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Show DESIGN Culletlbatch preheating will be accomplished using an advanced raining-bed preheater technology developed by Tecogen. The raining bed technology provides high heat transfer effectiveness in a compact unit. Figure 6 illustrates the preheater concept. Batch and cullet, falling freely through the heat exchanger, increase in temperature as they come in direct contact with the rising hot combustion gases. The material residence time is increased and dispersed flow is ensured by interaction with deflector baffles. Hot gases rise in the open area between the baffles ensuring good contact between the batchlcullet and the gas. The baffles deflect the batch and cullet across the flow of rising g(C , ~s creating a series of cross flow heat exchange paths which allow the heat exchanger performance to approach that of a counter flow heat exchanger. Th!? batch and cullet are collected at the base of the unit and fed directly to the furnace charger. t 'he culletlbatch preheater will be designed to operate utilizing the furnace combustion products, either from an air-fuel or oxygen-fuel combustion system, or from an auxiliary burner system. The auxiliary burner will permit independent operation of the preheater for shakedown and checkout purposes. As discussed earlier, recirculation of the preheater off-gas will be utilized to control the inlet gas temperature. Many factors must be taken into account in the design of the raining bed heat exchanger, among the most important design parameters are: cullet and batch size distribution, gas and material flow rates, gas inlet temperature, preheater height, internal configuration - baffle number, spacing, size and angle, preheater active height and batch constituent softening temperatures. In addition, the physical configuration of the preheater must be designed to be compatible with the plant layout especially with the plant batchlcullet material handling system. BENEFITS TO PRODUCTION The raining bed concept provides important advantages over other preheating methods. Among the advantages are: counter-current heat exchange; short residence time; no stored material capacity in the heat exchanger; a small footprint; and ease of retrofit onto existing furnaces . Of primary importance is that the unit does not contain an inventory of culletlbatch material within the heat exchanger. Material falls freely through the system eliminating the possibility of plugging. Other benefits to production are: increased pull rates as a result of being able to add more energy to the furnace without increasing the furnace temperature; and increased life of the furnace if the pull rate is maintained the same and the furnace temperature is decreased. DEMONSTRA TED PERFORMANCE The pilot unit installed at Tecogen in Waltham, MA was recently demonstrated to personnel from Coming and Praxair to familiarize them with the operation of the unit and to address concerns they had with the process. The unit was run for two day-long periods with inlet gas temperatures of 1300°F and batchlcullet temperatures of greater than 1000°F. The batchlcullet mixture was a soda/lime/silica mixture prepared for use in the Coming Charleroi #6 furnace in Charleroi, PA. Exhaust gases from the unit were monitored for ,rticulate content with an Isokinetic probe. Particulate losses were measured at 0.02% of the batchlcullet feed rate. Exhaust gas temperatures ranged from 280°F to 380°F depending on the ratio of gas to solids. 3 |
