GR1010037B - Control method of compressor unit, compressor unit and compression stage - Google Patents

Abstract

The present application discloses a control method of a compressor unit that is installed in a ship and compresses a target gas that is a boil off gas sucked from an LNG storage tank of the ship. In the control method, at a time of driving the compressor unit, when it is determined that the target gas in a storage lank connection flow path connected to the LNG storage tank is in a predetermined low-pressure state, the bypass valve is opened and the target gas is returned to the storage tank connection flow path through a bypass line.

Description

COMPRESSOR UNIT CONTROL METHOD, COMPRESSOR UNIT AND STAGE

COMPRESSION

Technical field

[0001]

The present invention relates to a method of controlling a compressor unit which supplies a target gas which is an evaporation loss gas from an LNG storage tank of a ship to a demand destination, and to a compressor unit. Background technique

[0002]

Conventionally, a compressor unit is developed which increases the pressure of an evaporation loss gas (hereafter referred to as "target gas") produced from liquefied natural gas (liquefied natural gas or LNG) and delivers the evaporation loss gas to a demand destination such as an engine or a generator (see JP 6371930 B1, JP 2011-517749 A and JP 2018-128039 A). To prevent excessive pressure build-up on a discharge side of a compression stage in the compressor unit, the compressor unit includes a bypass line to return the target gas upstream (see TP 6371930 B1 and TP 2011-517749 A). In general, when the pressure on the discharge side of the compression stage exceeds a predetermined limit, a bypass valve located in the bypass line opens and a high-pressure target gas returns upstream. As a result, the pressure on the discharge side of the compression stage is reduced and the load on the compression stage is reduced.

[0003]

At the same time, the amount of target gas produced in an LNG storage tank that stores LNG may decrease due to various factors. If the pressure of the target gas in a storage tank connection flow path connected to the LNG storage tank drops too much, the load on a first compression stage in the compressor unit may increase too much. As described above, even if the pressure on the discharge side of the compression stage is controlled not to increase excessively as in the related art described above, an increase in the load on the compression stage cannot be avoided in some cases.

Summary of the invention

[0004]

An object of the present invention is to provide a technique for supplying a target gas to a demand destination without excessively increasing the load on a compression stage of a compressor unit even with the production of a small amount of target gas.

[0005]

A control method according to one aspect of the present invention is used to control a compressor unit which is installed on a ship and compresses a target gas which is an evaporation loss gas produced in an LNG storage tank of the ship. The compressor unit includes a plurality of compression stages which successively increase the pressure of the target gas, a bypass line which extends from one end connected to a storage tank connection flow path which connects a first compression stage to the LNG storage tank to bypass a part of the plurality of compression stages and a bypass valve which is located in the bypass line. Another end of the bypass line is connected to a section of flow path between compression stages which are adjacent to each other. The compressor unit further includes another bypass line one end of which is connected to the flow path section and the other end of which is on a downstream side of the flow path section for bypassing one or two or more compression stages and another bypass valve placed on the other bypass line. The control method includes, during operation of the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low pressure state, opening the bypass valve and returning the target gas to the storage tank connection flow path via of the bypass line to reduce target gas pressure in the flow path section and increase target gas pressure in the storage tank connection flow path. The control method also includes, when it is determined that the target gas in the flow path portion is in a predetermined low pressure state, opening the other bypass valve and returning the target gas to the flow path portion through the other bypass line to reduce the pressure of the target gas in a flow path where the other end of the other bypass line is located and the pressure increase of the target gas in the flow path section. A low pressure side limit in a case where it is determined that the target gas in the flow path section is in the predetermined low pressure state is greater than a low pressure side limit in a case where it is determined that the target gas in the storage tank connection flow path is to the preset low pressure condition.

[0006]

A control method according to another aspect of the present invention is used to control a compressor unit which is installed on a ship and compresses a target gas which is an evaporation loss gas produced in an LNG storage tank of the ship. The compressor unit includes a plurality of compression stages which sequentially increase a target gas pressure, a bypass line which extends from one end connected to a storage tank connection flow path which connects a first compression stage to the LNG storage tank to bypass a part of the plurality of compression stages and a bypass valve which is located in the bypass line. Another end of the bypass line is connected to a section of flow path between compression stages which are adjacent to each other. The control method includes, during operation of the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low pressure state, opening the bypass valve and returning the target gas to the storage tank connection flow path via of the bypass line, when it is determined to be out of the low pressure state, closing the bypass valve and determining whether or not the target gas in the flow path portion is in a predetermined high pressure state, and when the target gas transitions to the state high pressure, which is caused by a decrease in the temperature of the target gas in the storage tank connection flow path, the opening of the bypass valve.

[0007]

A compressor unit according to another aspect of the present invention is used for the control method described above. The compressor unit includes the plurality of compression stages, a drive unit which drives the plurality of compression stages, the bypass line, the bypass valve, the other bypass line, the other bypass valve, a pressure sensor which detects the pressure of a gas target gas in the storage tank connection flow path, another pressure sensor which detects the pressure of the target gas in the flow path section, and a control unit which compares a pressure value obtained from the pressure sensor with the low pressure side limit of the target gas in the storage tank connection flow path, and when it is determined that the target gas in the storage tank connection flow path is in the low pressure state, performs a check to open the bypass valve and which compares a pressure value received from the other pressure sensor to the limit low pressure side of the target gas in the flow path section and the When it determines that the target gas in the flow path section is in a predetermined low pressure state, it performs control to open the other bypass valve.

[0008]

A compressor unit according to another aspect of the present invention is used for the control method described above. The compressor unit includes the plurality of compression stages, a drive unit which drives the plurality of compression stages, the bypass line, the bypass valve, a pressure sensor which detects the pressure of a target gas in the storage tank connection flow path, another a pressure sensor which detects the pressure of the target gas in the flow path section and a control unit which, upon determining, based on the pressure obtained from the pressure sensor, that the target gas in the storage tank connection flow path is in the low pressure state , performs a check to open the bypass valve, and when determined to be out of the low pressure state, performs a check to close the bypass valve, and which, when determined, compares a pressure value received from the other pressure sensor to the limit low pressure side of the target gas in the flow path section and when determined that the target gas in the flow path section is in a predetermined low pressure state, performs control to open the other bypass valve, based on the pressure received from the other pressure sensor, that the target gas transitions to a predetermined high pressure state, which is caused by a decrease in target gas temperature in the storage tank connection flow path, performs a control to open the bypass valve.

[0009]

A plurality of compression stages according to another aspect of the present invention is used in the compressor unit described above.

[0010]

The technique described above can provide the target gas to a demand destination without excessively increasing a load on the compression stage of the compressor unit even by producing a small amount of the target gas.

[0011]

The objectives, features and advantages of the compressor unit described above will be apparent from the following detailed description and accompanying drawings.

Brief description of the blueprints

[0012]

FIG. 1 is a schematic flow diagram of a compressor unit,

FIG. 2 is a schematic flow diagram illustrating a method of controlling a bypass valve in the compressor unit;

FIG. 3 is a schematic flow diagram illustrating a method of controlling the bypass valve in the compressor unit, and

FIG. 4 is a schematic flow diagram of a compressor unit.

Description of implementations

[0013]

FIG. 1 is a schematic flow diagram of a compressor unit 100. The compressor unit 100 will describe with reference to FIG. 1.

[0014]

The compressor unit 100 is installed on a ship (not shown) which has an LNG storage tank 101 that stores liquefied natural gas (LNG). The compressor unit 100 is configured to suck in a target gas which is an evaporation loss gas produced in the LNG storage tank 101 and compress the sucked target gas. In particular, the compressor unit 100 is configured to increase the pressure of the target gas to about 300 barG (30 MPaG) and to supply the target gas whose pressure has been increased to a demand destination. In the following description, the terms "upstream" and "downstream" are used based on the direction of flow of the target gas.

[0015]

The compressor unit 100 is a reciprocating compression mechanism and includes a flow path 110 in which the target gas flows to the demand destination, a plurality of compression stages 201 to 205 which sequentially increase the pressure of the target gas, a plurality of coolers 281 to 284 and a drive unit (not shown). The drive unit includes a drive source (electric motor, internal combustion engine or other similar machine) and a crank mechanism which transmits the power of the drive source to the first through fifth compression stages 201 to 205. In FIG. 1, the compressor unit 100 is illustrated as an assembly which includes components depicted within a line with two dots and a dash.

[0016]

The upstream end of the flow path 110 is connected to an upper portion of the LNG storage tank 101 to allow an evaporation loss gas produced in the LNG storage tank 101 to enter the flow path 110. A downstream end of the flow path 110 is connected to the demand destination . The flow path 110 includes a storage tank connection flow path 111 , a stages connection flow path 113 , and a demand destinations connection flow path 114 .

[0017]

The storage tank connection flow path 111 is connected to the LNG storage tank 101 and guides the evaporation loss gas to the first compression stage 201 of the compressor unit 100. The compressor unit 100 includes two first compression stages 201 and thus the storage tank connection flow path 111 includes a main pipe 111C extending from the LNG storage tank 101 and branch sections 111 A, 111 B branching from the main pipe 111C. These branch sections 111A, 111B are connected to the first compression stages 201, respectively. That is, the first two compression stages 201 are respectively connected to the two branch sections 111A, 111B so as to be parallel to each other. The compressor unit 100 may comprise a single first compression stage 201.

[0018]

The stage connecting flow path 113 consists of a plurality of flow paths connecting the first through fifth compression stages 201 to 205 to allow the target gas to flow from one compression stage to the next compression stage. On an upstream side of the stage connection flow path 113, the connection portions with the first compression stages 201 are the branch portions 113A, 113B, respectively. The second through fifth compression stages 202 through 205 are located in other portions of the stage connection flow path 113. The second through fifth compression stages 202 through 205 are arranged in series to sequentially increase the pressure of the target gas compressed in the first compression stage 201.

[0019]

The demand destination link flow path 114 is a flow path that connects the fifth compression stage 205 to the demand destination.

[0020]

The crank mechanism includes a piston head connected to a tappet of each of the first through fifth compression stages 201 to 205. The crank mechanism is configured to change a rotation of a crankshaft into a reciprocating motion of the piston head for the purpose of reciprocating. of the plunger and a piston connected to a distal end of the plunger.

[0021]

Coolers 281 to 284 are positioned in the stage connection flow path 113 and the demand destination connection flow path 114 to cool the target gas compressed in the second through fifth compression stages 202 to 205. The coolers 281 to 284 are configured to they exchange heat with the cooling water which has a temperature lower than that of the target gas.

[0022]

The cooler 281 is attached to a flow path portion between the second compression stage 202 and the third compression stage 203 in the stage connecting flow path 113. The cooler 282 is attached to a flow path portion between the third compression stage 203 and the fourth compression stage 204 in stage link flow path 113. Cooler 283 is attached to a flow path portion between fourth compression stage 204 and fifth compression stage 205 in stage link flow path 113. Cooler 284 is attached to demand destination link flow path 114.

[0023]

The compressor unit 100 is configured to perform control to adjust the pressure of the target gas in the storage tank connection flow path 111, the stage connection flow path 113, and the demand destinations connection flow path 114. The control-related sections used for pressure control will be described below.

[0024]

Compressor unit 100 includes bypass lines 411 to 413, bypass valves 421 to 423, pressure sensors 431 to 434 and a control unit 414. [0025]

The bypass line 411 is connected to the storage tank connection flow path 111 and the stage connection flow path 113 to bypass the first compression stage 201 and the second compression stage 202. One end of the bypass line 411 is connected to the main pipe 111C of the flow path storage tank connection 111. The other end of the bypass line 411 is connected to the stage connection flow path 113 between the cooler 281 and the third compression stage 203.

[0026]

The bypass line 412 is configured to bypass the third compression stage 203. One end of the bypass line 412 is connected to a flow path portion between the cooler 281 and the third compression stage 203 in the stage connection flow path 113 (i.e., the flow path portion to which the other end of the bypass line 411 is connected). The other end of the bypass line 412 is connected to a flow path section between the cooler 282 and the fourth compression stage 204 in the stage connection flow path 113.

[0027]

The bypass line 413 is configured to bypass the fourth compression stage 204 and the fifth compression stage 205. One end of the bypass line 413 is connected to the flow path portion between the cooler 282 and the fourth compression stage 204 in the stage connection flow path 113. The other end of the bypass line 413 is connected to the flow path connecting demand destinations 114 on a downstream side of the cooler 284 .

[0028]

Bypass valves 421 through 423 are attached to bypass lines 411 through 413, respectively. Bypass valves 421 through 423 are electrically connected to control unit 414. Bypass valves 421 through 423 are configured to allow adjustment of the opening rate of these bypass valves under the control of control unit 414.

[0029]

The pressure sensor 431 is attached to the main pipe 111C of the storage tank connection flow path 111. The pressure sensor 431 is configured to detect the pressure of the target gas in the storage tank connection flow path 111 (ie, the pressure of the target gas produced in LNG storage tank 101) and to generate a detection signal indicating a detected pressure (hereinafter "detected pressure").

[0030]

The pressure sensor 432 is attached to the flow path portion between the cooler 281 and the third compression stage 203 in the stage connection flow path 113. The pressure sensor 432 is configured to sense the pressure of the target gas in the flow path portion between the cooler 281 and of the third compression stage 203 and produce a detection signal indicative of a detected pressure. The detected pressure obtained from the pressure sensor 432 indicates the pressure of the target gas drawn into the third compression stage 203 .

[0031]

The pressure sensor 433 is attached to the flow path portion between the cooler 282 and the fourth compression stage 204 in the stage connection flow path 113. The pressure sensor 433 is configured to sense the pressure of the target gas in the flow path portion between the cooler 282 and of the fourth compression stage 204 and produce a detection signal indicative of a detected pressure. The detected pressure obtained from the pressure sensor 433 indicates the pressure of the target gas drawn into the fourth compression stage 204 .

[0032]

Pressure sensor 434 is attached to the demand destination connection flow path 114. The pressure sensor 434 is configured to sense the pressure of the target gas in the demand destination connection flow path 114 and generate a detection signal indicative of a sensed pressure.

[0033]

Control unit 414 is electrically connected to bypass valves 421 to 423 and pressure sensors 431 to 434. Control unit 414 is configured to receive detection signals from pressure sensors 431 to 434 and determine the opening rate of bypass valves 421 to 423 based on the detection signals received. The control unit 414 can be configured as a software or as a special purpose circuit.

[0034]

Below will describe an operation of the compressor unit 100 and a flow of the target gas with reference to FIGS. 1 to 3. FIGs. 2 and FIG. 3 are schematic flow diagrams illustrating a method of controlling the bypass valve 421. FIG. 2 illustrates a control method for eliminating a predetermined low pressure condition in the storage tank connection flow path 111. FIG. 3 illustrates a control method for eliminating a predetermined high pressure condition between the second compression stage 202 and the third compression stage 203 in the stage connection flow path 113.

[0035]

During operation of the compressor unit 100, the target gas is repeatedly aspirated and depressed in the first through fifth compression stages 201 through 205. The target gas depressed in the second through fifth compression stages 202 through 205 passes through the coolers 281 through 284 for cooling. After a compression process in the first through fifth compression stages 201 to 205 and a cooling process in the coolers 281 to 284, the target gas is supplied to a demand destination. During these processes, the pressure of the target gas in the flow path 110 is obtained from the pressure sensors 431 to 434. Normally, when the suction pressure and the discharge pressure in each of the first through fifth compression stages 201 to 205 are within a normal range, bypass valves 421 to 423 are closed. However, when the suction pressure and the discharge pressure deviate from the normal range, the control unit 414 controls the bypass valves 421 to 423 based on the pressures detected by the pressure sensors 431 to 431 and adjusts the pressure of the target gas in the flow path 110 .

[0036]

It will first describe the control of the opening rate of the bypass valve 421. During operation of the compressor unit 100, the amount of a target gas produced in the LNG storage tank 101 may decrease due to various factors. Accordingly, the pressure of the target gas in the storage tank connection flow path 111 is reduced. The bypass valve 421 to eliminate a low pressure condition of the storage tank connection flow path 111 is controlled as illustrated in FIG. 2.

[0037]

During operation of the compressor unit 100, the pressure sensor 431 detects the pressure of the target gas in the storage tank connection flow path 111. The control unit 414 compares a pressure obtained from the pressure sensor 431 with a predetermined limit of the low pressure side (step S110). When it is determined that the pressure of the target gas in the storage tank connection flow path 111 is lower than the low pressure side limit, that is, when it is determined that the target gas is in a low pressure state, the control unit 414 opens the bypass valve 421 ( step S120). If the pressure sensed by the pressure sensor 431 is not lower than the low pressure side limit, the bypass valve 421 is kept closed. The low pressure side limit is, for example, about 0 barG (0 MPaG). When the load on the first compression stage 201 is in an acceptable range even if a low-pressure target gas is sucked in, the low-pressure side limit can be less than 0 barG.

[0038]

As the bypass valve 421 opens, the high-pressure target gas compressed in the first compression stage 201 and the second compression stage 202 flows into the storage tank connection flow path 111 through the bypass line 411. As a result, the pressure of the target gas in the path section flow between the second compression stage 202 and the third compression stage 203 decreases, while the target gas pressure in the storage tank connection flow path 111 increases.

[0039]

The control unit 414 continuously or intermittently compares the pressure detected by the pressure sensor 431 with the low pressure side limit after opening the bypass valve 421 (step S130). If the pressure detected by the pressure sensor 431 is lower than the low pressure side limit, the bypass valve 421 is kept open (step S120). The process loop of steps S120 and S130 continues until the pressure sensed by the pressure sensor 431 is greater than or equal to the low pressure side limit. When the pressure detected by the pressure sensor 431 becomes greater than or equal to the low pressure side limit, the bypass valve 421 closes (step S140).

[0040]

While the bypass valve 421 is open (step S120), the opening rate of the bypass valve 421 is sequentially adjusted based on the comparison of the low pressure side limit with the pressure detected by the pressure sensor 431. Specifically, in the control unit 414, the rate opening time of the bypass valve 421 increases according to the range of the difference between the sensed pressure and the low pressure side limit. Accordingly, when the pressure of the storage tank connection flow path 111 is too low, the amount of target gas returning to the storage tank connection flow path 111 through the bypass line 411 increases, and thus the pressure in the storage tank connection flow path 111 can recover quickly.

In addition, when the pressure of the storage tank connection flow path 111 approaches the low pressure side limit, the opening rate decreases, and thus it is possible to prevent the target gas from excessively returning to the storage tank connection flow path 111.

[0041]

Next, it will describe the control performed when the target gas between the second compression stage 202 and the third compression stage 203 in the stage connection flow path 113 is in a high pressure state with reference to FIG. 3. In the compressor unit 100, for example, when the temperature of the target gas in the storage tank connection flow path 111 decreases, the overall work of the compressor unit 100 may be excessive.

[0042]

During operation of the compressor unit 100, the pressure sensor 432 detects the pressure of the target gas in the flow path portion between the second compression stage 202 and the third compression stage 203. The control unit 414 compares a pressure obtained from the pressure sensor 432 with a predetermined high pressure side limit (step S210). When it is determined that the pressure of the target gas is greater than the high pressure side limit, that is, when it is determined that the target gas is in a high pressure state, the control unit 414 opens the bypass valve 421 (step S220). If the pressure sensed by the pressure sensor 432 is lower than or equal to the high pressure side limit, the bypass valve 421 is kept closed. The limit of the high pressure side is set, for example, equal to 11 barG.

[0043]

As the bypass valve 421 opens, the high-pressure target gas compressed in the first compression stage 201 and the second compression stage 202 flows into the storage tank connection flow path 111 through the bypass line 411. As a result, the pressure of the target gas in the path section flow between the second compression stage 202 and the third compression stage 203 decreases, while the target gas pressure in the storage tank connection flow path 111 increases.

[0044]

The control unit 414 continuously or intermittently compares the pressure detected by the pressure sensor 432 with the high pressure side limit after opening the bypass valve 421 (step S230). If the pressure detected by the pressure sensor 432 is higher than the high pressure side limit, the bypass valve 421 is kept open (step S220). The process loop of steps S220 and S230 continues until the pressure sensed by the pressure sensor 432 is lower than or equal to the high pressure side limit. When the pressure detected by the pressure sensor 432 becomes lower than or equal to the high pressure side limit, the bypass valve 421 closes (step S240).

[0045]

While the bypass valve 421 is open (step S220), the opening rate of the bypass valve 421 is sequentially adjusted based on the comparison of the high pressure side limit with the pressure detected by the pressure sensor 432. Specifically, in the control unit 414, the rate opening time of the bypass valve 421 increases according to the range of the difference between the sensed pressure and the high pressure side limit. Accordingly, when the pressure of the target gas in the flow path portion between the second compression stage 202 and the third compression stage 203 is too high, the amount of the target gas returning to the storage tank connection flow path 111 through the bypass line 411 increases and thus the pressure in the flow path section may decrease rapidly. In addition, when the pressure in the flow path portion approaches the high pressure side limit, the opening rate decreases, and thus it is possible to prevent the target gas from excessively returning to the storage tank connection flow path 111.

[0046]

As described above, in the compressor unit 100, the pressure of the target gas at both ends of the bypass line 411 is obtained from the pressure sensors 431, 432.

When the target gas is in a low-pressure state at the end of the bypass line 411 located in a low-pressure side flow path (storage tank connection flow path 111 ) and when the target gas is in a high-pressure state at the end of the bypass line 411 located in a high pressure side flow path (flow path segment between the second and third compression stages 202 and 203), the opening rate of the bypass valve 421 is controlled.

[0047]

Next, it will describe the control of the opening rate of the bypass valves 422, 423. An opening control similar to the control of the opening rate of the bypass valve 421 is performed on the bypass valves 422, 423. Regarding the control of the opening rate of the bypass valve 422, the control unit 414 receives the pressures on a suction side and a discharge side of the third compression stage 203 which is bypassed by the bypass line 412 (pressures detected by the pressure sensors 432, 433). When the pressure detected by the pressure sensor 432 is lower than the predetermined limit of the low pressure side, that is, when the target gas is in a low pressure state, or when the pressure detected by the pressure sensor 433 is higher than the predetermined limit of the high pressure side, that is, when the target gas is in a high pressure state, the control unit 414 opens the bypass valve 422. The low pressure side limit and the high pressure side limit set in the bypass valve 422 are respectively larger from the low pressure side limit and the high pressure side limit set at bypass valve 421.

[0048]

Regarding the control of the opening rate of the bypass valve 423, the control unit 414 receives a pressure on a suction side of the fourth compression stage 204 and a pressure on a discharge side of the fifth compression stage 205 which is bypassed by the bypass line 413 (pressures that detected by the pressure sensors 433, 434). When the pressure sensed by the pressure sensor 433 is lower than the predetermined limit of the low pressure side or when the pressure sensed by the pressure sensor 434 is higher than the predetermined limit of the high pressure side, the control unit 414 opens the bypass valve 423. The low pressure side limit and the high pressure side limit set at the bypass valve 423 are respectively greater than the low pressure side limit and the high pressure side limit set at the bypass valve 422.

[0049]

The embodiment of the present invention has been described above. If the target gas in the storage tank connection flow path 111 is in a low pressure state, the bypass valve 421 opens to prevent an excessive load on the first and second compression stages 201, 202. In addition, if the target gas in the flow path portion between the second and third compression stages 202 and 203 is in a low pressure state, the bypass valve 422 opens to prevent an excessive load on the third compression stage 203. Similarly, if the target gas in the flow path portion between the third and fourth compression stages 203 and 204 are in a low pressure state, the bypass valve 423 opens to prevent an excessive load on the fourth and fifth compression stages 204, 205.

[0050]

In addition, when the target gas is in a high-pressure state in the flow path portion between the second and third compression stages 202 and 203, the bypass valve 421 is opened. In this way, an excessive load on the first and second compression stages 201 is reduced. , 202. Similarly, if the target gas is in a high-pressure state in the flow path portion between the third and fourth compression stages 203 and 204, the bypass valve 422 opens to prevent an excessive load on the third compression stage 203. If the target gas is in a high pressure state in the demand destination connection flow path 114, the bypass valve 423 opens to prevent an excessive load on the fourth and fifth compression stages 204, 205.

[0051]

The disclosed embodiments should be considered in all respects as indicative and not restrictive. The subject matter of the present invention is defined not by the above description, but by the claims and is intended to include all modifications within the scope of the subject matter and concepts equivalent to the claims.

[0052]

In the embodiment described above, when the amount of target gas produced in the LNG storage tank 101 decreases, the pressure detected by the pressure sensor 431 also decreases, so that the difference between the pressures detected by the pressure sensors 431 and 432 increases. At step S110 in FIG. 2, alternatively, the difference between the pressure detected by the pressure sensor 43 1 and the pressure detected by the pressure sensor 432 may be calculated, and the low pressure condition may be determined based on whether the range of the calculated difference exceeds or not a predetermined upper pressure difference limit value. When it is determined that the target gas in the storage tank connection flow path 111 is in a low pressure state, step S120 in FIG. 2 and bypass valve 421 opens.

[0053]

In the embodiment described above, when it is determined whether or not the target gas is out of the low pressure state (step S120), a value greater than the low pressure side limit may be used as the determination value. When determining whether or not the target gas is out of the high pressure state (step S220), a value smaller than the high pressure side limit may be used as the determination value.

[0054]

In the embodiment described above, the opening rate of the bypass valve 421 can be adjusted based on the ratio of the pressure sensed by the pressure sensor 431 (or the pressure sensor 432) to the low pressure side limit (or the high side limit pressure). This description applies to the bypass valves 422, 423. When precise control of the opening rate is not required, the bypass valves 421 to 423 can be controlled from two values, i.e., a fully closed condition and a fully open condition. This description applies to bypass valves 422, 423.

[0055]

In the present embodiment, as illustrated in FIG. 4, bypass line 411 may be connected to flow path 110 (i.e., storage tank connection flow path 111 and demand destinations connection flow path 114) to bypass the first through fifth compression stages 201 through 205. Alternatively, a line bypass can be placed in each of the compression stages 201 to 205. As described above, the bypass line can be changed as appropriate.

[0056]

With respect to the embodiment described above, the number of compression stages to be used may be less than five (for example, three) or may be greater than five (for example, six).

[0057]

The method of controlling a bypass valve according to the embodiment described above can also be applied to other screw compressors or turbochargers. In this case, power can be transmitted to a compression stage using a gear mechanism instead of a crank mechanism in a compressor unit. Power can be transmitted directly from a drive source to the compression stage.

[0058]

The embodiment described above mainly includes a compressor unit having the following configuration.

[0059]

A control method according to an aspect of the embodiment described above is used to control a compressor unit which is installed on a ship and compresses a target gas which is an evaporation loss gas produced in an LNG storage tank of the ship. The compressor unit includes a plurality of compression stages which sequentially increase the pressure of the target gas, a bypass line which extends from one end connected to a storage tank connection flow path which connects a first compression stage to an LNG storage tank to bypass a part of the plurality of compression stages and a bypass valve which is located in the bypass line. Another end of the bypass line is connected to a flow path section between the compression stages which are adjacent to each other. The compressor unit further includes another bypass line one end of which is connected to the flow path section and the other end of which is on a downstream side of the flow path section for bypassing one or two or more compression stages and another bypass valve placed on the other bypass line. The control method includes, during operation of the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low pressure state, opening the bypass valve and returning the target gas to the storage tank connection flow path through the bypass line to reduce the target gas pressure in the flow path section and increase the target gas pressure in the storage tank connection flow path. The control method also includes, when it is determined that the target gas in the flow path portion is in a predetermined low pressure state, opening the other bypass valve and returning the target gas to the flow path portion through the other bypass line to reduce pressure of the target gas in the flow path in which the other end of the other bypass line is located and the pressure increase of the target gas in the flow path segment. The low-pressure side limit in the case where the target gas in the flow path section is determined to be in the predetermined low-pressure state is greater than the low-pressure side limit in the case where the target gas in the storage tank connection flow path is determined to be in preset low pressure condition.

[0060]

According to the configuration described above, when the bypass valve opens, a part of the target gas returns to the storage tank connection flow path through the bypass line, while the pressure of the target gas in the storage tank connection flow path increases. As a result, it is possible to prevent excessive pressure reduction in the storage tank connecting flow path and reduction of an excessive load in the compression stage bypassed by the bypass line.

[0061]

In the configuration described above, the opening rate of the bypass valve is adjusted based on the result of the comparison between a predetermined value and the pressure of the target gas in the storage tank connection flow path. The opening rate of the other bypass valve is adjusted based on the result of the comparison between a predetermined value and the pressure of the target gas in the flow path section.

[0062]

According to the configuration described above, the opening rate of the bypass valve is adjusted based on the result of the comparison between a predetermined value and the pressure of the target gas in the storage tank connection flow path, and thus it is possible to adjust the amount of the target gas returning in the storage tank connection flow path through the bypass line.

[0063]

A control method according to another aspect of the embodiment described above is used to control a compressor unit which is installed on a ship and compresses a target gas which is an evaporation loss gas produced in an LNG storage tank of the ship. The compressor unit includes a plurality of compression stages which successively increase the pressure of the target gas, a bypass line which extends from one end connected to a storage tank connection flow path which connects a first compression stage to the LNG storage tank to bypass a part of the plurality of compression stages and a bypass valve which is located in the bypass line. Another end of the bypass line is connected to a section of flow path between compression stages which are adjacent to each other. The control method includes, during operation of the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low pressure state, opening the bypass valve and returning the target gas to the storage tank connection flow path via of the bypass line to reduce the pressure of the target gas in the flow path section and increase the pressure of the target gas in the storage tank connection flow path when it is determined to be out of the low pressure state, closing the bypass valve and determining whether the target gas in the flow path section is or is not in a predetermined high-pressure state, and when the target gas goes to the high-pressure state caused by a decrease in the temperature of the target gas in the storage tank connection flow path, the opening of the bypass valve.

[0064]

According to the configuration described above, it is possible to prevent an excessive increase in the pressure of the target gas in a flow path on a downstream side of the storage tank connection flow path and to reduce an excessive load in the compression stage bypassed by the bypass line.

[0065]

In the configuration described above, the opening rate of the bypass valve in the case where it is determined to be in the predetermined low pressure state is adjusted based on the result of the comparison between a predetermined value and the pressure of the target gas in the storage tank connection flow path. The opening rate of the bypass valve in the case where it is determined to be in the predetermined high pressure state is adjusted based on the result of the comparison between a predetermined value and the pressure of the target gas in the flow path section.

[0066]

A compressor unit according to another aspect of the embodiment described above is used for the control method described above. The compressor unit includes the plurality of compression stages, a drive unit which drives the plurality of compression stages, the bypass line, the bypass valve, the other bypass line, the other bypass valve, a pressure sensor which detects the pressure of a gas target gas in the storage tank connection flow path, another pressure sensor which detects the pressure of the target gas in the flow path section, and a control unit which compares a pressure value obtained from the pressure sensor with the limit of the low pressure side of the target gas in the storage tank connection flow path and when it is determined that the target gas in the storage tank connection flow path is in the low pressure state, it performs a check to open the bypass valve and which compares a pressure value received from the other pressure sensor to the limit of the low pressure side of the target gas in the flow path section and when it is determined that the target gas in the flow path portion is in a predetermined low pressure state, it performs control to open the other bypass valve.

[0067]

A compressor unit according to another aspect of the embodiment described above is used for the control method described above. The compressor unit includes the plurality of compression stages, a drive unit which drives the plurality of compression stages, the bypass line, the bypass valve, a pressure sensor which detects the pressure of a target gas in the storage tank connection flow path, another a pressure sensor which detects the pressure of the target gas in the flow path section and a control unit which, upon determining, based on the pressure obtained from the pressure sensor, that the target gas in the storage tank connection flow path is in the low pressure state , performs a check to open the bypass valve, and when determined to be out of the low pressure state, performs a check to close the bypass valve, and which, when determined, based on a pressure received from the other pressure sensor, that the target gas transitions to a predetermined high-pressure state which is induced by a meq ation of the target gas temperature in the storage tank connection flow path, performs a check to open the bypass valve.

A number of compression steps as described above are used in the method.

The technique described in para compressor installed on a ship.

to with another view of the implementation that

compressor blade described above. above implementation applies to a unit

Claims (7)

Claims 1. A method of controlling a compressor unit which is installed on a ship and compresses a target gas which is an evaporation loss gas produced in an LNG storage tank of the ship, with the compressor unit including: a plurality of compression stages which successively increase the pressure of the target gas, a bypass line extending from one end connected to a storage tank connection flow path connecting a first compression stage to the LNG storage tank to bypass a portion of the plurality of compression stages, and a bypass valve positioned in the bypass line, another end of the bypass line is connected to a flow path section between compression stages which are adjacent to each other, with the compressor unit additionally comprising: another bypass line one end of which is connected to the flow path section and the other end of which is on a downstream side of the flow path section to bypass one or two or more compression stages, and another bypass valve placed in the other bypass line, the control method comprising: during operation of the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low pressure state, opening the bypass valve and returning the target gas to the storage tank connection flow path through the bypass line for reducing the target gas pressure in the flow path section and increasing the target gas pressure in the storage tank connection flow path, and when it is determined that the target gas in the flow path section is in a predetermined low pressure state, opening the other bypass valve and returning the target gas to the flow path section through the other bypass line to reduce the pressure of the target gas in a path flow where the other end of the other bypass line is located and the pressure increase of the target gas in the flow path section where a limit of the low pressure side in a case in which it is determined that the target gas in the flow path section is in the predetermined low pressure state is greater than a limit of the low pressure side in a case in which it is determined that the target gas in the tank connection flow path storage is in the preset low pressure state. 2. The control method according to claim 1, wherein the opening rate of the bypass valve is adjusted based on the result of the comparison between a predetermined value and the pressure of the target gas in the storage tank connection flow path, and the opening rate of the other bypass valve is adjusted based on the result of the comparison between a predetermined value and the pressure of the target gas in the flow path section. 3. A method of controlling a compressor unit which is installed on a ship and compresses a target gas which is an evaporation loss gas produced in an LNG storage tank of the ship, with the compressor unit including: a plurality of compression stages which successively increase the pressure of the target gas, a bypass line extending from one end connected to a storage tank connection flow path connecting a first compression stage to the LNG storage tank to bypass a portion of the plurality of compression stages, and a bypass valve positioned in the bypass line, another end of the bypass line is connected to a flow path section between compression stages which are adjacent to each other, with the control method including: during operation of the compressor unit, when it is determined that the target gas in the storage tank connection flow path is in a predetermined low pressure state, opening the bypass valve and returning the target gas to the storage tank connection flow path through the bypass line; when determined to be out of the low pressure condition, closing the bypass valve, and determining whether or not the target gas in the flow path portion is or is not in a predetermined high pressure state, while the target gas transitions to the high pressure state caused by a decrease in temperature of the target gas in the storage tank connection flow path , the opening of the bypass valve. 4. The control method according to claim 3, wherein the opening rate of the bypass valve in the case where it is determined to be in the predetermined low pressure state is adjusted based on the result of the comparison between a predetermined value and the pressure of the target gas in the storage tank connection flow path, and the opening rate of the bypass valve in the case where it is determined to be in the predetermined high pressure state is adjusted based on the result of the comparison between a predetermined value and the pressure of the target gas in the flow path section. 5. A compressor unit used for the control method according to claim 1 or 2, the compressor unit comprising: the number of compression stages, a drive unit which drives the plurality of compression stages, the bypass line, the bypass valve, the other bypass line, the other bypass valve, a pressure sensor which detects the pressure of the target gas in the storage tank connection flow path, another pressure sensor which detects the pressure of the target gas in the flow path portion, and a control unit which compares a pressure value obtained from the pressure sensor with the low pressure side limit of the target gas in the storage tank connection flow path and when it is determined that the target gas in the storage tank connection flow path is in the low pressure state; performs the control to open the bypass valve and which compares a pressure value obtained from the other pressure sensor to the low pressure side limit of the target gas in the flow path section and when it is determined that the target gas in the flow path section is in a predetermined low pressure condition, performs the control to open the other bypass valve. 6. A compressor unit used for the control method according to claim 3 to 4, the compressor unit comprising: the number of compression stages, a drive unit which drives the plurality of compression stages, the bypass line, the bypass valve, a pressure sensor which detects the pressure of the target gas in the storage tank connection flow path, another pressure sensor which detects the pressure of the target gas in the flow path portion, and a control unit which, when it is determined, based on the pressure received from the pressure sensor, that the target gas in the storage tank connection flow path is in the low pressure state, performs a control to open the bypass valve and when it is determined to be out of the low pressure state, performs control to close the bypass valve, and when it is determined, based on the pressure received from the other pressure sensor, that the target gas is transitioning to a predetermined high pressure state, which is caused by a decrease in temperature of the target gas in the storage tank connection flow path, performs a check to open the bypass valve. 7. The number of compression stages used in the compressor unit according to claim 5.