PDD_19_EDM3 - Process Design Decisions(PDD Prof B V Babu...

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Unformatted text preview: Process Design Decisions (PDD) Prof B V Babu Process Design Decisions Copyright © 2008-2009 B V Babu, BITS-Pilani LECTURE - 19 Process Design Decisions (PDD) Prof B V Babu Economic Decision Making • Recap • Material Balances – Exact material balance calculations – Approximate material balance calculations – Solvent loss calculations tream cost calculations: acetone ater system Copyright © 2008-2009 B V Babu, BITS-Pilani – Stream cost calculations: acetone-water system – Cost of solvent lost • Summary Process Design Decisions (PDD) Prof B V Babu Design of Gas Absorber System: Flow sheet TION BER Air Solvent (Water ) (77 F=25 C or less) Acetone COOLANT Copyright © 2008-2009 B V Babu, BITS-Pilani Fig. 1 Flow sheet of gas absorption HEAT DISTILLAT ABSORB Acetone + Water Acetone + Air (Gas feed having solute) Water + traces of Acetone COOLANT POLLUTION TREATMENT Sewer Process Design Decisions (PDD) Prof B V Babu Rules of Thumb • H2: It is desirable to recover more than 99% of all valuable materials (we normally use 99.5% recovery as a first guess) • H3: For an isothermal, dilute absorber, choose the olvent flow rate ( such that = .4 G Copyright © 2008-2009 B V Babu, BITS-Pilani solvent flow rate ( L ), such that L = 1.4 mG Process Design Decisions (PDD) Prof B V Babu Exact Material Balances • With these rules of thumb, it is a straight forward task to calculate the material balances • For the acetone-water system at 77 F (25 C) and 1 atm – Fugacity coefficient, γ s = 6.7 – Vapour pressure of acetone in air, P o s = 229 mmHg. ir flow rate, 687 mol/hr Copyright © 2008-2009 B V Babu, BITS-Pilani – Air flow rate, G = 687 mol/hr • So that, • Solvent flow rate (L) = 1.4 mG = 1.4 x 2.02 x 687 = 1943 mol/hr 02 . 2 760 ) 229 ( 7 . 6 = = = = T o s s s P P x y m γ s o s s s T x P y P γ = Process Design Decisions (PDD) Prof B V Babu Exact Material Balances • For a 99.5% recovery of acetone in the gas absorber, – The acetone lost = 0.005 (10.3) = 0.05 mol/hr • And the acetone flow to the distillation column, – 0.995 (10.3) = 10.25 mol/hr Copyright © 2008-2009 B V Babu, BITS-Pilani • If 99.5% of acetone entering the still is recovered overhead, – Then acetone as distillate = 0.995 (10.25) =10.20 mol/hr Process Design Decisions (PDD) Prof B V Babu Exact Material Balances • Also if the product composition of acetone is specified to be 99%, – Then the amount of water in the product stream (distillate) will be mol/hr 10 . ) 20 . 10 ( 99 . 99 . 1 = & ¢ £ ¥- = Copyright © 2008-2009 B V Babu, BITS-Pilani • Then the bottom flows of acetone and water are – Acetone: 0.005 (10.25) = 0.05 mol/hr – Water: 1943 - 0.1 = 1942.9 mol/hr ¡ ¤ Process Design Decisions (PDD) Prof B V Babu Acetone Recovery Flow Sheet: Exact Material Balance TION BER Air (687 mol/hr)+ Acetone lost (0.05 mol/hr) Water (25 C, 1943 mol/hr) Acetone...
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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_19_EDM3 - Process Design Decisions(PDD Prof B V Babu...

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