Carbon and nitrogen emissions rates and heat transfer of an indirect pyrolysis biomass cookstove

Highlights: • CO emissions have a non-linear dependency on the pyrolysis fuel consumption rate. • NO emissions rates are a function of the rate of release of fuel bound nitrogen. • Firepower is positively and strongly correlated to pyrolysis fuel consumption rate. • CO emissions reductions are achieved at the expense of the speed of cooking. -- Abstract: Cookstoves, where fuel is pyrolyzed or gasified, have received much attention due to their potential to reduce environmental and household air pollution (HAP). In this study, an indirect pyrolysis cookstove was investigated to determine how operating conditions influence carbon and nitrogen emission rates and heat input to the cooking water. Multiple linear regression models were developed based on time-resolved measurements. The rate of pyrolysis fuel consumption emerged as the primary driver for the production of CO and NO emissions and heating of water. This parameter alone explained over 70% of the variation in the models for CO, NO and the water heating rate. The CO emission rate had a non-linear dependency on the rate of pyrolysis fuel consumption (R² = 0.70, p < 0.0001), likely because high pyrolysis fuel consumption produced conditions with insufficient air flow for the conversion of C to CO₂. NO emission rates were mainly affected by the rate of N release from the pyrolysis fuel (R² = 0.74, p < 0.0001). However, the pyrolysis temperature also affected the rate of production of NO, accounting for 4% of its variation. The water heating rate has a linear relationship to the rate of pyrolysis fuel consumption (R² = 0.69, p < 0.0001). CO and NO emission rates depend on the speed of cooking and the choice of fuel, as well as on the amount of pyrolysis fuel used. Reduction of CO emissions and increase in efficiency are possible through stove design changes while choosing low-nitrogen pyrolysis fuel can lower NO emissions.