Effects of operational mode on particle size and number emissions from a biomass gasifier cookstove

Interest in the size distribution of particles emitted from biomass cookstoves stems from the hypothesis that exposure to ultrafine particles is more detrimental to human health than exposure to accumulation mode or other size regimes. Previous studies have reported that gasifier cookstoves emit smaller particles than other cookstove designs under steady operating conditions. In the present study, the number size distribution of particles emitted from a forced-air gasifier cookstove was measured at 1 Hz as the stove transitioned between several steady and transient operating modes. During normal operation, when the stove functioned as a top-lit updraft gasifier, the distribution was bimodal, with peaks at 10 nm and 40 nm, when a pot of water was on the stove. The distribution became unimodal with a peak at 10 nm when the pot was removed. Once the fuel bed had completely gasified and the secondary flame extinguished, the concentration of particles increased and the peak in number concentration shifted to approximately 80 nm. After refueling, when the stove operated as a conventional updraft gasifier, the peak in number concentration decreased to 10 nm. When the secondary flame extinguished a second time, the peak in number concentration increased to approximately 100 nm before decreasing to 20 nm during the char burn-out phase. These results demonstrate that changes in operational mode influence the combustion process and produce distinct changes in the size distribution and rate of particle emissions. Copyright © 2018 American Association for Aerosol Research

学界针对生物质炉灶（biomass cookstoves）排放颗粒物的粒径分布展开研究的动机，源于"超细颗粒物（ultrafine particles）暴露对人体健康的危害程度高于积聚模态（accumulation mode）或其他粒径范围颗粒物暴露"这一假说。既往研究显示，在稳态运行工况（steady operating conditions）下，气化式炉灶（gasifier cookstoves）排放的颗粒物尺寸小于其他结构形式的炉灶。本研究针对一台强制送风气化式炉灶（forced-air gasifier cookstove），在其切换多种稳态与瞬态运行模式（transient operating modes）的过程中，以1赫兹（1 Hz）的采样频率对其排放颗粒物的数浓度粒径分布（number size distribution）进行了测量。正常运行且锅具置于炉灶上时，该炉灶以顶燃上行床气化炉（top-lit updraft gasifier）模式工作，其颗粒物粒径分布呈双峰（bimodal）特征，峰值分别位于10 nm与40 nm处。移除锅具后，粒径分布转为单峰（unimodal）分布，峰值位于10 nm处。当燃料床（fuel bed）完全气化、二次火焰（secondary flame）熄灭后，颗粒物数浓度升高，数浓度峰值粒径偏移至约80 nm。重新加料后，炉灶以传统上行床气化炉模式运行，数浓度峰值回落至10 nm。当二次火焰第二次熄灭时，数浓度峰值升至约100 nm，随后在焦渣燃尽阶段（char burn-out phase）降至20 nm。上述结果表明，运行模式的变化会影响燃烧过程，并使颗粒物排放的粒径分布与排放速率产生显著差异。版权所有©2018 美国气溶胶研究协会（American Association for Aerosol Research）