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Consider automation to check shell-and-tube heat exchanger design

03.01.2014  |  Shende, S. ,  Technip, Mumbai, India

This automated checklist tool can be used to quickly check the acceptability of your design configuration based on the various project, client and services requirements.

Keywords: [heat exchanger] [models] [heat transfer]

Plant operating experience over the years has led clients to be more demanding with regard to equipment design. This experience is expressed in client specifications, codes and standards. Heat exchanger design must meet requirements stipulated in:

  • Equipment standards
  • Design basis and client specifications applicable for the contract
  • Use of specialty expertise available with the designer (best practices, etc.)
  • Requirements from the process licensor.

These requirements exist in addition to the basic requirements of heat transfer area and pressure drop. They are maintained by heat exchanger designers in the form of a checklist, and applied during design development. The checklist can become quite extensive to cover various parameters that influence thermal design. It is used with every exchanger on the project, with the number of exchangers rising to 100-plus for large projects like refineries and cracking units.

In many designers’ experience, the use of this checklist, although essential, can be monotonous and time-consuming. Furthermore, the checklist cannot be incorporated into general-purpose thermal design software. To assist the designer, an Excel Visual Basic for Applications (VBA)-based tool has been developed.

The checklist is established in an Excel format at the start of the project. These requirements can be easily modified for each service, client or project. The user must apply it to a commercially available software program’s design output,1 and the program will display warning messages for violations of requirements. This helps the thermal designer quickly check the acceptability of each exchanger design, improving productivity.

However, this automation process does not replace the manual check that is required before finalizing the exchanger configuration. The methodology for automating a checklist for a shell-and-tube heat exchanger design in commercially available software is discussed here.

Software output checking tool

The software allows the facility to export output reports in an Excel format. The exported report is a fixed format. It contains most of the parameters required for reviewing software output. The tool makes use of the exported Excel file to read the parameters required for checking. The flowchart for the programming section is shown in Figs. 1 and 2.

 
  Fig. 1. Algorithm used for checking applicability.


 
  Fig. 2.  Algorithm used for verification.


The checking tool consists of a requirements spreadsheet and a mapping spreadsheet. The requirements spreadsheet is used to define various checks required for software output.

Any checklist point can be split into two parts; one is applicability, and the other is verification. An example is a checklist point indicating, “Cooling water velocity in the tube side should be greater than 6 ft/s.” This checkpoint is applicable only for the exchangers that have cooling water on the tube side, and the program verifies velocity only for these exchangers. The verification conditions are defined similarly to the applicability conditions.

A mapping spreadsheet contains the mapping of all the software output parameters with their corresponding cell locations in the exported software output files. The worksheet tab name, the cell row number and the cell column number for each parameter of the software output are specified in this worksheet. The file needs to be set only once.

Background VBA code will read the location of each parameter from this mapping sheet. Therefore, when a user wants to check the tube-side velocity, the program will read the location of the cell that contains tube-side velocity from the mapping file.

Some parameters are not reported in a single cell, but rather spread out over many cells. These parameters are “shell-side monitor” and “tube-side monitor.” These parameters are reported in a particular row, although they are spread across many cells over different worksheet tabs. For this parameter, the value is written as “multiple” in the mapping file. When the program reads the location as “multiple,” it knows that the parameter should be checked for multiple columns from the software output.

To define applicability and verification, the software output parameters listed in the mapping spreadsheet are used as a dropdown list. The selection process is split into two selections, for user convenience. Users must select the output report name as it appears in the software output. Accordingly, the options are displayed to the user for the next selection. Each software parameter can be uniquely specified through these two selections.

The comparison rules are also listed in a separate worksheet and are used as a dropdown menu. The various comparison conditions hardcoded in the program are equal to, greater than, less than, list, between and contain. These comparison conditions are self-explanatory.

Tables 1–3 show the methods of translating typical checklist points in an automated manner:

1. Tube-side cooling water velocity should be between 6 ft/s and 9 ft/s (Table 1).

 


2. Inlet-nozzle dynamic pressure (measured as Rho v2) should be greater than shell entrance Rho v2. This checklist condition is applicable to all exchangers. For such checkpoints, a dummy applicability condition is defined that is evaluated to be true for all exchangers (Table 2).

 


3. Tube length should be 8 ft, 10 ft, 12 ft, 16 ft or 20 ft (Table 3).

 


User calculation spreadsheet

A worksheet is created to read the software output values for additional user-defined calculations. This worksheet also makes use of software parameters listed in the mapping spreadsheet. Each software parameter is accessed in a similar way, as a means of defining applicability and verification.

The values of the software parameter will appear in a specific cell in the corresponding row of the worksheet. This cell can be linked to any other user-defined calculation. The final result should then be linked in the requirements spreadsheet to define the verification condition.

When the program executes, it initially updates the parameters from software output to the requirements spreadsheet. As a result, all user-defined calculations are automatically updated. The updated values are then used for verification.

A file-browse dialogue box is added as a user interface to enable easy browsing and selection of the software output file to be checked.

Takeaway

The automated checklist tool is useful in the thermal design of heat exchangers. It can be used to quickly check the acceptability of the design configuration based on various project, client and services requirements. The use of this tool helps increase the productivity of the thermal designer.

Furthermore, it is easy to customize the tool for various projects, clients and services. A customized tool reduces checking time to 50% for exchangers, which normally have 60–70 checklist points. This concept may be extended for the use of a checklist with commercial software. HP

ACKNOWLEDGMENT

The author thanks Mr. Mohan Chitale for initiating this effort and taking it to finalization. The author also thanks Technip management for supporting this work.

NOTE

1 Heat Transfer Research Inc. (HTRI) is a for-profit research consortium focused on studying heat transfer and related thermal phenomena.

The author 
  Sumedhkumar Shende is a senior heat transfer engineer at Technip in Mumbai, India. He has over 10 years of experience in the design of heat transfer equipment, especially shell-and-tube heat exchangers. Mr. Shende holds a bachelor’s degree in mechanical engineering from Nagpur University in India, and a master’s degree in mechanical engineering from the Indian Institute of Technology Kharagpur in India




Have your say
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Jan.Edin
10.30.2014

Nothing mention about the possibility of tube ruputure.
I will be happy to help.
Jan

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