Fully integrated NF-thermal seawater desalination process and equipment
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Abstract
An optimal thermal seawater desalination process is disclosed, which combines two or more substantially different water pretreatment processes in a unique manner and in a special configuration, hereto unknown to prior desalination arts, to produce a high yield of high quality fresh water, including potable water. In this process a two stage NF membrane pretreatment unit (NF2) with an energy recovery turbo charger (TC) device in between the stages or equipped with an energy recovery pressure exchanger (PX) is synergistically combined with at least one thermal desalination unit to form a dual hybrid of NF2-Thermal (FIG. 4), or alternatively the two stage NF2 unit is synergistically combined with a two stage SWRO unit (SWRO2) with an energy recovery TC in between the stages or combined with one stage SWRO (SWRO1) equipped with an energy recovery TC or PX system and the reject from the SWRO2 or SWRO1 unit is made make-up to a thermal unit to form a tri-hybrid of NF2-SWRO2 reject-Thermal (FIG. 5). In both the cases of di- or trihybrids the thermal unit is equivalent to a multistage flash distillation (MSFD) or multieffect distillation (MED) or vapor compression distillation (VCD) or thermal reheat (RH) evaporator.
Typically a process of this invention using the two stage NF2 initial pretreatment step will perform a semi-desalination step by reducing feed TDS by about 35 to 50%, but most important, especially to the thermal seawater desalination process, it removes the water recovery limiting, scale forming hardness ions of Ca++ and Mg++ by better than 80% and their covalent anions of sulfate to better than 95% and bicarbonate to about 65%. The removal of scale forming hardness ions, especially SO4=, and bicarbonates allowed for the operation of thermal unit in the above hybrids at top brine temperature (TBT) much greater than its present TBT limit by the singular conventional process of 120° C. for MSFD and operation of MED or VCD or RH unit at TBT much higher than their present TBT limit of 65-70° C., with many advantages gained by this process over prior art sweater desalination processes. The process of this invention exceeds all prior thermal seawater desalination arts in efficiency, including water yield, product water recovery ratio and unit water cost as well as in energy consumption per unit product which is equivalent or less than other efficient prior art seawater thermal desalination processes. By this process, an NF product recovery ratio of 75 and 80% or better is achieved from the high salinity Gulf sea (TDS≈45,000 ppm) and about an equal product recovery ratio is also obtained from the SWRO or thermal unit when it is operated on NF product for a total water recovery ratio in excess of 52% for seawater
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Citations
62 Claims
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1. to 23. (canceled)
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24. An optimal desalination process in which saline water, containing a high concentration of hardness scale forming ionic species, microorganisms, particulate matter and a high concentration of total dissolved solids, TDS, is passed under pressure through a two stage nanofiltration membrane, NF2, units coupled via an energy recovery turbocharger, TC, unit placed in between the stages to produce a first water product, NF permeate, and NF reject, wherein the said first water product having reduced content of said ionic species and from which is removed microorganisms, particulate matter and scale forming hardness ions, but having all sulfate, SO4= and bicarbonate, HCO3−
- ions are nearly totally removed from it, and thereafter passing said first water product through a thermal seawater distillation, desalination, unit to produce from it a second water product, distillate, of potable quality and brine discharge, blow down.
- View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39)
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40. An optimal desalination process in which saline water, containing a high concentration of hardness scale forming ionic species, microorganisms, particulate matter and a high concentration of total dissolved solids, TDS, is passed under pressure through a two stage nanofiltration membrane, NF2, units which are coupled via an energy recovery turbocharger, TC, unit placed inbetween the two stages to produce a first water product, NF permeate, and NF brine reject, wherein the first water product having reduced content of said ionic species and from which is removed microorganisms, particulate matter and nearly all scale forming hardness ions, but having all sulfate, SO4=, and bicarbonate, HCO3−
- , ions are nearly totally removed from it, and thereafter passing said first water product through a two stage seawater reverse osmosis units, SWRO2, where the two stages are coupled via an energy recovery TC unit to produce from them, the SWRO2, a third water product, SWRO permeate, of potable quality and a fourth water SWRO reject, consisting of second stage SWRO reject, having increased salinity but drastically reduced hardness, and thereafter passing said fourth water product reject through a thermal distillation unit to form a second water product, distillate, of potable quality and a brine discharge blow down.
- View Dependent Claims (41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62)
Specification