Approach to carbon dioxide capture and storage at ambient conditions

Carbon dioxide (CO2) capture and storage experiments were conducted at ambient conditions in varying weight % sodium carbonate (Na2CO3) solutions. Experiments were conducted to determine the optimal amount of Na2CO3 in solution for CO2 absorption. It was concluded that a 2% Na2CO3 solution, by weight, was the most efficient solution. The 2% Na2CO3 solution is able to absorb 0.5 g CO2/g Na2CO3. These results led to studies to determine how the gas bubble size affected carbon dioxide absorption in the solution. Studies were conducted using ASTM porosity gas diffusers to vary the bubble size. Gas diffusers with porosities of fine, medium, and extra coarse were used. Results found that the medium porosity gas diffuser was the most efficient at absorbing CO2 at 50%. Variation in the bubble size concluded that absorption of carbon dioxide into the sodium carbonate solution does depend on the bubble size, thus is mass transfer limited. Once the capture stage was optimized (amount of Na2CO3 in solution and bubble size), the next step was to determine if carbon dioxide could be stored as a calcium carbonate mineral using calcium rich industrial waste and if the sodium carbonate solution could be simultaneously regenerated. Studies of CO2 sequestration at ambient conditions have shown that it is possible to permanently sequester CO2 in the form of calcium carbonate using a calcium rich industrial waste. Studies have also shown that it is possible to regenerate a fraction of the sodium carbonate solution.

HEALTH AND SAFETY ISSUES IN THE WORKPLACE: THE CASE OF CAMEROON TEA ESTATE (CTE), A RISK COMMUNICATION APPROACH

In 2002, motivated largely by the uncontested belief that the private sector would operate more efficiently than the government, the government of Cameroon initiated a major effort to privatize some of Cameroon’s largest, state-run industries. One of the economic sectors affected by this privatization was tea production. In October 2002, the Cameroon Tea Estate (CTE), a privately owned, tea-cultivating organization, bought the Tole Tea Estate from the Cameroon Development Corporation (CDC), a government-owned entity. This led to an increase in the quantity of tea production; however, the government and CTE management appear not to have fully considered the risks of privatization. Using classical rhetorical theory, Richard Weaver’s conception of “god terms” (or “uncontested terms”), and John Ikerd’s ethical approach to risk communication, this study examines risks to which Tole Tea Estate workers were exposed and explores rhetorical strategies that workers employed in expressing their discontent. Sources for this study include online newspapers, which were selected on the basis of their reputation and popularity in Cameroon. Analysis of the data shows that, as a consequence of privatization, Tole Tea Estate workers were exposed to three basic risks: marginalization, unfulfilled promises, and poor working conditions. Workers’ reactions to these risks tended to grow more emotional as management appeared to ignore their demands. The study recommends that respect for labor law, constructive dialogue among stakeholders, and transparency might serve as guiding principles in responding to the politics of privatization in developing countries.

RAPID SPACE TRAJECTORY GENERATION USING A FOURIER SERIES SHAPE-BASED APPROACH

With the insatiable curiosity of human beings to explore the universe and our solar system, it is essential to benefit from larger propulsion capabilities to execute efficient transfers and carry more scientific equipment. In the field of space trajectory optimization the fundamental advances in using low-thrust propulsion and exploiting the multi-body dynamics has played pivotal role in designing efficient space mission trajectories. The former provides larger cumulative momentum change in comparison with the conventional chemical propulsion whereas the latter results in almost ballistic trajectories with negligible amount of propellant. However, the problem of space trajectory design translates into an optimal control problem which is, in general, time-consuming and very difficult to solve. Therefore, the goal of the thesis is to address the above problem by developing a methodology to simplify and facilitate the process of finding initial low-thrust trajectories in both two-body and multi-body environments. This initial solution will not only provide mission designers with a better understanding of the problem and solution but also serves as a good initial guess for high-fidelity optimal control solvers and increases their convergence rate. Almost all of the high-fidelity solvers enjoy the existence of an initial guess that already satisfies the equations of motion and some of the most important constraints. Despite the nonlinear nature of the problem, it is sought to find a robust technique for a wide range of typical low-thrust transfers with reduced computational intensity. Another important aspect of our developed methodology is the representation of low-thrust trajectories by Fourier series with which the number of design variables reduces significantly. Emphasis is given on simplifying the equations of motion to the possible extent and avoid approximating the controls. These facts contribute to speeding up the solution finding procedure. Several example applications of two and three-dimensional two-body low-thrust transfers are considered. In addition, in the multi-body dynamic, and in particular the restricted-three-body dynamic, several Earth-to-Moon low-thrust transfers are investigated.