Viability assessment of enhancing dry cooling systems using thermal storage ponds
Master Thesis
2014
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University of Cape Town
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Abstract
Dry cooled systems are employed to reject heat in modern power plants. Unfortunately, these cooling systems become less effective under windy conditions and when ambient temperatures are high. One proposed solution to this problem is to augment the cooling capacity of the dry cooled system by means of utilizing evaporative cooling ponds which can be operated in parallel during adverse ambient conditions. This study investigates a concept for a South African power station. The system utilises waste-water from evaporation ponds which will supply a surface condenser connected in parallel to the dry cooled system. The development of this system requires an accurate model to predict the transient thermal response of the pond. No such pond model is available in open literature due to the pond under consideration having a unique size as well as size to depth ratio. Various heat transfer modes are numerically modelled for large evaporation ponds, including free surface evaporation which is a transient and complex phenomenon. Evaporation at the surface is the primary heat and only mass transfer driver. The modified Ryan equation proposed by an experimentally validated study was used to estimate evaporation on the surface. Convection is modelled using a correlation that was derived and experimentally tested for applications in the natural environment. Heat transfer via conduction to the ground is solved using a one dimensional finite difference solution to the heat conduction equation, and radiation is modelled using widely accepted correlations. These correlations were coupled and implemented into a computer model using C++. Through numerical analysis the relevance and accuracy of each transfer mode was rigorously analysed. Once validated, the intended loading conditions at the power station were imposed onto the pond model in order to assess its cooling viability. It is concluded that the pond not only poses a sustainable and environmentally neutral cooling augmentation device, but is also cost effective.
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Includes bibliographical references
Reference:
Gosai, P. 2014. Viability assessment of enhancing dry cooling systems using thermal storage ponds. University of Cape Town.