Steam for Seattle

District heating system supplies steam to several downtown buildings.
By Lisa Gibson | February 22, 2011

Weaving their way through a maze of piping, knobs and gauges, tour participants at the Pacific West Biomass Conference & Trade Show saw firsthand how steam is produced and distributed to more than 200 downtown Seattle buildings.

Seattle Steam is a privately owned district heating system that supplies 600,000 pounds of steam per hour to hospitals, hotels and other structures through an 18-mile pipeline to Seattle Central Business District and First Hill Neighborhoods. The plant uses a 60 percent waste wood feedstock, the rest comprised of natural gas and oil.

During the tour, Seattle Steam President Stan Gent took the participants to the large, round combustion chamber, warning them of the high temperature even on the outside of the chamber. “The combustion of the fuel is probably the easiest part of what we do,” Gent said.

Participants also got a look at the plant’s storage, handling, grinding and screening processes located across the street from the plant. A grey silo dwarfing all the buildings around it holds 250 tons of wood, roughly one day’s worth of feedstock. Each truck load brings in 20 to 25 tons, emptying it inside the cemented and unheated drop-off area adjacent to the silo. The facility also controls odor and dust, Gent said.

Attendees descended a grated stairway into an area where machines grind and screen the biomass until all the material is three inches or smaller. From there, the tour continued through a tunnel where the feedstock is blown under the street to the combustion chamber. The pressure, power and force of the equipment could be felt through vibrations throughout the room.

Seattle Steam also has a natural gas-fired plant just blocks away that Gent hopes will be an operating combined-heat-and-power plant by 2012. The company has a federal grant for $19 million to help with the costs and hopes to produce 35 megawatts of electricity and 25 megawatts of heat at about 90 percent efficiency, he said.

—Lisa Gibson