WO2016059996A1

WO2016059996A1 - Bog compression equipment and reciprocating compressor control method

Info

Publication number: WO2016059996A1
Application number: PCT/JP2015/078199
Authority: WO
Inventors: 正悟長根
Original assignee: 株式会社Ihi
Priority date: 2014-10-15
Filing date: 2015-10-05
Publication date: 2016-04-21
Also published as: JP6256815B2; JPWO2016059996A1

Abstract

BOG compression equipment is provided with multiple first reciprocating compressors (12), multiple second reciprocating compressors (14), an intermediate pipe (16), a rated maximum flow detector (18), and a unit number-controlling unit (20a). Respective rated maximum BOG flows that can flow into the intermediate pipe (16) from multiple sites are detected by the rated maximum flow detector (18). On the basis of the rated maximum flows from the multiple sites, the unit number-controlling unit (20a) controls the number of second reciprocating compressors (14) to be operated.

Description

BOG compression equipment and reciprocating compressor control method

The present disclosure relates to a BOG compression facility for compressing boil-off gas (BOG) generated in a storage tank for low-temperature liquefied gas, and a control method for a reciprocating compressor.

In storage tanks for low-temperature liquefied gases such as LNG, LEG, and LPG, a large amount of boil-off gas (Boil Off Gas, hereinafter referred to as “BOG”) is generated during storage due to external heat input.
Therefore, in order to prevent the pressure in the storage tank from rising, a BOG compression facility for compressing BOG has been proposed and used (for example, Patent Documents 1 to 3).

Patent Document 1 discloses a high-pressure compressor having a suction valve with an unloader and a counterbalanced reciprocating compressor.
Patent Document 2 discloses a BOG high-pressure compressor and a reliquefaction device.
Patent Document 3 discloses a BOG multistage positive displacement compressor.

JP 2002-115663 A JP 2008-286211 A JP 2012-122352 A

The counterbalanced reciprocating compressor, the BOG high-pressure compressor, and the BOG multistage positive displacement compressor disclosed in Patent Documents 1 to 3 are hereinafter referred to as “two-stage reciprocating compressors”.
The reciprocating compressor is characterized by a large compression ratio and high operating efficiency compared to a turbo compressor.
The two-stage reciprocating compressor can drive the low-pressure piston and the high-pressure piston with a single drive source (for example, a motor) to compress the BOG generated in the storage tank to a high pressure (for example, 4 to 6 MPa).

BOG compressed with a two-stage reciprocating compressor is processed by sending it to a customer (for example, a power plant). The BOG may be compressed to a high pressure (eg, 4 to 6 MPa) depending on the application of the BOG at the customer (eg, gas turbine fuel).

However, the two-stage reciprocating compressor has a problem that the load fluctuation is large because the load is greatly different between the low pressure compression and the high pressure compression.

On the other hand, the single-stage reciprocating compressor has only a low-pressure piston or a high-pressure piston, and therefore has a feature of low load fluctuation and high operating efficiency.

Therefore, the BOG generated in the storage tank is compressed to a high pressure (for example, 4 to 6 MPa) using a reciprocating compressor (for example, a single-stage reciprocating compressor) having a large compression ratio, small load fluctuation, and high operating efficiency. Can be considered.

However, the pressure of BOG generated in the storage tank is very low (for example, normal pressure to 0.02 MPa). Therefore, in order to compress to a high pressure (for example, 4 to 6 MPa), it is conceivable to arrange low-pressure and high-pressure reciprocating compressors in series and provide an intermediate pipe therebetween.
In addition, it can also compress to a high pressure by single stage compression using the reciprocating compressor for high pressures.

In addition, the flow rate of BOG generated in the storage tank varies greatly depending on the storage tank usage and the season (change in temperature, etc.). Therefore, it is conceivable to install a plurality of reciprocating compressors for low pressure and high pressure, respectively, and control the number of operating reciprocating compressors according to the situation.

However, compared with the space volume above the storage tank, the volume of the intermediate pipe is small (for example, about 1 to 5% of the space volume above the storage tank), and the reciprocating compressor is activated and stopped for a long time (for example, 30 to 60). Seconds). For this reason, if an imbalance occurs in the gas flow rates of the low-pressure and high-pressure reciprocating compressors, the pressure in the intermediate pipe between them suddenly rises or falls, and the control of the number of operating high-pressure reciprocating compressors follows the pressure fluctuation. There was a possibility that it could not be done.

An object of the present disclosure is to provide a control method for a BOG compression facility and a reciprocating compressor that can suppress an imbalance in gas flow rate and prevent a sudden change in pressure in a pipe.

According to one aspect of the present disclosure, a plurality of first reciprocating compressors that compress BOG generated in a storage tank to a first pressure;
A plurality of second reciprocating compressors that compress the first pressure BOG to a second pressure;
An intermediate pipe communicating the discharge side of the first reciprocating compressor and the suction side of the second reciprocating compressor;
A rated maximum flow rate detector that detects the rated maximum flow rate of the BOG that can flow into the intermediate pipe from a plurality of locations;
A BOG compression facility is provided that includes a number control device that controls the number of operating second reciprocating compressors based on the rated maximum flow rate from the plurality of locations.

According to another aspect of the present disclosure, the BOG compression facility described above is prepared,
The rated maximum flow rate detector detects the rated maximum flow rate of BOG that can flow into the intermediate pipe from the plurality of locations,
A control method for a reciprocating compressor is provided, wherein the number control device controls the number of operating second reciprocating compressors based on the rated maximum flow rate from the plurality of locations.

According to the present disclosure, the number of operating units of the plurality of second reciprocating compressors is controlled by the number control device based on the rated maximum flow rates of the BOGs from a plurality of locations that can flow into the intermediate pipe. The second reciprocating compressor can be started or stopped before the pressure fluctuation occurs.
Therefore, the followability of the control of the number of operating units of the second reciprocating compressor is enhanced, so that an imbalance in the gas flow rate can be suppressed and a sudden change in the pipe pressure can be prevented.

1 is an overall system diagram of a BOG compression facility according to an embodiment of the present disclosure. It is a schematic diagram which shows the specific example of a single stage type reciprocating compressor. It is a schematic diagram which shows another specific example of a single stage type reciprocating compressor. It is explanatory drawing of the capacity | capacitance adjustment by a single stage type reciprocating compressor. It is a block diagram of a number control apparatus. It is a whole flow figure of the number control method of a reciprocating compressor by an embodiment of this indication. It is a block diagram of a capacity | capacitance adjustment apparatus. 1 is an overall flow diagram of a capacity adjustment method for a reciprocating compressor according to an embodiment of the present disclosure. It is explanatory drawing which shows the relationship between the total gas flow volume G and the operating capacity W.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

Hereinafter, in the present disclosure, “flow rate” means “weight flow rate” unless otherwise specified. The “rated maximum flow rate” means a “maximum flow rate” (that is, a maximum weight flow rate) preset for each device.
“Number control” means control for changing the number of operating units. The number of operating units is an integer having a minimum value of 1 during operation.
“Capacity adjustment” means control for changing the operating capacity of an operating reciprocating compressor. The “operating capacity” is the weight flow rate of gas that can be compressed by the reciprocating compressor in operation.
Therefore, the “maximum operating capacity” of the reciprocating compressor means “rated maximum flow rate”.

FIG. 1 is an overall system diagram of a BOG compression facility according to an embodiment of the present disclosure.
In this figure, 1 is a low-temperature liquefied gas such as LNG, LEG, LPG, 2 is a storage tank, 3 is a supply line for low-temperature liquefied

gas

1, 4 is a pump, 5 is an evaporator, 6 is a gas transfer line, and 7 is a merge Tube 8 is a customer.

With this configuration, the low-temperature liquefied gas 1 stored in the storage tank 2 is supplied to the pump 4 by the supply line 3, the low-temperature liquefied gas 1 is pressurized by the pump 4, and the low-temperature liquefied gas 1 is evaporated by the evaporator 5. The evaporated gas (for example, natural gas) can be supplied to the customer 8.

The customer 8 is, for example, a power plant, and low temperature liquefied gas 1 having a pressure of 4 to 6 MPa (hereinafter referred to as “high pressure”) is supplied to the customer 8 as fuel for a boiler or a gas turbine.

The BOG compression facility of the present embodiment includes a first control device 10, a first pressure detector 11, a plurality of first reciprocating compressors 12, a plurality of second reciprocating compressors 14, an intermediate pipe 16, and a rated maximum flow rate detector 18. And a second control device 20.
In addition, you may comprise the 1st control apparatus 10, the rated maximum flow volume detector 18, and the 2nd control apparatus 20 with a single control apparatus (for example, computer).

The pressure of BOG generated in the storage tank 2 is low (for example, normal pressure to 0.02 MPa). Hereinafter, the pressure of BOG generated in the storage tank 2 is referred to as “the 0th pressure P0”.

In FIG. 1, the upper part of the storage tank 2 and the suction side of the first reciprocating compressor 12 are connected by a BOG discharge line 15.
The plurality of first reciprocating compressors 12 are arranged in parallel and each sucks BOG generated in the storage tank 2 through the BOG discharge line 15 and compresses it to the first pressure P1. The first pressure P1 is an intermediate pressure (for example, 1 to 3 MPa).
The number of first reciprocating compressors 12 is five in this figure, but may be two to four or six or more.

The first pressure detector 11 is provided in the upper part of the storage tank 2 or in the BOG discharge line 15 and detects the pressure of the BOG (the 0th pressure P0) generated in the storage tank 2.
The first control device 10 is, for example, a computer (PC), and receives BOG pressure data detected by the first pressure detector 11. Based on the received pressure data, the first controller 10 controls the plurality of first reciprocating compressors 12 so that the zeroth pressure P0 falls within a preset pressure range (for example, normal pressure to 0.02 MPa). To do.

The time taken to start and stop the first reciprocating compressor 12 is, for example, 30 to 60 seconds. However, since the space volume in the upper part of the storage tank 2 is very large compared to the volume of the intermediate pipe 16 (for example, 20 to 100 times the volume of the intermediate pipe 16), the pressure is detected by the first pressure detector 11. Even if the first reciprocating compressor 12 is started or stopped later, the pressure fluctuation in the storage tank 2 can be followed.
Therefore, the upper pressure of the storage tank 2 can be maintained within a preset pressure range by the first control device 10 and the first pressure detector 11.

In FIG. 1, the plurality of second reciprocating compressors 14 are arranged in parallel and each compresses the BOG of the first pressure P1 compressed by the first reciprocating compressor 12 to the second pressure P2. The second pressure P2 is preferably a high pressure (eg, 4 to 6 MPa) that matches the customer 8 (eg, a power plant).
The number of second reciprocating compressors 14 is set so that the entire amount of BOG supplied from the intermediate pipe 16 can be compressed. The number of second reciprocating compressors 14 is three in this figure, but may be two or four or more.

The intermediate pipe 16 is a gas pipe that communicates the discharge side of the plurality of first reciprocating compressors 12 and the suction side of the plurality of second reciprocating compressors 14.
The volume of the intermediate pipe 16 is very small as compared with the space volume above the storage tank 2, for example, about 1 to 5% of the space volume of the storage tank 2. However, the present embodiment is not limited to this volume, and for example, a gas reservoir may be provided in the intermediate pipe 16.

In this example, off-gas flows into the intermediate pipe 16 from processes 9 other than the first reciprocating compressor 12. The off gas should have substantially the same composition as BOG.
Here, the process 9 means a process or equipment for generating off-gas by the storage system for the low-temperature liquefied gas 1.
In addition, the process 9 is not limited to the process in the BOG compression equipment of this embodiment, Other processes and equipment may be sufficient as long as off-gas (for example, BOG) generate | occur | produces. Further, the process 9 is only one place in this example, but may be two places or more.

The discharge sides of the plurality of second reciprocating compressors 14 are connected to the junction pipe 7 described above via high-pressure gas lines 17.
With the above-described configuration, the plurality of first reciprocating compressors 12 compress the BOG generated in the storage tank 2 to the first intermediate pressure P1, and the plurality of second reciprocating compressors 14 compress the BOG having the first pressure P1. Can be compressed to a high second pressure P2. The BOG compressed to the second pressure P <b> 2 merges with the gas from the evaporator 5 in the merge pipe 7 and is supplied to the customer 8.

The rated maximum flow rate detector 18 detects the rated maximum flow rate of the BOG that can flow into the intermediate pipe 16 from a plurality of locations.
Here, the plurality of locations are the first reciprocating compressor 12 in operation. The number of first reciprocating compressors 12 in operation is the number based on the control signal of the number of operating units by the second control device 20. Moreover, when the process 9 exists, the above-mentioned plurality of locations may further include the process 9. In this case, the rated maximum flow rate of BOG that can flow into the intermediate pipe 16 from the process 9 is known in advance, and the storage device (not shown) of the first control device 10, the second control device 20, or the rated maximum flow rate detector 18. ) Is stored.
Further, “can flow in” means that it is not necessary to actually flow in, and it is sufficient that it can flow in.

The rated maximum flow rate of the first reciprocating compressor 12 is the maximum operating capacity when the operating capacity W is adjustable. The rated maximum flow rate of the process 9 is the maximum value when the inflow amount from the process 9 varies.

In FIG. 1, the intermediate pipe 16 is provided with a total gas flow rate detector 13 and a second pressure detector 19.
The total gas flow rate detector 13 detects the total gas flow rate G flowing into the intermediate pipe 16 (that is, the weight flow rate actually flowing in), and outputs it to the second control device 20.
The second pressure detector 19 detects the pressure of the BOG in the intermediate pipe 16 and outputs it to the second control device 20.

The second control device 20 includes a number control device 20a and a capacity adjustment device 20b.

The number control device 20a is based on the rated maximum flow rate from the plurality of locations (the first reciprocating compressor 12 being operated, or the first reciprocating compressor 12 being operated and the process 9), as described above. Control the number of operating units. The number of operating units is set so that the entire amount of BOG supplied from the intermediate pipe 16 can be compressed.

The capacity adjusting device 20b adjusts the operating capacity W of each second reciprocating compressor 14 during operation based on the total gas flow rate G flowing into the intermediate pipe 16.

For example, when the operating capacity W of the second reciprocating compressor 14 can be adjusted, the operating capacity W of the second reciprocating compressor 14 in operation is adjusted, and the sum is obtained from the total gas flow rate G flowing into the intermediate pipe 16. Is also controlled to be larger.

1, the BOG compression facility of this embodiment further includes a recycle line 21 and a return gas flow rate control valve 22.

The recycle line 21 is a piping line that bypasses the second reciprocating compressor 14 and communicates the discharge side with the intermediate piping 16. In this example, the recycle line 21 directly communicates the high-pressure gas line 17 and the intermediate pipe 16 described above, but the discharge side and the suction side of the second reciprocating compressor 14 may be directly communicated.
Moreover, the recycling line 21 is not limited to one, and may be two or more.

The return gas flow rate control valve 22 is provided in the recycle line 21 and controls the gas flow rate returning from the discharge side of the second reciprocating compressor 14 to the intermediate pipe 16. This control is preferably set so that the pressure of the intermediate pipe 16 detected by the second pressure detector 19 falls within a preset pressure range (for example, the first pressure P1 ± α and α are arbitrary pressures).
The second pressure detector 19 is omitted, a pilot control valve is used as the return gas flow rate control valve 22, and the return gas flow rate control valve is set at the pressure of the intermediate pipe 16 (pilot pressure) without going through the second control device 20. 22 may be directly controlled.

Even when the gas flow rate (weight flow rate) processed by the plurality of second reciprocating compressors 14 is larger than the gas flow rate (weight flow rate) flowing into the intermediate pipe 16, the above-described recycle line 21 and the return gas flow rate control valve 22 The pressure in the intermediate pipe 16 can be controlled within a preset pressure range.

Even if the capacity adjustment described above is performed, the flow rate of gas flowing into the intermediate pipe 16 is smaller than the flow rate of gas flowing out, so that flow rate imbalance occurs. However, this imbalance can be eliminated by the recycle line 21 and the return gas flow control valve 22 described above.

2A and 2B are schematic views showing a specific example of a single-stage reciprocating compressor.

In the single-stage reciprocating compressor of FIG. 2A, two cylinders C are opposed to each other, and two pistons D are driven by a single drive source M (for example, a motor), and each piston D is reciprocated. Thus, gas is compressed at a total of four locations.
Each cylinder C is provided with an unload valve V that returns compressed gas to the suction side, and one or both of compressions by reciprocation of each cylinder C can be unloaded (no load). Yes.
Therefore, the single-stage reciprocating compressor of FIG. 2A can change the operating capacity W to five stages by the combination of on / off of the four unload valves V (only a part is shown). Hereinafter, these five stages of operation capacity W are referred to as 0, first capacity W1, second capacity W2, third capacity W3, and fourth capacity W4 from the smallest. The fourth capacity W4 is the maximum operating capacity.

In the single-stage reciprocating compressor of FIG. 2B, four cylinders C are arranged radially, and four pistons D are driven by a single driving source M (for example, a motor). The gas is compressed at a total of 4 points.
Each cylinder C is provided with an unload valve V for returning the compressed gas to the suction side so that each cylinder C can be unloaded (no load).
Therefore, the single stage reciprocating compressor of FIG. 2B also changes the operating capacity W to five stages by the combination of on / off of the four unload valves V (only a part is shown) as in FIG. 2A. Can do.

It should be noted that the number of variable capacity steps of the single-stage reciprocating compressor is not limited to the above-described five stages, and may be two stages (that is, only on / off), three, four stages, or six stages or more.

The first reciprocating compressor 12 is not limited to the single-stage reciprocating compressor described above, and may be a multi-stage reciprocating compressor. The maximum operating capacities of the plurality of first reciprocating compressors 12 may be the same or different.
The second reciprocating compressor 14 is preferably the above-described single-stage reciprocating compressor. The maximum operating capacities of the plurality of second reciprocating compressors 14 may be the same or different.

FIG. 3 is an explanatory diagram of capacity adjustment by one single-stage reciprocating compressor. This figure is a diagram showing the relationship between the load factor 0, A1, A2, A3, 100%, the operating capacity W, and the processing flow rate when the capacity can be changed in five stages. The processing flow rate means a gas flow rate processed by one single-stage reciprocating compressor. In FIG. 3, the symbol g indicates the maximum flow rate (hereinafter referred to as the processable flow rate g) that can be processed by the single-stage reciprocating compressor having the corresponding operating capacity W (that is, the load factor). This processable flow rate g is equal to the corresponding operating capacity W.
As shown in this figure, the combination of on / off of the above-described four unload valves V (only a part is shown) corresponds to each stage of load factor 0, A1, A2, A3, 100%. The operating capacity W can be adjusted in five stages of 0, W1, W2, W3, and W4 (in this example, the capacity difference between any adjacent steps is W1). The load factors 0, A1, A2, A3, and 100% are, for example, 0, 25, 50, 75, and 100% of the maximum operating capacity.

FIG. 4 is a configuration diagram of the number control device 20a.
The number control device 20 a is, for example, a computer (PC), and includes a storage device 23, a calculation device 24, and an output device 25.
The storage device 23 is a memory such as a RAM, a ROM, or a hard disk.
The arithmetic device 24 is a CPU, for example.
The output device 25 is, for example, an output terminal or an output relay.

The control method for the reciprocating compressor according to the present embodiment is executed by the second control device 20. This control method performs unit control and capacity adjustment described below. However, the capacity adjustment may not be performed, and in this case, the capacity adjustment device 20b may be omitted.

(Unit control)
The number control device 20a, that is, the arithmetic device 24 includes a maximum total gas flow rate prediction unit 24a, a command number calculation unit 24b, and a command output unit 24c.

FIG. 5 is an overall flowchart of the method for controlling the number of reciprocating compressors according to this embodiment.
In this figure, the method of the present embodiment includes steps (steps) S1 to S8.

In step S1, the above-described BOG compression facility is prepared.
In step S2, the rated maximum flow rate detector 18 detects the rated maximum flow rate of BOG that can flow into the intermediate pipe 16 from a plurality of locations.

In step S3, the maximum total gas flow rate prediction unit 24a predicts the maximum total gas flow rate Gmax based on the rated maximum flow rates from the plurality of locations described above.
The plurality of locations described above include the first reciprocating compressor 12 in operation. In addition, the 1st reciprocating compressor 12 which is not drive | operating (namely, being stopped) is excluded.
When the plurality of locations described above further include the process 9, in step S3, based on each rated maximum flow rate detected in step S2 and the rated maximum flow rate of the process 9 stored in the storage device described above, The maximum total gas flow rate prediction unit 24a predicts the maximum total gas flow rate Gmax.
For example, three of the five first reciprocating compressors 12 are in operation, the rated maximum flow rates (that is, the maximum operating capacity) are G1, G2, and G3, and the rated maximum flow rate of the process 9 is G9. In some cases, the maximum total gas flow rate Gmax is obtained by Gmax = G1 + G2 + G3 + G9 (1).
Here, when the operating capacity W of the first reciprocating compressor 12 can be changed to, for example, the above-described five stages, the rated maximum flow rate means the fourth capacity W4. The operating capacity W of the first reciprocating compressor 12 during operation may be any of 0, W1, W2, W3, and W4.

In step S4, the command number calculation unit 24b calculates the command number N of the second reciprocating compressor 14 from the maximum total gas flow rate Gmax.
That is, the command number calculation unit 24b calculates the command number N of the second reciprocating compressor 14 from the maximum total gas flow rate Gmax and the rated maximum flow rate X (that is, the maximum operating capacity) of each second reciprocating compressor 14.
For example, the command number N of the second reciprocating compressor 14 is obtained by N = ROUNDUP (Gmax / X) (2). The function “ROUNDUP” means rounding up to an integer.

When the rated maximum flow rates X1, X2, and X3 of the plurality of second reciprocating compressors 14 are different and priority is set for each second reciprocating compressor 14, the command number calculation unit 24b gives priority. The second reciprocating compressor 14 may be selected in descending order. At this time, the sum of the rated maximum flow rates of the selected second reciprocating compressor 14 is set to exceed the above-described maximum total gas flow rate Gmax.
The priority should be based on operating efficiency, maintainability, lifespan, and the like.

Even when the first reciprocating compressor 12 in operation operates at the rated maximum flow rate (that is, the maximum operating capacity) by the number control method of the above-described embodiment, the total of the maximum rated flow rates of the N second reciprocating compressors 14 Exceeds the above-mentioned maximum total gas flow rate Gmax. Accordingly, the entire amount of BOG supplied from the intermediate pipe 16 can be compressed by the N second reciprocating compressors 14.

In steps S5 to S8, the command output unit 24c compares the current operating number N2 of the operating second reciprocating compressor 14 with the calculated commanded number N, and the operating operating number N2 is calculated. Is commanded to increase or decrease the operating number N2 (or so that the operating number N2 approaches the designated number N).

That is, when the command number N exceeds the operating number N2 (YES) in step S5, the command output unit 24c outputs a command to increase the number of operating units N2 in step S6. Due to this increase command, the number N2 of the second reciprocating compressors 14 is changed to N2 + 1.
After outputting the additional command, the process returns to step S3.

Further, in step S7, the command output unit 24c outputs a reduction command for reducing the operating number N2 in step S8 when the number of units less than the current operating number N2 exceeds the command number N (YES). With this command to reduce the number of units, the number N2 of the second reciprocating compressors 14 is changed to N2-1.
After outputting the reduction command, the process returns to step S3.

If NO in steps S5 and S7, neither an increase command nor a decrease command is output, and the number N2 of the second reciprocating compressors 14 is maintained without change.

By the steps S5 to S8 described above, the operating number N2 in operation can be made to coincide with the commanded number N calculated. As a result, even when the first reciprocating compressor 12 in operation is operated at the rated maximum flow rate (that is, the maximum operating capacity), the total of the maximum rated flow rates of the N second reciprocating compressors 14 is the maximum total gas described above. Exceeding the flow rate Gmax, the entire amount of BOG supplied from the intermediate pipe 16 can be compressed.

(Capacity adjustment)
When the operating capacity of the second reciprocating compressor 14 can be adjusted stepwise to two or more operating capacities different from each other, the capacity adjusting device 20b has one or both of the following (1) and (2). I do.
(1) The current operation of each second reciprocating compressor 14 in which the total gas flow rate G to the plurality of second reciprocating compressors 14 in operation (that is, the total gas flow rate G flowing through the intermediate pipe 16) is in operation. When the total sum Ws of the capacities (that is, the processable flow rate g) is exceeded, at least one of the operating capacities of the plurality of second reciprocating compressors 14 being operated is switched to the maximum operating capacity side.
(2) The total gas flow rate G is smaller than the total current operating capacity Ws of each second reciprocating compressor 14 in operation, and a value obtained by subtracting the total gas flow rate G from the total Ws (Ws−G ) Is larger than the switchable amount of the operation capacity of the second reciprocating compressor 14 (that is, the operation capacity is switched in steps of one stage as shown in FIG. 3), each second reciprocal compression during operation The operating capacity of the plurality of second reciprocating compressors 14 in operation is switched to the minimum operating capacity side while maintaining the operating capacity of the machine 14 at a value greater than zero.

That is, the capacity adjusting device 20b is configured such that the total operation capacity (processable flow rate g) of FIG. 3 in each second reciprocating compressor 14 in operation is the total gas to the plurality of second reciprocating compressors 14 in operation. Set to exceed flow rate G.
In the present embodiment, the capacity adjustment by the capacity adjustment device 20b is performed on some or all of the plurality of second reciprocating compressors 14 that are operating by the number control performed by the number control device 20a described above. .

FIG. 6 is a configuration diagram of the capacity adjustment device 20b.
The capacity adjustment device 20b is, for example, a computer (PC), and includes a storage device 33, a calculation device 34, and an output device 35.
The storage device 33 is a memory such as a RAM, a ROM, or a hard disk.
The computing device 34 is a CPU, for example.
The output device 35 is, for example, an output terminal or an output relay.

The capacity adjustment device 20b, that is, the calculation device 34 includes a first capacity adjustment unit 34a and a second capacity adjustment unit 34b.

FIG. 7 is an overall flowchart of the capacity adjustment method for the reciprocating compressor according to the present embodiment.
In this figure, the method of the present embodiment includes steps (steps) S11 to S18.

In step S11, the above-described BOG compression facility is prepared.
In step S <b> 12, the total gas flow rate detector 13 detects the total gas flow rate G actually flowing into the intermediate pipe 16.

Steps S13 to S18 show the capacity adjustment method of the reciprocating compressor according to this embodiment. Hereinafter, this capacity adjustment will be described.

When the number of second reciprocating compressors 14 that are in operation is one, the capacity adjusting device 20b has an operating capacity W (that is, a processable flow rate g) as shown in FIG. The operating capacity W is set so as to exceed the gas flow rate G.

When there are two or more second reciprocating compressors 14 in operation, the total operating flow W of the second reciprocating compressor 14 in operation is the total gas flow rate G actually flowing into the intermediate pipe 16. The operating capacity W of each second reciprocating compressor 14 during operation is set so as to exceed.
For example, when two or more units are operating and there is no priority, the operation capacity W (processable flow rate) shared by each second reciprocating compressor 14 with respect to the total gas flow rate G actually flowing into the intermediate pipe 16. g) is set as appropriate, and is set so that the sum of the N operating capacities W (see FIG. 3) exceeds the total gas flow rate G.

When the number of second reciprocating compressors 14 in operation is N (N ≧ 2) and there is a priority order, the capacity adjusting device 20b has each second reciprocating device 14 in operation so as to satisfy all the following conditions. The operating capacity W of the compressor 14 is adjusted.
(A) The total operation capacity W of the second reciprocating compressor 14 in operation exceeds the total gas flow rate G flowing into the intermediate pipe 16.
(B) The load factor of the second reciprocating compressor 14 is higher in descending order of priority. That is, priorities are set in advance for the plurality of second reciprocating compressors 14 in operation, and the second reciprocating compressor 14 having a higher priority has a higher operating capacity (load factor).
(C) The operating capacity (load factor) of all the second reciprocating compressors 14 in operation is greater than zero.
The priority should be based on operating efficiency, maintainability, life, etc.

With this configuration, the following effects can be obtained.
By (A), since the sum total of the operation capacity W of the 2nd reciprocating compressor 14 in operation is larger than the total gas flow rate G which flows into the intermediate pipe 16, the pressure rise of the intermediate pipe 16 can be prevented.
Since the total operation capacity W of the second reciprocating compressor 14 in operation is larger, the pressure in the intermediate pipe 16 is reduced. However, since the recycle line 21 and the return gas flow control valve 22 are provided, the negative pressure is increased. Can be prevented.
By (B), the load factor of the 2nd reciprocating compressor 14 with high priority (for example, operation efficiency) can be made high, and the whole operation efficiency etc. can be raised.
By (C), it can prevent that the 2nd reciprocating compressor 14 is drive | operated by zero operation capacity, and can maintain the driving | running performance of the 2nd reciprocating compressor 14. FIG.

FIG. 8 is an explanatory diagram showing the relationship between the total gas flow rate G and the operating capacity W.
In this figure, the left side shows the total gas flow rate G flowing into the intermediate pipe 16, and the right side shows the operating capacity W of the three second reciprocating compressors 14 in operation.
In the right three units, the first priority K from the top is No. 1, the second is No. 2, and the third is No. 3. The hatched portion on the right side indicates the actual gas flow rate, and the blank portion indicates the unloaded portion of the operating capacity W.
The operating capacity W of each second reciprocating compressor 14 in FIG. 8 can be changed in five stages: 0, W1, W2 = 2W1, W3 = 3W1, W4 = 4W1.

In this example, the first operating capacity W from the top is W4, the second is W3, the third is W1, satisfies the relationship of W4 + W3 + W1> G, and satisfies the condition (A).
Further, W4>W3> W1, and the condition (B) is satisfied.
Further, W4, W3, W1 ≧ W1, and the condition (C) is satisfied.

Hereinafter, with reference to FIG. 7 and FIG. 8, the adjustment method of the operation capacity W of each 2nd reciprocating compressor 14 is demonstrated concretely.

As shown in FIG. 8, when there are two or more second reciprocating compressors 14 in operation (three in this example), the total operating capacity W of the second reciprocating compressor 14 in operation is The total gas flow rate G actually flowing into the intermediate pipe 16 is set to be exceeded.

(1) When the priority order K is from 1 to N-1 by the first capacity adjustment unit 34a (YES in step S13), the operating capacity W of each second reciprocating compressor 14 in descending order of the priority order K. Are set in steps S14 to S16 as follows.

In step S14, the first capacity adjustment unit 34a calculates the sum ΣWA of the operating capacities W from the priority order 1 to (K−1) with respect to the priority order K. ΣWA means the sum of the operating capacities W of the second reciprocating compressor 14 having a higher priority than the priority K being calculated.
For example, in FIG. 8, the first unit has the highest priority, and there is no higher priority, so the first ΣWA is zero. Further, since the second one from the top has the second highest priority and one higher priority, ΣWA is the first operating capacity W4.

In step S15, the first capacity adjustment unit 34a calculates the sum ΣWB of the minimum capacities (the above-described first capacities W1) from (K + 1) to N with respect to the priority order K. The minimum capacity is an adjustable minimum capacity greater than zero. ΣWB is calculated on the assumption that all the second reciprocating compressors 14 having a lower priority than the second reciprocating compressor 14 being calculated have the minimum capacity. This assumption is for ensuring the operating capacity W of the second reciprocating compressor 14 during operation to be equal to or greater than the minimum capacity.
For example, in FIG. 8, the first unit has the highest priority, and there are two units with lower priority, so the first ΣWB is 2W1. Also, the second one from the top has the second priority, and there is one lower priority, so the second ΣWB is W1.

In step S16, the first capacity adjustment unit 34a adjusts the operating capacity W with respect to the priority order K based on the remaining capacity obtained by subtracting ΣWA and ΣWB from the total gas flow rate G. When the remaining capacity is equal to or greater than the maximum operating capacity of the second reciprocating compressor 14 with priority K, the first capacity adjusting unit 34a sets the operating capacity of the second reciprocating compressor 14 to the maximum operating capacity. You can do it. When the remaining capacity is smaller than the maximum operating capacity of the second reciprocating compressor 14 with priority K, for example, the first capacity adjusting unit 34a determines the operating capacity of the second reciprocating compressor 14 from the remaining capacity. The operating capacity may be set large and closest to the remaining capacity.
For example, in FIG. 8, the top one has the highest priority, and W satisfying W> G−ΣWA−ΣWB = G−0−2W1 exceeds W4. In this case, the operating capacity W is adjusted to W4.
The second one from the top has the second highest priority, and W satisfying W> G−ΣWA−ΣWB = G−W4−W1 exceeds W2 but less than W3. In this case, the operating capacity W is adjusted to W3.

By adjusting the operating capacity W described above, the operating capacity W of the second reciprocating compressor 14 having a higher priority and the minimum capacity of the second reciprocating compressor 14 having a lower priority being secured are being calculated. The operating capacity W of the second reciprocating compressor 14 can be set to the maximum.

(2) The operating capacity W of the second reciprocating compressor 14 is set as follows by the second capacity adjusting unit 34b when the priority order K is N (NO in step S13).

In step S17, the second capacity adjusting unit 34b calculates the sum ΣWC of the operating capacities W from the first to the (N−1) th for the priority N. ΣWC means the sum of the operating capacities W of all the second reciprocating compressors 14 having a higher priority than the N-th second reciprocating compressor 14.
For example, in FIG. 8, the one on the top of the third has the third priority, and there is no lower priority, so ΣWC is W4 + W3.

In step S18, the second capacity adjustment unit 34b adjusts the Nth operation capacity W to a value larger than the remaining capacity obtained by subtracting ΣWC from the total gas flow rate G. For example, the second capacity adjustment unit 34b adjusts the Nth operation capacity W to an operation capacity that is larger than (G-ΣWC) and closest to (G-ΣWC).
As a result, the operating capacity W of all the second reciprocating compressors 14 having high priority is secured, and the operating capacity W of the Nth second reciprocating compressor 14 is set to be equal to or greater than the minimum capacity greater than zero. be able to.
For example, in FIG. 8, the third unit from the top has the third priority, and W satisfying W> G−ΣWA−ΣWB = G−W4−W3 is smaller than W1. In this case, the operating capacity W is adjusted to W1.

According to the apparatus and method of the above-described embodiment, the BOG generated in the storage tank 2 is compressed to the first pressure P1 by the plurality of first reciprocating compressors 12, and the first reciprocating compressor 14 is used to compress the first BOG. The BOG at the pressure P1 can be compressed to the second pressure P2.
Therefore, the BOG generated in the storage tank 2 can be compressed to a high pressure (for example, 4 to 6 MPa) using a reciprocating compressor.

Further, since the number of operating units of the plurality of second reciprocating compressors 14 is controlled by the number control device 20a based on the rated maximum flow rate of BOG from a plurality of places that can flow into the intermediate pipe 16, the pressure fluctuations in the intermediate pipe 16 Before this occurs, the second reciprocating compressor 14 can be started or stopped early.
Accordingly, the followability of the control of the number of operating units of the second reciprocating compressor 14 is enhanced, so that an imbalance in the gas flow rate can be suppressed and a sudden change in the pressure in the pipe can be prevented.

Further, since the operation capacity W of each second reciprocating compressor 14 in operation is adjusted by the capacity adjustment device 20b based on the total gas flow rate G actually flowing into the intermediate pipe 16 from a plurality of locations, The operating capacity W can be adjusted early before the pressure fluctuation occurs.
Accordingly, the followability of the capacity adjustment of each second reciprocating compressor 14 is enhanced, so that an imbalance in the gas flow rate can be suppressed and a sudden change in the pipe internal pressure can be prevented.

The BOG compression facility according to the above-described embodiment may be described as in the following supplementary notes 1 to 8.

(Appendix 1)
BOG compression equipment
A plurality of first reciprocating compressors that compress BOG generated in the storage tank to a first pressure;
A plurality of second reciprocating compressors that compress the first pressure BOG to a second pressure;
An intermediate pipe communicating the discharge side of the first reciprocating compressor and the suction side of the second reciprocating compressor;
A rated maximum flow rate detector that detects the rated maximum flow rate of the BOG that can flow into the intermediate pipe from a plurality of locations;
A number control device for controlling the number of operating second reciprocating compressors based on the maximum rated flow rate from the plurality of locations.

(Appendix 2)
In the above supplementary note 1, the number control device is:
A maximum total gas flow prediction unit for predicting a maximum total gas flow from each of the rated maximum flows;
A command number calculator for calculating a command number of the second reciprocating compressor based on the maximum total gas flow rate;
A command output unit that compares the current operating number of the second reciprocating compressor with the commanded number and commands an increase or decrease in the operating number so that the current operating number matches the commanded number; .

(Appendix 3)
In Supplementary Note 2, the command number calculation unit calculates the command number from the maximum total gas flow rate and the rated maximum flow rate of each of the second reciprocating compressors,
The command output unit outputs a command to increase the number of operating units when the commanded number exceeds the current operating number, and reduces the number of operating units when the number less than the current operating number exceeds the commanded number Output reduction command.

(Appendix 4)
In the above supplementary note 1, the BOG compression facility described above includes a recycle line that bypasses the second reciprocating compressor and communicates the discharge side with the intermediate pipe.
A return gas flow rate control valve that is provided in the recycle line and controls a gas flow rate that returns from the discharge side of the second reciprocating compressor to the intermediate pipe.

(Appendix 5)
In any one of Appendices 1 to 4, the operating capacity of each of the second reciprocating compressors can be adjusted stepwise to two or more different operating capacities,
A total gas flow detector for detecting the total gas flow actually flowing into the intermediate pipe from the plurality of locations;
A capacity adjusting device that adjusts the operating capacity of each of the second reciprocating compressors that are operating under the control of the number of operating units based on the total gas flow rate.

(Appendix 6)
In Appendix 5, the capacity adjusting device is
(1) At least one of the plurality of second reciprocating compressors in operation when the total gas flow rate flowing through the intermediate pipe exceeds the total operating capacity of the second reciprocating compressors in operation. Or (2) the total gas flow rate G is smaller than the total operating capacity Ws of the second reciprocating compressors in operation, and the total Ws When the value (Ws−G) obtained by subtracting the total gas flow rate G is larger than the switchable amount of the operation capacity of the second reciprocating compressor, the operation capacity of each of the second reciprocating compressors in operation is less than zero. While maintaining the large value, the operating capacity of at least one of the plurality of second reciprocating compressors in operation is switched to the minimum operating capacity side.

(Appendix 7)
In Appendix 5, when there are two or more second reciprocating compressors in operation and priority is set for each of the plurality of second reciprocating compressors in operation,
(A) The total operating capacity of the second reciprocating compressor in operation exceeds the total gas flow rate flowing into the intermediate pipe,
(B) the second reciprocating compressor having a higher priority has a higher operating capacity, and
(C) The operating capacity of all the second reciprocating compressors in operation is greater than zero.
The capacity adjusting device adjusts an operating capacity of each of the second reciprocating compressors.

(Appendix 8)
In Supplementary Note 5, the capacity adjusting device has N second reciprocating compressors in operation (N ≧ 2), and each of the plurality of second reciprocating compressors in operation is assigned a priority. If
In order of priority, the operating capacity from the first to the Kth (1 ≦ K ≦ N−1) is the sum of the operating capacity from the total gas flow to the first to the (K−1) th. And a first capacity adjustment unit that adjusts based on the remaining capacity obtained by subtracting the sum of the minimum capacity greater than zero from the (K + 1) th to the Nth,
A second capacity adjustment unit that adjusts the N-th priority operation capacity to a value larger than the remaining capacity obtained by subtracting the sum of the operation capacity from the first to the (N−1) th unit from the total gas flow rate. And having.

The method for controlling the number of reciprocating compressors according to the above-described embodiment may be described as the following

supplementary notes

9 and 10.

(Appendix 9)
In the reciprocating compressor unit control method,
Prepare the BOG compression facility in Appendix 1 above,
The rated maximum flow rate detector detects the rated maximum flow rate of BOG that can flow into the intermediate pipe from the plurality of locations,
The number control device controls the number of operating second reciprocating compressors based on the rated maximum flow rate from the plurality of locations.

(Appendix 10)
In the above supplementary note 10, the total gas flow rate detector detects the total gas flow rate actually flowing into the intermediate pipe from the plurality of locations,
The plurality of second reciprocating compressors compress the first pressure BOG to a second pressure,
The operating capacity of each of the second reciprocating compressors that are operating under the control of the number of operating units is adjusted in two or more steps by a capacity adjusting device based on the total gas flow rate.

It should be noted that the present disclosure is not limited to the above-described embodiment, is shown by the description of the scope of claims, and further includes all modifications within the meaning and scope equivalent to the description of the scope of claims.

C Cylinder D Piston Gmax Maximum total gas flow rate G1, G2, G3 Rated maximum flow rate g Processable flow rate M Drive source (motor)
P0 0th pressure (low pressure)
P1 First pressure (medium pressure)
P2 Second pressure (high pressure)
V Unloading valve W Operating capacity W1 1st capacity W2 2nd capacity W3 3rd capacity W4 4th capacity 1 Low temperature liquefied gas 2 Storage tank 3 Supply line 4 Pump 5 Evaporator 6 Gas transfer line 7 Merge pipe 8 Demand destination (power generation Place)
9 Process 10 First control device 11 First pressure detector 12 First reciprocating compressor 13 Total gas flow detector 14 Second reciprocating compressor 15 BOG discharge line 16 Intermediate piping 17 High-pressure gas line 18 Rated maximum flow detector 19 2 Pressure detector 20 Second control device 20a Number control device 20b Capacity adjustment device 21 Recycle line 22 Return gas flow rate control valve 23 Storage device 24 Arithmetic device 24a Maximum total gas flow rate prediction unit 24b Command number calculation unit 24c Command output unit 25 Output Device 33 Storage device 34 Computing device 34a First capacity adjustment unit 34b Second capacity adjustment unit 35 Output device

Claims

A plurality of first reciprocating compressors that compress BOG generated in the storage tank to a first pressure;
A plurality of second reciprocating compressors that compress the first pressure BOG to a second pressure;
An intermediate pipe communicating the discharge side of the first reciprocating compressor and the suction side of the second reciprocating compressor;
A rated maximum flow rate detector that detects the rated maximum flow rate of the BOG that can flow into the intermediate pipe from a plurality of locations;
A BOG compression facility comprising: a number control device that controls the number of operating second reciprocating compressors based on the rated maximum flow rate from the plurality of locations.
The number controller is
A maximum total gas flow prediction unit for predicting a maximum total gas flow from each of the rated maximum flows;
A command number calculator for calculating a command number of the second reciprocating compressor based on the maximum total gas flow rate;
A command output unit that compares the current operating number of the second reciprocating compressor with the commanded number and commands an increase or decrease in the operating number so that the current operating number matches the commanded number; The BOG compression facility according to claim 1.
The command number calculation unit calculates the command number from the maximum total gas flow rate and the rated maximum flow rate of each second reciprocating compressor,
The command output unit outputs a command to increase the number of operating units when the commanded number exceeds the current operating number, and reduces the number of operating units when the number less than the current operating number exceeds the commanded number The BOG compression facility according to claim 2, which outputs a reduction command.
A recycle line that bypasses the second reciprocating compressor and communicates the discharge side with the intermediate pipe;
2. The BOG compression facility according to claim 1, further comprising: a return gas flow rate control valve that is provided in the recycle line and controls a gas flow rate returning from the discharge side of the second reciprocating compressor to the intermediate pipe.
The operating capacity of each of the second reciprocating compressors can be adjusted stepwise to two or more different operating capacities,
A total gas flow detector for detecting the total gas flow actually flowing into the intermediate pipe from the plurality of locations;
5. A capacity adjusting device that adjusts the operating capacity of each of the second reciprocating compressors that are operating under the control of the number of operating units based on the total gas flow rate. The BOG compression equipment as described in the item.
The capacity adjusting device is
(1) At least one of the plurality of second reciprocating compressors in operation when the total gas flow rate flowing through the intermediate pipe exceeds the total operating capacity of the second reciprocating compressors in operation. Or (2) the total gas flow rate G is smaller than the total operating capacity Ws of the second reciprocating compressors in operation, and the total Ws When the value (Ws−G) obtained by subtracting the total gas flow rate G is larger than the switchable amount of the operation capacity of the second reciprocating compressor, the operation capacity of each of the second reciprocating compressors in operation is less than zero. The BOG compression facility according to claim 5, wherein the operating capacity of at least one of the plurality of second reciprocating compressors in operation is switched to the minimum operating capacity side while maintaining a large value.
When there are two or more second reciprocating compressors in operation and priority is set for each of the plurality of second reciprocating compressors in operation,
(A) The total operating capacity of the second reciprocating compressor in operation exceeds the total gas flow rate flowing into the intermediate pipe,
(B) the second reciprocating compressor having a higher priority has a higher operating capacity, and
(C) The operating capacity of all the second reciprocating compressors in operation is greater than zero.
The BOG compression facility according to claim 5, wherein the capacity adjusting device adjusts an operating capacity of each of the second reciprocating compressors.
In the capacity adjustment device, when the second reciprocating compressor in operation is N units (N ≧ 2), and priority is set for each of the plurality of second reciprocating compressors in operation,
In order of priority, the operating capacity from the first to the Kth (1 ≦ K ≦ N−1) is the sum of the operating capacity from the total gas flow to the first to the (K−1) th. And a first capacity adjustment unit that adjusts based on the remaining capacity obtained by subtracting the sum of the minimum capacity greater than zero from the (K + 1) th to the Nth,
A second capacity adjustment unit that adjusts the N-th priority operation capacity to a value larger than the remaining capacity obtained by subtracting the sum of the operation capacity from the first to the (N−1) th unit from the total gas flow rate. The BOG compression facility according to claim 5, comprising:
Preparing the BOG compression facility according to claim 1;
The rated maximum flow rate detector detects the rated maximum flow rate of BOG that can flow into the intermediate pipe from the plurality of locations,
A control method for a reciprocating compressor, wherein the number control device controls the number of operating second reciprocating compressors based on the rated maximum flow rate from the plurality of locations.
The total gas flow detector detects the total gas flow actually flowing into the intermediate pipe from the plurality of locations,
The plurality of second reciprocating compressors compress the first pressure BOG to a second pressure,
The operation capacity of each of the second reciprocating compressors that are operating under the control of the number of operating units is adjusted in two or more steps by a capacity adjustment device based on the total gas flow rate. The control method of the reciprocating compressor as described.