Research On Coal-fired Power Plants Near-zero Emission Technologies And Applications

China’s energy resources can be characterized as "rich in coal,not abundant oil,and very little natural gas.” The Chinese coal-dominated energy matrix is difficult to change in the short-term.At present,coal for power generation accounts for about 50% of the total coal consumption in China.This has resulted in environmental pollution issues,especially air pollution has become increasingly prominent due to the extensive use of coal.Thus,vigorously promoting the clean and efficient use of coal is an inevitable requirement of China’s energy security,byusing safe,efficient,low-carbon modern energy systems.This thesis focuses on coal utilization in Chinese coal-fired power plants using near-zero emissions technology.The near-zero emissions technology is designed to achieve the same emissions standards than natural gas turbine cycle units for particulate matter,SO₂ andNOx.The associated regulation is called “Emissions standard of air pollutants for thermal power plants”（GB13223-2011）,which was published on January 1,2012.The emissions concentration limits for dust,SO₂ and NOx from coal-fired power plants are 5,35 and 50 mg/Nm³,respectively.This thesis discusses the feasibility of near-zero emissions standards under the current power plants conditions in China.A technical roadmap for near-zero emissions has been introduced,which follows a strategy of that includes low-nitrogen combustion;selective catalytic reduction;low-temperature economizer;low-temperature electrostatic precipitator,high efficiency wet desulfurization and wet electrostatic precipitator.Zhejiang Zhoushan Unit 4 is a unit that has completed a near-zero emission engineering demonstration with the first wet electrostatic precipitator made in China.Unit 1 in Hebei Sanhe power plant also has completed the technological retrofitted of near-zero emission.The project is an environmental demonstration project of coal-fired power generating units recognized by the National Energy Bureau.Emission reduction effect is significant after retrofitted.Emission concentration of dust has been down to 0.23 mg/m³ in unit 4 in Sanhe power plant after the retrofitted.The near-zero emission technology has been applied to over 56 coal-fired units（28504MW）in nationwide,and national or local environmental monitoring units confirmed that the emissions from 56 units have all reached the near-zero emission standards.Several typical case ofnear-zero emissions were studies.The thesis studied the emissions of 300MW（350MW）subcritical units,350 MW supercritical units,600 MW subcritical units,660 MW supercritical units and1000 MW ultra-supercritical units.Although,the results of long-term run show that the concentration of pollutant emissions have been affected a little under different operating loads and coal qualities,the concentrations of dust、SO₂、NOx still meet the near-zero emission standards.The effects of different pollutant control units on PM_2.5 and SO₃ emissions are reported in this thesis.Results show that wet electrostatic precipitators have a very high removal efficiency of PM_2.5,PM10,and SO₃.PM_2.5,PM10,SO₃ removal efficiency is in the range of 98.37,97.31 and 42.23%,respectively.Desulfurization and dust removal integrated devices have demonstrated a synergistic effect on dust removal.Dust removal efficiency increases from 35% to 85% under rated load conditions with such integrated device.After a low-temperature economizer is put into operation,SO₃ concentration was seen to decrease from 15.35 to 8.27mg/m³,and SO₃ removal efficiency increases from 25.88 to 46.12%.The cost analysis of some 300 1000 MW units were also carried out.Operating costs increased 0.26¹.13 cents/kWh from retrofitted the standardized emission set up（limit concentrations of dust,SO₂,NOx from coal-fired power plants were 20,50,100 mg/m³）to the near-zero emission set up.The cost analysis show that the near-zero emissions coal-fired power plant is cheaper than that of gas turbine power plant.In order to study the reduction effect of air pollutants emission before and after near-zero emissionsretrofitted.The thesis utilized the emission data of coal-fired power plants in 2013 from Ministry of Environmental Protection,China Electricity Council and local government.If all coal-fired power plants of China achieve the near-zero emission standards,the reduction emissions of dust,SO₂,NOx emissions are 95.3%,94.3%,92% of the total emissions in the coal-fired power plants.This thesis has proved that the technology roadmap of near-zero emission in the coal-fired power plants is feasible and it can be achieved by theequipment which made in China.The economy also has a comparative advantage.The environmental effects and social benefits are remarkable.The coal-fired power plants with near-zero emission can achieve the emissions standards of the natural gas turbine units,consistent with the “ coal is transformed into electricity by tightly controlled combustion with high technology” in Environmental Protection Law.The electric from coal-fired power plants with near-zero emission is a “safe,clean,economic” energy.