Excess air influence on the thermal efficiency of domestic boilers burning pine pellets
Andrea Pinto1; Tânia Ferreira2; João Paiva1
1 Politécnico de Viseu; 2 Universidade do Porto
doi:10.20906/CPS/COB-2015-1293
Resumo
This work studied how the standard settings defining excess air used in common domestic boilers burning pine pellets influence the thermal efficiency. Commercial and ENplus certified pine pellets were burned in a boiler varying the amount of air supplied to the combustion process in three nominal thermal loads: reduced, medium and high. Initial essays were performed using the manufacturer's indicated parameter of air regulation for each load. As previous works had shown that the excess air value was way too high, thus affecting negatively the combustion process, experiments were carried out were the amount of air was progressively reduced. Simultaneously, the pollutant emissions of O2, CO, CO2, NOx and NO were measured to allow determining the excess air value for each essay. Boiler thermal efficiency increases by lowering the excess air, e.g., thermal efficiency of the medium load increased from 62 to 79% with excess air values decreasing from 565 to 193%, respectively. CO emissions reductions accompanied this excess air decrease. To define the excess air value that would point out maximum thermal efficiency, experiments were carried out so that gases dew-point temperature was attained. In so doing, slightly higher values of thermal efficiency were obtained but at the expense of extremely high pollutant emissions.
Palavras-chave: excess air; thermal efficiency; combustion; pellets