JP5378064B2 - Operation method of air temperature type vaporizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operation method for an air temperature vaporizer capable of performing continuous operation while removing frost causing the deterioration of heat-transfer performance due to adhesion to a finned heat transfer tube by blowing out and mechanically removing the frost adhered by wind power without stopping the operation of the vaporizer. <P>SOLUTION: In the operation method, the finned heat transfer tube 11 is vertically arranged longitudinally and laterally to let a cryogenic liquefied gas flow from the lower part of the finned heat transfer tube 11 upward. When operating vaporization, the outside air is dropped on the outside of the finned heat transfer tube 11 from the upper part to the lower part so as to evaporate the cryogenic liquefied gas, an ejecting air supply tube 31 is vertically arranged at the center of four finned heat transfer tubes 11 adjoining longitudinally and laterally. Blowing nozzles 32, 33 are provided at the outer periphery of the ejecting air supply tube 31 at a plurality of stages vertically. When the frost adhered to the finned heat transfer tube 11 reaches a predetermined thickness, air is ejected from the blowing nozzle at a frost deposited surface collision speed of 4 m/s or more so that the deposited frost is blown out by air injected from a blow nozzle and an avalanche is caused in the frost deposited to the finned heat transfer tube 11 with the frost blown and to perform continuous vaporization while removing the frost. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an operation method of an air temperature type vaporizer such as LNG, and in particular, an air temperature at which the air temperature type vaporizer can be continuously operated by efficiently defrosting frost adhering to the heat transfer surface of the air temperature type vaporizer. The present invention relates to a method of operating a vaporizer.

  There is an air temperature type vaporizer as a type of equipment for vaporizing or heating a low temperature liquid such as liquefied natural gas (LNG), liquid nitrogen, liquid oxygen or the like.

  This air temperature type vaporizer will be described by taking an air temperature type vaporizer installed at an LNG satellite base as an example. As shown in Patent Document 1, the air temperature type vaporizer is vertically perpendicular to the outer periphery of the heat transfer tube. The finned heat transfer tube is provided with a number of fins, and the finned heat transfer tubes are arranged vertically and horizontally, and the LNG is vaporized in the front-stage finned heat-transfer tube group, and the latter-stage finned heat-transfer tube Each finned heat transfer tube is connected so as to heat the NG vaporized in the group to near normal temperature.

  That is, the LNG stored in the storage tank of the satellite base is arranged in the vertical direction from the inlet pipe arranged at the bottom to the finned heat transfer pipe arranged in the horizontal direction through the distribution pipe, and from the finned heat transfer pipe in each row. LNG flows upward through the finned heat transfer tube group in the preceding stage, the outside air flows downward between the finned heat transfer tubes, and the LNG evaporates by exchanging heat with the air flowing downward. The NG evaporated in the finned heat transfer tube group in the preceding stage was collected in the upper manifold of the finned heat transfer tube arranged in the vertical direction, and sequentially arranged in the vertical direction in the finned heat transfer tube group in the subsequent stage. The finned heat transfer pipe flows while meandering up and down, is collected in a collecting pipe arranged at the lower part, and is supplied from the collecting pipe to the demand system through an outlet pipe.

  In an air temperature type vaporizer that vaporizes LNG used in conventional LNG satellite bases, etc., if the vaporization operation is performed for a long time, moisture in the atmosphere condenses on the heat transfer tube with fins and adheres to the heat transfer surface. Usually forms frost and ice.

  Since the frost adhering to the heat transfer tubes and fins becomes a very large heat transfer resistance when it becomes thick, the vaporization ability is extremely reduced. For this purpose, the frost that regularly adheres is removed by heating and melting with warm water or the like to form a bare pipe to restore the heat transfer capability.

  Also, when removing the attached frost, the operation is stopped and the recovery operation is performed. Therefore, in order to maintain the capacity as a base, a vaporizer with the same capacity as the stop device is installed as a switching device, and the switching operation is performed. Yes.

  Therefore, at least one regeneration standby vaporizer is installed as a switch at the LNG satellite base. Furthermore, a spare carburetor is generally installed in case of failure. The air temperature type LNG vaporizer is operated by switching to a spare unit every 4 hours for performance degradation due to frost formation on normal heat transfer tubes.

  In general, the increase in the frosting thickness is greater in the tip portion of the fin where the air flow is strongly applied in the heat transfer tube having the fin plate than in other portions. The frosting thickness on the fins is about 20 mm on both sides of the tip at a normal outside air flow speed (about 1 m / s). For this reason, the flow of air at the center is prevented from flowing into the fin plate and the surface of the heat transfer tube inside the tips of the fins, and this is a factor that deteriorates the heat transfer performance.

  Moreover, the hot water used to melt the adhering frost on the heat transfer tubes is made with steam generated by a water heater or a boiler, sprayed on the heat transfer tubes, and melted by the sensible heat. However, even if the water is sprayed, if the humidity of the atmosphere is low or the temperature is low, the heat of the hot water may be lost by heat or heat transfer to the atmosphere, and about half of the heat stored in the hot water may be lost. It's not expensive.

  Furthermore, hot water for melting frost is generally circulated for effective use of heat, but used hot water is contaminated by the atmosphere and other causes, so it cannot be heated directly with a water heater. Absent. In this case, the heating water for the water heater and the warm water for frost are used as separate systems by indirectly heating the hot water for frost with the heating water for the water heater, so that equipment costs, maintenance costs, and fuel costs are required. Becomes expensive.

  Defrosting frost with warm water is usually performed at intervals of 4 hours, so it is not necessary to perform defrosting operation automatically even if the frost does not thicken due to weather conditions and heat transfer performance does not deteriorate. This increases the operating cost by using hot water.

JP 2008-274975 A Japanese Patent Laid-Open No. 57-122272 Japanese Patent Laid-Open No. 08-5207

  On the other hand, in Patent Documents 2 and 3, as defrosting means for frost adhered to the cooler, a high-speed jet or compressed air from a compressor is blown onto the heat transfer surface at a wind speed of 30 m / sec, and frost adhering to the heat transfer surface is removed. It has been proposed to defrost by forcibly blowing.

  However, a small cooler can be defrosted with compressed air or the like, but an air temperature type vaporizer such as an LNG vaporizer has a vertical and horizontal width of about 2 m and a height of 4 to 5 m. The inner diameter of the heat tube is 20 mm, the fin width is about 50 mm, and the outer diameter of the fin tip is 135 mm. Blowing off the frost formed using the techniques of Patent Documents 2 and 3 with compressed air substantially requires a large amount of compressed air. Impossible.

  Therefore, the object of the present invention is to solve the above-mentioned problems, and to remove frost that adheres to the finned heat transfer tube and causes deterioration of heat transfer without stopping the operation of the vaporizer, An object of the present invention is to provide an operation method of an air temperature type carburetor which can be blown away and mechanically removed for continuous operation.

In order to achieve the above object, according to the first aspect of the present invention, finned heat transfer tubes are erected vertically and horizontally, and a low-temperature liquefied gas is allowed to flow upward from the lower portion of each finned heat transfer tube and the outside of the finned heat transfer tube. In the operation method of the air temperature type vaporizer in which the outside air is lowered from the upper part to the lower part to evaporate the low-temperature liquefied gas and vaporized, the finned heat transfer tube is placed in the center of the four finned heat transfer tubes adjacent vertically and horizontally. A jet air supply pipe extending from the lower part to the upper part is erected, and a plurality of jet nozzles are provided in the vertical direction on the outer periphery of the jet air supply pipe to prevent heat transfer deterioration due to frost adhering to the finned heat transfer pipe at an NG temperature. When the temperature of the NG drops below the set temperature (−40 to −50 ° C.) , air is injected from the blow nozzle so that the collision speed of the frosting surface is 4 m / s or more. Sky jetted by blowout nozzle Operation of an air-temperature type vaporizer characterized by blowing off the frost that has been frosted at the same time and generating avalanche on the frost attached to the heat transfer tube with fins, and performing continuous vaporization operation while defrosting. Is the method.

In the invention of claim 2 , the low-temperature liquefied gas is LNG, the length of the finned heat transfer tube is 4 to 5 m, and the blowing nozzles on the outer periphery of the blowing air supply pipe are formed in two or three stages at intervals of several meters. It is a driving | running method of the air temperature type vaporizer | carburetor of Claim 1 .

According to the invention of claim 3 , a finned heat transfer tube is formed by providing eight fin plates with a width of 40 to 80 mm at an angle of 45 degrees on the outer periphery of a heat transfer tube having an inner diameter of 20 to 25 mm. A plurality of vertical and horizontal erected pipes at intervals of ˜200 mm, and a jet air supply pipe having an inner diameter of 20 to 25 mm is erected at the center of the finned heat transfer pipes adjacent to the vertical and horizontal sides, and 1.5 m, 3 m, The operation method of the air temperature type | mold vaporizer of Claim 2 which formed the blowing nozzle in the position of 4 m.

According to the invention of claim 4 , the blowout nozzle is between the fins of the heat transfer tube blowing nozzle for injecting air downward toward the four adjacent finned heat transfer tubes and the fins of the finned heat transfer tubes adjacent in the horizontal or vertical direction. The operation method of the air temperature type | mold vaporizer of Claim 3 which consists of a blowing nozzle for fins injected so that air may hit toward.

  According to the present invention, when defrosting the frost adhered to the finned heat transfer tube, it is 4 m / s or more from the blow nozzle provided in a plurality of stages in the height direction of the blown air supply pipe without stopping the vaporizer operation. By blowing air at a frosting surface collision speed for a short time (several seconds), the frost at that position is blown away, and an avalanche is generated in the frost below and the frost is scraped off. By recovering the heat transfer performance, the vaporizer can be operated continuously. Moreover, the installation cost of a vaporizer and the running cost for defrosting can also be reduced.

1 shows an embodiment of the present invention, in which (a) is a cross-sectional view of a finned heat transfer tube, (b) is a left side view, (c) is a front view, and (d) is a plan view. (A) is sectional drawing which shows arrangement | positioning of the heat exchanger tube with a fin in FIG. 1, and an injection air supply pipe, (b) is a perspective view of an injection air supply pipe. (A) is a figure which shows the air supply system which supplies blown air to a heat transfer tube with two rows of fins, and an injection air supply pipe, (b) is a schematic diagram which blows air on the heat transfer tube with a fin. In this invention, it is a figure which shows the defrost operation system at the time of performing a defrost operation. In this invention, it is a figure which shows the relationship between the cool air fall speed | rate and frost density when the surface temperature of a finned heat exchanger tube is made into a parameter. In this invention, it is a figure which shows the relationship between the frost formation cooling surface temperature and frost formation density of a heat exchanger tube with a fin. In this invention, it is a figure which shows the relationship between a wind speed and the thickness (frost growth) of frost. In this invention, it is a figure which shows the relationship between the thickness of the frost adhering to the heat exchanger tube with a fin, and an overall heat transfer coefficient.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  First, the air temperature type vaporizer 10 and its defrosting device 30 used in the operation method of the air temperature type vaporizer of the present invention will be described with reference to FIG.

  As shown in FIG. 1 (a), the finned heat transfer tube 11 is configured by providing fins 13 that are radially vertical at an angle of 45 degrees on the outer periphery of a heat transfer tube 12 having an inner diameter of 20 to 25 mm, in the drawing, an inner diameter of 20 mm. The In this example, the number of fins 13 is eight, and the fin width is 40 to 80 mm, which is 50 mm in the drawing, and is provided along the length (5 m) of the heat transfer tube 12.

  As shown in FIGS. 1 (b) to 1 (d), the air temperature type vaporizer 10 is configured with a plurality of finned heat transfer tubes 11 arranged vertically and horizontally at intervals of 150 to 200 mm. Each finned heat transfer tube 11 is connected so that LNG is vaporized by the finned heat transfer tube group 11F and the NG vaporized by the finned heat transfer tube group 11R is heated to near room temperature.

  That is, an inlet pipe 14 connected to a discharge pipe (not shown) connected to the bottom of the storage tank of the satellite base is arranged, and the inlet pipe 14 has a portion extending in the left-right direction as shown in FIG. A pipe 15 is connected, and a collecting pipe 16 is arranged at the rear stage on the outlet side facing the front-side distribution pipe 15 on the inlet side, and an outlet pipe 17 is connected to the collecting pipe 16.

  A lower manifold 18 extending to the rear stage side is connected to the distribution pipe 15 according to the arrangement interval of the finned heat transfer tubes 11, and the finned heat transfer tubes 11 are connected to the lower manifold 18 in four rows toward the outlet side in the figure, The upper manifold 19 is connected to the upper part of the finned heat transfer tube 11, thereby configuring the finned heat transfer tube group 11 </ b> F.

  The upper manifold 19 is connected to the upper part of the finned heat transfer tube 11 on the front stage side of the rear finned heat transfer tube group 11R through the connecting pipe 20, and the lower end of the finned heat transfer tube 11 is connected to the next through the bend pipe 21. The finned heat transfer tube 11 is connected to the next finned heat transfer tube 11, and the upper portion of the next finned heat transfer tube 11 is connected to the next finned heat transfer tube 11 via the bend tube 21. The finned heat transfer tubes 11 are connected to each other, and the lower ends of the finned heat transfer tubes 11 at the final stage are connected to the collecting tube 16 via the joint tubes 22 to form the finned heat transfer tube group 11R at the subsequent stage.

  Although not described in detail, the finned heat transfer tubes 11 have a structure in which a lower part, an intermediate part, and an upper part are appropriately connected to each other by a connecting member.

  The LNG from the storage tank is supplied from the inlet pipe 14 through the distribution pipe 15 to the finned heat transfer pipe group 11F through the lower manifold 18. That is, LNG is supplied from the finned heat transfer tubes 11 arranged in the horizontal direction and the finned heat transfer tubes 11 in the row to the finned heat transfer tubes 11 arranged in the vertical direction. The ambient air is cooled by the LNG supplied to the finned heat transfer tube group 11F, so that the outside air flows downward between the finned heat transfer tubes 11 of the finned heat transfer tube group 11F (lowering speed; 1 to 2 m / second). In the meantime, heat is exchanged with LNG to evaporate LNG. At this time, the LNG vaporization region extends from the lower end of each finned heat transfer tube 11 to a predetermined height, and NG evaporated in the vaporization region flows above the heat transfer tube 12 and is heated while the NG rises.

  The NG evaporated in the finned heat transfer tube 11F of the finned heat transfer tube group 11F is collected in the upper manifold 19 and sequentially connected in series by the bend tube 21 in the finned heat transfer tube group 11R downstream from the connection pipe 20. The vertical finned heat transfer pipe 11 flows while meandering up and down, while being heated up to near the atmospheric temperature, collected in a collecting pipe 16 disposed in the lower part, and from the collecting pipe 16 through an outlet pipe 17 to a demand system. To be supplied.

  In the present invention, between the finned heat transfer tubes 11 of the air temperature type vaporizer 10, in particular, between all the finned heat transfer tubes 11F of the front finned heat transfer tube group 11F and the latter finned heat transfer tube group. An ejection air supply pipe 31 of the defrosting device 30 is provided between some or all of the finned heat transfer tubes 11 on the front stage side of 11R, and removed from the ejection air supply tube 31 toward the finned heat transfer tubes 11. By blowing frost air, the frost adhering to the finned heat transfer tube 11 is defrosted to recover the heat transfer performance, thereby enabling continuous vaporization operation.

  Below, the defrosting apparatus 30 which consists of the ejection air supply pipe | tube 31 is demonstrated.

  (1) The defroster 30 of the present invention mechanically removes frost adhering to the finned heat transfer tube 11 by blowing off the frost with wind power without stopping the operation.

  (2) Since the heating in the air temperature type vaporizer 10 is mainly due to heat transfer by natural convection (downflow) due to cooling of the air, the descending speed is also relatively slow, about 1-2 m / s. . The relationship between the wind speed and the frost density will be described with reference to FIG.

  FIG. 5 shows that when the heat transfer surface temperature of the finned heat transfer tube 11 is −110 ° C. (▲), −75 ° C. (■), −40 ° C. (●), the descending speed is 0.5 m / s. The relationship of the frost formation density at 1.1 m / s was obtained by experiment.

  In FIG. 4, if the heat transfer surface temperature is low, the frost density is small, and if the descending speed is slow, the frost density is also light. At low speeds of about 1 to 2 m / s, the frost density is the density of ice. It turns out that it becomes very light with about 1/5.

  Usually, the finned heat transfer tube 11 has a length of about 5 m, the temperature of the heat transfer surface is different in the height direction, and the initial wind speed from the upper part and the final speed of the lower part are also different. FIG. 6 shows the relationship between the frost cooling surface temperature as the heat transfer surface and the frost density.

  In FIG. 6, the ● mark indicates an initial wind speed of 0.6 m / s, and the ▪ mark indicates an end speed of 0.9 m / s.

  Usually, the region of the main vaporization temperature of LNG is −145 ° C. to −40 ° C., and in this temperature region, it is understood from FIG. 5 that the frost density change with respect to the frost cooling surface temperature as the heat transfer surface is small. .

  FIG. 7 shows an example of the relationship between the wind speed at the descending speed and the frost thickness (frost growth in 4 hours) of the finned heat transfer tube 11. When the wind speed is 2 m or less, the frost thickness is 4 mm. It turns out that it becomes the following.

  From the above, it can be seen that at a descending speed of about 1 to 2 m / s, the growth of frost is as thin as an average of 4 mm or less and the density of frost is very light. Accordingly, the adhesion force of frost to the finned heat transfer tube 11 is also weak, so when the impinging wind against the frosting surface of about 4 m / s or more is applied by the defrosting device 30, the attached frost is blown off, An avalanche occurs below the position and the frost is scraped off to the lower end, leaving only all of the frost or about 2 mm of frost.

  Therefore, the heat transfer performance can be recovered by blowing frost on the heat transfer tube surface with the jet air.

  (3) When the frost formation thickness on the heat transfer tube is up to 2 mm, the overall heat transfer coefficient becomes larger than that of the bare tube due to frost formation, and then gradually decreases in inverse proportion to the increase in frost thickness.

FIG. 8 shows the relationship between the thickness of frost adhered to the finned heat transfer tube 11 and the overall heat transfer coefficient [kW / m ² K].

  From FIG. 8, the overall heat transfer coefficient is higher when frost adheres than the bare pipe, the overall heat transfer coefficient is maximum at 1 mm, the same overall heat transfer coefficient as that of the bare pipe at 2 mm, and then gradually decreases to 10 mm. The thickness is 1/5 of the bare tube.

  Here, since the increasing speed of the frosting thickness is approximately proportional to the time, when the same air temperature type vaporizer as the conventional four-hour switching vaporizer is used, the defrosting device 30 is within two hours. Thus, it can be seen that the operation can be continued without stopping the operation by blowing air once to remove the frost.

(4) The average overall heat transfer coefficient of the air temperature carburetor design is about 3.5 kW / m ² K at the final frost thickness. The corresponding frost thickness is about 11 mm. Therefore, if the defrosting is performed as described in the item (3), the overall heat transfer coefficient becomes equal to or higher than the design overall heat transfer coefficient.

  Based on the knowledge of the above (1) to (4), the blown air supply pipe 31 is provided with two or three stages of air blowing nozzles in the vertical direction, and the frosting surface collision wind speed is 4 m / s or more and 15 m from the nozzles. By blowing the air below / s about once every 2 hours, the frost attached to the finned heat transfer tube 11 at the nozzle position is blown off, and when the blown off frost falls, it adheres below the blowing part. The frost that has become an avalanche phenomenon can be easily scraped off to the frost at the lower end.

  The defrosting device 30 of the present invention will be described with reference to FIGS.

  First, in the defrosting device 30, a main air supply pipe (150A) 36 is connected to a total air supply pipe (200A) 35 to which an on-off valve 34 is connected, and the main air supply pipe 36 is connected to the heat transfer pipe 11 with fins, In particular, an air supply header 37 is provided so as to traverse the lower part of the finned heat transfer tube group 11 </ b> F at the front stage and extend in the middle of the row of the finned heat transfer tubes 11, and a jet air supply pipe is provided in the air supply header 37. 31 is provided and configured to stand vertically.

  The blast air supply pipe 31 will be further described. First, as shown in FIG. 2 (a), when the finned heat transfer pipe 11 is arranged with a vertical and horizontal interval of 150 mm and the fin outer diameter is 132 mm, the blast air supply is provided. The tube 31 is disposed perpendicularly to the center of the arrangement of the finned heat transfer tubes 11, and the outer diameter of the jet air supply tube 31 is formed to be the same as or slightly larger than the outer diameter of the heat transfer tube 12.

  FIG. 2B shows a perspective view of the blast air supply pipe 31. The upper end of the blast air supply pipe 31 has three stages in the vertical direction and four blowout nozzles 32 in the circumferential direction and the diameter direction. Two blow-off nozzles 33 are formed in the same manner. The blowout nozzles 32 and 33 are formed by drilling in the blast air supply pipe 31, but nozzle-shaped ones may be attached.

  When the height of the finned heat transfer tube 11 is 4.5 to 5 m, the first stage nozzles 32 and 33 from the lower end of the finned heat transfer tube 11 are 1.5 m, and the second stage nozzles 32 and 33 are approximately 3 m and 3rd stage blowing nozzles 32 and 33 are arranged to be about 4 m high.

  The blow nozzles 32 and 33 are provided at four locations in the circumferential direction with a hole diameter of the heat transfer pipe side blow nozzle 32 toward the heat transfer pipe 12 of 3 mm, and the fin side blow nozzle 33 blown between the fins 13 has a hole diameter of 2 mm. Thus, two locations are provided so as to face each other in the diameter direction. The blowing nozzles 32 and 33 are arranged apart from each other so that the hole diameters do not overlap.

  The fin side blowing nozzle 33 collides between the fins 13 as shown in FIG. 2A because the blown air collides between the fins 13 when the nozzles 33 are positioned on both of the jet air supply pipes 31 facing each other between the fins 13. The fin-side blowing nozzles 33 of the adjacent jet air supply pipes 31 are arranged in different directions so as to jet in directions orthogonal to each other, and are prevented from interfering with the blown wind, so that they adhere to the tips of the fins 13. The frost that tends to be thick can be easily blown away.

  Further, the heat transfer tube side blowing nozzle 32 faces the fins 13 inclined by 45 degrees with respect to the vertical and horizontal arrangement directions of the heat transfer tubes 12, and further obliquely downward as shown in FIG. By providing it so as to incline, avalanche is likely to occur along the heat transfer tubes 12 and the fins 13 when blown off against the frost attached to the heat transfer tubes 12 and the fins 13. Further, as shown in FIG. 2B, the fin-side blowing nozzle 33 is provided at a position slightly higher than the position of the heat transfer tube side blowing nozzle 32, thereby being influenced by the blowing air from the heat transfer tube side blowing nozzle 32. The frost adhered to the tips of the fins 13 facing each other is blown away, and the blown frost and the frost blown off by the heat transfer tube side blowing nozzle 32 are merged on the surface of the fin 13 to form a heat transfer tube. A frost avalanche phenomenon is generated on the surfaces of the fins 12 and the fins 13, whereby the frost attached to the entire surface of the finned heat transfer tube 11 can be scraped downward.

  The collision speed of the heat transfer tube 12 of the heat transfer tube side blowing nozzle 32 determines the initial speed of ejection so that the air speed at the time of the collision is 4 m / s or more and 15 m / s or less.

  The region of the main vaporization temperature of LNG at the LNG satellite station is -145 ° C to -80 ° C. As shown in FIG. 6, the change in frost density during this period is approximately 20% due to the difference in speed between the initial stage and the final stage, and air is ejected by providing a plurality of stages in the height direction with the blowing nozzles 32 and 33. By doing so, an avalanche phenomenon is generated and defrosting can be performed.

  FIG. 4 is a diagram showing a defrosting operation system when performing the defrosting operation of the present invention.

  FIG. 4 shows the finned heat transfer tube 11 in the longitudinal direction of the finned heat transfer tube group 11F in the preceding stage, and the LNG passes through the discharge tube 40 and the control valve 41, and passes through the inlet pipe 14 and the distribution pipe 15 through the lower manifold. 18 is supplied from the lower manifold 18 from the lower part of each finned heat transfer tube 11, and LNG is overheated by the outside air descending there to become NG, and the NG is passed through the upper manifold 19 and the connecting pipe 20 to the subsequent stage. It is supplied to the NG superheater tube which is the heat transfer tube 11 with fins of the heat transfer tube group 11R with fins.

  Further, as described in the defrosting device 30, the defrosting air is supplied from the open / close valve 34 to the total air supply pipe 35 and from the main air supply pipe 36 to the air supply header 37, and from each air supply header 37 in the vertical direction. Are supplied to the blast air supply pipes 31, and are blown out from the blow nozzles 32 and 33 of the blast air supply pipe 31.

  Here, the temperature of NG flowing into the finned heat transfer tube 11 of the finned heat transfer tube group 11R in the subsequent stage is detected by the connecting tube 20 or the NG temperature controller (TIRC) 42 connected downstream thereof, and the NG temperature adjustment is performed. The temperature dropped below the temperature set in advance by a total of 42 (the temperature at which the thickness of the frost frosted on the finned heat transfer tube 11 is about 4 mm and the NG set temperature set within a range of −50 to −40 ° C.). At that time, the on-off valve 34 is opened for a short time (about 3 seconds, 2 to 4 seconds), and air is blown out from the blowing nozzles 32 and 33 of each of the jet air supply pipes 31 to perform a defrosting operation. Frost operation can be performed. The NG temperature controller 42 is preferably provided in any one of the connecting pipes 20 aligned in the lateral direction, particularly in the central portion where the heat exchange rate is low. The connecting pipe 42 may be provided. When a plurality of the NG temperature controllers 42 are provided, the opening / closing valve 34 is opened when any of the NG temperature controllers 42 reaches the NG set temperature.

  The thickness of the frost that forms on the heat transfer tube 11 with fins when the defrosting operation is started is about 4 mm, and air is blown out from the three-stage blowing nozzles 32 and 33 to cause an avalanche phenomenon of frost. Thus, defrosting can be performed effectively.

  This defrosting due to avalanche will be further described.

  First, Table 1 shows the result of obtaining the injection amount of the blown gas (nitrogen gas) for each frost temperature necessary for frost removal by an experimental device that simulates a vaporizer.

  This experimental apparatus is a cylinder with a diameter of 14 mm, and the cylinder is cooled in the range of −40 to −150 ° C., and frost is grown to a thickness of 4 mm. The nozzle diameter is 3 mm, the nozzle length is 20 mm, the nozzle The cylinder surface distance was set to 100 mm, and the injection gas from the nozzle was injected so as to be perpendicular to the center of the cylinder, and when the frost could be removed, the injection gas amount, the injection speed Uo, and the spread average speed Ux of the injection gas were shown. Is.

  From Table 1, it can be seen that when the frost surface temperature is −40 ° C., the injection speed is higher, but the lower the temperature, the lower the injection speed.

  Here, the process of LNG vaporization and frost formation in the case of the vaporizer which puts LNG from the lower part of the finned heat exchanger tube 11 is as follows.

  Initially, the lower part of the heat transfer tube 12 is rapidly cooled, the surface temperature of the heat transfer tube 12 becomes −70 ° C. or less, and frost formation is solidified at a low temperature, so that the density is relatively light and weak. At this time, since the heat transfer area of the upper heat transfer tube 12 is large, the temperature is almost close to room temperature. As the frost formation thickness of the lower heat transfer tube 12 increases with the passage of time, the heat input to the LNG decreases, so the vaporization region in the heat transfer tube 12 moves upward and the temperature decreases. Accordingly, the density of frosting on the upper side is lightened and the bonding strength is also weakened.

  As can be seen from FIGS. 5 and 6, the density of frost increases as the temperature of the frosting surface increases. For this reason, since the binding force of frost also becomes high, the air ejection speed | velocity which can be defrosted also becomes large as shown in Table 1.

  In the vicinity of the outlet of the heat transfer tube 12 of the front-stage finned heat transfer tube group 11F, the time when the temperature of the vaporized gas is normally about −40 ° C. is the time when switching to the rear-stage finned heat transfer tube group 11R. At this time, the frosting surface temperature of the upper heat transfer tube 12 of the heat transfer tube 12 of the heat transfer tube group 11F with the previous stage fins is inferior to the evaporation region because of the heat transfer to the gas inside, so the temperature difference increases. Get higher. Since the temperature can be estimated to be −20 ° C. to −30 ° C., it becomes heavier than the frost density in the vaporized region and the adhesion strength is increased, but the frost thickness is thin.

  The vaporizer 10 is normally used by shifting from the lower end of the heat transfer tube to a height of 3/4 to 2/3 to the vaporization region successively, and the remaining upper tube is used for heating the vaporized gas. Considering such characteristics of the heat transfer tube 12, it can be seen that the vaporization ability is improved by defrosting the heat transfer performance in the vaporization region below the heat transfer tube 12.

  Accordingly, when the temperature is high, the frost formation in the upper heating region is caused by the adhering frost on the surface of the heat transfer tube 12 being melted at the high temperature of the internal gas from the downstream and falling off with the adhering frost thereon. When the melted water falls along the tube surface, it touches the lower heat transfer surface and freezes to adhere as a thin ice film. However, since thin ice has a larger heat transfer than frost, it is considered not to be a problem as a heat transfer resistance. Moreover, since this ice film becomes extremely low temperature due to the rise of the vaporization region of the heat transfer tube 12, it has been confirmed that the ice film peels and collapses due to a difference in temperature expansion from the attached heat transfer surface. As such, it is not a big problem.

  Since the temperature of the internal LNG in the vaporization region is a low temperature of −70 ° C. or less, the binding force of frost formation is small, and it is easy to blow off with the blown air and to cause collapse (avalanche).

  Therefore, it is considered that if the avalanche is generated in the frost at a height corresponding to this temperature of the heat transfer tube 12, the ability of the vaporizer is almost recovered.

  From the above consideration, for example, in the case of the heat transfer tube 12 having a length of 5 m, the collision height of the blown air is about 3 to 3.5 m, and further about 1 m upward from the position to ensure defrosting. The avalanche phenomenon can be ensured by providing the blowing nozzles 32 and 33 so as to collide with the position and the position of 1.5 m below.

  The frosting in the vaporization region can be defrosted at a slow collision wind speed (about 4.1 m / s). However, in the present invention, the collision wind speed (about 6.3 ° C.) that can be removed even by frosting in the heating region (−40 ° C.). 2 m / s). However, the present invention is not limited to this.

  The speed of the blown air is determined so that the collision speed of the blown air to the frosting surface is equal to or higher than the speed shown in Table 1 where defrosting is possible from the distance between the frosting surface and the jetting point.

  During the operation of the vaporizer, the air is descending through the space surrounded by the heat transfer tubes, so that the collapsed frost is easily brought along with the air.

  As described above, in the present invention, blasting is performed by blowing a plurality of stages in the height direction of the finned heat transfer tube 11 from the blowing nozzles 32 and 33 of the blast air supply tube 31, particularly by blowing air in the vicinity of the LNG vaporization region. By generating an avalanche of this, almost all the frost adhering to the finned heat transfer tube 11 can be removed, and the vaporizer can be continuously operated.

  Assuming that the demand for NG is 10 tons / h at the satellite base, 15 air temperature type carburetors 10 are conventionally installed and vaporized with 10 units, and the remaining 5 units are used for switching. Then, since continuous operation is possible, only one unit can be installed as an emergency and 11 air temperature vaporizers 10 can be installed. Also, at 5 tons / h, 8 units are installed in the past, 5 units are vaporized, and the remaining 3 units are used for switching. However, in the present invention, 6 vaporizers 10 including 1 emergency unit are sufficient. Equipment costs can be greatly reduced. In addition, since defrosting during operation can be performed with a slight amount of air, a conventional watering device is not required, and the equipment and the running cost of defrosting can be reduced.

DESCRIPTION OF SYMBOLS 10 Air temperature type vaporizer 11 Heat transfer pipe with fin 12 Heat transfer pipe 13 Fin 30 Defroster 31 Blowing air supply pipe 32,33 Blowing nozzle

Claims (4)

The finned heat transfer tubes are erected vertically and horizontally, and a low-temperature liquefied gas is allowed to flow upward from the lower part of each finned heat-transfer tube and the outside air is lowered from the upper part to the lower part of the finned heat-transfer tube. In the operation method of the air temperature type vaporizer that performs the vaporization operation by evaporating, a jet air supply pipe extending from the lower part to the upper part of the finned heat transfer pipe is installed at the center of the four finned heat transfer pipes adjacent vertically and horizontally, A plurality of blow nozzles are provided in the vertical direction on the outer periphery of the blown air supply pipe, heat transfer deterioration due to frost adhering to the finned heat transfer pipe is detected by the temperature of the NG, and the temperature of the NG is set to a set temperature (-40 to 40). −50 ° C.) When the air pressure drops below, the air is injected from the blowing nozzle so that the collision speed of the frosting surface is 4 m / s or more, and the frost formed by the air injected from the blowing nozzle is blown off. With that blow Been frost, the method of operating air temperature vaporizer, characterized in that the continuous vaporization operation while defrosting by generating avalanche frost adhering to the heat pipe heat transfer finned. A low-temperature liquefied gas is LNG, a 4~5m length of finned heat transfer tubes, air temperature according to claim 1, wherein the outer peripheral blowing nozzles of the jet air supply pipe is formed 2 or 3-stage by the number-m intervals How to operate the vaporizer. Eight fin plates with a width of 40 to 80 mm are provided on the outer periphery of a heat transfer tube with an inner diameter of 20 to 25 mm at an angle of 45 degrees to constitute a heat transfer tube with fins, and a plurality of heat transfer tubes with fins are arranged vertically and horizontally at intervals of 150 to 200 mm. Standing up and installing a blown air supply pipe having an inner diameter of 20 to 25 mm at the center of the finned heat transfer pipes vertically and horizontally, and a blow nozzle at positions 1.5 m, 3 m and 4 m from the lower end of the blown air supply pipe The operating method of the air temperature type | mold vaporizer of Claim 2 formed. The blowing nozzle is such that air hits between the fins of the heat transfer tube adjacent to the horizontal or vertical direction and the blow nozzle for the heat transfer tube that injects air downward toward the adjacent four finned heat transfer tubes. The operation method of the air temperature type | mold vaporizer of Claim 3 which consists of a blowing nozzle for fins which injects into a pipe.

Images