High-Tech Energy Comes to an old Standby

Seattle Steam is converting its plant from natural gas to wood waste to help reach carbon neutrality.

By Lucy Bodilly

University Mechanical Contractors lifted the new combustor into place through a holein the roof. (Photo courtesy of University Mechanical Contractors)

The company that provides one of the most efficient sources of energy available in downtown Seattle is becoming even more resourceful.

By June, Seattle Steam will use recycled urban wood waste to power its downtown Seattle facility. The plant, originally built in 1906, provides heat to 64% of the square footage in the downtown Seattle core core and three major hospitals through its 18-mi pipeline.

When the plant first opened, it used coal to fuel its plant. Now it will use old pallets, wood construction debris and tree trimmings. Only clean wood will be accepted. The city of Seattle has given incentives for companies with wood waste in the form of higher dumping fees for those who still take waste it to the dump.

The steam is pushed through the system at 150 lbs of pressure and reaches the customer at 355 degrees F°. Each customer uses heat exchangers to convert the heat from the steam into its own HVAC system.

“The new system uses high technology, says Stan Gent, Seattle Steam CEO. “We are able to burn the waste at 2000° F by injecting air and fuel and get almost complete combustion.”

Most major cities have this type of district heating, but Seattle has one of the largest in the world, says Gent.

The conversion came about for a variety of reasons. The price of natural gas, which The price of natural gas, which the company was using, was on the rise. “We wanted to be able to meet the state cap and trade rules that we expect will require mandatory reporting of carbon emissions by 2010,” Gent says. “By 2012 we have to be carbon neutral.”

The new system, being built by University Mechanical of Mukilteo, Wash., will reduce carbon emissions by 60%. Wood waste is considered carbon neutral because even though wood releases carbon when it’s burned, the chemical element is eventually absorbed by trees.

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Building the System

Similar combustion systems are used at lumber mills and wood-processing plants across the country, but at mills, the excess energy isn’t used as an energy source.

Several steps were necessary before the new combustor could be put into place, says Dave Johnson, University Mechanical business development director. The updated plant requires two buildings, one on each side of Union Street, only a block from the Seattle waterfront. Steam generation takes place on the south side of the street.

“Right now there is just a concrete slab on the surface above a fuel storage tank,” Johnson says.

The unused underground storage tank is being converted into the holding area for fuel and ash. A utilador, a system of pipes that runs between the two buildings, will be used to convey fuel to the combustor. Ash is sent back to the storage area along the same utilador.

When the plant is in operation, wood waste will be stored in the old tank, and literally blown under the street, via the utilador.

Seismic improvements on the plant structure were finished in 2000, but to install the new combustor, the foundation was improved.

Construction so close to Elliot Bay is an automatic problem. The water table is only a few feet below the surface because of is done. The plant will start running on wood waste in May or June,“ Johnson says. Seattle Steam’s next project will be to recover waste heat from Seattle’s manufacturing district near Harbor Island and use it to heat nearby buildings.

The original steam plant was built in 1906.

Seattle Steam water coming down the hill from the upper reaches of downtown Seattle and the incoming tides. University Mechanical had to keep the dewatering pumps going while it installed grout micropiles to strengthen the building foundation to support the added weight of the new system.

University Mechanical installed the new combustor by cutting a hole in the roof of the existing building. It took one of the largest cranes available to lift the combustor into place in five sections.

“The last few weeks have been some of the most difficult for the project,” Johnson says. During one of the coldest weeks on record, University Mechanical worked with Seattle Steam personnel to commission the plant. Now the facility will still run on natural gas until the waste wood storage facility.

“I went to Copenhagen and discovered that 98% of the buildings were heated without burning fuel,” Gent says. “When you make electricity in the U.S., you just throw away the excess energy.