METHOD FOR CALCULATING THE STRENGTH AND THE SERVICE LIFE OF A PROCESS APPARATUS THROUGH WHICH FLUID FLOWS

Abstract

The invention relates to a method for calculating the strength and the service life of a process apparatus through which fluid flows, wherein: temperatures existing at a plurality of different points of the apparatus are measured at a first time point in order to obtain temperature measurement values (201); the temperature measurement values are used as constraints in a finite element method (203) in order to determine mechanical stresses existing at a plurality of different points in the material of the apparatus as stress values (204); the remaining service life of the material of the apparatus is determined from the obtained stress values (205); the remaining service life of the material of the apparatus is determined also in dependence on data regarding the apparatus that were determined at a second time point (207), which second time point is earlier than the first time point.

Claims

1. A method for calculating the strength and the service life of a process apparatus through which fluid flows, wherein at a first time point temperatures prevailing at a plurality of different points of the apparatus are measured in order to obtain temperature measurement values, wherein the temperature measurement values are input into a finite element method as boundary conditions, in order to determine mechanical stresses prevailing at a plurality of different points in a material of the apparatus as stress values, wherein a remaining service life of the material of the apparatus is determined from the obtained stress values, wherein the remaining service life of the apparatus is further determined as a function of data relating to the apparatus determined at a second time point which is earlier than the first time point.

2. The method according to claim 1, wherein the data relating to the apparatus comprise the results of finite element methods determined at the second time point.

3. The method according to claim 1, wherein the data relating to the apparatus further comprise temperature measurement values and/or temperature calculation values and/or mechanical stresses and/or strains and/or a remaining service life which were respectively determined at the second time point.

4. The method according to claim 1, wherein temperature distributions in the apparatus are obtained as temperature measurement values.

5. The method according to claim 1, wherein the temperature measurement values are obtained by means of fiber-optic temperature sensors, in particular by means of fiber Bragg grating sensors.

6. The method according to claim 1, wherein the boundary conditions for the finite element method are obtained in the form of the temperature measurement values during the ongoing operation of the apparatus.

7. The method Method according to claim 1 any one of the preceding wherein the execution of the finite element method and/or the determination of the mechanical stress and/or the determination of the remaining service life are carried out during the operation of the apparatus and/or in a remote computing unit.

8. The methodaccording to claim 1, wherein the process apparatus through which a fluid flows is designed as a heat exchanger, in particular as a plate heat exchanger or spiral or coiled heat exchanger, or as a column or as a container for phase separation.

9. The method according to claim 1, wherein no thermo-hydraulic simulation model is created, wherein the finite element method and the determination of mechanical stress are carried out without a thermo-hydraulic simulation model, wherein, in particular, boundary conditions for the finite element method are not determined by a thermo-hydraulic simulation model.

10. A computing unit with means for carrying out the method according to claim 1.

11. A computing program that causes a computing unit to perform the method according to claim 1 when it is executed on the computing unit.

12. A machine-readable storage medium having a computer program according to claim 11 stored on it.

Description

DESCRIPTION OF THE FIGURES

[0046] FIG. 1 shows, schematically and in perspective, a process apparatus through which a fluid flows designed as a plate heat exchanger, the remaining service life of which can be determined in accordance with a preferred embodiment of a method according to the invention.

[0047] FIG. 2 shows a preferred embodiment of a method according to the invention as a block diagram.

DETAILED DESCRIPTION OF THE DRAWING

[0048] FIG. 1 shows an external view of a process apparatus here taking the form of plate heat exchanger 1. The plate heat exchanger has a cuboid central body 8 with a length of, for example, several meters and a width or height of, for example, approximately one or a few meters. Attachments 6 and 6a are visible on top of the central body 8, on its sides, and underneath the central body 8. The attachments 6 and 6a located underneath the central body 8 and on the side facing away from the side depicted are partially concealed.

[0049] A fluid or process stream can be supplied to or removed again from the plate heat exchanger by connecting pieces 7. The attachments 6 and 6a serve for distributing the fluid introduced through the nozzles 7, or for collecting and concentrating the fluid to be removed from the plate heat exchanger. The various fluid streams then exchange thermal energy within the plate heat exchanger.

[0050] The plate heat exchanger shown in FIG. 1 is designed to feed fluid streams past each other in separate passages for the purpose of heat exchange. One part of the streams can be guided past one another in opposite directions, another part crosswise or in the same direction.

[0051] The central body 8 is essentially an arrangement of separating plates, heat exchange profiles (so-called fins) and distributor profiles. Separating plates and layers with profiles alternate. A layer having a heat exchange profile and distributor profiles is called a passage.

[0052] The central body 8 thus has passages and separating plates arranged alternately parallel to the flow directions. Both the separating plates and the passages are usually made of aluminum. To their sides, the passages are closed off by side strips made of aluminum, so that a side wall is formed by the stacking design with the separating plates. The outside passages of the central body are closed off by a cover made of aluminum (cover plate) lying parallel to the passages and the separating plates.

[0053] Such a central body 8 can be produced, for example, by applying a solder to the surfaces of the separating plates and then stacking the separating plates and the passages on top of each other alternately. The covers cover the stack 8 at the top or bottom. The central body has then been soldered by heating in an oven.

[0054] At the sides of the plate heat exchanger, the distributor profiles have distributor profile accesses (so-called headers or half-shells). The fluid may be introduced through these from the outside into the associated passages via the attachments 6 and 6a and connecting pieces 7 or also removed again. The distributor profile accesses are concealed by the attachments 6 and 6a.

[0055] The plate heat exchanger is equipped with a sufficient number of temperature sensors 10, here taking the form of fiber Bragg grating sensors, in order to capture temperature profiles or temperature fields or temperature profiles as temperature measurement values. Although in FIG. 1 the temperature sensors 10 have relatively large distances between each other, in practice these are advantageously closely distributed in order to be able to measure the temperature distribution with sufficient resolution.

[0056] The temperature sensors 10 are coupled in a data-transmitting manner to a computing unit 20, which may be designed, for example, as a control device of the heat exchanger 1. The computing unit 20 is in turn coupled to a remote computing unit 30 (“cloud”) in a data-transmitting manner, which is designed in particular as a server, expediently as part of a remote, distributed computing unit system in the sense of cloud computing. The control device 20 is expediently in communication with the remote computing unit 30 via a network 25, in particular via the Internet.

[0057] In FIG. 2, a preferred embodiment of a method according to the invention is schematically represented as a block diagram, in the course of which a remaining service life of the heat exchanger 1 is determined.

[0058] In a step 201, temperature profiles or temperature fields of the heat exchanger 1 are captured as temperature measurement values by means of the fiber Bragg grating sensors 10 and transmitted from the sensors 10 to the computing unit 20.

[0059] In step 202, such temperature measurement values are transmitted from the computing unit 20 to the remote computing unit or to the cloud 30.

[0060] In the remote computing unit 30, a finite element method is executed in step 203 as a function of the captured temperature measurement values. The temperature measurement values, which are captured on-line during the ongoing operation of the heat exchanger 1, are used here as boundary conditions for the finite element method.

[0061] In step 204, mechanical stresses prevailing at different locations in the heat exchanger 1 are determined as results of the finite element method from the remote computing unit 30. In the course of the finite element method, the heat exchanger 1 is divided into finite number of sub-regions or finite elements. At the transition between the individual finite elements the physical or thermo-hydraulic behavior of the entire heat exchanger 1 is simulated by predetermined continuity conditions. In the remote computing unit 30, a complex system of partial differential equations is thus numerically solved in the course of the finite element method in order to determine the mechanical stress in the heat exchanger 1 as a result.

[0062] In step 205, a remaining service life of the heat exchanger 1 is determined in the remote computing unit 30 as a function of this determined mechanical stress.

[0063] The service life of the heat exchanger 1 is largely determined on the basis of the number of stress changes of a certain magnitude which occur, for example, during start-up, when changing between different operating scenarios or as a result of process disturbances caused, for example, by machine or valve faults.

[0064] The remaining service life of the heat exchanger 1 can therefore be estimated in step 205 as a function of the mechanical stress or stress levels or stress curves prevailing in the material of the heat exchanger 1 determined in step 204.

[0065] For detailed explanations of how mechanical stresses of a heat exchanger can be determined with the aid of the finite element method and how the remaining service life of a heat exchanger can be determined from mechanical stresses, reference is made at this point, for example, to Freko, 2014 (Freko “Optimization of lifetime expectance for heat exchangers with special requirements” Proc. IHTC15 9791, 2014), Wang et al, 2006 (Wang, C. G. and S. Shan, Review of metamodeling techniques in support of engineering design optimization, J. Mechanical Design (2006)), Hölzl, 2012 (Hölzl, Reinhold. 2012. Lifetime estimation of aluminum plate fin heat exchangers. in: Proceedings of the ASME 2012 Pressure Vessels & Piping Division Conference) and to patents EP 1 830 149 B1 and U.S. Pat. No. 7,788,073 B2.

[0066] The steps 203 to 205, i.e. the execution of the finite element method, the determination of mechanical stress and the determination of the remaining service life, are carried out by the remote computer unit 30 on-line, that is to say during operation of the heat exchanger 1.

[0067] Furthermore, in step 206, the remote computing unit 30 stores the temperature measurement values received in step 202 along with the results of steps 203 to 205, that is, the executed finite element method, the determined mechanical stress and the determined remaining service life, for example, in a memory unit in the remote computing unit 30.

[0068] Such stored data are used at a later time point for a renewed determination of the remaining service life, indicated by reference sign 207 when in other words steps 203 to 205 are carried out again at a later time point.

[0069] A self-learning algorithm is thus provided which recognizes process boundary conditions already analyzed and finite element methods already carried out in the past and makes use of results that are already available.

[0070] The preferred embodiment of the present invention shown in FIG. 2 thus relates to a method for continuously determining the service life consumption of process apparatuses such as the heat exchanger 1 which are subjected to thermal stress, on the basis of sufficiently many temperature measurements or sufficiently precise determination of the temperature field, e.g. by means of fiber Bragg grating sensors, in the course of an automated finite element analysis and by means of a self-learning algorithm.

[0071] Thereby, as industrial, thermo-hydraulic boundary conditions for the finite element method for stress analysis performed in step 203, on-line measurements from step 201 are used directly instead of complex thermo-hydraulic simulation models.

[0072] The action chain from the measurement 201 via the finite element method 203, the stress analysis 204 and the service life assessment 205 is automated, for example as a concurrent cloud service, in particular in the course of a self-learning algorithm, which recognizes process boundary conditions already analyzed in the past and FEM analyzes carried out and uses results (207) that are already available.

[0073] The algorithm can operate, for example, according to the following operating principle: If a current temperature measurement or a temperature distribution or temperature gradient distribution defined by currently measured temperature measurement values is sufficiently similar to a temperature or temperature gradient distribution already measured in the past and deviates from this at most by a predetermined maximum permissible deviation or uncertainty, it will be possible to use the corresponding result relating to the service life influence already determined in the past.

[0074] Alternatively, the case may arise that a temperature or temperature gradient distribution defined by currently measured temperature measurement values is not sufficiently similar to a temperature or temperature gradient distribution already measured in the past and thus deviates from all temperature or temperature gradient distributions already measured in each case by more than the predetermined maximum permissible deviation or uncertainty. If, however, in this case the current temperature distribution lies between two temperature distributions already determined in the past, the results of which have already been investigated with regard to the service life influence, then an interpolation will expediently be carried out. Otherwise, a rigorous recalculation will take place for the current temperature distribution.

[0075] An apparatus-related on-line service life analysis is thus made possible, which does not represent a stress regression of thermo-hydraulically simulated process states, but enables a continuous and self-learning service life analysis in real plant operation.