Kimberly-Clark hosts biomass CHP plant tour
Paper product and pulp manufacturer Kimberly-Clark opened the doors at its Everett, Wash., mill to allow more than 60 guests attending BBI International’s Pacific West Biomass Conference & Trade Show a first-hand account of the operations of its biomass combined-heat-and-power plant.
The Snohomish County Public Utility District and the mill—then owned by Scott Paper—jointly began construction of the $115 million cogeneration facility in 1993. The PUD provided the capital and owns the project in addition to receiving the electrical output. Kimberly-Clark provided construction management and operates/maintains the facility, receiving steam for its tissue mill processes. The facility came online in 1995.
Though the facility possesses five boilers, it typically runs two of them and the others are reserved for backup, said Kimberly-Clark chemical engineer Nathan Pearson. One of the two boilers burns spent liquor from the pulp mill, and the other burns wood waste. Both can burn natural gas if needed, as all of the reserve boilers do. Pierson said the reserve boilers are typically only run about 15 to 20 days per year. “Our main focus isn’t generating electricity, it’s making paper, so we need these backups to continue to make steam if something goes down with the other boilers,” said Asset Manager Isaac Osborn.
The plant utilizes about 2,300 tons of wood waste each day to generate 711,000 pounds of steam per hour and 38.6 megawatts (MW) of electricity, via a 52-MW GE turbine generator. “It’s really loud, but it’s very impressive to see something that can spin at 3,600 RPMs [revolutions per minute],” Pearson said.
Fuel is delivered to the plant in trucks or via barge, according to Osborn. “Spot checks of fuel are done as it comes in to make sure it is clean wood, but we rely on our vendors to make sure it meets standards,” he said. The plant’s main source of fuel is land clearing debris—about half—and the rest is saw mill residue such as bark and clean demolition and construction debris.
In a simplified description, before being combusted in the boiler, wood fuel is sent through a disc screen for over-sized separation and metal separation, which eliminates anything from nails to spoons, with two magnetic belt conveyors, according to Pearson. The plant’s “run-around system” sends a more than necessary amount of fuel onto the conveyors, part of which drops into the boiler and the rest recirculates. “This way, if there is a problem the boiler continues to be fed the extra fuel so steam production is constant,” Pearson said. Moisture content of the fuel can vary from 25 to 70 percent.
Osborn said the company is currently paying anywhere from $30 to $50 per ton of wood fuel. “It all depends on who we’re buying it from and the quality of the fuel,” he said.
The Kimberly-Clark CHP plant was one of three stops during BBI International’s Pacific West Biomass Conference & Expo in Seattle, Jan. 10-12.