Apr 20, 2016
The integration of a biomass gasifier with an existing coal-fired boiler has become a success at Vaskiluodon Voima’s power plant in Vaasa, Finland.
The world’s largest biomass gasification plant started its commercial operation in early 2013. This is the first time ever that biomass gasification has been adopted to replace fossil fuels on such a large scale.
Vaskiluodon Voima Oy is a utility company jointly owned by EPV Energia Oy and Pohjolan Voima Oy. It operates two combined heat and power (CHP) plants in western Finland, one in Vaasa and the other in Seinäjoki. The Vaasa power plant has a capacity of 230 MW of electricity and 175 MW of district heat. It features a pulverized coal boiler that consumed from 320,000 to 600,000 tons of coal per year before the installation of the gasifier.
The main targets for the investment were to increase the use of renewable energy in production and reduce coal consumption by 25–40% as well as to allow the plant to use multiple fuels and thus optimize fuel costs. After going through several alternatives, Vaskiluodon Voima decided to convert its existing high-efficiency production unit to use gasified biomass instead of building a new one.
The new 140 MW gasification plant features Valmet’s innovative concept for gasifying and utilizing biomass. The delivery included a fuel yard, a large-scale belt dryer, a circulating fluidized bed (CFB) gasifier, modification and integration work on the existing coal-fired boiler, and an extension to the Valmet DNA automation system with advanced applications. Having everything from one supplier ensured a perfect match of solutions.
The gasification plant was built as part of the existing coal-fired power plant and integrated with the pulverized coal boiler. The gasifier feeds the boiler with product gas that is combusted together with coal.
“By adding a gasifier, it was possible to keep the original coal-firing capacity online and maintain a 100% coal-firing possibility. For the customer, this was a safe solution. Nothing old was dismantled. Additionally, only minor modifications were needed in the existing Benson-type boiler, although it had originally been built for coal firing only,” says Juhani Isaksson, Product Manager Gasification, Valmet.
The gasifier is fueled with forest residues, stumps and round wood. Peat is used as a backup fuel. The utilization of biomass that comes from a radius of 100 km around the plant has created new jobs in the area, and thus boosted the local economy.
|As the moisture content and heat value in various bio-fuels vary a lot, more detailed information about them is needed. As each fuel load arrives, it is registered into the Valmet Fuel Data Manager application, which is integrated with the plant’s Valmet DNA automation platform that has automated and facilitated all the important tasks related to bio-fuels. Valmet DNA offers a real-time monitoring window to the control room and office.
“We have succeeded very well in reaching our targets, and the outcome has exceeded our expectations,” states Matti Loukonen, Plant Manager at Vaskiluodon Voima. “Most importantly, product gas has become a new fuel in our fuel range.”
Thanks to biomass gasification, the company now has the capability to replace about 25–50% of the coal with local biomass, depending on the boiler load.
In fact, the figures are higher. Trial runs carried out in September 2014 proved that the boiler can be fueled solely with product gas. Since then, the boiler has been run purely on product gas when the load is low during autumn and spring.
Vaskiluodon Voima has been very satisfied with Valmet’s gasification technology. “An availability of 98–99% has been very high. We are currently increasing the gasifier capacity from 140 to 180 MW in cooperation with Valmet. It is about fine-tuning the equipment and finding new ways to run it. No new investment is needed for this capacity increase.”
Another main target for the investment was to reduce emissions – and this has been achieved, too. Through biomass gasification, the plant has been able to lower its CO2 emissions by approximately 230,000 tons per year. SO2 emissions are also lower.
“Our future challenge lies with NOx emissions. We need to decide how to stay under the new EU limit values after the transition period. We are currently considering options such as a SCR or SNCR method – or perhaps another gasifier,” Loukonen says.
The cooperation between Vaskiluodon Voima and Valmet has been mutually fruitful. “We have been very pleased with Valmet. It has been a proactive partner for us in developing cleaner combustion and now in increasing gasifier capacity.”
Vaskiluodon Voima intends to further increase its use of biomass. “We have a strong belief in biomass combustion. It represents the future,” Loukonen adds.