EP426Chemical Process Design and Optimization

Chapter 3a - Separation train synthesis.Introduction

Assess Primitive Problem

Steps in Process Design and Retrofit

Development of Base-case

Plant-wide Controllability Assessment

Detailed Design, Equipment sizing, Cap.

Cost Estimation, Profitability Analysis,

Optimization

Detailed Process Synthesis -Algorithmic

Methods

SECTION B

Section B: Algorithmic Methods

Introduction

Almost all chemical processes require the separation of chemical species (components), to: purify a reactor feed recover unreacted species for recycle to a reactor separate and purify the products from a reactor

Frequently, the major investment and operating costs of a process will be those costs associated with the separation equipment

For a binary mixture, it may be possible to select a separation method that can accomplish the separation task in just one piece of equipment. However, more commonly, the feed mixture involves more than two components, involving more complex separation systems

Example 1. Specification for Butenes Recovery

Design for Butenes Recovery System

100-tray column C3 & 1-Butene in distillate

Propane and 1-Butene recovery

Pentane withdrawn as bottoms

n-C4 and 2-C4=s cannot be separated by ordinary distillation (=1.03), so 96% furfural is added as an extractive agent ( 1.17).

n-C4 withdrawn as distillate.

2-C4=s withdrawn as distillate. Furfural is recovered as bottoms and recycled to C-4

Separation is Energy Intensive

Unlike the spontaneous mixing of chemical species, the separation of a mixture of chemicals requires an expenditure of some form of energy

Separation of a feed mixture into streams of differing chemical composition is achieved by forcing the different species into different spatial locations, by one or a combination of four common industrial techniques:

the creation by heat transfer, shaft work, or pressure reduction of a second phase that is immiscible with the feed phase (ESA – energy separating agent)

the introduction into the system of a second fluid phase (MSA – mass separating agent). This must be subsequently removed.

the addition of a solid phase upon which adsorption can occur

the placement of a membrane barrier

Common Industrial Separation Methods

Separation Method

Phase of the feed

Separation agent

Developed or added phase

Separation principle

Equilibrium flash

L and/or V Pressure reduction or

heat transfer

V or L difference in volatility

Distillation L and/or V Heat transfer or shaft work

V or L difference in volatility

Gas Absorption

V Liquid absorbent

L difference in volatility

Stripping L Vapor stripping agent

V difference in volatility

Extractive Distillation

L and/or V Liquid solvent and heat transfer

V and L difference in volatility

Azeotropic Distillation

L and/or V Liquid entrainer and heat transfer

V and L difference in volatility

4-Separation TrainsDESIGN AND ANALYSIS II - (c) Daniel R. Lewin9

Common Industrial Sep.Methods (Cont’d)

Separation Method

Phase of the feed

Separation agent

Developed or added phase

Separation principle

Liquid-liquid Extraction

L Liquid solvent

Second liquid

Difference in solubility

Crystalli-zation

L Heat transfer

Solid Difference in solubility or

m.p.

Gas adsorption

V Solid adsorbent

Solid difference in adsorbabililty

Liquid adsorption

L Solid adsorbent

Solid difference in adsorbabililty

Membranes L or V Membrane Membrane difference in permeability

and/or solubility

Common Industrial Sep.Methods (Cont’d)

Separation Method

Phase of the feed

Separation agent

Developed or added phase

Separation principle

Supercritical extraction

L or V Supercritical solvent

Supercritical fluid

Difference in solubility

Leaching S Liquid solvent

L Difference in solubility

Drying S and L Heat transfer

V Difference in volatility

EndNext Class: Part II