Use of almond residues for domestic heating. Study of the combustion parameters in a mural boiler

The combustion process of almond residues in a 12 kW mural boiler for domestic heating was studied. The fuels used were three residues of almond (almond tree pruning, almond shell, and almond peel) and one forest pellet recommended by the boiler manufacturer. Previously, the fuels were characterised by means of the higher heating value and, 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 employed 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, air excess coefficient and efficiency). The behaviour shown by almond tree pruning and almond shell was similar to that of the forest pellet, but almond peel didn't burn well in this boiler, and moreover the ashes accumulated in the fireplace impeding the combustion process. The boiler efficiencies obtained with the maximum fuel mass flow (100%) and minimum draught (0%) were 88.3%, 85%, 78.5% for almond tree pruning, almond shell, and almond peel, respectively. The obtained efficiency with the forest pellet was 90.5%. The optimum residue mixture was almond tree pruning (75%) and forest pellet (25%), with a boiler efficiency of 87.9% for a mass flow and draught of 100% and 0%, respectively.