Steam pressures, equilibrium

Melt Formation. The equilibrium steam pressures for Reactions 12, 13, and 14 are shown in Figure 8. The eutectic in the binary system CaO-Ca(OH)2, is at 1454°F. and corresponds to the point where curves... 

Using Kirby s data and familiar first order kinetics, the relationship shown in Figure II was derived. This was tested at temperatures up to 280 C (corresponding to 916 Ibs/sq in. equilibrium steam pressure) in 0.25 inch-diameter copper tubing reactors. In these batch experiments. 0.6 g of... 

Figure 4.1 Equilibrium steam pressure for Mg(0H)2=MgCM-H20 [381]. Typical reactions between nickel and support are listed in Table 4.2.

Pore distribution in general is calculated according to the desorption isotherm, which is a desorption process with equilibrium steam pressure descending and adsorption volume reducing. The relationship between the total adsorption quantity and pore radius is shown in Fig. 7.8. The relationship between the differential values of adsorption quantity vs. pore radius is the so-called pore distribution curve, as shown in Fig. 7.9. 

A two-stage steam jet is to be used on a large vacuum system. It is estimated that 9 kg of air must be removed from the system per hour. The leaving vapors will contain water vapor at a pressure equivalent to the equilibrium vapor pressure of water at 15°C. If a suction pressure of 2.0 in. Hg absolute is to be maintained by the jet, estimate the pounds of steam required per hour to operate the jet. 

The enthalpy change for this polymerization is AWp = —6.5 Real mor. The polymerization reaction in this problem is finished at a fixed steam pressure (1 atm). The equilibrium concentration of H2O in the polymer melt varies with temperature and steam pressure in this case. Tlte enthalpy of vaporization of H2O is about 8 Real mol . Compare the limiting values of number average molecular weight of the polyamide produced at 280 and 250°C final polymerization temperatures. Hint Recall that the variation of an equilibrium constant K with temperature is given by r/(ln K)/d /T) = —AH/R, where AH is the enthalpy change of the particular process and R is the universal gas constant. Calculate Ki and the equilibrium concentration of H2O in the melt at 250°C and use Eq.(10-8).]... 

There is experimental evidence [81] that K decreases with increasing concentration of water, but for ranges of molecular weight of particular interest, K is essentially constant. For at least a wide range of polyamides, K has a value of roughly 250 to 350 after extrapolation to 280°C [81]. The equilibrium water concentration in a particular polyamide held under fixed conditions of steam pressure is characteristic of that polymer. At... 

The approximate temperature distribution in a multiple-effect evaporator is under the control of the designer, but once built, the evaporator estabhshes its own equilibrium. Basically, the effects are a number of series resistances to heat transfer, each resistance being approximately proportional to 1/Ur. The total available temperature drop is divided between the effects in proportion to their resistances. If one effect starts to scale, its temperature drop will increase at the ejq)ense of the temperature drops across the other effects. This provides a convenient means of detecting a drop in heat-transfer coefficient in an effect of an operating evaporator. If the steam pressure and final vacuum do not change, the temperature in the effect that is scaling will decrease and the temperature in the preceding effect will increase. 

Occluded water is not in equilibrium with the atmosphere and is therefore insensitive to changes in humidity. Heating a solid containing occluded water may cause a gradual diffusion of the moismre to the surface, where it evaporates. Frequently, heating is accompanied by decrepitation, in which the crystals of the solid are suddenly shattered by the steam pressure created from moisture contained in the internal cavities. 

The phase equilibrium diagrams for the two binary systems CaO-Ca(OH)2 and Ca(OH)2-CaC03 are shown in Figures 9 and 10, respectively. The latter system particularly shows a remarkably low melting eutectic at 1180°F. At this temperature the steam pressure from Equation... 

The low melting eutectics in the CaO-Ca (OH) 2-CaC03 system undoubtedly explain the formation of melts in the gasifier at temperatures of 1500°-1600°F. whenever the steam pressure exceeds the critical value of 13 atm. The equilibrium data above clearly show that Ca(OH)2 cannot exist as a solid phase under these conditions at such low steam pressures. Liquids with melting points below 1600°F. must exist in the above ternary systems where the activity of Ca(OH)2(l) is sufficiently... 

If CaO is present, the steam partial pressure should not exceed the equilibrium decomposition pressure of Ca(OH)2 since the conversion of... 

In amidation, equilibrium is favorable even in the presence of water. In order to avoid loss of diamine in the early stages of pol3unerization with a resultant imbalance, the first step of pol3onerization is carried out under pressure at elevated temperature. Hexamethylenediammonium adipate with or without water is heated in a closed reactor at about 200°C and autogeneous pressure. Reaction takes place to form amide links and water and proceeds far enough to fix at least one end of all reactants. The steam pressure is then bled off and the temperature raised to 260-300 C to finish the reaction and produce high-molecular-weight polymer. 

The tests discussed thus far, while important in defining the effects expected from an alkali metal-water reaction, have involved large quantities of water and comparatively little alkali metal. In the event of water leakage into sodium in a heat-transfer system, the sodium would be in excess. To investigate the effects of a sodium-water leak in heat transfer systems, a small test system was operated at KAPL. The system consisted of a water boiler using one double-walled tube with flowing sodium on the tube side, boiler water on the shell side, and mercury as the third fluid. In each test run a hole was fabricated in the outside tube. After the boiler reached equilibrium conditions, steam pressure of 100 pounds per square inch and 475 to 500 F. sodium temperature, the inner tube was completely parted by a tensile load applied to a preformed peripheral notch. 

Moisture content of the surface plate layers depends on water vapour or steam pressure in the atmosphere above the plate. With decrease of air access to the plates, the moisture in the surface plate layers begins to evaporate thus opening the capillaries. Water from the inner plate parts diffuses towards the plate surface in an attempt to restore the moisture equilibrium throughout the plate volume (Fig. 8.27a). Consequently, the largest capillaries in the plate interior are evacuated, too. Thus, the processes illustrated in Fig. 8.26c and 8.26d proceed across the whole plate volume. 

Nevertheless, up to that point (i.e., up to the equilibrium), total pressure positively affects the CO conversion because it increases the reaction rate. However, the addition of steam effects the rate of forward reaction. Addition of more amount of steam than the stoichiometric ratio improves the CO conversion by pushing the equilibrium towards right. Figure 1.2 shows the effect of steam to CO ratio (R) and temperature on the equilibrium CO conversion for the WGSR. In the adiabatic single bed reactor, the CO conversion is thermodynamically limited - as the reaction proceeds the heat of reaction increases the... 

Saturator desaturator systems go far to improve the economics of CO shift conversion, provided that the gases are available in a cold condition. If the CO content of a gas containing some 45% CO, 45% H2 and 5% CO2 is to be reduced to 3 %, the Kp figure of 0.114 calculated for 430 C (410°C operating temperature plus 20 °C deviation from equilibrium) leads to a steam demand of approximately 1.47 mol per mol of gas, consisting of about 1.06 mol of equilibrium steam plus 0.41 mol of conversion steam. Hence, for a shift conversion unit operating at for instance 60 bar, almost 3 kg of steam at a pressure of not less than 63 bar would have to be provided per m of carbon mtxioxide to be shifted. 

A closed insulated cylinder is divided into parts by a piston that is held into place by latches. One compartment is evacuated, the other contains steam at 7.5 bar, 300 °C. The latches are removed and the gas expands to fill the entire volume of the cylinder. When the system reaches equilibrium, its pressure is 1 bar. Determine the final temperature. 

System pressure is controlled by the pressurizer, where steam and water are maintained in thermal equilibrium. Steam is formed by energizing immersion heaters in the pressurizer, or is condensed by the pressurizer spray to limit pressure variations caused by contraction or expansion of the reactor coolant. 

The discussion of iodine partition coefficients in this section relates solely to a gas phase consisting of saturated steam which is in thermal equilibrium with liquid water. With increasing steam temperatures and pressures, dissociated compounds such as Csl also exhibit an increasing volatility with steam according to the measurements reported by Styrikovich and Martynova (1963), NaCl shows a partition coefficient of 10 to 10 at a steam pressure of 7 MPa. Beyond the critical temper-... 

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