Page 235 - Mechanical Engineers' Handbook (Volume 4)

224 Furnaces

At present market prices, the power needed to concentrate pure oxygen for enrichment
to 35% will cost more than the fuel saved, even with metallurgical oxygen from an in-plant
source. As plants are developed for economical concentration of oxygen to around 90%, the
cost balance may become favorable for very-high-temperature furnaces.
In addition to fuel savings by improvement of available heat ratios, there will be addi-
tional savings in recuperative furnaces by increasing preheated air temperature at the same
net heat demand, depending on the ratio of heat transfer by convection to that by gas radiation
in the furnace and recuperator.

7 THERMAL PROPERTIES OF MATERIALS
The heat content of some materials heated in furnaces or used in furnace construction is
shown in the chart in Fig. 6, in units of Btu/lb. Vertical lines in curves represent latent
heats of melting or other phase transformations. The latent heat of evaporation for water in
flue gas has been omitted from the chart. The specific heat of liquid water is, of course,
about 1.
Thermal conductivities in English units are given in reference publications as: (Btu/
(ft hr))/( F/in.) or as (Btu/(ft hr))/( F/ft). To keep dimensions consistent, the latter term,
2
2
1
abbreviated to k Btu/ft hr F will be used here. Values will be ⁄12th of those in terms of
F/in.

Figure 6 Heat content of materials at temperature. 1