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Show 10 20 Stack ( • ) and 15 Jacket (*) 10 Losses (o/o) 5 0 90 Efficiency 85 (o/o) 80 75 H A > First Generation • J A ) Second Generation Oj • ••• a a a * * k A A Error Band (Typical) o o °oo o 10,000 11,000 J + 12,000 19,000 Firing Rate (Btu/hr) 20,000 21,000 FIGURE 3. EFFICIENCY AND STACK AND JACKET LOSSES FOR FIRST- AND SECOND-GENERATION PROTOTYPES The differences among individual efficiency values over the full range of firing rates tested were well within the typical error band of plus or minus 3 percent. The average values of 78.2 and 78.8 percent at low and high firing rates, respectively, were also similar. (Treating the data at low and high firing rates as two groups of redundant measurements reduces the uncertainty in the average values for the groups to the neighborhood of one percent, according to the methods of Schenck (5j.) Thus, overall system efficiency was largely insensitive to firing rate for the range tested. Stack losses at high firing rate averaged 15.1 percent, somewhat higher than the 13.6 percent average at low firing rate. Rougnly 10 percent of these losses are due to the latent heat of the water vapor in the flue gas. The balance consists of sensible heat loss, which is largely a function of exit-gas temperature. The boiler and recuperator heat-transfer areas were somewhat oversized for the gas flow at the lower firing rate, accounting for the reduced sensible heat losses. |