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Our company is regarded as a famous single-tube rotary dryer supplier and industrial rotary dryer manufacturer in China.
Processing capacity: 2.5-50 t/h
Application area: industries of slag, sand, construction materials, metallurgy, chemical engineering, coal and minerals.
Applied materials: slag, clay, limestone, ardealite, dry-mixed mortar, grain slag, coal slime, etc.
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On occasion, the bad quality achieved in the output products can be related to perturbations in the drying processes, such as fluctuations in the initial moisture and thickness of product or accumulation of noncondensable gases in the drum with local bad heat transfer. Consequently, the choice of the drum dryer is important. The most common types are the single-drum cylinder, the double-drum dryer, and the twin-drum dryer. A single-drum dryer consists of hollow metal cylinders mounted on a horizontal axis and mechanically rotated with variable speed control. The drum is heated by steam, hot water, or other heating medium condensing on its inside surface, the drying effect being obtained by the transfer of heat from the inside of the drum through its metallic wall to a film of material spread over its external surface . Important aspects considered when using single-drum dryers are uniform thickness of the film applied to the drum surface, the speed of rotation, and heating temperature . All of these factors affect the drying rate of the dryer, and, consequently, several types of drum dryers have been developed
A double-drum dryer consists of two cylinders (drums) of equal diameter rotating very close together in opposite directions. The material to be dried is fed into the wedge-shaped space between the drums using a distribution pipe. Heat is transferred from the hot drum surfaces to the wet material. The rotation of the cylinders causes the material in the pool to pass through the narrow space between them, dividing the material into two films, which after drying are removed in the form of thin sheets by scraper blades spanning the whole width of the drums. The most significant factors in the efficiency of a double-drum dryer are the steam pressure, drum rotation speed, level of pool between the drums, gap between drums, and conditions of the feed material, including concentration, physical characteristics, and temperature at which the material reaches the drum surface . Furthermore, these double-drum dryers can handle a wider range of products, and usually offer better economy, more efficiency, higher production, and fewer operating labor requirements than other equipments
Finally, a twin-drum dryer also has two drums, but they rotate away from each other at the top. Single- and double-drum dryers are largely used for drying fruits and vegetables, while twin-drum dryers are particularly adapted for drying materials, such as solutions of inorganic salts (which are crystal bearing or crystal forming), and for drying materials yielding dusty products
Drum drying: in drum drying, the heated surface is the envelope of a rotating horizontal metal cylinder. The cylinder is heated by steam condensing inside, at a pressure in the range of 200 to 500 kPa bringing the temperature of the cylinder wall to 120–155°C. The wet material is applied on the drum surface as a relatively thin layer by a variety of different methods to be described later. The dried product is removed from the drum with the help of a blade (Figure 22.13). In vacuum drum drying, applied to materials highly sensitive to heat, the drum and its accessories are enclosed in a vacuum chamber. Drum drying is extensively used in the production of instant mashed potatoes, pre-cooked cereals, soup mixtures and low-grade milk powder
Belt drying: in this application, the heated surface is a metal belt conveyor heated by contact or radiation by hot elements installed on both sides. In one case, known as ‘foam-mat drying’, the belt is used for drying concentrated juices. Because of the high viscosity of the feed material, mass transfer is important right from the start of the process. In order to improve mass transfer, the concentrates are first foamed and placed on the belt as a porous mat. Some of the tomato powders available in commerce are made by foam-mat drying of tomato paste. Belt drying can also be carried-out under vacuum (Figure 22.14)
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