Carbon Capture & Storage Industry - Carbon Capture

CCS is, by definition, a multi-stage process. You have to capture, transport, and then store the carbon. Let's start by breaking down the activities and technologies used across the steps, starting with capture. Actually, let's go one step back, to the emissions themselves. The type of capture technology will depend on the source of the emissions. Some of the big emissions culprits are large industrial sites, like refineries, power plants, cement factories, and steel mills, for example. Here, CO2 can be isolated and captured in high volumes and high concentrations, right at the source. There are multiple pathways for carbon capture here. Collectively, they're described as point source capture. Other sources are highly dispersed and much harder to isolate. Cars, planes, individual homes, and so on. These emissions cannot be feasibly captured at the source. They have to be captured later on, from the open atmosphere. This is called direct air capture, or DAC, the least efficient of the pathways. Why? The plane atmosphere has a very low carbon concentration, just around 0.04 percent. Exhaust from a factory, a point source, conversely, is closer to 4 to 40 percent carbon, a hundred to a thousand times atmospheric levels. That's why point source capture is more economical. In this camp, there are several viable pathways. The specific approach used will depend on the industrial site in question. First, whether the site is a new build or a retrofit of an existing site. If it's a retrofit, fewer options are available, and the most cost-effective pathway is to capture CO2 as it exits the smokestack. This is called post-process capture, or post-combustion capture. While easier to install, this is not the most efficient. These flue gases need to be purified of impurities like nitrogen, water vapor, and pollutants. Water vapor is a particularly concerning culprit. Why? While both CO2 and water are relatively harmless, they form a corrosive acid when mixed together. This acid can damage the metal in the pipeline and injection well infrastructure later in the process. CO2 isn't officially captured until it's refined to meet certain purity specifications, and post-combustion capture requires the most work here. For new builds, you can design cleaner approaches into the system itself, reducing the need for refining steps and increasing process efficiency. The specific approach will then depend on a second site-specific factor, the process in question. Is it fossil fuel combustion, where we burn fuels for their energy content, or is it some other chemical reaction that emits CO2 as a byproduct? When the reaction in question is fossil fuel combustion, like in gas power plants, there are two viable approaches. One is to burn the fuel under special conditions, in pure oxygen, called oxy-fuel combustion. This emits a stream of CO2 with no impurities or nitrogen. The other method is to strip the carbon from the fuel before it is burned, known as pre-combustion capture. Hydrocarbons, such as natural gas, can be converted into a mixture of H2 and CO2. The H2 gets burned as a clean fuel, and the CO2 gets captured. When it's not combustion, and instead other chemical reactions are the the best path is to capture the CO2 as soon as it's produced in the chemical process flow, and ideally before it's mixed with other gases. This is sometimes called inherent process capture or process-integrated capture. It's like post-capture, but you don't wait until the very end. Regardless of the pathway, capturing carbon is an energy-intensive process. Even in the most efficient cases, like a new-build gas power plant using pre-combustion capture, 10-20% of the energy produced by the plant will be needed to run the carbon capture activities. This energy penalty is a major reduction in plant efficiency. Plus, only about 90% of emissions are captured. The remaining 10% is typically too costly and inefficient to pursue. Post-capture is even less efficient, requiring up to 30% of the plant's energy. DAC is the least efficient of all, and makes the most sense when powered by renewable energy sources, like wind or solar. Otherwise, you're just burning fuels to capture emissions. Nonetheless, DAC may have an important role to play, since it's the only solution for all those emissions that can't be addressed via point-source means.