CN114349195B - A marine seawater desalination system and working method taking into account carbon dioxide recovery - Google Patents

Abstract

The invention discloses a marine seawater desalination system taking carbon dioxide recovery into account and a working method thereof. In the flue gas treatment unit, high-temperature flue gas generated by an internal combustion engine is subjected to oxidation catalytic reduction, a mixture of high-temperature carbon dioxide, nitrogen and water vapor generated after reduction is subjected to waste heat recovery and temperature reduction, then enters an adsorption device for drying, and then enters a gas compressor after heat exchange between a heat exchanger and LNG cold energy, wherein part of high-pressure liquid carbon dioxide is directly collected, the other part of high-pressure liquid carbon dioxide with pressure enters an energy recovery device for pressure conversion with raw seawater to be changed into gas state again, then enters the gas compressor for circulation, and the converted high-pressure seawater forms fresh water through a reverse osmosis membrane. The invention realizes zero carbon emission and sea water desalination functions of the internal combustion engine by utilizing the critical pressure of carbon dioxide and the pressure conversion of the raw sea water to ensure that the raw sea water can reach the pressure required by the reverse osmosis membrane to work without a high pressure pump.

Description

A marine seawater desalination system and working method taking into account carbon dioxide recovery

technical field

The invention relates to the fields of environmental protection and energy efficient utilization, in particular to a marine seawater desalination system and working method that take into account carbon dioxide recovery.

Background technique

Seawater desalination devices are divided into reverse osmosis devices and seawater distillation devices in principle. From the perspective of seawater desalination projects that have been built and applied around the world, reverse osmosis membrane method accounts for 65%. From a domestic point of view, by the end of 2018, 103 seawater desalination projects had been built across the country, with a water production scale of more than 900,000 m³/d, of which about 570,000 m³/d was produced by membrane reverse osmosis seawater desalination, accounting for 63.3% of the total water production. %, in an absolute dominance. With the commercialization of reverse osmosis seawater desalination technology, the application of this technology on ships is becoming more and more extensive.

In the reverse osmosis membrane seawater desalination system, after the seawater is treated by the pretreatment device to the specified water quality, it is pressurized by a high-pressure pump and sent to the reverse osmosis membrane separation device. Part of the pressurized high-pressure seawater overcomes the osmotic pressure and passes through the reverse osmosis membrane to become fresh water, and the other part of the seawater with increased salt concentration is discharged from the reverse osmosis separation device as concentrated seawater. However, in the seawater desalination process of the reverse osmosis membrane, due to the high salt content of the seawater, the reverse osmosis process requires a relatively large pressure, so the seawater desalination process undoubtedly consumes a lot of energy, and the main energy consumption is the increase of the influent water by the high-pressure pump. Pressure energy consumption, usually the operating pressure of the high pressure pump is as high as 5Mpa~6Mpa.

In order to reduce this part of energy consumption, in the prior art, the water pressure in the deep sea is used to replace the pumping pressure of the high-pressure pump in the conventional reverse osmosis device, so as to complete the desalination of seawater, but this method usually requires the device to be installed at a depth greater than 200 meters. In the deep sea, operation and maintenance are difficult and difficult to implement. Therefore, it is urgent to develop a system that can replace high-pressure pumps and recycle pressure.

The application number is 201310002417.7, and the invention patent titled "a thermal film coupled seawater desalination system" discloses a thermal film coupled seawater desalination system, which is used to reduce the energy consumption of the thermal film coupled seawater desalination system. The system includes a seawater pretreatment unit, a reverse osmosis unit, and a low-temperature multi-effect unit. A steam turbine is installed on the steam inlet pipeline, and the steam turbine is connected in series with the high-pressure pump shaft of the reverse osmosis unit. The high-pressure pump is driven to work by steam expansion, providing The utilization rate of steam heat energy reduces the electric energy consumed by the high-pressure pump. In this system, the steam turbine is used to work to drive the high-pressure pump to work, although the power consumption is reduced, but the energy consumption of the steam turbine is increased, and the energy consumption of the reverse osmosis membrane seawater desalination system is not reduced.

Contents of the invention

The technical problem to be solved by the present invention is to provide a marine seawater desalination system that takes into account the recovery of carbon dioxide, by using the flue gas processing unit to capture and recover the carbon dioxide generated by the internal combustion engine, and at the same time using the critical pressure of carbon dioxide to perform pressure conversion with seawater to achieve reverse osmosis membrane The pressure conditions required for seawater desalination realize zero carbon emissions of internal combustion engines and fresh water preparation.

The present invention adopts following technical scheme for realizing above-mentioned purpose of the invention:

A marine seawater desalination system taking into account carbon dioxide recovery, including a flue gas treatment unit, an energy conversion unit and a seawater desalination unit;

The flue gas treatment unit includes: an LNG inlet, an LNG pump, an internal combustion engine, a flue gas catalytic converter, a waste heat recovery device, an adsorption device, and a heat exchanger. The LNG inlet is connected to the left interface of the LNG pump through a pipeline, and the LNG The right interface of the pump is connected to the upper interface of the heat exchanger through a pipeline, and the lower interface of the heat exchanger is connected to the lower interface of the internal combustion engine through a pipeline, and the internal combustion engine is connected with the flue gas catalytic converter, waste heat recovery device, adsorption Device and heat exchanger connections;

The energy conversion unit includes: a compressor, a pressure sensor I, a pressure sensor II, a PLC controller, a first electric control valve, a second electric control valve, an expansion valve, a separator, a nitrogen outlet, a liquid carbon dioxide outlet, and an energy recovery device I. Check valve, filter, raw seawater inlet, the left interface of the compressor (8) is connected to the heat exchanger through a pipeline, and the right interface of the compressor is connected to the lower interface of the pressure sensor I through a pipeline , the upper interface of the pressure sensor 1 is connected to the PLC controller through a signal cable, and the PLC controller is connected to the first electric control valve and the second electric control valve respectively through a signal cable at the same time. The upper interface of the electric control valve is connected to the right interface of the compressor through a pipeline, the lower interface of the first electric control valve is connected to the separator through a pipeline, the upper interface of the separator is the nitrogen outlet, and the lower The interface is the outlet of the liquid carbon dioxide, the pressure sensor II is also connected to the PLC controller through a signal cable, the left interface of the expansion valve is connected to the lower interface of the pressure sensor I through a pipeline, and the right interface of the expansion valve is The interface is connected to the lower interface of the pressure sensor II through a pipeline, the upper interface of the second electric control valve is connected to the right interface of the expansion valve through a pipeline, and the lower interface of the second electric control valve is connected to the energy source through a pipeline. The a interface of the recovery device 1, the b interface of the energy recovery device 1 is connected to the lower interface of the compressor through a pipeline, and the d interface of the energy recovery device 1 is connected to the check valve through a pipeline, and the check valve Connecting the filter and the raw seawater inlet sequentially through pipelines;

The seawater desalination unit includes a primary reverse osmosis membrane, the c interface of the energy recovery device 1 is connected to the primary reverse osmosis membrane through a pipeline, and the right interface of the primary reverse osmosis membrane is connected to the fresh water collection box through a pipeline .

Preferably, the fuel in the internal combustion engine is natural gas, the heat exchanger is a plate heat exchanger, and the heat exchanger is provided with flue gas channels and LNG channels.

Preferably, the flue gas catalytic converter is provided with a catalyst and a reducing agent, the catalyst is a metal oxide or a zeolite molecular sieve, and the reducing agent is urea or liquid ammonia.

Preferably, a steam pipeline is arranged inside the waste heat recovery device, and the waste heat recovery is used for heat supply or power generation.

Preferably, an adsorbent is provided in the adsorption device, and the adsorbent is activated carbon or activated alumina.

Preferably, the nitrogen outlet is provided with a gas storage tank, and the liquid carbon dioxide outlet is provided with a liquid storage tank.

Preferably, the expansion valve is a gas expansion valve, which plays the role of throttling and reducing pressure.

Preferably, the seawater desalination unit is also provided with a secondary reverse osmosis membrane, an energy recovery device II, a booster pump and a concentrated seawater outlet, and the lower interface of the primary reverse osmosis membrane is connected to the energy recovery device II through a pipeline. c interface of the energy recovery device II, the d interface of the energy recovery device II is connected to the left interface of the concentrated seawater outlet through a pipeline, the a interface of the energy recovery device II is connected to the upper interface of the filter through a pipeline, and the energy recovery device II The b interface of II is connected to the left interface of the booster pump through a pipeline, the right interface of the booster pump is connected to the left interface of the secondary reverse osmosis membrane through a pipeline, and the right interface of the secondary reverse osmosis membrane is connected through a pipeline Connect the freshwater collection tank.

Preferably, both the energy recovery device I and the energy recovery device II are work-exchanging pressure recovery components with a piston inside, and two cavities are arranged on the left and right sides of the piston in the energy recovery device I, and the energy There are two cavities above and below the piston in the recovery device II.

Preferably, an energy storage water wheel is provided at the lower interface of the secondary reverse osmosis membrane, and the other interface of the energy storage water wheel is connected to the compressor shaft.

According to another aspect of the present invention, there is provided a working method for marine desalination of seawater taking into account carbon dioxide recovery, specifically comprising:

(a) The LNG inlet is vaporized by the LNG pump for the internal combustion engine to do work, and the flue gas generated by the combustion of the internal combustion engine is reduced in the flue gas catalytic converter, and the mixture of high-temperature nitrogen, water vapor and carbon dioxide after reduction After entering the waste heat recovery device, the consumed heat is cooled to 50°C~60°C, and then after the adsorption device absorbs water vapor, it enters the heat exchanger and the cold energy released by the vaporization of LNG is cooled to 25°C~30°C for the second time. Finally, nitrogen and carbon dioxide gas enter the compressor to increase the pressure to 5Mpa~7Mpa.

(b) When the pressure sensor I detects that the pressure reaches 7Mpa, the PLC controller drives the first electric control valve to liquefy a part of carbon dioxide and then flows out through the lower interface of the separator, that is, the outlet of the liquid carbon dioxide, Nitrogen then flows out from the nitrogen outlet; when the pressure sensor II detects that the carbon dioxide pressure passing through the expansion valve is 5Mpa~6Mpa, the PLC controller drives the second electric control valve to make the other part with pressure The carbon dioxide enters the energy recovery device I, and the raw seawater enters the filter through the raw seawater inlet to remove colloids and suspended impurities in the raw seawater, and then enters the energy recovery device I through the check valve and is connected with the pressurized The carbon dioxide undergoes pressure conversion. After the conversion, the high-pressure liquid carbon dioxide turns into a gaseous state and enters the compressor again. The original seawater enters the first-stage reverse osmosis membrane after the pressure is raised to separate fresh water, and the fresh water generated flows into the fresh water collection tank through pipelines. .

(c) The pressurized concentrated seawater discharged from the primary reverse osmosis membrane and the raw seawater diverted by the filter enter the energy recovery device II again for pressure conversion and discharge, and the discharged pressurized concentrated seawater passes through The booster pump is pressurized to 5Mpa~6Mpa and enters the secondary reverse osmosis membrane to separate fresh water, and at the same time, the high-pressure concentrated seawater discharged from the secondary reverse osmosis membrane drives the energy storage type water wheel to rotate and do work for the compressor to work .

By adopting the above technical scheme, the present invention at least includes the following beneficial effects:

1. Through the coupling of the flue gas treatment unit and the energy conversion unit, the present invention efficiently utilizes the critical pressure of carbon dioxide, avoids pressure leakage, enhances energy recovery and utilization, and collects liquid carbon dioxide while preparing fresh water. In the energy conversion device, the carbon dioxide after pressure conversion with the original seawater enters the compressor cycle again, which not only avoids environmental pollution caused by direct discharge, but also improves the recovery rate of carbon dioxide, which can reach more than 90%.

2. The present invention uses the critical pressure of carbon dioxide in the energy conversion unit and the original seawater to perform pressure conversion in the energy recovery device, avoiding the extra energy consumed by the high-pressure pump used in the traditional reverse osmosis membrane seawater desalination system, and can reduce power consumption by 30% .

3. The present invention utilizes the cooling capacity of LNG and seawater to directly capture the carbon dioxide produced during the combustion of natural gas, without the use of secondary refrigerant, the system is simple and efficient, and realizes zero-carbon emission of the internal combustion engine.

4. In the present invention, the concentrated seawater with high pressure discharged through the secondary permeable membrane passes through the energy storage water wheel to do work to drive the compressor to work, which reduces the additional driving energy consumption of the compressor to a certain extent.

Description of drawings

Fig. 1 is a schematic diagram of the structure and principle of a marine seawater desalination system taking into account carbon dioxide recovery according to the present invention.

Reference signs: LNG inlet 1, LNG pump 2, internal combustion engine 3, flue gas catalytic converter 4, waste heat recovery device 5, adsorption device 6, heat exchanger 7, compressor 8, pressure sensor I9, pressure sensor II10, first Electric control valve 11, second electric control valve 12, expansion valve 13, energy recovery device I14, energy recovery device II15, primary reverse osmosis membrane 16, secondary reverse osmosis membrane 17, booster pump 18, energy storage water wheel 19. Original seawater inlet 20, filter 21, check valve 22, concentrated seawater outlet 23, fresh water collection tank 24, nitrogen outlet 25, liquid carbon dioxide outlet 26, separator 27, PLC controller 28.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be further described in detail below in conjunction with the drawings in the embodiments of the present invention. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

As shown in Figure 1, a marine seawater desalination system and working method taking into account carbon dioxide recovery, including a flue gas processing unit, an energy conversion unit and a seawater desalination unit.

The flue gas treatment unit includes: LNG inlet 1, LNG pump 2, internal combustion engine 3, flue gas catalytic converter 4, waste heat recovery device 5, adsorption device 6, heat exchanger 7, and the LNG inlet 1 is connected to the The left interface of the LNG pump 2, the right interface of the LNG pump 2 are connected to the upper interface of the heat exchanger 7 through a pipeline, the lower interface of the heat exchanger 7 is connected to the lower interface of the internal combustion engine 3 through a pipeline, and the LNG passes through the LNG pump. 2 is vaporized for the internal combustion engine 3 to do work, and the internal combustion engine 3 is sequentially connected to the flue gas catalytic converter 4, waste heat recovery device 5, adsorption device 6 and heat exchanger 7 through pipelines, so that the flue gas generated by the internal combustion engine 3 is converted into flue gas. The reduction is carried out in the device 4. After reduction, the mixture of high-temperature nitrogen, water vapor and carbon dioxide is cooled to 50°C~60°C by the heat consumed in the waste heat recovery device 5, and then enters the heat exchanger after being adsorbed by the adsorbent in the adsorption device 6. 7 and the cold energy released by the vaporization of LNG for secondary cooling to 25°C~30°C. The adsorbent is activated carbon or activated alumina, and a catalyst and a reducing agent are provided in the flue gas catalytic converter 4. The catalyst is metal oxide or zeolite molecular sieve, and the reducing agent is urea or liquid ammonia.

Wherein, the heat exchanger 7 is a plate heat exchanger, and the heat exchanger 7 is provided with flue gas passages and LNG passages. Compared with the shell-and-tube heat exchanger, under the same pressure loss, the plate heat The heat transfer coefficient of the device is generally 2 to 3 times higher.

At the same time, a steam pipeline is provided inside the waste heat recovery device 5, and the waste heat recovery is used for heat supply or power generation.

The energy conversion unit includes: a compressor 8, a pressure sensor I9, a pressure sensor II10, a PLC controller 28, a first electric control valve 11, a second electric control valve 12, an expansion valve 13, a separator 27, a nitrogen outlet 25, Liquid carbon dioxide outlet 26, energy recovery device I14, check valve 22, filter 21, raw seawater inlet 20;

As shown in Figure 1, the left interface of the compressor 8 is connected to the right interface of the heat exchanger 7 through a pipeline, and the right interface of the compressor 8 is connected to the lower interface of the pressure sensor 19 through a pipeline, and the pressure The upper interface of the sensor 19 is connected to the lower left interface of the PLC controller 28 through a signal cable, and the left interface of the PLC controller 28 is connected to the right interface of the first electric control valve 11 through a signal cable. The upper interface of the control valve 11 is connected to the right interface of the compressor 8 through a pipeline, and the lower interface of the first electric control valve 11 is connected to the left interface of the separator 27 through a pipeline. The upper interface of the separator 27 is The nitrogen outlet 25, the lower interface of the separator 27 is the liquid carbon dioxide outlet 26, the left interface of the expansion valve 13 is connected to the lower interface of the pressure sensor I9 through a pipeline, and the right interface of the expansion valve 13 is Connect the lower interface of the pressure sensor II10 through a pipeline, the upper interface of the pressure sensor II10 is connected to the lower right interface of the PLC controller 28 through a signal cable, and the right interface of the PLC controller 28 is connected to the The right interface of the second electric control valve 12, the upper interface of the second electric control valve 12 is connected to the right interface of the expansion valve 13 through a pipeline, wherein the expansion valve 13 is a gas expansion valve, which plays a role in throttling and depressurization The lower interface of the second electric control valve 12 is connected to the a interface of the energy recovery device I14 through a pipeline, and the b interface of the energy recovery device I14 is connected to the lower interface of the compressor 8 through a pipeline. The d interface of the energy recovery device I14 is connected to the upper interface of the check valve 22 through a pipeline, the lower interface of the check valve 22 is connected to the upper interface of the filter 21 through a pipeline, and the lower interface of the filter 21 is connected to the upper interface of the filter 21 through a pipeline. A pipeline is connected to the raw seawater inlet 20.

A gas storage tank is provided at the nitrogen outlet 25, and a liquid storage tank is provided at the liquid carbon dioxide outlet 26 to recover nitrogen and liquid carbon dioxide.

The energy recovery device I14 is a work-exchanging pressure recovery component with a piston inside. There are two cavities on the left and right of the piston in the energy recovery device I14. When high-pressure liquid carbon dioxide enters the left cavity, the piston is pushed to move to the right This increases the pressure of sea water.

The seawater desalination unit includes: a primary reverse osmosis membrane 16, a secondary reverse osmosis membrane 17, an energy storage water wheel 19, an energy recovery device II15, a booster pump 18, a concentrated seawater outlet 23, and a fresh water collection tank 24. The left interface of the first-level reverse osmosis membrane 16 is connected to the c interface of the energy recovery device I14 through a pipeline, and the right interface of the first-level reverse osmosis membrane 16 is connected to the fresh water collection tank 24 through a pipeline. The lower interface of 16 is connected to the c interface of the energy recovery device II15 through a pipeline, and the concentrated seawater with pressure passing through the reverse osmosis membrane is reused, and the d interface of the energy recovery device II15 is connected to the outlet of the concentrated seawater through a pipeline 23, the a port of the energy recovery device II15 is connected to the upper port of the filter 21 through a pipeline, and the b port of the energy recovery device II15 is connected to the left port of the booster pump 18 through a pipeline. The right interface of the booster pump 18 is connected to the left interface of the secondary reverse osmosis membrane 17 through a pipeline, and the right interface of the secondary reverse osmosis membrane 17 is connected to the fresh water collection tank 24 through a pipeline.

The lower interface of the secondary reverse osmosis membrane 17 is provided with an energy storage type water wheel 19, and the other interface of the energy storage type water wheel 19 is connected to the compressor 8, so that the high-pressure concentrated seawater discharged by the secondary reverse osmosis membrane 17 By driving the energy storage type water wheel 19 to rotate and do work, the electrical energy is stored for the operation of the compressor 8 .

Wherein, the energy recovery device II15 is a work-exchanging pressure recovery component, with a piston inside and two cavities above and below the piston. When high-pressure liquid carbon dioxide enters the left cavity, the piston is pushed to move to the right so that the seawater Pressure rises.

Nitrogen and carbon dioxide gas produced by the flue gas treatment system enter the compressor 8 to increase the pressure to 5Mpa~7Mpa. When the pressure sensor 19 detects that the pressure reaches 7Mpa, the PLC controller 28 drives the first The electric control valve 11 liquefies a part of carbon dioxide and flows out through the lower interface of the separator 27, that is, the liquid carbon dioxide outlet 26, and nitrogen flows out through the nitrogen outlet 25. When the pressure sensor II10 detects that the gas passes through the expansion valve When the carbon dioxide pressure of 13 is 5Mpa~6Mpa, the PLC controller 28 drives the second electric control valve 12 to make another part of the carbon dioxide with pressure enter the energy recovery device I14, and the raw seawater passes through the raw seawater inlet 20 Enter the filter 21 to remove the colloid and suspended impurities in the original seawater, and then enter the energy recovery device I14 through the check valve 22 to perform pressure conversion with the pressured carbon dioxide, and the high-pressure liquid carbon dioxide becomes a gaseous state and enters again In the compressor 8, the raw seawater enters the first-stage reverse osmosis membrane 16 to separate fresh water after the pressure is raised, and the fresh water produced flows into the fresh water collection tank 24 through a pipeline.

Usually, the pressure of the concentrated seawater discharged from the primary reverse osmosis membrane 16 can reach 4.8Mpa~5.8Mpa, and this part of the concentrated seawater with pressure and the raw seawater after passing through the filter 21 will enter the energy recovery device II15 again After the pressure conversion, the discharged concentrated seawater with pressure is pressurized to 5Mpa~6Mpa by the booster pump 18 and enters the secondary reverse osmosis membrane 17 to separate fresh water. From the secondary reverse osmosis membrane 17 The discharged high-pressure concentrated seawater drives the energy storage water wheel 19 to rotate and do work for the compressor 8 to work, and so on.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within range.

In the description of the present invention, it should be noted that the positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer" etc. is based on the positional relationship shown in the drawings , are only for the convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred elements must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.

Claims (8)

1. The marine seawater desalination system capable of recovering carbon dioxide is characterized by comprising a flue gas treatment unit, an energy conversion unit and a seawater desalination unit, wherein the flue gas treatment unit comprises: LNG entry (1), LNG pump (2), internal-combustion engine (3), flue gas catalytic converter (4), waste heat recoverer (5), adsorption equipment (6), heat exchanger (7), LNG entry (1) pass through the pipe connection LNG pump (2) left side interface, LNG pump (2) right side interface pass through the pipe connection heat exchanger (7) go up the interface, the lower interface of heat exchanger (7) passes through the pipe connection internal-combustion engine (3) lower interface, internal-combustion engine (3) with flue gas catalytic converter (4), waste heat recoverer (5), adsorption equipment (6) and heat exchanger (7) are connected in proper order;

the energy conversion unit includes: the device comprises a gas compressor (8), a pressure sensor I (9), a pressure sensor II (10), a PLC (programmable logic controller) (28), a first electric control valve (11), a second electric control valve (12), an expansion valve (13), a separator (27), a nitrogen outlet (25), a liquid carbon dioxide outlet (26), an energy recovery device I (14), a check valve (22), a filter (21) and an original seawater inlet (20), wherein the left interface of the gas compressor (8) is connected with the heat exchanger (7) through a pipeline, the right interface of the gas compressor (8) is connected with the lower interface of the pressure sensor I (9) through a pipeline, the upper interface of the pressure sensor I (9) is connected with the PLC (28) through a signal cable, the PLC (28) is simultaneously connected with the first electric control valve (11) and the second electric control valve (12) through signal cables, the upper interface of the first electric control valve (11) is connected with the right interface of the gas compressor (8) through a pipeline, the lower interface of the first electric control valve (11) is connected with the lower interface of the separator (27), the upper interface of the separator (27) is the nitrogen outlet of the separator (25), the pressure sensor II (10) is also connected with the PLC (28) through a signal cable, the left interface of the expansion valve (13) is connected with the lower interface of the pressure sensor I (9) through a pipeline, the right interface of the expansion valve (13) is connected with the lower interface of the pressure sensor II (10) through a pipeline, the upper interface of the second electric control valve (12) is connected with the right interface of the expansion valve (13) through a pipeline, the lower interface of the second electric control valve (12) is connected with the a interface of the energy recovery device I (14) through a pipeline, the b interface of the energy recovery device I (14) is connected with the lower interface of the air compressor (8) through a pipeline, the d interface of the energy recovery device I (14) is connected with the check valve (22) through a pipeline, and the check valve (22) is sequentially connected with the filter (21) and the raw seawater inlet (20) through a pipeline;

the sea water desalination unit comprises a first-stage reverse osmosis membrane (16), wherein a c interface of the energy recovery device I is connected with the first-stage reverse osmosis membrane (16) through a pipeline, and a right interface of the first-stage reverse osmosis membrane (16) is connected with a fresh water collecting box (24) through a pipeline; the seawater desalination unit is internally provided with a second-stage reverse osmosis membrane (17), an energy recovery device II (15), a booster pump (18) and a concentrated seawater outlet (23), wherein the lower interface of the first-stage reverse osmosis membrane (16) is connected with the c interface of the energy recovery device II (15) through a pipeline, the d interface of the energy recovery device II (15) is connected with the concentrated seawater outlet (23) through a pipeline, the a interface of the energy recovery device II (15) is connected with the upper interface of the filter (21) through a pipeline, the b interface of the energy recovery device II (15) is connected with the left interface of the booster pump (18) through a pipeline, the right interface of the booster pump (18) is connected with the left interface of the second-stage reverse osmosis membrane (17) through a pipeline, and the right interface of the second-stage reverse osmosis membrane (17) is connected with the fresh water collection box (24) through a pipeline; an energy storage water wheel (19) is arranged at the lower interface of the secondary reverse osmosis membrane (17), and the other interface of the energy storage water wheel (19) is connected with the compressor (8) through a shaft.

2. The marine seawater desalination system with carbon dioxide recovery as claimed in claim 1, wherein the fuel in the internal combustion engine (3) is natural gas, the heat exchanger (7) is a plate heat exchanger, and a flue gas channel and an LNG channel are arranged in the heat exchanger (7).

3. The marine seawater desalination system with carbon dioxide recovery as claimed in claim 1, wherein a catalyst and a reducing agent are arranged in the flue gas catalytic converter (4), the catalyst is a metal oxide or zeolite molecular sieve, and the reducing agent is urea or liquid ammonia; and a steam pipeline is arranged in the waste heat recoverer (5).

4. The marine seawater desalination system with carbon dioxide recovery as claimed in claim 1, wherein the adsorption device (6) is provided with an adsorbent, and the adsorbent is activated carbon or activated alumina.

5. A marine desalination system with carbon dioxide recovery as claimed in claim 1, wherein the nitrogen outlet (25) is provided with a gas storage tank and the liquid carbon dioxide outlet (26) is provided with a liquid storage tank.

6. A marine desalination system with carbon dioxide recovery as claimed in claim 1, wherein the expansion valve (13) is a gas expansion valve.

7. The marine seawater desalination system with carbon dioxide recovery as claimed in claim 1, wherein the energy recovery device I (14) and the energy recovery device II (15) are power exchange type pressure recovery components, a piston is arranged in the energy recovery device I (14), two cavities are arranged on the left and right sides of the piston in the energy recovery device I (14), and two cavities are arranged on the upper side and the lower side of the piston in the energy recovery device II (15).

8. A marine seawater desalination working method taking carbon dioxide recovery into consideration is characterized by comprising the following steps:

(a) The LNG inlet (1) is gasified by the LNG pump (2) and then is supplied to the internal combustion engine (3) to do work, the smoke generated by the combustion of the internal combustion engine (3) is reduced in the smoke catalytic converter (4), the mixture of nitrogen, water vapor and carbon dioxide with high temperature after reduction enters the waste heat recoverer (5) to be cooled to 50-60 ℃ by the consumed heat, then the water vapor is adsorbed by the adsorption device (6) and then enters the heat exchanger (7) to be cooled to 25-30 ℃ for the second time with the cold energy released by the LNG gasification, and finally the nitrogen and the carbon dioxide gas enter the gas compressor (8) to increase the pressure to 5-7 mpa;

(b) When the pressure sensor I (9) detects that the pressure reaches 7Mpa, the PLC (28) drives the first electric control valve (11) to liquefy part of carbon dioxide and then flow out through a liquid carbon dioxide outlet (26) which is the lower interface of the separator (27), and nitrogen flows out through a nitrogen outlet (25); when the pressure sensor II (10) detects that the pressure of the carbon dioxide passing through the expansion valve (13) is 5 mpa-6 mpa, the PLC (28) drives the second electric control valve (12) to enable the other part of the carbon dioxide with pressure to enter the energy recovery device I (14), raw seawater enters the filter (21) through the raw seawater inlet (20) to remove colloid and suspended impurities in the raw seawater, then enters the energy recovery device I (14) through the check valve (22) to perform pressure conversion with the carbon dioxide with pressure, high-pressure liquid carbon dioxide after conversion is changed into a gaseous state again to enter the air compressor (8), the raw seawater enters the first-stage reverse osmosis membrane (16) to separate fresh water after pressure elevation, and the generated fresh water flows into the fresh water collecting box (24) through a pipeline;

(c) The method comprises the steps that concentrated seawater with pressure discharged by a first-stage reverse osmosis membrane (16) and raw seawater which is shunted by a filter (21) are discharged after pressure conversion in an energy recovery device II (15), the discharged concentrated seawater with pressure is pressurized to 5-6 mpa by a booster pump (18) and enters a second-stage reverse osmosis membrane (17) to separate fresh water, and meanwhile, high-pressure concentrated seawater discharged by the second-stage reverse osmosis membrane (17) drives an energy storage water wheel (19) to rotate to do work so as to enable the air compressor (8) to work.

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