JP7022245B1 - Compressor unit and control method of compressor unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an increase in pressure in a flow path on a storage tank side when a low temperature gas flows into a compressor unit from a storage tank. SOLUTION: A compressor unit 100 has a reciprocating type compression stages 201 to 206 for sequentially boosting a target gas from a storage tank 101, a bypass flow path 301 for bypassing at least the first compression stage 201, and a bypass flow path 301. The downstream pressure provided in the flow path to which the bypass valve 311 provided in the above, the upstream pressure sensor 401 and the temperature sensor 403 provided in the storage tank connecting flow path 111, and the inlet side end portion 322 of the bypass flow path 301 are connected. The sensor 402, the opening adjustment unit 441 that controls the opening degree of the bypass valve 311 so that the detection pressure P2 of the downstream pressure sensor 402 approaches the set pressure PS1, and the set pressure PS1 when the detection temperature T1 of the temperature sensor 403 drops. A compressor unit equipped with a set pressure changing unit 431 to be raised. [Selection diagram] Fig. 1

Description

The present invention relates to a compressor unit and a method for controlling the compressor unit.

A compressor unit installed on an LNG carrier that boosts boil-off gas generated from LNG (liquefied natural gas) in a storage tank and supplies it to a demand destination such as an engine is known. Patent Document 1 describes a plurality of compressors, a bypass flow path connecting a suction side flow path and a discharge side flow path, an adjustment valve provided in the bypass flow path, and a control unit for controlling the opening degree of the adjustment valve. , A compressor unit including a pressure gauge provided in the discharge side flow path is disclosed. In the compressor unit of Patent Document 1, the opening degree of the adjusting valve of the bypass flow path is controlled by the command value set according to the pressure difference between the pressure of the discharge side flow path and the target pressure. Further, in Patent Document 2 and Patent Document 3, a bypass flow path provided so as to bypass the compression stage, a bypass valve provided in the bypass flow path, and a control device for adjusting the opening degree of the bypass valve are provided. The compressor unit provided is disclosed.

Japanese Unexamined Patent Publication No. 2017-129112 Japanese Patent No. 6294243 Japanese Unexamined Patent Publication No. 2018-103954

By the way, in the compressor units of Patent Documents 1 to 3, a bypass flow path straddling the first compression stage is provided. In such a compressor unit, the opening degree of the bypass valve on the bypass flow path may be controlled so that the pressure on the discharge side of the first compression stage becomes the set pressure. The set pressure is set in consideration of the balance between the compression ratio of the first compression stage and the compression ratio of the other compression stages.

On the other hand, the set pressure is set in consideration of the intake temperature of the boil-off gas (for example, 40 ° C.) normally assumed when the compressor unit is in steady operation. However, the temperature of the boil-off gas may fluctuate, and the boil-off gas having a temperature lower than the above temperature may be sucked by the first compression stage.

Generally, when the temperature of the boil-off gas decreases, the gas density increases, so that the processing amount of the first compression stage increases. In this case, if the set pressure is set based on the above-mentioned normally assumed suction temperature of the boil-off gas, the flow rate of the gas returned through the bypass flow path tends to increase, and the pressure in the flow path on the storage tank side tends to increase. May rise.

Therefore, the present invention is to suppress an increase in pressure in the flow path on the storage tank side when a low-temperature gas flows from the storage tank into the compressor unit.

The compressor unit in the present disclosure is installed in a ship, and is a compressor unit that recovers a target gas, which is a boil-off gas, from the LNG storage tank of the ship and supplies at least a part of the target gas to a demand destination. This compressor unit includes a plurality of reciprocating compression stages that sequentially boost the target gas, a crank mechanism that drives the piston of each compression stage, a bypass flow path that bypasses at least the first compression stage, and the bypass flow. A bypass valve provided on the road, an upstream pressure sensor provided in the storage tank connection flow path connecting the LNG storage tank and the first compression stage, a temperature sensor provided in the storage tank connection flow path, and the storage tank. A downstream pressure sensor provided in a flow path downstream of the connection flow path to which the inlet side end of the bypass flow path is connected, and a predetermined pressure detected by the downstream pressure sensor. It is provided with an opening degree adjusting unit for controlling the opening degree of the bypass valve, and a set pressure changing unit for increasing the set pressure when the detection temperature of the temperature sensor decreases.

In the compressor unit configured in this way, when the temperature of the target gas flowing into the compressor unit from the LNG storage tank drops, the set pressure change unit changes the set pressure to a higher pressure. Then, the opening degree of the bypass valve is adjusted by the opening degree adjusting unit with the set pressure changed to a higher pressure as the target pressure of the detected pressure of the downstream pressure sensor. Therefore, it is difficult for the target gas to be returned from the discharge side flow path to the storage tank connection flow path through the bypass flow path, so that an increase in the flow rate of the target gas returning to the storage tank connection flow path can be suppressed. As a result, when the temperature of the inflowing target gas becomes low, it is possible to prevent the pressure in the storage tank connecting flow path from increasing.

When the detection temperature of the temperature sensor becomes equal to or lower than the predetermined temperature, the set pressure changing unit may maintain the set pressure as the set pressure corresponding to the predetermined temperature.

In this embodiment, a predetermined lower limit is set as the temperature for changing the set pressure in the set pressure changing unit. Therefore, since the set pressure does not become higher than the pressure corresponding to the predetermined temperature, it is possible to prevent the set pressure from rising too much. As a result, it is possible to suppress an increase in the power of the compressor unit.

The set pressure changing unit may increase the set pressure as the detection pressure of the upstream pressure sensor rises.

In this aspect, when the pressure in the storage tank connecting flow path rises due to an increase in the amount of boil-off gas generated or the like, the set pressure is changed to a higher pressure. As a result, the flow rate of the target gas returned from the discharge side flow path to the storage tank connection flow path through the bypass flow path can be suppressed. Therefore, it contributes to the suppression of the pressure increase in the storage tank connection flow path.

A safety valve provided in the flow path to which the inlet side end of the bypass flow path is connected and whose operating pressure is set to a constant value is further provided, and the set pressure changing unit operates the safety valve with respect to the set pressure. An upper limit pressure that is a predetermined value lower than the pressure may be set.

In this embodiment, the set pressure changing unit sets an upper limit pressure to the set pressure so that the set pressure, which is the target pressure of the second pressure sensor, does not come too close to the operating pressure of the safety valve. This makes it possible to prevent the pressure in the flow path provided with the safety valve from momentarily reaching the operating pressure even when the discharge amount from the compression stage fluctuates. That is, it is possible to prevent an unintended operation of the safety valve.

The temperature sensor may be provided between the outlet side end of the bypass flow path and the first compression stage in the storage tank connection flow path.

In this embodiment, the temperature sensor provided at a position closer to the suction port of the first compression stage can accurately detect the temperature of the target gas flowing into the first compression stage.

The method for controlling the compressor unit according to the present invention is a method for controlling a compressor unit installed in a ship and recovering a target gas which is a boil-off gas from the LNG storage tank of the ship and supplying at least a part of the target gas to a demand destination. be. The compressor unit includes a plurality of reciprocating compression stages that sequentially boost the target gas, a bypass flow path that bypasses at least the first compression stage, a bypass valve provided in the bypass flow path, and the LNG storage tank. It is provided with a storage tank connection flow path for connecting the first compression stage and the first compression stage. In the control method of the compressor unit, the pressure of the target gas flowing through the storage tank connection flow path is detected by an upstream pressure sensor, the temperature of the target gas flowing through the storage tank connection flow path is detected by a temperature sensor, and the storage tank connection flow is detected. The pressure of the target gas flowing through the flow path on the downstream side of the path to which the inlet side end of the bypass flow path is connected is detected by the downstream pressure sensor, and the detection pressure of the downstream pressure sensor is predetermined. The opening degree of the bypass valve is adjusted so as to reach the set pressure, and when the detection temperature of the temperature sensor decreases, the set pressure is increased.

According to the compressor unit in the present disclosure, when a low-temperature gas having a high gas density flows into the compressor unit from the storage tank, it is possible to suppress an increase in pressure in the flow path on the storage tank side.

It is a schematic block diagram of the compressor unit which concerns on 1st Embodiment. It is a relationship diagram which shows the relationship between the detected pressure of the upstream pressure sensor and the set pressure in the compressor unit which concerns on 1st Embodiment. It is a flowchart which shows schematic | control method of the controller which concerns on 1st Embodiment. It is a block diagram which shows a part of the compressor unit which concerns on 2nd Embodiment. It is a relationship diagram which shows the relationship between the detected pressure of the upstream pressure sensor and the set pressure in the compressor unit which concerns on 2nd Embodiment. It is a schematic block diagram of the compressor unit which concerns on 3rd Embodiment.

(First Embodiment)
FIG. 1 is a schematic configuration diagram of the compressor unit 100 according to the first embodiment. The compressor unit 100 will be described with reference to FIG.

The compressor unit 100 is installed on a ship (not shown) having a storage tank 101 in which LNG (Liquefied Natural Gas) is stored. The compressor unit 100 is configured to recover the target gas, which is the boil-off gas generated in the storage tank 101, boost the pressure to, for example, about 300 barG, and supply the boosted target gas to a predetermined demand destination 600. .. In the following description, the terms "upstream" and "downstream" are used with respect to the flow direction of the target gas.

The compressor unit 100 includes a gas flow path 110 through which a target gas flows from a storage tank 101 toward a demand destination 600, a plurality of compression stages (first compression stage 201 to sixth compression stage 206) for sequentially boosting the target gas, and a plurality of compression stages (first compression stage 201 to sixth compression stage 206). A drive unit (not shown) for driving each compression stage 201 to 206 is provided. The gas flow path 110 is provided with two first compression stages 201, and second to sixth compression stages 202 to 206 are sequentially provided on the downstream side of the two first compression stages 201.

The drive unit includes a drive source (motor, engine, etc.) and a crank mechanism that transmits the power of the drive source to the first compression stage 201 to the sixth compression stage 206. The crank mechanism has a plurality of crossheads connected to the piston rods of the first compression stage 201 to the sixth compression stage 206, respectively. The crank mechanism is configured to reciprocate the piston rod and the piston connected to the tip of the piston rod by changing the rotation of the crankshaft into the reciprocating movement of the crosshead. The first compression stage 201 to the sixth compression stage 206 are reciprocating type, respectively.

The first compression stage 201 to the sixth compression stage 206 are a cylinder portion, a piston housed in the cylinder portion, a piston ring attached to the piston, and a piston rod extending from the piston and connected to the crank mechanism, respectively. (Not shown). A rod packing is provided on the cylinder portion. The first compression stage 201 to the fifth compression stage 205 are oil-free compression stages in which lubricating oil is not supplied to the piston ring and rod packing, and the sixth compression stage 206 supplies lubricating oil to the piston ring and rod packing. It is a refueling type compression stage.

The gas flow path 110 supplies the target gas to the storage tank connection flow path 111 into which the target gas flows from the storage tank 101, the plurality of stage connection flow paths 112 to 116 between the plurality of compression stages 201 to 206, and the demand destination 600. The demand destination supply channel 117 and the like are included.

The storage tank connection flow path 111 is connected to the upper part of the storage tank 101 and is bifurcated and connected to two first compression stages 201. That is, the two first compression stages 201 are configured to be parallel to each other.

The stage connection flow path 112 is configured to flow the target gas from the two first compression stages 201 to the second compression stage 202. That is, the stage connection flow path 112 extends from the two first compression stages 201 and joins one flow path to be connected to the second compression stage 202.

The stage connection flow path 113 connects the second compression stage 202 and the third compression stage 203. The stage connection flow path 114 connects the third compression stage 203 and the fourth compression stage 204. The stage connection flow path 115 connects the fourth compression stage 204 and the fifth compression stage 205. The stage connection flow path 116 connects the fifth compression stage 205 and the sixth compression stage 206.

The stage connection flow path 116 includes an on-off valve 352 for opening and closing the flow of the target gas from the fifth compression stage 205 to the sixth compression stage 206, and a target gas from the sixth compression stage 206 to the fifth compression stage 205. An intermediate check valve 353 and an intermediate check valve 353 are provided to prevent backflow. The intermediate check valve 353 is arranged between the on-off valve 352 and the sixth compression stage 206.

The demand destination supply flow path 117 connects the sixth compression stage 206 and the demand destination 600. The demand destination supply flow path 117 includes a check valve 354 that prevents the backflow of the target gas from the demand destination 600 to the sixth compression stage 206, and a discharge flow path for leading the surplus target gas to the combustion equipment 500. 118 is connected. The discharge flow path 118 is provided with a discharge valve 355 for opening and closing the flow of the target gas to the combustion equipment 500.

A plurality of coolers 212 to 216 are provided in the plurality of stage connection flow paths 112 to 116 and the demand destination supply flow path 117. Each of the plurality of coolers 212 to 216 is configured to exchange heat with the cooling water having a temperature lower than that of the target gas.

The cooler 212 is provided in the stage connection flow path 113 so as to cool the target gas discharged from the second compression stage 202. The cooler 213 is provided in the stage connection flow path 114 so as to cool the target gas discharged from the third compression stage 203. The cooler 214 is provided in the stage connection flow path 115 so as to cool the target gas discharged from the fourth compression stage 204. The cooler 215 is provided on the upstream side of the on-off valve 352 in the stage connection flow path 116 so as to cool the target gas discharged from the fifth compression stage 205. The cooler 216 is provided on the upstream side of the check valve 354 in the demand destination supply flow path 117 so as to cool the target gas discharged from the sixth compression stage 206.

The compressor unit 100 further includes bypass flow paths 301 to 304 for returning the target gas from the downstream side to the upstream side, and a reliquefaction line 119 for reliquefying the target gas and returning it to the storage tank 101. ..

The bypass flow path 301 is formed so as to extend from the inlet side end portion 322 connected to the stage connection flow path 113 to the outlet side end portion 321 connected to the storage tank connection flow path 111. The inlet side end portion 322 is arranged on the downstream side of the cooler 212 in the storage tank connection flow path 111. That is, the bypass flow path 301 connects the stage connection flow path 113 and the storage tank connection flow path 111 so as to bypass the first compression stage 201 and the second compression stage 202.

Similarly, the bypass flow path 302 is formed so as to extend from the inlet side end connected to the stage connection flow path 114 to the outlet side end connected to the stage connection flow path 113, and the third compression stage 203 is formed. Bypassing. The bypass flow path 303 is formed so as to extend from the inlet side end connected to the stage connection flow path 116 to the outlet side end connected to the stage connection flow path 114, and is formed in the fourth compression stage 204 and the fifth compression. Bypassing stage 205. The bypass flow path 304 extends from the inlet side end connected to the demand destination supply flow path 117 to the outlet side end connected to the stage connection flow path 116, and bypasses the sixth compression stage 206. ing.

Bypass valves 311 to 314 are provided in the bypass flow paths 301 to 304, respectively. The bypass valves 311 to 314 receive a signal from the controller 420 described later so that the detected pressure of the target gas at the inlet side end of the bypass flow paths 301 to 304 becomes a set pressure which is a predetermined target pressure, and the opening degree is increased. It is configured to be adjusted.

The reliquefaction line 119 is formed so as to extend from the inlet side end connected to the upstream side of the intermediate check valve 353 in the stage connection flow path 116 toward the liquefaction facility (for example, heat exchanger) shown in the figure. ing.

The compressor unit 100 includes an upstream pressure sensor 401 and a temperature sensor 403, a second pressure sensor 412 functioning as a downstream pressure sensor 402, a third to sixth pressure sensors 413 to 416, and a controller 420. ..

The upstream pressure sensor 401 and the temperature sensor 403 together with the outlet side end portion 321 of the bypass flow path 301 in the storage tank connection flow path 111 in order to detect the pressure and temperature of the target gas in the suction side flow path of the first compression stage 201. It is arranged between the first compression stage 201 and the first compression stage 201.

The second pressure sensor 412 (downstream pressure sensor 402) detects the gas pressure in the discharge side flow path of the second compression stage 202, that is, the gas pressure at the inlet side end portion 322 of the bypass flow path 301, in order to detect the stage connection flow. It is provided on the downstream side of the cooler 212 on the road 113.

The third pressure sensor 413 is provided on the downstream side of the cooler 213 in the stage connection flow path 114. The fourth pressure sensor 414 is arranged between the cooler 215 and the on-off valve 352 in the stage connection flow path 116. The fifth pressure sensor 415 is arranged between the intermediate check valve 353 and the sixth compression stage 206 in the stage connection flow path 116. The sixth pressure sensor 416 is arranged between the cooler 216 and the check valve 354 in the demand destination supply flow path 117.

A signal indicating the detected pressure P1 output from the upstream pressure sensor 401, a signal indicating the detected temperature T1 output from the temperature sensor 403, and a detected pressure P2 output from the second pressure sensor 412 (downstream pressure sensor 402) are used. The indicated signal is transmitted to the controller 420.

The controller 420 is composed of a microcomputer including a ROM, a RAM, a CPU, and the like. A control program that causes the controller 420 to function as the set pressure changing unit 431 and the opening degree adjusting unit 441, and a predetermined relational expression are stored in the ROM or the like of the controller.

Here, the relational expression includes a detection pressure P1 (that is, a pressure on the suction side of the first compression stage 201) and a detection temperature T1 (that is, a temperature on the suction side of the first compression stage 201) and a second compression stage 202. It represents the relationship with the set pressure PS1 in the stage connection flow path 113 on the discharge side. The set pressure changing unit 431 is configured to derive the set pressure PS1 from the detected pressure P1 and the detected temperature T1 with reference to the relational expression, and change the opening setting value of the bypass valve 311 so as to be the set pressure PS1. Has been done.

FIG. 2 is a diagram showing the relationship between the set pressure PS1, the detected pressure P1, and the detected temperature T1. In FIG. 2, the horizontal axis shows the detected pressure P1 and the vertical axis shows the set pressure PS1. In the region A shown by the shaded parallelogram in FIG. 2, the set pressure PS1 is set based on the detected pressure P1 and the detected temperature T1.

The lower side CE11 of the region A in FIG. 2 shows the change of the set pressure PS1 with respect to the detected pressure P1 when the detected temperature T1 is a constant temperature T11. The temperature T11 corresponds to the upper limit temperature of the assumed target gas temperature, and is 40 ° C. in the present embodiment. If the target gas having a temperature exceeding the temperature T11 temporarily flows in, it is based on the relationship between the detected pressure P1 and the set pressure PS1 (relationship indicated by the side CE11) when the temperature is T11. The set pressure PS1 is calculated.

The upper side CE13 of the region A in FIG. 2 shows the change of the set pressure PS1 with respect to the detected pressure P1 when the detected temperature T1 is a constant temperature T13. The temperature T13 is lower than the temperature T11, and is 20 ° C. in the present embodiment. In reality, a gas having a temperature lower than the temperature T13 may flow in. When the temperature of the target gas is equal to or lower than the temperature T13, the set pressure PS1 is calculated based on the relationship between the detected pressure P1 and the set pressure PS1 (relationship indicated by the side CE13) when the temperature is T13.

The linear portion CE12 located between the sides CE11 and CE13 and having the same inclination as these shows the change of the set pressure PS1 with respect to the detected pressure P1 when the detected temperature T1 is a constant temperature T12. The temperature T12 is a temperature between the temperature T11 and the temperature T13. As described above, in the region A, the linear portion having the same inclination as the sides CE11 and CE13 indicates the change of the set pressure PS1 with respect to the detected pressure P1 when the detected temperature T1 is a constant temperature.

In the set pressure changing unit 431, when the detected temperature T1 is constant, the setting is changed so that the set pressure PS1 linearly increases with respect to the increase in the detected pressure P1 of the upstream pressure sensor 401. The relationship between the detected pressure P1 and the set pressure PS1 is represented by a straight line such as the sides CE11 and CE13 in FIG. That is, when the pressure of the target gas on the suction side of the first compression stage 201 rises, the compressor unit 100 sets the target pressure of the target gas on the discharge side of the second compression stage 202 according to the increase width of this pressure. It is configured to be high.

In the region A in FIG. 2, as the detected temperature T1 of the temperature sensor 403 decreases, a straight line representing the relationship between the detected pressure P1 and the set pressure PS1 is represented so as to translate upward in the vertical axis direction. .. That is, the set pressure changing unit 431 is configured to increase the set pressure PS1 as the detected temperature T1 decreases. That is, in the compressor unit 100, when the temperature of the target gas on the suction side of the first compression stage 201 drops, the target pressure of the target gas on the discharge side of the second compression stage 202 is set according to the temperature drop. It is configured to be high.

Here, a specific example in which the set pressure PS1 is changed will be described with reference to FIG. For example, assuming that the detection temperature T1 of the target gas on the suction side of the first compression stage 201 is T11 and the detection pressure P1 of the target gas on the suction side is in the state of P11 (state B), the pressure P21 is set as the set pressure PS1. Is set.

Assuming that the detection temperature T1 is T11 and the detection pressure P1 is in the state of P12 (state C), the pressure P22 is set as the set pressure PS1. Assuming that the detection temperature T1 is T12 and the detection pressure P1 is in the state of P11 (state D), the pressure P23 is set as PS1 as the set pressure. Assuming that the detection temperature T1 is T12 and the detection pressure P1 is in the state of P12 (state E), the pressure P24 is set as PS1 as the set pressure.

The opening degree adjusting unit 441 compares the set pressure PS1 set by the set pressure changing unit 431 with the detected pressure P2 of the second pressure sensor 412 (downstream pressure sensor 402), and compares the detected pressure of the second pressure sensor 412. It is configured to control the opening degree of the bypass valve 311 so that P2 becomes the set pressure PS1.

For example, when the detection pressure P2 of the second pressure sensor 412 is higher than the set pressure PS1, the opening degree adjusting unit 441 increases the opening degree of the bypass valve 311 in order to increase the gas flow rate of the bypass flow path 301. do. When the detected pressure P2 of the second pressure sensor 412 is lower than the set pressure PS1, the opening degree of the bypass valve 311 is reduced in order to reduce the gas flow rate of the bypass flow path 301.

(Operation explanation and control method)
Here, the operation when the compressor unit 100 is driven will be described. When the compressor unit 100 is driven, the on-off valve 352 is open, while the discharge valve 355 is closed, and the storage tank 101 and the demand destination 600 communicate with each other via the gas flow path 110. In this state, each compression stage 201 to 206 is driven.

The target gas supplied from the storage tank 101 to the storage tank connection flow path 111 passes through the compression steps in the first compression stage 201 to the sixth compression stage 206 and the cooling steps in the coolers 212 to 216 to the demand destination supply flow path 117. Derived. Further, a part of the target gas flowing through the stage connection flow path 116 is returned from the reliquefaction line 119 to the reliquefaction facility (not shown). The target gas of the demand destination supply flow path 117 is led out to the demand destination 600, and when a surplus is generated in the target gas, the discharge valve 355 is opened, and the surplus target gas is transferred from the discharge flow path 118 to the combustion equipment 500. Derived.

The compressor unit 100 may return a part of the target gas flowing through the stage connection flow paths 113 to 116 and the demand destination supply flow path 117 from the downstream flow path to the upstream side flow path by the bypass flow paths 301 to 304. It is configured to be possible. As a result, it is possible to flexibly respond to changes in the demand amount of the target gas of the demand destination 600.

In the first compression stage 201 and the second compression stage 202, a part of the target gas of the stage connection flow path 113 is connected to the storage tank via the bypass flow path 301 provided with the bypass valve 311 whose opening degree can be adjusted by the controller 420. It is possible to return to the flow path 111. In the third compression stage 203, a part of the target gas of the stage connection flow path 114 can be returned to the stage connection flow path 113 via the bypass flow path 302 provided with the bypass valve 312. In the fourth compression stage 204 and the fifth compression stage 205, a part of the target gas of the stage connection flow path 116 can be returned to the stage connection flow path 114 via the bypass flow path 303 provided with the bypass valve 313. It is said that. In the sixth compression stage 206, a part of the target gas of the demand destination supply flow path 117 can be returned to the stage connection flow path 116 via the bypass flow path 304 provided with the bypass valve 314.

Here, attention will be paid to the bypass valve 311 of the bypass flow path 301 straddling the first compression stage 201 and the second compression stage 202, and a control method when the controller 420 adjusts the opening degree of the bypass valve 311 will be described.

FIG. 3 shows a flowchart of a control method when the controller 420 adjusts the opening degree of the bypass valve 311.

First, the compressor unit 100 starts operation in response to a command to start operation, the target gas of the storage tank connection flow path 111 is sucked into the first compression stage 201, and the stage connection flow path 113 is sucked from the second compression stage 202. The compressed target gas is discharged. At this time, the controller 420 receives the signals of the detected pressure P1 and the detected temperature T1 from the upstream pressure sensor 401 and the temperature sensor 403 (step S100). The controller 420 also receives a signal of the detected pressure P2 from the second pressure sensor 412.

The controller 420 derives the set pressure PS1 based on the relational expression for deriving the set pressure PS1 with the detected pressure P1 and the detected temperature T1 as parameters and the values acquired from the upstream pressure sensor 401 and the temperature sensor 403 (step S200). ). This relational expression is set so as to fit within the region A in FIG. The opening degree adjusting unit 441 adjusts the opening degree of the bypass valve 311 so that the received detection pressure P2 approaches the set pressure PS1 derived from the relational expression (step S300).

As described above, in the compressor unit 100, when the detected temperature T1 becomes lower than the temperature T11 (upper limit temperature), the set pressure PS1 is changed to a higher value and the opening degree of the bypass valve 311 is adjusted. It will be done. Therefore, it becomes difficult for the target gas of the stage connection flow path 113 to be returned from the bypass flow path 301 to the storage tank connection flow path 111. Therefore, even if the processing amount of the target gas in the first compression stage 201 and the second compression stage 202 is increased by inhaling the target gas at a low temperature, the increase in the flow rate of the target gas returned to the storage tank connection flow path 111 is large. It is suppressed. As a result, it is possible to prevent the pressure of the storage tank connecting flow path 111 from becoming excessively high.

Further, in the compressor unit 100, when the set pressure changing unit 431 changes the set pressure PS1, if the detection temperature T1 of the temperature sensor 403 is equal to or lower than the preset lower limit temperature T13, the set pressure PS1 is set. The value is maintained according to the temperature T13. As a result, an excessive increase in the set pressure PS1 is suppressed, and deterioration of the pressure balance between the compression stages 201 to 206 due to an increase in the discharge pressures of the first compression stage 201 and the second compression stage 202 is suppressed. As a result, an increase in the power of the compressor unit can be suppressed.

Further, in the compressor unit 100, even when the pressure of the storage tank connection flow path 111 rises due to the increase in the amount of boil-off gas generated (regardless of the change in the detection temperature T1), the set pressure changing unit 431 detects it. The set pressure PS1 is changed to a higher value in proportion to the pressure P1. Therefore, an increase in the flow rate of the target gas returned to the storage tank connection flow path 111 is suppressed. As a result, it is possible to prevent the pressure of the storage tank connecting flow path 111 from becoming excessively high.

(Second Embodiment)
The compressor unit 100 according to the second embodiment will be described with reference to FIGS. 4 and 5. Here, the same components as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

In the second embodiment, the compressor unit 100 is provided with a safety valve 351 in the stage connection flow path 113, and an upper limit pressure is provided in the set pressure PS1 changed by the set pressure changing unit 431. It is different from the first embodiment. Other configurations of the compressor unit 100 are the same as those of the first embodiment.

As shown in FIG. 4, the safety valve 351 is arranged between the second compression stage 202 and the cooler 212 in the stage connection flow path 113 to which the inlet side end portion 322 of the bypass flow path 301 is connected. The safety valve 351 opens when the pressure in the stage connection flow path 113 rises abnormally and reaches a predetermined operating pressure P30 set in the safety valve 351 to release the gas in the stage connection flow path 113 to a predetermined location. It is a safety device to escape to.

As shown in FIG. 5, the controller 420 has an upper limit pressure P26 which is a predetermined value lower than the operating pressure P30 in the set pressure PS1 so that the set pressure PS1 does not come too close to the operating pressure P30 of the safety valve 351. It is remembered. As a result, the region A in FIG. 2 is corrected so as not to exceed the upper limit pressure P26.

For example, when the detected temperature T1 is the temperature T13, the detected pressure P1 changes from the state of the pressure P15 (state L) to the state of the pressure P16 higher than the pressure P15 (state M), and further higher than the pressure P16. It is assumed that the pressure P17 has changed to the state (state N). When changing from the state L to the state M, the set pressure changing unit 431 changes the set pressure PS1 from the pressure P25 to a pressure higher than the pressure P25 according to the change of the detected pressure P1 from the pressure P15 to the pressure P16. The upper limit pressure at this time is the upper limit pressure P26 which is lower than the operating pressure P30 of the safety valve 351 by a predetermined value. Then, even if the state M changes to the state N, since the set pressure PS1 has reached the upper limit pressure P26, the set pressure changing unit 431 maintains the set pressure PS1 at the upper limit pressure P26.

As a result, even when the processing amount of the target gas in the second compression stage 202 increases due to the fluctuation of the required amount of the target gas from the demand destination, the pressure of the stage connection flow path 113 provided with the safety valve 351 is instantaneous. It is possible to prevent the safety valve 351 from reaching the operating pressure P30. That is, it is possible to prevent the safety valve 351 from operating unintentionally.

Although the description of other configurations, actions and effects will be omitted, the description of the first embodiment can be incorporated into the second embodiment.

(Third Embodiment)
The compressor unit 100 according to the third embodiment will be described with reference to FIG. Here, the same components as those of the first embodiment and the second embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

The compressor unit 100 according to the third embodiment is composed of oil-free first to fifth compression stages 201 to 205. In the demand destination supply flow path 117, the upstream end of the reliquefaction line 119 is connected to a portion downstream of the fifth compression stage 205 and upstream of the check valve 354. A discharge flow path 118 for leading the surplus target gas to the combustion equipment 500 is connected to the stage connection flow path 114. The fourth pressure sensor 414 is arranged on the suction side of the fourth compression stage 204 in the stage connection flow path 114, and the fifth pressure sensor 415 is arranged on the downstream side of the cooler 216 in the demand destination supply flow path 117. In this case, the sixth compression stage 206, the bypass flow path 304, the bypass valve 314, the sixth pressure sensor 416, the intermediate check valve 353, and the on-off valve 352 are omitted. Other configurations are almost the same as those of the first embodiment.

Also in the compressor unit 100 according to the third embodiment, when the detected temperature T1 becomes lower than the temperature T11 (upper limit temperature), the set pressure PS1 is changed to a higher value as in the first embodiment. The opening degree of the bypass valve 311 is adjusted. Therefore, it becomes difficult for the target gas of the stage connection flow path 113 to be returned from the bypass flow path 301 to the storage tank connection flow path 111. Even when the processing amount of the target gas in the first compression stage 201 and the second compression stage 202 becomes large by inhaling the target gas at a low temperature, the increase in the flow rate of the target gas returned to the storage tank connection flow path 111 is suppressed. To.

Although the description of other configurations, actions and effects will be omitted, the description of the first embodiment can be incorporated into the third embodiment.

Further, in the first to third embodiments, when the detection temperature T1 is constant, the set pressure PS1 does not necessarily increase at a constant rate of increase with respect to the increase in the detection pressure P1 (change represented by a straight line in FIG. 2). It doesn't have to change. For example, the set pressure PS1 may be changed so as to increase stepwise with respect to an increase in the detected pressure P1. Alternatively, it may change in a curvilinear manner or may change so as to increase discontinuously.

Further, in the first to third embodiments, the bypass flow path 301 is provided so as to bypass the first compression stage 201 and the second compression stage 202, but the bypass flow path 301 is not limited to this. The bypass flow path 301 may be configured to bypass from the first compression stage 201 to the compression stage downstream of the third compression stage 203 or the third compression stage 203.

It should be understood that the embodiments disclosed this time are exemplary in all respects and are not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

100 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・Stage connection flow path 117 ・ ・ ・ ・ ・ ・ ・ ・ Demand destination supply flow path 201 ～ 206 ・ ・ ・ ・ ・ ・ ・ ・ 1st to 6th compression stages 301 ～ 304 ・ ・ ・ ・ ・ ・ Bypass flow path 311 ～ 314 ・ ・ ・ ・ ・ ・ ・ ・ Bypass valve 351 ・ ・ ・ ・ ・ ・ ・ ・ Safety valve 401 ・ ・ ・ ・ ・ ・ ・ ・ Upstream pressure sensor 402 ・ ・ ・ ・ ・ ・ ・ ・ Downstream pressure sensor 403 ····························································································································································································・ ・ ・ Demand destination P1, P2 ・ ・ ・ ・ ・ ・ ・ ・ Detected pressure T1 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Detected temperature PS1 ・ ・ ・ ・ ・ ・ ・ ・ Set pressure

Claims (6)

A compressor unit installed inside a ship that recovers the target gas, which is boil-off gas, from the LNG storage tank of the ship and supplies at least a part of it to the demand destination.
Multiple reciprocating compression stages that sequentially boost the target gas,
The crank mechanism that drives the piston of each compression stage,
With a bypass flow path that bypasses at least the first compression stage,
A bypass valve provided on the bypass flow path and
An upstream pressure sensor provided in the storage tank connection flow path connecting the LNG storage tank and the first compression stage, and
The temperature sensor provided in the storage tank connection flow path and
A downstream pressure sensor provided in a flow path downstream of the storage tank connection flow path and to which the inlet side end of the bypass flow path is connected.
When the detected pressure of the downstream pressure sensor is higher than the predetermined set pressure, the gas flow rate of the bypass flow path is increased, while when the detected pressure of the downstream pressure sensor is lower than the set pressure, the bypass flow path of the bypass flow path is increased. An opening adjustment unit that controls the opening of the bypass valve so as to reduce the gas flow rate ,
A set pressure changing unit that raises the set pressure when the detection temperature of the temperature sensor drops,
Compressor unit with. The compressor unit according to claim 1, wherein the set pressure changing unit maintains the set pressure at the set pressure corresponding to the predetermined temperature when the detected temperature of the temperature sensor becomes equal to or lower than the predetermined temperature. .. The compressor unit according to claim 2, wherein the set pressure changing unit increases the set pressure according to an increase in the detected pressure of the upstream pressure sensor. A safety valve provided in the flow path to which the inlet side end of the bypass flow path is connected and whose operating pressure is set to a constant value is further provided.
The compressor unit according to claim 3, wherein the set pressure changing unit sets an upper limit pressure of the set pressure, which is lower than the operating pressure of the safety valve by a predetermined value. The compressor unit according to any one of claims 1 to 4, wherein the temperature sensor is provided between the outlet side end of the bypass flow path and the first compression stage in the storage tank connection flow path. It is a control method of a compressor unit installed in a ship and recovering a target gas which is a boil-off gas from the LNG storage tank of the ship and supplying at least a part of the target gas to a demand destination.
The compressor unit includes a plurality of reciprocating compression stages that sequentially boost the target gas, a bypass flow path that bypasses at least the first compression stage, a bypass valve provided in the bypass flow path, and the LNG storage tank. A storage tank connection flow path for connecting the first compression stage and the first compression stage.
The pressure of the target gas flowing through the storage tank connection flow path is detected by the upstream pressure sensor, and the pressure is detected.
The temperature of the target gas flowing through the storage tank connection flow path is detected by a temperature sensor, and the temperature is detected.
The pressure of the target gas flowing through the flow path downstream of the storage tank connection flow path and connected to the inlet side end of the bypass flow path is detected by the downstream pressure sensor.
When the detected pressure of the downstream pressure sensor is higher than the predetermined set pressure, the gas flow rate in the bypass flow path is increased, while when the detected pressure of the downstream pressure sensor is lower than the predetermined set pressure, the bypass flow is increased. Adjust the opening of the bypass valve so as to reduce the gas flow rate in the road .
A method for controlling a compressor unit, which increases the set pressure when the detection temperature of the temperature sensor decreases.

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