EP3179192A1 - Method for determining a state of a heat exchanger device - Google Patents

Abstract

A method for determining a state of a heat exchanger device (10), which comprises means for heat transfer by means of at least one process stream, wherein a thermohydraulic simulation of the at least one process stream through at least one passage (14) in the heat exchanger means (10) for determining temperature and / or heat transfer coefficient profiles of the means for heat transfer takes place.

Description

The invention relates to a method for determining a condition, such as a strength of a heat exchanger device. In this case, for example, plate heat exchangers are considered and further proposed methods for producing a heat exchanger and / or a process plant. Moreover, the invention relates to a method for operating heat exchangers or heat exchangers or process plants.

It is desirable to predict the mechanical and thermal stress of elements in process plants, such as air separation or gas liquefaction plants, to estimate their life, maintenance or durability. This requires simulation methods that realistically simulate the operation of the system and provide state variables of the elements installed in the system. In most cases, these simulation methods are computationally extremely expensive or they do not provide sufficiently precise data.

It is therefore an object of the present invention to provide improved simulation capabilities.

This object is achieved by a method having the features of claim 1. The dependent claims name optional further education.

Accordingly, a method for determining a state of a heat exchanger device having means for heat transfer by means of process streams is proposed. In this case, a thermohydraulic simulation of one or more process streams takes place through one or more passages in the heat exchanger device for the determination of temperature and / or heat transfer coefficient profiles of the means for heat transfer.

The one or more process streams may be material streams and in particular may be formed by fluid streams of a respective process fluid or by energy flows. In this respect, in one embodiment, a method for determining a state of a heat exchanger device having means for heat transfer by means of fluid streams of a process fluid is proposed, in which a thermohydraulic simulation of the fluid flows of the process fluid through passages in the heat exchanger device for determining temperature and / or Heat transfer coefficient profiles of the means for heat transfer takes place.

The process fluid is in particular a fluid medium of a cryogenic plant, such as liquids, liquefied gases or gas mixtures. It is conceivable, for example, water, liquefied petroleum gas, liquefied air or air separation products.

The state to be determined of the heat exchanger device is in particular a thermohydraulic state. It is also conceivable to determine a strength state.

The term used in the plural term "means" is to be understood as a generic name, so that not necessarily several structural elements for heat transfer are necessary.

As a heat exchanger device usually applies a device which is adapted to transfer heat from a first to a second side. It is also possible to speak of a heat exchanger device which has structural means. Strictly speaking, there is no "exchange" of heat, but a quantity of heat is transferred, which is why in the following also referred to by a heat exchanger.

In principle, the term "heat exchanger" in the sense of this description also includes devices that transmit or conduct heat. In this respect, a so-called heat pipe or a heat pipe can be regarded as a heat exchanger device. Also, a heat-conducting element in a system, so a means for heat transfer, can be understood as a heat exchanger device.

As a heat exchanger device also applies a so-called regenerator, in which heat first - for example, a first fluid withdrawn and - is stored and the heat then - for example, to a second fluid - is discharged.

In embodiments, the heat exchange device is configured to transfer an amount of heat from a first fluid to a second fluid. One speaks also of a recuperator.

The proposed method refers to general devices that can transfer heat,

There is a thermohydraulic determination of temperature profiles in passages of the heat exchanger, which can vary over time. These dynamic temperature profiles are required as boundary conditions of the structural mechanics calculation. This is e.g. performed using finite element methods (FEM). The determined temperature profiles can be present on structural elements of the heat exchanger, which conduct the process fluid. However, man can also speak of temperature or heat transfer coefficient profiles of the respective process fluid flows.

In the thermohydraulic simulation, preferably temporally variable temperature boundary conditions and / or heat transfer coefficient profiles, in particular at the means for heat transfer, are determined. In further developments of the method, concentration and / or vapor content profiles of the process fluid are also determined. By determining the aforementioned profiles with the aid of thermohydraulic simulation, the profiles serving as boundary conditions for further determination methods for the heat exchanger or heat exchanger, a reliable determination of the state is made possible with reduced computational effort. As part of the simulation, thermodynamic states and fluid-dynamic states in the heat exchanger device or a process-engineering system are thus simultaneously determined.

The temporally varying temperature boundary conditions are in embodiments using a model for a phase transition of the process fluid, for a separation of components of the process fluid or a separation of Components of the process fluid, determined for a Auffüllvorgang with the process fluid and / or fluid dynamic instabilities of the process fluid.

In embodiments, for thermal-hydraulic simulation, a respective passage with a coupled means for heat transfer is imaged onto a one-dimensional model system with a process stream feed, a heat transfer path and a process stream outfeed, along the heat transfer path a particular one-dimensionally extended body with a heat capacity is applied.

Preferably, in the thermal hydraulic simulation, a heat capacity value and / or a heat transfer value for the one-dimensional expanded body are increased stepwise or continuously to ensure numerical convergence of the one-dimensional model system.

• Erfassen mehrerer, vorzugsweise aller, Passagen eines Wärmetauschers und/oder einer verfahrenstechnischen Anlage mit jeweils einem Anfangspunkt und einem Endpunkt, wobei ein jeweiliger Anfangs- oder Endpunkt einer Prozessstromeinspeisung oder einer Prozesstromausspeisung entspricht;
• Erfassen von Knoten zwischen den erfassten Passagen, wobei an einem Knoten mehrere Anfangs und/oder Endpunkte zusammenlaufen;
• Zuordnen eines eindimensionalen Modells zu jeder erfassten Passage;
• Festlegen von Drücken des Prozessfluids an Prozesstromausspeisungen und den Knoten; und
• Durchführen einer räumlich und zeitlich diskretisierten computerimplementierten Berechnung der bzw. des eindimensionalen Modells zum Bestimmen der Temperatur- und/oder Wärmeübergangskoeffizientenprofile.

In embodiments, the method comprises at least one or more and preferably all of the following steps:

• Detecting a plurality, preferably all, passages of a heat exchanger and / or a process plant, each having a start point and an end point, wherein a respective start or end point corresponds to a process stream feed or a process stream feed;
• Detecting nodes between the detected passages, wherein a plurality of start and / or end points converge at a node;
• Associating a one-dimensional model with each detected passage;
• Setting pressures on the process fluid to process power outlets and the node; and
• Performing a spatially and temporally discretized computer-implemented calculation of the one-dimensional model or models for determining the temperature and / or heat transfer coefficient profiles.

Preferably, in the sense of a Navier-Stokes' description, a complete spatially resolved thermodynamic state in one dimension is taken into account in terms of simulation technology. That means mass, momentum and energy balances are considered one-dimensional. In this respect one can say that to the thermohydraulic Simulation a respective passage is described using one-dimensional Navier-Stokes equations.

Preferably, adiabatic boundary conditions are used at the start and end points of, for example, a metal element bounded passage or at a process stream feed and a process stream outfeed to the metal. In other words, it is assumed that no heat transport takes place within the metal in the direction of flow of the process fluid.

In the corresponding one-dimensional simulation, variants of the method include terms which describe a temporal mass enrichment of the process fluid, a spatial mass transport of the process fluid, a reaction rate, a temporal impulse accumulation of the process fluid, a spatial impulse transport of the process fluid, a spatial pressure gradient, a spatial friction Influences of gravity on the process fluid, a temporal energy enrichment of the process fluid, a spatial enthalpy transport of the process fluid, an expansion work of the process fluid, friction dissipation and / or a heat input or acoustic input from the outside.

Embodiments of the method are used to forecast a lifetime of parts of a process plant, such as a heat exchanger, under the influence of thermal changes during operation of the plant. One speaks also of a lifetime consumption analysis. According to a variant of the method, the state of the heat exchanger device is determined as a life consumption in the manner of a Wöhler curve, wherein a stress in dependence on a number of operating cycles of the heat exchanger device is determined.

The means for heat transfer may comprise a pipe, a plate, a separating plate, a profile part, a lamella or a rib.

Preferably, the simulation takes into account a Joule-Thompson effect of the process stream in the passages.

In the implementation of the method is carried out in particular a temporal and local discretization.

The state of the heat exchanger device is optionally determined by means of a finite element method (FEM) for a structural analysis of the state as a function of the variable temperature boundary conditions. In this case, voltage states (locally and temporally distributed) of the heat exchanger device can be determined.

There is also proposed a method of manufacturing a plant or heat exchanger device, wherein structural parameters of the heat exchanger device are determined as a function of a specific state as a result of the method for determining a state of the heat exchanger device of the type to be produced. In this case, at least one structural parameter is in particular a solder joint, a material thickness or a material selection.

By a prior simulation, for example, certain operating conditions for the heat exchanger, and a corresponding state determination as a lifetime consumption analysis, the design of the system or the heat exchanger can be adjusted so that an improved life expectancy occurs. For example, fins, length or width specifications, layer patterns, two-phase feeds or other design measures can be taken. Manufacturing is to be understood as meaning that existing plants are modified with, for example, installed heat exchangers in order to achieve improved simulated or predicted lifetimes. In this respect, it is also possible to speak of a method for converting a system or heat exchanger device if a change in the system takes place on the basis of simulations carried out.

Furthermore, a method for operating a system or heat exchanger device is proposed, wherein operating parameters are defined as a function of a specific state as a result of the aforementioned method for determining a state of the heat exchanger device, and wherein an operating parameter is in particular a pressure, a maintenance interval or a replacement time of means for heat transfer.

By a simulation, for example, certain operating situations or operating histories for the heat exchanger or the system, and a corresponding state determination as a lifetime consumption analysis, the design or operation of the system or the heat exchanger can be adjusted so that an improved life expectancy occurs. The simulation thus enables optimized operation of systems comprising heat exchangers.

Furthermore, a computer program product is proposed which causes the execution of the method or methods explained above on a program-controlled device. It is conceivable, for example, the implementation using a computer or a control room computer for a process plant. The determination of the (thermo-hydraulic) state of the respective heat exchanger can be implemented in the manner of a process simulator. As a result, interactions of the considered heat exchanger with other parts of the system can be taken into account, in particular modular. The process simulator can be part of a simulation software.

A computer program product, such as a computer program means may, for example, be used as a storage medium, e.g. Memory card, USB stick, CD-ROM, DVD, or even in the form of a downloadable file provided by a server in a network or delivered. This can be done, for example, in a wireless communication network by the transmission of a corresponding file with the computer program product or the computer program means.

The method (s) are in particular software-implemented, and in the following also synonymously is spoken by a simulation software and / or a process simulator.

It is also proposed a user interface for such a process simulator. The user interface then includes a display device configured to visually represent a network of passages, first selection means for selecting a displayed passage, second selection means for assigning a one-dimensional model to a selected passage, and third selection means for assigning simulation parameters to the one-dimensional model assigned to the selected passage, the user interface being communicatively coupled to the process simulator.

Preferably, the user interface display device is further configured to display multiple variants of one-dimensional models for selection, the variants including consideration of a temporal mass enrichment of the process fluid, a bulk mass transport of the process fluid, a reaction rate, a temporal impulse accumulation of the process fluid, a spatial impulse transport of the process fluid, a spatial pressure gradient, a spatial friction, effects of gravity on the process fluid, a temporal energy enrichment of the process fluid, a spatial enthalpy transport of the process fluid, an expansion work of the process fluid, friction dissipation and / or a heat input or an acoustic entry from the outside for the respective passage allow.

A simulation facility then includes at least one process simulator and user interface as described above and below, and the user interface passes the selected and assigned indications for the selected passages, the respective assigned one-dimensional model variants, and the assigned simulation parameters to the process simulator.

Further possible implementations of the invention also include not explicitly mentioned combinations of features or embodiments described above or below with regard to the exemplary embodiments. The skilled person will also add individual aspects as improvements or additions to the respective basic form of the invention.

• Fig. 1 zeigt schematisch und perspektivisch einen Plattenwärmeübertrager von außen mit einigen Anbauten.
• Fig. 2 zeigt den Plattenwärmeübertrager aus Figur 1 mit einem teilweise weggelassenen Abdeckblech ohne die Anbauten.
• Fig. 3 zeigt schematisch und perspektivisch eine Passage aus dem Plattenwärmeübertrager der Fig. 1 und 2.
• Fig. 4 zeigt eine Darstellung für ein Passagenmodell.
• Fig. 5 zeigt Diagramme mit möglichen Start-Temperaturverteilungen in einer Passage.
• Fig. 6 - 10 zeigen Simulationsergebnisse für verschiedene Ausführungsformen von Wärmeübertragern.
• Fig. 11 zeigt ein Ablaufdiagramm für ein Ausführungsbeispiel eines Simulationsverfahrens zum Bestimmen von Zuständen eines Wärmeübertragers.
• Fig. 12 zeigt eine schematische Darstellung für ein Ausführungsbeispiel eines Prozesssimulators zum Bestimmen von Zuständen eines Wärmeübertragers.
• Fig. 13 zeigt eine schematische Darstellung für ein Ausführungsbeispiel einer Benutzerschnittstelle für einen Prozesssimulator nach Fig. 12.
• Fig. 14 zeigt ein Ablaufdiagramm für ein weiteres Ausführungsbeispiel eines Simulationsverfahrens zum Bestimmen von Zuständen eines Wärmeübertragers.
• Fig. 15 zeigt ein Ablaufdiagramm für ein Ausführungsbeispiel eines Verfahrens zum Betreiben einer verfahrenstechnischen Anlage.

Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the embodiments of the invention described below. Furthermore, the invention will be explained in more detail by means of preferred embodiments with reference to the attached figures.

• Fig. 1 shows schematically and in perspective a plate heat exchanger from the outside with some attachments.
• Fig. 2 shows the plate heat exchanger FIG. 1 with a partially omitted cover plate without the attachments.
• Fig. 3 shows schematically and in perspective a passage from the plate heat exchanger of Fig. 1 and 2 ,
• Fig. 4 shows a representation for a passage model.
• Fig. 5 shows diagrams with possible start temperature distributions in one passage.
• Fig. 6 - 10 show simulation results for different embodiments of heat exchangers.
• Fig. 11 shows a flowchart for an embodiment of a simulation method for determining states of a heat exchanger.
• Fig. 12 shows a schematic representation of an embodiment of a process simulator for determining states of a heat exchanger.
• Fig. 13 shows a schematic representation of an embodiment of a user interface for a process simulator Fig. 12 ,
• Fig. 14 shows a flowchart for another embodiment of a simulation method for determining states of a heat exchanger.
• Fig. 15 shows a flowchart for an embodiment of a method for operating a process plant.

In the figures, the same or functionally identical elements have been given the same reference numerals, unless stated otherwise.

Fig. 1 shows as an example of a heat transfer device, a plate heat exchanger 10 from the outside. The plate heat exchanger 10 has a central cuboid 8 with a length L of about 6 m and a width or height B, H of 1.2 m each. On top of the cuboid 8, on its sides and below the cuboid 8, one recognizes attachments 6 and 6a. Below the cuboid 8 and on the side facing away from the illustrated page are also such essays 6 and 6a. However, these are partially obscured. Through nozzle 7, the plate heat exchanger 10, a process fluid, for example, water, supplied or this be removed again. Thus, when flowing through, a process stream is obtained. The attachments 6 and 6a serve to distribute the water introduced through the nozzles 7 or to collect and to concentrate the water to be taken from the plate heat exchanger 10. Within the plate heat exchanger 10, the various water streams then exchange heat.

The in Fig. 1 shown plate heat exchanger 10 is designed to pass more than two process streams in separate passages for heat exchange with each other. A part of the streams can be passed in opposite directions, another part crosswise. To further illustrate, the simplified situation is considered where two process streams flow past each other in separate alternating passages. In principle, larger numbers of process streams can also be handled and taken into account in a simulation.

In Fig. 2 you can see how the plate heat exchanger 10 is constructed inside. Essentially, it is a cuboid 8 of separating plates 1 and internals to improve the heat transfer 2, so-called fins 2, or distribution profiles 3. Separators 1 and 2 or 3 layers having layers alternate. A layer comprising a heat exchange profile 2 and distributor profiles 3 is called passage 14 (such a passage is in FIG Fig. 3 shown and described below).

The cuboid 8 thus has alternately parallel to the flow directions lying passages 14 and dividers 1. Both the dividers 1 and the passages 14 are made of aluminum. On their sides are the passages 14 through bars 4 made of aluminum, so that a side wall is formed by the stacking construction with the dividing plates 1. The outer passages 14 of the cuboid 8 are covered by a parallel to the passages and the partitions 1 lying cover 5 made of aluminum.

The cuboid 8 is produced by applying a solder to the surfaces of the separating plates 1 and then alternately stacking the separating plates 1 and the passages 14. The covers 5 cover the stack 8 up or down. Subsequently, the stack 8 has been soldered by heating in a stack 8 comprehensive furnace. In the dimensioning of the solder joints or the material thicknesses, in particular methods can be used which predict or calculate strength states of the elements of the heat exchanger 10. For example, weaknesses or particularly stress-loaded elements can then be amplified during manufacture. In order to be able to determine in particular stress distributions at the passages 14, it is desirable to simulate the dynamic temperature distributions and / or profiles of the local heat transfer coefficient profiles occurring as a result of the process flows.

On the sides of the plate heat exchanger 10, the distributor profiles 3 distributor profile access 9. Through this, the water can be introduced from the outside as process fluid into the associated passages 14 via the attachments 6 and 6a and nozzles 7 or also removed again. In the FIG. 2 shown distributor profile 9 are in Fig. 1 covered by the essays 6 and 6a.

Fig. 3 shows one of the passages 14 of the in the Fig. 1 and 2 shown plate heat exchanger. The direction of flow of the water is indicated by arrows. At one distributor profile access 9, the water flows in to be distributed in the associated distributor profile 3 over the entire width of the passage 14. Subsequently, the water flows through the heat exchange profile 2 and is concentrated after the heat exchange from the other distributor profile 3 on the output side distributor profile access 9. On its long and short sides, the passage 14 is bounded by the bars 4.

To promote turbulence of the water and thus the heat transfer favor, are formed in the heat exchange profiles 2 in the example as serrated fins.

Depending on the temperatures generated by the process streams flowing through the plate heat exchanger 10 during operation, the dividing plates 1 and the profiles 2 and 3 undergo thermal expansion changes. This can lead to thermal stresses that can fatigue the plate heat exchanger 10 and eventually damage.

By means of a thermohydraulic simulation of the temperature distribution based on these heat flows in the plate heat exchanger 10, the stress distribution is determined in particular by means of a structural mechanical calculation. Based on these simulated stress distributions, it is possible to estimate failure risks, design improved plate heat exchangers 10 and, in particular, optimize operating modes.

In order to determine the stress distribution in a plate heat exchanger, first of all the spatial and temporal temperature distribution is determined by means of a thermohydraulic simulation and from this the stress distribution is calculated.

In order to determine the time-varying temperature boundary conditions, in particular at the means for heat transfer, a determination of the respective temperature and / or heat transfer coefficient profiles is essentially carried out. As simplistic assumptions, one-dimensional Navier-Stokes equations for the passages may be assumed in embodiments.

Furthermore, it is preferably taken into account: an accumulation of energy in the process fluid, dissipation, correlations according to HTRI, HTFS, VDI etc. or correlations that can be defined by the user of the corresponding simulation software, eg: α = α ( x ( z )) , α = α ( ṁ ( z )) where x is the mass fraction of steam, z is the position in the passage and m is the mass flow. Furthermore, the momentum dynamics can be taken into account as needed.

For the energy balance, a simplified variant of the simulation method for the 1-D heat capacity is assumed: $$\rho c_p\frac{\partial T}{\partial t}+v\rho c_p\frac{\partial T}{\partial z}=\dot{q}\mathrm{,}$$

Here, c _{p are} the specific heat capacity, ρ the process fluid density, T the temperature, v the speed of the process fluid , z the one-dimensional position, and q̇ a heat input as heat flow line density. The equation (1) corresponds to a heated pipe or a passage, for example, the length L.

Fig. 4 shows an example of three passages S1, S2, S3 and a partition wall 11 with a heat capacity CW. A respective passage, eg S3, has a fluid inlet 13 and a fluid outlet 12. Between the passages S1, S2, S3 and the heat capacity CW (or heat capacities) heat transfer is described as a one-dimensional extended heat flux density profile. In order to simulate a branch, for example, in the manner of a supply or withdrawal 15, pass the two passages S1 and S2 at the point 15 or a. For all passages a one-dimensional modeling is used. In this case, the start temperature distribution can be set arbitrarily. Using the example of the passage S2, the length L along the one-dimensional axis z is indicated. With respect to equation (1), the heat input for the passage S2 would be denoted by q̇CW, S2 .

Adiabatic boundary conditions can be used for the heat conduction of the one-dimensionally assumed partition wall (for example made of metal), that is to say: $$\frac{\partial T}{\partial z}{|}_{z=0.z=L}=\mathrm{0th}$$

In this respect, temperature changes in the partition wall 11 along the flow directions of the fluids in the passages S1, S2, S3 are neglected. In variants of the proposed method, other boundary conditions can be used or a heat transfer in partitions can be included in the simulation.

Fig. 5 shows two examples of an initial temperature distribution as a function of the position z. On the left a start temperature distribution is shown, which comes from a stationary assumed energy balance and on the right an arbitrarily assumed distribution. The initial distribution can z. B. be used for one of the passages.

wobei F eine Funktion gemäß dem zweiten Term aus Gleichung (1) ist, a, b entsprechende Vorfaktoren und der hochgestellte Querstrich für das Integralmittel (integraler Mittelwert) gemäß $\bar{f}=f\left(x*\right)=\frac{1}{\left|\omega \right|}{\int }_{\omega }f\left(x\right)\mathit{dx}$

steht. Die Stellen z⁺ und z^- geben die Grenzen des Kontrollvolumens w an. Es erfolgt nun eine Diskretisierung im Ortsraum z-Richtung der Passagenlänge L. Aufeinanderfolgende Punkte z_i und z_i+1 der Diskretisierung bilden den jeweiligen Kontrollraum z⁺ und z^-. Bei der räumlichen Diskretisierung wird für den in eckigen Klammern angegebenen Ausdruck in Gleichung (2) die Erfüllung einer Courant-Friedrichs-Levy-Bedingung verlangt. Man erhält so ein quadratisches Gleichungssystem für Differenzialgleichungen in der Zeit.In the following Fig. 6 - 10 Simulation results are given. For this purpose, the differential equations of the hyperbolic conservation equation (1) to be solved were converted into an integral equation of the following form: $$a\frac{\partial \tilde{T}}{\partial t}+b\left[F\left(z^{+}\right)-F\left(z^{-}\right)\right]=\dot{\widetilde{q\left(T\right)}}.$$

where F is a function according to the second term of Eq. (1), a, b are corresponding precursors and the superscript bar for the integral means (integral mean) according to FIG $\tilde{f}=f\left(x*\right)=\frac{1}{\left|\omega \right|}{\int }_{\omega }f\left(x\right)\mathit{dx}$

stands. The digits z ⁺ and z ^- indicate the limits of the control volume w. A discretization now takes place in the positional space z-direction of the passage length L. Successive points z _i and z _{i + 1 of} the discretization form the respective control space z ⁺ and z ^- . In the case of spatial discretization, the expression given in square brackets in equation (2) requires the fulfillment of a Courant-Friedrichs-Levy condition. This gives a quadratic system of equations for differential equations in time.

The temporal discretization takes place, for example, with the aid of a BDF method (Backward Differentiation Formula), which is not discussed in detail here. BDF methods for solving differential equations are known.

The 6 and 7 show results from the applicant's investigations for a so-called aluminum Brazed Plate Fin Heat Exchanger (PFHE) in its longitudinal direction. In the left part of FIG. 6 the z-axis is shown vertically. A scenario was simulated in which the warm process fluid flow (feed in top left 13, outfeed down right 12) fails through the heat exchanger. To compare the starting conditions (t = 0 s), the results according to the prior art are plotted according to the simulation software Aspen MUSE. You recognize a good one Match for the start condition. In Fig. 7 the temporal and local course of the metal temperatures is reproduced as a 3D representation.

The 8 and 9 show results from investigations by the applicant for a so-called Shell and Tube Heat Exchanger (STHE) 16. In such heat exchangers tube bundle 18 are surrounded by an outer jacket wall 17. The z-axis is horizontal and a scenario has been simulated where one of the two process streams fails ( Fig. 8, Fig. 9 ). For comparison are in Fig. 8 the temperature curves for t = 0 s according to the prior art according to the simulation software HTRI X is plotted. In Fig. 9 The right-hand diagram shows the temperature difference between the tube bundle and the heat exchanger jacket after the failure of the process fluid flow according to the one-dimensional modeling or simulation.

The Fig. 10 shows results from the applicant's investigations for a so-called Coil Wound Heat Exchanger (CWHE) 19. In such heat exchangers 19 wound tube bundles are enclosed by an outer shell. The upper left part of Fig. 10 shows an image of a corresponding heat exchanger. In Fig. 10 the temperature curves for t = 0 s for the warm process flow (shell side, (a)) and three cold pipe fractions (c) - (d) (solid lines) are plotted against the results of the simulation software GENIUS (x). It shows for the stationary initial state a match. Furthermore, the temperature profile of the three process streams in the wound heat exchanger 19 is shown for three times (t = 100 s, 200 s, 800 s).

The temporal temperature curves and heat transfer coefficient profiles can now serve as input data for a structural-mechanical stress analysis, so that a strength state of the respective heat exchanger can be determined taking into account thermohydraulic properties.

In Fig. 11 some process steps for a corresponding method are summarized. The method is carried out, for example, with the aid of a process simulator, which can be implemented as a computer program on a computer system, such as a PC. The Fig. 12 illustrates a possible embodiment for a process simulator. to Operation of the process simulator may serve a user interface. An example of an appropriate interface is one of Fig. 13 shown. In the following, a variant of the simulation method based on Fig. 11 - 13 explained.

The Indian Fig. 12 indicated process simulator 20 has a calculation module 21, a plurality of model modules 22 ₁ - 22 _N , a memory module 23 and simulation modules 24 ₁ - 24 ₃ . The modules 21-24 are implemented, for example, as software-implemented routines, program parts or functions. The process simulator 20 may be part of a software library. A hardware implementation is also conceivable in which the functions of the modules or units explained below are hardwired, implemented as ASICs or even FPGAs.

To operate the process simulator 20 by an operator is an in the Fig. 13 indicated user interface 25 communicatively coupled to the process simulator 25. The user interface 25 and the process simulator 20 form a simulation device to determine conditions of heat exchangers by means of a thermo-hydraulic simulation.

The user interface 25 includes a display device 26 configured to visually represent a network of passages S _{i of} a heat exchanger, first selection means for selecting a displayed passage, second selection means for assigning a one-dimensional model to a selected passage, and third selection means for assigning simulation parameters to the one-dimensional model assigned to the selected passage. The user interface 25, for example, displays various variants of one-dimensional models 27 ₁ -27 _N for selection and further enables a set of simulation parameters to be assigned to a respective selected model for a passage, the process simulator 20 then performing corresponding simulations through the simulation module 24 ₁ .

First, in the first step St1 passages 14 in the system, such as in the heat exchanger of Fig. 1-3 , identified. The respective passages are mapped as one-dimensional systems with a process fluid inlet, a heat transfer path and a process fluid exit, as shown in FIG Fig. 4 is indicated. For this purpose, the user interface 25 has a display device 26, the For example, a display in the manner of a monitor or touch screen includes. The display 26 displays a network of passages S _i , each with a starting point and an end point, possible nodes where several passages adjoin one another, the partitions with potential heat capacities CW and other possible elements of the process plant to be considered. In the Fig. 12 are simplified passages S _i indicated by dashed arrows, with end points or outlets correspond to the respective arrowhead.

The user can now select a passage (see arrow P1 in Fig. 13 ) and assign a suitable one-dimensional model. The selection is made for example by an input of a command or by a mouse click as a selection means on the passage shown.

The user interface 25 selects several possible models 27 ₁ - 27 _N. For example, the model for a heated pipe indicated in equation (1) may be assigned to the selected passage. This is indicated by the arrow P2.

Then the user can set simulation parameters that apply to the selected passage. For this selection means 29, for example, clickable buttons are provided. For example, the length of the passage and the pressure of the process fluid present at the outfeed are determined (arrows P4 and P5). Further possible simulation parameters are, for example, a process fluid velocity, a heat flow line density, a number of interpolation points along the length for the spatial discretization, a fluid temperature at the inlet or a heat capacity. Further simulation parameters are conceivable, the quantities to be assigned depending on the selected one-dimensional model.

The process simulator 20 has corresponding model modules 22 ₁ - 22 _N , wherein a model module 22 _{i is} set up to perform a one-dimensional, spatially and temporally independent discrete numerical calculation according to the model "i" taking into account associated simulation parameters. The one-dimensional models 27 ₁ - 27 _N that can be selected via the user interface 25 are implemented by the model modules 22 ₁ - 22 _{N in} terms of computing technology.

The user interface 25 now transfers the respective model selection together with the associated defined simulation parameters for the passages to the process simulator 20. For this purpose, for example, a description language or a script similar to a VHDL code can be used. The defined simulation parameters are stored in the memory module 23 and can be called by the calculation module 21.

In step St2 ( Fig. 11 ) is now a simulation of the process fluid flow and the temperature distribution based on Navier-Stokes equations. In the process simulator 20, the simulation module 24 ₁ accesses the model modules 22 ₁ - 22 _N and the simulation parameters present in the memory module 23 and carries out the respective numerical calculations. As a result, in step St3, dynamic temperature distributions are obtained on the surfaces of the heat exchanger elements such as plates, pipes, attachments, dividing plates, etc.

The simulation in step St2 preferably includes terms that include a time mass enrichment of the process fluid, a spatial mass transport of the process fluid, a reaction rate, a temporal impulse accumulation of the process fluid, a spatial impulse transport of the process fluid, a spatial pressure gradient, a position-dependent friction, and the effects of gravity on the process fluid, a temporal enthalpy enrichment of the process fluid, a spatial enthalpy transport of the process fluid, an expansion work of the process fluid, friction dissipation, and / or describe a heat input from the outside. For this purpose, in the process simulator 20 corresponding model modules 22 ₁ - 22 ₁ , for example, as simulation routines held, which can be retrieved from the (first) simulation module 24 ₁ and used. In each case one-dimensional conservation equations (in particular for mass, momentum and energy) and thermodynamic equations of state (in particular for density, temperature, pressure and energy) are used.

$$\frac{\partial }{\partial t}\left(\rho u\right)+\frac{\partial }{\partial z}\left({\mathit{\rho u}}^2\right)=-\frac{\partial }{\partial z}p+\frac{\partial }{\partial z}\sigma +\rho g\sin \left(\mathrm{\Theta }\right)$$

$$\frac{\partial }{\partial t}\left(\rho e\right)+\frac{\partial }{\partial z}\left(\rho eu\right)=-p\frac{\partial }{\partial z}u+\sigma \frac{\partial }{\partial z}u+\frac{U}{A_c}\dot{\bar{q}}$$

For compressible fluids, the Navier-Stokes equations can be summarized as follows: $$\frac{\partial }{\partial t}{c}_j+\frac{\partial }{\partial z}\left(c_{j}u\right)={\dot{r}}_j\mathrm{with\; j}=1.....\mathrm{nc}$$

$$\frac{\partial }{\partial t}\left(\rho u\right)+\frac{\partial }{\partial \mathrm{<figure-callout\; id="2"\; label="z\; \rho u"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">z\; </figure-callout>}}\left({\mathit{\rho u}}^{}\right)\left({\mathit{}}^2\right)=-\frac{\partial }{\partial z}p+\frac{\partial }{\partial z}\sigma +\rho G\sin \left(\mathrm{\Theta }\right)$$

$$\frac{\partial }{\partial t}\left(\rho e\right)+\frac{\partial }{\partial z}\left(\rho eu\right)=-p\frac{\partial }{\partial z}u+\sigma \frac{\partial }{\partial z}u+\frac{U}{A_c}\dot{\tilde{q}}$$

die Wärmeflussdicht in W/m², A die Querschnittsfläche in m² und U der Umfang. Die Dichte, Geschwindigkeit etc. sind dabei auf das Prozessfluid als Ganzes bezogen. Insofern ist die Dichte ρ zum Beispiel die Mischdichte des gesamten strömenden Fluids mit seinen Bestandteilen.Here, c _j = n _j / V is the molar density in mol / m ³ for the fluid component j, nc the number of fluid components (dimensionless), ρ the density in kg / m ³ , u the speed in m / s, e the specific internal energy in J / kg, pe the energy density in J / m ³ , θ the angle of attack in rad, ρ · g · sin (θ) the hydrostatic stress in Pa / m, σ the friction tensor in N / m ² , p the Pressure in Pa,

the heat flux density in W / m ² , A the cross-sectional area in m ² and U the circumference. The density, speed etc. are related to the process fluid as a whole. In this respect, the density ρ is, for example, the mixing density of the entire flowing fluid with its constituents.

The sizes can in principle also be stated for each fluid component j and be used as a basis for the simulation. For example, a segregation of the components or constituents of the respective process fluid can thus also be detected.

Here, the first term in the mass-conservation equation (3) stands for mass enrichment, the second for mass transport, and the right-hand side corresponds to the reaction rate. In the momentum conservation equation (4), the first term on the left side is for momentum accumulation, the second term for impulse transport. On the right side of equation (4), the first term considers acceleration due to a pressure gradient, the second term friction, and the third term gravity. The variables given in the model equations can be used in particular as simulation parameters.

wobei ε der volumetrische Dampfanteil ist.Depending on the desired accuracy of the simulation but also taking into account the computational effort, some of the terms can be neglected. It will in particular also assume that the process fluid is homogeneous, or vapor (vap) and the liquid (liq) flow at the same speed: $$\rho ={\rho }_{\mathit{vap}}\epsilon +{\rho }_{\mathit{liq}}\left(1-\epsilon \right).$$

where ε is the volumetric vapor fraction.

For example, in solving the equations, it is independently discretized and spatially discretized. As a result, the resulting computational effort can be reduced. In the time direction, a BDF method for numerical solution is preferably used. Locally a finite volume method can be used.

When starting the simulation by the process simulator 20, heat capacity values and / or heat transfer value for the one-dimensional extended body are initially disregarded and increased only slowly, stepwise or continuously, to numerically converge the one-dimensional model system realized with the aid of the model modules 22 ₁ -22 _N will ensure. That is, it is started by a non-heat coupled model system, and heat transport is ramped up to the desired value according to the particular simulation parameter.

Compared with conventional CFD (computational fluid dynamics) methods, the complexity is greatly reduced due to the simplification of one-dimensional phenomena. It can be a low-cost simulation that provides reliable values.

The boundary conditions provided by the simulation module 24 ₁ in step St3 are now used for further calculations and simulation of structural mechanical properties of the heat transfer means installed in the heat exchanger. Thus, temperature and / or heat transfer coefficient profiles of the means for heat transfer are obtained, which can be used in subsequent FEM calculations (step St4).

The second simulation module 24 _{2 of} the process simulator 20 is set up to perform a corresponding FEM method. For example, the second leads Simulation module 24 ₂ a method according to the EP 1 830 149 B1 by which reference is hereby made to the full extent (incorporated by reference).

• Berechnen von Temperaturspannungen des Plattenwärmetauschers 10 im Inneren des Wärmetauschers während dessen Betriebs mittels einer dreidimensionalen numerischen Simulation; und
• Bestimmen der Festigkeit des Plattenwärmetauschers auf der Basis der berechneten Temperaturspannungen.

In the structural mechanical determination of temperature-induced stresses or the strength of a heat exchanger, the following method steps can be performed, wherein for simplicity a plate heat exchanger 10 with dividers 1 and 2 profiles (see. Fig. 1 ) is looked at:

• Calculating temperature stresses of the plate heat exchanger 10 inside the heat exchanger during its operation by means of a three-dimensional numerical simulation; and
• Determine the strength of the plate heat exchanger based on the calculated temperature stresses.

• Modellieren des Profilteiles 2 als ein den Raum zwischen den Trennblechen 1 homogen ausfüllender Metallblock, welcher sich an einer seiner Seiten in einem wärmeleitfähigen Kontakt mit dem Trennblech 1 befindet;
• Bestimmen des über das Prozessfluid vermittelten Gesamtwärmeeintrages in das Profilteil 2 und in das angrenzende Trennblech 1 mit einem Wärmeeintrag von dem Fluid in das Profilteil 2 mit anschließender Wärmeleitung durch das Profilteil 2 und von dem Profilteil 2 in das angrenzende Trennblech 1; und
• Einbringen einer dem ersten Wärmeeintrag entsprechenden Wärmemenge in eine erste Fläche innerhalb des Metallblocks. Das Verfahren weist insbesondere Korrekturfaktoren zur Anpassung des Schichtmodells.

In the three-dimensional numerical simulation of the temperature stresses, the spatial temperature distribution in the profiles 2 and in the partitions 1 is determined by creating and using a layer model of a part of one of the profiles 2 in contact with one of the partitions 1. The three-dimensional numerical simulation then includes the steps:

• Modeling the profile part 2 as a metal block homogeneously filling the space between the dividing plates 1, which is in heat-conductive contact with the separating plate 1 on one of its sides;
• Determining the mediated via the process fluid total heat input in the profile part 2 and in the adjacent partition plate 1 with a heat input from the fluid in the profile part 2 with subsequent heat conduction through the profile part 2 and of the profile part 2 in the adjacent partition 1; and
• Introducing a quantity of heat corresponding to the first heat input into a first area within the metal block. In particular, the method has correction factors for adapting the layer model.

For example, the FEM calculations yield stress curves, comparative stress data, or similar state determining quantities that can be used to estimate the lifetime of particular elements in the heat exchanger.

In the optional step St5 therefore a lifetime, for example, determined by a sheet in the heat exchanger. The third simulation module 24 ₃ is set up to calculate a lifetime consumption of the system or of the heat exchanger as a function of the structural mechanical determination of temperature-induced voltages. A corresponding simulation system, such as the process simulator 20, is thus based on the combination of the thermo-fluid dynamic simulation with a finite element analysis and lifetime estimation.

A finite element analysis for lifetime estimation, as it is done in steps St4 and St5 or by the simulation modules 24 ₂ and 24 ₃ , is, for example, in R. Hölzl: "Lifetime estimation of aluminum plate fin heat exchangers", Proceedings of the ASME 2012 Pressure Vessels & Piping Division Conference (PVP2012), July 15-19, 2012, Toronto, Ontario, Canada [PVP2012-78343], which is incorporated herein by reference (incorporated by reference).

In Fig. 14 FIG. 3 is a flowchart for another embodiment of an advanced simulation method for determining states of a heat exchanger.

In step St21, critical operating scenarios are identified and defined with regard to thermal stresses and thus to the expected service life of the heat exchanger. For example, startup or shutdown scenarios can be determined.

In step St22 to St24, based on the scenario definition, the thermohydraulic modeling, validation and simulation of the corresponding heat exchanger (s). The effects considered in the simulation are the same as those explained for steps St2, St3 above.

In step St25, dynamic temperature and heat transfer coefficient profiles are created as a result of the simulations. These represent the input data for the subsequent structural mechanical calculations, which are performed in step St26. The structural mechanics calculations provide, for example, fatigue curves for the calculated operating scenarios, from which the expected lifetime consumption for the individual scenarios (step St27) is determined. In Consequently, for the entirety of the defined operating scenarios, the resulting total lifetime consumption for the heat exchanger under consideration can be determined (step St28).

The simulation results of the aforementioned analyzes can be used to achieve a sufficient longevity of heat exchangers through adjustments. The findings may lead to a changed design of a heat exchanger, to changed or optimized control concepts of the plant, to special operating instructions for the operating personnel, to the implementation of alarms or additional or modified process engineering circuits.

The Fig. 15 schematically shows an application of a process simulator 20 to support a plant controller 30 in a method for operating a process plant 40. Usually, the plant controller 30 controls by means of control signals CT the system, such as a cryogenic plant for air separation, gas liquefaction or the like. The system controller 30 receives measurement or sensor signals MS from measuring sensors in the system. For example, temperatures, pressures and flows are detected and evaluated by the plant controller 30 so that intended operations can be set.

In Fig. 15 Furthermore, a process simulator 20 is provided, which performs a simulation of the completed operations or modifications of the planned operations. How to Fig. 11 1, a life cycle consumption estimate is made (see step St5) so that an operating procedure or parameter may be changed by the plant controller 30 to allow for improved or extended operating time, for example with a prolonged maintenance interval. For this purpose, the process simulator 20 provides lifetime estimates LD to the plant controller 30 or operating personnel. As part of a maintenance cycle, the further operation can take place with the improved operating parameters or the improved operating sequence. The system controller 30 then outputs possibly modified control signals CT '. Consequently, the operation of the plant 40 is optimized depending on the simulation by the process simulator 20.

The process simulator 20 may, for example, in the maintenance intervals hints for operating recommendations to be changed for the operator, but it also It is conceivable that on the basis of the simulation results LD, the system controller 30 automatically makes adjustments to the respective operating sequence or to the operating parameters.

In this respect, production, planning, design, conversion or operation of a process plant can be carried out as a function of the thermo-hydraulic simulation, as described above. It is also possible to determine structural parameters, such as a choice of material, plate thicknesses, tube lengths or the like, before the production of the system or of the heat exchanger.

Although the present invention has been described with reference to embodiments, it is variously modifiable. It can z. As heat exchangers are considered to have other than the geometries shown.

1

Trennblech

2

Wärmeaustauschprofil

3

Verteilerprofil

4

Balken

5

Abdeckung

6,6a

Aufsatz

7

Stutzen

8

zentraler Quader/Stapel

9

Verteilerprofilzugang

10

Plattenwärmetauscher

11

Trennwand

12

Austritt/Ausspeisung

13

Eintritt/Zuspeisung

14

Passage

15

Abzweig/Ausspeisung

16

PFHE-Wärmeübertrager

17

Mantel

18

Rohre

19

STHE-Wärmeübertrager

20

Prozesssimulator

21

Berechnungsmodul

22₁ - 22_N

Modellmodul

23

Speichermodul

24₁ - 24₃

Simulationsmodul

25

Benutzerschnittstelle

30

Anlagensteuerung

40

verfahrenstechnische Anlage

CT

Steuersignale

CW

Wärmekapazität

MS

Messdaten

LD

Simulationsergebnis

S1 - S3

Passage

St1 - St28

Verfahrensschritt

Used reference signs:

1

Divider

2

Heat exchange profile

3

distribution profile

4

bar

5

cover

6,6a

essay

7

Support

8th

central cuboid / stack

9

Distributor profile access

10

Plate heat exchanger

11

partition wall

12

Leak / blowdown

13

Admission / feeding in

14

passage

15

Branch / outfeed

16

PFHE heat exchanger

17

coat

18

Tube

19

Sthe heat exchanger

20

process simulator

21

calculation module

22 ₁ - 22 _N

model module

23

memory module

24 ₁ - 24 ₃

simulation module

25

User interface

30

system control

40

Process engineering plant

CT

control signals

CW

heat capacity

MS

measurement data

LD

simulation results

S1 - S3

passage

St1 - St28

step

Claims (15)

Method for determining a state of a heat exchanger device (10), which has means for heat transfer with the aid of at least one process flow, wherein a thermo-hydraulic simulation of the at least one process flow by at least one pass (14) in the heat exchanger device (10) for determining temperature and / or heat transfer coefficient profiles of the means for heat transfer takes place. The method of claim 1, wherein the at least one process stream comprises a material flow, in particular a fluid flow of a respective process fluid, or an energy flow. The method of claim 1 or 2, wherein in the thermo-hydraulic simulation time-varying temperature boundary conditions and / or heat transfer coefficient profiles, in particular at the means for heat transfer, are determined. The method of claim 3, wherein the time-varying temperature boundary conditions are determined using a model for a phase transition of the process fluid, for a separation of constituents of the process fluid, for a filling process with the process fluid and / or for fluid dynamic instabilities of the process fluid. Method according to one of claims 1 - 4, wherein for the thermal-hydraulic simulation, a respective passage (14) with a coupled means for heat transfer to a one-dimensional model system with a process stream feed (13), a heat transfer path (S3) and a process flow outfeed (12) is mapped wherein along the heat transfer path (S3) a body (11) with a heat capacity (CW) is applied. Method according to claim 5, wherein for the thermo-hydraulic simulation a respective passage (14) is described by means of one-dimensional Navier-Stokes equations. The method of claim 5 or 6, wherein the one-dimensional simulation includes terms describing a temporal mass enrichment of the process fluid, a spatial mass transport of the process fluid, a reaction rate, a temporal impulse accumulation of the process fluid, a spatial impulse transport of the process fluid, a spatial pressure gradient, a spatial friction, influences of gravity on the process fluid, a temporal energy enrichment of the process fluid, a spatial enthalpy transport of the process fluid, an expansion work of the process fluid, friction dissipation, and / or a heat input from the outside. A method according to any one of claims 1-7, wherein the state of the heat exchanger means (10) is determined as a life consumption in the manner of a Wöhler curve, wherein a stress is determined in dependence on a number of operating cycles of the heat exchanger means (10). Method according to one of claims 1-8, wherein the means for heat transfer comprise a pipe, a plate, a separating plate, a profile part, a lamella, a rib or a device for heat storage. The method of any of claims 1-9, wherein the simulation takes into account a Joule-Thompson effect of the process stream on the passages. Method according to one of claims 1 - 10, wherein in the implementation of the method, a temporal and local discretization takes place. Method according to one of claims 3 - 11, wherein the state of the heat exchanger device (10) by means of a finite element method (FEM) for a structural analysis of the state as a function of the variable temperature boundary conditions is determined. Method according to one of claims 1 - 12, wherein spatially and temporally distributed voltage states of the heat transfer device (10) are determined. A method for producing a heat exchanger device (10), wherein structural parameters of the heat exchanger device (10) in dependence on a certain state as a result of the method according to any one of claims 1-13 are fixed, wherein a structural parameter is in particular a solder joint, a material thickness or a material selection. A method of operating a heat exchanger device (10) wherein operating parameters are determined in accordance with a particular condition as a result of the method of any one of claims 1-13, wherein an operating parameter is, in particular, a pressure, a maintenance interval, or a replacement time of heat transfer means.

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