Cycling furnaces

Instrument response Atomization volts Atomization time Charring time Charring cycle Furnace Recorder... 

I % or belter that can be expected for flame or plasma atomization. Furthermore, because of the healing-cooling cycles, furnace methods arc slow — typically requiring several minutes per element. A final disadvantage is that the analytical range is relatively narrow, usually less than two orders of magnitude. As a result, electrothermal atomization is the method of choice when flame or plasma atomization provides inadequate detection limits. 

Electrode consumption for ferrous melting a-c furnaces usually averages 2.5—6 kg/1 of molten metal dependent on the particular furnace practices. D-c furnaces have electrode consumptions that are about 30% lower for similar operations. A typical energy consumption for a typical high productivity ministeel mill practice is 400 kW h/t. In comparison, power consumptions exceeding 600 kW h/t ia foundries is not unusual because of longer furnace cycle times. 

Medium-sized loads are often processed ia a beU furnace, as shown ia Figure 2. The operation of this furnace is opposite to that of an elevator furnace the work load is placed on a stationary hearth and the furnace is lowered over the hearth. BeU furnaces are often arranged with two or more bases (hearths) which permit more efficient use of the furnace because one base can be unloaded/loaded as the furnace carries out a heating cycle on another base. 

The furnace charge consists of 2iac—lead siater, metallurgical coke, and recirculating metallic drosses and flux. The charge cycle is fully automatic. Hoist... 

The retorts must be opened, the reaction products removed, and the retorts filled with raw materials and resealed. The typical cycle is 8—10 hours. Capacity is controlled by the number of retorts used and the number of furnaces available. The metal crowns are removed, remelted, and cast iato iagots, or alloyed and then cast. 

The process operates at 1200°C and < 400 Pa (3 tort) and has a cycle time of 20—24 hours. The reactor is opened at the flange and the metal removed. Energy usage in the furnace is 7-7.3 kWh/kg magnesium. A similar process is used by Brasmag (Minas Givras, Bra2il) (56). 

Eig. 8. Cost of electricity (COE) comparison where represents capital charges, Hoperation and maintenance charges, and D fuel charges for the reference cycles. A, steam, light water reactor (LWR), uranium B, steam, conventional furnace, scmbber coal C, gas turbine combined cycle, semiclean hquid D, gas turbine, semiclean Hquid, and advanced cycles E, steam atmospheric fluidized bed, coal E, gas turbine (water-cooled) combined low heating value (LHV) gas G, open cycle MHD coal H, steam, pressurized fluidized bed, coal I, closed cycle helium gas turbine, atmospheric fluidized bed (AEB), coal J, metal vapor topping cycle, pressurized fluidized bed (PEB), coal K, gas turbine (water-cooled) combined, semiclean Hquid L, gas turbine... 

Limitations in the material of constmction make it difficult to use the high temperature potential of fuel hiUy. This restriction has led to the insertion of gas turbines into power generation steam cycles and even to the use of gas turbines in preheating air for ethylene-cracking furnaces. 

The first direct-arc furnace in the United States was a single-phase two-electrode rectangular furnace of 4-t capacity at the Halcomb Steel Company (Syracuse, New York), which made its first heat in 1906. A similar but smaller furnace was installed two years later at the Firth-Sterling Steel Company in McKeesport, Pennsylvania. In 1909, a 15-t three-phase furnace was installed in the South Works of the Illinois Steel Company, in Chicago, Illinois, which was, at that time, the largest electric steelmaking furnace in the world. It was the first round instead of rectangular furnace and operated on 25-cycle power at 2200 V. 

Isothermal annealing can be conveniendy adapted to continuous annealings usually in specially designed furnaces. This is commonly referred to as cycle annealing. 

This is the equiUbrium estabflshed at the end of each smelting cycle. By this time, a considerable proportion of the tin produced in the heat-up stages has been drained from the furnace and only the metal remaining in the furnace at the final tapping time comes into equiUbrium with the slag (3). 

Vacuum Brazing Furnace. The cross sections of a vacuum brazing furnace of the beU-jar type are shown in Eigures 15 and 16. Contamination is very low even when rapidly cycled from one work load to the next. The beU jar can serve on one hearth while another hearth is being loaded for the next operation. 

Offset design gives ready access along the axis of the hot 2one. This design permits routine operation and cycling of the furnace without sacrificing control of containination, access, and speed for condensables or noncondensables. 

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. 

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