JP3670528B2 - Boil-off gas processing method and apparatus for low-temperature liquefied gas - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a boil-off gas treatment method and apparatus for low-temperature liquefied gas for extracting and pressurizing boil-off gas (hereinafter referred to as BOG) generated in a tank of low-temperature liquefied gas such as LNG and supplying it to a customer. It is.
[0002]
[Prior art]
Conventionally, as a low-temperature liquefied gas boil-off gas processing method as described above, for example, a processing method disclosed in Japanese Patent Laid-Open No. 3-92700 is generally known.
[0003]
In the process disclosed in this publication, the BOG generated in the tank is specially heated by preheating the BOG before reaching the compressor in the process of pressurizing and supplying the BOG to the supply pressure to the customer. The BOG can be pressurized using a room-temperature type screw compressor without using a cryogenic compressor having a structure. Specifically, a suction gas heater is provided in the processing line, and heat exchange is performed between the low-temperature BOG before reaching the compressor in the heater and the high-temperature cooling water discharged from the compressor. The BOG is heated.
[0004]
[Problems to be solved by the invention]
However, the conventional boil-off gas processing method as described above has the following problems.
[0005]
First, in order to exchange heat between the cooling water circulation system of the compressor and the BOG supply system, the load fluctuation of the compressor (that is, the fluctuation of the BOG flow rate) and the fluctuation of the cooling water flow rate are affected by the heating performance of the BOG. Affects. That is, the balance of heat exchange is lost due to the flow rate balance between the cooling water and the BOG being lost, and as a result, the heating of the BOG may be insufficient. For this reason, in order to maintain the balance of heat exchange, dedicated equipment and control for maintaining the flow rate balance are required, which is one of the causes for increasing the size and complexity of the processing equipment and the control system.
[0006]
In addition, a suction gas heater and a pump for circulating cooling water are introduced to enable the use of a normal screw compressor (ie, for normal temperature operation) as a compressor. It is conceivable that low-temperature BOG that is insufficiently heated is introduced into the compressor as it is due to insufficient water flow or the like, and as a result, the compressor becomes inoperable. Therefore, in the past, in preparation for such troubles, a cooling water circulation pump and a suction gas heater spare machine have been incorporated in the processing line in advance, which also causes an increase in the size of the processing equipment. Yes.
[0007]
Furthermore, since it takes a considerable amount of time for the cooling water temperature to rise sufficiently after the compressor is started, preheating the cooling water using a dedicated start-up heater that uses steam as a heat source in order to reduce the time required. This also contributes to an increase in the size of the processing equipment.
[0008]
The present invention has been made to solve the above-described problems, and provides a low-temperature liquefied gas boil-off gas processing method and apparatus that can improve the reliability of the processing equipment while simplifying the processing equipment. The purpose is to do.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the boil-off gas processing method for low-temperature liquefied gas according to the present invention uses boil-off gas extracted from a tank storing low-temperature liquefied gas such as liquefied natural gas to supply pressure to a customer by a compressor. in BOG processing method of the low-temperature liquefied gas pressurized to above into the compressor is sucked and BOG discharged into the discharge-side passage through heat exchanger direct heat exchange from Rubo Iruofugasu the compressor through the suction side passage In this way, the boil-off gas before being sucked into the compressor is heated , and when the compressor is started, the air in the suction side passage is compressed and discharged before the boil-off gas is sucked. The air is preheated by returning air to the suction side passage after passing through the heat exchanger (claim 1).
[0010]
In this way, if direct heat exchange is performed between the boil-off gas discharged from the compressor and the boil-off gas before being sucked into the compressor, the gas flow rate before being sucked into the compressor and the compressor Since the flow rate of the discharged gas is linked, the balance of heat exchange is naturally maintained even if the load fluctuates in the compressor. In addition, prior to the intake of the boil-off gas, the heat exchanger can be quickly preheated using the exhaust heat of the compressor. In the description of claim 1, “directly” means that no heat medium is interposed.
[0011]
In order to solve the above problems, the boil-off gas processing apparatus for low-temperature liquefied gas of the present invention has a boil-off gas processing line from a tank for storing low-temperature liquefied gas such as liquefied natural gas to a customer through a compressor. A low-temperature liquefied gas boil-off gas processing device that pressurizes the boil-off gas extracted from the tank to the supply pressure to the customer by the compressor, and distributes the part from the tank to the compressor in the processing line A heat exchanger that directly exchanges heat between the boil-off gas that flows and the boil-off gas that circulates from the compressor to the customer, and a portion of the processing line that extends from the tank to the heat exchanger and a heat exchanger a bypass line which bypasses the pos- sibly portion demander from the state of connecting each said processing line to said tank and demander, the processing And a switching means for switching the line to a state of forming a circulation path for shutting off the line from the tank and the demand destination and cooperating with the bypass line to circulate the discharge fluid from the compressor through the heat exchanger. and those which (claim 2).
[0012]
According to this apparatus, the boil-off gas extracted from the tank is introduced into the compressor through the heat exchanger. At this time, while passing through the heat exchanger, heat is exchanged with the boil-off gas discharged from the compressor and heated to a predetermined temperature. In this way, if direct heat exchange is performed between the boil-off gas discharged from the compressor and the boil-off gas before being sucked into the compressor, the gas flow rate before being sucked into the compressor and the compressor Since the flow rate of the discharged gas is linked, the balance of heat exchange is naturally maintained even if the load fluctuates in the compressor. Furthermore, according to this configuration, when the compressor is started by starting the compressor and operating the compressor, high-temperature compressed air circulates in the circulation path, thereby heating the heat exchanger. . By circulating the discharge air from the compressor in this way, it becomes possible to quickly preheat the heat exchanger by directly using the exhaust heat of the compressor, and there is no need to provide a special heater or the like.
[0013]
In the configuration of claim 2 Symbol placement, as the compressor in case of providing the oil-cooled screw compressor, downstream of the heat exchanger in the flow direction of the boil-off gas discharged from at least the compressor the cooling oil of the compressor included in the boil-off gas is desirable to be provided with oil separator for separating from the gas (claim 3).
[0014]
In this way, the oil component is likely to condense as the temperature of the boil-off gas decreases through the heat exchanger, so that the cooling oil contained in the boil-off gas is effectively collected and recovered. Is possible.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
[0016]
Figure 1 shows a form of implementation of the BOG processing apparatus according to the present invention. This BOG processing apparatus is an apparatus applied to a receiving base for LNG (liquefied natural gas), for example, and has a tank 10 for storing LNG.
[0017]
The tank 10 is connected to an LNG line L ₁ for taking out LNG. Although not shown, the LNG taken out from the tank 10 through the LNG line L ₁ is, for example, pressurized to a predetermined pressure (for example, 10 kg / cm ² ) by a pump and then branched into a low pressure line and a high pressure line. . Of these, LNG in the low-pressure line is vaporized by a low-pressure vaporizer, and then supplied to a low-pressure customer (for example, a power plant) through a mixing tank or the like. On the other hand, the LNG in the high-pressure line is further pressurized by a pump (for example, after being pressurized to about 70 kg / cm ² ), then vaporized by a high-pressure vaporizer and supplied to a high-pressure customer (for example, a city gas pipeline). It has become so.
[0018]
In addition to the LNG line L ₁ , the tank 10 is connected to a low pressure side BOG line L ₂ (hereinafter referred to as a low pressure side line L ₂ ) for deriving BOG generated in the tank 10. The other end of the low-voltage side line L ₂ is connected to the suction port of the compressor 12 for pressurizing the BOG, in its middle, in order from the tank 10 side, the switch valve 13, heat exchanger 14 In addition, a filter 16 is interposed. Thus, the is sucked into the compressor 12 the BOG generated in the tank 10 through the low-voltage side line L _2, and is configured to heat the BOG in the heat exchanger 14 in the process. The configuration of the heat exchanger 14 will be described in detail later.
[0019]
The compressor 12 is a room temperature type BOG compressor, and in this embodiment, for example, an oil-cooled screw compressor is used.
[0020]
On the other hand, a high-pressure side BOG line L ₃ (hereinafter referred to as a high-pressure side line L ₃ ) is connected to the discharge port of the compressor 12. The other end of the high pressure side line L ₃ is connected to the mixing tank, and an oil separator 18, the heat exchanger 14, and a flow rate adjusting valve 20 are interposed in the middle of the high pressure side line L _3. ing.
[0021]
That is, the low pressure side line L ₂ constitutes the suction side passage of the present invention, the high pressure side line L ₃ constitutes the discharge side passage of the present invention, and the low pressure side line L ₂ and the high pressure side line L ₃ constitute the present invention. The processing line is configured.
[0022]
FIG. 2 shows a specific configuration of the heat exchanger 14.
[0023]
This heat exchanger 14 is a so-called multi-tube heat exchanger. As shown in this figure, the heat exchanger 14 has a hollow container body 14a, and two fluid chambers 30a and 30b (first fluid chamber 30a and second fluid) partitioned by a fixed tube plate 31 therein. Chamber 30b), and two ports 32, 34 and 36, 38 on the inlet side and the outlet side are provided corresponding to the fluid chambers 30a, 30b, respectively. In particular, for the second fluid chamber 30b, the fluid chamber 30b is further divided into two upper and lower unit chambers by the partition plate 42, and the ports 36 and 38 communicate with the upper and lower unit chambers, respectively.
[0024]
In the first fluid chamber 30a, a plurality of U-shaped tubes 44 projecting from the fixed tube plate 31 and communicating with the upper and lower unit chambers of the second fluid chamber 30b are arranged side by side (in FIG. These tubes 44 are supported by the support plate 40, and the labyrinth shape from the port 32 to the port 34 is supported by the support plate 40 in the first fluid chamber 30a. The flow path is formed.
[0025]
The end portion communicating with the opening and closing valve 13 of the low pressure side line L ₂ relative to the inlet side port 32 of the first fluid chamber 30a is also in the filter 36 of the low-voltage side line L ₂ relative to the outlet side port 34 While the communicating end portions are respectively connected, the end portion communicating with the oil separator 18 of the high pressure side line L _{3 with} respect to the inlet side port 16 of the second fluid chamber 30 b is also connected to the high pressure side with respect to the outlet side port 38. End portions communicating with the flow rate control valve 20 of the line L ₃ are respectively connected.
[0026]
That is, the low-temperature BOG before being sucked into the compressor 12 flows through the labyrinth-shaped flow path in the first fluid chamber 30a (indicated by a white arrow in the figure), while the high temperature discharged from the compressor 12 BOG flows through the second fluid chamber 30b and the tube 44 (indicated by broken arrows in the figure), that is, before the BOG flows through the tube 44 before being sucked into the compressor 12. Heat exchange is performed directly between the BOG and the BOG discharged from the compressor 12, whereby the BOG before being sucked into the compressor 12 is heated.
[0027]
In FIG. 1, a return line L _{11 for} collected oil is led out from the oil separator 18, and this return line L ₁₁ is connected to the oil return port of the compressor 12. The return line L ₁₁ is provided with a three-way valve 22, an oil pump 23, and a filter 24 in order from the oil separator 18 side, and a branch line L ₁₂ branches from between the three-way valve 22 and the oil pump 23. This branch line L ₁₂ is connected to the three-way valve 22. A heat exchanger 26 is interposed in the branch line L ₁₂ , and a cooling water supply line L ₁₃ is connected to the heat exchanger 26.
[0028]
The structure of the oil separator 18 which is interposed in the return line L ₁₁ is not limited particularly in the present invention, in those embodiments, the configuration of the oil separator 18, as shown in FIG. 3 is adopted ing.
[0029]
That is, the oil separator 18 has a horizontally long container main body 18a as shown in the figure, and the first oil sump chamber 50 partitioned by the partition plate 53a, the partition plate 53b, and the element 54 in the container main body 18a. The second oil sump chamber 52 partitioned by the above and a labyrinth-shaped passage 56 formed between them. The first oil sump chamber 50 is provided with a BOG inlet-side port 58 and an oil outlet port 62, while the second oil sump chamber 52 is provided with a BOG outlet-side port 60. The end portion of the side line L _{3 on} the compressor 12 side is connected to the oil outlet port 62 and the return line L ₁₁ is connected to the outlet side port 60, and the end portion of the high pressure side line L _{3 on} the heat exchanger 14 side is connected. ing.
[0030]
As a result, when BOG is introduced into the oil separator 18, the oil contained in the BOG adheres to the partition plate 53 b, drops into droplets, and is stored in the first oil sump chamber 50, and is compressed through the return line L _11. 12 is returned. The BOG is led out to the outside through the first oil sump chamber 50, the element 54, and the second oil sump chamber 52, and is guided to the heat exchanger 14.
[0031]
In the configuration as described above, the BOG generated in the tank 10 is extracted to the low-pressure side line L ₂ and sucked into the compressor 12 through the heat exchanger 14 and the filter 16. At this time, for example, −130 ° C. BOG is heated to about −50 ° C. through the heat exchanger 14 and then sucked into the compressor 12.
[0032]
The BOG sucked into the compressor 12 is pressurized to a supply pressure (10 kg / cm ² ) for a low-pressure demand destination, and after oil is removed through the oil separator 18, Sent to the mixing tank. At this time, the 100 ° C. BOG discharged from the compressor 12 is made to be about 25 ° C. through the heat exchanger 14 and then sent to the mixing tank.
[0033]
Incidentally, separated from the BOG in the oil separator 18, the collected oil is returned to the compressor 12 through the return line L _11. At this time, when the operating temperature of the compressor 12 becomes high, the three-way valve 22 is switched and the oil is returned to the compressor ₁₂ through the branch line L12. As a result, heat is exchanged between the oil and the cooling water supplied from the cooling water supply line L ₁₃ in the heat exchanger 26 to cool the oil, and the oil is returned to the compressor 12 to return to the compressor 12. The cooling action is promoted. Although not described specific configuration of the heat exchanger 26 which is interposed in the branch line L ₁₂ and the like, for example, a similar multi-tube heat exchanger as shown in FIG. 2 Used.
[0034]
According to the BOG processing apparatus described above, the BOG before being sucked into the compressor 12 is heated by exchanging heat between the BOGs flowing in the same system (processing line). As with conventional devices that exchange heat between the BOG flowing through the system and the compressor cooling water, the BOG is heated well without providing special equipment to deal with compressor load fluctuations. can do. That is, in the processing line, the flow rate of BOG before being sucked into the compressor 12 and the flow rate of BOG discharged from the compressor 12 are linked, and the flow rate balance of the BOG before and after the compressor is always kept constant. Be drunk. Therefore, even when a load change occurs in the compressor 12, the balance of heat exchange by heat exchange is naturally maintained, and BOG is good without providing dedicated equipment for maintaining the flow rate balance as in the conventional device. Can be heated.
[0035]
Therefore, according to the BOG processing apparatus as described above, a rational configuration is achieved in which the BOG can be satisfactorily heated without providing a dedicated facility for dealing with the load fluctuation of the compressor. Thus, the apparatus configuration can be simplified.
[0036]
In addition, cooling is caused by a trouble in the cooling water circulation system, for example, a failure of the pump for circulating the cooling water, as in the conventional device that heats the BOG by performing heat exchange between the BOG flowing in the independent system and the cooling water. Insufficient flow of water occurs, and as a result, there is no fear that low-temperature BOG that is insufficiently heated will be sucked into the compressor. In this respect, there is also an effect that the reliability of the apparatus is high. Moreover, since there is no influence on the heating performance of the BOG due to troubles in the cooling water circulation system, it is not necessary to provide a spare machine such as a pump for circulating cooling water in preparation for such troubles. Thus, the apparatus configuration can be simplified.
[0037]
Contact name in the BOG processing apparatus, the oil separator 70 is provided between the heat exchanger 14 and the flow regulating valve 20 of the high-pressure side line L _3, heat and closing valve 13 in the low-pressure side line L ₂ A bypass line 28 is provided to connect a portion between the exchanger 14 and a portion between the oil separator 70 and the flow rate adjusting valve 20 in the high pressure side line L _3, and an open / close valve 29 is interposed in the bypass line 28. It is installed. When the on-off valve 13 of the low-pressure side line L ₂ and the flow rate adjustment valve 20 of the high-pressure side line L ₃ are both fully closed, and the on-off valve 29 of the bypass line 28 is fully opened, the low-pressure side line L ₂ , a circulation path is formed by the high-pressure side line L ₃ and the bypass line 28. That is, the switching means of the present invention is constituted by the opening / closing valve 13, the flow rate adjusting valve 20, and the opening / closing valve 29.
[0038]
Further, a line L ₁₄ for deriving the oil collected in the oil separator 70 and a line L ₁₅ for deriving the oil accumulated in the second oil sump chamber 52 of the oil separator 18 (not shown in detail) are provided. These lines L ₁₄ and L ₁₅ are joined and connected to a return line L ₁₆ connected to the compressor 12.
[0039]
In the BOG processing apparatus of the second embodiment configured as described above, the following start heat-up operation for preheating the heat exchanger 14 is performed before entering the normal BOG processing operation. . Specifically, the opening / closing valve 13 of the low pressure side line L ₂ and the flow rate adjustment valve 20 of the high pressure side line L ₃ are both fully closed, while the opening / closing valve 29 of the bypass line 28 is fully opened, as described above. A circulation path is formed. Then, when the compressed air is discharged by starting the compressor 12, the compressed air circulates in the circulation path, and thereby the heat exchanger 14 is heated.
[0040]
Then, after the start-up heat operation, the on-off valve 13 and the flow rate adjusting valve 20 are switched to fully open, and the on-off valve 29 is switched to fully closed, and a normal BOG processing operation is performed.
[0041]
That is, by preheating the heat exchanger 14 by the start-up heat operation as described above and then shifting to the BOG processing operation, the BOG passing through the heat exchanger 14 can be heated satisfactorily even immediately after the start of the BOG processing. It has become.
[0042]
As described above, according to this embodiment, the BOG can be heated well immediately after the start of the process, and thereby the low temperature BOG can be reliably prevented from being sucked into the compressor 12. is there.
[0043]
Moreover, in accordance with the implementation of this, and by utilizing waste heat of the compressor 12 directly by circulating the compressed air discharged from the compressor 12 as described above so as to preheat the heat exchanger 14 Therefore, the heat exchanger 14 can be quickly preheated without providing a special heater or the like as in the conventional apparatus. Therefore, as compared with the conventional apparatus, there is an effect that the apparatus configuration can be further simplified because a special heater is not required.
[0044]
Further, in the apparatus of this embodiment, the two oil separators 18 and 70 are arranged so as to collect oil doubly, so that the oil in the BOG is better removed and collected. There is also an effect that can be done.
[0045]
In particular, the downstream side of the heat exchanger 14 to place the oil separator 70, the BOG temperature through the heat exchanger 14 drops since so as to pass through the oil separator 70, the oil in the oil separator 70 Condensation is promoted and oil is collected well. Therefore, the contained oil that cannot be collected by the oil separator 18 because it is vaporized can be collected well by the oil separator 70 .
[0046]
In the embodiment of each BOG processing apparatus described above, a multi-tubular heat exchanger is used as the heat exchanger 14, but the type of the heat exchanger 14 is not limited to this, and for example, a serpentine type Various heat exchangers such as a heat exchanger, a double tube heat exchanger, a vanette heat exchanger, and a jacket heat exchanger can be applied.
[0047]
Moreover, it is not necessary to provide an oil separator 70 between the heat exchanger 14 and the flow regulating valve 20 in the high pressure side line L ₃ servants Always, when only the oil separator 18 can be sufficiently collected oil, This may be omitted. The specific configuration of the oil separators 18 and 70 may be any configuration as long as the oil contained in the BOG can be collected satisfactorily. The configuration described in the embodiment (only the oil separator 18 will be described). Is not limited to).
[0048]
In addition, the specific configurations of the other low-pressure side line L ₂ and high-pressure side line L ₃ are not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention. Needless to say.
[0049]
【The invention's effect】
As described above, in the boil-off gas processing in which the boil-off gas extracted from the tank is pressurized to the supply pressure to the customer by the compressor, the present invention discharges the boil-off gas before being sucked into the compressor and the compressor. By directly exchanging heat with the pressurized boil-off gas and heating the former boil-off gas, the balance of heat exchange by heat exchange is naturally maintained even when load fluctuations occur in the compressor. Therefore, there is no need to provide a dedicated facility or the like for correcting an imbalance in heat transfer due to load fluctuations of the compressor as in the conventional apparatus. Therefore, there is an effect that the apparatus configuration can be simplified as compared with the conventional apparatus while the boil-off gas is heated well.
[0050]
Further, unlike the conventional apparatus, the heating performance of the boil-off gas is not deteriorated due to a trouble in the cooling water circulation system of the compressor, and there is an effect that the reliability of the apparatus is high in this respect.
[Brief description of the drawings]
Is a circuit diagram showing an embodiment of implementation of BOG processing apparatus according to the present invention; FIG.
FIG. 2 is a schematic cross-sectional view showing a configuration of a heat exchanger.
FIG. 3 is a schematic cross-sectional view showing a configuration of an oil separator .
[Explanation of symbols]
10 Tank 12 Compressor 14 Heat Exchanger 18 Oil Separator (Oil Separator)
20 Flow control valve 22 Three-way valve 23 Oil pump 24 Filter 26 Heat exchanger L ₁ LNG line L ₂ Low pressure side BOG line L ₃ High pressure side BOG line L ₁₁ Return line L ₁₂ Branch line L ₁₃ Cooling water supply line

Claims (3)

In the boil-off gas processing method of low-temperature liquefied gas, the boil-off gas extracted from the tank storing low-temperature liquefied gas such as liquefied natural gas is pressurized to the supply pressure to the customer by the compressor.
BOG before inhalation into the compressor by using a heat exchanger and a boil-off gas discharged into the discharge-side passage from the to the compressor is sucked Rubo Iruofugasu a compressor to direct heat exchange through the suction side passage When the compressor is started, the air in the suction side passage is compressed and discharged before the boil-off gas is sucked, and the compressed air passes through the heat exchanger and is then discharged to the discharge side. A boil-off gas treatment method for low-temperature liquefied gas, wherein the heat exchanger is preheated by returning from the passage to the suction side passage . It has a boil-off gas treatment line from a tank that stores low-temperature liquefied gas such as liquefied natural gas to the customer through the compressor, and the boil-off gas extracted from the tank is supplied to the customer by the compressor. In boil-off gas processing equipment for low-temperature liquefied gas that is pressurized to
A heat exchanger that directly exchanges heat between the boil-off gas that circulates from the tank to the compressor and the boil-off gas that circulates from the compressor to the customer in the processing line, and the processing line Among them, a bypass line that bypasses a portion from the tank to the heat exchanger and a portion from the heat exchanger to the customer, a state in which the processing line is connected to the tank and the customer, and the processing line to the tank And a switching means for switching to a state of forming a circulation path for shutting off from the customer and for circulating the discharge fluid from the compressor through the heat exchanger in cooperation with the bypass line. A low-temperature liquefied gas boil-off gas processing apparatus. An oil-cooled compressor is provided as the compressor, and at least downstream of the heat exchanger in the flow direction of the boil-off gas discharged from the compressor, the cooling oil of the compressor contained in the boil-off gas is the same gas. that it comprises a oil separator for separating from the claim 2 Symbol placement BOG processing apparatus low-temperature liquefied gas, characterized in.

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