TPS 2024: Carbon-Capture Plants with Gas Turbines

At TPS 2024, folks from Siemens Energy, including Lukas Biyikli, R&D Portfolio Manager of Integrally Geared Compressors, and Mike Welch, Industry Marketing Manager, presented on the Integration of CO₂ Capture Plants with Open Cycle Gas Turbines.

The industry is familiar with carbon-capture technologies’ ability to remove CO₂ from flue gas streams. Still, the challenges of providing the flue gas in the correct conditions and supplying the energy required for the CO₂ capture process are less well-known.

The speakers addressed these challenges by first reviewing the most common types of carbon-capture technologies, such as solvent- and potassium-carbonate systems, and then explored how open-cycle gas turbines could achieve similar results.

Technology Selection

Welch began with a clarification regarding the role of gas turbines in carbon capture: they can achieve decarbonization by firing low-carbon fuels and their plants can be equipped with post-combustion capture technology. Despite these carbon capabilities, users typically favor traditional technologies over gas turbines for capture applications, citing low CO₂ concentration in exhaust (3-4%) and high exhaust gas temperatures as the primary challenges.

He outlines several considerations for choosing carbon-capture technologies, including:

• Desire capture rate
• CO₂ capture amount

• Available space at location
• Energy and water availability
• Impact of NOx and SOx on solvent life and replacement rate

According to Welch, carbon capture is a difficult process when using gas turbines: “The only certain thing about CO₂ capture is that you’ll need a lot of space and it’ll cost you a lot of money—it’s not a cheap solution. Most of the processes are designed to operate at low ambient temperatures, so you become limited to the available technologies when operating with a gas turbine. There are only a few [technologies] that don’t require cooling of the gas turbine exhaust and most of the emerging technologies can’t support large-scale turbines.”

Available Systems

Despite the inherent challenges of running current carbon-capture technologies in conjunction with gas turbines, there are many available systems in use today. The most common are amine-based systems, which utilize proven solvents to absorb CO₂ with low toxicity and low energy demand for desorption. However, these solutions have large footprints and long construction times, with higher energy demand for absorption. Welch goes on to list specific systems and their respective benefits and drawbacks.

Modular Amine Towers: Often applied to smaller emitters that generate less than 1,000 tons of CO₂ per day. With a smaller footprint, towers have shorter construction times and can be used at space-constrained sites, such as offshore platforms.

Rotating Packed Beds: Features enhanced CO₂ adsorption through centrifugal force, but generally lower capture rates at approximately 100 tons per day.

Potassium Carbonate: Proven for gas processing and scalable to large CO₂ capture volumes. The energy demand is similar to amine towers, but these systems can use hot water for solvent desorption. On the downside, potassium carbonate operates with low flue gas inlet temperatures.

Hot Potassium Carbonate: Unlike typical potassium carbonate, it operates at high flue gas temperatures in a pressurized process. It can generate its own electricity and gas turbine supplementary firing can increase CO₂ concentration.

Membranes: These are also proven for gas processing but struggle when applied to gas turbines, as multiple modules are required to achieve the desired capture rate and purity. Membrane contactor modules are a hybrid solution combined with amine solvents.

Cryogenics: Freezes CO₂ out of the flue gas stream.

Electrochemical: Electroswing adsorption can be used on gas streams with any CO₂ concentration and, according to electrochemical operators, can selectively capture NOx and SOx.

CO₂ Compression and Utilization

Biyikli continued the discussion by outlining the basics of CO₂ compression and utilization processes following capture. Although compression is the primary electricity consumer in carbon-capture plants, it is a critical step for transportation via pipeline—the most economical way to move CO₂ from Point A to Point B. The main equipment for compression applications is reciprocating, single-shaft, and integrally geared compressors.

“Most of the capture technologies work at atmospheric pressure, yet the best way to transport CO₂ is at 100-200 bar,” said Biyikli. “This is why the compression takes such a significant amount of energy, particularly for compression that’s happening downstream of the capture plant. Once the CO₂ is in supercritical state, you might need a booster station to raise it from 80 bar to around 150 bar, for example.”

After CO₂ is compressed and transported, it can be stored or utilized in a variety of ways; however, it must be noted that around 95% of CO₂ from current capture plants is stored rather than repurposed. In terms of storage, it’s most often sequestered in underground geological formations such as aquifers, caves, and depleted reservoirs.

On the utilization end, Welch said that CO₂ can be converted into specialty chemicals and high-value products, such as methanol when combined with hydrogen gas, animal feed, Omega 3, and astaxanthin.

In summary, Welch said: “There’s no one-size-fits-all option, as every technology has its advantages and drawbacks, and you must do your own site-specific, process-specific research. Size also does matter, whether it’s the amount of CO₂ you’re trying to capture or the space you have. Capture costs of less than $100 per ton look feasible.”