Field evaluation of pollutant emissions and reduction effects of biomass pellets burning in improved heating stoves in rural China

Biomass pellets burning can improve the efficiency of heating stoves, compared with traditional raw coal, thereby to achieve clean heating in rural areas of China. Most previous studies focused on short-term testing, which cannot reveal the actual emission of stoves the whole day. The current on-site measurements on pollutant emissions are still lacking. Taking a demonstration village of biomass pellets and supporting stoves in a county of Heilongjiang Province as an example, this study aims to investigate the pollutant emissions of biomass pellets using 24-hour field measurement method, and further to evaluate the emission reduction effect, when using biomass pellets to replace raw coal for heating. A portable residential stove on-site pollutant emissions testing system was used, particularly equipped with real-time sensors to measure the emissions of CO, CO2, SO2, NOx and PM2.5. A dilution channel was also equipped, including a PM2.5 cyclone, and the filter loading compartments for PM2.5 collection. The dilution sampling method was used to simulate the process of high-temperature mixing smoke from the exhaust chimney in atmosphere. This system can effectively record the entire combustion of residential stoves, and the pollution emissions 24 hours a day, while in-situ monitor the actual pollution emission levels of residential stoves. The results showed that the emission concentration of pollutant that emitted from the combustion of biomass stoves relatively fluctuated less than that of raw coal stoves. The emission factors of pollutant from raw coal stoves and manual/automatic feeding biomass stoves were 0.17, 0.11, 0.10 g/MJ for PM2.5; 5.54, 4.32, 2.53 g/MJ for CO; 0.05, 0.04, 0.03 g/MJ for SO2, and 0.08, 0.08, 0.11 g/MJ for NOx. The emission factors of PM2.5, CO, and SO2 from the automatic and manual feeding biomass stoves reduced by 41.2%, 54.3%, 20.0%, and 35.3%, 22.1 %, 40.0%, respectively, compared with the raw coal stove. In contrast, the NOx emission factor of automatic feeding biomass stoves increased. The total amount of pollutant was calculated from the different combinations of stoves and fuel, in order to evaluate the emission reduction effects of pollutant from two biomass stoves. The results showed that: compared with raw coal stoves, the reduction ratio of CO, SO2, and PM2.5 emission in the manual feeding biomass stove were 19.38%, 27.01%, and 33.41%, respectively, where the reduction effect of CO emission was significant (P<0.05). The reduction ratio of pollutants CO, SO2 and PM2.5 that emitted from the automatic feeding biomass stove were 52.77%, 41.35% and 39.79%, respectively, in which the reduction effect of CO emission was also significant (P<0.05). However, the total average household amount of NOx that emitted from the automatic and manual feeding biomass stoves increased by 46.14% and 6.69%, respectively, compared with the raw coal stove. Surveys and interviews were conducted with residents in areas, where biomass clean stoves were promoted. It was found that the publicity of environmental protection and technical training for residents have become urgent to promote the utilization of such biomass stoves, and thereby to ensure the effective implementation of clean heating policies.