Rabble

Mu/tihearth Furnace. Multihearth furnaces are most often used for incineration of municipal and industrial sludges, and for generation and reactivation of char. The main components of the multihearth are a refractory-lined shell, a central rotating shaft, a series of soHd flat hearths, a series of rabble arms having teeth for each hearth, an afterburner (possibly above the top hearth), an exhaust blower, fuel burners, an ash removal system, and a feed system. 

The feed is normally introduced to the top hearth where the rabble arms and teeth attached to the central shaft rotate and spiral soflds across the hearth to the center, where an opening is provided and the soflds drop to the next hearth. The teeth of the rabble arms on the hearth spiral the soflds toward the outside to ports that let the soflds drop down to the next hearth. Soflds continue downward, traversing each hearth until they reach the bottom and the ash is discharged. The primary advantage of this system is the long residence time in the furnace controlled by the speed of the central shaft and pitch of the teeth. 

Multiple-Hea.rth Roasters. The circular types consist of a series of hearths arranged vertically in such a way that the ore entering the top is rabbled and dropped down from hearth to hearth, until it is completely oxidized. The hearths are usually stationary and the plows revolve, such as in the Wedge, Herreshoff, Ord, Skinner, and other roasters (21). In other furnaces, the hearths revolve and the rabbles are fixed, eg, the deSpirlet and its modification, the Barrier. 

A conventional circular-wedge roaster consists of a brick-lined steel shell with hearths arched gendy upward from the periphery to a central shaft. The brick hearths may number from 8 to 16 and are ca 1 m apart. The central steel shaft (ca 1.2 m in diameter) revolves at 1 rpm or less carrying two rabble arms per hearth. These rabbles, cooled with air or water, plow the ore from the outside to the center of the hearth where it is dropped to the next hearth for plowing in the opposite direction. The calcine thus proceeds to the bottom where it is dropped into a conveyor. The sulfide sulfur at this point is ca 3.5% (22). 

The flash roaster is flexible ia handling various flotation concentrates and reaching the degree of desulfurization desired, ie, 0.5—3.0% sulfate sulfur. Waste heat is easily recovered. However, grinding and rabbling must be done mechanically. 

Plasticity can be studied using a device known as the Gieseler plastometer. A constant torque is appHed to a shaft with rabble arms imbedded in coal in a cmcible heated at a fixed rate. The rate of rotation of the shaft indicates the duidity of the coal and is plotted as a function of the coal temperature. These curves, as shown in Figure 8, have a well-defined peak for coking coals usually near 450°C. Softening occurs at 350—400°C. At a normal heating rate of 3°C/min, the duid hardening may be complete by 500°C. 

Roasting . Roasting has been largely abandoned ia modem copper smelters, ia which this function is combiaed with the smelting furnace. In older systems, the multiple-hearth roaster is a brick-lined tower having horizontal brick hearths. The concentrate is iatroduced at the top hearth, where rotating arms with rabble blades turn it over and move it to holes ia the hearth. The concentrate is transferred successively to lower hearths and finally... 

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. 

Feuer-kammer, /. fire chamber, fire box. -kitt, m. fireproof cement, -kriicke,/. furnswe rake, rabble, -kunst,/. pyrotechnics, -leihing,/. priming, train (MU.) fire control, feuerlos, a. fireless, lusterless. 

Haken. m. hook clasp, catch Puddling) rabble. 

Eratze, /. scraper rabble rake skimmer card (for wool, etc.) scrapings. 

Ruhr-fass, n. churn (J/ to/.) dolly tub. -form, /. form or shape of stirrer, -frischen, n. (Metal.) puddling. -geschwindigkeit, /. velocity of stirring. -tUikchen, n. small stirring hook, -haken, m. stirring implement, rake, rabble, poker, -holz, n. wooden stirrer, stirring stick, paddle. 

Ruhrofen, m. (Afetal.) rabble furnace. Rubrrmde, /. Simarouba bark. 

Ruhr-schaufel, /. stirring paddle, -scheit, n. paddle, rake, stirrer spatula, -spatel, m. stirring spatula, -stab, m. stirring rod, stirring pole, paddle, rabble, -stativ, n. stirring stand, -tank, m. ablating tank. 

---