System for simultaneous recovery of purified water and dissolved solids from impure high TDS water

Abstract

The present system is for simultaneous recovery of purified water and dissolved solids from impure high TDS water (1) which is achieved in a single step and eliminates the use of external thermal energy for making the system significantly efficient. It eliminates the use of boiler, cooling tower that reduces the overall capital cost and continuous requirement of external thermal energy for making system efficient. The simultaneous recovery of the purified water and solids from high TDS input effluent reduce the energy intensity of the system. Said system provides a vacuum system as heat pump which enables the system to be self-sufficient in thermal energy requirements for evaporation process and reduces GHG emissions significantly.

Claims

1. A system for simultaneous recovery of purified water and dissolved solids from impure high TDS (total dissolved solids) water, comprising: an impure high TDS water input feeder; a vacuum cum heat pump; a plurality of passages, comprising first through eighth passages; a plurality of heat exchangers; a flash vessel; a plurality of pumps; a centrifugal separator; a screw feeder and induction type heating system; wherein: the impure high TDS water input feeder provides an entry of the impure high TDS water into the vacuum cum heat pump; the vacuum cum heat pump enables compression and pre heating of the impure high TDS water using: a water injection system, compression units, and a reheating system, the water injection system is provided to control and monitor temperature of discharge from each of the compression units which compresses water vapor received from the flash vessel through the sixth passage and generates a vacuum in the flash vessel upgrading low pressure water vapor to steam at a higher pressure, thereby acting as a heat pump; wherein the compression units: are connected to the preheating system which provides pre heating of the impure high TDS water by increasing a temperature of the impure high TDS water by 5-10° C.; wherein the vacuum cum heat pump is connected to the plurality of heat exchangers, the plurality of heat exchangers are provided to exchange heat from steam generated in the system and condensing the steam to liquid; wherein the plurality of heat exchangers comprises a first heat exchanger and a second heat exchanger; wherein: the first heat exchanger receives steam from the vacuum cum heat pump through the second passage; the first heat exchanger provides the conversion of steam into the purified water and the steam condensed in the first heat exchanger is used to preheat a recirculating solution coming through the eighth passage and the first heat exchanger is further connected to the flash vessel through the fifth passage; the second heat exchanger receives the purified water produced from steam from the first heat exchanger through the third passage using pressure of about 250-300 kPaA from a P3 pump (6A); wherein the second heat exchanger is used to cool the purified water, wherein the second heat exchanger discharges the purified water, from the system; the second heat exchanger receives feed impure high TDS water through the first passage from the vacuum cum heat pump which is connected to the second heat exchanger through the first passage; wherein the second heat exchanger provides preheating of feed impure high TDS water by extracting heat from the purified water coming from the first heat exchanger; wherein the second heat exchanger is connected to the flash vessel through the fourth passage; the flash vessel is provided to receive premixed recirculation stream with feed impure high TDS water from a junction formed at an intersection of the fourth and fifth passages wherein three separate phases of the premixed recirculation stream with feed impure high TDS water are formed, water vapor at a top as first phase, liquid water saturated with dissolved solid content as a second phase and solids as a third phase; wherein the water vapor generated as the first phase is passed through the sixth passage to be recycled through the vacuum cum heat pump in a present closed loop system for simultaneous recovery; the flash vessel is further connected to the centrifugal separator through the seventh passage by using pressure from a P7 pump (6B); and the centrifugal separator is provided to receive the second and third phases from the flash vessel using pressure of about 250-300 kPaA from the P7 pump (6B); the centrifugal separator separates a liquid phase and a solid phase; the centrifugal separator is connected to the screw feeder and induction type heating system for evaporating moisture present in solids and removing the solids from the system simultaneously.

2. The system as claimed in claim 1, wherein the plurality of passages are provided to channelize steam and liquid generated in the system for further processing; wherein: the first passage is provided to channelize feed impure high TDS water from the vacuum cum heat pump to the second heat exchanger, the second passage is provided to channelize steam from the vacuum cum heat pump to the first heat exchanger, the third passage is provided to channelize the purified water from the first heat exchanger to the second heat exchanger, the fourth passage is provided to channelize feed impure high TDS water from the second heat exchanger to the flash vessel, the fifth passage is provided to channelize recirculation liquid stream from the first heat exchanger to the flash vessel, the sixth passage is provided to channelize water vapor generated by flash of the recirculation stream as well as the feed impure high TDS water from the flash vessel to the vacuum cum heat pump, the seventh passage is provided to channelize liquid and solid content of the feed impure high TDS water from the flash vessel to the centrifugal separator, the seventh passage is provided to channelize solid from the centrifugal separator to screw feeder and induction type heating system, and the eighth passage is provided to channelize recirculation stream from the centrifugal separator to the first heat exchanger.

3. The system as claimed claim 2, wherein the plurality of pumps are provided to pressurize the recirculation stream, which is a mixture of a saturated solution of dissolved salts in water and solid, being treated in the system; wherein the P3 pump (6A) is placed on the third passage and pumps pressurized condensate received from the first heat exchanger to the second heat exchanger through the third passage and the P7 pump (6B) is placed on the seventh passage which pumps pressurized recirculation stream from the flash vessel to the centrifugal separator through the seventh passage.

4. The system as claimed in claim 3, wherein the plurality of heat exchangers are selected from a plate and frame type heat exchanger, or a spiral type heat exchanger.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1: Shows diagrammatic representation of present system for simultaneous recovery of purified water and dissolved solids from impure high TDS water; and

(2) FIG. 2: Is a table showing a reduction in fossil energy consumption, and hence GHG emissions, in the range of 50-100% as compared to the prior art.

MEANING OF REFERENCE NUMERALS OF SAID COMPONENT PARTS OF PRESENT INVENTION

(3) 1: System for simultaneous recovery of purified water and dissolved solids from impure high TDS water 2: Effluent input feeder 3: Vacuum cum heat pump 3A: Water injection 3B: Compression units 3C: Preheating system P: Plurality of Passage 4: Plurality of Heat exchanger 4A: First Heat exchanger 4B: Second Heat exchanger 5: Flash vessel 6: Plurality of pumps 6A: P3 Pump 6B: P7 Pump 7: Centrifugal separator 8: Screw feeder Induction type heating system

BRIEF DESCRIPTION OF THE INVENTION

(4) The embodiment of the present invention is to provide a system for simultaneous recovery of purified water and dissolved solids from impure high TDS water (1) which is achieved in a single step and without using any external thermal energy thereby making the system significantly efficient.

(5) Main embodiment of the present invention provides a system for simultaneous recovery of purified water and dissolved solids from impure high TDS water (1) as shown in FIG. 1; said system mainly comprises of: Effluent input feeder (2) Vacuum cum heat pump (3) Passage (P) Plurality of Heat exchanger (4) Flash vessel (5) Plurality of pumps (6) Centrifugal separator (7) Screw feeder and Induction type heating system (8)

(6) Wherein

(7) Referring to FIG. 1 said effluent input feeder (2) provides the entry of the high TDS water effluent. Said effluent input feeder (2) is connected to vacuum cum heat pump (3). Said vacuum cum heat pump (3) comprises of: Water injection (3A) Compression units (3B) Preheating system (3C)

(8) Wherein; said compression units (3B) are placed in series to provide the steam pressure of 80-150 kPaA. The compression units (38) compress the water vapour from flash vessel (5) through passage (P6) wherein compression units (3B), also achieve the generation of vacuum in the flash vessel (5) and upgrades low pressure water vapor to steam at higher pressure, and by this means it acts as a heat pump. Said compression units (3B) are connected to water injection (3A) which control and monitor said compression units (3B) discharge temperature at each stage of compression. The compression units (3B) are further connected to preheating system (3C) to provide preheating of feed effluent (2) by increasing its temperature by 5-10° C.

(9) Said vacuum cum heat pump (3) is further connected to plurality of heat exchanger (4). Said plurality of heat exchangers (4) are mainly selected from plate and frame or spiral type of heat exchanger. The vacuum cum heat pump (3) is connected to first heat exchanger (4A) to provide the steam through passage (P2); wherein the first heat exchanger (4A) provides the conversion of steam into liquid state of purified water. The purified water produced in first heat exchanger (4A) is connected to the second heat exchanger (4B) through the passage (P3) with P3 pump (6A) before getting discharged as product water stream from the system. Steam condensed in first heat exchanger (4A) preheats the recirculating solution coming through passage (P8) and is further connected to flash vessel (5) through passage (P5). The feed effluent stream coming from vacuum cum heat pump (3) is connected to second heat exchanger (4B) through passage (P1). The second heat exchanger (4B) further preheats the feed effluent by extracting heat from product water stream coming from first heat exchanger (4A) and is connected to through passage (P4) with junction (PJ) where it is connected to flash vessel (5) through passage (P5); wherein passages (P4 and P5) merge at junction (PJ) to provide pre-mixed effluent to flash vessel (5). The flash vessel (5) creates three separate phases i.e. water vapor at the top layer as a first phase, liquid water saturated with dissolved solid content (second phase), mixed with solids (third phase), as bottom layer. The flash vessel (5) is further connected with vacuum cum pump heat (3) through passage (P6); wherein water vapor generated in the flash vessel (5) is further recycled at said vacuum cum heat pump (3). The flash vessel (5) is connected to centrifugal separator (7) through passage (P7); through a P7 pump (6B); to provide the separation of liquid water saturated with solids and a solid phase from the mixed phase obtained in flash vessel (5). The centrifugal separator (7) is connected to screw feeder and induction type heating system (8); to provide the evaporation of the moisture present in solids and solid get removed from the system simultaneously. The centrifugal separator (7) is further connected to first heat exchanger (4A) through passage (P8) to provide the recycle stream of liquid of effluent which is preheated in first heat exchanger (4A) and further connected to flash vessel (5) through passage (P5) and the cycle repeats. Thus the simultaneous recovery of the purified water and solids is achieved.

(10) Another embodiment of the present invention provides an automated system for simultaneous recovery of purified water and dissolved solids from impure high TDS water as shown in FIG. 1;

(11) The control means provides control on operating parameters of different components such as pressure difference, temperature difference and TDS content of the purified water. Further control means is connected with SCADA (Supervisory Control and Data Acquisition) which provides the measuring and comparing of the set values for the parameters. Said SCADA is connected with PLC (Programmable Logic Controller) and provides the control of the parameters.

(12) Further control means are connected to the computer where the parameters continuously get fed. Said computer is connected to HMI (Human Machine Interface) panels which act as an interphase for operator guidance during the startup and shut down operations. Further computer is connected through a suitable internet connection which provides capability for remotely monitoring the operations.

(13) Working of the Present Invention:

(14) Referring to FIG. 1 with respect to present invention; the working steps are as under: 1. The high TDS effluent enters into the system (1) through effluent input feeder (2) and effluent passes to the vacuum cum heat pump (3) wherein it further enters in the preheating system (3C) where it gets preheated at temperature of about 45-50° C. 2. The steam generated from said vacuum heat pump (3) passes to first heat exchanger (4A) through the passage (P2) where the steam generated by heat pump is converted to liquid water (purified water) and the recirculating effluent, entering through passage (P8), gets preheated and recirculates back to flash vessel (5) through passage (P5). 3. The second heat exchanger (4B) receives purified water from first heat exchanger (4A) through passage (P3) using pressure from P3 pump (6A) at about 250-300 kPaA pressure; wherein the heat of said purified water, enables heating of input feed (coming from preheating system (3C) via passage (P1)) effluent to about 80-95° C. within second heat exchanger (4B). 4. Effluent from second heat exchanger (4B) and recycled stream from first heat exchanger (4A) through passages (P4 and P5) respectively reaches flash vessel (5); wherein, passages (P4 and P5) merges at junction (PJ) to allow the Effluent and recycled water to mix; forming pre-mixed effluent. A small portion of the pure water from second heat exchanger (4B) is directed to water injection (3A) to be used for cooling the water vapour that passes through series of compression units (3B). 5. The flash vessel (5) operates under vacuum in the range of 1-80 kPaA pressure. Meanwhile, the water evaporation is ensued in the flash vessel (5) wherein the premixed effluent gets divided into three separate phases i.e. with water vapor (first phase) at the top layer, liquid water (second phase) saturated with dissolved solid content mixed with suspended solids (third phase) as bottom layer. Unlike the prior arts, wherein the evaporation takes place within the heat exchangers; present invention involves this evaporation and separation stage in the flash vessel (5) which obviates problem related to choking of heat exchanger tubes and thus provides ease and reliability in continuous operation of the system. 6. Wherein the water vapor generated in the flash vessel (5) is recycled to vacuum cum heat pump (3) by entering in the compression units (3B) through passage (P6) and the bottom layer of liquid water saturated with dissolved solid content and having suspended solids passes to the centrifugal separator (7) by using pressure from P7 pump (6B). The P7 pump (6B) pressurizes the mixture of liquid effluent and solid content to about 300-400 kPaA pressure. After centrifugal separation, the solids are removed from the system using screw conveyer with heater (8) and the separated liquid is recycled to first heat exchanger (4A) through passage (P8) to get heated with the heat of steam. 7. Water vapour within the compression units (3B) achieve pressure of 80-150 kPaA after compression wherein water from second heat exchanger (4B) is used to control the temperature within said compression units (3B). Moreover, the pressure difference is controlled to confirm the temperature difference between flash vessel effluent and steam condensing in the first heat exchanger (4A) is in the range of 20-60° C. 8. The interstage temperature is constantly monitored and controlled through the water injection system (3A) during the process of compression of water vapour through compression units (3B). Thus, the compression units (3B) achieves dual objectives of the generation of vacuum in the flash vessel and upgrades low pressure water vapor to steam at higher pressure, and by this means it acts as a heat pump. Therefore; the system doesn't need any additional apparatus for heating the effluent and reduce the energy and cost of the system. 9. Through the above steps, the purified water from the present system comes out from the second heat exchanger (4B) at about 40-50° C. temperature; which is low TDS water (it contains, generally, less than 50 ppm but not more than 500 ppm).

Working of Alternative Embodiment

(15) The alternative embodiment of the present invention; which involves automatic monitor and control of the present system using control means wherein the operating parameters of different components like pressure difference, temperature difference, levels, flow of effluent and TDS content of the purified water are continuously measured and monitored.

(16) The control means uses SCADA (Supervisory Control and Data Acquisition) for measuring and comparing the set values for the parameters and controlling them using PLC.

(17) Various electrical drives of the motors are controlled through VFDs (variable frequency drives), and all the operating parameters of the system are controlled through the control of these VFDs by PLC.

(18) The operating parameters are continuously fed to a computer through PLC controller and such computer is connected to a HMI (Human Machine Interface) panel which acts as an interphase for operator guidance during the startup and shut down operations. The computer is connected through a suitable internet connection to remotely monitor the operations.

(19) Following table summarizes the test data on a pilot system of the present invention:

(20) TABLE-US-00001 Parameter Units Trial-1 Trial-2 Trial-3 Trial-4 Feed rate Liter/hr. 50 50 50 50 Feed TDS PPM 25000 25000 50000 50000 Flash pressure kPaA 15 30 15 30 Pure water flow Liter/hr. 48 47.8 47 46.9 Pure water TDS PPM 70 50 60 65 Solids recovered Kg/hr. 1.5 1.5 2.9 3.0 (prior to final moisture removal) Power consumption Kwh/liter 76 67 74 68 of system of feed

Comparison of Prior Art and Present Invention

(21) A typical prior art and the present invention are hereby compared in the below table to clearly bring out the technical differences between the prior art and the present invention.

(22) A comparison is done between the prior art and our invention in two parts viz. (1) Heat pumps for steam generation and (2) ZLD systems. Following tables clearly depict the major technical differences between prior art and our invention

(23) A) Heat Pump:

(24) TABLE-US-00002 Sr. Prior art No. Parameter (STEAM GLOW) Present invention 1 Heat pump fluid used R245fa & R134a Water 2 Operating pressure Very high Sub-atmospheric to pressure near atmospheric is is used used 3 Type of compressor Twin screw Twin or tri-lobe type used vapour compression system used for vacuum systems 4 Steam generation 200-700 kPaA 80-150 kPaA pressure( kPaA) 5 COP of heat pump 2.5-3.2 >7 and upto10 (indicator of energy efficiency)
B) Zero Discharge Process:

(25) TABLE-US-00003 Sr. Present invention No. Parameters Prior Art (simultaneous recovery) 1 Number of Multiple stage Single stage separate (simultaneous recovery processes of water and solids) required 2 Recovery of Water recovered in Simultaneous recovery water and multiple stages of of all the water and solids process and solids solids in the single recovered in last stage process process. 3 Type of heat Shell and tube Plate and frame type exchanger used type for MVR and or spiral heat for supply of MEE system. exchanger. heat for water Agitated shell Heat supplied used evaporation with thin film of for sensible heating liquid on shell of water and no for ATFD. evaporation happens Heat supplied used in exchanger. for latent heat of evaporation. 4 Location of Heat exchangers Flash vessel water evaporation 5 Operating For MVR and MEE the operating pressure it is in vacuum to pressure for water for heat almost atmospheric side in the heat exchangers pressure and exchanger is ATFD is almost 150-250 kPaA atmospheric. 6 Temperature MVR and MEE type It is in the range differential systems have very of 40-60° C. between low in the range boiling liquid of 5-12° C. and condensing and in Vacudest steam system it is maximum 35° C. 7 Utilities Boiler and cooling Only electric supply required for tower apart from is required, no other operating the electric supply utility support system systems is required to operate the system 8 Water recovery <90% >95% as % feed 9 Environment GHG emission If renewable power is impact by way cannot be used than there would of GHG avoided be no GHG emission. emission Even for non-renewable power sources, emission reduction can be in range of 50-60%.
3) GHG Emission:

(26) Present invention offers very high energy efficiency compared to prior arts and accordingly it results in substantial reduction in GHG emissions.

(27) Energy efficiency can be explain from following table with the example of processing effluent with 5% TDS for recovery of pure water and solids:

(28) TABLE-US-00004 Sr. Prior Our No. Parameters art invention 1 Steam consumption, kg/KL 309 0 2 Power consumption, kwh/KL 39 70 3 Water recovery, % of feed 88 95

(29) The table provides the comparison between prior art and present invention for power consumption, steam consumption and % water recovery; wherein said comparison assumes conservative figure for power consumption in our invention and in many cases it can be much lower also. However, this figure is used to highlight energy savings even in conservative case.

(30) In order to understand the macro economic impact, in terms of ultimate fossil fuel consumption and hence GHG emissions, following possible scenarios for energy supply in economy are considered for comparison of present invention with prior art. These scenarios are as follows:

(31) TABLE-US-00005 Sr. No. Parameters Case-1 Case-2 Case-3 Case-4 1 Fossil fuel Coal Coal Gas Gas used for boiler 2 Boiler  80  80  85 85 efficiency, % 3 Power generation parameters: Fuel used Coal Coal Gas None Technology Conventional Super- Combined Renewable critical cycle Heat rate 2500 2100 1700  0 (NCV basis), kcals/kwh

(32) Based on these four scenarios for energy supply in economy, the reduced fossil energy consumption and hence reduced environmental impact (in terms of GHG emissions) in present invention vis-à-vis prior arts is summarized in FIG. 2.

(33) FIG. 2 presents only four scenarios as typical examples, it can be done for any other permutation and combination of energy mix and the savings would work out to be of similar magnitude. As can be seen from the above, the present invention helps in reducing fossil energy consumption and hence GHG emissions in the range of 50-100% compared to prior arts.

Advantages of the Invention

(34) 1. Present invention has water evaporation process without any external thermal energy input which makes it significantly more efficient and reduces GHG emissions significantly. 2. Present invention has simultaneous recovery of the purified water and solids from high TDS input water thus provide simple processes and reduce the energy intensity of the system. 3. Present invention doesn't require support utilities like boiler and cooling tower which reduces the overall capital cost and, also, cost of continuous requirement of external thermal energy thereby making system efficient. 4. Heat supplied is used for sensible heating of water and evaporation of water takes place in flash vessel thereby obviating problem of choking of heat exchanger tubes 5. By preventing the problem of chocking of heat exchanger tubes it provides ease and reliability in continuous operation of the system. 6. The system requires very low electrical energy and no thermal energy to operate thereby making the system self-sufficient. 7. Present invention can be made completely automated operating system with possibilities for remotely controlled operations. 8. Present invention operates under vacuum and heat pump which needs compression to pressure which is slightly higher than atmospheric pressure thereby making invention efficient and cost effective and yet it helps in achieving high temperature differential between boiling liquid and condensing steam. 9. The invention results in compact preassembled and may be containerized system to operate as “plug and play” system which results in less requirement of land and civil works costs. 10. The invention is simple, user friendly and yet efficient. 11. The invention provides a significantly efficient and cost effective system that can be installed at large as well as small and medium sized industries and providing versatility for large scale applications to help in achieving sustainable development of economies. 12. Present invention need small land area for the process and thus reduces civil works costs.

Applicability of Present Invention

(35) Purified water and dissolved solids are recovered from any impure water stream with high TDS content; including, but not limited to, from industrial effluent waters; by a process developed wherein the impure water is evaporated under vacuum and water vapour generated are upgraded as steam, using a unique integration of vacuum system as heat pump, to be self-sufficient in thermal energy requirements for evaporation process.

(36) The invention provides wide scale application for water recovery, recycles, reuse and reduced GHG emissions; which will help in Sustainable Economic Development.

(37) There are various applications of the present system; which includes, but not limited its application for ZLD operations but can also be useful in following other similar applications: Desalination of sea water Purification of any other impure water source to produce process or even DM water for application in process industries Production of purified water for pharmaceutical industries Recovery of dissolved solids from their solutions in water (may be as by product or even main product) Preconcentration of solutions of dyes/chemicals prior to their spray drying so as to reduce the cost of drying Preconcentration of milk or any other fruit/vegetable juice before their spray drying to produce dry powder product