JP2008075705A - Method of starting low temperature liquefied gas pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of starting a low temperature liquefied gas pump, reliably exhausting residual gas or vaporizing gas from the low temperature liquefied gas pump, eliminating the occurrence of pulsation when starting the low temperature liquefied gas pump and the trouble of discharge pressure not rising up to specified pressure, and surely and efficiently feeding low temperature liquefied gas. <P>SOLUTION: The low temperature liquefied gas pump 12 is started as its blow valve 18V remains opened during pre-cooling. When the pressure of the low temperature liquefied gas discharged from the low temperature liquefied gas pump 12 to a discharge pipe 17 gets to preset pressure, the blow valve 18V is closed with a pressure switch 21 to start the feeding of the low temperature liquefied gas to a feeding destination. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for starting a cryogenic liquefied gas pump, and more specifically, cryogenic liquefaction when transferring cryogenic liquefied gas such as liquid oxygen, liquid nitrogen, and liquid argon stored in a cryogenic liquefied gas storage tank to a tank lorry or another storage tank. The present invention relates to a method for starting a gas pump.

  When the low-temperature liquefied gas stored in the low-temperature liquefied gas storage tank is transferred to a tank lorry or the like by the low-temperature liquefied gas pump, a suction pipe that connects the bottom of the low-temperature liquefied gas storage tank and the suction side of the low-temperature liquefied gas pump via a suction valve; A low-temperature liquefied gas transfer device including a liquid supply pipe that connects a discharge side of the low-temperature liquefied gas pump and a low-temperature liquefied gas supply destination via a liquid supply valve is used. When transferring low-temperature liquefied gas in the low-temperature liquefied gas storage tank with this low-temperature liquefied gas transfer device, before starting the low-temperature liquefied gas pump, before and after starting the low-temperature liquefied gas pump, It is necessary to pre-cool the pipes and valves to the low-temperature liquefied gas temperature, and the delivery of the low-temperature liquefied gas is started after confirming that the pre-cooling has been completed.

As a method for confirming the completion of pre-cooling of the low-temperature liquefied gas pump and automatically starting the low-temperature liquefied gas pump, a reflux path having an upward flow path is provided at the downstream position of the low-temperature liquefied gas pump, and A sensor is provided to detect that the low-temperature liquefied gas has passed in liquid form.When this sensor detects that the low-temperature liquefied gas has passed in liquid form, it is determined that pre-cooling has been completed, A method for opening and closing a valve to start liquid feeding has been proposed (see, for example, Patent Document 1).
Japanese Patent Publication No. 63-7271

  However, in the method described in Patent Document 1, even if the low-temperature liquefied gas passes through the sensor portion in a liquid state, a slight amount of gas remains inside the low-temperature liquefied gas pump, piping, or valves, or the vaporized gas is generated when the pump is started. Or the like, pulsation occurs, and the discharge-side pressure of the low-temperature liquefied gas pump may not rise to a predetermined pressure. For this reason, precooling and pump start-up are repeatedly performed, and the amount of low-temperature liquefied gas released may increase.

  Therefore, the present invention can reliably discharge residual gas and vaporized gas in the low-temperature liquefied gas pump, etc., causing problems such as pulsation when the low-temperature liquefied gas pump is started and discharge pressure does not rise to the specified pressure. It is an object of the present invention to provide a starting method of a low-temperature liquefied gas pump that can eliminate the low-temperature liquefied gas reliably and efficiently.

  In order to achieve the above object, the method of starting the low-temperature liquefied gas pump according to the present invention includes a suction pipe connecting a low-temperature liquefied gas storage tank and a suction side of the low-temperature liquefied pump, a discharge side of the low-temperature liquefied gas pump, and a low-temperature liquefied gas feed. In the start-up method of the low-temperature liquefied gas pump in the low-temperature liquefied gas transfer device having a liquid feed pipe connected to the liquid tip, the suction valve provided in the suction pipe and the upstream of the liquid feed valve provided in the liquid feed pipe Open the discharge valve provided in the pipe branched from the side, after circulating the low-temperature liquefied gas pump from the low-temperature liquefied gas storage tank through the low-temperature liquefied gas storage tank, pre-cooled the low-temperature liquefied gas pump, start the low-temperature liquefied gas pump, When the discharge side pressure of the low temperature liquefied gas pump becomes a preset pressure, or the differential pressure between the suction side pressure and the discharge side pressure of the low temperature liquefied gas pump is preset. When it becomes a force to close the discharge valve is characterized in that to start the liquid feed to the liquid feed destination.

  The discharge valve includes a bypass valve of a bypass pipe branched from the liquid supply pipe upstream of the liquid supply valve and connected to the low-temperature liquefied gas storage tank, and a blow pipe branched from the liquid supply pipe upstream of the liquid supply valve The discharge side pressure of the low temperature liquefied gas pump is a pressure in the pipe from the low temperature liquefied gas pump to the liquid feed valve, and the set value of the differential pressure is the low temperature liquefied gas pump It is calculated from the head of the gas pump and the density of the low-temperature liquefied gas.

  According to the start method of the low temperature liquefied gas pump of the present invention, the bypass valve and the blow valve are kept open even when the low temperature liquefied gas pump is started. The vaporized gas generated along with this can be discharged from the bypass pipe or blow pipe along with the low-temperature liquefied gas. When these gases are discharged and the discharge side pressure of the pump or the differential pressure between the suction side and the discharge side of the pump reaches a predetermined pressure, the bypass valve and the blow valve are closed, and liquid feeding is started. The discharge pressure rises smoothly, and stable start-up and operation are possible. In addition, unstable conditions such as cavitation do not continue to cause significant damage to the pump, and the amount of low-temperature liquefied gas released can be minimized, reducing low-temperature liquefied gas loss. Can do.

  FIG. 1 is a system diagram showing an example of a low temperature liquefied gas transfer device for carrying out the starting method of the low temperature liquefied gas pump of the present invention.

  The low-temperature liquefied gas transfer device is configured to increase the low-temperature liquefied gas stored in the plurality of low-temperature liquefied gas storage tanks 11 and 11 to a predetermined pressure by a low-temperature liquefied gas pump 12 and transfer it to a liquid destination such as a tank truck. Each low-temperature liquefied gas storage tank 11 has a bottom outlet pipe 13 having an outlet valve 13V, a manual valve 14V, a pressure evaporator 14E, and a pressure setting valve 14P, and a pressure connecting the tank lower part and the tank upper part. An adjustment path 14 and a top pressure release path 15 having a pressure setting valve 15P are provided. In addition, illustration of the low temperature liquefied gas introduction pipe provided in each low temperature liquefied gas storage tank is omitted.

  The low-temperature liquefied gas pump 12 includes a suction pipe 16 connected from the pump suction side to the outlet pipe 13 of each low-temperature liquefied gas storage tank 11 via a suction valve 16V, and a liquid feed valve from the pump discharge side to a liquid feed destination such as a tank lorry. A liquid supply pipe 17 connected via 17V is provided. From the upstream side of the liquid supply valve 17V of the liquid supply pipe 17, a blow pipe 18 having a blow valve 18V and a bypass pipe 19 connected to the upper portion of each low-temperature liquefied gas storage tank 11 via a bypass valve 19V are branched. ing.

  When the low-temperature liquefied gas transfer device formed in this way supplies low-temperature liquefied gas to the liquid destination, before starting the low-temperature liquefied gas pump 12, the outlet valve 13V of the one low-temperature liquefied gas storage tank 11, the intake valve The low temperature liquefied gas in the low temperature liquefied gas storage tank 11 is circulated through the outlet pipe 13, the suction pipe 16, the low temperature liquefied gas pump 12, the liquid feed pipe 17 and the bypass pipe 19. At this time, the gas vaporized by cooling the low-temperature liquefied gas pump 12 and the pipes 13, 16, 17, 19, etc. returns to the same low-temperature liquefied gas storage tank 11 through the bypass pipe 19. By opening the blow valve 18V and allowing the gas to flow through the blow pipe 18 before the pre-cooling is completed, the vaporized gas flows into the liquid discharge reservoir 20 along with the flow of the low-temperature liquefied gas, and is discharged from the exhaust port 20a to the atmosphere. . If the low-temperature liquefied gas is a valuable gas, a re-liquefier can be installed on the secondary side of the liquid discharge reservoir 20 and recovered into the low-temperature liquefied gas storage tank 11. The blow valve 18V may be opened from the beginning of precooling, and the precooling method is not particularly limited.

Next, when there is almost no amount of gas released from the blow valve 18V, the bypass valve 19V is closed, and the low temperature liquefied gas pump 12 is started with the blow valve 18V set to a preset valve opening. As a result, the low-temperature liquefied gas sucked from the suction pipe 16 is pressurized to some extent by the low-temperature liquefied gas pump 12 and flows into the liquid discharge reservoir 20 from the liquid feed pipe 17 through the blow pipe 18. At this time, even if there is residual gas in the pump or piping, or vaporized gas is generated, the pressure on the pump discharge side is released via the liquid discharge reservoir 20, so the residual gas and the like are at a low temperature. Along with the flow of the liquefied gas, it flows into the discharge reservoir 20 and is discharged. If the _CV value of the blow valve 18V is appropriately selected, it is not necessary to set the valve opening degree of the blow valve 18V when the pump is activated.

  When the gas is discharged from the low-temperature liquefied gas pump 12 and each pipe line, the pressure in the discharge pipe 17 on the pump discharge side is stabilized at a predetermined pressure. When the pressure in the discharge pipe 17 reaches a preset pressure, the pressure switch 21 provided on the upstream side of the liquid feed valve 17V of the liquid feed pipe 17 is actuated to close the blow valve 18V and open the liquid feed valve 17V. Thus, the transfer of the low-temperature liquefied gas from the liquid supply pipe 17 to the liquid supply destination starts. In the drawing, the pressure switch 21 on the pump discharge side is taken out from the liquid feeding pipe 17, but it may be upstream of the bypass valve 19 </ b> V of the bypass pipe 19. Moreover, the attachment position of the blow pipe 18 may be between the position where the bypass pipe 19 branches from the liquid feed pipe 17 and the liquid feed valve 17V, or may be upstream of the bypass valve 19V of the bypass pipe 19.

  Note that the bypass valve 19V of the bypass pipe 19 may remain closed or may be opened and closed in the same manner as the blow valve 18V. Further, the blow valve 18V may be manually closed when the pressure of the liquid feeding pipe 17 is monitored and becomes a predetermined pressure. Further, instead of opening / closing the blow valve 18V, the bypass valve 19V may be opened / closed.

  FIG. 2 is a system diagram showing a second embodiment, and instead of the pressure switch 21 provided in the liquid feeding pipe 17, a difference operated by the differential pressure between the suction side pressure and the discharge side pressure of the low temperature liquefied gas pump 12. An example in which a pressure switch 22 is provided is shown. In addition, the same code | symbol is attached | subjected to the component same as the component of the said 1st form example, and detailed description is abbreviate | omitted.

  In this embodiment, after starting the low-temperature liquefied gas pump 12 in the same manner as described above, the gas is discharged from the system and the pressure on the discharge side is increased by the difference in pressure between the suction side pressure and the discharge side pressure of the pump. When the differential pressure reaches a preset pressure, the differential pressure switch 22 is actuated, and the liquid feed is started by closing the blow valve 18V and opening the liquid feed valve 17V as described above. is doing. Further, as shown in the present embodiment, by determining the start of liquid feeding based on the differential pressure before and after the low temperature liquefied gas pump 12, even when the pressure in the low temperature liquefied gas storage tank 11 fluctuates greatly, the start of liquid feeding is always performed. It can be performed at an optimal time and does not increase the amount of low-temperature liquefied gas released.

  The reason for this will be described with reference to FIGS. Note that the performance curve of the pump is generally such that when the fluid is an incompressible fluid and the influence of viscosity is negligible, the horizontal axis represents the flow rate Q and the vertical axis, as shown in FIG. 4, regardless of the type of fluid. Although the axis can be displayed as a single curve with the pump head (head) H as the axis, in FIG. 3, the vertical axis is displayed as the pressure P on the discharge side for convenience.

  For example, when the internal pressure of the low-temperature liquefied gas storage tank 11 is 0.2 MPa, the pressure P1 on the pump suction side is substantially equal to the internal pressure of the low-temperature liquefied gas storage tank 11, and when the low-temperature liquefied gas pump 12 is operated, the pressure on the pump discharge side is P2. It becomes. The difference between the pressure P2 on the pump discharge side and the pressure P1 on the pump suction side at this time is defined as a differential pressure ΔP. If the internal pressure of the low-temperature liquefied gas storage tank 11 increases to 0.3 MPa, the pump suction side becomes pressure P1 ′, and the operation of the low-temperature liquefied gas pump 12 causes the pump discharge side to become pressure P2 ′. A differential pressure between the pump discharge side pressure and the pump suction side pressure at this time is represented by ΔP ′. If the volume flow Q of the pump does not change from the pump performance curve and the density change is almost negligible, since the pump head is the same, ΔP = ΔP ′, so the internal pressure of the low-temperature liquefied gas storage tank 11 increases. However, the differential pressure between the suction side pressure and the discharge side pressure of the pump does not change, but the pump discharge side pressure increases.

  For this reason, when the pressure switch 21 that operates at the pump discharge side pressure is used as a criterion for closing the blow valve 18V, the appropriate operation timing differs depending on the internal pressure of the low-temperature liquefied gas storage tank 11. For example, if the pressure switch is set to a pressure equal to P2 in FIG. 3, when the pump suction pressure starts to increase from 0.3 MPa and the pump discharge pressure reaches P2, that is, the pressure switch 21 is When the operation is started and the blow valve 18V is closed to start liquid feeding, the pulsation is generated or continues because the gas remaining in the pump or the like and the vaporized gas generated when the pump is started are not reliably discharged. there is a possibility. On the other hand, when the internal pressure of the low temperature liquefied gas storage tank 11 decreases and the pump discharge pressure does not reach P2 due to the pressure increase from less than 0.2 MPa, the pressure switch does not operate and valuable low temperature liquefied gas is removed. It will be wasted. By using the differential pressure switch 22 that operates by the differential pressure between the pump suction side pressure and the pump discharge side pressure, the pressure increase of the low-temperature liquefied gas pump 12 can be detected more accurately, so that liquid feeding can be started at an optimal time. It is possible to start and operate the pump stably without increasing the amount of valuable low temperature liquefied gas released.

Furthermore, when setting the differential pressure between the pump suction side pressure and the pump discharge side pressure, selecting the differential pressure to be set according to the type of low-temperature liquefied gas can start liquid feeding in a stable state. The amount of low-temperature liquefied gas released can be reduced. When the pump head (head) of the pump is H and the density of the fluid is ρ, the differential pressure ΔP between the suction side and the discharge side of the pump can be obtained by H = ΔP / ρ, so that liquid argon (Ar) FIG. 5 shows the relationship between the volume flow rate Q of liquid oxygen (O ₂ ) and liquid nitrogen (N ₂ ) and the differential pressure ΔP between the suction side and the discharge side of the pump. The density ρ on the pump suction side of the low-temperature liquefied gas is determined by the type of the low-temperature liquefied gas and the pressure and temperature conditions on the pump suction side. The blow valve 18V can be programmed to close when approximate to a value determined from the relationship between the density ρ and the known lift H obtained from the performance curve.

For example, when the pump fluid is liquid nitrogen and the pump suction pressure P1 is saturated at 0.2 MPaG, the enthalpy h1 at that time is 22.1 kJ / kg and the liquid density ρ1 is 755.5 kg / m ³ . Next, when the discharge pressure is adjusted so that the differential pressure ΔP is 1.0 MPa (discharge pressure P2 = 1.2 MPaG), the head H is 135.0 m. If the flow rate Q at this time is 50% and the pump efficiency is 50%, the power loss (Lloss) is substantially the same as the theoretical power, so the enthalpy increase Δh due to the power loss is Lloss / (ρ1 · Q) = ρ1 · Q・ H / 101.97 / (ρ1 · Q) = 135 / 10.97 = 1.3 kJ / kg, the enthalpy h2 on the discharge side is 23.4 kJ / kg, and the liquid density ρ2 at this time is 757.3 kg / kg At m ³ , the difference from the liquid density ρ1 on the suction side is as small as 0.2%.

  Therefore, if there is no extra heat intrusion, the differential pressure ΔP when the pump rotates at the rated speed can be predicted from the pressure and liquid density on the pump suction side. As a method to stabilize the start-up of the pump that transfers the low-temperature liquefied gas that is easily affected, the differential pressure ΔP obtained from the density ρ of the low-temperature liquefied gas and the pump head H obtained from the performance curve is selected as the set value and measured. It is preferable to set so that the blow valve 18V is closed by determining that the differential pressure has reached that value.

When the discharge side fluid approaches saturation due to other heat intrusion, the discharge side liquid density decreases. For example, the liquid density ρ2 ′ when the discharge pressure P2 = 1.2 MPaG is saturated is 636. 7 kg / m ³ , nearly 20% smaller than ρ2. Since the pump head H is 135 m (= constant) regardless of the density of the fluid, the discharge pressure does not increase to 1.2 MPaG and the predicted value of the differential pressure ΔP is not reached if there is excessive heat penetration. By detecting in this way, the timing for closing the blow valve 18V can be adjusted more accurately, and even in a case where cavitation occurs due to a decrease in suction pressure accompanying a decrease in the liquid level in the low temperature liquefied gas storage tank 11, the pump is more appropriately Can be stopped. Furthermore, if the rotation speed data of the pump is input, the same confirmation can be made even in the middle of starting.

It is a systematic diagram which shows one example of the low temperature liquefied gas transfer apparatus for enforcing the starting method of the low temperature liquefied gas pump of this invention. It is a systematic diagram which shows a 2nd form example. It is a figure which shows the relationship between the flow volume in a pump, and a pump head (lifting head). It is a figure which shows the relationship between the flow volume in a pump, and the pressure of the discharge side. It is a figure which shows the relationship between each volume flow in liquid argon, liquid oxygen, and liquid nitrogen, and the differential pressure | voltage of the suction side of a pump, and a discharge side.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Low temperature liquefied gas storage tank, 12 ... Low temperature liquefied gas pump, 13 ... Outlet pipe, 13V ... Outlet valve, 14 ... Pressure regulation path, 14E ... Pressure evaporator, 14P ... Pressure setting valve, 14V ... Manual valve, 15 ... Release Pressure path, 15P ... Pressure setting valve, 16 ... Suction pipe, 16V ... Suction valve, 17 ... Liquid feed pipe, 17V ... Liquid feed valve, 18 ... Blow pipe, 18V ... Blow valve, 19 ... Bypass pipe, 19V ... Bypass valve 20 ... Release reservoir, 20a ... Exhaust port, 21 ... Pressure switch, 22 ... Differential pressure switch

Claims (6)

  A low-temperature liquefied gas transfer device comprising a suction pipe that connects a low-temperature liquefied gas storage tank and a suction side of a low-temperature liquefied pump, and a liquid-feed pipe that connects a discharge side of the low-temperature liquefied gas pump and a low-temperature liquefied gas destination. In the starting method of the low-temperature liquefied gas pump in the above, the suction valve provided in the suction pipe and the discharge valve provided in a pipe branched from the upstream side of the liquid supply valve provided in the liquid supply pipe are opened, and the low-temperature liquefaction gas When the low-temperature liquefied gas pump is precooled by circulating low-temperature liquefied gas from the low-temperature liquefied gas storage tank to the gas pump, the low-temperature liquefied gas pump is started, and the discharge side pressure of the low-temperature liquefied gas pump becomes a preset pressure. The method for starting a low-temperature liquefied gas pump is characterized in that the discharge valve is closed and liquid feeding to the liquid feeding destination is started.   A low-temperature liquefied gas transfer device comprising a suction pipe that connects a low-temperature liquefied gas storage tank and a suction side of a low-temperature liquefied pump, and a liquid-feed pipe that connects a discharge side of the low-temperature liquefied gas pump and a low-temperature liquefied gas destination. In the starting method of the low-temperature liquefied gas pump in the above, the suction valve provided in the suction pipe and the discharge valve provided in a pipe branched from the upstream side of the liquid supply valve provided in the liquid supply pipe are opened, and the low-temperature liquefaction gas After the low-temperature liquefied gas pump is pre-cooled by circulating the low-temperature liquefied gas from the low-temperature liquefied gas storage tank to the gas pump, the low-temperature liquefied gas pump is started, and the differential pressure between the suction side pressure and the discharge side pressure of the low-temperature liquefied gas pump A starting method for a low-temperature liquefied gas pump, wherein when the set pressure is reached, the discharge valve is closed and liquid feeding to the liquid feeding destination is started.   3. The operation method of the low temperature liquefied gas pump according to claim 2, wherein the set value of the differential pressure is calculated from a head of the low temperature liquefied gas pump and a density of the low temperature liquefied gas.   The said discharge valve is a bypass valve of a bypass pipe branched from the liquid supply pipe upstream of the liquid supply valve and connected to the low-temperature liquefied gas storage tank. To start the low-temperature liquefied gas pump.   4. The starting method for a low-temperature liquefied gas pump according to claim 1, wherein the discharge valve is a blow valve provided in a blow pipe branched from a liquid feed pipe upstream of the liquid feed valve. .   The discharge valve is divided into a bypass valve of a bypass pipe branched from the liquid supply pipe upstream of the liquid supply valve and connected to the low-temperature liquefied gas storage tank, and a blow pipe branched from the liquid supply pipe upstream of the liquid supply valve. The method for starting a low-temperature liquefied gas pump according to any one of claims 1 to 3, wherein the blow valve is provided.

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