JPWO2018225683A1 - Liquefied fuel gas vaporization system and liquid heat medium temperature control method therefor - Google Patents

Abstract

A liquefied fuel gas vaporization system (X1) for vaporizing a fuel gas as a fuel gas from liquefied fuel gas and supplying it to the combustion device (5) 2) circulating the liquid heat medium between the heat recovery unit (4) for recovering the exhaust heat of the combustion device (5) by the liquid heat medium, the heat recovery unit (4) and the vaporizer (2) And a heat medium circulation line (62, 63), and the heat medium circulation line (62, 63) is discharged from the liquid heat medium that has passed through the heat recovery section (4) and the vaporizer And a mixing unit (71, 72) for mixing the liquid heat medium which has not passed through the heat recovery unit (4).

Description

  The present invention relates to a liquefied fuel gas vaporization system for heating and vaporizing a liquefied fuel gas such as liquefied natural gas with a liquid heat medium such as water, and supplying the vaporized gas as a fuel gas to a combustion apparatus.

  Gas engines are diesel engines and are widely used in generators, automobile engines, marine engines and the like. Gas engines are narrower in stable combustion area between knocking area and misfire area than liquid fuel diesel engines, and are more sensitive to conditions such as excess air ratio, charge air temperature, fuel gas composition, and fuel gas temperature. There is a problem that the combustion state is affected. For this reason, in general, a gas engine uses a governor (speed governor) to prevent a large change in engine rotation speed due to a minute change in engine load.

  In a facility that supplies natural gas fuel to a combustion apparatus such as a gas engine, LNG (liquefied natural gas) is stored in a fuel storage tank at a low temperature of -160 ° C or less, heated by a vaporizer or the like to be vaporized and gasified. As a heat source of the vaporizer, for example, water (liquid heat medium) is used.

  In Patent Document 1, in a marine gas engine (dual fuel engine) as a combustion apparatus, engine cooling water (engine cooling water) is directly supplied to the heating gas of a carburetor in order to supply fuel gas efficiently and safely. It is used as Since there is no such thing as a fuel injection pump in a gas engine, if the gas fuel temperature changes, the amount of gas fuel supplied at standard conditions (0 ° C, atmospheric pressure) changes, the calories supplied change, and the governor adjustment function Will be lost. Therefore, for example, when the fuel gas temperature changes rapidly, there is a problem that the governor can not control. On the other hand, when the natural gas supply system according to the prior art is used as it is, in the case of a marine diesel engine such as a marine diesel engine where load fluctuation largely changes as a gas engine, the amount of fuel gas according to the output of the engine It could not be supplied to the engine at (e.g. ± 5 ° C).

  Patent Document 1: Japanese Patent Application Laid-Open No. 2015-147508

  The present invention has been conceived under such circumstances, and using only the exhaust heat of the combustion apparatus without using means for forced heating and cooling, it is discharged from the vaporizer and burned. It is a main object to provide a liquefied natural gas vaporization system suitable for supplying a gaseous fuel (natural gas) supplied to an apparatus in a predetermined temperature range.

  The liquefied natural gas vaporization system provided by the first aspect of the present invention is for vaporizing liquefied fuel gas and supplying it to a combustion apparatus, wherein the liquefied fuel gas is vaporized by heating and vaporizing it with a liquid heat medium. A heat recovery unit for recovering the exhaust heat of the combustion apparatus by the liquid heat medium, and a heat medium circulation line for circulating the liquid heat medium between the heat recovery unit and the vaporizer. The heat medium circulation line is provided with a mixing unit for mixing the liquid heat medium discharged from the vaporizer and not passing through the heat recovery unit with the liquid heat medium passed through the heat recovery unit. It is done.

  Preferably, the heat medium circulation line includes a low temperature side line for sending the liquid heat medium having a relatively low temperature discharged from the vaporizer to the heat recovery unit, and the heat recovery unit passed through the heat recovery unit. A high temperature side line for sending the liquid heat medium which is high temperature to the vaporizer, the mixing unit has one end connected to the low temperature side line and the other end connected to the high temperature side line 1 Includes a bypass line.

  Preferably, the gas temperature detection unit that detects the temperature of the fuel gas discharged from the vaporizer, and the temperature of the fuel gas detected by the gas temperature detection unit fall within a predetermined range from the target temperature. And a first temperature control unit configured to control a flow rate of the liquid heat medium supplied to the high temperature side line through the first bypass line.

  Preferably, one end of the mixing unit is connected closer to the heat recovery unit than the connection point of the first bypass line in the low temperature side line, and the other end is connected to the first bypass line in the high temperature side line. A second bypass line connected closer to the heat recovery portion than a portion, and provided between the first bypass line and the second bypass line in the high-temperature side line, the temperature of the liquid heat medium Through the second bypass line so that the temperature of the heat medium temperature detecting unit for detecting the temperature of the liquid heat medium and the temperature of the liquid heat medium detected by the heat medium temperature detecting unit are maintained at a substantially constant temperature within a predetermined range. And a second temperature control unit for controlling the flow rate of the liquid heat medium mixed in the high temperature side line.

  Preferably, the combustion device is a dual fuel engine for ships.

  Preferably, a temperature maintenance chamber provided between the first bypass line and the second bypass line in the high temperature side line is further included, and the heat medium temperature detection unit is provided in the temperature maintenance chamber. ing.

  Preferably, the heat recovery unit includes a heat exchanger provided between the low temperature side line and the high temperature side line, and in the heat exchanger, the cooling water from the combustion device and the low temperature side line are The heat exchange is performed with the flowing heat medium.

  Typically, the fuel gas is natural gas and the heat medium is water.

  According to a second aspect of the present invention, a liquid heat medium temperature control method is provided for use in a liquefied fuel gas vaporization system for vaporizing liquefied fuel gas and supplying it to a combustion apparatus. According to the method, the liquid heat medium is circulated between the vaporizer which heats and vaporizes the liquefied fuel gas with the liquid heat medium, and the heat recovery unit which recovers the exhaust heat of the combustion apparatus, and The liquid heat medium that has been discharged and has not passed through the heat recovery unit is mixed with the liquid heat medium that has passed through the heat recovery unit so that the temperature of the liquid heat medium after mixing falls within a predetermined range. Control.

  Typically, the fuel gas is natural gas and the heat medium is water.

  The liquefied fuel gas vaporization system relatively passes the low temperature side line for sending the liquid heat medium, which is relatively low temperature, discharged from the vaporizer to the heat recovery unit, and the heat recovery unit. A heat medium circulation line including a high temperature side line for sending the liquid heat medium having a high temperature to the vaporizer, and a first bypass whose one end is connected to the low temperature side line and whose other end is connected to the high temperature side line A line, a gas temperature detection unit for detecting a temperature of fuel gas discharged from the vaporizer, and a flow rate of the liquid heat medium supplied to the high temperature side line through the first bypass line; 1 temperature control unit, one end is connected closer to the heat recovery unit than the connection portion of the first bypass line in the low-temperature side line, and the other end is connection of the first bypass line in the high-temperature side line A second bypass line connected closer to the heat recovery section than the first heat recovery section, and the high temperature side line between the first bypass line and the second bypass line, and A heat medium temperature detection unit to be detected; and a second temperature control unit to adjust the flow rate of the liquid heat medium that is mixed with the high temperature side line by passing through the second bypass line; The temperature control unit is supplied to the high temperature side line through the first bypass line such that the temperature of the fuel gas detected by the gas temperature detection unit falls within a predetermined range from the target temperature. The flow rate of the liquid heat medium is adjusted, and the second temperature adjustment unit is configured to maintain the temperature of the liquid heat medium detected by the heat medium temperature detection unit at a substantially constant temperature within a predetermined range. 2 passing through the bypass line Adjusting the flow rate of the liquid heat medium to be mixed to the high temperature side line.

  The liquefied fuel gas vaporization system further includes a temperature maintenance chamber provided between the first bypass line and the second bypass line in the high temperature side line, and the heat medium temperature detection unit detects the temperature. Provided in the maintenance chamber, mixed in the high temperature side line through the second bypass line so that the temperature of the liquid heat medium in the temperature maintenance chamber is maintained at a substantially constant temperature within a predetermined range Control the flow rate of the liquid heat medium.

  The first temperature control unit is configured to supply the liquid heat medium supplied to the high temperature side line through the first bypass line so as to be within 15 to 50 ° C., which is ± 5 ° C. from the target temperature of the fuel gas. The second temperature control unit controls the flow rate of the liquid heat medium so that the temperature of the liquid heat medium detected by the heat medium temperature detection unit is maintained at a substantially constant temperature within the range of 25.degree. C. to 60.degree. The flow rate of the liquid heat medium, which passes through the second bypass line and is mixed with the high temperature side line, is adjusted.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

It is a schematic block diagram which shows one Embodiment of the liquefied natural gas vaporization system which concerns on this invention. It is a graph showing the characteristic of gas fuel consumption change to gas engine operation time. It is a graph showing the characteristic of the natural gas temperature change emitted from the carburetor to gas fuel consumption. It is the schematic which shows the state which changed the position of the temperature control part.

  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.

  FIG. 1 shows an embodiment of a liquefied natural gas vaporization system according to the present invention. The liquefied natural gas vaporization system X1 of this embodiment includes a fuel storage tank 1, a vaporizer 2, a buffer tank 3, a heat recovery unit 4 (heat exchanger), and lines connected thereto. . The liquefied natural gas vaporization system X1 supplies a fuel gas to the combustion device 5. The combustion device 5 may be, for example, a ship engine, and is mounted on a bottom portion of the ship. Also, the fuel gas may be, for example, natural gas. In the following, for the sake of simplicity, the description will be made assuming that the combustion device 5 is a ship engine and the fuel gas is a natural gas.

  The fuel storage tank 1 is for storing liquefied natural gas (LNG) to be a fuel. The fuel storage tank 1 has a double surrounding wall, and a heat insulating material is filled between the two surrounding walls and the pressure is reduced to a vacuum to block the heat of entry from the outside air. . In the fuel storage tank 1, LNG is stored at a temperature of -160 ° C or less. Although the details will be described later, the fuel storage tank 1 receives the natural gas generated by vaporization of the LNG in the vaporizer 2 through the gas line 67 in a state of being pressurized to about 0.7 MPaG.

  A fuel supply line 61 is connected to the lower portion of the fuel storage tank 1. The fuel supply line 61 is a flow path for transferring the LNG delivered from the fuel storage tank 1 to the carburetor 2. The fuel supply line 61 is provided with a shutoff valve 611.

  A gas extraction line 612 is connected to the upper portion of the fuel storage tank 1. The gas extraction line 612 is for extracting the gas in the space in the fuel storage tank 1 and flowing it to the fuel supply line 61 when the fuel storage tank 1 is refilled with LNG. The gas extraction line 612 is provided with a shutoff valve 613.

  The vaporizer 2 is for evaporating and vaporizing LNG using a liquid heat medium (hereinafter, simply referred to as “heat medium”) as a heating source. The vaporizer 2 includes a heat medium container 21 and heat transfer tubes 22 and 23 disposed inside the heat medium container 21.

  The heat medium container 21 is a sealed container for containing a heat medium for heating and vaporizing the LNG in the heat transfer tube 22. The heat medium can be replenished. Examples of the heat medium include water.

  In the present embodiment, the heat medium container 21 has a structure in which a substantially bell-shaped container body 212 is mounted on a disc-shaped bottom plate 211, and the container body 212 and the bottom plate 211 sandwich bolts for sealing and bolts. Integrated and fixed. According to such a configuration, when carrying out a periodic inspection required by high pressure gas or the laws and regulations of the ship, if the heat medium is extracted and the bolt is removed, the bell-shaped container body 212 can It is possible to directly inspect the heat transfer pipes 22 and 23 simply by pulling up the fuel supply line 61) and the heat medium pipe (heat medium circulation lines 62, 63, etc. described later) (the heat medium circulation lines 62, 63 and the like).

  The heat medium circulation lines 62 and 63 are connected to the heat medium container 21. The heat medium circulation lines 62 and 63 circulate the heat medium between the vaporizer 2 and the heat recovery unit 4. The heat medium circulation line 62 is connected to the bottom plate 211 of the heat medium container 21 and is a flow path for sending the heat medium having passed through the heat recovery unit 4 to the heat medium container 21 (vaporizer 2). The heat medium circulation line 63 is connected to the bottom plate 211 of the heat medium container 21 and is connected to the overflow pipe 24 penetrating the bottom plate 211 in a sealed state. The heat medium which has been supplied via the heat medium circulation line 62 and has passed through the inside of the heat medium container 21 is discharged to the heat medium circulation line 63 via the overflow pipe 24. Although the details will be described later, the heat medium discharged from the heat medium container 21 is reheated in the heat recovery unit 4 and supplied again to the heat medium container 21 (vaporizer 2) to be circulated and used. The heat medium circulation line 62 is provided with a circulation pump 621.

  The heat medium passing through the heat recovery unit 4 and flowing through the heat medium circulation line 62 has a relatively high temperature. The heat medium passing through the heat medium container 21 (vaporizer 2) and flowing through the heat medium circulation line 63 has a relatively low temperature. Therefore, the heat medium circulation line 62 can also be called a high temperature side line, and the heat medium circulation line 63 can also be called a low temperature side line.

  In the present embodiment, two bypass lines 71 and 72 are connected to the heat medium circulation lines 62 and 63, respectively. One end of each of the bypass lines 71 and 72 is connected to the heat medium circulation line 63 (low temperature side line), and the other end is connected to the heat medium circulation line 62 (high temperature side line). Each of the bypass lines 71 and 72 is a flow path for mixing the heat medium that has passed through the heat recovery unit 4 with the heat medium that has been discharged from the vaporizer 2 and has not passed through the heat recovery unit 4. Here, the temperature of the heat medium flowing through the bypass lines 71 and 72 is lower than the temperature of the heat medium flowing through the heat medium circulation line 62. The connection point of the bypass line 72 to the heat medium circulation line 63 is closer to the heat recovery unit 4 than the connection point of the bypass line 71 to the heat medium circulation line 63. Further, the connection point of the bypass line 72 to the heat medium circulation line 62 is closer to the heat recovery unit 4 than the connection point of the bypass line 71 to the heat medium circulation line 62.

  In the present embodiment, a temperature control unit 73 is provided at the connection point of the bypass line 71 to the heat medium circulation line 62. The temperature control unit 73 adjusts the flow rate of the heat medium to be mixed with the heat medium circulation line 62 through the bypass line 71 and includes, for example, a three-way valve. The temperature control unit 73 passes the bypass line 71 based on the temperature of the natural gas detected by the gas temperature detection unit 641 described later, and the flow rate of the heat medium mixed in the heat medium circulation line 62 (high temperature side line) Adjust the

  Further, in the present embodiment, a temperature control unit 74 is provided at the connection point of the bypass line 72 to the heat medium circulation line 62. The temperature control unit 74 adjusts the flow rate of the heat medium that is mixed with the heat medium circulation line 62 through the bypass line 72 and includes, for example, a three-way valve. In the present embodiment, the temperature control unit 74 passes the bypass line 72 to the heat medium circulation line 62 (high temperature side line) so that the heat medium temperature detected by the heat medium temperature detection unit 622 falls within a predetermined range. Adjust the flow rate of the heat medium to be mixed. The heat medium temperature detection unit 622 is provided between the connection point with the bypass line 72 (additional bypass line) and the connection point with the bypass line 71 in the heat medium circulation line 62. In the present embodiment, a temperature maintenance chamber 623 is provided between the connection between the heat medium circulation line 62 and the bypass line 72 and the connection between the bypass line 71 and the connection. A predetermined amount of heat medium is accommodated in the temperature maintenance chamber 623, and the heat medium temperature detection unit 622 detects the temperature of the heat medium in the temperature maintenance chamber 623.

  The heat transfer tube 22 is a flow path through which the LNG introduced into the heat medium container 21 flows, and is wound, for example, in a coil shape. The upstream end of the heat transfer tube 22 penetrates the bottom plate 211 of the heat medium container 21 and is connected to the fuel supply line 61. A gas line 64 is also connected to the bottom plate 211 of the heat medium container 21. The downstream end of the heat transfer tube 22 penetrates the bottom plate 211 and is connected to the gas line 64.

  The LNG in the heat transfer tube 22 is heated by the heat medium present in the surrounding area to be vaporized and vaporized, and the vaporized natural gas is discharged to the gas line 64 leading to the outside of the heat medium container 21. The downstream end of the gas line 64 is connected to the buffer tank 3. Natural gas vaporized in the heat transfer tube 22 is fed to the buffer tank 3 via the gas line 64.

  Here, when water is used as the heat medium, water flows, for example, in a temperature range of 20 to 60 ° C. in the heat medium container 21 (vaporizer 2). The natural gas vaporized in the heat transfer tube 22 is heated to, for example, a temperature range of 15 to 50 ° C., preferably 20 to 45 ° C., and discharged to the gas line 64 at a pressure of about 0.70 MPaG.

  In the present embodiment, a gas temperature detection unit 641 is provided at a portion near the heat medium container 21 (vaporizer 2) in the gas line 64. The gas temperature detection unit 641 detects the temperature of the natural gas discharged from the vaporizer 2.

  The heat transfer tube 23 is a flow path through which the LNG introduced into the heat medium container 21 flows, and is wound, for example, in a coil shape. The heat transfer tube 23 raises the pressure in the space portion inside the fuel storage tank 1 by the vaporized natural gas. The upstream end of the heat transfer tube 23 penetrates the bottom plate 211 of the heat medium container 21 and is connected to the fuel supply line 66. The fuel supply line 66 branches off from the middle of the fuel supply line 61. The fuel supply line 66 is provided with a shutoff valve 661. A gas line 67 is also connected to the bottom plate 211 of the heat medium container 21. The downstream end of the heat transfer tube 23 penetrates the bottom plate 211 and is connected to the gas line 67. The gas line 67 is provided with a pressure control valve 671.

  Natural gas vaporized in the heat transfer tube 23 is sent to the fuel storage tank 1 through the gas line 67. In the gas line 67, the gas pressure is pressurized, for example, to 0.75 MPaG. This pressurized pressure is the pressure for supplying LNG from the fuel storage tank 1 and is a gas fuel supply pressure source necessary for the marine gas engine 5 (diesel engine) which is an internal combustion engine.

  The buffer tank 3 is a sealed container capable of containing natural gas. The buffer tank 3 is used to absorb load fluctuation of the consumption gas amount of the combustion device 5 (gas engine for ships) of the latter stage with respect to the natural gas fuel fed in by the gas line 64. For example, when the combustion apparatus is an internal combustion engine, the configuration in which natural gas is stored by the buffer tank 3 is effective in absorbing load fluctuations. A gas line 65 is connected to the buffer tank 3. The gas line 65 is provided with a pressure control valve 651. In the pressure control valve 651, the natural gas flowing through the gas line 65 is depressurized to a pressure suitable for consumption by the ship gas engine 5 in the subsequent stage.

  The natural gas passed through the gas line 65 is supplied to the marine gas engine 5. The marine vessel gas engine 5 is, for example, a dual fuel engine (a dual fuel diesel engine), and is switched on from liquid fuel mode to gas fuel mode after being activated by liquid fuel such as heavy oil, and gas fuel is supplied. . The gas fuel supplied to the marine vessel gas engine 5 is burned through the governor 51 (speed governor) with a consumption amount corresponding to the output of the marine vessel gas engine 5.

  During operation, the marine vessel gas engine 5 is cooled while circulating engine cooling water by a cooling water pump 681 or an engine driven pump 682 (driven by the engine 5). The engine cooling water is circulated in a temperature range of 55 to 90 ° C. while repeating exhaust heat recovery and cooling in a steady operation state. The engine cooling water leaving the marine vessel gas engine 5 is introduced into the heat recovery unit 4 while the temperature is detected by the cooling water temperature detection unit 683 through the cooling water circulation line 68.

  The heat recovery unit 4 is for recovering the exhaust heat of the marine gas engine 5 with a heat medium. In the present embodiment, the heat recovery unit 4 is configured by an indirect heat exchanger. In the heat recovery unit 4, the heat medium discharged from the vaporizer 2 and flowing through the heat medium circulation line 63 exchanges heat with the engine cooling water flowing through the cooling water circulation line 68, and the exhaust heat of the marine gas engine 5 is heated It will be collected in the medium.

  The engine cooling water removed by the heat recovery unit 4 is further cooled by seawater by the cooler 684 and mixed with part of the engine cooling water flowing through the cooling water bypass line 686 while being controlled by the cooling temperature control valve 685. Then, the pressure is raised again by the cooling water pump 681 or the engine driven pump 682 and supplied to the marine gas engine 5.

  Next, a method of controlling the temperature of the heat medium circulating between the vaporizer 2 and the heat recovery unit 4 during operation of the liquefied natural gas vaporization system X1 will be described.

  The heat medium discharged from the vaporizer 2 and flowing through the heat medium circulation line 63 has a relatively low temperature due to heat exchange with the LNG or vaporized natural gas in the heat transfer tube 22 in the vaporizer 2. The heat medium flowing through the heat medium circulation line 63 recovers the exhaust heat of the marine gas engine 5 by passing through the heat recovery unit 4 and is temporarily stored in the temperature maintenance chamber 623 after the heat medium temperature rises. Ru. The temperature of the heat medium in the temperature maintenance chamber 623 is detected by the heat medium temperature detection unit 622, and part of the heat medium flowing through the heat medium circulation line 63 passes through the bypass line 72 so that the heat medium temperature becomes constant. The flow rate is adjusted by the temperature control unit 74 and mixed with the heat medium in the heat medium circulation line 62. In this way, a heat medium having a substantially constant temperature (hereinafter referred to as "basic temperature heat medium" as appropriate) is produced. In the present embodiment, the heat medium stored in the temperature maintenance chamber 623 is the basic temperature heat medium. The temperature of the basic temperature heat medium is set to a predetermined temperature, for example, in a temperature range of 25 to 60 ° C.

  With respect to the basic temperature heat medium which has reached a constant temperature using the temperature control unit 74, the heat medium discharged from the vaporizer 2 by the temperature control unit 73 located on the downstream side thereof (heat medium circulation A part of the heat medium flowing through the line 63 is mixed via the bypass line 71. The degree of the mixing is adjusted so that the temperature of the heat medium after mixing is lower than the set temperature of the basic temperature heat medium, and the temperature detected by the gas temperature detection unit 641 becomes the target temperature. The temperature of the heat medium after the mixing is adjusted to a predetermined temperature, for example, in a temperature range of 20 to 60 ° C.

In the present embodiment, the mixing of the low temperature heat medium by the temperature control unit 74 and the temperature control unit 73 is performed on the upstream side of the circulation pump 621. This is effective in quantifying the amount of heat medium after mixing using the characteristics of the circulation pump 621. For example, in the case of a carburetor 2 having an output of 1,200 kw for a ship gas engine 5 and having a vaporization capacity of about 400 kg / h for natural gas fuel supply, a heat medium circulation amount of 15 m ³ / h or more is appropriate is there.

  On the other hand, the flow rate of the LNG flowing from the fuel storage tank 1 to the carburetor 2 (heat transfer pipe 22) is determined by the consumption of the gas fuel in the marine gas engine 5. When there is a load fluctuation of the marine gas engine 5, the gas fuel consumption also fluctuates correspondingly.

  Inside the heat transfer tube 22, for example, when the pressure is 0.7 MPaG, LNG of about -130 ° C. is vaporized and then heated to a temperature range of 15 to 50 ° C., preferably 20 to 45 ° C. . In the present embodiment, the temperature of the natural gas discharged from the vaporizer 2 is detected by the gas temperature detection unit 641 in the vicinity of the vaporizer 2. Then, the detected temperature of the natural gas discharged from the vaporizer 2 becomes the target temperature within the temperature range of the fuel gas (for example, 25 ± 5 ° C. to 40 ± 5 ° C.) suitable to be supplied to the marine gas engine 5 Thus, the temperature of the heat medium supplied to the vaporizer 2 via the heat medium circulation line 62 is controlled.

  Next, with reference to FIG. 2, the change characteristic of the gas fuel consumption with respect to the operation time of the gas engine 5 for ships will be described. First, after the ship gas engine 5 (two-fueled diesel engine) is started and operated in the liquid fuel mode, the liquid fuel mode is changed to the gas fuel mode to shift to the operation of the gas engine. At that time, the gas fuel consumption switches from 0 to 100% in about 30 seconds as shown by the rising line at the left end of FIG. By this switching, the engine cooling water is already circulated in the cooling water circulation line 68 in the liquid fuel mode, and from the state cooled by the seawater by the cooler 684, the heat recovery unit 4 changes to a state where the heat medium recovers the exhaust heat. . The function of exhaust heat recovery by the heat recovery unit 4 is that the heat medium corresponding to the heat of vaporization of the liquefied natural gas is deprived of more heat from the heat medium as the gas fuel consumption increases, and the heat medium returned from the vaporizer 2 As the temperature starts to fall, it automatically changes to the state of recovering more exhaust heat from the engine coolant.

  In addition, when the gas fuel consumption increases, the temperature of the natural gas discharged from the vaporizer 2 is detected by the gas temperature detection unit 641, and the temperature adjusting unit 73 reduces the temperature of the gas coming out of the vaporizer 2. It operates to reduce the mixing amount of the medium. As a result, the temperature of the heat medium circulated toward the vaporizer 2 rises and the heating capacity increases following the increase in the amount of vaporization of LNG. Therefore, in the heat medium circulation lines 62 and 63, the temperature control unit 74 always operates by detecting the temperature of the heat medium in the temperature maintenance chamber 623 and sets the predetermined temperature within the temperature range of 25 to 60 ° C. A heat transfer medium must be prepared.

  Contrary to the above-mentioned operation in which the gas fuel consumption (engine load) rises to 100%, when the engine load decreases and the gas fuel consumption of the gas engine decreases, 100% gas fuel consumption as shown in FIG. 2 The amount may drop to a minimum of 19% gas fuel consumption (equivalent to 15% for engine load) as engine load decreases. At this time, in the liquefied natural gas vaporization system X1, the operation of preparing the basic temperature heat medium is always performed by the temperature control unit 74, so the temperature of the basic temperature heat medium is reduced even if the amount of consumption of vaporization heat of LNG decreases. Never change. Therefore, even if the gas fuel consumption decreases, the temperature of the natural gas discharged from the vaporizer 2 does not become higher than the temperature of the basic temperature heat medium. It is safe. The same operation as described above is performed even when the gas engine (gas engine for ships 5) is switched from the gas fuel mode to the liquid fuel mode and the vessel enters a stop state. As described above, when the liquefied natural gas vaporization system X1 is operated, an operation to maintain the temperature of the natural gas discharged from the vaporizer 2 always at the target temperature required by the gas engine is performed.

  The vaporizer 2 has a structure in which a heat transfer tube 22 in the form of a coil is immersed in a heat medium container 21 accommodating a heat medium. The heat medium flowing from the lower part of the heat medium container 21 ascends while circulating along the inner wall of the heat medium container 21 and passes through the overflow pipe 24 penetrating the center from the upper part of the heat medium container 21 to circulate the external heat medium. Flow into line 63. Since the size of the vaporizer 2 is fixed no matter how the load of the gas fuel consumption, ie, the amount of vaporized gas, fluctuates, the total heat transfer area formed by the heat transfer tubes 22 in the heat medium container 21 is constant. is there. Therefore, when the gas fuel consumption decreases, the amount of vaporized natural gas delivered from the heat transfer pipe 22 to the engine 5 decreases (that is, the amount of vaporized natural gas remaining in the heat transfer pipe 22 increases). The heat transfer area of (the region where LNG or LNG and the vaporized gas are mixed) decreases, and the heat transfer area of the gas heating unit (the region where only the vaporized natural gas is present) increases. On the other hand, the amount of heat medium contained in the vaporizer 2 (heat medium container 21) is constant regardless of the gas fuel consumption. Therefore, when the load of the gas fuel consumption decreases, the degree of temperature drop of the heat medium due to the cooling in the vaporizer 2 becomes smaller, and the temperature difference between the heat medium and the LNG in the heat transfer tube 22 becomes large. The temperature of the vaporized natural gas discharged from the vaporizer 2 rises. On the other hand, when the gas fuel consumption increases, the heat transfer area of the evaporation unit increases and the heat transfer area of the gas heating unit decreases. At the same time, the temperature drop of the heat medium increases, the temperature difference between the heat medium and the LNG in the heat transfer tube 22 shrinks, and the heat transfer slows down, and the temperature of the natural gas discharged from the vaporizer 2 decreases. The present invention has been made by focusing on such characteristics of the carburetor 2 of a fixed capacity when the gas fuel consumption fluctuates.

Next, with reference to FIG. 3, the change characteristic of the temperature of the natural gas discharged from the vaporizer 2 with respect to the gas fuel consumption will be described. FIG. 3 shows that the vaporization capacity of LNG in the vaporizer 2 is about 400 kg / h and the lift amount of the circulation pump 621 is 20 m ³ / h so that it can be adapted to the ship gas engine 5 with an output of 1,200 kw. In some cases, it represents the temperature change of the natural gas discharged from the vaporizer 2 with respect to the gas fuel consumption. FIG. 3 shows five examples in which the heat medium temperature (the temperature of the basic temperature heat medium) is different, and the curves respectively indicate the basic temperature heat medium adjusted to each predetermined temperature by the temperature control unit 73 to the vaporizer 2. It shows how the temperature of the natural gas discharged from the vaporizer 2 changes with respect to the gas fuel consumption which changes due to the load fluctuation of the gas engine when it is fed. In FIG. 3, the case of the basic temperature heat transfer medium is 45 ° C., 40 ° C., 35 ° C., 30 ° C. and 25 ° C., respectively. The load of the gas engine is usually 15% when the maximum load factor is 100%, and the corresponding load factor of the gas fuel consumption is 19% when the maximum load factor is 100%. Therefore, if the maximum gas fuel consumption is about 400 kg / h, the minimum is about 76 kg / h.

First, as an example shown in FIG. 3, when the basic temperature heat medium of 45 ° C. is flowed to the vaporizer 2 at a flow rate of 20 m ³ / h, when the gas fuel consumption is the smallest (fuel load rate 19% In the case of an engine load factor of 15%), the temperature of the natural gas discharged from the vaporizer 2 is about 45 ° C., which is almost the same as the heat medium temperature. However, when the amount of gas fuel consumption increases and the amount of vaporized gas increases, the temperature of the natural gas discharged from the vaporizer 2 falls to 34 ° C. at the maximum fuel load ratio of 100%. At this time, the temperature of the heat medium discharged from the vaporizer 2 is cooled in the vaporizer 2 and dropped to about 41.degree.

  Therefore, when it is desired to set the target value of the gas fuel temperature of the gas engine to 40 ° C., the temperature control unit 74 adjusts the temperature of the basic temperature heat medium to 45 ° C., and the gas fuel consumption changes with the change of the gas engine load. That is, while detecting the temperature of the natural gas discharged from the vaporizer 2, the temperature is adjusted so that the temperature of the natural gas discharged from the vaporizer 2 (the detected temperature at the gas temperature detection unit 641) becomes 40.degree. What is necessary is just to increase / decrease the mixing amount of the heat medium (heat medium which is relatively low temperature) which flows through the bypass line 71 in the part 73. When the gas fuel consumption is the lowest (fuel load rate 19%), the temperature control unit 73 adjusts the heat medium after mixing to about 40 ° C., and the gas fuel consumption is maximum (fuel load rate 100%) If the temperature control unit 73 is adjusted so that the temperature of the heat medium supplied to the vaporizer 2 is about 45.degree. C. (specifically, the mixing of the low temperature side heat medium via the bypass line 71) Stop). At this time, even if the gas fuel consumption rapidly increases to 100%, the temperature of the natural gas discharged from the vaporizer 2 does not fall below 34 ° C., and the gas fuel consumption rapidly decreases. Also, the temperature of the natural gas discharged from the vaporizer 2 does not exceed 45 ° C., which is the temperature of the basic temperature heat transfer medium. As a result, the target value 40 ° C. ± 5 ° C. of the gas fuel temperature can be almost achieved.

  Further, when the target value of the gas fuel temperature of the gas engine is set to 27 ° C., the temperature control unit 74 controls the temperature of the basic temperature heat medium to 35 ° C. The temperature of the natural gas discharged from the vaporizer 2 may be adjusted to 27 ° C. by increasing or decreasing. When the gas fuel consumption is the lowest (fuel load ratio 19%), the temperature control unit 73 adjusts the heat medium after mixing to about 27 ° C., and the gas fuel consumption is maximum (fuel load ratio 100%) When the temperature of the heat medium supplied to the vaporizer 2 is about 35.degree. C., the temperature control unit 73 is adjusted. As a result, even if the gas fuel consumption rapidly increases to 100%, the temperature of the natural gas discharged from the vaporizer 2 does not fall below 20 ° C., and the gas fuel consumption decreases sharply. Also, the temperature of the natural gas exhausted from the vaporizer 2 does not exceed 35.degree. Therefore, the target value 27 ° C. ± 5 ° C. of the gas fuel temperature can be almost achieved.

  As understood from the above, it is useful to prepare the basic temperature heat medium by the adjustment of the temperature control unit 74, and it works effectively to determine the temperature of the natural gas discharged from the vaporizer 2. Although FIG. 3 shows only the curves according to the temperatures of the five basic temperature heat transfer media, the technique according to the present invention can operate at any temperature from 25 ° C. to 60 ° C. The gas engine can be supplied with gas fuel at a stable temperature.

  As described above, it is necessary to set the temperature of the basic temperature heat transfer medium at any temperature in the temperature range of 25 ° C. to 60 ° C. If the target temperature of the natural gas (gas fuel) discharged from the vaporizer 2 is determined, it is assumed how the temperature of the natural gas discharged from the vaporizer 2 changes according to the change in the gas fuel consumption. Then, the arithmetic mean value of the gas temperature and the temperature of the basic temperature heat medium in the case of the 100% load factor where the gas fuel consumption is the largest becomes the target value of the gas fuel temperature. Based on an example shown in FIG. 3, when the temperature of the basic temperature heat medium is 45 ° C., the gas temperature is 34 ° C. when the gas fuel consumption amount is 100% at maximum, and the gas temperature (34 ° C.) The arithmetic mean value of the basic temperature and the temperature of the basic heat medium (45 ° C.) is about 40 ° C. When the responsiveness of the temperature control unit 73 is good, the target temperature of the gas fuel is set as described above, and the actual temperature of the gas fuel is in the range of the target temperature of the gas fuel ± 5 ° C. by performing the control described above. It can fit almost.

  Here, even if the engine load fluctuates, if the height of the engine coolant temperature is small and stable, the change in the amount of heat recovered by the heat recovery unit 4 becomes small, and the temperature of the basic temperature heat medium is 25 ° C. The temperature is almost constant in the temperature range of 60 ° C., and the variation range is also small. Further, when the amount of heat transfer medium circulating through the vaporizer 2 is large, the change width of the heat transfer medium temperature in the vaporizer 2 becomes small even if the change in gas fuel consumption is large. It becomes possible to control stably the temperature of the natural gas discharged from 2. In such a case, the operation of the temperature control unit 74 can be stopped or the temperature control unit 74 can be eliminated.

  As mentioned above, although the embodiment of the present invention was described, the scope of the present invention is not limited to the above-mentioned embodiment, and all the changes within the range described in each claim are the scope of the present invention. Included.

  For example, the structure of the vaporizer is not limited to the heat medium tank type vaporizer described in FIG. 1, but any vaporizer that can circulate the heat medium to vaporize the liquefied natural gas Any structure may be employed.

  In addition, with regard to the mounting position of the temperature control units 73 and 74, if the mixing point of the heat medium is near the circulation pump 621, the temperature control units 73 and 74 are changed as shown in FIG. The control units 73 and 74 may be configured to change the flow direction of the heat medium.

X1 liquefied natural gas vaporization system 1 fuel storage tank 2 vaporizer 21 heat medium container 211 bottom plate 212 container body 22 heat transfer tube 23 heat transfer tube 24 overflow tube 3 buffer tank 4 heat recovery unit (heat exchanger)
5 Gas engine for ships 51 Governor 61 Fuel supply line 611 shutoff valve 612 Gas extraction line 613 Shutoff valve 62 Heat medium circulation line (high temperature side line)
621 Pump for circulation 622 Heat medium temperature detection unit 623 Temperature maintaining chamber 63 Heat medium circulation line (low temperature side line)
64 gas line 641 gas temperature detection unit 65 gas line 651 pressure control valve 66 fuel supply line 66 shutoff valve 67 gas line 671 pressure control valve 68 cooling water circulation line 681 cooling water pump 682 engine driven pump 683 cooling water temperature detection unit 684 cooler 685 Cooling control valve 686 Cooling water bypass line 71 Bypass line (1st bypass line)
72 bypass line (second bypass line)
73 Temperature control unit (1st temperature control unit)
74 Temperature control unit (second temperature control unit)

Claims (14)

A liquefied fuel gas vaporization system for vaporizing liquefied fuel gas and supplying it to a combustion device, comprising:
A vaporizer that vaporizes liquefied fuel gas by heating it with a liquid heat medium;
A heat recovery unit that recovers the exhaust heat of the combustion apparatus with the liquid heat medium;
A heat medium circulation line for circulating the liquid heat medium between the heat recovery unit and the vaporizer;
The heat medium circulation line is provided with a mixing unit for mixing the liquid heat medium discharged from the vaporizer and not passing through the heat recovery unit with the liquid heat medium passed through the heat recovery unit. There is a liquefied fuel gas vaporization system. The heat medium circulation line is a relatively high temperature which has passed through the heat recovery unit, a low temperature side line for sending the liquid heat medium which is relatively low temperature discharged from the vaporizer to the heat recovery unit, and the heat recovery unit. A high temperature side line for sending the above liquid heat medium to the above vaporizer;
The liquefied fuel gas vaporization system according to claim 1, wherein the mixing part includes a first bypass line connected at one end to the low temperature side line and at the other end to the high temperature side line. A gas temperature detection unit that detects the temperature of the fuel gas discharged from the vaporizer;
The flow rate of the liquid heat medium supplied to the high temperature side line through the first bypass line is set so that the temperature of the fuel gas detected by the gas temperature detection unit falls within a predetermined range from the target temperature. The liquefied fuel gas vaporization system according to claim 2, further comprising: a first temperature control unit to control. The mixing unit is connected such that one end is closer to the heat recovery unit than the connection portion of the first bypass line in the low temperature side line, and the other end is more connected than the connection portion of the first bypass line in the high temperature side line. Including a second bypass line connected closer to the heat recovery unit;
A heat medium temperature detection unit provided between the first bypass line and the second bypass line in the high temperature side line for detecting the temperature of the liquid heat medium;
The liquid mixed in the high temperature side line passing through the second bypass line such that the temperature of the liquid heat medium detected by the heat medium temperature detection unit is maintained at a substantially constant temperature within a predetermined range The liquefied fuel gas vaporization system according to claim 3, further comprising: a second temperature control unit that controls a flow rate of the heat medium. And a temperature maintaining chamber provided between the first bypass line and the second bypass line in the high temperature side line,
The liquefied fuel gas vaporization system according to claim 4, wherein the heat medium temperature detection unit is provided in the temperature maintenance chamber.   The liquefied fuel gas vaporization system according to any one of claims 1 to 5, wherein the combustion device is a dual fuel engine for ships.   The heat recovery unit includes a heat exchanger provided between the low temperature side line and the high temperature side line, and in the heat exchanger, the cooling water from the combustion device and the heat medium flowing through the low temperature side line The liquefied fuel gas vaporization system according to any one of claims 2 to 6, wherein heat exchange is performed between them.   The liquefied fuel gas vaporization system according to any one of claims 1 to 7, wherein the fuel gas is a natural gas.   The liquefied fuel gas vaporization system according to any one of claims 1 to 8, wherein the heat medium is water. In a liquefied fuel gas vaporization system for vaporizing liquefied fuel gas and supplying it to a combustion device,
The liquid heat medium is circulated between a vaporizer that heats and vaporizes liquefied fuel gas with a liquid heat medium, and a heat recovery unit that recovers the exhaust heat of the combustion apparatus,
The liquid heat medium discharged from the vaporizer and not passing through the heat recovery unit is mixed with the liquid heat medium passed through the heat recovery unit, and the temperature of the liquid heat medium after mixing is predetermined The liquid heat medium temperature control method of a liquefied fuel gas vaporization system controlled so that it may become in a range.   The liquid heat medium temperature control method according to claim 10, wherein the fuel gas is natural gas and the heat medium is water. The liquefied fuel gas vaporization system relatively passes the low temperature side line for sending the liquid heat medium, which is relatively low temperature, discharged from the vaporizer to the heat recovery unit, and the heat recovery unit. A heat medium circulation line including a high temperature side line for sending the liquid heat medium which is at a high temperature to the vaporizer;
A first bypass line having one end connected to the low temperature side line and the other end connected to the high temperature side line;
A gas temperature detection unit that detects the temperature of the fuel gas discharged from the vaporizer;
A first temperature control unit for controlling a flow rate of the liquid heat medium supplied to the high temperature side line through the first bypass line;
One end is connected closer to the heat recovery portion than the connection portion of the first bypass line in the low temperature side line, and the other end is closer to the heat recovery portion than the connection portion of the first bypass line in the high temperature side line Connected to the second bypass line,
A heat medium temperature detection unit provided between the first bypass line and the second bypass line in the high temperature side line for detecting the temperature of the liquid heat medium;
And a second temperature control unit for controlling the flow rate of the liquid heat medium to be mixed with the high temperature side line by passing through the second bypass line.
The first temperature control unit is supplied to the high temperature side line through the first bypass line such that the temperature of the fuel gas detected by the gas temperature detection unit falls within a predetermined range from the target temperature. Control the flow rate of the liquid heat medium
The second temperature control unit passes the second bypass line so as to maintain the temperature of the liquid heat medium detected by the heat medium temperature detection unit at a substantially constant temperature within a predetermined range. The liquid heat medium temperature control method according to claim 11, wherein the flow rate of the liquid heat medium mixed in the side line is adjusted. The liquefied fuel gas vaporization system further includes a temperature maintenance chamber provided between the first bypass line and the second bypass line in the high temperature side line,
The heat medium temperature detection unit is provided in the temperature maintenance chamber, and the second bypass line is provided so that the temperature of the liquid heat medium in the temperature maintenance chamber is maintained at a substantially constant temperature within a predetermined range. The liquid heat medium temperature control method according to claim 12, wherein the flow rate of the liquid heat medium that is passed through and mixed with the high temperature side line is adjusted. The first temperature control unit is configured to supply the liquid heat medium supplied to the high temperature side line through the first bypass line so as to be within 15 to 50 ° C., which is ± 5 ° C. from the target temperature of the fuel gas. Adjust the flow rate of
The second temperature control unit passes through the second bypass line such that the temperature of the liquid heat medium detected by the heat medium temperature detection unit is maintained at a substantially constant temperature within a range of 25 to 60 ° C. The liquid heat medium temperature control method according to claim 12 or 13, wherein the flow rate of the liquid heat medium mixed in the high temperature side line is adjusted.

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