CN110325793B

CN110325793B - Boiler, boiler system, and method for operating boiler

Info

Publication number: CN110325793B
Application number: CN201880011465.3A
Authority: CN
Inventors: 寺原贵澄; 高本健太; 天野英辉
Original assignee: Mitsubishi Heavy Industries Marine Machinery and Equipment Co Ltd
Current assignee: Mitsubishi Heavy Industries Marine Machinery and Equipment Co Ltd
Priority date: 2017-02-28
Filing date: 2018-02-07
Publication date: 2021-03-23
Anticipated expiration: 2038-02-07
Also published as: KR20190104574A; WO2018159245A1; EP3591293A4; CN110325793A; EP3591293A1; JP6957165B2; JP2018141584A; KR102314907B1; DK3591293T3; EP3591293B1

Abstract

The purpose of the invention is to be able to process a boil-off gas while utilizing the energy of the boil-off gas. The boiler is supplied with boil-off gas generated in an LNG tank storing LNG, and is provided with a burner (23) for burning the boil-off gas. The burner (23) has a continuous discharge igniter and an intermittent discharge igniter (43) which emits sparks at a higher frequency than the continuous discharge igniter (56) at the time of ignition. An intermittent discharge type igniter (43) is used in a boiler for treating boil-off gas.

Description

Boiler, boiler system, and method for operating boiler

Technical Field

The invention relates to a boiler, a boiler system and a method for operating the boiler.

Background

The LNG carrier fills LNG (Liquefied Natural Gas) in an LNG tank and carries the LNG. Since the LNG filled in the LNG tank has a low vaporization temperature, a large amount of vaporized gas (boil-off gas) is generated in the LNG tank due to the influence of outside air temperature and the like during the navigation of the LNG carrier. When boil-off gas is generated in the LNG tank, the pressure of the LNG tank rises, but the boil-off gas is mainly consumed by a main engine of the LNG carrier or the like, and the pressure in the LNG tank is appropriately maintained. In addition, when the boil-off Gas is not processed by the main engine or the like of the LNG carrier, the boil-off Gas is burned by a Gas Combustion Unit (GCU) or the like, thereby preventing a pressure increase in the LNG tank. As an LNG carrier provided with such a device, there is an LNG carrier described in patent document 1.

Patent document 1 discloses an LNG carrier provided with a gas burner downstream of an LNG storage tank. In the LNG carrier described in patent document 1, when the operation of the boil-off gas reliquefaction apparatus is stopped, the pressure of the LNG tank is increased by the boil-off gas (boil-off gas) generated in the LNG tank, and when the pressure becomes equal to or higher than a set safe pressure, the boil-off gas (boil-off gas) is sent to a gas burner (GCU) to be burned and incinerated.

Further, there is an LNG carrier that burns boil-off gas generated in an LNG tank in a boiler. Patent document 2 discloses a conventional boiler that burns boil-off gas.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4563420

Patent document 2: japanese laid-open patent publication No. 4-46892

Problems to be solved by the invention

However, in the structure of patent document 1, only the evaporated gas is burned and incinerated in the GCU, and therefore, the energy of the evaporated gas cannot be effectively utilized.

In addition, the conventional boiler for burning the boil-off gas as disclosed in patent document 2 is provided with only one type of ignition device for igniting the burner provided in the boiler. In order to burn the boil-off gas in the boiler, ignition of the burner needs to be differentiated according to the conditions in the boiler and the LNG tank. However, since only one type of ignition device is provided in the conventional boiler, the redundancy of the ignition device is low, and it is not possible to distinguish between the use of the ignition device according to the situation in the boiler and the LNG tank.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a boiler, a boiler system, and a method for operating a boiler, which can process boil-off gas and utilize energy of the boil-off gas.

Means for solving the problems

In order to solve the above problems, the boiler system, and the method for operating the boiler according to the present invention employ the following technical means.

A boiler according to an aspect of the present invention is a boiler to which boil-off gas generated in a fuel tank storing fuel is supplied, and includes a burner that burns the boil-off gas, the burner including a first ignition device and a second ignition device that emits sparks at a higher frequency than a frequency at which sparks are emitted at a time of ignition of the first ignition device.

In the above configuration, the boil-off gas generated in the fuel tank is supplied to the boiler. This enables the boil-off gas generated in the fuel tank to be burned in the boiler. Therefore, the boil-off gas can be treated without providing a dedicated device (GCU or the like) for burning the boil-off gas, and the steam can be generated by using the energy of the boil-off gas.

In the above configuration, the burner includes the first ignition device and the second ignition device that generates sparks at a higher frequency than the first ignition device. Since the frequency of sparks generated by the second ignition device at the time of ignition is higher than the frequency of sparks generated by the first ignition device at the time of ignition, the load at the time of ignition is large, and the spark plug is more easily consumed than the first ignition device. In contrast, the first ignition device generates sparks at a lower frequency than the second ignition device, and therefore, the spark plug is less likely to be consumed than the second ignition device. In this way, the burner is provided with ignition means having different characteristics. Therefore, by using the ignition devices having different characteristics according to the conditions in the boiler and the fuel tank, the vapor can be appropriately combusted to generate steam, and the product life of the ignition device can be extended.

In the boiler according to one aspect of the present invention, the second ignition device may be used when combustion of the boil-off gas is started in the burner.

If the vapor gas is generated in the fuel tank and the pressure in the fuel tank becomes high, the fuel tank may be damaged. Therefore, when the pressure in the fuel tank is reduced by performing the combustion process on the boil-off gas, if the pressure in the fuel tank becomes a threshold pressure that is smaller than a pressure at which the fuel tank may be damaged by a predetermined value, the boil-off gas needs to be rapidly combusted. Therefore, when the evaporated gas is subjected to combustion treatment, it is preferable that the time until ignition of the burner is short. In the above configuration, the second ignition device is used when the evaporation gas is burned. The second ignition device can ignite in a shorter time than the first ignition device, and therefore, the boil-off gas can be rapidly burned. Therefore, the boiler can burn the evaporated gas, and the pressure in the fuel tank can be appropriately maintained at a predetermined value or less.

In the boiler according to one aspect of the present invention, the first ignition device may be used when the pressure of the steam in the steam drum is increased by the combustion of the burner.

When the boil-off gas is burned by the boiler in a state where the steam pressure in the steam boiler drum is low, the boiler may become overloaded. Further, since the boiler is overloaded, the amount of the evaporated gas to be burned in the boiler is limited, and there is a possibility that the combustion process cannot be performed on a desired amount of the evaporated gas. Therefore, when the steam pressure in the steam drum is insufficient when the boil-off gas is burned in the boiler, it is necessary to increase the steam pressure in the steam drum. In the above configuration, the first ignition device is used when the pressure in the steam drum is increased. Thus, the second ignition device, which is more likely to be damaged than the first ignition device, can be eliminated when the steam pressure in the steam drum is increased. Therefore, the frequency of use of the second ignition device can be reduced, and the product life of the second ignition device can be prolonged.

A boiler system according to an aspect of the present invention is a boiler system including the above-described boiler, and includes: the boiler barrel pressure detection mechanism detects the steam pressure in the steam boiler barrel; a tank pressure detection mechanism that detects a pressure in the fuel tank; a target pressure reaching time calculation unit that calculates a time until the steam pressure in the steam drum reaches the target steam pressure, based on the steam pressure in the steam drum detected by the drum pressure detection means and the target steam pressure in the steam drum that is the steam pressure at which the combustion of the evaporation gas is performed; a predetermined pressure reaching time calculation unit that calculates a time until the pressure in the fuel tank reaches the predetermined pressure based on the pressure in the fuel tank detected by the tank pressure detection means and the predetermined pressure in the fuel tank that is the pressure at which the boil-off gas is supplied to the fuel tank; an ignition timing calculation unit that calculates an ignition timing such that the vapor pressure in the steam boiler drum becomes the target vapor pressure when the pressure in the fuel tank becomes the predetermined pressure, based on the target pressure reaching time calculated by the target pressure reaching time calculation unit and the predetermined pressure reaching time calculated by the predetermined pressure reaching time calculation unit; and an ignition control means for igniting the burner by the first ignition device at the ignition timing calculated by the ignition timing calculation section to start boosting of the steam pressure in the steam drum.

In the above configuration, when the pressure in the fuel tank becomes a predetermined pressure at which the boil-off gas is supplied to the boiler, the burner is ignited so that the steam pressure in the steam boiler tube becomes a target pressure. Therefore, when the boil-off gas is burned by the boiler, the steam pressure in the steam drum can be made a steam pressure sufficient for burning the boil-off gas, and the boiler can be prevented from being overloaded due to the steam pressure of the boiler not reaching the target steam pressure, so that the boil-off gas can be burned appropriately. Further, depending on the conditions of the marine weather, the amount of boil-off gas generated in the fuel tank, that is, the tendency of the pressure of the fuel tank to rise varies, and therefore, when the pressure increase of the boiler is started based only on the predetermined pressure in the fuel tank, the start of combustion of the boil-off gas may not be reached. In the above configuration, the ignition timing is calculated based on the detected pressure in the fuel tank so that the vapor pressure in the vapor drum becomes the target vapor pressure when the pressure in the fuel tank becomes the predetermined pressure. Therefore, when the pressure in the fuel tank reaches the predetermined pressure, the pressure increase of the steam pressure in the steam drum to the target pressure is completed, and therefore, the boil-off gas can be quickly supplied to the boiler and burned, and the pressure in the fuel tank can be reduced. The predetermined pressure is, for example, a threshold pressure that is smaller than a pressure at which the fuel tank may be damaged by a predetermined value.

In the above configuration, the time until the pressure in the fuel tank reaches the predetermined pressure is calculated, and the burner in the steam drum is ignited in advance so as to match the time until the pressure in the fuel tank reaches the predetermined pressure, thereby increasing the steam pressure in the steam drum to a target pressure state. In this way, since the pressure of the steam in the steam drum is increased according to the rate of increase of the pressure in the fuel tank, it is not necessary to constantly maintain the steam pressure in the steam drum at a high pressure in order to combust the boil-off gas. Therefore, as compared with a boiler system in which a high-pressure state is maintained so that boil-off Gas can be treated all the time, the time for operating the boiler at a high pressure can be shortened, and the consumption of fuel (MGO (Marine Gas Oil) or the like) in the boiler can be reduced.

A method of operating a boiler according to an aspect of the present invention is a method of operating a boiler supplied with boil-off gas generated in a fuel tank storing fuel, the method including: a pressure raising step of igniting a burner provided in the boiler by a first ignition device to raise a pressure of steam in a steam drum by combustion of the burner; and a combustion step of igniting the burner by a second ignition device after the pressure increasing step, and combusting the evaporated gas in the burner, wherein the frequency of sparks generated by the second ignition device at the time of ignition is higher than the frequency of sparks generated by the first ignition device at the time of ignition.

Effects of the invention

According to the present invention, the boil-off gas can be treated in the boiler while the energy of the boil-off gas can be utilized.

Drawings

Fig. 1 is an overall configuration diagram of a system mounted on a ship according to an embodiment of the present invention.

Fig. 2A is a longitudinal sectional view showing a burner of an embodiment of the present invention.

Fig. 2B is a vertical cross-sectional view showing the burner according to the embodiment of the present invention, and is a view showing a state where the intermittent discharge type igniter is pulled up.

Fig. 3 is a bottom view illustrating the burner of fig. 2A.

Fig. 4 is a longitudinal sectional view showing a main part of the burner of fig. 2A.

Fig. 5 is a graph showing the rise of pressure in the steam drum of fig. 1.

Fig. 6 is a graph showing a rise in pressure within the LNG tank of fig. 1.

Detailed Description

Hereinafter, an embodiment of a boiler, a boiler system, and a method for operating a boiler according to the present invention will be described with reference to the drawings.

As shown in fig. 1, the boiler system according to the present embodiment is applied to, for example, an LNG carrier 2 including a gas-fired main engine 10. The LNG carrier 2 is mounted with an LNG tank (fuel tank) 3 that stores LNG, a boiler 4 that burns boil-off gas generated in the LNG tank 3 to generate steam, an economizer 5 that recovers heat of exhaust gas generated by the main engine 10 to generate steam, and a control device 6 that controls the boiler 4.

The boil-off gas generated in the LNG tank 3 is supplied to the main engine 10, the power generation co-combustion engine (not shown), the reliquefaction device 15, and the like by the first supply compressor 13 provided in the boil-off gas supply pipe 12. In the main engine 10 and the mixed combustion engine for power generation, the supplied boil-off gas is combusted to obtain a driving force. In the reliquefaction device 15, the boil-off gas is reliquefied by compressing and cooling the boil-off gas, and the reliquefied boil-off gas is returned to the LNG tank 3 via the return pipe 16.

Further, a part of the boil-off gas generated in the LNG tank 3 is supplied to the boiler 4 via a boil-off gas supply pipe 17 connecting the LNG tank 3 and the boiler 4. The boil-off gas supply pipe 17 is provided with a second supply compressor 18 used when supplying the boil-off gas to the boiler 4, and a vent pipe 19 for releasing the boil-off gas to the atmosphere. The LNG tank 3 is provided with an in-tank pressure gauge (tank pressure detection means) 20 for detecting the pressure in the LNG tank 3. The tank pressure gauge 20 transmits the acquired pressure in the LNG tank 3 to the tank control device 40.

The boiler 4 includes a furnace (not shown), a steam drum 21 disposed above, and a water drum 22 disposed below. The furnace includes a burner 23 (see fig. 2A), and combustion is performed in the furnace. When the burner 23 is ignited in the furnace and the feed water is heated in the boiler 4, the water rises from the lower water drum 22 to the upper steam drum 21, and the gas and liquid are separated by the steam drum 21. The steam drum 21 is provided with an in-drum pressure gauge (drum pressure detection mechanism) 24 for measuring the steam pressure in the steam drum 21. The drum internal pressure gauge 24 transmits the acquired steam pressure in the steam drum 21 to the control device 6. Further, a boiler steam supply pipe 28 for supplying the steam separated in the steam drum 21 to the turbine 26 for power generation, the condenser 27, the steam-using equipment, and the like is connected to the steam drum 21. A generator 29 is coupled to a rotating shaft of the power generation turbine 26, and the generator 29 generates power by the rotational force of the power generation turbine 26. The steam discharged from the power generation turbine 26 is supplied to the condenser 27 via the steam discharge pipe 30.

The economizer 5 is provided with two stages, and generates steam by exchanging heat between water and combustion exhaust gas discharged from the main engine 10. The economizer 5 and the steam drum 21 are connected by an economizer steam supply pipe 32. The economizer steam supply pipe 32 supplies the gas-liquid generated in the economizer 5 to the steam drum 21. The separated steam is supplied to each device such as the power generation turbine 26 through the boiler steam supply pipe 28 in the steam drum 21. The water drum 22 and the economizer 5 are connected by a water supply pipe 33. The water supply pipe 33 supplies water in the water drum 22 to the economizer 5 by a pump 34 provided at an intermediate position. Further, a separate steam-water separator 35 may be provided to separate the gas and liquid generated by the economizer 5 in the steam-water separator 35. In this case, as shown by a broken line in fig. 1, the economizer 5 and the steam separator 35 are connected by an economizer steam supply pipe 36 and a water supply pipe 37. The steam generated in the economizer 5 is supplied to the steam-water separator 35 through an economizer steam supply pipe 36. The water supply pipe 37 supplies water in the steam separator 35 to the economizer 5 by a pump 38 provided at an intermediate position. In the present embodiment, two economizers 5 are provided, but the number of the economizers 5 may be one, or may be three or more.

In the present embodiment, the boiler system is configured by the boiler 4, the control device 6, the in-tank pressure gauge 20, the in-drum pressure gauge 24, and the like.

Next, the burner 23 provided in the furnace of the boiler 4 will be described in detail with reference to fig. 2A to 4.

As shown in fig. 2A and 2B, the burner 23 includes a main burner 41 for forming a flame in the furnace, a pilot burner 42 for igniting the main burner 41, and an intermittent discharge type igniter (second ignition device) 43.

The main burner 41 includes an oil supply portion for supplying oil, a gas supply portion for supplying an evaporation gas, and an air passage for supplying combustion air.

The oil supply unit includes an oil supply pipe 47 through which oil supplied from an oil supply device (not shown) through the oil supply path 11 (see fig. 1) flows. The oil supply pipe 47 is formed of a cylindrical member extending in the vertical direction at substantially the center of the burner 23, and oil flows downward from above inside. The oil supply pipe 47 is disposed so that the lower end portion thereof is located in the furnace. A tip 48 is provided at the lower end of the oil supply pipe 47, and the oil passing through the tip 48 is sprayed into the furnace. Examples of the supplied oil include light oil and heavy oil.

The gas supply unit includes a gas supply chamber 49 connected to the boil-off gas supply pipe 17 through which the boil-off gas from the LNG tank 3 flows, and 5 gas distribution pipes 50 extending downward from the gas supply chamber 49. As shown in fig. 3, the 5 gas distribution pipes 50 are disposed at equal intervals so as to surround the oil supply pipe 47. As shown in fig. 2A and 2B, the gas distribution pipes 50 are disposed so that the lower end portions thereof are located in the furnace. A nozzle 51 is provided at the lower end of the gas distribution pipe 50, and the evaporation gas is jetted into the furnace by the nozzle 51.

The air passage is provided so as to cover the periphery of the oil supply pipe 47 and the gas distribution pipe 50. The air passage includes a cylindrical air passage portion 52 extending vertically, a cylindrical burner block 53 extending downward from the lower end of the air passage portion 52, and a plurality of turning vanes 54 provided in the burner block 53. As shown by arrows in fig. 2A and 2B, the air passage portion 52 circulates combustion air supplied from an air supply device (not shown) therein. A cylindrical burner block 53 is attached to a lower portion of the air passage portion 52, an upper portion of an inner peripheral surface of the burner block 53 extends substantially in the vertical direction, and a lower portion of the inner peripheral surface is formed so as to expand in diameter as it advances toward the furnace center side. That is, the lower portion of the burner block 53 is a hollow portion having a truncated conical shape. The plurality of turning vanes 54 are interposed between the gas distribution pipe 50 and the outer peripheral surface of the oil supply pipe 47, and are arranged at equal intervals in the circumferential direction of the oil supply pipe 47.

As shown in fig. 2A and 2B, pilot burner 42 extends in parallel with oil supply pipe 47 of main burner 41 in the vicinity of main burner 41, and is disposed so that the lower end thereof is located above the lower ends of oil supply pipe 47 and gas distribution pipe 50. As shown in fig. 4, the pilot burner 42 includes an oil supply pipe 55 extending in the vertical direction and through which oil flows, a continuous discharge type igniter (first ignition device) 56 extending substantially in parallel with the oil supply pipe 55, and a pilot burner body 57 provided so as to cover the oil supply pipe 55 and the continuous discharge type igniter 56. The oil supply pipe 55 allows oil supplied from an oil supply pump (not shown) to flow therethrough. Further, a tip 58 is provided at the lower end of the oil supply pipe 55, and the oil passing through the tip 58 is sprayed. The continuous discharge type igniter 56 is connected to an igniter cable 59, and is continuously discharged by electricity from the igniter cable 59. The lower end portion of the continuous discharge type igniter 56 is bent so as to be disposed vertically below the lower end of the oil supply pipe 55. That is, the oil sprayed from the oil supply pipe 55 is discharged from the lower end portion of the continuous discharge type igniter 56, whereby the pilot burner 42 is ignited. A flame is formed downward from the pilot burner 42. The flame is formed such that the lower end of the flame is located below the lower ends of the oil supply pipe 47 and the gas distribution pipe 50. That is, the oil or gas discharged from the oil supply pipe 47 or the gas distribution pipe 50 is ignited by the formed flame.

As shown in fig. 2A and 2B, the intermittent discharge type igniter 43 is disposed in the vicinity of the main burner 41 so as to extend in the vertical direction and be inclined so that the lower side approaches the main burner 41. The lower end portion of the intermittent discharge type igniter 43 is intermittently discharged by electricity. The intermittent discharge type igniter 43 is supported to be movable up and down by a predetermined distance. At the time of ignition, as shown in fig. 2A, the lower end portion of the intermittent discharge type igniter 43 is disposed below the lower ends of the oil supply pipe 47 and the gas distribution pipe 50. As a result, the lower end portion of the intermittent discharge type igniter 43 is discharged to the oil or gas sprayed from the oil supply pipe 47 or the gas distribution pipe 50, and ignition is performed. After ignition, as shown in fig. 2B, the lower end is pulled upward so as to be positioned above the lower ends of the oil supply pipe 47 and the gas distribution pipe 50. By pulling up the igniter after ignition in this way, the lower end of the intermittent discharge type igniter 43 is prevented from being damaged by the flame of the main burner 41.

The frequency of sparks emitted by the intermittent discharge type igniter 43 at the time of ignition is higher than that of the continuous discharge type igniter 56 that ignites the pilot burner 42. Specifically, the intermittent discharge type igniter 43 discharges at a voltage of about 1500V, and intermittently emits sparks until the ignition of the main burner 41 is completed, and continuously emits sparks 20 times for 1 second until the ignition is completed. The continuous discharge type igniter 56 discharges at a voltage of approximately 10000V, and maintains an ignition state until the ignition of the pilot burner 42 is completed. That is, the number of sparks emitted from the continuous discharge igniter 56 is only one.

The intermittent discharge type igniter 43 ignites the main burner 41 by directly spraying the oil sprayed from the oil supply pipe 47 of the main burner 41 or the gas sprayed from the gas distribution pipe 50 with the spark discharged from the intermittent discharge type igniter 43. On the other hand, ignition of the main burner 41 by the pilot burner 42 is performed by the flame of the pilot burner 42 ignited by the discharge of the continuous discharge type igniter 56. That is, the continuous discharge type igniter 56 indirectly ignites the main burner 41 via the flame of the pilot burner 42. Specifically, the continuous discharge type igniter 56 requires many steps such as the following for igniting the main burner 41: the oil supply device that feeds oil to the oil supply pipe 55 is driven, the pilot burner 42 is ignited by the continuous discharge type igniter 56 after the oil is made to flow through the oil supply pipe 55, and the ignition to the main burner 41 is performed after the ignition of the pilot burner 42 is confirmed. Therefore, the indirect ignition of the main burner 41 by the continuous discharge igniter 56 takes a longer time than the direct ignition of the main burner 41 by the intermittent discharge igniter 43.

The control device 6 includes: a target pressure reaching time calculation unit that calculates a time until the steam pressure in the steam drum 21 reaches a target steam pressure Pb 2; a predetermined pressure reaching time calculation unit that calculates a time until the pressure in the LNG tank 3 reaches a predetermined pressure Pset; an ignition timing calculation unit that calculates an ignition timing Ts for the main burner 41 so that a vapor pressure in the vapor drum 21 becomes a target vapor pressure Pb2 when the pressure in the LNG tank 3 becomes a predetermined pressure Pset; and ignition control means for igniting the main burner 41 at the ignition timing Ts calculated by the ignition timing calculation unit and starting the pressure increase of the steam pressure in the steam drum 21.

The controller 6 is configured by, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a computer-readable storage medium, and the like. Further, as an example, a series of processes for realizing various functions are stored in a storage medium or the like in the form of a program, and the CPU reads the program from a RAM or the like and executes processing and arithmetic processing of information, thereby realizing various functions. The program may be installed in advance in a ROM or other storage medium, provided in a state of being stored in a computer-readable storage medium, distributed via a wired or wireless communication mechanism, or the like. The computer-readable storage medium refers to a magnetic disk, an optical magnetic disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like.

The target pressure reaching time calculating unit calculates a target pressure reaching time Tr, which is a time until the steam pressure Pb1 in the steam drum reaches the target steam pressure Pb2, based on the steam pressure Pb1 in the steam drum 21 obtained by the drum internal pressure gauge 24 and the target steam pressure Pb2 in the steam drum 21, which is the steam pressure at which the combustion of the boil-off gas can be performed in the boiler 4.

Specifically, first, a graph showing the time until the steam pressure stored in the steam drum 21 of the control device 6 reaches a predetermined steam pressure from a state of 0bar is read (see fig. 5). Next, using this graph, a time Tb2 until the target steam pressure Pb2 is reached and a time Tb1 until the steam pressure Pb1 in the steam drum 21 is reached, which are obtained by the drum inside pressure gauge 24, are obtained. Then, the time Tb1 until the steam pressure Pb1 in the steam drum 21 obtained by the drum inside pressure gauge 24 is subtracted from the time Tb2 until the target steam pressure Pb2 is reached, and the target pressure reaching time Tr is calculated.

Specifically, in the present embodiment, the target steam pressure Pb2 is set to 16 bar. Therefore, time Tb2 taken until target steam pressure Pb2 becomes 2.5 h. At this time, when the steam pressure Pb1 in the steam drum 21 obtained by the drum internal pressure gauge 24 is 3bar, the time Tb1 until the steam pressure Pb1 becomes 1.8h, and therefore 2.5(Tb2) -1.8(Tb1) are calculated, and the target pressure reaching time Tr is calculated to be 0.7 h.

This control is an example, and the method of calculating the target pressure reaching time Tr is not limited to this method, as long as it is based on the steam pressure Pb1 and the target steam pressure Pb2 obtained by the boiler inside pressure gauge 24. For example, other graphs may be used as the graph showing the time until the steam pressure in the steam drum reaches a predetermined steam pressure from a state of 0 bar.

As shown in fig. 6, the predetermined pressure reaching time calculation unit calculates a predetermined pressure reaching time Tpset, which is a time until the pressure in the LNG tank 3 reaches the predetermined pressure Pset, based on the pressure in the LNG tank 3 detected by the in-tank pressure gauge 20 and the predetermined pressure Pset in the LNG tank 3, which is the pressure at which the boil-off gas is supplied to the LNG tank 3. The predetermined pressure Pset is, for example, a threshold pressure that is smaller than a pressure at which the fuel tank may be damaged by a predetermined value. In the present embodiment, 10kPa is set.

Specifically, when the pressure in the LNG tank 3 starts to rise from the tank pressure gauge 20, this information is acquired. Then, after 1 hour, the pressure P1 in the LNG tank 3 is again obtained from the tank pressure gauge 20. The pressure increase rate Pt in the LNG tank 3 per hour is set to P1. Next, the predetermined pressure reaching time Tpset is calculated by dividing the predetermined pressure Pset by the pressure increase rate Pt.

Specifically, when the pressure in the LNG tank 3 rises slowly and Pt is 0.5 (Pt 1 shown in fig. 6), the predetermined pressure Pset is divided by 0.5, and the predetermined pressure reaching time Tpset is calculated as 20h (T1 shown in fig. 6). When the pressure increase is rapid and Pt is 0.75 (Pt 2 shown in fig. 6), the predetermined pressure Pset is divided by 0.75, and the predetermined pressure reaching time Tpset is calculated as 15h (T2 shown in fig. 6).

This control is an example, and the method of calculating the predetermined pressure reaching time Tpset is not limited to this method as long as it is based on the steam pressure Pb1 in the steam drum 21 and the target steam pressure Pb2 in the steam drum 21. For example, the interval between the acquisition of the pressure in the LNG tank 3 may be shorter than 1 hour or longer than 1 hour.

The ignition timing calculation unit calculates the ignition timing Ts so that the vapor pressure in the steam drum 21 becomes the target vapor pressure Pb2 when the pressure in the LNG tank 3 becomes the predetermined pressure Pset, based on the target pressure attainment time Tr in the steam drum 21 calculated by the target pressure attainment time calculation unit and the predetermined pressure attainment time Tpset in the LNG tank 3 calculated by the predetermined pressure attainment time calculation unit. The ignition timing Ts is a time from the present time to the start of the pressure increase of the steam drum 21 of the boiler 4. That is, the boosting is started after Tsh from the current time.

Specifically, the target pressure reaching time Tr in the steam drum 21 is calculated by subtracting the predetermined pressure reaching time Tpset in the LNG tank 3. For example, when the predetermined pressure reaching time Tpset is 15h and the target pressure reaching time Tr is 0.7h, the ignition timing Ts is 14.3 h.

The ignition control means compares a time T from the current time to a predetermined pressure reaching time Tpset with an ignition timing Ts, and when Ts reaches T, sends a signal to the continuous discharge type igniter 56 or the like to ignite the main burner 41 by the pilot burner 42. Then, the pressure increase of the steam pressure of the steam drum 21 is started.

Next, the operation of the present embodiment will be described with reference to fig. 1, 2A, and 2B.

First, a case where the combustion process is performed on the evaporation gas (evaporation gas processing mode) will be described. When steam is not generated, the boiler 4 performs a warm-up operation by circulating steam through the heating coil 61 in the water drum 22 so that the pressure in the steam drum 21 is maintained at about 3 bar. When the in-tank pressure gauge 20 detects a pressure rise in the LNG tank, a signal is sent from the in-tank pressure gauge 20 to the cargo tank control device 40. Upon receiving a signal from the in-tank pressure gauge 20, the tank control device 40 sends a signal to start the boil-off gas processing mode to the control device 6. When receiving a signal from the tank control device 40, the control device 6 starts the boil-off gas processing mode. When the evaporated gas treatment mode is started, the control device 6 performs the above control to calculate the ignition timing Ts. The time T from the current time to the time Tpset at which the predetermined pressure reaches the time Tpset is compared with the ignition timing Ts, and when Ts is greater than T, the ignition control mechanism transmits a signal to the pilot burner 42.

The pilot burner 42 that receives the signal drives an oil supply device that supplies oil to the oil supply pipe 55, ejects the oil from the oil supply pipe 55, and drives the continuous discharge type igniter 56 to start discharge. In this way, the pilot burner 42 is ignited to form a flame. When the pilot burner 42 confirms that a flame is formed, the control unit drives the oil supply device that supplies oil to the oil supply pipe 47 by the main burner 41, and ejects oil from the oil supply pipe 47. The injected oil is ignited by the flame of the pilot burner 42, and thereby the main burner 41 forms a flame. When ignition of the main burner 41 is confirmed, supply of oil to the pilot burner 42 is stopped, and the pilot burner 42 is extinguished. Thus, the pressure increase of the boiler 4 is started, and the pressure in the boiler 4 is increased (pressure increasing step). When the flame is formed by the main burner 41, the evaporated gas may be used as fuel instead of oil. In this case, instead of discharging oil from the oil supply pipe 47, the evaporation gas is discharged from the gas distribution pipe 50 and ignited by the flame of the pilot burner 42.

When the pressure of the boiler 4 is increased to the target steam pressure Pb2, i.e., 16bar, the supply of oil to the main burner 41 is stopped, the main burner 41 is temporarily turned off, and the boiler 4 is in a standby state for performing combustion processing of the evaporated gas. After a signal indicating the amount of boil-off gas to be processed (for example, 1200kg/h) is transmitted from the cargo tank control device 40 to the control device 6, the boil-off gas flows from the LNG tank 3 into the gas supply chamber 49 through the boil-off gas supply pipe 17. The evaporation gas flowing into the gas supply chamber 49 is distributed to 5 gas distribution pipes 50, and is ejected from the lower ends of the gas distribution pipes 50. At this time, the intermittent discharge type igniter 43 is moved so that the lower end thereof is located below the lower end of the gas distribution pipe 50 substantially simultaneously (see fig. 2A). When the movement is completed, the intermittent discharge type igniter 43 intermittently discharges the gas and ignites the evaporated gas discharged from the gas distribution pipe 50. Thereby, the main burner 41 forms a flame. When ignition of the main burner 41 is confirmed, the intermittent discharge type igniter 43 stops discharging and moves so that the lower end thereof is positioned above the lower end of the gas distribution pipe 50 (see fig. 2B). Steam is generated using combustion gas generated by the flame of the main burner 41. In this way, the boiler 4 generates steam while performing combustion processing on the evaporated gas (combustion process).

Next, when steam is generated in the boiler 4 (normal mode) outside the evaporated gas treatment mode, the main burner 41 is ignited by the pilot burner 42, and steam is generated in the boiler 4. When the boiler 4 is stopped, steam is passed through the heating coil 61 in the water drum 22 to perform the warm-up operation.

According to the present embodiment, the following operational effects are exhibited.

In the present embodiment, the boil-off gas generated in the LNG tank 3 is supplied to the boiler 4. This enables the boil-off gas generated in the LNG tank 3 to be burned in the boiler 4. Therefore, the evaporated gas can be treated without providing a special device (for example, a gcu (gas combustion unit) or the like) for burning the evaporated gas, and the steam can be generated by using the energy of the evaporated gas. The generated steam is used for power generation in the power generation turbine 26, steam-using facilities, and the like, and therefore energy efficiency of the entire LNG carrier 2 can be improved.

The burner 23 includes a continuous discharge igniter 56 and an intermittent discharge igniter 43 which emits sparks at a higher frequency than the continuous discharge igniter 56. Since the intermittent discharge type igniter 43 directly ignites the main burner 41, ignition can be performed in a shorter time than in a case where the main burner 41 is indirectly ignited by the pilot burner 42 having the continuous discharge type igniter 56.

On the other hand, since the frequency of sparks generated by the intermittent discharge type igniter 43 at the time of ignition is higher than that of the continuous discharge type igniter 56, the load at the time of ignition is large, and the spark is more likely to be damaged than the continuous discharge type igniter 56. Since the intermittent discharge type igniter 43 has a high frequency of generating sparks at the time of one ignition, it is more easily consumed than the continuous discharge type igniter 56 which performs only one spark at the time of one ignition. Further, since the frequency of sparks generated at the time of ignition of the continuous discharge igniter 56 is lower than that of the intermittent discharge igniter 43, the spark is less likely to be damaged and consumed than the intermittent discharge igniter 43. However, since the ignition of the main burner 41 by the continuous discharge type igniter 56 is indirect ignition requiring many steps such as the ignition of the pilot burner 42 by the continuous discharge type igniter 56, a longer time is required until the ignition than the direct ignition by the intermittent discharge type igniter 43.

In this way, the burner 23 is provided with ignition means having different characteristics. Therefore, by using the ignition devices having different characteristics according to the conditions in the boiler 4 and the LNG tank 3, the boil-off gas can be appropriately combusted to generate steam, and the ignition devices can be provided with redundancy to extend the product life.

If boil-off gas is generated in the LNG tank 3 and the pressure in the LNG tank 3 becomes high, the LNG tank 3 may be damaged. Therefore, when the pressure in the LNG tank 3 is reduced by performing the combustion process on the boil-off gas, if the pressure in the LNG tank 3 becomes the predetermined pressure Pset that is a threshold pressure that is smaller than the pressure at which the LNG tank 3 may be damaged by a predetermined value, the boil-off gas needs to be rapidly combusted. Therefore, when the evaporated gas is subjected to combustion treatment, it is preferable that the time until ignition of the main burner 41 is short. In the present embodiment, the intermittent discharge type igniter 43 is used when the evaporation gas is burned. Since the intermittent discharge type igniter 43 can be ignited in a shorter time than the pilot burner 42 using the continuous discharge type igniter 56, the evaporation gas can be rapidly burned. Therefore, the boiler 4 can appropriately maintain the pressure in the LNG tank 3 at or below the predetermined pressure Pset by performing the combustion process on the boil-off gas.

When the boil-off gas is burned by the boiler 4 in a state where the steam pressure in the steam drum 21 is low, there is a possibility that the boiler 4 becomes overloaded. Further, since the boiler 4 becomes overloaded, the amount of the combustion processing performed on the boil-off gas in the boiler 4 is limited, and there is a possibility that the combustion processing cannot be performed on a desired amount of the boil-off gas. Therefore, when the steam pressure in the steam drum 21 is insufficient when the boil-off gas is burned by the boiler 4, it is necessary to increase the steam pressure in the steam drum 21. In such a case, there is no need to ignite the main burner 41 particularly quickly. In the present embodiment, the pilot burner 42 using the continuous discharge type igniter 56 is used for increasing the pressure in the steam drum 21. Thus, the intermittent discharge type igniter 43, which is more likely to be damaged than the continuous discharge type igniter 56, is not used when the steam pressure in the steam drum 21 is increased. Therefore, the frequency of use of the intermittent discharge type igniter 43 can be reduced, and the product life of the intermittent discharge type igniter 43 can be extended. Further, as described above, when the pressure of the steam in the steam drum 21 is increased, there is no need to ignite the main burner 41 particularly quickly, and therefore, there is no problem even if ignition is performed by the pilot burner 42 using the continuous discharge type igniter 56 having a longer time until ignition than the intermittent discharge type igniter 43.

When the pressure in the LNG tank 3 becomes the predetermined pressure Pset at which the boil-off gas is supplied to the boiler 4, the main burner 41 is ignited so that the steam pressure in the steam drum 21 becomes the target steam pressure Pb 2. Therefore, when the boil-off gas is burned by the boiler 4, the steam pressure in the steam drum 21 can be made a steam pressure sufficient to burn the boil-off gas, so that the boiler 4 can be prevented from being overloaded and the boil-off gas can be burned appropriately. Further, when the pressure in the LNG tank 3 reaches the predetermined pressure Pset, the vapor pressure in the vapor drum 21 is brought into a state of the target vapor pressure Pb2, so that the boil-off gas can be quickly supplied to the boiler 4 and burned, thereby reducing the pressure in the LNG tank 3.

Further, when the pressure in the LNG tank 3 reaches a predetermined pressure, the steam pressure in the steam drum 21 is raised to a target steam pressure Pb2, so that it is not necessary to maintain the steam pressure in the steam drum 21 at a high pressure at all times in order to combust the boil-off gas. Therefore, the energy consumption of the boiler 4 can be reduced.

The present invention is not limited to the inventions of the above embodiments, and can be modified as appropriate within a scope not departing from the gist thereof. For example, in the above-described embodiment, the example in which the vaporized gas is ignited by the intermittent discharge type igniter 43 has been described, but the ignition may be performed by the pilot burner 42 when the intermittent discharge type igniter 43 fails or the like. In addition, when the pilot burner 42 fails, the main burner may be ignited by the intermittent discharge type igniter 43 to increase the pressure of the steam drum 21 of the boiler 4. With such a configuration, the ignition device of the main burner 41 can be made redundant.

In addition, when the generation of steam in the economizer 5 is insufficient, the boiler 4 may be operated at a low load to supplement the steam necessary for the LNG carrier 2. In this configuration, since a low-load auxiliary boiler (such as a port boiler) normally mounted on the LNG carrier 2 can be omitted from being mounted on the LNG carrier 2, the space inside the LNG carrier 2 can be saved.

Description of the symbols

3 LNG tank (Fuel tank)

4 boiler

6 control device

17 boil-off gas supply pipe

20 tank inner pressure gauge (tank pressure detection mechanism)

21 steam boiler barrel

23 burner

24 boiler barrel inner pressure gauge (boiler barrel pressure detecting device)

41 main burner

42 pilot burner

43 intermittent discharge type igniter (second ignition device)

47 oil supply pipe

50 gas distribution pipe

55 oil supply pipe

56 continuous discharge type igniter (first ignition device)

Claims

1. A boiler to which boil-off gas generated in a fuel tank storing fuel is supplied, the boiler comprising:

a burner that burns the boil-off gas; and

a steam drum for accommodating steam inside,

the burner has a first ignition device and a second ignition device, the second ignition device emitting sparks at a higher frequency when ignited than the first ignition device,

the second ignition device is used when the boil-off gas is caused to start combustion in the burner,

the first ignition device is used when starting the pressure increase of the steam pressure in the steam drum caused by the combustion of the burner.

2. A boiler system comprising the boiler according to claim 1, the boiler system comprising:

a drum pressure detection mechanism that detects the steam pressure within the steam drum;

a tank pressure detection mechanism that detects a pressure in the fuel tank;

a target pressure reaching time calculating unit that calculates a time until the steam pressure in the steam drum reaches the target steam pressure, based on the steam pressure in the steam drum detected by the drum pressure detecting means and the target steam pressure in the steam drum that is the steam pressure at which the combustion of the evaporation gas is performed;

a predetermined pressure reaching time calculation unit that calculates a time until the pressure in the fuel tank reaches the predetermined pressure, based on the pressure in the fuel tank detected by the tank pressure detection means and the predetermined pressure in the fuel tank that is the pressure at which the boil-off gas is supplied to the fuel tank;

an ignition timing calculation unit that calculates an ignition timing such that the vapor pressure in the steam boiler drum becomes the target vapor pressure when the pressure in the fuel tank becomes the predetermined pressure, based on the target pressure reaching time calculated by the target pressure reaching time calculation unit and the predetermined pressure reaching time calculated by the predetermined pressure reaching time calculation unit; and

and ignition control means for igniting the burner by the first ignition device at the ignition timing calculated by the ignition timing calculation unit to start boosting of the steam pressure in the steam drum.

3. An operation method of a boiler supplied with boil-off gas generated in a fuel tank storing fuel, the operation method comprising:

a pressure raising step of igniting a burner provided in the boiler by a first ignition device to raise a pressure of steam in a steam drum by combustion of the burner; and

and a combustion step of igniting the burner by a second ignition device after the pressure increasing step, and performing combustion by the evaporated gas in the burner, wherein a frequency of sparks generated by the second ignition device at the time of ignition is higher than a frequency of sparks generated by the first ignition device at the time of ignition.