Gasification of Coal and Biomass Char Using a Superheated Steam Flame

Gasification of coal or biomass can produce hydrogen rich synthetic gas (syngas) for use in fuel cells, liquid fuels or chemicals. While coal gasification is well established, biomass gasifiers have been hindered by costs and difficulties such as tar and ash deposition. Ultra-Superheated Steam (USS) has been proposed as an economical method to maximise gasification temperatures and hydrogen yields. A novel entrained flow USS gasification system showed promise with coal in a previous investigation.
The main objectives were to investigate how a USS gasification system produced high hydrogen yields and feedstock conversion within a short residence time. Secondly, apply the system to biomass gasification for sustainable hydrogen production.
The principle tasks were to identify the factors affecting the product composition, and experimentally compare the conversion and yields from coal and biomass materials. Numerical software was used to investigate gas and particle behaviour inside the burner.
Coal and a unique high ash softwood char were successfully gasified. Char yielded up to 34.9%mol H2 and 25.1%mol CO in the dry gas, demonstrating higher conversion and yields than coal despite lower feedstock heating value and feeding rates. Biomass ash was considered to catalyse char conversion. No detrimental effect was observed from ash deposition, which was dry and easily removed.
A fluid model mapped temperature distribution, showing good correlation with validation measurements and supporting the observation that wall temperature greatly affected particle conversion. Particle residence times were inversely proportional to particle diameter and density.
High ash biochar showed greater conversion than coal. Economic analysis revealed the system would be most competitive on an existing site with available feedstocks and steam. A longer reactor would increase time for homogeneous reactions to play a greater role. With further development this technology has potential to produce hydrogen competitively on a commercial scale.