Combustion optimisation of biomass residue pellets for domestic heating with a mural boiler

The purpose of this study was to optimise the combustion process of different residues in a 11.6 kW mural boiler for domestic heating. The fuels used were pellets from three biomass residues (tomato, olive stone and cardoon (Cynara cardunculus L.)) and the forest pellet recommended by the boiler manufacturer. Previously, the fuels were characterised by means of the higher heating value, proximate and ultimate analyses. The influence of the residue type, fuel mass flow, draught and residue mixture on the combustion parameters was studied. A TESTO 300 M-I analyzer was used to determine the principal parameters of the combustion process (CO2, CO and O2 contents, fumes temperature, not-burnt gaseous and sensitive heat losses in the fumes, volumetric flow rate and velocity of the fumes, air excess coefficient, efficiency). The behaviour of the three residues is similar to that of the forest pellet. The boiler efficiencies obtained with the maximum fuel mass flow (100%) and minimum draught (0%) were 90%, 90.5%, 89.7% and 91.6% for tomato, forest, olive stone and cardoon pellets, respectively. The optimum residue mixture was tomato (75%) and forest (25%) with a boiler efficiency of 92.4% for a mass flow and draught of 75% and 0%, respectively.