Linings in furnaces

Portland cement is such an alternative. Formed by chemical reactions, it is an inexpensive product and is used in large volumes. There is a wide gap between the attributes of ceramics and Portland cement, however. Ceramics exhibit superior mechanical properties compared to cements. Ceramics are far more stable in acidic and high temperature environments, but cements are not. Thermal stability of cements is poor, while ceramics are refractory and are used at very high temperature, such as linings in furnaces. Cements are porous, but ceramics can be very dense. 

The major application for magnesia is as a refractory lining in furnaces. In lesser quantities, it is made into a well-known milky solution and ingested. It is also used to manufacture other ceramics such as chrome-free spinels. Nonchrome spinel is not available in nature on an industrial scale. At Asahi Glass, spinel is produced by electrofusing magnesia with alumina. 

Most of the MgO is used as a refractory lining in furnaces, to make a milky solution for ingestion, and for the manufacture of nonchrome spinel. 

A furnace is a device (enclosure) for generating controlled heat with the objective of performing work. In fossil-fuel furnaces, the work appHcation may be direct (eg, rotary kilns) or indirect (eg, plants for electric power generation). The furnace chamber is either cooled (waterwaH enclosure) or not cooled (refractory lining). In this article, furnaces related to metallurgy such as blast furnaces ate excluded because they ate coveted under associated topics (see... 

Fresh reducing gas is generated by reforming natural gas with steam. The natural gas is heated in a recuperator, desulfurized to less than 1 ppm sulfur, mixed with superheated steam, further preheated to 620°C in another recuperator, then reformed in alloy tubes filled with nickel-based catalyst at a temperature of 830°C. The reformed gas is quenched to remove water vapor, mixed with clean recycled top gas from the shaft furnace, reheated to 925°C in an indirect fired heater, and injected into the shaft furnace. For high (above 92%) metallization a CO2 removal unit is added in the top gas recycle line in order to upgrade the quaUty of the recycled top gas and reducing gas. 

Dead-burned dolomite is a specially sintered or double-burned form of dolomitic quicklime which is further stabilized by the addition of iron oxides. Historically, it was used as a refractory for lining steel furnaces, particularly open hearths, but as of this writing is used primarily in making dolomite refractory brick (see Refractories). 

Equipment. The standard equipment in magnesium foundries consists of large stationary brick-lined reverbatory furnaces which can hold up to 10—15 t of molten magnesium. Reverbatory furnaces are furnaces in which heat is suppHed by burning a fuel in a space between the reactants and the... 

As of the mid-1990s all commercial phosphoms is manufactured at a few sites around the world. Significant production occurs in Idaho and Montana in the United States, in the Netherlands, in Kazakstan, and in China smaller production occurs in Prance, Russia, and India. A large amount of furnace capacity has been shut down worldwide because of cost pressure from electric power costs, phosphate derived from purified wet acid, and detergent phosphate bans legislated in the Western World. However, as of late 1995, additional production is stiU being brought on line in China. 

Schemes to control the outlet temperature of a process furnace by adjusting the fuel gas flow are shown in Figure 13. In the scheme without cascade control (Fig. 13a), if a disturbance has occurred in the fuel gas supply pressure, a disturbance occurs in the fuel gas flow rate, hence, in the energy transferred to the process fluid and eventually to the process fluid furnace outlet temperature. At that point, the outlet temperature controller senses the deviation from setpoint and adjusts the valve in the fuel gas line. In the meantime, other disturbances may have occurred in the fuel gas pressure, etc. In the cascade control strategy (Fig. 13b), when the fuel gas pressure is disturbed, it causes the fuel gas flow rate to be disturbed. The secondary controller, ie, the fuel gas flow controller, immediately senses the deviation and adjusts the valve in the fuel gas line to maintain the set fuel gas rate. If the fuel gas flow controller is well tuned, the furnace outlet temperature experiences only a small disturbance owing to a fuel gas supply pressure disturbance.

RCF is sold in a variety of forms, such as loose fiber, blanket, boards, modules, cloth, cements, putties, paper, coatings, felt, vacuum-formed shapes, rope, braid, tape, and textiles. The products are principally used for industrial appHcations as insulation in furnaces, heaters, kiln linings, furnace doors, metal launders, tank car insulation, and other uses up to 1400°C. RCF-consuming industries include ferrous and nonferrous metals, petrochemical, ceramic, glass, chemical, fertiH2er, transportation, constmction, and power generation/incineration. Some newer uses include commercial fire protection and appHcations in aerospace, eg, heat shields and automotive, eg, catalytic converters, metal reinforcement, heat shields, brake pads, and airbags. 

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. 

Where is naphthenic acid corrosion found Naphthenic acid corrosion occurs primarily in crude and vacuum distillation units, and less frequently in thermal and catalytic cracking operations. It usually occurs in furnace coils, transfer lines, vacuum columns and their overhead condensers, sidestream coolers, and pumps. 

The control valve in the delivery line to the furnace was also closed. Unfortunately, this valve was bypassed by the line through the heat exchanger. In the heat of the moment, no one remembered to close the valve in the bypass line. In addition, the check (nonreturn) valve did not hold. The return flow of oil from the furnace was stopped by closing a hand valve next to the furnace, which was about 30 m from the fire. Afterward, another EIV was installed in the pump delivery line. 

The first step in the production of synthesis gas is to treat natural gas to remove hydrogen sulfide. The purified gas is then mixed with steam and introduced to the first reactor (primary reformer). The reactor is constructed from vertical stainless steel tubes lined in a refractory furnace. The steam to natural gas ratio varies from 4-5 depending on natural gas composition (natural gas may contain ethane and heavier hydrocarbons) and the pressure used. 

The main advantages of electrothermal atomisers are that (a) very small samples (as low as 0.5 pL) can be analysed (b) often very little or no sample preparation is needed, in fact certain solid samples can be analysed without prior dissolution (c) there is enhanced sensitivity, particularly with elements with a short-wavelength resonance line in practice there is an improvement of between 102- and 103-fold in the detection limits for furnace AAS compared with flame AAS. 

Electrical conductivity The electrical conductivity of refractories is important when they are used in electric furnaces. Except for graphite and metals, all other refractories are poor conductors of electricity. Graphite is a highly refractory material, and is used for electrodes and furnace linings in all high-temperature electric furnaces. Metals are not important as refractories in electric furnaces, but copper wires or busbars, for example, are utilized to carry current to the graphite electrodes. 

As the assembled molds are being placed on the pour-off lines, the scrap metal is melted in the furnace. Molten metal from the furnace is brought to the molds on the pouring lines in a refractory lined pouring ladle. Once poured, the molds are allowed to cool before being sent to the shakeout processes. At the shakeout, the castings are separated from the sand mold. The sand is sent to a reclamation system so that it can be reused in the molding process. 

Duplex (1) An integrated steelmaking process in which iron is converted to steel in a Bessemer furnace with a basic lining, and the molten product is transferred to a basic lined arc furnace in which the remaining impurities are oxidized. Developed in Germany and widely used there and elsewhere around 1900. 

Pyral A process for destroying toxic waste oiganochlorine compounds. The wastes are mixed with carbon and sodium carbonate and injected into a graphite-lined arc furnace. Metallic sodium, formed by reduction of the sodium carbonate by the carbon, attacks the chlorinated organic compounds, forming sodium chloride. Developed by Hydro-Quebec in the late 1980s but not yet commercialized. 

In principle two similar crucibles containing respectively a sample of the alloy under investigation and an inert reference specimen are cooled (or heated) together in a furnace. By means of conveniently inserted thermocouples it is possible to follow (1) the continuous reference temperature trend of the reference specimen, (2) the temperature trend of the specimen under examination and (3) the temperature difference (A 7 ) between the two. If, at a certain temperature, there is a change in the structure of the sample (that is, if a boundary line in the corresponding phase diagram is crossed), a variation in the slope of the temperature vs. time curve is recorded. As a consequence the A7 vs. time curve (or vs. temperature) shows a deviation from the baseline. The temperatures at which such deviations are observed are used to build the phase diagram. 

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