THAPAR UNIVERSITY Chemical Reaction Engineering-2,UCH601 MAY 2015 PAPER Notes | EduRev

Created by: Ankita Sarai

: THAPAR UNIVERSITY Chemical Reaction Engineering-2,UCH601 MAY 2015 PAPER Notes | EduRev

 Page 1


Name: 	 Thapar University, Patiala 	 Roll No.: 	 
Department of Chemical Engineering 
B.E. ChE (VI Semester) MEG Sfrc 	 UCH601: Chemical Reaction Engineering — II 
May 2015 (28/05/2015) 	 Instructor: Dr. Vijaya Kumar Bulasara 
Duration: 3 hours (2:00-5:00 PM) 	 Max. Marks: 45 
Instructions: 
1. Write your name and roll number at the top of the question paper. 
2. Answer all questions in the given sequence only. 
3. Any missing data may reasonably be assumed. 
4. No queries are entertained during the examination. 
1) Calculate the time needed to burn to completion the particles of graphite (R = 5 mm, pB = 2.2 
g/cm3, ks  = 20 cm/s) in an 8% oxygen stream. For the high gas velocity used, assume that film 
diffusion does not offer any resistance to transfer and reaction. Reaction temperature is 900°C 
and the total pressure is 1 atm (graphite is of pure carbon with no inerts present). 	 (4) 
2) Two small samples of solids are introduced into a constant environment oven and kept there 
for one hour. Under these conditions the 4 mm particles are 58% converted, the 2 mm 
particles are 87.5% converted. Particles remained as hard solids during reaction. Find the rate-
controlling mechanism for the conversion of solids. Also, find the time needed for complete 
conversion of 1 mm particles in this oven. 	 (4) 
3) A solid feed consisting 30% of 50 gm particles, 40% of 100 gm particles, and 30% of 200 p.m 
particles is to be reacted with a fluidizing gas in a steady flow fluidized bed reactor. The times 
needed for complete conversion of these particles are 5, 10, and 20 min, respectively. The 
elutriation velocity constant is estimated to be x = 500/R2  min-1, where R is the particle radius 
in microns. Find the conversion of solids in the reactor for a feed rate of 1 kg solids/min, if the 
bed holdup is 10 kg solids. The solids are hard and unchanged in size and weight during the 
reaction. The change in gas-phase composition across the bed is negligible. 	 (8) 
4) Particles of uniform size are 60% converted on the average when flowing through a single 
fluidized bed. Particles are unchanging in size with chemical reaction controlling. What would 
be the conversion, if the output from this reactor is introduced into a second rector of same 
size and same gas environment? 	 (4) 
5) In a non-catalytic gas—solid reaction, z cc 1213  and the particles remained as hard solids during 
the reaction. For a mixture of two different sized particles R and 2R, determine the 
contribution of ash layer resistance for the particles of size (a) R and (b) 2R. 	 (5) 
6) A fluid—particle reaction 'A + V2B 	 products' follows unreacted-core model with the 
chemical reaction step rate controlling and the time needed for complete conversion (2) of the 
particles in a batch reactor is 1 h. Find the fractional conversion of solids (XB), if the RTD of 
solids in the contactor is approximated by the following curve. 	 (5) 
7 
0 0.5 
	? t, hr 
15 
Page 1 of 2 
Page 2


Name: 	 Thapar University, Patiala 	 Roll No.: 	 
Department of Chemical Engineering 
B.E. ChE (VI Semester) MEG Sfrc 	 UCH601: Chemical Reaction Engineering — II 
May 2015 (28/05/2015) 	 Instructor: Dr. Vijaya Kumar Bulasara 
Duration: 3 hours (2:00-5:00 PM) 	 Max. Marks: 45 
Instructions: 
1. Write your name and roll number at the top of the question paper. 
2. Answer all questions in the given sequence only. 
3. Any missing data may reasonably be assumed. 
4. No queries are entertained during the examination. 
1) Calculate the time needed to burn to completion the particles of graphite (R = 5 mm, pB = 2.2 
g/cm3, ks  = 20 cm/s) in an 8% oxygen stream. For the high gas velocity used, assume that film 
diffusion does not offer any resistance to transfer and reaction. Reaction temperature is 900°C 
and the total pressure is 1 atm (graphite is of pure carbon with no inerts present). 	 (4) 
2) Two small samples of solids are introduced into a constant environment oven and kept there 
for one hour. Under these conditions the 4 mm particles are 58% converted, the 2 mm 
particles are 87.5% converted. Particles remained as hard solids during reaction. Find the rate-
controlling mechanism for the conversion of solids. Also, find the time needed for complete 
conversion of 1 mm particles in this oven. 	 (4) 
3) A solid feed consisting 30% of 50 gm particles, 40% of 100 gm particles, and 30% of 200 p.m 
particles is to be reacted with a fluidizing gas in a steady flow fluidized bed reactor. The times 
needed for complete conversion of these particles are 5, 10, and 20 min, respectively. The 
elutriation velocity constant is estimated to be x = 500/R2  min-1, where R is the particle radius 
in microns. Find the conversion of solids in the reactor for a feed rate of 1 kg solids/min, if the 
bed holdup is 10 kg solids. The solids are hard and unchanged in size and weight during the 
reaction. The change in gas-phase composition across the bed is negligible. 	 (8) 
4) Particles of uniform size are 60% converted on the average when flowing through a single 
fluidized bed. Particles are unchanging in size with chemical reaction controlling. What would 
be the conversion, if the output from this reactor is introduced into a second rector of same 
size and same gas environment? 	 (4) 
5) In a non-catalytic gas—solid reaction, z cc 1213  and the particles remained as hard solids during 
the reaction. For a mixture of two different sized particles R and 2R, determine the 
contribution of ash layer resistance for the particles of size (a) R and (b) 2R. 	 (5) 
6) A fluid—particle reaction 'A + V2B 	 products' follows unreacted-core model with the 
chemical reaction step rate controlling and the time needed for complete conversion (2) of the 
particles in a batch reactor is 1 h. Find the fractional conversion of solids (XB), if the RTD of 
solids in the contactor is approximated by the following curve. 	 (5) 
7 
0 0.5 
	? t, hr 
15 
Page 1 of 2 
7) 
A solid catalyzed reaction A + B 
	 R + S' is to be conducted in a fluidized bed reactor. 
The feed rate of 'A' is 50 mol/min and the reactor is operated at 40 atm and 640°C. The feed 
consists of 30% 'A', 45% '13' and 25% inerts. Find the weight of catalyst necessary to achieve 
65% conversion of the limiting reactant. Take —r 
	 0.87 PAPB
mol/kg.rnin and 
1+1.39 P R  A-  1.038 P A  
ignore pressure drop in the reactor. 
	 (5) 
8) 
The concentration of an undesirable impurity 'A' in air is to be reduced from 0.7% to 0.01% 
using a liquid containing reactant 'B' (C
B  = 50 mol/m3
). Find the height of the tower required 
for counter current operation at 1 atm pressure (r). Also, determine the concentration of the 
exit stream of liquid and draw the concentration profiles at different heights of the tower 
showing the reaction plane. The reaction A(g)+B(1) -k Products(l) is instantaneous. Data: 
kAga = 32000 mol/h.m3.atm; 
kma = kBla = 0.1/h; HA = 125x10'6  atm.m3/mol; G = 1x105  
mol/h.m2; L = 7x105  mol/h.m2; CT = 56000 mol/m3. 	 (10) 
Note: 
For fluid—particle reactions conducted in a CSTR, the following correlations may be used. 
+ 1 (,)3 
1 r 
2!W 3!W 4!W 
a= 
(1_ 19 (1
2 
4.  41 (1 3  
5 t 	 420 t • 	 4620 t 
? 1-1 B  = —
1
r_ 
r
)— I  (1 2 + I  (1 3 — 
4 t 	 20 t) 120 t ) 
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