By Huang Qili
Member of the Chinese Academy of Engineering
Former Chief Engineer, SGCC Northeast China Grid Company
Coal is the Foundation of the Energy Mix in China
China is the largest coal producer and consumer in the world. In 2012, China produced 3.65 billion tonnes of coal. By the end of 2010, China’s proven coal reserves were 114.5 billion tonnes, approximately 13.3% of the total proven global reserves. Coal accounts for over 96% of China’s fossil energy reserves, and coal output accounts for more than 85% of all fossil energy output. Since 1990, the proportion of coal production and consumption in China’s total energy mix has always been greater than 70%, considerably higher than the approximately 20% in the U.S. and about 30% globally. It is predicted that, in 2030, China’s coal consumption will still account for more than 55% of its primary energy.
At the end of 2012, China’s total installed power generation capacity was 1,144.9 GW, of which 758 GW was from coal-fired power plants. Hydro power contributed 248.9 GW (including pumped storage of 20.31 GW) accounting for 21.7% of installed capacity. There were 38.27 GW of gas power, accounting for 3.3% of the installed capacity. The 12.57 GW of nuclear power contributed 1.1% of installed capacity. Wind and solar power contributed 60.83 GW (5.3%) and 3.28 GW (0.3%), respectively. These statistics are shown graphically in Figure 1. In 2012, coal’s contribution to China’s energy production was a larger percentage than its share of the installed capacity; the electricity production of coal-fired power plants was 3,680 billion kWh, accounting for 73.9% of the total 4,980 billion kWh of electricity produced.1
Coal has been in the past, and will continue to be, the dominant energy source for China, which can be largely attributed to the large proven coal reserves. Table 1 provides predictions for China’s coal-fired power generation installed capacity for 2015–2050.2 Because coal in China will play a continued role in the energy mix, those who construct and operate coal-fired power plants must lead the way toward high-efficiency, clean, and low-carbon utilization of coal in China.
Strategic Development of Coal-Fired Power in China
As China continues its industrial modernization and urbanization over the coming decades, coal-fired power plants will play a critically important role in making the energy mix of China cleaner and more efficient. According to the Development Planning Department of the National Energy Administration, from 2010 to 2050 China will consume approximately 150 billion tonnes of coal, of which approximately 99 billion tonnes, or 66%, will be used for power generation.3 As coal-fired power generation continues to develop, it is necessary to put a strong emphasis on further improving efficiency and reducing the emissions of criteria pollutants and greenhouse gases simultaneously. To accomplish this, it is necessary to think comprehensively about the strategy for coal-fired power development from a macroenergy perspective.
Several strategic suggestions for improving coal-fired power plants in China are offered below.
(1) The development of coal-fired power plants should be based on giving equal attention to “innovation” and “promotion” (i.e., widespread adoption). China’s new power plants should be designed and built to be the most efficient in the world. For existing plants, the best technology options must be implemented to improve efficiency and reduce emissions. China also should support the development of clean coal technologies and then, once they are commercial, make these technologies widely available to the power generation industry.
There are already examples of improving efficiency and reducing emissions through technology. Today, pulverized coal and circulating fluidized bed boiler technologies are widely used and considered to be well-developed power generation technologies in China; the larger scale units with higher steam temperatures and pressures have dramatically increased the efficiency of China’s fleet of coal-fired power plants. With further technology-based innovations, highly advanced ultra-supercritical pulverized coal plants and large-scale circulating fluidized beds power plants will continue to increase efficiency and reduce overall emissions. Today, China already operates some of the most efficient power plants in the world. It’s very important to apply mature and advanced technologies widely and enhance the overall coal-fired power generation technology in China.
(2) Coal should be efficiently utilized for different purposes to make full use of its potential. Therefore, China should strive to develop advanced ultra-supercritical generating units with higher steam parameters and increased efficiency. At the same time, we should develop staged coal conversion to produce liquid fuels and chemicals. Finally, technologies should be implemented to recycle heat, precious metals, and other byproducts of coal combustion and gasification that might otherwise be considered waste.
By fully exploring the conversion pathways of different components in coal (C, H, O, N, S), researchers will develop new ways to convert coal into desired products. Conversion of coal can be realized by combining the coal pyrolysis, gasification, and combustion processes. Through these different pathways, low-cost coal gas, tar, and steam can be produced as coproducts of a single system. When coal is gasified to create syngas, it can be used for the production of chemicals or used as a fuel. Tar from gasification can be broken down into various kinds of aromatic hydrocarbons, alkanes, and phenols, and it also can be made into gasoline, diesel, and other products through hydrogenation. The steam generated from coal can be used for power generation and heat. The ash resulting from coal combustion contains aluminum, vanadium, gallium, and other precious metals which may be obtained through extraction. Through these pathways, the energy and resources in coal can be used in such a way that waste is minimized.
The coal-to-chemicals industry should focus on coal as a resource while the coal-fired power generation industry should focus on the energy contribution from coal. China should integrate the coal-to-chemicals industry and coal-fired power generation industry to realize the most efficient use of coal through the cogeneration of power, chemicals, thermal energy, coal gas, and precious metals, all based on coal as the starting material.
(3) Energy from fossil fuels and emerging renewable energy power generation should be jointly developed to create hybrid power systems. In the past few years, wind and solar power have developed rapidly in China. However, electricity production from these sources is largely intermittent and unstable. Moreover, renewable energy potential and proximity to energy demand vary significantly. In addition to wind and solar, hydro power is strongly influenced by seasonal and regional characteristics. How best to integrate renewables, which are greatly affected by weather and seasons, with stable coal-fired power plants poses significant design and managerial challenges. These challenges must be solved through research and development, and should be solved so as to make full use of renewable energy and the high-efficiency of coal-fired units.
Key Technologies for the Continued Advancement of High-Efficiency Coal-Fired Power Generation
Advanced Ultra-supercritical Coal-fired Power Generation Technology
Since the beginning of the 21st century, China has made great advancements in improving coal-fired power generation. The first 1 GW ultra-supercritical coal-fired unit was placed in operation at the end of 2006 at the Zhejiang Yuhuan Power Plant. Since then, orders for 1 GW ultra-supercritical units are known to have far exceeded 100. By the end of July 2012, 46 units had been constructed and are operating. China has become a world leader in the number of installed and ordered large-scale (i.e., >1 GW) ultra-supercritical units.
Once ultra-supercritical power generation with 600°C steam temperatures was considered commercially mature, several countries launched plans to develop advanced ultra-supercritical power plants with steam temperatures above 700°C (e.g., the European AD700 plan, the American A-USC (760) plan, and the Japanese A-USC). The purpose of these plans is to increase coal-fired power generation efficiency to more than 50%. In addition, on July 23, 2010, the Chinese National Energy Administration announced the establishment of a “National Innovation Union of 700°C Ultra-supercritical Coal-fired Power Generation Technology,” formally launching China’s 700°C ultra-supercritical technology development plan. This plan is mainly focused on research related to the optimal design of unit systems and major equipment as well as the development of the necessary thermally resistant alloys.5,6 Construction of the 700°C steam temperature demonstration project is expected to begin in 2018; the targeted demonstration completion date is approximately 2020. The government should make great efforts to support relevant scientific research and project demonstrations, such as the ultra- supercritical demonstration, to support technology development. In addition, the government should also encourage widespread implementation of these highly efficient plants after they reach commercial maturity.
Shanghai Waigaoqiao Power Plant is an example of an ultra-supercritical plant that is already in operation. This plant is equipped with 2×1,000 MW ultra-supercritical units; construction and initial operation of these units were completed in March and June 2008, respectively. For these units, the designed coal consumption rate was 295 g/kWh with a design net efficiency of 41.6%. Subsequent to the initial power plant design and construction, several technological innovations were made, such as energy-saving desulfurization technology, elastic regenerative technology, steam heating launching technology, operation optimization and energy saving and comprehensive treatment technology of solid particle erosion, etc. Based on these improvements, the net unit efficiency has been improving year-after year. By the end of 2011, with an overall capacity factor of 75%, the actual net coal consumption rate was 276 g/kWh and the net plant efficiency was 44.5% (including desulfurization and denitration). Based on the original design, the plant efficiency would be nearly 46.5%, which is a 5% increase over the design value, demonstrating that energy savings and emissions reductions were simultaneously achieved.5-6
Circulating Fluidized Bed (CFB) Combustion
China is an international leader in technology development for circulating fluidized bed combustion for power generation. Because CFBs have unique advantages with regards to fuel adaptability, load following, emissions reductions, and operating costs, it is likely that the utilization of CFBs will continue. Currently, the total installed capacity of the CFBs in China is 73 GW, accounting for approximately 17% of the total coalfired power generation installed capacity.7 New CFBs are becoming increasingly efficient, larger, more reliable, and have decreasing emissions. The world’s largest and most efficient 600 MW supercritical CFB was placed into operation at the end of 2012.7
Through technical innovation related to evaluation of the gas-solids flow regime, Tsinghua University demonstrated substantial improvement of electricity utilization, combustion efficiency, and availability ratio. The technology demonstrated at Tsinghua University leads the way in the advancement of CFBs for power generation. It can be expected that, within this century, coal-fired CFB technology will experience continued development, and become increasingly important for obtaining high-efficiency coal-fired power generation.
Polygeneration Based on Coal Gasification
Generating synthesis gas after gasification of coal is the foundation for polygeneration (or coproduction). Using coal as the feedstock, polygeneration technologies can result in a range of products, such as electricity, chemicals, heat, liquid fuels, and natural gas. Both electricity and higher value products (e.g., chemical products and fuel gas used by urban residents) can be produced at the same facility. Integrated gasification and combined cycle (IGCC) technology is a combination of gasification used for the production of clean coal-based electricity production. Electricity generation based on IGCC has demonstrated significantly lower emission levels and can also facilitate the separation of CO2.
Power plants that implement polygeneration operate in such a way that they achieve the goals of efficient electricity production and full utilization of coal as a resource. This technology offers benefits across multi-disciplinary fields, and it is one of the best options for the high-efficiency, clean, and low-carbon utilization of coal. Therefore, development and demonstration of polygeneration facilities should be supported in such a way to promote the technology and increase the number of demonstration projects. China should strongly support research and development to tackle the problems facing polygeneration (such as overcoming issues with the combustion gas turbine and high-efficiency combustion chamber, etc.) so as to move polyproduction toward commercial maturity.
Use Coal and Renewable Energy as Hybrid Power Generation Options
In this century, China should begin to modify its energy mix to increasingly include clean energy options such as renewables. We should combine fossil energy with renewable energy to encourage the mutual development of coal-fired power and renewable energy generation. Renewable energy could assist the development of fossil energy and fossil energy could drive the development of renewable energy. For example, the heat energy produced by solar energy can enter the regeneration system of a coal-fired power plant to replace part of regenerative extraction steam; power generated by renewables such as solar, wind, and small hydro power can enter the local power plant’s electricity utilization system to supply more power without changing the levels of coal combustion; renewables could also be used to save coal capacity while still creating the same amount of total power. The huge regeneration system and power plant electricity utilization system of large-capacity coal-fired units can absorb the fluctuations associated with wind and solar power. If the geographical placement of the coal-fired power generation, renewable energy, and the power grid are considered together in comprehensive planning, the instability and geographical limitations associated with renewable energy can be mitigated to ensure the safe and high-efficiency operation of power generation systems based on both coal and renewables.
China’s energy reserves have predetermined that coal will dominate the energy mix in China for the foreseeable future. Coal-fired power plants account for an overwhelming majority of the installed power capacity in China. Making efforts to develop and promote high-efficiency, clean, and low-carbon coal-fired power generation technology has great significance to promote the scientific development of coal-fired power generation. This is an important policy that is directly related to the sustainable development of the national economy.
1. National Power Planning Research Center. Forecast of Power Generation Capacity and Power Demand Development of China in the Future, China Energy News, 2013-02-18 (1).
2. Huang Qili, Gao Hu, Zhao Yongqiang. China’s Medium and Long-term (2030, 2050) Development Strategic Objective and Approach of Renewable Energy, Chinese Engineering Science, 2011, 13(6): 88–94.
3. Xu Gang, TianLonghu, Liu Tong, et al. Analysis on CO2 Emission Reduction Strategy in China’s Electric Power Supply, Proceedings of the Chinese Society for Electrical Engineering, 2011, 31(17), 1–8.
4. Han Zhenxing, Liu Shi, Li Zhihong, et al. Coal Combustion Technology Comparison with Different Types of Power Generating Units, Thermal Power Generation, 2012, 41(2), 1–3, 7.
5. Feng Weizhong. Energy Saving Technology of Waigaoqiao Phase III 1GW Ultra-supercritical Unit, Energy Research & Utilization, 2011, (6): 42–47.
6. Zhang Yanping, Cai Xiaoyan, Huang Shuhong. Research and Development Status of Material in 700