Gasification is a promising technique for transforming solid biomass into a gas that can be used to produce renewable heat, power, fuels or chemicals. Biomass materials, such as forestry residues, can be high moisture, heterogeneous mixtures with low bulk density - properties that make them difficult to handle and convert. Consequently, this means that feedstock pre-treatment is usually necessary in order to facilitate its conversion by gasification. Pre-treatments methods, which include comminution, drying, pelletization, torrefaction, or carbonization will affect the properties of the biomass which will affect their gasification in a fluidized bed. The objective of this thesis was to determine how biomass pre-treatment can influence gasification in a fluidized bed. A single forestry residue was processed using five pre-treatment process levels: sieving (as a surrogate for comminution), drying (moisture content), pelletization, torrefaction, and carbonization. The fractions derived from these processes were gasified in a small pilot-scale air blown bubbling fluidized bed gasifier (feed rate 8 – 25 kg/h). The particle size and form had an impact on the gas composition, tar content, and cold gas efficiency of the gasification. Over the conditions tested, the finest fraction produced a gas with a H2/CO ratio of 0.36 – 0.47 containing 7 – 59 g/m3 tar (gravimetric) at a cold gas efficiency of 30 - 41%. The pellets on the other hand yielded a gas with a H2/CO ratio of 0.89 - 1.14, containing 3 – 37 g/m3 tar (gravimetric) at a cold gas efficiency of 41 – 60%. Drying, torrefaction and carbonization also had an impact on the gasification performance. Carbonization was able to reduce the yield of tar (as measured by gas chromatography) by more than 95% relative to the parent material. Finally, four different forestry residues were gasified in a large pilot-scale bubbling fluidized bed with air and steam-oxygen mixtures (feed rate 200 – 245 kg/h) in order to assess whether the comminution effect could be observed at the large scale. One feedstock with a significant portion of small particles showed the expected effects compared to the feed materials with large feed particles: lower H2/CO ratio, greater tar yield, lower cold gas efficiency while the other feed material containing a substantial amount of small particles did not show these effects.

A considerable number of modeling studies for the investigation of sulfur retention in atmospheric bubbling fluidized bed combustors have been carried out and well documented in the literature. Despite 30 years of intensive study of sulfation process in fluidized bed combustors and numerous laboratory studies, there are still many uncertainties and disagreements on the subject. In addition, modeling sulfur retention performance of Turkish lignites with high sulfur, volatile matter and ash contents has not drawn much attention to date. Recent trend in utilization of indigenous lignites in fluidized bed boilers necessitated investigation of pollutant emissions and adaptation of fluidized bed combustion technology to these lignites. In an attempt to achieve this objective, a system model, previously developed and tested for the prediction of the combustion behavior of fluidized bed combustors was extended to incorporate sulfur retention. The predictive accuracy of the model was assessed by applying it to the prediction of the behavior of METU 0.3 MWt ABFBC test rig burning indigenous lignites in their own ashes, and comparing its predictions with measurements taken on the same rig. Sulfur dioxide concentration predictions throughout the combustor were found to be in good agreement with the experimental data except for the small discrepancy between predictions and measurements in the bed section. Measurements and model predictions revealed that recyling enhances calcium utilization significantly by increasing the sorbent residence time leading to higher sulfur retention efficiencies. The system model proposed in this study proves to be a useful tool in qualitatively and quantitatively simulating the processes taking place in an atmospheric fluidized bed combustor.

Bibliography: leaves 290-303 / xxi, 303 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1993?

Thesis (doctoral)--University of New South Wales, 1997.

Thesis (Ph. D.)--University of Adelaide, Dept. of Chemical Engineering, 1989. / Includes bibliographical references (208-218).

Thesis (M.S.)--Ohio University, June, 1998. / Title from PDF t.p.

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xiv, 98 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 91-98).

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains x, 98 p. : ill. (some col.) + 1 video file. Includes a video file (29 sec.). Includes abstract. Includes bibliographical references (p. 91-92).

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xi, 100 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 83-86).

Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains xiii, 104 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 86-87).