Type of CHP system: Grate fired boiler

Plant owner: Umeå Energi Group owns Dåva combined power and heating station. Umeå Energi Group is wholly owned by Umeå Muinicipality.

Commissioned: 1999

Status of plant: Commercial

Contractor details:

Main contractors:

Machinery – Svenska Von Roll and Götaverken Miljö (contsortium)

Construction – Konte

Land – NCC Anläggning.

Manufacturer:

Boiler and fire grate – von Roll

Steam turbine – Allen Steam Turbines

Support burner – Saacke

Fabric filter (textile)- Flebu

Scrubbers – Munders / Bete

Heat pumps – Sulzer.

Power generation: Steam turbine

Main fuel: MSW

Dåva power and heating station only use waste as fuel. A small amount of oil is also used during heating of the boiler and to make sure that the temperature in the incinerator keeps high (850 degrees Celcius) during operation. Dåva power and heating station is annual allowed to to burn 175 000 tons of waste. In the year of 2002 about 123 000 tons of waste and 845 m3 oil were consumed. In the future the consumption of waste is going to increse because of the plants additional availability. The availability has increased because of a new establishment that cools of the district heating water when the demand of heat is low. This new establishment was built in the year of 2003 and can cool off about 20 MW of heat and make it possible to operate Dåva even during summer. This also makes it possible to produce electricity all year around. Sometimes the storage of waste is growing too much during the summer and this problem is also solved with the new cooling establishment. The cooling establishment cools off heat in a big heat exchanger where the surrounding air is warmed up. Waste is not an uniform fuel and the energy- and moist-content can fluctuate from time to time.

Dåva power and heating station only use waste as fuel. A small amount of oil is also used during heating of the boiler and to make sure that the temperature in the incinerator keeps high (850 degrees Celcius) during operation. Dåva power and heating station is annual allowed to to burn 175 000 tons of waste. In the year of 2003 about 160 000 tons of waste and 700 m3 oil were consumed. The availability has increased because of a new establishment that cools of the district heating water when the demand of heat is low. This new establishment was built in the year of 2003 and can cool off about 20 MW of heat and make it possible to operate Dåva even during summer. This also makes it possible to produce electricity all year around. The cooling establishment cools off heat in a big heat exchanger where the surrounding air is warmed up.

Nominal capacities & efficiencies:

Thermal input, biomass & waste: 65 MW

Total thermal input, incl. fossil fuels: 65 MW

Gross electrical output: 12 MWe

Net electrical output: 6 MWe

Heat output: 58 MJ/s

Electrical efficiency, gross: 18,4 %

Electrical efficiency, net: 9 %

Overall efficiency, gross: 108 %

The nominal overall efficiency is counted for the boiler (flue gas condensation excluded). Flue gas condensation 15 MW

How is plant controlled:

The plant is controlled by heat demand most of the year. In summertime when the demand of heat is low the power produktion controlles the plant. Before the cooling establishment was built the plant was put out of operation during summertime. The Dåva combined power and heating station produce heat to the district heating network in the first place. If the amount of heat seemes to be too small the electricity production will be reduced to make sure that enough heat can be delivered.

Heat backup:

Umeå Energi have several other plants which can be used to procuce heat to the customers when the demand of heat is large. We have two biofuel boilers, 18 and 30 MW. Besides these three base load stations, Dåva combined power and heat station included, we have several oil boilers and a number of electric boilers around the city to use when it is cold in the winter or when back-up is needed because of problems with the base load stations. The total effect that can be delivered on the main district heating network is 365 MW.

Heat usage: Heating and cooling

Energy usage:

The heat is used in the district heating network in Umeå City. Some 70 % of the total indoor area in the city is heated with district heating.The extension of the heating networks will continue at least in the next few years. During the summer when the demand of heat is low some amount of heat is used to run an absorption refrigerating machine. The product is cold water which is used in the district cooling network. The request of district cooling in summertime is growing. It´s also very good for the enterprise to get applications for the heat even during the summer when it  almost isn’t any demand for heating. The electricity is suppiled to the national grid.

District heat coverage (% of total demand in DH network): 40 %

DH inlet temperature: 85-120 °C

DH return temperature: 45-65°C

Heat storage size: The accumulation tank contain 18 000 m3 of water. It can hold 600 to 1000 MWh depending on temperature of the water. m3

Hours of full load that the heat storage can meet: The heat storage can at most deliver 50 MW heat. The storage can deliver heat at this rate in about 20 hours.

Fuel storage: The bunker can hold about 6000 m3 or 2000 tons of waste. This storage corresponds in a normal case to 4 days operation of full load.

Waste water:

The wet flue gas purification generates waste water. This water treats in a water purification unit. When the purified water finaly flows out to the receiving body of water it contains very small quantity of pollution. During 2003 the amount of 43 000 m3 purified water were blown out to Umeå River.

The water purification unit consists of several steps. The water is neutralized, ammonia is reduced and heavy metals precipitates and flocculates in two steps. After these steps the water enters the lamella sedimentation. Before the water flows out to the Umeå River it finally  pass a sand filter. The sludge from the lamella sedimentation and the sand filter are mixed with the fly ash from the fabric filter (the Bamberg method) and are taken to the landfill.

Ash discharge:

Flyash are mixed up with sludge from the water purification unit. This is called the Bamberg method. This stable Bamberg cakes are taken to the landfill. Some of the slag is used for constructions and some are taken to the landfill. The work continues to find new applications for the slag.

Plant description:

Dåva combined power and heating station is one of the worlds most energy-efficient and environmentally acceptable plant using waste as a fuel. The plant is located in Umeå in nothern Sweden and produces district heating and electricity from the incineration of sorted waste. The output is 70 MW, of which 12 MW is supplied as electricity to the national grid. Thanks to a combination of innovative solutions the efficiency is high. The exess heat from electricity production is recovered and heat pumps are being used to recycle the heat contained in in the flue gases.

Dåva was commissioned in 2000 after a two-year construction period. The plant was a necessary reinvestment in Umeå´s district heating system. The city is growing, and if nothing had been done Umeå would soon have found itself facing an acute power deficit. Dåva combined power and heating plant is the largest individual environmental investment ever undertaken in Umeå. The environmental gains are both local and global. The plant includes a number of new tecnical systems for incineration and flue gas cleaning, which have resulted in a significantly reduced environmental impact compared with previous production methods. For example a textile barrier filter with active carbon is used ahead of the wet flue gas cleaning stage with no possibility of bypass operation.

Dåva combined power and heating station is more than a energy production facility. It performs another task which is as least important – environmentally acceptable waste handling. With this new plant , Umeå Energi can offer the region´s municipalities and businesses a solution to their waste problems.  Umeå Energi operates in two dynamic lines of business, energy and communication. The enterprise is wholly owned by Umeå Municipallity. Umeå Energi runs several plants in consideration to produce heat to the district heating nerwork.

Fuel feeding system:

The bunker is a deep shaft that can hold up to 6000 m3 or 2000 tons of waste and functions as a short-term storage area. Two grip jaw traverse cranes capable of lifting 4,5 tons each lift, mix and drop the waste into a large funnel. The funnel is simply a sheet metal funnel but is equiped with a pusher at the bottom. The purpose of the pusher is to push the fuel down into the boiler in accurately-measured quantities.

Turbine:

The Dåva combined power and heating station produce heat to the district heating network in the first place. If the amount of heat seemes to be too small the electricity production will be reduced to make sure that enough heat can be delivered.

Steam data:

Steam pressure: 40 bar

Steam temperature: 400 degree Celcius

Steam production: 78 tons/h

Flue gas cleaning:

Dåva is equipped with one of the worlds best flue gas cleaning systems. The cleaning process startes in the boiler. Some of the flue gases return to the boiler in order to reduce the amount of nitric oxides. Ammonia is injected into the upper part of the boiler for the same reason. Before the first step in cleaning commences, active carbon is also added. The finaly powered carbon dust is used to bind dioxins and heavy metals. The fabric filter is the first step in the actual cleaningprocess. It´s made up of 1 620 fabric-lineed tubes through which the 150 degree (Celsius) flue gases must pass. The dust, the active carbon and everything which fastened on the carbon particles is collected and taken to an ash silo. The quencher is the next step for the flue gases. In the quencher the gases meet water and the temperature decreases to about 55 degrees Celsius. Now the gases enter the acid  scrubber. In the acid scrubber  the flue gases are cleaned from hydrogen cloride. The next step is the sulphur scrubber. In the sulphur scrubber lime solution is injected at three levels. The sulphur in the flue gases reacts with the lime and the result is calcium sulphite which, thanks to the air blasted into it, quickly change to calcium sulphate- i.e. gypsum. The gypsum is taken to the landfill. The condensation scrubbers extract addiotional heat from the gases and account for as much as 15 MW of the total effekt of the plant´s 70 MW. Heat pumps in these scrubbers lower the temperature to 35 degrees Celcius. The reheater rise the temperature to 65 degrees to help  the flue gases rise just a bit above the top of the smoke-stack. Before the flue gas enters the smoke-stack it passes through a noise damper. The waste water from the flue gas cleaning process is purified in a water purification unit (describes in the waste water section).

Cooling system:

Two heat exchangers (condensors) turn the steam heat into the cooled return water in the distribution network. The steam is cooled off in the condensors with the district heating water. The district heating water leaves the condensor at a temperature of 85 to 120 degrees Celcius.

Staff:

Two persons are needed to operate the plant during the day an two during the night. During daytime another 9 persons work at the plant. When necessary other people also can be called in. It´s hard to tell exactly how many full time employees that works at Dåva. Umeå Energi runs several plants and most of the employees works at other plants as well. The Umeå Energi Group has totally about 260 employees.

Total capital cost: € 73,000,000

Data collected and quality assured by: Swedish Biomass Association.

Contact person: Johan Vinterbäck