Page 234 - Mechanical Engineers' Handbook (Volume 4)

6 Oxygen Enrichment of Combustion Air 223

Figure 5 Available heat ratios for combustion of methane with 110% air containing 35% O 2 . 1

For combustion with other than 110% of net air demand, the corrected available heat
can be calculated as follows. For methane with preheated air at 1000 F and flue gas out at
2000 F and 150% net air supply:
Available heat from Fig. 1 in Chapter 20 0.59
Add excess air 0.18 (1.5 1.1) 0.072
0.41 (1.5 1.1) 0.164
Net total at 150% 0.498
Available heats for fuel gas mixtures can be calculated by adding the fractions for either
fuel and dividing by the combined volume. For example, a mixture of one-quarter coke oven
gas and three-quarters blast furnace gas is burned with 110% combustion air preheated to
1000 F, and with flue gas out at 2000 F. Using data from Table 3 and Figs. 3 and 4,
CO (539 0.25 134.75) (0.49 0.17) 88.93
BF (92 0.75 69.00) (0.21 0.144) 24.43
HHV 203.75 Available 113.36
Net: 113.36/203.75 0.556 combined HHV

6 OXYGEN ENRICHMENT OF COMBUSTION AIR
The available heats of furnace fuels can be improved by adding oxygen to combustion air.
Some studies have been based on a total oxygen content of 35%, which can be obtained by
adding 21.5 scf pure oxygen or 25.45 scf of 90% oxygen per 100 scf of dry air. The available
heat ratios are shown in the chart in Fig. 5.