Steam superheated

This is an endothermic reaction accompanied by an increase in the number of moles. High conversion is favored by high temperature and low pressure. The reduction in pressure is achieved in practice by the use of superheated steam as a diluent and by operating the reactor below atmospheric pressure. The steam in this case fulfills a dual purpose by also providing heat for the reaction. 

Fats are hydrolysed to glycerol and fatty acids by boiling with acids and alkalis, by superheated steam and by the action of lipases. If alkalis are used for hydrolysis, the fatty acids combine with the alkalis to form soaps. Alkaline hydrolysis is therefore sometimes called saponification. 

Two large Superheated Steam outlet headers with potential stmctural integrity problems, belonging to 2 600 MW multifuel ENEL power Units, have been submitted to continuous AE... 

Appreciable quantities are also obtained as a by-product in the manufacture of hydrogen from naphtha-gaseous hydrocarbons. In this process the gaseous hydrocarbon and superheated steam under a pressure of about 10 atmospheres and at a temperature of 1000 K are passed over a nickel-chromium catalyst. Carbon monoxide and hydrogen are produced ... 

The effect of superheated steam may be illustrated by reference to baizaldehyde, which boils at 178° at 760 mm. It distils with steam at 97-9° (Pj = 703-5 mm. and pg = 56-5 mm.) and the distillate contains 32-1 per cent, of benzaldehyde by weight. If one employs steam superheated to 133°, the vapour pressure of benzaldehyde (extrapolated from the boUing point - pressure curve) is 220 mm. hence pj = 540 (water), Pg = 220 (benzaldehyde), and... 

In practice superheated steam is generally employed for substances with a low vapour pressure (< 5-1 mm.) at 100°. Thus in the recovery of the products of nitration or aromatic compounds, the ortho derivative e.g., o-nitrophenol) can be removed by ordinary steam distillation the... 

The theory of, and the apparatus for, distillation with superheated steam are described in Section 1,7. 

I) The a-naplithylamine may also be isolated directly from the neutralised reaction mixture by distillation with superheated steam (Section 1,6). 

The use of dry, superheated steam, although not es.sential, considerably reduces the time of distillation. 

Disposal. Fluorine can be disposed of by conversion to gaseous perfluorocarbons or fluoride salts. Because of the long atmospheric lifetimes of gaseous perfluorocarbons (see Atmospheric models), disposal by conversion to fluoride salts is preferred. The following methods are recommended scmbbing with caustic solutions (115,116) reaction with soHd disposal agents such as alumina, limestone, lime, and soda lime (117,118) and reaction with superheated steam (119). Scmbbing with caustic solution and, for dilute streams, reaction with limestone, are practiced on an industrial scale. 

The unit Kureha operated at Nakoso to process 120,000 metric tons per year of naphtha produces a mix of acetylene and ethylene at a 1 1 ratio. Kureha s development work was directed toward producing ethylene from cmde oil. Their work showed that at extreme operating conditions, 2000°C and short residence time, appreciable acetylene production was possible. In the process, cmde oil or naphtha is sprayed with superheated steam into the specially designed reactor. The steam is superheated to 2000°C in refractory lined, pebble bed regenerative-type heaters. A pair of the heaters are used with countercurrent flows of combustion gas and steam to alternately heat the refractory and produce the superheated steam. In addition to the acetylene and ethylene products, the process produces a variety of by-products including pitch, tars, and oils rich in naphthalene. One of the important attributes of this type of reactor is its abiUty to produce variable quantities of ethylene as a coproduct by dropping the reaction temperature (20—22). 

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. 

Steam treatment imparts increased corrosion resistance for ferrous P/M parts. The parts are heated to 400—600°C and then exposed to superheated steam. After cooling, the parts are usually oil dipped to further increase corrosion and wear resistance, and to enhance appearance (see Corrosion and CORROSION control). Heat treated parts are seldom steam treated because annealing reduces hardness and tensile strength. 

The objective in packaging cool sterilized products is to maintain the product under aseptic conditions, to sterilize the container and its Hd, and to place the product into the container and seal it without contamination. Contamination of the head space between the product and closure is avoided by the use of superheated steam, maintaining a high internal pressure, spraying the container surface with a bactericide such as chlorine, irradiation with a bactericidal lamp, or filling the space with an inert sterile gas such as nitrogen. 

In the catalytic steam reforming of natural gas (see Fig. 2), the hydrocarbon stream, principally methane, is desulfurized and, through the use of superheated steam (qv), contacts a nickel catalyst in the primary reformer at ca 3.04 MPa (30 atm) pressure and 800°C to convert methane to H2. 

The superheated steam generated in the superheater section is coHected in a header pipe that leads to the plant s high pressure steam turbine. The steam turbine s rotor consists of consecutive sets of large, curved, steel aHoy disks, each of which anchors a row of precision-cast turbine blades, also caHed buckets, which protmde tangentiaHy from the shaft and impart rotation to the shaft when impacted by jets of high pressure steam. Rows of stationary blades are anchored to the steam turbine s outer sheH and are located between the rows of moving rotor blades. 

Sodium Chloride. Sodium chloride, a corrodent of many materials, is the archetype contaminant and has been studied more than other salts. The solubiUty of sodium chloride in superheated steam is shown at the conditions of a typical steam turbine expansion in Figure 14. The solubiUties were measured in the region of higher solubiUty (9). As the steam expands, sodium chloride becomes considerably less soluble. The solubiUty, S, in parts per biUion (ppb) can be represented by equation 3 ... 

A good summary of the behavior of steels in high temperature steam is available (45). Calculated scale thickness for 10 years of exposure of ferritic steels in 593°C and 13.8 MPa (2000 psi) superheated steam is about 0.64 mm for 5 Cr—0.5 Mo steels, and 1 mm for 2.25 Cr—1 Mo steels. Steam pressure does not seem to have much influence. The steels form duplex layer scales of a uniform thickness. Scales on austenitic steels in the same test also form two layers but were irregular. Generally, the higher the alloy content, the thinner the oxide scale. Excessively thick oxide scale can exfoHate and be prone to under-the-scale concentration of corrodents and corrosion. ExfoHated scale can cause soHd particle erosion of the downstream equipment and clogging. Thick scale on boiler tubes impairs heat transfer and causes an increase in metal temperature. 

Superheated steam results when steam is heated to a temperature higher than that which would produce saturated steam. The equiUbrium between hquid and vapor is destroyed, and the steam behaves as a gas. It loses its abiUty to condense into moisture when in contact with the cooler surface of the article to be sterilized. This process resembles dry-heat sterilization more than steam sterilization and, under ordinary time—temperature conditions for steam sterilization, does not produce stetihty. 

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