There is a range of feed materials available for the production of Ti02 pigment. These range from natural materials like ilmenite and rutile to synthetic materials like synthetic rutile. There is a large increase in the price of titaniferous feed materials as the Ti02content of the material increases. To take advantage of the difference in price between chloride grade slag and natural rutile a process was developed to increase the Ti02 content of chloride grade slag from ~85% to more than 95%. This beneficiated titania slag product (BTS) should be ideal as feed material to the chloride pigment process. Initially several processes were evaluated. Particular emphasis was placed on the slag pre-treatment procedure. This was necessary as impurities could only be leached with difficulty from as-cast slag. A suitable pre-treatment procedure would render the impurities easily leachable, while the titanium is retained in an insoluble form. The results indicated that a process consisting of oxidation and reduction roasting would satisfy these requirements. Detailed process development was then undertaken on this process. The first phase of the process development was conducted in a coal fired fluid bed roaster. This allowed a set of semi optimised process parameters to be established, but the highest Ti02 content that could be achieved was 94%. A second stage of process development was under taken under more controlled conditions, using a small fluid bed reactor connected to a gas mixing system. Based on the results in this phase of the process development a new set of optimum process parameters was established. They are oxidation at 850°C for 1.5 h in an atmosphere containing 8% O2; reduction at 850°C for 10 min in a 100% CO atmosphere and leaching in boiling 20% hydrochloric acid for 12 h. Under these conditions it was possible to produce BTS containing > 97% Ti02. During oxidation of titania slag several important morphological changes occur. These are the conversion of the original M305 phase in the slag to a mixture of rutile/anatase, hematite and ferric M305. In the process the iron in the slag migrates to the outside surfaces of the slag particles where it is easily accessible during leaching. The iron containing phases are converted to ilmenite during reduction and during leaching the ilmenite is removed. This yields the BTS product. As the oxidation roast appeared to be a very important of the BTS process it was decided to investigate the mechanism of titania slag oxidation. A mechanism based on the nucleation energy that is required to form the relevant phases during oxidation was proposed. This mechanism was tentatively confirmed through selected experiments. / Thesis (PhD)--University of Pretoria, 2009. / Materials Science and Metallurgical Engineering / unrestricted

The Council for Scientific and Industrial Research (CSIR) in South Africa is developing a process to produce titanium tetrachloride from a low-grade material such as ilmenite. Titanium tetrachloride can then be used as feed material for titanium metal or pigment-grade titanium dioxide production. Titanium tetrachloride is commercially produced by chlorinating synthetic rutile (<92% TiO2) or titanium dioxide slag (<85% TiO2) at ~900 ˚C. A drawback of chlorination at this temperature is that any constituents other than TiO2 will end up as hazardous waste material. A characteristic step in the CSIR’s proposed process is to nitride titanium dioxide contained in the feed material before it is sent for chlorination. The chlorination of the resulting titanium nitride is achieved at a much lower temperature (~200 ˚C) than that of the existing titanium dioxide chlorination reaction. An added advantage of the low-temperature chlorination reaction is that chlorine is selective mostly towards titanium nitride and metallic iron, which means that any other constituents present are not likely to react with the chlorine. The result is reduced chlorine consumption and less hazardous waste produced. The nitrided ilmenite must, however, be upgraded by removing all iron before it can be sent for chlorination. Commercial ilmenite upgrading processes, called synthetic rutile production, also require the removal of iron and other transition metals before chlorination. A literature review of existing ilmenite upgrading processes revealed four possible process options that could remove iron from nitrided ilmenite. Two of these process options, the Becher and Austpac ERMS SR processes, are proven process routes. The other two are novel ideas – one to passivate iron contained in the nitrided ilmenite against chlorination and the other to use ammonium chloride (as used in the Becher process) as a stoichiometric reactant to produce a ferrous chloride solution. A preliminary experimental evaluation of these process options indicated that the Austpac ERMS SR process is the most viable option for removing iron from nitrided ilmenite. The Austpac ERMS SR process was therefore selected as a template for further process development. A detailed Austpac ERMS SR process review found that two process units in the Austpac ERMS SR process could be used in a process that separates iron from nitrided ilmenite. These are the Enhanced Acid Regeneration System and the Direct Reduced Iron process units. The review also concluded that another leach unit would have to be developed. It was therefore necessary to further investigate the dissolution of nitrided ilmenite in hydrochloric acid. A detailed experimental evaluation of nitrided ilmenite dissolution in hydrochloric acid found that hydrochloric acid could be used as the lixiviant to selectively remove iron from nitrided ilmenite. The dissolution of metallic iron in 90 ˚C hydrochloric acid reached levels of at least 96% after only 60 minutes. An average “combined resistance” rate law was found that could be used to describe this dissolution reaction. The observed activation energy and Arrhenius pre-exponential factor were found to be equal to 9.45 kJ.mol-1 and 30.8 s-1 respectively. The Austpac ERMS SR process review and experimental results described above were then combined and used to propose a process that could be employed to remove iron from nitrided ilmenite. The proposed process was modelled using the Flowsheet Simulation module in HSC Chemistry 7.0 / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2010. / Chemical Engineering / MEng (Chemical Engineering) / unrestricted

The definition of polar codes given by Arikan is explicit, but the construction complexity is an issue. This is due to the exponential growth in the size of the output alphabet of the bit-channels as the codeword length increases. Tal and Vardy recently presented a method for constructing polar codes which controls this growth. They approximated each bit-channel with a “better” channel and a “worse” channel while reducing the alphabet size. They constructed a polar code based on the “worse” channel and used the “better” channel to measure the distance from the optimal channel. This thesis considers the knowledge gained from the perspective of the “better” channel. A method is presented using iterative upgrading of the bit-channels which successively results in a channel closer to the original one. It is shown that this approach can be used to obtain a channel arbitrarily close to the original channel, and therefore to the optimal construction of a polar code. / Graduate / 0984 / 0544 / arash.ghayoori@gmail.com

An investigation into the performance of several combined gas-steam power generating plants’ cycles was undertaken at the School of Engineering and Technology at the University of Hertfordshire and it is predominantly analytical in nature. The investigation covered in principle the aspect of the fundamentals and the performance parameters of the following cycles: gas turbine, steam turbine, ammonia-water, partial oxidation and the absorption chiller. Complete thermal analysis of the individual cycles was undertaken initially. Subsequently, these were linked to generate a comprehensive computer model which was employed to predict the performance and characteristics of the optimized combination. The developed model was run using various input parameters to test the performance of the cycle’s combination with respect to the combined cycle’s efficiency, power output, specific fuel consumption and the temperature of the stack gases. In addition, the impact of the optimized cycles on the generation of CO2 and NOX was also investigated. This research goes over the thermal power stations of which most of the world electrical energy is currently generated by. Through which, to meet the increase in the electricity consumption and the environmental pollution associated with its production as well as the limitation of the natural hydrocarbon resources necessitated. By making use of the progressive increase of high temperature gases in recent decades, the advent of high temperature material and the use of large compression ratios and generating electricity from high temperature of gas turbine discharge, which is otherwise lost to the environment, a better electrical power is generated by such plant, which depends on a variety of influencing factors. This thesis deals with an investigation undertaken to optimize the performance of the combined Brayton-Rankine power cycles' performance. This work includes a comprehensive review of the previous work reported in the literature on the combined cycles is presented. An evaluation of the performance of combined cycle power plant and its enhancements is detailed to provide: A full understanding of the operational behaviour of the combined power plants, and demonstration of the relevance between power generations and environmental impact. A basic analytical model was constructed for the combined gas (Brayton) and the steam (Rankine) and used in a parametric study to reveal the optimization parameters, and its results were discussed. The role of the parameters of each cycle on the overall performance of the combined power cycle is revealed by assessing the effect of the operating parameters in each individual cycle on the performance of the CCPP. P impacts on the environment were assessed through changes in the fuel consumption and the temperature of stack gases. A comprehensive and detailed analytical model was created for the operation of hypothetical combined cycle power and power plant. Details of the operation of each component in the cycle was modelled and integrated in the overall all combined cycle/plant operation. The cycle/plant simulation and matching as well as the modelling results and their analysis were presented. Two advanced configurations of gas turbine cycle for the combined cycle power plants are selected, investigated, modelled and optimized as a part of combined cycle power plant. Both configurations work on fuel rich combustion, therefore, the combustor model for rich fuel atmosphere was established. Additionally, models were created for the other components of the turbine which work on the same gases. Another model was created for the components of two configurations of ammonia water mixture (kalina) cycle. As integrated to the combined cycle power plant, the optimization strategy considered for these configurations is for them to be powered by the exhaust gases from either the gas turbine or the gases leaving the Rankine boiler (HRSG). This included ChGT regarding its performance and its environmental characteristics. The previously considered combined configuration is integrated by as single and double effect configurations of an ammonia water absorption cooling system (AWACS) for compressor inlet air cooling. Both were investigated and designed for optimizing the triple combination power cycle described above. During this research, tens of functions were constructed using VBA to look up tables linked to either estimating fluids' thermodynamic properties, or to determine a number of parameters regarding the performance of several components. New and very interesting results were obtained, which show the impact of the input parameters of the individual cycles on the performance parameters of a certain combined plant’s cycle. The optimized parameters are of a great practical influence on the application and running condition of the real combined plants. Such influence manifested itself in higher rate of heat recovery, higher combined plant thermal efficiency from those of the individual plants, less harmful emission, better fuel economy and higher power output. Lastly, it could be claimed that various concluding remarks drawn from the current study could help to improve the understanding of the behaviour of the combined cycle and help power plant designers to reduce the time, effort and cost of prototyping.

This report describes the development and testing of the upgraded Control and Monitoring (C&amp;Mu) system for the TOFOR neutron spectrometer. TOFOR is currently performing plasma diagnostics for the JET experimental fusion reactor. The purpose of the C&amp;Mu system is to enable monitoring of the amplitude dependent time delays of TOFOR. In order to perform this monitoring function the C&amp;Mu system must comprise a pulsed light source with variable intensity and a reference time signal. In this work a reference time signal has been retrieved from a laser comprising a motorized polarizer. This has been accomplished by installing a photomultiplier tube and a beamsplitter cube. The beamsplitter cube splits the laser light into two parts and directs one part into the photomultiplier tube. The photomultiplier tube converts the light into an electrical reference time signal. A control program has been developed for the motorized polarizer, enabling the user to vary the intensity of the light over the interval from 0% to 100%. The C&amp;Mu system has been performance tested and it was found that the time resolution of the system is about 0.1ns and the time stability of the system is about 0.12ns over 27 hours. The system is more than adequate to monitor variations in time delays at TOFOR of several nanoseconds, over a full JET day. The C&amp;Mu system is ready to be installed on TOFOR.