High Temperature Carbonization Furnace

A smoke pencil should be used to check for ingress of air. The furnace can be correctly balanced by adjusting the body flow of N2 at the furnace inlet end to such a level that, when looking down into the furnace muffle, the atmosphere is not entirely clear but, at the same time, smoke is not forced out from the outlet end. It is essential to maintain a slight cloudy atmosphere, as this permits the correct concentration of HCN to build up within the furnace, significantly improving the carbon fiber strength. 

If Na is present in the precursor fiber, it will tend to form NaCN and it is important to wear the correct protective clothing and face mask when dealing with such residues. To conserve water supplies, it is common to use a recirculation water cooling system with a water cooling tower. This water must be treated and routinely checked for legionella bacteria to prevent any outbreak of Legionnaires disease. 

The fiber will burn as it exits the furnace and enters the plant atmosphere unless sufficient cooling is applied. 

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Most of the coke produced in the United States today comes from the high-temperature carbonization of coal. The coke is used pnmarily by the metallurgical industries as a fuel and in the rendering of iron from iron ore m the blast furnace... 

Having established the feasibility of niobium metal production by the carbothermic reduction of niobium pentoxide under temperature and pressure conditions readily attainable in the laboratory and in industry, the principles of efficient process execution may now be examined. In a high-temperature vacuum furnace operation, the quantity of gas that is to be pumped off can influence the choice of the vacuum process. When the reduction of niobium pentoxide with either carbon or niobium carbide is attempted according to the following overall equations ... 

Samples are oven dried at 100°C after which they are weighed in order to measure water content. TC and TS are measured by introducing dried samples to the Carbon Sulfur (CS) automatic analyzer (Eltra CS-800) instrument. Subsequently, 2g of each sample is introduced in preweighed high temperature porcelain crucibles and is introduced to a high temperature muffle furnace for the removal of carbonates at 900C. Samples are then introduced to the CS automatic analyzer for measurement of organic residual carbon. 

Coke. Metallurgical coke is obtained by high-temperature carbonization of coal. It is a poorly graphitized form of carbon it is mainly used in blast furnace for steel manufacture (see Iron, 5.10). 

The CMS membranes are prepared by carbonizing (under pyrolysing conditions) the precursor membranes in a high temperature tube furnace, as shown in Figure 15.4. The step-by-step method (several dwells) most commonly used as the protocol for the carbonization process is described elsewhere. Many researchers report different carbonization conditions in their research works illustrating very well that each precursor will need different protocols in order to be pore tailored for specific applications. " The carbonization process is the most important step for fabrication of CMS membranes and is used to tailor the pore size and structure of the carbon membranes. Therefore, how to control the carbonization conditions is crucial for the resulting CMS membrane performance. Su and Lua reported that the statistical 2" factorial... 

This reaction equilibrium is favored at low temperatures, and most of the carbon monoxide is converted to carbon dioxide in a high-temperature shift furnace (HTS) operating at 350 to 450°C. This step is followed by low-temperature conversion of the remaining carbon monoxide to carbon dioxide in a low-temperature shift converter (LTS) after cooling. The usual catalyst for the low-temperature shift converter is copper oxide supported on zinc oxide and alumina. 

Pure metals are separated from ores primarily with heat. This is done in a high-temperature blast furnace. By adding reactants like limestone and coke (a carbon residue) to break hydrogen bonding and release the bonded metals, individual metals can be collected. Figure 12.1 shows a simple blast furnace. 

This is the basis of the extraction of iron on an industrial scale in a blast furnace. Carbon monoxide is a more powerful reducing agent at low temperatures than carbon, but at high temperatures carbon is the more powerful reducing agent. 

A fuel specimen of 1 to 10 pL is injected by syringe into a 950 to 13(K) C high-temperature tube furnace that contains metallized carbon. Oxygen-containing compounds... 

The absorption cell. A few elements, such as the alkali metals, have appreciable vapour pressures at easily attainable temperatures and may be studied by using sealed absorption cells of glass or quartz. However, for astro-physical applications there is considerable interest in the elements of the first transition series, e.g. manganese, iron, cobalt, and nickel. For these elem.ents suitable vapour pressures are only attained at temperatures above 2000 K and the standard technique involves the use of a carbon furnace introduced by King (1922) as the absorption cell. At high temperatures, carbon is one of the few suitable materials since it reacts only slowly with most metals and has a low vapour pressure. 

High process temperatures generally not achievable by other means are possible when induction heating of a graphite susceptor is combined with the use of low conductivity high temperature insulation such as flake carbon interposed between the coil and the susceptor. Temperatures of 3000°C are routine for both batch or continuous production. Processes include purification, graphitization, chemical vapor deposition, or carbon vapor deposition to produce components for the aircraft and defense industry. Figure 7 illustrates a furnace suitable for the production of aerospace brake components in a batch operation. 

Chrome—nickel alloy heating elements that commonly ate used in low temperature furnaces are not suitable above the very low end of the range. Elements commonly used as resistors are either silicon carbide, carbon, or high temperature metals, eg, molybdenum and tungsten. The latter impose stringent limitations on the atmosphere that must be maintained around the heating elements to prevent rapid element failure (3), or the furnace should be designed to allow easy, periodic replacement. 

The furnace is constmcted with a steel shell lined with high temperature refractory (see Refractories). Refractory type and thickness are deterrnined by the particular need. Where combustion products include corrosive gases such as sulfur dioxide or hydrogen chloride, furnace shell temperatures are maintained above about 150—180°C to prevent condensation and corrosion on the inside carbon steel surfaces. Where corrosive gases are not present, insulation is sized to maintain a shell temperature below 60°C to protect personnel. 

Some phosphides, such as titanium phosphide [12037-65-9] TiP, can be prepared bypassing phosphine over the metal or its haUde. Reaction of phosphine with heavy metal salt solutions often yields phosphines that may contain unsubstituted hydrogens. Phosphides may also be prepared by reducing phosphoms-containing salts with hydrogen, carbon, etc, at high temperatures, the main example of which is the by-product formation of ferrophosphoms in the electric furnace process for elemental phosphoms. Phosphoms-rich phosphides such as vanadium diphosphide [12037-77-3] may be converted to lower phosphides, eg, vanadium phosphide [12066-53-4] by thermal treatment. 

A number of high temperature processes for the production of titanium carbide from ores have been reported (28,29). The aim is to manufacture a titanium carbide that can subsequently be chlorinated to yield titanium tetrachloride. In one process, a titanium-bearing ore is mixed with an alkah-metal chloride and carbonaceous material and heated to 2000°C to yield, ultimately, a highly pure TiC (28). Production of titanium carbide from ores, eg, ilmenite [12168-52-4], EeTiO, and perovskite [12194-71 -7], CaTiO, has been described (30). A mixture of perovskite and carbon was heated in an arc furnace at ca 2100°C, ground, and then leached with water to decompose the calcium carbide to acetjdene. The TiC was then separated from the aqueous slurry by elutriation. Approximately 72% of the titanium was recovered as the purified product. In the case of ilmenite, it was necessary to reduce the ilmenite carbothermaHy in the presence of lime at ca 1260°C. Molten iron was separated and the remaining CaTiO was then processed as perovskite. 

The principles pertaining to carbon blast furnace hearths apply as well to submerged-arc furnace hearths. In some processes, such as in d-c arc furnaces, the electrical conductance of carbon is a most important factor. The long life of carbon linings in these appHcations is attributable to carbon s exceptional resistance to corrosive slags and metals at very high temperatures. 

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