CN112539091A

CN112539091A - LNG cold energy cascade comprehensive utilization system and method for dual-fuel power ship

Info

Publication number: CN112539091A
Application number: CN202011403800.XA
Authority: CN
Inventors: 姚寿广; 张子敬; 冯国增; 刘锐
Original assignee: Jiangsu University of Science and Technology
Current assignee: Jiangsu University of Science and Technology
Priority date: 2020-12-02
Filing date: 2020-12-02
Publication date: 2021-03-23
Anticipated expiration: 2040-12-02
Also published as: CN112539091B

Abstract

The invention discloses an LNG cold energy cascade comprehensive utilization system of a dual-fuel power ship, which adopts horizontal three-level nested Rankine cycle power generation to utilize LNG fuel cold energy step by step for power generation, and uses a third level transcritical CO₂Rankine cycle and storageThe cold circulation, the refrigeration house and the air conditioner are connected in parallel, so that four working modes of realizing the electricity generation and the cold energy utilization of the refrigeration house required in spring, autumn and winter, realizing the comprehensive utilization of the electricity generation and the cold energy of the refrigeration house and the air conditioner required in summer, realizing the normal operation of the refrigeration house maintained by the cold storage system when the ship is stopped in spring, autumn and winter for a short time, and realizing the normal operation of the refrigeration house and the air conditioner maintained by the cold storage system when the ship is stopped in summer for a short time are formed together. By effectively integrating the LNG/diesel engine dual-fuel main engine cylinder jacket cooling water loop and the high-temperature flue gas cooling loop, the system can improve the cooling performance on the basis of meeting the ship requirements through the adjustment of corresponding functional modules according to the working conditions of different time and space

Comprehensive utilization rate and reduced operation cost.

Description

LNG cold energy cascade comprehensive utilization system and method for dual-fuel power ship

Technical Field

The invention belongs to the technical field of ships, and particularly relates to a liquefied natural gas cold energy cascade comprehensive utilization system and method for a dual-fuel power container ship.

Background

In the 21 st century, people face huge environmental pollution problems and traditional energy exhaustion crisis, energy conservation and emission reduction become the subject of development of the current era, and the requirement of the international maritime organization on the emission of ship pollutants is increasingly strict. Compared with the traditional fuel, LNG (liquefied Natural gas) is used as the ship fuel, the SOX emission of the LNG is reduced by 100%, the NOx emission is reduced by 92%, and the CO2 emission is reduced by 23%. And the global natural gas reserves are very abundant, and based on the advantages, the LNG must become the first choice of global future ship fuel.

The main advantages of LNG for transport and storage are that LNG is 600 times less voluminous than gaseous NG and has a density of about 400kg/m³Making the energy density of LNG significantly higher than NG. During transport and storage, the LNG is maintained at almost atmospheric pressure and a temperature of-162 ℃. The LNG used in the sailing process of a dual fuel powered vessel needs to be re-vaporized to gaseous natural gas. The cold energy contained in the LNG is very large, and 830kJ of cold energy can be released by vaporization of each kilogram of LNG, but most of LNG powered ships cannot reasonably utilize the cold energy in the process of using the LNG, and the cold energy is selected to be discharged into seawater or cylinder water, so that great energy waste is caused. Considerable economic and environmental benefits must be gained if the portion of the cold energy released by the vaporization of LNG can be reasonably utilized or recovered.

At present, a lot of research results are available at home and abroad for the utilization of cold energy of LNG, however, most of the results use simple vaporization technology at land LNG terminals, have large scale and are not suitable for being applied to ships. Of course, there are a few processes for realizing LNG cold energy cascade utilization for ships, which mainly include:

(1) chinese utility model patent CN 204415698U provides a multistage system of utilizing of on-board LNG, including dual-fuel diesel engine, natural gas turboexpander generator, first heat exchanger, second heat exchanger, LNG storage tank, cabin evaporimeter, third heat exchanger, methane turboexpander generator and sea water pump, the dual-fuel diesel engine connects gradually natural gas turboexpander electricity generation, first heat exchanger, second heat exchanger and LNG storage tank through the pipeline, and methane turboexpander generator connects gradually second heat exchanger and third heat exchanger through the pipeline to form closed circulation pipeline, sea water pump and cabin evaporimeter are connected in the third heat exchanger left side. The system applies LNG cold energy to ship power generation, low-temperature seawater is used as a heat source of Rankine cycle, cylinder sleeve water is finally used for heating LNG and directly expanding the LNG, system income is low, and a large amount of energy is wasted.

(2) Chinese utility model patent CN 207006622U proposes a cold energy cascade utilization system of LNG carrier, including LNG force (forcing) pump, compressor, nitrogen making circulation system, two-stage rankine cycle power generation system, sea water desalination circulation system, low temperature freezer circulation system, high temperature freezer circulation system, boats and ships air conditioning system and steam turbine exhaust steam heating device. Although the system has the characteristics of compact structure, energy consumption saving, low cost, wide application range and the like, before the seawater desalination module is placed in a low-temperature cold storage, the LNG temperature is still low, the heat exchange temperature difference of the heat exchanger is large, so that the cold energy recovery efficiency is also low,

energy efficient utilization is not fully achieved.

(3) The Chinese patent CN 109268095A provides an LNG fuel cold energy comprehensive utilization method and system for a dual-fuel power ship, which comprises an LNG liquid storage tank, an LNG pump and a single-stage LangThe system comprises a positive cycle power generation system, a low-temperature refrigeration house system, a seawater desalination system, a high-temperature refrigeration house system and an air conditioning system. The invention is suitable for the dual-fuel power ship, but the LNG temperature span for providing cold energy for the air conditioning module is overlarge, and on one hand, the overlarge temperature difference causes

The loss is increased, and on the other hand, the requirement of the ship air conditioner on the cold load is excessive, so that the energy is wasted, namely, the LNG cold energy is not efficiently utilized in a gradient manner.

In addition to the above patents, many of them are designed for a single function on a ship, and do not realize efficient utilization of the LNG cold energy on an LNG-powered ship.

As can be seen from the above reports, many studies on LNG cold energy utilization for ships have been made, but there are some disadvantages, but the studies on LNG cold energy utilization using large container ships as prototype ships are still blank, and most of container LNG power ships discharge a large amount of cold energy into seawater or cylinder liner water during LNG use, which causes environmental pollution and energy waste.

Disclosure of Invention

The invention aims to solve the problems and the defects in the prior art and provides a LNG cold energy cascade comprehensive utilization system and method for a dual-fuel power ship.

According to the invention, the LNG fuel cold energy is utilized for power generation step by adopting the horizontal three-stage nested Rankine cycle power generation, and the third-stage transcritical CO2 Rankine cycle is connected in parallel with the cold accumulation cycle, the refrigeration house and the air conditioning cycle, so that four different system working modes are formed together. By effectively integrating the LNG/diesel engine dual-fuel main engine cylinder jacket cooling water loop and the high-temperature flue gas cooling loop, the system can improve the cold energy and cold on the basis of meeting the corresponding refrigeration requirements of the ship by adjusting corresponding functional modules according to the working conditions under different time-space conditions

The comprehensive utilization rate of the ship is reduced, and the operating cost of the ship is reduced.

In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:

a dual-fuel power ship LNG cold energy cascade comprehensive utilization system comprises:

the LNG evaporation side comprises an LNG storage tank 1, an LNG booster pump 2, a cold source input end 301 of a first-stage LNG heat exchanger 3, a cold source output end 302 of the first-stage LNG heat exchanger 3, a cold source input end 401 of a second-stage LNG heat exchanger 4, a cold source output end 402 of the second-stage LNG heat exchanger 4 and an LNG splitter 5 which are sequentially connected through pipelines, wherein NG is divided into three streams after coming out of the splitter 5, and the first stream is connected with a first valve 32, a cold source input end 601 of a third-stage LNG heat exchanger 6 and a cold source output end 602 of the third-stage LNG heat exchanger 6 and then flows into a host through an LNG combiner 30; the second strand is connected with the second valve 33, the cold source input end 1801 of the cold storage heat exchanger 18 and the cold source output end 1802 of the cold storage heat exchanger 18, and then is divided into two streams by the LNG flow divider 21, one stream is connected with the sixth valve 37, the cold source input end 2301 of the air conditioning heat exchanger 23 and the cold source output end 2302 of the air conditioning heat exchanger 23, and then is converged into the LNG junction station 26, the other stream is directly connected with the fifth valve 36 and the LNG junction station 26, the NG coming out of the LNG junction station 26 is connected with the cold source input end 2901 of the LNG temperature regulator 29 and the cold source output end 2902 of the LNG temperature regulator 29, and finally flows into the host through the LNG junction station; the third branch is connected with the fourth valve 35, the cold source input terminal 2801 of the cold accumulation tank 28 and the cold source output terminal 2802 of the cold accumulation tank 28, and then flows into the host through the LNG junction box 30.

The first-stage Rankine cycle power generation unit comprises a heat source output end 304 of a first-stage LNG heat exchanger 3, a first-stage power generation working medium pump 7, a cold source input end 403 of a second-stage LNG heat exchanger 4, a cold source output end 404 of the second-stage LNG heat exchanger 4, a cold source input end 603 of a third-stage LNG heat exchanger 6, a cold source output end 604 of the third-stage LNG heat exchanger 6, a cold source input end 801 of a first-stage cooling water heat exchanger 8, a cold source output end 802 of the first-stage cooling water heat exchanger 8, a first-stage turbine expander 9 and a heat source input end 303 of the first-stage LNG heat exchanger 3 which are sequentially connected through pipelines to form a closed. The first stage turboexpander 9 drives the first stage generator set to work.

The second-stage Rankine cycle power generation unit comprises a heat source output end 406 of the second-stage LNG heat exchanger 4, a second-stage power generation working medium pump 10, a cold source input end 605 of the third-stage LNG heat exchanger 6, a cold source output end 606 of the third-stage LNG heat exchanger 6, a cold source input end 1101 of the second-stage cooling water heat exchanger 11, a cold source output end 1102 of the second-stage cooling water heat exchanger 11, a second-stage turbo expander 12 and a heat source input end 405 of the second-stage LNG heat exchanger 4 which are sequentially connected through pipelines to form a closed loop. The second stage turboexpander 12 drives the second stage power generating unit to operate.

The third-stage transcritical Rankine cycle power generation unit comprises a heat source output end 608 of a third-stage LNG heat exchanger 6, a third-stage power generation working medium pump 13, a cold source input end 1401 of a heat regenerator 14, a cold source output end 1402 of the heat regenerator 14, a cold source input end 1501 of a high-temperature flue gas heat exchanger 15, a cold source output end 1502 of the high-temperature flue gas heat exchanger 15, a third-stage turbine expander 16, a heat source input end 1403 of the heat regenerator 14, a heat source output end 1404 of the heat regenerator 14 and a heat source input end 607 of the third-stage LNG heat exchanger 6 which are sequentially connected through pipelines to form a closed loop. The third stage turboexpander 16 drives the third stage power generating unit to work.

Freezer + air conditioner circulation refrigeration unit, freezer + air conditioner circulation refrigeration unit is including the freezer circulation and the air conditioner circulation of establishing ties, wherein the freezer circulation is including 18 heat source output terminals 1806, freezer refrigeration working medium pump 19, freezer refrigeration working medium evaporimeter 20 and the 18 heat source input terminals 1805 of freezer heat exchanger that loop through the pipe connection, the air conditioner circulation is including heat source output terminals 2306, air conditioner refrigeration working medium pump 24, air conditioner refrigeration working medium evaporimeter 25 and the heat source input terminals 2305 of air conditioner heat exchanger 23 through pipe connection. The refrigeration storage refrigeration working medium evaporator 20 and the air conditioner refrigeration working medium evaporator 25 absorb heat through evaporation and reduce the temperature.

The cold accumulation circulating unit comprises a cold accumulation tank 28 heat source output end 2803, a cold accumulation circulating working medium pump 17, a third valve 34, a cold source input end 1803 of a cold storage heat exchanger 18, a cold source output end 1804 of the cold storage heat exchanger 18 and a cold accumulation circulating working medium shunt 22 which are sequentially connected through a pipeline, cold accumulation circulating working medium coming out of the cold accumulation circulating working medium shunt 22 is divided into two streams, one stream is connected with an eighth valve 39, the cold source input end 2303 of an air conditioning heat exchanger 23 and the cold source output end 2304 of the air conditioning heat exchanger 23 and then flows into a cold accumulation circulating working medium junction device 27, the other stream is directly connected with a seventh valve 38 and the cold accumulation circulating working medium junction device 27, and the cold accumulation circulating working medium coming out of the cold accumulation circulating working medium junction device 27 flows back to the cold. The cold energy in the cold accumulation tank 28 is transferred to the cold storage heat exchanger 18 and the air conditioning heat exchanger 23 through the cold accumulation working medium, and then transferred to the cold storage refrigeration working medium evaporator 20 and the air conditioning refrigeration working medium evaporator 25 through the cold storage heat exchanger 18 and the air conditioning heat exchanger 23.

The cooling water side comprises cooling water flowing out of the ship main engine, and is divided into three flows through the cooling water splitter 31, wherein one flow is connected with a heat source input end 803 of the first-stage cooling water heat exchanger 8 and a heat source output end 804 of the first-stage cooling water heat exchanger 8; one is connected with a heat source input end 1103 of the second-stage cooling water heat exchanger 11 and a heat source output end 1104 of the second-stage cooling water heat exchanger 11; and one is connected to the heat source input 2903 of the LNG temperature controller 29 and the heat source output 2904 of the LNG temperature controller 29. The cooling water transfers heat to working media of each cold source through the three heat exchangers respectively.

And the high-temperature flue gas side comprises high-temperature flue gas flowing out of the ship waste heat boiler, and is connected with a heat source input end 1503 of the high-temperature flue gas heat exchanger 15 and a heat source output end 1504 of the high-temperature flue gas heat exchanger 15. The high-temperature flue gas transfers heat to a third-stage power generation working medium through the high-temperature flue gas heat exchanger 15.

Further, a first-stage power generation working medium is arranged in the first-stage Rankine power generation cycle; a second-stage power generation working medium is arranged in the second-stage Rankine power generation cycle; a third-stage power generation working medium is arranged in the third-stage Rankine power generation cycle; a refrigeration working medium of the refrigeration house is arranged in the refrigeration cycle of the refrigeration house; an air-conditioning refrigeration working medium is arranged in the air-conditioning refrigeration cycle; a cold accumulation medium is arranged in the cold accumulation tank; the cold accumulation circulation is provided with a cold accumulation circulation working medium.

Further, the dew point of the first-stage power generation working medium is lower than that of the second-stage power generation working medium, and the dew point of the second-stage power generation working medium is lower than that of the third-stage power generation working medium.

Furthermore, the first-stage to third-stage power generation working media, the refrigeration working medium of the refrigeration house, the refrigeration working medium of the air conditioner, the cold accumulation medium and the cold accumulation circulating working medium are all refrigerants.

Furthermore, the first-stage power generation working medium is R1150, the second-stage power generation working medium is R1270, the third-stage power generation working medium is carbon dioxide, the refrigeration working medium of a refrigeration house is R600, the refrigeration working medium of an air conditioner is CL2-C1, the cold storage medium in the cold storage tank is 53% ethylene glycol, and the cold storage circulating working medium is 60% ethylene glycol.

The working method of the LNG cold energy cascade comprehensive utilization system of the dual-fuel power ship is divided into four working modes according to requirements.

The cold energy utilization of the power generation and the refrigeration house required in spring, autumn and winter is realized, and the working mode of the system is as follows:

the first valve 32, the second valve 33 and the fifth valve 36 are opened, and the third valve 34, the fourth valve 35, the sixth valve 37, the seventh valve 38 and the eighth valve 39 are closed, so that the usable power generation and cold storage cold energy utilization system in spring, autumn and winter is realized.

LNG flow path: the LNG fuel is pressurized by an LNG booster pump 2 after coming out of an LNG storage tank 1, then sequentially enters a primary LNG heat exchanger 3 and a secondary LNG heat exchanger 4 for heat exchange, LNG absorbs heat and is heated, the vaporized LNG enters an LNG splitter 5 in a gaseous state, NG is divided into two streams, one stream exchanges heat with a tertiary LNG heat exchanger 6, and then the LNG enters a ship host through an LNG confluence device 30; one strand exchanges heat with a refrigeration house heat exchanger 18, then enters an LNG temperature regulator 29 to exchange heat with cylinder jacket cooling water after passing through an LNG diverter 21, a fifth valve 36 and an LNG confluence device 26, is converged into one strand with NG flowing through a third-stage Rankine cycle through the LNG confluence device 30 after the temperature reaches the air inlet requirement of a ship main engine, and is connected to the air inlet of a power ship main engine.

A first-stage Rankine power generation unit: the first-stage power generation working medium coming out of the first-stage turbo expander 9 enters the first-stage LNG heat exchanger 3 to exchange heat with LNG and then is condensed, then is pressurized by the first-stage power generation working medium pump 7, enters the second-stage LNG heat exchanger 4 to exchange heat with the second-stage power generation working medium and is heated up, enters the third-stage LNG heat exchanger 6 to exchange heat with the third-stage power generation working medium, then is continuously heated, enters the first-stage cooling water heat exchanger 8 to exchange heat with cylinder jacket cooling water and is evaporated, and then enters the first-stage turbo expander 9 in a gaseous state to perform expansion work to complete circulation.

A second-stage Rankine power generation unit: the second-stage power generation working medium from the second-stage turbo expander 12 enters the second-stage LNG heat exchanger 4 to exchange heat with the first-stage power generation working medium and LNG and condense, is pressurized by the second-stage power generation working medium pump 10, then enters the third-stage LNG heat exchanger 6 to exchange heat with the third-stage power generation working medium and raise the temperature, then enters the second-stage cooling water heat exchanger 11 to exchange heat with cylinder jacket cooling water and evaporate, and then enters the second-stage turbo expander 12 in a gaseous state to perform expansion and work so as to complete circulation.

A third-stage Rankine power generation unit: the third-stage power generation working medium from the third-stage turbo expander 16 enters the heat regenerator 14 to exchange heat with the condensed and pressurized third-stage power generation working medium, then the temperature of the third-stage power generation working medium is reduced, then the third-stage power generation working medium enters the third-stage LNG heat exchanger 6 to exchange heat and condense, is pressurized by the third-stage power generation working medium pump 13, then sequentially enters the heat regenerator 14 to be preheated, enters the high-flue gas heat exchanger 15 to exchange heat with flue gas and evaporate, and then enters the third-stage turbo expander 16 in a gaseous state to perform expansion and work doing. The temperature of the high-temperature flue gas is reduced after heat exchange with the third-stage power generation working medium.

Freezer refrigeration cycle unit: the refrigeration house refrigeration working medium from the refrigeration house refrigeration working medium evaporator 20 enters the refrigeration house heat exchanger 18 to exchange heat with the NG, then the temperature is reduced, the refrigeration house refrigeration working medium enters the refrigeration house refrigeration working medium evaporator 20 to release cold energy after being pressurized by the refrigeration house refrigeration working medium pump 19, and finally the cold energy flows back to the refrigeration house heat exchanger 18 to complete circulation.

Cooling water side: cooling water flowing out of the marine main engine is divided into three streams through the cooling water splitter 31, and one stream exchanges heat with a first-stage power generation working medium through the first-stage cooling water heat exchanger 8 and is cooled; one strand exchanges heat with a second-stage power generation working medium through a second-stage cooling water heat exchanger 11 and is cooled; one stream is passed through LNG thermostat 29 to exchange heat with NG and cool down.

High-temperature flue gas side: the high-temperature flue gas flowing out of the ship waste heat boiler exchanges heat with carbon dioxide through the high-temperature flue gas heat exchanger 15 and is cooled.

The comprehensive utilization of the cold energy of the power generation, the refrigeration house and the air conditioner which are needed in summer is realized, and the working mode of the system is as follows:

the first valve 32, the second valve 33 and the sixth valve 37 are opened, and the third valve 34, the fourth valve 35, the fifth valve 36, the seventh valve 38 and the eighth valve 39 are closed, so that the comprehensive utilization system of the cold energy of the power generation, the refrigeration house and the air conditioner, which can be used when the air conditioner needs to be used in summer, is realized.

LNG flow path: the LNG fuel is pressurized by an LNG booster pump 2 after coming out of an LNG storage tank 1, then sequentially enters a primary LNG heat exchanger 3 and a secondary LNG heat exchanger 4 for heat exchange, LNG absorbs heat and is heated, the vaporized LNG enters an LNG splitter 5 in a gaseous state, NG is divided into two streams, one stream exchanges heat with a tertiary LNG heat exchanger 6, and then the LNG enters a ship host through an LNG confluence device 30; one strand exchanges heat with a refrigeration house heat exchanger 18, then exchanges heat with an air conditioner heat exchanger 23 through an LNG (liquefied natural gas) shunt 21 and a sixth valve 37, enters an LNG temperature regulator 29 after passing through an LNG confluence device 26 to exchange heat with cylinder jacket cooling water, and is converged into one strand with NG flowing through a third-stage Rankine cycle through an LNG confluence device 30 after the temperature reaches the air inlet requirement of a ship main engine and then is connected to the air inlet of a power ship main engine.

Air-conditioning refrigeration cycle unit: the air-conditioning refrigeration working medium from the air-conditioning refrigeration working medium evaporator 25 enters the air-conditioning heat exchanger 23 to exchange heat with the NG, then the temperature is reduced, the air-conditioning refrigeration working medium is pressurized by the air-conditioning refrigeration working medium pump 24, enters the air-conditioning refrigeration working medium evaporator 25 to release cold energy, and finally flows back to the air-conditioning heat exchanger 23 to complete circulation.

Thirdly, realizing the short-time ship stopping and shutdown in spring, autumn and winter and using the cold accumulation system to maintain the normal operation of the cold storage house, wherein the working mode of the system is as follows:

the third valve 34 and the seventh valve 38 are opened, and the first valve 32, the second valve 33, the fourth valve 35, the fifth valve 36, the sixth valve 37 and the eighth valve 39 are closed, so that the ship is stopped and the cold accumulation system is used for maintaining the normal operation of the cold storage warehouse in spring, autumn and winter.

A cold storage circulation unit: when the ship is shut down and stopped in navigation, the system does not convey NG for the ship main engine any more, so that the LNG line is completely closed, and the cold storage system is continuously cooled through the cold storage tank. The condensed cold accumulation medium in the cold accumulation tank 28 absorbs heat by melting in a form of transferring cold energy to a cold accumulation circulating working medium, and the cold accumulation circulating working medium exchanges heat with the cold storage heat exchanger 18 and heats up through a third valve 34 under the pushing of the cold accumulation circulating working medium pump 17; then passes through the flow divider 22, the seventh valve 38, the flow combiner 27, and finally flows back to the cold accumulation tank 28 to complete the cycle.

Fourthly, realizing that the short-time ship stopping and shutdown in summer use the cold accumulation system to maintain the normal operation of the refrigeration house and the air conditioner, and the working mode of the system is as follows:

the third valve 34 and the eighth valve 39 are opened, and the first valve 32, the second valve 33, the fourth valve 35, the fifth valve 36, the sixth valve 37 and the seventh valve 38 are closed, so that the ship is stopped and the cold accumulation system is used for maintaining the normal operation of the refrigeration storage and the air conditioner in summer.

A cold storage circulation unit: when the ship is shut down and stopped in navigation, the system does not convey NG for the ship main engine any more, so that the LNG line is completely closed, and the cold storage system and the air conditioning system are continuously cooled through the cold storage tank. The condensed cold accumulation medium in the cold accumulation tank 28 absorbs heat by melting in a form of transferring cold energy to a cold accumulation circulating working medium, and the cold accumulation circulating working medium exchanges heat with the cold storage heat exchanger 18 and heats up through a third valve 34 under the pushing of the cold accumulation circulating working medium pump 17; then exchanges heat with the air-conditioning heat exchanger 32 through the flow divider 22 and the eighth valve 39, finally flows back to the cold accumulation tank 28 after passing through the flow combiner 27 to complete the circulation.

Further, the working method further comprises a short startup cold accumulation process, and the working mode of the system is as follows: opening a fourth valve 35, closing a first valve 32, a second valve 33, a third valve 34, a fifth valve 36, a sixth valve 37, a seventh valve 38 and an eighth valve 39, pressurizing LNG fuel from an LNG storage tank 1 by an LNG booster pump 2, sequentially entering a first-stage LNG heat exchanger 3 and a second-stage LNG heat exchanger for heat exchange 4, absorbing heat and raising temperature of the LNG, entering an LNG diverter 5 in a gaseous state after vaporization, and then entering a cold storage tank 28 for heat exchange with a cold storage medium, wherein the LNG temperature is raised to the intake requirement of a marine main engine and flows into the marine main engine through an LNG flow combiner 30; the cold accumulation medium absorbs the cold energy of the NG and then condenses into a solid state, and the solid state is stored in the cold accumulation tank to be used as a standby cold source.

Further, the LNG fuel is lifted to

30MPa is used as the air inlet of the ship main engine.

Further, when the air conditioner needs to be used in summer, the first valve 32, the second valve 33 and the sixth valve 37 are opened, and the third valve 34, the fourth valve 35, the fifth valve 36, the seventh valve 38 and the eighth valve 39 are closed, so that the NG exchanges heat with the cold storage heat exchanger 18 and then exchanges heat with the air conditioner heat exchanger 23, and the comprehensive utilization system of the cold energy of the power generation + the cold storage + the air conditioner is realized; when the air conditioner is closed in spring, autumn and winter, the first valve 32, the second valve 33 and the fifth valve 36 are opened, the third valve 34, the fourth valve 35, the sixth valve 37, the seventh valve 38 and the eighth valve 39 are closed, at the moment, the NG directly enters the LNG temperature regulator 29 after exchanging heat with the cold storage heat exchanger 18, and the usable power generation and cold storage cold energy utilization system in spring, autumn and winter is realized.

Further, when the ship is shut down and stopped in navigation, the system does not convey NG for the ship main engine any more, and the cold storage circulating working medium circularly exchanges heat with the refrigeration house and the air conditioner to maintain the normal operation of the refrigeration house and the air conditioner. If the off-time is summer, the third valve 34 and the eighth valve 39 are opened, the first valve 32, the second valve 33, the fourth valve 35, the fifth valve 36, the sixth valve 37 and the seventh valve 38 are closed, the condensed cold accumulation medium in the cold accumulation tank 28 transfers cold energy to the cold accumulation circulating working medium in a melting and heat absorption manner, and the cold accumulation circulating working medium is pushed by the cold accumulation circulating working medium pump 17 to exchange heat with the cold storage heat exchanger 18, then continuously exchanges heat with the air conditioner heat exchanger 23, and finally flows back to the cold accumulation tank 28; if the shutdown time is spring, autumn or winter, the third valve 34 and the seventh valve 38 are opened, the first valve 32, the second valve 33, the fourth valve 35, the fifth valve 36, the sixth valve 37 and the eighth valve 39 are closed, the condensed cold accumulation medium in the cold accumulation tank 28 transfers cold to the cold accumulation circulating working medium in a melting and heat absorption manner, the cold accumulation circulating working medium exchanges heat with the cold storage heat exchanger 18 under the driving of the cold accumulation circulating working medium pump 17, and the cold accumulation circulating working medium directly flows back to the cold accumulation tank 28 after coming out of the cold storage heat exchanger 18.

Compared with the prior art, the invention has the advantages that:

1. according to the invention, LNG fuel cold energy is utilized step by step for power generation by adopting horizontal three-level nested Rankine cycle power generation, cylinder jacket cooling water generated by a ship main engine is utilized as a heat source in the first-level Rankine power generation cycle and the second-level Rankine power generation cycle, and high-temperature flue gas generated by the ship main engine is utilized as a heat source in the third-level Rankine power generation cycle, so that the cascade utilization of the LNG cold energy and the utilization of low-grade waste heat for power generation are realized;

2. trans-critical CO of the third stage₂Rankine cycle and cold accumulation cycle and refrigeration houseThe air conditioners are circularly connected in parallel, so that four different system working modes are formed together: the electricity generation and cold energy utilization system of the cold storage house available in spring, autumn and winter; the comprehensive utilization system of the power generation, the refrigeration house and the cold energy of the air conditioner is available when the air conditioner needs to be used in summer; the ship is stopped for a short time in spring, autumn and winter, and the cold accumulation system is used for maintaining the normal operation of the refrigeration house; the cold storage system is used for maintaining the normal operation of the refrigeration house and the air conditioner when the ship is stopped and stopped in short time in summer, so that the system can improve the cold on the basis of meeting the corresponding refrigeration requirement of the ship through the adjustment of the corresponding functional module

Comprehensive utilization rate and reduced operation cost of the ship.

Drawings

FIG. 1 is a schematic flow chart of the present invention;

wherein: the LNG power generation system comprises an LNG storage tank 1, an LNG booster pump 2, a first-stage LNG heat exchanger 3, a second-stage LNG heat exchanger 4, an LNG diverter 5, a third-stage LNG heat exchanger 6, a first-stage power generation working medium pump 7, a first-stage cooling water heat exchanger 8, a first-stage turbine expander 9, a second-stage power generation working medium pump 10, a second-stage cooling water heat exchanger 11, a second-stage turbine expander 12, a third-stage power generation working medium pump 13, a regenerator 14, a high-temperature flue gas heat exchanger 15, a third-stage turbine expander 16, a cold storage circulating working medium pump 17, a cold storage heat exchanger 18, a cold storage refrigerating working medium pump 19, a cold storage refrigerating working medium evaporator 20, a cold storage refrigerating working medium divider 21, a cold storage circulating working medium divider 22, an air conditioning heat exchanger 23, an air conditioning working medium pump 24, an air conditioning refrigerating working medium evaporator 25, an air conditioning refrigerating working medium evaporator 26, an LNG combiner 27, a cold circulating working, 28. the system comprises a cold storage tank, a LNG temperature regulator, a LNG confluence device, a cooling water splitter, a first valve, a second valve, a third valve, a fourth valve, a fifth valve, a sixth valve, a seventh valve, a sixth valve.

Detailed Description

The invention is further elucidated with reference to the drawings and the embodiments.

As shown in fig. 1, the LNG cold energy cascade comprehensive utilization system for a dual-fuel powered ship of the present invention includes:

the first valve 32, the second valve 33, and the fifth valve 36 are opened, and the third valve 34, the fourth valve 35, the sixth valve 37, the seventh valve 38, and the eighth valve 39 are closed.

LNG flow path: the LNG fuel from an LNG storage tank 1 is 450kPa and-162 ℃, the LNG vaporization flow required by the air intake of a ship main engine is 5440kg/h, the LNG fuel is pressurized to 30MPa by an LNG booster pump 2, the power consumption of the LNG booster pump 2 is 129kW, the LNG fuel enters a primary LNG heat exchanger 3 to exchange heat with a primary power generation working medium R1150 to-87 ℃, then enters a secondary LNG heat exchanger 4 to exchange heat with a secondary power generation working medium R1270 and LNG to-45 ℃, and is vaporized to a gaseous state, then the LNG fuel is averagely divided into two streams by an LNG splitter 5, and one stream passes through a first valve 32 and then enters a tertiary LNG heat exchanger 6 to exchange heat with a tertiary power generation working medium carbon dioxide to 2; one strand of the mixed flow enters the cold storage heat exchanger 18 through the second valve 33 to exchange heat with a cold storage circulating working medium R600 to minus 30 ℃, then enters the LNG temperature regulator 29 through the LNG diverter 21, the fifth valve 36 and the LNG confluence device 26 to exchange heat with cylinder jacket cooling water to 2 ℃, and finally two strands of the mixed flow are converged into one strand through the LNG confluence device 30 and enter the ship main engine to be combusted.

A first-stage Rankine power generation unit: the first-stage power generation working medium R1150 with the flow rate of 1692kg/h and the temperature of 210kPa to-16 ℃ coming out of the first-stage turbo expander 9 enters the first-stage LNG heat exchanger 3 to exchange heat with LNG, is condensed to-145 ℃, is pressurized to 2000kPa by the first-stage power generation working medium pump 7, consumes 2.138kW of power by the first-stage power generation working medium pump, enters the second-stage LNG heat exchanger 4 to exchange heat with the second-stage power generation working medium R1270 to-87 ℃, enters the third-stage LNG heat exchanger 6 to exchange heat with the third-stage power generation working medium carbon dioxide to 2 ℃, enters the first-stage cooling water heat exchanger 8 to exchange heat with cylinder jacket cooling water to 85 ℃, enters the first-stage turbo expander 9 in a gas state to do work to complete_o

A second-stage Rankine power generation unit: 149 kPa-30 ℃ second-stage power generation working medium R1270 from the second-stage turbo expander 12 with the flow rate of 1223kg/h enters the second-stage LNG heat exchanger 4 to exchange heat with the first-stage power generation working medium R1150 and LNG to-40 ℃, is pressurized to 3500kPa by the second-stage power generation working medium pump 10, enters the third-stage LNG heat exchanger 6 to exchange heat with the third-stage power generation working medium carbon dioxide to 2 ℃, enters the second-stage cooling water heat exchanger 11 to exchange heat with cylinder jacket cooling water to 85 ℃, and then enters the second-stage turbo expander 12 in a gaseous state to perform expansion and work to complete circulation.

A third-stage Rankine power generation unit: the flow rate of the third-stage power generation working medium carbon dioxide which is 3251kPa and 30 ℃ and comes out of the third-stage turbo expander 16 is 1576kg/h, the third-stage power generation working medium carbon dioxide enters the heat regenerator 14 to exchange heat with the low-temperature carbon dioxide after condensation and pressurization to 8 ℃, then enters the third-stage LNG heat exchanger 6 to be condensed to-10 ℃, is pressurized to 18MPa by the third-stage power generation working medium pump 13, then sequentially enters the heat regenerator 14 to be preheated to 15 ℃, enters the high-flue gas heat exchanger 15 to exchange heat with flue gas to 160 ℃, and then enters the third-stage turbo expander 16 in a gaseous state to perform expansion and work to complete circulation.

Freezer refrigeration cycle unit: the flow rate of the refrigeration house refrigeration working medium R600 with the temperature of between 260kPa and 25 ℃ from the refrigeration house refrigeration working medium evaporator 20 is 3099kg/h, the temperature is reduced to-35 ℃ after the refrigeration house refrigeration working medium R600 enters the refrigeration house heat exchanger 18 to exchange heat with the NG, then the refrigeration house refrigeration working medium R20 is pressurized to 1000kPa after passing through the refrigeration house refrigeration working medium pump 19, then the refrigeration house refrigeration working medium R20 releases cold energy, and finally the cold energy flows back to the refrigeration house heat exchanger 18 to complete circulation.

Cooling water side: the cooling water flowing out of the marine main engine is divided into three flows through the cooling water splitter 31, wherein the temperature of the cooling water is 90 ℃, the flow rate of the cooling water is 24920kg/h, one flow is subjected to heat exchange with a first-stage power generation working medium through the first-stage cooling water heat exchanger 8, and the temperature is reduced to 70 ℃; one strand exchanges heat with a second-stage power generation working medium through a second-stage cooling water heat exchanger 11, and the temperature is reduced to 70 ℃; one stream is passed through LNG temperature regulator 29 to exchange heat with NG, reducing the temperature to 70 ℃.

High-temperature flue gas side: the temperature of the high-temperature flue gas flowing out of the ship waste heat boiler is 165 ℃, the flow rate is 65720kg/h, the high-temperature flue gas exchanges heat with carbon dioxide through the high-temperature flue gas heat exchanger 15, and the outlet temperature is 150 ℃.

the first valve 32, the second valve 33, and the sixth valve 37 are opened, and the third valve 34, the fourth valve 35, the fifth valve 36, the seventh valve 38, and the eighth valve 39 are closed.

LNG flow path: the LNG fuel from an LNG storage tank 1 is 450kPa and-162 ℃, the LNG vaporization flow required by the air intake of a ship main engine is 5440kg/h, the LNG fuel is pressurized to 30MPa by an LNG booster pump 2, the power consumption of the LNG booster pump 2 is 129kW, the LNG fuel enters a primary LNG heat exchanger 3 to exchange heat with a primary power generation working medium R1150 to-87 ℃, then enters a secondary LNG heat exchanger 4 to exchange heat with a secondary power generation working medium R1270 and LNG to-45 ℃, and is vaporized to a gaseous state, then the LNG fuel is averagely divided into two streams by an LNG splitter 5, and one stream passes through a first valve 32 and then enters a tertiary LNG heat exchanger 6 to exchange heat with a tertiary power generation working medium carbon dioxide to 2; one strand of the LNG-cooled water enters the refrigeration house heat exchanger 18 after passing through the second valve 33 to exchange heat with a refrigeration house circulating working medium R600 to minus 30 ℃, then enters the air conditioner heat exchanger 23 through the LNG diverter 21 and the sixth valve 37 to exchange heat with an air conditioner refrigerating working medium CL2-C1 to 2 ℃, then enters the LNG temperature regulator 29 after passing through the LNG combiner 26 to exchange heat with cylinder jacket cooling water, the temperature reaches the air inlet temperature of a main engine, and finally the two strands of the LNG-cooled water are converged into one strand through the LNG combiner 30 to enter a main engine of a ship to be combusted.

A first-stage Rankine power generation unit: the first-stage power generation working medium R1150 with the flow rate of 1692kg/h and the temperature of 210kPa and-16 ℃ coming out of the first-stage turbo expander 9 enters the first-stage LNG heat exchanger 3 to exchange heat with LNG, is condensed to-145 ℃, is pressurized to 2000kPa by the first-stage power generation working medium pump 7, consumes 2.138kW of power by the first-stage power generation working medium pump, enters the second-stage LNG heat exchanger 4 to exchange heat with the second-stage power generation working medium R1270 to-87 ℃, enters the third-stage LNG heat exchanger 6 to exchange heat with the third-stage power generation working medium carbon dioxide to 2 ℃, enters the first-stage cooling water heat exchanger 8 to exchange heat with cylinder jacket cooling water to 85 ℃, enters the first-stage turbo expander 9 in a gas state to do work to complete the

Air-conditioning refrigeration cycle unit: the flow rate of the air-conditioning refrigeration working medium CL2-C1 at the temperature of 15 ℃ and 260kPa from the air-conditioning refrigeration working medium evaporator 25 is 2304kg/h, the temperature is reduced to 5 ℃ after the air-conditioning refrigeration working medium CL enters the air-conditioning heat exchanger 23 to exchange heat with NG, then the air-conditioning refrigeration working medium CL is pressurized to 1000kPa by the air-conditioning refrigeration working medium pump 24, then the air-conditioning refrigeration working medium CL enters the air-conditioning refrigeration working medium evaporator 25 to release cold energy, and finally the air-conditioning refrigeration.

the third valve 34 and the seventh valve 38 are opened, and the first valve 32, the second valve 33, the fourth valve 35, the fifth valve 36, the sixth valve 37 and the eighth valve 39 are closed.

A cold storage circulation unit: when the ship is shut down and stopped in navigation, the system does not convey NG for the ship main engine any more, so that the LNG line is completely closed, and the cold storage system is continuously cooled through the cold storage tank. The condensed 53 percent of glycol in the cold accumulation tank 28 absorbs heat through melting in a mode of transmitting cold energy to 60 percent of glycol of cold accumulation circulating working medium, the temperature of the cold accumulation circulating working medium 60 percent of glycol is-40 ℃ after heat exchange, the cold accumulation circulating working medium passes through a third valve 34 under the push of a cold accumulation circulating working medium pump 17 and then exchanges heat with a cold storage heat exchanger 18, and the temperature is raised to-30 ℃; then passes through the flow divider 22, the seventh valve 38, the flow combiner 27, and finally flows back to the cold storage tank 28 to complete the cycle.

Freezer refrigeration cycle unit: the flow rate of the refrigeration house refrigeration working medium R600 with the temperature of between 260kPa and 25 ℃ from the refrigeration house refrigeration working medium evaporator 20 is 3099kg/h, the temperature is reduced to-35 ℃ after the refrigeration house refrigeration working medium R600 enters the refrigeration house heat exchanger 18 and exchanges heat with 60% glycol, then the refrigeration house refrigeration working medium R600 is pressurized to 1000kPa through the refrigeration house refrigeration working medium pump 19, then the refrigeration house refrigeration working medium R20 enters the refrigeration house refrigeration working medium evaporator 20 to release cold energy, and finally the cold energy flows back to the refrigeration house heat.

the third valve 34 and the eighth valve 39 are opened, and the first valve 32, the second valve 33, the fourth valve 35, the fifth valve 36, the sixth valve 37 and the seventh valve 38 are closed.

A cold storage circulation unit: when the ship is shut down and stopped in navigation, the system does not convey NG for the ship main engine any more, so that the LNG line is completely closed, and the cold storage system and the air conditioning system are continuously cooled through the cold storage tank. The condensed 53 percent of glycol in the cold accumulation tank 28 absorbs heat through melting in a mode of transmitting cold energy to 60 percent of glycol of cold accumulation circulating working medium, the temperature of the cold accumulation circulating working medium 60 percent of glycol is-40 ℃ after heat exchange, the cold accumulation circulating working medium passes through a third valve 34 under the push of a cold accumulation circulating working medium pump 17 and then exchanges heat with a cold storage heat exchanger 18, and the temperature is raised to-30 ℃; then exchanges heat with the air-conditioning heat exchanger 32 through the flow divider 22 and the eighth valve 39, the temperature is raised to 2 ℃, and then flows back to the cold accumulation tank 28 through the confluence device 27 to complete the circulation.

Air-conditioning refrigeration cycle unit: 260kPa and 15 ℃ air-conditioning refrigeration working medium CL2-C1 from the air-conditioning refrigeration working medium evaporator 25 with the flow rate of 2304kg/h enters the air-conditioning heat exchanger 23 to exchange heat with 60% glycol, then the temperature is reduced to 5 ℃, then the air-conditioning refrigeration working medium is pressurized to 1000kPa by the air-conditioning refrigeration working medium pump 24, then the air-conditioning refrigeration working medium enters the air-conditioning refrigeration working medium evaporator 25 to release cold energy, and finally the cold energy flows back to the air-conditioning heat exchanger 23 to complete circulation.

The working method also comprises the step of realizing a short startup cold accumulation process, and the working mode of the system is as follows: opening a fourth valve 35, closing a first valve 32, a second valve 33, a third valve 34, a fifth valve 36, a sixth valve 37, a seventh valve 38 and an eighth valve 39, pressurizing LNG fuel from an LNG storage tank 1 by an LNG booster pump 2, sequentially entering a first-stage LNG heat exchanger 3 and a second-stage LNG heat exchanger for heat exchange 4, absorbing heat and raising temperature of the LNG, entering an LNG diverter 5 in a gaseous state after vaporization, and then entering a cold storage tank 28 for heat exchange with a cold storage medium, wherein the LNG temperature is raised to the intake requirement of a marine main engine and flows into the marine main engine through an LNG flow combiner 30; the cold accumulation medium absorbs the cold energy of the NG and then condenses into a solid state, and the solid state is stored in the cold accumulation tank to be used as a standby cold source.

Claims

1. The utility model provides a dual fuel power ship LNG cold energy cascade comprehensive utilization system which characterized in that includes:

the LNG evaporation side comprises an LNG storage tank (1), an LNG booster pump (2), a cold source input end (301) of a first-stage LNG heat exchanger (3), a cold source output end (302) of the first-stage LNG heat exchanger (3), a cold source input end (401) of a second-stage LNG heat exchanger (4), a cold source output end (402) of the second-stage LNG heat exchanger (4) and an LNG diverter (5) which are sequentially connected through pipelines, wherein NG is divided into three streams after coming out of the diverter (5), and the first stream is connected with a first valve (32), a cold source input end (601) of a third-stage LNG heat exchanger (6) and a cold source output end (602) of the third-stage LNG heat exchanger (6) and then flows into a host through an LNG combiner (30); the second strand is connected with the second valve (33), the cold source input end (1801) of the refrigeration house heat exchanger (18) and the cold source output end (1802) of the refrigeration house heat exchanger (18), and then is divided into two streams through the LNG diverter (21), one stream is connected with the sixth valve (37), the cold source input end (2301) of the air-conditioning heat exchanger (23) and the cold source output end (2302) of the air-conditioning heat exchanger (23), and then is converged into the LNG combiner (26), the other stream is directly connected with the fifth valve (36) and the LNG combiner (26), the NG coming out of the LNG combiner (26) is connected with the cold source input end (2901) of the LNG temperature regulator (29) and the cold source output end (2902) of the LNG temperature regulator (29), and finally flows into a host through the LNG combiner (30; the third branch is connected with a fourth valve (35), a cold source input end (2801) of the cold accumulation tank (28) and a cold source output end (2802) of the cold accumulation tank (28), and then flows into the host through an LNG confluence device (30);

the first-stage Rankine cycle power generation unit comprises a heat source output end (304) of a first-stage LNG heat exchanger (3), a first-stage power generation working medium pump (7), a cold source input end (403) of a second-stage LNG heat exchanger (4), a cold source output end (404) of the second-stage LNG heat exchanger (4), a cold source input end (603) of a third-stage LNG heat exchanger (6), a cold source output end (604) of the third-stage LNG heat exchanger (6), a cold source input end (801) of a first-stage cooling water heat exchanger (8), a cold source output end (802) of the first-stage cooling water heat exchanger (8), a first-stage turbo expander (9) and a heat source input end (303) of the first-stage LNG heat exchanger (3), wherein the first-stage turbo expander (9) drives a first-stage generator set to work;

the second-stage Rankine cycle power generation unit comprises a heat source output end (406) of a second-stage LNG heat exchanger (4), a second-stage power generation working medium pump (10), a cold source input end (605) of a third-stage LNG heat exchanger (6), a cold source output end (606) of the third-stage LNG heat exchanger (6), a cold source input end (1101) of a second-stage cooling water heat exchanger (11), a cold source output end (1102) of the second-stage cooling water heat exchanger (11), a second-stage turbo expander (12) and a heat source input end (405) of the second-stage LNG heat exchanger (4) which are sequentially connected through pipelines to form a closed loop, and the second-stage turbo expander (12) drives a second-stage generator set to work;

the third-stage transcritical Rankine cycle power generation unit comprises a heat source output end (608) of a third-stage LNG heat exchanger (6), a third-stage power generation working medium pump (13), a cold source input end (1401) of a heat regenerator (14), a cold source output end (1402) of the heat regenerator (14), a cold source input end (1501) of a high-temperature flue gas heat exchanger (15), a cold source output end (1502) of the high-temperature flue gas heat exchanger (15), a third-stage turbine expander (16), a heat source input end (1403) of the heat regenerator (14), a heat source output end (1404) of the heat regenerator (14) and a heat source input end (607) of the third-stage LNG heat exchanger (6), wherein the third-stage turbine expander (16) drives a third-stage generator set to work;

the refrigeration house and the air conditioner circulating refrigeration unit comprise refrigeration house circulation and air conditioner circulation which are connected in series, wherein the refrigeration house circulation comprises a heat source output end (1806) of a refrigeration house heat exchanger (18), a refrigeration house refrigeration working medium pump (19), a refrigeration house refrigeration working medium evaporator (20) and a heat source input end (1805) of the refrigeration house heat exchanger (18) which are sequentially connected through a pipeline, the air conditioner circulation comprises a heat source output end (2306) of an air conditioner heat exchanger (23), an air conditioner refrigeration working medium pump (24), an air conditioner refrigeration working medium evaporator (25) and a heat source input end (2305) of the air conditioner heat exchanger (23) which are connected through a pipeline, and the refrigeration house refrigeration working medium evaporator (20) and the air conditioner refrigeration working medium evaporator (25) absorb heat through evaporation to cool;

the cold accumulation circulating unit comprises a heat source output end (2803) of a cold accumulation tank (28), a cold accumulation circulating working medium pump (17), a third valve (34), a cold source input end (1803) of a cold storage heat exchanger (18), a cold source output end (1804) of the cold storage heat exchanger (18) and a cold accumulation circulating working medium shunt (22) which are sequentially connected through a pipeline, the cold accumulation circulating working medium coming out of the cold accumulation circulating working medium shunt (22) is divided into two flows, one flow is connected with an eighth valve (39), a cold source input end (2303) of an air conditioner heat exchanger (23) and a cold source output end (2304) of the air conditioner heat exchanger (23), then flows into a cold accumulation circulating working medium confluence device (27), the other branch of the cold accumulation circulating working medium confluence device is directly connected with a seventh valve (28) and the cold accumulation circulating working medium confluence device (27), and the cold accumulation circulating working medium from the cold accumulation circulating working medium confluence device (27) flows back to a heat source input end (2804) of a cold accumulation tank (28) to form a closed loop.

2. The LNG cold energy cascade comprehensive utilization system of the dual-fuel power ship as claimed in claim 1, characterized in that the system further comprises a cooling water side, the cooling water side comprises cooling water flowing out of a ship main engine, and the cooling water is divided into three streams through a cooling water splitter (31), and one stream is connected with a heat source input end (803) of the first-stage cooling water heat exchanger (8) and a heat source output end (804) of the first-stage cooling water heat exchanger (8); one is connected with a heat source input end (1103) of the second-stage cooling water heat exchanger (11) and a heat source output end (1104) of the second-stage cooling water heat exchanger (11); and one strand of the cooling water is connected with a heat source input end (2903) of the LNG temperature regulator (29) and a heat source output end (2904) of the LNG temperature regulator (29), and the cooling water respectively transfers heat to working media of each cold source through the three heat exchangers.

3. The LNG cold energy cascade comprehensive utilization system of the dual-fuel power ship of claim 1, characterized in that the system further comprises a high-temperature flue gas side, the high-temperature flue gas side comprises high-temperature flue gas flowing out from a ship waste heat boiler, the high-temperature flue gas side is connected with a heat source input end (1503) of the high-temperature flue gas heat exchanger (15) and a heat source output end (1504) of the high-temperature flue gas heat exchanger (15), and the high-temperature flue gas transfers heat to a third-stage power generation working medium through the high-temperature flue gas heat exchanger (15).

4. The LNG cold energy cascade comprehensive utilization system of the dual-fuel power ship as claimed in claim 1, wherein a first-stage power generation working medium is arranged in the first-stage Rankine power generation cycle; a second-stage power generation working medium is arranged in the second-stage Rankine power generation cycle; a third-stage power generation working medium is arranged in the third-stage Rankine power generation cycle; a refrigeration working medium of the refrigeration house is arranged in the refrigeration cycle of the refrigeration house; an air-conditioning refrigeration working medium is arranged in the air-conditioning refrigeration cycle; a cold accumulation medium is arranged in the cold accumulation tank; the cold accumulation circulation is provided with a cold accumulation circulation working medium.

5. The LNG cold energy cascade comprehensive utilization system of the dual-fuel power ship as claimed in claim 4, wherein the dew point of the first-stage power generation working medium is lower than the dew point of the second-stage power generation working medium, and the dew point of the second-stage power generation working medium is lower than the dew point of the third-stage power generation working medium.

6. The LNG cold energy cascade comprehensive utilization system of the dual-fuel power ship as claimed in claim 4, wherein the first-stage to third-stage power generation working media, the refrigeration working media of the refrigeration house, the refrigeration working media of the air conditioner, the cold accumulation media and the cold accumulation circulating working media are all refrigerants.

7. The LNG cold energy cascade comprehensive utilization system of the dual-fuel power ship as claimed in claim 4, wherein the first-stage power generation working medium is R1150, the second-stage power generation working medium is R1270, the third-stage power generation working medium is carbon dioxide, the refrigeration working medium of the refrigeration house is R600, the refrigeration working medium of the air conditioner is CL2-C1, the cold storage medium in the cold storage tank is 53% ethylene glycol, and the cold storage circulating working medium is 60% ethylene glycol.

8. A working method of an LNG cold energy cascade comprehensive utilization system of a dual-fuel power ship is characterized by comprising four working modes according to requirements:

the first valve (32), the second valve (33) and the fifth valve (36) are opened, and the third valve (34), the fourth valve (35), the sixth valve (37), the seventh valve (38) and the eighth valve (39) are closed, so that the usable power generation and refrigeration house cold energy utilization system in spring, autumn and winter is realized;

LNG flow path: LNG fuel is pressurized by an LNG booster pump (2) after coming out of an LNG storage tank (1), and then sequentially enters a first-stage LNG heat exchanger (3) and a second-stage LNG heat exchanger (4) for heat exchange, LNG absorbs heat and is heated, the vaporized LNG enters an LNG flow divider (5) in a gaseous state, NG is divided into two flows, one flow passes through a first valve (32), then exchanges heat with a third-stage LNG heat exchanger (6), and then enters a ship host through an LNG flow combiner (30); one strand of the LNG flow-converging device passes through a second valve (33), then exchanges heat with a refrigeration house heat exchanger (18), then passes through an LNG flow divider (21), a fifth valve (36) and an LNG flow-converging device (26), enters an LNG temperature regulator (29) to exchange heat with cylinder jacket cooling water, and is converged into one strand with NG flowing through a third-stage Rankine cycle through the LNG flow-converging device (30) after the temperature reaches the air inlet requirement of a ship main engine and then is connected to the air inlet of a power ship main engine;

a first-stage Rankine power generation unit: the first-stage power generation working medium from the first-stage turboexpander (9) enters a first-stage LNG heat exchanger (3) to exchange heat with LNG and then is condensed, then is pressurized by a first-stage power generation working medium pump (7), enters a second-stage LNG heat exchanger (4) to exchange heat with a second-stage power generation working medium and is heated, enters a third-stage LNG heat exchanger (6) to exchange heat with the third-stage power generation working medium and then is continuously raised in temperature, enters a first-stage cooling water heat exchanger (8) to exchange heat with cylinder jacket cooling water and is evaporated, and then enters the first-stage turboexpander (9) in a gas state to perform expansion and work to complete circulation;

a second-stage Rankine power generation unit: the second-stage power generation working medium from the second-stage turbo expander (12) enters a second-stage LNG heat exchanger (4) to exchange heat with the first-stage power generation working medium and LNG and condense, is pressurized by a second-stage power generation working medium pump (10), then enters a third-stage LNG heat exchanger (6) to exchange heat with the third-stage power generation working medium and raise the temperature, then enters a second-stage cooling water heat exchanger (11) to exchange heat with cylinder jacket cooling water and evaporate, and then enters the second-stage turbo expander (12) in a gaseous state to perform expansion and work so as to complete circulation;

a third-stage Rankine power generation unit: the third-stage power generation working medium from the third-stage turbo expander (16) enters a heat regenerator (14) to exchange heat with the condensed and pressurized third-stage power generation working medium, then the temperature is reduced, then the third-stage power generation working medium enters a third-stage LNG heat exchanger (6) to exchange heat and condense, after being pressurized by a third-stage power generation working medium pump (13), the third-stage power generation working medium enters the heat regenerator (14) in sequence to be preheated, enters a high-smoke heat exchanger (15) to exchange heat with smoke and evaporate, then enters the third-stage turbo expander (16) in a gas state to be expanded and applied to complete circulation, and the temperature of the high-temperature smoke is reduced after exchanging;

freezer refrigeration cycle unit: the refrigeration house refrigeration working medium from the refrigeration house refrigeration working medium evaporator (20) enters the refrigeration house heat exchanger (18) to exchange heat with the NG, then the temperature is reduced, the refrigeration house refrigeration working medium is pressurized by the refrigeration house refrigeration working medium pump (19), enters the refrigeration house refrigeration working medium evaporator (20) to release cold energy, and finally flows back to the refrigeration house heat exchanger (18) to complete circulation;

cooling water side: cooling water flowing out of a marine main engine is divided into three streams through a cooling water splitter (31), and one stream exchanges heat with a first-stage power generation working medium through a first-stage cooling water heat exchanger (8) and is cooled; one strand exchanges heat with a second-stage power generation working medium through a second-stage cooling water heat exchanger (11) and is cooled; one is subjected to heat exchange with the NG through an LNG temperature regulator (29) and is cooled;

high-temperature flue gas side: the high-temperature flue gas flowing out of the ship waste heat boiler exchanges heat with carbon dioxide through a high-temperature flue gas heat exchanger (15) and is cooled;

the first valve (32), the second valve (33) and the sixth valve (37) are opened, and the third valve (34), the fourth valve (35), the fifth valve (36), the seventh valve (38) and the eighth valve (39) are closed, so that the comprehensive utilization system of the cold energy of the power generation, the refrigeration house and the air conditioner, which can be used when the air conditioner needs to be used in summer, is realized;

LNG flow path: LNG fuel is pressurized by an LNG booster pump (2) after coming out of an LNG storage tank (1), and then sequentially enters a first-stage LNG heat exchanger (3) and a second-stage LNG heat exchanger (4) for heat exchange, the LNG absorbs heat and is heated, the LNG enters an LNG flow divider (5) in a gaseous state after being vaporized, the NG is divided into two flows, one flow exchanges heat with a third-stage LNG heat exchanger (6), and then the two flows enter a ship host through an LNG flow combiner (30); one strand exchanges heat with a refrigeration house heat exchanger (18), then exchanges heat with an air conditioner heat exchanger (23) through an LNG (liquefied natural gas) shunt (21) and a sixth valve (37), then enters an LNG temperature regulator (29) to exchange heat with cylinder jacket cooling water after passing through an LNG confluence device (26), and is converged into one strand with NG flowing through a third-stage Rankine cycle through the LNG confluence device (30) after the temperature reaches the air inlet requirement of a ship main engine and is connected with the main engine of a power ship to enter air;

air-conditioning refrigeration cycle unit: the air-conditioning refrigeration working medium from the air-conditioning refrigeration working medium evaporator (25) enters the air-conditioning heat exchanger (23) to exchange heat with the NG, then the temperature is reduced, the air-conditioning refrigeration working medium is pressurized by the air-conditioning refrigeration working medium pump (24), enters the air-conditioning refrigeration working medium evaporator (25) to release cold energy, and finally flows back to the air-conditioning heat exchanger (23) to complete circulation;

the third valve (34) and the seventh valve (38) are opened, and the first valve (32), the second valve (33), the fourth valve (35), the fifth valve (36), the sixth valve (37) and the eighth valve (39) are closed, so that the ship is stopped and the cold storage system is used for maintaining the normal operation of the refrigeration house in spring, autumn and winter in a short time;

a cold storage circulation unit: when the ship is shut down and stopped in navigation, the system does not convey NG for the ship host, so that the LNG line is completely closed, the cold storage system is continuously cooled through the cold storage tank, the condensed cold storage medium in the cold storage tank (28) transfers cold energy to the cold storage circulating working medium in a melting and heat absorption mode, and the cold storage circulating working medium exchanges heat with the cold storage heat exchanger (18) and heats up under the pushing of the cold storage circulating working medium pump (17) through the third valve (34); then sequentially passes through a flow divider (22), a seventh valve (38) and a flow combiner (27), and finally flows back to a cold accumulation tank (28) to complete circulation;

the third valve (34) and the eighth valve (39) are opened, and the first valve (32), the second valve (33), the fourth valve (35), the fifth valve (36), the sixth valve (37) and the seventh valve (38) are closed, so that the ship is stopped and the cold storage system is used for maintaining the normal operation of the refrigeration house and the air conditioner in summer;

a cold storage circulation unit: when the ship is shut down and stopped in navigation, the system does not convey NG for the ship host, so that the LNG line is completely closed, the cold storage system and the air conditioning system are continuously cooled through the cold storage tank, the condensed cold storage medium in the cold storage tank (28) transfers cold energy to the cold storage circulating working medium in a melting and heat absorption mode, and the cold storage circulating working medium exchanges heat with the cold storage heat exchanger (18) and heats up under the pushing of the cold storage circulating working medium pump (17) through the third valve (34); then the heat exchange is carried out with the air-conditioning heat exchanger (23) through the flow divider (22) and the eighth valve (39), and finally the heat exchange flows back to the cold storage tank (28) through the flow combiner (27) to complete the circulation;

air-conditioning refrigeration cycle unit: the air-conditioning refrigeration working medium from the air-conditioning refrigeration working medium evaporator (25) enters the air-conditioning heat exchanger (23) to exchange heat with the NG, then the temperature is reduced, the air-conditioning refrigeration working medium is pressurized by the air-conditioning refrigeration working medium pump (24), enters the air-conditioning refrigeration working medium evaporator (25) to release cold energy, and finally flows back to the air-conditioning heat exchanger (23) to complete circulation.

9. The operating method of claim 8, further comprising implementing a transient startup cold storage process, wherein the system operates by: opening a fourth valve (35), closing a first valve (32), a second valve (33), a third valve (34), a fifth valve (36), a sixth valve (37), a seventh valve (38) and an eighth valve (39), pressurizing LNG fuel after coming out of an LNG storage tank (1) through an LNG booster pump (2), sequentially entering a first-stage LNG heat exchanger (3) and a second-stage LNG heat exchanger for heat exchange (4), absorbing heat and raising temperature of LNG, enabling the LNG to enter an LNG diverter (5) in a gaseous state after being vaporized, and then entering a cold storage tank (28) for heat exchange with a cold storage medium, wherein the LNG temperature is raised to the air inlet requirement of a ship host, and the LNG flows into the ship host through an LNG combiner (30); the cold accumulation medium absorbs the cold energy of the NG and then condenses into a solid state, and the solid state is stored in the cold accumulation tank to be used as a standby cold source.