Patent Application
20240238727
Purification and concentration of salt brines is often required for industries such as chlor-alkali. Typically, purification is achieved chemically by processes such as softening, and dewatering is performed by evaporation. These processes are energy, chemical, waste, and capital intensive. The chlor-alkali industry requires sodium chloride feed solutions in excess of 250 part per thousand (ppt) with low levels of magnesium calcium, and sulfate. Removal of calcium and magnesium from the brine typically is achieved by the addition of Na2CO3 to form CaCO3 solid, followed by the addition of NaOH to form Mg(OH)2 solid. The solution must be filtered and acidified with HCl before use and a large amount of sludge is formed. Alternately, Ca and Mg can be removed by crystallization, but this requires expensive, energy consuming equipment, loses a portion of the NaCl, and produces a concentrated waste brine.
A membrane process for achieving high salt brines was described in U.S. Published Patent Application No. 20150014248 filed 11 Jul. 2014 to Herron, Beaudry and Lampi (Herron Membrane Process), which is incorporated herein, in its entirety, by this reference. The Herron Membrane Process is like reverse osmosis (RO) in that it uses high pressure to force water through a semipermeable membrane. RO is limited in the amount of water it can remove since commercial membrane systems are limited to pressures of at most 120 bar due to materials issues. This pressure can at most produce a 110 ppt NaCl solution because of the osmotic pressure of the solution. The membrane and process in the Herron Membrane Process uses a more permeable nanofiltration membrane that allows salt to slowly permeate through the membrane, which creates a saline permeate. The osmotic potential of salt on the permeate side allows more water to be forced from the feed solution so that the difference in osmotic pressures between the feed and the permeate is equal to the applied pressure.
It was proposed that a salt solution be dewatered as much as possible with RO then the RO retentate be fed to a series of nanofiltration elements at high pressure to produce a final retentate with osmotic pressures far above the applied pressure. The saline permeate is substantially less salty than the retentate, so the permeate can be dewatered by RO or returned to the feed of the nanofiltration elements.
The process of high pressure nanofiltration to concentrate salt brines, discussed in the Herron Membrane Process, is incorporated herein, in its entirety, by this reference. The Herron Membrane Process describes the equipment and transport equations pertinent to the concentration of single component brines to osmotic pressures higher than the applied osmotic pressure.
An additional provisional patent application No. 63/150,772 filed on 18 Feb. 2021 by Herron, Beaudry and Lampi which describes energy and equipment savings by the appropriate reinjection of nanofiltration permeate is also incorporated, in its entirety, by reference.
The high-pressure nanofiltration process can also be used to purify salt streams. Of particular interest to the chlor-alkali industry, is the separation of calcium, magnesium, and sulfate impurities from high concentration sodium chloride solutions. In the nanofiltration process, divalent cations such as Ca++, Mg++ and SO4− permeate the membrane much more slowly than monovalent cations such as Na+ and Cl− so during the process, the ratio of divalent to monovalent cations increases in the retentate and decreases in the permeate. This has been applied to the reduction of magnesium in brines for the solar evaporation harvesting of lithium from salar ponds. A PCT International Patent Application No. PCT/US2020/058879 filed on 4 Nov. 2020 directed to the above subject matter is incorporated herein, in its entirety, by this reference.
Concentration and purification of brines for the chlor-alkali industry is a useful example of the benefits of the process. In the Middle East, electricity costs are low and numerous seawater desalination installations produce large amounts of brine which are expensive to dispose of. It has been proposed to concentrate the desalination brine to use as a feed to chlor-alkali plants. Further concentration of the brine has the added benefit of recovering more water from the seawater.
Removal of calcium, magnesium and sulfate from chlor-alkali feed brine is valuable in that it reduces fouling of chlor-alkali electrocells and reduces the amount of concentrated NaCl brine that must be purged.
Embodiments disclosed herein are directed to a three step combination of nanofiltration and reverse osmosis that can concentrate seawater or other mixed salt streams to high concentrations with low levels of calcium, magnesium and sulfate.
In one or more embodiments, a method of producing desalinated seawater includes nanofiltrating seawater to reduce calcium, magnesium, and sulfate therein, introducing permeate from the nanofiltration step as a feed to reverse osmosis followed by a progressive nanofiltration array, feeding the lower salinity permeate from the introducing permeate step to another reverse osmosis (RO) system, and feeding retentate from the feeding step to a progressive nanofiltration system that concentrates the brine to an appropriate salinity.
More particularly, the first step of the process includes nanofiltration of seawater to reduce calcium, magnesium, and sulfate. Numerous species such as strontium, phosphate, and silica are also reduced, but they are of less importance to the quality of the chlor-alkali brine extracted from seawater.
The second step is the introduction of the permeate from the first step as the feed to reverse osmosis followed by a progressive nanofiltration array. The second step feed is concentrated to a small volume of high strength brine with a high proportion of divalent ions. The permeate from the second step nanofiltration membranes becomes the feed to the third step. Water from the RO membranes is suitable for industrial or municipal use.
The third step feeds the lower salinity permeate from the second step nanofiltration to another RO system. The retentate from the step three RO is fed to a progressive nanofiltration system which concentrates the brine to an appropriate salinity. Permeate from the step three nanofiltration elements, as well as the high salinity permeate from step two nanofiltration, are fed to either the step three RO or to appropriate places in the step three nanofiltration train.
In an embodiment, a method of producing desalinated seawater includes nanofiltrating seawater to reduce calcium, magnesium, and sulfate therein. The method includes introducing permeate from the nanofiltration step as a feed to a first reverse osmosis system followed by a first progressive nanofiltration array, thereby forming a lower salinity permeate and a higher salinity permeate having a salinity greater than the lower salinity permeate. The method includes feeding the lower salinity permeate to a second RO system, thereby forming a retentate. The method includes feeding the retentate from the second RO system to a second progressive nanofiltration system that concentrates brine in the retentate to within at least a predetermined salinity.
In an embodiment, a system for reducing at least one of magnesium, calcium and/or sulfate from sodium chloride brine is disclosed. The system includes a first NF system positioned to receive at least filtered seawater fed by a pump, and configured to produce a first retentate and a first permeate. The system includes a first RO system positioned to be fed the first permeate from the first NF system and configured to produce at least a second retentate and desalinated water. The system includes a second NF system positioned to be fed the second retentate from the first RO system and configured to produce one or more additional permeates. The system includes a second RO system positioned to be fed at least one permeate of the one or more additional permeates from the second NF system to produce at least a fourth retentate and additional desalinated water. The system includes a third NF system positioned to be fed at least the fourth retentate from the second RO system to produce one or more further permeates and a final retentate that is substantially free of divalent ions.
In an embodiment, a method for reducing at least one of magnesium, calcium and/or sulfate from sodium chloride brine is disclosed. The method includes feeding at least filtered seawater to a first NF system, thereby producing a first retentate and a first permeate. The method includes feeding the first permeate from the first NF system to a first RO system, thereby producing at least a second retentate and desalinated water. The method includes feeding the second retentate from the first RO system to a second NF system, thereby producing one or more additional permeates. The method includes feeding at least one permeate of the one or more additional permeates from the second NF system to a second RO system, thereby producing at least a fourth retentate and additional desalinated water. The method includes feeding at least the fourth retentate from the second RO system to a third NF system, thereby producing one or more further permeates and a final retentate that is substantially free of divalent ions.
Features from any of the disclosed embodiments may be used in combination with one another, without limitation. In addition, other features and advantages of the present disclosure will become apparent to those of ordinary skill in the art through consideration of the following detailed description and the accompanying drawings.
The drawings illustrate several embodiments of the present disclosure, wherein identical reference numerals refer to identical or similar elements or features in different views or embodiments shown in the drawings.
Embodiments disclosed herein are related to systems and methods for reducing one or more (e.g., all) of magnesium (Mg), calcium (Ca), and/or sulfate (SO4) from sodium chloride (NaCl) brine during concentration by high-pressure nanofiltration. In at least one, some, or all embodiments, a combined, three-stage, nanofiltration (NF)/reverse osmosis (RO) system separates a mixed salt solution (e.g. feed solution) into water, streams of combined mixed salts, and a concentrated salt solution substantially free of divalent ions. The feed solution is seawater, according to an embodiment. The concentrated salt solution that is substantially free of divalent ions results in the technical of effect of providing feedstock for industrial processes and/or the chlor-alkali industry.
In at least one, some, or all embodiments, a method of producing desalinated seawater includes nanofiltrating seawater to reduce calcium, magnesium, and sulfate therein. The method also may include introducing permeate from the nanofiltration step as a feed to reverse osmosis followed by a progressive nanofiltration array. The method also may include feeding the lower salinity permeate from the introducing permeate step to another RO system. The method also may include feeding retentate from the feeding step to a progressive nanofiltration system that concentrates the brine to an appropriate salinity.
The model of the behavior of multiple species can predict the behavior of only two species (along with chloride). The modeling procedure was to first to estimate the removal of sulfate by treating all cations as sodium. This analysis showed sulfate is largely removed in the first step and the modeling was performed by ignoring sulfate, lumping sodium and potassium, calcium and magnesium, and modeling the water as a two-cation solution. The model also assumes that nanofiltration elements are selected with permeabilities that provide a constant flux of 10 liters/m2/hr (lmh). It was assumed that all elements are 8040 spiral wound design with 40 m2 membrane.
In at least one, some, or all embodiments, an antiscalant is added to the seawater, and the resulting initial solution is fed to banks of NF elements operating at 40 bar pressure in a first NF system 110 that produces a retentate (e.g., a concentrate) and a first permeate (A). The antiscalant may include a dianionic polyelectrolyte (DAPE), such as poly[disodium 3-(N,N-diallylamino)propanephosphonate. The retentate from the first NF system 110 is high in divalent ions and is disposed of. The first permeate (A) from the first NF system 110 passes on to a second step 200 of the process, shown in
In an example, the schematic modeled in
The schematic modeled in
Turning now to
More specifically, the second step 200 starts with the first permeate (A) from the first step 100 pumped (e.g., at about 70 bar) to the first RO system 250, which produces water or other solution (e.g., about 114 m3/hr of water), according to an embodiment. The flow of the second retentate from the first RO system 250 may be about 51.4 m3/hr and have salinity higher (e.g., 71.6 ppt) than the first permeate (A) fed to the first RO system 250, according to an embodiment. The second NF system 210 of the second step 200 passes the second retentate from the first RO system 250 through multiple (e.g., three) arrays of NF elements, according to an embodiment. The first array 211 of NF elements in the second NF system 210 may include 7 banks in parallel with 8 elements per bank. The second array 212 of NF elements in the second NF system 210 may include three banks in parallel, each having 16 elements in series. The third array 213 of NF elements in the second NF system 210 may include a single bank of 16 elements in series.
The first array 211 of NF elements in the second NF system 210 produces a retentate that leaves (e.g., at about 29 m3/hr) the first array 211 of NF elements in the second NF system 210 having a higher salinity (e.g. about 107 ppt) than the second retentate fed into the first array 211 of NF elements in the second NF system 210. The second array 212 of NF elements in the second NF system 210 produces a retentate that leaves (e.g., at about 9.8 m3/hr) the second array 212 of NF elements in the second NF system 210 having a higher salinity (e.g., about 170 ppt) than the retentate from the first array 211 of NF elements in the second NF system 210 that is fed to the second array 212 of NF elements in the second NF system 210. The third array 213 of NF elements in the second NF system 210 produces a third retentate that leaves (e.g., at about 3.4 m3/hr) the third array 213 of NF elements in the second NF system 210 having a salinity (e.g., 230 ppt) higher than the retentate from the second array 212 of NF elements in the second NF system 210 that is fed to the third array 213 of NF elements in the second NF system 210. The level of Mg (e.g., 7 ppt) in the third retentate may be at least 5 times, at least 10 times, or at least 15 times greater than the level of Mg (0.5 ppt) in the second retentate fed into the second NF system 210. Substantially all of the sulfate (e.g., at least about 75%, at least about 90%, or at least about 99% of the sulfate) which permeated the first NF system 110 (e.g., in the first permeate) in the first step 100 is in the third retentate.
The permeate from the first array 211 of NF elements in the second NF system 210 and the permeate from the second array 212 of NF elements in the second NF system 210 are combined to produce an third permeate (C) having a flow (e.g., of about 41.6 m3/hr) and a salinity (e.g., about 48.8.ppt) higher than the salinity (about 22.2 ppt) of the first permeate fed into the first RO system 250 but lower than the salinity (about 71.6 ppt) fed into the first array 211 of NF elements of the second NF system 210. The permeate from the first array 211 of NF elements in the second NF system 210 may have a lower salinity (e.g., 26 ppt) than the salinity (e.g., about 75.3) of the permeate from the second array 212 of NF elements to which the permeate from the first array 211 of NF elements is combined. The second permeate (B) from the third array 213 of NF elements of the second NF system 210 is produced (e.g., about 6.4 m3/hr) having a higher salinity (e.g., 139 ppt) than the third permeate, as well as a higher salinity than the second retentate fed into the first array 211 of NF elements in the second NF system 210. Both the second permeate (B) and the third permeate (C) streams are passed to the third step 300 the process, shown in
Turning now to
More specifically,
In some embodiments, the third step 300 of
In some embodiments, the fourth retentate from the second RO system 350 is combined with a higher salinity fifth permeate from another portion of the third NF system 310 (e.g., from the second array 312 of NF elements in the third NF system 310) to form a feed (e.g., about 127.8 m3/hr) for the third NF system 310 having a higher salinity (e.g., about 83.7 ppt) than the salinity (e.g., about 48.8 ppt) of the third permeate, the salinity (e.g., about 43.3 ppt) of the feed for the second RO system 350, and/or the salinity (e.g., about 68 ppt) of the fourth retentate output by the second RO system 350. The third NF system 310 may include multiple (e.g., three) arrays of NF elements. In some embodiments, the first array 311 of NF elements of the third NF system 310 has 18 banks of elements with 8 elements in series per bank. This first array 311 of NF elements in the third NF system 310 may produce (e.g., at about 57.6 m3/hr) the fourth permeate having a salinity (e.g., about 39.4 ppt) lower than the feed for the first array of NF elements 311 in the third NF system 310. This first array 311 of NF elements in the third NF system 310 also may produce (e.g., about 70.2 m3/hr) a retentate having a salinity (e.g., about 120 ppt) higher than the salinity (e.g., about 48.8 ppt) of the third permeate, the salinity (e.g., about 43.3 ppt) of the feed for the second RO system 350, the salinity (e.g., about 68 ppt) of the fourth retentate output by the second RO system 350, and/or the salinity (e.g., about 83.7 ppt) of the feed for the first array 311 of NF elements in the third NF system 310.
The retentate from the first array 311 of NF elements in the third NF system 310 may be combined with the (high salinity) second permeate (B) from the second step 200 to feed the second array 312 of NF elements in the third NF system 310. A sixth permeate from the third array 313 of NF elements of the third NF system 310 also may be combined with at least one (e.g., both) of second permeate (B) and the retentate from the first array 311 of NF elements of the third NF system 310 to create a feed (e.g., about 98 m3/hr) for the second array 312 of NF elements in the third NF system 310 having a higher salinity (e.g., about 131 ppt) than the retentate first array 311 of NF elements in the third NF system 310. The second array 312 of NF elements in the third NF system 310 may include 9 banks of NF in parallel with 18 elements in series per bank. The second array 312 of NF elements of the third NF system 310 may produce (e.g., about 64.8 m3/hr) a fifth permeate having a salinity (e.g., about 99 ppt) less than the salinity (e.g., about 131 ppt) of the feed for the second array 312 of NF elements in the third NF system 310. The second array 312 of NF elements of the third NF system 310 also may produce (e.g., about 33.2 m3/hr) a retentate having a salinity (e.g., about 194 ppt) that is greater than the salinity (e.g., about 131 ppt) of the feed for the second array 312 of NF elements in the third NF system 310.
The retentate from the second array 312 of NF elements of the third NF system 310 may be fed to the third (e.g., last) array 313 of NF elements in the third NF system 310, which may include 3 banks in parallel and with each bank having 18 elements in series. The third array 313 of NF elements in the third NF system 310 may produce (e.g., about 21.6 m3/hr) a sixth permeate having a salinity (e.g., about 164 ppt) that is less than the salinity (e.g., about 194 ppt) of the feed for the third array 313 of NF elements in the third NF system 310, but greater than the salinity (e.g. about 139 ppt) of the second permeate (B) and greater than the salinity (e.g., about 48.8) of the third permeate (C). The third array 313 of NF elements in the third NF system 310 also may produce (e.g., about 11.6 m3/hr) a fifth (or final) retentate having a salinity (e.g. about 250 ppt) at least about four times or five times greater than the salinity of the initial solution, at least about 1.5 times greater than the salinity (e.g. about 139 ppt) of the second permeate, and/or at least about four or five times greater than the salinity (e.g., about 48.8) of the third permeate (C). The magnesium concentration in the final retentate may be about 0.1 ppt or less.
Considering the system as a whole, in an example, 238 m3/hr seawater is separated into 150 m3/hr water, 11.6 m3/hr 250 ppt NaCl, 3.4 m3/hr mixed salts at 230 ppt, and 72 m3/hr of mixed salt at 89 ppt. The total power consumption, assuming 80% efficient pumps, is 1180 KW.
Features from any of the disclosed embodiments may be used in combination with one another, without limitation. In addition, other features and advantages of the present disclosure will become apparent to those of ordinary skill in the art through consideration of the following detailed description and the accompanying drawings.
As used herein, the term “about” or “substantially” refers to an allowable variance of the term modified by “about” or “substantially” by ±10% or ±5%. Further, the terms “less than,” “or less,” “greater than,” “more than,” or “or more” include, as an endpoint, the value that is modified by the terms “less than,” “or less,” “greater than,” “more than,” or “or more.”
While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting.
This application claims priority to U.S. Provisional Patent Application No. 63/155,494 filed on Mar. 2, 2021, the disclosure of which is incorporated herein, in its entirety, by this reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/018350 | 3/1/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63155494 | Mar 2021 | US |
