OCR Text |
Show house (batch feeding end of the compartment) the raw materials are fed into a molten mass of glass having a temperature near 2600- 2900F. The batch materials react, melt and disappear into the liquid glass after floating about one-third to one-half of the length of the melter. As the molten glass moves on through the melting zone it is fined (trapped gasses and bubbles are removed) and the melt homogenizes. The glass is essentially free of bubbles when it reaches the end of the melting chamber. Then the glass passes through a submerged refractory tunnel (throat) into the refiner where it is cooled to approximately 2300F. In a container furnace the glass then flows through shallow refractory lined channels called forehearths to the machines. The welght of material introduced is approximately 15% greater than the weight of the glass withdrawn. The loss is due to f.usion loss. The weight loss is primarily due to carbon dioxide from the limestone and soda ash in the batch. Furnaces generally have 3 parts. The melter where raw material is melted and glass produced; the refiner where glass is reduced to a lower temperature; the forehearth were the glass is channeled to a specific machine while its temperature is accurately and precisely adjusted to forming requirements. Typical furnace designs: There are 4 basic types of furnaces with the main difference found in the melting section rather than in the refiner or forehearth. The different types of furnaces used in the glass container segment include the following: Direct fired furnaces Regenerative Side Port Regenerative End Port All Electric Furnace The most basic type of melting unit is what is commonly termed direct-fired or unit melter. This furnace has a rectangular melting zone with burners along each side with direct venting of combustion products to outside air with no preheating of the combustion air. This type of furnace, which is least efficient and of low output capability has very limited applications in the glass industry. The most common type of melter is the regenerative type in which the combustion air is pre-heated in 2 refractory packed chamber. In the most common type of regenerative furnace, known as the side port furnace there is a regenerator or heat recovery chamber at each side of the melting area.In a cycle the combustion air is being preheated in one chamber while hot combustion products are being utilized to heat 24 the packing of the other chamber. The furnace is operated for about 15-30 minute cycles in each direction. Another common type of regenerative furnace is the end port furnace. In this type furnace, the two regenerator chambers, in6tead of being placed one on each side of the furnace, are placed side by side at the batch filling end of the furnaces. The fires, instead of passing directly across the furnace, as in the side port, describe a "u" flame across the melter surface. The cycling between the two regenerators is as described in the side port furnace. The waste gases in these regenerator furnaces are generally between 800 and 1200F as they leave the regenerator systems compared to 2800F for a direct fired furnace without a regenerator system. The fourth type of furnace is an all electric melter. Since glass is a poor conductor in its molten state, it can be heated by its own resistance by passing electric current through it. An all electric furnace is essentially a basin with electrodes inserted in the sides or bottom. Current is passed from one electrode to another. The surface may be near atmospheric temperature and may be completely covered with raw batch materials. There are no combustion products. Generally such fur.naces are used for lower production volumes. ~he energy required for the various types of glass melters may be generalized as follows: Direct fired - no waste heat recovery - 9 to 12 million BTU/ton glass Regenerative - Small regenerators - little insulation - 6.5 to 10 willion BTU/ton Regenerative - Large regenerative - heavily insulated - 5 to 7.5 million BTU/ton All electric - 800 to 1100 kwh/ton In a given furnace the I!Wre glass produced the less heat is required per ton because the holdiu& heat is divided among more tons. There are some variations on the regenerative furnaces including the Sorg deep refiner, the four pass regenerator and others. In the regenerative side port and end port furnaces, ",~hich are most typical the operations are quite si1!lllar. The electric or cold top furnaces in use are for limited ranges of sizes. The limits are around 200 tons of glass per day. The gas fired furnaces range up to the 700 plus tons per day. |