JNTU II B-Tech I Semester Supplimentary Examinations,Chemical Process Calculations November 2008


JNTU II B.Tech I Semester Supplimentary Examinations, November 2008

Chemical Process Calculations

(Chemical Engineering) SET-3



1. A natural gas has the following composition, all figures being in volumetric percent:

Methane CH4 —83.5%. Ethane C2H6—-12.5% Nitrogen N2——4.0% Calculate:

(a) Composition in mole percent

(b) Composition in weight percent:

(c) Average molecular weight

(d) Density at standard conditions as pounds per cubic feet


2. A volume of moist air of 1000 cubic meters at a total pressure of 750 mmHg and a temperature of 400C contains water vapor in such proportions that its partial pressure is 25 mmHg. Without the total pressure being changed, the temperature is reduced to 100C and some of the water vapor removed by condensation. After cooling it is found that the partial pressure of water vapor is 10 mmHg. Using partial pressure method, calculate:

(a) The volume of gas after cooling and

(b) The weight of water removed


3. (a) What is steam distillation? Write about the applications of steam distillation

in process industry.

(b) Explain how the steam distillation temperature is computed for any system


4. Air at a temperature of 200C and pressure 750 mm Hg has a relative humidity of 80%

(a) Calculate the molal humidity of air.

(b) Calculate the humidity of this air if its temperature is reduced to 100C and its pressure increased to 2.38 atm, condensing out some of the water.

(c) Calculate the weight of water condensed from 28 m3 of gas.

(d) Calculate the final volume of wet air leaving. Data: Vapor pressure of H2O at

200C is 17.5 mm Hg and at 100C is 9.2 mm Hg.


5. (a) A cotton mill dries a water soaked fabric in a drier from 54% to 9% moisture. How many kg of water are removed by drying operation per 1200 kg of feed.

(b) A gas containing 2% NH3, 25.4% N2 and the rest H2 is flowing in a pipe. To measure the flow rate an ammonia rich gas containing 96% NH3, 3% H2 and 1% N2 is sent at a rate of 100 cc/min. The concentration of NH3 in the down stream is 6%. Find the flow rate of gas at inlet.


6. (a) A solution of sodium chloride in water is saturated at a temperature of 150C.

Calculate the weight of NaCl that can be dissolved by 100 kg of this solution if it is heated to 650C.

(b) Define the following terms:






7. The solid municipal waste can be burned to a gas of the following composition (on a

dry basis): CO2 = 9.2% ; CO = 1.5%; O2 = 7.3%; N2 = 82.0. What is the enthalpy difference for this gas per pound mol between the bottom and the top of the stack if the temperature at the bottom of the stack is 550 0F and the temperature at the top is 2000F. Ignore the water vapor in the gas. The heat capacity equations are given as.


N2 : Cp = 6.895 + 0.7624 X 10?3T – 0.7009 X 10 ?7 T2

O2 : Cp = 7.104 + 0.7851 X 10 ?3T – 0.5528 X 10 ?7 T2

CO2 : Cp = 8.448 + 5.757 X 10 ?3T + 21.59 X 10 ?7 T2 + 3.059X10 ?10T3

CO : Cp = 6.865 + 0.8024 X 10 ?3T + 0.7367 X 10 ?7 T2


8. Calculate the theoretical flame temperature of the gas containing 30% CO and

70% N2 when burnt with 200% excess air, both air and gas being at 25 0C. Heat

of formation in cal/gm mole at 25 0C of CO2 = -94052 ; CO = -26912. Average specific heat in cal/gm mol 0K; CO2 = 12.10; O2 = 7.9; N2 = 7.55.



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