by Ansh Motiani What is Carbon Capture Technology? Carbon capture and storage (CCS) is an emerging emission reduction technology that captures carbon carbon dioxide emissions from sources and either reuses it or stores it, preventing it from entering the atmosphere. Areas of storage include oil and gas reservoirs, unmineable coal seams, any structures that have stored crude oil, natural gas, brine, and carbon dioxide over millions of years. The concept of carbon capture has been in use for years in the oil and gas industries as a way to enhance oil and gas recovery. It has only recently been utilized for environmental reasons. Currently, most research focuses on carbon capture at fossil fuel-powered energy plants, the majority of the contributors to man-made CO2 emissions. Some researchers propose the idea of a future in which all new power plants employ this carbon capture technology. How does it work? There are three main steps to CCS: trapping and separating theCO2 from other gases, transporting it to a storage location, and making sure it stays far away from the atmosphere. A fossil fuel power plant generates power burning fossil fuels to generate heat that turns water into steam. As a result, the steam turns a turbine connected to an electricity generator in a process called combustion. Carbon is extracted from this process in three basic ways: post-combustion, precombustion, and oxy-fuel combustion. Post-Combustion In post-combustion capture, CO2 is extracted after the fossil fuel is burned. The burning of these fossil fuels creates substances known as flue gases that include CO2, water vapor, sulfur dioxide, and nitrogen oxide. In this process of carbon capture, the CO2 is captured and separated from the flue gases. This is the process that currently in use to remove CO2 from natural gas due to its ease of implementation. Older power plants can be fitted with filters that help trap CO2 as it travels up a chimney or smokestack. Generally, this filter is a solvent that absorbs carbon dioxide. It can later be heated, releasing water vapor, leaving behind a concentrated stream of CO2. This method of carbon capture can reduce power plants’ carbon emissions by 80 to 90 percent. However, this process requires a large amount of energy to compress the gas enough for transport. Pre-Combustion In pre-combustion carbon capture, CO2 is trapped before the burning of fossil fuels where it is diluted by other flue gases. The process starts when coal, oil, or natural gas is heated in pure oxygen, creating a mix of carbon monoxide and hydrogen. This mixture is treated in a catalytic converter with steam, producing more hydrogen and carbon monoxide. These gases are sent to the bottom off a flask where they naturally begin to rise. A chemical known as amine is poured onto the top, binding with the CO2 and making it fall to the bottom of the flask, while the hydrogen continues to rise out of the flask. After this, the amine/CO2 mixture is heated, separating the two, allowing the CO2 to be collected and stored This method of carbon capture is already in use for natural gas and provides a much higher concentration of CO2 than post-combustion. Although it is lower in cost, precombustion cannot be retrofitted to older power plant generators. Like post combustion, it also reduces emissions into the atmosphere by 80 to 90 percent. Oxy-fuel Combustion In oxy-fuel combustion carbon capture, the power plant burns fossil fuels in oxygen, resulting in a gas mixture comprising of steam and CO2. The two are then separated by cooling and compressing the gases. Although the current cost of this method is high due to the necessity of oxygen, researchers are exploring new techniques to reduce the cost. This method can reduce emissions into the atmosphere by 90 percent. Transporting the Carbon Dioxide Following the separation and capture of CO2, it must be transported to a storage site. Currently, the method of transporting CO2 is through a pipeline. There are more than 1,500 miles of CO2 pipelines in the US today, mostly used to enhance oil production. Although the pipelines can transport CO2 in their gaseous, liquid, and solid states, pipelines generally transport it in its gaseous state as this is the most cost effective. Compressors throughout the pipe push the gas through. It is also possible to transport CO2 in its liquid form using ships or tankers, but the cargo tanks must be pressurized and refrigerated. CO2 pipeline under construction Tanker specialized for transporting liquid CO2 Carbon Storage There are two places where carbon is stored: underground and underwater. Estimates project that the planet can store up to 10 trillion tons of carbon dioxide, equivalent to about 100 years of storage of all human-created emissions. Underground Storage Also known as geological sequestration, underground storage is a popular way to store carbon. Due to the high pressure deep underground, CO2 behaves more like a liquid than gas. Because it can seep into porous rocks, a great amount can be stored in a small area. Basalt formations, also known as volcanic rock, are the most suitable for storing CO2. Basalt is one of the most common types of rock in the earth’s crust. After CO2 injection, the basalt eventually turns into limestone, another type of rock. Generally, rocks found in oil and gas reservoirs are best for geological sequestration because they have overlying rocks that form a seal, keeping the gas contained. Underwater Storage
The ocean is also a viable option for CO2 storage. Experts claim that if the CO2 is released at depths greater than 11,482 feet, the CO2 will compress and fall to the ocean floor. This method is mostly untested, and there are many concerns about the safety of marine life and the permanent storage of the carbon. Sources: https://www.energy.gov/carbon-capture-utilization-storage https://science.howstuffworks.com/environmental/green-science/carbon-capture4.htm https://www.theguardian.com/environment/interactive/2008/jun/12/carbon.capture https://www.greenfacts.org/en/co2-capture-storage/l-2/3-capture-co2.htm#1 Images: http://www.directindustry.com/prod/asco-carbon-dioxide/product-38377-1636862.html https://www.icb.csic.es/en/gi/co2-capture-oxy-fuel-combustion/ http://www.fossiltransition.org/pages/post_combustion_capture_/128.php https://www.pnnl.gov/science/highlights/highlight.asp?id=537 http://www.directindustry.com/prod/asco-carbon-dioxide/product-38377-1636862.html
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AuthorsAnsh Motiani, Andrew Vittiglio, Charles Kirby, and Benjamin Yurovsky
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April 2021
CategoriesEnvironmental Tech
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