Carbon capture technologies as a clean energy option
Point carbon capture is one of many clean energy transition options. It refers to the process of capturing carbon at the source from heavy industries like power, steel, cement, and chemicals. The exhaust gases are in a contained environment and CO2 concentration is also relatively high (10-30% by volume), making a case for carbon capture plants to be established as an extended arm closer to the site. However, this inflates the cost of operations.
Capturing CO2 from the atmosphere, or direct air capture, is relatively more challenging than point carbon capture as the volume of air is huge while concentration of CO2 is extremely low. However, the major advantage of this approach is that plants can be constructed anywhere on the planet. For instance, the plant can be constructed somewhere closer to an abandoned mine where CO2 can be sequestered.
Several factors need to be considered before selecting the carbon capture technology, such as volume of the gas to be treated, concentration of CO2, impurities present, power required, effluents and wastes, and cost. Well-established technologies such as absorption, adsorption, membrane separation, and cryogenic distillation that are used for gas separation and purification in industries are often recommended. New technologies like chemical looping and microbial or algal systems are also being explored for carbon capture. The appropriate technology can be adopted based on the requirements.
Each technology has its pros and cons. For instance, technologies like absorption and cryogenic distillation are mature and CO2 recovery is high (> 95%), but they are energy-intensive (4-10 MJ/kg CO2). On the other hand, adsorption and membrane separation are less energy-intensive (0.5-6 MJ/kg CO2), but recovery is lower (80-90%). Another crucial factor to be considered in the entire process is the cost of transportation and storage of CO2. The current practice is to store CO2 in saline formations and depleted oil and gas reservoirs. The need of the hour is to offset the cost of capture by utilizing CO2 for applications in enhanced oil recovery, fertilizers, polymers, food processing, industrial gases, and liquid fuels. Lastly, environmental sustainability of the process including the materials used and their lifecycle should be considered while selecting the technology.