Advanced technology resolves CO2 emission reduction crisis
Advanced technology resolves CO2 emission reduction crisis
口 Zhang Xinping Zhang Wang Zhang Jianli/China University of Petroleum (East China)
张新平 张王 张建丽/中国石油大学 (华东)
With the high development of industry and people's dependence on fossil fuels, the emission of CO2 is increasing day by day, which produces a greenhouse effect and increases the global temperature. It is generally believed that when climate change is below 2°C, positive and negative effects are basically coexisting; once it exceeds 2°C, the positive effects are greatly reduced or do not exist; and when it reaches 3°C-4°C, it is basically negative. impact, and the effect of negative impact is significantly intensified. Almost all scientists believe that the increase in carbon dioxide emissions will bring more adverse consequences such as droughts, floods, land desertification, heat waves, diseases, rising sea levels and species extinction, resulting in serious environmental and ecological crises.
In order to reduce CO2 emissions, slow down the greenhouse effect and protect the global environment, all countries in the world are making unremitting efforts. The world's first "United Nations Framework Convention on Climate Change" to comprehensively control CO2 and other greenhouse gas emissions stipulates that developed and developing countries have "common but differentiated responsibilities" for emission reduction; more in the "Kyoto Protocol" It puts forward specific emission reduction requirements for developed countries; now the Copenhagen Climate Conference has brought CO2 emission reduction to the forefront again, requiring both developed and developing countries to reduce emissions. The CO2 problem has caused serious political and economic pressure on countries.
The current emission reduction measures are mainly to improve energy utilization, develop new energy and increase carbon sinks. These measures can alleviate the greenhouse effect to a certain extent, but there are certain limitations to solve the problem of a large amount of CO2 emissions within a certain period of time. Therefore, many scientists in developed countries have proposed CO2 capture and storage technologies, and believe that CO2 geological storage is the most realistic and effective way to reduce CO2 emissions.
The primary link of CO2 sequestration
The basic idea of CO2 sequestration technology is to inject CO2 separated from centralized emission sources (power plants, steel plants, etc.) into deep underground formations with appropriate sealing conditions for isolation. It mainly includes the following links: First, the use of adsorption, absorption, low temperature and membrane systems and other technologies to capture and separate the waste gas from large-scale centralized emission sources (power plants, steel plants, etc.) to obtain pure CO2, which is compressed by compressors. Then it reaches the required state; then it is sent to the isolation site through a pipeline or other transportation methods; finally, the pressure is adjusted and injected into the deep underground, as shown in Picture 1.
Capture systems are generally divided into four categories: post-combustion capture systems, pre-combustion capture systems, oxy-combustion systems, and industrial processing. The capture technology currently being vigorously developed is mainly aimed at CO2 emitted by power stations. There are mainly three technical routes, as shown in Picture 2: post-combustion decarbonization, pre-combustion decarbonization and oxy-fuel combustion technology.
The post-combustion capture system is a system that captures CO2 from the fuel gas produced by the combustion of the fuel in the air; the pre-combustion capture system is to gasify the CO2-containing fuel into a fuel (a mixture of hydrogen and carbon monoxide), and through the reaction The post-generated CO2 is collected; the oxygen-enriched combustion system burns the fuel in an oxygen-enriched environment, and the CO2 after combustion is easily separated.
At present, there are five main methods for capturing CO2: adsorption method, absorption method, low temperature method, membrane system method, and hydrate method.
Three major areas
Especially suitable for CO2 storage
As can be seen from Picture 2, the underground storage sites of CO2 mainly include oil and gas fields, coal fields and saline aquifers. The first two can increase the production of oil and gas and coalbed methane while sequestering them.
CO2 is stored in oil and gas fields, and CO2 is injected into the oil and gas layers that have been exploited. Under high pressure conditions, CO2 promotes the flow of oil and gas to production wells, thereby increasing the recovery rate of oil and gas. Part of the CO2 dissolves in the unexploited oil and gas or is stored in the formation pores. In the past, some abandoned gas fields were used for backup storage of natural gas, and these related technologies can be used for CO2 storage. Currently, there has been commercial application of CO2 injection into nearby gas reservoirs for enhanced gas recovery (EGR) for geological storage. The technology is well understood, but the rollout is limited. Storing CO2 in depleted fields is inexpensive to develop, and traps have proven effective. As early as the early 1970s, CO2 was extracted from natural reservoirs in the western United States and transported by pipeline to Texas for injection into reservoirs for enhanced oil recovery (IEA, 2003). Through CO2-EOR, the output of 8%-15% of the original reserves can be obtained, so that the total recovery factor can reach 50% on average, and 2.4-3 tons of CO2 can be stored to produce 1 ton of oil.
Buried in coal seams, in coal measure strata, there are generally coal seams abandoned for technical or economic reasons, such as unminable thin coal seams, deep coal seams buried beyond the final mining line, and coal seams with severe structural damage, etc. These unminable coal seams are another potential geological formation for sequestering CO2. When CO2 is injected into such a coal seam, similar to the process of using activated carbon to filter impurities in air and water, they diffuse in the pores of the coal seam and are eventually adsorbed by the coal body. Experiments have shown that the adsorption capacity of the coal surface for CO2 is about twice that of the adsorption capacity for methane. According to this characteristic, when CO2 is injected into the coal seam, it can effectively replace methane while sequestering CO2, so that the methane in the adsorbed state can be converted into a free state, which can greatly enhance the output rate of coalbed methane and improve the output of coalbed methane.
Sequestration of CO2 in saline aquifers, injection into deep saline aquifers Sequestration is to store CO2 in deep saline aquifers to prevent short-term or long-term (hundreds to thousands of years) release of CO2 into the atmosphere. It is technically feasible to inject CO2 into water layers, just like injecting CO2 into oil and gas fields for enhanced oil recovery. The demonstration project for sequestration of associated CO2 water layers in the Sleiper gas field in Norway is a good proof.
The brine layer is a sedimentary rock composed of carbonatite or sandstone with a certain porosity and permeability. The pores are filled with brine, and generally the upper part has a good trap structure. After CO2 is injected into the groundwater layer, it is buried in the stratum by dissolving, reacting with the rock minerals in the stratum and trapped by the good upper caprock.
Technology areas that need to be broken through
The CO2 delivery system is an important link between the capture and permanent storage sites. From the perspective of system optimization, the research on CO2 transportation technology is still insufficient, so the CO2 transportation process needs to be further optimized to maximize the energy efficiency and reduce the cost of the process.
If the CO2 gas source is far away from the production site, the transportation method and the equipment used must be carefully selected according to the actual situation of the CO2 gas source and other factors. CO2 can be delivered in bulk by truck, rail or ship, or by pipeline. As with other gases, it is most convenient and economical to transport CO2 in a liquid or critical dense phase. The two preferred transport modes for CO2 are pipeline transport and tanker (specialized CO2 gas storage vessel) transport. Under normal circumstances, since the CO2 injection site is generally far from its recovery site, pipeline transportation is the most effective transportation method. For extremely long-distance maritime transportation, shipping may also be a more economical transportation method.
Based on the technology and experience of the petroleum industry, the drilling, completion and monitoring technologies of CO2 injection wells have a certain foundation. The design and construction of CO2 injection wells is very similar to the design and construction of gas injection wells in oil and gas extraction projects. The main difference is that the construction of CO2 injection wells requires higher pressure resistance and corrosion resistance of down-drilling components. The injection of CO2 in a single-phase state, generally in a supercritical state, is not only conducive to injection, but also inhibits the formation of hydrates.
When CO2 is buried underground, the physical and chemical reactions of CO2 injected into the reservoir should be monitored, and the most important thing is to monitor the potential migration of CO2 inside and outside the reservoir. Collecting production data samples is the main way to monitor CO2 migration in the reservoir. "Sampling" provides data on downhole pressures, injected volumes, reservoir gases and fluids.
The greenhouse effect caused by the massive emission of CO2 has caused a series of environmental and ecological problems; it has also brought political and economic pressure to countries. The research found that the CO2 geological storage technology is feasible in solving the CO2 emission problem. As the most realistic and effective emission reduction method, CO2 capture and storage technology is increasingly favored by people.
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CO2 emission reduction crisis, greenhouse effect, environmental and ecological crisis, emission reduction requirements, political and economic pressure, improving energy efficiency, developing new energy, CO2 capture and storage technology, capture system, post-combustion decarbonization, pre-combustion Decarbonization, Oxygen-enriched Combustion Technology, Oxygen-enriched Combustion System, Brine Sequestration, Coal Sequestration, CO2 Delivery System, Supercritical State.
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