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 ug on the gasification properties, were investigated using CPFD analysis. The results showed that when the gasification temperature increased from 700 °C to 900 °C, the mole fractions of CO and H2 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⋅Nm−3 to 4.35 MJ⋅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 H2 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 H2 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 ug value increasing from 0.15 m⋅s−1 to 0.75 m⋅s−1, the molar fraction of H2 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 ug, the molar concentrations of H2 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.