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 Copyright © 2008-2009 B V Babu, BITS-Pilani – Destination of Light ends – 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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This note was uploaded on 02/29/2012 for the course CHEMICAL 332 taught by Professor Profb.v.babu during the Spring '09 term at Birla Institute of Technology & Science.

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

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