Rotary kilns basics

The direct American process is basically a metallurgical operation. Ziac oxide ores are reduced usiag coal (qv) ia a rotary kiln at temperatures of 1000—1200°C to 2iac metal. At these temperatures the produced 2iac metal evaporates and is oxidi2ed with air to ZnO ia the upper part of the kiln. 

After thorough mixing, the mixture is roasted in a mechanical furnace, usually a rotary kiln. An oxidizing atmosphere is essential, and the basic reaction of a theoretical chromite is... 

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... 

The process is basically a rotary kiln design. Waste is first pretreated and then inserted in the rotary kiln, where it is incinerated with air. The chlorinated hydrocarbons are converted into H2O, CO2 and HCl. After that, in a wet scrubber the HCl is recovered as aqueous HCl. If needs be, natural gas or liquid energy carriers can be added in order to reach the necessary high temperatures in the afterburner. 

Peniakoff A process for extracting aluminum from bauxite or other aluminous ores. The ore is roasted with coke and sodium sulfate in a rotary kiln at 1,200 to 1,400°C this converts the aluminum to sodium aluminate, which is leached out with dilute sodium hydroxide solution. The basic reactions are ... 

The product is heated in a rotary kiln causing the excess lead oxide to react with the basic lead chromate, forming tetrabasic lead chromate ... 

Sato, A., Tsuchiya, I., Takahashi, H., Ishii, T., Takebayashi, K. and Kawakami, T., Effect of thermal shock on the structural changes of the basic refractories for cement rotary kiln , Taikabutsu Overseas, 1986 8(1) 37-9. 

Barthel, H. and Kaltner, E., The basic lining of cement rotary kilns to conform to changed requirements , Proc. 2ndInt. Conf. on Refractories, Tokyo, 2, 1987. 

Less than 15% of the ore is transformed into chromium compounds, principally chromates, dichromates, chromium(VI) oxide, chromium(III) oxide, and so on. Alkaline oxidative roasting of chromite in rotary kilns yields sodium chromate (see equation 1), which is leached out with water and typically converted into sodium dichromate with sulfimc acid (equation 2) or carbon dioxide (equations). Fiuther treatment of sodium dichromate with sulfuric acid yields chromium(VI) oxide ( chromic acid ), while its reduction (with carbon, sulfur, or anuuo-nium salts) produces chromium(III) oxide. Finally, basic chromium(III) salts, for example Cr(0H)S04, which are used as tanning agents for animal hides, also result from reduction of sodium dichromate. Heterogeneous chromium catalysts are used for the polymerization of ethylene. 

Indirectly heated, horizontally arranged, rotary kiln for Thermal Desorption and low temperature carbonisation of the 0 5 mm input basic material, containing the following technical characteristics ... 

During the last 25 years a variety of processes have been developed for the thermal degradation of tyres in order to recover valuable components from rubber wastes.120-125 Stirred tanks, rotary kilns, fixed beds, fluidized beds and tray systems are examples of reactor types used for the thermal degradation of tyres. Several of these processes are now being used on a pilot plant and industrial scale. Basically, three fractions are derived from the thermal decomposition of tyres gases, liquid oils and solid residues. In the past, the influence of the reaction conditions and the reactor type were studied in order to maximize... 

After the system described above was devised, the Onahama smelter was expanded, and a commercial magnesia-base absorption system developed by the company was applied to the reverberatory furnace gases (27). As described (27), the process is essentially the same as the Chemico-Basic process (33) although equipment details are not reported. The magnesium sulfite is decomposed in a rotary kiln in the presence of added carbon. The magnesia is returned to the absorption process, and the rich kiln gas stream (13-15% sulfur dioxide) is sent to a sulfuric acid plant. 

The rapid growth of the Basic Oxygen Steelmaking process in the 1960s required kilns which could produce a 6 to 40 mm quicklime, with a relatively high reactivity, low residual % CaCOs and low sulfur content. Initially, much of this new demand was met by Calcimatic and rotary kilns. 

One particular rotary kiln manufacturer uses an integral shredder at the bottom of the waste feed hopper. This system is termed an auger feeder. It basically serves to process waste into a size that is compatible with the kiln dimensions. 

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. 

A sulfoferrite-bearing clinker may be produced in a rotary kiln at burning temperatures of 1200-1350 °C. Its phase composition may vary—depending on the basicity of the raw meal and its gypsum content—in the following range C FgS, 10-55% CjFS, 0-60% C2S, 25-40% calcium aluminoferrite phase and other constituents, 5-30%. In commercial sulfofenite clinkers the composition of the sulfoferrite phases may vary as follows 3CF.(0.75-1.5)CS and C2F(0.8-1.5)CS. About 5-15% of sulfofenite clinker is combined with ordinary Portland chnker and calcium sulfate to obtain sulfofenite cement. 

D. Gregurek, Investigation of basic and non-basic bricks after the rotary kiln test carried out for Stillwater Mining Company, Columbus, Montana, U.S.A. (Internal RHI report. Technology Center Leoben, Austria, 2012). 

Chapter 2 Basic Description of Rotary Kiln Operation... 

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