DESC:FIELD
The present disclosure relates to an absorption-based multi-effect evaporative system which is generally used in water desalination plants or for wastewater treatment processes.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
A desalination system and certain conventional wastewater treatment processes rely on evaporation to separate water from contaminants. In desalination, heat is used to evaporate seawater, leaving salts and impurities behind, which are then removed when the vapor is condensed. Similarly, wastewater treatment systems use evaporation to eliminate effluent and recover water. These processes often implement multiple evaporators to achieve Zero Liquid Discharge (ZLD), ensuring that only pure water is separated while waste is concentrated. However, conventional evaporators commonly rely on a significant amount of high-pressure steam as the primary heat source. This results in considerable energy consumption and operating expenses. Additionally, in many conventional systems, the heat produced during the evaporation process is often not efficiently captured or reused, leading to significant energy waste. This inefficiency contributes to both higher operational costs and greater environmental impact.
Moreover, the high steam consumption in evaporators escalates operational costs and contributes substantially to environmental issues by emitting greenhouse gases.
A multi-effect evaporators (MEE) with TVR (Thermal Vapor Recompression) uses thermal vapor recompression, which relies on the energy from high-pressure vapor or steam to reheat the vapor within the system. It is more energy-efficient than other conventional evaporators, as it recycles vapor, reducing steam consumption. However, the MEE with TVR consumes a larger amount of steam as its primary energy source. Further, flash vessels are insertion at each stage of the system in the MEE setups leading to a significant increase in the space required for the equipment. This space-intensive configuration also results in higher capital expenditure.
There is, therefore, felt a need to provide an absorption-based multi-effect evaporative system for seawater or wastewater treatment processes that overcomes the above-mentioned drawbacks, or at least provides an alternative solution.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide an absorption-based multi-effect evaporative system that minimizes energy consumption.
Another object of the present disclosure is to provide an absorption-based multi-effect evaporative system that optimizes the utilization of heat generated during evaporation by employing heat recovery mechanisms, ensuring minimal wastage and maximizing overall system efficiency.
Still another object of the present disclosure is to provide an absorption-based multi-effect evaporative system that reduces greenhouse gas emissions.
Yet another object of the present disclosure is to provide an absorption-based multi-effect evaporative system that improves cost-effectiveness by lowering operational expenses associated with steam generation and enhancing overall system performance.
Still another object of the present disclosure is to provide an absorption-based multi-effect evaporative system that improves desalination efficiency and output quality while mitigating the environmental impact and operational costs.
Yet another object of the present disclosure is to provide an absorption-based multi-effect evaporative system that reduces space requirements and provides a compact design.
Still another object of the present disclosure is to provide an absorption-based multi-effect evaporative system that eliminates the need for flash vessels, reducing construction complexity and costs.
Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to an absorption-based evaporative system. The system comprises a generator configured to receive a dilute absorbent solution and a steam input, the dilute absorbent solution is boiled using the steam input to generate refrigerant vapors, steam condensate and a strong absorbent solution, a multi-effect evaporative unit disposed downstream of the generator, the multi-effect evaporator unit comprises a plurality of evaporators connected in series, each of the evaporators is configured to receive and circulate the refrigerant vapors through a plurality of tubes of corresponding evaporator, also configured to receive a feed solution and sprays it over the tubes of the evaporator, wherein the feed solution absorbs heat from the refrigerant vapors to generate a concentrate solution and discharge a condensate stream.
The absorption-based evaporative system further comprises an absorber unit. The absorber unit is configured downstream of the multi-effect evaporator unit to receive refrigerant vapors from the multi-effect evaporator unit. Then, receive the strong absorbent solution from the generator, and spray the strong absorbent solution over a plurality of tubes of the absorber unit to absorb the refrigerant vapors into the strong absorbent solution to produce the dilute absorption solution. the system furthermore includes at least one heat recovery unit fluidically connected between the generator and the absorber unit. The heat recovery unit is configured to exchange heat between the dilute absorption solution exiting the absorber unit and at least one of the strong absorbent solutions or the steam condensate exiting the generator.
In an embodiment of the present disclosure, the system includes a condenser disposed downstream of the multi-effect evaporator unit and configured to receive at least a portion of the refrigerant vapors exiting the multi-effect evaporator unit to generate a first condensate.
In an embodiment of the present disclosure, the at least one heat recovery unit includes a first heat recovery unit configured to heat a first stream of the dilute absorption solution using the strong absorbent solution exiting the generator and a second heat recovery unit configured to heat a second stream of the dilute absorption solution using the steam condensate exiting the generator.
In an embodiment of the present disclosure, a first water stream is supplied to the plurality of tubes of the absorber unit, the first water stream absorbs heat generated during the refrigerant vapor absorption process in the absorber unit to generate a hot water stream that exits from the absorber unit and supplied to at least one evaporator of the multi-effect evaporator unit.
In an embodiment of the present disclosure, the multi-effect evaporator unit comprises a plurality of heat exchangers downstream of each of the evaporators, the plurality of heat exchangers configured to heat the feed solution using the condensate steam exiting from the corresponding evaporator.
In an embodiment of the present disclosure, the multi-effect evaporator unit includes a first evaporator configured to receive the refrigerant vapor from the generator and circulate through the plurality of tubes, receive the feed solution from the plurality of heat exchangers and spray over the tubes, wherein the feed solution absorbs heat from the refrigerant vapor to obtain a first refrigerant vapor, a first concentrate solution, a first condensate stream, and discharge the first water stream; a second evaporator configured to receive and circulate the first refrigerant vapor through a plurality of tubes, receives the first concentrate solution and sprays it over the tubes to absorb heat from the first refrigerant vapor to obtain a second concentrate solution, a second condensate stream, and a second refrigerant vapor.
The multi-effect evaporator unit further includes a third evaporator configured to receive and circulate the second refrigerant vapor through a plurality of tubes, receive the second concentrate solution and spray it over the tubes to absorb heat from the second refrigerant vapor to obtain a third concentrate solution, a third condensate stream, and a third refrigerant vapor; a fourth evaporator is configured to receive and circulate the third refrigerant vapor through a plurality of tubes, receives the third concentrate solution and sprays it over the tubes to absorb heat from the third refrigerant vapor to obtain a fourth concentrate solution, a fourth condensate stream, and a fourth refrigerant vapor.
In an embodiment of the present disclosure, the absorption-based multi-effect evaporative system further comprises a first pumping unit configured to transfer the fourth concentrated solution from the multi-effect evaporator unit to further downstream processes, a second pumping unit configured to transfer the feed solution from a feed storage tank to the first evaporator of the multi-effect evaporator unit through the plurality of heat exchangers, a third pumping unit is configured to transfer the condensate ejected from the condenser and the fourth heat exchanger to further downstream processes, a fourth pumping unit is configured to transfer the first water stream from the multi-effect evaporator unit to the absorber unit and a fifth pumping unit is configured to transfer the dilute absorbent solution from the absorber unit to the generator through the at least one heat recovery unit.
In an embodiment of the present disclosure, the dilute absorbent solution is made of water and lithium bromide.
In an embodiment of the present disclosure, the steam input provided to the generator has a temperature in the range of 150 °C to 180 °C, and the refrigerant vapor generated from the generator has a temperature in the range of 75 °C to 110°C.
In an embodiment of the present disclosure, the first water stream has a temperature in the range of 65 °C to 85 °C and the hot water stream has a temperature in the range of 70 °C to 90°C
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The absorption-based multi effect evaporative system, of the present disclosure, will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates a schematic diagram of a conventionally used system for providing zero liquid discharge (ZLD) of wastewater/effluent by using a four-evaporator system coupled with a thermal vapor re-compressor (TVR) and flash vessels.
Figure 2 illustrates a schematic diagram of a system in accordance with the present disclosure for providing zero liquid discharge (ZLD) of wastewater/effluent by using a multi-effect evaporative system coupled with a single-effect vapor absorption cycle.
LIST OF REFERENCE NUMERALS USED IN DETAILED DESCRIPTION AND DRAWING
Reference no. Reference
100’ Conventional multi-effect evaporative system
1’ discharge vapors
2’ thermal vapor re-compressor
3’ first-effect evaporator
3a’ High pressure steam
4’ feed solution
5’ first effect heat exchanger
6’ re-circulation pump-1
7’ flash vessel-1
8’ Concentrate solution generated from flash vessel-1
9’ second-effect evaporator
10’ refrigerant vapors generated from flash vessel-1
11’ recirculation pump-2
12’ Flash vessel-2
13’ concentrate solution generated from flash vessel-2
14’ third-effect evaporator
15’ refrigerant vapors generated from flash vessel-2
16’ recirculation pump-3
17’ flash vessel-3
18’ concentrate solution generated from flash vessel-3
19’ fourth-effect evaporator
20’ refrigerant vapors generated from flash vessel-3
21’ recirculation pump-4
22’ flash vessel-4
23’ concentrate solution generated from flash vessel-4
24’ refrigerant vapors generated from flash vessel-4
25’ condenser
25a’ cooling water
27’ process pump
28’ fourth effect heat exchanger
29’ Condensate discharged from fourth-effect evaporator
30’ third effect heat exchanger
31’ Condensate discharged from third-effect evaporator
32’ second effect heat exchanger
33’ Condensate discharged from second-effect evaporator
34’ Condensate discharged from first-effect evaporator
35’ Total condensate
36’ Process pump
100 Absorption-based multi-effect evaporative system in accordance with the present disclosure
50 Multi-effect evaporator unit
1 Low-temperature heat exchanger (LTHE)
2 Heat recovery (HR) unit
3 Generator
3a Steam input
3b Steam condensate
3c strong absorbent solution
4 Refrigerant vapors
5 First evaporator
5a Tubes of the first evaporator
6 Feed solution
7 First concentrate solution
8 Second evaporator
8a Tubes of the second evaporator
9 First refrigerant vapor
10 Second concentrate solution
11 Third evaporator
11a Tubes of the third evaporator
12 Second refrigerant vapor
13 Third concentrate solution
14 Fourth evaporator
14a Tubes of the fourth evaporator
15 Third refrigerant vapor
16 Fourth concentrate solution
17 First pumping unit
18 Fourth refrigerant vapor
19 Second part of the fourth refrigerant vapor
20 Absorber unit
20a Tube of the absorbent unit
21 First part of the fourth refrigerant vapors
22 Condenser
22a Cooling water inlet
22b Cooling water outlet
23 First condensate discharged from the condenser
24 Second pumping unit
25 Fourth heat exchanger
26 Condensate discharged from the third heat exchanger
27 Fourth condensate stream
28 Third heat exchanger
29 Third condensate stream
30 Condensate discharged from the second heat exchanger
31 Second heat exchanger
32 Second condensate stream
33 Condensate discharged from the first heat exchanger
34 First heat exchanger
35 First condensate stream
36 Second condensate discharged from the fourth heat exchanger
37 Third pumping unit
38 First water stream
39 Fourth pumping unit
40 hot water stream
41 Fifth pumping unit
42 Dilute absorbent solution
42a First stream of the dilute absorbent solution
42b Second stream of the dilute absorbent solution
44 Condensate outlet for further processes
46 Concentrate outlet for further processes

DETAILED DESCRIPTION
The present disclosure relates to an absorption-based multi-effect evaporative system.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to a person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, elements, modules, units, and/or components, but do not forbid the presence or addition of one or more other features, elements, components, and/or groups thereof.
Conventional desalination and wastewater treatment systems often rely on evaporation to separate water from contaminants, requiring large amounts of high-pressure steam as the primary heat source. This results in high energy consumption, increased operational costs, and significant energy losses due to unused heat. Additionally, the heavy reliance on steam contributes to greenhouse gas emissions, posing environmental challenges.
Multi-effect evaporators (MEE) with Thermal Vapor Recompression (TVR) improve energy efficiency by recycling vapor and reducing steam consumption. However, they still rely heavily on high-pressure steam, leading to substantial energy use. Additionally, the inclusion of flash vessels in each stage increases space requirements, making the system space-intensive and resulting in higher capital costs.
Figure 1 illustrates a schematic diagram of a conventional multi-effect evaporator (MEE) system (100’) for providing zero liquid discharge (ZLD) of wastewater/effluent by using a four-effect evaporator system coupled with a thermal vapor re-compressor (2’). The conventional system (100’) comprises a first-effect evaporator (3’), a second-effect evaporator (9’), a third-effect evaporator (14’), and a fourth-effect evaporator (19’), a condenser (25’), a thermal vapor re-compressor (2’), a first effect heat exchanger (5’), a second effect heat exchanger (32’), a third effect heat exchanger (30’) and a fourth effect heat exchanger (28’). In the conventional system (100’), the feed solution (4’) is entered into the first effect evaporator (3’) through a series of heat exchangers (25’, 28’, 31’, 34’) The thermal vapor re-compressor (2’) is provided with high-pressure steam (3a’) having a temperature in the range of 155 °C to 175 °C and suction vapor which is in the temperature range of 85 °C to 95 °C is typically taken from flash vapor coming from the flash vessel -1 (7’) of the first effect evaporator (3’).
The resultant discharge vapors (1’) coming from the thermal vapor re-compressor (TVR) (2’) which are in the temperature range of 105 °C to 110°C are sent through the heat exchanger shell of the first effect evaporator (3’). The discharge vapors (1’) act as a heating source for the feed solution (4’) coming from the first effect heat exchanger (5’) which is passed through the heat exchanger tubes by the re-circulation pump-1 (6’). The feed solution (4’) is re-circulated continuously through the first effect evaporator (3’) tubes and gets heated. This Heated effluent is allowed to flash in the flash vessel-1 (7’) thus concentrating it and becoming a concentrate solution (8’). The concentrate solution (8’) is then transferred to the second effect evaporator (9’). The refrigerant vapors (10’) generated from the flash vessel-1 (7’) of the first effect evaporator (3’) are sent through the heat exchanger shell of the second effect evaporator (9’) which is used as a heating source for the concentrate solution (8’) coming from the recirculation pump-2 (11’) which is passed through the heat exchanger tubes. The concentrate solution (8’) is re-circulated continuously through the second effect evaporator (9’) tubes and gets heated. This Heated effluent is allowed to flash in the flash vessel-2 (12’) thus concentrating it and becoming a concentrate solution (13’). The concentrate solution (13’) is then transferred to the third-effect evaporator (14’). The refrigerant vapors (15’) generated from the flash vessel-2 (12’) of the second-effect evaporator (9’) are sent through the heat exchanger shell of the third-effect evaporator (14’) which is used as a heating source for the concentrate solution (13’) coming from the recirculation pump-3 (16’) which is passed through the heat exchanger tubes. The concentrate solution (13’) is re-circulated continuously through the third-effect evaporator (14’) tubes and gets heated. This Heated effluent solution is allowed to flash in the flash vessel-3 (17’), thus concentrating it and becoming a concentrate solution (18’). The concentrate solution (18’) is then transferred to the fourth-effect evaporator (19’). The refrigerant vapors (20’) generated from the flash vessel-3 (17’) of the third-effect evaporator (14’) are sent through the heat exchanger shell of the fourth-effect evaporator (19’) which is used as a heating source for the concentrate solution (18’) coming from the recirculation pump-4 (21’) which is passed through the heat exchanger tubes. The concentrate solution (18’) is re-circulated continuously through the fourth-effect evaporator (19’) tubes and gets heated. This Heated effluent is allowed to flash in the flash vessel-4 (22’) thus concentrating it and becoming a concentrate solution (23’). The final concentrate solution (23’) is transferred for further process.
The refrigerant vapors (24’) generated from the flash vessel-4 (22’) are sent to the condenser (25’), where it condenses and drains out as the condensate (26’), by rejecting its heat to the cooling water (25a’) which is flowing on the tube side. The feed solution (4’) which is at room temperature is pumped by the process pump (27’) through the fourth effect heat exchanger (28’) where it gains the heat rejected by the condensate (29’). The feed solution (4’) coming out from the fourth effect heat exchanger (28’) is then sent to the third effect heat exchanger (30’) where it gains the heat rejected by the condensate (31’). The feed solution (4’) coming out from the third effect heat exchanger (30’) is then sent to the second effect heat exchanger (32’) where it gains the heat rejected by the condensate (33’). The feed solution (4’) coming out from the second effect heat exchanger (32’) is then sent to the first effect heat exchanger (5’) where it gains the heat rejected by the condensate (34’). The total condensate (35’) is pumped by a process pump (36’) for further processing.
The MEE system (100’) depicted in Figure 1 is more energy efficient than the other conventional system. However, the MEE system (100’) with TVR (2’) consumes a larger amount of steam as its primary energy source. Further, the inclusion of flash vessels at each stage of the system (100’) leads to a significant increase in the space required for the equipment.
Therefore, the present disclosure provides a multi-effect evaporative system coupled with a single-effect vapor absorption cycle. The absorption-based multi-effect evaporative system of the present disclosure will now be described in detail with reference to Figure 2. The present embodiment does not limit the scope and ambit of the present disclosure.
The present disclosure provides the absorption-based multi-effect evaporative system (hereinafter referred to as the ‘system 100’). The system (100) according to the present disclosure comprises a generator (3). The generator is configured to receive a dilute absorbent solution (42) and a steam input (3a). The generator utilizes the steam input (3a) to boil the dilute absorbent solution (42) to generate refrigerant vapors (4). The steam input (3a) acts as a heating source that passes through a plurality of tubes of the generator (3) to boil the dilute absorbent solution and leave the generator (3) as a steam condensate, whereas the dilute absorbent solution after gaining the heat from the high-temperature steam input generates refrigerant vapors and becomes a strong absorbent solution (3c).
In an embodiment, the steam input (3a) provided to the generator (3) has a temperature in the range of 150 °C to 180 °C, and the refrigerant vapor (4) generated from the generator (3) has a temperature in the range of 75 °C to 110 °C.
The system (100) according to the present disclosure further includes a multi-effect evaporator unit (50) disposed downstream of the generator (3). The multi-effect evaporator unit (50) comprises a plurality of evaporators (5, 8, 11, 14....N) connected in series. Each of the evaporators (5, 8, 11, 14....N) is configured to receive the refrigerant vapors (4, 9, 12,15…N) and circulate the refrigerant vapors through a plurality of tubes (5a, 8a, 11a, 14a…Na) of the corresponding evaporator. Further, each of the evaporators (5, 8, 11, 14....N) is configured to receive a feed solution (6) and spray it over said tubes (5a, 8a, 11a, 14a…Na). As a result, the feed solution (6) sprayed over the tubes absorbs heat from the refrigerant vapors (4, 9, 12, 15…N) to generate a concentrate solution (7, 10, 13, 16…N) and discharge a condensate stream (35, 32, 29, 27…N). Herein, the refrigerant vapors (4) in the generator are generated due to the boiling of the dilute absorbent solution in the generator, whereas the subsequent refrigerant vapors (9, 12, 15…N) are generated from the feed solution (6).
The system (100) according to the present disclosure includes an absorber unit (20) positioned downstream of the multi-effect evaporator unit (50). The absorber unit (20) is configured to receive refrigerant vapors (19) from the multi-effect evaporator unit (50). The absorber unit also receives the strong absorbent solution from the generator (3) and sprays it over a plurality of tubes (20a) of the absorber unit. The strong absorbent solution inside said absorber unit absorbs the refrigerant vapors (19) received from the multi-effect evaporator unit (50) to become the dilute absorbent solution. The absorber unit (20) facilitates the refrigerant vapor absorption process to convert the strong absorbent solution into the dilute absorbent solution.
The absorber unit (20) is strategically positioned between the multi-effect evaporator unit (50) and the generator (3) in order to facilitate the single-effect vapor absorption cycle.
In an exemplary embodiment, the last evaporator (14) of the multi-effect evaporator unit (50) generates the refrigerant vapor (18). The first part (21) is fed to a condenser unit (22) and the second part (19) of the refrigerant vapor (18) is passed toward the absorber unit (20) to carry out the refrigerant vapor absorption process.
In an embodiment, the absorber unit is configured to receive a first water stream (38) from the multi-effect evaporator (50) and circulate it through the plurality of tubes (20a) of said absorber unit (20). The first water stream (38) absorbs heat generated during the refrigerant vapor absorption process in the absorber unit (20) to generate a hot water stream (40). The hot water stream (40) is further supplied to at least one evaporator (5, 8, 11, 14...N) of the multi-effect evaporator unit (50).
In an embodiment, the dilute absorbent solution produced in the absorber unit (20) is collected at the bottom sump of the absorber unit (20). The collected dilute absorbent solution is fed to the generator (3) through at least one heat recovery unit (1, 2).
The heat recovery unit (1, 2) is fluidically connected between the generator (3) and the absorber unit (20). The heat recovery unit (1, 2) is configured to exchange heat between the dilute absorption solution (42) exiting from the absorber unit (20) with at least one of the streams containing the strong absorbent solution (3c) or the steam condensate (3b) exiting from the generator (3).
In an embodiment, the heat recovery unit (1, 2) includes a first heat recovery unit (1) and a second heat recovery unit (2). The first heat recovery unit (1) is configured to receive a first stream (42a) of the dilute absorption solution (42) from the absorber unit (20) and the strong absorbent solution (3c) from the generator (3). The first recovery unit facilitates the exchange of heat between the first stream (42a) and the strong absorbent solution (3c).
In an embodiment, the first heat recovery unit (1) is a low-temperature heat exchanger operating at a temperature in the range of 60 °C to 160 °C.
The second heat recovery unit (2) is configured to receive a second stream (42b) of the dilute absorption solution (42) from the absorber unit (20) and the steam condensate (3b) from the generator (3). In the second recovery unit (2), the steam condensate ejects heat to the second stream (42b) to obtain a heated second stream. The steam condensate (3b) cooled before discharging to the condensate tank.
In an embodiment, the system (100) comprises a condenser. The condenser is positioned downstream of the multi-effect evaporator unit (50). The condenser is configured to receive the first part (21) of the refrigerant vapors (18) exiting from the multi-effect evaporator unit (50) to generate a first condensate (23).
In an embodiment, the multi-effect evaporator unit (50) of the system (100) includes a plurality of heat exchangers (34, 31, 28, 25,…N). In the multi-effect evaporator unit (50), the plurality of heat exchangers (34, 31, 28, 25,…N) is positioned downstream of each of the evaporators (5, 8, 11, 14.....N). The plurality of heat exchangers (34, 31, 28, 25,…N) is configured to heat the feed solution (6) using the condensate stream (35, 32, 29, 27….N) exiting from the corresponding evaporator (5, 8, 11, 14.....N).
In an exemplary embodiment, the heat exchanger (34) is positioned downstream of the evaporator (5). Similarly, the heat exchanger (31) is positioned downstream of the evaporator (8), the heat exchanger (28) is positioned downstream of the evaporator (11), and the heat exchanger (25) is positioned downstream of the evaporator (14).
The heat exchangers (34, 31, 28, 25) exchange the heat between the corresponding condensate stream (35, 32, 29, and 27) discharged from the corresponding evaporator (5, 8, 11, 14) with the feed solution (6) passing through the heat exchanger (34, 31, 28, 25).
In an embodiment, the multi-effect evaporator unit (50) includes four evaporators arranged in a series, a first evaporator (5), a second evaporator (8) downstream of the first evaporator (5), a third evaporator (11) downstream of the second evaporator (8), a fourth evaporator (14) downstream of the third evaporator (11).
The first evaporator (5) is configured to receive the refrigerant vapor (4) from the generator (3) and circulate the refrigerant vapor (4) through the plurality of tubes (5a). The first evaporator (5) is further configured to receive the feed solution (6) from the plurality of heat exchangers (25, 28, 31, 34….N) and spray the feed solution (6) over said tubes (5a) of the first evaporator (5). The feed solution (6) during spraying absorbs heat from the refrigerant vapor (4) to obtain the first refrigerant vapor (9), the first concentrate solution (7), a first condensate stream (35), and discharge the first water stream (38).
The second evaporator (8) is configured to receive the refrigerant vapor (9) from the first evaporator (5) and circulate the first refrigerant vapor (9) through a plurality of tubes (8a). The second evaporator (8) is further configured to receive the first concentrate solution (7) and sprays it over the tubes (8a) of the second evaporator (8). The first concentrate solution (7) absorbs heat from the first refrigerant vapor (9) to obtain a second concentrate solution (10), a second condensate stream (32), and a second refrigerant vapor (12).
The third evaporator (11) is configured to receive the second refrigerant vapor (12) from the second evaporator (8) and circulate the second refrigerant vapor (12) through a plurality of tubes (11a). The third evaporator (11) is further configured to receive the second concentrate solution (10) and spray it over said tubes (11a) of the third evaporator (11). The second concentrate solution (10) absorbs heat from the second refrigerant vapor (12) to obtain a third concentrate solution (13), a third condensate stream (29), and a third refrigerant vapor (15).
The fourth evaporator (14) is configured to receive said third refrigerant vapor (15) from the third evaporator (11) and circulate the third refrigerant vapor (15) through a plurality of tubes (14a). The fourth evaporator (14) is further configured to receive the third concentrate solution (13) and spray it over the tubes (14a) of the fourth evaporator (14). The third concentrate solution (13) absorbs heat from the third refrigerant vapor (15) to obtain a fourth concentrate solution (16), a fourth condensate stream (27), and a fourth refrigerant vapor (18).
The fourth concentrate solution (16) is fed downstream for further processing, the fourth condensate stream (27) leaves the fourth heat exchanger (25) and is collected at the condensate outlet (44), and the fourth refrigerant vapor (18) is split into two parts, first part (21) is fed to the condenser (22) and the second part (19) is fed to the absorber unit (20).
In an embodiment, the system (100) is configured with a pumping unit for the delivery of different types of solutions used in the system (100). In which a first pumping unit (17) is configured to transfer the fourth concentrated solution (16) from the multi-effect evaporator unit (50) to further downstream processes (46).
A second pumping unit (24) is configured to transfer the feed solution (6) from a feed storage tank to the first evaporator (5) of the multi-effect evaporator unit (50) through the plurality of heat exchangers (25, 28, 31, 34…N).
A third pumping unit (37) is configured to transfer the condensate (23, 36) ejected from the condenser (22) and the fourth heat exchanger (25) to further downstream processes (44).
A fourth pumping unit (39) is configured to transfer the first water stream (38) from the multi-effect evaporator unit (50) to the absorber unit (20).
A fifth pumping unit (41) is configured to transfer the dilute absorbent solution (42) from the absorber unit (20) to the generator (3) through the at least one heat recovery unit (1, 2).
In an embodiment, the dilute absorbent solution (42) is made of water and lithium bromide. The dilute absorbent solution is a combination of refrigerant and absorbent material, wherein the refrigerant is water and the absorbent material is at least one selected from lithium bromide, sodium hydroxide, zinc bromide, calcium bromide, sodium chloride and other halides, and the like.
In an embodiment, the first water stream (38) has a temperature in the range of 65 °C to 85 °C and said hot water stream (40) has a temperature in the range of 70 °C to 90 °C.
The system (100) is thus used in Chemical Industries, Food & Beverages, Automobile Industries and Pharmaceuticals where wastewater treatment is required. The system (100) advantageously configures the multi-effect evaporator with the single-effect vapor absorption cycle using the absorber unit.
The system (100) delivers substantial benefits, including 25% to 30% reductions in energy consumption, achieved through the efficient management of steam, hot water, exhaust, and gas usage. Moreover, it ensures 20% to 30% lower power consumption, significantly enhancing operational efficiency. Additionally, the system (100) helps to lower upfront costs with a 10% to 15% reduction in initial investment, while also contributing to long-term savings and environmental sustainability. These combined advantages make it a highly cost-effective and eco-friendly solution.
Therefore, in comparison to the conventional system (100’), the system (100) in accordance with the present disclosure uses part of the saturated steam produced in the last effect evaporator of the Multi-effect evaporator unit(50), which is low-grade heat used as a heat source for the absorption process in the absorber unit (20) to produce hot water stream (40), which in turn is used as a heat source to the first evaporator (5) of the multi-effect evaporator unit (50) along with the refrigerant vapors (4) generated from the generator (3), to reduce the overall energy consumption.
Further, the need for flashing in a flash vessel is eliminated. Thus, removing the flash vessel has led to cost savings. In addition, due to the elimination of the flash vessel, the total construction of the absorption-based multi-effect evaporator system (100) would be in SKID mounted and the need for raising feed temperature above the boiling point in each of the evaporator (5, 8, 11, 14…N) is eliminated which will reduce the required steam pressure in each stage.
In addition, the cooling water flow (Cooling tower capacity) requirement also reduced significantly. Water evaporation loss will also be reduced significantly. Re-circulation pumps used in conventional MEE systems are not required for our proposed invention and hence the power consumption of the system (100) reduced significantly.
The pumping units used in the system are a canned motor pump type which eliminates the need for a double mechanical seal in the centrifugal pumps along with a seal water cooling system. Furthermore, in a conventional MEE system (100’), it is very difficult to maintain the Vacuum in a steady state condition, whereas an advanced purging system is considered to maintain the required vacuum in each stage at a steady state condition in the system (100) in accordance with the present disclosure.
The comparison table of the conventional system (100’) with the system (100) in accordance with the present disclosure is given below:
Description Units Conventional system (100’) The system (100)
feed solution flow rate kg/hr 2500 2500
Water Evaporation capacity kg/hr 2175 2175
Total Solids in Feed solution % 5.2 5.2
Effluent Outlet Flow rate kg/hr 325 325
Effluent Outlet Concentration % 40 40
Steam consumption @ 6 kg/cm2(g) kg/hr 620 400
Cooling water inlet/outlet temperature °C 32 / 38 32 / 38
Cooling water flow rate m3/hr 56 33
The provided comparison table clearly illustrates that the absorption-based multi-effect evaporative system (100) consumes less steam compared to the conventional system (100’). Additionally, it is notable that the flow rate of cooling water is lower in the system (100) compared to the conventional system (100’). The system (100) does not alter the cooling water inlet/ outlet temperature.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment but are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

TECHNICAL ADVANCES AND ECONOMIC SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to the absorption-based multi-effect evaporative system, that:
• minimizes energy consumption;
• optimizes the utilization of heat generated during evaporation by employing heat recovery mechanisms;
• ensures minimal wastage and maximizes overall system efficiency;
• reduces greenhouse gas emissions;
• improves cost-effectiveness by lowering operational expenses associated with steam generation and enhancing overall system performance;
• improves desalination efficiency and output quality while mitigating the environmental impact and operational costs;
• offers a compact, skid-mounted design, simplifying installation and reducing space requirements; and
• eliminates the flashing in a flash vessel.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Throughout this specification the word “comprises”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, or group of elements, but not the exclusion of any other element, or group of elements.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation. ,CLAIMS:WE CLAIM:
1. An absorption-based multi-effect evaporative system (100) comprising:
• a generator (3) configured to receive a dilute absorbent solution (42) and a steam input (3a); boil said dilute absorbent solution (42) using said steam input (3a) to generate refrigerant vapors (4), steam condensate (3b) and a strong absorbent solution (3c);
• a multi-effect evaporator unit (50) disposed downstream of said generator (3), said multi-effect evaporator unit comprising a plurality of evaporators (5, 8, 11, 14.....N) connected in series; each of said evaporators (5, 8, 11, 14.....N) configured to receive and circulate said refrigerant vapors (4, 9, 12, 15,…N) through a plurality of tubes (5a, 8a, 11a, 14a…Na) of corresponding evaporator; receive a feed solution (6) and spray it over said tubes (5a, 8a, 11a, 14a…Na), wherein said feed solution (6) absorbs heat from said refrigerant vapors (4, 9, 12, 15 …N) to generate a concentrate solution (7, 10, 13, 16…N) and discharge a condensate stream (35, 32, 29, 27…N);
• an absorber unit (20) configured downstream of said multi-effect evaporator unit (50) to receive refrigerant vapors (19) from said multi-effect evaporator unit (50), receive said strong absorbent solution (3c) from said generator (3) and spray said strong absorbent solution (3c) over a plurality of tubes (20a) of said absorber unit (20) to absorb said refrigerant vapors (19) into said strong absorbent solution (3c) to produce said dilute absorption solution (42);
• at least one heat recovery unit (1, 2) fluidically connected between said generator (3) and said absorber unit (20), said heat recovery unit (1, 2) configured to exchange heat between said dilute absorption solution (42) exiting said absorber unit (20) and at least one of said strong absorbent solution (3c) or said steam condensate (3b) exiting said generator (3).
2. The system (100) as claimed in claim 1, wherein said system (100) includes a condenser (22) disposed downstream of said multi-effect evaporator unit (50) and configured to receive a first part (21) of the refrigerant vapors (18) exiting the multi-effect evaporator unit (50) to generate a first condensate (23).
3. The system (100) as claimed in claim 1, wherein said at least one heat recovery unit (1, 2) includes:
• a first heat recovery unit (1) configured to heat a first stream (42a) of said dilute absorption solution (42) using said strong absorbent solution (3c) exiting said generator (3);
• a second heat recovery unit (2) configured to heat a second stream (42b) of said dilute absorption solution (42) using said steam condensate (3b) exiting from said generator (3).
4. The system (100) as claimed in claim 1, wherein a first water stream (38) is supplied to said plurality of tubes (20a) of said absorber unit (20), said first water stream (38) absorbs heat generated during the refrigerant vapor absorption process in said absorber unit (20) to generate a hot water stream (40) that exits from said absorber unit (20) and supplied to at least one evaporator (5, 8, 11, 14..N) of said multi-effect evaporator unit (50).
5. The system (100) as claimed in claim 1, wherein said multi-effect evaporator unit (50) comprises a plurality of heat exchangers (34, 31, 28, 25,…N) downstream of each of said evaporator (5, 8, 11, 14.....N), said plurality of heat exchangers (25, 28, 31, 34…N) configured to heat said feed solution (6) using said condensate stream (35, 32, 29, 27 …N) exiting from said corresponding evaporator (5, 8, 11, 14.....N).
6. The system (100) as claimed in any one of the preceding claims, wherein said multi-effect evaporator unit (50) includes:
• a first evaporator (5) is configured to receive said refrigerant vapor (4) from said generator (3) and circulate through said plurality of tubes (5a), receive said feed solution (6) from said plurality of heat exchangers (25, 28, 31, 34…N) and sprays over said tubes (5a), wherein said feed solution (6) absorbs heat from said refrigerant vapor (4) to obtain a first refrigerant vapor (9), a first concentrate solution (7), a first condensate stream (35), and discharge said first water stream (38).
• a second evaporator (8) is configured to receive and circulate said first refrigerant vapor (9) through a plurality of tubes (8a), receives said first concentrate solution (7) and sprays over said tubes (8a) to absorb heat from said first refrigerant vapor (9) to obtain a second concentrate solution (10), a second condensate stream (32), and a second refrigerant vapor (12).
• a third evaporator (11) is configured to receive and circulate said second refrigerant vapor (12) through a plurality of tubes (11a), receives said second concentrate solution (10), and sprays over said tubes (11a) to absorb heat from said second refrigerant vapor (12) to obtain a third concentrate solution (13), a third condensate stream (29), and a third refrigerant vapor (15).
• a fourth evaporator (14) is configured to receive and circulate said third refrigerant vapor (15) through a plurality of tubes (14a), receives said third concentrate solution (13) and sprays over said tubes (14a) to absorb heat from said third refrigerant vapor (15) to obtain a fourth concentrate solution (16), a fourth condensate stream (27), and a fourth refrigerant vapor (18).
7. The system (100) as claimed in any of the preceding claims, wherein
i. a first pumping unit (17) is configured to transfer the fourth concentrated solution (16) from said multi-effect evaporator unit (50) to further downstream processes (46);
ii. a second pumping unit (24) is configured to transfer said feed solution (6) from a feed storage tank to said first evaporator (5) of said multi-effect evaporator unit (50) through said plurality of heat exchangers (25, 28, 31, 34…N);
iii. a third pumping unit (37) is configured to transfer said condensate (23, 36) ejected from said condenser (22) and said fourth heat exchanger (25) to further downstream processes (44);
iv. a fourth pumping unit (39) is configured to transfer said first water stream (38) from said multi-effect evaporator unit (50) to said absorber unit (20); and
v. a fifth pumping unit (41) is configured to transfer said dilute absorbent solution (42) from said absorber unit (20) to said generator (3) through said at least one heat recovery unit (1, 2).
8. The system (100) as claimed in claim 1, wherein said dilute absorbent solution (42) is made of water and lithium bromide.
9. The system (100) as claimed in claim 1, wherein said steam input (3a) provided to said generator (3) has a temperature in the range of 150 °C to 180 °C, and said refrigerant vapor (4) generated from said generator (3) has a temperature in the range of 75 °C to 110 °C
10. The system (100) as claimed in claim 1, wherein said first water stream (38) has a temperature in the range of 65 °C to 85 °C and said hot water stream (40) has a temperature in the range of 70 °C to 90 °C.
Dated this 04th Day of February 2025

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
OF R. K. DEWAN & CO.
AUTHORIZED AGENT OF APPLICANT