Design and development of bubbling fluidized bed gasifier for hydrogen enriched syngas from agricultural waste biomass

Abstract

The bubbling fluidized bed gasifier (BFB) was designed to operate at atmospheric pressure with a capacity of 5 kg/h (24 kWth) for gasification of locally grown agro-residues mustard stalk (MS), Bengal gram stalk (BGS), and wheat straw (WS). The gasifier performance was determined using air, air+ steam as gasification agent at different operating parameters such as as temperature (750 oC, 800 oC, 850 oC, and 900 oC); equivalence ratio (0.25, 0.3 0.35, and 0.5), particle size (lt0.6 mm, 0.6-1.0 mm and 1.0-1.4 mm); bed material (sand and olivine), and S/B ratio (0.3, 0.4 ad 0.5). The operating parameters have a strong influence on the gaseous composition, syngas yield (and#947;gas), carbon conversion efficiency (CCE), higher heating value (HHVg) and thermal efficiency (and#951;th) for all three biomasses. Types of biomass also affect gasification due to the difference in characteristic properties. Biomass as a fuel and its characteristic properties play an important role in gasification as they influence the product gas composition and yield during biomass gasification. Mustard stalk (MS) exhibited better gasification performance while wheat straw (WS) had a little inferior performance compared to mustard stalk (MS) and Bengal gram stalk (BGS). The introduction of steam into the gasification process has a major impact on the performance of gasifiers and especially on H2 generation as the S/B ratio increased from 0.3 to 0.5, the hydrogen content (%vol) and hydrogen yield (and#947;H2) increased significantly. It has been observed that the catalytic bed (olivine) has a moderate influence on gas composition compared to the sand bed. Olivine was found to be effective in tar reduction between 36-41%. FTIR analysis showed that the tars generated from all three biomasses have functional groups including phenolic, aromatic compounds, aliphatic chains and oxygenated functional groups. Contd.....