Tunnel dryer

Pulse combustion dryer Tunnel dryer Band dryer Impingement dryer Rotary dryer Huid bed dryer Hash dryer Spray dryer Drum dryer (pastes)... 

Tunnel dryers are shown in Fig. 3.15a. Wet material on trays or a conveyor belt is passed through a tunnel, and drying takes place by hot air. The airflow can be countercurrent, cocurrent, or a mixture of both. This method is usually used when the product is not free flowing. 

Reaction times can be as short as 10 minutes in a continuous flow reactor (1). In a typical batch cycle, the slurry is heated to the reaction temperature and held for up to 24 hours, although hold times can be less than an hour for many processes. After reaction is complete, the material is cooled, either by batch cooling or by pumping the product slurry through a double-pipe heat exchanger. Once the temperature is reduced below approximately 100°C, the slurry can be released through a pressure letdown system to ambient pressure. The product is then recovered by filtration (qv). A series of wash steps may be required to remove any salts that are formed as by-products. The clean filter cake is then dried in a tray or tunnel dryer or reslurried with water and spray dried. 

In paste drying the leather is spread on glass or porcelain plates and held in place with a low strength water-soluble paste. The plates are on a conveyor and the drying is done in a drying tunnel. The dryer usually has several temperature- and humidity-controUed zones to control the rate of drying and to prevent overdrying. 

Air Drying Equipment. Tunnel kiln dryers (70) are long furnaces comprised of several zones of different temperature, humidity, and air flow through which the ware travels on a moving car or belt. These kilns afford continuous processing. Periodic kiln cross-circulation dryers (70) are box furnaces in which ware is stacked on permanent racks or on a car that can be shuttled in and out of the furnace. Fans or jets are used to circulate heat uniformly through the ware. The process is not continuous, but production rates can be enhanced by shuttling multiple cars. 

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. 

Drying times range from a few seconds in spray dryers to 1 hr or less in rotary dryers and up to several hours or even several days in tunnel shelf or belt dryers. 

Unless employed by one of the specialist equipment manufacturers, the chemical engineer is not normally involved in the detailed design of proprietary equipment. His job will be to select and specify the equipment needed for a particular duty consulting with the vendors to ensure that the equipment supplied is suitable. He may be involved with the vendor s designers in modifying standard equipment for particular applications for example, a standard tunnel dryer designed to handle particulate solids may be adapted to dry synthetic fibres. 

Fig. 2.9. Basic types of freeze drying chambers. A, bell jar or vertical cylinder b, rectangular or cylindrical chamber with one (or 2) door(s) c, tunnel dryer, in which the trays are transported in and out by a system (shown as a carrier on a monorail).

Skeins of a synthetic fibre are dried from 46 per cent to 8.5 per cent moisture on a wet basis in a 10 m long tunnel dryer by a countercurrent flow of hot air. The air mass... 

The drying unit consisted of 3 sections of tunnel dryers that were Independently controlled for temperature. Drying temperatures were maintained mostly at 70°C, 50°C, and 60°C in the 3 sections, respectively. 

AREA Loading freeze dryer Room No. (Class WO) Reference sampling point Loading freeze dryer Room No. Class (100/1000) Reference sampling point Solution Room Room No. (Class 100) Reference sampling point Sterilization tunnel Room No. (Class 100) Reference sampling point ... 

Drying with Changing Humidity of Air in a Tunnel Dryer A granular material deposited on trays or a belt is moved through a tunnel dryer countercurrently to air that is maintained at 170°F with steam-heated tubes. The stock enters at 14001bdry/hr with W = 1.16 lb/lb and leaves with O.llb/lb. The air enters at 5% relative humidity (Hg = 0.0125 lb/lb) and leaves at 60% relative humidity at 170°F Hg = 0.203 lb/lb). The air rate found by moisture balance is 7790 lb dry/hr ... 

The length of tunnel needed depends on the space needed to ensure proper circulation of air through the granular bed. If the bed moves through the dryer at 10 ft/hr, the length of the dryer must be at least 42 ft. 

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