In: Chemistry
QUESTION 1. Cool and condense benzene for storage (F&R 8.38)
At OzChem plant, benzene vapour is processed as a reagent. The plant produces benzene as a vapour (at 5780C, 1 atm), which is cooled and converted to a liquid at 250C in a continuous condenser that operates at 1 atm pressure (the pressure drop is negligible). The liquid condensate from the condenser is transferred at a rate of 150 mol/s into storage tanks. Calculate the rate (in kW) at which heat must be transferred from the benzene in the condenser.
To find rate of heat transfer from benzene in the condenser,
we have benzene vapour temp. = 578C
Cooled to 25
C
T1 = 25C
& T2 =
578
C
Molar flowrate of condensate is 150 mol/s
Here benzene vapor is condensed to liquid so phase change must be considered.
Boiling point of Benzene is 80C
at 1 atm so From 578
C
to 80
C
Specific Heat capacity will be considered and no phase will change
at 80
C,
At 80
C
latent heat of phase change will be considered and from
80
C
to 25
C
cooling no phase will be change.
Q1 = From 578C
to 80
C
Cp = 135.69 J/mol*K
Q1 = m Cp (T2-T1)
Q1 = 150 (135.69) (578-80)
= 1013.6043 kW
Q2 = m
= 390 kJ/kg
Let convert flowrate from mol/s to kg/s
m=150 mol/s = 150* 78 g/s = 11.7 kg/s
Q2 = m = 11.7 * 390 =
4563 kJ/s = 4563 kW
Q3 = m Cp (T2-T1)
= 150 * (135.69) (80-25)
= 1119.4425 kW
Total Heat Transferred during condensation,
Q = Q1+Q2+Q3
=1013.6043+4563+1119.425
= 6696.0293 kW