A methane recovery system and method for LNG carriers

Abstract

This invention discloses a methane recovery system and method for LNG carriers. The system involves introducing main engine exhaust into a scrubbing and cooling tower, where it reacts chemically with scrubbing water. The separated methane is then returned to the ship's main engine for combustion. The resulting acidic scrubbing water flows into a circulation tank under gravity. Within the circulation tank, the scrubbing water stratifies: the oily residue at the top overflows into an oil residue treatment system; the middle layer of scrubbing water flows back to the scrubbing and cooling tower via a cooling circulation pipe for reuse; and the sludge deposited at the bottom of the tank is discharged into a sludge discharge treatment system. This method not only successfully separates and recovers methane from the main engine exhaust but also safely discharges particulate matter, oil residue, and other impurities from the exhaust, preventing environmental pollution.

Description

Technical Field

[0001] This invention relates to the field of marine technology, and in particular to a methane recovery system and method for LNG carriers. Background Technology

[0002] New low-carbon fuels, represented by LNG (liquefied natural gas), have become an important trend in the development of marine propulsion. As a clean fuel, LNG has significant advantages in reducing atmospheric pollutants such as NOx, SOx, and PM. However, methane escape is a problem in the operation of common low-pressure injection LNG engines. Methane is a potent greenhouse gas, with a greenhouse effect 25 times stronger than CO2. Although LNG-powered dual-fuel engines reduce CO2 emissions by 20% compared to traditional engines, the greenhouse effect of low-pressure injection LNG-powered ships is still higher than that of traditional engines. Therefore, if the methane escape problem in marine applications cannot be effectively solved, it will become a significant obstacle to the further promotion and application of LNG dual-fuel engines in the marine sector.

[0003] Existing methane escape control technologies involve sending the desulfurized exhaust gas from the main engine into a catalytic oxidation reactor, where the escaped methane is removed. While this technology reduces greenhouse gas emissions, the methane escaping from the main engine exhaust gas is not recycled by the dual-fuel main engine, resulting in wasted energy and high costs for catalysts and equipment. Summary of the Invention

[0004] In view of this, the present invention provides a methane recovery system and method for LNG carriers to solve the problem of methane recovery from main engine exhaust gas.

[0005] An LNG carrier methane recovery system includes the ship's main engine, exhaust economizer, scrubbing cooling tower, and circulation tank. The exhaust port of the ship's main engine is connected to the air inlet of the exhaust gas economizer through a first exhaust pipe, the exhaust port of the exhaust gas economizer is connected to the air inlet of the lower part of the washing and cooling tower through a second exhaust pipe, and the exhaust port of the top of the washing and cooling tower is connected to the air inlet of the ship's main engine through an air inlet pipe, so as to form a methane recycling loop. The bottom of the washing cooling tower is equipped with a circulation cabinet, which is connected to the washing cooling tower through a washing water cooling circulation pipeline. This allows the acidic washing water formed after the washing water sprayed down from the top of the washing cooling tower reacts with the exhaust gas entering the tower to be neutralized in the circulation cabinet. The neutralized washing water is then returned to the washing cooling tower through the washing water cooling circulation pipeline. The circulating cabinet is connected to the alkaline dosing pump group through the first filling pipe. The circulating cabinet is also connected to a sewage discharge treatment system for discharging the sewage deposited at the bottom of the circulating cabinet and purifying the discharged sewage. A replenishment pipe is connected between the sewage discharge treatment system and the circulating cabinet. The circulating cabinet is also connected to an oil residue treatment system for discharging oil floating on the surface of the washing water inside the cabinet.

[0006] Preferably, the washing water cooling circulation pipeline includes a cooler, a first cooling circulation pipe and a second cooling circulation pipe. The hot side inlet of the cooler is connected to one end of the first cooling circulation pipe, the other end of the first cooling circulation pipe is connected to the liquid outlet of the circulation tank, a circulating water pump is installed on the first cooling circulation pipe, the hot side outlet of the cooler is connected to one end of the second cooling circulation pipe, and the other end of the second cooling circulation pipe is connected to the liquid inlet at the top of the washing cooling tower.

[0007] Preferably, the waste discharge and treatment system includes a discharge chamber, a water treatment unit, a discharge pipe, a first discharge pipe, and a second discharge pipe. The discharge chamber is connected to the discharge port of the circulation tank through the discharge pipe. The discharge port of the discharge chamber is connected to the inlet of the water treatment unit through the first discharge pipe. A discharge pump is installed on the first discharge pipe. The first outlet of the water treatment unit is connected to the second discharge pipe. The end of the second discharge pipe extends to the outside of the ship. A discharge valve is installed on the second discharge pipe. One end of the replenishment pipe is connected to the second discharge pipe, and the other end is connected to the replenishment port of the circulation tank.

[0008] Preferably, the waste discharge treatment system further includes a neutralization unit for detecting the pH of impurities in the discharge chamber and neutralizing the wastewater in the discharge chamber. The first inlet of the neutralization unit is connected to the alkali dosing pump group through the second injection pipe, the second inlet of the neutralization unit is connected to the outlet of the discharge chamber through the first injection pipe, and the outlet of the neutralization unit is connected to the inlet of the discharge chamber through the second injection pipe.

[0009] Preferably, a water quality detection unit for detecting the quality of the liquid to be discharged in the pipe is connected to the second discharge pipe, and the water quality detection unit is installed on the pipe on the inlet side of the discharge valve.

[0010] Preferably, the waste discharge and treatment system further includes a first return pipe, one end of which is connected to the second outlet of the water treatment unit and the other end is connected to the return port of the discharge chamber.

[0011] Preferably, the waste discharge treatment system further includes a second return pipe, one end of which is connected to one of the valve ports of the discharge valve and the other end of which is connected to the return port of the discharge chamber.

[0012] Preferably, the oil sludge treatment system includes an oil separator, an oil sludge compartment, an overflow pipe, a first drain pipe, an oil supply pipe, and an oil discharge pipe. The inlet of the oil separator is connected to the overflow port of the circulation tank through the overflow pipe. The drain port of the oil separator is connected to the venting chamber through the first drain pipe. The sludge discharge port of the oil separator is connected to the oil sludge compartment through the oil supply pipe. The oil discharge port of the oil sludge compartment is connected to an oil discharge pipe, and an oil sludge pump is installed on the oil discharge pipe.

[0013] Preferably, the oil sludge treatment system further includes a drain pipe, one end of which is connected to the sludge discharge port of the water treatment unit and the other end of which is connected to the sludge inlet of the oil sludge compartment.

[0014] A method for recovering methane in an LNG carrier methane recovery system specifically includes the following steps: The exhaust gas from the ship's main engine enters the washing and cooling tower from the bottom through the first exhaust pipe, the exhaust gas economizer, and the second exhaust pipe. At the same time, washing water is sprayed down from the top of the washing and cooling tower. The washing water washes the upward-flowing exhaust gas and forms acidic washing water. The acidic washing water flows from the bottom of the washing and cooling tower into the circulation tank. The washing water in the circulation tank flows into the washing water cooling circulation pipeline for cooling and then flows back to the washing and cooling tower. Meanwhile, the methane discharged from the top of the washing and cooling tower re-enters the ship's main engine through the intake pipe. When the acidity of the washing water in the circulating tank exceeds the set value, add alkaline solution to the circulating tank to neutralize it. When the washing water level in the circulating tank exceeds the overflow port of the circulating tank, the oil floating on the surface of the washing water automatically flows into the oil residue treatment system, which processes and discharges the oil residue. When the amount of sludge deposited at the bottom of the circulating tank reaches a set amount, the sludge is discharged to the sludge discharge treatment system, which separates, purifies, and discharges the discharged wastewater.

[0015] Preferably, the specific steps of the wastewater discharge treatment system for separating, purifying, and discharging discharged wastewater are as follows: Dirt at the bottom of the circulating cabinet enters the discharge chamber along with some of the washing water through the discharge pipe; The discharge pump draws out the wastewater from the venting chamber and sends it to the water treatment unit for purification. The water quality testing unit tests the quality of the purified water. If the water quality meets the standards, it is discharged to the outside of the ship through the second discharge pipe or transported to the circulation tank through the replenishment pipe. If the water quality does not meet the standards, the water that does not meet the standards is returned to the venting chamber through the second return pipe for circulation and purification. During the purification process of the wastewater discharged by the water treatment unit, if the amount of wastewater supplied by the discharge pump exceeds the maximum treatment capacity of the water treatment unit, the excess wastewater will be returned to the discharge chamber through the first return pipe. Impurities filtered out by the water treatment unit are discharged into the oil sludge tank through the drain pipe.

[0016] Preferably, after the sludge at the bottom of the circulating cabinet enters the discharge chamber along with some of the washing water through the discharge pipe, the neutralization unit extracts the discharged wastewater in the discharge chamber through the first injection pipe and detects the acidity and alkalinity of the discharged wastewater. If the acidity and alkalinity of the discharged wastewater exceed the set value, the alkaline dosing pump group adds alkaline solution to the neutralization unit to neutralize the acidity and alkalinity of the discharged wastewater. The neutralized discharged wastewater flows back into the discharge chamber through the second injection pipe.

[0017] Preferably, the specific steps for the oil residue treatment system to treat and discharge oil are as follows: Oil floating on the surface of the washing water in the circulating tank flows automatically into the oil separator along with some of the washing water through the overflow pipe. After the mixture of oil and washing water is allowed to settle and separate in the oil separator, the oil deposited at the bottom of the oil separator is transported to the oil residue tank through the oil transfer pipe, while the washing water on the surface of the oil in the oil separator is transported to the venting tank through the first drain pipe. The oil sludge tank regularly drains the oil inside through the drain pipe to transfer barrels, which are then sent to a professional processing facility for disposal after the ship docks.

[0018] The beneficial effects of this invention are: 1. This invention introduces the main engine exhaust gas into a scrubbing cooling tower, where it undergoes a chemical reaction with the scrubbing water. The separated methane is then returned to the ship's main engine for combustion, while the resulting acidic scrubbing water flows into a circulation tank under gravity. The scrubbing water in the circulation tank is stratified, with the oil at the top flowing into the oil residue treatment system through its overflow outlet, the middle layer of scrubbing water flowing back to the scrubbing cooling tower for reuse through the scrubbing water cooling circulation pipe, and the sludge deposited at the bottom of the tank being discharged into the sludge discharge treatment system. This not only successfully separates methane from the main engine exhaust gas for recycling but also safely discharges particulate matter, oil residue, and other impurities from the exhaust gas, avoiding environmental pollution.

[0019] 2. In this invention, a first return pipe is added between the water treatment unit and the discharge chamber. When the discharge pump pumps the discharged sewage in the discharge chamber to the water treatment unit, if the amount of discharged sewage supplied by the discharge pump exceeds the maximum treatment capacity of the water treatment unit, or if the internal pressure of the water treatment unit is too high, the excess discharged sewage can be returned to the discharge chamber through the first return pipe to ensure water treatment efficiency and effect, and to ensure the normal operation of the water treatment unit. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the present invention.

[0022] The meanings of the labels in the diagram are as follows: 1 is the main engine; 2 is the exhaust gas economizer; 3 is the scrubber cooling tower; 4 is the circulation tank; 5 is the cooler; 6 is the alkali injection pump set; 7 is the venting tank; 8 is the water treatment unit; 9 is the neutralization unit; 10 is the water quality testing unit; 11 is the oil separator; 12 is the oil sludge tank; 13 is the oil sludge pump. 14 is the first exhaust pipe, 15 is the second exhaust pipe, 16 is the air intake pipe, 17 is the first filling pipe, 18 is the second filling pipe, 19 is the liquid replenishment pipe, 20 is the first cooling circulation pipe, 21 is the second cooling circulation pipe, 22 is the circulating water pump, 23 is the drain pipe, 24 is the first discharge pipe, 25 is the second discharge pipe, 26 is the discharge pump, 27 is the discharge valve, 28 is the first liquid injection pipe, 29 is the second liquid injection pipe, 30 is the first return pipe, 31 is the second return pipe, 32 is the overflow pipe, 33 is the first liquid drain pipe, 34 is the oil supply pipe, 35 is the oil discharge pipe, and 36 is the sewage discharge pipe. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0024] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0025] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0026] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0027] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two components. They can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0028] To better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

[0029] This invention provides a methane recovery system for LNG carriers, comprising a ship's main engine 1, an exhaust gas economizer 2, a scrubbing cooling tower 3, and a circulation tank 4. The exhaust port of the ship's main engine 1 is connected to the air inlet of the exhaust gas economizer 2 through the first exhaust pipe 14, the exhaust port of the exhaust gas economizer 2 is connected to the air inlet at the bottom of the washing cooling tower 3 through the second exhaust pipe 15, and the exhaust port at the top of the washing cooling tower 3 is connected to the air inlet of the ship's main engine 1 through the air inlet pipe 16, so as to form a methane recycling loop. The bottom of the washing cooling tower 3 is provided with a circulation cabinet 4. The circulation cabinet 4 is connected to the washing cooling tower 3 through a washing water cooling circulation pipeline. This allows the acidic washing water formed after the washing water sprayed down from the top of the washing cooling tower 3 reacts with the exhaust gas entering the tower to be neutralized in the circulation cabinet 4. The neutralized washing water is then returned to the washing cooling tower 3 through the washing water cooling circulation pipeline. The circulating cabinet 4 is connected to the alkaline dosing pump group 6 through the first filling pipe 17. The circulating cabinet 4 is also connected to a sewage discharge treatment system for discharging the sewage deposited at the bottom of the circulating cabinet and purifying the discharged sewage. The sewage discharge treatment system is connected to the circulating cabinet 4 by a replenishment pipe 19. The circulating cabinet 4 is also connected to an oil residue treatment system for discharging oil floating on the surface of the washing water inside the cabinet.

[0030] The exhaust gas from the ship's main engine 1 enters the washing and cooling tower 3 from the bottom through the first exhaust pipe 14, the exhaust gas economizer 2, and the second exhaust pipe 15. At the same time, washing water is sprayed down from the top of the washing and cooling tower 3. The washing water flowing from top to bottom comes into full contact with the exhaust gas flowing from bottom to top. The washing water reacts chemically with CO2, NOx, etc. in the exhaust gas, turning into acidic washing water containing H2CO3, H2NO3, H2NO4, particulate matter, and oil residue. Methane is discharged from the top of the washing and cooling tower 3 and re-enters the ship's main engine 1 through the air inlet pipe 16 for combustion.

[0031] The acidic washing water in the washing cooling tower 3 flows from the bottom of the tower into the circulation tank 4 under the action of gravity. The washing water in the circulation tank 4 flows into the washing water cooling circulation pipeline for cooling and then flows back to the washing cooling tower 3.

[0032] Specifically, the washing water cooling circulation pipeline includes a cooler 5, a first cooling circulation pipe 20, and a second cooling circulation pipe 21. The hot side inlet of the cooler 5 is connected to one end of the first cooling circulation pipe 20, and the other end of the first cooling circulation pipe 20 is connected to the liquid outlet of the circulation tank 4. A circulating water pump 22 is installed on the first cooling circulation pipe 20. The hot side outlet of the cooler 5 is connected to one end of the second cooling circulation pipe 21, and the other end of the second cooling circulation pipe 21 is connected to the liquid inlet at the top of the washing cooling tower 3.

[0033] The circulating water pump 22 pumps the washing water out of the circulating tank 4 and delivers it to the cooler 5 through the first cooling circulation pipe 20. After the washing water is cooled in the cooler 5, it is sent back to the washing cooling tower 3 through the second cooling circulation pipe 21 to spray down from the top of the tower. This cycle is repeated to wash the exhaust gas.

[0034] The washing water cooling circulation pipeline also includes a pH sensor, which can detect the acidity of the washing water in the circulation tank 4. When the acidity of the washing water in the circulation tank 4 exceeds the set value, the system controls the alkaline dosing pump group 6 to add to the circulation tank 4 to neutralize the acid and alkali of the washing water in the circulation tank 4.

[0035] As the washing water circulates into the washing cooling tower 3 to chemically react with the NOx in the continuous exhaust gas, the washing water mixed with oil residue and particulate matter enters the circulation tank 4. Over a long period of time, the sediment (particulate matter and other impurities) at the bottom of the circulation tank 4 will increase. When the sediment reaches a certain amount, it is necessary to discharge the sediment into the sewage discharge treatment system. Alternatively, the sediment can be discharged into the sewage discharge treatment system periodically.

[0036] When sediment is released, a certain amount of washing water (i.e., released wastewater) will enter the waste release and treatment system along with the sediment.

[0037] The waste discharge and treatment system includes a discharge chamber 7, a water treatment unit 8, a discharge pipe 23, a first discharge pipe 24, and a second discharge pipe 25. The discharge chamber 7 is connected to the discharge port of the circulation tank 4 through the discharge pipe 23. The discharge port of the discharge chamber 7 is connected to the inlet of the water treatment unit 8 through the first discharge pipe 24. A discharge pump 26 is installed on the first discharge pipe 24. The first outlet of the water treatment unit 8 is connected to the second discharge pipe 25. The end of the second discharge pipe 25 extends to the outside of the ship. A discharge valve 27 is installed on the second discharge pipe 25. One end of the replenishment pipe 19 is connected to the second discharge pipe 25, and the other end is connected to the replenishment port of the circulation tank 4.

[0038] The sediment in the circulation tank 4, along with a certain amount of washing water, flows from the vent pipe 23 into the vent chamber 7. The discharge pump 26 draws out the vented sewage from the vent chamber 7 and transports it to the water treatment unit 8 for purification. After the vented sewage is treated to meet the standards, it is discharged to the outside through the second discharge pipe 25, or a portion or all of the clean water is supplied to the circulation tank 4 as makeup water through the replenishment pipe 19 to replenish the liquid loss in the circulation tank 4.

[0039] Preferably, a water quality detection unit 10 is connected to the second discharge pipe 25 to detect whether the water quality of the liquid to be discharged in the pipe meets the standards. The water quality detection unit 10 is installed on the pipeline on the inlet side of the discharge valve 27.

[0040] The waste discharge and treatment system can also be equipped with a second return pipe 31 between the second discharge pipe 25 and the discharge chamber 7. One end of the second return pipe 31 is connected to one of the valve ports of the discharge valve 27, and the other end is connected to the return port of the discharge chamber 7. In this way, when the water quality in the second discharge pipe 25 is not up to standard, the water in the second discharge pipe 25 can be passed into the second return pipe 31 and flow into the discharge chamber 7 to continue the next round of water treatment.

[0041] If the water treatment capacity of the water quality testing unit fails to meet the standard for a period of time, the fresh water pipe of the water treatment unit is turned on to backwash the filter screen or filter membrane of the water treatment unit with fresh water. The sewage or wastewater generated by backwashing also flows into the discharge chamber 7 through the second discharge pipe 25 and the second return pipe 31.

[0042] In other embodiments, a first return pipe 30 may be added between the water treatment unit 8 and the discharge chamber 7. One end of the first return pipe 30 is connected to the second outlet of the water treatment unit 8, and the other end is connected to the return port of the discharge chamber 7. In this way, when the discharge pump 26 pumps the discharged sewage from the discharge chamber 7 to the water treatment unit 8, if the amount of discharged sewage supplied by the discharge pump 26 exceeds the maximum treatment capacity of the water treatment unit 8, or if the internal pressure of the water treatment unit 8 is too high, the excess discharged sewage can be returned to the discharge chamber 7 through the first return pipe 30 to ensure water treatment efficiency and effectiveness.

[0043] In addition, in other embodiments, a neutralization unit 9 may be added to the waste discharge treatment system. Since the discharged wastewater from the circulation tank 4 into the discharge chamber 7 may still be acidic, or the impurities such as particulate matter in the water may be acidic, the neutralization unit 9 is needed to neutralize the acidity and alkalinity of the discharged wastewater in the discharge chamber 7.

[0044] The first inlet of the neutralization unit 9 is connected to the alkali dosing pump group 6 through the second injection pipe 18, the second inlet of the neutralization unit 9 is connected to the outlet of the venting chamber 7 through the first injection pipe 28, and the outlet of the neutralization unit 9 is connected to the inlet of the venting chamber 7 through the second injection pipe 29.

[0045] After the sludge at the bottom of the circulating cabinet 4 enters the discharge chamber 7 along with some of the washing water through the discharge pipe 23, the neutralization unit 9 extracts the discharged wastewater in the discharge chamber 7 through the first injection pipe 28 and detects the acidity and alkalinity of the discharged wastewater. If the acidity and alkalinity of the discharged wastewater exceed the set value, the alkaline dosing pump group 6 adds alkaline solution to the neutralization unit 9 to neutralize the acidity and alkalinity of the discharged wastewater. The neutralized discharged wastewater flows back into the discharge chamber 7 through the second injection pipe 29 for subsequent water treatment.

[0046] Oil residue or oil will float on the surface of the washing water in the circulation tank 4. When the level of the washing water exceeds the overflow port on the circulation tank 4, the oil residue or oil on the surface of the washing water will automatically flow into the oil residue treatment system from the overflow port of the circulation tank 4.

[0047] The oil sludge treatment system includes an oil separator 11, an oil sludge compartment 12, an overflow pipe 32, a first drain pipe 33, an oil supply pipe 34, and an oil discharge pipe 35. The inlet of the oil separator 11 is connected to the overflow port of the circulation tank 4 through the overflow pipe 32. The drain port of the oil separator 11 is connected to the venting compartment 7 through the first drain pipe 33. The sludge discharge port of the oil separator 11 is connected to the oil sludge compartment 12 through the oil supply pipe 34. The oil discharge port of the oil sludge compartment 12 is connected to the oil discharge pipe 35, and an oil sludge pump 13 is installed on the oil discharge pipe 35.

[0048] Oil floating on the surface of the wash water in the circulation tank 4 flows automatically into the oil separator 11 through the overflow pipe 32 along with some of the wash water. After the mixture of oil and wash water settles and separates in the oil separator 11, the oil deposited at the bottom of the oil separator 11 is transported to the oil sludge tank 12 through the oil transfer pipe 34, while the wash water on the surface of the oil in the oil separator 11 is transported to the venting tank 7 through the first drain pipe 33. The oil sludge tank 12 periodically discharges the oil inside to the transfer tank through the oil drain pipe 35, and after the ship docks, it is sent to a professional treatment facility for disposal.

[0049] In other embodiments, a drain pipe 36 may be added between the water treatment unit 8 and the oil sludge compartment 12. One end of the drain pipe 36 is connected to the sludge discharge port of the water treatment unit 8, and the other end is connected to the sludge inlet of the oil sludge compartment 12. In this way, the residues and other pollutants generated by the water treatment unit 8 when treating the discharged sewage in the discharge compartment 7 can be discharged into the oil sludge compartment 12 for storage through the drain pipe 36.

[0050] This invention also provides a method for methane recovery in an LNG carrier's methane recovery system, specifically including the following steps: The exhaust gas discharged from the main engine 1 enters the washing cooling tower 3 from the bottom through the first exhaust pipe 14, the exhaust gas economizer 2, and the second exhaust pipe 15. At the same time, washing water is sprayed down from the top of the washing cooling tower 3. The washing water washes the upward-flowing exhaust gas and forms acidic washing water. The acidic washing water flows from the bottom of the washing cooling tower 3 into the circulation tank 4. The washing water in the circulation tank 4 flows into the washing water cooling circulation pipeline for cooling and then flows back to the washing cooling tower 3. Meanwhile, the methane discharged from the top of the washing cooling tower 3 re-enters the main engine 1 through the air inlet pipe 16.

[0051] As the washing water circulates into the washing cooling tower 3 and continuously reacts chemically with the exhaust gas, the acidity of the liquid in the circulation tank 4 becomes stronger and stronger. In order to ensure the cleaning effect of the exhaust gas and improve the methane removal effect, when the acidity of the washing water in the circulation tank 4 exceeds the set value, it is necessary to control the alkaline dosing pump group 6 to add alkaline solution to the circulation tank 4 to neutralize the acid and alkali.

[0052] As the washing water circulates into the washing cooling tower 3 and continuously reacts chemically with the exhaust gas, more and more sediment accumulates in the circulation tank 4. When the amount of sediment deposited at the bottom of the circulation tank 4 reaches a set amount, the sediment needs to be discharged to the sediment discharge treatment system. The sediment discharge treatment system separates, purifies, and discharges the discharged wastewater.

[0053] Specifically, the wastewater treatment system performs the following steps for separating, purifying, and discharging wastewater: First, the dirt at the bottom of the circulating cabinet 4 enters the discharge chamber 7 along with some of the washing water through the discharge pipe 23; Then, the discharge pump 26 draws out the discharged sewage from the discharge chamber 7 and sends it to the water treatment unit 8 for purification. The water quality testing unit 10 tests the water quality after purification. If the water quality meets the standards, it is discharged to the outside through the second discharge pipe 25 or transported to the circulation tank 4 through the replenishment pipe 19. If the water quality does not meet the standards, the water that does not meet the purification standards is returned to the discharge chamber 7 through the second return pipe 31 for circulation and purification. During the purification process of the discharged wastewater by the water treatment unit 8, if the amount of discharged wastewater supplied by the discharge pump 26 exceeds the maximum treatment capacity of the water treatment unit 8, the excess discharged wastewater will be returned to the discharge chamber 7 through the first return pipe 30. Impurities filtered out by water treatment unit 8 are discharged into oil sludge tank 12 through drain pipe 36.

[0054] When the sludge at the bottom of the circulating tank 4 enters the discharge chamber 7 along with some of the washing water through the discharge pipe 23, if the amount of discharged sewage exceeds the carrying capacity of the discharge chamber 7, the discharged sewage exceeding the receiving capacity of the discharge chamber 7 will be temporarily stored in the oil sludge chamber 12 through the discharge branch pipe 36. After the discharged sewage in the discharge chamber 7 is purified and discharged by the water treatment unit, it will flow back to the discharge chamber 7 through the oil drain pipe 35 and the return liquid pipe 37.

[0055] Preferably, since the wastewater discharged from the circulation tank 4 into the discharge chamber 7 may still be acidic, or the particulate matter and other impurities in the water may be acidic, after the sludge at the bottom of the circulation tank 4 enters the discharge chamber 7 along with some of the washing water through the discharge pipe 23, the neutralization unit 9 extracts the wastewater from the discharge chamber 7 through the first injection pipe 28 and detects the pH of the wastewater. If the pH of the wastewater exceeds the set value, the alkali dosing pump group 6 adds alkali to the neutralization unit 9 to neutralize the wastewater. The neutralized wastewater then flows back into the discharge chamber 7 through the second injection pipe 29. After the wastewater in the discharge chamber 7 is neutralized, the above water treatment steps are repeated.

[0056] When the washing water level in the circulation tank 4 exceeds the overflow port of the circulation tank 4, the oil floating on the surface of the washing water automatically flows into the oil residue treatment system, which then processes and discharges the oil residue.

[0057] The specific steps of the oil residue treatment system for treating and discharging oil are as follows: Oil floating on the surface of the washing water in the circulating tank 4 flows automatically into the oil separator 11 through the overflow pipe 32 along with some of the washing water; After the mixture of oil and washing water is allowed to settle and separate in the oil separator 11, the oil deposited at the bottom of the oil separator 11 is transported to the oil residue tank 12 through the oil transfer pipe 34, while the washing water on the surface of the oil in the oil separator 11 is transported to the venting tank 7 through the first drain pipe 33.

[0058] Oil sludge tank 12 periodically drains the oil inside through oil drain pipe 35 to transfer barrels, which are then sent to a professional treatment facility for disposal after the ship docks.

[0059] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A methane recovery system for an LNG carrier, characterized in that, It includes the ship's main engine (1), exhaust gas economizer (2), scrubbing cooling tower (3) and circulating cabinet (4). The exhaust port of the ship's main engine (1) is connected to the air inlet of the exhaust gas economizer (2) through the first exhaust pipe (14), the exhaust port of the exhaust gas economizer (2) is connected to the air inlet at the bottom of the washing cooling tower (3) through the second exhaust pipe (15), and the exhaust port at the top of the washing cooling tower (3) is connected to the air inlet of the ship's main engine (1) through the air inlet pipe (16) to form a methane recycling loop. The bottom of the washing cooling tower (3) is provided with a circulation cabinet (4). The circulation cabinet (4) is connected to the washing cooling tower (3) through a washing water cooling circulation pipeline. This allows the acidic washing water formed after the washing water sprayed down from the top of the washing cooling tower (3) and the exhaust gas entering the tower to be neutralized in the circulation cabinet (4). The neutralized washing water is then returned to the washing cooling tower (3) through the washing water cooling circulation pipeline. The circulating cabinet (4) is connected to the alkaline dosing pump group (6) through the first filling pipe (17). The circulating cabinet (4) is also connected to a sewage discharge treatment system for discharging the sewage deposited at the bottom of the circulating cabinet and purifying the discharged sewage. A replenishment pipe (19) is connected between the sewage discharge treatment system and the circulating cabinet (4). The circulating cabinet (4) is also connected to an oil residue treatment system for discharging oil floating on the surface of the washing water inside the cabinet.

2. The LNG carrier methane recovery system according to claim 1, characterized in that, The washing water cooling circulation pipeline includes a cooler (5), a first cooling circulation pipe (20) and a second cooling circulation pipe (21). The hot side inlet of the cooler (5) is connected to one end of the first cooling circulation pipe (20), and the other end of the first cooling circulation pipe (20) is connected to the liquid outlet of the circulation cabinet (4). A circulating water pump (22) is installed on the first cooling circulation pipe (20). The hot side outlet of the cooler (5) is connected to one end of the second cooling circulation pipe (21), and the other end of the second cooling circulation pipe (21) is connected to the liquid inlet at the top of the washing cooling tower (3).

3. The LNG carrier methane recovery system according to claim 1, characterized in that, The waste discharge and treatment system includes a discharge chamber (7), a water treatment unit (8), a discharge pipe (23), a first discharge pipe (24), and a second discharge pipe (25). The discharge chamber (7) is connected to the discharge port of the circulation tank (4) through the discharge pipe (23). The discharge port of the discharge chamber (7) is connected to the inlet of the water treatment unit (8) through the first discharge pipe (24). A discharge pump (26) is installed on the first discharge pipe (24). The first outlet of the water treatment unit (8) is connected to the second discharge pipe (25). The end of the second discharge pipe (25) extends to the outside of the ship. A discharge valve (27) is installed on the second discharge pipe (25). One end of the replenishment pipe (19) is connected to the second discharge pipe (25), and the other end is connected to the replenishment port of the circulation tank (4).

4. The LNG carrier methane recovery system according to claim 3, characterized in that, The waste discharge treatment system also includes a neutralization unit (9) for detecting the acidity or alkalinity of impurities in the discharge chamber (7) and neutralizing the wastewater in the discharge chamber (7). The first inlet of the neutralization unit (9) is connected to the alkaline dosing pump group (6) through the second injection pipe (18), the second inlet of the neutralization unit (9) is connected to the outlet of the discharge chamber (7) through the first injection pipe (28), and the outlet of the neutralization unit (9) is connected to the inlet of the discharge chamber (7) through the second injection pipe (29).

5. The LNG carrier methane recovery system according to claim 3, characterized in that, The second discharge pipe (25) is connected to a water quality detection unit (10) for detecting the quality of the liquid to be discharged in the pipe. The water quality detection unit (10) is installed on the pipeline on the inlet side of the discharge valve (27).

6. The LNG carrier methane recovery system according to claim 3, characterized in that, The waste discharge and treatment system also includes a first return pipe (30), one end of which is connected to the second outlet of the water treatment unit (8) and the other end is connected to the return port of the discharge chamber (7).

7. The LNG carrier methane recovery system according to claim 3 or 6, characterized in that, The waste discharge treatment system also includes a second return pipe (31), one end of which is connected to one of the valve ports of the discharge valve (27), and the other end is connected to the return port of the discharge chamber (7).

8. The LNG carrier methane recovery system according to claim 3, characterized in that, The oil sludge treatment system includes an oil separator (11), an oil sludge compartment (12), an overflow pipe (32), a first drain pipe (33), an oil supply pipe (34), and an oil discharge pipe (35). The inlet of the oil separator (11) is connected to the overflow port of the circulation tank (4) through the overflow pipe (32). The drain port of the oil separator (11) is connected to the venting compartment (7) through the first drain pipe (33). The sludge discharge port of the oil separator (11) is connected to the oil sludge compartment (12) through the oil supply pipe (34). The oil discharge port of the oil sludge compartment (12) is connected to the oil discharge pipe (35), and an oil sludge pump (13) is installed on the oil discharge pipe (35).

9. The LNG carrier methane recovery system according to claim 8, characterized in that, The oil sludge treatment system also includes a drain pipe (36), one end of which is connected to the sludge discharge port of the water treatment unit (8) and the other end is connected to the sludge inlet of the oil sludge compartment (12).

10. A method for recovering methane from an LNG carrier methane recovery system according to any one of claims 1-9, characterized in that, Specifically, the following steps are included: The exhaust gas discharged from the main engine (1) enters the washing cooling tower (3) from the bottom through the first exhaust pipe (14), the exhaust gas economizer (2) and the second exhaust pipe (15). At the same time, the washing water sprays down from the top of the washing cooling tower (3). After the washing water washes the exhaust gas flowing upward, it forms acidic washing water. The acidic washing water flows from the bottom of the washing cooling tower (3) into the circulation tank (4). The washing water in the circulation tank (4) flows into the washing water cooling circulation pipeline for cooling and then flows back to the washing cooling tower (3). At the same time, the methane discharged from the top of the washing cooling tower (3) re-enters the main engine (1) through the air inlet pipe (16). When the acidity of the washing water in the circulating tank (4) exceeds the set value, an alkaline solution is added to the circulating tank (4) to neutralize the acid and alkali. When the washing water level in the circulating tank (4) exceeds the overflow port of the circulating tank (4), the oil floating on the surface of the washing water automatically flows into the oil residue treatment system, and the oil residue treatment system treats and discharges the oil. When the amount of sludge deposited at the bottom of the circulating cabinet (4) reaches the set amount, the sludge is discharged to the sludge discharge treatment system, which separates, purifies and discharges the discharged wastewater.

11. The recovery method of the methane recovery system for an LNG carrier according to claim 10, characterized in that, The specific steps of the wastewater discharge treatment system in separating, purifying, and discharging discharged wastewater are as follows: The dirt at the bottom of the circulating cabinet (4) enters the discharge chamber (7) along with some of the washing water through the discharge pipe (23); The discharge pump (26) draws out the wastewater in the venting tank (7) and sends it to the water treatment unit (8) for purification. The water quality testing unit (10) tests the water quality after purification. If the water quality meets the standard, it is discharged to the outside of the ship through the second discharge pipe (25) or transported to the circulation tank (4) through the replenishment pipe (19). If the water quality does not meet the standard, the water that does not meet the standard is returned to the venting tank (7) through the second return pipe (31) for purification through circulation. During the purification process of the discharged sewage by the water treatment unit (8), if the amount of discharged sewage supplied by the discharge pump (26) exceeds the maximum treatment capacity of the water treatment unit (8), the excess discharged sewage will be returned to the discharge chamber (7) through the first return pipe (30). Impurities filtered out by the water treatment unit (8) are discharged into the oil sludge tank (12) through the drain pipe (36).

12. The recovery method of the methane recovery system for LNG carriers according to claim 11, characterized in that, After the dirt at the bottom of the circulating cabinet (4) enters the discharge chamber (7) along with some of the washing water through the discharge pipe (23), the neutralization unit (9) extracts the discharged sewage in the discharge chamber (7) through the first injection pipe (28) and detects the acidity and alkalinity of the discharged sewage. If the discharged sewage exceeds the set value, the alkaline dosing pump group (6) adds alkaline solution to the neutralization unit (9) to neutralize the discharged sewage. The neutralized discharged sewage flows back to the discharge chamber (7) through the second injection pipe (29).

13. The recovery method of the methane recovery system for an LNG carrier according to claim 10, characterized in that, The specific steps of the oil residue treatment system for treating and discharging oil are as follows: Oil floating on the surface of the washing water in the circulating tank (4) flows into the oil separator (11) automatically through the overflow pipe (32) along with some of the washing water. After the mixture of oil and washing water is allowed to settle and separate in the oil separator (11), the oil deposited at the bottom of the oil separator (11) is transported to the oil residue tank (12) through the oil transfer pipe (34), while the washing water on the surface of the oil in the oil separator (11) is transported to the venting tank (7) through the first drain pipe (33). The oil sludge tank (12) regularly discharges the oil inside through the oil drain pipe (35) to the transfer tank, which is then sent to a professional treatment facility for disposal after the ship docks.

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