Effect of the air flows ratio on energy behavior and NOx emissions from a top-lit updraft biomass cookstove

Abstract

Biomass as an energy source for three-stone cookfires is commonly used for cooking and heating rural and isolated households in developing countries; therefore, indoor air quality decreases. In this work, the effect of the air flows ratio (combustion air/gasification air, CA/GA: 2.8, 3.0, and 3.2), and the start type, cold (CS), and hot (HS), on the energy behavior and emissions from a forced-draft top-lit updraft (TLUD) cookstove, using wood pellets as fuel, is studied. Furthermore, the gasification process was thermodynamically characterized. The TLUD cookstove assessment was carried out following a modified water boiling test (WBT). The highest thermal efficiency of the cookstove was 26.74%. The lowest specific CO, NOx, and total suspended particle matter (TSPM) emissions were 1.8 g/MJd, 106 mg/MJd, and 78.32 mg/MJd, respectively; this was attributed to a proper mixture between the producer gas and the combustion air. The gasification process showed a better energy yield under the hot start due to the preheating induced in the cookstove reactor. The optimal values of the producer gas heating value (LHVpg), cold gas efficiency (CGE), and the biochar yield (Y char) were 3.53 MJ/Nm3, 58.61%, and 12.49%, respectively. Here, an opposite effect was found for the air flows ratios assessed. The cookstove behavior improved as the mixture between CA and GA was suitable, achieving the maximum at CA/GA = 3.0. However, the NOx emissions increased with the increment of CA/GA ratios (from 2.8 to 3.2). Therefore, future works must address the NOx emission reduction without penalizing performance or permanent emissions from the TLUD cookstoves.