Steam formation

The activity loss measured here is caused by recrystallizations. This was demonstrated by using scanning electron microscopy to determine nickel crystallite size in the same catalyst samples. These tests revealed that the catalyst used in demonstration plants has only a slight tendency to recrystallize or sinter after steam formation and loss of starting activity. 

For the smelt-water case. Nelson suggested the water in contact with the very hot smelt was, initially, separated by a thin vapor film. Either because the smelt cooled—or because of some outside disturbance— there was a collapse of the vapor film to allow direct liquid-liquid contact. The water was then heated to the superheat-limit temperature and underwent homogeneous nucleation with an explosive formation of vapor. The localized shocks either led to other superheat-limit explosions elsewhere in the smelt-water mass or caused intense local mixing of the smelt and water to allow steam formation by normal heat transfer modes. 

No explosions resulted if the water depth were less than about 5 cm. Splatter and steam formation were observed instead. 

Aqueous phase reforming of glycerol in several studies by Dumesic and co-workers has been reported [270, 275, 277, 282, 289, 292, 294, 319]. The first catalysts that they reported were platinum-based materials which operate at relatively moderate temperatures (220-280 °C) and pressures that prevent steam formation. Catalyst performances are stable for a long period. The gas stream contains low levels of CO, while the major reaction intermediates detected in the liquid phase include ethanol, 1,2-pro-panediol, methanol, 1-propanol, propionic acid, acetone, propionaldehyde and lactic acid. Novel tin-promoted Raney nickel catalysts were subsequently developed. The catalytic performance of these non-precious metal catalysts is comparable to that of more costly platinum-based systems for the production of hydrogen from glycerol. 

Fig. 13. Quartz ai>d amorphous silica solubility vs. temperature along the vapour saturation curve. The dashed lines show the silica concentration in water initially in equilibrium with quartz during adiabatic boiling to 100 C and subsequent cooling. The increase in aqueous silica concentrations during boiling is the consequence of steam formation. Amorphous silica saturation (shown by the dots) is attained at 188 C in the case of the 300 C aquifer water, but at 94 C in the case of the 200 C aquircr water. It was assumed that the pH of the water is not raised sufficiently during boiling to cause significant ionization of the aqueous silica. If some ionization had occurred, amorphous silica saturation would be reached at lower temperatures than those indicated in Fig. 13.

At some inlet air temperature, however, internal steam formation will cause "ballooning" of the drying droplet. Ballooning results in a very high surface to volume ratio for the powder and, therefore, greater flavor losses. Apparently 280 C is not adequate to produce ballooning. 

In the opinion of most investigators, in connection with the prevalent chloride-sulfuric acid composition of volcanogenic waters iron is transported in them mainly in the form of hydrochloric and sulfuric acid complexes. Only in deep hot springs containing a large amount of COj does iron presumably migrate in the form of bicarbonate complexes. Evidence for this is the formation of iron-bearing carbonate (ankerite) in zones below the limit of steam formation, while chiefly carbonates without iron (cdlcite) are formed in the near-surface zone. 

Decrepitation is a process in which a crystalline material containing occluded water suddenly explodes during heating because of a buildup in internal pressure resulting from steam formation. 

Circular volcano -shaped deposits can occur as a result of bubble formation in connection with boiling heat transfer and these deposits can act as nucleation points for further evaporation and deposition. As the process of deposition continues, the surface conditions will be modified and the scale may contain fissures, so that steam formation may occur within the deposit. The process is generally referred to as wick boiling that may influence the mechanism of heat transfer. The process of scale formation under boiling conditions is complex. 

In the 1980s, more attention has been increasingly paid to improving the physical properties, such as mechanical strength, stiffness, resistance to thermal deformation, and so forth, of the fiber-plastic composite products. It was recognized that moisture in cellulosic fiber leads to steam formation in the compounder and the extruder, increases porosity of the final product and decreases its density, accelerates the oxidation of the hot melt during processing, and makes the final product weaker and less durable. 

The proiecticn of fine zirconium or titanium powders by moistening with water requires the presence of at least 25% of water. If less water is present, the metal might not only be ignitible but the combustion may be extremely violent because of steam formation and reaction of metal and water. Actual use of water in the form of hydrated salts has been claimed for pyrotechnic purposes. ... 

If the average particle size is at least 10 /u, the hazard in handling zirconium in the dry state is regarded as small. The fine powders are shipped, and wherever possible, processed under water. If, however, the amount of water present is small (less than 20%), any accidental ignition has been said to have more serious consequences than results from burning in a dry state because of the violently explosive action caused by steam formation and reaction with the water as the oxidizer. 

When applying fabric filters, condensation problems need to be prevented. Condensation may cause a deposition of dust, clogging and/or a tearing of the filter. The addition of cooling water to the sand needs to be done in a controlled way in order to minimise steam formation. The dew point of the airflow may be increased through heating with gas burners. 

Case 4 Physical Wear, Some Atmospheres, Liquid Slag or Scale, Leaking Cooling Water These also can be bad for refractories. After installation of castable, rammed, and gunned refractories, a long, slow dryout period is necessary to prevent spalling or explosions from steam formation within the refractories. 

A3. The difference is many more hours for dryout than for warm-up because dryout must slowly cause moisture to migrate to the surface and evaporate without sudden steam formation below the refractory surface, which could cause small explosions that can blow off the surface. 

Keiser C, Wyss P, Rossi RM. Analysis of steam formation and migration in firefighters protective clothing using X-ray radiography. Int J Occup Saf Ergon 2010 16(2) 217-29. 

Withdrawing a control rod reduces the neutron absorption and increases core reactivity. Reactor power then increases until the increased steam formation just balances the change in reactivity caused by the rod withdrawal. The increase in boiling rate ends to raise reactor pressure, causing the initial pressure regulator fo open the turbine admission valves sufficiently to maintain a constant pressure. When a control rod is inserted, the converse effect occurs. 

Figure 7.6. Release of I, Cs, Ag, and In in steam formation of Agl from initially present Csl...

Mg,Fe,AI)3(AI,Si),0, (0H),. nH20. Heating to about 300 C causes the mineral to exfoliate and expand due to the steam formation from water between the layers. Vermiculite is used in light concrete and as insulating material. 

Figure 11.15 shows a flowsheet of the circulation process of the oxidation of natural gas in a three-section reactor with a heat removal between the oxidation stages by means of a steam formation. The resultant steam is used to heat the distillation columns, whereas its excess can be offered to an external consumer. The discharge gases can also be used for energy production. 

Kutepov, A. M. et al. Hydrodynamics and heat exchange at steam formation. M. Higher school. 1977. 

Kutepov, A. M. Hydrodynamics and Heat Exchange at Steam Formation. Higher school 1977. 

The system is comprised of three water circuits. The first is pressurized water that flows through the reactor core. The water picks up heat from the nuclear fuel and its temperature rises. The pressure in this loop is high enough to prevent steam formation. 

Their actions further reduced core cooling and increased steam formation. 

Griffin [1, 2] was the first to use starch as filler in synthetic plastics. Polyethylene films containing starch and other items based on this technology are available on the market. In this technology starch addition is restricted to a maximum of 10% by weight. The starch has to be dried to under 1% moisture to avoid steam formation during extrusion processes, and the starch granules are surface-treated (with silanes, for example) to increase the compatibility of the hydrophilic starch with the hydrophobic plastic matrix. 

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