Carbon dioxide BOG (boil-off gas) recirculation system for marine engine

Abstract

A carbon dioxide BOG recirculation system for a marine engine integrates a shipborne carbon capture system, a carbon dioxide storage tank, an engine scavenging box, an oxygen concentration sensor and a control unit. The shipborne carbon capture system efficiently captures and recovers carbon dioxide in exhaust gas of the marine engine through the steps of pretreatment, absorption, desorption, compression, liquefaction storage and the like, and the carbon dioxide is liquefied and stored in a carbon dioxide storage tank. The stored carbon dioxide BOG is utilized, and the flow of the BOG introduced into the scavenging box of the engine is accurately adjusted through the pressure control valve, so that the oxygen concentration in the scavenging box is adjusted in real time, the combustion performance of the engine is optimized, the energy utilization efficiency is improved, and greenhouse gas emission is remarkably reduced; and an oxygen concentration sensor in the oxygen concentration control unit works cooperatively with the control unit, so that real-time monitoring and accurate regulation and control of the oxygen concentration are realized. The method not only accords with the development trend of global energy conservation and emission reduction and green shipping, but also helps to promote technical innovation and industrial upgrading of the shipping industry.

Description

Technical Field

[0001] The invention relates to the technical fields of marine diesel engine exhaust system design and ship carbon capture technology, and in particular to a marine engine carbon dioxide (BOG) recycling system. Background Art

[0002] When a ship engine burns fuel, the exhaust gas recirculation (EGR) system is used to reduce the oxygen concentration in the engine scavenging air, which helps to improve combustion stability, avoid premature combustion and deflagration of the fuel gas, further increase the compression ratio, improve engine combustion performance and improve engine exhaust emissions.

[0003] In order to meet the challenge of global climate change, shipboard carbon capture systems have been widely introduced to reduce carbon dioxide emissions from engine exhaust. The system can efficiently capture carbon dioxide from exhaust gas, and after compression and condensation, the liquid carbon dioxide is safely stored in a dedicated storage tank. However, during the long-term storage of liquid carbon dioxide, boil-off gas (BOG) will inevitably be produced. If these carbon dioxide BOGs are not properly handled and leak directly into the atmosphere, they will seriously aggravate the greenhouse effect and pose a potential threat to the environment.

[0004] The current technical field lacks effective solutions for the leakage and efficient utilization of carbon dioxide BOG in the storage unit of the shipboard carbon capture system. There is no literature report on how to properly handle and utilize these BOG to reduce its environmental impact and explore its potential recycling value.

[0005] In view of this, in view of the defects of the existing technology, it is urgent to develop a BOG recycling system and its supporting working method, which should be able to be efficiently integrated into the storage unit of the shipboard carbon capture system. Through this system, not only can the leakage problem of carbon dioxide BOG be effectively solved, but also the efficient recovery and reuse of BOG can be achieved, thereby achieving dual benefits in environmental protection and resource conservation, filling the gap of the existing technology in this field. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a BOG recirculation system for a marine engine, which optimizes the operating efficiency of the engine and reduces emissions by utilizing the carbon dioxide BOG in a storage unit of a shipboard carbon capture system.

[0007] The technical solution of the present invention is as follows:

[0008] A BOG recirculation system for a marine engine is characterized in that it comprises:

[0009] A shipboard carbon capture system 7 for capturing carbon dioxide from engine exhaust, comprising a pretreatment unit, an absorption unit, a desorption unit, a compression unit and a liquefaction storage unit;

[0010] Carbon dioxide storage tank 8: connected to the liquefied storage unit, used to receive and store the treated carbon dioxide;

[0011] Engine scavenging box 1: connected to the marine engine, used to receive the treated waste components and carbon dioxide BOG;

[0012] A pressure control valve 4 is connected between the carbon dioxide storage tank and the engine scavenging air box and is used to adjust the flow rate of carbon dioxide BOG entering the engine scavenging air box;

[0013] An oxygen concentration control unit, comprising an oxygen concentration sensor 2 and a control unit 3, wherein the oxygen concentration sensor is used to monitor the oxygen concentration in the engine scavenging box 1 in real time and transmit a signal to the control unit, and the control unit 3 adjusts the opening of the pressure control valve 4 according to the received oxygen concentration signal to control the amount of carbon dioxide BOG introduced;

[0014] Among them, the engine exhaust gas is introduced into the shipboard carbon capture system after passing through the supercharger, and after being cooled by the pretreatment unit and absorbing carbon dioxide by the absorption unit, the remaining flue gas components are directly discharged into the outside atmosphere; the organic amine liquid after absorbing carbon dioxide is stored in the carbon dioxide storage tank after being desorbed by the desorption unit, compressed by the compression unit and liquefied by the liquefaction storage unit; the carbon dioxide BOG in the carbon dioxide storage tank is introduced into the engine scavenging box through the pressure control valve, so as to reduce the oxygen concentration content in the cylinder of the engine supercharger.

[0015] Furthermore, the pretreatment unit is used to remove nitrogen oxides in the exhaust gas and cool the exhaust gas to about 40°C.

[0016] Furthermore, the absorption unit absorbs carbon dioxide by spraying an organic amine liquid.

[0017] Furthermore, the desorption unit uses heating to desorb the organic amine liquid after absorbing carbon dioxide to obtain pure carbon dioxide gas.

[0018] Furthermore, the liquefied storage unit compresses, condenses and liquefies the pure carbon dioxide gas obtained by desorption and stores it in the carbon dioxide storage tank. The temperature of the liquefied carbon dioxide is -25°C and the pressure is 2200 kPa.

[0019] Furthermore, the opening of the pressure control valve is adjusted in real time according to the signal of the oxygen concentration sensor. When the oxygen concentration is higher than a preset threshold, the opening of the pressure control valve is increased; when the oxygen concentration is lower than the preset threshold, the opening of the pressure control valve is reduced.

[0020] Furthermore, the exhaust gas volume of the marine engine is 76000 kg / h, the engine scavenging air flow rate is 74440 kg / h, and the introduction amount of carbon dioxide BOG is 80 kg / h.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) By utilizing the BOG in the carbon dioxide storage tank, the carbon dioxide in the storage tank is suppressed from escaping, and the oxygen concentration in the scavenging gas is reduced, the engine compression ratio is increased, the combustion performance is improved and deflagration is avoided, and the pollutant concentration in the engine exhaust gas is reduced.

[0023] 2) The shipboard carbon capture system effectively captures and recovers carbon dioxide from engine exhaust, which not only reduces greenhouse gas emissions, but also reuses the recovered carbon dioxide in the form of BOG in the engine scavenging process, optimizing the engine's combustion efficiency and improving the overall energy efficiency.

[0024] 3) With the help of an oxygen concentration control unit, including an oxygen concentration sensor and an intelligent control unit, real-time monitoring and precise control of the oxygen concentration in the engine scavenge box are achieved. According to the changes in oxygen concentration, the opening of the pressure control valve is automatically adjusted to ensure that the oxygen concentration in the scavenge box remains in the optimal range, which not only avoids incomplete combustion caused by excessively high oxygen concentration, but also prevents engine performance degradation caused by too low oxygen concentration. By accurately controlling the oxygen concentration in the scavenge box, it helps to reduce fluctuations during engine operation, improve engine stability and reliability, extend engine service life, and reduce maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the BOG recirculation system for a marine engine of the present invention

[0026] Legend: 1-engine scavenge air box; 2-oxygen concentration sensor; 3-control unit; 4-pressure control valve; 5-air cooler; 6-supercharger; 7-onboard carbon capture system; 8-carbon dioxide storage tank. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below in conjunction with the embodiments and drawings, but this should not be used to limit the protection scope of the present invention.

[0028] See also Figure 1 , Figure 1The schematic diagram of the marine engine BOG recirculation system of the present invention is shown in the figure, which is a marine engine BOG recirculation system, which optimizes the engine's operating efficiency and reduces emissions by utilizing the carbon dioxide BOG in the shipboard carbon capture system storage unit. The following is a detailed explanation of each part of the technical solution:

[0029] The onboard carbon capture system 7 is responsible for capturing carbon dioxide from engine exhaust gas, including a pretreatment unit, an absorption unit, a desorption unit, a compression unit and a liquefaction storage unit;

[0030] The carbon dioxide storage tank 8 is used to store the liquefied carbon dioxide, which is released when needed and enters the engine scavenging air box 1 as BOG.

[0031] Engine scavenging air box 1: directly connected to the marine engine, used to receive BOG from the carbon dioxide storage tank 8 to reduce the oxygen concentration in the cylinder of the engine supercharger.

[0032] Oxygen concentration control unit: includes an oxygen concentration sensor 2 and a control unit 3; wherein the oxygen concentration sensor 2 is used to monitor the oxygen concentration in the engine scavenging box 1 in real time, and the control unit 3 adjusts the opening of the pressure control valve 4 according to the signal of the oxygen concentration sensor 2.

[0033] Workflow:

[0034] The engine exhaust gas first passes through a supercharger 6 to increase its pressure, and then enters the onboard carbon capture system 7.

[0035] In the pretreatment unit, the exhaust gas is cooled to a suitable temperature (such as 40°C) and impurities such as nitrogen oxides are removed.

[0036] The cooled waste gas enters the absorption unit and absorbs carbon dioxide by spraying organic amine liquid. The absorbed waste gas (mainly containing nitrogen, etc.) is discharged into the atmosphere.

[0037] The organic amine liquid after absorbing carbon dioxide enters the heat exchanger for preheating, using the main and auxiliary machine pressurized air as the heat source. The preheated organic amine liquid enters the desorption unit for heating and desorption to obtain pure carbon dioxide gas.

[0038] After being compressed, condensed and liquefied, the pure carbon dioxide gas is stored in a carbon dioxide storage tank 8. The temperature of the liquefied carbon dioxide is -25°C and the pressure is 2200 kPa.

[0039] The BOG in the carbon dioxide storage tank is passed into the engine scavenge air box 1 through the pressure control valve 4. The flow of BOG is regulated by the pressure control valve, which is connected to the oxygen concentration sensor on the scavenge air box to achieve linkage control.

[0040] When the oxygen concentration in the engine scavenging box 1 is higher than the preset threshold, the oxygen concentration sensor 2 sends a high alarm signal. After receiving the signal, the control unit 3 increases the opening of the pressure control valve 4 to increase the amount of BOG introduced, thereby reducing the oxygen concentration in the scavenging box 1.

[0041] On the contrary, when the oxygen concentration is lower than the preset threshold, the oxygen concentration sensor sends a low alarm signal. After receiving the signal, the control unit reduces the opening of the pressure control valve to reduce the amount of BOG entering and prevent the oxygen concentration from being too low and affecting the normal operation of the engine.

[0042] Example:

[0043] The exhaust gas volume of the ship engine is 76000 kg / h. The exhaust gas is passed into the supercharger 6, and the nitrogen oxides in the exhaust gas are removed by the pretreatment unit of the shipboard carbon capture system 7, and the exhaust gas is cooled to about 40°C.

[0044] The cooled exhaust gas from the main engine enters the absorption tower, where it is sprayed with organic amine liquid to fully absorb carbon dioxide. The exhaust gas after carbon dioxide absorption is discharged into the atmosphere through the absorption tower. The organic amine liquid after carbon dioxide absorption is preheated by the heat exchanger, which uses the main and auxiliary engine boosted air as the heat source. The cooled boosted air returns to the scavenging box. The preheated organic amine liquid enters the desorption tower for desorption to obtain pure carbon dioxide gas. The gas is compressed, condensed and liquefied and then stored in the carbon dioxide storage tank 8. The temperature of the liquefied carbon dioxide is -25°C and the pressure is 2200kPa.

[0045] The carbon dioxide storage tank 8 is connected to the engine scavenging box 1 through the pressure control valve 4, and the engine scavenging flow rate is 74440kg / h. The carbon dioxide BOG in the carbon dioxide storage tank 8 is passed into the engine scavenging box 1 through the pressure control valve 4, and the BOG flow rate is 80kg / h. The pressure control valve 4 is connected to the oxygen concentration sensor 2 on the engine scavenging box 1, and the control unit 3 realizes linkage control. The opening of the pressure control valve is usually 100%, but it will be adjusted in real time according to the signal of the oxygen concentration sensor to ensure that the oxygen concentration in the scavenging box remains within an appropriate range.

[0046] The marine engine BOG recirculation system of the present invention not only reduces the oxygen concentration in the engine scavenging air, improves the combustion performance and efficiency of the engine, but also achieves the reduction of carbon dioxide emissions and the recycling of resources.

Claims

1. A marine engine carbon dioxide BOG recirculation system, characterized in that: include: A shipboard carbon capture system 7 for capturing carbon dioxide from engine exhaust, comprising a pretreatment unit, an absorption unit, a desorption unit, a compression unit and a liquefaction storage unit; Carbon dioxide storage tank 8: connected to the liquefied storage unit, used to receive and store the treated carbon dioxide; Engine scavenging box 1: connected to the marine engine, used to receive the treated waste components and carbon dioxide BOG; A pressure control valve 4 is connected between the carbon dioxide storage tank and the engine scavenging air box and is used to adjust the flow rate of carbon dioxide BOG entering the engine scavenging air box; An oxygen concentration control unit, comprising an oxygen concentration sensor 2 and a control unit 3, wherein the oxygen concentration sensor 2 is used to monitor the oxygen concentration in the engine scavenging box 1 in real time and transmit a signal to the control unit, and the control unit 3 adjusts the opening of the pressure control valve 4 according to the received oxygen concentration signal to control the amount of carbon dioxide BOG introduced; Among them, the engine exhaust gas is introduced into the shipboard carbon capture system after passing through the supercharger, and after being cooled by the pretreatment unit and absorbing carbon dioxide by the absorption unit, the remaining flue gas components are directly discharged into the outside atmosphere; the organic amine liquid after absorbing carbon dioxide is stored in the carbon dioxide storage tank after being desorbed by the desorption unit, compressed by the compression unit and liquefied by the liquefaction storage unit; the carbon dioxide BOG in the carbon dioxide storage tank is introduced into the engine scavenging box through the pressure control valve, so as to reduce the oxygen concentration content in the cylinder of the engine supercharger.

2. The marine engine carbon dioxide BOG recirculation system according to claim 1, characterized in that: The pre-treatment unit is used to remove nitrogen oxides in the exhaust gas and cool the exhaust gas to about 40°C.

3. The marine engine carbon dioxide BOG recirculation system according to claim 1, characterized in that: The absorption unit absorbs carbon dioxide by spraying organic amine liquid.

4. The marine engine carbon dioxide BOG recirculation system according to claim 1, characterized in that: The desorption unit uses heating to desorb the organic amine liquid after absorbing carbon dioxide to obtain pure carbon dioxide gas.

5. The marine engine carbon dioxide BOG recirculation system according to claim 1, characterized in that: The liquefied storage unit compresses, condenses and liquefies the pure carbon dioxide gas obtained by desorption and stores it in the carbon dioxide storage tank. The temperature of the liquefied carbon dioxide is -25°C and the pressure is 2200 kPa.

6. The marine engine carbon dioxide BOG recirculation system according to claim 1, characterized in that: The opening of the pressure control valve is adjusted in real time according to the signal of the oxygen concentration sensor. When the oxygen concentration is higher than a preset threshold, the opening of the pressure control valve is increased; when the oxygen concentration is lower than the preset threshold, the opening of the pressure control valve is reduced.

7. The marine engine carbon dioxide BOG recirculation system according to claim 1, characterized in that: The exhaust gas volume of the marine engine is 76000 kg / h, the engine scavenging air flow rate is 74440 kg / h, and the introduction amount of carbon dioxide BOG is 80 kg / h.

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