How to switch BOG compressor

Abstract

To provide a switching method for BOG compressors capable of shortening a switching work time of the BOG compressors.SOLUTION: The present invention relates to a switching method for BOG compressors 1 for discharging, in a case where one of a plurality of BOG compressors 1 connected in parallel to an LNG tank 3 is defined as A machine 1A, another of the plurality of BOG compressors 1 connected in parallel to the LNG tank 3 is defined as a B machine 1B and BOG in the LNG tank 3 is being discharged by the A machine 1A, the BOG in the LNG tank 3 by the B machine 1B in place of the A machine 1A. In the switching method for the BOG compressors 1, the B machine 1B is activated while the A machine 1A is being actuated. Next, after a capacity adjustment of the B machine 1B becomes 100%, a capacity adjustment of the A machine 1A is decreased gradually to 25%. Next, the A machine 1A is stopped after the lapse of a predetermined time from the activation of the B machine 1B.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a BOG compressor switching method for switching between a plurality of BOG compressors connected to an LNG tank. [Background technology]

[0002] As is conventionally known, LNG (liquefied natural gas) transported from a production site by an LNG ship is transported while being kept at an extremely low temperature of -162°C or less, and then is received into an LNG tank through piping, during which a large amount of BOG (boil-off gas) is generated. Furthermore, the LNG stored in the LNG tank generates BOG due to the influence of the external environment. The BOG in the LNG tank is then discharged from the LNG tank by a BOG compressor, mixed with natural gas vaporized in an LNG vaporizer, and used as fuel for gas turbines, etc.

[0003] A plurality of BOG compressors are connected to a plurality of LNG tanks. During maintenance of an operating BOG compressor (e.g., Unit A), the compressor is switched to another BOG compressor (e.g., Unit B) that is not in operation, and the BOG in the LNG tank is discharged by the switched BOG compressor (e.g., Unit B) (see Patent Document 1).

[0004] Fig. 3 is a diagram showing a conventional BOG compressor switching operation process (switching operation process from Unit A to Unit B). As shown in Fig. 3, first, an operator checks with a monitor that the pressure in the LNG tank is within the normal control range (for example, 6.86 kPa) (first step: S101).

[0005] Next, the operator manually adjusts the discharge capacity (volume of discharged gas) of units A, C, and D among the multiple BOG compressors (units A to D). This will exclude the number control of Units A, C, and D (number control will be turned off). (Second step: S102).

[0006] Next, the worker manually adjusts Unit A and increases the pressure in the LNG tank by reducing the amount of BOG in the LNG tank being discharged by Unit A (e.g., by reducing the BOG discharge capacity to 25%) (third step: S103). This LNG tank pressure accumulation work is carried out when switching from Unit A to Unit B, while Unit A is in operation (for example, Discharge capacity (BOG discharge capacity) was reduced to 25% and Unit B was operated. Discharge setting capacity This work took into consideration the drop in pressure inside the LNG tank when operating at 100% for 15 minutes (performing predetermined operations when starting Unit B) (work that took into consideration the fact that LNG tanks are vulnerable to negative pressure). For example, it took approximately 10 to 30 minutes to increase the pressure inside the LNG tank from 6.86 kPa to 7.06-7.16 kPa.

[0007] Next, Unit B is manually started (fourth step: S104). When the operator turns on the operation switch of Unit B, Discharge setting capacity 100% from After reaching 0%, about one minute later, the outlet valve of Unit B opens fully and Unit B starts up. After one minute has passed since Unit B started up, Discharge setting capacity 0% from It will be 100%. Then, 15 minutes after the start of Unit B, the lamp indicating that Unit B is ready for adjustment (condition adjustment permission lamp) will light up. Unit B, manual The number of units controlled is excluded upon startup.

[0008] Next, the worker checks that the condition control permission lamp of Unit B is on, and then stops Unit A (fifth step: S105). This will result in a state where only Unit B is operating.

[0009] Next, the worker selects the number control of Unit B and executes the number control. This puts Unit B in a "unit control usable state." (6th step: S106). When a BOG compressor is manually operated, the number control is excluded. Therefore, by selecting (using) the number control of the manually operated BOG compressor, the number control becomes available.

[0010] Next, the worker enables the number control of the stopped machine A (seventh step: S107). This enables the number control of Unit A to be enabled. However, in order for unit control to be in use, the status must be switched to automatic operation, so at this point, unit control for Units A, C, and D is still unavailable.

[0011] Next, the operator checks that the pressure in the LNG tank is being controlled within the normal control range by the monitor (eighth step: S108).

[0012] Next, the worker The status of Units A, C, and D are put into automatic operation. This puts Unit Control Available State into which the status and unit control of all Units A to D are automatically managed by the computer (ninth step: S109).

[0013] As described above, the switchover work from Unit A to Unit B is completed through the first to ninth steps (S101 to S109). Note that, upon completion of the switchover work from Unit A to Unit B, the BOG in the multiple LNG tanks is discharged mainly by Unit B. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] JP 2008-286211 A Summary of the Invention [Problem to be solved by the invention]

[0015] However, the conventional BOG compressor switching method shown in FIG. 3 requires approximately 10 to 30 minutes for the LNG tank pressure accumulation operation and a long time (approximately 25 to 45 minutes) for the compressor switching operation. From the perspective of improving the efficiency of the compressor switching operation, therefore, there was a need to review the BOG compressor switching operation process and shorten the BOG compressor switching operation time.

[0016] Therefore, the present invention provides a BOG compressor switching method that can shorten the time required for switching the BOG compressor. [Means for solving the problem]

[0017] The present invention relates to a method of switching the BOG compressor 1 for discharging the BOG in the LNG tank 3 from Unit B 1B instead of Unit A 1A when one of the BOG compressors 1 connected in parallel to an LNG tank 3 is Unit A 1A and the other of the BOG compressors 1 connected in parallel to the LNG tank 3 is Unit B 1B and the BOG in the LNG tank 3 is being discharged from Unit A 1A. The switching method of the BOG compressor 1 according to the present invention includes the following steps: While the A unit 1A is in operation, the B unit 1B is started. Next, the B-unit 1B Discharge setting capacity After reaching 100%, the A-1A Discharge capacity gradually reduced to 25% Next, from the start of Unit B 1B After the time has elapsed until operation has stabilized, the Unit B status adjustment permission lamp will light up. This will then cause Unit A 1A to be shut down. Effect of the Invention

[0018] The BOG compressor switching method of the present invention eliminates the need for LNG tank pressure accumulation work and reduces the work time required for LNG tank pressure accumulation work, thereby reducing the time required for BOG compressor switching (from Unit A to Unit B). [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a configuration diagram of a BOG treatment facility used to explain a BOG compressor switching method according to the present invention. [Diagram 2] FIG. 2 is a process diagram of the BOG compressor switching method according to the present invention. [Diagram 3] FIG. 1 is a process diagram of a switching method for a BOG compressor according to a conventional example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0021] Fig. 1 is a configuration diagram of a BOG treatment facility 2 used to explain a method for switching a BOG compressor 1 (1A to 1D) according to this embodiment. Fig. 2 is a work flow diagram of the method for switching a BOG compressor 1 (1A to 1D) according to this embodiment.

[0022] (Outline of BOG treatment facility) As shown in FIG. 1, in the BOG treatment equipment 2, LNG (liquefied natural gas) in multiple (six in this embodiment) LNG tanks 3 is pumped out by a pump 4 to a first LNG pipe 5, which is then combined into a single second LNG pipe 6, and the LNG in the second LNG pipe 6 is then supplied to multiple (five in this embodiment) LNG vaporizers 7.

[0023] In addition, in the BOG treatment facility 2, a plurality of (four in this embodiment) BOG compressors 1 (units A to D: 1A to 1D) are connected in parallel to a plurality of LNG tanks 3, and one BOG compressor 1 normally discharges BOG from the plurality of LNG tanks 3. The BOG from each LNG tank 3 is discharged into a first BOG pipe 8 and then collected into a single second BOG pipe 10, and is then supplied by the BOG compressor 1 to a fuel supply pipe 13 via an outlet valve 11 and a third BOG pipe 12. In this embodiment, the units A to D 1A to 1D have the same discharge capacity (amount of discharged gas).

[0024] The natural gas vaporized by the LNG vaporizer 7 is discharged into a fuel supply pipe 13, and then mixed with the BOG sent by the BOG compressor 1 and used as fuel for a gas turbine 14.

[0025] (BOG compressor switching process) Hereinafter, a switching method for the BOG compressor 1 according to this embodiment will be described with reference to FIG.

[0026] As shown in FIG. 2, first, an operator checks with a monitor that the pressure in the LNG tank 3 is within a normal control range (for example, 6.86 kPa) (first step: S1).

[0027] Next, the worker manually controls the status of Units A 1A, C 1C, and D 1D (second step: S2). By manually controlling the status of Units A 1A, C 1C, and D 1D, the number control of Units A 1A, C 1C, and D 1D is excluded (the number control is turned off).

[0028] Next, the worker starts up unit B 1B while unit A 1A is in operation (third step: S3). After starting up Unit B 1B, the worker confirms that Unit B 1B operates according to a predetermined program. In other words, after starting up Unit B 1B, the worker confirms that Unit B 1B operates according to a predetermined program. Discharge setting capacity Confirm that the output voltage of Unit B 1B changes from 100% to 0%, and that approximately one minute after the start-up operation, the outlet valve 11 opens fully and Unit B 1B starts up. In addition, the operator confirms that the output voltage of Unit B 1B changes from 100% to 0%, and that approximately one minute after the start-up operation, the outlet valve 11 opens fully and Unit B 1B starts up. Discharge setting capacity Check that it goes from 0% to 100%.

[0029] Next, the worker Discharge setting capacity After reaching 100%, A-1A Discharge capacity Gradually decrease (step by step from 100% to 75%, 50%, and 25%) (fourth step: S4). Discharge capacity The decrease operation is not limited to being performed stepwise as in this embodiment, but may be performed in a non-stepwise manner. In this way, the switching method of the BOG compressor 1 according to the present embodiment is Discharge capacity By gradually reducing the flow rate, it becomes possible to suppress the fluctuation of the flow rate of BOG flowing out of LNG Tank 3. Then, the workers Discharge capacityThe BOG discharge amount at 125% of the total is equal to or greater than a specified value (a value derived from the relationship between the volume of Unit A 1A and Unit B 1B and the amount of discharged gas, for example, the BOG flow rate is 15t / h (15 tons per hour) or more. ) Check on the monitor that the BOG compressor 1 is working properly. In the discharge capacity BOG flow rate (reference value) teeth As follows: That is, the BOG compressor 1 has the following features: Discharge capacity At 25%, the BOG flow rate is 4t / h, Discharge capacity At 50%, the BOG flow rate is 6t / h, Discharge capacity At 75%, the BOG flow rate is 9t / h, Discharge capacity At 100%, the BOG flow rate is 13t / h.

[0030] Next, the operator confirms that the condition control permission lamp (not shown) of Unit B 1B is lit after a predetermined time (15 minutes in this embodiment) has elapsed since the startup operation of Unit B 1B, and then stops Unit A 1A (fifth step: S5). This causes the system to transition to a state in which only Unit B 1B is in operation. Note that the BOG compressor 1 (Unit B 1B) is in operation immediately after startup. Discharge setting capacity Even if the capacity is 100%, the flow rate will not be as it would be under normal circumstances (when stable operation has been taking place for some time since startup), so Unit A 1A must continue operating until the capacity adjustment permission lamp of Unit B 1B lights up.

[0031] Next, the operator selects and executes "Unit Quantity Control" for Unit B 1B. This puts Unit B 1B in a "unit control usable state." (Sixth step: S6). When the BOG compressor 1 is manually operated, the control of the number of units is excluded. Therefore, by selecting (using) the control of the number of units, the control of the number of units becomes available.

[0032] Next, the operator selects (uses) the unit number control for the A machine 1A (seventh step: S7). This enables the number control of Unit A to be enabled. However, in order for unit control to be in use, the status must be switched to automatic operation, so at this point, unit control for Units A, C, and D is still unavailable.

[0033] Next, the operator checks that the pressure in the LNG tank 3 is being controlled within the normal control range by the monitor (eighth step: S8).

[0034] Next, the worker A Unit 1A, C Unit 1C, D Unit 1D The condition of the machine will be adjusted automatically. This will put all units A to D into a "unit control usable state" where the status and unit control will be automatically managed by computer. (9th step: S9).

[0035] As described above, the switching operation from Unit A 1A to Unit B 1B in this embodiment is completed through the first to ninth steps (S1 to S9). Note that, upon completion of the switching operation from Unit A 1A to Unit B 1B, the BOG in the multiple LNG tanks 3 is discharged by one Unit B 1B under normal circumstances.

[0036] In addition, in this embodiment, Discharge setting capacity Even one minute after starting, when the temperature is between 0% and 100%, the temperature of the cylinder head is high. Discharge capacity By adjusting the BOG discharge from LNG tank 3 (by adjusting the volume using Unit A 1A), the pressure drop in LNG tank 3 can be reduced even if the conventional LNG tank pressure accumulation process (S103) performed manually by Unit A is omitted. of We were able to keep it to a level where it didn't cause any problems.

[0037] (Effects of the embodiment) The switching method of the BOG compressor 1 according to this embodiment as described above eliminates the need for pressure accumulation work in the LNG tank 3, and can reduce the work time of about 10 to 30 minutes required for pressure accumulation work in the LNG tank 3, thereby reducing the time required for switching the BOG compressor 1 (switching from Unit A 1A to Unit B 1B).

[0038] In addition, the switching method of the BOG compressor 1 according to this embodiment is the same as that of the B unit 1B. Discharge setting capacity After reaching 100%, A-1A Discharge capacityBy gradually decreasing the flow rate from 100% to 75%, 50%, and 25%, it becomes possible to suppress fluctuations in the flow rate of BOG flowing out from the LNG tank 3. As a result, according to the switching method of the BOG compressor 1 of this embodiment, when switching from Unit A 1A to Unit B 1B, the ratio of BOG and natural gas in the fuel supplied to the gas turbine 14 is stabilized, calorific fluctuations in the fuel supplied to the gas turbine 14 can be suppressed, and the operating state (combustion state) of the gas turbine 14 is stabilized. [Explanation of symbols]

[0039] 1...BOG compressor, 1A...Unit A, 1B...Unit B, 3...LNG tank

Claims

1. A BOG compressor switching method for discharging BOG from an LNG tank using Unit B instead of Unit A when one of a plurality of BOG compressors connected in parallel to an LNG tank is designated Unit A and another of the BOG compressors connected in parallel to the LNG tank is designated Unit B, the method comprising the steps of: While the A unit is in operation, the B unit is started. Next, after the discharge set capacity of the B unit reaches 100%, the discharge capacity of the A unit is gradually decreased to 25%; Next, when the time has elapsed from the start of Unit B until operation has stabilized, Unit A is stopped. A method for switching a BOG compressor.

2. The discharge capacity of the A-type unit is gradually reduced in the order of 100%, 75%, 50%, and 25%.

2. The method for switching a BOG compressor according to claim 1.

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