Demonstration of wood/coal co-firing in a spreader stoker

The Forest Service of the U.S. Department of Agriculture is sponsoring a series of demonstrations of wood/coal co-firing in stoker boilers. The first demonstration was conducted in 1997 in an industrial traveling-grate stoker boiler and the second in May 1999 in a spreader stoker boiler operated by the National Institute of Occupational Safety and Health (NIOSH) at the Bruceton Research Laboratory. The principal wood used in both demonstrations was tub-ground broken pallets. In the first phase of the NIOSH demonstration, four five-ton loads of wood/coal mixtures, varying from 3% to 12% wood (by Btu content), were combusted. The second phase of this demonstration was a 50-hour test using a 10% wood/coal blend delivered in two 20-ton loads. It has been concluded from both demonstrations that (1) a 10% wood/coal blend burns acceptably in the boiler, but (2) tub-ground urban wood is unacceptably difficult to feed through the grill above the delivery pit and through the spreader stokers. A method is being sought to acquire urban waste wood, having a more chip-like nature, to use in further testing and for commercialization.