Industry Guidelines for Setting the CO₂ Specification in CCUS Chains

This Introduction to the guidelines will guide you through the suite of work packages which cover the full CCUS value chain, from capture of industrial sources of CO₂ and transportation via different options through to geological storage. Additional key work packages are included which underpin the entire CCUS chain, including Thermodynamics, Reaction Chemistry and Materials & Corrosion.

Key contents of this report include:

• The objective of the JIP and introduction to the team of industry and research contributors.
• A summary of the suite of JIP Work Packages.
• A step-by-step methodology for setting a CO₂ Specification with worked case study example.

The Thermodynamic Work Package provides a comprehensive and systematic analysis of the thermodynamic impact of impurities within CO₂ and offers guidelines for selecting the most appropriate equations of state and benchmark data for modelling CO₂ systems. The work package also identifies the knowledge gaps and the potential risks associated with the lack of data and inaccurate modelling.

The work package uses the models developed at Heriot Watt University in their thermodynamics tool HWPVT. These models include cubic, multiparameter, and hybrid equation-of-states, as well as models for transport properties and solid formation. These models are considered as the state-of-the art for CO₂ thermodynamics.

The work package has gathered the experimental data available in the literature for CO₂ binary mixtures and some multicomponent mixtures, and compares them with the predictions of the HWPVT models. The results show the accuracy and limitations of different models for different properties and impurities. The work package also provides pseudo-experimental data that can be used by end-users to check the quality of their own models.

Key contents of the Thermodynamics Report includes:

• Generation of a representative list of impurities that can exist in CO₂ streams, categorized by their nature and behaviour.
• 1.5 million experimental data points were gathered from literature for over 30 CO₂ impurities and a gap analysis was performed on the availability of experimental data.
• Error margins between an advanced modelling tool and available experimental data is reported.
• Guidelines for selecting the most appropriate modelling approach.

Impurities within CO₂ streams can chemically react with their environment and with each other to create products which can adversely affect CCUS design and operation. Some reactions may produce products which cause plugging and injectivity issues, whilst others may impact material integrity through corrosion and cracking.

This Chemical Reactions Report was developed with expertise from IFE and key contents include:

• Identification of the main reactions occurring within CCUS chains and categorization into acid formation, sulphur producing and solid forming reactions.
• A review of solubility and precipitation of impurities and reaction products in dense and gaseous CO₂ phases, such as water, glycols, alcohols, sulphur, acids, ammonium carbamate, and salts.
• A summary of published data and available reaction models.
• A summary of published CO₂ specifications and recommendations comparing the maximum concentrations for various impurities, including H₂O, H₂S, CO, O₂, SO_X, NO_X, and NH₃.
• Suggestions for further research to address current knowledge gaps.

CO₂ streams in CCUS projects can originate from various sources, such as power plants, industrial emitters, and natural gas production and may use different capture technologies, such as pre-combustion, post-combustion, and oxyfuel. These sources and technologies can result in different types and levels of impurities in the CO₂, such as water, oxygen, nitrogen, sulphur and hydrogen compounds. These impurities can affect the phase behaviour, corrosivity, and integrity of the materials used within the CCUS chain.

The Materials & Corrosion work package guidelines outlines the main challenges and recommendations for materials selection and corrosion control for each element of the CCUS chain, based on the available standards, guidelines, and research data.

These Materials & Corrosion guidelines were developed with expertise from Shell and key contents include:

• Impact of impurities on low temperature embrittlement and running ductile fracture in pipelines.
• Selection of corrosion resistant alloys and non-metallic materials for specific conditions.
• Controlling the CO₂ specification to prevent acid and sulphur drop-out.
• Applying a risk-based approach and integrity operating windows for each corrosion loop, and conducting testing and monitoring of the CO₂ composition and corrosion rates.
• Identification for gaps in current knowledge and guidance for future research.

Safety and environmental management considerations are paramount throughout the CCUS chain. This work package explores the effects impurities may have on potential CO₂ releases and dispersion and to provide guidance on effective modelling and risk review.

This Safety & Environment report was developed with support from DNV and key contents include:
• A review of CO₂ exposure safety limits and threshold data applied to occupational health and safety assessment worldwide and the impact of impurities on CO₂ toxicity and safety thresholds.
• A review of consequence and risk-based assessment methodologies and tools for modelling CO₂ releases, including the application use of safety distances and exclusion zones as safeguards for CCUS infrastructure.
• A demonstration of the effect of impurities on CO₂ dispersion modelling using the DNV PHAST model for different environmental conditions and release scenarios.

CO₂ streams from different industries have a wide variance in CO₂ concentration and can be accompanied by a range of different impurities.

The Capture & Conditioning work package provides guidance on the types of impurities expected in CO₂ streams and their impact on carbon capture technologies and presents processes typically used to remove impurities from CO₂ streams.

Key contents of the report include:

• The range of impurities which may be anticipated from different industry sources.
• A review of flue gas impurity measurement methods.
• A review of the main carbon capture technologies.
• The impact of impurities on the performance of CO₂ capture and conditioning processes.
• A review of data from test facilities such as Technology Centre Mongstad on expected impurity levels from CO₂ capture plants.
• Feedback from Capture Licensors on modelling software limitations and prediction of impurities in CO₂ product streams.
• A review of impurity removal technologies.
• The impact of impurities on liquefaction processes.
• A decision flow chart for CO₂ purification and liquefaction requirements.
• A flow chart methodology for selection of capture and & conditioning processes.
• Gaps in knowledge and guidance for future research.

Compression and pumping are essential for pressurising CO₂ for processing and transport and ultimately to meet the injection pressures required for geological storage. Compression and pumping cover a range of CO₂ phases from liquid and vapour through to supercritical conditions. Impurities can directly affect the thermodynamic and physical properties of CO₂ and can impact materials and seal selection.

The Compression & Pumping work package explores the impact of impurities on compression and pumping equipment design and operation.

Key contents of the report include:

• An introduction of the use of pumps and compressors across the CCUS chain.
• A review of the non-ideal behaviour of CO₂ and the impact of impurities on the design and performance of rotating equipment.
• A discussion on the factors that influence compressor and pump design and selection, such as pressure ratio, interstage cooling, seal type, material selection and operating point.
• Addition of case studies to demonstrate the impact of impurities on CO₂ pumping and compression.

Confident measurement and control of CO₂ through the CCUS chain relies on traceably accurate and reliable metering and sampling. Impurities present in the CO₂ stream can affect this accuracy and understanding the precise composition, nature and the consequences of impurities present is important for regulatory reporting, custody transfer, commercial allocation, process control and storage measurement, monitoring and verification (MMV).

The Metering & Sampling work package provides a detailed discussion of the various available metering technologies and suitable analysis techniques (online and offline) applicable for the various impurities present in the CCUS gas streams.

The Metering report was prepared with support from TÜV SÜD National Engineering Laboratory (NEL). Key contents include:

• Flow measurement upstream of capture plant: The report describes the direct and indirect methods for measuring the mass of CO₂ entering the capture plant, and the techniques for determining the biogenic fraction of the captured CO₂.
• Flow measurement downstream of capture plant: The report discusses the design considerations and the available technologies for measuring the flow of CO₂-rich streams downstream of the capture plant, and the quality assurance requirements for accurate and reliable measurement.
• Flow meter calibration strategies: The report explores various calibration strategies for flow meters, such as proving using process medium, using transferrable laboratory medium, and non-flow calibration methods, and their advantages and limitations.
• Standards and regulations for CCUS measurements: The report summarises the existing standards, guidelines and regulations and identifies the gaps and challenges that need to be addressed to facilitate the development and implementation of CCUS projects.

• Sampling locations: Identification of appropriate sampling locations across the CCUS chain including additional points that may be required for regulatory, fiscal, or operational purposes.
• Sampling methods: A review of direct and indirect sampling methods for CO₂ streams across the CCUS chain. It also provides guidance on general considerations for effective sampling.
• Analysis methods: A review of techniques for online and offline analysis of CO₂ impurities, such as gas chromatography, liquid chromatography, mass spectrometry, spectroscopy, and sensors. It also recommends the suitable techniques for different impurities based on their concentration range, sensitivity, selectivity, and performance criteria.

The Pipeline Transport work package discusses how the presence of impurities can affect phase behaviour, water solubility and hydrate formation of CO₂ streams, and how these factors can influence the design and operation of CO₂ pipelines.

The report was technically supported by Fluxys and key contents include:

• A review and comparison of applicable codes and standards on CO₂ pipeline design and identification of gaps and challenges.
• The impact of impurities on the pipeline operating envelope and management of two-phase CO₂ transport.
• Suitability of repurposing existing pipelines and umbilicals for CO₂ transmission in the presence of different impurities.
• Material selection and corrosion management: Guidance on selecting materials for CO₂ pipelines, considering the corrosion and cracking risks associated with different impurities and conditions. It also recommends corrosion monitoring and mitigation strategies for ensuring long-term integrity.
• Brittle and ductile fracture propagation and arrest in CO₂ pipelines, and the effects of hydrogen impurities on the fracture toughness and fatigue performance of pipeline materials. It includes methods for fracture control assessment and material qualification.
• Pre-commissioning and operation: Best practices for pre-commissioning, line-filling, venting, and managing off-specification fluid in CO₂ pipelines. It also highlights the challenges and uncertainties involved in these processes and the need for further research and development.

Impurities present in CO₂ can affect shipping operations through their impact on phase behaviour, solubility and potential for chemical reactions affecting the material integrity and solid formation.

The Ship Transport work package explores the current knowledge of the impact of impurities with respect to corrosion, cargo handling and management.

The report was technically supported by DNV and key contents include:

• A review of existing industry guidelines and standards for CO₂ shipping and highlights ongoing initiatives by IMO, SIGTTO, and ZEP to develop guidance for CO₂ ship and terminal operators.
• A discussion of publicly available CO₂ specifications for ship-based transport.
• A discussion on the current practice and specifications for ship-based transportation of liquified gases and the implications of impurities to the design and operation of CO₂ carriers.
• A discussion on the considerations on shipping of CO₂ streams: including CO₂ transport conditions, material selection for CO₂ applications and the implications of impurities to the design and operation of CO₂ carriers.
• The report also identifies knowledge gaps and recommends areas for further research such as impurity solubility limits, potential chemical reactions and acid drop-out at low temperatures.

The Geological Storage work package explores the physical and chemical impacts of impurities within reservoirs, including the effects on capacity, injectivity and integrity of the storage complex.

This work package/report was supported with input from NGI and IFE and key contents include:

• Review of geological impacts from CO₂ impurities, such as enhanced mineral dissolution or precipitation, changes in CO₂ properties, interfacial tension, phase boundaries, microbial activity, storage performance and particulates. A risk impact summary table for each of the impurities is included.
• Recommendations to storage asset owners to conduct a system and supply chain impurity review, a system modelling of CO₂ properties and phase behaviour, and laboratory and pilot trials of representative systems to determine the optimal CO₂ specification for their reservoirs.
• A review of existing standards and guidelines for setting CO₂ composition for geological storage and identification of knowledge gaps and areas for further work research, including guidance on CO₂ contaminants, the variability of CO₂ composition along the CCUS chain, the site-specific characteristics of the reservoir and the caprock, and the long-term behaviour and interactions of CO₂ impurities in the subsurface.

To meet a CO₂ specification for a CCUS chain may require the removal or reduction of impurities. Minimising the cost of additional conditioning is a key part of providing a safe and cost effective CCUS chain. This Economics work package provides guidelines for calculating the levelized cost of CO₂ abatement (LCOA) for different capture and impurity removal technologies and identifies several factors that can influence the LCOA of a CCUS project.

Also provided are order of magnitude costs and LCOA data for some of the main impurity removal technologies, such as dehydration, oxygen removal, cryogenic distillation, flue gas desulphurisation, selective catalytic reduction, hydrogen sulphide removal, and mercury removal. Trade-offs between the cost of impurity removal and the cost of designing the CCUS system to tolerate the impurity are also discussed.