Type of CHP system: Gasification

Lahden Lämpövoima Oy biofuel gasifier connected to pulverised coal-fired boiler.

Plant owner: Plant owner is Lahden Lämpövoima Oy. Local energy utility Lahti Energia Oy owns 100% of the shares of Lahden Lämpövoima Oy.

Commissioned: (reconstructed):1976 (1997)

Status of plant: Commercial

Contractor details:

Gasifier delivered by Foster Wheeler Energia Oy.

The fuel handling system was supplied by Roxon Oy.

Power generation: Steam turbine

The CFB gasifier consists of the inside refractory-lined steel vessel, where fuel is gasified in a hot fluidised gas-solid particle suspension. Biofuels and REF will be converted to combustible gas at atmospheric pressure at the temperature of about 850 °C. The hot gas flowing through the uniflow cyclone will be cooled down in the air pre-heater before feeding to the main boiler. Simultaneously, the gasification air is heated up. Fluidised bed material like sand and limestone are needed in the gasifier process.

The boiler is a Benson type once through boiler. The gasification product gas is burned in the boiler.

In 1986, the plant was furnished with a gas turbine connected to the heat exchanger preheating the boiler feed water. The maximum energy output of the gas turbine is 49 MWe, when the outside temperature is -25°C. The maximum power capacity of the Power Station is 200 MWe in condensing power mode (including the boiler, gasifyer and the gas turbine) and the maximum district heat production is 250 MW. The boiler uses about 2500 GWh/a (280,000 ton/a) of coal and about 100 GWh of natural gas.

Main fuel: Multifuel (more biofuels and/or peat)

In the beginning the gasifier fuel consisted of mainly biofuels like bark, wood chips, saw dust and uncontaminated wood waste. Now also REF from households and industry is used. Gas turbine is fuelled with natural gas and the boiler with coal, natural gas and gasifier product gas.

Nominal capacities & efficiencies:

Thermal input, biomass & waste: 50 MW

Total thermal input, incl. fossil fuels: 500 MW

Net electrical output: 200 MWe

Heat output: 250 MJ/s

Electrical efficiency, gross: 35 %

Overall efficiency, gross: 85 %

Power to heat ratio: 0,6

Nominal thermal input (biomass) depends on the fuel, it is typically 40 – 70 MWt. Total nominal thermal input capacity of the plant icludes the entire process (also gas turbine).

How is plant controlled: Plant is basically a base-load power station. Partly the price of electricity in Nordic electricity market also controls the plant use.

Heat backup: There are other power plants and heating plants in city of Lahti connected to the DH-network. They are used as back up and peak boilers.

Heat usage: Heating only

Energy usage: Heat is used for district heating in the city of Lahti. Electricity is sold through the owner, Lahti Energia Oy.

DH inlet temperature: 80-120 °C

DH return temperature: 50-60°C

Heat storage size: 10000 m3

Hours of full load that the heat storage can meet: 10

Fuel storage:

The gasification plant has one fuel storage. The volume of the intermediate storage is 3000 m3. The form of the storage silo is retangular.

Fuels are transported to the power plant on trucks. There is one receiving hall for REF and one receiving station for incoming biofuels. The REF hall is equipped with a receiving pit having a lamella feeder to control the flow of fuel to a crusher. Coarse biofuel from the wood refining industry is also fed through the REF -system. The trucks tip the REF and coarse material on the floor of the hall or directly into the pit.

The other receiving bunker is for the fine material, like saw dust and milled peat. These fuels are taken to the site by trucks equipped with chain unloading system. The truck can drive “through” the receiving tunnel. The discharging takes place on a flat chain conveyor, which drops the fuels on the screen. Accepted fraction falls down onto the chain conveyor at the bottom of bunker. Over sized particles are moved back to the REF hall for pre-crushing.

Ash discharge:

Ash is used for landscaping and also partly landfilled. As a local very large landfill will be closed soon, big amounts of ash will be used for landscaping the landfill area in near future.

Plant description:

The Lahti power plant went into operation in 1976. Originally, the plant was heavy oil fired, but in 1982 the plant was modified for coal firing. In 1986, a gas turbine generator set was installed at the plant. In 1997 a new biomass gasifier was connected to the coal-fired boiler. Gasification enables the utilisation of locally available low-price biofuels and recycled fuels, equivalent to an energy content of 400 GWh (100 000 – 130 000 tonnes) annually. It reduces maximum of 20% of the plant’s annual coal consumption. Also the use of natural gas has been reduced down to 100 GWh annually. The plant is operated by Lahden Lämpövoima, a local power company producing power and district heat for the town of Lahti. The gasifier was supplied by Foster Wheeler Energia Oy. The gasification plant project received financial support from the European energy demonstration programme Thermie.

In 2003 Kymijärvi power plant was awarded an SFS-EN ISO 9001-2000 certificate for quality system in the field of energy production and power plant operation and an SFS-EN ISO 14001:1996 certificate for environmental system in the field of energy production and power plant operation.

Sources: Biomass CFB gasifier connected to a 50 MWt steam boiler fired with coal and natural gas – Thermie demonstration project in Lahti in Finland, by Matti Kivelä, Jorma Nieminen and Juha Palonen.

Fuel feeding system:

The REF and coarse biofuel are crushed in the slowly rotating crusher. The underground conveyor from the first receiving bunker transports REF and biofuels from the crusher.

The underground conveyor lifts the fuels to belt conveyor provided with magnetic separator. The belt feeds a disc screen. The overflow falls down into the final crusher, while the accepted fuel fraction and crushed material are transported by a chain conveyor into the intermediate storage. The fuel storage silo is used also for homogenisation of fuel mixture before the feed of the gasifier. The storage is unloaded by the screw reclaimer.

There are two feeding silos (of 20 m3 total) on the both sides of the gasifier. The material is dosed into the gasification chamber through to block feeders

Gasifier: Atmospheric fluidised bed gasifier.

Gas quality: 2.2 MJ/kg (with moist fuels, appr.50%) or even 4.5 MJ/kg when the fuel includes a lot of plactic materials.

Gas cleaning: Fuel gas is used without cleaning in the boiler. Limestone is used in fluidised bed when needed.

Turbine: Back pressure turbine

Steam data: 125 kg/s, 540°C, 170 bar

Cooling system: River water is used when condensing power is generated.

Flue gas cleaning:

Coal utilized contains only 0.3 -0.5% sulphur, plant is not equipped with a sulphur removal system. The burners are provided with flue gas circulation and staged combustion to reduce NOx-emissions. Plant is equipped with electric precipitator.

Staff: The company employes a staff of approx. 52 persons. The number of O&M personnel is 46.

Electricity sale info: Electricity is sold through the parent company Lahti Energia.

Total capital cost: € 12,000,000

Total costs (including gasifier, fuel preparation system, civil works, instrumentations, control system and electricication) were about 12 million euros.

Gasifier 8 million euros and fuel receiving system 4 million euros.

Data collected and quality assured by: VTT Processes.

Contact person: Kati Veijonen