What are the different methods of carbon capture and storage?
Carbon capture and storage (CCS) is a technology that aims to mitigate climate change by capturing carbon dioxide emissions from power plants and industrial sources, and then storing it underground. There are three main methods of CCS: post-combustion capture, pre-combustion capture, and oxy-fuel combustion.
Long answer
-
Post-combustion capture: This method captures carbon dioxide after the fuel has been burned. It is the most widely applicable technique as it can be retrofitted to existing power plants. The process involves removing carbon dioxide from flue gas using solvents or adsorbents. The captured CO2 is then compressed, transported, and stored in geological formations such as deep saline aquifers or depleted oil and gas reservoirs.
-
Pre-combustion capture: This method involves gasifying the fuel prior to combustion to produce a mixture of hydrogen and carbon monoxide known as syngas. The syngas undergoes a shift reaction to convert carbon monoxide into more hydrogen and carbon dioxide. The separated CO2 can be captured before combustion occurs. Pre-combustion capture is commonly used in integrated gasification combined cycle (IGCC) power plants.
-
Oxy-fuel combustion: In this method, fossil fuels are burned in an oxygen-rich environment instead of regular air. By using pure oxygen for combustion, it produces a concentrated stream of carbon dioxide that can be easily captured without the need for extensive separation processes involved in post-combustion methods. After capturing the concentrated CO2, it is compressed, transported, and stored underground.
In all three methods, once the CO2 is captured, it goes through compression to reach a supercritical state for transportation via pipelines or other means to the storage site. Storage options include deep saline aquifers (porous rock formations filled with salty water), depleted oil and gas fields (where oil or natural gas was previously extracted), and deep coal seams. The storage of CO2 must be done carefully to ensure integrity and prevent leakage back into the atmosphere.
Furthermore, it is worth mentioning that CCS involves a significant energy penalty due to the capture and compression processes, which can offset some of the benefits. However, ongoing research and development aim to improve efficiency and lower costs associated with these methods.