Modeling and thermodynamic optimization of distributed combined heat and power system based on biomass chemical looping hydrogen generation process

Abstract

Distributed biomass combined heat and power (CHP) system is becoming an important way to use local biomass for ensuring regional energy supply and reducing CO2 emissions. In this work, a high-efficient CHP system based on a new separated-type biomass gasification process is proposed. The gasification system includes a chemical looping hydrogen generation (CLHG) process combined and a tar catalytic steam reforming (TCSR) unit, in which the general CLHG process includes a fuel reactor (FR), a steam reactor (SR) and an air oxidation reactor (AR), but in this study, the AR is removed and instead, the FR is decoupled into two reaction stages, namely, pyrolysis and gasification. In addition, the biomass pyrolysis-gasification-hydrogen generation (BPGH) combined cycle system is established by using oxygen carrier to couple pyrolysis, gasification and hydrogen generation stages. The TCSR process is used to convert volatiles generated by pyrolysis into syngas. To maximize thermodynamic efficiency of the system, the influences of temperature for the catalytic steam reforming (TCSR) and the ratio of steam to carbon (S/C) on the overall energy and exergy efficiency are mainly studied. The results show that the overall energy and exergy efficiencies reach the highest values of 75.93% (LHV) and 32.61%, respectively, when TSCR=800 °C and S/C = 3 while the net power generation energy and exergy efficiencies are 27.43% (LHV) and 27.54%, respectively.