Submitted to: Fuel
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/5/2014
Publication Date: 5/16/2014
Citation: Martin, J.A., Boateng, A.A. 2014. Combustion performance of pyrolysis oil/ethanol blends in a residential-scale oil-fired boiler. Fuel. 133:34-44. Interpretive Summary: In order to curb greenhouse gas emissions and promote U.S. energy independence, renewable energy sources must be developed to replace nonrenewable fossil fuels. A major potential source of renewable energy is biomass, i.e. nonliving plant and animal matter such as crop residues, woody materials, and animal wastes. Biomass can be converted into a liquid fuel via pyrolysis, in which the biomass undergoes rapid heating in an oxygen-free environment. The major product of this process is a dense, combustible liquid known as bio-oil or py-oil. Py-oil has several properties that make it unsuitable as a fuel in most combustion systems, but it has the potential to be upgraded into a drop-in transportation fuel similar to diesel fuel. However this will take time-consuming research and a more immediate application of py-oil would help to sustain its production. To this end, py-oil can be blended with ethanol to reduce its undesirable properties, and py-oil/ethanol blends could replace #2 fuel oil in home heating applications such as boilers, furnaces, and water heaters. In this study, several different py-oil/ethanol blends were tested in a residential boiler and compared with #2 fuel oil. It was found that a blend of 20% py-oil and 80% ethanol could be used as a replacement for #2 fuel oil with only minor adjustments to the boiler. The type of biomass used to produce the py-oil had a great effect on the boiler’s emissions of NOx, a harmful atmospheric pollutant. The results of this work demonstrate an immediate potential use of py-oil that could increase the level of renewable fuel in the U.S. fuel supply.
Technical Abstract: 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.