Hydrogen Production via Gasification of Biomass Fuels

摘要

This paper presents experimental results of decomposition tests for biomass to hydrogen conversion. The gasification process was found to yield improved char conversion and higher levels of H_2 and CO for various CO_2 recycle ratios. Carbon monoxide production from steam gasification was enhanced by increasing the CO_2 input flow rates. The evolution of H_2 gas only became significant at high gasification temperatures above 600 ℃ for the woody biomass samples studied. Using TGA, GC, AAS, SEM/EDX, and Calorimetry we studied the nature of the biomass composition and ash residue, and the mass decay of biomass sources including various woods and grasses. These were poplar, oak, sugar maple, white pine, spruce, Douglas fir, pine needles, maple bark, alfalfa and cordgrass. Hydrogen, carbon dioxide and methane gas evolution as a function of temperature was also quantified. The woods and grasses had similar TGA curves with a third constant mass step during gasification and completed mass loss by 900-1000 ℃. Two distinct regimes of mass decay, representing pyrolysis and gasification and char burnout, were found to correlate well with the two corresponding gas evolution regimes for CO and H_2. The SEM/EDX analyses showed high levels of K, Mg, and P in the ash residue. The mineral content of the biomass sources, and particularly the high alkaline content of the grassy feedstocks used in the present study, were held responsible for the corrosion of the quartz TGA furnace. This composition necessitates the careful selection and possible need for preprocessing of biomass fuels to minimize corrosion of the operating equipment. Gasification prior to high temperature combustion enables the removal of the corrosive ash elements such as potassium and chloride that would otherwise be problematic.