Colmac Energy's Secret to Success: Reliability and Maximum Uptime
Maximizing uptime and throughput are key factors enabling the country's largest biomass power plant to consistently turn a profit.
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.
This attention to detail is critical because if a boiler were to go down for any reason, including the interruption of the biomass transport line, the cost to Colmac in terms of lost productivity would be substantial. Donaldson estimates it at $5,000 per hour per boiler.
When a plant is shut down, the adverse impact goes beyond lost power output. "You can't shut down the fuel flow when a plant goes down," Donaldson says. "If you send the fuel away, it gets used someplace else and it's hard to acquire again."
"We continue to push the envelope on the reliability of our system," he says. "We used to change our rotary valves every three months. Now, because of Precision Machine's experience with advanced metallurgy and quality control, we do so only once per year, and we're looking at ways to improve the reliability beyond that. The payoff is in lower costs and increased efficiency." The Colmac plant runs an efficiency of 92 percent to 95 percent whereas other plants run between 82 percent and 85 percent. Using equipment with longer operating lifetimes also helps Donaldson keep the cost of maintaining spare parts inventories under control.
"We can't increase our plant's output," Donaldson adds. "We're limited by the original boiler design to 47 MW. The only way that we can improve the financial returns from our process is to increase the system's reliability, which translates to more continuous uptime. And when it comes to maximizing, Precision Machine engineers it into every one of their products."
Tony McNeil is the sales manager for Precision Machine and Manufacturing Inc. Reach him at firstname.lastname@example.org or (541) 484-9841.