Integrated water washing and carbonization pretreatment of typical herbaceous and woody biomass: Fuel properties, combustion behaviors, and techno-economic assessments

Abstract

Thermal pretreatment of biomass is crucial for its efficient utilization. Two types of common biomass were selected for integrated water washing and carbonization pretreatment, specifically water washing-torrefaction (WT) and hydrothermal carbonization (HTC), respectively. The fuel properties, combustion characteristics, and representative ash-related pollutant PM10 (particulate matter with aerodynamic diameter of 10 μm or less) emission performance were evaluated. The results indicated that both the WT and HTC had beneficial effects in improving the fuel properties and combustion characteristics, and also alleviated severe ash-related problems of biomass. Then the modeling of mass and energy balance under auto-thermal conditions was established based on the experimental data. Subsequently, economic evaluations were performed at three plant capacities. The net present value (NPV) increased with upscaling, with the production of pine biochar (WTP) at 1000 kg/h capacity having the highest NPV value of 7.76 M€ and lowest cost of production (COP) value of 9.1 €/GJ. The NPV was most dependent on the biochar/hydrochar price, whereas the variations in electricity price, working hours of the plant, and number of workers together dominated the COP. Furthermore, the effect of carbon tax illustrated that WT was more affected than HTC; the COP was approximately zero under the carbon-neutral scenario.