Optimising biomass combustion for heat and power generation
Almost half of the EU’s energy demand is taken up by heating and cooling, with bioheat responsible for almost 90 % of all renewable heat in 2017. Tapping the heat generated during biomass combustion to generate electricity and heating in a combined heat and power (CHP) plant, works well for medium- and large-scale units. Many of these can be found around Europe, especially in Scandinavia. The EU-supported Biofficiency project was set up to optimise the production of bioenergy from biomass-fired CHP plants, resulting in a design for a next-generation biomass CHP plant which the project’s industrial partners plan to commercialise.
Producing higher-quality biofuels
In contrast to the traditional fossil fuels used in thermal power stations, biomass is a non-uniform feedstock. Its composition varies depending on type, origin and season and can contain harmful inorganic elements such as chlorine, sodium and potassium. These can cause problems during high-temperature steam production. Problems include leaving an insulating layer of ash on exchange surfaces which increases operating costs due to maintenance and shutdowns. To render previously challenging material usable, and remove harmful elements, Biofficiency investigated three different pre-treatment technologies: torrefaction with and without washing, hydrothermal carbonisation and steam explosion of biomasses prior to combustion. Secondly, the project studied the use of mineral additives that capture problematic components in the gas phase of combustion and so prohibit harmful reactions in the boiler. Both approaches were tested at scales from laboratory to full scale, in two different firing systems (pulverised fuel and fluidised bed). The testing ensured they would work in real-life applications. Models also allowed the team to simulate combustion behaviour and ash formation to understand the processes in more detail. After demonstrating that their techniques did enhance combustion performance in biomass boilers, the team delivered a design for a CHP plant, with higher steam temperatures of up to 600 °C at medium to large scale (approximately 300 MWth fuel input). As well as being very efficient, their new technique could significantly reduce emissions compared to coal-fired plants and smaller biomass CHP plants, at a competitive cost. The project also explored and evaluated uses for biomass ash to prevent it becoming landfill. One possible use identified was as an ingredient in construction materials, such as geopolymers.
Meeting future demand
Bioenergy is not only highly efficient for combined heat and electric power production, it can also significantly reduce CO2 emissions when compared to fossil fuels. This is especially true for the heating sector, where it can reduce the reliance on coal if used in medium- to large-scale CHP stations, which are much more efficient than small-scale heating systems. While more technologically complex, bioenergy offers a viable alternative to renewables, such as wind or solar. As bioenergy does not depend on fluctuating weather conditions, it is better able to meet the needs of a demand-driven heat supply to private homes connected to heating networks. Medium- to large-scale bioenergy for electricity and combined industrial or district heating is predicted to increase by 160 % in 2020 compared to 2010, while carbon emission quotas are becoming stricter. “Finding new ways to efficiently utilise cheap and currently unused feedstocks are necessary in order to meet this increased demand,” says Sebastian Fendt, project coordinator.
Keywords
Biofficiency, biomass, heat, cooling, energy, renewables, feedstock, bioenergy, electricity, carbon emissions, combustion
