Furnaces, industrial continuous furnace

Firing of Enamels. Firing can be carried out in intermittent box-type furnaces or continuous furnaces. The dryer and the furnace form one continuous unit or function as separate units in the continuous firing process. Most industrial furnaces are fiber-lined (low thermal mass), which lowers cost and downtime between firing schedules. 

Figure 9.5 shows an example of a large industrial continuous furnace. The classic use is for firing bricks, pottery, tiles, and whitewares. Similar furnaces are used in the production of advanced ceramics such as multilayer ceramic chip capacitors. 

The MPFs and the LICs are similar to equipment utilized in industry. The furnaces utilize commercially available components, such as burners, refractory, and thermocouples. With good maintenance, similar furnaces in industry can continue to be operated for three decades or longer. 

FIGURE 9.5 A large continuous furnace used in industry to produce traditional ceramic products and advanced ceramics such as multilayer chip capacitors. 

The previous improvements will make a continuous furnace flexible and profitable. The savings can be even more if done properly from the start. With industrial furnaces, it is usually true that Only the low bidder wins in a low-cost deal. (See chap. 8 for sample heating curves illustrating these points.)... 

Continuous liquid flow furnaces include boiler furnaces, fluid heaters (such as Dow-therm heaters), evaporators, cookers, and many liquid heaters used in the chemical process industries. (See figs. 1.12 and 4.25.) The tubing through which the liquid fluids flow is often built as an integral part of the furnace, for which many textbooks are readily available therefore, they will not be discussed at length here. 

Fig. 6.19. Load temperature versus time (or furnace length) in a continuous furnace before use of data acquisition to modify the design, control, and operation. From Ruark, Ralph, Making the Connection, Ceramic Industry, /o. 150, No. 1, Jan. 2000, p. 14. Reproduced with permission.

Robert A. Shannon has more than 50 years experience with engineering work. He has been North American Mfg. Co. s authority on steel reheat furnaces, soaking pits, and forging furnaces. He continues private consulting relative to his extensive experience with steel reheat, pelletizing, forging, heat treating, catenary furnaces, and industrial boilers. 

Although urine remained the only source of the element for nearly 100 years after its discovery, it had been replaced by bones by the end of the eighteenth century. Supplies of the latter soon proved to be inadequate, but fortunately substantial phosphate mineral deposits were quickly found. This enabled serious commercial production of phosphorus compounds from these ores to commence in Europe about 1850, when wet process phosphoric acid became available. In 1888, a major development took place when Readman invented the electric furnace method for the continuous production of the element directly from phosphate ores. In 1890, the first industrial electric furnace came into use at Oldbury in England, and this was followed by similar production at Niagara Falls, USA. 

The fertilizer industry continues to improve its products to give higher and higher yields of nutrient to plants. Triple Super Phosphate fertilizer is made by first treating phosphate ore with sulfuric acid to make a crude form of phosphoric acid that is often referred to as green acid, because it is colored green and not because it has not been cured or ripened. The green acid is also called wet acid, to differentiate it from phosphoric acid made from elemental phosphorus. Phosphoric acid produced from elemental phosphorus is the purest of acids and it is called furnace acid. 

High process temperatures generally not achievable by other means are possible when induction heating of a graphite susceptor is combined with the use of low conductivity high temperature insulation such as flake carbon interposed between the coil and the susceptor. Temperatures of 3000°C are routine for both batch or continuous production. Processes include purification, graphitization, chemical vapor deposition, or carbon vapor deposition to produce components for the aircraft and defense industry. Figure 7 illustrates a furnace suitable for the production of aerospace brake components in a batch operation. 

These furnaces may operate batchwise or continuous. In the batch, intermittent, or periodic types, the content is heated at the desired temperature for the stipulated time and then removed. In the continuous type, the charge moves at a predeterrnined rate through one or more heating 2ones to emerge in most cases at the end opposite the point of entry. Figures 9 and 10 are representative examples of typical, industrial refractory-wall furnaces. 

Industrial furnaces may be operated in batch or continuous mode. 

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