Tube Bundles for A Shell Tube Heat Exchanger in A Refinery

Tube Bundles for a Shell Tube Heat Exchanger in a Refinery

In a refinery, shell tube heat exchangers are critical for processes like distillation, cracking, and heat recovery, with tube bundles serving as the core component for heat transfer.

Tube Bundle Structure and Core Components

A tube bundle in a shell tube heat exchanger consists of:

Tubes：

Arranged in parallel within the shell, forming the primary heat transfer surface.

Connected to tube sheets at both ends, which separate the tube side and shell side fluids.

Tube Sheets：

Thick metal plates (often forged) with drilled holes for tube insertion, welded or expanded into place.

Designed to withstand pressure differences between tube and shell sides.

Support Structures：

Baffles：Horizontal or vertical plates that guide shell-side fluid flow, enhance turbulence, and support tubes to prevent vibration (e.g., segmental baffles, orifice baffles).

Tie Rods and Spacers：Maintain spacing between baffles and ensure bundle rigidity.

Header/Channel：

Distributes tube-side fluid to the tubes (e.g., multi-pass configurations use partition plates in headers to direct flow).

Key Parameters

Tube Diameter：Common sizes: 19 mm (3/4") or 25 mm (1") OD, with wall thicknesses (1.2-2.5 mm) depending on pressure and corrosion.

Pitch (Tube Spacing)：Typically 1.25-1.5x tube OD; larger pitches for fouling fluids (e.g., heavy oil) to ease cleaning.

Pass Configuration：1-pass, 2-pass, or 4-pass tubes to increase fluid velocity and heat transfer (e.g., 2-pass tubes for higher tube-side heat transfer coefficients).

Materials for Refinery Applications

1. Tube Materials

Carbon Steel (e.g., ASTM A179, A192)：Suitable for non-corrosive fluids (e.g., steam, light hydrocarbons) below 400°C.

Stainless Steel (304, 316, 321)：Resists corrosion from sulfur-containing oils, acids, and high-temperature oxidation (e.g., 316L for sour crude processing).

Nickel Alloys (Inconel, Hastelloy)：For extreme conditions (e.g., >600°C, high-pressure hydrogen environments in hydrocracking units).

Copper Alloys (Brass, Cupronickel)：Used in coolers with seawater or freshwater (e.g., condenser tubes in refinery cooling systems).

2. Tube Sheet Materials

Low-alloy steel (ASTM A387) for high-temperature service, clad with stainless steel or nickel alloys for corrosion resistance.

Weld overlay or explosive cladding to protect against tube-side and shell-side corrosion.

Refinery Process Applications

1. Crude Oil Preheating Train

Function：Heat crude oil using hot products from distillation columns before entering the furnace.

Tube Bundle Design：

Triangular pitch for high heat transfer in shell-side (hot oil) and tube-side (crude oil).

Stainless steel tubes (316L) to resist sulfuric corrosion from crude oil.

Segmental baffles with 25-35% cut to balance heat transfer and pressure drop.

2. Vacuum Tower Condensers

Function：Condense vacuum tower overhead vapors (light hydrocarbons) using cooling water.

Tube Bundle Design：

Square pitch for easy cleaning of tube outer surfaces (water-side fouling).

Cupronickel (Cu-Ni 90/10) tubes to resist chloride-induced corrosion from cooling water.

Multi-pass tube arrangement to increase water velocity and prevent scaling.

3. Catalytic Cracking Unit (FCCU) Heat Exchangers

Function：Recover heat from reactor effluent to preheat feedstock or generate steam.

Tube Bundle Design：

High-alloy steel tubes (e.g., 321 SS) to withstand high temperatures (450-550°C) and coking.

Close tube spacing with anti-vibration baffles to prevent fluid-induced vibration from high-velocity gases.