JP2015105740A - Condensing and mixing device, condensing and mixing method, boil-off gas reliquefying apparatus and boil-off gas reliquefaction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a condensing and mixing device and a condensing and mixing method for effectively condensing boil-off gas and mixing it with low temperature liquid, and to provided a boil-off gas reliquefying apparatus and a boil-off gas reliquefaction method capable of effectively achieving reliquefaction of boil-off gas.SOLUTION: A condensing and mixing device 2 includes: memory means 18 prestoring correspondence relationship between pressure of mixed liquid and saturation temperature at that pressure as a first correspondence relationship A and prestoring correspondence relationship between the allowable minimum value of super-cooling degree of the mixed liquid and a sub-flow flow rate ratio attained by dividing a flow rate of the sub-flow with a sum of flow rate of main flow and flow rate of sub-flow as a second correspondence relationship B; and control means 17 for controlling a flow rate of the prescribed sub-flow by adjusting a degree of opening of a sub-flow adjustment valve 14 so as to cause the super-cooling degree of the mixed liquid to become larger than the prescribed minimum value on the basis of measured values of each of flow rate of the prescribed sub-flow, temperature and pressure of the prescribed mixed liquid while referring to the prescribed first correspondence relationship A and the prescribed second correspondence relationship B.

Description

  The present invention relates to a condensing and mixing device, a condensing and mixing method, an evaporating gas reliquefaction device, and an evaporating gas reliquefaction method, in which vapor and a low temperature liquid are brought into contact with each other to condense and liquefy the vapor and mix it with the low temperature liquid.

  When low temperature liquid such as liquefied natural gas (LNG) is stored in a tank, a part of the low temperature liquid in the tank evaporates due to heat input to the tank from the outside, and evaporated gas is generated in the tank. When the low-temperature liquid is LNG, an evaporating gas mainly composed of methane is generated.

  The generated evaporative gas can be compressed as it is and supplied to the demand side as city gas, but the compression power becomes very large. Therefore, in order to reduce such power, it can be considered that the evaporated gas is re-liquefied and pressurized in a liquid state and then gasified again to be supplied as city gas. In order to reliquefy, evaporative gas is compressed and cooled, and as a cooling method, evaporative gas is cooled by the cold heat of LNG discharged as a low temperature liquid from the tank, that is, compressed. Patent Documents 1 and 2 disclose a method of cooling evaporative gas by exchanging heat with LNG.

  Patent Document 1 discloses a method (indirect heat exchange method) in which compressed evaporative gas is cooled by heat exchange with LNG in a heat exchanger. However, in this indirect heat exchange method that requires a heat exchanger, a large heat exchanger is required to secure a sufficient heat transfer area for heat exchange, and there is a problem that the equipment becomes large and costs increase. . Furthermore, since heat transfer is indirect through the heat transfer surface, improvement in heat transfer performance on this heat transfer surface is also required.

  On the other hand, Patent Document 2 discloses a method (direct contact heat exchange method) in which compressed evaporative gas is blown into an LNG pipe and directly brought into contact with LNG to exchange heat, and evaporative gas is blown into LNG. As an injection method, an apparatus is disclosed in which one evaporative gas supply nozzle is arranged in the LNG pipe so as to be in a direction orthogonal to the flow direction of the discharge LNG flowing in the LNG pipe or in a direction opposite to the flow direction of the LNG. The evaporative gas supply nozzle is bent in an L shape in the LNG pipe, and the discharge port of the nozzle is located on the center line of the LNG pipe so that the evaporative gas is directed in the direction opposite to the flow of LNG. Is discharged. The discharged evaporative gas is cooled by heat exchange with LNG, condensed, liquefied and mixed with LNG.

  Since the direct contact heat exchange method of Patent Document 2 exchanges heat without passing through the heat transfer surface, the heat transfer performance at the interface where both the LNG and the evaporation gas are in contact with each other is improved. However, in the direct contact heat exchange system, the liquefaction efficiency is poor due to insufficient contact and mixing of the evaporating gas and the low temperature liquid due to the difference in density between the evaporating gas as the gas and the LNG as the low temperature liquid. Prone. In order to improve the efficiency, there is a demand for an efficient condensing and mixing device that mixes gaseous evaporative gas and low-temperature liquid LNG to condense and mix evaporative gas. It is difficult to say that sufficient evaporating gas and liquid LNG can be contacted and mixed, and desired liquefaction performance can be ensured.

  When the condensing and mixing device is capable of completely and uniformly condensing the evaporative gas and the low-temperature liquid, the condensate and the low-temperature liquid in which the evaporative gas is condensed are uniformly mixed as a mixed liquid, and the temperature of the mixed liquid Is lower than the saturation temperature (the maximum temperature at which the evaporating gas condenses under the pressure at that time). At this time, evaporative gas does not exist in the liquid mixture and is in a liquid state.

  When evaporating gas is blown into the low-temperature liquid, and evaporating gas is brought into contact with the liquid to cool and condense, the temperature of the mixed liquid rises from the temperature of the low-temperature liquid before mixing. The amount of evaporative gas blown into the low-temperature liquid is the maximum amount until the temperature of the mixed liquid of evaporative gas and low-temperature liquid rises to the saturation temperature (until the mixture becomes saturated). Can be blown in as. If an amount of evaporating gas exceeding this amount is blown, evaporating gas bubbles are present in the liquid mixture, which causes a problem.

  Actually, since the condensing and mixing device cannot completely and uniformly condense and mix, the temperature of the liquid mixture should be lower than the saturation temperature in order to prevent the presence of evaporating gas bubbles in the liquid mixture. The amount of evaporating gas blown into the low temperature liquid is reduced. The difference between the actual temperature of the liquid mixture (the temperature of the liquid mixture flowing out from the condensing and mixing apparatus) and the saturation temperature is called the degree of supercooling.

  In order to make the liquid mixture flowing out from the condensing and mixing device into a liquid state, it is necessary to maintain a predetermined degree of supercooling, and therefore, it is necessary to limit the amount of evaporating gas blown into the low-temperature liquid. Yes. Here, if the condensing and mixing performance in the condensing and mixing apparatus can be improved, the liquid mixture can be made into a liquid state even if the degree of supercooling is small, the amount of evaporation gas blown can be increased, and the processing capacity of the condensing and mixing apparatus can be increased. It can be expected to improve.

  Patent Document 3 discloses a condensing and mixing device that generates hot water by injecting steam as evaporating gas into water as low-temperature liquid flowing through a mixing chamber in a pipe, condensing the steam, and mixing it with water. ing. This condensing and mixing device is provided with a fixed swirl vane for imparting swirl to water in the mixing chamber, and the efficiency of mixing water and steam is improved by the fixed swirl vane.

JP 55-145897 JP 08-173781 JP 7-116486 A

  However, when the vapor evaporative gas is pressurized and brought into direct contact with the low-temperature liquid, if sufficient condensing and mixing performance is not ensured, the evaporative gas merged with the low-temperature liquid is not completely liquefied and bubbles remain without being liquefied. If it is supplied to the liquid feed pump in a state, not only liquid feeding becomes difficult, but it also causes a failure of the liquid feed pump. Further, in the condensing and mixing apparatus provided with the swirl imparting mechanism that improves the condensing and mixing performance as in Patent Document 3, the fluid in the condensing and mixing apparatus passes through the fixed swirling blades, so that the pressure loss of the condensing and mixing apparatus increases. There is a problem.

  In view of such circumstances, the present invention increases the pressure of gaseous evaporative gas, and when this evaporative gas is brought into direct contact with a low temperature liquid such as LNG for reliquefaction, the evaporative gas is effectively condensed to a low temperature liquid. It is an object of the present invention to provide a condensing and mixing apparatus for mixing, a condensing and mixing method, and an evaporating gas reliquefaction apparatus and an evaporating gas reliquefaction method capable of effectively realizing reliquefaction of evaporating gas.

  According to the present invention, the above-described problems are solved by the condensing and mixing apparatus according to the first and second aspects of the invention, the evaporative gas reliquefaction apparatus according to the third aspect, the condensing and mixing method according to the fourth aspect, and the second aspect. It is solved by the evaporative gas reliquefaction method according to the fifth invention.

<First invention>
The condensing and mixing apparatus according to the first aspect of the invention injects evaporative gas generated from the low temperature liquid into the main flow formed by the flow of the low temperature liquid, condenses the evaporative gas, and mixes it with the main temperature low temperature liquid.

  In such a condensing and mixing apparatus, in the first invention, a tubular body having an axis in the direction in which the low-temperature liquid flowing from upstream to downstream is circulated as the main stream is formed, and a part of the main stream is divided upstream of the tubular body. A tangential inlet for receiving the substream obtained by the flow is formed, and a swirl flow forming portion for generating a swirl flow with respect to the main flow by the subflow, and the swirl flow formation downstream of the swirl flow forming portion A venturi tube positioned on an extension line of the axis of the portion, receiving a low-temperature liquid forming the swirling flow from the swirling flow forming portion, and forming an evaporating gas hole for receiving the evaporating gas on a tube wall of the venturi tube. And a mixing tube section that condenses the evaporated gas and mixes with the low-temperature liquid forming the swirling flow to generate a mixed liquid.

<Second invention>
The condensing and mixing apparatus according to the second aspect of the invention injects evaporative gas generated from the low-temperature liquid into the main flow formed by the flow of the low-temperature liquid, condenses the evaporative gas, and mixes it with the main-stream low-temperature liquid.

  In such a condensing and mixing apparatus, in the second invention, a tubular body having an axis in the direction in which the low-temperature liquid flowing from upstream to downstream is circulated as the main stream is formed, and a part of the main stream is separated upstream of the tubular body. A tangential inlet for receiving the substream obtained by the flow is formed, and a swirl flow forming portion for generating a swirl flow with respect to the main flow by the subflow, and the swirl flow formation downstream of the swirl flow forming portion A venturi tube positioned on an extension line of the axis of the portion, receiving a low-temperature liquid forming the swirling flow from the swirling flow forming portion, and forming an evaporating gas hole for receiving the evaporating gas on a tube wall of the venturi tube. A mixing tube section that condenses the evaporative gas and mixes with the low-temperature liquid that forms the swirling flow to generate a mixed liquid, a main flow meter that measures the flow rate of the main flow flowing into the swirling flow forming section, and Flow in the swirl flow forming section A secondary flow meter for measuring the flow rate of the secondary flow, a secondary flow adjustment valve for adjusting the flow rate of the secondary flow, a liquid mixture thermometer for measuring the temperature of the liquid mixture flowing out of the mixing pipe section, and the A mixed liquid pressure gauge for measuring the pressure of the mixed liquid, a correspondence relation between the pressure of the mixed liquid and the saturation temperature at the pressure as a first correspondence relation, and a minimum allowable supercooling degree of the mixed liquid; Storage means for preliminarily storing a correspondence relationship with a secondary flow rate ratio obtained by dividing the flow rate of the secondary flow by the sum of the flow rates of the main flow and the secondary flow, and the first correspondence relationship And referring to the second correspondence relationship, based on the measured values of the main flow rate, the secondary flow rate, the temperature and pressure of the mixed solution, the degree of supercooling of the mixed solution is less than the minimum value. Adjust the flow rate of the secondary flow by adjusting the opening of the secondary flow control valve so that it increases. It is characterized in that a control means for controlling.

  In the second invention, the control means is based on the measured values of the flow rate of the main flow, the flow rate of the secondary flow, the temperature and the pressure of the mixed liquid while referring to the first correspondence relationship and the second correspondence relationship. By controlling the flow rate of the side flow, the supercooling degree of the mixed liquid is always larger than the minimum value of the supercooling degree, so that the evaporated gas is surely condensed and effectively mixed with the low temperature liquid. Can do. Here, the “minimum value of the degree of supercooling” is the smallest value of the degree of supercooling that prevents the mixture from containing steam.

  In the second invention, the control means refers to the first correspondence relationship stored in the storage means, derives the saturation temperature corresponding to the measured value of the pressure of the mixed liquid, Supercooling degree calculating means for calculating a difference between the measured value of the temperature of the mixed liquid as the degree of supercooling of the mixed liquid, and the sum of the measured value of the main flow rate and the measured value of the substream flow rate. The subflow flow rate ratio calculating means for calculating the subflow flow ratio by dividing the measured value of the flow rate, and the calculated value of the supercooling degree is the minimum supercooling degree in the second correspondence relationship stored in the storage means. When the calculated value of the degree of supercooling is less than or equal to the minimum value compared to the value, the secondary flow is such that the calculated value of the degree of supercooling is greater than the minimum value with reference to the second correspondence relationship. The flow rate ratio is derived as a target value, and the opening of the secondary flow control valve is adjusted so that the calculated value of the secondary flow rate ratio follows the target value. Preferably has a sidestream flow rate adjusting means for increasing the flow rate of the larger to the side stream.

  Here, as described above, the “substream flow rate ratio” is a ratio obtained by dividing the substream flow rate by the sum of the main flow rate and the substream flow rate, and is formed in the swirl flow forming portion. This represents the strength of the swirling flow, that is, “swirl strength”. When there is a swirling flow, the minimum value of supercooling is lower than when there is no swirling flow, and the minimum value of subcooling decreases as the side flow rate ratio (swirl strength) increases (Fig. 3). That is, by generating a swirling flow with respect to the main flow by the side flow, and as the swirling strength increases, the degree of supercooling decreases, and the mixing performance of the condensing and mixing apparatus improves.

<Third invention>
The evaporative gas reliquefaction apparatus according to the third aspect of the invention mixes the evaporative gas generated from the low temperature liquid stored in the storage tank with the low temperature liquid by injecting it into the low temperature liquid discharged from the storage tank and condensing it. Re-liquefy.

  In this evaporative gas reliquefaction apparatus, the third invention comprises the condensing and mixing apparatus according to the first invention or the second invention, a delivery pump for sending out the low temperature liquid from the storage tank, and an evaporating gas compressor for compressing the evaporating gas. The low-temperature liquid is supplied to the swirl flow forming portion of the condensing and mixing device by the delivery pump, and the evaporating gas is injected into the mixing tube portion of the condensing and mixing device by the evaporative gas compressor. .

  According to the evaporative gas reliquefaction apparatus having the condensing and mixing apparatus according to the second aspect of the invention, the degree of supercooling of the mixed liquid is always greater than the minimum value as in the case of the second aspect. It can be condensed and efficiently mixed into a cryogenic liquid for reliquefaction.

<Fourth Invention>
In the condensing and mixing method according to the fourth aspect of the invention, the evaporative gas generated from the low temperature liquid is injected into the main flow formed by the flow of the low temperature liquid, and the evaporative gas is condensed and mixed with the main flow low temperature liquid.

  In such a condensing and mixing method, in the fourth invention, the main flow rate measurement step for measuring the flow rate of the low-temperature liquid flowing as the main flow from upstream to downstream, and the low temperature flowing as a side flow obtained by dividing a part of the main flow A substream flow rate measuring step for measuring the flow rate of the liquid, and the mainstream cryogenic liquid is circulated in the tubular body, and the substream cryogenic liquid is injected in a tangential direction of the tubular body, and the mainstream is introduced by the substream. A swirl flow forming step for generating a swirl flow with respect to the liquid, and the evaporating gas is injected into a venturi tube that receives the low-temperature liquid in which the swirl flow is formed in the swirl flow forming step, and the evaporative gas is condensed and swirled. A mixing step of mixing the low-temperature liquid formed with the flow to generate a mixed solution, a mixed solution temperature measuring step of measuring the temperature of the mixed solution, a mixed solution pressure measuring step of measuring the pressure of the mixed solution, The above The first correspondence that is the correspondence between the pressure of the liquid and the saturation temperature at that pressure, and the minimum value of the allowable subcooling of the mixed liquid and the sum of the flow rates of the main flow and the substream, While referring to the second correspondence relationship that is the correspondence relationship with the side flow rate ratio obtained by dividing the flow rate, the measured values of the main flow rate, the secondary flow rate, the temperature and pressure of the mixed liquid And a control step of controlling the flow rate of the side flow so that the degree of supercooling of the mixed liquid is greater than the minimum value.

  In the fourth invention, the control step refers to the first correspondence relationship, derives the saturation temperature corresponding to the measured value of the mixed liquid pressure, and then derives the saturated temperature derived value and the measured temperature of the mixed liquid. The subcooled flow rate is calculated by subtracting the measured value of the secondary flow rate from the sum of the measured value of the main flow rate and the measured value of the secondary flow rate. The sub-flow rate ratio calculation step for calculating the sub-flow rate ratio, and the calculated value of the supercooling degree is compared with the minimum value of the supercooling degree in the second correspondence relationship. When the value is equal to or lower than the value, the second correspondence relationship is referred to, and a subflow flow rate ratio in which the calculated value of the degree of supercooling is larger than the minimum value is derived as a target value. It is preferable to have a secondary flow rate adjustment step of increasing the secondary flow rate so as to follow the target value.

<Fifth invention>
The evaporative gas reliquefaction method according to the fifth aspect of the present invention is to mix evaporative gas generated from the low temperature liquid stored in the storage tank into the low temperature liquid by injecting it into the low temperature liquid discharged from the storage tank and condensing it. Re-liquefy.

  In this evaporative gas reliquefaction method, the fifth invention comprises the steps described in the condensing and mixing method according to the fourth invention, a delivery step for sending out the cryogenic liquid from the storage tank, and an evaporative gas compression step for compressing the evaporative gas. The low temperature liquid is supplied to the tubular body in the delivery step, and the evaporation gas is injected into the venturi tube in the evaporation gas compression step.

  In the present invention, as described above, the flow of the low-temperature liquid in the secondary flow is controlled by the control means or the control process so that the degree of supercooling of the mixed liquid always becomes larger than the minimum value. It is possible to reliably condense and effectively mix and re-liquefy in the low temperature liquid, and it is possible to prevent the pump from being damaged due to the evaporating gas flowing into the pump as a gas. Further, the reliquefaction of the evaporative gas is completed efficiently in a short time, and as a result, the apparatus configuration can be made compact.

It is a schematic block diagram of the evaporative gas reliquefaction apparatus of one Embodiment apparatus of this invention. (A) is a schematic block diagram of the condensation mixing apparatus used for the evaporative gas reliquefaction apparatus of FIG. 1, (B) is BB sectional drawing of (A). It is a figure which shows the relationship between the minimum value of the supercooling degree of a liquid mixture, and a subflow flow rate ratio (swirl strength).

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of an evaporative gas reliquefaction apparatus including a condensing and mixing apparatus as an embodiment of the present invention.

  In FIG. 1, reference numeral 1 denotes an evaporative gas reliquefaction device according to the present embodiment, which has a condensing and mixing device 2 having a structure shown in detail in FIG. Connected to the left side) are a delivery pump 3 for delivering a cryogenic liquid 25 to the condensing and mixing device 2 and an evaporative gas compressor 4 for injecting evaporative gas 26.

  The cryogenic liquid 25 is, for example, a part of liquefied natural gas (LNG) stored in a tank (not shown), and the evaporative gas 26 is, for example, a part of liquefied natural gas in the tank. Is a boil-off gas (BOG) generated by evaporation.

  As seen in FIG. 1, the cryogenic liquid 25 is delivered by the delivery pump 3 and flows into the condensation and mixing device 2. The evaporative gas 26 compressed by the evaporative gas compressor 4 is injected into the low-temperature liquid 25 flowing in the condensing and mixing apparatus 2.

  A booster pump 5 is connected to the outlet side of the condensing and mixing device 2 and condenses and mixes the evaporated gas 26 condensed after being injected into the low temperature liquid 25 and mixed with the low temperature liquid 25 in a liquefied state. The mixed low temperature liquid (hereinafter referred to as “mixed liquid”) discharged from the apparatus 2 is pressurized. For example, if the low-temperature liquid 25 is liquefied natural gas, the pressurized liquid mixture is sent to the vaporizer, gasified again, and sent to the demand side as city gas.

  As shown in FIG. 2A, the condensing and mixing apparatus 2 includes a main flow pipe 6 that circulates a low-temperature liquid 25 that flows from the upstream side toward the downstream side as a main flow, and a low temperature branched from the main flow pipe 6. A subflow pipe 7 that circulates the liquid 25 as a substream; a swirl flow forming portion 8 that receives the main stream and the low-temperature liquid of the subflow and generates a swirl flow with respect to the main stream by the subflow; and the swirl flow Receiving the low-temperature liquid 25 and the evaporative gas 26, condensing the evaporative gas 26 and mixing it with the low-temperature liquid 25 to produce a mixed liquid, and the mixed liquid flowing out of the mixed pipe section 9 downstream And a mixed liquid pipe 10 to be circulated to the side.

  The condensing and mixing device 2 further includes a main flow meter 11 and a main flow adjusting valve 12 provided in the main flow pipe 6, a sub flow meter 13 and a sub flow adjusting valve 14 provided in the sub flow pipe 7, and a mixed liquid pipe. 10 stores a mixed liquid pressure gauge 15 and a mixed liquid thermometer 16, a control unit 17 for controlling the flow rates of the main flow and the substream, and data referred to in the control by the control unit 17. Storage means 18.

  Hereinafter, the structure of each part of the condensation mixing apparatus 2 will be described. As shown in FIG. 2A, the secondary flow pipe 7 is branched from the main flow pipe 6 on the upstream side of the swirl flow forming portion 8, and a part of the main flow flowing in the main flow pipe 6 is divided. The obtained secondary flow is circulated toward the swirl flow forming portion 8. The swirl flow forming portion 8 is a tubular body having an axis in the direction from the upstream to the downstream (left and right in FIG. 2A), and is connected to the downstream end of the main flow tube 6. A tangential inlet 8A to which the downstream end of the subflow pipe 7 is connected is formed in the tube wall of the swirling flow forming section 8, and the cryogenic liquid 25 forming the subflow is supplied to the tangential inlet 8A. 8 A is received in the tangential direction of the swirl flow forming portion 8. As a result of receiving the subflow in the tangential direction in this manner, a swirl flow is formed with respect to the main flow by the subflow in the swirl flow forming portion 8 (see FIG. 2B). The cryogenic liquid flowing in the side flow pipe 7 can be injected into the tangential inlet 8A with the flow momentum originally provided by the delivery pump 3, but in order to obtain the momentum more reliably, It is preferable to provide a pump in the pipe 7.

  The mixing tube portion 9 receives from the swirl flow forming portion 8 a horizontal cylindrical casing 19 connected to the downstream end of the swirl flow forming portion 8 and a low-temperature liquid 25 housed in the casing 19 and forming swirl flow. It has a venturi tube 20 and an insert 21 inserted in a space between the casing 19 and the venturi tube 20. The axis of the mixing tube portion 9 is located on an extension line of the axis of the swirl flow forming portion 8 (see the axis X in FIG. 2A).

  The casing 19 has an inlet portion 19A on the upstream side in the flow direction of the cryogenic liquid 25, an outlet portion 19B on the downstream side, and a storage portion 19C in which the venturi tube 20 is stored and disposed at an intermediate position therebetween. The inlet portion 19A and the outlet portion 19B have the same inner diameter, and the inner diameter is increased in the accommodating portion 19C. The central axes of the inlet portion 19A, the outlet portion 19B, and the accommodating portion 19C are located on the same straight line (see the axis X in FIG. 2A). The accommodating portion 19C has an inner diameter larger than the outer diameter of the venturi tube 20, forms a space around the venturi tube 20, and is an insert 21 made of a woven or knitted fibrous metal wire such as stainless steel. Are distributed and inserted in this space. Further, an evaporating gas injection part 19D that opens upward is formed at an upper upstream side position of the housing part 19C, and the evaporating gas 26 fed from the evaporating gas compressor 4 is supplied to the evaporating gas injection part 19D. To accept. In the condensing and mixing apparatus 2 shown in FIG. 2 (A), the evaporative gas injection part 19D has an opening formed at the upper upstream side position of the accommodating part 19C, but the position of the evaporative gas injection part 19D is not limited to this. Alternatively, an opening may be formed at a position upstream of the side portion of the accommodating portion 19C.

  The venturi tube 20 has mounting flanges 20D and 20E projecting radially outward on both sides in the direction of the axis X, and the venturi tube 20 and the mounting flanges 20D and 20E are placed in the housing portion 19C of the casing 19, respectively. It is attached so that the axis X of the inlet 19A and the outlet 19B of the casing 19 coincides and is positioned on one straight line.

  The inner diameter of the venturi tube 20 has a reduced diameter portion 20A located on the inlet portion 19A side of the casing 19, a throat portion 20B located immediately after the reduced diameter portion 20A, and an expanded portion extending from the throat portion 20B toward the outlet portion 19B. The diameter portion 20C is sequentially formed. The diameter-reduced portion 20A has a curved surface and the inner diameter is relatively abruptly reduced to narrow the flow path cross-sectional area, and the diameter-expanded portion 20C is expanded so as to recover the inner diameter over a long distance in the axis X direction. The throat portion 20B is formed by connecting the reduced diameter portion 20A and the enlarged diameter portion 20C with a smooth curve so as to have a low resistance to the flow of the low-temperature liquid, and is formed with a minimum diameter so as to have a minimum flow path cross-sectional area. Has been.

  A large number of small-diameter evaporation gas holes 20C-1 are formed in the enlarged diameter portion 20C at a plurality of positions in the circumferential direction and the liquid flow direction. Each evaporative gas hole 20C-1 is formed so as to penetrate the tube wall of the venturi pipe 20 in the radial direction, and is inclined inward in the axial direction toward the radial inward. As will be described later, the evaporation gas 26 injected from the evaporation gas injection part 19D is dispersed from the plurality of evaporation gas holes 20C-1 and sucked into the enlarged diameter part 20C. As a result, the evaporative gas 26 is condensed in the swirling low temperature liquid 25 flowing in the enlarged diameter portion 20C and mixed with the swirling low temperature liquid 25 to generate a mixed liquid.

  The mixed liquid pipe 10 is connected to the downstream end of the outlet part 19B of the casing 19 of the mixing pipe part 9, and the mixed liquid generated in the mixed pipe part 9 is directed to the downstream side, that is, the booster pump 5 side. To distribute.

  The main flow meter 11 and the main flow regulating valve 12 are provided in the main flow pipe 6 respectively. The main flow meter 11 measures the flow rate of the mainstream cryogenic liquid 25 flowing in the main flow pipe 6 and flowing into the swirl flow forming unit 8. The main flow regulating valve 12 can adjust the main flow rate by adjusting the opening degree under the control of the control means 17 described later. Further, the secondary flow meter 13 and the secondary flow adjustment valve 14 are provided in the secondary flow pipe 7 respectively. The side flow meter 13 measures the flow rate of the side-stream cryogenic liquid 25 injected into the swirling flow forming unit 8 through the side flow pipe 7. The subflow adjusting valve 14 can adjust the flow rate of the subflow by adjusting the opening degree under the control of the control means 17 described later. The mixed liquid pressure gauge 15 and the mixed liquid thermometer 16 are provided in the mixed liquid pipe 10, respectively, and measure the pressure and temperature of the mixed liquid flowing out of the mixed pipe portion 9 and flowing in the mixed liquid pipe 10, respectively. .

  The storage means 18 uses the data of the correspondence between the pressure of the liquid mixture and the saturation temperature at that pressure as the first correspondence A, and the allowable minimum value of the degree of subcooling of the liquid mixture and the side flow rate ratio (swirl) Strength) is stored in advance as second correspondence B (see FIG. 3). The data of the first correspondence relationship A and the second correspondence relationship B is referred to by the control means 17 when controlling the flow rate of the secondary flow, as will be described later. Here, the “minimum value of the degree of supercooling” is the smallest value of the degree of supercooling that prevents the mixture from containing steam. The smaller the minimum value of the degree of supercooling, the closer the temperature at which the mixed solution is cooled so that no vapor exists in the mixed solution is close to the saturation temperature. The degree of supercooling is calculated by the supercooling degree calculating means as the difference between the derived value of the saturation temperature and the measured value of the temperature of the mixed liquid. The “substream flow rate ratio” is the ratio of the substream flow rate to the sum of the mainstream flow rate and the substream flow rate. It is calculated by dividing the measured value of the flow rate of the secondary flow by the sum of the measured value of the flow rate. Further, the storage means 18 preferably stores the first correspondence relationship A in the form of, for example, a relational expression between the pressure of the liquid mixture and a saturation temperature, a relationship diagram, or a steam table.

  FIG. 3 is a diagram showing a relationship between the minimum value of the degree of supercooling of the mixed liquid and the side flow rate ratio (swirl strength), that is, the second correspondence relationship B. As shown in FIG. 3, the minimum value of the degree of subcooling of the mixed liquid becomes smaller when the side flow rate ratio is 0, that is, when there is swirling, compared to the case where there is no swirling, and The minimum value and the secondary flow rate ratio (swirl strength) have a relationship that the minimum value of the degree of supercooling decreases as the secondary flow rate ratio increases. That is, as the side flow rate ratio increases, the minimum value of the degree of supercooling decreases, the temperature of the liquid mixture in the liquid state in which no vapor exists in the liquid mixture approaches the saturation temperature, and the mixing performance of the condensing and mixing apparatus improves.

  As shown in FIG. 2A, the control means 17 includes a supercooling degree calculating means 22 for calculating the degree of supercooling of the mixed liquid, a subflow flow rate ratio calculating means 23 for calculating a subflow flow ratio, and a main flow. And a flow rate adjusting means 24 for adjusting the opening degree of each of the adjusting valve 12 and the auxiliary flow adjusting valve 14. The supercooling degree calculation means 22 refers to the first correspondence A stored in the storage means 18 and derives the saturation temperature corresponding to the measured value of the pressure of the mixed liquid, The difference from the measured value of the temperature of the mixed solution is calculated as the degree of supercooling of the mixed solution. The secondary flow rate ratio calculating means 23 calculates the secondary flow rate ratio by dividing the measured value of the secondary flow by the sum of the measured value of the primary flow and the measured value of the secondary flow. The flow rate adjusting unit 24 compares the calculated value of the degree of supercooling with the minimum value of the degree of supercooling in the second correspondence relationship B (see FIG. 3) stored in the storage unit 18. When the calculated value is equal to or less than the minimum value, the second correspondence relationship B is referred to, and a subflow rate ratio in which the calculated value of the degree of supercooling is larger than the minimum value is derived as a target value. The flow rate of the secondary flow is increased by increasing the opening of the secondary flow adjustment valve 14 so that the calculated value of the secondary flow rate ratio follows the target value.

  Next, the evaporative gas reliquefaction apparatus 1 configured as described above and its operation will be described with reference to FIGS.

  First, a part of a cryogenic liquid (for example, LNG) 25 in a tank (not shown) is sent out by the delivery pump 3 and introduced into the condensing and mixing apparatus 2. The evaporative gas generated in the tank is boosted to a pressure (intermediate pressure) between the atmospheric pressure and the city gas operating pressure (4 to 7 MPa) by the evaporative gas compressor 4 and then introduced into the condensing and mixing apparatus 2. Is done.

  The low-temperature liquid 25 introduced into the condensing and mixing device 2 flows through the main flow pipe 6 as a main flow and directly flows into the swirl flow forming unit 8. A part of the mainstream low-temperature liquid flowing through the main flow pipe 6 flows as a subflow through the subflow pipe 7 and is injected in the tangential direction from the tangential inlet 8A of the swirl flow forming portion 8. The cryogenic liquid 25 that has directly flowed into the swirling flow forming portion 8 flows in the direction of the axis X, and the cryogenic liquid injected from the tangential inlet 8A flows in the circumferential direction to generate a swirling flow with respect to the main flow. Therefore, on the downstream side of the tangential inlet 8A, the low-temperature liquid 25 flowing in the direction of the axis X from the upstream side is also affected by the swirling flow, and the entire low-temperature liquid 25 flowing in the swirling flow forming unit 8 swirls. A flow is formed. In the present embodiment, the flow rates of the main flow and the sub flow are controlled by adjusting the opening degrees of the main flow adjustment valve 12 and the sub flow adjustment valve 14 by the control means 17.

  The cryogenic liquid 25 that has been swirled in the swirling flow forming section 8 flows into the venturi pipe 20 through the inlet 19A provided in the casing 19 of the mixing pipe section 9 that accommodates the venturi pipe 20, and is reduced in diameter. It flows through the part 20A, the throat part 20B and the enlarged diameter part 20C and reaches the outlet part 19B of the casing 19. The low-temperature liquid 25 flowing in the Venturi tube 20 increases the flow velocity at the reduced diameter portion 20A, reaches the maximum flow velocity at the throat portion 20B, and then gradually decreases the flow velocity at the expanded diameter portion 20C, but downstream at the expanded diameter portion 20C. Since the maximum inner diameter at the end (the right end in FIG. 2A) is also smaller than the inner diameter of the inlet portion 19A, the flow velocity at the enlarged diameter portion 20C is higher than the flow velocity at the inflow of the inlet portion 19A, and therefore the pressure is lower. Therefore, a suction force is provided to the evaporation gas hole 20C-1.

  On the other hand, the evaporative gas 26 is pressurized by the evaporative gas compressor 4 and is injected into the casing 19 through an evaporative gas injection part 19D provided in the casing 19 of the condensing and mixing apparatus 2. In the accommodating portion 19C of the casing 19 that accommodates the venturi tube 20, an insert 21 is inserted on the outer periphery of the venturi tube 20, and is pumped by the evaporative gas compressor 4 from the evaporative gas injection portion 19D. The injected evaporative gas 26 is buffered by the insert 21 and diffuses over the entire circumference and the entire length of the venturi 20 in the accommodating portion 19C.

  As described above, the low temperature liquid 25 flowing through the enlarged diameter portion 20C of the venturi pipe 20 brings about a suction force to the evaporative gas hole 20C-1 due to the venturi phenomenon, so that the evaporated gas diffused in the accommodating portion 19C. 26 is sucked and introduced from each evaporating gas hole 20C-1 into the enlarged diameter portion 20C. As shown in FIG. 2A, the evaporative gas hole 20C-1 is inclined upstream in the radial inward direction, so that the evaporative gas that has flowed in opposes the flow of the mainstream cryogenic liquid 25 in the venturi tube 20. It joins under low resistance without any problems. At this time, since the mainstream cryogenic liquid 25 forms a swirling flow, the evaporative gas 26 is sufficiently mixed with the cryogenic liquid 25 both in the circumferential direction and in the radial direction.

  The evaporative gas 26 sucked and introduced into the enlarged diameter portion 20C is mixed in the low temperature liquid and cooled by the low temperature liquid. As a result of the cooling, the evaporated gas is condensed and reliably liquefied, and flows downstream as a part of the low temperature liquid 25. The low-temperature liquid containing the evaporated gas re-liquefied in this way is boosted by the booster pump 5 and brought to the vaporizer, then vaporized by the vaporizer and sent to the demand side as city gas.

  Next, the control operation of the flow rate of the side flow by the control means 17 in the condensing and mixing apparatus 2 will be described. In this embodiment, when the evaporative gas reliquefaction apparatus 1 is operated with the main flow adjustment valve 12 open and the sub flow adjustment valve 14 closed, the sub flow adjustment valve 14 is opened as necessary. A control operation when a side flow is injected into the swirling flow forming unit 8 to form a swirling flow will be described.

  The supercooling degree calculation means 22 of the control means 17 refers to the first correspondence relationship A stored in the storage means 18 and saturates corresponding to the measured value of the pressure of the mixed liquid measured by the mixed liquid pressure gauge 15. The temperature is calculated, and then the difference between the calculated saturation temperature and the measured value of the temperature of the liquid mixture measured by the liquid mixture thermometer 16 is calculated as the degree of supercooling. Further, the side flow rate ratio calculating means 23 is the sum of the measurement value of the main flow rate measured by the main flow meter 11 and the measurement value of the sub flow rate measured by the sub flow meter 13. The measured value of the flow rate is divided to calculate the side flow rate ratio (turning strength).

  The flow rate adjusting unit 24 compares the calculated value of the degree of supercooling calculated by the degree of supercooling calculating unit 22 with the minimum value of the degree of supercooling in the second correspondence B stored in the storage unit 18. As a result of this comparison, when the calculated value of the degree of supercooling is larger than the minimum value, it can be said that the evaporated gas is mixed in the low temperature liquid without being present as bubbles in the low temperature liquid. Therefore, the flow rate adjusting means 24 does not perform control for opening the subflow adjusting valve 14. That is, since a substream is not injected into the swirl flow forming unit 8, a state in which a swirl flow is not formed with respect to the main flow is maintained.

  On the other hand, when the calculated value of the degree of supercooling is equal to or less than the minimum value, bubbles of evaporating gas remain in the mixed solution flowing out from the mixing tube portion 9, and the mixed solution becomes a gas-liquid two-phase flow. It can be said. In such a state, if the evaporative gas is condensed on the downstream side of the condensing and mixing device 2, the safe operation of the entire evaporative gas reliquefaction device 1 is hindered, such as the occurrence of a water hammer action.

  Therefore, the flow rate adjusting means 24 refers to the second correspondence B, derives the subflow flow rate ratio so that the calculated value of the degree of supercooling is larger than the minimum value, and sets the subflow flow rate ratio as a target value. The opening degree of the secondary flow adjustment valve 14 is adjusted so that the calculated value of the secondary flow rate ratio calculated by the calculation means 23 follows the target value. As a result, the sub-flow low-temperature liquid adjusted to an appropriate flow rate is injected tangentially into the swirl flow forming unit 8 to form a swirl flow with respect to the main flow, thereby reducing the degree of supercooling of the mixed liquid. Accordingly, the evaporated gas can be reliably condensed and mixed with the low temperature liquid without remaining in the low temperature liquid.

  As a specific example of the above-described control operation, the flow rate of the mixed liquid is changed greatly from the state in which the swirl flow is not formed (the swirl strength is 0%) and the supercooling degree of the mixed liquid is operated at 5 ° C. First, the case where the temperature of the mixed liquid is increased will be described. In this case, it is necessary to increase the flow rate of the evaporating gas blown into the venturi tube 20, but as can be seen from FIG. 3 showing the second correspondence B, the degree of supercooling of the mixed solution is minimized (5 ° C.). Therefore, if it remains as it is, bubbles of evaporated gas remain in the mixed solution, and the flow rate of evaporated gas cannot be increased.

  Therefore, the minimum value of the degree of supercooling is reduced by forming the swirl flow by injecting the subflow low temperature liquid into the swirl flow forming portion 8 in the tangential direction with the subflow adjustment valve 14 open. Increase the temperature. As shown in FIG. 3, when the temperature of the mixed liquid is increased by 2 ° C. (increase from 5 ° C. to 3 ° C.), the side flow rate ratio (swirl strength) is adjusted to about 35%. The flow rate of the flow is adjusted to enhance the evaporative gas condensation and mixing performance so that evaporative gas bubbles do not remain in the mixture. The application of such swirling causes an increase in the pressure loss of the fluid in the condensing and mixing apparatus 2 and increases the power of the pump to be supplied. Therefore, the imparting of swirling should be performed only when the degree of supercooling of the mixed liquid is reduced. Is desirable. In this way, by providing swirl only when necessary, it is possible to suppress an increase in pressure loss to a minimum as compared with the case where a device such as a fixed swirl blade is provided, and unnecessarily reduce energy consumption. An increase can be prevented.

  As described above, the turning control as described above is performed when the amount of evaporating gas to be condensed and mixed in the low temperature liquid is increased. In addition, the control of the swirl imparting may increase the temperature of the resulting mixed liquid, for example, when water as a low temperature liquid is mixed with water vapor as an evaporating gas to produce hot water as a mixed liquid. It is also effective when desired.

  In the present embodiment, the flow rate of the low-temperature liquid in the secondary flow is controlled so that the degree of supercooling of the liquid mixture is always greater than the minimum value. It can be liquefied, and evaporative gas can be prevented from flowing into the pump as a gas and causing trouble in the pump. In addition, since it is not necessary to provide a device such as a conventional fixed swirl blade for imparting swirl, the pressure loss of the condensing and mixing device can be minimized, and the reliquefaction of the evaporative gas can be efficiently performed in a short time. In addition, the apparatus configuration can be made compact.

  In the present embodiment, the control means 17 controls both the main flow regulating valve 12 and the sub flow regulating valve 14, but instead, only the sub flow regulating valve 14 is controlled. Good.

  Moreover, in this embodiment, although the condensation mixing apparatus 2 is arrange | positioned in the horizontal direction, you may arrange | position in the vertical direction. Since the condensing and mixing device 2 is arranged in the vertical direction, the low-temperature liquid 25 is circulated downward in the vertical direction, and the evaporative gas flows in from the horizontal direction. Gas condensation and mixing is performed more stably.

  Further, in the present embodiment, the calculated value of the degree of supercooling is compared with the minimum value of the degree of supercooling in the second correspondence B, and the side flow rate ratio is set such that the calculated value of the degree of supercooling is larger than the minimum value. The flow rate of the secondary flow is adjusted as the target value, but the target system is required to set the secondary flow rate ratio that is larger than the value obtained by adding a constant value to the minimum value of the degree of subcooling. The safety factor may be reflected.

DESCRIPTION OF SYMBOLS 1 Evaporative gas reliquefaction apparatus 2 Condensation mixing apparatus 3 Delivery pump 4 Evaporative gas compressor 8 Swirling flow formation part 9 Mixing pipe part 11 Main flow flow meter 13 Subflow flow meter 14 Subflow adjustment valve 15 Mixed liquid pressure gauge 16 Mixed liquid temperature Total 17 Control means 18 Storage means 20 Venturi tube 20C-1 Evaporating gas hole 22 Subcooling degree calculating means 23 Subflow flow rate ratio calculating means 24 Substream flow rate adjusting means 25 Low temperature liquid 26 Evaporating gas

Claims (7)

In a condensing and mixing apparatus that injects evaporative gas generated from a cryogenic liquid into a main stream formed by the flow of the cryogenic liquid, condenses the evaporative gas and mixes it with the mainstream cryogenic liquid,
A tubular body having an axial line in the direction in which the low-temperature liquid flowing from upstream to downstream flows as the main stream, and a tangential direction that receives a substream obtained by dividing a part of the main stream upstream from the tubular body. A swirl flow forming portion that forms an swirl flow with respect to the main flow by the side flow;
A venturi tube positioned on the extension line of the axis of the swirl flow forming unit downstream from the swirl flow forming unit; receives a low-temperature liquid forming the swirl flow from the swirl flow forming unit; A condensing unit comprising: an evaporating gas hole for receiving the evaporating gas on a tube wall; and a mixing tube unit that condenses the evaporating gas and mixes with the low-temperature liquid forming the swirling flow to generate a mixed liquid. Mixing equipment. In a condensing and mixing apparatus that injects evaporative gas generated from a cryogenic liquid into a main stream formed by the flow of the cryogenic liquid, condenses the evaporative gas and mixes it with the mainstream cryogenic liquid,
A tubular body having an axial line in the direction in which the low-temperature liquid flowing from upstream to downstream flows as the main stream, and a tangential direction that receives a substream obtained by dividing a part of the main stream upstream from the tubular body. A swirl flow forming portion that forms an swirl flow with respect to the main flow by the side flow;
A venturi tube positioned on the extension line of the axis of the swirl flow forming unit downstream from the swirl flow forming unit; receives a low-temperature liquid forming the swirl flow from the swirl flow forming unit; An evaporating gas hole for receiving the evaporating gas is formed on a tube wall, and a mixing tube part that condenses the evaporating gas and mixes with the low-temperature liquid forming the swirling flow to generate a mixed liquid;
A main flow meter for measuring the flow rate of the main flow flowing into the swirl flow forming section;
A secondary flow meter for measuring the flow rate of the secondary flow flowing into the swirl flow forming section, and a secondary flow adjustment valve for adjusting the flow rate of the secondary flow;
A liquid mixture thermometer for measuring the temperature of the liquid mixture flowing out from the mixing pipe section, and a liquid mixture pressure gauge for measuring the pressure of the liquid mixture;
The correspondence between the pressure of the liquid mixture and the saturation temperature at that pressure is used as the first correspondence, and the sum of the minimum value of the allowable subcooling of the liquid mixture and the flow rates of the main and substreams Storage means for preliminarily storing the correspondence relationship with the secondary flow rate ratio obtained by dividing the flow rate of the flow as a second correspondence relationship;
While referring to the first correspondence relationship and the second correspondence relationship, the degree of supercooling of the mixed solution based on the measured values of the main flow rate, the secondary flow rate, the temperature and pressure of the mixed solution, respectively. And a control means for controlling the flow rate of the secondary flow by adjusting the opening of the secondary flow control valve so that the value is larger than the minimum value. The control means refers to the first correspondence relationship stored in the storage means, derives the saturation temperature corresponding to the measured value of the pressure of the mixed liquid, and then determines the derived value of the saturation temperature and the temperature of the mixed liquid. A degree of supercooling calculating means for calculating the difference from the measured value as the degree of supercooling of the mixed solution;
A secondary flow rate ratio calculating means for calculating the secondary flow rate ratio by dividing the measured value of the secondary flow rate by the sum of the measured value of the primary flow rate and the measured value of the secondary flow rate;
When the calculated value of the degree of supercooling is compared with the minimum value of the degree of supercooling in the second correspondence relationship stored in the storage means, and the calculated value of the degree of supercooling is equal to or less than the minimum value, Referring to the second correspondence relationship, a subflow flow rate ratio in which the calculated value of the degree of supercooling is larger than the minimum value is derived as a target value, and the calculated value of the subflow flow rate ratio follows the target value. The condensing and mixing apparatus according to claim 2, further comprising: a secondary flow rate adjusting means for increasing the flow rate of the secondary flow by increasing the degree of opening of the secondary flow adjustment valve. In an evaporative gas reliquefaction apparatus that mixes and reliquefies the low temperature liquid by injecting and condensing evaporative gas generated from the low temperature liquid stored in the storage tank into the low temperature liquid discharged from the storage tank.
A condensing and mixing apparatus according to any one of claims 1 to 3, a delivery pump for delivering a low-temperature liquid from a storage tank, and an evaporative gas compressor for compressing evaporative gas, wherein the delivery pump condenses the low-temperature liquid. An evaporative gas reliquefaction device, wherein the evaporative gas is supplied to a swirl flow forming portion of a mixing device and injected into the mixing tube portion of the condensing and mixing device by the evaporative gas compressor. In a condensing and mixing method of injecting evaporative gas generated from a cryogenic liquid into the main stream formed by the flow of the cryogenic liquid, condensing the evaporative gas and mixing it with the mainstream cryogenic liquid,
A main flow rate measurement step for measuring the flow rate of the low-temperature liquid flowing as the main flow from upstream to downstream;
A substream flow rate measuring step for measuring the flow rate of the cryogenic liquid flowing as a substream obtained by diverting a part of the mainstream;
A swirling flow forming step of causing the mainstream cryogenic liquid to flow through the tubular body, injecting the substream cryogenic liquid in a tangential direction of the tubular body, and generating a swirling flow with respect to the mainstream by the subflow; ,
The evaporative gas is injected into a venturi tube that receives the low-temperature liquid in which the swirl flow is formed in the swirl flow forming step, and the evaporated gas is condensed and mixed with the low-temperature liquid in which the swirl flow is formed. A mixing step to produce;
A mixed liquid temperature measuring step for measuring the temperature of the mixed liquid;
A mixed liquid pressure measuring step for measuring the pressure of the mixed liquid;
The first correspondence that is the correspondence between the pressure of the liquid mixture and the saturation temperature at that pressure, and the sum of the minimum value of the allowable subcooling of the liquid mixture and the flow rates of the main and substreams. Measure each of the flow rate of the main flow, the flow rate of the secondary flow, the temperature and the pressure of the mixed liquid while referring to the second correspondence relationship corresponding to the flow rate ratio of the secondary flow obtained by dividing the flow rate of the flow. And a control step of controlling the flow rate of the side flow so that the degree of supercooling of the mixed liquid is larger than the minimum value based on the value. The control step refers to the first correspondence relationship, derives the saturation temperature corresponding to the measured value of the mixed liquid pressure, and then calculates the difference between the derived value of the saturated temperature and the measured value of the temperature of the mixed liquid. A supercooling degree calculating step for calculating the supercooling degree of the mixed liquid;
A sub-flow rate ratio calculating step of calculating a sub-flow rate ratio by dividing the measured value of the sub-flow rate by the sum of the measured value of the main flow rate and the measured value of the sub-flow rate;
When the calculated value of the degree of supercooling is compared with the minimum value of the degree of supercooling in the second correspondence relationship, and the calculated value of the degree of supercooling is equal to or less than the minimum value, refer to the second correspondence relationship, Deriving the sub-flow flow rate ratio so that the calculated value of the degree of supercooling is larger than the minimum value as the target value, and increasing the flow rate of the sub-flow so that the calculated value of the sub-flow flow rate ratio follows the target value. The condensing and mixing method according to claim 5, further comprising a substream flow rate adjusting step. In the evaporative gas re-liquefaction method in which the evaporative gas generated from the low-temperature liquid stored in the storage tank is injected into the low-temperature liquid discharged from the storage tank and condensed to mix and re-liquefy the low-temperature liquid.
A process according to the condensation mixing method according to claim 5 or 6, a delivery process for sending a low-temperature liquid from a storage tank, and an evaporative gas compression process for compressing evaporative gas,
An evaporative gas reliquefaction method characterized in that a cryogenic liquid is supplied to the tubular body in the delivery step and the evaporative gas is injected into the venturi tube in the evaporative gas compression step.

Images