Thermal oxidizer rotary kiln

Calcination. Calcination involves a low (<1000° C) temperature soHd-state chemical reaction of the raw materials to form the desired final composition and stmcture such as perovskite for BaTiO and PZT. It can be carried out by placing the mixed powders in cmcibles in a batch or continuous kiln. A rotary kiln also can be used for this purpose to process continuously. A sufficiendy uniform temperature has to be provided for the mixed oxides, because the thermal conductivity of powdered materials is always low. 

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. 

Multiple effects evaporation-steam and/or oil, multiple hearth and rotary kiln incineration, and other special thermal oxidation systems. 

The Pyretron thermal destruction technology is a burner system designed to be used in conjunction with any conventional transportable or fixed rotary kiln incinerator and is intended to increase the efficiency of conventional incineration. The commercially available technology controls the heat input during incineration by controlling excess oxygen available to oxidize hazardous waste. 

Other treatment systems consist of utilizing a reactor for the neutralization process, employing a rotary kiln to thermally destroy the calcium carbide and acetylene, and the oxidation of the slag by introducing small amounts of oxygen into the molten material. As of this date, technical problems associated with these methods have prevented their use, and require that more research needs to be done. 

A second major type of reactor involves thermal destruction of the calcium carbide. At about 1,S00°F, both calcium carbide and acetylene are thermally oxidized. Therefore, a system such as a rotary kiln could be used for thermal destruction of the reactivity characteristics. The additional benefit of thermal destruction is that it will also effectively deal with potential sulfide reactivity problems. Large chunks of metals often included in the desulfurization slag will tend to be a problem for many types of thermal units. Concern over air emissions and cost are other hurdles to the use of thermal systems for calcium carbide desulfurization slag. 

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

Nitric oxide (NOx) is one of the main pollutants in combustion systems and rotary kilns are no exception particularly for pulverized fuel combustion. NOx formation depends on three factors, namely (i) the amount of nitrogen present in the fuel, (ii) the combustion temperature, and (iii) the stoichiometric conditions for the combustion reaction. Hence NOx production is classified into fuel NOx, thermal NOx, and prompt NOx. Some of the mechanisms for the formation of these species during pulverized coal combustion in rotary cement kilns have been described in commercial CFD packages (e.g., FLUENT, CINAR). 

Wet mixes are usually dried before calcination. Calcination is performed continuously in rotary or tunnel kilns, or batchwise in directly fired drum or box furnaces. The temperature at which the mixed metal oxide pigments are formed can be reduced by adding mineralizing agents [3.75]. In the case of chromium rutile pigments, addition of magnesium compounds [3.81] or lithium compounds [3.80] before calcination improves thermal stability in plastics. 

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