JP4634727B2 - Low duty compressor control method for LNG ship - Google Patents

Description

  The present invention relates to a control method for a low duty compressor mounted on an LNG ship, and more particularly to a control method for controlling an operating point of a low duty compressor so as not to enter a surge control zone.

  Conventionally, in an LNG carrier, evaporative gas generated from liquefied natural gas [LNG (cargo liquid)] in a cargo tank (Boil Off Gas) during transportation of LNG [BOG] That's it. ] As a fuel gas for the main boiler.

  FIG. 4 is a system diagram of a gas combustion apparatus that supplies such BOG as fuel gas to the main boiler. As shown in the figure, the BOG 12 generated from the cargo liquid 11 in the tank 10 is compressed by the low duty compressor 14 via the fuel pipe 13, and the BOG 16 discharged to the discharge pipe 15 is heated to a predetermined temperature by the gas heater 17. Thereafter, the flow rate is adjusted by the gas control valve 18 and supplied to the burner 20 of the main boiler 19. As shown in FIG. 5, the low duty compressor 14 is provided with an inlet guide vane (hereinafter referred to as “IGV”) at the suction port, and a fan 22 provided on the downstream side is connected to the motor. By rotating at 23, the BOG 12 is discharged as a BOG 16 pressurized to a predetermined pressure.

  On the other hand, the main boiler 19 is usually provided with a plurality of burners 20, and the number of combustions is appropriately controlled in accordance with a load (necessary steam amount) that changes according to the operating state of the main turbine. For example, in the case of the main boiler 19 provided with three burners 20 as shown in the figure, when the main turbine is at 100% load, the three burners 20 are burned, and when the load decreases, the two burners 20 are When it is burned and the load is further reduced, the opening degree of the two burners 20 is reduced, or in some cases, the burner 20 is burned. In this way, the combustion state of the main boiler 19 is controlled so that three to one burner 20 is appropriately combusted according to the load. In addition, since two main boilers 19 are usually provided, the number of burner burners is controlled.

  When the number of burners burned in the main boiler 19 changes in this way, the gas supply amount from the discharge pipe 15 is controlled by the gas control valve 18, so that the resistance in the discharge pipe 15 changes to enter the discharge pipe. This causes pressure fluctuations. Since the BOG 16 in the discharge pipe 15 is pressurized and supplied by the low duty compressor 14, the amount of BOG 16 discharged from the low duty compressor 14 corresponding to the control of the gas control valve 18 is a signal from the control device 24. Although it is adjusted, when the gas supply amount is controlled by the gas control valve 18, the operating point of the low duty compressor 14 (the operating state where the predetermined volume flow rate and the predetermined outlet pressure are reached) is quickly lowered to adjust the discharge flow rate. This is difficult, and a surging phenomenon may occur in the low duty compressor 14 due to an increase in pressure in the discharge pipe 15.

  Therefore, a surge control valve 25 is provided to return the BOG 16 in the discharge pipe 15 on the downstream side of the low duty compressor 14 to the fuel pipe 13 on the upstream side of the low duty compressor 14 so that a surging phenomenon does not occur.

FIG. 6 is a surge control graph in the conventional low duty compressor control method. As shown by the solid line in this figure, the surge line S ₁₀ controlled by the surge control valve 25 is first provided at the inlet of the low duty compressor 14. Control is performed such that the rotational speed is increased to a predetermined outlet pressure while the IGV 21 is fully opened, and then the volumetric flow rate is increased to increase the outlet pressure by increasing the rotational speed. The horizontal axis of FIG. 6 shows the volumetric flow rate per time, and the vertical axis shows the output pressure. In the example shown in the figure, the volume flow rate is large up to 12000 rpm, but the rotation speed increases so that the output pressure increases slowly, and the rotation speed increases from 12000 rpm to the maximum rotation speed of 24000 rpm so that the output pressure increases greatly. Surge line S ₁₀ is set.

Also, this way the low duty compressor 14 controlled by the surge line S ₁₀ a, the advance surge control line SC ₁₀ as the operating point does not exceed a surge line S ₁₀ are set. The two-dot chain line shown in the figure is the surge control line SC _10. By setting the surge control line SC ₁₀ with a predetermined margin with respect to the surge line S ₁₀ , the output pressure at the operating point is set to the surge line S _10. The surge control valve 25 opens at the surge control line SC ₁₀ before reaching the BOG 16 and the operating point of the low duty compressor 14 enters the surge control zone SCZ ₁₀ (between the surge line S ₁₀ and the surge control line SC ₁₀ ). The surging phenomenon is prevented from entering.

As this type of conventional technology, there is a configuration in which liquefied natural gas in a tank is vaporized by a vaporizer, and the vaporized gas is compressed by a compressor and then heated by a heater and supplied to a boiler (for example, , See Patent Document 1).
Japanese Utility Model Publication No. 57-110000 (first page, FIG. 2)

However, the pressure rise due to pipe resistance changes caused by changes in burner combustion number of main boiler 19 as described above, such as the resistance curve R ₁₀ indicated by the chain line in FIG. 6, the surge control line SC at the time of burner three combustion _Although it is far from _10, it approaches the surge control line SC10 when two burners are burned, and is very close when the opening of the two burners is reduced or when one burner is burned, and the IGV 21 is fully opened to rotate. Near the low speed at which the number starts to increase, the resistance curve R ₁₀ may enter the surge control zone SCZ ₁₀ , causing a situation where the BOG combustion by the main boiler 19 is not stable.

  That is, when the opening degree is reduced during the combustion of two burners or when the pressure in the discharge pipe 15 fluctuates during the combustion of a single burner, the gas pressure in the discharge pipe 15 is a gas required on the main boiler 19 side. The pressure becomes higher than the pressure, and the surge control valve 25 is opened and the BOG 16 is released. However, depending on the operation state, the surge control valve 25 is frequently opened and closed, causing a phenomenon that it is difficult to sufficiently follow and the surge control valve 25 It becomes difficult to suppress the surging phenomenon. In addition, depending on the pressure fluctuation, the surge control valve 25 is always open, and surge control may not be possible.

That is, the gas supply amount to the main boiler 19 whose operating state changes according to the load of the main turbine is adjusted by the low duty compressor 14, but when the number of burners burned decreases, the low duty compressor 14 Since the operating point frequently enters or enters the surge control zone SCZ ₁₀ , a surging phenomenon occurs in the low duty compressor 14 and there are many situations where gas combustion in the main boiler 19 cannot be stabilized. End up.

  Therefore, development of a control method capable of stably controlling the low duty compressor 14 in the LNG ship is desired.

  The invention described in Patent Document 1 relates to an apparatus for co-firing a gas obtained by vaporizing liquefied natural gas and a gas (BOG) vaporized in a tank, and control of a compressor that compresses BOG. No measures have been taken.

Therefore, in order to solve the above problems, the present invention supplies boil-off gas generated in the LNG tank to a plurality of burners provided in the main boiler after being pressurized by a low duty compressor, and changes depending on the operating state of the main turbine. in low duty compressor control method in LNG carriers Ru is burned by changing the combustion number of the burner according to the load, a low duty while opening the opening of the inlet guide vanes provided in the low duty compressor to a predetermined opening degree Rotational speed control is performed to increase the rotational speed of the compressor to a predetermined outlet pressure by a set increase amount, and when the predetermined outlet pressure is reached, the rotational speed of the low duty compressor is gradually increased to a set value by the set increase amount. , Gradually open the inlet guide vane to the fully open position with the set amount In by performing the opening control for opening the same time, low duty compressor discharge pipe resistance increasing as the driving point of the low duty compressor is the surge line and the settings amount set in advance away from the surge line Control is performed so as not to enter the surge control zone between the surge control line set in advance so as not to exceed the surge line .

In addition, the boil-off gas generated in the LNG tank is pressurized by a low-duty compressor and supplied to a plurality of burners provided in the main boiler, and the number of combustions of the burner is changed according to the load that changes depending on the operating state of the main turbine. In the low-duty compressor control method for an LNG ship that burns, the rotational speed of the low-duty compressor is increased by a predetermined increment while opening the inlet guide vane provided in the low-duty compressor to a predetermined opening. When the predetermined outlet pressure is reached, the opening of the inlet guide vane is released to the set amount with the rotation speed kept constant, and the opening degree is controlled until the rotation speed reaches the set value. When the set value is reached, the rotation speed is set with the inlet guide vane opening kept constant. The number of rotations is controlled to increase to the set value.When the number of rotations reaches the set value, the opening of the inlet guide vane is released to the set value with the number of rotations kept constant. alternating rows Ukoto and the rotation speed control and opening degree control of controlling the opening degree until the discharge pipe resistance of low duty compressor so as to increase the setting amount set in advance away from the surge line Control may be performed so that the operating point of the low duty compressor does not enter a surge control zone between the surge line and a surge control line set in advance so as not to exceed the surge line .

  Since the present invention is controlled by the means described above so that the operating point does not enter the surge control zone of the low duty compressor, the low duty compressor can be stably operated.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a surge control graph in the low duty compressor control method according to the first embodiment of the present invention. The horizontal axis of the figure indicates the volumetric flow rate per time, and the vertical axis indicates the output pressure. FIG. 3 is a graph schematically showing a part of the surge line in the low duty compressor control method shown in FIGS. The configuration of the LNG ship adopting such a control method is the same as the system diagram shown in FIG. 4 and the cross-sectional view shown in FIG. To explain.

In the first embodiment, opening control for controlling the opening of the IGV 21 provided in the low duty compressor 14 with a set amount, and rotation speed control for controlling the rotation of the low duty compressor 14 with a set increase amount, By alternately performing the surge line S ₁ away from the discharge pipe resistance (resistance curve R ₁₀ ) of the low duty compressor 14, the operating point of the low duty compressor 14 is prevented from entering the surge control zone SCZ ₁ .

  That is, at the start of operation, the rotational speed of the low duty compressor 14 is set to a predetermined increase amount while the opening of the IGV 21 provided in the low duty compressor 14 is opened from the minimum to a predetermined opening (for example, 20% opening). Increase to outlet pressure (in this example about 1.2 bar). When a predetermined outlet pressure is reached, the opening of the IGV 21 is opened to a set amount (for example, 60% opening) with the rotation speed kept constant, and the rotation speed reaches a set value (in this example, 12000 rpm). Opening control is performed until it reaches. When the rotational speed reaches the set value, the rotational speed control is performed to increase the rotational speed to a set value (in this example, about 17000 rpm) with a set increase amount while keeping the opening of the IGV 21 constant. When the rotation speed reaches the set value, the opening of the IGV 21 is opened to a set amount (for example, fully open at 100%) with the rotation speed kept constant, and the rotation speed is set to the set value (in this example, 18000 rpm). Opening control is performed until the value is reached. Then, when the rotational speed reaches the set value, the rotational speed control is performed to increase the rotational speed to the set value (in this example, 24000 rpm) with a set increase amount while keeping the opening of the IGV 21 constant.

Thus, in the first embodiment, the opening control of the IGV 21 and the rotation speed control of the low duty compressor 14 are alternately performed so that the operating point of the low duty compressor 14 does not enter the surge control zone SCZ ₁ . Therefore, as shown in FIG. 3, the surge line S ₁ at a position where the volume flow rate of the low duty compressor 14 is smaller than that of the conventional surge line S ₁₀ (two-dot chain line in FIG. 3) (lower left portion in FIG. 1). (The thin solid line in FIG. 3) can increase the outlet pressure away from the resistance curve R ₁₀ (dashed line), and the surge line S ₁ thereafter can also move away from the resistance curve R _10, so the surge control zone SCZ ₁ can be given a margin with respect to the pipe resistance curve R ₁₀ . Therefore, even if the pipe burner the number of main boiler 19 is changed resistance is changed, by absorbing changes between the resistor curves R ₁₀ and the surge control line SC _1, the surge operating point of the low duty compressor 14 Since the control zone SCZ ₁ can be prevented from entering, the boil-off gas combustion by the main boiler 19 can be stabilized.

  Note that the opening setting amount of the IGV 21 in the first embodiment is an example, and may be set as appropriate according to the performance of the low duty compressor 14 and the like. Further, the set increase amount of the rotational speed is also an example, and may be appropriately set according to the performance of the low duty compressor 14 or the like.

  FIG. 2 is a surge control graph in the low duty compressor control method according to the second embodiment of the present invention. Also in this figure, the horizontal axis indicates the volumetric flow rate per time, and the vertical axis indicates the output pressure. 3 also schematically shows a part of the surge line in the low duty compressor control method shown in FIG. The configuration of the LNG ship adopting this control method is also the same as the system diagram shown in FIG. 4 and the cross-sectional view shown in FIG. explain.

In the second embodiment, opening control for controlling the opening of the IGV 21 provided in the low duty compressor 14 with a set amount, and rotation speed control for controlling the rotation of the low duty compressor 14 with a set increase amount, By simultaneously performing the surge line S ₂ so as to be separated from the discharge pipe resistance (resistance curve) of the low duty compressor 14, the operating point of the low duty compressor 14 is prevented from entering the surge control zone SCZ ₂ .

  That is, at the start of operation, the rotational speed of the low duty compressor 14 is set to a predetermined increase amount while the opening of the IGV 21 provided in the low duty compressor 14 is opened from the minimum to a predetermined opening (for example, 20% opening). Increase to outlet pressure (in this example about 1.2 bar). Then, when the predetermined outlet pressure is reached, the rotational speed is gradually increased to the set value (in this example, 24000 rpm) by the set increase amount, and the opening degree of the IGV 21 is fully opened by the predetermined set amount ( The opening degree control for gradually opening the opening degree to 100% is simultaneously performed.

Thus, in the second embodiment, since as the operating point of the opening control and low duty compressor 14 speed control and a low duty compressor 14 carried out at the same time of the IGV21 from entering the surge control zone SCZ ₂ As shown in FIG. 3, the surge line S ₂ at the position where the volumetric flow rate of the low duty compressor 14 is lower than that of the conventional surge line S ₁₀ (two-dot chain line in FIG. 3) (lower left portion in the figure) (FIG. 3). 3, the outlet pressure can be increased so that the uppermost thick solid line is separated from the resistance curve R ₁₀ , and the subsequent surge line S ₂ can also be separated from the resistance curve R ₁₀ as a whole. SCZ ₂ can be given a margin with respect to the pipe resistance curve R ₁₀ . Therefore, even if the pipe burner the number of main boiler 19 is changed resistance is changed, by absorbing changes between the resistor curves R ₁₀ and the surge control line SC _2, surge operating point of the low duty compressor 14 Since the control zone SCZ ₂ can be prevented from entering, the boil-off gas combustion by the main boiler 19 can be stabilized.

  The opening setting amount of the IGV 21 in this second embodiment is also an example, and may be set as appropriate according to the performance of the low duty compressor 14 and the like.

As described above, according to the control method of the low duty compressor 14 according to the first and second embodiments, the operating point of the low duty compressor 14 can be prevented from entering the surge control zones SCZ ₁ , SCZ _2. The boil-off gas combustion at 19 can be stabilized and burned from a low load to a high load. Further, since the low duty compressor 14 can be controlled so as not to cause a surging phenomenon even by a change in the pipe resistance of the discharge pipe 15, it is possible to make the discharge pipe 15 have a small diameter.

  The above-described embodiment shows an example, and various modifications can be made without departing from the spirit of the present invention, and the present invention is not limited to the above-described embodiment.

  The low-duty compressor control method for an LNG ship according to the present invention is useful for an LNG ship in which the operating situation of the main boiler changes to cause a surging phenomenon in the low-duty compressor.

It is a surge control graph in the low duty compressor control method which concerns on 1st Embodiment of this invention. It is a surge control graph in the low duty compressor control method which concerns on 2nd Embodiment of this invention. It is the graph which showed typically a part of surge line in the low duty compressor control method shown in FIGS. It is a systematic diagram which shows an example of a structure of the LNG ship which employ | adopts this invention. It is sectional drawing of the low duty compressor in the systematic diagram shown in FIG. It is a surge control graph in the conventional low duty compressor control method.

Explanation of symbols

10 ... Tank 11 ... Cargo liquid 12 ... BOG
DESCRIPTION OF SYMBOLS 13 ... Fuel pipe 14 ... Low duty compressor 15 ... Discharge piping 16 ... BOG
17 ... gas heater 18 ... gas control valve 19 ... main boiler 20 ... burner 21 ... inlet guide vanes 22 ... fan 23 ... Motor 24 ... controller 25 ... surge control valves _{S 1, S 2, S 10} ... surge line SC _1, SC ₂ , SC ₁₀ ... Surge control line SCZ ₁ , SCZ ₂ , SCZ ₁₀ ... Surge control zone R ₁₀ ... Resistance curve

Claims (2)

The boil-off gas generated in the LNG tank is pressurized by a low-duty compressor and supplied to a plurality of burners provided in the main boiler. in low duty compressor control method in LNG carriers Ru is,
Increasing the number of rotations of the low duty compressor to a predetermined outlet pressure while opening the opening of the inlet guide vane provided in the low duty compressor to a predetermined opening, and when the predetermined outlet pressure is reached, Rotational speed control is performed to gradually increase the rotational speed of the low-duty compressor to the set value by the set increment , and simultaneously opening control is performed to gradually open the inlet guide vane to the fully opened position by the predetermined set amount. We are, the operating point of the low duty compressor preset so as not to exceed the surge line and the surge line discharge pipe resistance of low duty compressor so as to increase the setting amount set in advance away from the surge line enter the surge control zone between the surge control line Low duty compressor control method in LNG carriers to odd controlled. The boil-off gas generated in the LNG tank is pressurized by a low-duty compressor and supplied to a plurality of burners provided in the main boiler. In the low duty compressor control method in the LNG ship
While opening the opening of the inlet guide vane provided in the low duty compressor to a predetermined opening, the rotation speed of the low duty compressor is increased by a set increment to a predetermined outlet pressure, and when the predetermined outlet pressure is reached, the rotation Open the inlet guide vane opening to a set amount with the number kept constant, and control the opening until the rotation speed reaches the set value.When the rotation speed reaches the set value, the opening of the inlet guide vane is adjusted. Rotational speed control is performed to increase the rotational speed up to the set value with the set increase amount in a constant state. When the rotational speed reaches the set value, the opening of the inlet guide vane to the set amount with the rotational speed kept constant in open rotational speed alternating rows Ukoto and the rotation speed control and opening degree control of controlling the opening degree until it reaches the set value, a low duty compressor discharge pipe resistance Surge control zone between the surge control line the operating point of the low duty compressor so as to increase the setting amount set in advance away from the surge line is preset so as not to exceed the surge line and the surge line A low-duty compressor control method for an LNG ship that is controlled so as not to enter.

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