A Swedish company has built a combined heat and power plant that is exemplary in terms of sustainability and design. Jo Stimpson reports.
In Sweden, it is common to live in a home with no boiler. Instead, district heating - where hot water is distributed to residential and commercial properties from a central heat generating plant - is widespread.
More than 50% of Swedish homes are heated in this way. The country’s first municipal district heating system was built in 1948, and it was in the 1960s that district heating systems really began to take off in Södertälje, a city south west of Stockholm.
The Södertälje municipality’s principal district heating plant is Igelsta, operated by energy company Söderenergi. Along with the Fittja plant in nearby Botkyrka and two other stand-by boiler stations, Igelsta has for many years produced around 1.8TWh of thermal energy per year and supplied heat to around 70,000 properties, including a rather well known customer - the world’s largest Ikea store.
“It was difficult to find where to unload and store all of the precast concrete. It was also hard to find the right contractors”
Staffan Dyrsch, project manager, WSP
Igelsta has already undergone some changes since coming on stream in 1982. It was originally fired with pulverised coal, but as climate change began to command attention in Sweden, Söderenergi looked for more environmentally friendly fuels. Peat and tall oil - a byproduct of wood pulp manufacturing - were introduced to the plant from 1992, and in 1994 one of the three boilers was converted to take solid fuels such as wood chips.
The fuel mix used by Söderenergi today includes 48% waste wood chips and 25% recovered waste materials.
Now Igelsta has undergone its biggest evolution yet. In May 2007 work to build a new combined heat and power (CHP) plant on the site began. This will be able to produce electricity rather than just heat, with a capacity to produce 200MW of district heating and 85MW of electricity - enough to supply around 110,000 homes.
CHP technology is extremely efficient. Fuel is burned to boil water, producing steam at 540°C which turns a turbine to generate electricity. The steam condenses back into extremely hot water and passes through a heat exchanger where it heats water in feed pipes to 110°C. Those pipes then take the heated water through the district heating system, which comprises 400km of pipelines in total and runs through individual homes, before returning to the plant at 40°C.
A smaller heat exchanger in each home uses the hot water in Igelsta’s pipes to heat that building’s own water supply. “The two waters never mix,” says WSP project manager Staffan Dyrsch. “We put a green food colouring in our water so we know if there’s a leak,and whether it’s our water.”
Igelsta’s CHP system offers low costs, high security of supply and minimal environmental impact. Electricity generated by the new CHP plant will save 450,000t of carbon emissions per year by replacing imports of coal and oil based electricity.
“Most of the problems were because people wanted to work on the same spot at the same time”
Staffan Dyrsch, project manager, WSP
The new plant was finished in late 2009 and the new boiler was inaugurated in March this year by King Carl Gustaf XVI.
The new plant only houses one large boiler compared to the old plant’s three smaller ones. The new 3,000t boiler is 50m tall and hangs suspended from the roof of a new 63m tall boiler hall. It was built to the south of the existing plant - which will remain in place to supplement the new plant if needed - at a cost of SKr2.4bn (£210M).
Consultant WSP was responsible for project management, design, construction management and installation co-ordination for the new structures. The project was divided into more than 55 different contracts, presenting the challenge of co-ordinating hundreds of workers. At one point, the number of people on site reached over 500.
“When we started the project there were cranes all over the place,” says Dyrsch.
The steel structures for the new buildings were the first to be built. The new silos were built afterwards using 2.4m long prefabricated concrete double tee wall sections arranged in a near-cylindrical shape, with a steel structure for the roof. The project used a total of 13,000m³ of concrete and 1,400t of steel. The generator and turbines were installed later, in June 2009.
Finding the right suppliers was a challenge. Part of the main boiler building was designed to be built using prefabricated concrete sections, but WSP had to look far afield to locate the right products. “We found it hard to find a company that would deliver concrete as prefabricated walls,” says Dyrsch. A Finnish company located 1,500km away was eventually chosen - but the small size of the site cause further problems.
“It was difficult to find where to unload and store it all,” Dyrsch says. “It was also hard to find the right contractors - but we did well.”
He also describes how a flash flood after exceptionally heavy rainfall caused temporary problems on site.
“There was water running down from the woods and onto the site - it was making big holes in the ground,” he says. Although the water ingress appeared suddenly overnight, the site’s proximity to Hallsfjärden, an inlet of the Baltic Sea, meant the problem had a relatively simple solution. “We had to make special arrangements to channel it down to the water.”
The striking design of the new plant is down to architects Scheiwiller Svensson Arkitekter. The red and grey colour scheme of the exterior extends indoors, with the main steel structure painted black, and other steel grey shades used throughout. Major pieces of equipment were painted red - the novelty of which was not lost on employees at Siemens, where the turbine was manufactured. “The workers really loved to work with a red turbine,” says Söderenergi communications manager Madeleine Engfeldt-Julin. “It was very important for Söderenergi that they wanted it to be a landmark,” says Dyrsch.
“We did a lot of work to make it look good.”
The fuel for the boiler comes in by road and also by sea, since Igelsta has its own quay. Due to the low energy density of the renewable fuels used, much more storage space is needed than if the plant were burning coal. Accordingly, a new warehouse was also built and the on-site quay was widened to take two ships instead of one, allowing more fuel to be delivered simultaneously.
Hundreds of people attended the new plant’s inauguration ceremony in March, and the project has been popular from the start.
Planning permission was granted very quickly, from the application being made in February 2006 to permission being granted in December that year.
“It was a real record time,” says Dyrsch. “It can take years if you don’t have public opinion with you. But we worked a lot on communications beforehand to prepare everybody for this.”
Preliminary operation at the new plant began in September 2009 with commercial operation starting in December 2009, ahead of the royal inauguration in March.
“It has really gone very well,” says Dyrsch. “There were a lot of small problems and coordination issues - but we could manage the problems. Most of them were because there was not a lot of space around the site.
People wanted to work on the same spot at the same time.”
Even the extremely heavy and long-lasting snows that fell in the region and lingered into the early months of 2010 did not derail the enthusiasm and optimism that surrounds the project.
“We are very happy,” says Engfeldt-Julin. “We have really had the opportunity to test the system with this weather.”