Production and Characterization of Biocoal for Coal-Fired Boilers

As part of PGE-EBC-MTU collaboration of the testing program to fire up to 100% of biocoal in the 600 MW Boardman boiler we produced samples from the seven biomass feedstock: Arundo Donax (AD), wheat waste, corn waste, woody hybrid poplar, and bark from hybrid poplar, woody pine, and bark from pine. The idea was to produce a few thousand tons of biocoal from woody and bark poplar for a 100% firing tests and from the other types to produce a 1000 tons of biocoal from each material that will be co-fired up to 10% with Powder River Basin coal. Biocoal is produced by a torrefaction which is a thermal process carried out in absence of oxygen. We have produced biocoal samples from the above biomass feedstock in two pilot facilities, one in Israel and another in Michigan. The torrefaction process comprises the following steps: (1) shredding and soil separation, (2) drying, (3) torrefaction, and (4) compaction to produce biocoal briquettes. Biocoal briquettes are essential for logistics, safety, operational, and economic considerations. The briquettes must be durable, water resistant and can be pulverized in common coal mills. The briquettes that we produced did indeed conform to these properties. A real operational challenge was working with absence of oxygen which essential for the torrefaction process as well as for safety considerations because the entire process occurs at elevated temperatures which biocoal can burn. A 30,000 t/year torrefaction facility has been constructed at the Boardman Plant site to produce biocoal required for the firing tests.