PCS TG 002 CO₂ Capture Systems Guidance_v1.0

Document Control

Document identification

• Document code: PCS-TG-002

• Title: Technical Guidance for CO₂ Capture Systems

• Scope: Guidance for engineering design, monitoring and verification of captured CO₂ quantities, CO₂ quality (purity/impurities/moisture), energy use and emissions accounting, venting and fugitives, calibration, uncertainty management, and reporting for capture systems under PCS

• Application: Supports application of the PCS CCS methodology and capture module and informs VVB assessment of capture MRV integrity

Version history and change log

Table DC-1. Revision history

Version	Date	Status	Summary of changes	Developed by	Approved by
v1.0	TBD	Draft	Release for public consultation	PCS	TBD

Superseded versions

No superseded versions for v1.0.

Governance note on versioning and archiving

Only the latest approved version of this Technical Guidance shall be used for new project registrations and related submissions. Superseded versions shall be archived and retained for traceability and audit purposes, including for projects registered under earlier versions where applicable, consistent with PCS governance rules.

Purpose and scope summary

Purpose

This Technical Guidance defines the technical expectations needed to measure, monitor, and report captured CO₂ quantities and quality reliably and consistently across capture technologies, supporting conservative and verifiable net climate benefit claims.

Scope summary

This guidance applies to CO₂ capture systems across point sources and DAC where relevant, and provides monitoring and reporting depth to support the CCS methodology suite under PCS.

Relationship to PCS standards and methodologies

This guidance supports the CCS methodology suite (including the capture module) and shall be read alongside applicable PCS requirements on MRV, safeguards, and governance. Where conflict exists, the PCS Framework, Program Manual, and applicable Methodology/Module prevail.

Chapter 1 - Introduction And Purpose Of Capture Guidance

1.1 Background and Rationale

1. Carbon dioxide capture is the foundational stage of any CCS project and determines the quantity, purity, and consistency of CO₂ available for transport and storage. Capture systems operate at the interface between industrial processes and the CCS chain, removing CO₂ from flue gases, process streams, or ambient air and delivering it in a conditioned form suitable for compression, transport, and geological storage. Because capture technologies vary widely in their engineering principles, operational conditions, and monitoring challenges, it is essential to have a dedicated guidance document that standardizes expectations across all project types applying to the Planetary Carbon Standard (PCS).

2. Capture facilities may operate continuously, cyclically, or intermittently depending on the industrial process they serve. They may rely on chemical absorption, solvent scrubbing, adsorbent cycles, membranes, cryogenic separation, oxyfuel combustion, or direct air capture systems. Each technology presents distinct performance characteristics, energy requirements, and measurement complexities. Despite these differences, all capture systems must meet common integrity, monitoring, and accounting requirements under PCS. This guidance provides the underlying scientific and engineering principles that allow these diverse technologies to be evaluated consistently.

1.2 Purpose of the Capture Technical Guidance

1. The purpose of the PCS Capture Technical Guidance is to define the technical expectations for the design, monitoring, verification, and reporting of CO₂ capture systems in order to ensure accuracy, transparency, and reproducibility of emissions reductions and removals claimed under PCS methodologies. Whereas the PCS CCS Methodology (PCS-MT-001) and Capture Module (PCS-MT-001-A) define what must be quantified and how CO₂ capture contributes to net reductions, this guidance document explains how capture facilities should operate in practice to meet those methodological requirements.

2. This guidance aims to ensure that capture processes remain well-characterized, measurable, and verifiable. It establishes acceptable approaches to determine CO₂ flow, purity, moisture content, energy use, and fugitive releases. It also defines engineering and operational standards that support long-term reliability and safety. The guidance provides clarity to project developers, VVBs, and host country authorities by laying out the expected protocols for instrumentation, calibration, data collection, operational transparency, and reporting.

1.3 Scope of Application

1. This guidance applies to all CO₂ capture systems submitted to PCS for registration, regardless of technology type or industrial sector. It includes point-source capture from power generation, cement manufacturing, steel production, hydrogen production, chemical processes, and refineries, as well as emerging technologies such as direct air capture (DAC). The guidance covers the full range of CO₂ sources including dilute gas streams, high-purity industrial streams, and atmospheric air.

2. The document provides technical expectations for:

1

Capture system performance and reliability.

Details: Expectations that systems operate predictably, maintain separation efficiency, and support accurate measurement of CO₂ output.

2

Monitoring of CO₂ quantities and quality.

Details: Requirements for flow metering, purity and impurity monitoring, moisture measurement, and sampling representativeness.

3

Measurement of energy and resource inputs.

Details: Defining the energy boundary, electricity/thermal metering, fuel use, and attribution methods for shared utilities.

4

Detection and quantification of fugitive emissions and venting.

Details: Leak detection programs, venting logs, mass-balance reconciliation, and event reporting.

5

Data quality and instrument calibration.

Details: Calibration schedules, data logging, missing data treatment, uncertainty quantification and traceability.

6

Operational record-keeping and reporting.

Details: Capture Monitoring Report components, archiving, and reporting of deviations and maintenance.

7

Risk and safety considerations relevant to CO₂ capture operations.

Details: Risk assessments, safety systems, emergency procedures, and material compatibility.

1. Although the specific design of a capture facility may vary widely, the principles and requirements described here apply universally.

1.4 Relationship to PCS Methodologies and Other Guidance

1. This Capture Technical Guidance is designed to function alongside several PCS documents. It supports the PCS CCS Methodology and the Capture Module by providing engineering depth and monitoring procedures. It complements the Geological Storage Technical Guidance by ensuring that the CO₂ delivered from the capture facility is suitable for transport and storage, particularly with respect to purity, moisture content, and impurity profiles.

2. The guidance also aligns with international standards such as ISO 27913 and ISO 27916, IPCC emissions accounting principles, and operational learnings from industrial CCS applications worldwide. It does not replace regulatory requirements in any jurisdiction but provides a harmonized technical basis for PCS validation and verification.

1.5 Importance of Capture Guidance for PCS Integrity

1. Accurate and reliable capture data is essential for determining the baseline scenario, calculating project emissions, and quantifying net CO₂ reductions or removals. Errors in measurement or inconsistent definitions of capture quantities can compromise the environmental integrity of carbon units issued by PCS. Because CO₂ capture is often the most energy-intensive and variable component of a CCS project, this stage requires greater clarity in monitoring and reporting than transport or storage.

2. The guidance ensures that CO₂ quantities are measured consistently across projects, that purity and moisture content are accounted for correctly, and that any CO₂ vented during routine operations or maintenance is captured in project emissions. It also strengthens the credibility of PCS by ensuring that capture technologies are deployed with a high level of technical rigor and transparency.

1.6 Structure of This Document

1. The guidance is organized to reflect the lifecycle and operational logic of capture systems. It begins by describing the major categories of capture technologies and their relevant engineering principles, followed by detailed requirements for monitoring CO₂ quantities and quality. The guidance then addresses energy use and fugitive emissions before outlining calibration, data quality requirements, and reporting expectations. Annexes contain technical specifications, example calculations, and references.

2. This structure enables project developers to design capture systems in accordance with PCS expectations and provides VVBs with a consistent basis for evaluating capture performance and MRV compliance.

Chapter 2 - Overview Of CO₂ Capture Technologies

2.1 Introduction

1. CO₂ capture technologies vary widely in terms of operating principles, industrial applications, energy requirements, and measurement challenges. Despite this diversity, all capture systems share a common purpose: to separate CO₂ from gas streams or ambient air at sufficient purity and consistency to allow for compression, transport, and geological storage. This chapter provides a technical overview of the primary categories of capture technologies used worldwide. The descriptions here are not meant to prescribe specific technologies but to establish a clear understanding of how each system operates and how it interfaces with the MRV requirements of the Planetary Carbon Standard (PCS).

2. Because the choice of technology affects everything from purity specifications to fugitive emissions and monitoring strategies, PCS requires developers to present a transparent and scientifically grounded description of the capture system in their Project Design Document. This chapter provides the conceptual foundation for those descriptions.

2.2 Chemical Absorption (Amine and Solvent-Based Capture)

1. Chemical absorption is the most widely deployed CO₂ capture technology globally, especially in post-combustion applications. It involves the selective reaction of CO₂ with a chemical solvent, typically amine-based, to form a weakly bound compound that can later be regenerated by applying heat. The process generally consists of an absorber, where flue gas contacts the solvent; a stripper or regenerator, where CO₂ is released through heating; and associated heat-exchange and solvent conditioning equipment.

2. The technology is suitable for dilute CO₂ streams such as those from power plants, cement kilns, or industrial boilers. Amine systems can achieve high capture efficiencies, often exceeding ninety percent under optimal operating conditions, although performance depends strongly on solvent quality, flue gas composition, and process control. The purity of captured CO₂ is typically high, but water vapor and trace impurities must be removed or conditioned downstream. Chemical degradation, solvent oxidation, and heat-stable salts are factors that may influence operational reliability and monitoring.

3. Chemical absorption systems require detailed monitoring of solvent circulation rates, CO₂ loading, regeneration energy consumption, and potential fugitive emissions from solvent degradation products or absorber vents. These factors make chemical absorption technologically mature but operationally complex.

2.3 Physical Solvent Systems

1. Physical solvent systems rely on the ability of certain liquids to absorb CO₂ without chemical reaction. CO₂ dissolves into the solvent at high pressures and is released upon depressurization. Examples include Selexol®, Rectisol®, and other proprietary solvents. These systems are most effective for high-pressure gas streams, such as syngas from pre-combustion processes or natural gas processing.

2. Physical solvents tend to have lower energy requirements for regeneration compared to amine systems, but they require high operating pressures to achieve meaningful absorption. Because no chemical bond is formed, impurities such as H₂S, COS, or other acid gases may also be captured simultaneously. Monitoring requirements focus heavily on pressure conditions, solvent circulation, and the purity and phase behavior of the captured CO₂ emerging from the regeneration step.

2.4 Solid Sorbent Capture

1. Solid sorbent capture involves materials such as zeolites, metal-organic frameworks, activated carbon, or proprietary sorbents that selectively adsorb CO₂. These sorbents release CO₂ when exposed to changes in temperature (temperature swing adsorption), pressure (pressure swing adsorption), or humidity. The technology tends to be modular and can be applied to industrial point sources or direct air capture systems.

2. Sorbent systems offer advantages in modularity, lower regeneration energy for some materials, and potential for selective CO₂ uptake. However, sorbent degradation, dust formation, and temperature sensitivity must be considered. Monitoring requirements include tracking adsorption capacity, regeneration cycles, thermal performance, and any CO₂ break-through events that reduce capture efficiency.

2.5 Membrane Separation

1. Membrane capture uses selective semi-permeable barriers that allow CO₂ to pass through faster than other gases, generating streams of enriched CO₂ and depleted flue gas. Membrane systems may be polymeric, inorganic, or hybrid. Their effectiveness depends on pressure gradients and membrane material properties.

2. Membrane systems are compact and mechanically simple but often require multi-stage configurations to achieve high CO₂ purity. They are better suited to streams with elevated CO₂ concentrations or where high pressure is available. Monitoring focuses on membrane performance degradation, pressure differentials, permeate purity, and the efficiency of compression systems downstream of the membranes.

2.6 Cryogenic Separation

1. Cryogenic systems remove CO₂ by cooling gas streams until CO₂ condenses or solidifies, allowing physical separation. This approach is energy-intensive but effective for gas streams with high initial CO₂ concentrations or when extremely high CO₂ purity is required. Cryogenic separation is common in certain industrial processes such as natural gas purification or liquefied gas production.

2. Because temperature control is central to cryogenic systems, monitoring requirements involve precise temperature measurement, refrigeration energy consumption, impurity freeze-out, and condensate management. The approach may also be integrated into oxyfuel combustion systems or other high-purity capture configurations.

2.7 Oxyfuel Combustion Capture

1. Oxyfuel systems burn fuel in nearly pure oxygen instead of air, generating a flue gas primarily composed of CO₂ and water vapor. After water removal, the resulting CO₂ stream can be captured with minimal purification. Oxyfuel combustion offers high CO₂ concentrations but requires an air separation unit to supply oxygen, which can be energy-intensive.

2. Monitoring must account for oxygen purity, combustion performance, and any nitrogen leakage that could reduce CO₂ concentration. Oxyfuel systems may also produce trace gases requiring downstream purification.

2.8 Pre-Combustion Capture (Syngas-Based Capture)

1. In pre-combustion capture, fuels are converted into syngas (CO + H₂), which is shifted to produce CO₂ and hydrogen. CO₂ is then captured, usually using physical solvents, and hydrogen is used for combustion or industrial processes. This approach produces CO₂ at high pressure and concentration, making capture efficient, but it is primarily applicable in integrated gasification combined cycle (IGCC) systems and hydrogen plants.

2. Monitoring must address syngas composition, shift reactor performance, solvent absorption behavior, and impurities such as sulfur compounds.

2.9 Direct Air Capture (DAC)

1. Direct air capture involves removing CO₂ directly from ambient air. DAC systems may use chemical solvents, solid sorbents, or electrochemical methods. Because atmospheric concentrations are extremely dilute, DAC operations require highly efficient sorbents and regeneration systems. They may also produce CO₂ with distinct impurity profiles and moisture characteristics compared to point-source capture.

2. Monitoring requirements include accurate measurement of captured CO₂ quantities, energy use (which may dominate emissions), air flow volumes, sorbent regeneration cycles, and temperature or humidity effects. DAC systems must demonstrate net-negative CO₂ removal after accounting for all process emissions.

2.10 High-Purity Industrial Sources

1. Certain industrial processes inherently produce nearly pure CO₂ streams, such as ammonia production, bioethanol fermentation, or natural gas processing. These sources require minimal separation, although conditioning, drying, and compression are still needed prior to transport and storage.

2. Even for high-purity streams, PCS requires precise measurement of CO₂ flow, impurity levels, and any venting events. The apparent simplicity of these systems does not eliminate monitoring obligations, especially where venting or maintenance shutdowns occur.

2.11 Relevance of Capture Technology Differences Under PCS

1. Although the PCS methodology quantifies captured CO₂ in a technology-neutral manner, the way CO₂ is produced, measured, purified, and conditioned varies significantly across capture systems. These differences influence how monitoring instruments are installed, how often calibrations are required, what impurities must be considered, and how plant performance is verified.

2. Understanding each technology's engineering basis allows project developers to design reliable monitoring systems and provides VVBs with the context necessary to validate measurements. The remainder of this guidance document builds on these concepts to establish detailed requirements for monitoring, purity management, energy use tracking, and performance documentation.

Chapter 3 - Engineering And Operational Requirements For CO₂ Capture Systems

3.1 Purpose of Engineering Requirements

1. Engineering requirements ensure that CO₂ capture systems operate reliably, safely, and consistently under the conditions defined in the PCS methodology. Although capture technologies differ widely, they all must be designed to support stable CO₂ separation, maintain predictable flow and purity, minimize losses, and allow accurate measurement of the quantities captured. The integrity of the entire CCS chain relies on the quality and consistency of the CO₂ stream produced at this upstream stage. For this reason, PCS establishes common engineering principles that apply universally across all capture installations.

2. The requirements described in this chapter do not prescribe specific technologies but define the performance, design, and monitoring expectations necessary to ensure alignment with PCS verification and reporting standards.

3.2 Fundamental Design Principles for Capture Systems

1. A CO₂ capture system must be engineered to operate within a defined performance envelope that ensures predictable separation efficiency, stable operating conditions, and consistent CO₂ quality. Each capture technology has specific thermodynamic and chemical requirements, but all systems must demonstrate that they can maintain stable pressure and temperature conditions, operate within equipment tolerances, and prevent operational instability that could compromise CO₂ purity or measurement reliability.

2. Capture systems should be designed to minimize variability in flow, reduce contaminant carryover, and prevent conditions that might lead to foam formation, sorbent degradation, membrane fouling, or other operational disruptions. The system must include provisions for controlling major process parameters such as solvent circulation rates, regeneration temperatures, vacuum levels, pressure differentials, air flow rates (for DAC), and reactor temperatures. These controls allow operators to maintain the system within optimal ranges and support accurate MRV.

3.3 CO₂ Conditioning and Processing Requirements

1. Following initial separation, CO₂ must often undergo further conditioning before it can be compressed and transported. The conditioning process may involve water removal, impurity reduction, dehydration, filtration, or temperature stabilization. Because impurities can influence corrosion, phase behavior, and storage reservoir suitability, the conditioning stage is a critical component of capture system design.

2. The system must provide reliable control of moisture content to avoid corrosive reactions during compression and to prevent hydrate formation in pipelines. When CO₂ streams contain oxygen, nitrogen, sulfur compounds, or trace hydrocarbons, the design must ensure that these impurities remain within acceptable limits for the transport and storage system. Monitoring and documentation of impurity levels must be incorporated into the design so that downstream operators and VVBs understand the composition of the delivered stream.

3.4 Instrumentation and Process Measurement Systems

1. A capture system must incorporate instrumentation capable of measuring the parameters necessary for accurate quantification of captured CO₂ and understanding process performance. Instruments must include flow meters, temperature and pressure sensors, purity analyzers, and energy-measurement equipment appropriate for the technology in use.

2. Instrumentation must be located at points in the process where representative measurements can be obtained without interference from multiphase conditions, condensates, or unstable flow regimes. For example, flow meters positioned downstream of dehydration units or immediately prior to compression often provide the most reliable measure of CO₂ output. In amine systems, instruments must be capable of monitoring solvent concentrations and CO₂ loading. In membrane systems, permeate and retentate lines must be equipped with sensors characterizing purity and flow.

3. The selection of instruments must consider expected variability, required measurement accuracy, and the potential for drift over time. Systems must include mechanisms for regular calibration, inspection, and data recording to ensure continuous reliability.

3.5 Operational Stability and Control Requirements

1. Capture processes must be operated with sufficient stability to ensure predictable CO₂ separation rates and quality. Operational stability refers to narrow and controlled fluctuations in pressure, temperature, flow, solvent composition, or sorbent performance. Instabilities such as sudden temperature excursions, equipment cycling, solvent foaming, or vacuum collapse may compromise CO₂ purity, reduce capture efficiency, and introduce errors in flow measurement.

2. Operators must have real-time visibility into key parameters and must implement control strategies that maintain the process within acceptable limits. This may include automated control loops, alarms, interlocks, or manual operational procedures. For technologies such as DAC, maintaining consistent air flow and sorbent regeneration cycles is essential for quantification accuracy.

3. The guidance emphasizes that stable operations are not only an engineering concern but also a monitoring requirement because unstable systems produce unreliable measurement data and increase uncertainty in reported values.

3.6 Corrosion, Material Compatibility, and Chemical Stability

1. CO₂ streams, especially those containing moisture or impurities, can cause corrosion in metallic components and chemical degradation of solvents, membranes, and sorbents. Capture systems must therefore be constructed using materials compatible with long-term exposure to CO₂, water, and process-specific contaminants such as SO₂, NOₓ, or oxygen. Acid gas impurities and dissolved oxygen can accelerate solvent degradation in chemical absorption systems and may lead to fouling or increased emissions.

2. Engineers must consider the full lifecycle of material exposure, including startup, shutdown, and transient phases. Components such as heat exchangers, absorber internals, stripper columns, pumps, and piping must be designed with appropriate corrosion allowances or protective coatings. Material selection must reflect expected operating temperatures, pH levels, and chemical loading. Failure to manage corrosion risks can compromise system reliability and introduce safety hazards.

3.7 Redundancy, Backup Systems, and Reliability Assurance

1. Capture facilities typically operate continuously and must maintain high uptime to provide consistent CO₂ supply for compression and storage. To achieve this, systems may require redundancy in critical components such as compressors, pumps, circulation blowers, analyzers, or valves. Backup systems reduce the risk of unexpected downtime and support continuous measurement and control.

2. Reliability assurance also requires systematic maintenance schedules, availability of spare parts, and contingency plans for equipment failures. These measures are not only operational necessities but also essential to maintaining high-quality monitoring and reducing uncertainties in captured quantities.

3.8 Safety, Emergency Shutdown, and CO₂ Handling Protocols

1. Capture systems must include engineering features and operational protocols that mitigate safety risks. High-concentration CO₂ streams, hot solvents, high-pressure equipment, oxygen-handling systems (in oxyfuel applications), and hazardous chemical environments pose safety risks requiring disciplined management.

2. Facilities must incorporate emergency shutdown procedures designed to isolate equipment, safely depressurize lines, and prevent uncontrolled releases of CO₂ or solvents. Operators must be trained to recognize and respond to situations such as compressor failures, absorber flooding, solvent degradation incidents, sorbent fires, or membrane ruptures. Adequate ventilation, gas detection systems, and emergency response plans must be implemented to protect personnel and equipment.

3.9 Integration With Downstream Transport and Storage Requirements

1. Capture system design must consider the demands of the downstream compression, transport, and storage systems. Purity, moisture content, phase behavior, and pressure requirements must align with the specifications of pipeline operators, shipping vessels, or injection facilities. If CO₂ impurities exceed storage tolerance levels, additional purification steps may be required. If moisture remains too high, hydrate formation may occur during pipeline transport. Engineers must therefore design capture conditioning systems with downstream needs in mind.

2. Operational interfaces between capture, transport, and storage systems—such as metering points, sampling ports, and data transfer protocols—must be designed to support PCS monitoring and verification.

3.10 Documentation of System Design and Operational Boundaries

1. Every capture project must produce a detailed engineering description of the system, identifying process flow diagrams, operating envelopes, equipment specifications, material selections, expected CO₂ compositions, and monitoring instrumentation layouts. The operational boundaries must be clearly defined, including minimum and maximum allowable conditions for pressure, temperature, flow, purity, and capture rate.

2. This documentation forms the basis for VVB validation and helps ensure that the project operates consistently throughout its lifecycle. It also provides the reference point against which deviations, anomalies, or significant design changes can be evaluated.

Chapter 4 - Measurement, Monitoring, And Verification Of Captured CO₂ Quantities

4.1 Purpose of Measurement and Verification Requirements

1. Reliable measurement and verification of captured CO₂ is fundamental to the environmental integrity of any CCS project. The quantity of CO₂ captured at the facility constitutes the starting point for all subsequent emission reduction calculations in the PCS methodology. Inconsistent, inaccurate, or poorly documented measurements at this stage undermine the credibility of the entire CCS chain. For this reason, PCS establishes clear expectations for how CO₂ flow, purity, moisture content, and vented or fugitive losses must be quantified.

2. The purpose of this chapter is to ensure that all capture projects—regardless of technology type—measure CO₂ in a traceable, accurate, and verifiable manner. The chapter sets out the required measurement principles, instrumentation approaches, sampling expectations, and integration with mass and energy balances.

4.2 Principles of CO₂ Quantification Under PCS

1. PCS requires that all captured CO₂ be measured as dry, compressed, and conditioned CO₂ at the point where it exits the capture system and enters the compression or transport stage.

2. This ensures consistency across different capture technologies and eliminates discrepancies caused by moisture, impurities, or unstable upstream conditions. Measurements must represent actual mass flow, not volumetric flow at uncontrolled conditions. The mass flow of CO₂ must reflect the true amount separated from the gas stream or air, adjusted for moisture and impurities.

3. Quantification must rely on direct measurement rather than theoretical estimates or manufacturer specifications. Continuous measurement is preferred whenever technologically feasible. Where continuous measurement is not possible, PCS requires justified measurement intervals with conservative assumptions. All measurements must be supported by calibration records and documented quality control procedures.

4.3 Placement of Flow Measurement Instruments

1. Flow meters or measurement devices must be positioned at a location that allows accurate and representative measurement of CO₂ output. The preferred position is downstream of any dehydration or purification equipment and upstream of compressors or transport interfaces. This ensures that the CO₂ stream is in a controlled thermodynamic state and free from entrained liquids that could bias readings.

2. For systems where CO₂ may still be saturated with moisture prior to compression, drying units may influence flow stability. In such cases, the installation point must be chosen so that the meter encounters a fully gaseous, stable-condition CO₂ stream. The measurement point must be included in engineering drawings and referenced in monitoring reports.

4.4 Requirements for Flow Measurement Accuracy and Reliability

1. The selected flow meter must be suitable for the conditions under which it operates, including CO₂ pressure, temperature, and purity. Acceptable technologies include Coriolis meters, ultrasonic meters configured for CO₂, and mass-flow devices designed for dense-phase operation. Differential-pressure meters may be used only if accompanied by appropriate flow conditioning.

2. Meters must have a documented accuracy consistent with the needs of PCS, and their performance must be maintained through routine calibration and verification. Calibration intervals must reflect the manufacturer’s specifications and the operating environment of the meter. Redundant or backup measurement systems may be appropriate in large-scale facilities or where flow interruptions are operationally unacceptable.

3. All metering equipment must record data at a frequency sufficient to detect operational irregularities and allow integration across measurement periods. Raw and processed data must be archived to support independent verification.

4.5 Measurement of CO₂ Purity and Impurity Composition

1. In addition to measuring CO₂ quantity, PCS requires periodic measurement of the CO₂ purity and impurity content. These measurements provide insight into process performance and support downstream compatibility with transport and storage systems. Purity refers to the mass fraction of CO₂ relative to other gases present, while impurity analysis must include common contaminants such as water vapor, nitrogen, oxygen, sulfur compounds, and hydrocarbons.

2. Purity and impurities must be measured using appropriate laboratory or online analytical equipment such as gas chromatographs, spectrometers, or moisture analyzers. Sampling must follow standardized procedures that maintain representativeness, especially when gas streams include trace contaminants that may condense under certain conditions. The results must be recorded at intervals suitable for detecting changes in capture performance.

3. These values must be used to adjust the mass flow of captured CO₂ to reflect dry, pure CO₂ content. This adjustment is necessary because impurities do not contribute to carbon storage and may impact the safety or integrity of transport and storage systems.

4.6 Measurement of Moisture Content

1. Moisture measurement is essential because water vapor contributes to mass flow readings but is not considered stored carbon under PCS. Excess moisture can also cause corrosion or hydrate formation downstream. Moisture levels must be measured using dew-point analyzers or equivalent instruments that provide reliable data for the conditions of the CO₂ stream.

2. Measurements must be taken at the same point as flow measurement or at a representative sampling location linked to the metering point. Moisture content must be incorporated into calculations so that the final reported quantity of CO₂ reflects dry mass only.

4.7 Determining Capture Efficiency and Internal Mass Balance

1. Although PCS quantifies net captured CO₂ at the outlet of the capture system, internal mass balance calculations remain essential. These calculations help identify losses, validate monitoring results, and provide a diagnostic tool for operational efficiency. Capture efficiency is determined by comparing the CO₂ removed from the inlet stream (or captured from air, in the case of DAC) with the quantity measured at the system outlet.

2. Mass balance discrepancies can indicate solvent degradation, sorbent exhaustion, membrane leakage, operational anomalies, or measurement inaccuracies. Therefore, PCS requires projects to document inlet CO₂ concentrations, outlet flow readings, and solvent or sorbent cycle conditions to the extent possible. These data support consistent verification and ensure system reliability.

4.8 Monitoring of Venting, Flaring, and Fugitive Emissions

1. All CO₂ that is separated from the gas stream but subsequently vented must be measured or estimated and included in project emissions. Venting may occur during startup, shutdown, maintenance, or emergency events. These emissions must be quantified using continuous or event-based monitoring, depending on system design.

2. Fugitive emissions, including leaks from pumps, compressors, piping, absorber columns, DAC fans, or membrane housings, must be identified and quantified using appropriate leak detection methods. Infrared imaging, handheld analyzers, or periodic facility inspections may be used, provided that the methods produce conservative and verifiable estimates. Fugitive emissions must be recorded, tracked, and integrated into the overall project emissions accounting.

3. PCS requires clear documentation of each venting or fugitive emission event, including its cause, magnitude, duration, and corrective actions taken. This ensures that capture quantities are not overstated.

4.9 Calibration, Data Integrity, and Quality Assurance

1. Reliable monitoring depends on rigorous calibration and quality control. All instruments used to measure flow, purity, moisture, temperature, or pressure must have documented calibration records. Calibration must be performed using traceable standards and at intervals that reflect both the manufacturer’s guidelines and site-specific operating conditions.

2. Data integrity must be ensured through secure data collection systems that preserve raw measurements, processing algorithms, timestamps, and calibration factors. PCS requires that any corrections to data—such as replacing missing values or addressing sensor failures—must be documented transparently, using conservative assumptions that do not inflate captured CO₂ quantities.

3. Quality assurance procedures must include checks for data continuity, validation of unexpected operational patterns, and reconciliation between flow measurements and mass balance indicators. VVBs must have access to all data necessary to independently evaluate measurement quality.

4.10 Integration With PCS MRV Requirements

1. The measurement and monitoring protocols defined in this chapter support the broader MRV framework outlined in the PCS methodology. Data collected from the capture system must feed into the Monitoring Report and support calculations of total captured CO₂, capture-related emissions, and net project benefits. Measurements must align with calibration records, operational documents, and any modifications to the capture system described in the Project Design Document.

2. This alignment ensures that MRV under PCS is coherent and defensible, enabling transparent validation and verification of captured quantities. High-quality data from the capture stage forms the foundation for trustworthy transport and storage stages and ultimately ensures the credibility of issued carbon units.

Chapter 5 - CO₂ Purity, Moisture, Impurities, And Conditioning Requirements

5.1 Purpose of Purity and Conditioning Requirements

1. The purity and conditioning of captured CO₂ directly affect the safety, operability, and environmental integrity of downstream transport and storage systems. Impurities influence CO₂ phase behavior, corrosion potential, energy requirements for compression, and the performance of geological storage reservoirs. Moisture, in particular, is a critical parameter because it can lead to hydrate formation, pipeline blockages, or acid-induced corrosion.

2. PCS therefore requires capture systems to produce CO₂ streams that meet defined quality expectations and to implement monitoring systems capable of verifying those qualities. Although purity specifications may vary across transport operators, geological formations, or regulatory jurisdictions, PCS establishes minimum technical expectations to maintain consistency and ensure safe integration into the CCS chain.

5.2 Understanding CO₂ Stream Composition

1. The CO₂ stream emerging from the capture system consists predominantly of carbon dioxide, but its exact composition depends on the capture technology, feed gas composition, and downstream processing steps. Chemical absorption systems may produce CO₂ containing water vapor, solvent carryover, degradation products, or small amounts of nitrogen and oxygen. Membrane systems may allow nitrogen or hydrogen to permeate depending on separation selectivity. Cryogenic systems typically produce very high purity CO₂, whereas physical solvent systems may co-absorb sulfur species or hydrocarbons.

2. Understanding the expected composition of the CO₂ stream is fundamental to selecting appropriate conditioning steps and determining monitoring needs. The project developer must provide a detailed description of expected impurities, their variability, and their relevance to downstream operations.

5.3 Moisture Content Requirements

1. Moisture content must be controlled to prevent corrosion and hydrate formation in pipelines or compression equipment. High moisture levels combined with CO₂ can form carbonic acid, which aggressively corrodes steel. In the presence of low temperatures during compression or transport, excessive moisture may freeze or form hydrates that block equipment.

2. CO₂ must be dehydrated to levels compatible with the transport and storage system. While specific tolerance levels depend on pipeline specifications and reservoir conditions, moisture is typically reduced to levels below a few hundred parts per million by volume. Moisture measurement must occur downstream of the dehydration system and close to the flow measurement point to ensure that readings are representative of the stream actually delivered to transport.

3. If moisture levels exceed acceptable limits, corrective actions must be implemented immediately and documented in monitoring reports.

5.4 Impurity Classes and Their Implications

1. Impurities fall into several classes, each with distinct implications for transport and storage. Non-condensable gases such as nitrogen, oxygen, and argon may influence CO₂ density and compressibility, increasing energy requirements for compression. Reactive species such as sulfur dioxide, nitrogen oxides, or hydrogen sulfide may create corrosive or toxic conditions. Hydrocarbons may alter phase behavior or present flammability concerns. Water-soluble impurities may affect groundwater chemistry in the unlikely event of leakage.

2. The developer must describe all expected impurities and their potential impact on operational safety and environmental protection. If impurities exceed the acceptable thresholds established by transport or storage operators, additional purification steps must be implemented.

5.5 Monitoring and Sampling for Impurities

1. Monitoring of impurity levels must occur at a location where the CO₂ composition is stable and representative of the stream entering the transport system. Sampling ports must be designed to prevent condensation, freezing, or contamination. Analytical methods must be appropriate for the impurities present and must include sufficient sensitivity to detect concentrations relevant to operational and environmental concerns.

2. Sampling frequency must be determined based on the variability of the capture process. Processes with stable operating conditions, such as high-purity industrial streams, may require less frequent sampling, while processes with fluctuating impurity levels may require daily or continuous monitoring.

3. The developer must ensure that all purity and impurity measurement methods are traceable, calibrated, and validated against reference standards. Deviations from expected impurity levels must be investigated promptly.

5.6 CO₂ Conditioning Requirements for Transport and Storage

1. Conditioning refers to the set of processes used to prepare the CO₂ stream for transport and injection. These may include drying, filtering, compressing, and removing specific impurities. Conditioning requirements must be aligned with transport specifications such as pipeline pressure class, allowable impurity thresholds, or shipping tank conditions. They must also be compatible with reservoir properties and geochemical conditions.

2. Conditioning steps must be engineered to maintain stable CO₂ flow and minimize operational variability. Temperature and pressure conditions must be controlled to prevent multiphase flow or condensation that would interfere with measurement accuracy. The developer must describe all conditioning stages and their operating principles, demonstrating how they ensure CO₂ compatibility with the downstream system.

5.7 CO₂ Specification Agreements With Downstream Operators

1. PCS recognizes that transport system operators and storage site managers may impose additional quality requirements beyond the minimum standards in this guidance. Developers must secure written specifications from these operators and demonstrate how their capture system meets those requirements. These specifications may address impurity tolerance limits, moisture content, maximum oxygen or nitrogen content, or allowable concentrations of sulfur compounds.

2. The developer must provide evidence that the CO₂ stream consistently meets these specifications and must report any deviations in the Monitoring Report. Failure to meet downstream quality requirements may affect transport safety or storage integrity and must be treated as a significant operational issue.

5.8 Temperature and Phase Behavior Considerations

1. The thermodynamic behavior of CO₂ determines its density, compressibility, and phase stability. Capture systems must ensure that CO₂ is delivered at conditions suitable for compression and transport. Sudden temperature swings or phase changes may interfere with measurement, cause hydrate formation, or damage equipment.

2. The developer must understand and document the phase envelope of the CO₂ mixture produced by the capture system, including any impurities that may alter phase behavior. Monitoring of temperature at the measurement point is essential for accurate density calculations and must be incorporated into the measurement system.

5.9 Handling of Off-Specification CO₂

1. Occasionally, capture systems may produce CO₂ that falls outside the acceptable purity or moisture limits. Such occurrences may result from operational instability, equipment failure, solvent degradation, membrane fouling, or other process deviations. PCS requires that off-specification CO₂ not be delivered to the transport system unless downstream operators explicitly approve its acceptance.

2. If off-specification CO₂ is vented or flared, the developer must quantify the associated emissions and document the reason for the deviation. Recurrence of off-specification CO₂ indicates deeper operational issues and must be addressed through maintenance, calibration, or redesign.

5.10 Documentation and Reporting of CO₂ Stream Quality

1. Developers must maintain clear and continuous records of CO₂ purity, moisture content, impurity levels, temperature, and pressure. All analytical results must be logged, archived, and presented in Monitoring Reports where required. Reports must include interpretive narratives that describe how CO₂ stream quality remained within acceptable limits and how any deviations were addressed.

2. The documentation must allow VVBs to confirm the reproducibility and credibility of reported values. Incomplete or inconsistent documentation may result in non-compliance findings during verification.

Chapter 6 - Energy Use, Performance Efficiency, And Emission Accounting

6.1 Role of Energy Use in CO₂ Capture Performance

1. Energy consumption is the defining operational characteristic of most CO₂ capture systems and represents a substantial contributor to project emissions. The energy required for solvent regeneration, steam production, compression, refrigeration, air movement (in DAC systems), and vacuum generation can significantly influence the net climate benefit of the capture process. For projects claiming emission reductions or removals under PCS, it is essential that energy use be accurately measured, attributed, and accounted for within the project boundary.

2. This chapter provides the guidance needed to measure energy consumption reliably, interpret its impacts on system performance, and incorporate associated emissions into PCS quantification procedures.

6.2 Defining the Energy Boundary of the Capture System

1. To accurately determine the emissions associated with capture operations, the energy boundary must be clearly defined. The boundary includes all energy streams required to operate the capture system but excludes energy used for unrelated industrial processes. Within the boundary fall electricity consumption, steam supply, cooling water pumping, natural gas used for regeneration heaters, air blowers in DAC systems, and any energy used by compressors upstream of the transport interface.

2. Energy metering must distinguish capture-related energy from the broader facility energy use. When energy is shared between processes, allocation methods must be transparent and based on a measurable, justifiable basis such as heat duty, flow contribution, or equipment service ratios. Failure to define the energy boundary correctly can distort emissions accounting and undermine the integrity of reported reductions.

6.3 Measurement of Electricity Consumption

1. Electricity is typically the most variable energy input in CO₂ capture systems. Fans, pumps, blowers, vacuum systems, refrigeration units, and control systems all draw electrical power. Measurement must be based on calibrated, continuous metering systems that record consumption at intervals appropriate to capture operational variability.

2. Electricity meters must be installed at the point where electrical supply enters the capture system boundary. Developers must ensure that reactive power, power factor variations, and equipment cycling do not distort measured consumption. Measurements must be time-synchronized with process data to allow correlation between operational conditions and energy use.

3. The measurement approach must be documented clearly so that VVBs can confirm the appropriateness of metering placement, accuracy class, and calibration frequency.

6.4 Measurement of Thermal Energy Consumption

1. Many capture systems depend heavily on thermal energy. Solvent regeneration in amine systems often requires steam, while sorbent systems may need heating during regeneration cycles. Cryogenic processes rely on refrigeration systems that effectively convert electrical input into thermal energy removal.

2. Thermal energy consumption must be measured directly where possible using steam flow meters, condensate metering, or heat-duty calculations. When thermal energy is delivered through a shared system, allocation methods must be transparent and supported by process engineering principles. The chosen method must reflect actual thermal demand rather than assumptions based on design values.

3. All thermal data must be recorded in units consistent with emissions factor calculations, typically in megawatt-hours or gigajoules.

6.5 Fuel Use and Onsite Combustion Emissions

1. Some capture facilities require direct fuel combustion to generate steam or heat. When natural gas, fuel oil, biomass, or other fuels are consumed within the capture boundary, the associated emissions must be quantified using appropriate emission factors or continuous emissions monitoring.

2. Fuel flow meters must be installed where feasible, and fuel composition must be measured or estimated based on supplier data. Combustion-related emissions must be included in the overall project emissions accounting and cannot be excluded unless specifically addressed in PCS baseline or project definitions.

6.6 Energy Efficiency and Capture Performance

1. The energy efficiency of a capture system reflects how effectively it separates CO₂ relative to the energy consumed. Although PCS does not prescribe minimum efficiency standards, efficiency is a key indicator of system health and performance stability.

2. Efficiency trends may reveal solvent degradation in chemical systems, membrane fouling in separation systems, or sorbent exhaustion in DAC systems. A decrease in efficiency without a corresponding change in inlet CO₂ concentration may indicate operational issues that require investigation.

3. Monitoring efficiency also supports broader policy understanding of CCS performance and encourages continuous improvement in system operations.

6.7 Emissions Associated With Energy Consumption

1. Captured CO₂ does not represent a net reduction unless emissions associated with the energy used for capture are less than the CO₂ removed from the gas stream or atmosphere. Energy-related emissions must therefore be carefully quantified. Electricity emissions must be calculated using grid emission factors or, where applicable, renewable energy certificates or direct renewable supply arrangements. Thermal emissions must reflect the carbon intensity of the heating source.

2. All emission factors must be documented, justified, and linked to credible sources such as national inventory reports or recognized international databases. When multiple emission factors exist for different time periods or operational modes, the developer must explain which factor applies and why.

6.8 Venting, Blowdown, and Restart Emissions

1. Energy-intensive systems may require periodic maintenance, solvent replacement, sorbent handling, or equipment shutdowns. During these periods, CO₂ may be vented or released. PCS requires quantification of these emissions even when they occur intermittently.

2. Venting emissions must be logged with clear timestamps, operating conditions, and reasons for occurrence. When vented volumes cannot be measured directly, mass-balance calculations or engineering estimates must be used. Developers must explain and justify all methods used to quantify venting emissions.

3. VVBs will review venting records carefully to ensure full accounting of losses.

6.9 Start-Up and Shut-Down Energy Use

1. Capture systems may require substantial energy during start-up, particularly for heating solvents, energizing refrigeration units, or establishing operating pressures. Shut-down conditions may also involve active cooling or depressurization. Although these periods may represent a small fraction of operating time, they can contribute significantly to emissions.

2. PCS requires that start-up and shut-down energy use be included within the capture system boundary. Measurement or estimation must be based on traceable data and documented engineering assumptions.

6.10 Mass and Energy Balance Validation

1. Mass and energy balances provide an independent check on the accuracy of measured CO₂ quantities and energy consumption. They allow operators and VVBs to verify that captured CO₂ volumes align with process flows, thermodynamic conditions, and energy inputs. Significant discrepancies may indicate errors in flow measurement, calibration drift, process instability, or unseen fugitive emissions.

2. Developers must maintain complete mass and energy balance records and incorporate them into Monitoring Reports. VVBs will evaluate these balances to determine whether reported values are credible.

6.11 Documentation and Reporting Requirements

1. All energy and emissions data must be recorded systematically, archived securely, and presented in the Monitoring Report. Reports must include explanations of operational conditions, energy trends, deviations from expected performance, and the implications for net project emissions. Energy-use narratives must demonstrate that the capture system operated efficiently and that any increases in consumption were investigated.

2. Documentation must include instrument specifications, calibration records, emission factor sources, allocation methods, and all supporting calculations. Transparency and interpretability are central to verifying net climate impact under PCS.

Chapter 7 - Fugitive Emissions, Venting, And Loss Accounting

7.1 Purpose of Fugitive and Venting Accounting

1. A CO₂ capture system does not operate in perfect isolation. Even in well-engineered facilities, small leaks, controlled vents, maintenance releases, and startup or shutdown episodes may cause CO₂ to escape into the atmosphere. These emissions reduce the effectiveness of the capture process and must be incorporated into the project’s net emission calculations. The purpose of this chapter is to ensure that all fugitive emissions and intentional or unintentional releases are quantified, recorded, and transparently reported in accordance with PCS requirements.

2. Fugitive accounting reinforces environmental integrity by ensuring that only net captured CO₂ is credited. Without this accounting, capture performance would be overstated, and climate benefits misrepresented.

7.2 Understanding Fugitive Emission Sources in Capture Systems

1. Fugitive emissions arise from multiple potential points in a capture facility. Although the magnitude of these emissions may vary depending on technology type, all capture systems share common vulnerabilities. Valves, flanges, joints, seals, compressors, blowers, solvent regeneration equipment, sorbent chambers, membrane housings, and low-pressure gas-handling sections may experience small losses. Over time, these small losses can accumulate and become a significant contributor to total emissions.

2. Additionally, specific technologies present characteristic emission patterns. Amine systems may release degraded solvent compounds or CO₂ through absorber vents. Solid sorbent systems may experience blow-through during regeneration cycles. Membrane systems may have measurable bypass flows if pressure conditions deviate from design. Understanding these typical behaviors allows operators to design more effective monitoring strategies.

7.3 Controlled Venting and Operational Releases

1. Capture operations may require controlled venting for safety, maintenance, or operational stability. Venting may occur during solvent change-outs, compressor maintenance, column depressurization, or emergency shutdown events. These releases must not be ignored or treated as anomalies. Instead, they must be quantified using direct measurement or defensible engineering calculations, documented with operational context, and incorporated into project emissions.

2. For each venting event, the operator must record the date, time, duration, reason, operating conditions, and estimated CO₂ content. If the vent contains entrained impurities or gaseous byproducts, these must be described. A well-maintained venting log strengthens the credibility of monitoring reports and allows VVBs to confirm that all CO₂ losses are accounted for.

7.4 Start-Up, Shutdown, and Transient Emissions

1. Start-up and shutdown conditions may produce emissions that differ in magnitude and behavior from steady-state operations. During start-up, equipment purging, heating or cooling, solvent conditioning, or pressure equalization may generate measurable releases. Shutdown may require depressurization or solvent stripping cycles that release CO₂-rich gas.

2. Because these transitions are often the most emission-intensive phases of capture operation, PCS requires that they be treated explicitly in emission accounting. Operators must measure, estimate, or otherwise quantify CO₂ released during these periods and must provide explanations of the operational causes. Start-up and shutdown emissions must be included in monitoring reports and are not exempted simply due to their intermittent nature.

7.5 Leak Detection and Monitoring Requirements

1. Leak detection must be proactive rather than reactive. All capture facilities must implement a leak detection and monitoring program (LDMP) that reflects the specific risks and design characteristics of the system. This program may include handheld detectors, fixed gas monitors, pressure-loss testing, mass balance evaluations, or infrared imaging. The monitoring approach must be tailored to the facility’s layout, emission sources, and potential high-risk zones.

2. Regular inspections must be conducted, and any leaks detected must be repaired promptly. All leak detection activities must be documented, including the method used, results obtained, and corrective actions taken. In cases where leaks cannot be measured directly, engineering estimation methods must be justified and recorded.

7.6 Quantifying Fugitive Emissions

1. Quantification of fugitive emissions must rely on measurable data wherever possible. Direct measurement through fixed sensors or portable analyzers provides the most accurate results, particularly for persistent or continuous leaks. However, some systems may rely on mass balance methods where measured CO₂ output is compared against expected capture levels to infer losses. When mass balance is used, the uncertainty must be acknowledged, and conservative assumptions applied.

2. Engineering estimation methods may be used when leaks are too small or too transient for direct measurement. These methods must be based on established engineering principles, equipment specifications, or recognized fugitive emission estimation protocols. The facility must maintain documentation showing how each estimate was derived and why it is considered reasonable.

7.7 Treatment of Solvent or Sorbent Degradation Emissions

1. In chemical and sorbent-based systems, degradation of the capture medium may result in the release of CO₂ or other gaseous byproducts. These emissions may occur through absorber vents, regeneration columns, or off-gas streams associated with solvent reclaiming operations. Such emissions must be quantified and incorporated into the overall fugitive emissions accounting.

2. If degradation products include compounds other than CO₂ that may influence environmental or occupational safety, these must also be documented. Although PCS focuses on CO₂ accounting, the presence of degradation products may signal system instability requiring maintenance or redesign.

7.8 Integration of Losses Into Net CO₂ Accounting

1. All losses—whether fugitive emissions, venting releases, or degradation-related emissions—must be subtracted from the gross CO₂ captured to determine the net CO₂ delivered to the transport system. This integrated accounting ensures that the overall system performance reflects actual CO₂ transfer rather than theoretical capture efficiency.

2. In the Monitoring Report, developers must present a clear reconciliation showing gross captured CO₂, all quantified losses, and the resulting net captured amount. VVBs will review these calculations to ensure completeness and consistency.

7.9 Documentation and Traceability Requirements

1. Developers must maintain detailed records of fugitive detection activities, venting logs, leak repairs, operational deviations, and any corrective actions undertaken. All entries must be time-stamped, linked to operational data, and traceable through the monitoring period. Documentation must allow VVBs to reconstruct events, validate estimates, and confirm that no significant losses were omitted.

2. Transparent recordkeeping also supports long-term facility learning, enabling operators to identify recurring patterns, equipment vulnerabilities, or operational conditions that lead to increased emissions.

7.10 Implications for Verification and Compliance

1. Fugitive and venting emissions are often the most scrutinized components during VVB verification. PCS requires that developers demonstrate a proactive approach to identifying and quantifying losses. Failure to account for emissions may undermine project credibility, result in verification findings, or prohibit issuance of carbon units for the monitoring period.

2. Compliance requires not only accurate quantification but also clear documentation and consistent application of monitoring methods. The chapter’s requirements ensure that all capture systems operate under a unified framework of transparency and technical rigor.

Chapter 8 - Data Quality, Instrument Calibration, And Uncertainty Management

8.1 Purpose of Data Quality Requirements

1. High-quality data is fundamental to the credibility of CO₂ capture reporting under PCS. Measurement results must be accurate, reproducible, traceable, and representative of actual operating conditions. Because capture systems often experience dynamic behavior—ranging from fluctuations in solvent loading to changes in gas composition—PCS requires a robust approach to data quality management. This chapter establishes the expectations for calibration, data handling, uncertainty management, and quality assurance practices that apply to all PCS capture projects.

2. PCS recognizes that measurement uncertainty cannot be eliminated, but it must be quantified, minimized, and transparently reported. The integrity of issued carbon units relies on this disciplined approach.

8.2 Minimum Data Quality Standards for PCS Capture Projects

1. All measurements related to CO₂ flow, purity, moisture content, energy use, and emissions must meet minimum standards of accuracy and precision. Instruments must be selected based on suitability for CO₂-rich streams and must operate within the manufacturer’s specified ranges. Data must be recorded at frequencies appropriate for the expected variability of each parameter, ensuring that transient or abnormal conditions are captured and understood.

2. Data quality must be evaluated continuously throughout the monitoring period. Whenever data gaps, anomalies, or inconsistencies occur, the operator must investigate the cause, document findings, and apply corrective measures. PCS requires transparent documentation of any data quality issues and their resolution.

8.3 Calibration Requirements for Measurement Instruments

1. All measurement devices—including flow meters, pressure sensors, purity analyzers, moisture sensors, temperature probes, and energy meters—must be calibrated according to the manufacturer’s recommendations or industry standards, whichever is more stringent. Calibration must occur at intervals that ensure drift does not materially affect measurement accuracy.

2. Calibration results must be documented, including the date, method, reference standard, and any corrective factors applied to the instrument. If calibration reveals deviations beyond acceptable tolerance, historical data must be assessed to determine whether corrections are required. Operators must retain calibration certificates for audit and verification purposes.

3. Instruments that cannot maintain stable calibration or show consistent drift must be repaired or replaced. A calibration schedule must be included in the Monitoring Report for VVB review.

8.4 Data Logging, Storage, and Traceability

1. Data must be logged using secure systems that ensure completeness, integrity, and traceability. Time-stamping is essential for correlating flow, purity, temperature, pressure, and energy readings, enabling coherent interpretation of system performance. Data storage solutions must include redundant backup systems to prevent loss.

2. Operators must ensure that data acquisition systems provide continuous recording without manual intervention. Manual data entry introduces risk of error and must be limited to exceptional cases, such as analytical laboratory results that cannot be integrated automatically. Any manually entered data must include audit trails.

3. Traceability requires that every data point can be linked to its measurement source, instrument, calibration history, and any transformations applied during processing.

8.5 Treatment of Missing or Invalid Data

1. Missing data may arise from instrument failure, calibration cycles, communication issues, or operational disruptions. PCS requires that missing or invalid data be clearly identified and explained in monitoring documentation.

2. If missing data represent a small fraction of the monitoring period, substitution using conservative estimation methods may be allowed, provided the estimation is justified and documented. For significant data gaps that impair the ability to quantify captured CO₂ reliably, the developer must notify the PCS Secretariat and may be required to take corrective actions before verification can proceed.

3. Under no circumstance may operators adjust or reconstruct data in a manner that obscures underlying measurement uncertainty or operational issues.

8.6 Ensuring Representativeness of Sampling and Measurement

1. Data must accurately reflect the conditions of the CO₂ stream delivered to the transport system. Sampling points must be placed at locations where the gas mixture is homogeneous and free of condensation or phase instability. Instruments must be shielded from vibration, temperature shocks, or contamination that could distort readings.

2. For impurity and moisture analyses, sampling procedures must ensure that samples remain representative from the moment of extraction to laboratory analysis. This may require specialized sample cylinders, controlled-temperature transport, or immediate analysis for sensitive parameters.

3. Representativeness is not a procedural formality; it is essential for accurate CO₂ accounting and ensuring downstream compatibility.

8.7 Uncertainty Quantification and Management

1. Uncertainty arises from instrument accuracy limits, calibration drift, variability in operating conditions, sampling errors, and analytical precision constraints. PCS requires that all major sources of uncertainty be identified, quantified where possible, and integrated into the assessment of captured CO₂.

2. Uncertainty may be expressed as a confidence interval or statistical range associated with flow, purity, or energy measurements. When multiple instruments contribute to a single parameter—such as density derived from pressure and temperature measurements—combined uncertainty must be considered.

3. Projects must demonstrate that uncertainty does not undermine the credibility of reported captured quantities. If uncertainty is unusually high for any parameter, the developer must investigate the cause and implement mitigation measures, which may include upgrading instruments, modifying sampling procedures, or enhancing data verification processes.

8.8 Validation of Measurement Systems Through Mass and Energy Balances

1. Mass and energy balances serve as powerful tools for validating measurement accuracy. A coherent balance confirms that the measured CO₂ output, the energy input, and the physical behavior of the capture system are consistent with engineering principles. Significant deviations in the balance indicate potential errors in measurement, unrecognized fugitive emissions, or operational instability.

2. PCS requires that operators maintain updated mass and energy balances and review them periodically to identify trends or discrepancies. These balances must be included in monitoring documentation for VVB review.

8.9 Requirements for Independent Verification

1. VVBs rely on data quality to form verification conclusions. PCS requires that measurement systems, calibration records, uncertainty analyses, and data handling procedures be made available during validation and verification. VVBs will assess whether instruments were properly calibrated, whether data were recorded consistently, and whether uncertainty has been treated conservatively.

2. If verification identifies gaps in data quality, the project may be required to re-measure specific parameters, adopt stricter controls, or adjust reported values to reflect uncertainty more accurately.

8.10 Documentation and Reporting of Data Quality Procedures

1. Each project must document data quality procedures in the Project Design Document and Monitoring Report. Documentation must include instrument specifications, calibration schedules, uncertainty analyses, data handling protocols, missing data treatments, and any corrective measures applied during the monitoring period.

2. Transparency in data quality practices enables VVBs and the PCS Secretariat to evaluate the robustness of the monitoring system. It also supports continuous improvement in capture operations by providing a clear record of how data quality has been maintained over time.

Chapter 9 - Risk Assessment For Capture Systems

9.1 Purpose of Risk Assessment in Capture Operations

1. Risk assessment is an essential component of any CO₂ capture project because the reliability of capture performance, the safety of personnel and equipment, and the credibility of monitoring depend on identifying and addressing operational vulnerabilities. Capture systems involve complex thermochemical and mechanical processes, high temperatures, high pressures, corrosive environments, and substantial energy flows. These characteristics create a range of risks that must be managed proactively.

2. This chapter sets out expectations for the systematic identification, evaluation, and mitigation of risks associated with CO₂ capture technologies. A robust risk assessment ensures that the capture system operates safely, that data remain trustworthy, and that the broader CCS chain is not compromised by failures or unplanned releases.

9.2 Overview of Risk Categories

1. Risks associated with CO₂ capture systems arise from interconnected physical, chemical, mechanical, and operational factors. Although specific risks vary with technology type, most capture facilities share several overarching categories of concern. These include process instability, equipment failure, corrosion, fouling, solvent or sorbent degradation, membrane rupture, material incompatibility, freeze-out events, and deviations in gas composition. Environmental and occupational hazards must also be considered, especially where capture chemicals, elevated temperatures, or high-pressure CO₂ streams are present.

2. A comprehensive risk assessment must examine each of these categories and determine how they interact under normal and abnormal operating conditions. This evaluation supports the design of monitoring systems and informs the selection of mitigation strategies to ensure operational stability.

9.3 Risks Associated With Chemical Absorption Systems

1. Chemical absorption systems present a characteristic set of risks related to solvent chemistry and thermal operation. Solvent degradation can reduce capture efficiency, alter CO₂ loading characteristics, and produce volatile byproducts that may contribute to fugitive emissions. Excessive temperatures in the regenerator can accelerate solvent breakdown or generate heat-stable salts. Foaming within the absorber column may reduce separation efficiency and cause solvent carryover into downstream equipment.

2. Corrosion is a persistent risk due to the presence of water, CO₂, oxygen, and degradation products. Equipment such as heat exchangers, pumps, and piping may require enhanced material specifications to prevent failures. Mechanical risks include flooding of columns, pump failures, and blockages caused by particulate formation.

3. These risks must be evaluated during design and monitored continuously during operation.

9.4 Risks in Solid Sorbent and Temperature/Pressure Swing Systems

1. Solid sorbent systems face risks associated with thermal cycling, sorbent fatigue, and dust formation. Repeated heating and cooling may alter sorbent structure or reduce adsorption capacity. In systems using fine particulate sorbents, dust formation can cause filter blockages or fouling of blowers and piping. Regeneration cycles may release concentrated CO₂ streams at temperatures that pose equipment or safety risks.

2. Temperature or pressure swing processes may experience incomplete regeneration due to operational instability, leading to reduced adsorption efficiency or CO₂ break-through. The risk assessment must consider the durability of sorbent materials, the control of thermal gradients, and the performance of valves and blowers essential to cycle management.

9.5 Risks in Membrane Separation Systems

1. Membrane systems are sensitive to pressure variations, fouling, and material degradation. Sudden pressure drops or pressure surges may damage membranes or reduce separation performance. Contaminants such as particulates, aerosols, or condensate droplets can foul membrane surfaces and reduce permeability. High concentrations of oxygen or aggressive impurities may alter membrane selectivity over time.

2. Because membrane performance directly influences CO₂ purity, any decline in performance may affect downstream transport and storage compatibility. Risk assessments must address the expected lifetime of membrane modules, the potential for mechanical failure, and the design of pre-treatment systems necessary to prevent fouling.

9.6 Risks in Cryogenic and High-Purity Separation Systems

1. Cryogenic processes face risks associated with extreme temperatures, potential freeze-out of impurities, and brittleness of materials exposed to cryogenic conditions. Blockages may occur when impurities solidify, and thermal stress may cause fractures in equipment not designed for low-temperature service.

2. High-purity CO₂ streams produced in cryogenic systems must also be monitored for oxygen or nitrogen contamination that may alter phase behavior. Temperature control is critical; fluctuations may cause rapid condensation or vaporization that destabilizes flow and measurement systems.

3. Risk assessments must evaluate the resilience of thermal control systems, insulation integrity, and the ability to manage cold-start or shutdown conditions safely.

9.7 Risks in Oxyfuel and Pre-Combustion Capture Systems

1. Oxyfuel systems present risks associated with handling high-purity oxygen, including fire hazards and accelerated oxidation of materials. The flue gas from oxyfuel combustion contains high moisture levels, creating additional corrosion concerns. Improper control of oxygen purity may affect combustion stability and CO₂ purity.

2. Pre-combustion systems face risks associated with syngas composition, catalyst performance in shift reactors, and sulfur contamination. High-pressure systems increase the consequences of equipment failure and require strict safety controls and leak detection systems.

3. These risks must be understood within the context of integrated industrial operations.

9.8 Cross-Cutting Mechanical and Operational Risks

1. Regardless of technology type, capture facilities must address common mechanical risks. Compressor failures can disrupt operations or result in CO₂ venting. Pump or blower failures may compromise separation efficiency. Valve malfunction may alter pressure balance and destabilize the system. Thermal exchange units may foul, reducing heat transfer efficiency and increasing energy use.

2. Operational risks include human error, inadequate maintenance, inconsistent feed gas composition, unexpected load fluctuations, and process upsets caused by upstream industrial systems. The risk assessment must evaluate how such events could influence capture stability, monitoring data, and emissions accounting.

9.9 Corrosion, Material Integrity, and Chemical Compatibility Risks

1. CO₂ capture systems often expose equipment to corrosive environments. The combined effects of CO₂, water, oxygen, and contaminants can create acidic conditions that degrade steel and other materials. Solvents and sorbents may produce breakdown products that accelerate corrosion or alter chemical behavior.

2. The risk assessment must evaluate the selection of materials, corrosion allowances, protective coatings, and expected equipment lifetime. It must also consider operating conditions that exacerbate corrosion risk, such as temperature excursions, moisture levels, and impurity concentrations. Preventive measures and monitoring plans must be included.

9.10 Environmental, Safety, and Occupational Risks

1. Capture facilities may involve hazardous chemicals, high-pressure systems, elevated temperatures, or confined spaces. Risks to workers and the environment must be evaluated comprehensively. Potential hazards include accidental releases of CO₂, solvent vapors, byproducts, or flammable compounds. Safety systems must include gas detection, alarms, ventilation, emergency shutdown procedures, and containment systems.

2. Environmental risks may include emissions of degradation products, solvent slip, or contaminated condensates. PCS requires that these risks be evaluated in conjunction with local environmental regulations and international safety standards.

9.11 Integration of Risk Assessment Into Monitoring and Operations

1. The findings of the risk assessment must inform the design of monitoring systems, operational control strategies, and maintenance schedules. Monitoring plans must target identified high-risk areas, and operational procedures must prioritize stability in parameters that influence risk.

2. Risk assessments must be revisited periodically as operational experience accumulates and as system performance evolves. Changes in feed gas composition, equipment upgrades, or new operating patterns may alter risk profiles and require adjustment of mitigation strategies.

9.12 Documentation and Reporting of Risk Assessment

1. The Project Design Document must include a comprehensive risk assessment that identifies major risks, explains their relevance, and describes mitigation measures. During the monitoring phase, the developer must document any incidents, near misses, operational deviations, or corrective actions taken. These records must be included in the Monitoring Report and reviewed by VVBs.

2. The risk assessment serves as a living reference that evolves with operational learning and supports continuous improvement throughout the capture project lifecycle.

Chapter 10 - Reporting Requirements For Capture Facilities

10.1 Purpose of Reporting Under PCS

1. Reporting is the mechanism through which project developers demonstrate compliance with PCS methodological requirements and provide transparent evidence of capture system performance. While monitoring generates the raw data needed to quantify CO₂ captured and emissions produced, reporting transforms that data into a coherent narrative that allows independent reviewers, including Validation and Verification Bodies (VVBs) and the PCS Secretariat, to assess whether the project operated reliably and within defined boundaries.

2. The reporting requirements outlined in this chapter ensure that information is communicated consistently across projects, enabling comparability and strengthening the integrity of carbon units issued under PCS.

10.2 Relationship Between Reporting and Monitoring

1. Monitoring and reporting are closely linked but remain distinct functions. Monitoring involves real-time data collection and continuous operational oversight, whereas reporting involves the interpretation, documentation, and formal presentation of those results. Reporting must therefore be comprehensive, structured, and sufficiently detailed to allow verification without requiring VVBs to reconstruct operational conditions from raw datasets alone.

2. The reporting framework ensures that deviations, anomalies, energy trends, and loss events are not only recorded but also explained and contextualized. Reporting is the gateway through which monitoring data becomes verifiable evidence.

10.3 Required Components of the Capture Monitoring Report

1. The Capture Monitoring Report (CMR) is the primary document through which developers communicate capture performance during each monitoring period. It must integrate operational data, interpretive analyses, and documented evidence. Each report must include:

1

A description of operating conditions during the monitoring period.

Includes periods of stability, operational transitions, maintenance events, or abnormal conditions.

2

Quantities of CO₂ captured.

Gross captured CO₂ at the measurement point; net captured CO₂ after deducting losses; supporting evidence such as flow meter readings, purity analyses, and calculation records.

3

CO₂ stream quality data.

Purity measurements, impurity profiles, moisture levels, and descriptions of any deviations from expected stream composition.

4

Fugitive, venting, and loss accounting.

Documentation of all losses, including venting during maintenance, leaks detected through the LDMP, and emissions associated with start-up or shutdown. Each loss must include a quantitative estimate and explanation.

5

Energy use and associated emissions.

Electricity and thermal energy consumption documented using calibrated meters, with emissions calculated based on approved emission factors.

6

Incidents, anomalies, and corrective actions.

Description of abnormal events or operational deviations, with cause, response, and resolution.

7

Uncertainty analysis and data quality assurance.

Calibration results, missing data treatments, and uncertainty evaluations.

8

Mass and energy balance summaries.

A reconciled mass and energy balance to support reported quantities.

10.4 Reporting of Operational Deviations

1. Operational deviations, whether planned or unplanned, must be fully disclosed. These may include changes in feed gas composition, capture rate reductions, equipment downtime, or variations in solvent or sorbent performance. The report must explain the cause of each deviation, how long it persisted, and whether it affected the accuracy of CO₂ capture measurement.

2. If deviations resulted in off-specification CO₂, unexpected venting, or inconsistent purity levels, the report must clearly document these occurrences and quantify impacts. PCS emphasizes that transparency is more important than operational perfection; undisclosed deviations undermine trust in the reporting system.

10.5 Reporting of Maintenance and Calibration Activities

1. Maintenance activities and calibration cycles influence data availability and measurement reliability. The report must describe all planned and unplanned maintenance that affected capture performance or monitoring instrumentation. This includes solvent replacements, membrane exchanges, sorbent regeneration interventions, pump or compressor maintenance, and shutdown events.

2. Calibration activities must be reported with sufficient detail to allow VVBs to confirm proper execution. If calibration reveals drift or errors, the developer must describe how historical data were corrected or interpreted.

10.6 Reporting of Emission Factors and Energy Attribution Methods

1. Emission factors used to convert energy consumption into CO₂ emissions must be documented clearly. The report must identify the source of each emission factor, the time period it applies to, and the rationale for its selection. For grid electricity, the emission factor may vary seasonally or annually; the justification must explain why the selected factor reflects actual consumption patterns.

2. Energy attribution methods must be explained when capture and non-capture processes share utilities. The report must include the engineering logic behind any allocation method and demonstrate that it does not underestimate capture-related emissions.

10.7 Reporting of Capture Efficiency and Performance Trends

1. Capture efficiency is an important indicator of system health and stability. The report must present efficiency trends over the monitoring period and interpret any fluctuations. Declining efficiency may suggest solvent degradation, sorbent fatigue, membrane fouling, or operational instability. Conversely, improvements may result from optimization or maintenance.

2. By presenting and interpreting efficiency trends, developers demonstrate an understanding of system behavior and provide evidence of active performance management.

10.8 Reporting Requirements for Direct Air Capture (DAC) Projects

1. DAC systems have unique performance characteristics and must provide additional reporting on:

• Air flow volumes

• Sorbent regeneration cycles

• Temperature and humidity impacts

• Net removal calculations after energy emissions

1. DAC reporting must also address the heightened importance of uncertainty due to lower CO₂ concentrations in inlet air. All DAC-specific variables must be documented with sufficient granularity to enable verification.

10.9 Archiving and Data Retention Requirements

1. PCS requires that all monitoring data, calibration records, maintenance logs, venting records, and supporting calculations be retained for the full duration of the project and any subsequent verification periods. Records must be stored securely and must remain accessible to VVBs and the PCS Secretariat upon request.

2. Electronic storage systems must include backup provisions, audit trails, and safeguards against data manipulation. The integrity of archived data ensures accountability and supports long-term project evaluation.

10.10 Final Reporting and Transition to Verification

1. At the end of each monitoring period, the developer must prepare the Capture Monitoring Report and submit it through the PCS Registry. The report must be complete, internally consistent, and supported by traceable evidence.

2. VVBs will evaluate the report against monitoring data, calibration records, and operational logs. Clear structure and transparency facilitate verification and reduce the risk of non-conformities. Only after successful verification may the CO₂ quantities reported in the capture stage be integrated into the full CCS issuance cycle.

Annex A - Capture Techniques And Operating Principles

A.1 Purpose

1. Annex A provides foundational technical explanations of the operating principles behind major CO₂ capture techniques. While the PCS Capture Guidance focuses on monitoring and operational requirements, this annex offers a deeper engineering context to support understanding of system performance, stability, and measurement challenges. These descriptions help project developers articulate design choices in their Project Design Document and assist VVBs in evaluating whether system behavior aligns with established scientific and engineering principles.

A.2 Chemical Absorption Systems (Amine and Solvent-Based Capture)

1. Chemical absorption relies on the reversible reaction between CO₂ and a chemical solvent. The process typically consists of an absorber, where flue gas contacts the solvent, and a regenerator or stripper, where heat is applied to release CO₂ from the solvent. Common solvents include mono-ethanolamine (MEA), methyl-di-ethanolamine (MDEA), piperazine, or blended proprietary formulations.

2. In the absorber, CO₂ molecules react with the solvent to form bicarbonates, carbamates, or other weakly bonded species. The solvent becomes “rich” in CO₂ and is then transferred to the regenerator. Heat supplied by steam or another thermal source breaks these chemical bonds, releasing high-purity CO₂ gas and regenerating the solvent for reuse.

3. Temperature, solvent concentration, residence time, and flue gas composition all influence separation performance. Chemical absorption systems require careful control to avoid solvent degradation, foaming, or corrosion. Their operating principles allow high separation efficiency even at low CO₂ concentrations, making them suitable for power generation and industrial combustion sources.

A.3 Physical Solvent Systems

1. Physical solvents rely on the solubility of CO₂ in certain organic liquids under high pressure rather than chemical bonding. CO₂ dissolves into the solvent in an absorber at elevated pressure and is released during depressurization.

2. The behavior of physical solvents is governed by Henry’s Law, whereby solubility increases with partial pressure. This makes physical solvents particularly effective in high-pressure streams such as natural gas processing or pre-combustion syngas treatment. Unlike chemical solvents, physical solvents require little or no heat for regeneration, as pressure reduction alone is sufficient to release absorbed CO₂.

3. Because the absorption does not involve chemical reactions, these systems typically have lower energy requirements but may be less effective for dilute streams. Proper design must account for co-absorption of impurities such as hydrogen sulfide or hydrocarbons.

A.4 Solid Sorbent Systems

1. Solid sorbent capture is based on materials that selectively adsorb CO₂ from a gas stream. Sorbents may include zeolites, activated carbon, metal–organic frameworks (MOFs), or proprietary engineered materials. Adsorption occurs at specific temperature and pressure conditions, and regeneration is achieved through temperature swing adsorption (TSA), pressure swing adsorption (PSA), or vacuum swing adsorption (VSA).

2. In TSA systems, CO₂ is adsorbed at lower temperatures and released during heating. In PSA systems, adsorption occurs at higher pressure, and regeneration occurs by reducing pressure. VSA operates by applying vacuum during regeneration.

3. These systems are modular, scalable, and widely used in gas purification and emerging DAC technologies. Their performance depends on sorbent surface area, pore structure, and thermal stability. Sorbents may degrade over time due to repeated cycling or exposure to moisture or contaminants, and system design must accommodate this.

A.5 Membrane Separation

1. Membrane systems separate CO₂ from gas mixtures by allowing CO₂ to permeate through a semi-permeable membrane faster than other components. The process operates based on differences in solubility and diffusivity of gas molecules within the membrane material.

2. Separation efficiency depends on the membrane’s intrinsic selectivity, the pressure gradient across the membrane, and temperature. Polymeric membranes are common but may experience performance decline due to plasticization or chemical exposure. Inorganic membranes offer greater thermal stability but are more expensive and less widely deployed.

3. Membrane systems are compact and have fewer moving parts than solvent systems, but often require multiple stages to achieve high purity. Effective pre-treatment is essential to remove particulates, moisture, aerosols, and contaminants that may foul or degrade membranes.

A.6 Cryogenic Capture and Phase-Change Separation

1. Cryogenic separation relies on cooling gas streams to temperatures where CO₂ liquefies or solidifies. At these temperatures, CO₂ can be physically separated from non-condensable gases. The process is energy-intensive due to refrigeration requirements, but it can produce CO₂ at very high purity and is well-suited to streams with high initial CO₂ concentrations.

2. Cryogenic capture may involve staged cooling, controlled expansion, and phase separation steps. Design challenges include managing freezing of impurities, maintaining cold-chain performance, and preventing thermal shocks that may damage equipment. Cryogenic systems are often used in industrial gas processing and LNG production where cold temperatures are already present.

A.7 Oxyfuel Combustion Capture

1. Oxyfuel combustion involves burning fuel in nearly pure oxygen instead of air, producing a flue gas composed mainly of CO₂ and water vapor. Once the water is condensed, the remaining gas stream is already CO₂-rich and requires minimal further separation.

2. Producing oxygen requires an air separation unit, which significantly affects energy use. Oxyfuel systems operate at elevated temperatures and may generate impurities depending on the combustion process and oxygen purity. The principles of oxyfuel capture involve controlling combustion stoichiometry, flue gas recycling for temperature moderation, and efficient heat integration.

3. Because the CO₂ concentration is high, oxyfuel capture can yield high capture efficiencies with relatively simple conditioning steps.

A.8 Pre-Combustion Capture (Syngas and Hydrogen Production)

1. Pre-combustion capture occurs when fuels are converted into syngas through gasification or reforming. Carbon monoxide is then shifted to CO₂ through a water–gas shift reaction, producing CO₂ and hydrogen. CO₂ is captured from the high-pressure, high-concentration syngas using physical or chemical solvents, while hydrogen serves as a clean fuel or feedstock.

2. Pre-combustion systems operate under high pressure, allowing efficient solvent-based capture. The operating principles involve catalytic reactions, heat integration, and careful control of gas compositions. These systems are common in hydrogen production and integrated gasification combined cycle (IGCC) applications.

A.9 Direct Air Capture (DAC) Systems

1. DAC systems remove CO₂ directly from atmospheric air despite extremely low ambient concentrations. They rely on solvents, solid sorbents, or electrochemical processes that selectively bind CO₂ from dilute air streams.

2. DAC systems must handle large volumes of air, requiring significant fan power or passive air contact designs. Sorbent regeneration requires thermal or electrical energy, and system performance depends on humidity, temperature, and sorbent stability.

3. The operating principles behind DAC emphasize selectivity, efficient regeneration, and energy optimization. Because DAC is inherently energy-intensive, detailed monitoring and high-accuracy measurement are central to PCS assessment of DAC performance.

A.10 High-Purity Industrial CO₂ Sources

1. Some industrial processes generate CO₂ at high concentration without significant separation effort. Examples include ammonia production, ethanol fermentation, and certain hydrocarbon processing streams. Although separation requirements are minimal, conditioning, purification, and metering remain necessary to ensure compatibility with transport and storage systems.

2. These systems operate by capturing naturally produced CO₂ rather than separating it from dilute flue gas. They are typically more stable but require careful attention to impurity control and measurement accuracy.

A.11 Summary of Operating Principles Across Technologies

1. While the technologies described in this annex differ significantly in their science and engineering, they share several common operating principles:

• Each requires control of thermodynamic conditions to maintain stable separation performance.

• Each benefits from predictable feed gas conditions and suffers performance degradation under unstable conditions.

• Each must manage impurities and moisture to ensure downstream compatibility.

• Each requires reliable monitoring systems to track flow, purity, temperature, pressure, and energy use.

1. Understanding these principles reinforces the need for rigorous, transparent MRV practices under PCS.

Annex B - Monitoring Equipment Specifications

B.1 Purpose

1. Annex B defines the technical specifications for monitoring equipment used in CO₂ capture systems under PCS. These specifications provide reference standards for project developers, operators, and Validation and Verification Bodies (VVBs) to ensure that measurements are accurate, traceable, and reliable throughout the project lifecycle.

2. The equipment listed here represents the preferred or acceptable instruments typically used in industrial gas measurement and CCS applications. Projects may use alternatives only if they meet or exceed the performance criteria established in this annex.

B.2 Flow Measurement Equipment

1. Flow measurement is one of the most critical components of CO₂ capture MRV. Instruments must provide high accuracy, maintain stability under varying pressures and temperatures, and operate reliably in CO₂-rich gas environments. The choice of flow meter depends on flow regime, pipeline conditions, and required accuracy.

Table B-1 — CO₂ Flow Measurement Devices and Specifications

Instrument Type	Typical Accuracy	Suitable Flow Regime	Installation Requirements	Notes for PCS MRV
Coriolis Mass Flow Meter	±0.1–0.2% of reading	Single-phase CO₂-rich streams; stable density	Minimal straight-run; avoid vibration; temperature compensation	Preferred PCS instrument due to high accuracy and direct mass measurement
Ultrasonic Flow Meter (Transit-Time)	±0.5%	Clean, conditioned CO₂; medium-to-large pipelines	Straight-run upstream/downstream; avoid pulsating flow	Suitable when Coriolis meters are impractical due to pipe size
Ultrasonic Flow Meter (Clamp-On)	±1–2%	Temporary or supplemental monitoring	Depends on pipe material and thickness	May be used for verification or redundancy
Differential Pressure Meter (Orifice/Venturi)	±1–3%	Stable gas flow; lower accuracy applications	Requires temperature and pressure correction; long straight-run	Acceptable only when higher-accuracy devices cannot be used
Vortex Meter	±1%	Clean gas flow; moderate pressure	Sensitive to vibration; requires stable flow	Not preferred, but allowed with justification

1. Coriolis meters remain the standard for PCS capture MRV because they directly measure mass flow and require minimal external correction. Ultrasonic meters may be used when pipeline diameter exceeds the feasible range for Coriolis units. Differential pressure meters must be justified due to higher uncertainty.

B.3 Purity and Impurity Monitoring Equipment

1. Purity measurements determine the percentage of CO₂ in the conditioned gas stream and form the basis for net CO₂ accounting. Impurity analysis is required to determine suitability for transport and storage.

Table B-2 — CO₂ Purity and Impurity Monitoring Equipment

Parameter	Instrument Type	Detection Range	Calibration Requirements	MRV Role
CO₂ purity	Gas chromatograph (GC)	0–100%	Calibration gases traceable to standards	Determines net CO₂ content
Moisture (H₂O)	Chilled mirror hygrometer	ppmv to %	Regular drift checks; temperature-stable environment	Critical for transport safety
Moisture (alternate)	Aluminum oxide (AlOx) sensor	ppmv	Quarterly calibration	Acceptable for continuous monitoring
Oxygen (O₂)	Electrochemical sensor or GC	ppmv–%	Temperature compensation; monthly verification	Impurity accounting and corrosion assessment
Nitrogen (N₂)	GC	% range	Use of certified calibration standards	Influences density and mass calculations
Sulfur species (SO₂, H₂S)	GC with sulfur detector	ppmv	Frequent calibration due to sensitivity	Required when sulfur impurities are expected
Hydrocarbons	FID-GC or IR analyzer	ppmv	Multipoint calibration	Relevant for storage compatibility

1. Purity and moisture measurement must reflect actual CO₂ composition at the measurement point. Instruments must be located downstream of conditioning systems to avoid distorted measurements due to phase instability.

B.4 Pressure, Temperature, and Density Measurement Equipment

1. Since density is required for converting volumetric flow to mass flow, accurate pressure and temperature measurements are essential. These instruments must be installed close to the flow meter.

Table B-3 — Pressure, Temperature, and Density Measurement Specifications

Parameter	Instrument Type	Accuracy Requirement	Installation Notes
Pressure	Digital pressure transmitter	±0.1% full scale	Install near flow meter; temperature-compensated
Temperature	RTD (Resistance Temperature Detector)	±0.1°C	Shield from external heat; ensure proper immersion
Density (derived)	Equation of state using P & T	Based on accuracy of P & T	Must use validated thermodynamic models

1. Density calculations must rely on equations of state suitable for CO₂ mixtures, such as Peng–Robinson or Span–Wagner. P&T sensors must have synchronized timestamps for accurate data pairing.

B.5 Energy Measurement Equipment

1. Energy use drives the emissions associated with capture processes. Accurate measurement of both electrical and thermal energy is required.

Table B-4 — Energy Measurement Devices

Energy Type	Instrument	Accuracy Requirement	Installation Notes	PCS Requirement
Electricity	Revenue-grade meter	±0.2%	Isolated feed for capture system preferred	Mandatory
Steam	Vortex or mass flow meter	±1–2%	Must monitor both supply and condensate return	Required for regeneration energy
Natural Gas	Ultrasonic or turbine meter	±1%	Correct for temperature and pressure	Required when fuel is used for heat
Compressed Air / Blower Power	Electrical metering	±0.2%	Must separate capture vs. plant loads	Required for DAC and membrane systems

1. Energy meters must be placed within the defined capture boundary to avoid double-counting or misallocation.

B.6 Calibration Standards and Minimum Frequencies

1. Calibration must occur frequently enough to ensure that drift does not materially affect measurement accuracy.

Table B-5 — Calibration Intervals and Requirements

Instrument	Minimum Calibration Frequency	Required Documentation
Flow meters	Annually or per manufacturer	Certificate, drift test
Gas chromatographs	Monthly or per drift	Calibration gas logs
Moisture analyzers	Quarterly	Sensor health checks
Pressure transmitters	Annually	Reference comparison report
Temperature sensors (RTDs)	Annually	Calibration certificate
Energy meters	Every 1–2 years	Verification test

1. If calibration reveals unacceptable drift, the operator must assess whether historical data require adjustments.

B.7 Installation and Operational Considerations

1. Proper installation ensures accurate, stable measurements. The following table summarizes typical requirements:

Table B-6 — Installation Requirements for Major Instruments

Instrument	Key Installation Considerations
Coriolis meters	Avoid vibration; maintain proper support; ensure single-phase flow
Ultrasonic meters	Provide straight-run pipe; avoid multiphase flow; maintain clean internal surfaces
GC sampling ports	Ensure isokinetic sampling; prevent condensation; stainless steel sample lines
Moisture analyzers	Locate downstream of dehydration; avoid cold spots
Pressure sensors	Minimize impulse line length; prevent liquid accumulation
RTDs	Install in thermowells; ensure immersion depth meets manufacturer guidance

1. Installation quality is as important as instrument quality. Even high-accuracy instruments produce unreliable data if installed incorrectly.

B.8 Recommended Instrumentation by Capture Technology

1. To support technology-specific monitoring needs, PCS recommends the following instrumentation by capture system:

Table B-7 — Recommended Instrument Set by Technology Type

Capture Technology	Critical Instruments	Special Considerations
Amine/solvent systems	Flow meter, purity analyzer, moisture sensor, solvent loading instrument	Sensitive to temperature instability and solvent degradation
Physical solvent systems	Flow meter, pressure sensors, impurity analyzer	Must monitor co-absorption of acid gases
Solid sorbent systems	Breakthrough detectors, thermal sensors, CO₂ purity analyzer	Must track regeneration cycle stability
Membrane systems	Pressure differential sensors, permeate/retentate analyzers	Fouling detection important
Cryogenic systems	Temperature sensors, dew-point analyzers, flow meter	Must maintain ultra-low temperature calibration
DAC systems	Air-flow meters, regeneration heat meters, CO₂ purity analyzer	Must account for dilute inlet CO₂ concentrations

1. This table ensures each technology receives proper instrumentation aligned with its operating principle and MRV sensitivity.

B.9 Data Output, Resolution, and Integration Requirements

1. Monitoring instruments must provide data at a resolution compatible with PCS reporting requirements. Data must be stored in digital format, time-synchronized, and archived securely. Operators must ensure that data from flow, pressure, temperature, and purity instruments can be integrated to compute mass flow accurately.

2. PCS encourages redundancy for critical measurements to reduce uncertainty.

B.10 Summary of Equipment Requirements

1. The equipment specified in this annex forms the technical backbone for PCS-compliant CO₂ capture monitoring. Adherence to these specifications ensures that reported captured quantities are credible, traceable, and verifiable, strengthening environmental integrity across the entire CCS chain.

Annex C - Performance Calculation Examples And Standardized Templates

C.1 Purpose Of Annex C

1. Annex C provides practical tools that support implementation of the PCS Capture Guidance. It includes:

• Example calculations for determining captured CO₂ mass

• Example calculations for purity corrections

• Templates for mass and energy balances

• Templates for operational logs, venting logs, and calibration summaries

• Illustrative uncertainty calculations

1. These examples do not replace project-specific engineering, but they demonstrate the required structure and logic expected in PCS-compliant monitoring and reporting.

C.2 Example Calculations

C.2.1 Example Calculation of Net Captured CO₂

Step 1 — Measure volumetric flow at actual conditions

Assume a flow meter provides:

• Volumetric flow rate: 3,000 Nm³/hour

• Temperature: 40°C

• Pressure: 15 bar

Step 2 — Convert to mass using density at actual conditions

Using a validated equation of state (e.g., Span–Wagner):

• Density of CO₂ at 40°C and 15 bar = 100 kg/m³

• Gross CO₂ mass flow = 3,000 Nm³/hr × 100 kg/m³ = 300,000 kg/hr

Step 3 — Apply purity correction

Measured purity (from GC): 97% CO₂

Adjusted mass flow = 300,000 kg/hr × 0.97 = 291,000 kg/hr

Step 4 — Subtract fugitive and venting losses

Total losses during the hour:

• Pipeline blowdown: 1,200 kg

• Solvent slip emissions: 600 kg

• Small leak estimated: 200 kg

Total losses = 2,000 kg

Step 5 — Net captured CO₂

Net = 291,000 kg – 2,000 kg = 289,000 kg/hr (net captured CO₂)

C.2.2 Example Purity Adjustment Table

Table C-1 — Purity Adjustment Example

Component	Concentration (%)	Contribution to Mass Flow
CO₂	97.0	Counted
N₂	1.5	Subtracted
O₂	0.5	Subtracted
H₂O	1.0	Subtracted

Net purity correction factor = 0.97

C.2.3 Example Efficiency Calculation (Chemical Absorption)

Input:

Flue gas CO₂ concentration = 12%

Flue gas flow = 500,000 Nm³/hr

CO₂ in treated gas (stack) = 1.5%

CO₂ removed = (12% – 1.5%) × 500,000 Nm³/hr = 0.105 × 500,000 = 52,500 Nm³/hr removed

Capture efficiency = 52,500 / (0.12 × 500,000) = 52,500 / 60,000 = 87.5%

C.2.4 Example Energy Emissions Calculation

Electricity consumption = 12,000 kWh/day

Grid emission factor = 0.55 tCO₂/MWh

Electricity emissions = 12 MWh × 0.55 = 6.6 tCO₂e/day

Steam consumption = 50 GJ/day

Emission factor = 0.056 tCO₂/GJ

Steam emissions = 50 × 0.056 = 2.8 tCO₂e/day

Total = 9.4 tCO₂e/day

C.2.5 Example Uncertainty Propagation

If:

• Flow meter uncertainty = ±0.15%

• Purity uncertainty = ±0.3%

• Temperature/pressure uncertainty contributes = ±0.1%

Total uncertainty (combined using root-sum-square):

√(0.15² + 0.3² + 0.1²) = √(0.0225 + 0.09 + 0.01) = √0.1225 = ±0.35%

PCS requires reporting uncertainty values when >0.5%, but documenting all uncertainties is recommended.

C.3 Standardized PCS Templates

C.3.1 Template: Mass Balance Summary

Table C-2 — Mass Balance Template

Parameter	Value	Method / Instrument	Notes
Gross CO₂ outflow		Flow meter	Before purity correction
CO₂ purity		GC analysis	Applied to mass
Adjusted CO₂ mass		Calculation	Purity corrected
Venting losses		Logs	Must include timestamps
Fugitive emissions		LDMP system	Direct or estimated
Net CO₂ delivered		Calculation	Used for PCS issuance

C.3.2 Template: Energy Balance Summary

Table C-3 — Energy Balance Template

Energy Type	Quantity	Instrument	Emission Factor	Resulting Emissions
Electricity		Meter
Steam		Flow meter
Fuel use		Gas meter
Other energy
Total emissions

C.3.3 Template: Venting and Fugitive Emissions Log

Table C-4 — Venting Log Template

Date & Time	Type of Release	Estimated CO₂ Mass (kg)	Measurement / Estimate Method	Cause	Corrective Action

C.3.4 Template: Calibration and QA/QC Summary

Table C-5 — Calibration Summary Template

Instrument	Calibration Date	Standard Used	Result	Adjustment Needed	Certification Reference

C.3.5 Template: Capture Efficiency Summary

Table C-6 — Efficiency Reporting Template

Parameter	Value	Source / Instrument	Notes
Inlet CO₂ concentration		Gas analyzer
Outlet CO₂ concentration		Stack analyzer
Gas flow rate (inlet)		Flow meter
Calculated captured CO₂
Capture efficiency (%)		Calculation

C.3.6 Template: Operational Summary for Monitoring Report

Table C-7 — Operational Summary Template

Operational Aspect	Summary Description	Evidence / Logs	VVB Notes
System uptime
Maintenance events
Deviations/anomalies
Corrective actions
Monitoring system stability

C.4 Guidance For Using Templates

1. Templates in this annex are intended to support standardized reporting across all PCS capture projects. Developers may expand or adapt the templates as needed, but they must ensure that:

• All required PCS data fields remain present

• Calculations are transparent and traceable

• All assumptions, formulas, and methodologies are documented

• Uncertainty is addressed appropriately

1. Independent verification.

Annex D - Glossary And Technical References For Capture Systems

D.1 Purpose

1. Annex D provides definitions of key terms used throughout the PCS Capture Technical Guidance and lists the scientific and engineering references that support the guidance. The glossary is intended to standardize terminology among project developers, operators, VVBs, and the PCS Secretariat. The reference section identifies authoritative sources that inform the technical expectations outlined in this document.

D.2 Glossary of Capture-Related Terms

• Amine Degradation: Chemical breakdown of amine solvents due to reaction with impurities, oxygen, heat, or other contaminants, often forming heat-stable salts and reducing solvent capacity.

• Breakthrough: The point at which CO₂ begins to appear in the treated gas stream of a sorbent or membrane system because the material or module is saturated or performance has degraded.

• Capture Efficiency: The percentage of CO₂ removed from the source gas relative to its original concentration or mass flow.

• Chilled Mirror Hygrometer: An instrument that measures moisture content by cooling a mirror until condensation forms. Used for accurate CO₂ moisture readings.

• Chemical Absorption: CO₂ capture through reversible reaction with chemical solvents such as amines.

• Compression Boundary: The interface where CO₂ leaves the capture system and enters the compression or transport system. This is the PCS measurement point.

• Dehydration: Removal of moisture from CO₂ after capture to prevent corrosion or hydrate formation in transport systems.

• Direct Air Capture (DAC): A capture technology that removes CO₂ directly from ambient air using sorbents, solvents, or chemical processes.

• Fugitive Emissions: Unintentional releases of CO₂ from valves, seals, equipment leaks, or other incidental pathways in the capture system.

• Gas Chromatograph (GC): An analytical instrument used to measure CO₂ purity and impurity composition in gas streams.

• Heat-Stable Salts: Compounds formed when amines react irreversibly with contaminants such as SO₂ or NOₓ. They reduce solvent performance and may increase corrosion.

• Mass Flow Meter: An instrument, such as a Coriolis meter, that measures mass directly rather than volume, providing highly accurate CO₂ flow measurement.

• Membrane Separation: A capture technology based on selective permeability of gases through a semi-permeable membrane.

• Moisture Analyzer: An instrument that measures water vapor concentration in CO₂, essential for evaluating transport and storage readiness.

• Off-Spec CO₂: CO₂ that does not meet required purity, moisture, or impurity thresholds for downstream transport or geological storage.

• Physical Solvent: A solvent that absorbs CO₂ through physical dissolution rather than chemical reaction.

• Pressure Swing Adsorption (PSA): A sorbent-based system where CO₂ is adsorbed at high pressure and released when pressure is lowered.

• Purity Correction: The adjustment applied to measured CO₂ flow to account for non-CO₂ components in the captured gas stream.

• Regeneration: The process by which solvents or sorbents release captured CO₂ and are restored for reuse, typically through heat, pressure changes, or vacuum.

• Solvent Slip: Carryover of solvent vapor or aerosols into the treated gas stream or vent, contributing to emissions and potential environmental impacts.

• Span–Wagner Equation of State: A thermodynamic model used to calculate CO₂ density under varying temperature and pressure conditions.

• Temperature Swing Adsorption (TSA): A sorbent regeneration method where CO₂ is released by heating the sorbent.

• Uncertainty Propagation: The calculation of overall measurement uncertainty by combining the uncertainties of individual measurement components.

• Venting: Intentional release of CO₂ during maintenance, safety procedures, or process transitions.

D.3 Scientific and Technical References

1. The following references underpin the technical and engineering foundations of the PCS Capture Guidance:

2. ISO 27913:2016 - Carbon dioxide capture, transportation and geological storage - Pipeline transportation systems.

3. ISO 27916:2019 - Carbon dioxide capture, transportation, and geological storage - Quantification and verification.

4. IEA Greenhouse Gas R&D Programme (IEAGHG) Technical Reports.

5. IPCC Special Report on Carbon Dioxide Capture and Storage (2005).

6. IPCC 2006 and 2019 Refinement Guidelines for National GHG Inventories.

7. CSLF (Carbon Sequestration Leadership Forum) Best Practice Manuals.

8. U.S. Department of Energy (DOE) NETL Reports.

9. ASHRAE and ISA Instrumentation Standards.

10. ASTM and API Standards for Gas Measurement.

11. Peer-Reviewed Journals (Energy Procedia, International Journal of Greenhouse Gas Control, Chemical Engineering Science).

D.4 Use of Glossary and References in PCS Verification

1. The glossary provides a reference framework for consistent terminology across all capture projects. The technical references inform engineering expectations and enable VVBs to evaluate whether systems comply with accepted scientific principles. Developers are encouraged to cite these references when describing system design, monitoring procedures, and calculation methods in their Project Design Documents and Monitoring Reports.