Heat Exchanger Design

Mechanical Engineering Department By Sharon Wenger

June 11, 2015

Heat Exchanger Design training

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OutlineIntroduction

Why we need to use a systematic approach to design heat exchangers

What factors are needed to design a quality heat exchanger

How do we approach that goal

What are a Process engineers responsibilities

What are the Mechanical engineers responsibilities

What tools are available in-house for heat exchanger design

Heat Exchanger design codes

An example of step by step design for a heat exchanger

Heat Exchanger Design training

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INTRODUCTION The objective of this training is to provide a concise review of the key issues involved in Heat Exchanger design. At the start of the heat exchanger design, process and mechanical considerations are crucial. It needs to be clearly understood what we want to achieve. The calculations in the software program relies on careful considered input. Engineering judgment must be used to evaluate both thermal and hydraulic the design results.

So what are the key parameters we should consider to produce a quality design?

The Data Sheet is the final product, all the hard work will be inputted here. When complete it is ready to be issued to vendors, manufactures for quote.

Client often decide which Vendors to select.

Therefore, we want to produce a quality design to demonstrate we know how to design heat exchangers.

How do we approach this goal? Process Considerations Mechanical Considerations Construction Considerations

Heat Exchanger Design training

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INTRODUCTION Process Considerations

− How many heat exchangers are required? − What duty? − What type of utility (air, water, steam, hot oil) is required?

Mechanical Considerations− What is the Lead Time and Cost?

Construction Considerations Not covered here

Heat Exchanger Design training

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Systematic Approach – the following steps are suggested

Optimization possibilities

Adapt Current new technologies

Compare approximate cost of configurations

Cost of utility requirements

Ho do we approach to design a quality heat Exchanger?

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Optimization possibilities

Is Optimization possible? Pinch Technology is one of the optimize heat exchanger design methods. The results of the pinch technology will targets for:

1. Calculate utility requirements

2. Estimate exchanger requirements

3. Overview of energy flows for entire process

4. Overall view of entire steam/power system

5. Potential energy saving in a process

6. Targets to aim for• Quantity of exchangers (# shells, total area)• Utility Capital cost targets

Process Considerations

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Data Extraction

To start the Pinch Analysis, we need to extract the necessary thermal data from process simulations as shown in Figure 1.

Figures (a) & (b) on next page shows an example represented by the two process Flow sheets. We now apply the pinch analysis principles to design the heat exchanger.

* Pinch Technology (JGCA-1303-0132)

Example: Condenser Design

Fig. 1

Fig. 1 Work Steps Required*

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Example: Condenser Design (Cont.)Process Flow Sheet

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Optimization possibilities Example: Condenser design (cont.)

Table 1 shows the thermal extraction data for Pinch Analysis. Streams 1 & 2 are hot steams (heat sources). Streams 3 & 4 are cold streams (heat sinks). Assume a minimum temperature difference of 10o C. The hot utility is steam at 200o C and the cold utility is cooling water in the range 25 o C to 30 o C. Figures (a) & (b) represent a graphical construction of the target for minimum energy consumption for the process.

Fig. 2 Construction of Composite CurvesTable 1

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Example: Condenser design (cont.)

The minimum energy target for the process. The hot and cold composite curves are now overlapped on one another. Fig. (a), separating them by the minimum temperature difference ∆Tmin = 10 C.

Fig. (b) shows the minimum hot utility (QHmin)

As you can see, using Pinch Analysis we are able to set targets for minimum energy consumption based on heat and material balance information prior to heat exchanger design. This allows us to quickly identify any energy saving at an early stage.

For more details refer to JGCA-1303-0132 Pinch Technology

DETERMINING THE ENERGY TARGETS

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The Pinch PrincipleThe point where ∆Tmin is observed is known as the “Pinch” and recognizing its implications allow energy targets to be realized in practice. One above and one below the pinch, as shown in Fig. (a). The system above the pinch requires a heat input, The system below the pinch rejects heat, so is a net heat source. To restore the heat balance, the hot utility must be increased by the same amount, that is, α units., therefore the cold utility requirement also increases by α units. In conclusion, the consequence of a cross-pinch heat transfer (α) is that both the hot and cold utility will increase by the cross-pinch duty (α).

DETERMINING THE ENERGY TARGETS

Example: Condenser design (cont.)

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Systematic Approach – the following steps are suggested There are two disciplines whose goal is to generate the HX datasheet. Process Engineer and Mechanical Engineer.

Process Responsibilities are:◦ Selection of heat transfer models◦ Define Fluid Composition for both shell side and tube side◦ Define Operating Pressure and Temperature◦ Define shell side and tube side allowable Pressure limits◦ Define shell side and tube side velocity limits.◦ Define Gravity or Density◦ Define Specific Heat◦ Define Viscosity, cp ◦ Define Fouling Factor for shell side and tube side◦ Define Thermal Conductivity◦ Define Latent Heat, (if phase change)◦ Complete optimum thermal design◦ Complete internal Process verification and checking and pass the Data Sheet to Mechanical

Ho do we approach to design a quality heat Exchanger?

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Optimizing Heat Exchanger Process and Cost Effectiveness

Mechanical engineer shall use the Data Sheet from process and import the data into COMPRESS. Then complete the mechanical design and complete the mechanical sections of the Data Sheet. Mechanical engineer responsibilities are:1. Confirm the type of exchanger configuration. 2. Set upper and lower design limits on shell diameter3. Set upper and lower design limits on tube length.4. Specify both shell and tube side layout5. Specify pitch, material, baffle cut, baffle spacing and clearances.6. Prepare Material Requisition7. Complete Technical Bid Evaluation on bids

Items 1 to 5 are covered in the following sections.

Mechanical

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Tools are available in-house for design the exchangers

There are two software programs in house 1) HTRI, 2) COMPRESS. HTRI is best used for process thermal design and to produce TEMA Datasheet. COMPRESS is used to design the complete exchanger. Tubesheet(s), tubes, expansion joint, shell, channels, flanges, head closures, nozzles, etc. COMPRESS will generate shell side & tube side hydrotest conditions based on the input design conditions.

There are four ways to create a heat exchanger in COMPRESS.1. Start from “File” and select “New heat exchanger”.2. Pressing “Ctrl T” on your keyboard3. Import an HTRI designed file4. To Start a File click on the heat exchanger icon found on the main menu

Mechanical Design Software

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Two methods are used in COMPRESS design. a) TEMA

b) UHX methods. When to use TEMA or UHX methods.

• When rating an existing exchanger built to TEMA. • When supplying new equipment where TEMA has been specified in addition to UHX.

Regardless which option is selected, for new exchanger design. ASME is mandatory for tubesheet design

COMPRESS Heat Exchanger introductionHow does COMPRESS work

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COMPRESS has a built in interface with HTRI.

COMPRESS can read and write HTRI’S Xist files

COMPRESS directly importing an existing HTRI file to complete the mechanical design

COMPRESS / HTRI interface enables shell and tube heat exchanger files design interchangeable

COMPRESS can analyze all components design conditions simultaneously

COMPRESS has built-in Design codes to check and evaluate components design conditions

• Such as ASME VIII UHX, TEMA, or both ASME VIII UHX & TEMA and more

How does COMPRESS work

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The following screenshots are example from COMPRESS

Exchanger design codes

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Example by import an HTRI designed file Before starting COMPRESS to design a heat exchanger, a few things are required. Open COMPRESS, on the lower right corner, select the Mode, units, Div. and revision to set up the calculation Mode.

https://support.codeware.com/link/portal/9185/9191/Article/352/COMPRESS-Heat-Exchanger-Tutorial

COMPRESS Heat Exchanger introduction

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Step 1: Start the Heat Exchanger Wizard

The following screenshots are example from COMPRESS

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This is the HTRI File Import Values. The color code indicate four results

The following screenshots are example from COMPRESS

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Step 2: Edit an existing Heat Exchanger

The following screenshots are example from COMPRESS

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The following screenshots are example from COMPRESS

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Report summary

The following screenshots are example from COMPRESS

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Report summary

The following screenshots are example from COMPRESS

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The following screenshots are example from COMPRESS

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The following screenshots are example from COMPRESS

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HTRI Fundamentals of Exchanger Design COMPRESS , BUILD 7500 COMPRESS REPORT RGX6_663-E016, Provided by -

Leonard Stephen Thill, san, Principal Piping – Lead Piping Stress Specialist, Stress & Static Equipment

References

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THE END

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Special Thanks