| OCR Text |
Show be ope~ated at high e~cess air levels to control the preheater inlet temperature. The added air is not desIrable because It adds to the burden on the down stream particulate cleaning system. Three operating scenarios were evaluated to determine the change in furnace performance and to predict. fuel and ox~gen savings with batch/cullet preheating. The first case (Case A) assumes there IS no change In the natural gas firing rate or in the furnace heat loss as the batch is preheated and there is a direct reduction in the amount of electric boost as the batch is preheated. The second case (Case B) assumes there is no change in electric boost and there is a reduction in fuel use as the batch is preheated. Furnace structural heat loss is also reduced to reflect the reduced firing rate and correspondingly lower furnace and refractory temperatures. Furnace structural heat loss is determined by a straight line fit between full load pull and zero pull heat losses with a 10% reduction in heat loss from 100% to 0% furnace pull. In both Cases A and B, the achievable batch/cullet preheat temperature can be limited by the amount of energy in the furnace exhaust products. This is especially true in Case B where the furnace exhaust products are reduced as the batch/cullet is preheated. In the third case (Case C), additional energy is added to the furnace exhaust by a supplemental burner so that the batch can be raised to its maximum preheat temperature. The maximum gas inlet temperature to the preheater is 1300'F in all cases. This temperature constraint is based on operating data obtained during testing of a fluidized bed batch preheater previously investigated by Tecogen and funded by the Gas Research Institute. F '·ure 9 provides a schematic representation of the flow streams used in the furnace energy bal' .) and Table 2 gives the assumptions used in the heat balance analysis. Oxygen costs have been estimated based on the oxygen plants sized for the particular furnaces4 • Tables 3, 4, and 5 are typical results of the analysis for a preheat temperature of 850'F. In Table 4, Furnace #2 is only able to supply enough heat to preheat the batch to 774°F. Figures 10 through 13 summarize the predicted electric boost reduction associated with Case A, and Figures 14 through 17 summarize the predicted fuel and oxygen use reduction predicted for Cases Band C. It is important to note that even with the more efficient oxygen-fuel combustion conditions, there is ample energy in the furnace exhaust to preheat the incoming batch charge. Only for the highly electric boosted furnace, Tank 2, is supplemental fuel firing required to achieve elevated batch temperatures. Although there is a dr~p off in fuel use reduction as the preheater is supplementally fired, see Figure 15, the oxygen use reduction continues at the higher rate since oxygen-fuel combustion in the furnace is being replaced by air-fuel combustion at the preheater. Similar predictions for fuel and electric boost reductions are presented in Figure 18 for the baseline air-fuel combustion configuration for Tank 4. 3.2 Preliminary Economic Evaluation To assist Corning in performing an economic evaluation of the preheater technology, size and cost estimates were made to incorporate culletlbatch preheating into the four evaluation furnaces. The results of this preliminary design summary are presented in Table 6 .for the oxygen-fuel configurations. Table 7 gives the detailed cost estimates for the correspondIng preheaters along with an estimate of the installation costs for the units. The actual cost for the preheater installation will be very site specific and therefore these n~~bers mus~ be vi~wed entirely as preliminary estimates. Interface requirements with the eXIstIng batchlng equIpment, exhaust 5 |
