DESC:FIELD OF INVENTION

[0001] The present invention is directed to a method for clarification of brine, and more particularly to an application of submerged membrane filtration system for the clarification of brine in chlor-alkali and other process industry.

BACKGROUND OF INVENTION

[0002]In a chloralkali industry caustic soda, chlorine, hydrogen are generally produced through membrane electrolysis process. The caustic soda lye or sodium hydroxide produced from the electrolyser will have a concentration in the range of 31- 33 %. This is further concentrated by evaporation to 47 – 48 %. As commonly known, the major raw materials required for producing caustic soda via membrane electrolysis process are power, water and industrial grade salt.

[0003]Industrial grade salt, containing calcium, magnesium, sulphate and insoluble as impurities, is dissolved in water and treated with chemicals for the removal of such impurities. Conventionally, in a membrane chloroalkali plant the sodium chloride brine which is the main raw material is purified with respect to calcium and magnesium impurities. During the purification steps, the soluble calcium and magnesium salts are made insoluble with the addition of sodium carbonate (soda ash)and sodium hydroxide (caustic soda).The precipitated impurities are allowed to settle in a clarifier. The over flow brine from the clarifier is passed through a media filter called the anthracite filter and finally polished with ultrafiltration or pre-coat filters that use alpha cellulose as pre-coat.

[0004] Hence, for the separation of these insoluble precipitates the treated brine undergoes various filtration steps before it is rendered suitable for feeding to the electrolysers. Furthermore, the brine is treated through ion-exchange resin columns to get ultrapure brine consisting of 290 – 305 gpl of sodium chloride. The purified brine is then fed to the electrolysers for the production of caustic soda, chlorine and hydrogen.

[0005]In order to overcome aforementioned limitations, there exists a need for requirement of a simplified process of brine filtration and treatment in chloroalkali industry that eliminates need of conventional anthracite filter, pre-coat filter or any pressurized membrane system, and obviate need for two stage filtration in the brine treatment cycle.

OBJECT OF THE INVENTION

[0006] The primary objective of the present disclosure is to provide a simplified, economical, sustainable and more efficient process and system of brine filtration and treatment in chloroalkali industry.

[0007] In one other objective of the present disclosure, a cost effective brine clarification process and system utilizing aspects of submerged membrane technology is proposed, which functions as an optimal substitute for conventional pre-coat filters by eliminating use of alpha cellulose or any other pressurized membrane system.

[0008] Another objective of the present disclosure is to provide a submerged membrane process and system for brine clarification having better antifouling, and mechanical properties.

[0009] Another objective of this disclosure is to provide a brine clarification process and system having reduced number of steps, excellent performance and high quality brine that gets directly processed without the anthracite, the ultrafiltration/pre-coat filter or any other pressurized membrane system.

[0010] Yet another objective of the disclosure is to provide an improved efficiency of electrolyzers by producing quality brine via submerged membrane clarification process.

[0011] Yet other objective of the present disclosure is to provide clarified brine obtained by a process that eliminated need of acid cleaning for considerable period of time as compared with conventional techniques that require almost daily or say periodic acid cleaning of the system.

[0012] It is another object of the present disclosure to provide brine clarification system utilizing optimum power levels when compared to conventional methods.

[0013] It is a further object of the present disclosure to provide extended life of submerged membrane system thereby reducing the down time of the brine clarification process.

[0014] It is another object of the present disclosure to provide eco-friendly submerged membrane system causing no adverse impact on surrounding environment.

[0015] In one other object of present disclosure, an arrangement of air agitation and backwash cycles for the submerged system to maintain the flux and produce brine of consistent quality on a sustained basis, is provided.

[0016] These and other objects will become apparent from the ensuing description of the present invention.

SUMMARY OF THE INVENTION

[0017] The present invention is directed to a system for brine clarification, comprising a tank configured to receive brine; a membrane system submerged in the tank configured to clarify the received brine; and a feed and backwash pump configured to deliver the clarified brine and use at least some portion of the clarified brine for backwash cycles.

[0018] In another preferred embodiment, the submerged membrane system is made of varying range of polymers including, but not limited to, polyethersulfone (PES), polyvinylidene fluoride(PVDF), polupropylene(PP), Teflon or any other plastic materials. Further, in another aspect of present disclosure the submerged membrane system has a pore size ranging from 0.01-1.0 microns, and the diameter of the membrane fiber ranging between 0.5 to 5 mm.

[0019] These and other aspects, features and advantages of the present invention will be described or become apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Fig. 1 shows a generic perspective view of the brine clarification system, in accordance with one preferred embodiment of the present disclosure.

[0021] Fig. 2 is tabular representation of recommended operational levels of various system parameters, in accordance with one preferred embodiment of the present disclosure.

[0022] Figs. 3(a) and 3(b)are tabular representation of the performance of the brine clarification system, in accordance with one preferred embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] Before the present process of brine clarification is described, it is to be understood that this disclosure is not limited to the particular system and method for brine clarification, as described, since it may vary within the specification indicated. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope of the present invention, which will be limited only by the appended claims. The words "comprising,""having,""containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. The disclosed embodiments are merely exemplary methods of the invention, which may be embodied in various forms.

[0024] In accordance with the first embodiment, a brine clarification process using submerged membrane technique is proposed. The submerged membrane is made of varying range of polymers vis-à-vis polyethersulfone (PES),polyvinylidene fluoride(PVDF), polupropylene(PP), Teflon or any other plastic materials. In one preferred embodiment, the pores-size of the membrane varies from 0.01 – 1.0 microns and the diameter of the membrane fiber ranging between 0.5 to 5mm, while the configuration can be of a single or multibore construction. The submerged membrane is made of material which is antifouling and hence achieves better performance with less frequent chemical cleaning compared to other technologies.

[0025] In one significant aspect of present disclosure, the submerged membrane cassettes broadly comprises of two end blocks that are placed in position with the help of tie-rods. Preferably, membranes are placed in ‘U’ shape, wherein the open end of all the membranes is terminated on the upper block from where the brine is sucked and purified. There are different types of sub-merged membrane of different configuration and material of construction commonly available for water and wastewater treatment applications. Primarily, the MBR membranes are made of polyether sulfone (PES), PP, Teflon, PVDF (polyvinylidene Fluoride) and other polymeric materials. Further, material of construction of tie rods, clamps and other metallic components are preferably constructed of SS316 L, Duplex stainless steel and titanium

[0026] In one preferred embodiment, membrane modules are modified to suit the brine (sodium chloride) by changing the metallic components which are compatible with the sodium chloride, and maintaining pH between 9 – 12. In one significant embodiment of present disclosure, the submerged membranes are operated in the brine stream, and have the following composition: sodium chloride, sodium sulphate, sodium chlorate, sodium carbonate, sodium hydroxide. More significantly, the concentration of aforementioned constituents is as follows: sodium chloride in range of 18-310g/l, sodium sulphate in range of 4-20g/l, sodium chlorate in range of 4-20g/l, sodium carbonate in range of 100-500ppm, and sodium hydroxide in range of 100-500ppm.

[0027] Further, the turbidity levels are maintained between 5-100 NTU, temperatures between 55-75 degree Celsius and density in range of 1.13-1.19.Next, uniform mixing and turbulence creation is achieved using air diffusers, for example, disc and tube type air diffusers, where the quantity of air is optimized at 0.5 – 2 cfm/sq.m of the membrane area, in accordance with one exemplary embodiment of present disclosure. Furthermore, the process flow involved filtration step, followed by backwash, and still again followed by filtration step, all of which can be varied for process optimization. The filtration time, in accordance with one working embodiment of present disclosure, is varied between 5 – 60 minutes, while the backwash time is varied between 5 – 60 seconds.
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[0028] In accordance with one embodiment, duplex stainless centrifugal pumps are employed for sucking the brine through the submerged membrane system. Previously, the submerged MBR membranes were suitable only for the water and wastewater treatment at ambient temperatures (of max 40 deg C); instead components like the tie-rods/other metallic components and the glue used for fixing the tie-rods in the membrane end caps are modified to suit high temperature operation with brine solution.

[0029] In one exemplary working embodiment of the present disclosure, a complete set up of system for brine clarification using membrane filtration technology is illustrated in Fig. 1. Accordingly, a large vessel or tank 10, preferably lined with rubber material, a feed line 1,plurality of rotameters 2 to measure volumetric flow rate of brine, a stainless steel duplex pump 20, on/off valves 30, a programmable logic controller (PLC) based timer 40, a level controller 50, air diffuser 60 and PVDF/PTFE/PES/PP made submerged membrane 70 of 24-35sq.m,common overflow and drain line 12 are arranged for brine clarification process.

[0030] The filtration and clarification process flow begins with the pump 20 sucking the brine 5 through the submerged membrane system 70 immersed in a mild steel rubber lined tank (MSRL) or any other tank 10 suitable for the brine application. The sucked brine is the clarified brine or the “product”. A part of the product brine is filled in the backwash tank 80 for use during the backwash cycle. The brine in the tank 10 enters from outside the membrane 70 fibers to inside the lumen and enters the pump 20 from the suction side 8. The clarified brine through the pump 20 comes out from the delivery end and is filled in the product collection tank.

[0031] The plant is operated by a PLC based timer 40, whereby at a programmed time, the filtration sequence stops and the backwash cycle starts with the product brine pumped from inside the lumen to outside. All the suspended particles settled on the membrane 70 gets dislodged during this cycle and collected in the MSRL tank 10. A portion of the brine in the tank 10 is purged out continuously to maintain the total suspended solids in the tank 10 at a constant level. Due to continuous filtration and backwash cycles the pressure build up as a result of the accumulation of the suspended solids on the membrane 70 surface is totally eliminated, and the system operates continuously without any chemical or acid cleaning.

[0032] Thereafter, the compressed air is purged inside the tank 10 via air line 23 to prevent the suspended solids settling on the membrane 70 surface and inside the tank 10. The tank 10 is provided with an overflow and the drain arrangement 12. The brine is continuous drained via the overflow and the drain arrangement 12 to maintain the suspended solids concentration in the tank 10. The excess brine if collected inside the tank 10 comes out of the overflow pipe and passes out through the drain line26.

[0033] In one exemplary embodiment, the submerged membrane 70 is operated through a PLC based timer 40, comprising steps of filtration for a period of 0-60 minutes and backwash for 0-10 minutes. The sequence of filtration and backwash with definite time intervals take place continuously resulting in continuous flow of clarified brine to the process. In general, the brine flow during backwash via backwash line 25is kept between 1.5 – 5 times the feed volumes. Further, various parameters such as flux, recovery, quality of brine, flow, filtration and backwash time, air quantity , type and design of air distributor, turbidity of brine in tank, type of membrane used and its material of construction, etc. are optimized and presented in table of Fig. 2 to obtain clarified brine of optimum quality.

[0034] More precisely, the trials for clarification of brine requires monitoring of parameters for feed and product streams are turbidity, total suspended solids (TSS), calcium and magnesium. The quality of brine obtained when compared with conventional systems that involved use of anthracite filter or ultrafiltration technique, is of matching quality, the results of which are presented in table of Fig. 3 (a) and 3(b).
[0035] Such a clarified brine can be obtained by a system that can be operated without any acid cleaning for approximately more than four months compared to the existing system that require almost a daily acid wash for the ultrafiltration unit and microfiltration membrane units and replacement for other pre-coat filtration units. Thus, while in the existing system the anthracite filters are backwashed on daily basis for regeneration, with the submerged membrane system both the anthracite and the Ultrafiltration unit or the microfiltration membrane units are eliminated. Further, the submerged membrane system is a low pressure operation and hence the power consumption in the membrane unit is less compared to the other existing membrane systems such as ultrafiltration system.
[0036] The foregoing description is a specific embodiment of the present disclosure. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.
,CLAIMS:We claim:

1. A system for brine clarification, comprising:
a tank configured to receive brine;
a membrane system submerged in the tank configured to clarify the received brine; anda feed and backwash pump configured to deliver the clarified brine and use at least some portion of the clarified brine for backwash cycles.

2. The system for brine clarification according to claim 1, further comprising a programmable logic controller based timer, configured to initiate the backwash cycle as the clarified brine is pumped via the feed and backwash pump to a final collection tank.

3. The system for brine clarification according to claim 1, further comprising an overflow and the drain arrangement to drain off the clarified brine to maintain concentration of suspended solids in the tank.

4. The system for brine clarification according to claim 1, further comprising air diffuser to receive and purge compressed air inside the tank to avoid settling of the suspended solids in the tank and on the membrane system.

5. The system for brine clarification according to claim 1, wherein the submerged membrane system is operated for up to 60 minutes to clarify the received brine.

6. The system for brine clarification according to claim 1, wherein the submerged membrane system is made of varying range of polymers including, but not limited to, polyethersulfone (PES),polyvinylidene fluoride(PVDF),polupropylene(PP), Teflon or any other plastic materials.

7. The system for brine clarification according to claim 1, wherein the submerged membrane system has a pore size ranging from 0.01-1.0 microns.

8. The system for brine clarification according to claim 1, wherein the feed and backwash pumpis configured to operate for 0-10 minutes.

9. The system for brine clarification according to claim 1, wherein the feed and backwash pump is configured to receive flow of brine at 1.5 to 5 times volume of brine.

10. The system for brine clarification according to claim 1, wherein the submerged membrane system further comprises:
a first end block and a second end block from where the brine is sucked and clarified; and one or more tie-rods are configured to terminate open ends of the first end block and the second end block.

11. The system for brine clarification according to claim 1, wherein the submerged membrane system includes sodium chloride, sodium sulphate, sodium chlorate, sodium carbonate, sodium hydroxide and a combination thereof.

12. The system for brine clarification according to claim 11, wherein concentration of the sodium chloride is in range of 18-310g/l.

13. The system for brine clarification according to claim 11, wherein concentration of the sodium sulphate is in range of 4-20g/l.

14. The system for brine clarification according to claim 11, wherein concentration of the sodium chlorate is in range of 4-20g/l.

15. The system for brine clarification according to claim 11, wherein concentration of the sodium carbonate is in range of 100-500ppm.

16. The system for brine clarification according to claim 11, wherein concentration of the sodium hydroxide is in range of 100-500ppm.

17. The system for brine clarification according to claim 1, wherein turbidity levels are maintained between 5-100NTU.

18. The system for brine clarification according to claim 4, wherein the compressed air received by the air diffusers is optimized in range of 0.5-2 cfm.sq.m.

19. The system for brine clarification according to claim 1, wherein the submerged brine system is configured to withstand temperatures upto 75 degree Celsius.

20. The system for brine clarification according to claim 1, further comprising membrane fibre having diameter size ranging between 0.5 to 5 mm.