Dual brine concentration for the beneficial use of two concentrate streams from desalination plant - Concept proposal and pilot plant demonstration

Abstract

A dual brine concentration concept is proposed and proved in a pilot plant demonstration with commercial membranes. To utilize the dissolved ions in seawater (45,000 mg/L) effectively for various applications, a nanofiltration (NF) system is introduced in the upstream of the reverse osmosis (RO) system, and a membrane brine concentration (MBC) system is introduced after RO to concentrate the RO brine to the desired point, i.e., 15 wt% (166,000 mg/L) and higher. In the proposed NF-RO-MBC system two valuable brines are produced: 1) Concentrate 1, which is highly concentrated and purified monovalent ion stream at a TDS of about 170,000 mg/L after HPRO and 2 stage OARO, and 2) Concentrate 2, which has a high concentration of divalent ions, such as 3.41 times the Ca and 5.17 times the Mg concentration compared to those in seawater. Based on the successful pilot demonstration data and performance evaluation of a novel NF membrane and a single OARO module, a commercial-scale NF-RO-MBC system was designed for the capacity of 1 mil. dry ton/year production of NaCl salt in the form of 169,000 mg/L concentrated brine. With the proposed configuration, 65.2 % of the seawater will be recovered as fresh water, 19.3 % will be Concentrate 1, and the remainder 15.5 % will be Concentrate 2. The specific electricity consumption of the NF-RO-MBC system is estimated as 6.90 kWh/t of the fresh water produced, and the techno-economic analysis estimated the production cost of fresh water as 0.57 USD/m3 and that of NaCl brine as 28.87 USD/dry t NaCl.