Pellet-fed semi-gasifier stoves in Rwanda approach gas-stove like performance: Field evaluation of climate- and health-relevant pollutant emissions

This research study was commissioned by the Clean Cooking Alliance and funded by the Climate & Clean Air Coalition to understand the in-field black carbon emissions from liquid, gas, and high-performing biomass stoves. This field study in Rwanda examined how higher performing stoves and fuels can potentially reduce the climate impacts from black carbon emissions.

Black carbon emissions occur due to the incomplete combustion of biomass and fossil fuels and are a significant source of both climate change and air pollution. Few studies have been conducted to measure the emissions reduction potential of the household use of liquid, gas, or high-performing biomass cookstoves. Though the laboratory data indicates that consistent use of higher performing cookstoves and fuels, at scale, could have a significant climate benefit, previous research shows that how cookstoves are used in households often greatly differs from the ideal settings in a lab. This study seeks to answer whether liquid, gas, and high-performing biomass cookstoves provide measurable climate benefits when used in households in Rwanda. 

The study, led by Andy Grieshop, PhD and his team from North Carolina State University, assessed the emissions from the Mimi Moto forced-draft pellet-fed semi-gasifier cookstove in urban and rural homes in Gisenyi, Rwanda. Emissions were sampled in-field during cooking events for the Mimi Moto, as well as traditional wood (three stove fire) and charcoal (coalpot/Jiko) cookstoves for comparison.

The team measured in-use emissions of pollutants including fine particulate matter (PM2.5), organic and elemental carbon (OC, EC), black carbon (BC), and carbon monoxide (CO) in 91 uncontrolled cooking tests (UCTs) of both pellet and baseline (wood; charcoal) stoves. They observed >90% reductions in most pollutant emission factors/rates from pellet stoves compared to baseline stoves. Pellet stoves performed far better than gasifier stoves burning unprocessed wood, and consistent with ISO tiers 4 and 5 for PM2.5 and CO, respectively. Pellet stoves were generally clean, but performance varied; emissions from the dirtiest pellet tests matched those from the cleanest traditional stove tests.

The real-time data suggest that events occurring during ignition and the end of testing (e.g., refueling, char burnout) drive high emissions during pellet tests. The researchers use the data to estimate potential health and climate cobenefits from stove adoption. This analysis suggests that pellet stoves have the potential to provide health benefits far above previously tested biomass stoves and approaching modern fuel stoves (e.g., LPG). Net climate impacts of pellet stoves range from similar to LPG to negligible, depending on biomass source and upstream emissions.