Page 187 - Chemical engineering design

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Note: in practice superheated steam would probably be generated, for use in a turbine
driving the air compressor. CHEMICAL ENGINEERING
Cooler-condenser
The sources of heat to be considered in the balance on this unit are:
Ž
1. Sensible heat: cooling the gases from the inlet temperature of 234 C to the required
Ž
outlet temperature (the absorber inlet temperature) 40 C.
2. Latent heat of the water condensed.
3. Exothermic oxidation of NO to NO 2 .
4. Exothermic formation of nitric acid.
5. Heat of dilution of the nitric acid formed, to 40 per cent w/w.
6. Sensible heat of the outlet gas and acid streams.
So that the magnitude of each source can be compared, each will be calculated separately.
Ž
Take the datum temperature as 25 C.
1. Gas sensible heat
The program ENERGY 1 was used to calculate the sensible heat in the inlet and outlet
gas streams. The composition of the inlet stream and the heat capacity data will be
the same as that for the WHB outlet given above. Outlet stream flows from flow-sheet,
converted to kmol/h:
Condenser outlet (6)

kmol/h
8.6
O 2
N 2 309.6
NO 6.75
NO 2 21.03
H 2 O 1.63
Temp. 313 K

Sensible heat inlet stream (5) D 2.81 GJ/h,
outlet stream (6) D 0.15 GJ/h.

2. Condensation of water
Water condensed D inlet H 2 O outlet H 2 O D 1161 29 D 1131.6 kg/h
Ž
Latent heat of water at the inlet temperature, 230 C D 1812 kJ/kg
The steam is considered to condense at the inlet temperature and the condensate then
cooled to the datum temperature.
6
Heat from condensation D 1131.6 ð 1812 D 2.05 ð 10 kJ/h
Sensible heat to cool condensate D 1131.6 ð 4.18 230 25
6
D 0.97 ð 10 kJ/h
6
Total, condensation and cooling D 2.05 C 0.97 10 kJ/h
D 3.02 GJ/h