Updraft Fixed Bed Gasification of Mesquite Fuel Using Air-Steam Mixture

Abstract

The mesquite woody species that dominate uncultivated lands in the south central Great Plains, U.S.A. (Texas, Oklahoma) may have the potential for bioenergy utilization. Gasification of woody biomass is an environmentally promising technology that provides an alternative to the use of fossil fuel. The objective of this study is to study enhancement of heat values of mesquite (Prosopis glandulosa) using an adiabatic fixed bed gasifier using air-steam as gasification medium and compare these values with those from other methods which include: air (N2:O2), CO2-O2 mixture, enriched air, blending biomass with high quality coal etc. The effects of steam/fuel ratio (S:F) and equivalence ratio (ER) on the gasification peak temperature (Tpeak), gas compositions, and gas higher heating value (HHV) were investigated. It is found that the Tpeak in air-steam gasification is lower than that of air gasification and the Tpeak decreased with the increase in the steam to fuel ratio (S:F). In addition, when S: F ratio increased from 0 to 0.45, the CO2 and H2 concentration increased while the CO percentage decreased. The mole composition of the end product gas contained: 8–19% CO, 4–15% H2, 1–3% CH4, and 10–18% CO2. The HHV of the mesquite gas was estimated to be in a range of 2800 kJ/Nm3 to 3800 kJ/Nm3. The HHV increased when the S: F increased from 0.15 to 0.3, and then it decreased when the S: F was increased from 0.3 to 0.45 and the highest value was obtained at S: F = 0.3 and ER = 2.7 (optimum). The HHV of the producer gas from air-steam gasification is found to be almost same as that produced from pure air gasification (2800–4000 kJ) and lower than that obtained from CO2:O2 mixture (79:21) gasification (4000 to 6000 kJ/Nm3). However, H2 rich producer gas was obtained with air steam mixture.

Carbon Dioxide Torrefaction of Woody Biomass

“…A slightly negative pressure was maintained within the reactor by means of a vacuum fan (10) to remove the gases produced during torrefaction as well as the medium used for torrefaction. A shell and tube heat exchanger type condenser (7) was used to condense out any condensables from the gases produced during torrefaction. Since some of the condensables were condensed along the pathway, an accurate quantification of the condensables was not made.…”

“…Analysis of Sauter Mean Diameter (SMD), defined according to eq 7, 33 will give a better understanding on the grindability of pretreated biomass. (7) where d p is the diameter of the particle collected in each sieve and N is the number of particles in each size group. shows the variation in Sauter Mean Diameter (SMD) of the samples torrefied in CO 2 and N 2 .…”

“…A good heat content coupled with increased availability makes it a renewable energy crop that can be used as fuel for direct combustion or gasification. 7 Harvesting the mesquite and utilizing it as a bioenergy feedstock has the following advantages. There are no planting, cultivation, irrigation, and fertilization costs for this naturally occurring species.…”

“…Both mesquite and juniper, which have invaded the grasslands, have a good heating value. A good heat content coupled with increased availability makes it a renewable energy crop that can be used as fuel for direct combustion or gasification . Harvesting the mesquite and utilizing it as a bioenergy feedstock has the following advantages.…”

Regimes of Nonpremixed Combustion of Hot Low-Calorific-Value Gases Derived from Biomass Gasification

“…1 Despite their low quality and low calorific value, such renewable materials are often attractive feedstocks for robust fixed-bed gasification processes. 2−4 The virtually unlimited diversity of potential feedstocks, from refuse derived fuels to wood materials, 5,6 organic residuals, 2,4 and preprocessed biomass; 5 however results in different gasification-derived gases. Industrial fixedbed biomass gasifiers always proceed with a presence of inert gases such as carbon dioxide or water vapor, which are constantly mixed with produced hydrogen, carbon monoxide, methane, and other combustible species.…”