heat ingeration of reactors

8/9/2019 Heat Ingeration of Reactors

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HEAT INTEGRATION OFREACTORSBy Siti Shawalliah Idris, AMIChemE

CPE 633 PROCESS ENGINEERING II


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Heat Integration Characteristics of Reactors

Adiabatic operation➢ Heat carriers➢ Cold shot

➢ Indirect heat transfer with the reactor➢ Quench


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Heat Integration Characteristics of Reactors (Cont’d)

Indirect heat transfer with the reactor


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Exothermic Reaction

A maximum can occur in the temperature at an intermediate pointbetween the reactor inlet and exit


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Endothermic Reaction

A minimum can occur in the temperature at an intermediate pointbetween the reactor inlet and exit


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For indirect heat transfer, the heat integration characteristicsof the reactor can broken down into the following three case:

If the reactor can be matched directly with other process stream,then the reactor profile should be included in the heat integrationproblem

If a heat transfer intermediate is to be used and cooling/heatingmedium is fixed, then the cooling/heating medium should beincluded and not the reactor profile itself

If a heat transfer intermediate is to be used but the temperatureof the cooling/heating medium should be included


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Batch reactor for a fixed rate ofheat transfer (exothermic reaction)A family of curves illustrates theeffect of increasing the rate ofheat removal and/or decreasingheat of reaction

Each individual curve assumes the

rate of heat transfer to the coolingmedium to be constant for thatcurve throughout the batch cycle


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Batch reactor for a fixedrate of heat transfer(endotherm)

Fixing the rate of heattransfer in a batch reactor isoften not the best way tocontrolic reaction)


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The heat duty on the heating/cooling medium is given by

Q react = −(Δ H streams+ Δ H react )

Q react = reactor heating or cooling requiredΔ H streams = enthalpy change between feed and product streamsΔ H react = reaction enthalpy


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Appropriate Placement of Reactors

Exothermic reactor


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Appropriate Placement of Reactors (Cont’d)

Exothermic reactor integrated below the pinch

Same hot utility: Cold utility increase!


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Exothermic reactor integrated above the pinch

Required hot utility is reduced by heat integration


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Endothermic Reactor


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Endothermic reactor integrated above the pinch

The process needs more hot utility!


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Endothermic reactor integrated below the pinch

Required cold utility is reduced


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The various streams associated with the reactor can becombined to form a grand composite curve for reactor

This can then be matched against the grand composite curvefor the rest of the process


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Case Study – Pthalic Anhydride


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Case Study – Phthalic Anhydride (Cont’d)

Stream Data


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GCC for the process


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Divides the GCC into twosections:

ReactorsRest of the process

Note:

Grand composite curve forreactor includes the reactorfeed and effluent streams.


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Match reactor against the process

Appropriately placed in this case


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What if the reactor is not appropriately placed?

Usually change rest of the process, not reactor, to get appropriateplacement .


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Heat Integration of Reactors (Cont’d)

Heat integration will always benefit by making hotstreams hotter and cold streams colder

This applies whether the heat integration is carried out directlybetween process streams or through an intermediate such as steam

Care should be taken when preheating reactor feeds within thereactor using the heat of reactionIf the exothermic reactor is appropriately placed above the pinchand feed start below the pinch, then the preheating within the reactoris cross-pinch heat transfer


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Heat Integration of Reactors – Summary

The appropriate placement for exothermic reactors is above the pinch

The appropriate placement for endothermic reactors is below the pinch

If the reactor is not appropriately placed ,then it is more likely that the

rest of the process would be changed to bring about appropriateplacement rather than changing the reactor

If changes to the reactor design are possible, then the simple criterion ofmaking hot streams hotter and cold streams colder can be used to bringabout beneficial changes


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Heat Integration of Reactors

Working Session


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Heat Integration of Reactors

How can we improve performance ?


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heat ingeration of reactors

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