On the Coast of Denmark, a Quietly High-Performing Woodchip Gasifier Is Producing District Heat and Power
Vølund Gasifier Plant and Town of Harboøre
Woodchip CHP and District Heating System
Heating Capacity (output): 4 MW (14MMBtu/hr)
Electrical Capacity: 1.6MW
Emissions Reduction and Combustion Control Equipment: Electrostatic precitator
Year Installed: 2000
Thermal Output: Hot water
District Heating Network Length: 10 km (6 miles)
District Heating Customers: 900
Vølund Gasifier Plant and Town of Harboøre PDF
A key goal, and an elusive one, in the worldwide quest to develop an efficient, reliable, clean gasifier to convert wood into electricity using an engine instead of a steam boiler, has been to build one that runs a dependable 4,000 hours per year.
In Jutland on the western coast of Denmark, a 1.6 MW (electric) gasifier system owned and operated by a subsidiary of the US firm Babcock & Wilcox has been running, very quietly, without promotion or much attention, more than 8,000 hours for each of the past several years.
Testifying to its quiet operation, there are usually no cars parked out front of the plant—just an operator’s bicycle, leaning against a wall.
“Most gasifiers are in the development stage,” notes Kim Jensen, assistant manager at Babcock & Wilcox’s Vølund plant in Harboøre, and one of two men who run the plant. “Ours has run more than 95 percent of the time, 8,300 hours per year.
“Is this plant very hard to take care of? Well, let’s just say we’ve gotten really good at golf.”
The plant converts woodchips into a gas that burns clean enough to fuel an internal combustion engine. Two engines in the plant burn that gas, producing rotary motion that drives a power generator.
The gasifier produces electricity, but Babcock & Wilcox treats the power as its second energy product. It gets heat, the primary product, from three sources: the heat that comes from the engines’ coolant, the heat that is pulled from the engine exhaust, and the heat produced by the cooling process that cleans the gas from the gasifier.
The product of all this heat capture is hot water for a district heating system that warms buildings in the Town of Harboøre a kilometer away. The total length of the Harboøre district heat network of buried piping is 10 kilometers (six miles).
Although most gasifier projects focus more on power production, the Harboøre plant works with the actual proportions of power and heat that it produces: more than twice as much heat as electricity. The system’s thermal output capacity is four MW, or 13.5 MMBtu/hour. Its electrical output is 1.6 MW, sold to the power grid. In the summer, when there is little demand for heat, little electricity is produced.
The system uses wood harvested from forests within a 20-30-kilometer (10-20-mile) radius of the plant. Using wood for energy is nothing out of the ordinary in a country so committed to renewable energy that windmills are a common sight on the western coast where the Vølund plant stands.
"It Works Perfectly"
“Woodchips are delivered into this bin, which holds enough fuel for four days,” explains Plant Manager Jørn Snejbjerg. “The electric eye of the overhead crane system continually locates the highest part of the chip pile and sends the crane there. It scoops up about a cubic meter of woodchips, travels to the back of the bin, and then drops the fuel into the receiving hopper. It’s all automatic and it works perfectly.”
“There aren’t many commercially operating wood gasifiers in the world running internal combustion engines for making electricity,” adds assistant manager Jensen. “This one is unusual because it can use green woodchips with no need for fuel drying, and the chips don’t have to be very uniform.”
The gasifier is a vertical cylinder that produces, along with the combustible gas, a thick, heavy tar.
“The tar from the gasifier is separated out by the gas coolers,” Jensen says. “We store it and then we burn it in the winter in an oil boiler, to get more heat output for the system. We have a treatment system for the water from the gas coolers. When we’re done it’s almost clean enough to drink.”
The plant has two backup boilers, one that can burn fuel oil as well as the waste tar, another that runs on natural gas.
The Harboøre plant was commissioned in 2000, and Vølund spent the first five years fine-tuning it for optimal performance. It has been since 2006, Snejbjerg and Jensen say, that the plant has been running more than 8,000 hours per year—so smoothly that the operators have spare time to improve their golf game.