(cont'd) 9.23 b. Basis : 1000 kg CaCO3 fed 10.0 kmol CaCO3 CaCO 3 (s) CaO(s) + CO 2 (g) 2CO + O 2 2CO 2
10 kmol CaCO3 25 oC 200 kmol at 900oC 0.75 N2 0.020 O2 0.090 CO 0.14 CO2
Product gas at 900oC n2 (kmol CO2 ) n3 (kmol N2 ) n4 (kmol CO)
n1 [kmol CaO(s)]
10 kmol CaCO 3 react n1 = 10.0 kmol CaO n2 = (014)(200) + . 10.0 kmol CaCO 3 react 1 kmol CO 2 4 kmol O 2 react 2 kmol CO 2 + = 46 kmol CO 2 1 kmol O 2 1 kmol O 2
n3 = (0.75)(200) = 150 kmol N 2 C balance: (10.0)(1) + (200)(0.09)(1) + (200)(0.14)(1) = 46(1) + n4 (1) n4 = 10.0 kmol CO
References : Ca(s), C(s), O 2 (g), N 2 (g) at 25 C
nin
^ H in
nout
^ H out
Substance (mol) (kJ/mol) (mol) (kJ/mol) ^ CaCO3 10.0 H1 - - CaO 10 - - -587.06 CO 2 28 46 -350.56 -350.56 ^ ^ 18 CO 10 H2 H2 ^ O 4.0 H - -
2 3
N2
o
150
^ H4
Table B.1
150
^ H4
^ ^ CaCO3 (s, 25 C) : H1 = (H fo ) CaCO3 (s)
= - 1206.9 kJ/mol
Table B.1, Table B.8
^ ^ ^ CO(g, 900o C) : H1 = (H fo )CO(g) + H CO (900o C)
o Table B.8
=
(-110.52 + 27.49) kJ/mol = -83.03 kJ/mol
^ ^ O 2 (g, 900 C) : H 2 = H O2 (900o C) = 28.89 kJ/mol ^ ^ N 2 (g, 900 C) : H 3 = H N2 (900 C) = 27.19 kJ/mol
o o Table B.8
Q = H =
F n H - n H I = 0.44 10 GH JK
i i i i out in
6
kJ
100 = 838% .
% reduction in heat requirement =
2.7 106 - 0.44 106 2.7 106
c.
The hot combustion gases raise the temperature of the limestone, so that less heat from the outside is needed to do so. Additional thermal energy is provided by the combustion of CO.
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