Problem 3 Calcination of 
In the electrolysis, anhydrous alumina is required. For this purpose  is calcined at 1700 K in rotary kiln. A kiln receives a damp filter cake of analyzing 55% and 45% total  (free and combined) and produce, pure Al2O3 as solid product. The fuel consumption is estimated to be 0.2Kg of fuel oil of composition  and  per Kg of alumina. Air for combustion is 20% excess than theoretical required. Assume complete combustion and heat losses 10% of heat input. Find
a) The volume of gases (At 1 atm, 273 K)leaving the kiln per 1000Kg of Al2O3 produced.
b) Wet and dry composition of flue gases.
c) Perform the heat balance and comment on the results. Assume reactants enter at 298K and products namely Al2O3 at 1000K and flue gases at 800K.
Solution: Basis of calculation 1000Kg calcine Al2O3
Calcination reaction:
Combustion reactions
Material balance gives volume of flue gases 
Flue gas analysis: |
on Wet basis (%) |
On dry basis (%) |
CO2 |
7.8 |
11.9 |
O2 |
2.5 |
3.7 |
N2 |
55.4 |
84.4 |
H2O |
34.3 |
- |
|
100% |
100% |
|
Heat balance gives the following result:
| |
Heat input (kcal) |
|
Heat output (kcal) |
| Combustion of fuel |
+2414120* |
Flue gases |
1362135 |
| Heat of decomposition |
– 2381370 |
Sensible heat in Al2O3 |
183431 |
| Heat available: |
2175983 |
Heat losses |
217598 |
| |
|
|
Total 1763164 kcal |
|
- + indicated heat input due to exothermic and - indicates heat absorption.
Heat balance indicates that there is 412819 kcal heat is surplus. This surplus heat may be utilized. If not then amount of fuel may be reduced as illustrated in problem 4
|
