An experimental investigation on biogases production from Chinese herb residues based on dual circulating fluidized bed

Abstract

In this paper, pyrolysis gasification experiment was carried out on a dual circulating fluidized bed gasifier using Chinese herb residues as raw material, and the effects of gasification temperature, the moisture content of raw materials, air equivalence ratio ER and steam to biomass mass ratio (S/B) on gasification characteristics were studied. The results show that the increase of gasification temperature can promote the gasification reaction and improve the gas production quality as well as the gasification efficiency. The rise of moisture content of raw materials leads to the decrease of the gasification temperature and φCO, the significant increase of φCO2, φH2, gas heat value and gasification efficiency all showed the tendency to increase first and then decrease. With the increase of ER, the combustible gas, especially φCO reduced continuously, leading to the gradual decrease of the calorific value of gas, φCO2, carbon conversion rate and gasification efficiency increased firstly and then decreased. A certain amount of steam ratio can improve the gas quality and the gasification efficiency, but excessive steam will restrain the gasification, S/B has a suitable threshold range. When the raw material moisture content was controlled between 5 and 10%, the gasification temperature was between 750 and 800 °C, ER 0.23–0.26 and S/B 0.4–0.6, the residue gasification system in dual circulating fluidized bed displays good gasification characteristics with more than 8 MJ/m3 the calorific value and 75% gasification efficiency. The results can provide a theoretical reference for the improvement of dual circulating fluidized bed gasification process and the further deepening utilization of Chinese herb residue resources.