CPFD modeling of air-steam gasification of brewer's spent grains in a bubbling fluidized bed

To explore the gasification characteristics of brewer's spent grains (BSGs) in a fluidized bed gasifier with air and water vapor as gasification agents, a numerical simulation model with computational particle fluid dynamics (CPFD) of 3D bubbling fluidized-bed gasifier was established, and gasification properties was investigated based on CPFD simulation. The thermogravimetric mass spectrometry (TG-MS) was used to investigate the main components in the volatiles released during the pyrolysis of BSGs, for providing benchmark data of gasification raw materials. The effects of temperature T, equivalence ratio ER, steam-to-BSGs mass ratio S/B and fluidization velocity u(g) on the gasification properties, were investigated using CPFD analysis. The results showed that when the gasification temperature increased from 700 degrees C to 900 degrees C, the mole fractions of CO and H-2 in the product gas increased from 9.80 % and 3.95 % to 16.00 % and 14.21 % respectively, and the low heating value of the product gas increased from 3.36 MJ center dot Nm(-3) to 4.35 MJ center dot Nm(-3). As ER value increased from 0.2 to 0.4, the carbon conversion fraction increased from 78.8 % to 85 %, but the molar fractions of H-2 and low heating value of the product gas both decreased. When S/B value increased from 0.3 to 0.7, the molar fraction of H-2 increased from 6.54 % to 11.76 %, while the molar fraction of CO and CH4 decreased from 13.59 % and 3.97 % to 11.37 % and 3.84 % respectively. With u(g) value increasing from 0.15 m center dot s(-1) to 0.75 m center dot s(-1), the molar fraction of H-2 and CO increased from 8.11 % and 9.61 % to 11.63 % and 17.01 % respectively, owing to strengthened particle mixing. However, with further increase of u(g), the molar concentrations of H-2 and CO above the splash zone both decreased, due to a portion of BSGs particles being brought out by fluidizing gas from the top outlet of the gasifier. The numerical simulation results were validated by the experiments in a bubbling fluidized-bed gasifier. They underestimated CO2 production, slightly overestimated the mole fraction of H-2 with a maximum error of 9.54 %, overestimated the mole fraction of CO in the vast majority of cases, and estimated the mole fraction of CH4 with a maximum error of only 6.67 %.