Analysis of the behaviour of pollutant gas emissions during wheat straw/coal cofiring by TG–FTIR

Abstract

The behaviour of pollutant gas emissions during the firing of wheat straw and coal blends was examined experimentally by using thermogravimetric analysis (TGA). Typical anthracite coal and wheat straw in central China were selected in this study. The ratio of coal to wheat straw by mass was set as 10:90, 15:85, 40:60 and 60:40 and the firing was carried using simulated air with oxygen and nitrogen gases. The emission characteristics of gas pollutants such as HCl, SO2, CO2 and NOx were determined by coupled Fourier transform infrared (FTIR) measurements. The results showed that HCl, SO2, CO2 and NOx emissions were closely related to the volatile combustion and char reacting stages. HCl emission was mainly released during the volatile combustion at the temperature between 220 and 450°C. The profiles of HCl against temperature exhibit a single-peak, and the HCl peak occurred at 310°C for all blends no matter what the ratio. The emission profiles of SO2, and NOx against temperature had the characteristic of two peaks. The first peak occurred around 320°C for all blends, and however the second peak shifted towards higher temperatures as the coal content was increased in the blends. The study showed that combining the straw and coal can produce better emission control by reducing the magnitude of the peak releases. The analysis showed that the blended sample with 40% coal and 60% straw by mass produced the lowest levels of HCl, NOx and SO2 gas emissions. The CO2 emission was mainly produced in the char combustion stage and purely increased with the carbon content in the blends.