EP3566794A1 - Lubricant, use of a lubricant and heat exchanger - Google Patents

Abstract

The invention relates to a lubricant for a cleaning device (10) of a heat exchanger (13) comprising at least 30% polytetrafluoroethylene, at least 0.5% graphite, and at least 0.5% molybdenum disulfide. Furthermore, the invention relates to a use of the lubricant for a cleaning device (10) of a heat exchanger (10) and a heat exchanger.

Description

The invention relates to a lubricant for a cleaning device of a heat exchanger, a use of a lubricant for friction reduction for a cleaning device of a heat exchanger and a heat exchanger. The invention is therefore particularly in the field of heat exchangers.

Heat exchangers for heating or for cooling a working medium are widely known from the prior art. Without restricting generality, the working medium natural gas will be considered in more detail below. Natural gas from soil reservoirs often has a particularly high percentage of unwanted accompanying substances and particularly high proportions of water. It is desirable to remove the impurities as well as the water content from the natural gas before it is used for further purposes. One possibility for this is the cooling of the natural gas in one or more steps to suitable low temperatures. In particular, in this case, a liquefaction of the natural gas may be appropriate.

During the cooling of natural gas, sediments on the heat transfer surfaces usually occur due to the aforementioned accompanying substances in the heat exchanger, the time course of such deposits depending on the operating conditions and the respective natural gas composition. The heat transfer surfaces must therefore be cleaned at certain intervals. For the reasons mentioned, however, it is difficult to specify generally valid cleaning intervals for the relevant heat exchangers.

Condensing and freezing impurities such as water, CO ₂ and hydrocarbon compounds separate on the heat transfer surfaces and thus reduce the heat transfer. Even at operating temperatures above the freezing point of water, it may also come to the heat transfer surfaces to form methane hydrate.

Cylinder tubes of heat exchangers can therefore be provided with a cleaning device, by means of which deposits from the heat transfer surfaces in the cylinder tubes can be removed mechanically. For example, the DE 10 2015 010 455 A1 such a cleaning device.

Such cleaning devices often have a high degree of friction and wear, as many conventional lubricants are not applicable to the prevailing in the heat exchanger temperature ranges. In addition, discharges of lubricant can lead to contamination of the working medium to be heated or cooled in the heat exchanger.

It is therefore the object of the present invention to provide a lubricant and a heat exchanger, which allow a reliable reduction of the friction of a cleaning device of a heat exchanger.

This object is achieved by a lubricant, a use of a lubricant and a heat exchanger having the features of the respective independent claims. Preferred embodiments are subject of the dependent claims and the description below.

In a first aspect, the invention relates to a lubricant for a cleaning device of a heat exchanger, comprising or consisting of at least 30% polytetrafluoroethylene, at least 0.5% graphite, and at least 0.5% molybdenum disulfide.

In a further aspect, the invention relates to the use of the lubricant according to the invention for friction reduction for a cleaning device of a heat exchanger.

In a further aspect, the invention relates to a heat exchanger with a cylinder tube and a cleaning device with a coaxially extending in the first cylinder tube threaded spindle, wherein on the threaded spindle a cleaning element is mounted such that by rotation of the threaded spindle, the cleaning element in the axial direction along the threaded spindle in the cylinder tube is displaceable. A first contact surface between the cleaning element and an inner wall of the cylinder tube and / or a second contact surface between the cleaning element and the threaded spindle are at least partially coated with a lubricant according to the invention.

The fact that the first and / or the second contact surface are at least partially coated with a lubricant means that the first and / or the second contact point are coated at least in places with the lubricant. In other words, it is not absolutely necessary, albeit advantageous, for the entire first contact surface and / or the entire second contact surface to be coated with the lubricant. In addition, points of the cylinder tube and / or the threaded spindle and / or the cleaning element may be coated with the lubricant, which do not form part of the first and / or the second contact surface.

The invention has the advantage that a reduction of the friction between the cylinder tube and / or the threaded rod can be achieved, whereby a material abrasion and / or wear on the cleaning device and / or on the heat exchanger can be avoided. This can in turn repair-related downtime or downtime can be reduced and / or a required maintenance can be reduced. Thus, the operating costs can be reduced.

Due to the reduced friction further, the required driving force for rotating the threaded rod can be reduced. Thus, for a heat exchanger with a lubricant coating according to the invention, a less powerful drive element or a less powerful motor may be sufficient than is required in conventional heat exchangers.

In addition, the invention has the advantage that with the lubricant according to the invention, even at very low temperatures, as prevail in particular in the cooling and / or liquefaction of gases in the heat exchanger, an effective reduction in friction can be achieved. In particular, the lubricant according to the invention is suitable for ensuring reliable lubrication of the surfaces provided therewith even at temperatures between 0 K and 273 K. In particular, the invention offers the advantage that the lubricant according to the invention can be used even at significantly lower temperatures than conventional lubricants based on oils and / or fats and therefore typically lose a high degree of lubricating action below a temperature of about 223 K, further freeze and / or solidify and thus almost completely lose their lubricating effect.

Preferably, the lubricant comprises at most 99% polytetrafluoroethylene and / or at most 50% graphite and / or at most 50% molybdenum disulfide or consists of these proportions. More preferably, the lubricant comprises at least 80% and at most 99% polytetrafluoroethylene and / or at least 0.5% and at most 2% graphite and / or at least 0.5% and at most 2% molybdenum disulfide or consists of these proportions. This offers the advantage that particularly advantageous properties of the lubricant can be achieved with regard to the lubricating effect and with regard to temperature stability. In particular, a high proportion of polytetrafluoroethylene can lead to particularly advantageous properties at low temperatures.

Preferably, the cylinder tube has on the inner wall at least one guide groove, wherein the first contact surface is at least partially formed by the guide groove. Thereby, a precise and controlled movement of the cleaning element can be achieved, which can be designed accordingly to follow upon rotation of the threaded spindle of the guide groove. In particular, the cleaning element may have one or more outer grooves, which may be designed to engage in the at least one guide groove of the cylinder tube.

The threaded spindle preferably has an external thread and the cleaning element has an internal thread which at least partially forms the second contact surface. This offers the advantage that by rotating the threaded rod about the longitudinal axis, which extends in the axial direction, leads to a movement of the cleaning element in the axial direction.

A layer thickness of the lubricant at the first contact surface and / or at the second contact surface is preferably at least 20 μm and at most 200 μm, particularly preferably at least 50 μm and at most 100 μm. The lubricant may be distributed in uniform thickness or in uneven thickness over the respective contact surface or at least a part thereof. Also can the lubricant may be disposed on the first contact surface in a different thickness or thickness than on the second contact surface. At the first contact surface and / or at the second contact surface, the lubricant may be applied on one side or on two sides. That is, at the first contact surface, the lubricant may be attached to the inner wall of the cylinder tube or in the at least one guide groove or on an outer surface of the cleaning element or both on the inner wall of the cylinder tube and in the at least one guide groove as well as on an outer surface of the cleaning element , Accordingly, the lubricant may be attached to the threaded spindle or to the cleaning element or both to the threaded spindle and to the cleaning element on the second contact surface.

The coating can be done for example by spray-sintering. The coating forms a PTFE (Teflon®) compound of solid state in which the dry lubricants graphite and MoS ₂ are arranged.

The cleaning element preferably comprises or consists at least partially of a carbon-comprising or consisting of carbon surface coating. In other words, the cleaning element has a different coating from the material, which, however, can also serve to reduce friction. Particularly preferably, the surface coating comprises or consists of a hydrogen-containing, amorphous carbon layer. This offers the advantage that a particularly good reduction in friction can be achieved by an interaction of the surface coating of the cleaning element with the lubricant.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is schematically illustrated by means of preferred embodiments in the drawings and will be described below with reference to the drawings.

Brief description of the figures

• FIG. 1 schematically shows a longitudinal section through a preferred embodiment of a heat exchanger.
• FIG. 2 shows a cylinder tube of a heat exchanger according to a preferred embodiment.
• FIG. 3 shows a cleaning element according to a preferred embodiment.

Detailed description of the figures

FIG. 1 schematically shows a longitudinal section through an embodiment of a heat exchanger 13, as it can be used in particular for cooling natural gas. In this simple embodiment, the heat exchanger 13 has an outer cylinder tube 1, which surrounds a cylinder tube, which is designed as a cooling coil 2. This cooling coil 2 has at least one, preferably spiral, channel 23 on its outer surface, which serves to guide a coolant. This channel 23 is generated by a corresponding helix 21 on the outer surface of the cooling coil 2. The inner surface of the hollow cylindrical cooling coil 2 has guide grooves 22 which serve to guide a cleaning element 12, which is also referred to as a scraper. For example, the cleaning element 12 may be formed as an ice scraper.

The heat exchanger 13 has a cleaning device 10, which has a threaded spindle 3 located in the interior of the cooling coil 2 and extending in an axial direction 100. The threaded spindle 3 is driven by a coupling element 30 and is mounted in a bearing point, which is preferably designed as an axial / radial mixing bearing 5. At the other end of the threaded spindle 3, this can be stored in a radial bearing, which is preferably designed as a plain bearing bush (not shown). At the other end of the heat exchanger 13 may also be present a thermally decoupled condensate reservoir and a heating element for heating condensate in the condensate reservoir to melt the discharged through the cleaning element 12 there condensate and dissipate.

By rotating the threaded spindle 3, the cleaning element 12 is displaced on the threaded spindle 3 along the cooling coil 2 in the axial direction. In the present example, a threaded spindle 3 is used for example with trapezoidal profile. A reversal of the direction of movement of the reamer 12 requires a reversal of the direction of rotation of the threaded spindle 3.

The cylinder tube or the cooling coil 2 is coated on the inner wall 2a with a lubricant, which serves to reduce the friction between the cleaning element 12 and the cooling coil 2, which form a first contact surface. The lubricant according to the invention comprises polytetrafluoroethylene, graphite and molybdenum sulfide. Alternatively or additionally, the inner wall 21 a of the cylinder tube or the cooling coil 2 facing the outside of the cleaning element 12 may be coated with the lubricant. Furthermore, the external thread of the threaded spindle 3 and / or the Innengwinde of the cleaning element 12 is coated with the lubricant to reduce friction at this point of contact.

During operation of the heat exchanger 13, for example, moist, contaminated working medium is introduced into the intermediate space between threaded spindle 3 and between cooling coil 2 or into the interior of the cylinder tube via a working medium inlet opening 14 on both sides and flows in the axial direction 100 to the working medium outlet opening (not shown) The working medium flows on the inner surface of the hollow cylindrical cooling coil 2 along the axial direction 100. Coolant is supplied to the space between the cooling coil 2 and the outer cylinder tube 1 via a coolant inlet opening 16 on both sides, the coolant being supplied to the other end of the heat exchanger 13 flows and leaves through the coolant outlet opening (not shown). In this case, the coolant flows spirally in the axial direction in the channel 23 formed between the outer cylindrical tube 1 and the cooling coil 2. The coolant removes heat from the cooling coil 2, which in turn removes heat from the working medium.

Due to the different pressure ratios between the cooling medium, for example nitrogen at a maximum of 10 bar, and the working medium, here CNG with impurities including nitrogen from 4 to 220 bar, nitrogen as a companion at high pressure (eg. At 10 bar) by liquid nitrogen at low Pressure (eg at 1 bar), caused by the different pressure-dependent phase transitions to liquefy and deposited. The heat exchanger 13 proposed here can thus also be used for the liquefaction of nitrogen.

For the purpose of cleaning the heat transfer surfaces, for example of water or ice in the first stage or of higher hydrocarbons, CO ₂ and / or other impurities, the threaded spindle 3 is rotated by a drive element via the coupling element in rotation. The cleaning element 12, which engages in the thread of the threaded spindle 3 and thereby forms a second contact surface, is thereby displaced in a translational movement in the axial direction. Due to the lubricant provided at the two contact surfaces, the movement of the cleaning element 12 can take place with little friction. On its way in the axial direction, the cleaning element 12 takes with it the aforementioned condensed accompanying substances. These are pushed into the same upon reaching the condensate reservoir at the other end of the heat exchanger.

It should be noted that the heat exchanger 13 explained here can be adapted and used not only for natural gas liquefaction but also for a large number of industrial applications with appropriate working media. The cleaning device 10 and / or the cleaning element 12 can be adapted as a little complex replacement parts to the needs of the respective applications and quickly replaced in the event of damage.

FIG. 2 shows a cylinder tube of a heat exchanger 13, which is designed as a cooling coil 2, according to a preferred embodiment. It can be seen that the channel 23 is generated by a corresponding cooling coil 2 on the outer surface of the cooling coil 2. The inner surface or inner wall 2a of the hollow cylindrical cooling coil 2 has guide grooves 22. This at least one guide groove 22 serves to guide a cleaning element or reamer 12 and is coated according to this preferred embodiment with inventive lubricant, so that the cleaning element 12 can be moved as low friction by the cooling coil 2 and by the guide grooves 22.

FIG. 3 shows a cleaning element 12 according to a preferred embodiment, as it can be used in the heat exchanger 13. Shown are the outer grooves 122 of the cleaning element 12, which correspond to the guide grooves 22 of the cooling coil 2 and engage in this. The internal thread 121 of the cleaning element 12 corresponds to the thread of the threaded spindle 3. The cleaning element 12 has recesses or milled slots 123. By the latter, the cleaning element 12 "teeth" or "claws", which prevent accumulate deposits in the thread and lead to a blocking of the cleaning element 12. The deposits can namely enter through the recesses or milled slots 123 into the intermediate space and fall downwards in the vertical position of the heat exchanger 13 in the direction of the condensate reservoir. Furthermore, the inner diameter of the reamer 12, which increases in the direction of movement of the cleaning, serves for easier insertion into the contaminated threaded spindle at the beginning of the cleaning process. The cleaning element 12 is provided according to this preferred embodiment with a surface coating, which consists of a hydrogen-containing, amorphous carbon layer. Furthermore, the coating consists of hydrogen-free, amorphous carbon layers in which the sp ³ -hybridized carbon bond fraction is higher than in the hydrogen-containing coatings. The surface coating may be limited to the outer surface and / or the outer grooves 122 and / or the inner thread 121 or be formed on the entire cleaning element 12. By the surface coating, the friction between the internal thread 121 and the threaded rod 3 and / or between the outer surface of the cleaning element and the inner wall 2a of the cooling coil 2 can be reduced. Optionally, the outer surface of the cleaning element 12 and / or the internal thread 121 may be provided with lubricant according to the invention in order to further reduce the friction.

reference numeral

1

Outer cylinder tube

2

cooling coil

2a

Inner wall of the cooling coil

3

screw

5

Axial / radial mixing camp

10

cleaning device

12

cleaning element

13

heat exchangers

14

Working fluid inlet port

16

Coolant inlet opening

21

Spiral on the outer surface of the cooling coil

22

guide

23

Channel of the cooling coil

30

coupling member

100

axial direction

121

Internal thread of the cleaning element

122

Outer groove of the cleaning element

123

milled

Claims (11)

A lubricant for a cleaning device (10) of a heat exchanger (13) comprising at least 30% polytetrafluoroethylene, at least 0.5% graphite, and at least 0.5% molybdenum disulfide. A lubricant according to claim 1, wherein the lubricant comprises at most 99% polytetrafluoroethylene and / or at most 50% graphite and / or at most 50% molybdenum disulfide. A lubricant according to claim 1 or 2, wherein the lubricant comprises at least 80% and at most 99% polytetrafluoroethylene, and / or wherein the lubricant comprises at least 0.5% and at most 2% graphite, and / or wherein the lubricant is at least 0.5% and at most 2% molybdenum disulfide. Use of a lubricant according to one of the preceding claims for friction reduction for a cleaning device (10) of a heat exchanger (13). Heat exchanger (13), comprising: a cylinder tube; - A cleaning device (10) with a coaxially extending in the first cylinder tube threaded spindle (3), wherein on the threaded spindle (3) a cleaning element (12) is mounted such that by rotation of the threaded spindle (3), the cleaning element (12) in the axial direction (100) is displaceable along the threaded spindle (3) in the cylinder tube; wherein a first contact surface between the cleaning element (12) and an inner wall (2a) of the cylinder tube and / or a second contact surface between the cleaning element (12) and the threaded spindle (3) are at least partially coated with a lubricant according to one of claims 1 to 3 , Heat exchanger (13) according to claim 5, wherein the cylinder tube on the inner wall (2a) has at least one guide groove (22) and wherein the first contact surface is at least partially formed by the guide groove (22). Heat exchanger (13) according to claim 5 or 6, wherein the threaded spindle (3) has an external thread and the cleaning element (12) has an internal thread (121) which at least partially form the second contact surface. Heat exchanger (13) according to one of claims 5 to 7, wherein a layer thickness of the lubricant at the first contact surface and / or at the second contact surface is at least 20 microns and at most 200 microns, preferably at least 50 microns and at most 100 microns. Heat exchanger (13) according to one of claims 5 to 8, wherein the cleaning element (12) at least partially comprises a carbon-comprising surface coating. A heat exchanger (13) according to claim 9, wherein the surface coating comprises a hydrogen-containing, amorphous carbon layer. A heat exchanger (13) according to claim 9, wherein the surface coating comprises a hydrogen-free, amorphous carbon layer consisting of more than 50% sp ³ -hybridized carbon.

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