Hearth zone

Countercurrent operation of shaft and rotary kiln furnaces leads to extensive heat transfer between feedstock and outgoing products. The sensible heat of the products remains within the system which enhances its thermal yield. Cocurrent operation shows none of these advantages yet it is a simple and efficient method to avoid tar problems. Indeed the tar is extensively cracked while moving through the hearth zone. Also the problem of wastewater is somewhat simplified. Crosscurrent operation is only seldom used. 

Furnace walking hearth Zones = A top, 0. bottom. Piece weight 2068 pounds... 

Before this treatment, the cassiterite content of the ore is increased by removing impurities such as clay, by washing and by roasting which drives off oxides of arsenic and sulphur. The crude tin obtained is often contaminated with iron and other metals. It is, therefore, remelted on an inclined hearth the easily fusible tin melts away, leaving behind the less fusible impurities. The molten tin is finally stirred to bring it into intimate contact with air. Any remaining metal impurities are thereby oxidised to form a scum tin dross ) on the surface and this can be skimmed off Very pure tin can be obtained by zone refining. 

The furnace (Fig. 2) maybe divided into four zones (from bottom to top). (/) Hearth and raceway as the coke descends through the furnace, it is heated by the ascending gases to about 1370°C. When it reaches the raceway in front of the tuyeres, it reacts immediately with the oxygen in the hot blast air. Equation 1, however, is actually the combination of coke combustion (eq. 6) and coke gasification (eq. 7, also referred to as solution loss). 

For practical reasons, the blast furnace hearth is divided into two principal zones the bottom and the sidewalls. Each of these zones exhibits unique problems and wear mechanisms. The largest refractory mass is contained within the hearth bottom. The outside diameters of these bottoms can exceed 16 or 17 m and their depth is dependent on whether underhearth cooling is utilized. When cooling is not employed, this refractory depth usually is determined by mathematical models these predict a stabilization isotherm location which defines the limit of dissolution of the carbon by iron. Often, this depth exceeds 3 m of carbon. However, because the stabilization isotherm location is also a function of furnace diameter, often times thermal equiHbrium caimot be achieved without some form of underhearth cooling. 

Even at 1,500 F, equilibrium eonstants for the first two reactions are high enough (about 10) to expect reaction to go essentially to completion except for kinetic-rate limitations. The reaction zone might be expected to be sized by volume of rabbled carbon bed, considering that the carbon gasification reactions that occur in it are governed by kinetics and are reaction-rate limited. Actually, it is sized by hearth area. The area exposed to the gases controls mass transfer of reactants from the gas phase to the carbon and heat transfer to support the endothermic reactions. 

Selenium is a significant component of the enzymatic system of the glutafion for antioxidant protection. It is included in the composition of 200 enzymes engaged in different biochemical reactions, demonstrates the immune-tropic, antiteratogenic and anticancer properties, betters the functional state of muscles, especially myocarditis, and takes part in hormones synthesis of the thyroid gland. Selenium s deficit in soil is the cause of hearth deficiency in endemic zones. 

Drop zone from heat treatment in Pithouse 1 3385-3078 Clay lined hearth inside a structure not far from deer bones. 

In the proprietary rotary hearth method of calcining coke, green coke is fed to the perimeter of the rotating circular table and gently moved toward the center of the hearth in a circular path by stationary rabbles. A combustion zone above the coke bed, formed by liberated volatiles, supplies the heat necessary for calcination. A rotating hearth furnace can also be equipped with energy efficient features, such as steam generation and air preheat. 

The steelmaking components of an open hearth furnace consist of a rectangular heating zone with a floor containing a long shallow depression of 200-500 tonnes capacity into which the charge is placed (Fig. 14.3). Gas or... 

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