Combustion performance of pyrolysis oil/ethanol blends in a residential-scale oil-fired boiler

A 40 kWth oil-fired commercial boiler was fueled with blends of biomass pyrolysis oil (py-oil) and ethanol to determine the feasibility of using these blends as a replacement for fuel oil in home heating applications. An optimal set of test parameters was determined for the combustion of these blends with minimal soot and carbon monoxide formation. These set parameters were used to compare the performance of blends of ethanol with different concentrations of py-oil (10%, 20%, and 30% py-oil by mass) and py-oil produced from different biomass feedstocks, including switchgrass, miscanthus, eucalyptus, pennycress, forest residues, and soiled animal bedding, using #2 fuel oil as a control. Performance was measured in terms of the total heat input, the axial temperature profile of the combustion chamber, the gross heat output, and heat losses to the flue gas. Exhaust gas was analyzed for O2, CO2, CO, NOx, and total hydrocarbon concentration. It was found that a blend of 20% py-oil/80% ethanol could be used as a fuel in residential boilers with minimal retrofitting. This blend ratio produced no detectable change in the CO and hydrocarbon emissions compared to #2 fuel oil. When the py-oil fraction of this blend was produced from biomass with low amounts of nitrogen such as eucalyptus, NOx emissions were reduced by 12% compared to #2 fuel oil. When the py-oil was produced from proteinaceous feedstocks the py-oil stability improved but high nitrogen led to an order of magnitude increase in NOx emissions.