CHEN 4470 – Process Design Practice

Dr. Mario Richard EdenDepartment of Chemical Engineering

Auburn University

Lecture No. 12 – Reboiler Selection and Design

February 16, 2012

Material Developed by Dr. Jeffrey R. Seay, University of Kentucky - Paducah

Distillation Modeling

Overview

• Purpose of Reboilers– Provide vapor flow up a column and acts as an

additional theoretical stage below the trays/packing

• Types of Reboilers– Thermosyphon– Forced circulation– Kettle– Internal reboiler (rarely used in continuous

columns)Proper reboiler design is critical to the optimum operation of a column!

Thermosyphon Reboiler

2-Phase Flow Region

All-Liquid Flow Region

• Return piping to the column must be sized for two-phase flow.

• Thermosyphons operate based on thermodynamic principles, rather than gravity.

• Therefore, design detail is important.

• Thermosyphon operation is simple, but they are often difficult to design for a wide operating range.

• Proper elevation is critical!

Forced Circulation Reboiler

• Forced circulation reboilers are designed to operate liquid full.

• Flashing occur as the liquid crosses the control valve.

• Valve should be located close to the column shell.

• Forced circulation reboilers offer greater operational flexibility than thermosyphons, yet have a smaller footprint than kettle reboilers.

• Elevation is less critical due to pump and control valve.

Kettle Reboiler

• Vapor-Liquid disengagement occurs in the vapor space, therefore return piping is sized for all-vapor flow.

• Proper elevation is critical to kettle reboiler operation.

• Kettles have a large footprint, but require less elevation than a thermosyphon.

• Works by gravity, rather than thermodynamics.

Cross Section ofKettle

All-Vapor Flow Region

All-Liquid Flow Region

Reboiler Design

Reboiler Selection Flowchart

Thermosyphon

Kettle

Forced Circulation

Cost Comparison of Reboiler Types

Reboilers in ASPEN Plus