Carbon Capture: What it is and cooling options identified

The Carbon Capture process is a method of removing Carbon Dioxide (CO₂) from the discharge of a power plant or other industrial facility that is burning fossil fuels (coal, natural gas, etc.) before it enters the atmosphere. That discharge is generally through a large stack, with the goal of capturing and removing CO₂ to reduce greenhouse gas emissions and thus mitigate climate change. 

The terms ‟Carbon Capture and Utilization” (CCU) and ‟Carbon Capture and Storage” (CCS) are part of a larger process generalization referred to as ‟Carbon Capture, Utilization and Sequestration” (CCUS). In simple terms, the CO₂ is captured, separated from an exhaust airstream, compressed, transported and then injected back into the ground, stored or used in other industrial or chemical processes.

Currently, the main uses for the captured CO₂ include:

• Enhanced oil recovery to help push out additional reserves
• A component for plastics and building materials

Among different technologies for Carbon Capture, liquid solvent (i.e. amine) is the most common and proven technology for capturing CO₂ from flue gas. Within the last few years, several other solvents have been developed by different licensors. Unlike traditional gas sweeting systems in carbon capture, the absorber column works at very low pressure, so effective cooling of flue gas and the solvent is essential for the performance of the system. In liquid solvent technology, separation, compression and transportation within the Carbon Capture systems require cooling at various process stages:

• Direct column cooling
• Rich/lean solution cooling
• Gas condensing
• Compressed gas cooling
• Supercritical CO₂ cooling

Three cooling technologies used in the Carbon Capture process include wet, hybrid (wet/dry) and dry systems. Alfa Laval offers product ranges in these technologies:

• WET: Wet Surface Air Coolers (WSAC^®)
• WET/DRY: Hybrid Air Coolers (HYAC)
• DRY: Air-Cooled Heat Exchangers (ACE)

Wet System

The Alfa Laval Wet Surface Air Cooler (WSAC) is an engineered-to-order closed loop evaporative cooling system. It is a highly efficient method of cooling liquids and condensing vapors in a wide variety of applications.

The WSAC is a more efficient heat transfer technology as compared to standard air-cooled heat exchangers or cooling tower/heat exchanger (shell-and-tube or plate-and-frame) systems.  

The advantages of a Wet Surface Air Cooler include:

• Lowest process outlet temperatures (5ºF-10ºF approach to ambient wet bulb) as compared to other technologies (lower temps will allow the absorber column to operate at 100% efficiency, even on the hottest days, while also reducing amine liquid hold-up volume)
• Increased system throughput while reducing upstream and downstream power requirements
• Lower parasitic energy consumption (less carbon footprint)
• Reduced freshwater consumption – process generated or condensed water can be used as makeup
• A first-stage evaporator to reduce plant discharge volume
• Less plot area than standard tower / heat exchanger systems

Wet/Dry (Hybrid) System

As with the WSAC, Alfa Laval Hybrid Air Cooler Systems (HYAC) offer compact and sustainable cooling for plants requiring high cooling capacity but with low water availability. An Alfa Laval HYAC solves the problem by switching between two operating modes: dry cooling and wet cooling, depending on the ambient temperature. By only engaging the wet cooling mode when required during hotter periods, both water consumption and installation space is minimized, while ensuring consistent output temperatures.

The HYAC Single Zone (SZ) model is intended for installations where temperature fluctuations in the ambient air cause insufficient cooling in traditional air-cooled heat exchangers. The HYAC Dual Zone (DZ) model is used in plants where increased cooling capacity is required. The first cooling zone in a HYAC DZ operates as a traditional air-cooled heat exchanger and the second zone as an evaporative cooler.

Both single and dual zone HYAC systems are optimized for minimal water usage. As with the WSAC, the HYAC systems can operate with poor quality (process generated) water allowing for higher cycles of concentration, reducing plant water discharge.

In addition to the advantages of a WSAC, the HYAC can also provide:

• Smaller footprint than separate wet and dry units
• Minimal water usage

Dry System

When there is absolutely no water available, a dry, air-cooled system is the best alternative. Alfa Laval ACE air heat exchangers will deliver high performance covering most applications in the Carbon Capture process. Alfa Laval can supply both standardized and fully customized, engineered-to-order solutions. Thanks to their flexible designs, these heat exchangers can be configured to match specific operating conditions, ensuring reliable operation, low operating costs and high performance.

The advantages of an Air-Cooled Exchanger include:

• No need for water
• Simple and lower capital cost

Cooling systems are an integral part of the CCUS process. Alfa Laval cooling technologies can help to improve process efficiency, reduce carbon footprint and provide water resource conservation.