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For a given coal gasification atmosphere, the reactions between fired alumina-chromia solid solution refractories and alkali (sodium and potassium) with and without sulfur at varying alkali concentrations were thermodynamically calculated using the SOLGASMIX-PV computer program and the results were experimentally confirmed. In addition, the kinetics of alkali diffusion into the refractory were experimentally determined as a function of time and temperature. The results, both experimental and theoretical, show formation of alkali-aluminate (Na₂O⋅Al₂O₃, K₂O⋅Al₂O₃) and β-alumina (Na₂O⋅11Al₂O₃, K₂O⋅11A₂O₃) compounds with formation of several metastable alkali compounds in a coal gasification environment. Sulfur did not appear to affect the reaction products. Alkali distribution into the alumina-chrome refractory is rapid and the formation of the Na₂O⋅Al₂O/K₂O⋅Al₂O₃ compounds cause large volume expansion from the reaction surface which causes poor thermal shock resistance and eventual refractory failure. The hot face of an alumina-chrome refractory in service in an alkali environment will be prone to failure by alkali attack. / Master of Science

An experimental test system was designed to simulate the operating conditions found in nonslagging coal gasifiers. The reaction products that form when refractory linings in coal gasifiers are exposed to alkali impurities (sodium or potassium) were experimentally determined. Analysis of selected physical and chemical properties of the reaction products, which typically form between the alkali and the refractory will lead to a better understanding of the mechanisms behind refractory failures associated with alkali attack. The reaction products sodium aluminate (Na₂O·Al₂O₃), N₂C₃A₅ (2Na₂O·3CaO·5A1₂O₃), nepheline (Na₂0·Al₂0₃·2SiO₂), potassium aluminate, (K₂Oâ·Al₂0₃), and kaliophilite (K₂O·Al₂0₃·2Si0₂) were synthesized and their solubility in water and coefficients of linear thermal expansion were: measured. Of the compounds tested, the formation of potassium aluminate would be the most detrimental to the gasifier lining. The linear thermal expansion of potassium aluminate was 2.05% from room temperature to 800°C, which was twice as large as the other compounds. Potassium aluminate also possessed the highest solubility in water which was 8.893/L at 90°C. / Master of Science

Three monolithic refractories (a 90+ wt.% alumina Castable, a 50+ wt.% alumina castable, and a 90+ wt.% alumina phosphate-bonded ramming mix) doped with up to 2.0 wt.% Fe and 2.0 Fe wt.% Fe₂O₃ were tested for CO disintegration in a 100 hr. test similar to. ASTM C-288. The effects of CO₂, NH₃, H₂, H₂S, and H₂O on CO disintegration were observed. Prefired samples of all three refractories were found to be susceptible to disintegration in a CO atmosphere when 0.5 wt.% Fe or more was added. Castables doped with up to 2.0 Fe wt.% Fe₂O₃ were not affected by CO, while the ramming mix doped with 1.5 Fe wt.% Fe₂O₃ or more was. H₂ and H₂O proved most effective in retarding CO disintegration in all three refractories. CO₂, H₂S, and NH₃, in descending order, also retarded CO disintegration in both castables. The retarding effect of up to 15% CO₂ in CO is questionable for the ramming mix. NH3 did not slow CO disintegration in this refractory and H₂S actually accelerated the disintegration process. The effect of gas pressure is also found to be especially important, for it greatly accelerates CO disintegration in all three monoliths and appears to be a more significant factor than the disintegration~inhibiting gases. An optimum iron-impurity size range, neither a maximum nor a minimum, for which CO disintegration resistance was greatest was also found for the 90+ wt.% alumina castable. / Master of Science

Yes / In order to evaluate the feasibility of using CO2 as a gasifying agent in the conversion of carbonaceous materials to syngas, gasification characteristics of coal, a suite of waste carbonaceous materials, and their blends were studied by using a thermogravimetric analyser (TGA). The results showed that CO2 gasification of polystyrene completed at 470 °C, which was lower than those of other carbonaceous materials. This behaviour was attributed to the high volatile content coupled with its unique thermal degradation properties. It was found that the initial decomposition temperature of blends decreased with the increasing amount of waste carbonaceous materials in the blends. In this study, results demonstrated that CO2 co-gasification process was enhanced as a direct consequence of interactions between coal and carbonaceous materials in the blends. The intensity and temperature of occurrence of these interactions were influenced by the chemical properties and composition of the carbonaceous materials in the blends. The strongest interactions were observed in coal/polystyrene blend at the devolatilisation stage as indicated by the highest value of Root Mean Square Interaction Index (RMSII), which was due to the highly reactive nature of polystyrene. On the other hand, coal/oat straw blend showed the highest interactions at char gasification stage. The catalytic effect of alkali metals and other minerals in oat straw, such as CaO, K2O, and Fe2O3, contributed to these strong interactions. The overall CO2 gasification of coal was enhanced via the addition of polystyrene and oat straw.

The gasification of carbonaceous fuel materials offers significant potential for the production of both energy and chemical products. Advancement of gasification technologies may be expedited through the use of computational fluid dynamics, as virtual reactor design offers a low cost method for system prototyping. To that end, a series of numerical studies were conducted to identify a computational modeling strategy for the simulation of coal gasification in fluidized bed reactors. The efforts set forth by this work first involved the development of a validatable hydrodynamic modeling strategy for the simulation of sand and coal fluidization. Those fluidization models were then applied to systems at elevated temperatures and polydisperse systems that featured a complex material injection geometry, for which no experimental data exists. A method for establishing similitude between 2-D and 3-D multiphase systems that feature non-symmetric material injection were then delineated and numerically tested. Following the development of the hydrodynamic modeling strategy, simulations of coal gasification were conducted using three different chemistry models. Simulated results were compared to experimental outcomes in an effort to assess the validity of each gasification chemistry model. The chemistry model that exhibited the highest degree of agreement with the experimental findings was then further analyzed identify areas of potential improvement. / Ph. D. / Efficient utilization of coal is critical to ensuring stable domestic energy supplies while mitigating human impact on climate change. This idea may be realized through the use of gasification systems technologies. The design and planning of next-generation coal gasification reactors can benefit from the use of computational simulations to reduce both development time and cost. This treatise presents several studies where computational fluid dynamics was applied to the problem of coal gasification in a bubbling fluidized bed reactor with focuses on accurate tracking of solid material locations and modeling of chemical reactions.

An investigation was undertaken to compare the kinetics of combustion and gasification reactions of chars prepared from two South African coals in different reaction atmospheres: air, steam, and carbon dioxide. The two original coals were characterised as vitrinite-rich (Greenside) and inertinite-rich (Inyanda) coals with relatively low ash content (12.5-16.7 wt. %, adb). Chars were prepared from the parent coals under nitrogen atmosphere at 900 °C. Characterisation results show that the volatiles and moisture were almost completely driven off from the parent coals, indicating that the pyrolysis process was efficient. Physicalstructural properties such as porosity and surface area generally increased from the parent coals to the subsequent chars. The heterogeneous char-gas reactions were conducted isothermally in a TGA on ~1 mm size particles. To ensure that the reactions are under chemical reaction kinetic control regime, different temperatures zones were selected for the three different reaction atmospheres. Combustion reactivity experiments were carried out with air in the temperature range of 387 °C to 425 °C; gasification reactivity with pure steam were conducted at higher temperatures (775 °C - 850 °C) and within 825 °C to 900 °C with carbon dioxide. Experimental results show differences in the specific reaction rate with carbon conversion in different reaction atmospheres and char types. Reaction rates in all three reaction atmospheres were strongly dependent on temperature, and follow the Arrhenius type kinetics. All the investigated reactions (combustion with air and gasification with CO2 and steam) were found to be under chemical reaction control regime (Regime I) for both chars. The inertinite-rich coals exhibit longer burn-out time than chars produced from vitrinite-rich coals, as higher specific reaction rate were observed for the vitrinite-rich coals in the three different reaction atmospheres. The determined random pore model (RPM) structural parameters did not show any significant difference during steam gasification of Greenside and Inyanda chars, whereas higher structural parameter values were observed for Greenside chars during air combustion and CO2 gasification (ψ > 2). However a negative ψ value was determined during CO2 gasification and air combustion of Inyanda chars. The RPM predictions was validated with the experimental data and exhibited adequate fitting to the specific rate of reaction versus carbon conversion plots of the char samples at the different reaction conditions chosen for this study. The activation energy determined was minimal for air and maximum for CO2 for both coals; and ranged from 127-175 kJ·mol-1 for combustion, 214-228 kJ·mol-1 and 210-240 kJ·mol-1 for steam and CO2 gasification respectively. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

An investigation was undertaken to compare the kinetics of combustion and gasification reactions of chars prepared from two South African coals in different reaction atmospheres: air, steam, and carbon dioxide. The two original coals were characterised as vitrinite-rich (Greenside) and inertinite-rich (Inyanda) coals with relatively low ash content (12.5-16.7 wt. %, adb). Chars were prepared from the parent coals under nitrogen atmosphere at 900 °C. Characterisation results show that the volatiles and moisture were almost completely driven off from the parent coals, indicating that the pyrolysis process was efficient. Physicalstructural properties such as porosity and surface area generally increased from the parent coals to the subsequent chars. The heterogeneous char-gas reactions were conducted isothermally in a TGA on ~1 mm size particles. To ensure that the reactions are under chemical reaction kinetic control regime, different temperatures zones were selected for the three different reaction atmospheres. Combustion reactivity experiments were carried out with air in the temperature range of 387 °C to 425 °C; gasification reactivity with pure steam were conducted at higher temperatures (775 °C - 850 °C) and within 825 °C to 900 °C with carbon dioxide. Experimental results show differences in the specific reaction rate with carbon conversion in different reaction atmospheres and char types. Reaction rates in all three reaction atmospheres were strongly dependent on temperature, and follow the Arrhenius type kinetics. All the investigated reactions (combustion with air and gasification with CO2 and steam) were found to be under chemical reaction control regime (Regime I) for both chars. The inertinite-rich coals exhibit longer burn-out time than chars produced from vitrinite-rich coals, as higher specific reaction rate were observed for the vitrinite-rich coals in the three different reaction atmospheres. The determined random pore model (RPM) structural parameters did not show any significant difference during steam gasification of Greenside and Inyanda chars, whereas higher structural parameter values were observed for Greenside chars during air combustion and CO2 gasification (ψ > 2). However a negative ψ value was determined during CO2 gasification and air combustion of Inyanda chars. The RPM predictions was validated with the experimental data and exhibited adequate fitting to the specific rate of reaction versus carbon conversion plots of the char samples at the different reaction conditions chosen for this study. The activation energy determined was minimal for air and maximum for CO2 for both coals; and ranged from 127-175 kJ·mol-1 for combustion, 214-228 kJ·mol-1 and 210-240 kJ·mol-1 for steam and CO2 gasification respectively. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015

The significance of hydrogen production is increasing as fossil fuels are being depleted and energy security is of increasing importance to the United States. Furthermore, its production offers the potential to alleviate concerns regarding global warming and air pollution. In this thesis we focused on examining the efficiency of hydrogen production from current biomass compared to that from fossil fuel coal. We explored the efficiencies of maximum hydrogen production from biomass and from coal under current technology, namely coal gasification and biomass pyrolysis, together with following-up technologies such as steam reforming (SR). Bio-oil, product from pyrolysis and precursor for steam reforming, is hard to define. We proposed a simulation tool to estimate the pyrolytic bio-oil composition from various biomasses. The results helped us understand the accuracy that is needed for bio-oil composition prediction in the case it is converted to hydrogen. Hydrogen production is energy intensive. Therefore, heat integration is necessary to raise the overall thermodynamic efficiencies for both coal gasification and biomass pyrolysis. The results showed that considering the ultimate energy source, sunlight, about 6-fold more sunlight would be required for the coal to hydrogen than that for biomass to hydrogen. The main difference is in the efficiency of conversion of the ancient biomass to coal and therefore, for modern mankind, this loss has already been incurred.

This thesis describes the development and experimental testing of a 100 kW dual fluidized bed biomass gasifier (also called a Fast Internally Circulating Fluidized Bed (FICFB) biomass gasifier). This steam-blown gasifier is being studied for its suitability within combined heat and power plant systems for the New Zealand forest products industry. This advanced design of gasifier has the ability to generate producer gas with a lower heating value (LHV) of 11.5-13.4 MJ/Nm3, which is two to three times higher than yielded by conventional gasification systems. This is accomplished because the gasification and combustion processes occur in two physically separated reactors. Several modifications to the gasifier were required after it was first constructed in order to achieve stable and reliable operation. Producer gas yields were measured through the use of helium as a tracer gas. A new simultaneous producer gas and tar sampling system was developed, allowing accurate samples to be obtained in a matter of minutes. Experimental testing included a cold testing exercise which provided valuable information on the circulation behaviour of the bed material and char within the gasifier. This helped in achieving stable and reliable operation of the plant. Producer gas yields of 14.6 Nm3/h were recorded with a fuel (radiate pine wood pellets) feed rate of 18.9 kgdry/h. The cold gas efficiency ranged from 16-40 % with limited heat recovery in place, but depended noticeably on the plant operating conditions especially gasification temperature. The amount of polycyclic aromatic hydrocarbon (PAH) tars measured in the producer gas ranged between 0.9-4.7 g/Nm3 with naphthalene and acenapthylene being the most abundant compounds. The moisture content of the producer gas was determined to be 0.9-1.2 g/gdry gas. It was found that a steam to biomass ratio of 0.45-0.7 kg/kgdry was most favourable for generating a 12-13.4 MJ/Nm3 producer gas while limiting the amount of steam generation. Gasification temperatures above 750 °C encouraged higher producer gas yields and higher cold gas efficiencies. The catalytic bed material olivine (forsterite olivine) was found to increase the producer gas yield by approximately 20 % compared to the non-catalytic bed material greywacke. The use of olivine meant higher cold gas efficiencies were achieved for a given wood feed rate.