# Anna University exam papers, B-tech. Degree examination – fifth sem – Chemical process calculations

##### CHEMICAL ENGINEERING, CHEMICAL PROCESS CALCULATIONS

Part A  (10 x 2 = 20 marks)

1. What are derived units.

2. Write the Expression for Vander Waals’ Equation of state.

3. Define the terms: Purging and Recycle.

4. What is meant by excess reactant?

5. Define: Relative Humidity and Percentage Humidity.

6. What is the use of Humidity chart?

7. What do you mean by sensible heat and latent heat?

8. What is Orsat Analysis?

9. What is meant by heat capacity?

10. Define heat of combustion.

Part B (5 x 16 = 80 marks)

11.i) Identify the limiting reactant, excess reactant, percentage excess and degree of completion for the following reactions.

a.      C + O2 ? CO2 where C and O2 are present in the mole ratio of 4:3.

b. An Ammonia synthesis gas containing N2 & H2 in the mole ratio of 1:4.

ii) A petroleum refinery burns a gas mixture containing C5H12 7%, C4H10 10%, C3H8 16%, C2H6 9%, CH4 55% and N2 3% at the rate of 200m3/hr at 4.5 bar pressure and 30°c temperature. The air rate is adjusted so that 15% excess air is used and under the conditions the ratio of moles of CO2 to CO is 20:1 in the flue gas.   Calculate a) m3/hr of air introduced at 30°c and 1 atmospheric pressure and b) Composition of flue gas on dry basis.

12.A

i) The value of ideal gas constant is 8314 J/Kg mole K. How many gram moles of Nitrogen will occupy 1000 m3 at a pressure of 112 x 103 n/m2 and a temperature of 400 K.

ii) Calculate the average molecular weight of flue gas having the following composition by volume. CO2 13.1%, O2 7.7% and N2 79.2%.

iii) Compare the pressure given by Ideal gas law and Vander Waals equation for 1 mole of CO2 occupying a volume of 381 x 105 m3 at 40°c. Given a = 0.3646m6 N/m2mole2 and b = 4.28 x 10-5m3/mole.

# OR

12.B

i) Air at a temperature of 20°c and pressure 0.987 x 105 N/m2 has a relative humidity of 80%. Calculate a) Molal humidity, b) Calculate the molal humidity if the temperature is reduced to 10°c and pressure increased to 2.38 x 105 N/m2 condensing some of water c) Calculate weight of condensed water from 28.3 m3 of original wet air in cooling and compressing to the conditions as mentioned in part (b) and d) Calculate final weight of wet air of part (c).

Given the vapour pressures at 20°c = 0.023 x 105 and 10°c = 0.0012 x 105 N/m2.

ii) A solid material with 15% by weight of water is dried to 7% by weight of water under the following conditions. Fresh air is mixed with recycled air and blown over the solid. Fresh air contains 0.01 Kg water/Kg dry air and the recycled air which is part of the air leaving the drier contains 0.1 Kg water / Kg dry air. The proposition of recycled air and fresh air are adjusted such that the mixture entering the drier contains 0.05 Kg water/ Kg dry air.

a) How many kgs of water are removed from 100 Kg of wet material fed to the drier.

b) How many kgs of dry air are in fresh feed per 100 kg of wet material.

c) How many kgs of dry air are recycled per 100 kg wet material.

13.A

i) The Orsat analysis of flue gas from an oil furnace is CO2 8%, CO 3% O2 4% and N2 85%. An analysis indicates that oil contains 78% by weight of Carbon and rest combustible Hydrogen and moisture. Air enters at 30°c and 1.013 bar. Assume air to be dry. Calculate a) % excess air used b) C – H2 ratio in fuel oil c) Volume of air used per 100 Kg of oil fired, d) Kg of moisture in flue gas kg of oil fired.

ii) What is meant by Theoretical air and % Excess air.

OR

13.Bi)  Ethylene glycol is produced from ethylene, air and water as follows.

2 C2H4 + O2 + 2 H2 O ? 2 (CH2OH)2 when 300% excess air and Stiochiometric quantity of water and ethylene are used, the process yields an aqueous solution containing 45 mole% of ethylene glycol and an off gas containing 6 mole% of CO2 which is produced by the side reactions as C2H4 + 3O2 ? 2 CO2 + 2 H2O and carries 0.03 moles of moisture per mole of dry gas. Calculate a) % of ethylene converted into process and b) % ethylene converted into ethylene glycol.

13.B

ii) A power plant burns coal having the following composition of C 65%, S 15% ash 10.5% rest moisture and combustible hydrogen. The stack gas analysis shows that 8.5% mole% of CO2 and SO2, 1.6 mole% of CO, 7.5 mole% O2 and rest N2. Ash contains 2% unburnt carbon but on sulphur. Calculate a) Fuel to air weight ratio, b) % Excess air used c) Combustion of H2 and moisture % in coal, d) Kg of flue gas per kg of coal burnt, e) Kg of ash produced per kg of coal burnt.

14.A

i) Calculate the heat required to raise the temperature of 28 kg of CO from 100°c to 1000°c. perform the calculation in the following ways. a) Integrate the expression for Cp and b) by using the mean heat capacity value. Cp for CO is given by the expression Cp = 6.35 + 1.811 x 10-3 T- 0.267×10-6 T2 where Cp is in Kcal/kg mole K and T is in K.

ii) State the Claysius Clapeyron equation. What is the use of this equation.

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14.B

i) State the Kityakowsky’s equation and Trouton’s rule.

ii) The analysis of 15000 m3 of a gas at standard conditions is as follows. SO2. 10%, O2 12%, N2 78%. How much heat must be added to raise the temperature from 30°c to 425°c. The mean molar heat capacity between 0°c and Tc is given below.

 Gas 30°c 425°c SO2 10.0 11.0 O2 6.96 7.32 N2 6.8 7.72

15.A

i) State the Hess’s law and its applications.

ii) Calculate the heat of reaction for the following reaction.

CO2 + 4H2 ? 2H2O + CH4 at 500°c with the data given below. Std. Heat of reaction at 25°c is – 39433 Kcal / Kgmole. Enthalpy values in Kcal / Kgmole are given below.

 Temp C CO2 H2 H2O CH4 25 218 172 200 210 500 5340 3499 4254 5730

# OR

15.B

i) Define a) Std. Heat of reaction, b) Heat of dilution, c) Heat of combustion, d) Heat of  ormation.

ii) Calculate the standard heat of reaction of CO + H2O ? CO2 + H2.

 Component CO H2 CO2 Hf in KJ — 110.6 — 242 — 394