Overview of Process Design

Chapter 4

Terry A. Ring

ChE

Where is Design used in Industry?

Where is Design used in Industry?

• De Novo Designs• Known Plants but different location or

larger size• Plant Improvement

– Debottlenecking Plant– Increase Plant Capacity– Increase Plant Efficiency– Decrease Costs– Pollution Minimization

Importance of Process Design

• In Preliminary Process Design– 98% Operating Costs Committed– 80% Capital Costs Committed

• Less than 10% $ Spent• Design is Very Important

• But why is this so?

How is Design Practiced• Process Conception• Preliminary Design

– Process Concepts– Process Economics

• Management decision to go forward• Intermediate Design

– P&ID’s– Ask vendors for prices major pieces of equipment

• Reactor, Separators, HX, Utilities, tank farms– Process Economics

• Management decision to go forward• Detailed Design

– Mechanical Engineering• Equipment + Supports

– Where are all the nuts and bolts

– Piping elevation– Electrical/Power Engineering– Utilities– Process Economics

• Management decision to go forward

Process Creation

• Chemical Reaction Routes

• Preliminary Database– MSDS – (Health and safety info.)

• Raw Materials• Reaction Products and Intermediates

– Thermo/phys properties (Expts and Predictions)

• Heats of Formation• VLE data, solubilities, etc.

– Chemical Prices (Chemical Market Reporter)

Operating costs

• Selection of Raw Materials

• Selection of Reaction Path to Product

• Determine Gross Profitability of Process

• Examples– Vinyl Chloride Manufacture (part of PVC plant)

• Example in your book

– Octane Manufacture (part of refinery)

Process Economics-I

• Macro View– Possible Reactions for vinyl chloride

• 1) C2H4 (ethylene) + Cl2 C2H3Cl (vinyl Chloride) + HCl• 2) C2H2 (acetylene) + HCl C2H3Cl• 3) C2H4 + Cl2 C2H4Cl2 C2H3Cl + HCl• 4) C2H2 + 2HCl + ½ O2 C2H4Cl2+H2O• C2H4Cl2 C2H3Cl +H2O• C2H2 + 2HCl + ½ O2C2H3Cl +H2O (overall)

• 5) C2H4 + Cl2 C2H4Cl2• C2H2 + 2HCl + ½ O2 C2H4Cl2+ H2O• 2 C2H4Cl2 2C2H3Cl + 2HCl• 2C2H4 + Cl2 + ½ O2 2C2H3Cl + H2O (overall)

Gross Profitability Analysis-1

• Start With Raw Material Costs and Product Prices

Gross Profitability Analysis-1

• For Each Reaction Determine the Profit to be made

• Gross Profit is – 22¢/lb(1) +18¢/lb (0.583)-18¢/lb(0.449)-11¢/lb(1.134)=11.94 ¢/lb

Gross Profitability Analysis-2

• Overview of Various Reactions

• Reaction 3 is most profitable!• How much do we make? Market Volume?http://nexant.ecnext.com/coms2/summary_0255-3041_ITM

Example of Market Information

http://www.ceramics.org/ASSETS/574195312DA149928805FFEA1242FECF/MaterialsReview_08_08.pdf

Process Synthesis-1

• Reaction 3 – Direct Chlorination– Pyrolysis

Consider Separations• VLE data

• Boiling Points

• Flash HCl from Rxn Products

Process Synthesis-1

• Separation System

Process Synthesis-3• Task Integration

– Reactor & Condenser

• Separations

Onion Model of Process Design

Overall Process

Octane Reaction

• 2C2H4 + C4H10 C8H18

• P= 5 psi, T=93C, X=98% Conversion

Preliminary Flow Sheet

Flash ΔP= 2 psi

Distillation

Purge Stream

With Heat Integration

Without Heat Integration

What else can be done?

• Where is the heat duty for the Flash vessel coming from?– Heat Exchanger coupling reactor feed to

reactor product.

• Do we really need the flash vessel?– Let distillation column do all the separation.

• Reactor heat duty– Exo or Endo reaction?– Where does it come from?

Onion Model of Process Design

Importance of Process Design

• In Preliminary Process Design– 98% Operating Costs Committed– 80% Capital Costs Committed

• Less than 10% $ Spent• Design is Very Important

• But why is this so?

Why

• In Preliminary Design– Decide on Raw Materials Operating Costs

– Decide Process• Reactor System Capital Costs• Separation System Capital Costs• Recycle System Capital Costs• Heat Integration Scheme Capital Costs• Utilities Operating Costs