Refractory walls

Refractory organics Refractory-wall furnaces Refrasil Refrigerant... 

Wall losses through most refractory walls are ca 10% of the heat suppHed by the fuel. Losses increase with rising operating temperature. In special cases, eg, in glass tanks, losses can be as high as 30—35%. In these instances, very high values are requked to maintain the refractory at a temperature below which it does not melt or coUapse. 

The fuels Hsted in Table 2 are generally representative of fuels to be encountered over the range of industrial furnaces and, depending on the type (cooled or refractory wall), exhibit operating temperatures considerably different from adiabatic values. The choice of fuel is dependent upon a number of factors including cost, availabiUty, cleanliness, emissions, reflabiUty, and operations. Small furnaces tend to bum cleaner, easier to use fuels. Large furnaces can more effectively use coal. 

These furnaces may operate batchwise or continuous. In the batch, intermittent, or periodic types, the content is heated at the desired temperature for the stipulated time and then removed. In the continuous type, the charge moves at a predeterrnined rate through one or more heating 2ones to emerge in most cases at the end opposite the point of entry. Figures 9 and 10 are representative examples of typical, industrial refractory-wall furnaces. 

The lshi2uka cell (39—41), another multipolar cell that has been ia use by Showa Titanium (Toyama, Japan), is a cylindrical cell divided ia half by a refractory wall. Each half is further divided iato an electrolysis chamber and a metal collection chamber. The electrolysis chamber contains terminal and center cathodes, with an anode placed between each cathode pair. Several bipolar electrodes are placed between each anode—cathode pair. The cell operates at 670°C and a current of 50 kA, which is equivalent to a 300 kA monopolar cell. 

Treatment of Refractory Walls Partially Enclosing a Radiating... 

T = absolute temperature. Subscript 1 (or G), radiating surface (or gas) temperature subscript E, exit-gas subscript o, base temperature subscript E, pseudoadiabatic flame temperature based on C averaged from to Te-U = overall coefficient of heat transfer, gas convec tion to refractory wall to ambient air. 

Treatment of Refractory Walls Partially Enclosing a Radiating Gas Another modification of the results in Table 5-10 becomes important when one of the surface zones is radiatively adiabatic the need to find its temperature can be eliminated. If surface A9, now called A, is radiatively adiabatic, its net radiative exchange with Aj must equal its net exchange with the gas. 

Treatment of radiative transfer in combustion chambers is available at varying levels of complexity, including allowance for temperature variation in both gas and refractory walls (Hottel and Sarofim,... 

Stirred-Chamber Model Refractory Wall LiOss Negligible... 

L/A /(GSi)rOTf = Lr, refractory-wall loss number (dimensionless)... 

Forced-convection pit furnaces are employed for heat-treating small metal parts in biuk. Small pieces are suspended in a mesh-bottom basket, while larger pieces are placed on racks. Air heating is by means of Nichrome electric coils set in refractory walls around the... 

Indirect-Fired Equipment (Fired Heaters) Indirect-fired combustion equipment (fired heaters) transfers heat across either a metallic or refractory wall separating the flame and products of combustion from the process stream. Examples are heat exchangers (dis-... 

An upper limit of die heat losses tluough the reaction container wall, usually in the form of a cylindrical ciiicible with an increasing diameter from bottom to top, by assuming that die whole reaction mixture achieves the hnal reaction teiiiperamre immediately, and heat losses occur dirough the ciiicible refractory walls by conduction. The solution of Fourier s equation... 

In the secondary production of aluminum, scrap is usually melted in gas- or oil-fired reverberatory furnaces of 14,000 to over 45,000 kg capacities. The furnaces have one or two charging wells separated from the main bath by a refractory wall that permits only molten metal into the main bath. The principal processing of aluminum-base scrap involves the removal of magnesium by treating the molten bath with chlorine or with various fluxes such as aluminum chloride, aluminum fluoride,... 

Refractory raw materials, 21 483-491 composition of, 21 484 87t Refractory sales, U.S., 21 507t Refractory-wall furnaces, 12 328, 330 Refrigerant-absorbent combinations, 21 525... 

In most heaters, the majority of the heat of combustion is radiated to the refractory walls. The glowing refractory walls then reradiate the heat to the heater tubes. 

Many older heaters have massive brick refractory walls. The weight of these walls greatly exceeds the weight of the heater s tubes. The massive brick refractory walls store a great deal of heat. This creates several operating problems. One such problem is that it takes many hours to bring such a heater up to its normal operating temperature. However, a far more serious problem occurs when the process flow to a heater is interrupted. 

When flow is first lost, the fuel to the heater is often automatically tripped off. But the refractory walls continue to radiate heat to the process tubes. It is rather like a large fly wheel. Even after we stop cranking the wheel, the rotational energy stored by the wheel keeps it spinning. Even when all the firing is stopped, the energy stored in the refractory walls continues to radiate heat to the process tubes. 

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