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Applications for Process Automation

Monitoring of Heat Exchangers using the HeatXchMon Function Block

Application Example

Warranty, Liability and Support

Heat Exchanger Monitoring <Beitrags-ID>

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Note The application examples are not binding and do not claim to be com-plete regarding the circuits shown, equipment and possibilities. The soft-ware samples do not represent a customer-specific solution. They only serve as a support for typical applications. You are responsible for ensur-ing that the described products are used correctly. These application ex-amples do not release you from your own responsibility regarding profes-sional usage, installation, operation and maintenance of the plant. When using these application examples, you acknowledge that Siemens cannot be made liable for any damage/claims beyond the scope described in the liability clause. We reserve the right to make changes to these application examples at any time without prior notice. If there are any deviations be-tween the recommendations provided in these application examples and other Siemens publications – e.g. catalogs – then the contents of the o-ther documents have priority.

Warranty, Liability and Support We accept no liability for information contained in this document.

Any claims against us – based on whatever legal reason – resulting from the use of the examples, information, programs, engineering and perform-ance data etc., described in this application example shall be excluded. Such an exclusion shall not apply in the case of mandatory liability, e.g. un-der the German Product Liability Act (“Produkthaftungsgesetz”), in case of intent, gross negligence, or injury of life, body or health, guarantee for the quality of a product, fraudulent concealment of a deficiency or breach of a condition which goes to the root of the contract (“wesentliche Ver-tragspflichten”). The damages for a breach of a substantial contractual obli-gation are, however, limited to the foreseeable damage, typical for the type of contract, except in the event of intent or gross negligence or injury to life, body or health. The above provisions do not imply a change in the burden of proof to the detriment of the orderer.

Copyright© 2010 Siemens Industry Sector IA. These application ex-amples or extracts from them must not be transferred or copied with-out the approval of Siemens. For questions about this document please use the following e-mail address:

mailto:[email protected]

mailto:[email protected]

Preface


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Preface

Objective of the Application The objective is performance monitoring and diagnostics of heat exchang-ers in the context of SIMATIC PCS 7 plant asset management. A low-cost solution can be achieved by intelligent combination and logical interpreta-tion of measured process values which are (mostly) already available in the DCS, in contrast to high-end condition monitoring systems based on dedi-cated additional sensors, e.g. vibration sensors or structure-borne sound sen-sors.

For heat exchanger monitoring, data for characteristic surfaces in clean and dirty state of the heat exchanger are required, that have to be generated by numerical simulation. These simulations are performed as a service by the Siemens department I IA AS PA EC in Frankfurt.

Main Contents of this Application Note The following issues are discussed in this application:

• How to implement heat exchanger monitoring.

• How to parameterize and commission heat exchanger monitoring.

• How to evaluate the monitoring results in the context of plant asset management.

Validity Valid for PCS 7 V6.1 and later versions. The application example is based on PCS 7 V7.0 SP1.

Table of Contents


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Table of Contents

Table of Contents ......................................................................................................... 4

1 Introduction Heat Exchanger Monitoring ..................................................... 6 1.1 Classification of Heat Exchangers .................................................................... 6 1.1.1 Classification with Respect to Physical Condition (Aggregate State) ............... 6 1.1.2 Classification with Respect to Structural Shape ............................................... 6 1.1.3 Classification with Respect to Flow Form ......................................................... 7 1.2 Application Area of Heat Exchanger Monitoring ............................................... 7 1.3 Functions .......................................................................................................... 9 1.3.1 Analysis and Characteristic Surface Displays of Heat Exchanger and its

Operating States .......................................................................................... 9 1.3.2 Diagnostic Functions ...................................................................................... 10 1.4 Typical Application Examples ......................................................................... 10

2 Implementation of Heat Exchanger Monitoring ......................................... 11 2.1 Installation of SIMATIC PCS 7 Add-on Product.............................................. 11 2.2 Configuration .................................................................................................. 11 2.2.1 Greenfield Engineering of the Complete Automation around a Heat Exchanger

(Based on Solution Template).................................................................... 11 2.2.2 Retrofitting of Monitoring in a Running Plant .................................................. 11 2.2.3 CFC Engineering ............................................................................................ 12

3 Parameter Specification and Commissioning ........................................... 16 3.1 Required Data of Heat Exchanger.................................................................. 16 3.1.1 Characteristic Surfaces of Heat Exchangers in Separate Function Blocks .... 16 3.1.2 Heat Exchanger Technical Data for HeatXchMon .......................................... 16 3.2 Parameter Input in Faceplate or CFC............................................................. 17 3.2.1 Data of Heat Exchanger ................................................................................. 17 3.2.2 Parameter Specification of Performance Monitoring ...................................... 17 3.2.3 Parameter Specification for Alarming and Performance Limits ...................... 18

4 Evaluations for Plant Asset Management .................................................. 20 4.1 Display in Faceplate ....................................................................................... 20 4.1.1 Display of Process Variables .......................................................................... 20 4.1.2 Characteristic Line Display ............................................................................. 21 4.1.3 Calculation Functions ..................................................................................... 23 4.1.4 Display of Operating Point .............................................................................. 24 4.2 Maintenance Request..................................................................................... 25 4.2.1 Specify Heat Exchanger Master Data............................................................. 25 4.2.2 Linking and Parameterization of AssetMon Function Block............................ 26

5 Simulation Example...................................................................................... 27

6 Summary ....................................................................................................... 31

Table of Contents


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7 History ........................................................................................................... 32

8 Literatur ......................................................................................................... 33

Introduction Heat Exchanger Monitoring


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1 Introduction Heat Exchanger Monitoring

1.1 Classification of Heat Exchangers

Definition from [4.], p. 11: Heat Exchangers are technical components, wherein warmer material flows give away some part of their thermal en-ergy, that is taken over by colder material flows. A product medium is to be heated or cooled using a service medium (e.g. hot steam, cooling water).

The following classification is based on [4.], p. 111.

1.1.1 Classification with Respect to Physical Condition (Aggregate State)

In general, the physical condition of product and service medium can be fluid, steam or gas respectively. The focus of heat exchanger monitoring is on fluid-fluid heat exchangers, but pure gas flows as product or service medium can also easily be handled.

Heat exchangers where the working principle is based on a change of physical state or that are intended to achieve a change of physical state, namely condensors and reboilers are special cases.

Such heat exchangers require specialized calculations for monitoring and therefore are no application area for the universal HeatXchMon function block.

1.1.2 Classification with Respect to Structural Shape

With respect to structural shape, recuperators are classified as

• tube bundle (shell and tube) heat exchangers

• plate heat exchangers.

1.1.2.1 Tube Bundle Heat Exchangers

These heat exchangers have a market share of 30-35%. Simulation calcu-lations are more straightforward due to well defined flow conditions. Clean-ing is easier, and therefore they are first choice if there is a tendency to fouling. Therefore they are interesting for asset management and preferred candidates for application of HeatXchMon.

With respect to type of construction, there are bare tube and fin-tube heat exchangers. There are also versions with straight tubes or tube spirals.

1.1.2.2 Plate Heat Exchangers

These heat exchangers have a market share of 40-45%. Flow conditions are more complicated and more difficult to simulate. Design, construction and calculations are different for each vendor. Before application of HeatXchMon it must be checked in each single case who has an appropri-ate simulation model for the calculation of characteristic surfaces.



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With respect to type of construction, there are fin-plates, spiral plates or multi-disks.

1.1.3 Classification with Respect to Flow Form

With respect to flow form, there are

• Single-pass heat exchangers

• Multi-pass heat exchangers

1.1.3.1 Single-Pass Heat Exchangers

There are concurrent flow, countercurrent flow, cross flow and flow division versions of heat exchangers. Simulation of single-pass heat exchangers is more straightforward due to well defined flow conditions.

1.1.3.2 Multi-pass Heat Exchangers

There are

• Tube bundles with concurrent or countercurrent flow or m-pass shell side or n-pass tube side

• Plate heat exchangers

Multi-pass heat exchangers are more difficult for simulation, due to compli-cated flow conditions. Therefore the calculation of characteristic surfaces is less straightforward.

1.2 Application Area of Heat Exchanger Monitoring

The PCS 7 Add-on product HeatXchMon offers a cost effective solution for monitoring and analysis of heat exchangers. Monitoring is based on intelli-gent evaluation of measured values and comparison with characteristic sur-faces of the heat exchanger. These characteristic surfaces are calculated beforehand via simulations of clean and dirty state of the heat exchanger, using technical data of the heat exchanger. Simulations are performed as part of a service package by Siemens I IA AS PA EC, Frankfurt.

The preferred application area of HeatXchMon is fluid-fluid tube bundle heat exchangers. Plate heat exchangers can be monitored if there is a suf-ficiently precise simulation program for the given type of heat exchanger. Heat exchangers involving a change of aggregate state (reboilers, conden-sors) can only be monitored by application specific versions of the HeatXchMon function block.

Heat exchanger performance can be reduced significantly by fouling. Foul-ing is a general term for all sorts of contaminations in heat exchangers, e.g. sedimentation, corrosion, reaction fouling, bio fouling. Contamination cre-ates a separation layer hindering heat transfer. This separation layer in-creases heat transfer resistance and reduces the heat transfer coefficient of heat exchangers.



HeatXchMon is applied for

• Detection of decreasing heat exchanger efficiency

• Early warning with respect to all types of fouling.

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T P,In

T

T

Serv

ice

Med

ium

Product Medium

T

F P

F S

T P,Out

T S,In T S,Out

F

F

T

Figure 1-1: Heat exchanger with process values

The function block needs the following six input variables:

• Flow service medium: Fs

• Inlet temperature service medium: TS,In

• Output temperature service medium: TS,Out

• Flow product medium: FP

• Inlet temperature product medium: TP,Out

• Output temperature product medium: TP,Out

For the calculations in the function block, only steady states of the process are evaluated.

The HeatXchMon function block needs two function blocks FB Char-Surf5D and FB CharRefSurf5D that realize the following characteristic sur-faces:

• CharRefSurf5D: five dimensional characteristic surface for heat flow in "realistic clean" reference state, i.e. with minimal fouling that fits to real measurement data. Four of the six measured variables can be consid-ered as input variables of the heat exchanger model, namely both inlet temperatures and both flows. The other two measured variables are output variables of the model, namely both outlet temperatures. The



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four input variables are the independent variables of the characteristic surface, while the fifth dimension is the dependant variable heat flow.

• CharSurf5D: five dimensional characteristic surface for heat flow in "maximal contaminated" state, i.e. the state that urgently requires clean-ing.

HeatXchMon includes its own messaging. It will generate messages for limit violations of the performance indicator (reserve of wear out) and devia-tions from expected heat flow characteristic in clean reference state. Mes-sage events are also provided as binary output variables for further proc-essing in CFC.

The function block it self has a purely diagnostic function where active in-terventions into heat exchanger operation are not provided. Therefore any application (also in form of re-vamping) does not induce danger of disturb-ing the process. If desired, active interventions can be achieved by evalua-tion of function block output variables.

1.3 Functions

The HeatXchMon function block offers the following functions [1.]:

1.3.1 Analysis and Characteristic Surface Displays of Heat Exchanger and its Operating States

• Calculation of heat flow for clean and maximal contaminated state from characteristic surfaces.

• Performance of heat transfer: display of reference heat flow (heat flow in clean reference state) depending on mass flow of service medium, displayed as two dimensional cut through the five dimensional charac-teristic surface. Display of actual heat flow at operating point and in maximal contaminated state.

• Calculation of key performance indicator (heat transfer performance, reserve of wear out) as an indicator of fouling.

The wear out reserve of the heat exchanger is defined such that it will show the value 100% in clean reference state and 0% in maximal contaminated state:



%100⋅−

−=

dirtyclean

dirtyact

QQQQ

HeatPerf&&

&&

HeatPerf = wear out reserve

actQ& = actual heat flow

dirtyQ& = heat flow in maximal contaminated state

cleanQ& = heat flow in clean reference state

Equation 1-1: Calculation of wear out reserve

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1.3.2 Diagnostic Functions

The function block offers the following diagnostic functions for warning op-erators in case of unfavorable operating states:

• Limit monitoring of wear out reserve Fouling.

• Monitoring of deviation of actual heat flow from reference heat flow in clean state decreasing heat exchanger efficiency.

• Monitoring of energy losses per day, with reference to heat flow in clean state waste of energy.

• Monitoring of financial losses per day, caused by energy losses waste of money.

1.4 Typical Application Examples

• Heat exchangers that tend to corrosion or sedimentation.

• Heat exchangers that are contaminated by micro organisms (bio foul-ing).

• Heat exchangers where fouling is caused by chemical reactions or re-action products (reaction fouling).

• Heat exchangers with bad or heavily fluctuating efficiency.

Implementation of Heat Exchanger Monitoring


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2 Implementation of Heat Exchanger Monitoring

2.1 Installation of SIMATIC PCS 7 Add-on Product

The installation of the SIMATIC PCS 7 Add-on Product is performed by the setup program of the delivery CD. After selection of the function block HeatXchMon in the blocks folder, the online help can be called via function key F1.

The function block can be installed in PCS 7 Version 6.1 or higher.

2.2 Configuration

With respect to engineering, two completely different use cases are dis-cussed: retrofitting heat exchanger monitoring in a running plant, or greenfield engineering of the complete automation around a heat ex-changer incl. monitoring.

2.2.1 Greenfield Engineering of the Complete Automation around a Heat Exchanger (Based on Solution Template)

In the most common application scenario the heat exchanger is integrated in a temperature control loop. There is a typical combination of actors and sensors, that (together with the heat exchanger) provide the equipment module "achieve or keep specified temperature of product medium and monitor it".

2.2.1.1 Tag Type Template TempControlHeatExchanger

A temperature control loop with heat exchanger controls the outlet tempera-ture of the product medium by manipulating the flow of the service medium.

If there is already a tag type template according to Figure 1-1 in the project, it makes sense to integrate the HeatXchMon function block into this tem-plate, because both service medium flow (=manipulated variable of tem-perature controller) and outlet temperature (=controlled variable of tempera-ture controller) are already available here.

2.2.2 Retrofitting of Monitoring in a Running Plant

In this case, the basic automation around the heat exchanger incl. tempera-ture control already exists.

The function block HeatXchMon is inserted into a CFC in the appropriate hierarchy folder of the technological hierarchy. Because HeatXchMon con-nects sensor signals from different existing measurement tags, you will typi-cally generate a new chart for it. This chart can be located in the hierarchy folder to which the heat exchanger belongs, or in a separate hierarchy tree "plant diagnosis" or "performance station". In a performance station similar to the PCS 7 maintenance station, target group specific information could be collected and displayed. While the maintenance station is targeted to



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maintenance personal, the target group for the performance station is plant managers, process and control engineers that are responsible for optimiz-ing plant operation.

2.2.3 CFC Engineering

The HeatXchMon function block, the related characteristic surface function blocks and the SteadyState function blocks are inserted into the desig-nated CFC via Drag&Drop from the block catalogue.

The positioning of the SteadyState function blocks in an OB (cyclic task) is depending on the positioning of the related analog driver blocks for process values. The HeatXchMon function block and the related characteristic sur-face function blocks (FB CharSurf5D and FB CharRefSurf5D) can be in-serted in a slower OB (e.g. OB30) to save CPU resources.

The HeatXchMon function block is connected to the related driver, SteadyState and characteristic surface function blocks as follows:

2.2.3.1 Connection to SteadyState Function Blocks

Heat exchanger monitoring is based on evaluation of heat balances in steady state, i.e. it is assumed that the amount of heat energy stored in product and service medium inside the heat exchanger is constant. There-fore the monitoring functions are evaluated only in steady state of complete heat exchanger, requiring steady state detection of all six process vari-ables. If some of the six variables, e.g. service medium inlet temperature are normally constant during operation, or fluctuate extremely slowly, it is sufficient to monitor stationarity of typically fast time-varying process values like e.g. inlet and outlet temperature of product medium and flow of service medium.

Steady state detection is performed by function block SteadyState that is provided together with HeatXchMon in the same library. The SteadyState function block is applied to detect steady states in a dynamic process. It analyses an input signal and decides without delay if this signal is in a steady state or not. Further information is provided in the online help of the SteadyState function block [2.].

One instance of SteadyState function block is required for each process value to be monitored. Each of them has to be connected in the following way:

• Process value at analog driver block input SteadyState.PV

The binary output variables SteadyState.Stationarity of all six instances are connected to six binary input variables (AND.IN1 ... AND.IN6) of an AND-block. The output variable AND.OUT is connected to HeatXch-Mon.SteadyState.



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2.2.3.2 Connection to Process Signals

The function block requires the following process values:

• Flow service medium input mpProd [kg/s]

• Inlet temperature service medium input TeProdIn [°C]

• Outlet temperature service medium input TeProdOut [°C]

• Flow product medium input mpServ [kg/s]

• Inlet temperature product medium input TeServIn [°C]

• Outlet temperature product medium input TeServOut [°C]

The process signals for the HeatXchMon function block are not directly ob-tained from the related analog input driver blocks, but from the output vari-ables SteadyState.FilteredPV of the respective SteadyState function blocks, in order to make use of the low-pass filtered measurement values for heat exchanger monitoring.

2.2.3.3 Connection to Characteristic Surface Function Blocks

The function block CharSurf5D that contains the characteristic surface data for maximal contaminated state is connected as follows:

• Process value flow product medium of SteadyState function block Stea-dyState.FilteredPV input CharSurf5D.X1

• Process value flow service medium of SteadyState function block SteadyState.FilteredPV input CharSurf5D.X2

• Process value inlet temperature product medium of SteadyState func-tion block SteadyState.FilteredPV input CharSurf5D.X3

• Process value inlet temperature service medium of SteadyState func-tion block SteadyState.FilteredPV input CharSurf5D.X4

• Output heat flow: CharSurf5D.Y input HeatXchMon.QpDirty

The function block CharRefSurf5D that contains the characteristic surface data for clean reference state is connected as follows:

• Process value flow product medium of SteadyState function block SteadyState.FilteredPV input CharSurf5D.X1

• Process value flow service medium of SteadyState function block SteadyState.FilteredPV input CharSurf5D.X2

• Process value inlet temperature product medium of SteadyState func-tion block SteadyState.FilteredPV input CharSurf5D.X3

• Process value inlet temperature service medium of SteadyState func-tion block SteadyState.FilteredPV input CharSurf5D.X4

• Output heat flow: CharSurf5D.Y input HeatXchMon.QpClean



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• Output reference coordinates for heat flow: CharSurf5D.Y_Ref input HeatXchMon.QpCleanRef

• Output reference coordinates for flow service medium: Char-Surf5D.X2_Ref input HeatXchMon.mpServRef

• Output scaling of four input variables: CharSurf5D.BarScaOut input HeatXchMon.BarScales



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Abbildung 2-1: Connection of HeatXchMon function block

Parameter Specification and Commissioning


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3 Parameter Specification and Commissioning

3.1 Required Data of Heat Exchanger

The technical data listed in the following sections are required for heat ex-changer monitoring and must be specified beforehand.

3.1.1 Characteristic Surfaces of Heat Exchangers in Separate Function Blocks

Data for characteristic surfaces of heat exchanger in clean and maximal contaminated state are required for heat exchanger monitoring. These data are stored in two function blocks.

• Function block FB CharSurf5D

This function block contains data for maximal contaminated state. It re-quires four process values as input variables: - Flow product medium ( X1) - Flow service medium ( X2) - Inlet temperature product medium ( X3) - Inlet temperature service medium ( X4)

The function block calculates the heat flow ( Y) in maximal contami-nated state at the actual operating point defined by the above variables.

• Function block FB CharRefSurf5D

This function block is derived from CharSurf5D and contains the data for clean state. It needs the same input variables. The function block calculates the reference heat flow ( Y) in clean state at the actual op-erating point. Moreover it calculates the heat flow in clean state ( Y_Ref) for five further interpolation points of service medium flow ( X2_Ref ), providing a characteristic line display in performance view of HeatXchMon faceplate.

Moreover the scaling ranges ( BarScaOut) for the four input variables of the characteristic surfaces are provided as output variables in a data structure. These ranges are used for bar graphs of the four input vari-ables in operating point view of HeatXchMon faceplate.

Both characteristic surface function blocks have no message generation and no faceplates for operation and control in WinCC.

3.1.2 Heat Exchanger Technical Data for HeatXchMon

The following data have to be provided:

• Specific heat capacity of service medium [kJ / kg / K]



• Specific heat capacity of product medium [kJ / kg / K]

3.2 Parameter Input in Faceplate or CFC

3.2.1 Data of Heat Exchanger

The behaviour of the given heat exchanger is represented by the character-istic surfaces in the instances of CharSurf5D and CharRefSurf5D. Those two function block instances have to be connected to the HeatXchMon in-stance.

Parameter specification at HeatXchMon:

• Specific heat capacity of service medium cpServ (CFC only)

• Specific heat capacity of product medium cpProd (CFC only)

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3.2.2 Parameter Specification of Performance Monitoring

The parameters for monitoring limits of key performance indicator (wear out reserve HeatPerf) can be specified in the standard view of the faceplate.

Figure 3-1: Key performance indicator monitoring

The calculation of heat flow in actual state can be performed in three differ-ent ways that can be selected via input variable SelHeatCalc (CFC only). The difference is that the calculation of heat flow is based on product side, service medium side or the mean value of both.



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• SelHeatCalc = 1: The heat flow in actual state corresponds to the heat flow entering product medium.

QpAct = QpProd = ABS (cpProd * mpProd * (TeProdOut - TeProdIn))

• SelHeatCalc = 2: The heat flow in actual state corresponds to the heat flow taken away from service medium.

QpAct = QpServ = ABS( -cpServ * mpServ * (TeServOut - TeServIn))

• SelHeatCalc = 3: The heat flow in actual state is calculated from the mean value of the heat flow entering product medium and the heat flow taken away from service medium.

QpAct = 0.5 * (QpProd + QpServ)

Ideally the calculations at product and service side will deliver the same re-sults. If one of the calculations is expected to deliver more reliable results, take only this calculation, otherwise take the mean value.

3.2.3 Parameter Specification for Alarming and Performance Limits

The wear out reserve (heat transfer performance) HeatPerf is permanently calculated according to equation 1-1 and can be observed in trend view of faceplate over longer time intervals.

For the heat transfer performance there is a monitoring of lower warning and alarm limits with option for suppression. Limits and suppression can be operated in the faceplate standard view or in CFC.

The performance limit monitoring is using a hysteresis to avoid chattering alarms if the actual value is fluctuating around the alarm limit.

In detail, there are the following parameters:

• Low warning limit for heat transfer performance (L_alarm) Heat-PeWL (in faceplate, standard view, or in CFC)

• Low alarm limit for heat transfer performance (LL_alarm) HeatPeAL (in faceplate, standard view, or in CFC)

• Hysteresis for heat transfer performance in [%] HeatPeHys (in face-plate, standard view, or in CFC)



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• Message suppression for low warning MeSuprWL (in faceplate, standard view, or in CFC)

• Message suppression for low alarm MeSuprAL (in faceplate, stan-dard view, or in CFC)

• General message suppression MSG_LOCK (CFC only)

• Message suppression for a number of CPU cycles after startup, to avoid nuisance alarms RUNUPCYC (CFC only)

• Upper and lower scale of bar graph MO_PVHR and MO_PVLR (CFC only)

If alarm limits are violated at runtime, the respective binary output variables of HeatXchMon function block are set to true:

• Violation of low warning limit HePeWL_Act = 1

• Violation of low alarm limit HePeAL_Act = 1

Internally, HeatXchMon calls the function block MEAS_MON. If the alarm limits are violated and there is no message suppression (MeSuprWL =0 bzw. MeSuprAL =0 und MSG_LOCK = 0), a warning or an alarm is gener-ated. Further input variables OOS, CSF, USTATUS and MSG_EVID are only intended for MEAS_MON. The meaning of these parameters can be found in MEAS_MON online help.

Evaluations for Plant Asset Management


4 Evaluations for Plant Asset Management

Different results of the calculations performed by HeatXchMon are relevant for different target groups working in a process plant, and differ with respect to appropriate reaction and urgency.

A diagnosis like heavy fouling that reduces the performance of the heat ex-changer drastically must be immediately alarming the operator.

Deviations of actual heat flow from reference heat flow in clean state induce beginning of fouling.

Following these considerations, it is reasonable to evaluate the information created by HeatXchMon in a target group oriented way.

4.1 Display in Faceplate

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4.1.1 Display of Process Variables

This view shows the actual values of temperatures, mass and heat flows.

Figure 4-1: Process variables (HeatXchMon faceplate, view process)

The following process variables are displayed:

• Temperature Product medium Inlet [°C] ( TeProdIn (input parameter of HeatXchMon)

• Temperature Product medium Outlet [°C]) TeProdOut (input pa-rameter of HeatXchMon)



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4.1

• Temperature Service medium Inlet [°C] TeServIn (input parameter of HeatXchMon)

• Temperature Service medium Outlet [°C] TeServOut (input pa-rameter of HeatXchMon)

• mass flow Product medium [kg/s] mpProd (input parameter of HeatXchMon)

• mass flow Service medium [kg/s] mpServ (input parameter of HeatXchMon)

• Heat flow in maximal contaminated state [kW]) QpDirty (output parameter of CharSurf5D, input parameter of HeatXchMon)

• Heat flow in clean state [kW]) QpClean (output parameter of CharRefSurf5D, input parameter of HeatXchMon)

• Heat flow in actual state [kW]) QpAct (output parameter of HeatXchMon)

• Energy prize [€/kWh] EnergyPrize

• Money loss per day [€ / day], caused by energy loss due to fouling, c.f. section 4.1.3 MoneyLossPerDay

.2 Characteristic Line Display

In the performance view of the faceplate the performance characteristic is displayed. The characteristic line shows the reference heat flow in clean state, depending on service medium mass flow. The reference heat flow (QpCleanRef) is calculated from the characteristic surface at five interpola-tion points of service medium mass flow (mpServRef), i.e. a two-dimensional cut through the five dimensional surface is visualized.

The actual heat flow is displayed as green dot (coordinates QpAct and mpServ) below the characteristic line. The heat flow in maximal contami-nated state is displayed as red dot (QpDirty and mpServ).



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Figure 4-2: Performance characteristic line

During operation, fouling and decreasing performance of the heat ex-changer makes the green dot moving slowly from the blue line towards the red dot.



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Figure 4-3: Example for heat transfer in clean state depending on both input temperatures as a three di-

mensional characteristic surface

Background information: a three dimensional cut through the five dimen-sional characteristic surface can be visually displayed, however not in a PCS 7 faceplate, but in other software tools, e.g. Simatic NeuroSystems. A (two dimensional) cut parallel to the X- or Y-axis through the three dimen-sional surface in Figure 4-3 will look qualitatively similar to the characteristic line in Figure 4-2, which is obvious at the edges of the surface.

4.1.3 Calculation Functions

• Calculation of relative deviation from reference heat flow in clean state

[%]

RelDevQp = (QpAct - QpClean) / QpClean * 100

• Calculation of energy loss per day [kWh / day] with reference to the heat flow in clean state

EnerLossPerDay = (QpClean - QpAct) * 24

• The specification of service medium energy prize EnergyPrize ( [€/kWh], CFC only) allows a calculation of money loss per day [€/day], caused by energy loss due to fouling MoneyLossPerDay



MoneyLossPerDay = EnerLossPerDay * EnergyPrize

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4.1.4 Display of Operating Point

The operating point view shows the position of the operating point by four bar graphs of the four input variables of the characteristic surfaces. The bars are scaled according to the value range of the characteristic surfaces.

Figure 4-4: Operating point of input variables

• Inlet temperature product medium TeProdIn upper limit TeProdHigh lower limit TeProdLow

• Inlet temperature service medium TeServIn upper limit TeServHigh lower limit TeServLow

• Mass flow product medium mpProd upper limit mpProdHigh lower limit mpProdLow

• Mass flow service mediums mpServ upper limit mpServHigh lower limit mpServLow



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4.2 Maintenance Request

A maintenance request announced by a maintenance message is not gen-erated by the HeatXchMon function block itself, but by the associated As-setMon function block . The AssetMon is a universal proxy function block for mechanic and process assets in the Maintenance Station of Simatic PCS 7. It is located in the hierarchy folder of the Maintenance Station and not in the normal plant hierarchy. Its faceplate therefore appears in the Maintenance Station and not in the Operator Station.

The Electronic Device Description (EDD) containing the master data of the heat exchanger is attached to the AssetMon block, allowing to access the heat exchanger like an intelligent field device in the context of asset man-agement.

4.2.1 Specify Heat Exchanger Master Data

In order to generate the EDD for a heat exchanger, you need a so called PLT-ID .

Die PLT-ID is a connection parameter between a PDM object (parameter data EDD) and the faceplate in the maintenance station. The PLT-ID is lin-ked to the PDM object. The PDM object is generated in the SIMATIC Man-ager as follows:

1. Select View > Process device plant view in SIMATIC Manager.

2. Select Insert > SIMATIC PDM > TAG.

3. Highlight the inserted TAG object and select the context menu com-mand SIMATIC PDM > Device Selection...

4. In the tree structure CFC > DATA_OBJECTS > CFC >, select Asset-Mon and close the dialog with "OK".

5. In the context menu select Open Object and enter all necessary data in the parameter assignment screen form.

6. Select File> Save.

7. The parameter assignment screen form is closed.

8. Select the TAG object and then Tools > SIMATIC PDM > Create PLT-ID.

You can then assign parameters for the generated PLT-ID at the associ-ated parameter "PLT_ID". Note: The PLT-IDs cannot be changed or de-leted individually.

Now maintenance requests and master data of the heat exchanger are dis-played together to maintenance personal.



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4.2.2 Linking and Parameterization of AssetMon Function Block

The heat transfer performance (wear out reserve) HeatPerf is related to fouling of the heat exchanger. It is defined such that it will show the value 100% in clean reference state and 0% in maximal contaminated state.

From the output side of the HeatXchMon function block, the binary output variables HePeWL_Act for violation of lower warning limit and HePeAL_Act for lower alarm limit can be further connected.

At the AssetMon block there are seven additional message input variables (MESSAGE1, ... MESSEGE7) that will cause generating a message if set to true. For a maintenance alarm or a maintenance request, the message input variables MESSAGE1 or MESSAGE2 can be used. The violation of the wear out reserve low warning limit could be a maintenance request. For this, the output HeatXchMon.HePeWL_Act must be connected to the input AssetMon.MESSAGE2. For a maintenance alarm, the output HeatXch-Mon.HePeAL_Act must be connected to input AssetMon.MESSAGE1.

Figure 4-5: Linking of AssetMon function block for a heat exchanger

Simulation Example


5 Simulation Example

There is a PCS 7 solution template for heat exchanger monitoring. It con-tains all relevant process values for heat exchanger monitoring.

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Figure 5-1: PCS 7 solution template for heat exchanger monitoring

The solution template includes the following functions together with the re-lated measurement tags:

• Flow sensor for service medium

Simulation Example


• Flow sensor for product medium

• Sensor for inlet temperature service medium

• Sensor for outlet temperature service medium

• Sensor for inlet temperature product medium

• Sensor for outlet temperature product medium

• Heat exchanger monitoring using HeatXchMon function block

• Detection of steady state of all process variables using SteadyState function block

• Maintenance management using AssetMon function block

The simulation example contains characteristic surface of a real heat ex-changer located at laboratories of Siemens I IA AS PA EC C CI in Frank-furt, Industry Park Höchst [5.].

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The heat exchanger is applied to heat a product flow of 400kg/h by about 20°C using a service medium. In nearly clean state the product reaches a temperature of 76.75°C, the heat transfer performance is nearly 100% and the actual operating point (green) is close to the blue characteristic line.

Figure 5-2: Heat exchanger in nearly clean state

Heat transfer will become worse due to fouling, i.e. the product does not reach the desired outlet temperature any more, and the service medium will give away less heat energy. (In case product temperature should be kept constant by a control loop, the controller had to send more service medium through the heat exchanger.)

Example: Reduce product outlet temperature in the simulation from 76.75°C to 76°C, and increase service medium outlet temperature from 75.5°C to 75.72°C. You can observe the green dot moving downwards, ap-proaching the red dot. After the transient has settled, HeatXchMon will cal-culate a heat transfer performance of 15% and generate a warning mes-sage.

Simulation Example


Figure 5-3: Heat exchanger in contaminated state

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Figure 5-4: Warning message for fouling of heat exchanger

HeatXchMon calculates a daily energy loss of 31514 kWh/day for this foul-ing state, which corresponds to financial losses of 3151.4 €/day if an (arbi-trary) energy prize of 0.1 €/kWh is assumed.

These values are display in process view of HeatXchMon faceplate (Figure 4-1).

Simulation Example


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Figure 5-5: Energy loss and financial losses due to fouling of heat exchanger

Summary


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6 Summary

An important prerequisite for heat exchanger monitoring is to supply data for characteristic surfaces in clean and contaminated state of the heat ex-changer to be monitored. The data is stored in the auxiliary function blocks CharRefSurf5D and CharSurf5D.

The function block HeatXchMon calculates the following variables that are not directly measured:

• Heat flow in actual, clean and maximal contaminated state.

• Wear out reserve (=100% in clean reference state, decreases with foul-ing, approaches 0 in maximal contaminated state.

Heat exchanger diagnostics works with the following logic to detect faulty operating conditions:

• Bad heat exchanger efficiency:

Is derived from deviations of actual heat flow from reference heat flow in clean state, and from calculation of energy loss per day with reference to heat flow in clean state.

• Fouling:

Is detected from violation of wear out reserve low limit.

History


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7 History Table 7-1 History

Version Date Changes

V1.0 April 2010 1st release

Literatur


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8 Literatur

[1.] Pfeiffer, B-M.: User Documentation of Heat Exchanger Monitoring. Sie-mens I IA&DT ATS 32, Jul. 2009.

[2.] Preusse, Chr.: Textvorschlag zur Online-Hilfe Funktionsbaustein Stea-dyState (derzeit nur deutsch verfügbar). I IA&DT ATS 32, Sep. 2007.

[3.] Online help function block AssetMon, PCS7 ES V7.0.1, I IA AS RD Khe, 2008.

[4.] Wagner, Walter: Wärmetauscher, Vogel Fachbuch, Würzburg, 2005.

[5.] Kirchberg, K-H., Schüler, M.: Modellbasierte Überwachung von Wärme-tauschern. Technical Report (German), A&D ATS 32 Karlsruhe, Dez. 2004.

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