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PDD_32_GS2 - Process Design Decisions(PDD Process Design...

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Process Design Decisions (PDD) Prof B V Babu Process Design Decisions Copyright © 2008-2009 B V Babu, BITS-Pilani LECTURE - 32
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Process Design Decisions (PDD) Prof B V Babu General Structure of the Flow Sheet Recap Strategy Combining VRS with LSS Liquid Separation System (LSS) Light ends Destination of Light ends Copyright © 2008-2009 B V Babu, BITS-Pilani Summary of Light ends Azeotropes with Reactants Applicability of Distillation Column Sequencing Alternatives to Distillation Economic Potential (EP 4 ) Summary
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Process Design Decisions (PDD) Prof B V Babu Strategy We design the vapor recovery system ( VRS ) before we consider the liquid separation system ( LSS ) Because each of the vapor recovery processes usually generates a liquid stream that must be further purified For the case of gas absorber, where we need to supply a solvent to the absorber Copyright © 2008-2009 B V Babu, BITS-Pilani We also introduce a new recycle loop between the separation systems Normally we need to estimate the size and cost of each unit to determine which is the cheapest
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Process Design Decisions (PDD) Prof B V Babu Strategy Vapor Recovery System Vapor Gas recycle Purge H 2 , CH 4 Copyright © 2008-2009 B V Babu, BITS-Pilani Reactor system Liquid Separation system Phase split Products H 2 , CH 4 Liquid Solvent Liquid recycle Toluene
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Process Design Decisions (PDD) Prof B V Babu Combining VRS with LSS If we use a partial condenser and a flash drum to phase- split the reactor effluent some of the lightest liquid components will leave with the flash vapor i.e., a flash drum never yields perfect splits and therefore will not be recovered in the liquid recovery system Copyright © 2008-2009 B V Babu, BITS-Pilani However, if there is only a small amount of vapor in the stream leaving the partial condenser And if the first split in the liquid separation is chosen to be distillation We could eliminate the phase splitter and feed the reactor effluent stream directly into the distillation column
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Process Design Decisions (PDD) Prof B V Babu Combining VRS with LSS The diameter of a distillation column with the two-phase feed will need to be larger than a column that follows a flash drum to handle the increased vapor traffic However, this increased cost may be less than the costs associated with Copyright © 2008-2009 B V Babu, BITS-Pilani using a vapor recovery system to remove the liquid components from the flash vapor stream There does not seem to be a heuristic available for making this decision and so we need to add another process alternative to our list with phase splitter & without phase splitter
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Process Design Decisions (PDD) Prof B V Babu Liquid Separation System The decisions that we need to make to synthesize the liquid separation system: 1. How should the light ends be removed if they might contaminate the product?
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