A butane-pentane splitter is to be designed to process 4200 lb/h of C3-C5 feed s

Question

A butane-pentane splitter is to be designed to process 4200 lb/h of C3-C5 feed subject to specifications of I. A maximum of 3 wt % iC5 in the distillate product The heat sink will be air (process design temperature to be 130°F) and 100 lb/in (gage) steam A maximum of 1 wt % C4 in the bottoms product will be used as the heat source in the reboiler. The feed to the column is given below omponent Propane (C3) Iso-Butane(iC4) Butane (C4) Iso-Pentane (iC5) Pentane (C5) 15 25 20 35 Find the flow rates of each component and their mole fractions in the top and bottom products? HINT First convert mass % to mole percent. Determine the key components and their separation. Assume that all Lighter-than-Light Key (LLK) go to the top product and all Heavier-than-Heavy Key (HHK) go the bottom. Note that this is an assumption, hence flow rates and compositions of LLK and HHK components should be written in brackets, since we will have to check this assumption later, but not when solving this problem. Problem # 5 For the above problem, select the type of condenser and find the terminal operating conditions of the distillation system. The terminal conditions desired are the temperature and pressure of distillate reflux drum 2. coumn overhead or top of column, assuming a 2.5 psia pressure drop in total condenser 3. column bottom/reboiler, assuming a 5 psia pressure drop in the distillation column

Explanation / Answer

For air as a Utility, area requires is maximum. Therefore condensor to be used is Plate Fin Heat exchanger.

1) Distillate reflux drum will be kept at atmosphere, Therefore, Pressure = 1 atm = 14.5 psia

Inlet of distillate-reflux drum =Outlet of Overhead condensor,

Since utility is air, Therefore, there will be a margin of 20 F between air and fluid temperature

Air temperature= 130 F

Therefore, distillate-reflux drum temperature = 130-20 =110 F

2) In the condensor, there is 2.5 Psia pressure drop,

Therefore, Overhead column pressure = 14.5+2.5 = 17 psia

Fin Plate Overhead heat exchanger is removing only latent heat to work efficiently

Therefore, Overhead column temperature = Saturation temperature=Condensor outlet temperature =110F

3) Column bottom pressure = Column top pressure + Pressure drop in column = 17+5=22psia

In reboiler, saturated Steam pressure =100 lb/inch2

=> Using steam table, temperature of steam = 329 F

For better heat transfer, Boiler fluid temperature = steam temperature - 20 = 329-20 = 309 F

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