Abstract
A unique laboratory scale auto-thermal moving bed gasifier was designed for studying the thermochemical conversion of coal-biomass blends. For this purpose, two coals (lignite and sub-bituminous), two biomass materials (corn stover and switchgrass), and their respective blends were used. Gasification characteristics of the fuels were evaluated with an emphasis on improving the producer gas composition. The efficiency and product gas compositions reveal that utilizing the inner stainless-steel tubing better promotes heat transfer upwards in the axial direction when compared to utilizing quartz insulation. The H2/CO ratio at the same operating conditions is much higher due to the increase in bed temperature and heat transfer upwards in the axial direction. This improved the overall efficiency by at least 20%. Using pure oxygen and steam, efficiency greater than 50% was obtained for blends with corn stover at steam to oxygen ratio of 2:1. Also, using air as the gasifying agent greatly improved the H2/CO ratios and overall efficiency in blends with corn stover. In contrast, blends with switchgrass were not very effective with respect to the overall gasification characteristics. Blending switchgrass with coal may not be viable option from the viewpoint of generating high quality producer gas for downstream operations.
Highlights
Energy is the cornerstone to economic stability and development
The efficiency and product gas compositions reveal that utilizing the inner stainless-steel tubing better promotes heat transfer upwards in the axial direction when compared to utilizing quartz insulation
It must be noted here that the percentage of hydrogen generated at same operating conditions is much higher due to the increase in bed temperature) and transfer of heat upwards in the axial direction and better heat utilization which improved the overall efficiency by at least 20% when the steam concentration was at its maximum in the gasifier
Summary
Energy is the cornerstone to economic stability and development. Fossil fuels have stimulated worldwide economic growth. Combustion of fossil fuels has driven the atmospheric concentration of carbon dioxide, the most significant greenhouse gas (GHG), and emission of environmentally harmful compounds (sulfur, nitrogen (N) and heavy metals) to levels not seen for several decades [1] [2]. It is expected to contribute significantly to the future energy needs in many nations [5] [6], especially in fast-developing countries such as China and India [5]. Fueled by the following factors, the past few years have seen an upsurge in interest in gasification of biomass [10]: 1) Reduction in greenhouse gas emissions caused due to the combustion of fossil fuels
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