Recovery of mineral salts and potable water from desalting plant effluents by evaporation. Part II. proposed simulation system for salt recovery

Salt recovery from rejected brines of the Al-Khobar Water Desalination Plant, Saudi Arabia, is studied through the simulation of a modified MSF system. Two phases of concentrations are planned: Phase I will concentrate the main effluent from 6.4 wt% total salt to 28.8%, while Phase II will use the effluents from Phase I as a feed to undergo further evaporation and cooling. NaCl and water are produced throughout this phase, while the end residue product will be essentially MgCl2, since it is the most soluble. A mathematical model is developed and used to perform stage-to-stage material and heat balance calculations. Concentrations of NaCl and MgCl2 in the streams entering and leaving a stage are determined by using the solubility correlation developed in Part I. Simulation results show that by using 5210 tons/h brine as a feed for Phase I, we can recover 4430 tons/h fresh water, 277 tons/h NaCl, and 502 tons/h bittern (in which the ratio of MgCl2/NaCl is increased to 12) as the very final products of the integrated scheme. This bittern provides 30 tons/h MgCl2 as an end product.