liquefied gas carrier

Abstract

To provide a liquified gas carrier capable of properly processing a surplus boil-off gas.SOLUTION: A liquified gas carrier comprises a hull propelled by rotating a propeller, a storage tank to store a liquified gas, a boiler system to generate steam, a steam turbine to convert steam energy to a power and to transmit the same to the propeller, and a control device. A boiler system includes a boiler mixing a boil-off gas generated in the storage tank with air, burning the same, and generating steam by heat from burning, a preheater to heat the air supplied to the boiler with heat of the exhaust gas exhausted from the boiler, and one of an air bypass flow path to supply the air to the boiler bypassing the preheater and an exhaust gas bypass flow path to exhaust the exhaust gas overboard bypassing the preheater. The control device increases at least one of the bypass amount of the air passing through the air bypass flow path and the bypass amount of the exhaust gas passing through the exhaust gas bypass flow path when the actual speed of the hull is greater than a preset target speed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to liquefied gas carriers. [Background technology]

[0002] Liquefied gas carriers are equipped with storage tanks for storing liquefied gas. The liquefied gas naturally evaporates in the storage tanks, generating boil-off gas. This boil-off gas can be effectively used as energy for a propulsion engine. For example, a propulsion engine has been devised in which boil-off gas is combusted in a boiler to generate steam, and the generated steam rotates a propeller for propulsion (see Patent Document 1 below).

[0003] In such propulsion engines, a preheater is sometimes provided in the boiler system. The preheater is a device that performs heat exchange between the exhaust gas discharged from the boiler and the air supplied to the boiler. By using this preheater, the heat of the exhaust gas can be recovered, thereby improving the efficiency of the boiler system. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-109738 Summary of the Invention [Problem to be solved by the invention]

[0005] However, depending on the situation, such as when the outside air temperature is high, boil-off gas may be generated in excess of what is necessary. In such cases, since discharging boil-off gas overboard is restricted, how to dispose of the excess boil-off gas becomes an issue. Therefore, an object of the present disclosure is to provide a liquefied gas carrier that can appropriately dispose of the excess boil-off gas. [Means for solving the problem]

[0006] A liquefied gas carrier according to one aspect of the present disclosure comprises a hull that is propelled by rotating a propeller, a storage tank that stores liquefied gas, a boiler system that generates steam, a steam turbine that converts the energy of the steam generated in the boiler system into power and transmits the converted power to the propeller, and a control device. The boiler system includes a boiler that mixes boil-off gas generated in the storage tank with air and burns it to generate steam using the heat from the combustion, a preheater that warms air to be supplied to the boiler using the heat of exhaust gas discharged from the boiler, and at least one of an air bypass passage that bypasses the preheater to supply air to the boiler, and an exhaust gas bypass passage that bypasses the preheater to discharge the exhaust gas overboard. When the actual speed of the hull is greater than a predetermined target speed, the control device increases at least one of the amount of air bypassed through the air bypass passage and the amount of exhaust gas bypassed through the exhaust gas bypass passage. [Effects of the Invention]

[0007] According to this configuration, the excess boil-off gas can be appropriately treated. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a liquefied gas carrier. [Figure 2] FIG. 2 is a flow diagram of the detour amount adjustment program. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Overall composition) A liquefied gas carrier 100 according to an embodiment will be described below. First, the overall configuration of the liquefied gas carrier 100 according to an embodiment will be described. FIG. 1 is a schematic diagram of the liquefied gas carrier 100. As shown in FIG. 1, the liquefied gas carrier 100 includes a hull 10, a storage tank 20, a boiler system 30, a steam turbine 40, and a control device 50. These components will be described in order below.

[0010] A propeller 11 is provided on the hull 10, and the hull 10 is propelled by rotating the propeller 11. The hull 10 includes a control panel 12 and a speedometer 13. The control panel 12 is a device that allows crew members to perform various operations and allows various settings to be made. The control panel 12 of this embodiment allows the speed (target speed) of the hull 10 to be set as desired. The speedometer 13 is a measuring device that measures the actual speed (actual speed) of the hull 10.

[0011] The storage tanks 20 are tanks that store liquefied gas. The liquefied gas carrier 100 of this embodiment is equipped with two storage tanks 20. However, the number of storage tanks 20 equipped in the liquefied gas carrier 100 is not limited. Furthermore, the shape and format of the storage tanks 20 are not limited. The liquefied gas stored in the storage tanks 20 may be, for example, liquefied petroleum gas (LPG), liquefied natural gas (LNG), liquefied hydrogen, etc.

[0012] Boil-off gas, which is vaporized liquefied gas, is naturally generated in the storage tank 20. The boil-off gas generated in the storage tank 20 is supplied to the boiler system 30 via the boil-off gas supply passage 21. The amount of boil-off gas naturally generated in the storage tank 20 varies depending on the situation at the time, such as the outside air temperature. Therefore, the amount of boil-off gas supplied to the boiler system 30 also varies depending on the situation at the time.

[0013] The boiler system 30 is a system that generates steam. The liquefied gas carrier 100 of this embodiment is equipped with two boiler systems 30. However, the number of boiler systems 30 equipped in the liquefied gas carrier 100 is not limited. The two boiler systems 30 have the same structure, and each includes a boiler 31, a preheater 32, an air bypass passage 33, and an exhaust gas bypass passage 34.

[0014] The boiler 31 is a facility that mixes boil-off gas with air, burns the mixture, and generates steam using the heat generated by the combustion. The boiler 31 is supplied with boil-off gas via the boil-off gas supply passage 21, and with air (outside air) via the air supply passage 35. Exhaust gas generated by the combustion of the boil-off gas is discharged from the boiler 31 to the outside of the ship via the exhaust gas discharge passage 36. Furthermore, a water pipe 37 is disposed inside the boiler 31. Water is supplied to the water pipe 37, and as the supplied water passes through the water pipe 37, it is heated by the heat generated by the combustion of the boil-off gas and turns into steam.

[0015] The preheater 32 is a facility that heats the air to be supplied to the boiler 31 using the heat of the exhaust gas discharged from the boiler 31. The preheater 32 is located on the air supply passage 35 and on the exhaust gas discharge passage 36. The exhaust gas flowing through the exhaust gas discharge passage 36 supplies heat to the air flowing through the air supply passage 35 when passing through the preheater 32. This recovers the heat of the exhaust gas, improving the efficiency of the boiler system 30.

[0016] The air bypass flow path 33 is a flow path that supplies air to the boiler 31, bypassing the preheater 32. The air bypass flow path 33 is arranged to connect a portion of the air supply flow path 35 upstream of the preheater 32 with a portion downstream of the preheater 32. A bypass air amount adjustment damper 38 is provided in the air bypass flow path 33. By changing the opening degree of the bypass air amount adjustment damper 38, the flow rate of air that bypasses the preheater 32 and is supplied to the boiler 31 (hereinafter referred to as the "bypass air amount") can be adjusted.

[0017] The exhaust gas bypass passage 34 is a passage that bypasses the preheater 32 and discharges the exhaust gas generated in the boiler 31 overboard. The exhaust gas bypass passage 34 is arranged to connect a portion of the exhaust gas discharge passage 36 upstream of the preheater 32 with a portion downstream of the preheater 32. The exhaust gas bypass passage 34 is provided with an exhaust gas bypass amount adjustment damper 39. By changing the opening degree of this exhaust gas bypass amount adjustment damper 39, it is possible to adjust the flow rate of exhaust gas that bypasses the preheater 32 and is discharged overboard (hereinafter referred to as the "exhaust gas bypass amount").

[0018] The steam turbine 40 is a facility that converts the energy of steam generated in the boiler system 30 into power and transmits the converted power to the propeller 11. Steam is supplied to the steam turbine 40 from the boiler 31 of each boiler system 30 via a steam supply passage 41. The torque of the propeller 11 fluctuates depending on the energy of the steam supplied to the steam turbine 40, and thus the speed of the hull 10 fluctuates.

[0019] The control device 50 is a device that controls each device equipped on the liquefied gas carrier 100. The control device 50 has a processor, a volatile memory, a non-volatile memory, an I / O interface, etc. The non-volatile memory of the control device 50 stores a detour amount adjustment program (described later) and various data, and the processor performs calculations using the volatile memory based on each program.

[0020] The control device 50 of this embodiment is electrically connected to the operation panel 12 and the speedometer 13, and can obtain the target speed and actual speed of the hull 10 based on signals received from these devices. Furthermore, the control device 50 is electrically connected to the air bypass volume adjustment damper 38 and the exhaust gas bypass volume adjustment damper 39, and can adjust the air bypass volume and exhaust gas bypass volume by sending control signals to these devices.

[0021] The functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor.

[0022] (Detour Volume Adjustment Program) Next, the bypass amount adjustment program will be described. The bypass amount adjustment program is a program that adjusts the bypass air amount and the bypass flue gas amount, and is executed by the control device 50. Here, one of the two boiler systems 30 will be described as the controlled object. However, in reality, the control device 50 controls both boiler systems 30. FIG. 2 is a flow diagram of the bypass amount adjustment program. Furthermore, it is assumed that the bypass air amount and the bypass flue gas amount are greater than zero when the bypass amount adjustment program starts to be executed. In other words, it is assumed that a certain amount of air and a certain amount of flue gas are flowing through the air bypass passage 33 and the exhaust gas bypass passage 34, respectively.

[0023] 2, when the bypass amount adjustment program is started, the control device 50 first determines whether another boiler system 30 (a boiler system 30 different from the boiler system 30 to be controlled) has stopped (step S1). Stopping the boiler system 30 includes both intentional and unintentional stopping. Whether the boiler system 30 has stopped can be determined based on the combustion temperature in the boiler 31, the temperature of the exhaust gas discharged from the boiler 31, the temperature of the steam supplied from the boiler 31 to the steam turbine 40, etc.

[0024] In step S1, if it is determined that the other boiler system 30 is stopped (NO in step S1), the control device 50 reduces the amount of bypass air and the amount of bypass exhaust gas (hereinafter, these will be collectively referred to simply as "bypass amount") and adjusts the amount of bypass to a predetermined minimum value (step S2). This allows more heat to be recovered from the exhaust gas discharged from the boiler 31, improving the efficiency of the boiler system 30. The minimum value may be zero or greater than zero.

[0025] When the other boiler system 30 is stopped, steam is generated only by the boiler system 30 to be controlled, resulting in an overall decrease in the energy of the steam supplied to the steam turbine 40. Therefore, in this embodiment, in such a case, the bypass amount is reduced in the boiler system 30 to be controlled, thereby improving the efficiency of the boiler system 30 to be controlled and suppressing the decrease in the energy of the steam supplied to the steam turbine 40.

[0026] On the other hand, if it is determined in step S1 that the other boiler systems 30 are not stopped (YES in step S1), the process proceeds to step S3. In step S3, the control device 50 acquires the target speed and actual speed of the hull 10. The control device 50 can acquire the target speed from the operation panel 12 and the actual speed from the speedometer 13. The target speed is set in advance before the detour amount adjustment program is executed.

[0027] Next, the control device 50 compares the target speed and the actual speed acquired in step S3 to determine whether the actual speed is greater than the target speed (step S4). If it is determined that the actual speed is greater than the target speed (YES in step S4), the control device 50 increases the amount of bypassing. This adjusts the efficiency of the boiler system 30 and suppresses an increase in the actual speed.

[0028] If the amount of boil-off gas generated increases due to an increase in the outside air temperature, for example, the amount of boil-off gas supplied to the boiler system 30 also increases accordingly. As a result, the energy of the steam supplied to the steam turbine 40 also increases, causing the actual speed of the hull 10 to exceed the target speed. In this case, reducing the amount of boil-off gas supplied is considered to suppress the actual speed of the hull 10, but this would result in excess boil-off gas. Therefore, in this embodiment, the amount of bypass is increased in such a case, and the efficiency of the boiler system 30 is adjusted (by increasing the amount of boil-off gas consumed), thereby essentially treating the excess boil-off gas.

[0029] On the other hand, if it is determined in step S4 that the actual speed is not greater than the target speed, that is, that the actual speed is smaller than or equal to the target speed (NO in step S4), the control device 50 reduces or maintains the bypass amount (step S6). Specifically, if it is determined that the actual speed is smaller than the target speed, the control device 50 reduces the bypass amount. This improves the efficiency of the boiler system 30, resulting in an increase in the actual speed. Note that if the actual speed falls below the target speed even after reducing the bypass amount, the liquefied gas in the storage tank 20 may be forcibly vaporized to generate boil-off gas, and the amount of boil-off gas supplied to the boiler system 30 may be increased. On the other hand, if it is determined that the actual speed is equal to the target speed, the control device 50 maintains the bypass amount without changing it. After the above-mentioned steps S1, S5, and S6 are performed, the process returns to step S1 and repeats each step.

[0030] (Variation) The liquefied gas carrier 100 according to this embodiment has been described above, but the configuration of the liquefied gas carrier 100 is not limited to the above. For example, the boiler system 30 described above includes both the air bypass passage 33 and the exhaust gas bypass passage 34, but may include only one of these passages. In this case, in the bypass amount adjustment program, the control device 50 may adjust either the bypass air amount or the bypass exhaust gas amount. Furthermore, even when the boiler system 30 includes both the air bypass passage 33 and the exhaust gas bypass passage 34, the control device 50 may adjust either the bypass air amount or the bypass exhaust gas amount. Specifically, instead of decreasing both the bypass air amount and the bypass exhaust gas amount, only one of them may be decreased. Furthermore, instead of increasing both the bypass air amount and the bypass exhaust gas amount, only one of them may be increased.

[0031] The liquefied gas carrier 100 may also be equipped with a condenser that returns a portion of the steam generated in the boiler system 30 to water without supplying it to the steam turbine 40. In this case, when the actual speed of the hull 10 exceeds the target speed, the amount of bypassing may be increased and the amount of steam returned to water by the condenser may be increased. Increasing the amount of steam returned to water in this way reduces the energy of the steam supplied to the steam turbine 40 (steam supply amount), and the actual speed of the hull 10 can be further reduced.

[0032] (summary) The first item disclosed in this specification is a liquefied gas carrier comprising a hull that is propelled by rotating a propeller, a storage tank that stores liquefied gas, a boiler system that generates steam, a steam turbine that converts the energy of the steam generated in the boiler system into power and transmits the converted power to the propeller, and a control device, wherein the boiler system includes a boiler that mixes boil-off gas generated in the storage tank with air and burns it to generate steam using the heat from the combustion, a preheater that warms air to be supplied to the boiler using the heat of exhaust gas discharged from the boiler, and at least one of an air bypass passage that bypasses the preheater to supply air to the boiler, and an exhaust gas bypass passage that bypasses the preheater to discharge the exhaust gas overboard, and the control device increases at least one of the amount of air bypassed through the air bypass passage and the amount of exhaust gas bypassed through the exhaust gas bypass passage when the actual speed of the hull is greater than a predetermined target speed.

[0033] According to this configuration, when excess boil-off gas is generated, the efficiency of the boiler system can be adjusted by increasing at least one of the amount of bypassed air and the amount of bypassed exhaust gas, thereby allowing the excess boil-off gas to be appropriately treated.

[0034] The second item disclosed in this specification is a ship comprising a hull that is propelled by rotating a propeller, a storage tank that stores liquefied gas, a plurality of boiler systems that generate steam, a steam turbine that converts the energy of the steam generated in the plurality of boiler systems into power and transmits the converted power to the propeller, and a control device, and each of the plurality of boiler systems has a boiler that mixes boil-off gas generated in the storage tank with air and burns it to generate steam by the heat of combustion, and a control device that controls the exhaust gas discharged from the boiler. a preheater that uses heat from a boiler system to heat the air to be supplied to the boiler; an air bypass passage that bypasses the preheater to supply air to the boiler; and at least one of an exhaust gas bypass passage that bypasses the preheater to discharge the exhaust gas overboard, wherein when some of the plurality of boiler systems stop, the control device reduces at least one of the bypass amount of air passing through the air bypass passage of the remaining boiler system and the bypass amount of exhaust gas passing through the exhaust gas bypass passage.

[0035] According to this configuration, even if some of the boiler systems among the plurality of boiler systems stop, the efficiency of the remaining boiler systems can be improved by reducing at least one of the bypass air amount and the bypass exhaust gas amount in the remaining boiler systems, thereby suppressing a decrease in the energy of the steam supplied to the steam turbine. [Explanation of symbols]

[0036] 10 Hull 11 Propeller 20 Storage Tank 30 Boiler System 31 Boiler 32 Preheater 33 Air bypass channel 34 Exhaust gas bypass flow path 40 Steam Turbine 41 Steam supply channel 50 Control device 100 Liquefied Gas Carriers

Claims

1. A hull that is propelled by rotating a propeller, a storage tank for storing liquefied gas; a boiler system for generating steam; a steam turbine that converts the energy of the steam generated in the boiler system into power and transmits the converted power to the propeller; a control device; The boiler system includes: a boiler that mixes the boil-off gas generated in the storage tank with air and burns the mixture to generate steam using heat from the combustion; a preheater that heats air to be supplied to the boiler using heat from exhaust gas discharged from the boiler; at least one of an air bypass flow path that bypasses the preheater and supplies air to the boiler, and an exhaust gas bypass flow path that bypasses the preheater and discharges the exhaust gas overboard, The control device increases at least one of the amount of air bypassed through the air bypass passage and the amount of exhaust gas bypassed through the exhaust gas bypass passage when the actual speed of the hull is greater than a predetermined target speed.

2. A hull that is propelled by rotating a propeller, a storage tank for storing liquefied gas; a plurality of boiler systems for generating steam; a steam turbine that converts the energy of steam generated by the plurality of boiler systems into power and transmits the converted power to the propeller; a control device; Each boiler system of the plurality of boiler systems comprises: a boiler that mixes the boil-off gas generated in the storage tank with air and burns the mixture to generate steam using heat from the combustion; a preheater that heats air to be supplied to the boiler using heat from exhaust gas discharged from the boiler; at least one of an air bypass flow path that bypasses the preheater and supplies air to the boiler, and an exhaust gas bypass flow path that bypasses the preheater and discharges the exhaust gas overboard, The control device, when some of the boiler systems among the plurality of boiler systems stop, reduces at least one of the amount of air bypassed through the air bypass passage of the remaining boiler systems and the amount of exhaust gas bypassed through the exhaust gas bypass passage.

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