EP3452773B1 - Method and apparatus for monitoring a heat exchanger - Google Patents

Description

The invention relates to a method for monitoring the degree of contamination of a heat exchanger and to a device for carrying out the method.

Heat exchangers are used in large numbers in an industrial environment and in many cases are operated almost without interruption over a long period of time. The heat exchangers get dirty during operation. For example, a medium to be cooled, in particular air, is used to introduce dirt into the heat exchanger. The dirt sticks to the interfaces of the heat exchanger. It reduces or hampers the flow of the medium in the heat exchanger and has a negative effect on the heat transfer resistance or the efficiency of the heat transfer between a cooling medium and the medium to be cooled. Ultimately, this increases the energy required to operate the heat exchanger. Regular cleaning of the heat exchanger is generally not planned today. The companies or operators of the heat exchanger cannot make any statements about the degree of soiling of the heat exchanger, the deterioration in efficiency as a result of the pollution or the time of the next scheduled or unscheduled cleaning.

Methods for monitoring heat exchangers with regard to their degree of contamination and devices designed for carrying out the method are, for example, from DE 10 2014 204 718 A1 , US 2016/047609 A1 , U.S. 5,226,285 A and US 2010/273118 A1 known The US 2010/273118 A1 shows a method according to the preamble of claim 1.

The object of the present invention is to provide a method for determining a degree of pollution and / or a deterioration in the efficiency of a heat exchanger as a result of pollution. The determination of the pollution or the change in efficiency should take place automatically with technical means during normal operation. A further object of the invention is to specify a device for carrying out the method.

To achieve the object, the method according to the invention has the features of independent claim 1.

According to the invention it is provided that during a learning operation in a cleaned reference operating state of the heat exchanger for one or preferably for several reference operating situations, the cooling work of an electric motor responsible for cooling is determined. After the end of the learning mode, the cooling work of the same electric motor is determined in a measuring mode of the method according to the invention in a working operating situation corresponding to the reference operating situation. After the learning operation and the measuring operation have been carried out, knowing the different cooling work in the measuring operation and in the cooling operation, a change in the efficiency of the heat exchanger is concluded. In particular, knowing a deterioration in the efficiency can determine how much more energy has to be applied for its operation due to the pollution of the heat exchanger. Knowing an average duration of cleaning the heat exchanger and typical costs for cleaning the heat exchanger, it can then be determined whether the continued operation of the soiled heat exchanger is economically less advantageous than carrying out a cleaning of the heat exchanger. In addition to the cleaning costs, the downtimes of the heat exchanger and the loss of production associated with the shutdown of the heat exchanger can be taken into account.

In particular, it can be provided that the learning mode is carried out once, while the measuring mode is carried out repeatedly. For example, the learning mode is carried out once after cleaning or when the heat exchanger is put into operation. The measuring operation is carried out periodically, for example, at the same or variable operating time intervals.

According to a further development of the invention, the cooling work for the electric motor in the learning mode and in the measuring mode is determined by determining the real power or the motor current of the electric motor. The real power or the motor current of the electric motor can be recorded comparatively easily and used to determine an electrical power consumption of the electric motor. The cooling work absorbed by the electric motor in a detection time interval results from the power consumption over time. The acquisition time interval can be selected to be the same size in learning mode and in measuring mode or it can be dimensioned differently.

According to an advantageous development, the invention provides that the determination of the cooling work is carried out in the learning mode and / or in the measuring mode after the heat exchanger is in a quasi-static or stationary operating state. For this purpose, the cooling work of the electric motor is determined after a reaction time of the heat exchanger with a constant power consumption of the electric motor, with a constant temperature of the medium to be cooled before and after the energy conversion and with a constant coolant temperature. The response time can be determined in different ways. For example, empirical values from the past can be used to conservatively estimate the response time. A value determined in this way for the reaction time of the heat exchanger can then be stored in a data memory and used before the method according to the invention is carried out. It is also provided that the parameters of the system relevant to determining the steady operating state, in particular the power consumption of the electric motor, the temperature of the medium to be cooled before and after the energy conversion and the coolant temperature are detected by sensors. The stationary operating state can then be derived from the parameters recorded in this way of the heat exchanger can be determined. The determination of the cooling work in the learning mode or in the measuring mode then follows.

In the learning mode, with the heat exchanger cleaned, the cooling work is preferably determined for a plurality of reference operating situations. In this respect, there is the possibility of comparing the cooling work of the electric motor determined during the measurement operation in a selected working operating situation with the value of the cooling work in one or more corresponding reference operating situations. For example, a working operating situation can resemble a reference operating situation, for example with regard to the temperature, the pressure and the volume flow of the medium to be cooled. For example, it can be provided that for a work situation for which no exact identical reference operating situation is documented in the data memory, the change in the efficiency of the heat exchanger is determined using an interpolation of the cooling work values determined for at least two reference operating situations stored in the data memory. The at least two reference operating situations considered for the interpolation can be included in the determination of the efficiency of the heat exchanger with the same or different weightings.

A device designed to achieve the object has the features of independent claim 10.

In particular, the device comprises a central measuring device and a plurality of heat exchangers, a plurality of sensors assigned to the heat exchangers being connected to the central measuring device and the sensors assigned to a single heat exchanger interacting with a computing unit of the central measuring device and a data memory of the central measuring device in such a way that for each individual Heat exchanger, a change in efficiency that occurs as a result of the pollution is compared by comparing the cooling work of an electric motor of the heat exchanger in question, determined in the measurement mode, and a value of the cooling work of the same heat exchanger stored in the data memory in a cleaned reference operating state. The central measuring device can in particular be provided remotely from at least individual heat exchangers. A point in time for carrying out cleaning can be determined individually for each heat exchanger under consideration.

According to a development of the invention, it can be provided that a decentralized control module is provided for each individual heat exchanger. The sensors assigned to the individual heat exchangers are then preferably connected to the decentralized control module. The decentralized control module is connected to the central measuring device via a data line, in particular a data bus. In this respect, the parameters determined using the sensors can be used by the decentralized control module can be collected or aggregated and validated. The values for the cooling work determined during the learning mode for the individual heat exchanger can also be stored in a data memory of the decentralized control module. For example, it can be provided that the change in efficiency is determined for all connected heat exchangers in the central measuring device. Even if the decentralized control modules are provided, the data memory for the cooling work of the electric motor determined during the learning mode can be assigned to the central measuring device.

According to the invention it can be provided that the principle of monitoring the energy-converting processes is broadly defined. For example, the power consumption of an electric motor can be monitored, which drives a propeller to provide an air flow. For example, an electric pump provided for circulating a gas or a liquid can be monitored. The circulated medium can be provided for heating or cooling a useful volume flow supplied to the heat exchanger. The method according to the invention can be applied to lamellar heat exchangers in which the increasing engine power of the fan is evaluated. It can also be used with tube bundle, plate, counterflow, cocurrent and crossflow heat exchangers in which a liquid medium is moved by an electrically driven pump. The electrical work of the pump in connection with the energy conversion performed is also evaluated.

It can further be provided that the principle of the monitoring of the energy-converting processes on which the method according to the invention is based is extended beyond the monitoring of electric motors. In particular, any other energy sources can be monitored with regard to their power balance. The energy consumption can, for example, be made available to the evaluation unit in a processed form. For example, the energy consumption of a gas burner provided for temperature control of a fluid can be recorded and compared with reference to the reference operating situation and the working operating situation. The other process parameters are recorded in the same way as the process variables described above.

Further advantages, features and details of the invention can be derived from the further subclaims and the following description. Features mentioned there can each be essential to the invention individually or in any combination. Features and details of the device described according to the invention naturally also apply in connection with the method according to the invention and vice versa. In this way, mutual reference can always be made to the disclosure of the individual aspects of the invention. The drawings serve only by way of example to clarify the invention and are not of a restrictive nature.

Figur 1

eine Prinzipdarstellung für einen Wärmetauscher, an dem das erfindungsgemäße Verfahren durchgeführt wird und

Figur 2

eine erfindungsgemäße Vorrichtung mit einer Zentralmesseinrichtung und einer Mehrzahl von Wärmetauschern.

The invention is explained in more detail below with reference to the accompanying drawings. Show:

Figure 1

a schematic diagram for a heat exchanger on which the method according to the invention is carried out and

Figure 2

a device according to the invention with a central measuring device and a plurality of heat exchangers.

Figure 1 shows a heat exchanger 1, to which a medium to be cooled is supplied via a first fluid channel 2 and a coolant is supplied via a coolant circuit 3. The coolant circuit 3 is assigned a coolant pump 4 which is operated by an electric motor 5 responsible for cooling. The coolant pumped around in the coolant circuit 3 has a coolant temperature T _k . The medium to be cooled, which is guided via the fluid channel 2, is fed to the heat exchanger 1 at an inlet temperature T _i and is removed at an outlet temperature T _o . With respect to the electric motor 5, the effective power P _M and the cooling power P _{K are} determined. To determine the active power PM, in particular the motor current i, the voltage u and the phase are determined.

According to the invention, it is provided that the cooling work J _R of the electric motor 5 responsible for cooling is initially determined in a learning mode in a cleaned reference operating state of the heat exchanger 1 for at least one and preferably for a plurality of reference operating situations and the values thus determined are stored in a data memory. Furthermore, at a later date in a measurement operation of the heat exchanger 1 determines a cooling work J _{B of} the electric motor in a working operating situation, which is characterized in that the heat exchanger has a different, in particular higher degree of pollution than in the learning mode. The working operating situation corresponds in particular to at least one reference operating situation. After the learning mode and the measuring mode have been carried out, a difference between a value of the cooling work J _B in the measuring mode and a value of the cooling work J _R in the learning mode is used to deduce a change in an efficiency of the heat exchanger. In particular, the values for the cooling work J _B in measuring mode and for the cooling work J _R in learning mode are determined after the heat exchanger 1 is in a quasi-static or steady state after a reaction time, which is characterized in that the electric motor 5 has a constant power consumption that the temperatures T _i , T _{o of} the medium to be cooled are constant before and after the energy conversion and that the coolant temperature T _{k is} constant.

On the basis of the change in the efficiency of the heat exchanger 1, a point in time is determined at which cleaning the heat exchanger 1 and returning it to the cleaned reference operating state is more economical than continuing to operate the uncleaned heat exchanger 1. In addition to the energy costs, in particular the downtime or the production stop can be taken into account which is associated with a shutdown of the heat exchanger. The costs for carrying out the cleaning in terms of personnel and material can also be taken into account or offset.

A device according to the invention for performing the method according to Figure 2 provides a central measuring device 6 and a plurality of heat exchangers 1.1, 1.2, 1.3, 1.4. A decentralized control module 7.1, 7.2, 7.3, 7.4 is assigned to each heat exchanger 1.1, 1.2, 1.3, 1.4. The decentralized control module 7.1, 7.2, 7.3, 7.4 of each individual heat exchanger 1.1, 1.2, 1.3, 1.4 interacts with a number of sensors, not shown, which serve in particular to measure the motor current i for the electric motor, the coolant temperature T _k , the temperature T _{i of} the medium to be cooled before the energy conversion and the temperature T _{o of} the medium to be cooled after the energy conversion. In each case, the decentralized control module 7.1, 7.2, 7.3, 7.4 is connected to the central measuring device 5 via a data bus 8. The measured values determined using the sensors are processed in the decentralized control module 7.1, 7.2, 7.3, 7.4, for example digitized and filtered, buffered or the like and transmitted to the central measuring device 6 via the data bus 8 to determine the changes in efficiency. The central measuring device 6 uses a computing unit (not shown) to determine the cooling work J _B in the current operating state and compares this with values for the cooling work J _{R of} the electric motor 5 stored in a data memory of the central measuring device 6 in the cleaned reference operating state of the heat exchanger 1.

According to an alternative, not shown embodiment of the invention, the decentralized control modules 7.1, 7.2, 7.3, 7.4 can be dispensed with. Likewise, instead of the data bus 8, any other suitable data link between the heat exchangers 1.1, 1.2, 1.3, 1.4 and the central measuring device 6 can be created.

According to the present exemplary embodiment of the invention, a volume flow V of the medium to be cooled through the fluid channel 2 of the heat exchanger 1 will remain constant or at least approximately constant in order to apply the measuring principle. The volume flow of the medium to be cooled through the fluid channel 2 is preferably not recorded. A constant pressure of the medium to be cooled is also not recorded.

According to an alternative example of the invention, the volume flow and a pressure of the medium to be cooled can vary. It is then provided that the variables are recorded and taken into account when determining the cooling work J _R , J _B.

The Figures 3 and 4 show alternative embodiments in which fluid channels 2 of a heat exchanger 1 are provided in a liquid bath 10 and through which the medium to be cooled flows. In Figure 3 the heat exchanger 1 is designed as a tube bundle heat exchanger. Figure 4 shows a plate heat exchanger. The liquid provided in the liquid bath 10 is tempered via an operating unit 9. For example, a gas burner can be provided as part of the operating unit 9, which is monitored with regard to its consumption data to evaluate an energy balance of the heat exchanger in the reference operating situation and the working operating situation and to determine the degree of pollution.

The same components and component functions are identified by the same reference symbols.

List of reference symbols

1

Heat exchanger

1.1

Heat exchanger

1.2

Heat exchanger

1.3

Heat exchanger

1.4

Heat exchanger

2

Fluid channel

3

Coolant circuit

4th

Coolant pump

5

Electric motor

6

Central measuring device

7.1

decentralized control module

7.2

decentralized control module

7.3

decentralized control module

7.4

decentralized control module

8th

Data bus

9

Operating unit

10

Liquid bath

T _k

Coolant temperature

T _i

Temperature of the medium to be cooled before the energy conversion

T _o

Temperature of the medium to be cooled after the energy conversion

i

Motor current

P _K

Cooling capacity

P _M

Real power of the electric motor

J _R

Performed work of the cooling electric motor in a cleaned reference operating state (learning mode) of the heat exchanger

J _B

Work performed by the cooling electric motor in a working operating state (measuring operation)

V

Volume flow of the medium to be cooled

Claims (13)

1. Method for monitoring a degree of soiling of a heat exchanger (1, 1.1, 1.2, 1.3, 1.4), comprising

   - learning operation, in which the cooling work (J_R) of an electric motor (5) responsible for cooling is determined in a cleaned or new reference operating state of the heat exchanger for at least one reference operating situation and stored in a data store, and

   - measurement operation, in which the cooling work (J_B) of the electric motor (5) is determined in a working operating situation corresponding to the at least one reference operating situation,

   a change in the efficiency of the heat exchanger (1, 1.1, 1.2, 1.3, 1.4) being ascertained, after the learning operation and measurement operation are carried out, from a difference between a value of the cooling work (J_B) during the measurement operation and the value of the cooling work (J_R) during the learning operation, characterised in that, using the change in the efficiency of the heat exchanger (1, 1.1, 1.2, 1.3, 1.4), a moment in time is determined at which cleaning the heat exchanger (1, 1.1, 1.2, 1.3, 1.4) and setting it back to the cleaned reference operating state is more economical than continuing to operate the uncleaned heat exchanger (1, 1.1, 1.2, 1.3, 1.4).
2. Method according to claim 1, characterised in that the cooling work (J_R, J_B) is determined during the learning operation and/or during the measurement operation once the temperature (T_o) of the medium to be cooled is no longer changing after the energy conversion, after a reaction time, when there is a constant power uptake (P) of the electric motor (5), a constant temperature (T_i) of the medium to be cooled before the energy conversion, and a constant coolant temperature (T_k).
3. Method according to either claim 1 or claim 2, characterised in that the effective power (P_W) of the electric motor is measured so as to determine the cooling work (J_R, J_B) during the learning operation and/or during the measurement operation.
4. Method according to any of claims 1 to 3, characterised in that the cooling work (J_R, J_B) is determined while a volume flow passed through the heat exchanger (1, 1.1, 1.2, 1.3, 1.4) and/or a pressure of the medium to be cooled are kept constant, and/or in that the volume flow (V) and/or pressure of the medium to be cooled are determined so as to determine the cooling work (J_R, J_B).
5. Method according to any of claims 1 to 4, characterised in that a detection time interval for determining the cooling work (J_R) during the learning operation and a detection time interval for determining the cooling work (J_B) during the measurement operation are the same size.
6. Method according to any of claims 1 to 5, characterised in that during the learning operation a plurality of reference operating situations are determined and the corresponding cooling work (J_R) is stored in the data store separately for the plurality of reference operating situations.
7. Method according to any of claims 1 to 6, characterised in that, for a working operating situation for which no exactly identical reference operating situation is documented in the data store, the change in the efficiency of the heat exchanger (1, 1.1, 1.2, 1.3, 1.4) is detected by interpolating the values of the cooling work (J_R) which have been determined for at least two reference operating situations which are stored in the data store, the at least two reference operating situations being incorporated into the determination of the efficiency of the heat exchanger (1, 1.1, 1.2, 1.3, 1.4) with the same or different weightings.
8. Method according to any of claims 1 to 7, characterised in that an end of the reaction time of the heat exchanger (1, 1.1, 1.2, 1.3, 1.4) is determined by measuring the power uptake (P) of the electric motor (5) and/or the temperature (T_i, T_o) of the medium to be cooled before and after the energy conversion and the coolant temperature (T_k) during the learning operation and/or during the measurement operation, and subsequently the cooling work (J_B, J_R) of the electric motor (5) is determined.
9. Method according to any of claims 1 to 8, characterised in that parameters for determining the reaction time and/or a duration of the learning operation are stored in the data store.
10. Device configured to carry out the method according to any of claims 1 to 9, wherein a central measurement device (6) and a plurality of heat exchangers (1, 1.1, 1.2, 1.3, 1.4) are provided, a plurality of sensors assigned to the heat exchangers (1, 1.1, 1.2, 1.3, 1.4) being connected to the central measurement device (6) and the sensors assigned to an individual heat exchanger (1, 1.1, 1.2, 1.3, 1.4) cooperating with a computing unit of the central measurement device (6) and with a data store of the central measurement device (6) in such a way that, separately for each individual heat exchanger (1, 1.1, 1.2, 1.3, 1.4), the change in efficiency is determined by comparing a value determined during measurement operation for the cooling work (J_B) of an electric motor (5) of the individual heat exchanger (1, 1.1, 1.2, 1.3, 1.4) in question and a value stored in the data store for the cooling work (J_R) of the same heat exchanger (1, 1.1, 1.2, 1.3, 1.4) for at least one reference operating situation, which is detected in a cleaned reference operating state.
11. Device according to claim 10, characterised in that the central measurement device (6) is provided remotely from at least individual heat exchangers (1, 1.1, 1.2, 1.3, 1.4) and/or in that a moment in time for carrying out cleaning can be determined for each connected heat exchanger (1, 1.1, 1.2, 1.3, 1.4) individually.
12. Device according to either claim 10 or claim 11, characterised in that a decentralised control module (7.1, 7.2, 7.3, 7.4), cooperating with the local sensors and/or the individual heat exchanger (1, 1.1, 1.2, 1.3, 1.4), is assigned to each individual heat exchanger (1, 1.1, 1.2, 1.3, 1.4), and/or in that the decentralised control module (7.1, 7.2, 7.3, 7.4) is data-linked to the central measurement device (6).
13. Device according to any of claims 10 to 12, characterised in that the decentralised control modules (7.1, 7.2, 7.3, 7.4) are connected to the central measurement device (6) via a bus system (8).

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