PDD_26_IOS - 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 - 26
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Process Design Decisions (PDD) Prof B V Babu Input Output Structure of the Flow Sheet Decisions for the Input-Output Structure Flow Sheet Alternatives Level-2 Decisions – Purification of feeds Copyright © 2008-2009 B V Babu, BITS-Pilani – Number of Product streams Summary
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Process Design Decisions (PDD) Prof B V Babu Decisions for the Input-Output Structure To understand the decisions required to fix the input- output structure of a flow sheet – We merely draw a box around the total process Thus, we focus our attention on what raw materials are fed to the process and what products and byproducts are moved Copyright © 2008-2009 B V Babu, BITS-Pilani removed Since, the raw materials costs fall normally in the range of 33-85% of the total processing costs , we want to calculate these costs before we add any other detail to the design
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Process Design Decisions (PDD) Prof B V Babu Flow Sheet Alternatives Almost every flow sheet has one of the two structures shown below: PROCESS Product By-product Feed Streams Fig. 1 (a) Copyright © 2008-2009 B V Babu, BITS-Pilani PROCESS Product By-product Purge Gas Recycle Feed Streams Fig. 1 (b)
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Process Design Decisions (PDD) Prof B V Babu Flow Sheet Alternatives For initial design calculations – We use the order-of-magnitude argument to say that the rule of thumb • That it is desirable to recover more than 99% of all valuable materials – Is equivalent to requiring Copyright © 2008-2009 B V Babu, BITS-Pilani • That we completely recover and then recycle all valuable reactants – Thus Fig. 1(a) indicates that no reactants leave the system If air & water are reactants in a process – They are sufficiently inexpensive compared to organic materials – That it might be cheaper to lose them in an exit stream rather – Hence, in a few rare cases, Fig. 1(a) might not be complete
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Process Design Decisions (PDD) Prof B V Babu Flow Sheet Alternatives The other situation in which commonly reactants have been lost from a process occurs – When we have a gaseous reactant , and – Either a gaseous feed impurity – Or a gaseous by-product produced by one of the reactions e want to recycle the aseous reactant Copyright © 2008-2009 B V Babu, BITS-Pilani We want to recycle the gaseous reactant But the inert-gas components must be purged from the process so that they do not continue to accumulate in the gas-recycle loop In the past, it was so expensive to separate gaseous mixtures that some reactant was allowed to leave the process in a gas-recycle and purge stream [ Fig. 1(b) ]
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Process Design Decisions (PDD) Prof B V Babu Flow Sheet Alternatives
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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_26_IOS - Process Design Decisions (PDD) Process Design...

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