Thesis (M.S.)--University of Iowa, 2009. / Thesis supervisor: Lea-Der Chen. Includes bibliographical references (leaves 110-114).

Although the general principles of biomass gasification are broadly understood, at a larger scale of operation (e.g. > 200 kg/h) there is a lack of confidence in the translation of the basic scientific concepts into a financially viable operation that satisfies regulatory requirements. Looking in particular at the operation of a down-draft type of gasifier, a number of challenges were identified and studied in greater detail. Gasification experiments were performed on wood and straw pellets in a small scale, 21 mm i.d. quartz-tube reactor. These provided useful insight into what was occurring inside the gasifier, and the complexity and roles of the various reaction zones. In order to perform on-line gas analysis measurements in real time, a method was developed which enabled a quadrupole mass spectrometer (QMS) to be used. This was tested in a laboratory environment, and then used on a commercial pilot-plant gasifier (150 to 250 kg/h). This enabled the composition of the gas to be monitored while the plant was started up, and then operated at various levels of gas flow through the plant. In general the concentrations measured during a stable operation were as follows: CO = 16.0 vol.%, H2 = 11.9 vol.%, CO2 = 15.8 vol.%, N2 = 54.1 vol.%, CH4 = 1.9 vol.%, O2 = 0.3 vol.%. Measurements of O2 concentrations in the gas stream on start-up provide useful information on conditions when a flammable atmosphere could exist in the lines/vessels. To help with the development of suitable gas clean-up strategies, the presence of two key sulphur species, H2S and carbonyl sulphide (COS), was studied in more detail. Experimental measurements were taken on the laboratory reactor (e.g. H2S = 286 ppmv, COS = 28 ppmv for gasification of refuse-derived fuel (RDF) pellets), and the commercial pilot-scale gasifier (e.g. H2S = 332 ppmv, COS = 12 ppmv). This data was also compared with theoretical thermodynamic predictions. The steam gasification of char was also studied in a laboratory 9.5 mm i.d. reactor, and kinetic expressions were determined for RDF-derived char. It was shown that high concentrations of H2 (20 vol.%) and CO (15 vol.%) can be achieved, and the temperature at which reactions were initiated was > 700 ºC, and significant at 900 ºC. Interestingly, the RDF-derived char (at carbon conversion from 10 to 70 %) appears to be more reactive than other biochars reported in the literature. However, at high conversion (> 50 %), its apparent reactivity decreases with carbon conversion, behaving in a similar manner to coal chars.

In this work, SCWG of glucose, cellulose and pinewood was studied at different operating conditions with and without catalyst. Three parameters studied included temperature (400, 470, 500 and 550oC), water to biomass weight ratio (3:1 and 7:1) and catalyst (Ni/MgO, Ni/activated carbon, Ni/Al2O3, Ni/CeO2/Al2O3, dolomite, NaOH, KOH, activated carbon and olivine), which were varied for gasification of glucose, cellulose and pinewood. By comparing the results from model compound (glucose and cellulose) with that from real biomass (pinewood), the mechanism of how the individual compounds are gasified was explored. For catalytic runs with glucose, NaOH had the best activity for improving H2 formation. H2 yield increased by 135% using NaOH compared to that for run without catalyst at 500oC with a water to biomass weight ratio of 3:1. At the same operating conditions, the presence of Ni/activated carbon (Ni/AC) contributed to an 81% increase in H2 yield, followed by 62% with Ni/MgO, 60% with Ni/CeO2/Al2O3 and 52% with Ni/Al2O3. For catalytic runs with cellulose, the H2 yield increased by 194% with KOH compared to that for run without catalyst at 400oC with a water to biomass ratio of 3:1. At the same operating conditions, the presence of Ni/CeO2/Al2O3 contributed to a 31% increase in H2 yield followed by a 28% increase with dolomite. When the water to biomass ratio was increased from 3:1 to 7:1, H2 yield from glucose gasification was increased by 40% and 33% at 400 and 500oC, respectively, and the H2 yield of cellulose gasification was increased by 44%, 11% and 22% at 400, 470 and 550oC, respectively. The higher heating value of the oil products derived from SCWG of both glucose and cellulose incresed in the presence of catalysts. As real biomass, pinewood was gasified in supercritical water at the suitable operation conditions (550oC with water to biomass ratio of 7:1) obtained from previous experiments, using three kinds of catalyst: Ni/CeO2/Al2O3, dolomite and KOH. At the same operating conditions, the gasification of pinewood had smaller yields of H2 (20 to 41%) compared with that from cellulose. The effect of the catalyst on H2 production from SCW in the absence of biomass was studied. The results showed that a trace amount of H2 was formed with Ni based catalyst/dolomite only while some CO2 was formed with Ni/AC. Most of the runs presented in this report were repeated once, some of the runs had been triplicated, and the deviation of all results was in the range of ±5%.

Thesis (M.E.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. 194-196). Also available via the World Wide Web.

The aim of this thesis is to describe the process of biomass gasification using gas simulating the composition of flue gas – a mixture of oxygen, carbon dioxide and water vapor. In the research part of the thesis the issue of gasification with the focus on fluidized bed gasification and the effect of the gasification medium used on the gasification process is discussed. In the practical part the thesis deals with the design, realization and evaluation of the experiment on a real device. The aim of the experiment is to determine the effect of the exact composition of the mixture of these three media on the gasification process and on the quality of the gas generated. The aim is to find the optimum composition for obtaining gas with the highest possible lower heating value, which contains as little tar as possible. At the end of the work, the results from the experiment are presented and described.

Mathematical models of gasification are suitable for predicting gas composition and its properties. The aim of the diploma thesis is to compile a mathematical model for biomass gasification. The first part deals with the description of gasification and the technologies used. Theoretical part consists of the search of modeling methods. Other theoretical part is devoted to the description of the model and equations presented in the thesis. Part of the assignment is a parametric study that shows changes in gas production and its properties when changing the parameters. Finally, the model is compared with the data obtained in the experiment on the fluid reactor biofluid 2.

This master’s thesis deals with the process of biomass gasification using mixture of CO and O2 as gasification agent. First part describes the gasification process itself, used devices, gasification medium and its influence on the generated gas. Following section covers the experimental part of the work, which is focused on change properties of the generated gas using different ratios of CO2, O2, H2O and air in the gasification mixture. This part also includes processing and evaluation of the results.

The possibility to extract bio-SNG from the product gas obtained from gasification of biofuel with a pressurized, oxygen-blown CFB gasifier connected to a heat and power station using only membrane separation was theoretically investigated. Selling the methane, instead of feeding it to the plant’s turbine(s), might mean that overall profitability is increased. The considered product gas mainly consists of H2, CO, CO2, H2O and CH4. By doing a literature review different membrane types were studied and it was concluded that for now only polymers may be of interest, due to high production costs for other membranes or for the fact they are still at laboratory stage. It was further determined though that neither membranes made of glassy polymers (fixed polymer chains) nor rubbery polymers (mobile polymer chains) are probably capable of separating the methane from the other gas components on their own. Glassy membranes will most likely have trouble separating CO from CH4 due to similarity in size of the two molecules, while a separation using rubbery membranes will result in at least H2 accompanying the methane. The rubbery polymers’ incapability of separating H2 from CH4 despite greatly differing condensation temperatures between the two components can be explained by the fact that rubbery membranes, apart from condensation temperature, also separate according to molecular diffusivity. If a multistep process with recirculation that combines both glassy and rubbery polymers is applied, satisfying results may be obtained. This, however, builds on a higher separation of CH4 and CO with rubbery membranes than condensation data indicates and needs to be further investigated with help of real life experiments and more advanced computation programs than used in this study.

The topic of master´s thesis is atmosferic gasification of biomass by the addition of oxygen and steam. The theoretical part is devoted to the description of biomass, process of gasification, kinds of gasification reactor and product gas. Further experiments are devised depending on the gasification medium and output temperature. In this case, the key aspect is the steam addition control. In the practical part, these experiments are performed in a fluidized bed reactor. Resulting values from samples of gas and tar are subsequently processed and evaluated.

Renewability and the carbonaceous basis of biomass provide potential for both energy and chemical production in biorefineries in a fashion similar to crude oil refineries. Biorefineries are envisaged as having a key role in the transition to a more sustainable industry, especially as a means to mitigate greenhouse gas (GHG) emissions. A biorefinery is a concept for the flexible, efficient, cost-effective and sustainable conversion of biomass through a combination of process technologies into multiple products. This implies that biorefineries must be integrated through designs that exploit the interactions between material and energy streams. The wide range of possibilities for biomass feedstock, processes and products poses a challenge to biorefinery design. Integrating biorefineries within evolving economic and environmental policy contexts requires careful analysis of the configurations to be deployed from early in the design stage. This research therefore focuses on the application and development of methodologies for biorefinery design encompassing process integration tools, economic and environmental sustainability analyses together. The research is presented in the form of papers published or submitted to relevant peer-reviewed journals, with a preamble for each paper and a final synthesis of the work as a whole. In a first stage, mass pinch analysis was adapted into a method for integration ofbiorefineries producing bioethanol as a final product and also utilising bioethanol asa working fluid within the biorefinery. The tool allows targeting minimum bioethanol utilisation and assessing network modifications to diminish revenue losses. This new application could stimulate the emergence of similar approaches for the design of integrated biorefineries. The thesis then moves to combine feedstock production models, process simulations in Aspen Plus® and process integration with LCA, to improve energy efficiency and reduce GHG emissions of biorefineries. This work, presented via two publications covering wheat to bioethanol and Jatropha to biodiesel or green diesel, provided evidence of the benefits of biorefinery integrationfor energy saving and climate change adaptation. The multilevel modelling approach is then further integrated into a methodologydeveloped for the combined evaluation of the economic potential and GHG emissions saving of a biorefinery from the marginal performances of biorefineryproducts. The tool allows assessing process integration pathways and targeting forpolicy compliance. The tool is presented via two further publications, the first drawing analogies between value analysis and environmental impact analysis inorder to create the combined Economic Value and Environmental Impact (EVEI)analysis methodology, the second extending this to demonstrate how the tool canguide judicious movement of environmental burdens to meet policy targets. The research embodied in this thesis forms a systematic basis for the analysis andgeneration of biorefinery process designs for enhanced sustainability. The toolspresented will facilitate both the implementation of integrated biorefinery designsand the cultivation of a community of biorefinery engineers for whom suchintegrated thinking is their distinctive and defining attribute.