Abstract
The high contents of disadvantageous elements contained in non-woody biomass are known to cause problems during small and large scale combustion, typically resulting in a higher risk of slagging, corrosion, and increased emissions. Mechanically leaching the respective elements from the biomass through a sequence of process steps has proven to be a promising solution.The florafuel process used here is comprised of size reduction followed by washing and subsequent mechanical dewatering of the biomass. Densification of the upgraded biomass into standardized pellets (Ø 6mm) enables an application in existing small-scale boilers. The presented combustion trials investigated the performance of pellets made from leached grass, foliage and a mixture of both in two small-scale boilers (<100 kWth) with slightly different technology (moving grate versus water-cooled burner tube) during a 4-h measurement period. Emissions were in accordance with German emissions standards except for NOx (threshold is 0.50 g/m3) in the case of pure grass pellets (0.51 g/m3) and particulate matter (PM) in all but one case (foliage, 13–16 mg/m3). An electrostatic precipitator (ESP) unit installed with one of the boilers successfully reduced PM emission of both the grass and mixture fuel below the threshold of 20 mg/m3 (all emission values refer to 13 vol.% O2, at standard temperature and pressure (STP)). Bottom ash composition and grate temperature profiles were analyzed and discussed for one of the boilers.
Highlights
According to the National Renewable Energy Action Plans of the European Union member states bioenergy is the largest contributor to the renewable energy targets for 2020 with 54.5% and energy from solid biomass will contribute 36% [1]
An electrostatic precipitator (ESP) unit installed with one of the boilers successfully reduced particulate matter (PM) emission of both the grass and mixture fuel below the threshold of 20 mg/m3 (all emission values refer to 13 vol.% O2, at standard temperature and pressure (STP))
The florafuel-treated grass and foliage had ash contents of 10.1 and 8.5% DM, respectively, which was a reduction due to the washing and leaching by 58% DM for grass and 40% DM for foliage (Table 1). In both cases, the ash content is considerably higher than in woody biomass which is largely due to the remaining amounts of Ca, Si, K, and Mg, even though they were reduced by the mechanical leaching process by 42%, 89%, 84%, and 62% DM, respectively
Summary
According to the National Renewable Energy Action Plans of the European Union member states bioenergy is the largest contributor to the renewable energy targets for 2020 with 54.5% and energy from solid biomass will contribute 36% [1]. 2020, will be driven by a low-carbon economy, or rather by a bio-economy based on the principle of cascading, more and more biomass will be utilized for non-energy purposes. This requires the efficient recovery of residue biomass, for e.g., heat production, as high-value biomass will be mainly used for material purposes. A smart utilization of bioenergy will be integrated with the other renewable energies and bio-based products, acknowledging that wind, solar, and bioenergy need to be complementary in order to achieve a 100% renewable heat and power production by the end of the century [2]
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