Assessment of low‐rank coal and biomass co‐pyrolysis system coupled with gasification

Abstract

To utilize low-rank coal and biomass in a highly efficient and environmental-friendly manner, a co-pyrolysis system coupled with char gasification is investigated. This system has five main units, namely, the drying and mixing, pyrolysis, cooling and separation, combustion, and gasification units, which are simulated by ASPEN plus based on experimental data. Results show that 37% of the pyrolysis char is burned to supply heat for pyrolysis and drying processes based on cascade utilization of heat energy, whereas the rest is sent to a gasifier. The sensitivity analysis is performed to investigate the impacts of steam and O2 injection on gas composition, gasification temperature, carbon conversion efficiency, heating value of gas during gasification, and gas production efficiency. The fractions of H2, CH4, CO, and CO2 demonstrate diverse variation tendencies with an increasing equivalence ratio and steam-to-char (S/C) ratio. However, carbon conversion efficiency reaches its peak of 99.91% when the equivalence ratio is approximately 4 regardless of S/C ratio. An equivalence ratio of 4 and S/C ratio of 0.15 are used as decent examples to calculate the mass balance and to simulate the overall system. Results show that 1000 kg/h coal and 500 kg/h biomass can produce 285.83 m3/h pyrolysis gas and 2580.78 m3/h gasification gas with low heating values of 8.20 and 9.746 MJ/m3, respectively.