Heat exchanger and method for suppressing gasket swelling

Abstract

To provide a heat exchanger capable of suppressing swelling of a gasket while suppressing damage of a heat transfer plate, and a method for suppressing swelling of a gasket.SOLUTION: A heat exchanger of the present invention is a plate-type heat exchanger in which a plurality of heat transfer plates is laminated with rubber gaskets between adjacent heat transfer plates, and a space is formed between the adjacent heat transfer plates through which liquid containing aromatic hydrocarbons can flow. A coating film that has elastic deformation followability and benzene resistance is formed on the surface of the gasket, and fastening members are provided for fastening the plurality of heat transfer plates so as to compress the gasket at a compression rate of 25.0[%] to 27.0[%].SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a heat exchanger and a method for suppressing swelling of a gasket. [Background technology]

[0002] It has been known that when a liquid containing aromatic hydrocarbons is introduced into a plate-type heat exchanger consisting of multiple stacked heat transfer plates, the gaskets between adjacent heat transfer plates absorb the aromatic hydrocarbons and expand in volume. This volumetric expansion of the gasket, commonly referred to as swelling, softens and deteriorates the gasket. This gasket swelling not only deteriorates sealing performance but also compresses the heat exchanger's components, particularly the plates. Continued gasket swelling can lead to plastic deformation of the heat transfer plates, resulting in liquid leakage from the heat exchanger. Patent Document 1 discloses a technology that attempts to change the gasket material. Patent Document 2 also discloses a technology that suppresses excessive gasket swelling by pre-immersing the gasket in oil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-132754 [Patent Document 2] Japanese Patent Application Publication No. 7-292140 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology disclosed in Patent Document 1 does not demonstrate cost-effectiveness, and from that perspective, it is unclear whether it is suitable for practical use. Furthermore, the technology disclosed in Patent Document 2 was unable to shorten the time it takes for the gasket to swell or reduce the volume expansion rate in an equilibrium state.

[0005] In addition, even if an emulsion breaker (surfactant), which is a chemical agent used to separate water (ammonia water) and oil (aromatic hydrocarbons such as tar), is added to the ammonia water in the upstream stage of the heat exchanger in an attempt to separate the aromatic hydrocarbons, it is difficult to separate them completely and swelling of the gasket occurs.

[0006] In conventional heat exchangers, gaskets are compressed at a compression ratio of 23.1% to 24.0%, but gasket swelling still occurs. While increasing the gasket compression ratio can suppress swelling, compression ratios above 24.0% can deform the plates due to the repulsive force from the gasket, potentially resulting in plate damage. Therefore, conventionally, gaskets are compressed at 24.0% or less. For this reason, traditionally, gaskets were used, assuming that gasket swelling was possible, and the heat exchanger was disassembled and replaced with new ones after a certain period of time. Historically, gasket replacement was required every six months. Because heat exchangers are deployed in large numbers in coal-fired chemical plants, the cost of gasket replacement and the impact of equipment downtime (heat loss) were considered problematic. Therefore, suppressing gasket swelling could reduce gasket replacement costs and the impact of equipment downtime (heat loss).

[0007] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a heat exchanger and a method for suppressing gasket swelling that can suppress damage to heat transfer plates while suppressing gasket swelling. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the heat exchanger of the present invention is a plate-type heat exchanger in which a plurality of heat transfer plates are stacked with rubber gaskets interposed between adjacent heat transfer plates, and a space is formed between the adjacent heat transfer plates through which a liquid containing aromatic hydrocarbons flows, and the heat exchanger is characterized in that a coating film having elastic deformation followability and benzene resistance is formed on the surface of the gasket, and fastening members are provided to fasten the plurality of heat transfer plates so as to compress the gasket at a compression rate of 25.0[%] to 27.0[%].

[0009] The heat exchanger according to the present invention is a plate-type heat exchanger for recovering low-temperature waste heat from circulating ammonia water circulating between a coke oven and a tar decanter, and is a bottom heat exchanger connected to the bottom of a reduced-pressure ammonia stripper for distilling excess ammonia water.

[0010] Furthermore, the method for suppressing gasket swelling according to the present invention is a method for suppressing gasket swelling in a plate-type heat exchanger in which a plurality of heat transfer plates are stacked with a rubber gasket interposed between adjacent heat transfer plates, and a space is formed between the adjacent heat transfer plates through which a liquid containing aromatic hydrocarbons flows, characterized in that a coating having elastic deformation followability and benzene resistance is applied to the surface of the gasket, the plurality of heat transfer plates are fastened together with fastening members, and the gasket is compressed at a compression rate of 25.0% to 27.0%. [Effects of the Invention]

[0011] The heat exchanger and the method for suppressing swelling of a gasket according to the present invention have the effect of suppressing swelling of the gasket while suppressing damage to the heat transfer plate. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing an example of an ammonia water treatment system according to an embodiment. [Figure 2]FIG. 2 is a perspective view that schematically shows the heat exchanger according to the embodiment. [Figure 3] FIG. 3 is a perspective view schematically showing the heat exchanger according to the embodiment in an exploded state. [Figure 4] FIG. 4 is a side view schematically showing the heat exchanger according to the embodiment in an exploded state. [Figure 5] FIG. 5 is a diagram showing an example of the structure of a coating film formed on the surface of a gasket. [Figure 6] FIG. 6 is a diagram showing a compression mechanism for the gasket test piece used in Example 1. [Figure 7] FIG. 7 is a graph showing the time course of the mass change rate of the gasket test piece. [Figure 8] FIG. 8 is a graph showing the change in hardness of the gasket test piece over time. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of a heat exchanger and a method for suppressing swelling of a gasket according to the present invention will be described, although the present invention is not limited to this embodiment.

[0014] FIG. 1 is a schematic diagram showing an example of an ammonia water treatment system using a heat exchanger according to an embodiment.

[0015] In the ammonia distillation system according to the embodiment, a portion of the excess ammonia distillate generated in the coke oven 2 is supplied to a reduced-pressure ammonia stripper 4 for distilling the excess ammonia distillate. The excess ammonia distillate supplied to the ammonia stripper 4 is sent from the bottom of the ammonia stripper 4 to the heat exchanger 1, where it is heated by heat exchange in the heat exchanger 1 and then returned to the bottom of the ammonia stripper 4. The heated excess ammonia distillate becomes ammonia-containing vapor under reduced pressure and reaches the top of the ammonia stripper 4. As a result, ammonia is removed from the excess ammonia distillate. Deammonia distillate, which is the excess ammonia distillate from which the ammonia has been removed, is discharged from the bottom of the ammonia stripper 4. The heat source for the heat exchanger 1 is the circulating ammonia distillate circulating between the coke oven 2 and the tar decanter 3, which is introduced into the heat exchanger 1 and used.

[0016] Fig. 2 is a perspective view schematically showing a heat exchanger according to an embodiment, Fig. 3 is a perspective view schematically showing a heat exchanger according to an embodiment in an exploded state, and Fig. 4 is a side view schematically showing a heat exchanger according to an embodiment in an exploded state.

[0017] The heat exchanger 1 according to the embodiment is a plate-type heat exchanger for recovering low-temperature waste heat from circulating ammonia water circulating between a coke oven 2 and a tar decanter 3, and is a bottom heat exchanger connected to the bottom of a reduced-pressure ammonia stripper 4 for distilling excess ammonia water. The heat exchanger 1 according to the embodiment is composed of a pair of nameplates 11a, 11b, a plurality of heat transfer plates 12 arranged between the nameplates 11a, 11b, a plurality of gaskets 13 arranged between adjacent heat transfer plates 12, a plurality of bolts 14, a plurality of nuts 15, and the like.

[0018] The heat exchanger 1 has a plurality of heat transfer plates 12 stacked side by side, a first space forming a flow path for a high-temperature medium, and a second space forming a flow path for a low-temperature medium between adjacent heat transfer plates 12, and performs heat exchange by allowing a high-temperature medium and a low-temperature medium to flow mutually between the first space and the second space. A gasket 13, which is a sealing member that maintains liquid-tightness, is disposed between adjacent heat transfer plates 12 to maintain the liquid-tight state.

[0019] The heat transfer plates 12 are integrated by being sandwiched between a pair of nameplates 11a, 11b. To sandwich the heat transfer plates 12 between the pair of nameplates 11a, 11b, a plurality of fastening members, namely a plurality of bolts 14 and a plurality of nuts 15, are used and are provided at predetermined intervals around the periphery of each of the pair of nameplates 11a, 11b. Note that the bolts 14 and nuts 15 are not shown in Figures 2 and 3.

[0020] 3, reference numeral 111 denotes a supply pipe that supplies circulating ammonia water, which is a high-temperature medium, to the heat exchanger 1, reference numeral 112 denotes a discharge pipe that discharges the circulating ammonia water from the heat exchanger 1, reference numeral 113 denotes a supply pipe that supplies excess ammonia water, which is a low-temperature medium, to the heat exchanger 1, and reference numeral 114 denotes a discharge pipe that discharges the excess ammonia water from the heat exchanger 1. In the heat exchanger 1 configured as described above, the circulating ammonia water supplied from the supply pipe 111 passes through a flow path 121 for flowing a high-temperature medium, the first space, a flow path 122, etc. of the heat exchanger 1, and is discharged from the discharge pipe 112. On the other hand, the excess ammonia water supplied from the supply pipe 113 passes through a flow path 123 for flowing a low-temperature medium, the second space, a flow path 124, etc. of the heat exchanger 1, and is discharged from the discharge pipe 114. In this way, heat exchange occurs between the circulating ammonia water (high-temperature medium) and the excess ammonia water (low-temperature medium) via the multiple heat transfer plates 12.

[0021] The heat exchanger 1 according to the embodiment has a structure in which heat transfer plates 12 and gaskets 13 are alternately arranged and sandwiched. The heat exchanger 1 prevents leakage of the liquid introduced into the heat exchanger by compressing the gaskets 13 in the grooves of the heat transfer plates 12 to tightly seal them. However, conventionally, compression is performed only for sealing purposes, not to prevent swelling, and is limited to 24.0% or less.

[0022] In the heat exchanger 1 according to the embodiment, the compression ratio of the gasket 13 is increased to prevent swelling of the gasket 13. For example, when the distance L between the pair of nameplates 11a and 11b is 1817 mm, the width Lp of the heat transfer plate 12 is 4.16 mm, and the number N of heat transfer plates 12 is 395, the total width of the gasket 13 is expressed as LN × Lp. Increasing the compression ratio of the gasket 13 from 23.1% to 25.0% reduces the distance L between the pair of nameplates 11a and 11b by 2.1 mm. Increasing the compression ratio of the gasket 13 from 23.1% to 27.0% reduces the distance L between the pair of nameplates 11a and 11b by 5.0 mm. Furthermore, by increasing the compression rate of the gasket 13 from 23.1% to 30.0%, the distance L between the pair of nameplates 11a and 11b is reduced by 7.5 mm.

[0023] As described above, by sandwiching the gasket 13 between the heat transfer plates 12 and increasing the compressive force, it is easy to obtain the effect of suppressing the swelling of the gasket 13. However, care must be taken because if the compressive force is increased too much, the repulsive force of the gasket 13 may become too large, which may accelerate the deformation of the heat transfer plates 12.

[0024] In the heat exchanger 1 according to the embodiment, the gasket 13 (rubber base material 131 described later) may be made of, for example, EPDM (ethylene propylene rubber), IIR (butyl) rubber, or fluororubber.

[0025] Here, it is possible to set the compression rate of the gasket 13 to 24.0% to 33.0% due to the structure of the heat exchanger 1. On the other hand, if the compression rate of the gasket 13 is 24.0% or more, there is a concern that swelling of the gasket 13 may cause deformation of the heat transfer plate 12 and even damage to the heat transfer plate 12. Therefore, in the heat exchanger 1 according to this embodiment, a coating for suppressing swelling is applied to the surface of the gasket 13.

[0026] FIG. 5 is a diagram showing an example of the structure of a coating film formed on the surface of the gasket 13. As shown in FIG.

[0027] As shown in FIG. 5, gasket 13 is formed by coating a rubber substrate 131 with a coating material made of binder 133 containing scaly filler 132, forming a coating film on the surface of gasket 13. This coating film forms a flexible, transparent thin film after deposition, and has adhesion to rubber substrate 131 and elastic deformation followability. Furthermore, the coating film has chemical barrier properties such as resistance to benzene because binder 133 contains scaly filler 132, which has high barrier properties, such as silica-based scaly filler or metallic scaly filler. The thickness of the coating film is preferably 90 μm or more and 110 μm or less, with 100 μm being suitable.

[0028] The flaky filler 132 may be, for example, flaky silica powder or flaky metal powder.

[0029] It is preferable to use, for example, a fluorine-containing resin as the binder 133. An example of the fluorine-containing resin is a solvent-based paint made of a copolymer of TFE (Tetrafluoroethylene), isobutylene, and hydroxybutyl vinyl ether. Another example of the fluorine-containing resin is a solvent-based paint made of a copolymer of TFE, vinyl versatate, and hydroxybutyl vinyl ether. Another example of the fluorine-containing resin is a solvent-based paint made of a copolymer of CTFE (Chloro Tri Fluoro Ethylene) and hydroxybutyl vinyl ether. Another example of the fluorine-containing resin is a solvent-based paint made of a copolymer of TFE, vinylidene fluoride, and hydroxybutyl vinyl ether.

[0030] It should be noted that a curing agent appropriate for the functional groups of the fluorine-containing resin can be selected and added to the binder 133. For example, when a fluorine-containing resin having hydroxyl groups is used as the binder 133, polyisocyanate compounds, melamine curing agents, urea resin curing agents, silicate compounds, isocyanate group-containing silane compounds, and polybasic acid curing agents can be used. Among these, polyisocyanate compounds are preferred because they provide an excellent balance of physical properties to the cured coating.

[0031] The method for applying the paint (binder 133 containing scaly filler 132) to the surface of rubber substrate 131 is not particularly limited, and for example, it can be applied using a known application device such as an air spray coating. After applying the paint (binder 133 containing scaly filler 132) to rubber substrate 131, a drying process is performed to form a coating film layer on the surface of rubber substrate 131. The drying conditions are not particularly limited, and are preferably, for example, 60°C to 150°C from the viewpoint of promoting the crosslinking reaction and protecting the urethane layer. The drying time may be set appropriately until the curing of the paint (binder 133) is completed.

[0032] In this embodiment, in a heat exchanger 1 that receives a liquid containing aromatic hydrocarbons (ammonia water), a coating is applied to the gasket 13, forming a coating film on the surface of the gasket 13 that has elastic deformation followability and benzene resistance. Furthermore, in the heat exchanger 1 according to this embodiment, multiple heat transfer plates 12 are fastened together with multiple bolts 14 and multiple nuts 15, which are fastening members, so that the gasket 13 is compressed at a compression rate of 25.0% to 27.0%. This significantly suppresses swelling of the gasket 13 in the heat exchanger 1 according to this embodiment. In other words, there is concern that the repulsive force of the gasket 13 increases due to increased fastening force, which may cause deformation of the heat transfer plates 12. However, in the heat exchanger 1 according to this embodiment, the swelling suppression effect of the coating on the gasket 13 makes it possible to increase the compression rate of the gasket 13 while suppressing deformation of the heat transfer plates 12 up to a compression rate of 27.0%. Furthermore, due to the compression of the gasket 13 and the swelling suppression effect of the coating, the period until leakage of the liquid (ammonia water) introduced into the heat exchanger 1 was extended by six months when the compression rate of the gasket 13 was 25.0% to 27.0% compared to when the compression rate was 23.1%. As a result, the heat exchanger 1 according to the embodiment can reduce repair costs and the impact of equipment shutdowns (heat loss) by extending the replacement cycle of the gasket 13. As described above, in order to obtain a sufficient swelling suppression effect while suppressing deformation of the heat transfer plate 12 due to compression, the compression rate of the gasket 13 is set to 25% or more and 27% or less, and more preferably 25.1% or more and 26.9% or less.

[0033] Example 1 Hereinafter, the configuration of the present invention will be described in detail based on an example in which the invention is applied to a gasket test piece made of EPDM (ethylene propylene rubber) for a plate-type heat exchanger.

[0034] FIG. 6 is a diagram showing a compression mechanism for the gasket test piece 201 used in Example 1.

[0035] In Example 1, the structure of a plate-type heat exchanger was simulated, and a pair of steel plates 202a, 202b sandwiching an EPDM gasket test piece 201 was fastened using a plurality of bolts 203 and a plurality of nuts 204. The compression ratios of the gasket test piece 201 were set to 23.1% and 24.0%, which are equivalent to the actual machine set values, and 25.0%, 27.0%, 30.0%, and 33.0%, which exceed the actual machine set values.

[0036] In Example 1, a gasket test piece 201 sandwiched between a pair of plates 202a and 202b and compressed was immersed in a liquid having the same composition as the liquid (ammonia water) introduced into the heat exchanger 1. Then, the mass change rate and hardness change of the gasket test piece 201 were measured 7 days after the start of immersion, 14 days after the start of immersion, and 21 days after the start of immersion. The compression rate of the gasket test piece 201 was obtained by dividing the change in thickness of the gasket test piece 201 before and after compression by the thickness of the gasket test piece before compression. The mass change rate was obtained by dividing the change in mass of the gasket test piece 201 before and after the immersion test by the mass of the gasket test piece 201 before immersion. The hardness of the gasket test piece 201 was measured using a measurement method in accordance with JIS K 6253, and the change in hardness before and after the immersion test was obtained.

[0037] The immersion liquid in which the gasket test piece 201 was immersed contained 1000 ppm to 4000 ppm of ammonia and 0 ppm to 1500 ppm of benzene, simulating the ammonia solution that is the liquid introduced into the heat exchanger 1. The gasket test piece 201 was prepared by cutting an EPDM gasket into a length of about 5 mm and compressing it by sandwiching it with the compression mechanism shown in Fig. 6. When neither compression nor sandwiching between the heat transfer plates 12 is performed, the mass increase rate and hardness change of the gasket test piece 201 reach equilibrium in about 7 days.

[0038] FIG. 7 is a graph showing the time course of the mass change rate of the gasket test piece 201. FIG. 8 is a graph showing the time course of the hardness change of the gasket test piece 201. In FIGS. 7 and 8, "coated" indicates that the surface of the gasket test piece 201 is coated with the paint described in the above embodiment, and a coating film having elastic deformation followability and benzene resistance is formed on the surface of the gasket test piece 20. The thickness of the coating film was 100 μm. In FIGS. 7 and 8, "uncoated" indicates that there is no coating film on the surface of the gasket test piece 201.

[0039] As shown in FIGS. 7 and 8, it was confirmed that by increasing the compression ratio of the gasket test piece 201, both the mass change rate and hardness change of the gasket test piece 201 were reduced.

[0040] Example 2 In Example 2, based on the results of Example 1, painted and unpainted gaskets were applied to actual heat exchangers with five different compression ratios: 24.0%, 25.0%, 27.0%, 30.0%, and 33.0%. The paint used to paint the gasket surface was the same as that described in the above embodiment. These heat exchangers were then used to exchange heat between liquids containing aromatic hydrocarbons for two years, and the deformation of the heat transfer plates and the presence or absence of leakage of the introduced liquid were observed. Table 1 shows the results after two years. In Table 1, "◯" indicates no leakage, "△" indicates leakage but no damage to the heat transfer plates, and "×" indicates leakage and damage to the heat transfer plates.

[0041] [Table 1]

[0042] As can be seen from Table 1, in the heat exchanger using an unpainted gasket, damage to the heat transfer plate and leakage occurred at all compression rates. On the other hand, in the heat exchanger using a painted gasket, the heat transfer plate deformed and liquid leaked at a compression rate of 24.0%. In the heat exchanger using a painted gasket, no leakage occurred at compression rates of 25.0% and 27.0%. In the heat exchanger using a painted gasket, the heat transfer plate deformed and liquid leaked at a compression rate of 30.0%. In the heat exchanger using a painted gasket, the heat transfer plate broke and leakage occurred at a compression rate of 33.0%.

[0043] As shown above, with an unpainted gasket, increasing the compression rate above 24.0% damages the heat transfer plate, and no swelling suppression effect is achieved. On the other hand, with a painted gasket, leakage is suppressed without damaging the heat transfer plate at a compression rate between 25.0% and 27.0%. This shows that compressing a painted gasket at a compression rate between 25.0% and 27.0% achieves a significant swelling suppression effect, extending the gasket's lifespan by six months. [Explanation of symbols]

[0044] 1 heat exchanger 2. Coke ovens 3 Tar Decanter 4. Ammonia Stripper 11a, 11b Nameplate 12 Heat transfer plate 13 Gasket 14 volts 15 Nut 111,113 Supply pipe 112,114 Discharge pipe 121,122,123,124 Distribution channels 131 Rubber base material 132 Scaly Filler 133 Binder 201 Gasket test piece 202a, 202b Plate 203 volts 204 Nut

Claims

1. A plate-type heat exchanger in which a plurality of heat transfer plates are stacked with rubber gaskets interposed between adjacent heat transfer plates, and a space through which a liquid containing aromatic hydrocarbons flows is formed between the adjacent heat transfer plates, a coating film having elastic deformation followability and benzene resistance is formed on the surface of the gasket by a swelling-suppressing coating material made of a binder using a fluorine-containing resin containing a silica-based scaly filler or a metal-based scaly filler; A heat exchanger characterized by comprising fastening members that fasten the plurality of heat transfer plates so as to compress the gasket at a compression rate of 25.0% to 27.0%.

2. A plate-type heat exchanger for recovering low-temperature waste heat from circulating ammonia water circulating between a coke oven and a tar decanter, 2. The heat exchanger according to claim 1, which is a bottom heat exchanger connected to the bottom of a reduced-pressure ammonia stripper for distilling excess ammonia water.

3. A method for suppressing gasket swelling in a plate-type heat exchanger in which a plurality of heat transfer plates are stacked with rubber gaskets interposed between adjacent heat transfer plates, and a space through which a liquid containing aromatic hydrocarbons flows is formed between the adjacent heat transfer plates, comprising: a coating having elastic deformation followability and benzene resistance is applied to the surface of the gasket using a swelling-suppressing coating material made of a binder using a fluorine-containing resin containing a silica-based scale-like filler or a metal-based scale-like filler; A method for suppressing swelling of a gasket, characterized in that a plurality of the heat transfer plates are fastened together with fastening members, and the gasket is compressed at a compression rate of 25.0% to 27.0%.

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