Material and Energy Balances - Process Calculations - Chemical Engineering Previous Year Questions

1

2007 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2007

For the same process, if fresh H₂O feed to the reactor is 600 mol/hr and wash water for scrubbing is 20 % of the condensables coming out of the reactor, the water flowrate in mols/hr from the distillation column as bottoms is

A

170

B

220

C

270

D

430

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2

2007 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2007

44 kg of C₃H₈ is burnt with 1160 kg of air (Mol. Wt. = 29) to produce 88 kg of CO₂ and 14 kg of CO.
C₃H₈ + 5 O₂ = 3 CO₂ + 4 H₂O
What is the percent excess air used ?

A

55

B

60

C

65

D

68

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3

2007 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2007

What is the % carbon burnt?

A

63.3

B

73.3

C

83.3

D

93.3

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4

2008 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2008

A 35 wt% Na\(_2\)SO\(_4\) solution in water, initially at 50°C, is fed to a crystallizer at 20°C. The product stream contains hydrated crystals Na\(_2\)SO\(_4\)·10H\(_2\)O in equilibrium with a 20 wt% Na\(_2\)SO\(_4\) solution. The molecular weights of Na\(_2\)SO\(_4\) and Na\(_2\)SO\(_4\)·10H\(_2\)O are 142 and 322, respectively. The feed rate of the 35% solution required to produce 500 kg/hr of hydrated crystals is

A

403 kg/hr

B

603 kg/hr

C

803 kg/hr

D

1103 kg/hr

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5

2008 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2008

600 kg/hr of saturated steam at 1 bar (enthalpy 2675.4 kJ/kg) is mixed adiabatically with superheated steam at 450°C and 1 bar (enthalpy 3382.4 kJ/kg). The product is superheated steam at 350°C and 1 bar (enthalpy 3175.6 kJ/kg). The flow rate of the product is

A

711 kg/hr

B

1111 kg/hr

C

1451 kg/hr

D

2051 kg/hr

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6

2008 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2008

A tank of volume \( 0.25 \ m^3 \) and height 1 m has water flowing in at \( 0.05 \ m^3/min \). The outlet flow rate is governed by the relation
\[ F_{out} = 0.1 h \]
where \( h \) is the height of the water in the tank in m and \( F_{out} \) is the outlet flow rate in \( m^3/min \).
The inlet flow rate changes suddenly from its nominal value of \( 0.05 \ m^3/min \) to \( 0.15 \ m^3/min \) and remains there. The time (in minutes) at which the tank will begin to overflow is given by

A

0.28

B

1.01

C

1.73

D

\(\infty \)

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7

2009 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2009

A dehumidifier (shown below) is used to completely remove water vapor from air.
Which ONE of the following statements is TRUE ?

A

Water is the ONLY tie component

B

Air is the ONLY tie component

C

BOTH water and air are tie components

D

There are NO tie components

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8

2010 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2010

A new linear temperature scale, denoted by °S, has been developed, where the freezing point of water is 200°S and the boiling point is 400°S. On this scale, 500°S corresponds, in degrees Celsius, to

A

100°C

B

125°C

C

150°C

D

300°C

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9

2010 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2010

A saturated solution at 30°C contains 5 moles of solute (M.W.=50 kg/kmol) per kg of solvent (M.W.=20 kg/kmol). The solubility at 100°C is 10 moles of the solute per kg of the solvent. If 10 kg of the original solution is heated to 100°C, then the weight of the additional solute that can be dissolved in it, is

A

0.25 kg

B

1 kg

C

2 kg

D

3.34 kg

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10

2010 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2010

The products of combustion of methane in atmospheric air (21% O₂ and 79% N₂) have the following composition on a dry basis.

Products	Mole %
CO₂	10.00
O₂	2.37
CO	0.53
N₂	87.10

The ratio of the moles of CH₄ to the moles of O₂ in the feed stream is

A

1.05

B

0.60

C

0.50

D

0.45

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11

2011 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2011

The following combustion reactions occur when methane is burnt. \( CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O \) \( 2CH_4 + 3O_2 \rightarrow 2CO + 4H_2O \) 20 % excess air is supplied to the combustor. The conversion of methane is 80 % and the molar ratio of CO to \( CO_2 \) in the flue gas is 1:3. Assume air to have 80 mol % \( N_2 \) and rest \( O_2 \). The \( O_2 \) consumed as a PERCENTAGE of \( O_2 \) entering the combustor is

A

20

B

62.5

C

80

D

83.3

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12

2011 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2011

An aqueous sodium chloride solution (10 wt %) is fed into a single effect evaporator at a rate of 10000 kg/hr. It is concentrated to a 20 wt % sodium chloride solution. The rate of consumption of steam in the evaporator is 8000 kg/hr. The evaporator capacity (kg/hr) and economy are

A

5000, 0.625

B

10000, 0.625

C

5000, 1.6

D

10000, 1.6

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13

2011 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2011

P, Q, R and S are four types of dangerous microbes recently found in a human habitat. The area of each circle with its diameter printed in brackets represents the growth of a single microbe surviving human immunity system within 24 hours of entering the body. The danger to human beings varies proportionately with the toxicity, potency and growth attributed to a microbe shown in the figure below:
A pharmaceutical company is contemplating the development of a vaccine against the most dangerous microbe. Which microbe should the company target in its first attempt?

A

P

B

Q

C

R

D

S

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14

2011 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2011

A container originally contains 10 litres of pure spirit. From this container 1 litre of spirit is replaced with 1 litre of water. Subsequently, 1 litre of the mixture is again replaced with 1 litre of water and this process is repeated one more time. How much spirit is now left in the container?

A

7.58 litres

B

7.84 litres

C

7 litres

D

7.29 litres

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15

2013 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2013

A reverse osmosis unit treats feed water (F) containing fluoride and its output consists of a permeate stream (P) and a reject stream (R). Let C_F, C_P, and C_R denote the fluoride concentrations in the feed, permeate, and reject streams, respectively. Under steady state conditions, the volumetric flow rate of the reject is 60 % of the volumetric flow rate of the inlet stream, and C_F = 2 mg/L and C_P = 0.1 mg/L. The value of C_R in mg/L, up to one digit after the decimal point, is

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16

2014 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2014

Carbon monoxide (CO) is burnt in presence of 200% excess pure oxygen and the flame temperature achieved is 2298 K. The inlet streams are at 25 °C. The standard heat of formation (at 25 °C) of CO and CO₂ are −110 kJ mol⁻¹ and −390 kJ mol⁻¹, respectively. The heat capacities (in J mol⁻¹ K⁻¹) of the components are
\(C_{P_{O_2}} = 25 + 14 \times 10^{-3} T\)
\(C_{P_{CO_2}} = 25 + 42 \times 10^{-3} T\)
where, T is the temperature in K. The heat loss (in kJ) per mole of CO burnt is __________

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17

2016 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2016

A liquid mixture of ethanol and water is flowing as inlet stream P into a stream splitter. It is split into two streams, Q and R, as shown in the figure below.
The flow rate of P, containing 30 mass% of ethanol, is 100 kg/h. What is the least number of additional specification(s) required to determine the mass flow rates and compositions (mass%) of the two exit streams?

A

0

B

1

C

2

D

3

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18

2016 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2016

A jacketed stirred tank with a provision for heat removal is used to mix sulphuric acid and water in a steady state flow process. H₂SO₄(l) enters at a rate of 4 kg/h at 25°C and H₂O(l) enters at a rate of 6 kg/h at 10°C. The following data are available:
Specific heat capacity of water = 4.2 kJ kg^-1 K^-1.
Specific heat capacity of aqueous solution of 40 mass% H₂SO₄ = 2.8 kJ (kg solution)^-1 K^-1.
Assume the specific heat capacities to be independent of temperature.
Based on reference states of H₂SO₄(l) and H₂O(l) at 25°C, the heat of mixing for aqueous solution of 40 mass% H₂SO₄ = – 650 kJ (kg H₂SO₄)^-1.
If the mixed stream leaves at 40°C, what is the rate of heat removal (in kJ/h)?

A

1802

B

2558

C

5702

D

6458

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19

2017 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2017

An aqueous salt-solution enters a crystallizer operating at steady state at 25°C. The feed temperature is 90°C and the salt concentration in the feed is 40 weight %. The salt crystallizes as a pentahydrate. The crystals and the mother liquor leave the crystallizer. The molecular weight of the anhydrous salt is 135. The solubility of the salt at 25°C is 20 weight %.

The feed flowrate required for a production rate of 100 kg/s of the hydrated salt, rounded to the nearest integer, is __________ kg/s.

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20

2017 · Chemical Engineering · Process Calculations · Material and Energy Balances

Chemical Engineering (CH) 2017

Reaction A → B is carried out in a reactor operating at steady state and 1 mol/s of pure A at 425°C enters the reactor. The outlet stream leaves the reactor at 325°C. The heat input to the reactor is 17 kW. The heat of reaction at the reference temperature of 25°C is 30 kJ/mol. The specific heat capacities (in kJ/mol.K) of A and B are 0.1 and 0.15, respectively.

The molar flowrate of B leaving the reactor, rounded to 2 decimal places, is __________ mol/s.

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