Steam partial pressure, effect

Because water will be present in this system, and is assumed immiscible with the other components, it will exert its own vapor pressure. This situation is similar to many systems where the liquid to be flashed enters below its dew point, and hence requires the use of steam to heat (sensible + latent) as well as steam for the partial pressure effect... 

Laboratory steam deactivations represent a significant compromise in the effort to simulate equilibrium catalyst. Since hydrothermal deactivation of FCC catalysts is not rapid in commercial practice, deactivation of the fresh catalyst in the laboratory requires accelerated techniques. The associated temperatures and steam partial pressures are often in substantial excess of those encountered in commercial units. In some instances, the effect of contaminant metals is measured by an independent test not affiliated with steam deactivation. In subsequent yields testing, interactions between different modes of deactivation may be overlooked. Finally, single mode deactivation procedures can not reproduce the complex profile of ages and levels of deactivation present in equilibrium catalyst. 

The effect of increasing H2O/CH4 ratio is to move the point of maximum rate towards higher values of steam partial pressure. Increasing the partial pressures of the other products has a similar effect. 

It is of interest and practical importance to show the situation where different feeds are introduced to the model with different steam partial pressures while the feed partial pressures of the other components are kept constant, which means of course, a change of the total pressure. The steam reformer tube chosen for simulation is 5 m long to illustrate the kinetic effects rather than the thermodynamic equilibrium effect since the assumption of constant temperature along the tube causes a fast approach to thermodynamic equilibrium of the mixture. 

Top Temperature. The temperature at the top of the tower must be just high enough to allow complete vaporization of the overhead product. A lower temperature will condense a part of the desired overhead product and incorporate it in the first side-draw product, and a higher temperature will cause the inclusion of high-boiling materials which are not desired in the overhead product. If the top of the tower is at atmospheric pressure and no steam is used, the 100 per cent point of the equilibrium vaporization curve of the overhead product is the top temperature. Such a rimple case is seldom encountered, and hence the top temperature at 760 mm must be corrected for the tower pressure and for the partial-pressure effect of steam or gas. 

In the condensation zone, the temperature may be computed with accuracy by means of the equilibrium condensation curve (Examples 4-5 and 4-6) of the oil vapor, corrected for the total pressure within the condenser and for the partial-pressure effect of the steam. In some... 

In this pyrolysis, sub atmospheric partial pressures are achieved by employing a diluent such as steam. Because of the corrosive nature of the acids (HE and HCl) formed, the reactor design should include a platinum-lined tubular reactor made of nickel to allow atmospheric pressure reactions to be mn in the presence of a diluent. Because the pyrolysate contains numerous by-products that adversely affect polymerization, the TFE must be purified. Refinement of TFE is an extremely complex process, which contributes to the high cost of the monomer. Inhibitors are added to the purified monomer to avoid polymerization during storage terpenes such as t7-limonene and terpene B are effective (10). 

The principle of Le Chatelier shows that when the pressure applied to a gaseous system is increased, dre equilibrium composition will chairge in order to reduce tire number of gaseous molecules. In the case of tire steam reforming of metlrane, the partial pressures of methane and steam will increase as the pressure is increased. In the water-gas reaction, where tire number of molecules is the same on both sides of the equation, the effect of increasing... 

Open or direct injection of steam into a distillation system at the bottom may be used to heat the mixture as well as to reduce the effective partial pressure of the other materials. In general, if steam is used to replace a reboiler, one tray is added to replace the reboiler stage, and from one-third to one or more trays may be needed to offset the... 

The presence of non-condensable gases in steam systems (e.g. air and CO2) will reduce the partial pressure of the steam, and hence its temperature, thus affecting the output of the appliance. A further adverse effect is the presence of a non-condensable gas at the inside surface of a heat emitter. These impede condensation and, hence, heat output. It is therefore imperative that suitable means are provided to prevent formation of CO2 and to evacuate all gases from the system. 

In a natural gas fueled PAFC, water is condensed out of the fuel stream going to the fuel cell to increase the partial pressure of hydrogen. In a coal gasification MCFC, water often is added to the fuel stream prior to the fuel cell to prevent soot formation. The addition of excess steam not only prevents the soot formation, but also causes a voltage drop of approximately 2 mV per each percentage point increase in steam content (45). The use of zinc ferrite hot gas cleanup can aggravate the soot formation problem because of the catalytic effect of the sorbent on carbon formation, and requires even higher moisture levels (46). 

The moistnre content or hnmidity of air has an important effect on the properties of the gaseons mixtnre. Steam in air at any relative hnmidity less than 100 percent mnst exist in a superheated condition. The satnration temperatnre corresponding to the actual partial pressure of the steam in air is called the dew point. This term arose from the fact that when air at less than 100 percent relative hnmidity is cooled to the temperatnre at which it becomes satnrated, the air has reached the minimnm temperatnre to which it can be cooled withont precipitation of the moistnre (dew). Dew point can also be defined as that temperatnre at which the weight of steam associated with a certain weight of dry air is adeqnate to saturate that weight of air. 

The first effect is illustrated when we blow across a bowl of hot soup, to cool the soup. Our breath displaces the steam vapors that are on top of the soup. This encourages more molecules of steam vapors to escape from the soup that is, the vapor pressure of the steam above the liquid soup is diminished, because steam is pushed out of the soup bowl with air. The correct technical way to express this idea is to say, The partial pressure of the steam, in equilibrium with the soup, is diminished. But our breath itself does not remove heat from the soup. The evaporation of steam from the soup, promoted by our breath, takes heat. Converting one pound of soup to one pound of steam requires 1000 Btu. This heat of evaporation comes not from our breath, but from the soup itself. The correct technical way to express this second effect is, The sensible-heat content of the soup is converted to latent heat of evaporation. ... 

Increasing recycle flow reduces the inlet, peak, and exit temperatures of the reactor. Pressure builds until the higher partial pressures of the reactants compensate for the lower specific reaction rate because of the lower temperatures. The higher velocities in the reactor tubes also increase the heat transfer coefficient, which means that the heat transfer rate does not decrease directly with the decrease in reactor temperatures. Remember, steam pressure (and temperature) is held constant in the openloop run. The net result of the various effects is that, with the fresh feed flowrates fixed, the reactor comes to a new steady-state condition, which has lower reactor temperatures but higher pressure. The net reaction rate and the heat transfer in the reactor remain the same. The... 

Figure 5 shows the boiler feedwater requirement for the waste heat boiler according to alternative I, and for alternative II, the quench water requirement, i.e. the amount of water which evaporates in the quench. The partial pressure of the water, which increases as a function of the total pressure, results in a corresponding increase in the steam concentration, which has a favourable effect on the exergy balance. 

The main aim of the present work has been to study the effects of the direct factors (which determine the coking rate in steam reforming) on the length of the induction period of coking and various ways of catalyst pretreatment (without or with the initiation of coking at a relatively high partial pressure of hydrocarbon) on the steady-state rate of coking,... 

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