Kilns and Hearth Furnaces

These units are primarily for high temperature services, the kilns up to 2500°F and the furnaces up to 4000°F. Usual construction is steel-lined with ceramics, sometimes up to several feet in thickness. Vertical kilns are used for materials that do not fuse or soften. 

Recovery of high concentrations of benzene from gas oils 

Phthallc anhydride from naphthalene or o-xylene 1D Maleic 4cld anhydride from benzene 

Cracking of chlorides such as FbCI2, NICIs, and AICI3 

Chlorination of ores of aluminum, titanium, nickel, cobalt, and tin 

Preparation of fluorides aluminum trifluoride, uranium tetra- and hexafluorides 

ADIPONITRILE + BYPRODUCTS + HIGH-BOILING RESIDUE + PHOSPHORIC ACID 

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Figure 1730. Kilns and hearth furnaces Walas, 1959). (a) Temperature profiles in a rotary cement kiln, (b) Space velocities in rotary kilns, (c) Continuous lime kiln for production of approximately 55tons/24hr. (d) Stirred salt cake furnace operating at 1000°F, 11-18 ft dia, 6-10 tons salt/24 hr. (e) Multiple-hearth reactor one with 9 trays, 16 ft dia and 35 ft high roasts 1250 lb/hr iron pyrite. (f) Siements-Martin furnace and heat regenerators a hearth 13 ft wide and 40 ft long makes 10 tons/hr of steel with a residence time of 10 hr.

Tubular Flow Reactors 569 Gas-Liquid Reactions 571 Fixed Bed Reactors 572 Moving Beds 574 Kilns and Hearth Furnaces 575 Fluidized Bed Reactors 579... 

Other examples of cylindrical lined vessels include blast furnaces, blast furnace stoves, basic oxygen furnaces, torpedo ladles, shaft kilns, multiple hearth furnaces, and rotary kilns. Some refractory lined vessels have refractory lined conical bottoms. When heated, the conical lining will want to displace upward. Therefore, the top mortar joint of the conical lining is critical. The cylindrical lining will be critical in restraining the upward expansion of the conical lining. At the ends of rotary kilns, restraint must be provided to contain and keep the kiln lining within the kiln shell. 

The ore is ordinarily ground to pass through a ca 1.2-mm (14-mesh) screen, mixed with 8—10 wt % NaCl and other reactants that may be needed, and roasted under oxidising conditions in a multiple-hearth furnace or rotary kiln at 800—850°C for 1—2 h. Temperature control is critical because conversion of vanadium to vanadates slows markedly at ca 800°C, and the formation of Hquid phases at ca 850°C interferes with access of air to the mineral particles. During roasting, a reaction of sodium chloride with hydrous siUcates, which often are present in the ore feed, yields HCl gas. This is scmbbed from the roaster off-gas and neutralized for pollution control, or used in acid-leaching processes at the mill site. 

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. 

Charcoal is produced commercially from primary wood-processing residues and low quaUty roundwood in either kilns or continuous furnaces. A kiln is used if the raw material is in the form of roundwood, sawmill slabs, or edgings. In the United States, most kilns are constmcted of poured concrete with a capacity of 40 to 100 cords of wood and operating on a 7- to 12-d cycle. Sawdust, shavings, or milled wood and bark are converted to charcoal in a continuous multiple-hearth furnace commonly referred to as a Herreshoff furnace. The capacity is usually at least 1 ton of charcoal per hour. The yield is - 25% by weight on a dry basis. 

Direct-fired combustion equipment is that in which the flamt of combustion are used to achieve the desired result by r and convection. Common examples include rotary kilns and open-hearth furnaces. Indirect-fired combustion equipment is that in wh e... 

The roasting process mostly applied to sulfidic sources is carried out in appliances of different types with different design features. Without describing their features and constructional details, it may simply be mentioned here that some of the widely acclaimed roasting units are traveling grate furnaces, multiple hearth furnace, rotary kilns, and fluid-ized-bed roasters. 

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