N2

Hcomb. air = f x fuel firing rate x h'aiI h'air at 100°F is found to be 1.2 Btu/ft3.

Hcomb.air = 13.0 x 403.8 103 x 1.2 = 6.3 x 106Btu/hr

The specific enthalpy of each of the flue-gas components at 2200°F is found from Figure 8.10 to be

Because each fuel has its own chemical composition, the stack-gas composition will be different for each fuel, as will the enthalpy flux: thus the calculation should be repeated for each fuel.

Flow path 1 represents the flow of product through the furnace.

prod. in prod prod prod. in

= 50 tons x 2000 lb/ton x 0.115 Btu/lb • (100-60)°F = 0.5 x 106 Btu/hr

Figure 8.10 Heat content vs. temperature.

prod. out prod prod prod. out

= 50 tons x 2000 lb/ton x 0.180 Btu/lb • °F (2000 - 60) °F = 34.9 x 106 Btu/hr

Flow path 2 is the cooling-water flow for the con veyor.

X 1 Btu/lb • °F X TcW,m = 600 gpm X 60 min/hr x 8.33 lb/gal x 1 Btu/lb • °F (100 - 60) °F = 12.0 x 106 Btu/hr HCW. out = gpm x 60 min/hr x 8.33 lb/gal x 1 Btu/lb • °F x tcw.out = 600 gpm x 60 min/hr x 8.33 lb/gal x 1 Btu/lb • °F (191 - 60) °F = 39.3 x 106 Btu/hr

The heat losses are then estimated from equation 8.11 as

Q = Hstack gas — Hf .1 — Hcomb. air + Hprod. out

- 12.0)106 = - 94.7 x 106 Btu/hr where Q includes not only the furnace surface losses but any unaccounted for enthalpy flux and all the inaccuracies of measurement and calculation.

Figure 8.9 shows the completed heat-balance diagrams for the reheat furnace. From that diagram we identify three waste-heat streams, as listed in Table 8.5.

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