Selection of Biomass Feedstock for Production of Biocoal for Coal-Fired Boilers

PGE in collaboration with EBC and MTU is carrying out a testing program to fire up to 100% of biocoal (torrefied biomass) in its 600 MW Boardman boiler. An important aspect of this program is the selection of suitable biomass feedstock from which biocoal will be produced, emphasizing potential problems of fouling and slagging in the boiler. We thoroughly tested seven different types of feedstock: Arundo Donax (AD), wheat waste, corn waste, woody hybrid poplar, and bark from hybrid poplar, woody pine, and bark from pine. It was found that all these material comprised significant amounts of soil (varying from 5–25% in weight) with low fusion temperatures and therefore must be avoided from flowing into the boiler. We developed a separation technology of the soil from the biomass and were able to obtain biomass feedstock only with the plant minerals. All separated biomass feedstock, from soil, showed mineral content that is respective to soil they grew at. Samples were characterized for ultimate and proximate analysis, ash content and analysis and fusion temperatures. AD, wheat, and corn showed high content of potassium and low flow temperatures and therefore may not be used at 100% firing test unless some of the mineral contents are removed to protect the boiler from corrosion and slagging. Woody and bark hybrid poplar were found to have high fusion temperatures; woody and bark pine showed flow temperatures around 2500°F. All four feedstock types can be used for 100% firing test, however, the ones which is mostly recommended are woody and bark hybrid poplar.