3. SOLVED EXAMPLE

Part 2: Mechanical design

(Part 1: Thermal design calculation is given in module #1)

The process design of shell and tube for single phase heat transfer solved in module #1 is continued for the mechanical design.

The minimum information required for the mechanical design of some important components of shell and tube exchanger is summarized below:

a. Shell side and tube side passes: 1 shell pass and 6 tube passes.

b. Number, type, size, and layout of tubes: Number of tubes 318; tube length 20΄ (6.096 m as per IS: 4503-1967 and IS:2844-1964 standards); tube OD 1΄΄ (25.4 mm); tube ID: 0.834΄΄ (21.2 mm); square pitch ; fixed tube sheet.

c. Shell diameter and head: Shell ID 31΄ (787.4 mm); torispherical head is selected;carbon steel for both shell and head.

d. Corrosion allowance: Corrosion allowance of 3 mm for carbon steel is taken as per IS:4503 for the service in the petroleum industries.

e. Design temperature and pressure: design temperature 1.1×160=176°F (80°C) (10% greater than the highest process fluid temperature is taken); design pressure 0.38 N/mm² (55 psia) (10% higher than the inlet pressure of both the streams).

f. Permissible stress, f =100.6 N/mm² for carbon steel.

i. Shell thickness calculation (refer section 2.3.1)

(2.1)

Including corrosion allowance 6.72 mm, use 8 mm thickness

(This value is in accordance to IS:4503 corresponding to the shell diameter)

ii. Torispherical head (refer section 2.3.2)

Crown radius, R_i = 787.4 mm (crown radius, R_i = D_s is considered)

Knuckle radius r_i =0.06 of R_i = 47.24 mm (knuckle radius r_i =6% of D_s is taken)

Inside depth of the head ( h_i) can be calculated as: