# Assignment 4

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```					Material and Energy Balances, 313a

Assignment # 4

Sept. 30, 2003,    Due date: Oct. 7, 2003

1. Multiple effect evaporators (vacuum) are used to produce concentrated solutions
of heat sensitive materials. In a three stage evaporator (shown below) the feed is
an aqueous solution containing 20% (wt) of material A. the desired product
contains 5% water. If the water removed from the second stage is 1000 kg/hr,
calculate the flow rate of feed, final product and intermediate streams.:

20% A
Evap 1
Evap 2                    Evap 3

40% A
75% A
95% A

Water 1000 kg/hr

2) A contact sulfuric acid plant produces 98% (wt) sulfuric acid by absorbing SO3 into a
97.3% (wt) sulfuric acid solution.
SO3 + H2O = H2SO4
A gas containing 8% (mole) SO3 (remainder inerts) enters the SO3 absorption tower at the
rate of 28 kgmol/hr. 98.5% of the SO3 is absorbed in the absorption tower. The sulfuric
acid (97.3% (wt)) solution is introduced into the top of the tower and 95.5 % (wt) sulfuric
acid from another part of the process is used as make-up acid as shown below. Calculate:
a) Tons per day of 95.5 % (wt) make-up acid solution
b) Tons per day of 97.3 % (wt) acid solution introduced into the top of the tower
c) Tons per day of 98 % (wt)      acid solution produced

H2SO4 97.3%
Water 2.7%

Absorption
tower
H2SO4 95.9%
Water 4.1%

SO3 8%                     H2SO4 98%
Inert 92%                  Water 2%

3) An isomerizer is a catalytic reactor that simply tends to rearrange isomers. The number
of moles entering an isomerizer is equal to the number of moles leaving.
A process as shown in Fig. Below has been designed to produce a p-Xylene-rich product
from an aromatic feed charge. All the compositions on the flow sheet are in mole percent.
The components are indicated as: A = ethyl benzene, B = o-xylene, C = m-Xylene, D =
p-xylene. Eight percent of A entering the distillation tower is removed in the top stream
for the tower. The ratio of the moles of fresh feed to the process as a whole to the moles
of product from the crystallizer is 1.63. Find:
a) the reflux ratio ( the ratio of moles of stream from the bottom of the
distillation tower per mole of feed to the tower).
b) The composition in mole percent of the product from the crystallizer
c) The moles leaving the isomerizer per mole of feed
Product
Product                                                               A 60%
B 6.5%
A 15%                                 A 4%                   A 7%                     C 16.5%
B 20%                                 B 29.4%                B 27%                    D 17%
C 50%                                 C 54%                  C 44.4%
D 15%                                 D 12.6%                D 21.6%

Isomerizer
Crystallizer

Distillation

4) The following data shows the exit gas analysis (water free basis) from the combustion
of a hydrocarbon oil (CxHy) in a furnace. The oil is burned with 10% excess oxygen. Is
the analysis right?
Air contains 21% oxygen and 79% nitrogen.
CO2 = 11.8%, CO = 5%, H2 = 1.5%, O2 = 1% N2 = 80.7%

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