Winter warmth from the forest
ANDRITZ recently added to Sweden’s environmental commitment by supplying a Combined Heat and Power (CHP) plant to keep residents of Mjölby warm in the winter – using renewable fuels from local forests.
Mjölby-Svartådalen Energi (M-SE) is a lean company that supplies district heating and electricity in Östergötland County, Sweden. It is also impressively green. Christer Kjellberg, Head of Projects at M-SE, says, “Last year, over 90% of our output was locally generated from renewables. We are setting records in this region, and even in Sweden.”
In the beginning, district heating was supplied to the 26,000 residents of Mjölby by oil-fired boilers. “Our existing boilers were becoming less efficient, and we needed more capacity,” Kjellberg says. “More importantly, by adding CHP capabilities, the income we produce from power production can be used to offset the costs of producing district heating.”
M-SE issued a tender to six companies for a new biomass power plant that would use wood chips, forest residues, and sawdust as fuel. The fuel for the plant comes from within a 30 km radius. Design capacity was to be 35 MW for heat, and 10 MW of electricity. ANDRITZ was selected to supply almost the complete plant and the contract was signed on September 12, 2013.
“Everything that is visible above the ground in the new plant came from ANDRITZ,” says Christian Lackinger, ANDRITZ Project Manager. “We delivered the EcoFluid BFB boiler, fuel handling system, flue gas cleaning system, steam turbine with auxiliaries, and the electrical systems.”
From rock to clay
“The actual construction of the plant was quite a challenge,” says Kjellberg. “In some places we had to blast out hard rock and in other places we had very soft clay, so we had to insert numerous piles to support the civil construction."
All challenges were overcome with excellent cooperation, according to Lackinger. The plant was fully taken over by M-SE in July 2016.
Production Manager Anders Ejhed says, “Start-up went well. It took us some time to tune and optimize, mostly focused on getting the biomass fuel mix right.”
Flexibility - a major feature of Mjölby
One of the main features of the new Mjölby plant is the flexibility to adjust the electrical output from the turbine according to where the energy output of the boiler is needed most, or is most economically viable. Lackinger explains, “In most plants, if you reduce electrical output, you also reduce district heating energy. The Mjölby plant is a bit different. We direct part of the steam to a heat exchanger that converts this steam input directly to district heating energy. This allows them to adapt to heating requirements from the community, fuel mixtures, and the need for electrical energy.”