DESIGN OF SHELL & TUBE HEAT EXCHANGERS.pptx

SHELL AND TUBE HE

1. DESIGN OF SHELL & TUBE HEAT EXCHANGERS

2. Session Schema Understanding of STHE Construction Basic Principles of Design Preliminary Design Decisions Exposure to standards General guidelines ,terminologies and definitions

3. Flow arrangements in Heat exchangers

4. Parallel-flow Heat Exchangers both the hot and cold streams enter the heat exchanger at the same end and travel to the opposite end in parallel streams. Energy is transferred along the length from the hot to the cold fluid so the outlet temperatures asymptotically approach each other.

5. Parallel Flow rapid initial rates of heat exchange near the entrance rapidly decrease as the temperatures of the two streams approach one another leads to higher energy loss during heat exchange Advantageous when two fluids are to be brought to nearly same temperature

6. Counter-flow Heat Exchangers the two streams enter at opposite ends of the heat exchanger and flow in parallel but opposite directions. Temperatures within the two streams tend to approach one another in a nearly linearly fashion resulting in a much more uniform heating pattern.

7. Counter Flow relatively uniform temperature differences and, consequently, lead toward relatively uniform heat rates throughout the length of the unit.

8. HAIRPIN HEAT EXCHANGERS Reliable Closures for design pressures up to 15,000 psi (1055 kg/cm 2 ) Independent tube-sheets for high-temperature differences, thermal shock. All connections on the same end for ease of piping. Moveable Support Brackets with slots for shell expansion and flexibility in installation. All Bolting is external. Large Radius U-bends for ease of cleaning and effective thermal expansion (no expansion joints).

9. HAIRPIN HEAT EXCHANGERS- THE PROCESS ADVANTAGE Hairpin heat exchangers utilize true counter-current flow to maximize the temperature differences between shellside and tubeside fluids, resulting in less surface area required for a given duty. This arrangement allows for a temperature cross (when the hot fluid outlet temperature is below the cold fluid outlet temperature) and a close temperature approach for maximum heat recovery.

10. STHE - A Schematic Diagram

11. Shell and tube heat exchanger (one shell pass and one tube pass)

12. Multiple pass heat exchangers

13. Multiple pass heat exchangers tube side fluid passes through once in parallel and once in counter flow 1-2 pass heat exchanger, indicating that the shell side fluid passes through the unit once, the tube side twice By convention the number of shell side passes is always listed first

14. Understanding STHE Construction

15. Understanding STHE Construction

16. Structure of the Heat exchanger Design Problem Identification of Problem Includes data like flow rates , pressures, temperatures, compositions Likelihood of fouling, difficulty in cleaning, special material requirements and unusual operating conditions Decision – configuration of the exchanger Selection of tentative set of design parameters Tube type, tube size, layout, shell diameter and length, baffle spacing etc. Rating of Design Thermal performance of the tentative configuration Pressure drop calculations Mechanical design and cost estimation

17. Allocation of Streams Heat Transfer Coefficient Low coefficient fluid on the shell side Fluid is highly corrosive Corrosive fluid should be put on tube side Fluid at high pressure Fluid at high pressure should be on tube side Not necessary to use heavy and expensive high pressure shell Fluid is severely fouling Fouling fluid should be put on tube side Easier to clean tube side Limited allowable pressure drop Stream with Lower allowable pressure drop limits should go to shell side

18. Selection of Shell Type –Thumb rules Most important factor in selecting shell type is the Thermal Stresses Fixed tube – no specific arrangement to relieve thermal stresses – can be used when T(inlet) is less than 27 c Fixed tube- rolled expansion joints in the shell – can be used when T(inlet) up to 87 c for moderate pressure shells U-tube bundles are a close solution to tube stress problem- as tubes are free to expand or contract independent of the shell

19. Fixed and floating heads design comparison

20. contd

21. Exposure to HX standards Code and Standards Sources Standards TEMA Standards (Tubular Exchanger Manufacturer’s Association) www.tema.org API (American Petroleum Institute) Standard 660 www.api.org Codes Section VIII Division 1 of ASME Boiler and Pressure Vessel Code Unfired Pressure Vessels Applies to pressure-containing envelope of shell and-tube heat exchangers www.asme.org

22. TEMA - Tubular Exchanger Manufacturers Association Heat Exchanger Designations HX sizes and types designated by numbers describing shell diameters and tube lengths Letters are used to describe the type of heads and shell Three classes of HX’s R: suited for severe requirements of petroleum and processing applications C: moderate commercial and general process applications B: chemical process service

23. TEMA- HE designations

24. TEMA- HX types (examples)

25. TEMA- HX types (examples)

26. TEMA- HX types (examples)

27. TEMA- HX types (examples)

28. TEMA- HX types (examples)

29. TEMA- HX types (examples)

30. Other Standards BS PD 5500 -   British Standards Institute ASME VIII/1- American Society of Mechanical Engineers API - American Petroleum Institute HEI – Heat Exchanger Institute

31. General guidelines, terminologies and definitions Tube Diameter The most common sizes used are 3/4"od and 1"od Use smallest diameter for greater heat transfer area with a normal minimum of 3/4"od tube due to cleaning considerations and vibration. 1/2"od tubes can be used on shorter tube lengths say < 4ft. The wall thickness is defined by the Birmingham wire gage (BWG).

32. TUBE DIMENSIONAL DATA

33. Tube Number and Length Select the number of tubes per tube side pass to give optimum velocity 0.9-1.52 m/s for liquids and reasonable gas velocities are 15-30 m/s If the velocity cannot be achieved in a single pass consider increasing the number of passes Tube length is determined by heat transfer required subject to plant layout and pressure drop constraints. To meet the design pressure drop constraints may require an increase in the number of tubes and/or a reduction in tube length. Long tube lengths with few tubes may give rise to shell side distribution problems. Minimum tube pitch should be 1.25 times outside dia of the tube.

34. Tube Layout, Pitch and Clearance Triangular pattern provides a more robust tube sheet construction. Square pattern simplifies cleaning and has a lower shell side pressure drop. Typical dimensional arrangements are shown below, all dimensions in inches.

35. Assignment Problem What is the required heat-transfer area for a parallel-flow shell-and-tube heat exchanger used to heat oil if the entering oil temperature is 15.6C , the leaving oil temperature is 48.9C, and the heating medium is steam 1378.8 kPa The overall coefficient of heat transfer U 141.9 W/(m2 C). How much heating steam is required if the oil flow rate through the heater is 6.3 L/ s, the specific gravity of the oil is 0.9, and the specific heat of the oil is 2.84 W/(m2 C)?

36. Assignment Fouling Considerations Corrosion Fouling

37. THANK YOU