Detecting deposition and / or pollution conditions on a sensor surface within a vessel or

Abstract

The invention relates to a detection device (1) for detecting deposits and / or contaminants on a sensor surface (3) within a vessel or a pipe having a flowing medium (40), the detection device (1) comprising: a detection section (25) having the sensor surface (3) and configured to be arranged within the vessel or within the pipe and to be in contact with the flowing medium (40), the invention relates to a sensor (1) comprising a reference surface (21), a heat-conducting base body (2) having a sensor surface (3) or in direct contact with the sensor surface, a heat source or cold source (7) arranged on the base body (2) for generating a main heat flow (Q1) between the heat source or cold source (7) and the sensor surface (3) and a secondary heat flow (Q2) between the heat source or cold source (7) and the reference surface (21), a first temperature sensor (4) arranged on the base body (2) at a first distance from the sensor surface (3) and a second temperature sensor (5) arranged on the base body (2) at a second distance from the sensor surface (3), the second distance being greater than the first distance, a temperature difference being ascertainable by means of the temperature sensors (4, 5), a heat-conducting coating (19), the invention relates to a detection device (1) comprising a base body (2) having a detection section (25), a covering body (19) which covers a portion of the base body (2) arranged outside the detection section and which has a reference surface (21), the reference surface (21) being part of the detection section (25), and an outer isolation (22) which separates the covering body (19) from the external surroundings thereof.

Description

Technical Field

[0001] The invention relates to a detection device for detecting deposits and / or contaminants on a sensor surface in a vessel or a pipe with a flowing medium. Another subject of the invention is a detection assembly for detecting deposits and / or contaminants of a flowing medium on the wall of a vessel or a pipe, the detection assembly having such a detection device. In addition, the invention also relates to a method for detecting deposits and / or contaminants on a sensor surface in a vessel or a pipe with a flowing medium using a first detection device. Background Art

[0002] DE 10 2009 009 592 A1 discloses that two temperature sensors are arranged on the outside of a pressure tube of a heat exchanger in an undulation in order to determine the heat flow between the two temperature sensors. In addition, a third temperature sensor is provided, wherein a further heat flow is determined using the temperatures measured by the three temperature sensors. The changes in the two heat flows over time are monitored and the contamination of the outside of the pressure tube is determined therefrom. A disadvantage of this method is that the contamination can only be determined if there is a temperature difference between the inside and the outside of the pressure tube. This temperature difference is caused by the process. This severely limits the reliable detection of deposits in all operating points of the pressure tube and greatly reduces the measurement accuracy.

[0003] WO 2014 / 099 755A1 describes a method for detecting deposits and / or contaminants caused by a liquid flowing medium on the surface of a heated sensor. The sensor is arranged in a conduction unit through which the medium flows, and comprises a heat-conducting block with a heating device, the main heat flow generated by the heating device flows to the sensor surface through the block. The secondary heat flow is lost to the surrounding environment via the side of the block opposite to the sensor surface. The deposits and / or contaminants on the sensor surface increase the thermal resistance in the main heat flow path, while the secondary heat flow is not affected by these deposits. The block comprises two temperature sensors, which are arranged at different distances from the sensor surface and can measure the temperature difference by these temperature sensors. If the temperature at the end of the secondary heat path (i.e., the ambient temperature) is constant, the temperature difference of the temperature sensors is linearly related to the thickness of the deposits on the sensor surface. Therefore, the method can determine the deposits and / or contaminants on the sensor surface by measuring the temperature difference of the heat-conducting block that guides the main heat flow. However, it has been found to be disadvantageous in this known method that if the properties of the medium to which the sensor surface is exposed change, such as changes in temperature, flow rate, viscosity or concentration of components of the medium, inaccuracies may occur when determining the thickness of the deposits and / or contaminants. In order to avoid these inaccuracies, WO 2014 / 099 755A1 proposes that the same medium as the sensor surface flows around the other sides of the heat-conducting block, so that the surrounding environment of the block has the same temperature as the temperature of the medium. Thus, the temperature change of the liquid medium affects not only the main heat flow but also the secondary heat flow, and they compensate each other. However, in such a case where there is flow around the sensor on all sides, additional pipes for the medium are required and a relatively large structural space is required. Summary of the invention

[0004] The object of the invention is to enable reliable detection of deposits and / or contamination situations using a compact detection device when the properties of the flowing medium causing deposits and / or contamination, such as temperature, flow velocity, viscosity and / or component concentration, change.

[0005] In order to achieve this object, a detection device for detecting deposits and / or contamination on a sensor surface in a vessel or a pipeline with a flowing medium is proposed, wherein the detection device comprises:

[0006] a detection section which has a sensor surface and is designed to be arranged within a vessel or within a pipeline and to be in contact with the flowing medium,

[0007] a thermally conductive substrate which has the sensor surface or is in direct contact with the sensor surface,

[0008] a heat source or a heat sink arranged on the substrate for generating a primary heat flux between the heat source or the heat sink and the sensor surface, and a secondary heat flux between the heat source or the heat sink and the reference surface,

[0009] a first temperature sensor arranged on the substrate at a first distance from the sensor surface and a second temperature sensor arranged on the substrate at a second distance from the sensor surface, wherein the second distance is greater than the first distance, wherein a temperature difference can be determined by means of the temperature sensors,

[0010] a thermally conductive covering which covers a portion of the base body arranged outside the detection section and has a reference surface,

[0011] Therein, the reference surface is part of the detection section, and the detection device comprises an outer insulation portion which isolates the enclosure from its external surroundings.

[0012] The heat-conducting substrate either has a sensor surface on which deposits and / or contaminants can be detected, or is in direct contact with the sensor surface. The first temperature sensor and the second temperature sensor are arranged at different distances from the sensor surface. The heat source or cold source arranged on the substrate can adjust the temperature gradient in the substrate, which is proportional to the main heat flow. When the sensor surface does not change, the temperature gradient is constant. Even if there are fewer deposits and / or contaminants on the sensor surface, it will cause an increase in thermal resistance, that is, a decrease in the main heat flow, and the increase in thermal resistance can be measured as a change in the temperature difference between the first temperature sensor and the second temperature sensor. Since the heat source or cold source is arranged on the substrate, the temperature difference between the first temperature sensor and the second temperature sensor can be adjusted in principle even when the temperature difference between the sensor surface and the surrounding environment of the substrate is small. Therefore, the contaminants or deposits on the sensor surface can be reliably detected. The detection device according to the present invention also includes a heat-conducting coating, which covers the substrate in an area outside the detection area, that is, outside the vessel or pipeline. The coating guides the secondary heat flow and has a reference surface, which (like the sensor surface) is arranged in a vessel or a pipe so as to be in contact with the flow medium to be monitored. The formation of deposits or contaminants on the sensor surface causes a measurable change in the ratio of the primary heat flow to the secondary heat flow. Therefore, the detection device according to the present invention can achieve reliable determination of the contaminant or deposit situation. According to the present invention, it is proposed that the detection section that is set up to be arranged in a vessel or a pipe and in contact with the flow medium has not only a sensor surface, but also a reference surface. In addition, the coating is isolated from the surrounding environment by an external isolation part. Therefore, the primary heat flow (flowing to the sensor surface) and the secondary heat flow (flowing to the reference surface) are both guided to the flow medium in the vessel or the pipe. Therefore, changes in the liquid (such as changes in temperature, flow rate, viscosity and / or component concentration) affect the primary heat flow and the secondary heat flow, and will not cause inaccuracies in detecting deposits and / or contaminants. The enclosure is isolated from the surroundings by an outer insulation, so that neither a liquid is required to flow around the enclosure nor active cooling or active heating is required. In the detection device according to the invention, additional pipes for the liquid or measures for temperature control of the enclosure can be omitted. This enables a compact design that saves structural space.

[0013] Unlike the prior art, for example, according to WO 2014 / 099 755 A1, deposits and / or contamination can also form on the reference surface, since in the detection device according to the invention the reference surface is in contact with the liquid. Since the secondary heat flow through the reference surface is lower than the main heat flow through the sensor surface, the temperature reached on the reference surface is lower than the temperature reached on the sensor surface, so that the formation of deposits and / or contamination on the reference surface can be kept as low as possible.

[0014] The flowing medium in the vessel or pipe may be a liquid medium or a gaseous medium, or may be a medium that is partly liquid and partly gaseous.

[0015] Preferably, the outer insulation isolates the enclosure from its external surroundings, so that the secondary heat flux is greater than the parasitic heat flux between the heat source or the heat sink and the surroundings through the enclosure and the outer insulation.

[0016] The covering body can be made of metal, for example. Preferably, the covering body is made of titanium. Alternatively, it can be provided that the covering body is made of plastic.

[0017] Preferably, the detection section is a detection surface. In this respect, the sensor surface and the reference surface can be arranged flush with each other.

[0018] If the detection device has a heat source, the heat source is preferably designed as an adjustable, particularly preferably controllable, and especially controlled heat source. If the detection device has a cold source, the cold source is preferably designed as an adjustable, particularly preferably controllable, and especially controlled cold source. The heating power or cooling power can be specified by an adjustable heat source or cold source. The advantage of this design is that the temperature at the sensor surface can be affected by adjusting the heat source or cold source. Therefore, the temperature of the sensor surface can be adapted to the temperature of the flowing medium applied to the sensor surface. In addition, the detection device can also be used to simulate heat transfer through the wall of a process vessel or process pipeline. For example, the calculated temperature at the reference point within the matrix can be adjusted so that the temperature corresponds to the temperature at the inner wall or outer wall of the process vessel or process pipeline. The distance between the reference point and the sensor surface can be selected in the following manner so that the distance (taking into account the thermal conductivity of the material) corresponds to the wall thickness of the wall of the process vessel or process pipeline.

[0019] A design solution that has proven to be advantageous for the design structure is that the heat source or the cold source and the first temperature sensor and the second temperature sensor are arranged along a virtual straight line.

[0020] The heat source can be designed as a heating element, for example, as an electric heating element, in particular a resistance heating element. The heat source can be designed as a Peltier element, for example.

[0021] Preferably, a first recess is provided in the base body, in which a first temperature sensor is arranged, and / or a second recess is provided, in which a second temperature sensor is arranged, and / or a third recess is provided, in which a heat source or a cold source is arranged. The provision of the recess enables the corresponding temperature sensor or the heat source or the cold source to be permanently fastened to the base body with less manufacturing effort. The third recess in which the heat source or the cold source is arranged is preferably arranged on the rear surface of the base body opposite to the sensor surface. The first recess and the second recess in which the temperature sensor is arranged are preferably arranged between the sensor surface and the rear surface. The first recess, the second recess and / or the third recess can be respectively designed as the bevel of the outer wall of the base body, especially in the shape of a cylinder. Alternatively, the first recess, the second recess and / or the third recess can be designed as a blind hole.

[0022] According to an advantageous design, the base body is rod-shaped, in particular has a circular cross section. Alternatively, it can be provided that the base body has a triangular, quadrilateral, pentagonal, hexagonal, heptagonal, octagonal or polygonal cross section.

[0023] An advantageous embodiment of the invention provides that the thermal conductivity of the substrate is isotropic and uniform. This means that the thermal conductivity of the substrate is the same over its entire extension range and is independent of the direction in which the heat conduction occurs. In this embodiment, a linear temperature curve can be achieved in the substrate from the heat source or the cold source to the sensor surface. The substrate is made in particular of one of the following materials: steel, copper, brass, in particular CuZn39Pb3 (formerly known as Ms 58).

[0024] According to a favorable design solution, the detection device includes a third temperature sensor, which is arranged on the substrate at a third distance from the sensor surface, wherein the third distance is greater than the second distance. Preferably, the heat source or cold source and the first temperature sensor, the second temperature sensor and the third temperature sensor are arranged along a virtual straight line. It is advantageous in the design structure that the substrate includes another recess, such as another blind hole, in which the third temperature sensor is arranged. Additional information can be obtained by the third temperature sensor, which further improves the detection of deposits and / or contaminants. For example, if the first temperature sensor or the second temperature sensor fails or cannot measure the temperature for other reasons, the third temperature sensor can be used instead of the first temperature sensor or the second temperature sensor. In addition, the temperature difference between the first temperature sensor and the second temperature sensor and the temperature difference between the second temperature sensor and the third temperature sensor can be determined. According to these temperature differences and the corresponding distances between the temperature sensors, the temperature gradient between the first temperature sensor and the second temperature sensor and the temperature gradient between the second temperature sensor and the third temperature sensor can be obtained. In an ideal case, these temperature gradients must be the same. If the temperature gradients differ from one another, it can be inferred from this that heat loss is occurring perpendicularly to the line between the heat source or heat sink and the sensor surface. This could indicate, for example, poor insulation or undesired intrusion of the medium into the detection device.

[0025] It is preferably provided that the heat source is arranged at a fourth distance from the sensor surface, wherein the fourth distance is greater than the second distance and, if appropriate, greater than the third distance.

[0026] A design of the invention which has proven to be advantageous is that the detection device comprises an isolating device surrounding the base body, the isolating device being arranged between the outer contour of the base body and the inner contour of the encapsulation body. In this design, the isolating device is located in the path of the second heat flow. Preferably, in the absence of deposits and / or contaminations on the sensor surface, the thermal resistance of the second heat path is higher than the thermal resistance of the first heat path.

[0027] A configuration is advantageous in which the insulating device surrounding the base body has the same thermal resistance on all sides of the base body. In particular, the insulating device has the same thermal resistance on the end side of the base body opposite the sensor surface and on the radial circumferential surface of the base body.

[0028] A favorable design scheme proposes that the insulating device surrounding the substrate has a bulk material or a porous material, such as a sponge. The bulk material preferably has particles with a particle size (volume equivalent spherical diameter) in the range of 1 micron to 10 mm, preferably in the range of 1 micron to 1 mm, particularly preferably in the range of 1 micron to 100 microns, for example in the range of 1 micron to 10 microns. The particle size distribution of the bulk material is preferably as uniform as possible. The bulk material preferably includes organic particles, such as foamed polyester alcohol, and / or inorganic particles, such as minerals, mineral acid salts, volcanic ash or clay minerals. Preferably, the bulk material is arranged in an immovable manner between the substrate and the coating.

[0029] An alternative advantageous design solution provides that the insulating device surrounding the base body comprises a gas or a gas mixture, or a gas or a gas mixture, which is enclosed between the base body and the encapsulating body. For example, the gas mixture can be air.

[0030] Preferably, the outer insulation has an insulation body. An advantageous design solution provides that the outer insulation that isolates the encapsulation body from the surrounding environment has glass wool and / or wood wool and / or rock wool.

[0031] In order to achieve the purpose stated at the beginning, a detection component for detecting deposits and / or contamination of a flowing medium on the wall of a vessel or a pipe is also proposed, the detection component having the above-mentioned detection device, wherein a detection section having a sensor surface and a reference surface is arranged as a part of the wall.

[0032] By using such a detection device, it is possible to reliably detect deposits and / or contamination of the flowing medium on the wall of a vessel or a pipe. The detection device is arranged as a part of the wall of the vessel or the pipe, so that the deposition phenomena occurring on the sensor surface of the detection device are the same as the deposition phenomena occurring on the remaining wall.

[0033] The wall is preferably an inner wall, ie the inner surface of a wall. Alternatively, the wall may be an outer wall, ie the outer surface of a wall, such as the outer wall of a flame tube.

[0034] The vessel or pipeline can be, for example, part of a heat transfer system, in particular a heat exchanger, a reactor or a jacketed cooler, or a pipeline located upstream or downstream of such a heat transfer system. The vessel or pipeline can be part of a chemical facility, in particular a petrochemical facility, for example part of an evaporator facility, a cooling tower or a shell and tube heat exchanger.

[0035] An advantageous design of the detection assembly is provided with a plurality of the above-mentioned detection devices, wherein the detection section of the corresponding detection device having the sensor surface and the reference surface is provided as a part of the wall. This design with a plurality of detection devices can realize a redundant design of the detection assembly on the one hand. In addition, by providing a plurality of detection devices, these detection devices can be used to detect different deposits. Therefore, by adjusting the heating power of each heat source of the detection device or the cooling power of each cold source to be different, the temperature on the corresponding sensor surface can be adjusted to be different. Thus, these detection devices can have different sensitivities to the deposits. For example, organic deposits and inorganic deposits can be distinguished.

[0036] As an alternative to or in addition to the above-described advantageous embodiments of the detection arrangement, the advantageous embodiments and features described in conjunction with the detection device may also be used alone or in combination.

[0037] Furthermore, a method for detecting deposits and / or contamination on a sensor surface in a vessel or a pipe with a flowing medium using a first detection device, the first detection device comprising:

[0038] a thermally conductive substrate which has the sensor surface or is in direct contact with the sensor surface,

[0039] a heat source or a heat sink arranged on the substrate, which generates a primary heat flow between the heat source or the heat sink and the sensor surface, and a secondary heat flow between the heat source or the heat sink and a reference surface,

[0040] a detection section which has a sensor surface and a reference surface and is arranged in the vessel or in the pipeline and is in contact with the flowing medium,

[0041] a thermally conductive covering which covers a portion of the base body arranged outside the detection section and has a reference surface,

[0042] - an external insulation that isolates the enclosure from its external surroundings, and

[0043] a first temperature sensor arranged on the substrate at a first distance from the sensor surface and a second temperature sensor arranged on the substrate at a second distance from the sensor surface, wherein the second distance is greater than the first distance,

[0044] In this case, a temperature difference is determined by means of a temperature sensor of the first detection device, and deposits and / or contamination on the sensor surface are detected based on the temperature difference.

[0045] This method can achieve the same effects and advantages as have already been explained in conjunction with the detection device according to the invention.

[0046] In the method, a temperature difference between a first temperature and a second temperature is determined. Particularly preferably, the change in the temperature difference over time is monitored. Deposits and / or contamination on the sensor surface can be inferred from the change in the temperature difference. Thus, a calibration measurement can be performed to initialize the detection device, in which a calibration temperature difference is determined. The temperature difference obtained by further measurements with the detection device can then be compared with the calibration temperature difference.

[0047] Preferably, the measure PFL for the amount or thickness of deposits and / or contaminants is determined as follows

[0048]

[0049] Where, ΔT 12_act is the currently measured temperature difference, ΔT 12_cal is the calibration temperature difference measured within the calibration range.

[0050] An advantageous embodiment of the method provides that the heat source is operated with a constant heating power or the heat sink is operated with a constant cooling power. By providing a constant heating power or cooling power, a temporally stable temperature gradient can be set in the base body, in particular between the first temperature sensor and the second temperature sensor (ignoring deposits on the sensor surface). In this respect, the deposits on the sensor surface can be inferred from the change in the temperature difference between the measured first temperature and the second temperature.

[0051] An alternative advantageous design provides that the heating power of the heat source or the cooling power of the heat sink is adjusted as a function of the temperature of the flowing medium causing the deposits and / or contamination. This results in a design in which the temperature of the heating device follows the temperature of the medium flowing in the vessel or pipe. This design is particularly advantageous in batch processes in which the temperature of the flowing medium changes as the batch process progresses.

[0052] The method according to the invention for detecting deposits and / or contamination on the surface of a sensor in a vessel or pipe with a flowing medium can also be used to determine deposits on the wall of a heat exchanger caused by a cooling medium, in particular a liquid cooling medium, which enables a heat exchange between a process medium and a cooling medium. For this purpose, it is not necessary to arrange a detection device in the heat exchanger. More precisely, according to an advantageous design of the method according to the invention, it is proposed that a first detection device is arranged in an inlet pipe or a discharge pipe of a heat exchanger filled with a cooling medium, wherein the heat exchanger is able to achieve a heat exchange between the process medium and the cooling medium through the heat exchanger wall, wherein the heating power of the heat source or the cooling power of the heat source is adjusted according to the process temperature of the process medium.

[0053] The following embodiment is preferred: Depending on the process temperature and the thermal conductivity of the heat exchanger wall and the wall thickness of the heat exchanger wall, a virtual distance to the sensor surface is determined in the base of the first detection device at which the process temperature must be reached in order to set a temperature on the sensor surface that is substantially the same as the temperature on the surface of the heat exchanger wall that is in contact with the cooling medium. Virtual distance x emul For example, use the following formula to calculate:

[0054] x emul =d w ·λ s / λ w

[0055] in

[0056] d w : Heat exchanger wall thickness

[0057] λ s : Thermal conductivity of the substrate of the detection device

[0058] λ w : Thermal conductivity of the heat exchanger wall.

[0059] The process temperature can be specified by the user, ie as a constant value or as a temperature profile. Alternatively, it is possible to measure the process temperature with a process temperature sensor and to determine the virtual distance x emul The measured process temperature is taken into account when

[0060] The following design is preferred: the heating power of the heat source or the cooling power of the heat sink is additionally adjusted as a function of the temperature determined by the first temperature sensor and the second temperature sensor, so that the process temperature is reached at a virtual distance from the sensor surface. The heating power P of the heat source is obtained as follows

[0061] P=λ s A s (T1-T2) / (x2-x1)

[0062] in

[0063] λ s : Thermal conductivity of the substrate of the detection device

[0064] A s : Cross-sectional area of ​​the substrate of the detection device

[0065] T1: First temperature

[0066] T2: Second temperature

[0067] x1: First spacing (position of the first temperature sensor)

[0068] x2: Second spacing (position of the second temperature sensor)

[0069] Here, according to the virtual spacing x emul , the distance between the temperature sensor and the sensor surface x1, x2 and the specified process temperature T P , the following target values ​​are specified for the first temperature T1 and the second temperature T2:

[0070] T1=T P / x emul x1

[0071] T2=T P / x emul x2

[0072] According to the advantageous design of the method, a third temperature is measured by a third temperature sensor, which is arranged on the substrate at a third distance from the sensor surface, wherein the third distance is greater than the second distance, wherein a first temperature gradient between the first temperature sensor and the second temperature sensor and a second temperature gradient between the second temperature sensor and the third temperature sensor are obtained, and preferably they are compared with each other. The first temperature gradient can be obtained based on the temperature difference between the first temperature and the second temperature and the distance between the first temperature sensor and the second temperature sensor. Similarly, the second temperature gradient can be obtained based on the temperature difference between the second temperature and the third temperature and the distance between the second temperature sensor and the third temperature sensor. In an ideal case, these temperature gradients must be the same. If the temperature gradients are different from each other, it can be inferred that heat loss occurs in the direction perpendicular to the straight line between the heat source or the cold source and the sensor surface. For example, this may indicate that the thermal insulation is poor or that the medium invades the detection device in an undesirable manner. Particularly preferably, a third temperature gradient between the first temperature sensor and the third temperature sensor is obtained. The third temperature gradient can be obtained based on the temperature difference between the first temperature and the third temperature and the distance between the first temperature sensor and the third temperature sensor. The third temperature gradient can be compared with the first temperature gradient and or the second temperature gradient. Ideally, these temperature gradients must also be identical.

[0073] According to a favorable design of the method, a temperature difference between the first temperature and the second temperature is obtained, and an additive is introduced into a process vessel or a process pipeline according to the obtained temperature difference. In this design, deposits can be identified in real time when they appear, and appropriate countermeasures can be taken immediately. Therefore, in response to the change in the obtained temperature difference, an additive can be introduced into the process vessel or the process pipeline to remove the identified deposits and / or contaminants. It is advantageous here that the introduction is carried out shortly after the deposit is identified, because at this time a possible crystallization reaction or polymerization reaction has not yet been fully completed. The additive can be a hardness stabilizer or a dispersant. Preferably, the amount of the introduced additive is adjusted according to the obtained temperature difference or the obtained temperature difference change, so as to achieve the additive dosage according to the contaminant situation. This can prevent excessive use of additives.

[0074] An advantageous design of the present invention provides that a second detection device is provided, which includes a second substrate, in particular in the form of a rod, having a second sensor surface, which is arranged as a part of the wall, wherein an additional first temperature is measured using an additional first temperature sensor arranged on the second substrate at an additional first distance from the second sensor surface, wherein an additional second temperature is measured using an additional second temperature sensor arranged on the second substrate at an additional second distance from the second sensor surface, wherein the additional second distance is greater than the additional first distance, and wherein a temperature gradient is generated between the additional first temperature sensor and the additional second temperature sensor using a second heat source or a second heat source arranged on the second substrate, wherein the first heat source or the first heat source is operated in such a way that a first surface temperature is adjusted on the first sensor surface, in particular in a range between 35°C and 40°C, and the second heat source or the second heat source is operated in such a way that a second surface temperature is adjusted on the second sensor surface, in particular in a range between 45°C and 55°C, which second surface temperature is different from the first surface temperature. By using the first detection device and the second detection device, it is possible in the method to distinguish different deposits and / or contaminants from each other and, if necessary, suppress them by different measures. For example, if the first surface temperature is adjusted to a range between 35°C and 40°C, in particular to 37°C, then organic deposits and / or contaminants are continuously deposited on the first sensor surface. If the second surface temperature is adjusted to a range between 45°C and 55°C, in particular to 50°C, then inorganic deposits and / or contaminants are continuously deposited on the second sensor surface. By comparing the temperature differences detected by the two detection devices, the composition of the deposits and / or contaminants formed in the vessel or pipe can be inferred. Preferably, the first surface temperature and the second surface temperature are adjusted so that the surface temperature difference between the first surface temperature and the second surface temperature is in the range of 1°C to 100°C, or in the range of 1°C to 75°C, in the range of 1°C to 50°C, or in the range of 1°C to 40°C, or in the range of 1°C to 30°C, or in the range of 1°C to 20°C, or in the range of 1°C to 10°C, or in the range of 1°C to 5°C, or in the range of 1°C to 3°C. For example, the surface temperature difference can be adjusted to 1°C or 2°C or 3°C or 4°C or 5°C or 6°C or 7°C or 8°C or 9°C or 10°C or 15°C or 20°C.

[0075] Preferably, a first temperature difference is determined by means of a first detection device, and a first additive is introduced into a process vessel or a process pipeline according to the first temperature difference determined; and a second temperature difference is determined by means of a second detection device, and a second additive is introduced into a process vessel or a process pipeline according to the second temperature difference determined. This solution provides the advantage that the supply of additives can be coordinated according to the composition of the detected deposits. In this way, overdosing can be effectively avoided. Alternatively or additionally, an alarm can be triggered according to the first temperature difference or the second temperature difference determined, or a process parameter can be adjusted according to the first temperature difference or the second temperature difference determined.

[0076] In this context, it is advantageous to provide a temperature profile of the flowing medium, wherein the profile comprises a current first process temperature and a future second process temperature, wherein the first surface temperature is the first process temperature and the second surface temperature is the second process temperature. In this embodiment, the course of the process can be simulated using the second detection device, so that deposits and / or contaminants that may occur in the future (ie at the second process temperature) can be detected before they actually occur in the course of the process.

[0077] As an alternative to or in addition to the above-described advantageous embodiments of the method, the advantageous embodiments and features described in conjunction with the detection device and / or the detection assembly can also be used in the method alone or in combination.

[0078] Further details, features and advantages of the invention will be apparent from the drawings and the following description of preferred embodiments with the aid of the drawings. The drawings illustrate only exemplary embodiments of the invention, which do not limit the inventive concept. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 A schematic cross-sectional view of a first embodiment of a detection device according to the invention is shown.

[0080] Figure 2 Show according to Figure 1 The detection equipment is shown and the main heat flows are highlighted.

[0081] Figure 3 A first exemplary embodiment of a detection arrangement having a detection device according to the invention is shown.

[0082] Figure 4 A second exemplary embodiment of a detection arrangement having a plurality of detection devices according to the invention is shown.

[0083] Figure 5 A diagram is shown to illustrate the process when simulating the heat transfer in a heat exchanger. DETAILED DESCRIPTION

[0084] In the various figures, identical components are always provided with the same reference symbols and are therefore generally only named or mentioned once in each case.

[0085] Figure 1 and Figure 2 The illustration in FIG. 1 shows a detection device 1 for detecting deposits and / or contaminants on a sensor surface 3 within a vessel or a pipe 11, which is filled with a flowing medium 40 along a flow direction F. The detection device 1 comprises a detection section 25, which is arranged within the vessel or within the pipe 11 and in contact with the medium 40, and can therefore also be referred to as an inner section. The detection section 25 comprises the sensor surface 3 and the reference surface 21. In addition, the detection device 1 also has an outer section 26 arranged outside the vessel or pipe 11.

[0086] The substrate 2 is designed to be rod-shaped and has a circular cross-section. With respect to its thermal conductivity, the substrate 2 is designed to be isotropic and uniform. In this respect, the substrate is a substantially cylindrical substrate 2. A plurality of (here exactly three) temperature sensors 4, 5, 6 are arranged on the substrate 2. Here, the first temperature sensor 4 is arranged on the substrate 2 at a first distance from the sensor surface 3, and the second temperature sensor 5 is arranged on the substrate 2 at a second distance from the sensor surface 3, the second distance being greater than the first distance. The third temperature sensor 6 is located on the substrate 2 at a third distance, the third distance being greater than the second distance. All temperature sensors are arranged on a common virtual straight line perpendicular to the sensor surface 3.

[0087] According to the present embodiment, the sensor surface 3 is designed as a separate end plate, which is made of metal, preferably titanium, for example. The substrate 2 is directly connected to the end plate. Alternatively, the sensor surface 3 can be a part of the substrate 2. An isolation device 8 is provided between the sensor surface 3 and the reference surface 21, which isolates the two surfaces thermally. The isolation device 8 can be made of PEEK, for example.

[0088] Another component of the detection device 1 is a heat source 7 arranged on the substrate, by means of which a temperature difference can be generated between the first temperature sensor 4 and the second temperature sensor 5 or between the second temperature sensor 5 and the third temperature sensor 6 or between the first temperature sensor 4 and the third temperature sensor 6. Alternatively, a cold source can also be provided instead of the heat source 7. According to the present embodiment, the heat source 7 is designed as an electric heating element, which can resistively heat the substrate. The heat source 7 is arranged at a fourth distance from the sensor surface 3, which is greater than the first distance, the second distance and the third distance. In the current embodiment, the heat source 7 is arranged on the rear surface of the substrate 2 which is arranged opposite to the sensor surface of the substrate 2. Therefore, a first thermal path is provided in the substrate 2 starting from the heat source 7 to the sensor surface 3, which first thermal path conducts the main heat flow, see Figure 2 .

[0089] The detection device 1 further comprises a covering 19 which covers the circumferential side of the base body 2 and the end side opposite the sensor surface 3. In this respect, the area of ​​the base body 2 arranged in the outer area 26 is covered by the covering 19, and only the detection section 25 is exposed. The covering 19 can be made of metal, in particular titanium, for example. A second heat path is provided via the covering 19, i.e., a secondary heat flow Q2 is guided from the heat source 7 through the covering 19 to the reference surface 21 of the covering 19, see Figure 2 .

[0090] An insulating device 9 is arranged between the base body 2 and the encapsulation body 19. The insulating device is designed as a bulk material or a porous material. Alternatively, the insulating device 9 can include a gas or a gas mixture, such as air. The outer contour of the encapsulation body 19 is isolated from the surrounding environment by an outer insulating part 22. The outer insulating part has an insulating body, which is composed of glass wool, for example.

[0091] The following relationship applies to Figure 2 The detection device 1 shown in FIG. 1 , wherein the heating device 7 has a power P and a temperature T H , and the flowing medium 40 has a temperature T W :

[0092] (1) (2) ΔT HW =T H -T W

[0093] (3) (4)

[0094] (5) (6)

[0095] (7)R th1 =R 1A +R 1B +R 1C +R 1F

[0096] (8)R th2 =R 2A +R 2B +R 2C +R 2F

[0097] P Heating power of heating device 7

[0098] Q1 Heat flow of path 1

[0099] Q2 Heat flow of path 1

[0100] T H The temperature of the heating device 7

[0101] T W Temperature of the flowing medium 40

[0102] ΔT HW The temperature difference between the heating device 7 and the flowing medium 40

[0103] R th1 Absolute thermal resistance of path 1

[0104] R th2 Absolute thermal resistance of path 2

[0105] R 1A Thermal resistance of the measuring rod of path 1

[0106] R 1B Thermal resistance of path 1 to the contact plate

[0107] R 1C Thermal resistance of the transition of path 1 to the flow medium 40

[0108] R 1F Thermal resistance of deposits (fouling) in path 1

[0109] R 2A Thermal resistance of the internal insulation section of path 2

[0110] R 2B Thermal resistance of housing sleeve of path 2

[0111] R 2C Thermal resistance of the transition of path 2 to the flowing medium 40

[0112] R 2F Thermal resistance of deposits (fouling) in path 2

[0113] Applicable to the measuring section with heat flow Q1 and measuring points P1 (first temperature sensor 4 with temperature T1) and P2 (second temperature sensor 5 with temperature T2) is:

[0114] (9)

[0115] T1 Temperature of substrate 2 at point P1

[0116] T2 Temperature of substrate 2 at point P2

[0117] ΔT 12 The temperature difference between points P1 and P2

[0118] R1 A_12 Thermal resistance between points P1 and P2 in the main thermal path 1

[0119] A measure for the amount or thickness of deposits and / or contaminants is the performance loss PFL in %. The performance loss is defined for a measurement without deposits (calibration = cal) and for the current measurement (act) as follows:

[0120] (10)

[0121] ΔT 12_act The current measured temperature difference

[0122] ΔT 12_cal The temperature difference measured during calibration (without deposits)

[0123] When using (9)(R 1A_12 From (10), we can conclude that:

[0124] (11)

[0125] And using (5) we can get

[0126] (12)

[0127] Under the following premise, that is, the thermal resistance in the primary heat path is smaller than the thermal resistance in the secondary heat path, and the impedance increase caused by the deposit is smaller than the impedance of the primary heat path

[0128] (13)R th2_cal >R th1_cal >R 1F , R 2F

[0129] Approximately applicable are:

[0130] (14)

[0131] Therefore, from (12) we can conclude:

[0132] (15)

[0133] Because it applies:

[0134] (16)R 1A , R 2A , R 1B , R 2B = Constant

[0135] So according to the assumption

[0136] (17)

[0137] Using (7), (8), and (15), we can obtain:

[0138] (18)

[0139] And using (13) we can get

[0140] (19)

[0141] K sensor constant

[0142] The metric PFL (performance loss) is therefore proportional to the thermal resistance of the deposit in the main thermal path:

[0143] (20)

[0144] Figure 3 FIG. 1 shows an embodiment of a detection assembly 10 for detecting the deposition of a flowing medium on an inner wall 12 of a process vessel or a process pipeline 11. The detection assembly 10 comprises a detection device 1 which can be configured to detect the deposition of a flowing medium on an inner wall 12 of a process vessel or a process pipeline 11. Figure 1 and Figure 2 The embodiment shown in FIG. 1 is designed. A recess is provided in the inner wall 12 of the pipeline 11, into which the detection device 1 extends with its detection section 25, so that the sensor surface 3 and the reference surface 21 are provided as part of the inner wall 12 of the process pipeline 11. A cooling medium or a process medium is transported in the pipeline 11 along the transport direction F. In this case, deposits 13 are formed on the inner wall 12 and deposits 13 are formed on the sensor surface 3, which deposits on the sensor surface can be associated with the deposits 13 on the inner wall 12 and can be detected by the detection device 1.

[0145] The heat source 7 of the detection device 1 is operated with a constant heating power in order to thereby generate a temperature gradient between the first temperature sensor 4 and the second temperature sensor 5. In order to monitor the deposit 13, the first temperature is measured by the first temperature sensor 4 of the detection device 1 and the second temperature is measured by the second temperature sensor 5 of the detection device 1. The above-mentioned measurement PFL is calculated in the evaluation unit 20 connected to the detection device 1. The measurement PFL is proportional to the thickness of the deposit on the inner wall 12. The evaluation unit 20 calculates this thickness and can transmit it to a superordinate system, such as a process control facility, via an interface 30.

[0146] according to Figure 3In a modification of the embodiment shown in , the detection device 1 is arranged in an inlet or outlet pipe 11 of a heat exchanger filled with a liquid cooling medium, wherein the heat exchanger is capable of heat exchange between a process medium and a cooling medium via the heat exchanger wall, wherein the heating power of the heat source or the cooling power of the heat sink is adjusted depending on the process temperature of the process medium. In this way, deposits on the wall of the heat exchanger due to the liquid cooling medium can be determined without the need to arrange the detection device inside the heat exchanger for this purpose. In this respect, it is a simulation of the process on the wall of the heat exchanger with the help of the detection device. Figure 5 The simulation is summarized graphically in and is based on the fact that the process temperature T P , thermal conductivity λ of the heat exchanger wall w and the wall thickness d of the heat exchanger w Based on these parameters of the heat exchanger and the process, a virtual distance x from the sensor surface 3 is determined in the base body 2 of the detection device 1 . emul , at which the process temperature must be reached in order to set a temperature on the sensor surface 3 that is substantially the same as the temperature on the surface of the heat exchanger wall that is in contact with the flowing coolant. emul It is calculated as follows:

[0147] x emul =d w ·λ s / λ w

[0148] The heating power P of the heat source 7 is adjusted as a function of the temperatures T1, T2 determined by the first and second temperature sensors 4, 5, so that at a virtual distance x from the sensor surface 3 emul The process temperature T P The heating power P of the heat source 7 is obtained as follows

[0149] P=λ s A s (T1-T2) / (x2-x1)

[0150] in

[0151] λ s : Thermal conductivity of the substrate of the detection device

[0152] A s : Cross-sectional area of ​​the substrate of the detection device

[0153] T1: First temperature

[0154] T2: Second temperature

[0155] x1: First spacing (position of the first temperature sensor)

[0156] x2: Second spacing (position of the second temperature sensor)

[0157] Here, according to the virtual spacing x emul , the distance between the temperature sensor and the sensor surface x1, x2 and the specified process temperature T P , the following target values ​​are specified for the first temperature T1 and the second temperature T2:

[0158] T1=T P / x emul x1

[0159] T2=T P / x emul x2

[0160] Figure 4 The illustration in FIG. 1 shows another embodiment of a detection assembly 10 for detecting the deposits of a process medium on the inner wall 12 of a vessel or a pipe 11, which is different from the embodiment of FIG. Figure 3 The embodiment shown in FIG. Figure 3 Unlike the detection device of the embodiment, in the present embodiment, a plurality of (here exactly two) detection devices 1, 1' are provided and arranged on the pipeline 11 in such a way that the respective sensor surface 3, 3' of the detection device 1, 1' is arranged as a part of the inner wall 12 of the pipeline 11. The two detection devices 1, 1' can be used to distinguish different deposits and / or contaminants from each other and, if necessary, suppress them by different measures. For example, if the first surface temperature of the first sensor surface 3 is adjusted to be in the range between 35° C. and 40° C., in particular to 37° C., then organic deposits and / or contaminants are continuously deposited on the first sensor surface 3. If the second surface temperature of the second sensor surface 3' is adjusted to be in the range between 45° C. and 55° C., in particular to 50° C., then inorganic deposits and / or contaminants are continuously deposited on the second sensor surface 3'. By comparing the temperature differences detected by the two detection devices 1, 1', for example in the evaluation unit 20, it is possible to infer the composition of the deposit 13 formed in the pipeline 11. Based on these findings, the composition of the additive which is introduced into the line 11 for decomposing the deposits 13 can be derived.

[0161] For example, the first detection device 1 may be used to obtain a first temperature difference and introduce a first additive into the pipe 11 according to the obtained first temperature difference, and the second detection device 1 ′ may be used to obtain a second temperature difference and introduce a second additive into the pipe 11 according to the obtained second temperature difference.

[0162] With regard to the above-described detection devices 1, 1', a method for detecting deposits and / or contamination on a sensor surface 3 in a vessel or pipe 11 with a flowing medium 40 can be performed using a first detection device 1, which comprises

[0163] a thermally conductive substrate 2 which has the sensor surface 3 or is in direct contact with the sensor surface,

[0164] a heat source or heat sink 7 arranged on the substrate 2, which generates a primary heat flux Q1 between the heat source or heat sink 7 and the sensor surface 3, and a secondary heat flux Q2 between the heat source or heat sink 7 and the reference surface 21,

[0165] a detection section which has the sensor surface 3 and the reference surface 21 and is arranged in the vessel or in the pipeline and is in contact with the flowing medium 40 ,

[0166] a thermally conductive covering 19 which covers a portion of the base body 2 arranged outside the detection section and has a reference surface 21,

[0167] an outer insulation 22 which isolates the enclosure 19 from its external surroundings, and

[0168] a first temperature sensor 4 arranged on the substrate 2 at a first distance from the sensor surface 3 and a second temperature sensor 5 arranged on the substrate 2 at a second distance from the sensor surface 3, wherein the second distance is greater than the first distance,

[0169] In this case, a temperature difference is determined by means of the temperature sensors 4 , 5 of the first detection device 1 , and deposits and / or contamination on the sensor surfaces are detected based on this temperature difference.

[0170] List of Reference Numerals

[0171] 1. Detection equipment

[0172] 2 Matrix

[0173] 3Sensor surface

[0174] 4 Temperature Sensor

[0175] 5. Temperature Sensor

[0176] 6 Temperature Sensor

[0177] 7 Heat Source

[0178] 8 Isolation device

[0179] 9 Isolation device

[0180] 10 Detection components

[0181] 11 Pipeline

[0182] 12 walls

[0183] 13 Sediment

[0184] 18 through holes

[0185] 19 Encapsulation

[0186] 20 evaluation units

[0187] 21 Reference surface

[0188] 22 External isolation

[0189] 25 detection section (internal section)

[0190] 26 External Segments

[0191] 30 interfaces

[0192] 40 Flowing medium (liquid)

[0193] FDelivery Direction

[0194] Q1 main heat flow

[0195] Q2 auxiliary heat flow.

Claims

1. A detection device (1) for detecting deposits and / or contamination on a sensor surface (3) in a vessel or a pipeline with a flowing medium (40), wherein: The detection device (1) comprises: a detection section having a sensor surface (3) and being designed to be arranged within the vessel or within the pipeline and to be in contact with the flowing medium (40), a thermally conductive substrate (2), which has the sensor surface (3) or is in direct contact with the sensor surface, a heat source or a heat sink (7) arranged on the substrate (2) for generating a primary heat flux (Q1) between the heat source or the heat sink (7) and the sensor surface (3), and a secondary heat flux (Q2) between the heat source or the heat sink (7) and a reference surface (21), a first temperature sensor (4) arranged on the substrate (2) at a first distance from the sensor surface (3) and a second temperature sensor (5) arranged on the substrate (2) at a second distance from the sensor surface (3), wherein the second distance is greater than the first distance, wherein a temperature difference can be determined by means of the temperature sensors (4, 5), a thermally conductive covering (19), which covers a portion of the base body (2) arranged outside the detection section and has the reference surface (21), It is characterized in that The reference surface (21) is part of the detection section, and the detection device (1) comprises an outer insulation (22) which isolates the enclosure (19) from its external surroundings.

2. The detection device (1) according to claim 1, characterized in that The outer insulating portion (22) isolates the encapsulating body (19) from its external surrounding environment, so that the secondary heat flux is greater than the parasitic heat flux between the heat source or the cold source and the surrounding environment through the encapsulating body (19) and the outer insulating portion (22).

3. The detection device (1) according to any one of the preceding claims, characterized in that The sheath (19) is made of metal, in particular titanium.

4. The detection device (1) according to any one of the preceding claims, characterized in that The detection section is a detection surface.

5. The detection device (1) according to any one of the preceding claims, characterized in that The heat source (7) or the cold source is designed as an adjustable heat source or cold source.

6. Detection device (1) according to any one of the preceding claims, characterized in that The base body (2) is rod-shaped, and in particular has a circular cross section.

7. Detection device (1) according to any one of the preceding claims, characterized in that The thermal conductivity of the substrate (2) is isotropic and uniform.

8. Detection device (1) according to any one of the preceding claims, characterized in that The detection device (1) comprises a third temperature sensor (6), which is arranged on the substrate (2) at a third distance from the sensor surface (3), wherein the third distance is greater than the second distance.

9. Detection device (1) according to any one of the preceding claims, characterized in that The heat source (7) is arranged at a fourth distance from the sensor surface (3), wherein the fourth distance is greater than the second distance and, if appropriate, greater than the third distance.

10. Detection device (1) according to any one of the preceding claims, characterized in that The detection device (1) comprises a separating device (8, 9) surrounding the base body (2), wherein the separating device is arranged between the outer contour of the base body (2) and the inner contour of the encapsulation body (19).

11. The detection device (1) according to claim 10, characterized in that The insulating device (8) surrounding the base body (2) has the same thermal resistance on all sides of the base body (2).

12. The detection device (1) according to claim 10 or 11, characterized in that The insulating device (8) comprises a bulk material or a porous material, such as a sponge.

13. A detection assembly (10) for detecting deposits and / or contamination of a flowing medium (40) on a wall (12) of a vessel or a pipeline (11), the detection assembly comprising a detection device (1) according to any one of the preceding claims, wherein: The detection section having the sensor surface (3) and the reference surface (21) is arranged as a part of the wall (12).

14. The detection assembly (10) according to claim 13, characterized in that A plurality of detection devices (1, 1') according to any one of claims 1 to 12, wherein a detection section of the respective detection device (1, 1') is arranged as a part of the wall (12).

15. A method for detecting deposits and / or contaminants on a sensor surface (3) in a vessel or a pipe (11) having a flowing medium (40) using a first detection device (1), the first detection device comprising: a thermally conductive substrate (2), which has the sensor surface (3) or is in direct contact with the sensor surface, a heat source or heat sink (7) arranged on the substrate (2), the heat source or heat sink generating a primary heat flux (Q1) between the heat source or heat sink (7) and the sensor surface (3), and a secondary heat flux (Q2) between the heat source or heat sink (7) and a reference surface (21), a detection section which has the sensor surface (3) and the reference surface (21) and is arranged in the vessel or in the pipeline and is in contact with the flowing medium (40), a thermally conductive covering (19), which covers a portion of the base body (2) arranged outside the detection section and has the reference surface (21), - an outer insulation (22) which isolates the enclosure (19) from its external surroundings, and a first temperature sensor (4) arranged on the substrate (2) at a first distance from the sensor surface (3) and a second temperature sensor (5) arranged on the substrate (2) at a second distance from the sensor surface (3), wherein the second distance is greater than the first distance, Therein, a temperature difference is determined by means of the temperature sensors (4, 5) of the first detection device (1), and deposits and / or contamination on the sensor surface are detected based on the temperature difference.

16. The method according to claim 15, characterized in that The heat source (7) operates at a constant heating power, or the heat sink operates at a constant cooling power.

17. The method according to claim 15, characterized in that The heating power of the heat source (7) or the cooling power of the heat sink (40) is adjusted according to the temperature of the flow medium (40).

18. The method according to claim 15, characterized in that The first detection device (1) is arranged in an input pipe or a discharge pipe of a heat exchanger filled with a flowing cooling medium (40), wherein the heat exchanger is capable of realizing heat exchange between a process medium and the cooling medium (40) via a heat exchanger wall, wherein the heating power of the heat source (7) or the cooling power of the heat sink is adjusted according to the process temperature of the process medium.

19. The method according to claim 18, characterized in that Based on the process temperature and the thermal conductivity of the heat exchanger wall and the wall thickness of the heat exchanger wall, a virtual distance from the sensor surface (3) is determined in the base body (2) of the first detection device, at which virtual distance the process temperature must be reached in order to adjust a temperature on the sensor surface (3) that is substantially the same as the temperature on the surface of the heat exchanger wall in contact with the cooling medium (40).

20. The method according to claim 19, characterized in that In addition, the heating power of the heat source (7) or the cooling power of the heat sink (7) is regulated as a function of the temperature determined by the first temperature sensor and the second temperature sensor, so that the process temperature is reached at the virtual distance from the sensor surface (3).

21. The method according to any one of claims 15 to 20, characterized in that A third temperature is measured using a third temperature sensor (6), which is arranged on the substrate (2) at a third distance from the sensor surface (3), wherein the third distance is greater than the second distance, and wherein a difference between the first temperature and the second temperature is compared with a difference between the second temperature and the third temperature.

22. The method according to any one of claims 15 to 21, characterized in that A temperature difference between the first temperature and the second temperature is determined, and an additive is introduced into a process vessel or a process pipeline (11) according to the determined temperature difference.

23. The method according to any one of claims 16 or 22, characterized in that A second detection device (1') is provided, which comprises a second base body, in particular in the form of a rod, which has a second sensor surface (3'), which is arranged as part of the wall, wherein a further first temperature is measured by means of a further first temperature sensor which is arranged on the second substrate at a further first distance from the second sensor surface (3'), wherein a further second temperature is measured using a further second temperature sensor which is arranged on the second substrate at a further second distance from the second sensor surface (3'), wherein the further second distance is greater than the further first distance, and wherein a temperature gradient is generated between the further first temperature sensor and the further second temperature sensor by using a second heat source or a second cold source arranged on the second substrate, The first heat source or the first cold source is operated in such a way that a first surface temperature is adjusted on the first sensor surface (3), in particular in the range between 35°C and 40°C, and the second heat source or the second cold source is operated in such a way that a second surface temperature is adjusted on the second sensor surface (3'), in particular in the range between 45°C and 55°C, the second surface temperature being different from the first surface temperature.

24. The method according to claim 23, characterized in that A temperature profile of the flow medium (40) is defined, wherein the profile includes a current first process temperature and a future second process temperature, wherein the first surface temperature is the first process temperature and the second surface temperature is the second process temperature.

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