Influence of sludge co-combustion on trace element emission characteristics in a coal-fired power plant

Sampled by EPA Method 29 and analyzed by Cold Atomic Absorption Spectroscopy and Inductively Coupled Plasma Spectroscopy, the concentrations of trace elements in the raw fuels, flue gas and by-product samples before and after sludge co-combustion in an ultra-low emission coal-fired unit were obtained, with the influence of sludge co-combustion on the emission characteristics of trace elements being investigated. The concentrations of Zn and Cu elements in sludge were high, which was 18.81times and 17.64times than that in the coal samples, respectively. The content of trace elements in the coal fed into the furnace after sludge co-combustion was generally increased. The mass balance rates of trace elements in the whole system, boiler system and air pollution control facilities of the whole process before and after sludge co-combustion were all within the acceptable range. The co-combustion of sludge had no obvious effect on the distribution characteristics of trace elements, and discharging with fly ash was the main emission pathway for trace elements. The proportion of trace elements emitted to the atmosphere through the stack was very small, no more than 0.43%. Except for Hg, the trace elements in the flue gas in the SCR inlet before and after sludge co-combustion mainly existed in the form of particles. The relative enrichment coefficients of trace elements in fly ash and bottom ash did not change significantly after sludge co-combustion. After the coordinated control of the whole-process air pollution control facilities, the emission concentrations of trace elements in the stack outlet before and after sludge co-combustion were 0~12.76µg/m3 and 0~14.97µg/m3, respectively. The emission concentrations of trace elements after sludge co-combustion meet the requirements of the US emission standards for harmful air pollutants from coal-fired generating units, the air pollution emission standards for coal-fired coupled sludge power plants in Shanghai, and the Ministry of Ecology and Environment's domestic waste incineration pollution control standards. The existing air pollution control system in coal-fired power plants had good adaptability to the emission control of trace elements under the condition of 6% sludge co-combustion ratio. © 2022 Chinese Society for Environmental Sciences. All rights reserved.