Process ovens with gas/oil burners are normally under positive pressure. In order to keep the smoke, fumes, products of combustion and volatile organic compounds from bleeding into the surrounding area, an exhaust fan is used. This fan can be quite small and is sized to match the amount of fresh air being supplied by the combustion blower. Electric element heaters use a small make-up air port and only exhaust enough air to maintain neutral pressure in the oven. In continuous oven designs, the exhaust fan is located at the extreme cold end of the oven in order to draw cool air into the oven to temper the exhaust air. It is common practice in oven design to size the oven exhaust fan at 10% of the oven recirculation volume. This can be further refined by splitting the exhaust volume in half and using two smaller fans in vestibules at the entrance and exit to a continuous oven. This practice is thought to reduce heat loss from the main oven zone.
Bearings and motors isolated from the process. Shaft seals with ceramic felt elements.
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