JP2018009630A - Carbon dioxide supply method and supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve energy efficiency in pressuring carbon dioxide to a pressure exceeding the critical pressure by a positive displacement pump, and sending it out.SOLUTION: Liquefied carbon dioxide stored in a supply tank 2 is sucked by a first positive displacement pump 3. The liquefied carbon dioxide is pressurized by the first positive displacement pump 3 so that it is pressurized to a pressure less than the critical pressure and sent out. The liquefied carbon dioxide in the first positive displacement pump 3 is cooled by a cooling device 4. The liquefied carbon dioxide sent out from the first positive displacement pump 3 is sucked by a second positive displacement pump 5. The liquefied carbon dioxide is pressurized by the second positive displacement pump 5 so that it is pressurized to a pressure over the critical pressure, and the carbon dioxide with the pressure over the critical pressure is sent out.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a carbon dioxide supply method and a supply system, and is suitable for supplying carbon dioxide having a pressure exceeding a critical pressure to an extruder for molding a foamed resin.

  Foamed resin molded from polystyrene resin or the like is manufactured as a general industrial product, and is used as, for example, a heat insulating material as a building material, or a packing material for food or electrical products. In the production of such a foamed resin, for example, a mixture of a polystyrene resin and a polyester resin is kneaded with carbon dioxide supplied as a foaming agent to an extruder and extruded at a high pressure while being adjusted to a suitable temperature. Foaming is performed by reducing the pressure after extrusion. That is, carbon dioxide is used as an inorganic physical foaming agent. At this time, since the resin is pressurized up to nearly 10 MPa (absolute pressure) in the extruder, the pressure of carbon dioxide supplied as a foaming agent to the extruder is set to 7.38 MPa (absolute pressure) which is a critical pressure. It is necessary to raise it to 10 MPa or more which is greatly exceeded.

  Therefore, a carbon dioxide supply system 101 as shown in the conventional example of FIG. 7 is used. The supply system 101 includes a supply tank 102 that stores liquefied carbon dioxide, and a positive displacement pump 103 connected to the supply tank 102.

  In the supply tank 102, the liquefied carbon dioxide has a liquid level L and is stored at a temperature of, for example, -20 ° C. and a pressure of 2.0 MPa (absolute pressure) corresponding to the saturated vapor pressure at that temperature. The supply tank 102 is cooled by a vacuum heat insulating layer 102a, and a coiled heat exchanger 104 is provided in the internal space. The ethylene glycol refrigerant 107 cooled to −30 ° C. to −25 ° C. by the refrigerator 106 is circulated between the coil heat exchanger 104 and the refrigerant tank 105 by the refrigerant pump 108.

  As the positive displacement pump 103, a diaphragm type metering pump is used. A plurality of positive displacement pumps 103 are connected in parallel to each other. The suction port 103 a of the positive displacement pump 103 is connected to the supply tank 102, and the discharge port 103 b is connected to the foamed resin extruder 109. The liquefied carbon dioxide stored in the supply tank 102 is sucked into the positive displacement pump 103 and is pressurized by the positive displacement pump 103, so that the pressure is increased to 10 MPa or more exceeding the critical pressure of 7.38 MPa. As a result, carbon dioxide having a pressure exceeding the critical pressure is sent to the extruder 109.

  The liquefied carbon dioxide sucked into the positive displacement pump 103 increases in saturated vapor pressure when the temperature rises due to frictional heat of the working part or intrusion heat from outside air before reaching the critical pressure, and a part of the liquefied carbon dioxide is vaporized. Occurs, and pressurization by the displacement pump 103 is inhibited. Therefore, by cooling the liquefied carbon dioxide in the positive displacement pump 103, the saturated vapor pressure is reduced and vaporization is suppressed. That is, the displacement pump 103 is covered with a cooling jacket 111, and the ethylene glycol refrigerant 113 cooled to −30 ° C. to −25 ° C. by the refrigerator 112 circulates between the cooling jacket 111 and the refrigerant tank 115 by the refrigerant pump 114. Be made. In addition, as disclosed in Patent Document 1, it has been proposed to cool the driving oil of a diaphragm metering pump with a refrigerant.

Japanese Patent Laid-Open No. 2002-13481

  The positive displacement pump 103 in the conventional supply system 101 pressurizes carbon dioxide from the accommodation pressure in the liquid state in the supply tank 102 to the delivery pressure exceeding the critical pressure to the extruder 109. Therefore, the conventional positive displacement pump 103 has a problem that the compression ratio is large, the frictional heat of the working part is increased accordingly, the energy required for cooling is correspondingly increased, and the energy efficiency is lowered.

  Also, when carbon dioxide is sent out using only the diaphragm type metering pump 103 as the positive displacement pump 103, it is suitable for sending out the metered amount with high accuracy. However, the housing becomes larger as the amount of feed increases, and the liquefied carbon dioxide inside from outside is increased. It becomes difficult to cool. Therefore, in order to increase the delivery amount, it is necessary to increase the number of positive displacement pumps 103 connected in parallel with each other, and there is a problem that energy efficiency is lowered.

  Furthermore, the upper limit of the pressure of the liquefied carbon dioxide stored in the supply tank 102 is restricted from the safety standard. Therefore, it is necessary to suppress the temperature rise of the liquefied carbon dioxide stored in the supply tank 102 using the refrigerator 106 or the like as described above, and this also causes a problem that the energy efficiency is lowered.

  An object of this invention is to provide the supply method and supply system of a carbon dioxide which can solve the said conventional problem.

  According to the carbon dioxide supply method of the present invention, liquefied carbon dioxide contained in a supply tank is sucked by at least one first positive displacement pump, and the liquefied carbon dioxide is pressurized by the first positive displacement pump. The pressure is raised to a pressure lower than the critical pressure, and the liquefied carbon dioxide is cooled in the first positive displacement pump, and the liquefied carbon dioxide sent from the first positive displacement pump is sent to at least one second volume. The pump is sucked in by a pump, and the second positive displacement pump is used to pressurize liquefied carbon dioxide to a pressure exceeding the critical pressure, and carbon dioxide having a pressure exceeding the critical pressure is sent out.

  According to the present invention, the first positive displacement pump and the second positive displacement pump pressurize the carbon dioxide stepwise from the accommodation pressure in the liquid state in the supply tank to the pressure exceeding the critical pressure. That is, conventionally, carbon dioxide is compressed and sent out in a single stage, but is compressed and sent out in multiple stages. Therefore, the compression ratio in each of the first positive displacement pump and the second positive displacement pump can be made smaller than that of the conventional one, and the frictional heat of each operating portion can be reduced. Further, by bringing the pressure of the liquefied carbon dioxide below the critical pressure stored in the supply tank close to the critical pressure by the first positive displacement pump, until the liquefied carbon dioxide reaches the critical pressure in the second positive displacement pump. Thus, the cooling energy necessary for suppressing the generation of bubbles due to the vaporization of a part of the liquefied carbon dioxide before the critical pressure is reached in the second positive displacement pump. It can be made as small as possible and can be made unnecessary. That is, in order to suppress the generation of bubbles in the liquefied carbon dioxide before reaching the critical pressure, the liquefied carbon dioxide is cooled in the first positive displacement pump in which the frictional heat of the operating portion is reduced as compared with the prior art. For example, the cooling energy required in the second positive displacement pump can be reduced and can be eliminated. Therefore, the total energy required for cooling can be reduced as compared with the prior art.

A carbon dioxide supply system according to the present invention includes a supply tank for storing liquefied carbon dioxide, and at least one first volume type connected to the supply tank so as to suck in the liquefied carbon dioxide stored in the supply tank. A pump, a cooling device for cooling liquefied carbon dioxide in the first positive displacement pump, and at least one second positive displacement pump connected in series to the first positive displacement pump, When the liquefied carbon dioxide is pressurized by the first positive displacement pump, the pressure is increased to a pressure lower than the critical pressure, and the liquefied carbon dioxide fed from the first positive displacement pump is sent to the second positive displacement pump. Inhaled by the pump, the second positive displacement pump pressurizes the liquefied carbon dioxide to a pressure exceeding the critical pressure and exceeds the critical pressure. Wherein the carbon dioxide forces are sent out.
According to the system of the present invention, the method of the present invention can be carried out.

In the method of the present invention, an intermediate tank is interposed between the first positive displacement pump and the second positive displacement pump, and liquefied carbon dioxide fed from the first positive displacement pump is supplied to the intermediate tank. It is preferable that after being accommodated, the second positive displacement pump sucks in and a part of the liquefied carbon dioxide accommodated in the intermediate tank is reduced in pressure by a pressure reducing valve to be returned to the supply tank.
As a result, the delivery flow rate of the first positive displacement pump can be made larger than the delivery flow rate of the second positive displacement pump, and the excess liquefied carbon dioxide can be recirculated to the supply tank via the intermediate tank. Since the temperature of the liquefied carbon dioxide recirculated to the supply tank is reduced by reducing the pressure, an increase in the temperature of the liquefied carbon dioxide contained in the supply tank can be suppressed. That is, the temperature rise of the liquefied carbon dioxide stored in the supply tank can be suppressed without using a refrigerator, and the energy required for cooling can be reduced.
Further, the liquefied carbon dioxide delivered from the first positive displacement pump is temporarily retained in the intermediate tank, and the liquefied carbon dioxide has a liquid level in the intermediate tank, and the gas phase exists above the liquid level. In addition, the buffer tank can absorb the pressure pulsation of the liquefied carbon dioxide delivered from the first positive displacement pump in the intermediate tank, and the pressure fluctuation of the carbon dioxide delivered from the second positive displacement pump can be reduced.
In this case, in order to carry out the method of the present invention, the system of the present invention connects an intermediate tank interposed between the first positive displacement pump and the second positive displacement pump, and connects the intermediate tank to the supply tank. A recirculation path; and a pressure reducing valve provided in the recirculation path. The liquefied carbon dioxide fed from the first positive displacement pump is sucked by the second positive displacement pump after being stored in the intermediate tank. The temperature of a part of the liquefied carbon dioxide stored in the intermediate tank is lowered by the pressure reducing valve, and the liquefied carbon dioxide decompressed by the pressure reducing valve is supplied to the supply tank through the reflux path. Preferably it is refluxed. Thereby, the temperature rise of the carbon dioxide in a supply tank by the intrusion heat from the outside is suppressed by the liquefied carbon dioxide recirculated to a supply tank.

Further, the liquefied carbon dioxide stored in the supply tank is maintained at a pressure within a certain range, a value corresponding to the pressure of the liquefied carbon dioxide in the intermediate tank is detected, and the pressure fluctuation of the liquefied carbon dioxide in the intermediate tank is detected. It is preferable to adjust the secondary pressure setting value of the pressure reducing valve in accordance with the detected value so as to be suppressed.
Thereby, the pressure fluctuation of the liquefied carbon dioxide in the intermediate tank can be reduced, and the pressure fluctuation of the carbon dioxide delivered from the second positive displacement pump can be reduced.
In this case, in order to carry out the method of the present invention, the system of the present invention comprises means for holding the liquefied carbon dioxide contained in the supply tank at a pressure within a certain range, and a value corresponding to the pressure of the liquefied carbon dioxide in the intermediate tank. A control device that adjusts the secondary pressure setting value of the pressure reducing valve in accordance with the value detected by the detection device so that the pressure fluctuation of the liquefied carbon dioxide in the intermediate tank is suppressed. Preferably it is provided.

It is preferable that a plunger metering pump is used as the first positive displacement pump, and a diaphragm metering pump is used as the second positive displacement pump.
The plunger metering pump that compresses liquefied carbon dioxide by the reciprocating drive of the plunger is a mechanical part of the drive unit required for a fixed discharge amount compared to the diaphragm metering pump that compresses by the movement of the diaphragm by the reciprocating drive of the drive shaft. Since the momentum can be increased, the discharge amount can be increased and the casing can be made thinner. Therefore, since the plunger type metering pump can reduce the casing in size compared to the diaphragm type metering pump, the cooling effect when the liquefied carbon dioxide in the pump chamber is cooled from the outside can be enhanced.
On the other hand, in the plunger type metering pump, since the plunger is slid with respect to the casing through the seal at the gland, the leakage of liquefied carbon dioxide from between the plunger and the casing increases as the pressure increases. In contrast, in the diaphragm metering pump, the diaphragm does not slide with respect to the casing at the time of compression. Therefore, the gland portion is unnecessary, the airtightness is improved, and the leakage of liquefied carbon dioxide can be reduced to improve the compression efficiency.
Since the second positive displacement pump in the present invention is used at a pressure higher than the critical pressure than the first positive displacement pump, the temperature of the liquefied carbon dioxide in the second positive displacement pump rises to about 30 ° C. or more. To do. Therefore, the second positive displacement pump can be operated in a state where the internal temperature is higher than the standard environmental temperature, and energy required for cooling can be reduced. Therefore, energy efficiency can be obtained by using a plunger metering pump that can increase the cooling effect as the first positive displacement pump, and a diaphragm metering pump with low leakage of liquefied carbon dioxide at high pressure as the second positive displacement pump. Can be increased.

  The number of the first positive displacement pumps may be single or plural. When the number of the first positive displacement pumps is plural, the first positive displacement pumps may be connected in parallel to each other.

  The number of the second positive displacement pumps may be single or plural. When there are a plurality of the second positive displacement pumps, the second positive displacement pumps may be connected in parallel to each other.

  According to the carbon dioxide supply method and supply system of the present invention, the energy efficiency when the carbon dioxide is raised to a pressure exceeding the critical pressure by the positive displacement pump and sent out can be improved.

The figure which shows the structure of the supply system of the carbon dioxide in embodiment of this invention. A sectional view of a plunger type metering pump in an embodiment of the present invention. III-III sectional view taken on the line of FIG. A sectional view of a diaphragm type metering pump in an embodiment of the present invention. The partial expanded sectional view of the diaphragm type | formula metering pump in embodiment of this invention. Carbon dioxide state diagram. The figure which shows the structure of the conventional carbon dioxide supply system.

  A carbon dioxide supply system 1 shown in FIG. 1 includes a supply tank 2 that stores high-pressure liquefied carbon dioxide that is used for industrially molding a foamed resin. The supply tank 2 of the present embodiment includes a pressure evaporator for holding the liquefied carbon dioxide at a pressure within a certain range, a pressure holding means such as a pressure regulator, and a cold insulation means such as a vacuum heat insulating layer 2a. A known cold evaporator can be used. The liquefied carbon dioxide stored in the supply tank 2 has a liquid level L. The supply tank 2 is suitable for storing a large amount of liquefied carbon dioxide so that the foamed resin can be industrially continuously produced, and the storage pressure of the liquefied carbon dioxide is limited in terms of strength. Therefore, the liquefied carbon dioxide is stored in the supply tank 2 at a pressure and temperature generally used, and the storage pressure and the storage temperature are balanced so that the storage pressure corresponds to the saturated vapor pressure at the storage temperature. It is preferable that the housing pressure and the housing temperature are maintained within a certain range. For example, the set value of the storage temperature of liquefied carbon dioxide in the supply tank 2 is −20 ° C., and the set value of the storage pressure is 2.0 MPa (absolute pressure) corresponding to the saturated vapor pressure at the set value of the storage temperature. As the housing temperature is raised and lowered with a certain fluctuation range so that the accommodation temperature becomes a set value by the operation of the tank 2, the accommodation pressure is raised and lowered with a certain fluctuation width so as to become the setting value. The constant fluctuation range of the storage temperature is preferably as small as possible, for example, ± 1 ° C. In this case, the constant fluctuation range of the storage pressure is ± so that the storage pressure corresponds to the saturated vapor pressure at the storage temperature. 0.1 MPa. As a result, the housing temperature is maintained at a value within the range of −20 ° C. ± 1 ° C., and the housing pressure is within the range of 2.0 MPa (absolute pressure) ± 0.1 MPa, corresponding to the saturated vapor pressure at the housing temperature. Is held at the value to be The storage temperature of the liquefied carbon dioxide in the supply tank 2 is not limited, but is preferably set to a value between −20 ° C. and −25 ° C. for economic efficiency, and the storage pressure is a saturated vapor pressure at the storage temperature. It is sufficient to correspond to.

  A suction port 3a of a plunger metering pump 3 is connected to the lower outlet 2b of the supply tank 2 as a first positive displacement pump. The liquefied carbon dioxide stored in the supply tank 2 is sucked by the plunger type metering pump 3. The plunger metering pump 3 pressurizes the liquefied carbon dioxide to a pressure lower than the critical pressure, and sends it out from the discharge port 3b. That is, the liquefied carbon dioxide is compressed by the plunger-type metering pump 3, so that the pressure and temperature are increased more than in the supply tank 2, and are sent close to the critical point.

  As the plunger type metering pump 3, a known one can be used. For example, as shown in FIGS. 2 and 3, the pump chamber 3e surrounded by the plunger 3c and the casing 3d in the plunger-type metering pump 3 has a suction port via a suction valve 3f constituted by a check valve that opens at the time of suction. It leads to the discharge port 3b through a discharge valve 3g constituted by a check valve that opens to 3a. The plunger 3c is reciprocated by a driving device (not shown) and slides with respect to the casing 3d through a seal such as an O-ring at the ground portion 3h. When the plunger 3c moves to the right as shown by a two-dot chain line in FIG. 2, the liquefied carbon dioxide in the pump chamber 3e is pressurized and sent out through the discharge valve 3g. As the plunger 3c moves to the left as shown by the solid line in FIG. 2, liquefied carbon dioxide is sucked into the pump chamber 3e via the suction valve 3f.

  In the plunger metering pump 3, a cooling device 4 is provided for cooling the liquefied carbon dioxide to −20 ° C. or less, for example. As the cooling device 4, a known device can be used. In order to cool the liquefied carbon dioxide through the cooling jacket 4 e that covers the casing 3 d of the plunger type metering pump 3, such as ethylene glycol stored in the refrigerant tank 4 a. The refrigerant 4b is cooled by the refrigerator 4c. The temperature of the refrigerant 4b may be set so as to prevent bubbles from being generated in the liquefied carbon dioxide in the plunger metering pump 3. For example, the refrigerant 4b cooled to −30 ° C. by the refrigerator 4c is cooled by the refrigerant pump 4d. The cooling jacket 4e is fed from the inlet 4e 'through the pipe, and is refluxed from the outlet 4e "through the pipe at -25 ° C.

  The liquefied carbon dioxide in the plunger-type metering pump 3 is cooled by the cooling device 4 so that the saturated vapor pressure is reduced, and part of the vaporized carbon dioxide is suppressed from being vaporized. That is, the saturated vapor pressure is reduced by cooling so that bubbles can be suppressed in the liquefied carbon dioxide before, during and after pressurization, and the effective suction head is made sufficiently large. When the pressure and heat loss of the liquefied carbon dioxide before pressurization in the plunger metering pump 3 are negligible because the pressure loss and heat loss in the piping between the supply tank 2 and the plunger metering pump 3 are negligible, the supply tank 2 The housing temperature and the housing pressure are preferably the same. The temperature of the liquefied carbon dioxide after pressurization in the plunger type metering pump 3 is a value between 30 ° C. and −25 ° C., and the pressure is a value between 7.0 MPa and 7.3 MPa (absolute pressure). Preferably it is done. For example, the liquefied carbon dioxide in the plunger-type metering pump 3 has a temperature of −20 ° C. and a pressure of 2.0 MPa (absolute pressure) corresponding to the saturated vapor pressure at that temperature in the suction port 3a before pressurization. In this case, the pressure is set to a value determined by the compression ratio of liquefied carbon dioxide by the plunger metering pump 3 at the discharge port 3b after pressurization, and the compression ratio is set to about 3.3 MPa (7.0 MPa). Absolute pressure).

  A diaphragm type metering pump 5 as a second positive displacement pump is connected in series to the plunger type metering pump 3 via a sealed intermediate tank 6, whereby the plunger type metering pump 3, the diaphragm metering pump 5, An intermediate tank 6 is interposed between the two. That is, the discharge port 3b of the plunger-type metering pump 3 is connected to the inlet 6a of the intermediate tank 6 via a pipe, and the suction port 5a of the diaphragm-type metering pump 5 is connected to the main outlet 6b of the intermediate tank 6 via a pipe. Is done. The number of diaphragm metering pumps 5 in this embodiment is plural, and each of the diaphragm metering pumps 5 is connected in parallel to each other and connected to different extruders 7.

  The liquefied carbon dioxide delivered from the plunger metering pump 3 is sucked by the diaphragm metering pump 5 after being stored in the intermediate tank 6. When the storage pressure of the liquefied carbon dioxide in the intermediate tank 6 is less than the critical pressure, and the pressure loss in the pipe between the plunger type metering pump 3 and the intermediate tank 6 is small and can be ignored, the pressure from the plunger type metering pump 3 The pressure is preferably equal to the delivery pressure, for example, about 7.0 MPa (absolute pressure). When the liquefied carbon dioxide is stored at a temperature lower than the critical temperature in the intermediate tank 6 and the heat loss in the pipe between the plunger type metering pump 3 and the intermediate tank 6 is small and can be ignored, it is sent out from the plunger type metering pump 3. It is preferable to be stored at a temperature equal to the temperature to be stored. The pressure of the liquefied carbon dioxide in the intermediate tank 6 is preferably a value between 7.0 MPa and 7.3 MPa (absolute pressure), the temperature is preferably a value between 30 ° C. and −25 ° C., and the temperature is − It is particularly preferable that the temperature is around 5 ° C. In order to prevent the temperature change of carbon dioxide in the intermediate tank 6, the intermediate tank 6 is covered with a heat insulating material to be kept cool, or a cooling jacket that covers the intermediate tank 6 is provided, and the refrigerant cooled by the refrigerator is referred to as a cooling jacket. You may circulate with a pump between refrigerant | coolant tanks.

  A reflux path 12 that connects the intermediate tank 6 to the supply tank 2 is provided, and a pressure reducing valve 8 is provided in the reflux path 12. One end of the reflux path 12 is connected to the reflux port 6 c of the intermediate tank 6, and the other end is connected to the upper inlet 2 c of the supply tank 2. A part of the liquefied carbon dioxide stored in the intermediate tank 6 is decompressed by the decompression valve 8, and the liquefied carbon dioxide decompressed by the decompression valve 8 is refluxed to the supply tank 2 through the reflux path 12. Therefore, the delivery flow rate of the liquefied carbon dioxide from the plunger metering pump 3 corresponds to the sum of the liquefied carbon dioxide suction flow rate by the diaphragm metering pump 5 and the liquefied carbon dioxide flow rate in the reflux path 12. The That is, the delivery flow rate (for example, 30 kg / h) of the liquefied carbon dioxide from the plunger-type metering pump 3 is set to be larger than the flow rate (for example, 6 kg / h) required for forming the foamed resin in the extruder 7. (For example, 24 kg / h) is returned to the supply tank 2. The pressure reducing valve 8 may be a known one capable of adjusting the secondary pressure setting value, for example, a valve body that moves due to the difference between the elasticity of the spring and the internal pressure of the supply tank 2 that is the secondary pressure, An actuator having an actuator for shifting the spring receiving member of the spring can be employed. As a result, the pressure reducing valve 8 can maintain the secondary pressure at the set value by moving the valve body against the elasticity of the spring so that the opening degree increases as the secondary pressure decreases. The secondary pressure set value can be adjusted by changing the spring elasticity by moving the spring receiving member with the actuator.

  Since the temperature of the liquefied carbon dioxide refluxed to the supply tank 2 is reduced by being reduced in pressure, the temperature of the liquefied carbon dioxide stored in the supply tank 2 is suppressed from rising due to heat entering from the outside. For example, the secondary pressure setting value of the pressure reducing valve 8 is made equal to the setting value of the storage pressure of liquefied carbon dioxide stored in the supply tank 2, and the intermediate tank 6 is set at 7.0 MPa (absolute pressure), for example, at −5 ° C. The stored liquefied carbon dioxide is depressurized by the pressure reducing valve 8 to, for example, 2.0 MPa (absolute pressure) and refluxed to the supply tank 2. Thereby, the temperature of the liquefied carbon dioxide in the intermediate tank 6 is lowered to a set value of the storage temperature of the liquefied carbon dioxide in the supply tank 2, for example, −20 ° C. It is suppressed. At this time, the temperature of the liquefied carbon dioxide to be refluxed changes along the boiling line connecting the triple point and the critical point in the relationship between the thermodynamic state quantity of carbon dioxide and the phase in FIG.

  A detection device 9 having a value corresponding to the pressure of liquefied carbon dioxide in the intermediate tank 6 is provided. The detection device 9 of the present embodiment uses a liquid level gauge that detects the height of the liquid level L ′ of liquefied carbon dioxide in the intermediate tank 6 as a value corresponding to the pressure of liquefied carbon dioxide. A pressure sensor that detects the pressure of the liquefied carbon dioxide itself may be used as the detection device 9.

  Even when the excess amount of the liquefied carbon dioxide obtained by subtracting the suction flow rate of the diaphragm type metering pump 5 from the delivery flow rate of the plunger type metering pump 3, the excess liquefied carbon dioxide suppresses the pressure fluctuation in the intermediate tank 6. A control device 10 that adjusts the secondary pressure set value of the pressure reducing valve 8 according to the value detected by the detection device 9 is provided so that the supply tank 2 can be refluxed.

That is, in a normal state where the excess amount of liquefied carbon dioxide is constant, a predetermined constant flow rate of liquefied carbon dioxide is returned to the supply tank 2 without fluctuation in pressure as an excess amount. The secondary pressure set value of the valve 8 is set to an initial value, and the pressure of the liquefied carbon dioxide in the intermediate tank 6 at this time is set as a reference pressure.
When the excess amount of liquefied carbon dioxide varies from a predetermined constant flow rate, the pressure of liquefied carbon dioxide in the intermediate tank 6 varies from the reference pressure in accordance with the amount of variation. The control device 10 outputs a control signal for operating the actuator of the pressure reducing valve 8 according to the difference between the detected pressure of the detecting device 9 and the reference pressure. Thereby, the secondary pressure setting value of the pressure reducing valve 8 is made larger than the initial value as the pressure of the liquefied carbon dioxide stored in the intermediate tank 6 rises above the reference pressure, and as the pressure falls below the reference pressure. The spring receiving member of the pressure reducing valve 8 is changed so as to be smaller than the initial value. Thereby, according to the change from the initial value of the secondary side pressure setting value of the pressure reducing valve 8, the flow volume of the liquefied carbon dioxide recirculated from the intermediate tank 6 to the supply tank 2 can be changed. Therefore, even if the excess amount of liquefied carbon dioxide fluctuates, the excess amount is recirculated to the supply tank 2 while suppressing the pressure fluctuation in the intermediate tank 6, and the flow rate and pressure fluctuation of the carbon dioxide delivered from the diaphragm metering pump 5 Can be prevented. When the detected pressure varies from the reference pressure, the control device 10 may output an alarm signal to an alarm device such as a warning lamp.

  The diaphragm type metering pump 5 pressurizes the liquefied carbon dioxide to raise the pressure to a pressure exceeding the critical point and shifts it to the supercritical state, and sends out the carbon dioxide in the supercritical state from the discharge port 5b. The discharge ports 5b of the diaphragm type metering pumps 5 are connected to the foamed resin extruders 7, respectively. By being compressed by the diaphragm metering pump 5, carbon dioxide is increased to, for example, 10 MPa (absolute pressure) or more, and the temperature is also raised to a value exceeding the critical temperature of 31.1 ° C. The extruder 7 forms, for example, a polystyrene resin foam plate. The temperature of carbon dioxide fed from the diaphragm metering pump 5 and supplied to the extruder 7 may be less than the critical temperature, and the diaphragm metering pump 5 pressurizes the liquefied carbon dioxide to a pressure exceeding the critical pressure. It is only necessary to increase the pressure and send out carbon dioxide having a pressure exceeding the critical pressure.

  A known pump can be used as the diaphragm metering pump 5. For example, as shown in FIGS. 4 and 5, the pump chamber 5e surrounded by one surface of the diaphragm 5c and the casing 5d in the diaphragm metering pump 5 is a suction port via a suction valve 5f configured by a check valve that opens at the time of suction. It leads to the discharge port 5b through a discharge valve 5g constituted by a check valve that opens to 5a. Further, the oil chamber 5h surrounded by the other surface of the diaphragm 5c, the casing 5d and the drive shaft 5k is an inflow constituted by a relief valve 5i constituted by a check valve opened at the time of pressurization and a check valve opened at the time of release of the pressure. It leads to a tank 5n of hydraulic oil 5m integrated in the casing 5 through a valve 5j. The drive shaft 5k is reciprocally driven by a drive device (not shown). The diaphragm 5c is deformed via the hydraulic oil 5m by the leftward movement of the drive shaft 5k in FIG. 4, so that the liquefied carbon dioxide in the pump chamber 5e is pressurized to a supercritical state and is extruded through the discharge valve 5g. The liquefied carbon dioxide is sucked into the pump chamber 5e through the suction valve 5f by the deformation of the diaphragm 5c which is sent to the machine 7 and released from the pressure by the rightward movement.

  A cooling device 11 for cooling carbon dioxide in the diaphragm metering pump 5 is provided. As the cooling device 11, a known device can be used. In order to cool the carbon dioxide through the cooling jacket 11e covering the casing 5d of the diaphragm type metering pump 5, the refrigerant 11b such as ethylene glycol accommodated in the refrigerant tank 11a. Is cooled to, for example, −30 ° C. by the refrigerator 11c, and the refrigerant 11b is sent from the inlet 11e ′ to the cooling jacket 11e via the pipe by the refrigerant pump 11d and refluxed at −25 ° C. via the pipe from the outlet 11e ″.

  The liquefied carbon dioxide before reaching the critical point in the diaphragm metering pump 5 is cooled by the cooling device 11 so that the saturated vapor pressure is reduced. That is, before the pressurization, during the pressurization until the critical point is reached, the saturated vapor pressure is reduced by cooling so as to suppress the generation of bubbles in the liquefied carbon dioxide, and the effective suction head is made sufficiently large. For example, when the liquefied carbon dioxide in the diaphragm metering pump 5 is small in pressure loss and heat loss in the pipe between the intermediate tank 6 and the diaphragm metering pump 5 and can be ignored, the liquefied carbon dioxide in the suction port 5a before pressurization As in 6, the temperature is −5 ° C. and the pressure is about 7.0 MPa (absolute pressure). The temperature of the liquefied carbon dioxide before pressurization in the diaphragm metering pump 5 is a value between 30 ° C. and −25 ° C., and the pressure is a value between 7.0 MPa and 7.3 MPa (absolute pressure). It is particularly preferable that the temperature is around -5 ° C. Thereby, it is suppressed that a part of liquefied carbon dioxide evaporates and a bubble is generated before reaching a critical point. In the case where the temperature of the liquefied carbon dioxide in the intermediate tank 6 is sufficiently low and a part of the liquefied carbon dioxide in the diaphragm metering pump 5 can be suppressed from being vaporized before the critical point is reached, it is possible to suppress the generation of bubbles. 11 may not be provided.

  According to the supply system 1, the liquefied carbon dioxide contained in the supply tank 2 is sucked by the plunger-type metering pump 3, and pressurized to a pressure lower than the critical pressure and sent out, and the delivered liquefied carbon dioxide is sent out. Is sucked by the diaphragm type metering pump 5 and pressurized to a pressure and temperature exceeding the critical point, the temperature is raised and the state is changed to the supercritical state, and the liquefied carbon dioxide in the supercritical state is sent out. That is, in the past, carbon dioxide was compressed and sent out in a single stage, whereas the plunger-type metering pump 3 and the diaphragm-type metering pump 5 were used to change the critical pressure from the accommodation pressure in the liquid state in the supply tank 2 to the carbon dioxide. Compressed and sent in two stages until the pressure exceeds.

  By pressurizing the carbon dioxide stepwise in this way, the compression ratio in each of the plunger-type metering pump 3 and the diaphragm-type metering pump 5 can be made smaller than before, and the frictional heat of each operating part can be reduced. Further, by bringing the pressure of the liquefied carbon dioxide stored in the supply tank 2 below the critical pressure close to the critical pressure by the plunger metering pump 3, until the liquefied carbon dioxide reaches the critical pressure in the diaphragm metering pump 5. Thus, the cooling energy required to suppress the vaporization of liquefied carbon dioxide before reaching the critical pressure in the diaphragm-type metering pump 5 can be reduced as much as possible. It is also possible to do. That is, if the liquefied carbon dioxide is cooled in the plunger metering pump 3 in which the frictional heat of the working part is reduced as compared with the prior art in order to suppress the vaporization of the liquefied carbon dioxide before reaching the critical pressure, the diaphragm metering is performed. Since the cooling energy required in the pump 5 can be reduced and can be eliminated, the total energy required for cooling can be reduced as compared with the conventional case.

  In addition, a part of the liquefied carbon dioxide stored in the intermediate tank 6 is decompressed and refluxed to the supply tank 2, and the temperature of the liquefied carbon dioxide that is refluxed is reduced by being decompressed. The temperature rise of the liquefied carbon dioxide can be suppressed. Thereby, the temperature rise of the liquefied carbon dioxide accommodated in the supply tank 2 can be suppressed without using a refrigerator, and the energy required for cooling can be reduced.

  The liquefied carbon dioxide delivered from the plunger-type metering pump 3 is temporarily retained in the intermediate tank 6, and the liquefied carbon dioxide has a liquid level L ′ in the intermediate tank 6, above the liquid level L ′. Due to the presence of the gas phase, the intermediate tank 6 can exhibit a buffering action for absorbing the pressure pulsation of the liquefied carbon dioxide delivered from the plunger metering pump 3, and the supercritical carbon dioxide delivered from the diaphragm metering pump 5. Pressure fluctuation can be reduced. Furthermore, the pressure fluctuation of the liquefied carbon dioxide in the intermediate tank 6 can be reduced by adjusting the secondary pressure setting value of the pressure reducing valve 8 according to the pressure of the liquefied carbon dioxide in the intermediate tank 6.

  The plunger-type metering pump 3 that compresses liquefied carbon dioxide by the reciprocating drive of the plunger 3c is required for a constant discharge amount as compared with the diaphragm-type metering pump 5 that compresses the diaphragm 5c by the reciprocating drive of the drive shaft 5k. Since the mechanical momentum of the drive unit can be increased, the discharge amount can be increased, and the casing can be thinned, so that the size can be easily reduced. Therefore, the plunger-type metering pump 3 can enhance the cooling effect when the liquefied carbon dioxide in the pump chamber 3e is cooled from the outside by making the casing 3d thinner and smaller than the diaphragm-type metering pump 5. On the other hand, in the plunger type metering pump 3, since the plunger 3c is slid with respect to the casing 3d through the seal in the ground portion 3h, the leakage of liquefied carbon dioxide from between the plunger 3c and the casing 3d is high. In comparison with the diaphragm type metering pump 5, the diaphragm 5c does not slide with respect to the casing 5d at the time of compression, so that the gland portion is unnecessary and the hermeticity is improved, and the leakage of liquefied carbon dioxide is reduced. Compression efficiency can be improved. Further, since the second positive displacement pump is used at a higher pressure than the first positive displacement pump, the temperature of carbon dioxide in the second positive displacement pump rises to about 30 ° C. or more. . Therefore, the second positive displacement pump can be operated in a state where the internal temperature is higher than the standard environmental temperature, and energy required for cooling can be reduced. Therefore, by using the plunger metering pump 3 that can increase the cooling effect as the first positive displacement pump, and using the diaphragm metering pump 5 with less leakage of liquefied carbon dioxide at high pressure as the second positive displacement pump, Energy efficiency can be increased.

The present invention is not limited to the above embodiment.
For example, a diaphragm type metering pump or a gear pump may be used as the first positive displacement pump, and a plunger type metering pump or a gear pump may be used as the second positive displacement pump.
The number of the first positive displacement pumps may be plural, and in this case, the first positive displacement pumps may be connected in parallel to each other.
The number of the second positive displacement pumps may be single.
Cooling the liquefied carbon dioxide in the diaphragm metering pump 5 by cooling the liquefied carbon dioxide in the intermediate tank 6 or lowering the temperature after cooling the liquefied carbon dioxide in the plunger metering pump 3 than in the above embodiment. May be unnecessary. When the ambient temperature is low and the liquefied carbon dioxide in the intermediate tank 6 is cooled, the cooling of the liquefied carbon dioxide in the second positive displacement pump may be unnecessary.

  2 ... Supply tank, 3 ... Plunger type metering pump (first positive displacement pump), 4 ... Cooling device, 5 ... Diaphragm metering pump (second positive displacement pump), 6 ... Intermediate tank, 8 ... Pressure reducing valve , 9 ... detecting device, 10 ... control device, 12 ... reflux path.

Claims (9)

Liquefied carbon dioxide contained in a supply tank is sucked by at least one first positive displacement pump,
By the first positive displacement pump, the liquefied carbon dioxide is pressurized to a pressure lower than the critical pressure and sent out.
Cooling the liquefied carbon dioxide in the first positive displacement pump;
Liquefied carbon dioxide delivered from the first positive displacement pump is sucked by at least one second positive displacement pump;
A method for supplying carbon dioxide, wherein the liquefied carbon dioxide is pressurized by the second positive displacement pump to a pressure exceeding the critical pressure, and carbon dioxide having a pressure exceeding the critical pressure is sent out. An intermediate tank is interposed between the first positive displacement pump and the second positive displacement pump;
The liquefied carbon dioxide delivered from the first positive displacement pump is sucked by the second positive displacement pump after being stored in the intermediate tank,
The method for supplying carbon dioxide according to claim 1, wherein a part of the liquefied carbon dioxide stored in the intermediate tank is reduced in temperature by a pressure reducing valve to be refluxed to the supply tank.   The liquefied carbon dioxide stored in the supply tank is maintained at a pressure within a certain range, a value corresponding to the liquefied carbon dioxide pressure in the intermediate tank is detected, and the pressure fluctuation of the liquefied carbon dioxide in the intermediate tank is suppressed. The method for supplying carbon dioxide according to claim 2, wherein the secondary pressure setting value of the pressure reducing valve is adjusted according to the detected value. A supply tank containing liquefied carbon dioxide;
At least one first positive displacement pump connected to the supply tank to suck in liquefied carbon dioxide contained in the supply tank;
A cooling device for cooling the liquefied carbon dioxide in the first positive displacement pump;
And at least one second positive displacement pump connected in series to the first positive displacement pump,
By the first positive displacement pump, liquefied carbon dioxide is pressurized and sent to a pressure lower than the critical pressure,
The liquefied carbon dioxide delivered from the first positive displacement pump is sucked by the second positive displacement pump,
A carbon dioxide supply system in which liquefied carbon dioxide is pressurized by the second positive displacement pump to a pressure exceeding a critical pressure, and carbon dioxide having a pressure exceeding the critical pressure is sent out. An intermediate tank interposed between the first positive displacement pump and the second positive displacement pump;
A reflux path connecting the intermediate tank to the supply tank;
A pressure reducing valve provided in the reflux path,
The liquefied carbon dioxide delivered from the first positive displacement pump is sucked by the second positive displacement pump after being stored in the intermediate tank,
A part of the liquefied carbon dioxide stored in the intermediate tank is reduced in temperature by being depressurized by the pressure reducing valve,
The carbon dioxide supply system according to claim 4, wherein the liquefied carbon dioxide decompressed by the pressure reducing valve is refluxed to the supply tank through the reflux path. Means for maintaining the liquefied carbon dioxide contained in the supply tank at a pressure within a certain range;
A detector for a value corresponding to the pressure of liquefied carbon dioxide in the intermediate tank;
The control apparatus which adjusts the secondary side pressure set value of the pressure-reducing valve according to the value detected by the detection device is provided so that the pressure fluctuation of liquefied carbon dioxide in the intermediate tank may be controlled. 5. The carbon dioxide supply system according to 5.   A plunger metering pump is used as the first positive displacement pump, and a diaphragm metering pump is used as the second positive displacement pump. Supply system.   The carbon dioxide supply system according to any one of claims 4 to 7, wherein the number of the first positive displacement pumps is plural, and each of the first positive displacement pumps is connected in parallel to each other.   The carbon dioxide supply system according to any one of claims 4 to 8, wherein the number of the second positive displacement pumps is plural, and each of the second positive displacement pumps is connected in parallel to each other.

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