Abstract
•Integration of a 10,000 m2 area solar pond in a salt work is investigated.•A mathematical model is used for LCZ temperature prediction.•A simple method is presented for salinity gradient development.•Economic and environmental benefits are evaluated through a parametric study.•Construction and operating costs of the solar pond are estimated.
The process of salt manufacture in a salt work in Sabzevar in Northeast Iran is presented. A multi-faceted application to integrate a salinity gradient solar pond as part of the salt work process is presented addressing the reduction of parasitic energy losses such as the energy used for salt rock crushing and saving the amount of fossil fuel (natural gas) needed for brine heating. The solar pond with an area of 100 × 100 m2 and depth of 3 m is proposed to be constructed on the site of salt work. A partitioning wall with some opening heights equal to the desired position of the interface of lower convective (LCZ) and non-convective zones (NCZ) in its lower section, divides part of the area of this pond, say 5 percent or 500 m2. The separated area is designated to act as a salt charger and salt storage. The rock salt deposited in the salt charger dissolves into the LCZ of the pond and produces hot saturated brine solution. Results indicate that 100 tons of pure salt may be obtained from the extraction of 320 m3 of hot saturated brine consisting of 73 wt% water and 27 wt% salt. This is the nominated daily salt production of the factory. The proposed system will help to streamline the process of salt manufacture and reduce the environmental footprint.
Using locally available meteorological data of Sabzevar, it is shown that such a pond may produce hot brine at an average temperature of 65 °C in summer and 37 °C in wintertime with a loading of 20% of the input irradiation. The gradient zone of the pond may be setup by placing a layer of low salinity water over saturated brine, allowing for salt diffusion to take place. Formation of large amplitude surface waves increases the salt diffusion and a salinity profile will develop in few months.
A parametric study was performed to assess the enviro and economic effects of the proposed 10,000 m2 solar pond. The amount of fresh water to be injected to the solar pond is calculated to compensate for evaporation of pond surface as well as production of concentrated brine containing 100 tons of salt per day. Computer simulation shows that about 59,000 MJ/day thermal energy may be extracted from the pond in June. This is equal to a saving of about 1,576 kg/day of methane. Considering the price of methane this would be a financial saving of 283 $/day. The rate of reduction in CO2 emission is estimated to be 4,335 kg/day in June. Considering a carbon price of 30 $/ton, the above reduction in CO2 will be equivalent to savings of 130 $/day related to the environment. These calculations are extended to all months of the year and results presented.
For demonstration, feasibility of using an existing old cylindrical fuel storage tank (2,000 m3, 3.3 m deep) as a container for a 600 m2 outdoor solar pond nearby the factory buildings, is proposed for pilot study. The shading effect is examined by scaling down a 3D model of the reservoir and its adjacent buildings for different months of the year, using Helidon device available at RMIT University of Australia. According to the simulation performed, it seems that the presence of buildings around the fuel tank does not have a significant shading effect on the surface of the demonstration solar pond.