CHEMICAL ENGINEERING: Industrial Grade Salt Recovery from Zero Liquid Discharge Process

February 1, 2019

A process that increases the water-recovery from reverse osmosis (RO) while producing a salt byproduct is being developed by Hyrec (Urla/Izmir, Turkey; The process, which uses osmotically assisted RO (OARO), could be especially beneficial in coal-to-chemicals (CTC) plants in China, which require large volumes of water, but are in water-stressed regions, says business development specialist Günseli Mendi. The process can also be used for concentrating waste brines generated in other industries, such as textiles, mining, and oil and gas, she says.

In OARO (diagram), permeate flows from the high-pressure side to the low-pressure side of the membrane, as in standard RO. However, unlike RO, OARO employs two feed streams. The first feed stream is the same RO feed stream, which is dewatered through the membranes, and leaves the module with increased concentration. Some part of this concentrated stream is then recycled back to the opposite side of the membranes as a second feed stream, diluted through the membranes and leaves the module with decreased concentration. The reduced osmotic-pressure difference between the feed and the permeate sides allows the treatment of ultra-saline feeds at pressures as low as 70 bars. Thus, OARO’s maximum recovery is not limited by the burst pressure of standard RO membranes, says Mendi.

Hyrec’s OARO process extends the range of RO to very high salinities, salinity ranges that have been dominated by thermal systems. Hyrec can concentrate brine up to saturation levels from a saline influent of about 40,000 parts per million (ppm) total dissolved solids (TDS), at a hydrostatic pressure of 70 bars. In such cases, it consumes approximately 6 kWh/m3 of recovered water. The OARO method significantly decreases operational and capital costs, compared to conventional electrodialysis, forward osmosis and mechanical vapor compression for brine concentration, says the company.

Since February 2018, Hyrec has been operating a near commercial-sized plant with a feed capacity of 7.35-m3/h. Industrial scale projects are expected to take place in conjunction with commercial partners from the U.S., Indonesia, Kuwait, Japan, India and Germany in mid-2019. “We plan to be in a fully commercial stage by the end of 2019,” says Mendi.

Originally  published for the Feb. 1 of “Chemical Engineering” magazine: