Rotary Kiln Principles

This paper presents the first experimental results for the solid motion inside a pilot-scale rotary kiln. Such data are useful to enable efficient pyrolysis reactions inside a rotary kiln to be carried out, through the prediction of residence time and material hold-up, and the evaluation of different surfaces and temperature profiles according to the operating conditions. In the first part, the pilot-scale rotary kiln and the principle of the experiments will be described. An original dynamic solid motion model will be presented in the second part, this dynamic model is derived from the original static model of Seaman [1], The static and dynamic experimental results are finally compared with the simulated results. 

The high capital investment cost of the Asahi process is due to the necessity for large absorbers, evaporators, crystallizers, dryers, rotary kiln crackers and screw decanter separators. The major operating and maintenance costs are electricity, fuel oil, steam and chemicals such as soda ash, EDTA and limestone. The requirement for consumption of large amounts of utilities is associated with the operation principle and design of the Asahi process. According to the economic evaluation, equipment required for N0X and SO2 absorption (such as packed-bed absorbers) accounts for 20% of total direct capital investment for treatment of dithionate ion (such as evaporator, crystallizer, dryer, and cracker) it accounts for about 40% and for treatment of nitrogen-sulfur compounds (such as screw decanter and cracker) it accounts for only 2%. 

Pyrolysis of agricultural residue was experimentally assessed as a fuel production process for farm applications. A rotary kiln (3.4 m by 0.165 m I.D.) was used due to its ease of operation, commercial availability, low operating costs and ease of start-up and shutdown. Ground oat straw and corn stover at less than 10% moisture were pyrolysed in an indirectly fired continuous-flow rotary kiln located at the University of Sherbrooke. The principle products were char and gas, less than 1% of the feed mass was converted to tar. Calorific values were about 17 MJ/kg for the feed, 26 MJ/kg for the char, and 12 MJ/m3 for the gas. Calculations indicate that the thermal efficiency of a self-sustaining process would be around 65%. 

We have examined the effect of kiln aerodynamics on fluid mixing and combustion. It is equally important to look at the aerodynamic effect on dust carryover from rotary kilns processing mineral materials. Although the principles behind particle motion are related to granular flow which will be covered in Chapter 4, the interaction of the flow of fluid in the freeboard and the active layer surface of the kiln bed is an aerodynamic phenomenon. 

For the design of the drive, tyres (riding rings), rollers, rotating seals and wall thicknesses the principles and criteria are basically the same as those for the rotary kiln itself. In view of the risk associated with overheating of the shell plate, the latter should be at least of a boiler plate grade. 

An alternative to placing electronic products waste in dumps and landfills is to destroy the waste by incineration. One type of incinerator is the rotary kiln that uses the energy from liquid, combustible hazardous waste to increase the temperature of the kiln for drying cement. The chemical industry disposes of high energy-capacity, flammable liquids in this manner. Incinerators that bum hazardous chemical waste must be monitored and achieve a destruction removal efficiency (DRE) rate of at least 99.99 percent of the principle organic hazardous constituents of the waste. 

Light-burned dolomite (or dolime) is produced in either rotary or shaft kilns. The principles are similar to those of making high calcium quicklime. Heat usages are presumably somewhat lower, owing to the lower heat of calcination of dolomite and its lower dissociation temperature. 

Rotary-hearth Kiln. A circular tunnel with a slowly rotating platform for conveyance of the ware through the kiln. An early example was the woodhall-DUCKHAM KILN (Brit. Pat. 212 585 23/2/23). The principle has since been adapted in the clark circle system of brickmaking introduced in Australia in 1953 and in some modern potterydecorating kilns. (This type of kiln is sometimes also known as a rotating-platform kiln.)... 

In process engineering terms the planetary cooler functions on the same principle as the rotary cooler. The cooling air rate corresponds to the secondary air supplied to the kiln. The air flow through the cooler is sustained by the kiln exit gas fan. 

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