ES2650243T3 - Heat exchanger plates with anti-dirt properties - Google Patents

Abstract

A plate with gasket for a plate heat exchanger, characterized in that said plate has a coating comprising silicon oxide, SiOx, which has an atomic ratio of O / Si> = 2, a carbon content> = 30% atomic and a coating layer thickness of 3-10 μm, whose coating was prepared by sol-gel processing and applied to at least a part of the plate, wherein said coating is applied to the surface of the joint designated to be in contact with at least one fluid when the plate is in a plate heat exchanger in use, and wherein said plate is made of a base material selected from titanium, nickel, copper, any alloy of those mentioned above, stainless steel or Carbon Steel.

Description

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

60

65

DESCRIPTION

Heat exchange plates with anti-dirt properties Field of the invention

The present invention relates to a plate for a plate heat exchanger, a plate filling, a plate exchanger and a method for producing a plate for a plate heat exchanger to improve the anti-dirt properties and facilitate the cleaning of exchangers of plate heat.

Background

In many industrial processes, the fouling of heat transfer equipment is worrying. In order to maintain satisfactory performance of the equipment with regular service and cleaning, it is necessary to eliminate the accumulation of deposits on the heat transfer plates. Deposits arise, for example, from fluids in the equipment, microbial growth and / or dirt.

The plate heat exchangers (ICP) in use can become dirty over time, which results in less heat transfer and a greater pressure drop, and thus results in a reduced overall performance of the heat exchanger. Therefore, heat exchangers that are not permanently attached must be opened and cleaned. Depending, for example, on the fluids used in the heat exchanger plates, they can get seriously dirty and make cleaning difficult, thus requiring strong detergents and / or a powerful mechanical cleaning for a substantial period of time to restore the heat exchanger's performance. Cleaning ICP can be slow and expensive. In addition, the process to which the ICP is normally connected may have to be closed during said ICP cleaning.

Heat exchanger plates are made of metal sheets. The base material, that is, the metals used, has a high surface-free energy that results in most liquids easily wetting the surface of the sheets.

In addition, when heat exchanger plates are produced, the operation of forming the sheet metal increases the surface roughness that is often associated with a faster accumulation of dirt deposits.

JP H09 178392 A refers to a plate for a plate heat exchanger having a coating comprising an oxide of Zr, Ti, Hf or Al, the coating of which was prepared by soldering processing, applied to at least part of the plate, dried and cured, to improve corrosion resistance.

GB 2 428 604 A describes a heat exchanger with a coating to reduce fouling caused by adhesion of particles to the surfaces of the heat exchanger. The coating comprises a siloxane-based network, the network comprising silicon atoms, oxygen atoms and fluorinated alkyl groups.

WO2009034359 describes the provision of a coating to reduce surface biosecurity in aquatic environments where the coating is applied through the use of plasma-assisted chemical vapor deposition (PACVD).

US20090123730 describes a surface of a heat exchanger to be welded by means of a flux, and said surface, in addition to the flow, is also provided with at least one more layer containing an additive. The additive is reacted to modify the surface during welding.

WO2008119751 describes the production of a hydrophobic capacitor coating in which the coating comprises sol-gel materials based, for example, on silicon oxide sol

JP2000345355 refers to the improvement of corrosion resistance and describes a film consisting of 55-99% by weight of SiO2 and 45-1% by weight of ZrO2, film that is formed using sun processing -gel.

US2006 / 0196644 describes a heat exchanger provided with a hydrophilic surface coating comprising a gel produced by sol-gel processing.

It would be desirable to find new ways to ensure less fouling of heat exchangers and their plates in order to keep the heat exchangers in operation for longer periods of time, as well as heat exchangers and easier to clean plates. In addition, a reduced downtime would be desirable for the processes in which ICPs are involved.

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

60

65

A problem encountered with currently known anti-dirt coatings is the low wear resistance of the coatings in applications with abrasive heat exchange media, for example, sand or other particulate material entering the ICP with heat exchange fluids . In addition, cracks in the coating may occur due to the torque and tensile forces acting on plate fillings in high pressure applications.

Summary of the invention

An object of the present invention is to provide improved plates for an ICP, which show reduced fouling of the plates when used in an ICP. Another objective is to achieve plates for an ICP that have an anti-dirt surface that is resistant to wear in abrasive environments and has a high resistance against cracking.

This objective is achieved by coating the plates with a sol-gel composition that results in reduced soiled plates of the plate when used in a heat exchanger. By applying a coating composition comprising a sol-gel material with organosilicon compounds to the heat exchange plate, both the surface free energy and the roughness are reduced, which results in the reduction of fouling and easy cleaning of the heat exchanger plates. In addition, the sol-gel coated ICP plates of the invention exhibit excellent wear resistance and have flexibility that reduces the risk of cracks in the coating.

The present invention also relates to a heat exchanger and a plate filling for plate heat exchangers comprising various heat transfer plates of the types defined herein.

The present invention further relates to a method of producing a heat transfer plate comprising the steps of:

a) forming a plate for a plate heat exchanger from a base material,

b) preparing a composition by sol-gel processing in at least a part of the plate, the composition of which comprises organosilicon compounds,

c) drying and / or curing said composition to form a coating comprising silicon oxide (SiOx).

Brief description of the drawings

Figure 1 is a schematic drawing of the M20 ICP plate filling with the relative position of the plates used in the tests, both of coated plates according to the present invention and of conventional uncoated plates.

Figure 2 shows images of plates according to the present invention and a conventional plate after disassembly after operation for 7 months.

Figure 3 is a schematic cross section of a plate for a plate heat exchanger having an anti-dirt coating according to the invention.

Detailed description of the invention

The coating used in accordance with the present invention may be referred to as a non-stick coating and facilitates cleaning of the plates of a dirty heat exchanger. The coated plates according to the present invention show a better heat transfer over time compared to the plates of a conventional heat exchanger since the latter get dirty much faster and, therefore, decrease the yield of heat transfer to a greater extent. The coating of the plates also results in a much smoother surface, which results in better flow characteristics. In addition, the pressure drop is reduced over time for a plate heat exchanger according to the present invention compared to conventional plate heat exchangers, since the accumulation of impurities, microorganisms and other substances is not as pronounced. .

The coated plates according to the present invention can be easily cleaned using simply high pressure washing with water. With a plate according to the present invention, there is no need for mechanical cleaning or cleaning that takes a long time using strong acids, bases or detergents, such as for example NaOH and HNO3.

In accordance with the present invention, a plate for use in a plate heat exchanger is coated with a composition comprising organosilicon compounds using a sol-gel process. The organosilicon compounds are starting materials used in the sol-gel process and are preferably silicon alkoxy compounds. In the sol-gel process, a sun becomes a gel to produce nanomaterials. Through the hydrolysis and condensation reactions, a three-dimensional network of molecules interspersed in a liquid is produced. The thermal processing stages serve to further process the gel in nanomaterials or nanostructures that

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

60

65

They result in a final coating. The coating comprising said nanomaterials or nanostructures mainly comprises silicon oxide, SiOx, which has an atomic ratio of O / Si> 1, preferably an atomic ratio of O / Si> 1.5-3, and more preferably O / Si> 2-2.5. A preferred silicon oxide is silica, SiO2. Silicon oxide forms a three-dimensional network that has excellent adhesion to the plates.

The coating of the present invention also has a carbon content such as that found in hydrocarbon chains. The hydrocarbons may or may not have functional groups such as those found in hydrocarbon chains or aromatic groups, for example, C = O, C-O, C-O-C, C-N, N-C-O, N- C = O, etc. Preferably, the carbon content is> 10% atomic, preferably> 20-60% atomic, and most preferably> 30-40% atomic. Hydrocarbons give flexibility and elasticity to the coating, which is especially important in plate heat exchangers with joints, since the plates move during operation due to the high pressures exerted on the plates in the plate filling. The hydrocarbon chains are hydrophobic and oleophobic, which results in the non-stick properties of the coating.

A schematic drawing of a plate for a plate heat exchanger provided with a silicon oxide gel sol coating is shown in Figure 3. Between the plate itself and the silicon oxide layer there is an interface between the coating siloxane and a metal oxide film of the plate. The volume of coating that follows said interface is the siloxane network with organic and hollow linker chains that confer flexibility to the coating. The outermost layer is a functional surface, that is, a hydrophobic / oleophobic surface for dirt reduction.

By combining a durable but flexible coating, a plate for a plate heat exchanger is achieved that has excellent non-stick properties and is also resistant to wear and cracks. The flexibility of the coating is especially important in plate heat exchangers provided with joints between the plates, since it is a well known problem that the plate filling is not rigid, which makes the plate coatings tend to crack when flexible plates move and bend in relation to each other, a phenomenon called "meandering".

In one embodiment of the present invention, at least one sun comprising organosilicon compounds is applied to the surface to be coated. The surface can be wetted / coated with the sun in any suitable way. It is preferable that the surface coating be applied by spraying, immersion or flooding. At least a part of one side of the heat exchanger plate must be coated. Alternatively, all surfaces of at least one side of a plate that are in contact with a fluid during use in an ICP are coated. In addition, at least one side of a heat exchanger plate may be completely coated. Alternatively, both sides of the plate may be coated. If both sides are coated, they can be partially or fully coated, in any combination. Naturally, more surfaces can be coated than surfaces intended to be in contact with the fluid. Preferably, all surfaces in contact with a fluid that results in fouling are coated. The joints may also be coated with the composition according to the present invention. The coating composition is preferably applied only to the surface of the joints designated to be in contact with at least one fluid when used in an ICP. In view of the foregoing, the coating composition according to the present invention can be applied to bare ICP plates or ICP plates with joints attached thereto. When described in the present application, the surfaces of plates and joints in contact with at least one fluid are intended to relate to surfaces in contact with the fluid or fluids within the heat exchanger.

In another embodiment, the method comprises a pretreatment of at least the surfaces on the heat exchanger plates to be coated with at least one sun. This pretreatment is also preferably carried out by immersion, flooding or spraying. Pretreatment is used to clean the surfaces to be coated in order to obtain greater adhesion of the latter coating to the heat exchanger plate. Examples of such pretreatments are treatment with acetone and / or alkaline solutions, for example, caustic solution.

In another embodiment, the method comprises thermal processing steps, for example, a drying operation can be carried out after a pretreatment and a drying and / or curing operation is often necessary after the actual coating of the plate with said sol . The coating is preferably subjected to heat using a conventional heating apparatus, such as for example ovens.

The composition comprising SiOx is applied to a plate to be used in a plate heat exchanger. The application of the composition is done by sol-gel processing. The resulting film of said composition on the plate is preferably between 1 and 30 gm thick. The thickness of the coated film is important for the use of the plate in a heat exchanger not permanently attached. A film thickness of less than 1 gm is considered not to be sufficiently resistant to wear, since the plates in a plate heat exchanger in use may move slightly relative to each other. This slight movement causes wear on the film and over time the coating will wear out. In addition, the thickness of the

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

film has an upper limit since the application of substances on the heat transfer plates influences the heat transfer and, therefore, the performance of the plate heat exchanger. The upper limit for the applied film is preferably 30 pm. Therefore, the film thickness of the silicon oxide sol-containing composition is 1-30 pm, preferably 1.5-25 pm, preferably 2-20 pm, preferably 2-15 pm, preferably from 2-10 pm and preferably from 3-10 pm.

The base material for the plates can be selected from various metals and metal alloys. Preferably, the base material is selected from titanium, nickel, copper, any alloy of those mentioned above, stainless steel and / or carbon steel. However, titanium, any alloy of those mentioned above or stainless steel is preferred.

Examples

In the search for a prolonged operating time of the equipment on the high seas, tests were carried out on ceramic coatings of low surface energy glass. Two low surface energy glass ceramic coatings, Layer 1 and Layer 2, were analyzed, and the results are presented below. Layer 1 is a silane-terminated polymer in butyl acetate and Layer 2 is a polysiloxane-urethane resin in naphtha / butylacetate solvent.

Phase A

The analysis documents the properties of the coatings with respect to the wetting and adhesion of the substrate, the contact angle, the thickness of the coating and the stability against 1.2% of HNO3 in H2O, 1% of NaOH in H2O and the Raw oil. The results are summarized below in Table 1.

Table 1

 Layer 1 Layer 2

 Substrate Moistening

 Excellent Excellent

 Substrate adhesion

 Al: 0/0 Stainless steel: 0/0 Ti: 0/0 (see below) Al: 0/0 Stainless steel: 0/0 Ti: 0/0 (see below)

 Contact angle measurements

 H2O: 102-103 ° H2O: 102-103 °

 Coating thickness

 4-10 pm 2-4 pm

 Stability

 1.2% HNO3 in H2O: 1.5 h at 75 ° C 1% NaOH in H2O: 3 h at 85 ° C Crude oil: 6 months at room temperature 1.2% HNO3 in H2O: 1.5 h at 75 ° C 1% NaOH in H2O: 3 h at 85 ° C Crude oil: 6 months at room temperature

Both coatings showed excellent wetting when spray applied onto stainless steel or titanium substrates.

The adhesion was determined by cross-sectional test / tape according to DIN EN ISO2409. The rating is from 0 (excellent) to 5 (terrible). 0 or 1 is acceptable, while 2 to 5 is not. The first digit indicates the classification after the cross section (1 pm grid) and the second digit gives a rating after the tape has been applied and removed again. To obtain the best adhesion for Layer 1 and Layer 2, substrates require pretreatment.

To obtain the best adhesion of Layer 1 on stainless steel, the substrate must be pretreated. The substrate is immersed in an alkaline cleaning detergent for 30 minutes. Then, the substrate is washed with water and demineralized water and dried before applying Layer 1 in half an hour to achieve optimum adhesion. Tests have shown that adhesion is reduced if substrate cleaning is carried out only with acetone. Pretreatment is also necessary for stainless steel substrates coated with Layer 2. This coating showed unaltered adhesion regardless of whether an alkaline detergent or acetone was used as pretreatment. If the pretreatment stage is neglected or not performed correctly, it will affect the adhesion of the coating.

Both coatings showed good stability in acidic conditions. The coatings were stable for 1 hour at 75 ° C and more than 24 hours at room temperature.

Under alkaline conditions, Layer 1 showed a better result than Layer 2. Layer 1 could withstand alkaline conditions for 3 hours at 85 ° C and Layer 2 for 2 hours at 85 ° C. Both coatings showed no decomposition or reduction in oleophobic properties after submerging for 6 months in

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

60

65

crude oil at room temperature. Phase B

M3 heat exchanger plates with gaskets were partially coated and then analyzed. To examine whether partially coated joints would jeopardize the operation of the ICP, these tests included pressure tests. It was concluded that the partial coating of the joints with the coatings had no impact on the operation. M3 plates were not operated with crude oil.

C phase

ICP plate coating

Layer 1 and Layer 2 were applied to a total of 30 M20 titanium heat exchange plates (measuring 175 x 62 cm) used in a crude oil cooler. All plates underwent a pretreatment that consisted of:

1. Immerse in liquid nitrogen (-196 ° C) to remove seals

2. Treatment with acid and alkaline solutions to remove dirt

3. High pressure washing of the plates with water

4. Assembling the ICP stack for pressure testing

5. Disassembly of the ICP battery. The plates are allowed to dry before application

This pretreatment was completed the day before Layer 1 and Layer 2 were applied to the plates. Consequently, this procedure did not follow the recommended approach as described in Phase A. As the plates were allowed to dry at room temperature, some plates were still wet. 15 plates were treated with Layer 1 and the remaining 15 plates with Layer 2 by spray coating. The heat exchanger plates were coated on both sides and then placed on a rack. Since the plates had glued joints, both the plates and the joints were coated. The final thickness of the film was measured in 24 gm and the coating was applied on both sides of the plates. Curing / drying was performed at elevated temperatures of 200 ° C or 160 ° C, respectively, for 1 hour and a half in an oven on site. Upon completion, the coated heat exchangers were weighed and the thickness of the coating was measured. It was noted that some plates had some imperfections and small coating defects.

All plates were marked with a unique number for later identification.

The heat exchanger plates were then assembled with the remaining 319 untreated plates. The coated plates were placed respectively in the front, center and end of the assembled unit and the position of the coated plates in the ICP stack is shown in Figure 1. The evaluation of the coated plates was performed after more than seven months of operation

The plates that later, after the completion of the operation at sea, were selected for a detailed analysis, were placed in the left positions (plate No. 3 and 6), center (plate No. 12 and 17) and right (plate # 22 and 29) in Figure 1.

Phase D

Determination of the content in the coating by XPS analysis

Three different Ti substrates coated with silicon oxide were analyzed before and after use by means of XPS (X-ray photoelectron spectroscopy), also known as ESCA (electron spectroscopy for chemical analysis). The XPS method provides quantitative chemical information, the chemical composition expressed in atomic%, for the outermost parts of 2-10 nm of the surfaces.

The measurement principle is that a sample, placed in high vacuum, is irradiated with well-defined X-ray energy that results in the emission of photoelectrons. Only those photoelectrons of the outermost surface layers reach the detector. By analyzing the kinetic energy of these photoelectrons, their link energy can be calculated, thus giving their origin in relation to the element and the electronic layer.

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

XPS spectra were recorded using a Kratos AXIS UltraDLD X-ray photoelectron spectrometer. Samples were analyzed using a monochromatic X-ray source of Al. The analysis area was per

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

below 1 mm2.

In the analysis, broad spectra were run to detect elements present in the surface layer. The relative surface compositions were obtained from the quantification of the detailed spectra executed for each element.

The following three samples were analyzed with XPS:

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

2. Silicon oxide (used) in Ti plate - coating on one side

3. Silicon oxide in stainless steel plate with DIN 1.4401, coating on both sides.

The analysis was performed in one position per sample, with the exception of sample 1, where two positions were analyzed. The results are summarized in Table 2 which shows the relative surface composition in atomic% and O / Si atomic ratio.

Table 2

 Sample

 O / Yes C O Yes N

 1 new (pt1)

 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) *

* weak peak in detailed spectra, signal close to noise level

As seen in Table 2, mainly C, O and Si were detected on the outermost surfaces, that is, 41.968.0% atomic, 19.5-34.3% atomic and 8.6-23.4% atomic .

Note that in the O / Si atomic ratios, the total amount of oxygen is used. This means that oxygen is also included in functional groups with carbon. On the contrary, for silica, the theory expects an O / Si ratio of 2.0 for pure SiO2 mass silica.

Inspection during operation

After four months of operation, a previous inspection was carried out at sea by thermography. Thermography of the middle region of the heat exchanger in operation. The identity of the two coating systems was assumed from the installation, but it was obvious that two groups of ICP plates show greater heat transfer compared to the rest of the ICP unit.

The inspection showed a temperature rise in the coated plates. The uncoated plates showed a lower operating temperature. The difference in temperature is presumed due to less dirt, therefore, a greater flow of crude oil in the coated region that produces an elevated temperature.

Inspection of plates after operation

The term dirt is used to describe deposits formed on ICP plates during operation. Dirt is waste and deposits formed by crude oil and consist of a waxy, organic part and a mineral / inorganic part.

Visual inspection revealed that the plates with the coating designated as Layer 1 were covered with the least amount of dirt on the side of the plate facing crude oil. In addition, the other coating system designated Layer 2 had a reduced amount of dirt on the side of the front plate of crude oil compared to the bare titanium surface, but to a lesser extent than Layer 1. The bare titanium plates in the end of the plate filling were completely covered with a thick layer of dirt derived from crude oil.

The images taken at sea during disassembly (Fig. 2) showed a significant reduction of fouling on both coated plates compared to uncoated plates.

By subtracting the average weight of a clean plate from the weight recorded for the individual dirty plates, the average amount of dirt was calculated by type of surface (table 3). It should be borne in mind that the weight of the coating was not compensated and, therefore, the actual reduction in fouling is slightly greater. For a T20-M plate, the heat transfer surface is 0.85 m2, so for a plate with a 4 pm thick coating on the front and back, the total volume is around 6.8 cm3 If it is estimated that the coating

5

10

fifteen

twenty

25

It is pure SIO2 (density 2.6 g / cm3), so the amount of coating per plate is approximately 20 g.

Table 3

 Surface

 Average fouling * (g) STDEV Reduction of fouling (%)

 Titanium

 585 125 -

 Layer 1

 203 48 65

 Layer 2

 427 144 27

For both coating systems, the fouling of the plates was more easily removed compared to the fouling adhered to the bare titanium surface, see Table 4. The difference in cleaning requirements was analyzed by manually cleaning the plates with a handkerchief. paper and by cleaning with high pressure water. Just cleaning the plates with a tissue showed that dirt was easily removed from the coated plates, unlike uncoated plates. By using a water jet, all dirt, with the exception of one or two small patches, could be removed from the coated surface of Layer 1. On the coated surface of Layer 2, there was more dirt after cleaning with Waterjet. This dirt looked like a slightly burned oil.

Some loss of coating was observed at the contact points, but in general the coated surface that had been in contact with the crude oil was in good condition.

On the sea-facing side, both coatings had deteriorated and could be removed quite easily.

Table 4

 Layer 1 Layer 2 Uncoated

 View

 very little dirt compared little dirt important dirt compared and extended

 Cleaning with a tissue

 very easy to clean the dirt very easy to clean the dirt the dirt was not removed

 High pressure water cleaning

 the plates appeared as new most of the dirt was removed even after attempts to manually remove the dirt, there is still a considerable layer

The tolerance of the coating to immersion in liquid nitrogen for joint removal was analyzed. A Layer 1 and a Layer 2 plate were treated in liquid nitrogen, at -196 ° C, to remove the rubber seals. The coatings do not seem to undergo extreme temperature changes. Subsequently, the plates were washed with high pressure water, which removed almost all the dirt. No delimitation or failure in the coating was observed for any of the coating systems.

Claims (4)

5 10 fifteen twenty 25 1. A plate with gasket for a plate heat exchanger, characterized in that said plate has a coating comprising silicon oxide, SiOx, which has an atomic ratio of O / Si> 2, a carbon content> 30% atomic and a coating layer thickness of 3-10 pm, which coating was prepared by sol-gel processing and applied to at least a portion of the plate, wherein said coating is applied to the surface of the joint designated to be in contact with at least one fluid when the plate is in a plate heat exchanger in use, and wherein said plate is made of a base material selected from titanium, nickel, copper, any alloy of those mentioned above, stainless steel or Carbon Steel. 2. A plate filling for a plate heat exchanger, characterized in that it comprises several plates of the types defined in claim 1. 3. A plate heat exchanger, characterized in that it comprises several heating plates of the type defined in claim 1. 4. Method for producing a gasket plate for a plate heat exchanger according to claim 1, comprising the steps of: a) form a plate of a base material, b) prepare a composition comprising organosilicon compounds by means of solder processing and apply it to at least a part of the plate, c) drying and / or curing said coating, after which the coating on the plate comprises silicon dioxide.