KR20140106604A - Shell and tube heat exchanger with improved anti-fouling properties - Google Patents

Abstract

The invention comprises a shell 2 with an inlet end cap 3 attached to a first end 4 and an outlet end cap 5 attached to a second end 6 of the shell 2, A bundle 7 is embedded within the shell 2 and the tube bundle 7 includes a plurality of parallel spaced tubes 8 across the interior of the shell 2 from a first end to a second end of the tube bundle Tubular heat exchanger 1 in which a plurality of baffles 11 are arranged inside the shell 2 to support the parallel spaced tubes 8 of the tube bundle 7. At least a portion of the multitubular heat exchanger is provided with a coating comprising silicon oxide (SiO _x ).

Description

[0001] SHELL AND TUBE HEAT EXCHANGER WITH IMPROVED ANTI-FOULING PROPERTIES [0002]

The present invention generally relates to a shell and tube heat exchanger that enables heat transfer between two fluids at different temperatures for various purposes. Specifically, the present invention relates to a multitubular heat exchanger coated to improve the anti-fouling properties, and in certain embodiments provided with certain structural features to ensure that coating remains in the multitubular heat exchanger in use.

In many industrial processes, contamination of heat exchange equipment is a major concern. In order to maintain the performance of the equipment satisfactorily, it is necessary to remove accumulated deposits on the heat transfer surface through regular maintenance and cleaning. Sediments arise, for example, from fluid, microbial growth and / or dust in equipment.

The multitubular heat exchanger can become contaminated over time, which reduces heat exchange and increases the pressure drop, thereby degrading the overall performance of the heat exchanger. For example, depending on the fluid used, the heat exchanger can be seriously contaminated and thus difficult to clean, and thus the performance of the heat exchanger requires a strong detergent and intensive mechanical cleaning over a considerable period of time. Cleaning can take a lot of time and money. Also, during the cleaning, the process associated with the multitubular heat exchanger may be stopped.

A multitubular heat exchanger is made of a metal with a high surface free energy that most liquids easily wet the surface.

In addition, when the surface of a heat exchanger is manufactured, the surface roughness increases due to the molding operation of the metal, which is usually associated with faster accumulation of contaminated sediments.

GB 2428604 discloses providing a coating on a multitubular heat exchanger to reduce contamination.

US20080073063 discloses a multitubular heat exchanger coated with a low surface energy material to reduce contamination.

In order to ensure that the heat exchanger continues to run for longer periods of time, it is desirable to find a new way of ensuring pollution reduction of the heat exchanger and its surface. It is also desirable to shorten the stopping time of the process associated with the multitubular heat exchanger.

A problem encountered with currently known antifouling coatings is that the abrasion resistance of the coating is poor in applications where abrasive heat exchange media, such as sand or other particulate materials, are introduced into a multitubular heat exchanger with heat exchange fluids. Also, in applications where high pressure is applied, cracks may occur in the coating due to the torque and tension acting on the multitubular heat exchanger.

It is an object of the present invention to provide a surface for an improved multitubular heat exchanger which exhibits surface fouling reduction characteristics when used in a multitubular heat exchanger. Another object is to obtain a surface for a multitubular heat exchanger having anti-fouling properties with abrasion resistance and high resistance to crack formation in a polishing environment.

The object is achieved by the provision of a tube bundle comprising a shell with an inlet end cap attached at a first end, an outlet end cap attached to a second end of the shell, a tube bundle embedded within the shell, Tubular heat exchanger comprising a plurality of parallel spaced tubes transverse to the interior of the shell from the end to the second end, the plurality of baffles being arranged inside the shell to support parallel spaced tubes of tube bundles. The multitubular heat exchanger is provided with a coating comprising silicon oxide (SiO _x ) having an atomic ratio O / Si of greater than 1, a carbon content of at least 10 atomic%, and a coating thickness of from about 1 to about 30 탆, Gel treatment and applied to at least a portion of the surface of the multistubular heat exchanger.

According to another aspect of the invention, the layer thickness of the coating on the multitubular heat exchanger is from 5 to 30 mu m, preferably from 2 to 20 mu m.

According to another aspect of the present invention, a coating comprising silicon oxide (SiO _x ) has an atomic ratio O / Si of O / Si ≧ 1.5-3, preferably O / Si ≧ 2-2.5.

According to another embodiment of the present invention, the composition has a carbon content ≥ 20-60 atomic%, preferably a carbon content ≥30-40 atomic%.

The multitubular heat exchanger is advantageous in that the contamination of the surface is remarkably reduced. By applying a coating composition comprising a sol-gel material having an organosilicon compound to the surface of a multitubular heat exchanger, the surface free energy and the roughness are lowered, thereby enabling the contamination reduction and easy cleaning of the surface of the multitubular heat exchanger . In addition, the surface of the sol-gel coated multitubular heat exchanger of the present invention exhibits excellent abrasion resistance and has the flexibility to reduce the risk of cracking in the coating. Further, it is possible to reduce the overall dimensions of the heat exchanger while maintaining the heat transfer performance of the multistub-type heat exchanger by the multitubular heat exchanger according to the present invention.

Further objects, features and advantages of the present invention will become apparent from the detailed description of various embodiments of the present invention presented with reference to the accompanying schematic drawings.

1 is a schematic view of a multitubular heat exchanger according to the present invention.
2 is a schematic cross-sectional view of the surface of a cylindrical multitubular heat exchanger having an antifouling coating according to the present invention.

1 is a side view of a multitubular heat exchanger 1 arranged in accordance with a preferred embodiment of the present invention. The multitubular heat exchanger 1 comprises a shell 2 in which an inlet end cap 3 is attached to the first end 4 of the shell 2. The outlet end cap (5) is attached to the second end (6) of the shell (2).

The cutout of the shell 2 exposes the tube bundle 7 built into the shell 2. The tube bundle (7) includes a plurality of parallel spaced tubes (8) across the interior of the shell (2) from a first end to a second end of the tube bundle. A plurality of baffles 11 are arranged in the interior of the shell 2 to support the parallel spaced tubes 8 of the tube bundle 7.

In operation, a first heat exchange fluid such as a hot medium or flue gas carrying waste heat is introduced into the shell 2 through the inlet. The first heat exchange fluid exits the shell (2) through the outlet through the passageway created by the baffle and through the shell (2). The second heat exchange fluid, which is heated in the heat exchanger (1), enters the inlet end cap (3) through the inlet. The second heat exchange fluid is heated by a first heat exchange fluid which passes into the tube bundle (7) and passes through the parallel spacing tube (8) and through the shell side of the heat exchanger (1). The second heat exchange fluid eventually travels from the tube bundle 7 to the outlet end cap 5 and exits the heat exchanger 1 through the outlet tube.

The coatings used in accordance with the present invention may be referred to as non-stick coatings and facilitate cleaning of the surface of the contaminated multitubular heat exchanger. The coated surface according to the present invention has better heat transfer over time than the conventional multitubular heat exchanger because the conventional multitubular heat exchanger is much more contaminated and thus the heat transfer performance is reduced to a greater extent . In addition, the coating on the surface results in a much more uniform surface and better flow characteristics. Also, in the multitubular heat exchanger according to the present invention, the pressure drop over time is reduced as compared with the conventional multistubular heat exchanger because accumulation of impurities, microorganisms and other substances is not large.

The coated multitubular heat exchanger according to the present invention can be easily cleaned by simply high pressure washing with water. Using a surface according to the present invention does not require excessive time consuming mechanical cleaning or cleaning with strong acids such as NaOH, HNO ₃ , strong bases or strong detergents.

In accordance with the present invention, the surface of the multitubular heat exchanger is coated with a composition comprising an organosilicon compound using a sol-gel process. The organosilicon compound is the starting material used in the sol-gel process, preferably a silicon alkoxy compound. In the sol-gel process, the sol is converted into a gel to produce a nanomaterial. Through the hydrolysis and condensation reaction, a three-dimensional network of interlayer molecules is produced in the liquid. The thermal treatment step serves to further treat the gel to be the nanomaterial or nanostructure that constitutes the final coating. The coating comprising the nanomaterial or nanostructure mainly comprises silicon oxide (SiO _x ) having an atomic ratio O / Si greater than 1, preferably from 1.5 to 3, and most preferably from 2 to 2.5 or more. Preferred silicon oxides are silica (SiO _2). Silicon oxide forms a three-dimensional network with excellent adhesion to the surface.

The coating of the present invention also has a carbon content as found in the hydrocarbon chain. The hydrocarbons may or may not have functional groups such as those found in hydrocarbon chains or aromatics such as C = O, C-O, C-O-C, C-N, N-C-O, Preferably, the carbon content is 10 atomic% or more, preferably 20 to 60 atomic% or more, and most preferably 30 to 40 atomic% or more. The hydrocarbons impart flexibility and elasticity to the coating. Hydrocarbon chains are hydrophobic and oleophobic, which makes the coatings non-tacky.

2 shows a schematic view of a surface 9 for a multitubular heat exchanger provided with a silicon oxide sol gel coating 10. Between the surface 9 itself and the silicon oxide layer there is an interface 11 between the siloxane coating and the metal oxide film on the surface 9. The coating bulk following the interface is a siloxane network 12 with voids and organic linker chains that impart flexibility to the coating. The outermost layer is a functional surface 13, a hydrophobic / oleophobic surface for reducing contamination.

The combination of durable and flexible coatings results in a surface for a multitubular heat exchanger with excellent non-tackiness and resistance to abrasion and cracking. The flexibility of the coating is particularly important to prevent cracking of the coating as the surfaces move relative to each other.

In one embodiment of the present invention, at least one sol comprising an organosilicon compound is applied to the surface to be coated. The surface can be wetted / coated with the sol in any suitable manner. The coating of the surface is preferably applied by spraying, dipping or flooding. At least a portion of one side of the multitubular heat exchanger surface is coated. As an alternative, all surfaces of at least one side of the surface in contact with the fluid are coated during use in a multitubular heat exchanger. Also, at least one side of the surface of the multitubular heat exchanger can be completely coated. Alternatively, both sides of the tube can be coated. When both sides are coated, both sides may be partially or entirely coated, or may be coated in any combination. Of course, more surfaces may be coated than surfaces intended to be in contact with the fluid. Preferably, all surfaces in contact with the contaminating fluid are coated.

In another embodiment, the method comprises at least pretreating the surface on the heat exchanger tube to be coated with at least one sol. This pretreatment is also preferably carried out by dipping, flooding or spraying. Pretreatment is performed to clean the surface of the coating to increase the adhesion of the subsequent coating to the heat exchanger tube. Examples of such pretreatment include treatment with acetone and / or alkaline solutions, such as caustic solutions.

In another embodiment, the method includes a heat treatment step, for example, a drying operation can be performed after the pre-treatment, and drying and / or curing operations are usually required after the sol tube is actually coated. The coating is preferably heated using conventional heating equipment such as, for example, an oven.

Compositions comprising SiO _x are applied to surfaces used in multitubular heat exchangers. Application of the composition is carried out by sol-gel treatment. The film of the composition thus obtained preferably has a thickness of 1 to 30 mu m. The thickness of the coated film is important for use in a multitubular heat exchanger. It is believed that film thicknesses less than 1 占 퐉 do not have sufficient wear resistance, as the surfaces of the multitubular heat exchangers in use can move slightly relative to each other. This slight movement wears the film, and over time the coating wears off. In addition, there is an upper limit on the thickness of the film because the application of the substance to the heat transfer surface affects the heat transfer and affects the performance of the multitubular heat exchanger. The upper limit of the thickness of the applied film is preferably 30 占 퐉. Therefore, the film thickness of the composition containing silicon oxide sol is preferably 1 to 30 占 퐉, preferably 1.5 to 25 占 퐉, preferably 2 to 20 占 퐉, preferably 2 to 15 占 퐉, preferably 2 to 10 占 퐉, Is 3 to 10 mu m.

The surface base material may be selected from a variety of metals and metal alloys. Preferably, the base material is selected from titanium, nickel, copper, any alloy of these metals, stainless steel and / or carbon steel. However, titanium, any alloy of these metals or stainless steel is preferred.

Although the various embodiments of the invention have been illustrated and described, it will be appreciated from the foregoing description that the invention is not so limited and may be implemented in other ways that are within the scope of the subject matter defined in the claims.

Example

To determine the long-term operating time of coastal facilities, tests were conducted on glass ceramic coatings with low surface energy.

Two low surface energy glass ceramic coatings, Coat 1 and Coat 2, were tested and the results are presented below. Coat 1 is a silane-terminated polymer in butyl acetate and Coat 2 is a polysiloxane-urethane resin in solvent naphtha / butyl acetate.

Step A

The analysis is intended for the H ₂ O in 1.2% HNO _3, H ₂ O and NaOH in oil within 1%, and records the properties of the coated substrate with respect to wettability and adhesiveness, the contact angle, the coating thickness and stability. The results are summarized in Table 1 below.

Court 1 Court 2 Substrate wettability Very good Very good Substrate adhesion Buy: 0/0
Stainless steel: 0/0
Ti: 0/0 (see below) Buy: 0/0
Stainless steel: 0/0
Ti: 0/0 (see below) Contact angle measurement H ₂ O: 102-103 [deg.] H ₂ O: 102-103 [deg.] Coating thickness 4-10 μm 2-4 μm stability 1.2% HNO _{3 in} H ₂ O: 1 h 30 min at 75 ° C
1% NaOH in H ₂ O: 3 hours at 85 ° C
Crude oil: 6 months at room temperature 1.2% HNO _{3 in} H ₂ O: 1 h 30 min at 75 ° C
1% NaOH in H ₂ O: 85 ° C for 2 hours
Crude oil: 6 months at room temperature

Both coatings exhibited excellent wettability when spray coated on stainless steel or titanium substrates.

The adhesive strength was measured by a crosscut / tape test according to DIN EN ISO 2409. Rated from 0 (very good) to 5 (very bad). 0 or 1 is acceptable and 2 to 5 are not. The first number indicates the score after the crosscut (1 mm grid) and the second number indicates the rating after the tape is applied and stripped again.

In order to obtain the maximum adhesive force for Coat 1 and Coat 2, the substrate required pre-treatment.

The substrate must be pretreated to obtain maximum adhesion of coat 1 on stainless steel. Immerse the substrate in an alkaline cleaning detergent for 30 minutes. The substrate is then washed with water and demineralized water and dried for a period of time not exceeding 30 minutes prior to application of the coat 1 to obtain an optimum adhesion. Tests showed that when the substrate was cleaned with acetone only, the adhesion decreased. Pretreatment is also required for stainless steel coated with Coat 2. Whether using an alkaline detergent as a pretreatment agent or acetone, the coating showed an unaffected adhesive force. If the preprocessing step is omitted or not performed correctly, it will affect the adhesion of the coating.

Both coatings exhibited excellent stability under acidic conditions. The coating was stable for one and a half hours at 75 ° C and more than 24 hours at room temperature.

Under alkaline conditions, coat 1 showed better results than coat 2. Coat 1 was able to withstand alkali conditions for 3 hours at 85 ° C and Coat 2 was able to withstand 2 hours at 85 ° C. The two coatings did not show degradation or degradation of properties after being immersed in crude oil for six months at room temperature.

Step B

Multi-tubular  Coating of Heat Exchanger Surface

Coat 1 and coat 2 were applied to a tube bundle. All tubes were pretreated with the following steps:

1. Immersion in liquid nitrogen (-196 DEG C)

2. Treatment with acid and alkaline solution to remove contamination

3. Wash tubing with water at high pressure

4. Assembling tube bundles for pressure testing

5. Disassembly of tube bundle. Allow tube to dry before application.

This pretreatment was completed the day before applying Coat 1 and Coat 2 to the tube. Therefore, this procedure does not follow the recommended method outlined in step A. Some tubes were still wet because the tubes were allowed to dry at room temperature. Fifteen tubes were treated with coat 1 by spray coating and the remaining 15 tubes were treated with coat 2. The tubes of the heat exchanger were coated on both sides. The final film thickness was 2 to 4 탆, and the coating was applied on both sides of the tube. Curing / drying was carried out at a high temperature of 200 ° C or 160 ° C for 1 hour 30 minutes in the field oven, respectively. After completion, the coated heat exchanger was weighed and the thickness of the coating was measured. Some tubes were observed to have some coating defects and small defects.

The tubes of the heat exchanger were then assembled with the remaining untreated tubes. The coated tubes were placed at the front, middle and end of the assembly. Evaluation of coated tubes was performed after an operating period exceeding 7 months.

Step C

XPS  Determination of coating content by analysis

Three different silicon oxide coated Ti substrates were analyzed before and after using XPS (X-ray photoelectron spectroscopy), also known as ESCA (Electron Spectroscopy for Chemical Analysis). The XPS method provides quantitative chemical information (chemical composition expressed in atomic%) for the outermost 2 to 10 nm of the surface.

A well defined x-ray energy was irradiated to a sample placed in a high vacuum state to release the photoelectrons. Only the photoelectrons from the outermost surface layer reached the detector. By analyzing the kinetic energy of these photoelectrons, it is possible to calculate the binding energy thereof, so that it can be grasped which element and the electron shell are derived from these photoelectrons.

XPS provides quantitative data on the elemental composition and the different chemical states of elements (different functional groups, chemical bonds, oxidation states). All elements except hydrogen and helium are detected, and the surface chemical composition thus obtained is expressed in atomic%.

Use keuratoseu Axis Ultra ^DLD (Kratos AXIS Ultra ^DLD) photoelectron spectroscopy XPS spectrum was recorded. Samples were analyzed using a monochromatic AI x-ray source. The analytical area was less than 1 mm2.

At the time of analysis, a broad spectrum was created to detect elements present in the surface layer. The relative spectra of each element were quantified to determine the relative surface composition.

The following three samples were analyzed by XPS.

1. Silicon oxide on Ti-plate (new) - Both sides coating

2. Silicon oxide on Ti-plate (conventional) - One side coating

3. Silicon oxide on DIN 1.4401 stainless steel sheet - Both sides coating

Analysis was performed at one location per sample, with the exception of Sample 1, which analyzed both locations. The results are summarized in Table 2, which shows the relative surface composition as atomic% and atomic ratio O / Si.

Sample O / Si C O Si N 1 New pt  One) 2.25 61.1 23.5 10.5 4.2 2 New pt  2) 2.30 61.0 23.9 10.4 4.1 2 Used 2.29 68.0 19.5 8.6 3.1 3 1.46 41.9 34.3 23.4 (0.2) ^*

* A weak peak in the detail spectrum, a signal close to the noise level

As can be seen from Table 2, mainly C, O and Si, i.e., 41.9 to 68.0 atomic% C, 19.5 to 34.3 atomic% O, and 8.6 to 23.4 atomic% Si were detected on the outermost surface.

The atomic ratio O / Si uses the total amount of oxygen. This means that the oxygen of the functional group containing carbon is also included. Otherwise, in the case of silica, in theory an O / Si ratio of 2.0 for bulk silica (SiO _{2 )} is expected.

Inspect tubes after operation

The term "contaminant" is used to refer to a deposit formed on a tube during operation. Contaminants are residues and sediments formed by crude oil, consisting of waxy organic and mineral / inorganic parts.

Visual inspection revealed that the tube with the coat marked Coat 1 was covered with a minimum amount of contaminants on the tube side facing the crude oil. In addition, other coating systems, denoted as coat 2, did not reach coat 1, but the contamination on the tube side facing the crude oil was reduced compared to the bare titanium surface.

The average amount of contamination by surface type was calculated by subtracting the average weight of the clean tube from the weight recorded for each contaminated tube (Table 3). The weight of the coating was not calibrated, so the actual contamination reduction rate is slightly higher. Assuming that the coating is pure SiO ₂ (density 2.6 g / cm ³ ), the amount of coating per tube is about 20 g.

surface Average pollution amount ^* (g) STDEV Contamination reduction rate (%) titanium 585 125 - Court 1 203 48 65 Court 2 427 144 27

In both coating systems, the contaminants in the tube were more easily removed than the contaminants attached to the titanium surface (see Table 4). The difference in cleaning requirements was tested by manually cleaning the tubes with tissue paper and washing with high pressure water. Tube cleaners using only dirt have shown that contaminants are very easily removed from coated tubes unlike uncoated tubes. By using water spray, all the contaminants except one or two pieces could be removed from the surface coated with coat 1. There were slightly more contaminants on the Coat 2 coated surface after the water spray cleaning. This contaminant had a slightly burned oil appearance.

Although some coating loss was observed at the point of contact, the coated surface that was in contact with the crude oil was generally in good condition.

On both sides facing the seawater, both coatings deteriorated and could be removed very easily.

Court 1 Court 2 Uncoated Exterior Relatively little contamination Pollution abatement Serious and extensive contamination Purging using tissue paper Very easy to remove contaminants Very easy to remove contaminants Contamination not removed High pressure water wash Tube looks new Most contaminants removed A significant layer still remains after attempts to remove the contaminants manually

The resistance of the coating to immersion in liquid nitrogen to remove the gasket was tested. One coat 1 and one coat 2 tube were treated in liquid nitrogen at -196 DEG C to remove the rubber gasket. The coating did not appear to have undergone excessive temperature changes. The tube was then rinsed with high-pressure water to remove almost all contaminants. No delimitation or coating failure was observed in both coating systems.

Claims (4)

And a second end portion 6 of the shell 2 is attached to the first end portion 4 of the tube bundle 7 so that the end end cap 5 is attached to the second end portion 6 of the shell 2, Is built into the shell 2 and the tube bundle 7 comprises a plurality of parallel spaced tubes (not shown) transversing the interior of the shell 2 from the first end 9 to the second end 10 of the tube bundle A shell and tube heat exchanger (1) comprising a plurality of baffles (11) arranged within a shell (2) to support parallel spaced tubes (8) of tube bundles (7) Lt;
Wherein said multitubular heat exchanger is provided with a coating comprising silicon oxide (SiO _x ) having an atomic ratio O / Si of greater than 1, a carbon content of at least 10 atomic% and a coating thickness of from about 1 to about 30 microns, - < / RTI > gel process and applied to at least a portion of the surface of the multistubular heat exchanger. The method of claim 1, wherein the layer thickness of the coating on the surface is in the range of 1.5 to 25 占 퐉, preferably 2 to 20 占 퐉, more preferably 2 to 15 占 퐉, more preferably 2 to 10 占 퐉, 3 to 10 [micro] m. The coating of claim 1 or 2, wherein the coating comprising silicon oxide (SiO _x ) has an atomic ratio O / Si of O / Si ≥1.5-3, preferably O / Si ≥2-2.5. . The multitubular heat exchanger according to any one of claims 1 to 3, having a composition of carbon content ≥ 20-60 atomic%, preferably carbon content ≥ 30-40 atomic%.

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