Energy conservation and emission reduction, and taking the path of low-carbon development are the best solutions to global climate change. As global coal consumption continues to grow, some scientists believe that the widespread adoption of carbon capture and storage technology is very important to the goal of limiting global warming to 2°C. Therefore, in the eyes of scientists around the world, new technologies for reducing carbon dioxide emissions are increasingly valued, among which carbon capture and storage technology has begun to become a hot topic. Among various emission reduction measures, carbon capture and storage technology is considered to be the "single technology with the greatest contribution." It is predicted that its contribution to global emission reduction will reach 20%, so it has attracted much attention from all countries. At present, there are more than 100 carbon capture and storage technology projects in operation or about to be operated around the world.
Carbon capture and storage technologies
Professor Pan Weiping, director of the Institute of Combustion Science and Environmental Technology at Western Kentucky University, said in a recent interview that carbon capture and storage refers to a technology that collects carbon dioxide produced by emission sources such as large power plants, steel mills, and chemical plants, and stores it in various ways to prevent it from being released into the atmosphere. The technology includes three links: carbon dioxide capture, transportation, and storage.
Carbon capture is the process of capturing carbon dioxide released into the atmosphere. There are three main ways to capture carbon dioxide: pre-combustion capture, rich gas combustion, and post-combustion capture. Regardless of the capture method used, in short, the gas generated by coal-fired power plants is collected, and after desulfurization, nitrogen oxides, etc., the carbon dioxide is separated and collected.
The second is carbon sequestration. When carbon dioxide is captured and compressed, it is compressed back into depleted oil fields or other safe underground places. "For example, in the process of oil extraction, carbon dioxide needs to be injected before oil can emerge." Pan Weiping said. Research on this technology can be traced back to 1975, when the United States injected carbon dioxide into the ground to increase oil production, but it was not until 1989 that the Massachusetts Institute of Technology began to study it as an environmental protection project to store carbon dioxide to reduce greenhouse gas emissions. It was not until recent years that this technology received more attention and research. It is considered to be an effective way to directly reduce the concentration of carbon dioxide in the air.
Regarding the specific methods of carbon capture, there are now more than 1,100 thermal power plants in the United States, which usually use post-combustion treatment technology. Pan Weiping introduced that there are two types of post-combustion treatment technologies: one is organic ammonia technology, which is currently a more mature technology, but it also has disadvantages: the capture efficiency of carbon dioxide is only 90%, and it consumes a lot of energy.
The second is ammonia absorption technology. Ammonia plus carbon dioxide becomes a small nitrogen fertilizer, which can be used as fertilizer for agricultural production. But not every thermal power plant can use this technology. It is limited by quantity. Otherwise, where can so many small nitrogen fertilizers be sold?
The third is pre-combustion treatment technology. New thermal power plants can use this technology. For example, a thermal power plant under construction in Dongguan, Guangdong, China, uses coal gasification cycle power generation technology as a whole. Its advantage is that the coal is gasified first. After coal gasification, the main products are hydrogen, carbon monoxide, etc., and hydrogen combustion will not produce carbon dioxide.
Pan Weiping said, "Now, many newly built thermal power plants in the United States use mixed combustion. Why? Because these power plants do not need to be equipped with additional equipment and use existing power generation equipment. The mixed combustion of coal and biomass can reduce carbon dioxide emissions. This is the most direct and fastest way in the short term.
Enhanced oil recovery may help combat climate change
Carbon capture technology has been used in the United States since the 1930s. For example, carbon dioxide is captured by chemical reactions in the smokestacks of power plants and factories, and then released by heating the chemicals. The carbon dioxide is then pressurized to become a liquid and pumped through pipelines to storage locations. Storage locations include underground gravel, saline aquifers, and old oil fields.
For decades, oil companies have been drilling for carbon dioxide underground in southwestern Colorado, and they will transport large amounts of carbon dioxide through pipelines to oil fields in western Tennessee. By injecting carbon dioxide, the aged oil can be used to produce more oil, and most of the carbon dioxide will be permanently stored in Tennessee.
In Missouri, a new gasification coal-fired power plant will begin collecting carbon dioxide in 2015 and transport it to oil fields in southern Missouri through a nearly 100-kilometer pipeline. The power plant will also be the first plant in the United States to implement carbon capture and storage. The project uses greenhouse gases produced by the burning of fossil fuels to help produce more fossil fuels. Although this move is far from an ideal solution to climate change, enhanced oil recovery can prove that carbon dioxide capture and storage technology is an important tool for addressing climate change.
"Fossil fuels are not going away anytime soon," said John Thompson, director of the Fossil Fuel Transition Project at the nonprofit Clean Air Task Force. "If we want to stop global warming, we need to find a way to use fossil fuels without emitting carbon dioxide. Currently, only carbon capture and storage can do that." The biggest challenge is scale, and aging oil wells have a huge demand for carbon dioxide. Thompson predicts that enhanced oil recovery will eventually require 33 billion tons of carbon dioxide, which is equivalent to decades of carbon dioxide emissions from all power plants in the United States.
Chris Jones, a chemical engineer at Georgia Institute of Technology, said: "In the short term, we may use more fossil fuels to develop carbon capture and storage technology. But this process is necessary, and we must continue to develop this technology through this process and make this technology more mature and efficient." But Jones also pointed out that carbon capture and storage is not just about burying carbon dioxide deep underground. The whole process will lead to the continued use of fossil fuels. In addition, pumping high-pressure liquids into the ground may lead to the risk of man-made earthquakes, and there is also the risk of accidental leakage of carbon dioxide. Because there is no way to prove that the captured and stored carbon dioxide will not leak out. For example, there is a village in Africa with a lake in it. After the carbon dioxide at the bottom of the lake leaked out, all the people and animals in the village suffocated to death, and the entire village disappeared.
The value of carbon technology cannot be ignored
Currently, cost is the main obstacle to the implementation of carbon capture and storage technology, and enhanced oil recovery is the main area for the widespread implementation of this technology and the reduction of its cost. Globally, carbon dioxide emissions exceed 35 billion tons per year, almost all of which come from coal, oil, and natural gas. According to the International Energy Agency, in order to achieve the goal of limiting global warming to 2 degrees Celsius, more than 100 carbon capture and storage projects will need to be built by 2020, reducing 270 million tons of carbon dioxide per year. However, there are currently only 60 planned or proposed projects, of which only 21 projects have started construction or operation. There are 34 planned or operational carbon capture and storage projects outside North America, most of which are located in Asia and Australia. According to the Global Carbon Capture and Storage Institute, public opposition to carbon capture and storage projects in European countries such as Germany has led to a drop in the number of projects in Europe from 14 planned projects in 2011 to 5 planned projects in 2014.
