Instrumentation and Evaluation of a Pilot Scale Fluidized Bed Biomass Gasification System

Abstract

A pilot scale fluidized bed biomass gasifier developed at Texas A&M University in College Station, Texas was instrumented with thermocouples, pressure transducers and motor controllers for monitoring gasification temperature and pressure, air flow and biomass feeding rates. A process control program was also developed and employed for easier measurement and control. The gasifier was then evaluated in the gasification of sorghum, cotton gin trash (CGT) and manure and predicting the slagging and fouling tendencies of CGT and manure. The expected start-up time, operating temperature and desired fluidization were achieved without any trouble in the instrumented gasifier. The air flow rate was maintained at 1.99 kg/min and the fuel flow rate at 0.95 kg/min. The process control program considerably facilitated its operation which can now be remotely done. The gasification of sorghum, CGT and manure showed that they contained high amounts of volatile component matter and comparable yields of hydrogen, carbon monoxide and methane. Manure showed higher ash content while sorghum yielded lower amount of hydrogen. Their heating values and gas yields did not vary but were considered low ranging from only 4.09 to 4.19 MJ/m3 and from 1.8 to 2.5 m3/kg, respectively. The production of hydrogen and gas calorific values were significantly affected by biomass type but not by the operating temperature. The high values of the alkali index and base-to acid ratio indicated fouling and slagging tendencies of manure and CGT during gasification. The compressive strength profile of pelleted CGT and manure ash showed that the melting (or eutectic point) of these feedstock were around 800 degrees C for CGT and 600 degrees C for manure. Scanning electron microscopy (SEM) images showed relatively uniform bonding behavior and structure of the manure ash while CGT showed agglomeration in its structure as the temperature increased. The instrumentation of the fluidized bed gasifier and employing a process control program made its operation more convenient and safe. Further evaluation showed its application in quantifying the gasification products and predicting the slagging and fouling tendencies of selected biomass. With further development, a full automation of the operation of the gasifier may soon be realized.