Evaluation of a biomass drying process using waste heat from process industries: A case study

Dry biomass provides considerable benefits for combustion, such as increased boiler efficiency, lower flue gas emissions and improved boiler operations, compared to fuels with high moisture. Drying is however an energy-intensive pre-treatment. Utilising low-grade, waste heat – of which large amounts are available from many process industries – could significantly reduce energy consumption. The integration of a drying process into a power station fuel system was investigated; the results are presented here. Waste heat from a process industry plant (100 MW output) was utilised as the heat source for drying. The biomass, pine chips at 60wt% moisture, was dried and could then be provided as the input fuel for a subsequent 40 MW power plant. The process consisted of a belt conveyor as the dryer and either flue gases or superheated steam (generated from the hot cooling water) as the heat source. Flue gas usage would result in lower capital costs (∼€2.5 m), but environmental issues, such as pollutant emissions must be considered. Superheated steam can combine short drying times, good heat recovery and environmental protection, but would entail greater capital costs (∼€3 m). A 3–4 year return on the initial investment was calculated for both technologies, but profitability was sensitive to fuel price.