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Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references and index.

<p>Environmental concerns about greenhouse gas emissions and energy security are the main drivers for the production of alternative fuels from bio-based feedstock. Dimethyl ether has attracted interest of many researches and is touted as “A fuel for the 21^st century” due to its versatility. However, the production of DME from biomass is dependent on the overall economics of its production.</p> <p>This thesis considers the application of semicontinuous distillation to improve the economics of the separation section in a biomass-to-DME facility. Semicontinuous distillation systems operate in a forced cycle to effect multiple separations using a single distillation column integrated with a middle vessel. The control system plays an integral role in the driving the forced cycle behaviour of the process in which no steady state exists.</p> <p>The separation section consists of a series of flash drums followed by a distillation train consisting of three (3) columns. In the first phase of this work, a semicontinuous system was developed to achieve the separation of the second and third distillation columns in the separation section. Rigorous models were used to simulate the semicontinuous system in which several control configurations were evaluated. The final control structure based on classic PI control was shown to achieve the specification objectives of the system and handle disturbances while avoiding weeping and flooding conditions. Optimization followed by an economic analysis showed that the semicontinuous system was economically preferable to the traditional continuous process for a range of DME production rates.</p> <p>Next, a semicontinuous system was developed to achieve the separation of the first and second distillation columns in the separation section. In this phase the application of semicontinuous distillation was extended to partial condenser configurations and the separation of biphasic mixtures. The control structure developed was effective in handling disturbance, attaining specification objectives while remaining with operational limits. An economic analysis, however, showed the traditional continuous configuration to be more economical for all DME production rates. Findings show that the operating cost is highly depending on the middle vessel purity so while uneconomical for this process it could result in favourable economics for less stringent purity specifications.</p> / Master of Applied Science (MASc)

A novel technique of drawing wire, i.e., dieless wire drawing, is described in which no conventional reduction dies are used. The wire is passed through a unit having stepped parallel bores filled with polymer melts, the smallest bore diameter being greater than the initial nominal wire diameter. The technique eliminates the need for a leader wire, prevents breakage during start-up, and eliminates the use of conventional reduction dies and, hence, the problem of die wear. An analysis has been developed for predicting the produced wire sizes for given drawing speeds, the pressure distribution within the unit and the drawing load during the drawing process. The performance of the drawing process is effected by means of the plasto-hydrodynamic action of the polymer melt within the unit. Heat is generated by mechanical dissipation during the drawing process. The effect of this upon the performance of the process is considered by coupling the energy equation into the analysis and allowing the polymer viscosity to be dependent on temperature. Agreement between the theory and experiment is found to be close. To further investigate the performance of the drawing process, an extensive experimental study has been undertaken, in which parameters such as drawing speeds, the temperature of the polymer and type of polymers are varied. Based on the theoretical and experimental results, a microcomputer-based control system for the dieless wire drawing process has been designed and built. A method with which the percentage reduction in area of the wire can be measured on line is proposed. Wires of desired qualities in terms of consistency in diameter over long lengths, or uniform change in area of the wire, are capable of being produced from the new system. A self-tuning controller for determinisic systems is proposed, which has the same structure as a conventional PID controller. The new self-tuning PID controller is based on a generalised self-tuning controller with pole assignment for deterministic systems. Simulation and experimental studies for several examples indicate that the new controller performs well and can be further improved to provide a fundamental method of tuning a PID controller.

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Thesis (DTech (Chemistry))--Cape Peninsula University of Technology, 2005 / A 2-factorial experiment, involving 3 levels of phosphorus (0, 40, and 80 kg P.ha-I ) as main treatment and 4 cropping systems (mono crop, maize/cowpea inter-row, maize/cowpea intra-row, and maize/cowpea intra-hole cropping) as sub-treatment was conducted in the field for 2 consecutive years in 2003 and 2004 to assess i) the effects of exogenous P supply and cropping system on the concentrations of plant-available nutrients in the rhizosphere of cowpea and maize; ii) the effect of exogenous P supply on tissue concentrations of minerals in nodulated cowpea and maize in mixed plant cultures iii) the effects of exogenous P supply and cropping system on plant growth and N2 fixation, and iv) the effects of exogenous P supply and cropping system on phosphatase activity and microbial biomass in the rhizosphere of cowpea and maize. At harvest, it was found that applying 40 or 80 kg P.ha-I significantly increased cowpea grain yields by 59-65% in 2003 and 44-55% in 2004. With maize, the increases in grain yield were 2037% in 2003 and 48-55% in 2004 relative to zero-P control. In both cropping seasons, the number of pod-bearing peduncles per plant, the number of pods per plant, the number of seeds per pod, and seed yield per cowpea plant were significantly increased with the application of exogenous P. In contrast, these parameters were all significantly depressed by mixed culture relative to mono crop cowpea. Intercropping maize with cowpea produced higher total yields per unit land area than the sole crop counterpart.