2011_L23_process optimisation

8/7/2019 2011_L23_process optimisation

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Optimisation Part 2Process

Dr Simon Smart

The University of Queensland

CHEE4024

Energy Systems in Sustainable Development


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Process Optimisation -Outlinen Considerations

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n Major Approaches

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n Environmental / Saftey Considerations

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n Summary

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Process Optimisation -Example

Too much wastewater

Biotreatmentplant at capacity

How to solve?Optimal

Solution?


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Process Optimisation -Example

Most obvioussolution is notalways best

Think outside

the box


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Considerations for ProcessDesign

OptimisedProcess

Current technologies

Risk

Safety

Environment

Alternatives

Capital Costs

Running Costs

Product Costs

Waste Products

Infinite number of solutionsNarrowing them down needs experience


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Process Design

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Early design stagesaccommodate forcurrent needs

n Creative designq Most obvious may

not be best

n Process simulationq

ASPEN, HYSYS,Matlab, etc.

What about plantsmade 50 years ago?

Can you see whatmight be more of aconcern in another50 years?


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Process Design

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Heuristics (rules of thumb)q Chemical reactions

q Mixing and recycling

q Separation

q T, P, and phase changeq Integration

n Mass

n Heat

There are 53 heuristicprinciples stated in Seider,Seader and Lewinsprocess principles book.


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Major Approachesn Various areas are classically approached for

optimisation:q Distillation heuristics

q Mass exchange networks (MENs)

q Heat exchanger networks (HENs)

n Co-current vs counter-current, pipe losses etcn Pinch analysis

q Reaction/separation staging

q Mass and energy recycle

q

Pumping, turbine and compressor networks (egHP/LP dual turbines)


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Operation PositioningExamplen Consider a process to make isobutane: n-C4H10 i---H--The feed is 20 mol% isobutane. Show the optimal pathway

n Solution:n

n

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Either option is valid on initial glance. On closer look, withdistillation column first, pure feed is sent to reaction operation

leading to higher conversion to isobutane. Need to look at effectiveness of distillation efficiency

and reaction kinetics simulated together to make decision

- 80 mol%nC4- 20 mol% iC4

n C4H10 iC4H10iC4

nC4

n C4H10 iC4H10

iC4

nC4

Option 1 Option 2


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Equipment Choice

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Chemicals and conditions tie closely withequipment choice.q Vessels: Height, diameter, orientation, pressure,

temperature, material of construction (MOC)q

Towers: as for vessels and tray number, heightand packing materialq Pumps: Driver type, flow, P, T, shaft power, MOCq Heat exchangers: Fluid, type, area, duty, no.

shell and tube passes, T, P, P and MOCq Fired heaters: Type, tube P and T, duty, radiant

and convective heat transfer are, MOC.

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Environmental Consideration

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Examples:q R134a refrigerantq Desulphurisation of dieselq Sulphur recovery

q CO2 reductionq Waste water treatmentq Soil remediationq Combined cycle power generation

q Waste conversion to acetone and isopropanolq Ethanol for petroleum from biomass


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Safety

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Safety is the most important design requirementn Improved product (energy) outcome can come fromchoice of safer systems.

n Safety costs money. Trade off actually considered bycompanies: Payouts vs safety implementation cost.

n Some industries impossible because safety tooexpensive to make competitive product.n Safety ties in with environment

q Bhopal, India, Dec 3, 1984: Union Carbide factory, waterflowed into tank with methyl isocyanate (MIC). Rapid T

rise caused boiling and MIC vapours escaped. Nonfunctional scrubbers and flares on safety system allowedrelease of 25t toxic MIC. Killed 3 800 people.

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Safe Design

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Fires and explosions prevented by inerting,ventilation, construction

n Relief devices

n Careful study of process: HAZOP, FMEA

n MSDS

n Ethical consideration

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Process Integration

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Holistic approach to process design,retrofitting and operation which emphasisesthe unity of the process

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n A trade off clearly exists between improvedefficiency and complexity (reliability, cost,etc)

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Quantify disturbancesn Flexibility

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Process Integration HeatExample

nHow to setupthis system?

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Process Integration HeatExample

nIs this the bestway?

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Why not?n

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2011_L23_process optimisation