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.

A considerable number of modeling studies for the investigation of sulfur retention in atmospheric bubbling fluidized bed combustors have been carried out and well documented in the literature. Despite 30 years of intensive study of sulfation process in fluidized bed combustors and numerous laboratory studies, there are still many uncertainties and disagreements on the subject. In addition, modeling sulfur retention performance of Turkish lignites with high sulfur, volatile matter and ash contents has not drawn much attention to date. Recent trend in utilization of indigenous lignites in fluidized bed boilers necessitated investigation of pollutant emissions and adaptation of fluidized bed combustion technology to these lignites. In an attempt to achieve this objective, a system model, previously developed and tested for the prediction of the combustion behavior of fluidized bed combustors was extended to incorporate sulfur retention. The predictive accuracy of the model was assessed by applying it to the prediction of the behavior of METU 0.3 MWt ABFBC test rig burning indigenous lignites in their own ashes, and comparing its predictions with measurements taken on the same rig. Sulfur dioxide concentration predictions throughout the combustor were found to be in good agreement with the experimental data except for the small discrepancy between predictions and measurements in the bed section. Measurements and model predictions revealed that recyling enhances calcium utilization significantly by increasing the sorbent residence time leading to higher sulfur retention efficiencies. The system model proposed in this study proves to be a useful tool in qualitatively and quantitatively simulating the processes taking place in an atmospheric fluidized bed combustor.

Bibliography: leaves 290-303 / xxi, 303 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1993?

Thesis (doctoral)--University of New South Wales, 1997.

Thesis (Ph. D.)--University of Adelaide, Dept. of Chemical Engineering, 1989. / Includes bibliographical references (208-218).

Thesis (M.S.)--Ohio University, June, 1998. / Title from PDF t.p.

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xiv, 98 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 91-98).

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xi, 100 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 83-86).

The Fluidised Bed Combustion (FBC) technology has been widely used internationally for power generation. This technology has good fuel flexibility and reduced S02 emissions with dry sorbent (Limestone or Dolomite) addition. South Africa has large reserves of coals that are difficult to combust in conventional pulverised fuel fired boilers. These reserves could be potential feedstocks for new build FBC boilers. The chemical composition of these coals is site specific and could have an impact on the combustion performance of the fuel. This necessitates the need for FBC coal tests in the presence of a sorbent. The objectives of this study were to investigate the changes in the production NO" SO" and the combustion efficiency of the three test coals under conditions of fluidised bed combustion, with the same sorbent. Tests with no sorbent were performed to evaluate the coals inherent calcium capabilities of capturing sulphur. Tests with varying ratios of sorbent were performed to evaluate the sorbent's capabilities for further levels of in-bed desulphurisation. The experimental equipment used in this investigation was the Eskom Fluidised Bed Test Facility (FBTF). This facility is a bubbling fluidised bed combustorlgasifier. The investigated bed temperature range was between 800 to 900°C, in intervals of 20°C. The operating pressure was 50kPa (gauge). The three coals were compared at CalS molar ratio of 1. Carbon in ash has shown to decrease with an increase in bed temperature for Coal A, Band C. The best performing coal in terms of least quantity of remaining carbon in ash was Coal A. The NO emissions increased for an increase in bed temperature for Coal A, Band C. The greatest NO emissions were recorded during Coal B tests. The N 20 emissions decreased with an increase in bed temperature for Coal A and B tests. Higher N 20 emissions were observed for Coal B than Coal A tests. In terms of S02 retention Coal C performed the best. The optimal operating bed temperature for S02 retention observed for the three coals was in the region of 800-860°C. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

Sulphur dioxide (S02) is an atmospheric pollutant that has the ability to negatively impact on local vegetation, farming activities and human health. South Africa's coal fired power stations release this pollutant into the atmosphere during the combustion of coal. Current coal fired power stations operating in South Africa are not required to install any form of S02 removal equipment however, the new Air Quality Act to be implemented in South Africa could change this situation. The use of Fluidised Bed Technology with the addition of limestone or dolomite (sorbent) has the ability to absorb and convert S02 from a gaseous phase into a solid phase for easy disposal. The objective of this study was to evaluate potential commercial sorbent sources in South Africa that could potentially be used for the reduction of S02 released into the atmosphere during fluidised bed combustion of coal. Eight commercially mined sorbents within a two hundred kilometre radius of large economically mineable coalfields were selected. The study was divided into two parts in order to identify any possible links between the physical and chemical composition of the sorbents and their performance under fluidised bed combustion conditions. In Part 1, the chemical composition of the sorbents was determined by X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) analysis. The sorbents hardness property was determined by Hardgrove Grindability Index (HGI) testing. The physical structure of the sorbent was analysed by both Petrographical and Scanning Electron Microscope (SEM) analysis of the original/parent sorbents. In Part 2, S02 absorption capability by the sorbents was determined through batch tests conducted in a 1.6m high stainless steel, 10kW electrically heated Atmospheric Fluidised Bed Reactor (AFBR). Three different bed temperatures (800, 850 and 900°C) and three different particle size ranges (425-500, 600-710 and 850-lOOOllm) were tested for each of the eight sorbents. The highest Maximum Sulphur Retention for all of the sorbents was found to occur at a temperature of 850°C and at the smallest particle size tested, 425-500llm. The best desulphurisation sorbent of the eight sorbents tested was found to be Sorb1 with a S02 Maximum Sulphur Retention of 92.30% and a Removal Efficiency of 84.54%. Additional tests were also performed on the sorbents to get a better understanding of their desulphurisation ability. For the area calculation on the performance test graphs, it was found that the sorbent that produced the best S02 removal efficiency was not necessarily the sorbent that had the highest maximum sulphur retention. For varying quantities of sorbent added to the AFBR, it was found that each sorbent had an optimum quantity that produced the best removal efficiency. However, for desulphurisation beyond certain limits any further increase in the amount of sorbent added to the AFBR resulted only in a marginal increase in the sorbent's S02 removal. The calcium and magnesium composition of the sorbents was found to have no noticeable influence on the sorbents ability to reduce S02. The silica and inherent moisture content of the sorbent showed signs whereby an increase in their compositions produced an increase in desulphurisation. The Hardgrove Grindability Index of the sorbents indicated that the softer the sorbent, the better the S02 reduction. The petrographical analysis performed on the eight sorbents showed no obvious reason for the difference between the sorbents ability to remove S02. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2006.