KR20120023406A - Apparatus and method for regasification of liquefied natural gas - Google Patents

Abstract

PURPOSE: An apparatus and a method for re-gasifying liquefied natural gas are provided to prevent corrosion not to use seawater for re-gasification, and increase energy efficiency by combining an indirect heating method with a heat medium fluid and a direct heating method with steam. CONSTITUTION: An apparatus for re-gasifying liquefied natural gas(100) comprises a boiler(140), a first heat exchanger(110), a second heat exchanger(120), and a third heat exchanger(130). The boiler generates steam using boil-off gas supplied from a liquefied natural gas storage tank(210). The first heat exchanger heat-exchanges liquefied natural gas with a heat medium fluid to re-gasify. The second heat exchanger heat-exchanges the re-gasified natural gas in the first heat exchanger with the steam generating in the boiler. The third heat exchanger allows to decrease clear water temperatures using the heat medium fluid passing through the first heat exchanger. The clear water cools a heat engine such as an engine of the ship etc.

Description

Apparatus and method for regasification of liquefied natural gas}

The present invention relates to an apparatus and a method for regasifying liquefied natural gas.

Natural gas is a main component of methane, fossil containing a small amount of ethane, propane and the like, and has recently been spotlighted as a low pollution energy source in various technical fields.

Efficient transportation methods that can transport the natural gas in large quantities from the production site to the demand site have been continuously examined, and recently, liquefied natural gas (LNG) carriers capable of liquefying natural gas and transporting it in large quantities are mainly studied. Is used.

In recent years, LNG regasification apparatuses installed in liquefied natural gas carriers or floating structures, regasifying liquefied natural gas with natural gas at sea, and supplying natural gas obtained through regasification to the land have been used.

For example, liquefied natural gas regasification vessels include LNG liquefied natural gas regasification vessels, LNG liquefied natural gas floating storage and regasification units, and LNG liquefied natural gas floating, production, storage and off-loading It can be installed in the offshore structure.

As a method of regasifying liquefied natural gas to natural gas in the regasification apparatus, a method of using seawater or a method of using a thermal medium such as glycol water may be used.

Recently, an indirect heating method is used in which the AL medium fluid is heated with steam supplied from a boiler and then heat exchanged between the heat medium fluid and the liquefied natural gas.

However, the above conventional technology has the following problems.

In the case of regasification using seawater, there is a problem that there are limitations according to various environmental regulations regarding seawater discharged from ships.

In addition, there is a problem that corrosion may occur in the internal pipe of the regasification device due to the suspended matter present in the seawater.

In addition, in the case of using the indirect heating method, since the heat amount of steam supplied from the boiler is indirectly transferred to the liquefied natural gas through the heat medium fluid, there is a problem that unnecessary heat loss occurs in the regasification process.

Embodiments of the present invention seek to provide an apparatus and method for regasifying liquefied natural gas that is free from environmental regulations and seawater corrosion problems.

In addition, an apparatus and method for regasifying liquefied natural gas that can reduce energy consumption by using a direct heating method and an indirect heating method are provided.

It is also an object of the present invention to provide a regasification apparatus and method for liquefied natural gas capable of supplying natural gas at a temperature suitable for use at a consumer.

In addition, the present invention provides a regasification apparatus and method for liquefied natural gas that can be reduced in size.

According to an aspect of the invention, the first heat exchanger for regasifying the liquefied natural gas to natural gas by heat-exchanging the heat medium fluid with the liquefied natural gas supplied from the liquefied natural gas storage tank; A second heat exchanger configured to heat the natural gas by heat exchanging the natural gas regasified by the first heat exchanger with steam supplied from a boiler; A third heat exchanger for exchanging heat medium fluid passing through the first heat exchanger with fresh water supplied from the fresh water tank; And a cooling unit for cooling the heating engine of the ship by using the fresh water passing through the third heat exchanger.

In addition, the heat medium fluid may pass through the third heat exchanger may be characterized in that the temperature is high.

The steam supplied from the boiler may be condensed in the second heat exchanger, and the condensed water generated in the second heat exchanger may be moved to the fresh water tank.

In addition, between the third heat exchanger and the cooling unit may be provided with a thermal media fluid detector for detecting whether the thermal media fluid outflow.

In addition, a portion of the fresh water passing through the cooling unit may be characterized in that it is supplied to the boiler.

In addition, the fresh water passing through the cooling unit may be moved to the fresh water tank.

According to another aspect of the invention, the transport line is transported liquefied natural gas or regasified natural gas; A first circulation line through which the heat medium fluid circulates; A second circulation line through which fresh water is circulated; A first heat exchanger provided at an intersection point of the transport line and the first circulation line, the first heat exchanger exchanging liquefied natural gas with a heat medium fluid to regasify it into natural gas; A second heat exchanger disposed in the transport line and heat exchanging steam supplied from the boiler and regasified natural gas; A third heat exchanger provided at an intersection point of the first circulation line and the second circulation line and exchanging heat medium fluid and fresh water passing through the first heat exchanger; And a cooling unit disposed on the second circulation line and including a cooling unit for cooling the heat generating engine of the vessel.

In addition, the second circulation line may be connected to a fresh water tank in which fresh water is stored, and steam supplied from the boiler may be condensed in the second heat exchanger and then moved to the fresh water tank.

In addition, a bypass line bypassing the third heat exchanger may be connected to the second circulation line so that fresh water may selectively pass through the third heat exchanger.

In addition, the fresh water supply line may be connected to the second circulation line so that the fresh water passing through the cooling unit may be supplied to the boiler.

In addition, the fresh water supply line may be connected to the fresh water tank so that the fresh water stored in the fresh water tank is selectively supplied to the boiler.

In addition, the second circulation line connecting the third heat exchanger and the cooling unit may be provided with a thermal media fluid detector for sensing the thermal media fluid.

In the third heat exchanger, heat may be transferred from the fresh water to the heat medium fluid.

In addition, the boiler may be characterized in that for generating steam using the evaporated gas generated in the storage tank.

According to another aspect of the invention, the first heat exchanger for regasifying the natural gas liquefied natural gas; A second heat exchanger for heating the regasified natural gas; And a cooling unit cooling the heat generating engine of the ship using fresh water, wherein the fresh water discharged from the cooling unit is heated by the condensed water supplied from the second heat exchanger, and is a thermal medium fluid supplied from the first heat exchanger. After cooling by liquefied natural gas can be provided to the regasification apparatus, characterized in that flowing back into the cooling unit.

In the second heat exchanger, steam supplied from the boiler may be condensed by losing heat to the regasified natural gas.

In addition, the fresh water discharged from the cooling unit may be heated by mixing with the condensed water in the fresh water tank.

According to another aspect of the invention, the step of regasifying the natural gas supplied from the storage tank to the natural gas by the first heat exchange with the heat medium fluid; And heating the regasified natural gas by a second heat exchange with steam supplied from a boiler, wherein the first heat-exchanged heat medium fluid is third heat exchanged with fresh water to cool the fresh water, and The fresh water may be provided with a regasification method of liquefied natural gas, characterized in that used for cooling the heating engine of the ship.

In addition, the fresh water cooling the heat generating engine may be heated by the condensed water condensed in the second heat exchange process.

Embodiments of the present invention can be free from environmental restrictions on seawater and corrosion problems by seawater by not using seawater for regasification.

In addition, energy efficiency may be increased by using a direct heating method using steam and an indirect heating method using a heat medium fluid.

In addition, since the liquefied natural gas is regasified and heated to be supplied to the consumer, there is an advantage that natural gas having a temperature suitable for use at the consumer can be supplied.

In addition, by using the latent heat of the heat medium fluid as the heat source for regasification, the flow rate of the heat medium fluid can be reduced, so that the size of the regasification device can be reduced.

1 is a view showing the configuration of a regasification apparatus of liquefied natural gas according to an embodiment of the present invention.
2 is a flow chart showing a regasification method of liquefied natural gas according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In addition, in describing the present invention, when it is determined that the detailed description of the related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

1 is a view showing the configuration of a regasification apparatus of liquefied natural gas according to an embodiment of the present invention.

Referring to FIG. 1, the regasification apparatus 100 of liquefied natural gas according to an exemplary embodiment of the present invention uses LNG supplied from a storage tank 210 to store liquefied natural gas (“LNG”). After regasification with natural gas (hereinafter referred to as "NG"), it is heated and supplied to the customer 300.

The regasification apparatus 100 is a marine vessel such as LNG liquefied natural gas regasification vessel (RV RV), LNG liquefied natural gas floating storage and regasification unit (FSRU), LNG liquefied natural gas floating, production, storage and off-loading (FPSO), etc. Can be installed on the structure.

In detail, the regasification apparatus 100 recovers the boiler 140, which generates steam using a boil of gas (BOG) supplied from the storage tank 210, and heat exchanges LNG with a heat medium fluid. The first heat exchanger 110, the second heat exchanger 120 to heat the NG generated in the first heat exchanger 110 with the steam generated in the boiler 140, the first heat exchanger The third heat exchanger 130 may be included to lower the temperature of the fresh water that cools the heat generating engine such as an engine of the ship by using the heat medium fluid that has passed through the gas 110.

Here, the storage tank 210, the first heat exchanger 110, the second heat exchanger 120 and the demand destination 300 may be connected by the LNG / NG transport line 101, the transport line LNG 101 or NG from which LNG is regasified may flow.

The LNG stored in the storage tank 210 may be supplied to the first heat exchanger 110 by the LNG high pressure pump 171 installed on the transport line 101. At this time, the LNG supplied to the first heat exchanger 110 may have a temperature of about -162 ℃. LNG may be regasified to about −50 ° C. to 0 ° C. in the first heat exchanger 110, and the regasified NG may be heated to about 0 ° C. to 20 ° C. in the second heat exchanger 120. .

The first heat exchanger 110 heat exchanges heat medium fluid with LNG. The thermal media fluid is moved along the first circulation line 103 circulating the first heat exchanger 110 and the third heat exchanger 130. The heat medium fluid is used for regasification of the LNG in the first heat exchanger 110, the temperature is lowered, and is heated in the third heat exchanger 130, thereby heating the first circulation line 103 within a predetermined temperature range. Circulate The first heat exchanger 110 may be provided at the intersection of the transport line 101 and the first circulation line 103.

In addition, a heat mediated fluid reservoir (not shown) may be provided on the first circulation line 103, and a pump 172 for circulating the heat mediated fluid may be provided.

The heat medium fluid circulating in the first circulation line 103 may be an evaporative fluid that maintains a gas state at room temperature such as propane and ammonia.

The NG regasified in the first heat exchanger 110 is heated in the second heat exchanger 120. The second heat exchanger 120 may be provided at the intersection of the steam supply line 102 extending from the transport line 101 and the boiler 140. The steam supply line 102 may extend from the boiler 140 to the fresh water tank 150 to be described later. Steam supplied from the boiler 140 passes through the second heat exchanger 120 and is condensed by taking heat into the regasified NG, and the condensed water in which steam is condensed may be introduced into the fresh water tank 150. In other words, steam passing through the second heat exchanger 120 may be condensed and phase-changed into condensed water, and latent heat of steam may be used to heat NG.

The boiler 140 is in communication with the storage tank 210 by the BOG supply line 211 extending from the upper portion of the storage tank 210, by burning the BOG supplied through the BOG supply line 211 Steam can be generated by heating water. Steam generated in the boiler 140 may have a temperature of about 200 ℃ to 250 ℃, it may be supplied to the second heat exchanger 120 along the steam supply line (102).

On the other hand, equipment such as engines, electronic devices installed in the ship is a heat generating engine that generates a lot of heat, it can be cooled by the fresh water circulating the fresh water tank 150. In detail, the fresh water tank 150 and the cooling unit 220 for cooling the heat generating engine may be connected by a second circulation line 104 in which fresh water flows, and the fresh water is formed along the second circulation line 104. Passing through the cooling unit 220 may cool the heat generating engine.

The third heat exchanger 130 is disposed on the second circulation line 104 and before the fresh water flowing through the second circulation line 104 flows into the cooling unit 220. 130 may be provided to be cooled. In addition, the third heat exchanger 130 is also used to regasification of the LNG serves to heat the heat medium fluid having a low temperature through heat exchange with fresh water. That is, the fresh water circulating in the second circulation line 104 may simultaneously perform a role of heating the heat medium fluid circulating in the first circulation line 103 and cooling the heat generating engine.

The third heat exchanger 130 may be disposed at the intersection of the first circulation line 103 and the second circulation line 104, the position of the third heat exchanger 130 is the fresh water tank ( 150 may be between the cooling unit 220.

A pump 173 for circulating fresh water may be provided between the fresh water tank 150 and the third heat exchanger 130 in the second circulation line 104.

In addition, a bypass flow path 104 ′ is further provided in the second circulation line 104 such that water supplied from the fresh water tank 150 may selectively bypass the third heat exchanger 130. Can be connected.

Meanwhile, in the second circulation line 104, the fresh water supply line 105 extending to the boiler 140 may be branched. The fresh water supply line 105 may be branched between the cooling unit 220 and the fresh water tank 150 so that the fresh water passing through the cooling unit 220 may be supplied to the boiler 140. At the intersection of the second circulation line 104 and the fresh water supply line 105, a valve for controlling a part or all of the fresh water flowing along the second circulation line 104 is supplied to the boiler 140. Can be.

In addition, the fresh water supply line 105 may be directly connected to the fresh water tank 150 (105 '). In this case, the fresh water supply line 105 may be provided with a valve for controlling the fresh water stored in the fresh water tank 150 to be selectively supplied to the boiler 140.

In addition, between the third heat exchanger 130 and the cooling unit 220 of the second circulation line 104, the heat-mediated fluid from the third heat exchanger 130, the second circulation line 104 A thermally mediated fluid detector 160 may be further provided to detect whether or not it has leaked out.

In detail, since the heat medium fluid may be in an explosive gas state in the third heat exchanger 130, when the heat medium fluid is mixed with fresh water due to breakage such as cracks in the third heat exchanger 130, the cooling may be performed. An explosion may occur while passing through the heating engine or the periphery of the heating engine in the unit 220. In order to prevent such a problem, the heat-mediated fluid detector 160 may be installed at the front end of the cooling unit 220, and when the heat-mediated fluid is mixed in fresh water, appropriate measures may be taken.

Hereinafter will be described the operation and effects of the liquefied natural gas regasification apparatus 100 according to an embodiment of the present invention having the configuration as described above.

LNG is supplied to the first heat exchanger 110 along the transport line 101 by the high pressure pump 171.

In the first heat exchanger 110, heat exchange between the heat medium fluid circulating in the first circulation line 103 and LNG occurs, and in this process, LNG absorbs heat from the heat medium fluid and is regasified to NG. For example, heat-borne fluids lose heat with LNG, resulting in lower temperatures. For example, in the first heat exchanger 110, LNG may absorb heat at a temperature of about −162 ° C. and regasify it to NG having a temperature of about −50 ° C. to 0 ° C., and the heat medium fluid may be about − Heat may be taken away at a temperature of 5 ° C. to 10 ° C. and cooled to a temperature of about −20 ° C. to 0 ° C. The heat medium fluid passing through the first heat exchanger 110 may be supplied to the third heat exchanger 130 along the first circulation line 103 to be used for cooling fresh water.

The NG regasified by the first heat exchanger 110 may be heated by steam supplied from the boiler 140 while passing through the second heat exchanger 120, and may be supplied to the demand destination 300. At this time, the steam supplied from the boiler 140 may be condensed by taking heat into the NG. For example, the regasified NG may be heated to about 0 ℃ to 20 ℃ in the second heat exchanger 120, the steam supplied from the boiler 140 is at a temperature of about 200 ℃ to 250 ℃ The heat may be deprived of NG and lowered to about 100 ° C to 150 ° C. The condensed water generated in the second heat exchanger 120 is supplied to the fresh water tank 150 along the steam supply line 102. The condensed water generated in the second heat exchanger 120 may be mixed with fresh water stored in the fresh water tank 150 to lower the temperature to about 20 ° C. to 50 ° C.

On the other hand, the heat medium fluid regasified LNG in the first heat exchanger 120 is supplied to the third heat exchanger 130 along the first circulation line (103). The third heat exchanger 130 heats and cools the fresh water supplied along the second circulation line 104 with a heat medium fluid. Fresh water flows from the fresh water tank 150 to the third heat exchanger 130 along the second circulation line 104, and deprives heat of the third heat exchanger 130 as a heat-mediated fluid. To 10 ° C.

In addition, the heat-mediated fluid may be used for regasification of LNG in the first heat exchanger 110 by being heated while passing through the third heat exchanger 130.

The fresh water cooled while passing through the third heat exchanger 130 is used as cooling water for cooling the heat generating engine in the cooling unit 220 and returns to the fresh water tank 150 along the second circulation line 104. can do. In addition, some of the fresh water cooling the heat generating engine may be supplied to the boiler 140 along the fresh water supply line 105 to be used to generate steam to be used in the second heat exchanger 120.

When the first heat exchanger 110 for regasification of LNG is not operated, the fresh water does not pass through the third heat exchanger 130 along the bypass line 104 ′ and immediately passes through the cooling unit ( 220 may be used to cool the heating engine.

In addition, the heat medium fluid absorbs heat from the fresh water in the third heat exchanger 130 to increase the temperature to about -5 ℃ to 10 ℃, the first heat exchanger along the first circulation line 103 110 may be supplied.

At this time, the heat-mediated fluid is moved to the first circulation line 103 at a higher pressure than atmospheric pressure by the pump 172, so that the boiling point is high, condensed through the first heat exchanger 110 The liquid may be in a liquid state and may evaporate while passing through the third heat exchanger 130 to be in a gaseous state.

2 is a flowchart illustrating a regasification method of liquefied natural gas according to an embodiment of the present invention.

Referring to FIG. 2, LNG supplied from the storage tank 210 is regasified by heat exchange with a heat medium fluid circulating in the first circulation line 103 in the first heat exchanger 110. Heat exchange in the first heat exchanger 110 may be referred to as first heat exchange (S110).

In the first heat exchange step S110, LNG is regasified to NG, and the regasified NG is supplied to the second heat exchanger 120. In the second heat exchanger 120, heat exchange of regasified NG and steam supplied from the boiler 140 occurs, and the heat exchange in the second heat exchanger 120 is referred to as a second heat exchange. It may be (S120).

Steam is condensed by the second heat exchange (S120) is stored in the fresh water tank 150, the heat-mediated fluid and the fresh water stored in the fresh water tank 150 is the third heat exchange (S110) Heat exchange in the heat exchanger (130). Heat exchange in the third heat exchanger 130 may be referred to as third heat exchange. The fresh water is lowered by the third heat exchange, and the fresh water having the lowered temperature may be returned to the fresh water tank 150 or may be supplied to the boiler 140 after being used to cool the heat generating engine (S130). .

According to the regasification apparatus 100 and the regasification method of the liquefied natural gas according to the embodiment of the present invention as described above, by not using the seawater for the regasification of LNG from the environmental restrictions on seawater and corrosion problems by seawater Can be free.

In addition, the bar is heated after regasifying LNG by using an indirect heating method using a heat medium fluid in the first heat exchanger 110 and a direct heating method using steam in the second heat exchanger 120. It is possible to directly provide the NG of the temperature required by the demand source (300).

In addition, since the cold heat contained in the fluid heat exchanged in the first heat exchanger 110 can be used to cool the fresh water used for cooling the heat generating engine, the regasification apparatus 100 of the liquefied natural gas is installed. It can increase the energy efficiency of the ship.

As described above as a specific embodiment of the regasification apparatus and method of liquefied natural gas according to an embodiment of the present invention, this is only an example, the present invention is not limited to this, the broadest in accordance with the basic idea disclosed herein It should be interpreted as having a range. Those skilled in the art can easily change the material, size, etc. of each component according to the application field, and can be combined / substituted the disclosed embodiments to implement a pattern of a timeless shape, but this also does not depart from the scope of the present invention will be. It will be apparent to those skilled in the art that various changes and modifications may be readily made without departing from the spirit and scope of the invention as defined by the appended claims.

100: regasification apparatus of liquefied natural gas 101: transport line
102 steam supply line 103 first circulation line
104: second circulation line 105: fresh water supply line
110: first heat exchanger 120: second heat exchanger
130: third heat exchanger 140: boiler
150: fresh water tank 160: thermal fluid detector
210: LNG storage tank 220: cooling unit
230: demand source

Claims (19)

A first heat exchanger configured to heat-exchange the liquefied natural gas with natural gas by heat-exchanging the liquefied natural gas and the heat-mediated fluid supplied from the liquefied natural gas storage tank;
A second heat exchanger configured to heat the natural gas by heat exchanging the natural gas regasified by the first heat exchanger with steam supplied from a boiler;
A third heat exchanger for exchanging heat medium fluid passing through the first heat exchanger with fresh water supplied from the fresh water tank; And
Apparatus for regasification of liquefied natural gas comprising a cooling unit for cooling the heat generating engine of the vessel using the fresh water passing through the third heat exchanger. The method of claim 1,
The thermal medium fluid passes through the third heat exchanger, the temperature of the liquefied natural gas, characterized in that the high temperature. The method of claim 1,
Steam supplied from the boiler is condensed in the second heat exchanger, the condensed water generated in the second heat exchanger is re-gasification apparatus of the liquefied natural gas, characterized in that for moving to the fresh water tank. The method of claim 1,
And a heat medium fluid detector for detecting whether a heat medium fluid is leaked between the third heat exchanger and the cooling unit. The method of claim 1,
Part of the fresh water passing through the cooling unit is supplied to the boiler regasification apparatus. The method of claim 1,
The fresh water passing through the cooling unit is regasified apparatus for liquefied natural gas, characterized in that moved to the fresh water tank. A transport line through which liquefied natural gas or regasified natural gas is transported;
A first circulation line through which the heat medium fluid circulates;
A second circulation line through which fresh water is circulated;
A first heat exchanger provided at an intersection point of the transport line and the first circulation line, the first heat exchanger exchanging liquefied natural gas with a heat medium fluid to regasify it into natural gas;
A second heat exchanger disposed in the transport line and heat exchanging steam supplied from the boiler and regasified natural gas;
A third heat exchanger provided at an intersection point of the first circulation line and the second circulation line and exchanging heat medium fluid and fresh water passing through the first heat exchanger; And
The regasification apparatus of the liquefied natural gas is disposed on the second circulation line and includes a cooling unit for cooling the heat generating engine of the vessel. The method of claim 7, wherein
The second circulation line is connected to a fresh water tank in which fresh water is stored,
Steam supplied from the boiler is condensed in the second heat exchanger and the re-gasification apparatus of the liquefied natural gas, characterized in that moved to the fresh water tank. The method of claim 7, wherein
And a bypass line bypassing the third heat exchanger is connected to the second circulation line so that fresh water can selectively pass through the third heat exchanger. The method according to any one of claims 7 to 9,
The second circulation line is a re-gasification apparatus of liquefied natural gas, characterized in that the fresh water supply line is connected so that the fresh water passing through the cooling unit can be supplied to the boiler. The method of claim 10,
The fresh water supply line is connected to the fresh water tank so that the fresh water stored in the fresh water tank is selectively supplied to the boiler. The method of claim 7, wherein
The second gas circulation line connecting the third heat exchanger and the cooling unit is provided with a thermal media fluid detector for detecting a thermal media fluid. The method of claim 7, wherein
In the third heat exchanger, the regasification apparatus of liquefied natural gas, characterized in that the heat is transferred from the fresh water to the heat medium fluid. The method of claim 7, wherein
The boiler is a regasification apparatus of liquefied natural gas, characterized in that for generating steam using the evaporated gas generated in the storage tank. A first heat exchanger for regasifying liquefied natural gas into natural gas;
A second heat exchanger for heating the regasified natural gas; And
It includes a cooling unit for cooling the heating engine of the ship using fresh water,
The liquefied natural water, which is discharged from the cooling unit, is heated by the condensed water supplied from the second heat exchanger, cooled by a heat medium fluid supplied from the first heat exchanger, and then flows back into the cooling unit. Device for regasification of gas. The method of claim 15,
In the second heat exchanger, the steam supplied from the boiler is condensed by losing heat to the regasified natural gas condensed natural gas. The method of claim 15,
The fresh water discharged from the cooling unit is heated by mixing with the condensed water in the fresh water tank regasification apparatus of liquefied natural gas. Regassing the liquefied natural gas supplied from the storage tank into natural gas by first heat exchanging the heat medium fluid; And
Heating the regasified natural gas by means of a second heat exchange with steam supplied from a boiler,
The first heat-exchanged heat medium fluid is a third heat exchange with fresh water to cool the fresh water, the cooled fresh water is used for cooling the heat generating engine of the vessel regasification method of liquefied natural gas. The method of claim 18,
The fresh water cooling the heat generating engine is heated by the condensed water condensed in the second heat exchange process.

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