With the continuous attention to environmental protection, energy conservation and emission reduction, pollutant control technology for coal-fired units also needs to be continuously upgraded to reduce pollutant emissions. The "Coal Energy Conservation and Emission Reduction Upgrade and Transformation Action Plan (2014-2020)" issued by the National Energy Administration in 2014 requires that the atmospheric pollutant emission concentration of coal-fired power units in eastern regions such as Shanghai meet the gas turbine emission limit. Shanghai also requires that the emission indicators of the unit after the renovation meet the ultra-clean emission requirements, that is, the concentrations of dust, SO2 and NOx are less than 5mg/Nm3, 35mg/Nm3 and 50mg/Nm3 respectively, and white smoke plumes are basically eliminated. Therefore, our company decided to carry out ultra-clean emission transformation. At present, very few units in China have completed ultra-clean emission transformation, especially those with dust concentrations less than 5mg/Nm3. Most of them use wet electrostatic precipitation. Although the emission concentration of conventional wet electrostatic precipitators meets the requirements, the investment is huge, the system is complex, the maintenance cost is high, and the output of the original induced draft fan cannot meet the transformation requirements. At the same time, on the million-class tower furnaces built in China, there are two technologies to achieve full-load denitrification: economizer separation arrangement and zero-number high-pressure heater. Both solutions have large investment, and our company's existing equipment does not have the ability to implement these two solutions. Through in-depth theoretical analysis and field research, our company has studied an innovative solution for ultra-clean emissions. This solution can achieve a dust emission concentration of less than 5 mg/m3 without installing wet electrostatic precipitator, eliminate white smoke plumes, and achieve full-load denitrification, improve denitrification efficiency, and effectively arrange heating surfaces to achieve heat exchange effects when the output of the induced draft fan is limited. The main contents of this innovative ultra-clean emission plan are: 1. A flue gas cooler is added between the air preheater and the electrostatic precipitator to reduce the flue gas temperature at the electrostatic precipitator inlet, reduce the flue gas temperature at the electrostatic precipitator inlet from 100℃-120 ℃ to 90℃, and reduce the specific resistance of dust, thereby reducing the dust concentration at the electrostatic precipitator outlet by about 30%, and can be controlled below 15mg/Nm3. At the same time, more efficient demister is adopted in the absorption tower to reduce the droplet concentration at the outlet of the absorption tower, so as to improve the dust removal efficiency of the absorption tower. Two-stage flue demister is installed in the flue, and the droplet concentration is reduced from 75mg/Nm3 in the original design to 15mg/Nm3. The dust removal efficiency of the absorption tower is improved from 30% to 60-70% at present. Therefore, the dust concentration at the chimney inlet is less than 5mg/Nm3. 2. In view of the phenomenon of white smoke plume, a flue gas heater is arranged at the entrance of the chimney, that is, the heat recovered by medium water in the flue gas cooler heats the flue gas at the entrance of the chimney in the flue gas heater to make its temperature rise to more than 80 ° C, so as to basically eliminate the white smoke plume. 3. For full load denitration, it is mainly to meet the flue gas temperature requirements for low load denitration operation. The economizer water side bypass is adopted to improve the flue gas temperature at the economizer outlet, i.e., part of feed water is directly led to the water wall descending pipe through the economizer bypass pipe, so as to reduce the medium flowing through the economizer, thus reducing the heat absorption of the economizer, improving the flue gas temperature at the economizer outlet, and realizing full load denitration. 4. In terms of denitrification efficiency, a half-layer catalyst was added to increase the denitrification efficiency to 90%, thus meeting the requirement of NOx emissions less than 50mg/Nm3. 5. The heat exchange tubes of the flue gas cooler use unique elliptical finned tubes, and the flow field simulation of the inlet flue of the flue gas cooler is carried out to minimize the flue resistance and meet the capacity requirements of existing induced draft fans. After the above-mentioned ultra-clean emission scheme transformation, after on-site measurements by the Environmental Protection Bureau and Xi'an Thermal Engineering Institute, the concentrations of dust, SO2 and NOx are less than 5mg/Nm3, 35mg/Nm3, and 50 respectively under various working conditions. mg/Nm3, achieving full-load denitrification without obvious smoke plumes.