The key ingredients of success for Colmac Energy Inc., operator of a 47 megawatt (MW) net biomass-fueled facility in the Coachella Valley of Riverside County, Calif., are the constant supply of quality landfill-diverted wood waste and the highest quality processing equipment. The plant, which has been in continuous operation since 1992, consumes approximately 325,000 tons per year of wood waste, landscape and right-of-way tree trimmings, broken pallets and used boxes. The company will accept construction waste, but no treated wood or painted materials. About 12 percent of the plant's fuel (40,000 tons per year) consists of locally collected agricultural residues that would otherwise have been disposed of by burning in open fields. And because of Colmac's plant, Riverside and San Bernardino counties are able to meet their state mandated recycling standard (AB939). Unlike companies that convert trash into power, Colmac processes only biomass material. Sixty to 80 trucks arrive at the facility each day coming in from a 200- to 250-mile radius, from east of Phoenix to south of Los Angeles. The trucks discharge up to 25 tons of biomass every five minutes. Upon arrival, the biomass material passes through separators that take out any ferrous materials, after which it is deposited into the first holding cell of a two-cell system. From that holding cell, it is transferred to an operating cell, from which it is broken down by grinding equipment prior to being fed into the boilers. No biomass fuel stays on site for more that 30 days at a time. Though Colmac takes care to make sure that the biomass provided by its suppliers is of high quality and is cut into small pieces so as to limit stress on the material handling machinery, the internal biomass feed system still sees considerable wear. "Biomass is among the hardest fuel sources on equipment," says Graeme Donaldson, Colmac's vice president and plant operations manager. Critical path transfer components must be selected and maintained with care to avoid failures that can shut down the whole line. In this area, maintaining close working relationships with equipment suppliers pays off. The Colmac site has been using screws and valves supplied by Precision Machine and Manufacturing Inc. of Eugene, Ore., since the current generating plant came on line in 1992. The plant now employs two sets of 12 metering bin screws (that feed the boilers), two sets of transfer screws, and two rotary valves per boiler, all provided by Precision Machine. Donaldson regularly consults with the company on things that Precision Machine can do to improve the reliability of the plant. "Precision Machine's valves last longer because they are built to tighter tolerances and the metallurgy has been designed to match the chemistry of our fuel," says Donaldson, who is an ex-marine materials engineer. read more