John L. Guillory’s research while affiliated with University of Louisiana at Lafayette and other places

Biomass torrefaction is a mild pyrolysis thermal treatment process carried out at temperatures between 200 and 300 °C under inert conditions to improve fuel properties of parent biomass. Torrefaction yields a higher energy per unit mass product but releases noncondensable and condensable gases, signifying energy and mass losses. The condensable gases (volatiles) can result in tar formation on condensing, hence, system blockage. Fortunately, the hydrocarbon composition of volatiles represents a possible auxiliary energy source for feedstock drying and/or torrefaction process. The present study designed a low-pressure volatile burner for torrefaction of pine wood chips and investigated energy recovery from volatiles through clean co-combustion with natural gas (NG). The research studied the effects of torrefaction pretreatment temperatures on the amount of energy recovered for various combustion air flow rates. For all test conditions, blue flames and low emissions at the combustor exit consistently signified clean and complete premixed combustion. Torrefaction temperature at 283–292 °C had relatively low volatile energy recovery, mainly attributed to higher moisture content evolution and low molecular weight of volatiles evolved. At the lowest torrefaction pretreatment temperature, small amount of volatiles was generated with more energy recovered. Energy conservation evaluation on the torrefaction reactor indicated that about 27% of total energy carried by the exiting volatiles and gases has been recovered by the co-fire of NG and volatiles at the lowest temperature, while around 19% of the total energy was recovered at the intermediate and highest torrefaction temperatures, respectively. The energy recovered represents about 23–45% of the energy associated with NG combustion in the internal burner of the torrefaction reactor, signifying that the volatiles energy can supplement significant amount of the energy required for torrefaction.

Biomass has received wide attention as a substitute for fossil fuel in the generation of energy because of its renewability and carbon neutrality. However, raw biomass combustion is hindered by physical properties such as low energy density and high moisture content. Biomass torrefaction is a mild pyrolysis thermal treatment process carried out at temperature of 200 to 300oC under inert conditions to improve the fuel properties of parent biomass. This yields a higher energy per unit mass product but releases non-condensable and condensable gases which results in energy and mass losses. The condensable gases (volatiles), can result in tar formation on condensing hence, system blockage. Fortunately, the hydrocarbon composition of volatiles also represents a possible auxiliary energy source for torrefaction. The present study investigated energy recovery from volatiles through clean co-combustion with NG for feedstock drying and/or the thermal treatment process of pine wood chips. The research also studied the effect of torrefaction pretreatment temperatures on the amount of energy recovered for various combustion air flow rates. For all test conditions, blue visual flames and low CO and NOx emissions at the combustor exit consistently signified clean and complete premixed combustion. Torrefaction temperature at 283-292 oC had relatively low energy recovered from volatiles, mainly attributed to higher moisture content evolution and low molecular weight of volatiles evolved. At lowest torrefaction pretreatment temperature, smaller amount of volatiles was generated with most energy recovered from the volatiles. Energy conservation evaluation on the torrefaction reactor indicated that about 40% of total energy carried by the exiting volatiles and gases has been recovered by the co-fire of NG and volatiles at the lowest temperature while 20% and 22% of the total energy were recovered at the intermediate and highest torrefaction temperature respectively.

This paper documents a simplified process model developed in connection with the Biomass Gasification Development program at the University of Louisiana at Lafayette. The numerical solution to the set of non-linear simultaneous equations arising from the analysis was implemented using the “Solver” feature of MS Excel®. It is designed to provide a rational first-pass basis for reactor sizing and process equipment selection yet is accessible and readily modifiable by a process engineer with an average programming background. The results follow trends with respect to the important variables (temperature, feedstock composition, etc.) in general agreement with experimental data reported for well-mixed, relatively isothermal reactors such as bubbling and circulating fluidized beds. The model generally overestimates the quantitative H2/CO ratio reported for most gasifiers which results in an underestimation of the product density. However, this does not appear to have a strong influence on energy factors (e.g., the gasifier chemical energy efficiency) and is considered sufficiently accurate for initial design and selection of gasification system components.