Solar pond optimization for improved salt production at lake Katwe, Uganda

Abstract

Salt mining and extraction have been existing in Uganda for a long period of time based on traditional methods. The salt is currently extracted in three salt mining sites i.e. Lake Katwe, Lake Kibiro and Lake Kasenyi. Among the three active mining sites, mining operations at Lake Katwe is vast and is a very highly rich salt mineral lake on a renewable basis. The salts are recoverable through over 10,000 salt pans located around the periphery of the lake which vary in surface area from less than 24 m 2 to around 400 m 2 , and in depth from 0.3 to 1 m. The salt pans employ rudimentally techniques and are set up haphazardly without any scientific guidelines which compromises the annual throughput from the solar salt works. In order to improve the design of the salt pans, the heat transfer dynamics of the salt pan have been numerically and experimentally studied in this research to optimize the salt pan depth. A representative salt pan located at the shores of Lake Katwe with a surface area of 62 m 2 and a depth of 0. 2 m was used in this study. The numerical model was implemented in the OpenFOAM software known as OpenFOAM6 where a 3D heat transfer salt pan model was studied using the Finite Volume Method under Lake Katwe climatic conditions. The model was governed by continuity, salt concentration, momentum, energy equations and the Boussinesq approximation. A field experiment that determined the temperature variation with depth and brine physical chemical properties was conducted for 5 consecutive days. The correctness of the model results was verified against experimental data. During the experimental study, the salt concentration of the salt pan brine remained constant and uniformly distributed. The density of the salt pan showed a relatively small change with time. The numerical simulation model revealed a thermal stratification along the salt pan depth and the salt concentration significantly remained constant with time. The top surface of the salt pan showed the lowest brine temperature (296.7 K) compared to the temperature (301.4 K) at the bottom. The model and the experimental salt concentration and temperature profiles were found

14 to be in good agreement. The sensitivity analysis on the effect of the salt pan depth on brine temperature was studied. It was revealed that the shallower the salt pan, the higher the rate of heat loss. This study revealed that an optimum salt pan depth to yield a higher salt quantity under Lake Katwe climatic conditions was at 0.1 m.