Formation features of benz(a)pyrene and nitrogen oxides when burning brown coal in boilers with liquid slag removal system

Abstract

In the article, the authors examine the experience of burning Kansk-Achinsk coal (KAC) in the boilers of the BKZ-320-140PT type at the CHPP-6 in Bratsk. The article considers the results of the experiments carried out at two boilers (b.u.No.5 and No.7), where the organization of aerodynamic processes is significantly different. These results are presented as the dependences of the concentrations of nitrogen oxides (NOx) and benz(a)pyrene (BaP), as well as the content of combustibles in fly-ash (Cf) on several parameters simultaneously, namely, the boiler load, the number of working dust collecting systems, and excess air. The following conclusions have been drawn: 1) two parameters have the most significant effect on the amount of BaP emissions – the scheme of entering drying gases into the combustion chamber and the excess air in the combustion chamber; 2) there is a certain relationship between BaP emissions and the content of combustibles in fly-ash: a lower Cf value corresponds to the mode with a lower concentration of BaP. It follows that BaP emissions can be reduced by measures reducing chemical and mechanical underburning (q3 and q4), primarily the turbulization of flue gases. The formula is proposed that clarifies the values of BaP emissions during vortex combustion. It is shown that the formation of NOx is also significantly affected by the same parameters as the formation of BaP, as well as the load of the boiler. The effect of these parameters is explained. Various technological measures are proposed to reduce pollutant emissions comprehensively by providing vortex combustion in the boilers with both liquid and solid slag removal systems.