Furnace Construction

The lead blast furnace consists of a rectangular shaft with sidewalls made up from a series of water-cooled hollow steel jackets. Refiactory lining is unnecessary since an accretion layer forms on the inner surface to protect the steel from attack. 

The shaft narrows at the bosh to the lower section containing the tuyeres. This allows for the reducing volume of the charge as coke is consumed and the sinter melts. In older furnaces the top shaft can be refractory brick within a steel shell, but the lower section around the tuyeres will be of water-jacketed construction. Furnaces constructed in this way tend to bum out the joint between the upper refractory and the lower water jackets and the full steel furnace was a significant improvement. It is also easier to remove accretions from the steel surface compared to refractories and this is a key advantage of a water jacketed furnace. 

The tuyeres are fitted through the jackets and are constmcted of copper, often fitted with stainless steel tips to reduce corrosion and erosion. The cold air blast is sufficient to keep the tuyere bodies cool. Jackets at the tuyere level can be refiactory lined on initial installation, but this is gradually replaced by acaetions. The influence of the tuyeres can cause bum out of jackets, particularly with oxygen enrichment of blast air, but this can be overcome by the projection of the tuyere further into the furnace. 

The lower section of the furnace sits on a hearth made up of several layers of refiactory brick and a castable refractory cmcible, all held within a steel frame. The constmction of the hearth and selection of the bricks and refractories used is critical to avoid leakage of molten lead and expansion of the brickwork, which can limit the operating life of the furnace before reconstmclion. If properly constmcted this is not a problem and hearth life can be determined more by the build up of accretions, which gradually restrict the flow of bullion to the tapping point. 

The width of the furnace at the tuyeres or lower section is set by the penetration of the air blast and is in the range of 1.2 to 2.0 m, but more commonly 1.5 to 1.8 m. The tuyeres are set at a height of around 450 mm above the furnace tap hole. The upper shaft width can be expanded to 2 to 3 m and the overall shaft height is around 5 to 6 m. Some experimentation with tuyere angle of inclination and distance above the hearth may be needed for each furnace to achieve the desired crucible temperature and lead content in slag. 

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Fig. 13. (a) Convection currents around electrically heated furnace tube (b) furnace construction to minimise convection (78). 

Phosphate Fertilizer Industry Granular Triple Superphosphate Storage Facilities Goal Preparation Plants Ferroalloy Production Facilities Steel Plants Electric Arc Furnaces Constructed after October 21, 1974, and on or before August 17,1983... 

Figs. 604 and G0C are a plan and section of the smelting furnace at present employed in the smelting of tin ores. In these figures, A Is the fire supplied through the door, B c is the bed of the furnace, constructed of five-... 

Furnace Design. Modem carbide furnaces have capacities ranging from 45,000 t/yr (20 MW) to 180,000 t/yr (70 MW). A cross-section of a 40 MW furnace, constructed in 1981, having a 300 t/d capacity is shown in Figure 2. The shell consists of reinforced steel side walls and bottom. Shell diameter is about 9 m and the height to diameter ratio is shallow at 0.25 1.0. The walls have a refractory lining of 0.7 m and the bottom has a 1-m layer of brick topped by a 1.5-m layer of prebaked carbon blocks. The steel shell is supported on concrete piers and cooling air is blown across the shell bottom. A taphole to withdraw the liquid carbide is located at the top of the carbon blocks. 

Anon,C EN 35,32 (Dec 23,1957)[New process for prepn of CaHa designed by Tennessee Eastman Co is briefly described. It involves high temp breakdown of satd hydrocarbons (such as natural gas) conducted in a special furnace (constructed of stabilized zirconium)... 

High density tungsten alloy machine chips are recovered by oxidation at about 850°C, followed by reduction in hydrogen at 700—900°C. Typically, the resultant powders are about 3- im grain size and resinter readily. There can be some pickup of refractory materials used in furnace construction, which must be controlled. This process is important commercially. For materials that may be contaminated with other metals or impurities, the preferred recovery process is the wet chemical conversion process used for recovery of tungsten from ores and process wastes. Materials can always be considered for use as additions in alloy steel melting. 

The spongy metal is now made into a paste with water, compressed into a mould, and either forged into a homogeneous bar by heating and hammering, or melted in an oxyhydrogen furnace constructed of lime. 

In addition to the characteristics of pyrolysis oils and burner settings, different furnace constructions were compared in the test runs. By insulating the forepart of the furnace the mean tenqierature levels of flame were increased and hence combustion inqiroved. 

Fireclay refractories are divided into several groups according to their properties and quality. The main criteria are refractoriness, AI2O3 content, porosity and strength. The complex of properties then determines the field of application. In addition to shaped ware, granular fireclay mixes are also manufactured for the preparation of mortars in furnace construction, for repairs or for monolithic linings. 

Carbon matrices are more suitable than polymers ones for applications at temperatures of 250 to 600°C. Above 600°C they are, however, (as are the C-fibers as such) only utilizable in inert atmospheres. C-fiber reinforced carbon matrix composites are particularly used in aircraft brakes, in fusion reactors and as a substitute for monolithic graphite. In addition they are utilized in the medical sector (implants), in furnace construction (heaters) and in energy conversion (heat exchangers). The market for carbon fiber/carbon matrix composites in 1993 was estimated to be ca. 250 t. 

The Castner process is characterized by more efficient energy utilization and by more uniform graphitization compared with the Acheson process. Disadvantageous is the more complex furnace construction and restrictions concerning the dimensions of the carbon articles. 

Powdered Coal.—The fuel is blown into the furnace so as to burn in suspension. Furnace construction is much the same as for oil, and combustion is very perfect. Dryers are employed to drive off moisture before grinding. On account of its lower moisture content, run-of-mine coal may be preferred to slack, in spite of its higher price. The chief cost is for fixed charges in the grinding and feeding equipment, and for power. From 50 cts. to 1 per ton seems to be... 

The results of tension tests upon refractories in the hot state are not available in the literature nor are data relating to the transverse strength of bricks and tiles. This is to be regretted since in many furnace constructions transverse loads must be considered. Again, it seems very probable that the compression test of firebricks will ultimately be replaced by one involving transverse stress. 

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