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Reducing the carbon footprint by 50%

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Reducing the carbon footprint by 50%

March 31, 2013 - 16:00
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BRUSSELS, April 1, 2013 (RISI) -Metsä Board's Kyro, Finland, mill now has access to a new combined heat and power (CHP) facility in late 2012 fuelled entirely with biomass: 80% wood-based and 20% peat. Natural gas is now used only for startups and in case of any disturbances. The objective is to provide competitive energy (steam and power) to the Kyro mill as well as district heat to the adjacent community of Hämeenkyrö.

The facility was built as a joint project by Pohjolan Voima, Leppäkosken Sähkö and Metsä Board. Pohjolan Voima was established in 1943 based on hydropower production. It then diversified into thermal power: oil at first followed by coal, nuclear and biofuel. In 2011, it produced 14.5 TWh of electricity, about 25% of Finland's total power production.

Pohjolan Voima is a privately-owned group of companies, producing heat and electricity. Its shareholders include forest products companies (61.5%), energy companies and municipalities. When first formed, it was totally owned by a group of forest products companies.

In the last 20 years, it has invested in 15 biomass-based power plants. This is the latest. Also known as the HaVo project, after Hämeenkyrön Voima, which is a subsidiary of Pohjolan Voima. It controls 84% of the company; the rest is owned by the local utility.

The decision to invest in the new boiler was made on March 17, 2011, although prep work had started in late 2010 with the demolition of the old power boiler. Space was exceptionally tight on the mill site but work proceeded without incident. Connections to the paper mill were reused. No work was needed for tie-ins as all are in basically the same place as they were with the old boiler.

Construction began in April 2011. The first tests were run in July 2012 and the plant was ready for commercial operation in October 2012. The Euro 50 million project included fuel handling (Raumaster), EcoFluid bubbling fluidized bed boiler (Andritz) and the automation (Metso).

The new boiler was fit into about the same space the old one occupied. It is the white building in the middle of the picture. The silos can be seen in the lower right

The main fuel is wood: stumps, bark, thinning, sawdust. An advantage for Metsä Board is that the wood comes from one of its sister companies, Metsä Forest, so that supply is virtually guaranteed. The company does not "vacuum" the forest floor for the residues. About 20% of residue is left to act as nutrients for future growth. In some more fragile forest areas, Metsä Forest collects no residue.

Peat use is supplementary, especially in the winter. Peat is also readily available. The boiler also uses pressed sludge from the paper mill.

The Raumaster receiving station is a single line with a capacity anywhere from 100-500 loose m3/hr. The material is screened and crushed and then sent to one of two 1,300-m3capacity silos. Peat is delivered already milled, in a granular form that can be quite dusty.

Wood is delivered by truck, about 20 loads daily. The first screening removes the football (soccer) ball sized particles. After the second screening the larger particles are removed and crushed. Samples are then tested for moisture content. Peat's moisture content is usually about 40%. Some wood (stumps for example) may test less than 30% while at the other extreme, bark may contain 60% moisture or more. Winter and summer conditions also can create a flux in moisture content.

Once delivered to the silos, the material is usually stored for about a day. There is a smaller (1-hr capacity) silo just before the boiler. The mill sledge is fed onto a belt conveyor and then directly into the boiler.

Even with constant delivery of biomass, noise is kept to a minimum as the mill abuts onto a residential area

Andritz supplied the PB105 model BFB unit that has a heating value of 3,500-5,100 Btu/lb. Fuel heat input is 370-410 million Btu/hr. Electrical capacity is 16 MW, of which 12 goes to the mill and the rest to the local utility

Steam flow is 231,000-254,000 lb /hr at a pressure of 1,220 psi and a temperature of 950°F. Feed water temperature is 316°F.

Fuel is fed to the boiler and then the steam produced is fed to a back pressure turbine (16-MW AEG unit installed in 1972). There is a steam accumulator for paper machine breaks and startups.

As well as the boiler, Andritz supplied the flue gas cleaning system with bag filters, field instrumentation and electrification. As noted dust can be a problem. To solve this, unloading is done in a closed room. There is a dust collection system and the dust is then burned.

For both bottom ash and fly ash, various options are being studied. As Juha Kouki, managing director of Hämeenkyrön Voima Oy, says, "Because we are still in startup, we first need to study the makeup of the ash."

The Metsä Board Kyro mill
With its two machines, Kyro produces 190,000 tonnes/yr of high quality coated folding boxboard as well as 105,000 tonnes/yr of wallpaper base paper. In 2011, the board machine went through a rebuild that included added 40,000 tonnes/yr of capacity. The machine’s products include Carta Elega and Avanta Prima, used in demanding beauty care and health care packaging applications.

There are two bag filter silos for flue gas cleaning. Each can handle 60-70% of capacity so there is some built in redundancy. Flue gas studies have shown that carbon dioxide emissions have fallen, and, there has been no increase in noise in the area, an important factor since the mill is adjacent to a residential area.

Kouki says that boiler life is expected to be 30 years or longer. The driving force for the project was the economy although environmental considerations also played an important role. The new boiler is expected to reduce the carbon footprint of Kyro's grades by 50%. Carbon dioxide emissions will be reduced by 100,000 tonnes/yr. This is part of Metsä Board's goal of cutting CO2emissions across the company by 30% by 2020 compared with 2009 levels.