process principles

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Cork Institute of Technology

Bachelor of Engineering (Honours) in Chemical & Process Engineering Stage 1

(NFQ Level 8)

Summer 2006

CE1.5 Process Principles

(Time: 3 Hours)

InstructionsAnswer FOUR questions.All questions carry equal marks.

Examiners: Mr. I. O SullivanProf. L. KershenbaumMr. D. O Connor

Q1 (a) In an article on measuring flow from pipes, the author calculated Q = 41 m3/s using the

formula

( )2

2

1

211

AA

1

ppgV2CAQ

=

Where

Q = volumetric flowrate, m3/s

C = dimensionless coefficient, 0.6

A1= area (2 m2)

A2`= area (5 m2)

V = specific volume, 10-3

m3/kg

P = pressure; (p1 p2) is 50 kPa

g = acceleration due to gravity (9.81 m/s2)

Was the calculation correct? Answer yes or no and briefly explain your answer.

(5 Marks)

(b) A cylindrical rod of Silica (SiO2) is heated to its melting point and a cylindrical thread

of silica 0.125 mm is drawn from the melt. By careful control of the temperature and

the tension on the string being drawn, long cylindrical threads of uniform diameter can

be obtained to make optical fibres.

(i) Calculate how much fibre (in km) can be drawn from one cylindrical rod of silica

1.0m in length and 2.5 cm in diameter. Also estimate the mass if the specific

gravity of silica is 2.25. (5 Marks)


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(ii) Before optical fibre is used, it is typically covered with a thin protective coating of

a polymer with density 1,740 kg/m3. How much polymer (kg) is needed to coat the

entire fibre? (5 Marks)

(c) Calculate all temperatures from the one given for scenario i to iv

(i) (ii) (iii) (iv)

F 140

R 500

K 298

C -40

(5 Marks)

(d) Pressure in a gas cell PGis measured with an inverted manometer as shown in figureQ1(d). The scale on the right hand side shows the distances in mm (not to scale) of the

liquid interfaces within the manometer. What is the pressure in the cell PG(mmHg) if

the pressure in tank 1 (P1) is 12.5 psia? NOTE: The temperature in the system is 300K.

Figure Q1(d)

(5 Marks)


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Q2 (a) Calculate the volume (ft3) occupied by 88 lb of CO2gas at 15 C and a pressure of

32.2 ft (abs) of water. (5 marks)

(b) 3000 m3/d of a gas mixture containing methane and n-butane at 21 C enters a

separation tower (stream F). The partial pressures at the inlet conditions are 103 kPa for

methane and 586 kPa for n-butane. In the separator 80% of the butane is removed via

stream L. The remaining butane leaves the tower at 38 C along with all of the methane

(stream V). The total pressure of exit stream V is 550 kPa. How many moles per day of

n-butane are removed from the feed gas in this process? What is the volumetric

flowrate of the gas at the exit? Assume a basis of 1 day.

(20 Marks)

Q3 (a) A sample of natural gas taken at 3500 kPa absolute and 120 C is separated by

chromatography at standard conditions. It was found by calculation that the grams of

each component in the gas were

Component (g)

Methane (CH4) 100

Ethane (C2H6) 240

Propane

(C3

H8)

150

Nitrogen (N2) 50

Total 540

What was the density of the original gas sample?

V

L


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Figure Q3(a)

Figure Q3(b)

(13 Marks)


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(b) The pressure gauge on an O2cylinder stored outside at 0 F in the winter reads 1375

psia. By weighing the cylinder (whose volume is 6.7 ft3you find that the net mass, that

is, the mass of the O2is 63.9 lb.

Using the Redlich-Kwong equation of state determine whether the pressure reading is

correct.

c

c

c

5.2

C

2

^^5.0

^

p

RT08664.0b

p

TR42748.0a

bVVT

a

bV

RTp

=

=

+

=

c

c

c

2

C

2

^

2^

p

RT

8

1b

p

TR

64

27a

bV

V

apRT

=

=

+=

(12 marks)

Q4 (a) For each of the conditions of temperature and pressure listed below for water, statewhether the water is in the solid phase, the liquid phase, the saturated state or in the

superheated state. Use the steam tables attached to this paper to assist in your

determinations.

State P (kPa) T (K) v (m3/kg)

1 2000 475 -

2 1000 500 0.2206

3 101.3 200 -

4 245.6 400 0.7308

5 1000 453.06 0.001127

6 200 393.38 0.8857

(6 marks)


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(b) A vessel that has a volume of 0.35 m3contains 2 kg of a mixture of liquid water and

water vapour at equilibrium with a pressure of 450 kPa. What is the quality of the water

vapour?

Hint: g^

f

^

vapour&liquid

^

VxV)x1(V +=

(8 marks)

(c) 1000 m3of air saturated with water vapour at 30 C and 99.0 kPa is cooled to 14 C and

compressed to 133 kPa. How many kg of water will condense out?

(11 marks)

Q5 (a) In the final stages of the industrial production of penicillin, air enters a dryer having a

dry bulb temperature of 34 C and a wet bulb temperature of 17 C. This moist airflows over the penicillin at a pressure of 1 atm and a flowrate of 4500 m

3/hr. 68.2 kg of

the penicillin/water feed is placed in the dryer at 34C with a moisture content of 80%

(of total mass) and leaves the dryer with a moisture content of 71.4%.

Calculate the outlet dry bulb temperature of the air assuming that adiabatic drying

occurs.

(15 marks)

(b) Air is being compressed from 100 kPa and 255K (where it has an enthalpy of489 kJ/kg) to 1000 kPa and 278 K (where it has an enthalpy of 509 kJ/kg).

The exit velocity of the air from the compressor is 60 m/s.

What is the power required (in kW) for the compressor if the load is 100 kg/hr?

Hint: Assume that the inlet air flowrate is negligible. (10 marks)


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Figure Q5(a)


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Q6 (a) Calculate the heat of vaporization of water at 3.5 C using the Clausius-Clayperon

equation. Compare the value calculated to an appropriate value from the steam tables.

mercury= 13590 kg/m3.

g = 9.81 m/s2

=

12

^

v

*

2

*

110

T

1

T

1

R303.2

H

p

plog

(10 marks)

(b) Determine the enthalpy change when 1 gmol of SO2gas is cooled from 538 C to 101

C at a pressure of 1 atm.

Data:Boiling point: -5 C

Melting point: -75.5 C

Latent heat of vaporization: 24940 J/gmol

Latent heat of fusion: 7401 J/gmol

Average liquid Cp: 1.28 J/gmolC

Average solid Cp: 0.958 J/gmolC

(8 marks)

(c) In a fluidised bed gasification system you are asked to find out the heat of formation of

a solid sludge of composition C5H2from the following data.

H kJ/gmol

C(s) + O2(g)CO (g) -110.4 kJ/gmolC

C(s) + O2(g)CO2(g) -394.1 kJ/gmolC

H2(g) + O2(g)H2O(g) -241.8 kJ/gmolH2

CO(g) + O2(g)CO2(g) -283.7 kJ/gmolCOH2O(g) + CO(g)H2(g) +CO2(g) -38.4 kJ/gmolH2O

C5H2(s) + 5 O2(g)5CO2(g) + H2O(l) -2110.5 kJ/gmolC5H2

HvapourizationH2O at 25C +43.911 kJ/gmolH2O

(7 marks)


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