Efficient and clean use of fossil energy under the "double carbon" goal



China's rapid economic development is the driving force behind the rapid growth of fossil energy production and consumption. Since 2005, China has been the largest emitter of energy-related carbon dioxide (CO2). Power and industry are the main battlefields of fossil energy consumption in China, and industries such as power, steel, building materials and chemical industry have therefore become large CO2 emitters in China. Therefore, the efficient use of fossil energy is the key to achieve the goal of carbon peak and carbon neutrality (hereinafter referred to as "double carbon") in China.

China's energy and resource endowment and incompatible energy structure, complex international environment, rapid and high-quality economic and social development and the need to cope with the change of gasification and other factors require that we must unswervingly promote the energy revolution. Especially under the requirements of the "dual carbon" goal, the task of CO2 emission reduction in the medium and long term development of energy is more clear, and it is necessary to comprehensively promote the large-scale development and utilization of clean energy and build a diversified clean energy supply system. Fossil energy is still the main source of energy, which needs total control and orderly replacement. To realize the efficient, clean and low-carbon use of fossil energy is the top priority in promoting the energy revolution and transformation, and building a clean, low-carbon, safe and efficient energy system.

Current situation of fossil energy utilization in China

Coal-fired power generation technology

Since the founding of New China, with the continuous investment and support of the state, coal-fired power generation technology has made great progress, and coal-fired power generation technology and equipment continue to develop in the direction of high parameters, large capacity and low emissions. At present, China has reached the world advanced level in ultra-supercritical coal-fired power generation technology, circulating fluidized bed combustion technology, and ultra-low emission technology of conventional flue gas pollutants. The coal consumption of coal-fired power units shows a gradual decreasing trend, but the decline of coal consumption gradually slows down due to the reduction of peak load and utilization time of the units (Table 1).

Clean coal-fired power generation. After more than 10 years of development, the discharge of conventional pollutants from coal-fired power generation has been effectively controlled. By the end of 2020, China has a total of 4,990 coal power units with an installed capacity of 1.08 billion kilowatts, and more than 950 million kilowatts of coal power units have reached the ultra-low emission limit. China has built the world's largest clean coal-fired power generation system, and conventional pollutants are no longer the main constraint on coal-fired power generation, and are currently working towards a near-zero level.

Efficient coal-fired power generation. In the past few decades, coal power units have been developing towards high parameters. Advanced ultra-supercritical power generation technology is the world's main coal-fired efficient power generation technology, which includes double reheat ultra-supercritical unit and ultra-supercritical circulating fluidized bed unit. Since the Tenth Five-Year Plan, China has deployed key projects and continued to support the research and development and application of ultra-supercritical power generation technology; During the "13th Five-Year Plan" period, six secondary reheating units were put into operation successively in Anyuan, Taizhou, Laiwu, Bengbu, Suqian and Jurong, with two types of steam parameters: 31 MPa/600℃/610℃/610℃ and 31 MPa/600℃/620℃/620℃. In addition, two ultra-supercritical 660 MW circulating fluidized bed coal-fired generating units in Weihe, Guizhou Province and Binchang, Shaanxi Province were started. In 2020, ultra-supercritical units will account for 26% of the total installed capacity of active coal power units in China, of which 137 are in service with 1,000 MW grade ultra-supercritical units, with an average coal consumption of 283.59 g/kWh for the overall power supply. At present, China has accumulated rich experience in the design, manufacturing and operation of ultra-supercritical generating units, and related technologies have achieved leapfrog development: as a whole, it is synchronized with the international advanced level, and the technical indicators such as power supply coal consumption and power generation efficiency of some units have achieved world leadership, and the development speed, installed capacity and number of units have ranked first in the world.

Industrial process combustion technology

Coal combustion and utilization forms in the industrial field are mainly coal-fired industrial boilers and industrial kilns.

Coal-fired industrial boilers. There are nearly 500,000 coal-fired industrial boilers in service in China, accounting for about 20% of the country's total coal consumption. At present, China's coal-fired industrial boilers are mainly chain stokers, and the actual operation combustion efficiency and boiler thermal efficiency are about 15% lower than the international advanced level. In recent years, circulating fluidized bed boiler technology has also been well applied, forming 35 t/h, 65 t/h, 75 t/h, 130 t/h, 240 t/h steam boiler series; In addition, some pulverized coal industrial boilers have been promoted and applied in the market. Compared with the chain furnace, the thermal efficiency of circulating fluidized bed and pulverized coal industrial boilers has been greatly improved, which has been close to 90%, and the original emission level of nitrogen oxides (NOx) has also been greatly reduced. However, due to the large number of coal-fired industrial boilers, there are still problems of high overall energy consumption and heavy pollution.

Industrial kiln. Coal is the main fuel and raw material of metallurgy, building materials and other basic industries, China's industrial furnace stock is huge, but due to backward technology and process equipment and other reasons, there are widespread problems such as low system thermal efficiency, high energy consumption, poor fuel adaptability, and high original pollutant emission concentration. Taking cement as an example, the number of dry cement clinker production lines in the country is about 1 500; The thermal efficiency of the core equipment of these production lines is generally low, the energy saving potential is large, and most of them have not achieved ultra-low emission of conventional pollutants, and discharged a large amount of CO2. In 2020, China's cement clinker output is 1.579 billion tons, cement output is 2.377 billion tons, and CO2 emissions from the cement industry account for nearly 14.3% of the total national emissions. The CO2 emissions of tons of cement and tons of cement clinker are about 616.6 kg and 865.8 kg respectively, and the emission reduction task is arduous. Therefore, the field of industrial furnaces is in urgent need of transformative technologies to promote the direction of energy conservation, environmental protection and effective improvement of resource utilization.

Coal conversion technology

In 2020, China's coal chemical industry (including coking) will use about 797 million tons of standard coal, accounting for about 28% of the country's coal consumption. According to the estimation of CO2 generated by the production process of coal conversion into chemical products, the annual CO2 emission is about 677 million tons, accounting for about 5.75% of the national carbon emissions.

In the past 10 years, China's coal conversion technology has made remarkable progress, mainly developing coal to clean fuels (such as coal to oil and coal to natural gas, etc.) and bulk and special chemicals (such as coal to methanol, olefin, ethylene glycol, etc.) two major categories of technology and products. The largest single coal processing capacity of China's coal gasification plant has reached 4 000 tons/day, which supports the development of modern coal chemical industry.

Coal to clean fuel. In the coal-to-oil field, a number of technology demonstration projects with independent intellectual property rights have been completed and put into operation. At present, 10 sets of coal-to-oil projects have been completed, and major projects such as indirect coal liquefaction of 4 million tons/year and direct coal liquefaction of 1.08 million tons/year have been successfully operated.

In terms of coal-to-natural gas, China has built four sets of coal-to-natural gas demonstration and industrialization projects, but low-cost coal gasification technology and methanation technology are still in the research and development stage, so the economic benefits of coal-to-synthetic natural gas products are poor, limiting the promotion and application.

Coal to bulk and specialty chemicals. Coal to olefin, coal to ethylene glycol and other technologies have made breakthroughs, has built 32 sets of coal (methanol) to olefin, 24 sets of coal to ethylene glycol demonstration and industrialization promotion projects, successful operation of 1.37 million tons/year coal to olefin and other large-scale modern coal chemical plant.

China's coal chemical industry technology is generally in the world's leading level, but large coal consumption, hard to deal with solid waste, carbon emission problems are still facing the development of China's coal chemical industry. In the coupled utilization of coal conversion, coal to special fuels, coal to oxygen compounds and other high-value compounds and degradable materials, there is still a need to further breakthrough key technologies, the formation of advanced complete sets of process technology, to achieve clean and efficient utilization of coal, and ensure oil and gas safety.

Oil and natural gas utilization technology

In 2020, the carbon emissions of China's oil and natural gas industry will account for 20.8% of the total carbon emissions, and the pressure to reduce emissions is greater under the "double carbon" goal.

Oil. The upstream and downstream carbon emissions of the petroleum and petrochemical industry chain account for a relatively high proportion, among which petroleum exploitation and refining are prominent processes with high energy consumption and high carbon emissions. In oil downstream applications, the use of petroleum fuel properties occupies a dominant position, while the proportion of chemicals is relatively low (generally less than 20%). Under the "dual carbon" goal, with the development of energy consumption from fuel to electrification, the fuel attribute of oil in terminal consumption will be greatly weakened in the future, and traditional oil utilization modes such as transportation oil will be gradually replaced by electrification. Therefore, the oil utilization process faces the pressure of energy efficiency improvement, substantial carbon reduction and deep adjustment of product structure.

Natural gas. Natural gas is mainly used as city gas, industrial fuel and raw material. City gas is mainly used for residential life, heating, and compressed natural gas (CNG) for vehicles. The industrial applications of natural gas mainly include metallurgy, building materials and chemical industry. Natural gas power generation is mainly used in peaking power plants and distributed cogeneration. Under the goal of "dual carbon", on the one hand, the utilization process of natural gas faces the challenge of improving efficiency and reducing carbon, and on the other hand, natural gas can actively play the role of "bridge" in the transition process of energy main body from fossil energy to non-fossil energy.

Fossil energy utilization faces new challenges under the goal of "dual carbon"

Challenge 1: There is an urgent need for flexible peak regulation of coal power to smooth the intermittency and volatility of renewable energy and ensure the stability and security of electricity. Building a new power system with new energy as the main body is the foundation, key and core of realizing "double carbon", and the energy status of coal will change from "main body" to "foundation" and then to "guarantee". In view of the characteristics of renewable energy power such as volatility, randomness, intermittent, long-term large capacity of advanced energy storage technology has not yet appeared, coal-fired power generation needs to give full play to the role of "stabilizer" and "ballast stone" in the energy system, in the process of energy structure transformation for the grid to absorb a large proportion of renewable energy to provide flexible peak load capacity. However, the existing coal-fired generating units are designed according to base load, which is difficult to operate in the mode of wide load and rapid load change, resulting in a serious shortage of flexible resources in China's power system, which affects the stability and security of power. It is urgent to develop and promote flexible peaking technology of coal-fired generating units to meet the major demand for renewable energy consumption of power grids.

Challenge 2: As the main fuel and raw material of basic industries, coal urgently needs to be low-carbon and efficient use to ensure the safety of the industrial chain. Coal is the main fuel and raw material for basic industries such as metallurgy and building materials. At present, China's industrial boiler and furnace stock is huge, there are widespread problems such as low thermal efficiency, high energy consumption, serious pollution and so on, while discharging a large amount of CO2; Reducing carbon emissions poses a challenge to the production energy of the industrial chain. We must step up energy conservation and emission reduction efforts, improve energy efficiency, and reduce the intensity of carbon emissions at the source.

Challenge 3: The international situation is complex, and there is an urgent need for coal-to-oil/gas chemicals to supplement and replace imports to ensure national oil and gas security. China's coal chemical industry assumes the role of energy security, especially in the current complex international situation, coal to oil/gas chemicals, the realization of oil/gas supplement and replace imports, is to ensure national oil/gas security needs. However, in China's coal chemical industry, the coal chemical process is too long, and the investment and operation cost are too high. High energy consumption and large carbon emission in the production process; The product structure is not reasonable, there are deficiencies in differentiation and high-end, and the product flexibility is not enough; The disposal cost of "three wastes" (waste water, waste gas, solid waste) in coal chemical industry is high. In the context of "dual carbon", the coal chemical industry must speed up the transformation and upgrading, and take the road of low-carbon technology and high-end products.

Challenge 4: Under the goal of "dual carbon", the status of oil/gas is redefined, facing challenges such as the transformation of utilization attributes, high-end products, and low-cost. Under the "dual carbon" goal, natural gas, as the cleanest fossil energy, will maintain rapid development, and will become the "bridge" of the transition from fossil energy to new energy, and play a pillar role in the future global energy development; However, its use faces the challenge of further improving energy efficiency and reducing carbon. Oil consumption is gradually reduced, and the property of raw materials is returned, and the use of oil is facing challenges such as high-end products and further reduction of costs.

Efficient and clean utilization of fossil energy under the goal of "double carbon"

In the context of the "dual carbon" goal and the energy revolution, in the process of establishing a new energy system, the comparative advantage of various energy sources will depend on the progress of their own technological innovation. It is necessary to base on the basic national conditions of coal, promote the clean and efficient use of coal and other fossil energy, and realize the transformation of energy supply entities in stages. Through the revolutionary innovation of coal, oil, natural gas and other fossil energy utilization technology, accelerate the transformation of coal resources from fuel attributes to raw material and fuel coupling attributes; Carry out technological innovation and demonstration of typical processes of coal combustion and conversion and utilization in power generation, industrial energy use and chemical industry, as well as technological innovation and demonstration of high-value utilization of natural gas combustion, to further improve the use of petroleum raw materials; Promote the complementary integration of fossil energy and renewable energy, achieve the improvement of system energy efficiency, ensure China's energy security and industrial chain security, and promote the low-carbon development of China's energy and related industries.

Development proposals for efficient and clean utilization of fossil energy under the "double carbon" goal

The efficient and clean utilization technology of fossil energy is the key to the transformation of the national energy structure, and is the key means and way to effectively support the realization of the "dual carbon" goal. In the context of the energy revolution and the new situation of the "double carbon" goal, vigorously develop the efficient and clean utilization of fossil energy technologies, promote the efficient combustion and transformation of coal, the efficient utilization of oil and gas, and the research and application of the "three wastes" treatment technology of coal chemical industry, and strengthen the coupling of the fuel and raw material properties of fossil resources, which is of great significance to achieve the transformation of the national energy structure.

5.1 Efficient coal combustion and low-carbon conversion technology

At this stage, coal is still the main body of energy in our country, technological change and innovation, technological transformation and tapping potential is the main focus of clean and efficient use of coal, the National Energy Administration issued the coal power unit transformation and upgrading implementation plan in the "three reform linkage" is the specific support policy. In order to realize the combination of coal utilization and breaking in the process of energy transformation under the goal of "dual carbon", it is necessary to vigorously develop the typical industrial process coal utilization reform technology suitable for carbon peak and carbon neutrality, strengthen the attributes of coal fuel and raw materials, improve the utilization level of coal stock, and promote the research and development and application of coal efficient and low-carbon technology in a safe and orderly manner. Under this objective and background, the Chinese Academy of Sciences has deployed the strategic pilot science and technology project (Class A) "Clean Coal Combustion and Low carbon utilization", aiming at the efficient and low carbon utilization of coal, strengthening the coupling utilization of coal fuel properties and raw material properties and equipment process strengthening as a means to strengthen the research and development of key technologies and engineering verification, and promoting technology engineering demonstration. To realize the reduction, low-carbon and clean utilization of coal, and provide technical support for building a safe, efficient, low-carbon and clean energy system.

Flexible peak regulation technology of coal-fired boiler. The rapid development of renewable energy generation has injected new vitality into the low-carbon transformation of China's energy system. Because of the fluctuation and intermittency of renewable power, it affects the safe and stable operation of power system. At present, there is no large-scale, low-cost, long-period advanced energy storage technology available, there is an urgent need for coal power deep flexible peak regulation technology to meet the needs of large-scale renewable energy access to the grid. Accelerate the development and application of deep flexible peak regulation technology, ultra-low load stable combustion technology, and efficient flexible power-heat dual supply technology for coal-fired boilers, so as to achieve deep peak regulation and rapid load change of boilers, and protect the high proportion of renewable energy power generation connected to the grid. In particular, after 2030, coal will gradually transition to basic energy and secure energy.