CHE111P Material Balance: Multiple Units [PDF]

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MATERIAL BALANCE INVOLVING MULTIPLE UNITS



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FLOWCHART – is a graphical representation of a process USES: ◦ ◦ ◦ ◦



1) 2) 3) 4)



Formulate material and energy balances. Troubleshooting Control of operation conditions Optimization of process



Indicates equipment sequence and flow of material  Shows block diagram/subsystems 



PROCESS FLOWSHEET



F2



F1 MIXER



EXAMPLE



W



L



D



FILTER



C



P DRIER



4



3



5



1



MIXING PT. - 2 OR MORE STREAMS OF DIFFERENT COMPOSITIONS



EXAMPLE



6 2



7 SPLITTING PT.



- 2 OR MORE STREAMS EXIT - ALL STREAMS HAVE THE SAME COMPOSITION



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Figure 11.8 shows a schematic for making fresh water from sea water by freezing. The pre-chilled sea water is sprayed into a vacuum at a low pressure. The cooling required to freeze some of the feed sea water comes from evaporated of a fraction of the water entering the chamber. The concentration of the brine stream, B, is 4.8% salt. The pure salt-free water vapor is compressed and fed to a melter at a higher pressure where the heat of condensation of the vapor is removed through the heat of fusion of the ice which contains no salt. As a result, pure cold water and concentrated brine (6.9%) leave the process as products. a) Determine the flow rates of streams W and D if the feed is 1000 kg per hour b) Determine the flow rates of streams C, B and A per hour?



EXAMPLE



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Several streams are mixed as shown in Figure P11.10. Calculate the flows of each stream in kg/s



EXAMPLE



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RECYCLE – material that leaves a process that is downstream and is returned to the same unit or upstream unit for processing again F



M



G



UNIT



SEPARATOR



P



R



RECYCLE, BYPASS & PURGE



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BYPASS – a stream that skips one or more units of the process, and goes directly to a downstream unit.



F



M



UNIT I



UNIT II



P



B



RECYCLE, BYPASS & PURGE



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PURGE – a stream bled off from the process to remove accumulation of inert of unwanted material that might build up in the recycle system. R



U S



F



M



UNIT



G



SEPARATOR



P



RECYCLE, BYPASS & PURGE



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Forty-five hundred kilograms per hour of 33.3% K2CrO4 solution is joined by a recycle stream of 36.4% K2CrO4 solution, and the combined stream is fed into an evaporator. The condensed stream leaving the evaporator contains 49.4% K2CrO4. This stream is then fed to a crystallizer where it is cooled, causing crystals of K2CrO4 to come out of the solution. The resulting solution and K2CrO4 are separated by a filter, dividing the product into two streams: the filter cake, which consists of K2CrO4 crystals and 36.4% K2CrO4 solution; and the filtrate, which is 36.4% K2CrO4. The K2CrO4 crystals account for 95% of the total mass of the filter cake. The filtrate is recycled to mix the feed. Calculate (a) the rate of evaporation, or the rate of water evaporated (b) the recycle ratio (mass flow rate of recycle/mass flow rate of fresh feed)



EXAMPLE



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In the preparation of the feedstock for a plant manufacturing gasoline, iso- and normal pentane are produced from the process below. Calculate the fraction of feed that passes through the iso-pentane tower.



EXAMPLE