Running kilns

The earliest continuous kilns (also known as running kilns or draw kilns) were fired using the mixed-feed principle (Fig. 16.3). Alternate layers of limestone and fuel (wood or coal) were charged into the top of the kiln and lime was removed through the drawing door. 

Run Kiln speed, rpm Bed height, cm Average axial particle velocity, m/h measured theoretical Number of mixers Number of particle falls ... 

Cost Data for Kilns Purchase prices, weights, and horsepower requirements of typical units are given in Table 12-21. Installed costs will run to from 300 to 500 percent of purchase cost. Maintenance will average 5 to 10 percent of the total installed cost per year but is dependent largely on the hfe of the refractoiy lining. 

No. 2 fuel oil is a petroleum distillate that may be referred to as domestic fuel oil or industrial fuel oil. Domestic fuel oil is usually lighter and straight-run refined it is used primarily for home heating and to produce diesel fuel. Industrial distillate is the cracked type, or a blend of straight-run and cracked. It is used in smelting furnaces, ceramic kilns, and packaged boilers. 

A glaze that is too thick may not harden totally. Also, it may not adhere to a clay piece. It can crack easily. If the glaze is too thin, it may also not adhere to a clay piece surface and may crack. A thin glaze may run off a piece in a kiln and unintentionally glaze it. 

Reactions such as the above have been used for the large-scale commercial production of WC by Kenna-metal, Inc. in a process called the Macro Process [28]. Thermodynamics for the analogous molybdenum reaction show that the reaction is highly exothermic (Table 3). The solid reactants are metered into a carbon-lined kiln to develop a self-sustained exothermic reaction. The reaction occurs in a pool of molten metal at temperatures above 2800 K. At the end of the run the kiln contents solidify into a lower heavy layer of carbide crystals and an upper slag layer of oxides. 

With the Conrad process [1-3] a set of experimental runs with a throughput of approximately 100-1000 kg/h with PVC contents of up to 3% in a 60 20 20 HDPE PP PS base mixture have been performed. Typically 70-80% of liquids and 1-3% of solids are obtained. In scavenging the chlorine from evolving gases by hot calcium oxide and before condensation of the liquid fraction with a content of about 25 ppm chlorine were possible. Similar results were obtained by treating the plastics in the kiln with calcium oxide during pyrolysis. A direct condensation without any calcium oxide treatment led to concentrations of up to 10000 ppm chlorine. 

In the mid-1990s BASF, Ludwigshafen and APME, Brussels had run experiments witli electronic scrap in cooperation with the BC-Berlin Consult plant in Liibben, Germany. The BC plant consisted of an indirectly heated rotary kiln with 300 mm inner diameter and 3 m heated length driven at 750-850°C [20, 21, 55]. Two types of material were investigated, a fine fraction and a typically shredded electronic scrap fraction. Up to... 

Table 20.3 Pyrolysis products from BC-rotary kiln runs [20]...

The quicklime removed from a lim -kiln during a day s run weighed 15,000 pounds. Assuming that the limestone used is pure calcium carbonate and that the calcination is complete, what weight of limestone is required to produce this quantity of lime, and what volume of carbon dioxide in cubic feet at standard conditions is liberated ... 

These conditions were followed for the first run, but some leaks at the oven were observed. As the catch of the facility could not be modified, we decided to decrease the heating rate from 20 C/min to 2°C/min hoping for a lower pressure in the kiln. Unfortunately, the leaks persisted. 

Continuously operating tunnel kilns heated with gas, oil or electricity, in which the articles travel through a well-defined temperature-time profile, are currently almost exclusively used for the manufacture of the mass-produced articles of the brick, refractory and crockery porcelain industries. Such kilns are 20 to 150 m long and have transit times between 1 and >72 h. Muffle kilns, which operate discontinuously, are still important for small production runs and specialty products. 

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