Gas cleaning is an essential step in many chemical processes. The reason for cleaning is to remove components that can damage equipment or inhibit further reactions. The treatment can include the removal of particulates, removal of one or more chemical species, or the conversion of one species to another. The gases include natural gases, combustion gases or synthesis gas (syngas). Of particular importance is the hot gas desulphurization (HGD) of syngas after gasification. This method of treatment offers potential energy and raw material savings to traditional ‘wet’ gas cleaning methods, such as physical or chemical absorption. Syngas is a valuable intermediate product because it can be processed into a number of different chemicals. These range from hydrocarbon chains (Fischer-Tropsch reactions), methanol, and ammonia (from hydrogen in the syngas). Methanol and ammonia are important raw materials to produce other chemicals. Syngas can be used for production of electricity via gas turbines in an Integrated Gasification Combined Cycle (IGCC) plant. In this study, a laboratory scale gasification and desulphurization unit was designed and constructed for removal of hydrogen sulphide (H2S) from syngas. The gasifier operates at moderately high temperature (700-900 °C) and low pressure (1-3 bar g) to produce syngas containing H2S (1-6 mol %) from a liquid hydrocarbon fuel mixture and oxygen. Desulphurization occurs in a fixed bed isothermal reactor (300-600 °C) whereby H2S is removed by chemical reaction with a sorbent. The fuel used was a mixture of methanol and ipropanethiol and the sorbent chosen was zinc oxide. The apparatus was tested to obtain a reliable experimental method. A series of experiments were conducted to determine two results: Firstly, to see the performance of the unit during repeated sorbent testing (i.e. a systematic experimental run programme). Secondly, to determine the effect of some process variables (temperature, flowrate and particle size) on the conversion of sorbent. GC analysis of the syngas showed consistent gas composition during the experiment, an important result which justifies this new method of syngas production from a liquid fuel. The final conversions from ZnO to ZnS ranged from 2-12 mole %. However, there was some variation under repeated conditions, which showed the need for additional method development. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

Scaling and corrosion cost industries all over the world millions of rands each year. Chemical treatment of water to prevent scale is expensive and can be hazardous. As a result industry is always looking for new, cheaper alternate methods of reducing scale. One such method is magnetic water treatment. Magnetic water treatment involves passing hard water (the main cause of scale) through a magnetic field. This method favors the precipitation of calcium carbonate in the form of aragonite instead of calcite. Aragonite is a softer, less tenacious material that does not adhere to the walls of pipes or heating surfaces. These particles remain in suspension and may settle out somewhere along the system where the velocity of the water has been reduced. A simple bench-top heating system was set up to determine whether magnetic treatment works and, if it does, to determine the optimum conditions under which it operates. A saturated solution of calcium carbonate was circulated through the heating system with, and without the magnets, so that comparisons could be made. The precipitate was analysed (via X-ray diffraction) to calculate the proportions of calcite and aragonite, while atomic absorption was used to test the hardness of the filtrate. This gave an indication of the effectiveness of the magnetic system. pH graphs and absorption graphs were plotted to compare the rates of precipitation. The precipitate was also observed under the electron microscope in order to view the different structures of calcite and aragonite. Experiments were carried out at different temperatures and different flow rates in order to test the effect of these parameters on the magnetic system. Results showed that the magnetic field increased the rate of precipitation and caused aragonite rather than calcite to be formed. This was in contradiction with most literature surveyed, which stated that magnetism increased the dissolution of calcium carbonate. Results indicated that the higher the temperature, the greater was the rate of precipitation and as a result, the greater the amount of aragonite formed, even without the magnets. Increased flow rate also increased the amount of aragonite formed. As a result hereof, conclusive results could not be obtained at high temperatures and high flow rates. / Thesis (M.Sc.Eng.)-University of Durban-Westville, 2004.

This project investigated the viscosity of heavy medium suspensions. Heavy medium suspensions are used extensively in the minerals processing industry for separation of valuable materials from gangue on the basis of density. Rheological profiles for ferrosilicon and magnetite suspensions were determined using a laboratory-scale viscometer developed in the School of Chemical Engineering, University of KwaZulu-Natal, Howard College Campus, Durban. Ferrosilicon suspensions with specific gravities ranging from 2.0-3.2 were investigated in the presence of clay, to simulate higher density separations such as those used in the diamond industry, where slime build up can be a problem. Magnetite suspensions were prepared at specific gravities ranging from 1.6 - 2.6 to simulate separation densities used in the coal cleaning industry. Mixtures of suspensions of fine magnetite, and coarse magnetite, were also prepared to see what the effect of a coarser medium would have on the viscosity of the suspensions. The effect of viscosity on the separation efficiency of heavy medium separations was also investigated, using a laboratory-scale Dense Medium Separator designed and developed in the department. Suspensions with specific gravities between 1.6 and 1.8 were used to separate coal samples in the following size ranges: - 4mm + 1mm; -1mm + 500um; and -4mm + 500um. The rheograms for ferrosilicon suspensions showed that at low shear rates the suspensions behaved as pseudo-plastic liquids, while at high shear rates the behaviour resembled that of dilatant fluids. At low specific gravities the behaviour of magnetite suspensions was pseudo Newtonian. For specific gravities greater than 2.0, the suspensions became pseudo-plastic. The effect of a locally available dispersant (DP001), on the viscosity of the heavy medium suspensions, was also investigated. For ferrosilicon / clay mixtures, a reduction in viscosity of up to 20 percent was achievable for some specific gravities and slimes level. It was also observed that the dispersant had little effect or none at all, on the viscosity of uncontaminated ferrosilicon suspensions. Addition of the dispersant to fine magnetite suspensions achieved viscosity reductions between 8 and 10 percent. It was observed that the presence of coarse magnetite reduced the viscosity of fine magnetite suspensions by as much as 40 % at certain coarser solid ratios. Adsorption tests using a UV spectrometer showed that there was little or no DP001 adsorbed onto the surfaces of uncontaminated ferrosilicon particles. The results showed that DP001 was adsorbed onto the surfaces of magnetite #1 particles, with almost half the amount of 1 g DP001 / kg Mag #1 added to a test suspension of specific gravity 2.2 being adsorbed. This explained why magnetite #1suspensions were more susceptible to DP001 addition compared to ferrosilicon suspensions. For some of the coal size ranges separated, it was observed that there was a reduction of approximately 22% in the separation efficiency of the process as the specific gravity was increased. For some of the coal samples, an improvement in separation efficiency between 11% and 17% was achievable with DP001 additions of Ig DP001/kg solids, and 2g DP001/kg solids. The presence of coarse magnetite media initially improved the separation efficiency by up to 50% for some coal samples. However, as DP001 was added, there was a decline in the separation efficiency. In conclusion, the measured rheological profiles of the suspensions were comparable with those found in literature. It was shown that media particle size distribution affects the viscosity of heavy medium suspensions. It was also shown that surface active agents can be used to reduce the viscosity of heavy medium suspensions. / Thesis (M.Sc.Eng)-University of KwaZulu-Natal, 2005.

No abstract available. / Thesis (M.Sc.Eng.)-University of Durban-Westville, 2000.

Vetiver grass is a viable vegetative absorbent and erosion barrier; in addition the valuable oils extracted from its roots are playing an increasing role in the perfume, food and pharmaceutical industries. The quantity and quality of oil extracted from the vetiver grass depends strongly on location of growth, and the extraction and separation techniques adopted. The aim of this research project is to evaluate whether the harvesting and extracting of essential oils from locally grown vetiver grass would be a feasible business idea, as well as, which extraction technique will give the highest yield of vetiver oil. The extraction methods tested are solvent extraction, hydro distillation and supercritical carbon dioxide extraction. Due to the lack of supercritical fluid extraction equipment available a large portion of the research project was on the design and setup of a supercritical fluid extraction unit. The experimental investigations undertaken using solvent extraction in a soxhlet apparatus with hexane as the extracting agent gave an average yield of +-1.6% for a 5 hour run which is slightly lower than the yield of 1.91% for a 5 hour run stated in literature. According to the experimental results, yields of up to approximately 2% for hexane extraction can be achieved by increasing the extraction time to 12 hours. The vetiver roots were also hydro-distilled in a clevenger apparatus for 16 hours (extraction time); this produced a yield of approximately 0.18 to 0.35%. According to literature hydrodistillation of vetiver roots in a similar apparatus resulted in an average yield of 1.8% for a 16 hour run. This showed that the heavier components of the vetiver oil were not released during the hydro-distillation extraction. Research shows that supercritical carbon dioxide extraction (SCE) produces the highest yields ranging from 2.9 to 3.74% when using the recommended parameters of 190 bar and 50°C. Experimentally a yield of approximately 2.3% was achieved by SCE at 180 bar and 40°C. This yield is lower than that seen in literature due to the lower operating temperature and pressure; however SCE gives a higher yield than the other methods tested in this investigation. The composition of the vetiver oil extracts were analysed using gas-chromatography techniques and this showed that a large percentage of nootkatone is present when using the hydro distillation technique, whilst a large percentage of zizanoic acid was present when using the solvent extraction technique. However a minimal percentage zizanoic acid with higher percentages of nootkatone and khusimol are present in the SCE extracts. The solvent extraction technique gives high yield with high percentage invaluable zizanoic acid whereas hydro-distillation gives very low yields but no zizanoic acid with high percentages valuable nootkatone and khusimol. SCE gives slightly higher yields of vetiver oil than solvent extraction and it contains very minimal zizanoic acid with higher percentages of nootkatone and khusimol. It was therefore concluded that SCE would be the best extraction method for these particular vetiver roots. For a pilot scale SCE extractor the total annual sales was estimated as R 453 420 and the total operating costs per annum were estimated to be R 4 839 813. Therefore from this preliminary feasibility study it is seen that the total operating costs far exceed the total annual sales and hence the business is not profitable. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

Liquid extraction, sometimes called solvent extraction, is the separation of the constituents of a liquid solution by contact with another insoluble liquid. It belongs to the class of countercurrent diffusional separation processes, where it ranks second in importance to distillation. There are many different types of columns that are available for liquid-liquid extraction and the reciprocating column (RPC) and vibrating plate column (VPE) are two types of mechanically aided columns. This research aims at developing a mathematical model for the prediction of NTUIHETS and the mass transfer coefficient, k-ox for the VPE based on the agitation level of the plates (af- the product of frequency and amplitude of the plate motion), the plate spacing and the flow rates which will allow for the simplification in the design of this type of column. There is a lot of research that has gone into the development of mechanically aided extraction columns but it is limited when it comes to the RPC and VPE and most of this research is devoted to the RPC. The system chosen is the acetone-toluene-water system with the acetone in toluene forming the feed that is dispersed in the column as it moves upward while the water moves as a continuous phase down the column. Experiments were conducted to evaluate the hydrodynamics of the droplets moving up the column (in terms of drop sizes, size distribution and dispersed phase holdup) and to evaluate the mass transfer that occurs (in order to evaluate NTU, HTU and k-ox) as well as the effect of mass transfer on the hydrodynamics of the system while varying the agitation levels and spacing of the plates in the column. Successful models were developed using some of the experimental data and these correlations were verified with additional data. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2010.

Critical properties, liquid vapour pressures and liquid viscosities are important thermophysical properties required for the design, simulation and optimisation of chemical plants. Unfortunately, experimental data for these properties are in most cases not available. Synthesis of sufficiently pure material and measurements of these data are expensive and time consuming. In many cases, the chemicals degrade or are hazardous to handle which makes experimental measurements difficult or impossible. Consequently, estimation methods are of great value to engineers. In this work, new group contribution methods have been developed for the estimation of critical properties, liquid vapour pressures and liquid viscosities of non-electrolyte organic compounds. The methods are based on the previous work of Nannoolal (2004) & Nannoolal et al. (2004) with minor modifications of structural group definitions. Critical properties, viz. critical temperature, critical pressure and critical volume, are of great practical importance as they must be known in order to use correlations based on the law of corresponding states. However, there is a lack of critical property data in literature as these data are difficult or in many cases impossible to measure. Critical property data are usually only available for smaller molecules of sufficient thermal stability. The proposed group contribution method for the estimation of critical properties reported an average absolute deviation of 4.3 K (0.74%), 100 kPa (2.96%) and 6.4 cm3.mol1 (1.79%) for a set of 588 critical temperatures, 486 critical pressures and 348 critical volumes stored in the Dortmund Data Bank (DDB (2006)), respectively. These results were the lowest deviations obtained when compared to ten well known estimation methods from literature. In addition, the method showed a wider range of applicability and the lowest probability of prediction failure and leads to physically realistic extrapolation when applied to a test set of components not included in the training set. For the estimation of the critical temperature using the new method, knowledge about the normal boiling point is required. If there is no information on the latter property, then the previous group contribution estimation method can be employed for estimation. Because of their great importance in chemical engineering, liquid vapour pressures have received much attention in literature. There is currently an abundance of experimental data for vapour pressures, especially for smaller molecules, but data are scarce or of low quality for larger and more complex molecules of low volatility. The estimation of liquid vapour pressures from molecular structure has met with very limited success. This is partly due to the high quality predictions required for vapour pressures for use in the design of for example distillation columns. This work presents a new technique for the estimation of liquid vapour pressures by developing a two-parameter equation where separate parameters model the absolute value and slope while at the same time the equation is able to approximate the nonlinearity of the curve. The fixed point or absolute value chosen was the normal boiling point for which a large amount of experimental data is available. A group contribution estimation of the slope was then developed which showed nearly no probability of prediction failure (high deviation). Employing experimental normal boiling points in the method, an absolute relative deviation of 6.2% in pressure for 1663 components or 68835 (68670 from DDB and 165 from Beilstein) data points was obtained. This result is in comparable accuracy or slightly higher in deviation than correlative models such as the Antoine and DIPPR equations (direct correlations). A test of the predictive capability by employing data that were not used in the training set also showed similar results. Estimations are possible up to the inflection point or a reduced normal boiling temperature of ±1.2. If there is no information about the experimental normal boiling point, two options are recommended to obtain this value. The first and more reliable is back-calculation using the known boiling point at other pressures and the estimated slope of the vapour pressure equation. Results in this case are similar to cases where experimental normal boiling points were used. The second possibility is to estimate the normal boiling point using the method developed previously. In this case, an absolute relative deviation of 27.0% in pressure is obtained. The saturated liquid viscosity is an important transport property that is required for many engineering applications. For this property, experimental data are limited to mostly simple and more common components and, even for these components the data often cover only a small temperature range. There have been many different approaches to estimate liquid viscosities of organic compounds. However, correlative and empirical methods are often the only or preferred means to obtain liquid viscosities. The technique used for the estimation of the liquid viscosity is similar to that in case of liquid vapour pressures, i.e. a two-parameter equation models the absolute value, slope and the non-linearity of the curve. As there was no convenient reference point at a standard viscosity available to model the absolute value (viscosity reference temperature), an algorithm was developed to calculate this temperature which was chosen at a viscosity of 1.3 cP. This work then presents a group contribution estimation of the slope and using calculated or adjusted reference temperatures, an absolute relative deviation of 3.4% in viscosity for 829 components or 12861 data points stored in the DDB was obtained. This result is in comparable accuracy or slightly higher in deviation than correlative models such as the Andrade and Vogel equations (direct correlations). The estimation method has an upper temperature limit which is similar to the limit in case of liquid vapour pressures. If no data are available for a viscosity close to 1.3 cP then, as in case of the vapour pressure estimation method, the temperature can be back calculated from data at other viscosity values. Alternately, the viscosity reference temperature can be estimated by a group contribution method developed in this work. This method reported an average absolute deviation of 7.1 K (2.5%) for 813 components. In case both the slope and absolute value were estimated for the liquid viscosity curve, an average absolute deviation of 15.3 % in viscosity for 813 components or 12139 data points stored in the DDB was obtained. The new method was shown to be far more accurate than other group contribution methods and at the same time has a wider range of applicability and lower probability of prediction failure. For the group contribution predictions, only the molecular structure of the compound is used. Structural groups were defined in a standardized form and fragmentation of the molecular structures was performed by an automatic procedure to eliminate any arbitrary assumptions. To enable comparison, chemical family definitions have been developed that allow one to automatically classify new components and thus inform the user about the expected reliability of the different methods for a component of interest. Chemical family definitions are based on the kind and frequency of the different structural groups in the molecule. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2006.

This thesis presents a chemical, microbiological and mathematical analysis of an anaerobic baffled reactor (ABR) treating domestic wastewater. The purpose of this study was to gain an understanding of the mechanisms of treatment of domestic wastewater in an ABR at pilot-scale, and to use this understanding to develop some guidelines for the design of ABR technology for the anaerobic treatment or pre-treatment of domestic wastewater. Previous research has been undertaken on ABR technology, but no detailed studies of the performance of an ABR on domestic wastewater at pilot-scale have been reported. In this thesis, operating data from a 3 000 ℓ pilot-scale ABR are presented and analysed. Two hypotheses were proposed: that (i) the baffled design of the reactor would facilitate phase separation whereby acidogenic and methanogenic processes predominate in different physical locations in the reactor; and (ii) the critical design parameter is the applied hydraulic retention time. The principle findings of this research were: • The pilot-scale ABR functioned as a solids retention device. Particulate material was retained through settling in the first compartment, forming a gel-like matrix. Reduction of solids occurred through anaerobic conversion to CH4 and CO2. • Partial phase separation of acidogenic and methanogenic communities was observed. • The major factor that controlled biomass washout rate and therefore reactor performance was upflow velocity in each compartment. At higher upflow velocities, slow growing microorganisms failed to establish, resulting in increased solids accumulation rates, while at lower upflow velocities, stable digestion proceeded. • Relatively poor treatment rates were obtained due to the low inherent alkalinity of waters in eThekwini municipality resulting in low operating pH values. • Insufficient pathogen reduction was observed indicating that post-treatment of effluent would be required. It was concluded that the benefit of the baffled design was related to the system’s solids retention characteristics and that the critical design parameters for an ABR domestic wastewater treatment unit were compartment upflow velocity and applied hydraulic retention time. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2009.

The models used in the prediction of activity coefficients are important tools for designing major unit operations (distillation columns, liquid-liquid extractors etc). In the petrochemical and chemical industry, well established methods such as UNIFAC and ASOG are routinely employed for the prediction of the activity coefficient. These methods are, however, reliant on binary group interaction parameters which need to be fitted to reliable experimental data. It is for this reason that these methods are often not applicable to systems which involve complex molecules. In these systems, typically solid-liquid equilibria are of interest where the solid is some pharmaceutical product or intermediate or a molecule of similar complexity (the term complex here refers to situations where molecules contain several functional groups which are either polar, hydrogen bonding, or lead to mesomeric structures in equilibrium). In many applications, due to economic and environmental considerations, a list of no more than 20 solvents is usually considered. It is for this reason that the objective of this work is to develop a method for predicting the activity coefficient of complex multifunctional compounds in some common solvents. The segment activity coefficient approaches proposed by Hansen, MOSCED and the NRTL-SAC models show that it should be possible to “interpolate” between solvents if suitable reference solvents are available (e.g. non-polar, polar and hydrogen bonding). Therefore it is useful to classify the different solvents into suitable categories inside which analogous behaviour should be observed. To accomplish this, a significant amount of data needs to be collected for the common solvents. Data with water as a solvent was freely available and multiple sources were found with suitable data. Both infinite dilution activity coefficient (y∞) and SLE (Solid-Liquid Equilibrium) data were used for model development. The y∞ data were taken from the DDB (Dortmund Data Bank) and SLE data were taken from Beilstein, Chemspider and DDB. The limiting factor for the usage of SLE data was the availability of fusion data (heat of fusion and melting temperature) for the solute. Since y∞ in water is essentially a pure component property it was modelled as such, using the experience gained previously by this group. The overall RMD percentage (in ln y∞) for the training set was 7.3 % for 630 compounds. For the test set the RMD (in ln y∞) was 9.1 % for 25 fairly complex compounds. Typically the temperature dependence of y∞ data is ignored when considering model development such as this. Nevertheless, the temperature dependence was investigated and it was found that a very simple general correlation showed moderate accuracy when predicting the temperature dependence of compounds with low solubility. Data for solvents other than water were very scarce, with insufficient data to develop a model with reasonable accuracy. A novel method is proposed for the alkane solvents, which allows the values in any alkane solvent to be converted to a value in the solvent hexane. The method relies on a first principles application of the solution of groups concept. Quite unexpectedly throughout the course of developing the method, several shortfalls were uncovered in the combinatorial expressions used by UNIFAC and mod. UNIFAC. These shortfalls were empirically accounted for and a new expression for infinite dilution activity coefficient is proposed. This expression is however not readily applicable to mixtures and therefore requires some further attention. The method allows for the extension of the data available in hexane (chosen since it is a common solvent for complex compounds). In the same way as the y∞ data in water, the y∞ data in hexane were modelled as a pure component property. The overall RMD percentage (in ln y∞) for the training set was 21.4 % for 181 compounds. For the test set the RMD (in ln y∞) was 11.7 % for 14 fairly complex compounds. The great advantage of both these methods is that, since they are treated as pure component properties, the number of model parameters grows linearly with the number of groups, unlike with mixture models (UNIFAC, ASOG, etc.) where it grows quadratically. For both the water and the hexane method the predictions of the method developed in this work were compared to the predictions of UNIFAC, mod. UNIFAC, COSMO-RS(OL) and COSMO-SAC. Since water and hexane are not the only solvents of practical interest, a method was developed to interpolate the alcohol behaviour based on the water and hexane behaviour. The ability to predict the infinite dilution activity coefficient in various solvents allowed for the prediction of various other properties, viz. air-water partition coefficient, octanol-water partition coefficient, and water-alcohol cosolvent mixtures. In most cases the predictions of these properties were good, even for the fairly complex compounds tested. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2009.

A three-stage Pressurized Fluidized Bed Combustor (PFBC) of principal dimensions, O,4Sm internal diameter by4m high was designed and fabricated to burn South African coals, with particular reference to coals unsuitable for burning in conventional boilers. The combustor which is the first of its kind and probably one of very few operational PFBCs in the world, was made of three jacketed sections positioned vertically one above the other and bolted together at the flanges. Distributor plates were located at the flanges which gave the combustor a multistage capability. A three, two, or one deep Fluidized Bed (FB) configurations were possible by removing the interstage distributors. Interstage solids circulation was made possible by the use of downcomers transporting solids downwards between the FBs. The solids were returned to the top FB using a pneumatic conveyor. The design of the PFBC was a sequence to a series of experimental and theoretical investigations which were carried out in order to provide us with the necessary PFBC design parameters. These investigations dealt with the following areas of research: (a) the development of a new type of cyclonic tuyere capable of transmitting through it high quantities of solids with the fluidizing gas, without choking, (b) the transfer and control of the downward flow of solids through downcomer pipes, (c) the control of the circulation of solids in a Circulatory system using a non-mechanical solids flow control valve, (d) the development of a new type of start up burner which could operate immersed under the solids, and (e) the combustion of coal in a small FB under batch conditions and the study of reaction kinetics of South African coals. On the basis of the results of the investigation in these research areas and the findings of research of individuals and of .organizations working in the field of fluidization technology the PFBC was designed, built, and successfully commissioned. A series of 12 runs, with each run lasting between 2 and 8 days, totalling more than 1500 hours, were carried out on the PFBC. Char and coal with ash content between 30 and 70 per cent were burnt in the combustor using various combinations of feeding ports and number of FBs. System pressures ranged between atmospheric and 6 bar(abs). For some of the runs the reactor was operated in a counter-current mode with solids and combustibles descending against the upflowing fluidizing air in order to study the effect that counter-current flow had on the efficiency of combustion. The combustion trials showed that the two-FB combustor, operated preferably without solids circulation, with the bottom FB acting as the main combustion cell and the top FB as a smuts burn-out cell, proved to be the most practical and most suitable combustor for burning South African high ash coals and fines or, in general, any low-grade carbonaceous materials of any size. With this configuration combustion efficiencies of up to 99 per cent, based on the combustibles in the feed and the ash, were achieved. The department computer (COC1700) was successfully linked with the PFBC for real time data logging and data processing. A mathematical model which was based on our research findings and the work of T.P. Chen and S.C. Saxena, C. Fryer and O.E. Potter, and D. Levenspiel was successfully developed and applied to the twoFB PFBC. The model describes the devolatilization and combustion of coal particles in the FB in accordance with a shrinking core type model and uses a population balance over all particles for the overall mass balance. The results from this model, which was put onto the computer, compared favourably with the experimental results and the model can be confidently used to predict the behaviour of the PFBC. It can also be easily adapted for use on any other single or multifluidized bed reactors provided that the assumptions made for the derivation of this mathematical model still hold. A mathematical model based on the work of H.C. Hottel and A.F. Sarofim, and L. Wender and G.T. Copper was also developed. This model describes the transfer of heat from the FB to the cooling coils using a stepwise heat and mass balance along the length of the cooling coil. Although this mathematical model was developed specifically for the cooling coils of our combustor it is strongly believed that it can also form the basis of a general purpose model. / Thesis (Ph.D.)--University of Natal, 1981.