Most biodiesel plants operate batch-wise using homogeneous alkali catalysts. Recently, several heterogeneous catalysts have been suggested in literature, as they have shown potential for overcoming most of the challenges associated with the application of homogeneous catalysts. Previous published techno-economic comparisons of the two technologies on large-scale processes located in the developed world, have revealed the economic superiority of heterogeneously catalysed processes. Hence, prospect exists for current homogeneously catalysed process plants to be converted to heterogeneously catalysed ones. The objective of this research was to investigate the actual cost benefit of converting a small-scale batch biodiesel plant from homogeneous to heterogeneous catalysed process. For this purpose, a small-scale batch biodiesel plant located in South Africa was taken as the base case homogeneous process. Aspen Batch Process Developer® software was used to perform the process simulations. The homogeneous process was converted to the heterogeneous one and results from process simulation were used to evaluate the economics of both processes, which were compared in terms of fixed capital cost, total manufacturing cost and profitability indicators. During economic evaluation, two types of cost factors were used: one prevailing in developed world and the other one relevant to South Africa. The sensitivity analysis of both processes was further performed in order to investigate the impact of some uncertain parameters on their profitability. Finally, a debottlenecking study was carried out. Results obtained from this study showed an increase in the annual throughput of biodiesel as well as significant savings in the total capital cost for the heterogeneous catalysed process relative to the homogeneous one. As regards the estimation of the total unit manufacturing cost of biodiesel, significant differences arose when using the two types of cost factors. Results of economic analyses estimated using cost factors relative to South Africa suggest an increase in the unit manufacturing cost of biodiesel while using the developed world’s cost factors suggests the opposite. This is due to the higher raw material and energy requirement for the CaO process, while knowing that the direct costs are a bigger proportion of the manufacturing costs estimated using the South African cost factors. Profitability and sensitivity analyses only provided positive results when estimated using the South African cost factors. In all cases, the heterogeneous catalysed process was found to be more promising than the homogeneous one over the prescribed project life. The study showed the importance of using cost factors relevant to a particular economic environment during techno-economic assessment of a process. It was also shown that there are economic benefits when replacing settling with centrifugation in biodiesel production processes. In summary, this thesis makes some important contributions. It presents the first process simulation for biodiesel production using Aspen Batch Process Developer® software and thereby proposes a methodology that is currently scarce in the literature. It also reports the first techno-economic analysis applied to the biodiesel field in South Africa and provides a preliminary insight to owners of biodiesel plants as regards the decision to convert or not their homogeneous catalysed plant to heterogeneous one.

Thesis submitted in fulfilment of the requirements for the degree Master Technologiae: Chemical Engineering In the Faculty of Engineering at Cape Peninsula University of Technology / Most biodiesel plants operate batch-wise using homogeneous alkali catalysts. Recently, several heterogeneous catalysts have been suggested in literature, as they have shown potential for overcoming most of the challenges associated with the application of homogeneous catalysts. Previous published techno-economic comparisons of the two technologies on large-scale processes located in the developed world, have revealed the economic superiority of heterogeneously catalysed processes. Hence, prospect exists for current homogeneously catalysed process plants to be converted to heterogeneously catalysed ones. The objective of this research was to investigate the actual cost benefit of converting a small-scale batch biodiesel plant from homogeneous to heterogeneous catalysed process. For this purpose, a small-scale batch biodiesel plant located in South Africa was taken as the base case homogeneous process. Aspen Batch Process Developer® software was used to perform the process simulations. The homogeneous process was converted to the heterogeneous one and results from process simulation were used to evaluate the economics of both processes, which were compared in terms of fixed capital cost, total manufacturing cost and profitability indicators. During economic evaluation, two types of cost factors were used: one prevailing in developed world and the other one relevant to South Africa. The sensitivity analysis of both processes was further performed in order to investigate the impact of some uncertain parameters on their profitability. Finally, a debottlenecking study was carried out. Results obtained from this study showed an increase in the annual throughput of biodiesel as well as significant savings in the total capital cost for the heterogeneous catalysed process relative to the homogeneous one. As regards the estimation of the total unit manufacturing cost of biodiesel, significant differences arose when using the two types of cost factors. Results of economic analyses estimated using cost factors relative to South Africa suggest an increase in the unit manufacturing cost of biodiesel while using the developed world’s cost factors suggests the opposite. This is due to the higher raw material and energy requirement for the CaO process, while knowing that the direct costs are a bigger proportion of the manufacturing costs estimated using the South African cost factors. Profitability and sensitivity analyses only provided positive results when estimated using the South African cost factors. In all cases, the heterogeneous catalysed process was found to be more promising than the homogeneous one over the prescribed project life. The study showed the importance of using cost factors relevant to a particular economic environment during techno-economic assessment of a process. It was also shown that there are economic benefits when replacing settling with centrifugation in biodiesel production processes. In summary, this thesis makes some important contributions. It presents the first process simulation for biodiesel production using Aspen Batch Process Developer® software and thereby proposes a methodology that is currently scarce in the literature. It also reports the first techno-economic analysis applied to the biodiesel field in South Africa and provides a preliminary insight to owners of biodiesel plants as regards the decision to convert or not their homogeneous catalysed plant to heterogeneous one.

The behavior of repairable equipment is often modeled under assumptions such as perfect repair, minimal repair, or negligible repair. However the majority of equipment behavior does not fall into any of these categories. Rather, repair actions do take time and the condition of equipment following repair is not strictly "as good as new" or "as bad as it was" prior to repair. Non-homogeneous processes that reflect this type of behavior are not studied nearly as much as the minimal repair case, but they far more realistic in many situations. For this reason, the quasi-renewal process provides an appealing alternative to many existing models for describing a non-homogeneous process. A quasi-renewal process is characterized by a parameter that indicates process deterioration or improvement by falling in the interval [0,1) or (1,Infinity) respectively. This parameter is the amount by which subsequent operation or repair intervals are scaled in terms of the immediately previous operation or repair interval. Two equivalent expressions for the point availability of a system with operation intervals and repair intervals that deteriorate according to a quasi-renewal process are constructed. In addition to general expressions for the point availability, several theoretical distributions on the operation and repair intervals are considered and specific forms of the quasi-renewal and point availability functions are developed. The two point availability expressions are used to provide upper and lower bounds on the approximated point availability. Numerical results and general behavior of the point availability and quasi-renewal functions are examined. The framework provided here allows for the description and prediction of the time-dependent behavior of a non-homogeneous process without the assumption of limiting behavior, a specific cost structure, or minimal repair. / Ph. D.