Vol. 11, No.2, pp.165-169 (2018)
Emission Reduction and Energy Saving of Electrostatic Precipitation Used for Coal-fired Boilers
B. Liu1, Q. Zheng2, C. Gao3, C. Du4, S. Wang5, S. Li1, J. Zhang3, T. Bao4, Y. Yang5, J. Wang6, P. Han5, and K. Yan2
1Dananhu Power Plant, China
2Zhejiang University, China
3Wangqu Power Plant, Shenhua Guoneng Energy Group Co. Lid., China
4Huaneng Beijing Thermal Co. Ltd., China
5Shenhua Guoneng Energy Group Co. Ltd., China
Abstract
Both cold and colder-side electrostatic precipitators (ESPs) are widely applied in China with coal-fired boilers. This paper mainly discusses effects of high-voltage power sources and rapping on emission reduction and energy saving when upgrading ESPs. According to the rapping techniques, ESPs can be divided into three groups, namely moving, top and side-bottom rapping ones. High-voltage (HV) power generators are mainly single-phase and three-phase transformer rectifiers (T/R) and high frequency switch power sources. Typical Chinese ESPs with four- and/or five-electrical fields have the specific collection area of around 80–136 m2/m3/s. The ash inlet load is in the range of 10–40 g/m3. Today, the best colder-side ESP performances with four and five fields are 10 mg/m3 and 5 mg/m3, respectively. For newly designed cold-side ESP used for 2 × 1100 MW coal-fired boilers, their ash outlet concentrations are ≤ 7 mg/m3 with the area of 136 m2/m3/s and inlet load of ≤ 30 g/m3. By optimizing the rapping and HV sources, both emission and energy costs can be significantly reduced. For an example, the PM10 (particles with diameters of less than 10 µ m) concentration at the ESP outlet drops from 62.9 mg/m3 to 15.8 mg/m3 after replacing single-phase T/Rs by using three-phase T/Rs and reducing flue gas temperature from 120 ℃ to 90 ℃. At the same time, PM2.5 (particles with diameters of less than 2.5 µ m) concentration drops from 23.8 mg/m3 to 1.6 mg/m3. For similar ESP with high-frequency power sources, PM10 and PM2.5 are around 51.8 mg/m3 and 15.1 mg/m3, respectively. For either high-resistivity or very sticky ash, traditional top rapping usually gives poor performance for the inlet field. Outlet emission can be reduced by at least of a factor of two by using hybrid top rapping for outlet and side bottom rapping for inlet fields. The moving field ESP is usually used as the last field with a gap distance of 460 mm. When applying 72 kV, its collection efficiency is around 40–50% with outlet of around 10.0 mg/m3. For 600 MW coal-fired boilers, PM10 emission always shows a minimum with the HV input power of about 1000 kVA.
Keywords - Electrostatic precipitator, high-voltage power sources, fine particle, collection efficiency