Master of Science / Department of Biological and Agricultural Engineering / Wenqiao Yuan / Gasification is an efficient way to produce energy from biomass, which has significant positive impacts on the environment, domestic economy, national energy security, and the society in general. In this study, a lab-scale updraft biomass gasifier was designed, built, and instrumented for stable gasification using low-bulk density biomass. Related accessories, such as a biomass feeder, inlet air temperature controller, air injection nozzle, and tar cracking system, were also developed to enhance gasifier performance. The effect of operation parameters on gasifier performance was studied. Two operational parameters, including air flow rate and feed-air temperature, were studied on three sources of biomass: prairie hay, sorghum biomass, and wood chips. Results showed that higher air flow rate increased tar contents in syngas for all three types. It was also found that different biomasses gave significantly different tar contents, in the order of wood chips>sorghum biomass>prairie hay. Feed-air temperature did not have a significant effect on tar content in syngas except for prairie hay, where higher feed air temperature reduced tar. A statistical model was implemented to study differences on syngas composition. Results showed that different biomasses produced syngas with different high heating value, e.g., wood chips > prairie hay > sorghum biomass. CO composition also showed differences by feed air temperature and biomass, e.g. prairie hay>wood chips>sorghum biomass, but H[subscript]2 did not show significant differences by either biomass type or operating conditions. Moreover, because of the downstream problems caused by tars in syngas such as tar condensation in pipelines, blockage and machinery collapse, an in-situ tar cracking system was developed to remove tars in syngas. The tar cracking device was built in the middle of the gasifier’s combustion using gasification heat to drive the reactions. The in-situ system was found to be very effective in tar removal and syngas enhancement. The highest tar removal of 95% was achieved at 0.3s residence time and 10% nickel loading. This condition also gave the highest syngas HHV increment of 36% (7.33 MJ/m[superscript]3). The effect of gas residence time and Ni loading on tar removal and syngas composition was also studied. Gas residence of 0.2-0.3s and Ni loading of 10% were found appropriate in this study.

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This thesis evaluates the possibility to use a iron-based catalyst as a pyrolysis vapour conversion catalyst. The iron catalyst was also compared with the mineral dolomite. The experiments were facilitated at Cortus Energy's demonstration plant in Koping, Sweden, by in situ instal- lation of the experimental setup to an outlet of the pyrolyser unit. The pyrolysis vapour from Cortus Energy was converted for a total of 8 hours by passing it through a packed bed reactor containing the iron-based catalyst while sampling gas and oil from the feed for analysis. The outset for the operation on the dolomite catalyst bed was the same as for the iron catalyst with a resulting collapse of the bed when the pyrolysis vapour was introduced. The permanent gases were analysed on site with a µ-GC unit while oil samples were condensed and analysed with GC-MS, H-NMR and Karl Ficher titration. The carbon laydown and surface area of the catalyst was determined as well as the phase changes of the catalyst surface with XRD. The results showed clear indications of bio-crude conversion with an eightfold increase of the H2 concentration of the synthetic gas from 3.38 % to 26.69 % on a dry gas basis. The oxygen to carbon (O:C) ratio decreased in the treated pyrolysis oil compared to the untreated oil while the hydrogen to carbon (H:C) ratio showed indications of dehydration of the oil. The gas and water content of the stream increased while 57.2 % of the oil was converted in the process. Lastly, the iron-based catalyst did not seem to favour the conversion of alkylated phenols.

Gasification is a process used to convert any carbonaceous species through heterogeneous reaction to obtain the desired gaseous products of H2 and CO which are used to make chemicals, liquid transportation fuels, and power. Both pyrolysis and heterogeneous gasification occur in commercial entrained-flow gasifiers at pressures from 4 to 65 atm with local gas temperatures as high as 2000 °C. Many gasification studies have been performed at moderate temperatures, heating rates, and pressures. In this work, both pyrolysis and char gasification experiments were performed on coal, petroleum coke, and biomass at conditions pertinent to commercial entrained-flow gasifiers. Rapid biomass pyrolysis experiments were performed at atmospheric pressure in an entrained-flow reactor for sawdust, switchgrass, corn stover, and straw mostly using a peak gas temperature of 1163 K at particle residence times ranging from 34 to 113 ms. Biomass pyrolysis was modeled using the Chemical Percolation Devolatilization model assuming that biomass pyrolysis occurs as a weighted average of its individual components (cellulose, hemicellulose, and lignin). Thermal cracking of biomass tar into light gas was included using a first-order model with kinetic parameters regressed in the current study. Char gasification rates were measured for biomass, petroleum coke, and coal in a pressurized entrained-flow reactor at high heating-rate conditions at total pressures between 10 and 15 atm. Peak centerline gas temperatures were between 1611 and 1879 K. The range of particle residence times used in the gasification experiments was 42 to 275 ms. The CO2 gasification rates of biomass and petroleum coke chars were measured at conditions where the reaction environment consisted of approximately 40 and 90 mol% CO2. Steam gasification rates of coal char were measured at conditions where the maximum H2O concentration was 8.6 mol%. Measured data was used to regress apparent kinetic parameters for a first-order model that describes char conversion. The measured char gasification rates were far from the film-diffusion limit, and are pertinent for pulverized particles where no internal particle temperature gradients are important. The modeling and measured data of char gasification rates in this research will aid in the design and efficient operation of commercial entrained-flow gasifiers, as well as provide validation for both existing and future models at a wide range of temperatures and pressures at high heating-rate conditions.