Experimental and Numerical Studies on Fluidized Bed Gasifier for Hydrogen Production

Abstract

Currently, there is a growing interest in various alternative energy sources driven by the global energy scenario and escalating crude oil prices. Renewable sources of energy, such as biomass, can be harnessed to produce energy-rich syngas. In this study, both numerical and experimental investigations were conducted on a lab-scale fluidized bed gasifier (3kg/hr) for sustainable hydrogen production. Initially, the effect of cold flow hydrodynamics was studied for the currently designed reactor. Co-gasification experiments involving rice husk, cashew husk, cashew shell, and their mixtures were performed in a lab-scale fluidized bed gasifier using air as the gasification agent. Overall, the results indicated an increase in cold gas efficiency, hydrogen content, and lower heating value (LHV) when biomass was blended. H2 content increased from 6.8% during gasification of RH to 8.23% during gasification of rice husk (RH) + cashew shell (CS) blends. LHV also increased from 3.3 MJ/m3 to 4.3 MJ/m3 during gasification of RH and RH+CS blends. This study demonstrated that challenges in individual biomass gasification could be addressed by blending with feed stocks containing higher alkali metals in its ash. Additionally, to enhance both LHV and H2 production, various gasification agents were employed in co-gasification experiments. CO- gasification of rice husk and cashew shell blends was performed using CO2/air and O2-enriched air mixture as the gasification agent. The overall results indicated an increase in CO and LHV compositions when O2-enriched air was used as the gasification agent. LHV increased from 4.36 MJ/m3 to 5.92 MJ/m3 during gasification with pure air and oxygen enriched air gasification. Numerical investigations with parametric studies were carried out for rice husk gasification using a steam and CO2-steam mixtures as the gasification agent. Mole composition for different gases and thermal efficiency were studied at different steam to biomass ratio (SBR) and temperature. Thermal efficiency increased from 68.5% to 73.5% when SBR was increased from 0-2. With the addition of CO2 resulted in higher CO production from 27 to 30%. Hence, the addition of CO2 helps in the conversion of CO2 to energy-rich CO in syngas and increasing the LHV. Experimental studies were not undertaken for CO2-steam gasification due to the highendothermic nature of the steam-CO2 mixture, posing challenges in maintaining a consistent temperature. The outcome of the parametric studies carried out in the present research work establishes a key technical basis for enhancing hydrogen and LHV in biomass gasification.