Continuous tunnels

Conventional Sintering Equipment. Like drying furnaces, sintering furnaces (29,76,85) can be periodic or continuous in nature. Periodic kilns offer greater flexibiHty continuous tunnel kilns are more economical. Advanced ceramics are typically siatered in high purity, controUed atmosphere furnaces by electric resistance heating. Ceramic furnaces used to fire traditional ceramic ware are generally heated with inexpensive natural gas, oil, wood, or coal. 

After dewatering the cmmb it is fed to the drying process which is usually carried out in a continuous tunnel dryer. The cmmb is spread on a perforated stainless steel bed through which hot air is passed to evaporate the remaining water. Typically, in the first portion of the dryer, air at 110—140°C is used, with lower temperatures being used as the product approaches dryness. A typical target for final moisture content is 0.5% or less. At the exit of the dryer the product is cooled and conveyed to a baler which shapes it into bales for packaging and shipment. 

Performance and Cost Data for Continuous Tunnel Dryers. 12-48... 

Design Methods for Continuous Tunnel Dryers In actual practice, design of a continuous through-circulation diyer is best based upon data taken in pilot-plant tests. Loading and distribution of solids on the screen are rarely as nearly uniform in commercial installations as in test diyers 50 to 100 percent may be added to the test diying time for commercial design. 

After a final rinse with clean water in tumbler washers, the cork moisture levels arc adjusted to 5.5 to 8% in continuous tunnel dryers to avoid growth of microorganisms on the washed corks. An ideal moisture level achieves a water activity unsuitable for mold growth, yet high enough to maintain the flexibility of the cork necessary for bottling. 

Wet leather containing 61 % water enters a continuous tunnel dryer and leaves at a rate of 485 Ibm/h containing 6.0% water. Dry air enters the dryer at 140 F and 1 atm, and the outlet air is at 130 F and 1 atm with a relative humidity of 50%. Calculate the rate at which wet leather enters the dryer and the volumetric flow rate of the inlet air (ft /h). 

In commercial practice, ceramic ware is dried in chamber dryers or in continuous tunnel dryers through which the ware is conveyed on cars. Efficient drying requires careful control of air temperature and humidity. The heat is usually transmitted to the ware surface by air convection or radiation from IR sources. Uniform drying is attained by suitable arrangement of the heat sources and by air circulation. 

Continuous tunnels are batch truck or tray compartments, operated in series. The solids to be processed are placed in trays or on trucks which move progressively through the tunnel in contact with hot gases. Operation is semicontinuous when the tunnel is filled, one truck is removed from the discharge end as each new truck is fed into the inlet end. In some cases, the trucks move on tracks or mono-rails, and they are usually conveyed mechanically, employing chain drives connecting to the bottom of each truck. 

Applications of tunnel equipment are essentially the same as those for batch tray and compartment units previously described, namely, practically all forms of particulate solids and large solid objects. Continuous tunnel or conveyor ovens are employed also for drying refractory shapes and for drying and baking enameled pieces. In many of these latter, the parts are suspended from overhead chain conveyors. 

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