Cool combination of heat, power and pellet production
In August 2015 the Swedish municipal energy company, Uddevalla Energi AB officially inaugurated its new 42 000 tonne-per-annum wood pellet plant. Built next to its 32 MW thermal municipal solid waste (MSW) fired combined heat and power (CHP) plant, Lillesjöverket, the new pellet facility utilises residual heat from the CHP during the summer period when the demand for district heating is low.
Tracing its roots back to 1857, Uddevalla Energi may well be one of the oldest municipal energy companies in Sweden. It also exemplifies some of the most modern out-of-the-box forward thinking. Whilst it may have taken a cue from its Swedish utility colleague Falu Energi och Vatten that also built a “summer” pellet plant to use residual heat from its CHP, there is a major difference. In Uddevalla the 32 MWth CHP is a municipal waste thermal treatment plant, which brings additional constraints into play.
– It’s the world’s first waste to energy powered pellet plant. By using residual heat to dry sawdust and shavings we in effect transfer energy from summer to winter when it is needed. This is an environmental and energy efficient way of operating the CHP, commented Roger Johansson, former CEO, Uddevalla Energi during his inauguration address.
Commissioned in 2009 Lillesjöverket has a permit to use up to 130 000 tonnes of combustible household waste, peat and wood-based fuels annually. This is collected from the town and surrounding municipalities. Located on the southwest coast of Sweden some 80 km north of Gothenburg, Uddevalla is in the heart of the popular Bohus-coast tourism region. From a waste management perspective this means that the local population increases significantly during the summer period. At the same time the demand for district heating is at its lowest and local environmental permitting regulations restrict the amount of cooling the waste-fired CHP can deploy. This in turn restricts the amount of waste treatment and power production.
On an annual basis the CHP plant uses around 110 000 tonnes of MSW fuel to supply about 200 GWh of heat and 60 GWh electricity. During the summer excess heat had to be cooled and production downscaled. The new pellet plant addresses this by providing a suitable heat demand during the warmer months enabling the CHP to run year round without the need for cooling or scaling-back fuel intake.
– Previously we cooled around 25 GWh of heat during the summer. Now we can use the heat excess and produce wood pellets. At the same we generate revenue from increased waste treatment capacity and power production, explained Fredrik Jostby, Pellet Business Manager for Uddevalla Energi.
Supplied as a turnkey plant by Estonia-based Hekotek AS, the SEK 180 million (≈ EUR 19 million) pellet plant investment includes property acquisition, site repurposing, and onsite pellet storage dimensioned for the current production output of 42 000 tonnes. The pellet plant will use around 230 000 m³ of softwood sawmill residues, roughly 50/50 spruce and pine from the region, supplied by Norway-based wood industry major Moelven AS. This is delivered by truck and stored on site.
– We receive 6-8 truck deliveries daily and since we only operate the pellet plant during the summer period we can store around 140 000 m3 of sawdust onsite, said Jostby.
An off-take agreement for around 60 percent of the production output has been struck with utility colleague Göteborg Energi with the remaining production destined for large industrial clients and heating networks in the region. Major component suppliers for the plant include Bruks for material handling, Stela for the belt-dryer, Fredrik Mogensen for the sieves and CPM for the pellet presses, the latter equipped with CPM’s novel press lubrication and cooling system.
Since the pellet facility is not operational year round, annual capacity is more difficult to estimate. However, according to Hekotek, the plant has a design capacity of 13 tonnes-per-hour, which can be increased in the future.
– The layout of the new plant is planned so that an extra press and a dryer can be easily added to the existing equipment complex, a hallmark of Hekotek design, explained Heiki Einpaul, Managing Director of AS Hekotek, during the inauguration.
– In principle one can say that what we do is simply capture and store uneeded energy from the summer and move it to the winter when its needed, concluded Fredrik Jostby.
Pellet plant start-up:
Lillesjöverket CHP start-up:
Annual heat production:
Annual power production:
Boiler & flue gas treatment:
SEK 180 million (c. EUR 19 million)
c. 42 000 tonnes
Bruks, Fredrik Mogensen (sieve)
3 x CPM (space for 4th), capacity c.13 t/hr
Stela, 16 MW 55 m, input 26.5 t/h output 13 t/hr @ 8%mc
Symaga 2 x 4 000 tonnes
2009 (boiler 2008)
SEK 900 million (c. EUR 93.7 million)
c. 200 GWh
c. 60 GWh
110 000 t/yr MSW, peat & wood waste (permit 130 000 t/yr)
Fisia Babcock Environment