The prime objective of a current research project at the University of Natal is to develop a novel autothermal fluidised bed coal gasifier which is capable of efficiently producing synthesis quality gas (rich in hydrogen and carbon monoxide) from discard of duff coal resources using air and steam as the reactant gases. The development of this gasifier was initially motivated to utilise the ever increasing supply of discard coal in South Africa which represents a significant potential source of energy and currently poses severe environmental pollution hazards caused by spontaneous combustion and wind erosion of the discard coal dumps. Recently, however, the gasifier has been considered for the conversion of more general coal resources in an Integrated Coal Gasification Combined Cycle process (IGCC) for the production of electricity. The knowledge of the kinetics of steam gasification of local coal resources is of vital importance to the design of this gasifier. However, no such kinetic data are available of which the author is aware. This thesis presents the following contributions to the overall knowledge of the gasifier (a) The development of a micro reactor to measure the rate of reaction of the steam gasification of coal-char at temperatures of up to l000oC and pressures up to 5 bar absolute; (b) Kinetic studies using the microreactor on the steam gasification of coal-chars derived from Bosjesspruit and Transvaal Navigation coal samples. The following principal results were obtained with Bosjesspruit coal-char : The rate of steam-char gasification is very sensitive to variations in the temperature of reaction in the range 840°C to 920°C. Neither the rate of steam-char gasification nor the product gas composition are affected by the steam partial pressure in the range 1.8 to 4.8 bar absolute; The concentrations of the H2 and CH4 components of the product gas stream rapidly approached their respective equilibrium compositions, whereas the concentrations of CO and CO2 gradually approach their respective equilibrium compositions during gasification at a rate which is typical of the stoichiometry of the Boudouard reaction. The average product gas composition is independent of the temperature of reaction in the range 840°C to 920°C and is approximately 49% H2, 32% CO, 17% CO2 and 2% CH4 on a molar basis; The steam gasification kinetic data are well described by a fundamental Arrhenius-type volumetric reaction model at (c) temperatures of up to 920°C. The value of the activation energy for the reaction is 146 kJ/gmol, which indicates that the gasification kinetics are controlled by the rates of the chemical reactions (ie. C + H2O = CO + H2 and C + CO2 = 2CO) at temperatures up to 920o C; There are no major differences between the kinetics measured for Bosjesspruit coal-char and those reported in the literature for foreign coal-chars. The experimental results obtained for the steam gasification of char derived from Transvaal Navigation coal show that the concentrations of both the Hz and the CH4 in the product gas stream rapidly attain their respective equilibrium values and remain approximately constant throughout gasification, whereas the concentrations of CO and CO2 gradually approach their respective equilibrium values during the course of gasification and almost attain equilibrium concentrations as the conversion of carbon nears completion. The rate of steam gasification of this char is therefore also controlled by the rate of the Boudouard reaction. The mathematical development of a steady-state, one-dimensional compartment model of the gasifier. The model is also presented in the form of a Fortran 77 computer program which is designed to run on a personal computer. The program is capable of simultaneously solving the overall material and energy balances of the gasifier to a tolerance of l% within 15 minutes when using a microprocessor which operates at 10 Mhz. (d) The gasifier simulation program is currently being used in the design of a pilot scale gasifier which is intended to demonstrate the capability of the process on a continous basis of operation. (e) Experimentation on the air-steam gasification of Bosjesspruit coal using a mini-pilot scale gasifier. These experiments have successfully demonstrated the feasibility of the production of a gas stream which is rich in hydrogen and carbon monoxide. The composition of the product gas stream compares well with the predictions of the simulation model of the gasifier. / Thesis (Ph.D.)-University of Natal, Durban, 1990.

The high temperature interactions of alkali metal compounds with solids present in coal conversion processes are investigated. A temperature and concentration programmed reaction method is used to investigate the mechanism by which organically bound alkali is released from carbonaceous substrates. Vaporization of the alkali is preceded by reduction of oxygen-bearing groups during which CO is generated. A residual amount of alkali remains after complete reduction. This residual level is greater for potassium, indicating that potassium has stronger interactions with graphitic substrates than sodium. Other mineral substrates were exposed to high temperature alkali chloride vapors under both nitrogen and simulated flue gas atmospheres to investigate their potential application as sorbents for the removal of alkali from coal conversion flue gases. The compounds containing alumina and silica are found to readily adsorb alkali vapors and the minerals kaolinite, bauxite and emathlite are identified as promising alkali sorbents. The fundamentals of alkali adsorption on kaolinite, bauxite and emathlite are compared and analyzed both experimentally and through theoretical modeling. The experiments were performed in a microgravimetric reactor system; the sorbents were characterized before and after alkali adsorption using scanning Auger microscopy, X-ray diffraction analysis, mercury porosimetry and atomic emission spectrophotometry. The results show that the process is not a simple physical condensation, but a complex combination of several diffusion steps and reactions. There are some common features among these sorbents in their interactions with alkali vapors: In all cases the process is diffusion influenced, the rate of adsorption decreases with time and there is a final saturation limit. However, there are differences in reaction mechanisms leading to potentially different applications for each sorbent. Bauxite and kaolinite react with NaCl and water vapor to form nephelite and carnegieite and release HCl to the gas phase. However, emathlite reacts to form albite and HCl vapor. Albite has a melting point significantly lower than nephelite and carnegieite; therefore, emathlite is more suitable for lower temperature sorption systems downstream of the combustors/gasifiers, while kaolinite and bauxite are suitable as in-situ additives.

Chemical kinetic mechanisms governing the fate of coal nitrogen in the fuel-rich stage of a pulverized-coal staged combustion process were investigated. Emphasis was on determination of the effects of coal rank, temperature and stoichiometric ratios on the speciation and rates of destruction of nitrogenous species and correlation of coal data by a unif1ed mechanism. The relative importance of homogeneous and heterogeneous mechanisms during post-flame interconversion reactions of the fuel nitrogen pool was quantified. Experiments with doped propane gas and a high- and low-grade coals, burned under a variety of conditions in a 2 Kg/h downflow combustor, yielded timeresolved profiles of temperature, major (H₂, CO, CO₂, O₂ and N₂), nitrogenous (NO, HeN and NH₃) and hydrocarbon (CH₄ and C₂H₂) species. These profiles allowed global mechanisms describing the speciation and destruction of fuel nitrogen species to be explored, using predictive models of increasing levels of sophistication. Fuel nitrogen speciation varied significantly from coal to coal and depended on stoichiometric ratio and temperature, which were varied independently. A general correlation describing the destruction rate of NO was derived from data. This rate, which was first-order in both NO and NH₃, was generally valid for all coals and all conditions examined. Fuel nitrogen interconversion reactions, especially destruction of NO and HeN, was predominantly homogeneous, but no single elementary reaction was controlling. Temperature quench down the combustor is the origin of OH equilibrium overshoot. Expressions for estimating the OH equilibrium overshoot as a function of the axial temperature decay along the combustor were derived both empirically and kinetically from fundamental considerations using data from doped propane gas runs. These expressions, together with available literature values of gas phase rate coefficients, could adequately describe the post-flame NO and HeN profiles of coal and gas runs. HeN profiles in the far postflame zone of the coal flames are strongly influenced by the slow release of nitrogen from the coal residue. This devolatilization plays a critical role in supplying the HeN that drives the multistep process converting fuel N into molecular nitrogen.

The use of black liquor gasification as an alternative to conventional chemical and energy recovery systems for spent liquors is an area of particular interest to the pulp and paper industry. The motivation to explore this technology is to improve the thermal efficiency of the recovery process by utilizing the energy content of the spent black liquor more effectively and provide chemical recovery for sodium and sulphur containing liquors for a local pulp and paper mill. A study of the available gasification technologies showed that the steam reforming process marketed by ThermoChem Recovery International is particularly suited to the mill in that it can handle a change to a sulphite pulping chemistry and also handle silica removal which is an inherent problem with the bagasse raw material that the mill uses. However the technology required further development and confirmation of process suitability before implementation at the mill. This aim of this project was to build and operate a gasifier based on the TRI concept to determine if this process is suitable for recovery of SASAQ black liquor from bagasse pulping. This included gaining an understanding of the process variables like the black liquor solids composition and the non-process element levels and required carrying out a mass balance on inorganic components across the reactor as well. The focus of this investigation was primarily on the front end of the project and entailed basic and detailed design of a pilot gasification unit. The pilot unit was subsequently constructed, commissioned and operated to prove the unit met the design intent. Preliminary results showing the conceptual proof of the technology are presented as well as performance tests showing the unit capability of gasifying a 3.1 1Ihr 60% solid content black liquor feed. Problematic areas that could influence the design of a scale-up unit were identified and highlighted for further development, with proposed solutions. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2005.

The pulp and paper industry uses pulping chemicals for the treatment of bagasse, straw and wood chips. Spent liquor or effluent liquor, with high carbon content is produced and sent to chemical recovery to recover pulping chemicals. In addition, energy from the spent liquor is recovered and utilised to generate steam for electricity supply, thereby reducing fossil fuel power consumption. Spent liquor is destroyed using conventional incineration technology, in a recovery furnace or recovery boiler, which is the heart of chemical recovery. These units have over the past few decades been prone to numerous problems and are a major concern to the pulp and paper industry. They pose a threat to the environment, are expensive to maintain and constitute a safety hazard. Thus the pulp and paper industry is now looking at a replacement technology; an alternative that will effectively regenerate pulping chemicals and recover energy for generating electricity, ultimately to make the plant energy self-sufficient. Gasification technology may be the chosen technology but is yet to be applied to the pulp and paper sector. However, this technology is not new. It has been integrated and used successfully in the petroleum industry for decades, with applications in coal mining and the mineral industry. The overall objective of tills study is to develop a better understanding of gasification using a pilot-scale fluidised bed reactor which was designed and developed at the University of Natal. The reactor, "the Gasifier", is operated at temperatures below the smelt limits of inorganic salts (<750°C) in the spent liquor. In this investigation, spent liquor is injected directly into an inert bed of alwninium oxide grit, which is fluidised by superheated steam. The atomized liquor immediately dries when it contacts the grit in the bed, pyrolyses and the organic carbon is gasified by steam. Pyrolysis and steam gasification reactions are endothennic and require heat. Oxidised sulphur species are partially reduced by reaction with gasifier products, which principally consist of carbon monoxide, carbon dioxide and hydrogen. The reduced sulphur is said to be unstable in the gasifier environment, and reacts with steam and carbon dioxide to form solid sodium carbonate and gaseous hydrogen sulphide. (Rockvam, 2001). The focus of this study will be to determine the Gasifier's ability to gasify spent liquor, from soda and sulphite pulping of bagasse, at different operating conditions. In addition, the fate of process and non-process elements will be investigated. The product gas generated in the gasification of spent soda and sulphite liquors consisted of hydrogen, carbon dioxide, carbon monoxide and methane. In the gasification of spent sulphjte liquor, hydrogen sulphide was also produced. The water-gas shift reaction, which was the main reaction, was found to be temperature dependent. In adilition, organic carbon conversion increased with temperature. Furthermore, most of the sulphur in the bed predominated in the form of hydrogen sulphide with very little sulphur in the form of sulphate. This indicated that gasification would reduce sulphate levels, which are responsible for dead load in a chemical recovery cycle. Finally, an important result was that the aluminium oxide grit was successfully coated. It was previously speculated that this would not be possible. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2004.

Gasification is a very efficient method of producing clean synthetic gas (syngas) which can be used as fuel for electric generation or chemical building block for petrochemical industries. This study performs detailed simulations of coal gasification process inside a generic two-stage entrained-flow gasifier to produce syngas carbon monoxide and hydrogen. The simulations are conducted using the commercial Computational Fluid Dynamics (CFD) solver FLUENT. The 3-D Navier-Stokes equations and seven species transport equations are solved with eddy-breakup combustion model. Simulations are conducted to investigate the effects of coal mixture (slurry or dry), oxidant (oxygen-blown or air-blown), wall cooling, coal distribution between the two stages, and the feedstock injection angles on the performance of the gasifier in producing CO and H2. The result indicates that coal-slurry feed is preferred over coal-powder feed to produce hydrogen. On the other hand, coal-powder feed is preferred over coal-slurry feed to produce carbon monoxide. The air-blown operation yields poor fuel conversion efficiency and lowest syngas heating value. The two-stage design gives the flexibility to adjust parameters to achieve desired performance. The horizontal injection design gives better performance compared to upward and downward injection designs.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Chemical Engineering), 25 May 2016 / The Integrated Gasification Combined Cycle (IGCC) is a promising technology in the power generation industry to increase efficiency and reduce environmental emissions associated with fossil fuels. The performance of the gasifier and its economic feasibility largely depends on the gasifier island and many problems experienced during gasification are associated with extreme operating conditions. There is, however, no evidence that the extreme operating conditions in the gasifier yield the maximum possible fuel gas heating value. The main objective of this research was, therefore, to develop a mathematical model to simulate and optimize the performance of the IGCC, particularly focusing on maximizing the fuel gas heating value. The work carried out in this thesis was divided into three parts. The first part presented a 1-D simulation model for a dry-fed entrained flow gasifier with oxygen and steam used as oxidizing agents. The model was then validated against published models for a similar reactor configuration and then extended to an existing entrained flow gasifier of Elcogas IGCC power plant in Puertollano, Spain. The second part presented the optimization model in which the objective function was to maximize the fuel gas heating value. The last part combined gasifier and the gas turbine models and evaluated the overall performance of the gas path. The formulated mathematical model which consisted of mass and energy balances of the system was solved in gPROMS platform in order to determine the optimum conditions of the gasifier. Multiflash for Windows was used to obtain the thermodynamic properties of gas phase. The model was first used to replicate three published simulation models, particularly focusing on the carbon conversion, cold gas efficiency, gasification peak temperature and gasifier exit gas temperature. The results obtained during optimization of the Elcogas entrained flow gasifier showed a 14% increase in fuel gas heating value was realized with a decrease of 519K in operating temperature. The pressure did not have a significant impact on the fuel gas heating value, with only less than 2% increase in heating value being achieved by changing the pressure from 2MPa to 5MPa. Owing to a decrease in operating temperature, the conversion was reduced from 97% to about 63% and that led to a decrease of almost 60% in O2 and 50% in steam used in the gasifier. The results also indicate an almost 2% increase in the efficiency of the gas turbine when burning the gas of the higher heating value. This was mainly due to the increase in the expander inlet temperature. The gas turbine exhaust temperature and the exhaust gas heat capacity also iii increased, thereby, increasing the amount of heat available in the heat recovery steam generator. There was also a 7% notable increase of the overall gas path efficiency. A reduction in operating temperature and pressure of the gasifier, therefore, guarantee an extended operating cycle of the gasifier, thereby, improving commercial attractiveness and competitiveness of the technology compared to other available power generation technologies. These new proposed operating conditions, which are less severe, therefore, signify a possible improvement availability and reliability of the IGCC power plant.

Thesis. 1977. Sc.D. cn--Massachusetts Institute of Technology. Dept. of Chemical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 222-228. / Sc.D.cn

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Chemical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography : leaves 146-149. / M.S.

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Chemical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography : leaves 75-76. / M.S.