LNG (Liquefied Natural Gas) ship flue gas waste heat and cold energy synergetic seawater recycling process

Abstract

The invention provides an LNG (Liquefied Natural Gas) ship flue gas waste heat and cold energy synergistic seawater recycling process, which relates to the technical field of ship energy and resource comprehensive utilization and comprises a flue gas treatment module, a seawater desalination module and a CO2 fixation module, the flue gas treatment module comprises a desulfurization tower, and an in-tower gasification heat exchange coil, a flue gas preliminary dehydration heat exchanger, a coalescence dehydration filter, a flue gas compressor, a deep dehydration heat exchanger and an activated carbon and molecular sieve adsorption tank which are arranged in the desulfurization tower, and the flue gas preliminary dehydration heat exchanger and the deep dehydration heat exchanger take LNG as a cold source; the flue gas is sequentially cooled to 0 DEG C or below, water vapor is deeply removed, innovative three-level cold energy utilization enables the cold energy recovery rate to reach 79.2%, the cold energy recovery rate is increased by 5.3 times compared with traditional seawater direct heating gasification which is smaller than 15%, and 1200 tons of standard coal can be saved for a single ship every year. LNG cold energy is used for driving seawater to crystallize and desalt at low temperature, electricity consumption is only 0.8 kWh / m < 3 > fresh water, compared with a traditional reverse osmosis method, the electricity consumption is greatly reduced, and the cost is reduced by 80%. The daily produced fresh water is 58m < 3 > in a real ship test, and the requirement of 200 sailors for water is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of comprehensive utilization of ship energy and resources, and more specifically, particularly relates to a process for synergizing seawater resources with waste heat and cold energy from flue gas of LNG ships. Background Art

[0002] At a time when the global shipping industry is booming, LNG (liquefied natural gas) ships, as an important means of energy transportation, have attracted much attention for their energy efficiency and environmental performance. Traditional LNG ships have many problems that need to be solved during operation, which seriously restricts the sustainable development of the shipping industry.

[0003] 1. Low efficiency of cold energy utilization: The traditional LNG gasification process is like a "cold energy black hole", and most of the cold energy is directly discharged and wasted. In the traditional seawater direct heating gasification process, the utilization rate of LNG cold energy is extremely low, usually less than 15%. This not only causes a huge waste of energy, but also makes the ship operation cost high. The discharge of a large amount of cold energy may also have a potential impact on the marine environment and destroy the thermal balance of the marine ecosystem.

[0004] 2. Severe waste of flue gas heat: Ship flue gas emissions carry a large amount of waste heat. The traditional treatment method is to discharge the flue gas directly, with a waste heat waste rate of up to 100%. This not only causes a waste of energy, but also leads to serious thermal pollution problems. Taking a 174,000 cubic meter LNG ship as an example, the thermal pollution caused by the direct discharge of flue gas waste heat is equivalent to the waste of 21,000 tons of standard coal each year, exacerbating the pressure of global warming.

[0005] 3. Seawater resources are not effectively utilized: Although ships sail on the sea, traditional processes have failed to effectively utilize seawater as a resource. Traditional seawater desalination methods, such as reverse osmosis, consume up to 4-6kWh / m³ of fresh water, are costly, and the equipment is complex and difficult to maintain. In addition, the demand for fresh water during ship operation can only rely on external purchases or limited onboard fresh water reserves, and cannot achieve self-sufficiency, facing the risk of insufficient fresh water supply when sailing in the ocean.

[0006] 4. CO2 emissions and treatment issues are prominent: CO2 emissions from ships are one of the important factors leading to global climate change. Direct CO2 emissions from traditional LNG ships are common, and there is a lack of effective capture and fixation measures. Even if some ship-borne carbon capture technologies are available, the cost is still high, usually >80 yuan / ton, which makes it difficult for shipping companies to widely adopt them due to cost considerations, resulting in high carbon emissions. At the same time, SO x and NO xEmissions of pollutants such as sulfur dioxide are likely to trigger pollution problems such as those on Iwo Jima, seriously affecting the marine ecological environment and air quality.

[0007] 5. Insufficient equipment adaptability and stability: Traditional ship-related equipment has poor adaptability under different operating conditions. For example, in the face of fluctuations in seawater temperature from 5 to 30 °C and flue gas load from 50% to 120%, traditional equipment is difficult to operate stably, with large fluctuations in freshwater production, unable to meet the stable needs of ships in different sea areas and operating conditions. Moreover, the service life of traditional equipment is short. For example, the membrane module has a life of only 24 months, with high maintenance costs, affecting the normal operation and economic benefits of ships.

[0008] 6. Limited economy and industry development: The above problems lead to high operating costs for ships. From energy waste to environmental protection fines, to equipment maintenance and freshwater outsourcing costs, etc., the economic benefits of the shipping industry are seriously affected. In addition, with the increasingly strict environmental protection standards such as carbon emissions by the International Maritime Organization (IMO), the traditional shipping model faces huge challenges, such as being unable to meet the IMO CII (Carbon Intensity Indicator) limit, seriously restricting the sustainable development of the industry.

[0009] In summary, traditional LNG ships have many drawbacks in terms of energy utilization, environmental protection, and economy. There is an urgent need for an innovative process to solve these problems and achieve green and efficient development of the shipping industry. The LNG ship flue gas waste heat and cold energy collaborative seawater resource utilization process of the present invention is developed based on such a background, aiming to break through the traditional technical bottlenecks and bring new development opportunities to the shipping industry. Summary of the Invention

[0010] In order to solve the above technical problems, the present invention provides an LNG ship flue gas waste heat and cold energy collaborative seawater resource utilization process to solve the above problems.

[0011] An LNG ship flue gas waste heat and cold energy collaborative seawater resource utilization process includes a flue gas treatment module, a seawater desalination module, and a CO2 fixation module; The flue gas treatment module includes a desulfurization tower and an in-tower vaporization heat exchange coil, a flue gas preliminary dehydration heat exchanger, a coalescing dehydration filter, a flue gas compressor, a deep dehydration heat exchanger, and an activated carbon + molecular sieve adsorption tank inside the desulfurization tower. The flue gas preliminary dehydration heat exchanger and the deep dehydration heat exchanger use LNG as the cold source to cool the flue gas to below 0 °C in sequence and deeply remove water vapor; The seawater desalination module includes a seawater primary heat exchanger, a seawater deicer, and a desalination device. The seawater primary heat exchanger uses the cold energy of LNG to pre-cool seawater to -5 °C, and the seawater deicer further cools it to -8 to -10 °C through an LNG freezing heat exchange tube to separate low-salt ice crystals for ship fresh water; The CO2 fixation module includes a tubular membrane concentration module, a distributor, a stirrer, a reaction crystallization tank and a plate and frame filter press. The tubular membrane concentration module increases the CO2 concentration in the flue gas to more than 50% (V / V). The high-concentration CO2 reacts with ammonia and concentrated seawater in the reaction crystallization tank at a low temperature of -10~-15°C to form bicarbonate. Through the distributor for spraying and mixing and the stirrer for strengthening mass transfer, the crystal salts are separated by the plate and frame filter press and then transported out. Preferably, the desulfurization tower is a packing-free empty tower structure, with a serpentine gasification heat exchange coil inside. LNG or low-temperature CH4 flows through the coil, and is heated to 5~15°C using the waste heat of the desulfurized spray seawater. The coil layout density is 20~30m 2 / m 3 Tower volume.

[0012] Preferably, a low-temperature dehydration filter is connected in series after the coalescing dehydration filter to filter the flue gas ice crystals at -10~-15°C. After dehydration, the flue gas dew point ≤ -40°C and the total water content < 10 ppm to avoid clogging of the membrane concentration module.

[0013] Preferably, the bottom of the seawater deicer is provided with deicing inclined plates with an inclination angle of 15~30°. The ice crystal sliding rate is 0.5~1.2 m / s. After separation, the salinity of the seawater increases from 3.5% to 5.0~6.5%, and the cold energy is recovered through a plate heat exchanger before entering the seawater concentration module.

[0014] Preferably, a spiral LNG refrigeration heat exchange tube is arranged in the reaction crystallization tank, with a temperature control accuracy of ±1°C. Combined with a stirrer rotation speed of 50~150 rpm, the solution supersaturation is maintained at 1.2~1.5 to promote the directional crystallization of bicarbonate, and the crystallization rate ≥ 85%.

[0015] Preferably, the filtrate tank of the plate and frame filter press is reinjected into the reaction crystallization tank through a circulation pump. The circulation volume accounts for 30~50% of the liquid volume in the tank, which is used to dilute the NH4⁺ concentration and supplement the reaction medium to avoid the precipitation of ammonium chloride.

[0016] Preferably, the LNG ship flue gas waste heat and cold energy collaborative seawater resource utilization process includes the following steps: S1: After the flue gas is desulfurized by the desulfurization tower, it is dehydrated preliminarily at -10°C and deeply dehydrated at -15°C in sequence, removing more than 99% of the water vapor; S2: LNG exchanges heat with seawater at -5°C, deicer at -10°C, and reaction crystallization tank at -15°C in sequence. After gasification, the low-temperature CH4 enters the coil in the tower and is heated to normal temperature using the waste heat of the desulfurized seawater; S3: The concentrated seawater with a salinity of 5~6.5% reacts with CO2 and NH3 at -10~-15°C for 40~60 min, controlling the pH value at 8.5~9.5 to generate sodium bicarbonate crystals; S4: After pressure filtration and dehydration, the water content of the crystalline salt is ≤ 10%, the recycling rate of the filtrate is ≥ 90%, the fresh water output rate of the system is 15 - 20%, and the CO2 fixation rate is ≥ 92%.

[0017] Preferably, the flue gas passes through an activated carbon + molecular sieve adsorption tank before the membrane concentration module to remove residual SO x / NO x to < 5 ppm, avoiding poisoning of the reaction system and extending the service life of the membrane module to more than 5 years.

[0018] Preferably, a gas washing buffer tank is arranged at the top of the reaction crystallization tank, and the unreacted CO2 is sprayed and washed with concentrated seawater. The concentration of the tail gas CO2 is < 0.2%, meeting the IMO Tier III emission standard.

[0019] Preferably, the temperature difference between the CH4 temperature at the outlet of the gasification heat exchange coil in the tower and the seawater in the desulfurization tower is ≤ 5 °C, the waste heat recovery rate is ≥ 75%. Compared with the traditional direct seawater gasification, the cold energy utilization rate is increased by more than 40%, and the system comprehensive energy efficiency ratio (COP) reaches 2.8 - 3.2.

[0020] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, the innovative three - stage cold energy utilization enables the cold energy recovery rate to reach 79.2%. Compared with < 15% of the traditional direct seawater gasification, it is increased by 5.3 times, and the annual energy consumption saved per ship is 1200 tons of standard coal. Using LNG cold energy to drive seawater low - temperature crystallization desalination, the power consumption is only 0.8 kWh / m³ of fresh water, which is significantly lower than that of the traditional reverse osmosis method, and the cost is reduced by 80%. The actual ship test shows a daily fresh water output of 58 m³, meeting the water use requirements of 200 crew members.

[0021] In the present invention, the serpentine coil in the desulfurization tower recovers waste heat, and the waste heat recovery rate is 75%, reducing a large amount of heat pollution compared with the traditional direct flue gas discharge. The non - packing design doubles the space utilization rate, the system COP reaches 3.12, and it still has high efficiency and stability under partial load, being superior to similar equipment In the present invention, the carbon capture rate is 92%, the annual CO2 fixation per ship is 6300 tons, and the emission reduction cost is only 18 yuan / ton, far lower than that of traditional ship - borne carbon capture. 2800 tons of industrial - grade bicarbonate are generated annually. Coupled with fresh water self - sufficiency, the annual comprehensive income per ship is 1.13 million yuan, far exceeding the power generation income of Comparative Example 2. The tail gas emissions fully meet the IMO Tier III standard, with strong environmental protection compliance In the present invention, under the fluctuations of seawater temperature from 5 - 30 °C and flue gas load from 50% - 120%, the fluctuation of fresh water production is < 12%, and it can adapt to different sea area temperatures. The pretreatment system effectively extends the service life of the membrane module to 62 months, and the maintenance cost is reduced by 60%. The inclined plate design of the de - icer avoids the risk of ice blockage, and there are 0 failures in the actual ship for 6 months. Description of the Drawings

[0022] Figure 1It is a schematic diagram of the process composition of the present invention; Figure 2 It is a schematic diagram of the flue gas treatment module in the present invention; Figure 3 It is a schematic diagram of the seawater desalination module in the present invention; Figure 4 It is a schematic diagram of the CO2 fixation module in the present invention; Figure 5 It is a schematic diagram of the desulfurization tower in the present invention; Figure 6 It is a schematic diagram of the coalescing dehydration filter in the present invention; Figure 7 It is a schematic diagram of the seawater ice breaker in the present invention; Figure 8 It is a schematic diagram of the reaction crystallization tank in the present invention; Figure 9 It is a schematic diagram of the plate and frame filter press in the present invention; Figure 10 It is a schematic diagram of the process flow of the present invention; Figure 11 It is a schematic diagram of the desulfurization tower in the process flow of the present invention; Figure 12 It is a schematic diagram of the tubular membrane concentration module in the process flow of the present invention; Figure 13 It is a schematic diagram of the reaction crystallization tank in the process flow of the present invention; Figure 14 It is a schematic diagram of the filtrate tank in the process flow of the present invention; Figure 15 It is a schematic diagram of the ice removal inclined plate in the process flow of the present invention. Detailed implementation manners

[0023] The following further describes the implementation manners of the present invention in detail with reference to the drawings and embodiments. The following embodiments are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0024] Please refer to Figure 1 - Figure 15 , the present invention provides an LNG ship flue gas waste heat and cold energy collaborative seawater resource utilization process, including a flue gas treatment module, a seawater desalination module and a CO2 fixation module; The flue gas treatment module includes a desulfurization tower and an in-tower vaporization heat exchange coil, a flue gas preliminary dehydration heat exchanger, a coalescing dehydration filter, a flue gas compressor, a deep dehydration heat exchanger and an activated carbon + molecular sieve adsorption tank inside. The flue gas preliminary dehydration heat exchanger and the deep dehydration heat exchanger use LNG as a cold source to cool the flue gas below 0°C in sequence and deeply remove water vapor; The seawater desalination module includes a primary seawater heat exchanger, a seawater de-icer, and a desalination device. The primary seawater heat exchanger uses the cold energy of LNG to pre-cool seawater to -5°C. The seawater de-icer further cools it to -8 to -10°C through LNG refrigeration heat exchange tubes, and separates low-salt ice crystals for ship fresh water. The CO2 fixation module includes a tubular membrane concentration module, a distributor, a stirrer, a reaction crystallization tank, and a plate and frame filter press. The tubular membrane concentration module increases the CO2 concentration in the flue gas to more than 50% (V / V). High-concentration CO2 reacts with ammonia and concentrated seawater in the reaction crystallization tank at a low temperature of -10 to -15°C to generate bicarbonate. Through the distributor for spraying and mixing and the stirrer for strengthening mass transfer, the crystal salts are separated by the plate and frame filter press and then transported out.

[0025] The desulfurization tower is a packing-free empty tower structure, with serpentine gasification heat exchange coils installed inside. LNG or low-temperature CH4 flows through the coils, and uses the waste heat of the desulfurized spray seawater to heat it to 5 to 15°C. The coil layout density is 20 to 30 m² / m³ of the tower volume. A coalescing dehydration filter is connected in series with a low-temperature dehydration filter to filter the flue gas ice crystals at -10 to -15°C. After dehydration, the flue gas dew point is ≤ -40°C, and the total water content is < 10 ppm to avoid clogging of the membrane concentration module. An ice removal inclined plate with an inclination angle of 15 to 30° is set at the bottom of the seawater de-icer, and the ice crystal sliding rate is 0.5 to 1.2 m / s. After separation, the salinity of the seawater increases from 3.5% to 5.0 to 6.5%, and the cold energy is recovered through a plate heat exchanger before entering the seawater concentration module.

[0026] Spiral LNG refrigeration heat exchange tubes are installed in the reaction crystallization tank, with a temperature control accuracy of ±1°C. Combined with a stirrer rotation speed of 50 to 150 rpm, the solution supersaturation is maintained at 1.2 to 1.5, promoting the directional crystallization of bicarbonate, and the crystallization rate is ≥85%. The filtrate pool of the plate and frame filter press is injected back into the reaction crystallization tank through a circulation pump, and the circulation volume accounts for 30 to 50% of the liquid volume in the tank, which is used to dilute the NH4⁺ concentration and supplement the reaction medium to avoid the precipitation of ammonium chloride.

[0027] The LNG ship flue gas waste heat and cold energy collaborative seawater resource utilization process includes the following steps: S1: After the flue gas is desulfurized by the desulfurization tower, it is dehydrated preliminarily at -10°C and deeply dehydrated at -15°C in sequence, removing more than 99% of the water vapor. S2: LNG exchanges heat with seawater at -5°C in the primary heat exchanger, -10°C in the de-icer, and -15°C in the reaction crystallization tank in sequence. After gasification, the low-temperature CH4 enters the coils in the tower and is heated to room temperature using the waste heat of the desulfurized seawater. S3: Concentrated seawater with a salinity of 5 to 6.5% reacts with CO2 and NH3 at -10 to -15°C for 40 to 60 minutes, controlling the pH value at 8.5 to 9.5 to generate sodium bicarbonate crystals. S4: After pressure filtration and dehydration, the water content of the crystal salt is ≤10%, the recycling rate of the filtrate is ≥90%, the fresh water output rate of the system is 15 - 20%, and the CO2 fixation rate is ≥92%.

[0028] Before the membrane concentration module, the flue gas passes through an activated carbon + molecular sieve adsorption tank to remove residual SO x / NO x to <5 ppm, prevent the reaction system from being poisoned, extend the service life of the membrane module to more than 5 years. A scrubbing buffer tank is set at the top of the reaction crystallization tank, and the concentrated seawater is used to spray and wash the unreacted CO2. The CO2 concentration in the tail gas is <0.2%, meeting the IMO Tier III emission standard. The temperature difference between the CH4 temperature at the outlet of the gasification heat exchange coil in the tower and the seawater in the desulfurization tower is ≤5°C, and the waste heat recovery rate is ≥75%. Compared with the traditional direct seawater gasification, the cold energy utilization rate is increased by more than 40%, and the system comprehensive energy efficiency ratio (COP) reaches 2.8 - 3.2.

[0029] Flue gas treatment module process: Desulfurization tower: The flue gas enters from the bottom of the tower and contacts the seawater sprayed from the top of the tower for reverse desulfurization. The layout density of the serpentine gasification heat exchange coil in the tower is 20 - 30 m² / m³. LNG or low-temperature CH4 absorbs the waste heat of the desulfurized seawater (temperature rises from 5°C to 15°C) in the coil, and the gasified low-temperature CH4 enters the coil in the tower. Finally, the temperature difference with the desulfurized seawater is ≤5°C.

[0030] Preliminary dehydration heat exchanger: The desulfurized flue gas (about 50°C) is indirectly heated with LNG (-162°C) and cooled to -10°C, and liquid water is precipitated.

[0031] Coalescence dehydration filter: Separate the liquid water, and the water content of the flue gas drops to 500 ppm.

[0032] Flue gas compressor: Pressurized to 1.2 bar to improve the subsequent membrane concentration efficiency.

[0033] Deep dehydration heat exchanger: The flue gas is secondarily heated with LNG to -15°C to form ice crystals.

[0034] Low-temperature dehydration filter: Filter the ice crystals, and the flue gas dew point is ≤ -40°C.

[0035] Activated carbon + molecular sieve adsorption tank: Remove residual SO x / NO x to <5 ppm to protect the membrane concentration module.

[0036] Energy flow: The LNG cold energy is successively used for primary dehydration (-10°C), deep dehydration (-15°C), and reaction crystallization (-15°C), and finally the waste heat of desulfurized seawater is recovered through the coil in the tower.

[0037] Principle of collaborative operation between modules: Cascaded utilization of cold energy: Seawater primary heat exchanger: The LNG pre-cools the seawater to -5°C, and the cold energy utilization rate reaches 35%.

[0038] Seawater de-icer: The LNG freezing heat exchange tube further cools down to -10°C, and low-salt ice crystals are precipitated.

[0039] Reaction crystallization tank: The LNG spiral heat exchange tube controls the temperature at -15°C to promote the crystallization of bicarbonate.

[0040] Linkage between the CO2 fixation module and the flue gas treatment module: Tube-type membrane concentration module: The CO2 concentration in the flue gas is increased to more than 50%.

[0041] Reaction crystallization tank: High-concentration CO2 reacts with concentrated seawater (salinity 5 - 6.5%) and NH3 at -10 to -15°C to form sodium bicarbonate crystals.

[0042] Control logic of key parameters: Flue gas treatment module: The primary dehydration temperature of the flue gas is controlled by the LNG flow regulating valve to ensure that the flue gas is cooled down to -10°C ± 0.5°C.

[0043] When the pressure difference of the low-temperature dehydration filter is > 0.1 bar, it will be automatically backwashed to prevent ice crystal blockage.

[0044] Seawater desalination module: The angle of the de-icing inclined plate is 15° - 30°, which is automatically adjusted according to the seawater salinity to ensure that the ice crystal sliding rate is 0.5 - 1.2 m / s.

[0045] CO2 fixation module: The pH value of the reaction crystallization tank is maintained at 8.5 - 9.5 through the NH3 flow regulating valve, and the supersaturation is jointly controlled by the stirring speed (50 - 150 rpm) and the LNG heat exchange tube flow.

[0046] Equipment connection relationship of the flue gas treatment module: The desulfurized flue gas (about 50°C) discharged from the top of the desulfurization tower enters the flue gas primary dehydration heat exchanger through the pipeline, exchanges heat with the LNG cold source and is cooled down to -10°C; the cooled flue gas enters the coalescing dehydration filter, and after separating the liquid water, it is pressurized to 1.2 bar by the flue gas compressor; the pressurized flue gas enters the deep dehydration heat exchanger, exchanges heat with the secondary LNG to -15°C to form ice crystals; the flue gas containing ice crystals is filtered by the low-temperature dehydration filter and then enters the activated carbon + molecular sieve adsorption tank to remove SO x / NO x ; The final dry flue gas (with a CO2 concentration of 3.5%) enters the tubular membrane concentration module, and after being concentrated to a CO2 concentration of over 50%, it enters the CO2 fixation module.

[0047] Material flow direction of the CO2 fixation module: The high-concentration CO2 flue gas from the outlet of the tubular membrane concentration module, ammonia (NH3), and concentrated seawater (salinity 5 - 6.5%) are sprayed into the reaction crystallization tank through a distributor; after the sodium bicarbonate crystals generated by the reaction are separated by a plate and frame filter press, the filtrate tank is recycled back to the reaction crystallization tank through a circulation pump, and the circulation volume accounts for 30 - 50% of the liquid volume in the tank.

[0048] Flue gas fan: Located at the inlet of the desulfurization tower, it is used to introduce the ship's flue gas into the system; Seawater circulation pump: Connects the desulfurization tower and the seawater primary heat exchanger to circulate and spray seawater; Membrane concentration inlet valve: Controls the flow rate of the flue gas entering the tubular membrane concentration module; Spiral LNG refrigeration heat exchange tube: Located inside the reaction crystallization tank to maintain the reaction temperature at -10~-15°C; Filter press feed pump: Transports the reaction liquid to the plate and frame filter press.

[0049] Example 1: Standard operating conditions (174,000 cubic meters LNG ship, flue gas volume 15000 Nm 3 / h): Module Key parameter Design value Measured value Flue gas treatment module Material / area of the desulfurization tower coil 316L stainless steel, 800 m² - Initial dehydration temperature / pressure 0℃, 1.05 bar(a) 0.2℃, 1.03 bar(a) Deep dehydration temperature / pressure -12℃, 1.2 bar(a) -11.5℃, 1.18 bar(a) Dew point of the flue gas after dehydration ≤-40℃ -42℃ Seawater desalination module Temperature of seawater after primary heat exchange -5℃ -4.8℃ Ice crystal salinity at the outlet of the deicer 0.8% (w / w) 0.75% Fresh water production 2.5 m³ / h 2.42 m³ / h <![CDATA[CO2 fixation module]]> <![CDATA[Membrane concentration of CO2 concentration]]> 50% (V / V) 52% Reaction temperature / time -12℃, 50 min -11.8℃, 48 min Bicarbonate crystallization rate ≥85% 87% Energy efficiency index LNG cold energy utilization rate 78% 79.2% System COP (waste heat + cold energy) 3.0 3.12 Example 2: High-load operating conditions (flue gas volume 20000 Nm³ / h, seawater temperature 30°C): Adjusted parameters: The flow rate of the LNG refrigeration heat exchange tube of the seawater de-icer is increased by 20%, and the stirring speed of the reaction crystallization tank is increased to 120 rpm.

[0050] Measured results: Fresh water production: 3.1 m³ / h (ice crystal salinity 0.9%), CO2 fixation rate 91.5% (1.5% lower than that in Example 1 because the reaction time is shortened to 40 min).

[0051] CH4 temperature at the outlet of the coil in the tower: 18°C (seawater inlet temperature 30°C → outlet 22°C, temperature difference 4°C, waste heat recovery rate 76%).

[0052] Example 3: Low-temperature sea area operating conditions (seawater temperature 5°C, flue gas SO x content 150 ppm): Adjusted parameters: The adsorption time of the activated carbon + molecular sieve tank is extended to 480 min (standard 360 min) to prevent SO x poisoning.

[0053] Measured results: Membrane module life: 62 months (54 months under standard conditions), SO x Residual < 3 ppm.

[0054] Ice crystal rate of the de-icer: 45% (when the seawater temperature is low, the ice formation increases by 10%), fresh water production 2.8 m³ / h.

[0055] Comparative Example 1: Traditional direct seawater gasification process: Index The present invention (Example 1) Comparative Example 1 Difference analysis LNG cold energy utilization rate 79.2% <15% (direct heat discharge) Cold energy waste reduced by 81% Fresh water production 2.42 m³ / h 0 (no desalination) Newly added ship fresh water self - sufficiency ability <![CDATA[CO2 emissions]]> 720 kg / h (fixed) 3200 kg / h (direct discharge) Emission reduction by 77.5% System energy consumption (kWh / m³ LNG) 18.5 28.3 Energy saving by 34.6% Equipment floor area 45 m² 30 m² (only gasification) +50% (but integrated seawater / flue gas treatment) Comparative Example 2: Single cold energy power generation + flue gas desulfurization (without seawater resource utilization): Defects: Cold energy power generation efficiency 22% (cold energy utilization rate of the present invention 79.2%), seawater not utilized, CO2 directly discharged.

[0056] Economy: Power generation income 0.15 yuan / m³ LNG, comprehensive income of the present invention (fresh water + carbonate) 0.82 yuan / m³ LNG.

[0057] Experimental verification: Experimental platform: A 147,000 m³ LNG carrier configured with the system of the present invention (parameters of Example 1).

[0058] Test item Test period Average value Standard value Compliance rate Flue gas desulfurization efficiency Continuous 72h <![CDATA[99.2% (SO2 < 10 ppm)]]> ≥98% 100% Low - temperature desalinated fresh water quality Once a day Conductivity <500 μS / cm Ship fresh water standard (<1000 μS / cm) 100% Bicarbonate purity Once a week <![CDATA[NaHCO3 ≥ 92% (impurities < 5%)]]> Industrial grade standard (≥90%) 100% System stability 6 months Fault shutdown: 0 times Design goal (<2 times / year) 100%

[0059] The present invention realizes through ternary synergy (flue gas waste heat + LNG cold energy + seawater) in the in-ship verification: The cold energy utilization rate is increased by 5 times (79.2% vs 15%), and the annual energy consumption savings is 1,200 tons of standard coal (for a 174,000 m³ LNG ship).

[0060] Seawater resource utilization: The daily fresh water supply per ship is 58 m³ (meeting the water use of 200 crew members), and the annual production of bicarbonate is 2,800 tons (worth about 840,000 yuan).

[0061] Environmental protection benefits: CO2 emissions reduction 77.5%, SO x / NO x Residual < 5 ppm, fully meeting the IMO Tier III emission standards.

[0062] Through the ternary collaborative innovation of cascaded utilization of LNG cold energy, recovery of flue gas waste heat, and seawater resource utilization, the present invention constructs a "cold - heat - water - gas" multi - energy flow coupling system at the ship end, breaks through the technical bottleneck of single - energy utilization in traditional LNG ships, and provides a replicable engineering paradigm for green shipping. The actual ship test data (such as in Example 1) shows that the system achieves a cold energy utilization rate of 79.2% on a 174,000 - cubic - meter LNG ship (traditional process < 15%), which is equivalent to reducing cold energy waste by 120 tons of standard coal per voyage (8,000 nautical miles); it produces 58 m³ of fresh water per day (meeting the water use of 200 crew members), and simultaneously fixes 17.3 tons of CO2, with the emission reduction rate increased by 77.5% compared to the traditional process. These data not only verify the technical feasibility but also mark the paradigm shift of ships from "energy - consuming units" to "resource - producing units".

[0063] In summary, the process of synergistic seawater resource utilization of flue gas waste heat and cold energy in LNG ships provided by the present invention, relying on the innovative ternary collaborative concept, successfully breaks through the limitations of energy utilization in traditional LNG ships, constructs an efficient multi - energy flow coupling system, and provides a highly valuable engineering example for the development of green shipping.

[0064] Through the close cooperation of three major modules: flue gas treatment, seawater desalination, and CO2 fixation, this process realizes the cascaded utilization of LNG cold energy, the effective recovery of flue gas waste heat, and the resource utilization of seawater. From the examples, it shows good performance under different working conditions. Whether it is standard working conditions, high - load working conditions, or low - temperature sea area working conditions, it can stably produce fresh water, fix CO2, and maintain a high cold energy utilization rate and system energy efficiency.

[0065] Compared with the traditional direct - heat vaporization process of seawater and the single cold - energy power generation + flue gas desulfurization process, the present invention has significant advantages. It not only greatly improves the LNG cold energy utilization rate, reduces cold energy waste, but also newly adds the ship's fresh - water self - supply ability, realizes the efficient emission reduction of CO2 and energy conservation and consumption reduction. Although the floor area of the equipment has increased, the integration of seawater and flue gas treatment functions brings higher comprehensive benefits.

[0066] The actual ship verification further proves the reliability and practicability of the present invention. All test indicators meet or exceed the standard values, the system has strong stability, and the number of fault shutdowns is zero. It has made major breakthroughs in cold energy utilization, seawater resource utilization, and environmental protection benefits, realizing the transformation of ships from simple "energy - consuming units" to "resource - producing units", providing solid technical support for promoting the shipping industry towards green and sustainable development, and having broad application prospects and promotion value.

[0067] The embodiments of the present invention are provided by way of example and description, and are not exhaustive or limit the present invention to the disclosed forms. Many modifications and variations are obvious to those of ordinary skill in the art. The embodiments are chosen and described in order to better illustrate the principles of the present invention and its practical applications, and to enable those of ordinary skill in the art to understand the present invention so as to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A process for synergistically utilizing the waste heat and cold energy of the flue gas of an LNG ship for seawater resource utilization, characterized in that: It includes a flue gas treatment module, a seawater desalination module and a CO2 fixation module; The flue gas treatment module includes a desulfurization tower and the in-tower gasification heat exchange coil, the preliminary flue gas dehydration heat exchanger, the coalescence dehydration filter, the flue gas compressor, the deep dehydration heat exchanger and the activated carbon + molecular sieve adsorption tank installed in the desulfurization tower. The preliminary flue gas dehydration heat exchanger and the deep dehydration heat exchanger use LNG as the cold source to cool the flue gas below 0°C in sequence and deeply remove water vapor; The seawater desalination module includes a seawater primary heat exchanger, a seawater deicer and a desalination device. The seawater primary heat exchanger uses the cold energy of LNG to pre-cool the seawater to -5°C. The seawater deicer further cools it to -8~-10°C through the LNG refrigeration heat exchange tube to separate low-salt ice crystals for ship fresh water; The CO2 fixation module includes a tubular membrane concentration module, a distributor, a stirrer, a reaction crystallization tank and a plate and frame filter press. The tubular membrane concentration module raises the CO2 concentration in the flue gas to more than 50% (V / V). The high-concentration CO2 reacts with ammonia and concentrated seawater in the reaction crystallization tank at a low temperature of -10~-15°C to generate bicarbonate. It is sprayed and mixed through the distributor and the mass transfer is strengthened by the stirrer. The crystal salt is separated by the plate and frame filter press and then transported out; 2. The co - utilization process of flue gas waste heat and cold energy of an LNG ship for seawater resource utilization according to claim 1, wherein, The desulfurization tower is a structure of a filler-free empty tower, with a serpentine gasification heat exchange coil installed inside. LNG or low-temperature CH4 flows through the coil, and its heat is used to heat it to 5~15°C by the waste heat of the desulfurized spray seawater. The coil layout density is 20~30m² / m³ of the tower volume; 3. The seawater resource utilization process for synergistically using the waste heat and cold energy of the flue gas of an LNG ship according to claim 1, characterized in that, A low-temperature dehydration filter is connected in series after the coalescence dehydration filter to filter the flue gas ice crystals at -10~-15°C. After dehydration, the flue gas dew point ≤ -40°C and the total water content < 10ppm to avoid blocking the membrane concentration module; 4. A process for synergistically utilizing the waste heat and cold energy of flue gas in an LNG ship for seawater resource utilization as described in claim 1, characterized in that, The bottom of the seawater deicer is provided with an ice removal inclined plate with an inclination angle of 15~30°. The ice crystal sliding rate is 0.5~1.2m / s. After separation, the salinity of the seawater is increased from 3.5% to 5.0~6.5%. The cold energy is recovered through a plate heat exchanger before entering the seawater concentration module; 5. A process for synergistic seawater resource utilization of LNG ship flue gas waste heat and cold energy as claimed in claim 1, characterized in that, A spiral LNG refrigeration heat exchange tube is installed in the reaction crystallization tank, with a temperature control accuracy of ±1°C. Combined with the stirrer rotation speed of 50~150rpm, the solution supersaturation is maintained at 1.2~1.5 to promote the directional crystallization of bicarbonate, and the crystallization rate ≥ 85%; 6. A process for synergistically utilizing the waste heat and cold energy of the flue gas of an LNG ship for seawater resourceization as claimed in claim 1, characterized in that, The filtrate tank of the plate and frame filter press is back-injected into the reaction crystallization tank through a circulation pump, and the circulation volume accounts for 30-50% of the liquid volume in the tank, which is used to dilute the NH4 + concentration and supplement the reaction medium to avoid the precipitation of ammonium chloride.

7. A process for synergistic seawater resource utilization of the flue gas waste heat and cold energy of an LNG ship according to any one of claims 1-6, characterized in that, It includes the following steps: S1: After the flue gas is desulfurized by the desulfurization tower, it is dehydrated preliminarily at -10°C and deeply dehydrated at -15°C in sequence to remove more than 99% of the water vapor; S2: LNG exchanges heat with seawater at -5°C, the deicer at -10°C, and the reaction crystallization tank at -15°C in sequence. After gasification, the low-temperature CH4 enters the tower coil and is heated to normal temperature by the waste heat of the desulfurized seawater; S3: The concentrated seawater with a salinity of 5~6.5% reacts with CO2 and NH3 at -10~-15°C for 40~60min, and the pH value is controlled at 8.5~9.5 to generate sodium bicarbonate crystals; S4: After the crystal salt is dewatered by filtration, the moisture content ≤ 10%, the filtrate recycling rate ≥ 90%, the system fresh water output rate is 15~20%, and the CO2 fixation rate ≥ 92%; 8. A process for synergistic seawater resource utilization of LNG ship flue gas waste heat and cold energy as claimed in claim 7, characterized in that, The flue gas passes through an activated carbon + molecular sieve adsorption tank before the membrane concentration module to remove residual SO x / NO x to less than 5 ppm.

9. A process for synergistically recycling seawater using the waste heat and cold energy of the flue gas of an LNG ship as claimed in claim 7, wherein A gas washing buffer tank is arranged at the top of the reaction crystallization tank, and the concentrated seawater is used to spray and wash the unreacted CO2, and the tail gas CO2 concentration < 0.2%; 10. A process for synergistic seawater resource utilization of LNG ship flue gas waste heat and cold energy as claimed in claim 7, characterized in that, The temperature difference between the CH4 temperature at the outlet of the vaporization heat exchange coil in the tower and the seawater in the desulfurization tower is ≤ 5°C, the waste heat recovery rate is ≥ 75%, compared with the traditional direct seawater heating for vaporization, the cold energy utilization rate is increased by more than 40%, and the comprehensive energy efficiency ratio of the system reaches 2.8 - 3.2.

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