Types of Rotary Kilns

Only rotary kilns are now used for the direct process the use of static furnaces has been discontinued. The zinc content of raw materials is between 60 and 75 %. There are two types of rotary kiln ... 

The second type of rotary kiln is shorter (5 m) and has a larger diameter (ca. 3 m). Charging is continuous, but the dezincified residues are removed batchwise. 

Typically two major types of rotary kilns are used for pyrolysis processes either internally or externally heated systems. For internally heated kilns a heat exchanger based on steam-... 

Calcination can be carried out in various types of process equipment such as fixed beds, moving beds, fluid beds, tunnel kilns, moving belts and rotary kilns. Because of their versatility rotary kilns are widely used in the catalyst manufacturing Industry both for calcination of zeolite powders and for calcination of shaped carriers and catalysts. Other types of equipment (e.g. moving belts) are used less frequently. Only the use of rotary kilns will be discussed. Various types of rotary kilns are found in commercial catalyst plants ... 

The dehydrochlorinated molten polymer in the molten polymer vessel is qnantitatively fed into the pyrolysis reactor (Figure 26.11), which is of rotary kiln type. It has a hot air jacket and ceramic balls inside to prevent coking problems, as shown on the Fignre 26.12. Thermal degradation is at 400°C and 5 kPa overpressure. 

The furnace has an adjustable rotation rate of 0.5-10 rpm. The kiln is heated externally. The sealing of rotary kilns is a difficult task, especially for a pyrolyzer. The internal pressure of the kiln is higher than atmospheric pressure. A special friction-type seal is required for a pyrolyzer operating at high temperature. Solid waste with different shapes, sizes, and heating values can be fed into rotary kilns in batches or continuously. 

Limestones that are relatively soft, are subject to thermal degradation, or produce a soft lime may not be suitable for calcining in shaft kilns. They may, however, be calcined in certain types of rotary or other kilns (see section 16.4.11),... 

The most common adsorbant used is granular or powdered activated carbon. This material, which is available from almost all forms of organic carbon-containing matter, is a microcrystalline nongraphite form of carbon. The production of activated carbon can be achieved by use of rotary kilns, hearth furnaces, or furnaces of the vertical shaft or fluidised bed type, and each is suitable for the generation of different pore size and the source of carbon. The pore volume and size are influenced by both the carbon source and method of production. The adsorption properties are directly related to the pore volume, pore size distribution and the nature of the functional groups on the surface of the carbon. Activation is achieved chemically, by treatment by dehydration with zinc chloride or phosphoric acid, or by treatment with steam, hot carbon dioxide or a mixture of both. The activated carbon is available in three basic forms, powder, granules or as cylindrical or spherical pellets. For solvent recovery systems the carbon is usually obtained from either wood charcoal, petroleum residues or coconut shells and is often used in the form of pellets. 

Two broad types of rotary furnace are used - the rotary kiln and the short rotary furnace. Rotary kilns are characterised by large length to diameter ratios of the order of 10 to 15 1, whereas for the short rotary furnace the length to diameter ratio rarely exceeds 1.5 1. 

Furthermore, in order not to reduce the width of shell plate between the openings too much, the latter are oval in shape and are protected by inserted sockets made of heat-resisting cast steel. In a sense, they correspond to the outlet sectors (nose sectors) of rotary kilns with other types of clinker cooler and are embedded in refractory lining material. The refractories that have achieved the best results in this... 

The model is now being used for scaling down the calcination of various types of catalysts requiring different kinetic models. Comparisons are being made between products obtained at different scales of rotary kilns and guidelines are being established for carrying out a representative calcination at the smallest conceivable scale. 

The ABS polymer is recovered through coagulation of the ABS latex. Coagulation is usually achieved by the addition of an agent to the latex which destabilizes the emulsion. The resulting slurry can then be filtered or centrifuged to recover the ABS resin. The wet resin is dried to a low moisture content. A variety of dryers can be used for ABS, including tray, fluid bed, and rotary kiln type dryers. 

Rotary Kiln Incinerators. The rotary kiln has been used to incinerate a large variety of Hquid and soHd industrial wastes. Any Hquid capable of being atomized by steam or air can be incinerated, as well as heavy tars, sludges, pallets, and filter cakes. This abiUty to accept diverse feeds is the outstanding feature of the rotary kiln and, therefore, this type of incinerator is often selected by the chemical and waste treatment industries. 

The latest installations incorporate a waste heat boiler in the off-gas cleaning system to recover sensible heat from the rotary kiln off-gas. There is sufficient sensible heat in the off-gas from the SL/RN process to generate 500 to 700 kWh/t of DRJ, depending on the type of reductant used. 

A more simplified description is a unit that combusts materials in the presence of oxygen at temperatures normally ranging from 800 to 1650°C. A typical configuration of an incinerator is shown in Figure 9. Typical types of incineration units that are discussed herein are catalytic oxidation, fluidized beds, hquid injection, multiple hearth furnaces, and rotary kiln. Thermal desorption is also discussed. However, an overview of the main factors affecting incinerator performance is presented first, below. 

Once an undesirable material is created, the most widely used approach to exhaust emission control is the appHcation of add-on control devices (6). Eor organic vapors, these devices can be one of two types, combustion or capture. AppHcable combustion devices include thermal iaciaerators (qv), ie, rotary kilns, Hquid injection combusters, fixed hearths, and uidi2ed-bed combustors catalytic oxidi2ation devices flares or boilers/process heaters. Primary appHcable capture devices include condensers, adsorbers, and absorbers, although such techniques as precipitation and membrane filtration ate finding increased appHcation. A comparison of the primary control alternatives is shown in Table 1 (see also Absorption Adsorption Membrane technology). 

Solid wastes arc disposed of by two basic methods. The first is by some type of dumping or landfill procedure the second is by incinerating (burning) the waste. This section focuses on incinerators, namely the rotary kiln, liquid injection, fuidized-bed, and multiple-hearth dc ices, which are the four types... 

Three different types of furnaces are generally in use for calcination. The shaft furnace is considered to be the most suited for calcining coarse limestone. Furnaces of the rotary kiln type are used for handling materials of mixed particle sizes and lumps which disintegrate during the process. Calcination can be carried out in a fluidized bed-reactor for materials of small and uniform particle size. These furnaces are usually fired with gas, oil or coke in some cases electric heating is resorted to. 

The roasting process mostly applied to sulfidic sources is carried out in appliances of different types with different design features. Without describing their features and constructional details, it may simply be mentioned here that some of the widely acclaimed roasting units are traveling grate furnaces, multiple hearth furnace, rotary kilns, and fluid-ized-bed roasters. 

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