Overcoming challenges in CCUS operations
By Amy Loi, Director at Emerson Automation Solutions
Monday, 01 August, 2022
Carbon capture, utilisation and storage (CCUS) is the process of capturing carbon dioxide (CO2) emissions at the source, or directly from the air, and preventing them from entering the atmosphere. Once captured, CO2 is then purified, liquefied and transported to a suitable storage location for long-term isolation from the atmosphere or utilised in a variety of industrial products.
The process of capturing carbon dioxide has been used within gas processing for decades to remove CO2 from natural gas to improve purity. Since the 1970s, captured CO2 has been injected into oil fields and utilised to enhance oil recovery. In more recent times, capture technology has been successfully coupled with underground injection and sequestration of CO2.
Emerson has decades of experience in engineering, operating and optimising industrial facilities, providing the foundation for its expertise in CCUS. Emerson understands the unique challenges posed by the needs of CCUS operations.
In Australia, Emerson has been involved in a major carbon capture project, working with the engineering contractor and end user from the early-stage front-end engineering design (FEED) stage to follow best practices in providing instrumentations required in different sections of the plant for critical measuring points and applications, while also enabling full automation of the plant.
The deployment of carbon capture and storage involves substantial capital and operational costs, presenting challenges to its commercial viability:
- Cost of implementation and operation: The upfront capital investment for capture technology, transport pipelines and geological storage is high, and significant energy and water usage is required to capture and compress the CO2.
- Transportation challenges: New infrastructure is required to safely carry liquefied CO2 to storage or utilisation sites, and significant energy is also required to compress the CO2 and to maintain high pressure and low temperature throughout the pipelines.
- Custody transfer: Reliable methods are needed to precisely measure large volumes of CO2 transferred between producers and consumers, as well as for reporting carbon tax credits and regulatory compliance.
Emissions challenges: Impurities in the CO2 stream, including water, can result in dangerous leaks and explosions as the compressed fluid rapidly expands to a gas.
Accurate instrumentation of the entire CCUS process is imperative to maintain safety and minimise operational costs.
The carbon capture process
Post-combustion amine-based absorption is the most mature carbon capture process. It consists of an absorber, where a chemical solvent captures CO2 from the flue gas, followed by a stripper where the chemical solvent is regenerated and the CO2 is extracted.
CO2 capture efficiency is dependent on the solvent circulation rate. By increasing the circulation rate, the energy required for the stripper reboiler is increased. There is a trade-off between the capture efficiency and energy cost to regenerate the solvent. The greatest challenge is to meet the targeted CO2 capture rate in an efficient manner.
Liquefaction is an essential process for long distance transportation of CO2 and consists of a series of compressor stages and cooling. Efficiency of the liquefaction process depends on reliable measurement and control. CO2 must be compressed to a pressure between 1,500 and 2,200 pounds per square inch (psi) for pipeline transportation. Compressors are key assets used across all phases of CCUS, with unexpected failures resulting in capacity outage, equipment damage, excessive maintenance and costs, and scheduling delays.
Maintaining CO2 in its liquid state is critical, but it has proven to be difficult. CO2 purity is important to maintaining a single phase without requiring extra energy. Impurities and humid conditions can cause the formation of dry ice, which result in corrosion and potential leaks.
Loss of containment
A leak, as a result of corrosion and erosion, is a significant concern during all stages of the CCUS process. In an amine carbon capture unit, carbonic acid attack is possible where water vapour condenses in the presence of CO2. Two-phase flow at the feed to the stripper also results in erosion concerns. Sheer rates, turbulence and steam velocities are also key for corrosion and erosion control. Within liquefaction, water content in CO2 can also lead to corrosion-based leaks and must be controlled.
CCUS Instrumentation Solutions
As for any industrial process, the success of a CCUS project depends on the accurate measurement of critical parameters throughout the process.
Accurate flow and phase measurement
At all points in the CCUS process, accurate measurement of the flow and density of the CO2 is essential. Volumetric flow measurement will be difficult due to the changes in CO2 phase and density. Direct mass flow measurement is the best option at these critical measuring points. Emerson’s portfolio of mass flow devices using Coriolis metering technology provides reliable CO2 measurement data in critical applications throughout the capture process.
The Coriolis meter’s ability to measure multiple variables, such as mass flow, density, temperature, drive gain (an indicator of phase fraction conditions) means that it is possible for these meters to continue measuring with entrained liquids in gas. This type of measurement works by combing data from the meter with readily available process variables, such as density of liquid and gas at standard conditions. It is possible to detect the presence of entrained water in the CO2 stream, so that action can be taken to mitigate the risk of corrosion.
In the amine unit, Coriolis density meters also help to automate lean amine concentration measurement to determine solvent circulation rate to achieve the desired capture efficiency at the lowest cost.
Emerson’s Micro Motion high-pressure Coriolis meters work reliably at the required pressure and no straight pipe run is required. This results in a compact custody metering skid, reduced engineering complexity and lower materials cost in the building of the CCUS system. The integrated metering skid complies with international custody transfer standards and has the accuracy suited for carbon credit trading purposes.
Throughout the entire process of carbon capture, liquefaction and transport, temperature is a key property of the CO2 that must be managed. Traditionally, accurate measurement of temperature requires the installation of thermowells into the process fluid streams in order to bring the temperature sensor in contact with the fluid; however, this method of measurement is complex to design and install, and increases the risk of process leaks — potentially defeating the purpose of a CCUS project.
Emerson’s Rosemount X-well Technology provides an accurate, reliable and non-intrusive temperature measurement at a lower cost while reducing the risk of process leaks by making it possible to achieve accurate process temperature data without the need for thermowell or process penetration. Using a thermal conductivity algorithm with an understanding of the conductive properties of the temperature measurement assembly and piping, this surface temperature sensor solution accurately measures internal temperature. This ensures the efficiency and safety of the CCUS process and the proper state of gases and liquids are maintained during processing, transport and storage.
Depending on the process from which the CO2 is being captured, various types of impurities other than water may be present in the gas stream.
Concentration and composition measurement of the CO2 purity and its impurities during the carbon capture process as well as further down the value chain are also important. Emerson’s gas analysers based on Quantum Cascade Laser technology offer fast, high-resolution spectroscopy measurements that provide near-live data and trend information for operators. This visibility into the process allows operators to take quick action if the impurity levels exceeded the required data set points.
Carbon capture success through automation
In the Australian CCUS project, Emerson was able to provide, along with critical instrumentation technology, the complete automation solution for the successful implementation of carbon capture, utilisation and storage.
Emerson’s advanced automation technologies, designed specifically to monitor and control the CCUS process, have helped the Australian CCUS project to ensure operational certainty by delivering advanced control, increased process visibility and actionable information for improved decision-making.
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