Field kilns

Various types of kilns evolved during the history of ceramic production fired brick walls were constructed for field kilns in contrast to periodic kilns, serving only for a limited production campaign round or tunnel kilns provide different features concerning the duration of the firing cycle or the temperature uniformity. A kiln with an oxygen-deficient atmosphere produces harder ceramics (and a different colour) than a kiln with an oxidising atmosphere. 

The early pot or field kilns (see section 16.3.2 for details) were generally wood-fired. Many operated on a batch basis, in which alternate layers of wood and stone were placed in the kiln before setting Ught to the wood at the base of the kiln. Others operated continuously, with alternate layers of wood and limestone being charged into the top of the kiln. 

Flare kilns, pot kilns and field kilns include a number of designs, which may be roughly cylindrical, rectangular or other suitable shapes (Fig. 16.2). Wood is placed on the grate beneath a crude stone arch (or arches). Progressively smaller lumps of stone are placed above the arch(es). The wood is lit and the rate of combustion is adjusted by controlling the air flow which enters via the ash pits. Ad-... 

Typical applications in the chemical field (Beaver, op. cit.) include detarring of manufactured gas, removal of acid mist and impurities in contact sulfuric acid plants, recovery of phosphoric acid mists, removal of dusts in gases from roasters, sintering machines, calciners, cement and lime kilns, blast furnaces, carbon-black furnaces, regenerators on fluid-catalyst units, chemical-recovery furnaces in soda and sulfate pulp mills, and gypsum kettles. Figure 17-74 shows a vertical-flow steel-plate-type precipitator similar to a type used for catalyst-dust collection in certain fluid-catalyst plants. 

The most important applications of solvent dehydration lie within the field of kiln drying for seasoning timber where substantial reductions in drying times have been achieved150 . 

Under USEPA s BIF mle, manufacturers are required to closely monitor numerous conditions in the kiln and to observe limits on the following aspects of the process (a) the maximum feed rate of hazardous waste fuel (b) the maximum feed rate of metals from both raw materials and fuels (c) the maximum feed rate of chlorine from raw materials and fuels (d) the maximum feed rate of raw materials (e) the maximum temperature at the inlet to the air pollution control devices (f) the maximum concentration of carbon monoxide and total hydrocarbons in the flue gas (g) the maximum temperature in the combustion zone or minimum temperature at the kiln inlet and (h) any decrease of pressure at the baghouses or any decline in the strength of the electric field of electrostatic precipitators (both are types of air pollution control devices). 

Electrostatic precipitators and baghouses are used to catch dust particles containing metals. Electrostatic precipitators use an electrical field to remove the particles. Baghouses use fiberglass filters, similar to vacuum cleaner bags, to catch them. The majority of theses particles, called cement kiln dust (CKD), are trapped by this equipment and returned to the kiln for incorporation into the cement clinker. Under USEPA s BIF rule. Southdown tests its cement kiln dust to judge whether it is hazardous. If the CKD does not meet the standards set under the BIF rule, it must be disposed of in accordance with USEPA s strict hazardous waste regulations. For that reason. Southdown does not accept fuels that would cause the waste CKD to fail this test. 

Archaeomagnetism can be considered a branch of Paleomagnetism specifically devoted to the dating of archaeological materials from the measurement of the remanent magnetization achieved by the iron oxide impurities present in clay after cooling of the ceramic artifact. This recording mechanism primarily provides information on the direction of the Earth s field at the time the artifact was fired or the kiln was last used. 

As a special topic, solids transport in a pilot-scale rotary kiln was studied and outlined in a paper of N. Descoins et al. Finally, two papers give examples on environmental aspects of this field. A nice overview on dust control and explosions in solids handling plants are given P. Wypych et al. with description of some own experimental results. Application... 

Tablets come into a somewhat different category. All that is ever wanted of them is their inscriptions and it is common practice to fire tablets so that they can be handled indefinitely. Should only clay be wanted for analysis an unscribed section can be set aside and left unfired. Any treatment to be given to tablets in the field depends on whether there is a kiln on the site or not and, if not, on how desperate the epigraphist is to read them on the spot.

The pyrolysis of tires based on rotary kiln technology started quite early in the 1970s. A field-scale rotary kiln at Rocky Flats is documented in [5]. Very new developments can be found in [6]. The rotary kiln developed by Faulkner has several distinct heating zones independent from each other. The system consists of a rotary feed cylinder that includes a screw-Uke flight extending from the inner wall of the feed cylinder. As the feed cylinder rotates, the flight directs the supply of vehicle tire pieces into the infeed end of the pyrolysis section. The temperature levels of the kiln zones decrease from a maximum of 800°C to 500°C at the end of the kiln. A separation of char and scrap steel... 

Some oilseeds are dried in the field with hot gases from oil burners. Copra is often dried in ovens or kilns fired by coconut shells. In each case, contamination with diesel fuel fumes or polyaromatic hydrocarbons is inevitable. The only question is to what extent. Some hydrocarbons occur naturally in plants and appear in plant products. Mineral oil contamination of vegetable oil was also associated with toxic oil syndrome (20). 

Thermal treatment appears to be the most readily available remedial action technology for dioxin. However, no data are available to confirm the maintainability, reliability and cost-effectiveness of transportable commercial systems. Through a competitive process, the USAF selected ENSCO Corporation for a full-scale field test of their rotary-kiln combustor. The test will be conducted at the NCBC, Mississippi and will involve treatment of approximately 9000 cubic yards of contaminated soil. An intense analytical program and engineering failure mode analysis will support the project. Testing is planned for November 1986 - March 1987. 

The furnace lens provides a 90° or 60° field of view in the same direction as the flame being blown from the burner. Operators can thus watch the complete flame (including length, shape, color, and direction) on the end of the pipe 12 feet away, the sidewalls, top, and bottom of the kiln, the clinker being formed, and the movement of material down the kiln. The camera s quartz lens can see 15-25 feet into the kiln, in contrast to the old vidicon cameras, which could only provide a hazy image over a distance of a few feet. Observing their remote screens, operators can adjust for the most efficient combustion— with pulverized coal igniting at the tip of the feed pipe. 

The furnace lens, flush with the interior wall of the lime kiln, provides a 90° or 60° field of view. The operator can view directly along the axis of the scope. Likewise, he or she can operate a motorized iris and spot filter in the lens to adjust the amount of light reaching the camera. 

To calculate the flue gas flow rate it is necessary to know the decarbonation degree of the hot meal (material coming from the lowermost stage into the kiln) the calculation has been based by assuming that 60% of the residual decarbonation is done in the kiln. The oxygen value at the kiln outlet is the average measure given by field instrumentations. The flue gas at the kiln outlet is composed by (see Table 31.31) ... 

One of Lewis strong interests was in combustion, kilns, and gas production. In the early 1920 s, Robert T. Haslam, who had joined the faculty after World War I, chose this part of Lewis interest as his area of specialization and began with Robert P. Russell of the Research Laboratory of Applied Chemistry to assemble material for a book. Fuels and their Combustion, an authoritative volume. This field was so important that Haslam considered the possibility of either a separate chemical engineering division in this area or perhaps a separate course. Fuel and gas engineering did, in fact, maintain a separate identity for a period of several years, but returned to chemical engineering in 1932. 

High-temperature rotary drum lime and cement kilns are of similar configuration to rotary drum furnaces and dryers discussed in section 4.2, except that they are of higher temperature construction and longer. This is a very specialized field. (See Perry The Rotary Cement Kiln, reference 64.) A shaft-type lime kiln is shown in figure 1.11. 

The ceramic industries are leading the way in kiln and furnace data-acquisition technology. Fixed noncontact thermocouples give only a general idea about the true thermal history of the molecules within a load. It behooves leaders within the industrial heating field to encourage cooperation with instrument and control experts by... 

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