Concentrated solar power development for milk pasteurization in rural South Africa

Mallet, James (2019-03)

Thesis (MEng)--Stellenbosch University, 2019.


ENGLISH ABSTRACT: This thesis explains the designs, technologies and testing procedures used to develop a low-cost parabolic solar reflector unit for the pasteurization of raw milk. Throughout Southern Africa there are large portions of the population that rely on milk as a source of nutrition and income. However, for those that do not have access to adequate infrastructure including electricity, this can pose challenges. Raw milk can be home to significant amounts of bacteria and pathogens, which can cause it to be potentially unsafe for consumption. Raw milk will also spoil in a short space of time, if not treated properly. The process of milk pasteurization involves heating it to specific temperatures for certain periods of time, and by doing so bacteria can be destroyed, increasing the lifespan of the milk. The energy required for this heating process can be problematic or resource dependant, but fortunately solar energy is abundant in Southern Africa. By utilizing a solar concentrating device, the energy needed for heating can be obtained directly from the sun at zero cost. A parabolic trough was designed to perform this function, which allows for continuous flow pasteurization. An important component in such a system is the receiver tube solar absorber coating, which is responsible for absorbing the concentrated energy. For this reason, additional analyses was done on a commercial selective solar absorber, black spray paint and a candle soot coating as potential low cost receiver tube coatings. These were characterized using UV-vis-NIR and Raman spectroscopy, HR-SEM, HR-TEM, EDS and XRD. The parabolic trough system was tested by heating water to the temperatures necessary for pasteurization. Each of the receiver tube solar absorber coatings were used, and temperatures above 75 °C were achieved with all of them. The system was then tested using milk, and the same temperature ranges were obtained, allowing the milk to be successfully pasteurized.

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