Steam acceleration

Reaction turbine design also makes use of steam jets (which are produced by steam flowing across static vanes), although the turbine has rotor discs that incorporate movable blades rather than buckets. The design utilizes the reactive force produced by steam accelerating through a nozzle (created by the combination of a stationary vane and a moving blade) to rotate the shaft. 

Morita et al. [222] compared bismuth molybdate (1/1) with U—Sb oxides (1 2) at 400°C in a continuous flow system. The methacrolein selectivity for U—Sb is significantly higher than in the case of Bi—Mo (see Table 20). These values increase slightly with increasing conversion of isobutene. Isobutene itself retards the oxidation. In contrast to the pro-pene oxidation, addition of steam accelerates the reaction up to a factor 4 with U—Sb and to a smaller degree with Bi—Mo. With the first catalyst, the activation energy decreases from 27 to 18 kcal mol-1 (0.23 atm steam). U—Sb seems to be less stable than Bi—Mo, but steam has a beneficial effect here too (Table 20). 

The motive steam accelerates to such a great velocity that it can exceed the speed of sound (that is, exceed sonic velocity). This tremendous increase in velocity of the steam represents a tremendous increase in the kinetic energy of the steam. The source of this kinetic energy is the pressure of the steam. 

Furthermore, the driving force for the phosphorus enrichment on the CV0)2P20 surface is not clear yet. In the study of Arnold and Sundaresan [10] on the influence of water on the catalytic properties of a non-equihbrated VPO catalyst the hydrophilicity of phosphorus was supposed to be a reason for it but this assumption has not yet been proven. It was found that the addition of water vapour to the feed lowers the overall activity towards butane oxidation and enhances the selectivity towards partial oxidation products. The addition of steam accelerated the formation of (V0)2P207 in the solid structure which originally contained approximately equal amounts of a-V0P04 and (V0)2P207 crystalline phases [10]. However, the (V0)2P207 phase is the only crystalline phase in an equilibrated VPO catalyst with a P V ratio of 1.1 as used in [10]. Recently Cavani and Trifiro emphasized [2] that only a study of equilibrated catalysts provides precise information on the relationships between activity and selectivity and the structural properties of vanadylpyrophosphate catalysts. 

The necessary presence of steam is disadvantageous, in that steam accelerates many solid state reactions [21]. In the presence of steam, the general rule that sintering becomes significant at ca 1/3 to 1/2 of the melting point of the solid [21] may indicate only an upper limit for the appearance of sintering. 

A comparison of Filtrol sintering curves obtained in vacuum and in steam is available in Fig. 22. Area values are plotted against temperature of treatment. It is apparent that steam accelerates the sintering... 

Minimum creep rate was reached in all tests. In air, creep strain rates were below 10 s at 1000 and 1100 °C, and ranged from 1.5 x 10 to 6.0 x 10 s at 1200 °C. The presence of steam has negligible effect on creep strain rates at 1000 °C. The presence of steam accelerates creep rates of N720/A by two orders of magnitude at 1100 °C. 

The cause of water and steam hammer is the same sudden deceleration of water in an enclosed system. In the examples cited above, the rapid and localized condensation of steam accelerates a slug of steam condensate upstream by producing a localized area of low downstream pressure. The high-velocity water slams into a piping elbow or an exchanger channel head and produces the clanging sound associated with water hammer. 

Water as an impurity accelerates the oxidation rate. Figure 4 compares growth curves for Si02 under dry and steam conditions. Halogens can also be introduced to the oxidation process, thereby reducing sodium ion contamination. This improves dielectric breakdown strength, and reduces interface trap density (15). 

Silica and Alumina. The manufacture of Pordand cement is predicated on the reaction of lime with siUca and alumina to form tricalcium sihcate [12168-85-3] and aluminate. However, under certain ambient conditions of compaction with sustained optimum moisture content, lime reacts very slowly to form complex mono- and dicalcium siUcates, ie, cementitious compounds (9,10). If such a moist, compact mixture of lime and siUca is subjected to steam and pressure in an autoclave, the lime—silica reaction is greatiy accelerated, and when sand and aggregate is added, materials of concrete-like hardness are produced. Limestone does not react with siUca and alumina under any circumstances, unless it is first calcined to lime, as in the case of hydrauhc lime or cement manufacture. 

Monobutylamines are easily soluble in water and hydrocarbons and can generally be steam distilled. These properties lead to uses in soaps for water and oil emulsions, and as corrosion inhibitors in steam boiler appHcations (see Corrosion and corrosion inhibitors Emulsions). Morpholine is also extensively used as a corrosion inhibitor in steam boiler systems. In addition, it is widely used as an intermediate in the production of delayed-action mbber accelerators. 

Special drying methods, such as superheated steam, solvent, vacuum, infrared radiation, and high frequency dielectric and microwave heating, are occasionally employed when accelerated drying is desired and the species being dried can withstand severe conditions without damage. None of these methods is of significant commercial importance. 

In most existing styrene processes, the catalyst is loaded into large, radial flow reactors, which are operated adiabaticaHy at low pressure and temperatures near 600°C. Heat is suppHed by superheated steam. During start-up, dehydrogenation begins slowly and accelerates as the Fe (HI) is reduced to Fe (II,III). The catalyst, which was red in color when fresh, turns to the characteristic black color of Fe O. ... 

Eor printing on polyester, the fixation conditions are more rigorous than on other disperse dyeable fibers, owing to the slower diffusion of disperse dyes in polyester. Eor continuous fixation the prints are exposed at atmospheric pressure to superheated steam of 170—180°C for 6—8 min. A carrier may be added to the print paste for accelerated and fliU fixation. Dry-heat fixation conditions of 170—215°C for 1—8 min are less popular for printed fabrics, but are sometimes employed because of lack of other equipment. 

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