The critical role of gas chromatography in CCUS success

Carbon capture initiatives are typically presented with a focus on new and emerging technologies, large scale capital projects, and ambitious decarbonization goals. Behind each successful carbon capture, utilization and storage (CCUS) project, however, there exists a much less visible, but equally important, foundation on which those projects depend—precise chemical composition measurement of gas streams.

For the power generation, cement, steel, refining, chemical and hydrogen production sectors, CCUS represents a primary method to reduce emissions associated with processes that are traditionally difficult or impossible to decarbonize.

Each of these sectors generates large volumes and continuous flows of CO₂ gases, creating ideal conditions for capturing these gases before they enter the atmosphere. As regulatory standards continue to be implemented at a rapid pace, and companies increase their commitment to addressing climate change, CCUS is rapidly evolving from a forward-looking concept to a necessity for operations.

The drivers behind this trend include economic and strategic factors. Increasingly, governments have developed regulations on emissions, pricing mechanisms for carbon, and incentives to drive development. In the U.S., the federal 45Q tax credit is a major source of funding for each ton of CO₂ captured and stored. Other global markets also provide similar subsidy structures or trade platforms. 

At the same time, many large-scale, industrial processors are aligned with net-zero targets through 2030–50, and require solutions that will let them continue to produce and meet their environmental goals.

Precise control 

While the strategic and regulatory case for CCUS is increasingly well-established, its successful implementation ultimately depends on precise process monitoring and control. However, the performance, reliability and cost-effectiveness of such technology largely depends on accurate descriptions of the gas streams involved. As such, process gas chromatography (GC) continues to be one of the primary tools for ensuring that CCUS systems are operating reliably, meeting all applicable regulatory requirements, and achieving their best performance.

Process gas chromatography 

Process GC is an analytical tool used to continuously measure the chemical make-up of a gas stream flowing through industrial equipment. One of the most significant advantages of using GC is the ability to analyze a complex gas mixture, and split it into individual components during a single measurement.

Understanding the chemical composition of a gas is important for several reasons. It’s important for maintaining  product quality, optimizing operating parameters, protecting staff working near the process area, and regulatory compliance.

The analyzer works by sampling a small amount of gas from a pipeline or process stream, and injecting it into a flow of carrier gas. This mixture moves through a column filled with a stationary phase material. Each component interacts with the stationary phase differently, causing it to move through the column at a distinct rate. As each separated component reaches the end of the column, it enters the detector, where it’s identified and quantified. The detector’s signal is processed by a computer to determine the concentration of each component in the sample. 

In carbon capture processes, large amounts of flue or process gases enter a capture unit. It’s imperative to  accurately separate and quantify the major components in the gas. However, one of the biggest obstacles is that different processing plants generate different gas mixes, while operating under different pressures, temperatures and impurity levels.

For flue gas analysis from a power plant, its analyzer typically tracks CO₂, O₂, N₂, SO_x. When analyzing gases during blue hydrogen or syngas production, it would likely follow H₂, CO, CH₄, CO₂ to ensure CO₂ removal is effective. In industrial off-gas and chemical looping systems, there could be many additional hydrocarbons and contaminates present requiring measurement and tracking.

Because of these factors, analytical equipment needs to be versatile. However, many plants use online analyzers that detect only one compound or element, so several are needed for more complex streams.

“The strength of GC lies in its ability to measure multiple components in a gas stream simultaneously, unlike individual gas analyzers that are limited to detecting one component at a time,” says Al Kania, business development manager at Valmet.

Accurate measurements guide decisions

Process GC systems must deliver enough accuracy to support effective CCUS implementation. Reliable, high-precision measurements let operators accurately determine system composition, providing a dependable foundation for downstream decisions.

With detailed compositional information, operators can effectively evaluate the performance of carbon capture processes, and make informed adjustments to improve absorption and stripping efficiency. Accurately measured process parameters give operators the confidence to make educated decisions regarding the system’s actual chemistry. In addition, using accurate measurements of the feedstock’s chemical composition, operators can make knowledgeable decisions about the effectiveness of the carbon-capture process, and identify opportunities to optimize absorption and stripping processes.

Accurately identifying and quantifying each component present in the gas stream is critical for managing amine degradation during CO₂ absorption. It’s also essential for mitigating corrosion risks by effectively controlling corrosive conditions, and operating compressors and pipelines safely at or below their design limits. These operations ensure that captured CO₂ meets specified purity standards for transportation and storage.

Validated, laboratory-grade compositional data is also necessary to meet many reporting requirements for regulations  related to carbon sequestration and to qualify for tax incentives.  “Process GCs are the established analytical method for meeting these requirements,” notes Kania.

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Guarding against analytical drift

Though advanced analyzers like GCs are sophisticated, small measurement inaccuracies can increase operationing costs, or cause the control system to make unnecessary adjustments to the process. These gradual shifts in accuracy—known as analytical drift—are caused by variables such as temperature, detector deterioration, contaminants and electronic stability issues. Analytical drift may occur even when the analyzer is regularly calibrated.

“If an instrument experiences analytical drift, it may report CO₂ concentrations that are either higher or lower than actual values. This can lead the system to incorrectly adjust absorber or regeneration conditions, resulting in increased energy consumption or reduced capture efficiency,” says Kania.

Accurate GC readings play an important role in minimizing operational and safety-related risks from hydrogen sulfide (H₂S) breakthroughs and oxygen (O₂) ingress. By maintaining their accuracy and reliability, GC instruments also provide timely and reliable information on gas mixture changes, so operators can act before situations escalate. 

GC design and construction

The design and construction of a process GC is also a factor in controlling drift. Industrial-grade products like Valmet’s Maxum II are designed to operate at -20 °C to 100 °C, and should be rated for use in corrosive and potentially explosive atmospheres where hazardous gases may be present.