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Show (AR = 24:1) nozzles. In recent work by Reddy, et.al.3 (1997) circular shaped nozzles were modified by attaching small triangular tabs at the exit plane to enhance the mixing and entrainment of the jet. In all efforts, the improvement in mass entrainment was significant when compared to circular nozzles. The subject presented herein deals with improving heat uniformity. Technologies are addressed which provide simple, affordable solutions to quality problems that are associated with the firing of high velocity burners. Non-circular shaped (slotted) burner nozzles are shown to improve mixing and entrainment in lab and field tests. 2.0 Background There are many varieties of ceramic and structural clay products that are direct fired in kilns. Types include dinner ware, sanitary ware, electronic ceramics and porcelains, refractories, ferrites, pottery, brick, tile, abrasives, and many other specialty products. Chemical reactions that occur during the firing process dictate, in part, the quality of the finished product. There are equally important chemical reactions that occur during the cooling of the product. Dinner ware is arguably the most critical in terms of quality, given the customer usage. There are two primary means of kiln firing: periodic and continuous. Periodic usually involves smaller, special type loads. Products that are the most sensitive to temperature uniformity normally are fired in periodic kilns. Continuous kiln firing is typical of larger production requirements. Figure 1 depicts the basic operation of a continuous, or tunnel kiln. Product is formed, stacked onto cars and travels through a dryer prior to entering the tunnel kiln. Burners are located at the center and toward the front (charge) end of the kiln. Exhaust from the burners travels opposite the movement of the product in a counter flow manner. Combustion products and any gaseous byproducts from the ware are transferred to a flue by a fan at the front of the kiln. Air used to cool the product is normally removed from the kiln and ducted to the dryer. A temperature versus time schedule is used for firing a product. It is unique to the product chemistry and kiln structure. Graphs are normally created by the experience and know how of the plant personnel. The kiln firing sections (i.e. preheat and furnace zones) are divided into a number of individual zones of control. Each zone will control a set of burners by modulating the fuel and/or air flow. The firing of each zone is accomplished by controllers that compare a thermocouple reading in the zone with a set point temperature. Thermocouples typically protrude through the crown. The set point temperature is selected which best represents the desired product temperature. Product temperature is periodically measured to adjust either the set points or the flow through individual burners. The temperature distribution of the product can vary significantly within a zone. For example, in firing brick it is not uncommon to measure a difference of 400°F between product located on the outside of stacking (package) and that which is at the bottom and center of the package. Large temperature differentials limit the speed, or push rate, of the product. Product temperature variance is the primary constraint during the phases of the firing that involve chemical reactions. It is generally known that the time to properly fire, and cool, one brick is approximately 4 TO ORYtR Figure 1 Continuous Tunnel Kiln |