Page 119 - Chemical engineering design

Composition of combustion gases
CO2 7.29 FUNDAMENTALS OF ENERGY BALANCES 99
H2O 4.00
O2 1.97
N2 41.98
ENERGY BALANCE
Take datum temp, To be 298 K
In
mols A B C D
Air O2 11.15 28.06 3.67E-06 1.743E-05 1.06E-08
N2 41.95 31.099 0.01354 2.675E-05 1.17E-08
mols ð Cp O2 312.869 4.1E-05 0.0001944 1.19E-07
N2 1304.455 0.567939 0.0011221 4.89E-07
SUM 1617.324 0.567979 0.0013165 6.08E-07
total
Energy kJ Tin 465789.30 23555.25 10482.593 1045.259 451671.39
To 481962.54 25219.43 11612.883 1198.17 467157.83
Diff 15486.44
Fuel sensible heat mass ð Cp ð Tin To D 4000
combustion mas ð cv D 3954000
total 3958000
Total energy in sensible C combustion: 3942513.6 kJ
Out mols A B C D
CO2 7.29 19.763 0.0733 5.52E-05 1.713E-08
H2O 4.00 32.19 0.0019207 1.054E-05 3.59E-09
O2 1.97 28.06 3.67E-06 1.743E-05 1.06E-08
N2 41.98 31.099 0.01354 2.675E-05 1.17E-08
mols ð Cp CO2 144.07227 0.534357 0.000402 1.248E-07
H2O 128.76 0.0076828 4.215E-05 1.44E-08
O2 55.2782 7.24E-06 3.434E-05 2.09E-08
N2 1305.536 0.568409 0.001123 4.9E-07
SUM 1633.6465 0.026377 0.0008 4.0E-7
Energy Tout 2.45EC06 29673.72 896937.56 506303.8 total 2811429.8
To 486826.65 1171.175 7032.9451 788.6988 491899.72
Diff 2319530.1
latent heat mass ð Lv D 35000
Total out D sensible C latent D 2354530.1
Cooling required D Heat in heat out D 1587983.5 kJ/100 kg fuel

3.15. UNSTEADY STATE ENERGY BALANCES
All the examples of energy balances considered previously have been for steady-state
processes; where the rate of energy generation or consumption did not vary with time and
the accumulation term in the general energy balance equation was taken as zero.
If a batch process is being considered, or if the rate of energy generation or removal
varies with time, it will be necessary to set up a differential energy balance, similar to the
differential material balance considered in Chapter 2. For batch processes the total energy
requirements can usually be estimated by taking as the time basis for the calculation 1
batch; but the maximum rate of heat generation will also have to be estimated to size any
heat-transfer equipment needed.