S. HARRIS, Emerson, Longmont, Colorado
Carbon dioxide (CO2) is emitted by various sources, from coal-fired power plants to internal combustion engines, which provide the energy our lives depend on. It has few uses by itself since it does not burn and is chemically inert, but it is the most significant contributor to our climate crisis. Consequently, with the technologies available today, one of the best solutions at the scale needed for global impact is carbon capture and storage (CCS), where CO2 is captured, compressed and forced into the ground, where it stays.
This is already happening in many areas globally. The Global CCS Institute and International Energy Agency (IEA) monitor new projects in all stages of planning and construction. Announcements reflect an increase in capacity is coming, but most projects are in the early stages (FIG. 1).
At the time of this publication, Gulf Energy Information’s Global Energy Infrastructure (GEI) database was tracking more than 440 active carbon capture projects around the world. These projects include carbon capture projects, hubs and storage facilities. Most carbon capture projects are in the U.S., followed by Western Europe. These two regions account for more than 70% of active carbon capture projects globally (FIG. 2).
In some areas around the world, governing bodies have instituted limitations on CO2 emissions. Companies can emit up to the established limits, and regulators are intending to incentivize reductions and/or penalize them when limits are exceeded. Also, companies are either granted permits by regulatory agencies to emit CO2, or they must purchase such permits. Some regions have alternatively chosen to incentivize reductions. For example, a long-standing cement plant will have a permit to release some thousands of tons per year (tpy) of CO2 equivalent (CO2e). If the plant can reduce its output below that figure, it may have an opportunity to sell the excess allowable emissions to another facility that is unable to stay within its limit.
The objective in these jurisdictions is to stay within the total emissions levels permitted for all industries, with reductions over time, but allowing companies that have a difficult time cutting emissions to continue operating if another company can compensate by reducing its output. This keeps total output below the aggregate maximum. This is the cap-and-trade concept, which is one example of an involuntary market.
An alternative market for the captured carbon and subsequent credits are the commitments by companies to reduce overall emissions, or even achieve net-zero operations. Such a company may choose to purchase CO2 removal credits to offset their emissions. These credits can be generated and sold by capturing emitted carbon and permanent sequestration.
For either system to work, a digital trail must be accurate for companies to buy and sell carbon, as explained below, starting at the capture source.
Sources of CO2. There are countless industrial or point sources of CO2 including:
Flue gas from any fossil fuel combustion equipment, including boilers, fired heaters, gas turbines and other sources
Output from calcination processes, such as cement and lime
Batch operations, such as a steel mill’s basic oxygen furnace, which creates enormous amounts of CO2
Reformation of fossil fuels, such as hydrogen (H2) production via steam methane reforming (SMR).
What differentiates these sources for CCS is the concentration of CO2 in the emissions stream. For example, a perfectly tuned boiler burning natural gas will have 20%─25% CO2 in its flue gas, at best, since it is diluted with atmospheric nitrogen that remains unchanged by the process. A cement kiln will have a higher proportion since it has CO2 driven out of the feedstock, plus from the combustion. Some applications produce streams of almost 100% CO2, such as the output from the carbon removal section of an SMR unit, or from fermentation-based alcohol production.
Increased concentration of CO2 improves the practicality and economics of CCS, avoiding the cost of removing contaminants, such as nitrogen, and reducing energy costs. Chemically-based carbon capture processes can be applied to nearly any stream, which often results in CO2 at concentrations near 100%, and overall recovery rates of more than 95% (FIG. 3). Most of these processes mix the gas stream with an organic solvent, ideally allowing just the CO2 to dissolve into the liquid, avoiding nitrogen and other gases. The solvent is then regenerated using heat, which drives CO2 out of the solution.
This is a proven and commercialized technology, but it requires significant capital investments (CAPEX), along with energy use and other operational expenses (OPEX), both of which rise as the CO2 concentration falls.
The opposite end of the concentration spectrum is direct air capture (DAC) where CO2 is simply drawn from ambient air. Normal CO2 levels are approximately 420 parts per million (ppm), so removing a meaningful amount means processing enormous volumes of ambient air.
Auditing emission credits trading. To understand carbon emission credits in a capped system, imagine that a community issues a standard trash can to each residence. Each house can fill the can but no more. A house that does not fill its trash can may give or sell unfilled space to neighbors over the limit. This is not harmful because the total amount is not exceeded, just redistributed.
The same applies to carbon emissions. A specific plant is given permits to emit a particular amount of carbon based on the nature and volume of production. If it does not reach that amount, it can sell its permitted surplus credits to another facility that is over its limit. The company buying the credits has a seemingly simple request, but in practice this can be a difficult question to answer: How do we prove to the relevant regulatory agency and/or credit markets that these are legitimate credits?
The burden of proof is on the seller. Consequently, monitoring CCS cannot be a haphazard effort with a few instruments cobbled together. If money is changing hands, or if emission credits are accepted, the relevant agencies and parties will want auditable proof of what has transpired (FIG. 4).
The carbon credit exchange value chain will eventually require the same level of precision and auditability as custody transfer for feedstocks coming into a facility and conventional products leaving it. The details of how regulatory agencies will certify credits are still being formulated, but there are enough precedents for handling custody transfer and measuring pollutants in other areas to anticipate what is coming.
If a facility is claiming emissions reduction as a credit for sale, then its continuous emissions monitoring system (CEMS) will supply the required data for gas composition. These systems are already in place in many regulated facilities today, such as power plants, and they are periodically audited in accordance with regulatory requirements, so this is perhaps the simplest area for gathering the required information.
Using the concentration measurements and calculating the ultimate tonnage of carbon credits requires precision mass flowmeters, typically using Coriolis technology, as these types of meters are adept at handling the potential complexity in dealing with CO2, especially when considering most long-range transport will be done in a dense phase (FIG. 5).
Analyzers must be able to measure CO2 in proportions up to 100% since some streams will likely be virtually pure. Technologies available today to make this measurement include tunable diode laser (TDL) and quantum cascade laser (QCL), both of which can also measure various other components necessary for CEMS applications.
Data collected from these and other instruments in the capture process must be integrated into a larger system capable of historizing and analyzing it so it can be presented to satisfy both parties in the transaction, as well as regulators (FIG. 6). This methodology is very similar to the custody transfer systems already in place worldwide, simplifying implementation in theory, but with unique challenges remaining.
Such a system supplies data that covers the distance from in-field assets to corporate management. Advanced control and analyticsc technology is designed to span this range by using a full suite of embedded applications that provide model predictive and real-time closed-loop process verification and control, adaptive loop tuning and advanced control applications. These solutions work in combination with solutions from the author’s company’s partner to accelerate innovation and ensure a verifiable digital thread for CCS.
The same data ultimately feeds an accounting system to handle the financial side, like custody transfer systems. Some companies will want to create such a system in-house, but as complexity increases, and as capture systems add multiple stakeholders, many companies will eventually adopt a pre-configured approach to save internal development time and cost. In any case, capturing carbon and monetizing the credits requires efficient operation and an auditable digital thread to ensure profitability.
This entire system of cloud computing and intelligent devices, along with an accounting system, provides the foundation for the financial side and auditing procedures, and it reduces risks for companies wanting to commercialize CO2 removal credits. It also speeds up project execution and optimizes processes across the complete credit trading value chain.
Capturing carbon and lowering emissions. The CCS process takes the CO2-rich gas stream, and instead of releasing it to the atmosphere, draws it into a system where it is compressed and transported to an appropriate site, typically via pipeline, or occasionally via truck or even tanker, where it is forced into the ground (FIG. 7).
In some cases, these are extinct oil or natural gas wells or other geological formations, with appropriate geologic conditions to provide permanent storage. These formations are thousands of meters below the surface, necessitating compression to 70 bar (1,015 psi) and higher, so the site’s capacity must be capable of keeping up with input. There are costs for transport and compression, along with a new sequestration well, which also requires permitting from the required agencies.
Where a given CCS site receives CO2 from various processes, both continuous and batch, some storage may be necessary to smooth out processing to match compressor capacity.
Selecting sources of carbon to capture. Most applicable combustion processes, such as fired heaters, are extensively instrumented to monitor throughput and efficiency (FIG. 8). Any that emit a significant flow of pollutants probably have a CEMS in place, although it might not be measuring CO2. Most existing CEMS are looking for other pollutants, such as sulfur dioxide and nitrogen oxides. Combustion management systems normally look for oxygen in flue gas to verify efficient combustion but do not monitor CO2.
So, what are the best analyzer technologies for measuring CO2? Laser-based gas analyzers offer a useful optical detection method using a narrowband laser light source. Utilizing TDL, and more recently QCL, these analyzers measure a range of frequencies in very targeted sections of the near- and middle-infrared (IR) spectrum (FIG. 9).
QCL lasers cover the mid-IR region, where high-sensitivity measurement of a broad range of gas components, including CO2, is now practical.
Rich stream processes. Other sources of carbon capture are processes that produce a stream of almost pure CO2 from a specific chemical or biological reaction, rather than combustion. The most common example is a steam methane reformer (SMR) in an ammonia plant or oil refinery (FIG. 10).
SMR is very energy intensive, consuming half the natural gas needed for fuel as compared to the amount used to generate H2. Consequently, it must be thoroughly instrumented, with sophisticated process control to maintain an acceptable level of efficiency and availability.
Custody transfer validation and transportation. Custody transfer for fuels, feedstocks and products at a facility uses instrumentation technologies, and it follows common practices accepted by all sides as valid. This same mindset and framework are critical throughout the CCS value chain for creating an auditable digital thread to verify and monetize carbon credits.
Custody transfer systems require the best possible measurement accuracy and reliability, which must comply with commercial and environmental regulations. Such systems depend heavily on flow computers and Coriolis mass flowmeters. A flow computer’s measurement history, along with meter verificationd, proves the flowmeter is functioning correctly, and this is foundational to efficient, auditable operations.
Taking a step back, in most cases, the captured CO2 must be transported via pipeline to sequestration facilities. It is paramount for both safety and measurement validation to monitor pipelines to reduce risks and ensure all captured carbon emissions are ultimately sequestered underground. Key solutions to accomplish these tasks are corrosion and erosion monitoring systemse, and a pipeline leak detection systemf.
These solutions are a critical component of the technology stack to transport CO2. These types of measurement technologies and software must be integrated with accounting processes for regulatory and tax reports. These types of reports require extensive data from many sources, including the CO2 source, delivery pathways, contracts, invoices, transportation information, custody transfer documentation and others. Data gathering and analysis platforms provide a means to automate visualization and reporting, while providing the flexibility to adapt as future requirements for CO2 trading mechanisms develop. A central data repository, often referred to as a data lake, stores all types of data required for reports and analytics, with integrated visualization to reduce the labor needed to create highly accurate, yet flexible, reports.
Future proofing. Cap-and-trade exchange mechanisms or open market trading for CO2 removal credits are still being formulated in most areas, but there are enough precedents in other similar areas to predict what they will look like. The required instrumentation and data analysis platforms are available today, and these will be the technology base going forward to create the required auditable digital thread.
As related above, an auditable digital thread for CCS is very similar to the custody transfer systems which are widely used throughout the process and other industries. It will function in much the same way, with the main differences found in the technologies required to measure carbon emissions, transport and storage—as opposed to traditional custody transfer systems that typically measure flows of fossil fuels.
Companies should be exploring the practicality of reducing their emissions by using CCS strategies, along with calculating the possible value of selling their excess reduction as a new income stream. Partnering with a single provider able to support all aspects of such a program can shorten the development time and ensure successful project execution. HP
NOTES
Emerson’s Micro Motion ELITE Peak Performance Coriolis flow and density meters
Emerson’s Rosemount™ X-STREAM Enhanced XEFD continuous gas analyzer
Emerson’s DeltaV™ advanced control and analytics
Emerson’s Smart Meter Verification
Emerson’s corrosion and erosion monitoring system
Emerson’s PipelineManagerTM
SETH HARRIS is the director of sustainability solutions sales in the Americas for Emerson. He has more than 19 yr of experience with Emerson across multiple industries, various sales functions including product, software and data management, and a personal foundation built on environmental sustainability that brings a unique depth to society’s decarbonization efforts. Harris earned a BS degree in chemical engineering from the University of Colorado.