The world’s largest biomass gasification plant located in Vaasa (FI) 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. The target for the investment was to use more renewable fuels in production and to reduce coal consumption by 25–40%. Vaskiluodon Voima, the local plant operator, also wanted to be able to use multiple fuels and thus optimise costs and environmental impact. Therefore, Vaskiluodon Voima decided to convert its existing high-efficiency production unit to use gasified biomass.
Valmet, the finish worldwide technology leader, delivered the biomass gasification plant that was built as part of the existing coal-fired power plant and integrated with the pulverised coal boiler. The gasifier feeds the boiler with product gas that is combusted together with coal. The 140 MW gasification plant delivery included a fuel yard, a large-scale belt dryer, a circulating fluidised bed (CFB) gasifier, modification and integration 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. Only minor modifications were needed in the existing Benson-type boiler, although it had originally been built for coal firing only.
The gasifier is fueled with forest residues, stumps and round wood. Peat is used as a backup fuel. The utilisation 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. “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. 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. Despite the modification, also the original coal-firing capacity of the boiler is still available when needed. For Vaskiluodon Voima, this was a risk-free solution.
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 tonnes per year. SO2 emissions are also lower. To monitor emissions, the plant uses the Valmet DNA emission monitoring tool. The application provides all necessary information for emission monitoring and reporting. “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 (selective catalytic reduction) or SNCR (selective non-catalytic reduction) method” Loukonen says.