Heat Ingeration of Reactors [PDF]

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CPE 633 PROCESS ENGINEERING II



HEAT INTEGRATION OF REACTORS By Siti Shawalliah Idris, AMIChemE



Heat Integration Characteristics of Reactors   



 



Adiabatic operation ➢ Heat carriers ➢ Cold shot ➢ Indirect heat transfer with the reactor ➢ Quench



Heat Integration Characteristics of Reactors (Cont’d) 



Indirect heat transfer with the reactor



Heat Integration Characteristics of Reactors (Cont’d) Exothermic Reaction



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



Heat Integration Characteristics of Reactors (Cont’d) Endothermic Reaction



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



Heat Integration Characteristics of Reactors (Cont’d) 



For indirect heat transfer, the heat integration characteristics of 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 integration problem







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







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



Heat Integration Characteristics of Reactors (Cont’d) 







Batch reactor for a fixed rate of heat transfer (exothermic reaction) A family of curves illustrates the effect of increasing the rate of heat removal and/or decreasing heat of reaction  Each



individual curve assumes the rate of heat transfer to the cooling medium to be constant for that curve throughout the batch cycle



Heat Integration Characteristics of Reactors (Cont’d) 



Batch reactor for a fixed rate of heat transfer (endotherm)  Fixing



the rate of heat transfer in a batch reactor is often not the best way to controlic reaction)



Heat Integration Characteristics of Reactors (Cont’d) 



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



Qreact = −(ΔHstreams+ΔHreact)  Qreact



= reactor heating or cooling required  ΔHstreams = enthalpy change between feed and product streams  ΔHreact = reaction enthalpy



Appropriate Placement of Reactors Exothermic reactor



Appropriate Placement of Reactors (Cont’d) Exothermic reactor integrated below the pinch



Same hot utility: Cold utility increase!



Appropriate Placement of Reactors (Cont’d) Exothermic reactor integrated above the pinch



Required hot utility is reduced by heat integration



Appropriate Placement of Reactors (Cont’d) Endothermic Reactor



Appropriate Placement of Reactors (Cont’d) Endothermic reactor integrated above the pinch



The process needs more hot utility!



Appropriate Placement of Reactors (Cont’d) Endothermic reactor integrated below the pinch



Required cold utility is reduced



Appropriate Placement of Reactors (Cont’d) 



The various streams associated with the reactor can be combined to form a grand composite curve for reactor  This



can then be matched against the grand composite curve for the rest of the process



Case Study – Pthalic Anhydride



Case Study – Phthalic Anhydride (Cont’d) 



Stream Data



Case Study – Phthalic Anhydride (Cont’d) 



GCC for the process



Case Study – Phthalic Anhydride (Cont’d) 



Divides the GCC into two sections: Reactors  Rest of the process 







Note:







Grand composite curve for reactor includes the reactor feed and effluent streams.



Case Study – Phthalic Anhydride (Cont’d) 



Match reactor against the process



Appropriately placed in this case



Case Study – Phthalic Anhydride (Cont’d) What if the reactor is not appropriately placed?



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



Heat Integration of Reactors (Cont’d) 



Heat integration will always benefit by making hot streams hotter and cold streams colder  This



applies whether the heat integration is carried out directly between process streams or through an intermediate such as steam  Care should be taken when preheating reactor feeds within the reactor using the heat of reaction  If the exothermic reactor is appropriately placed above the pinch and feed start below the pinch, then the preheating within the reactor is cross-pinch heat transfer



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



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



If the reactor is not appropriately placed ,then it is more likely that the rest of the process would be changed to bring about appropriate placement rather than changing the reactor If changes to the reactor design are possible, then the simple criterion of making hot streams hotter and cold streams colder can be used to bring about beneficial changes



Working Session Heat Integration of Reactors



Heat Integration of Reactors How can we improve performance ?