Superheated solvent vapor

Superheated solvent vapor may be used to provide additional heat for the cooker. 

Note that the application of superheated solvent vapor is the most time-consuming process step, and with that the total cycle time approaches one-half hour. Compare this to the example of Table 2.7 and Figtue 2.44 where, for... 

Dark blue - superheated solvent vapor sprayed on parts. Maroon — flush chamber with clean dry air. 

Ohzawa et al. [53,54] also considered the solution of Eq. (60). However, they did not solve for concentration as a function of r and z but, instead, averaged the solution of Eq. (11-35). This gave them average concentration vs z distance. The average concentration curve they obtained did not match the shapes either of Fig. 11-11 or of industrial data [49]. Other dry-spinning mass-transfer studies include those of Yoshida and Hyodo [55], who studied the use of superheated solvent vapor as a drying atmosphere and Tokahashi and Watanabe [56], who made rough experimental measurements of solvent content in spun fibers. 

The raffinate phase containing asphalt and a small amount of solvent flows from the bottom of the rotating disc contactor to the asphalt mix heater. The hot, two phase asphalt mix from the heater is flashed in the asphalt mix flash tower where solvent vapor is taken overhead, condensed, and collected in the low pressure solvent receiver. The remaining asphalt mix flows to the asphalt stripper where the remaining solvent is stripped overhead with superheated steam. The asphalt stripper overhead vapors are combined with the overhead from the deasphalted oil stripper, condensed, and collected in the stripper drum. The asphalt product is pumped from the stripper and is cooled by generating low pressure steam. 

Practical Considerations Removal of nonaqueous solvents from a material presents several practical challenges. First, solvents are often flammable and require drying either in an inert environment, such as superheated steam or nitrogen, or in a gas phase comprised solely of solvent vapor. The latter will occur in indirect or... 

A third example of specific microwave effects is the phenomenon of macroscopic superheating." Solvents will boil only when they are in contact with their own vapor and, if this is not the case, they can be heated to above their normal (atmospheric) boiling point without the onset of boiling. This phenomenon can be appreciated when heating a degassed solvent in a pristine reaction vessel using microwave... 

Convection is possibly the most common mode of drying particulate or sheet-form or pasty solids. Heat is supplied by heated air or gas flowing over the surface of the solid. Heat for evaporation is supplied by convection to the exposed surface of the material and the evaporated moisture carried away by the drying medium. Air (most common), inert gas (such as N2 for drying solids wet with organic solvent), direct combustion gases, or superheated steam (or solvent vapor) can be used in convective drying systems. 

The enthalpy of the liquid Zq is increased by the amount A/t, without any change of concentratioa In this way point 1 can be found. This point represents the enthalpy of the two-phase system with the phases vapor at x = 0 and liquid L with concentration Xj and pressure p, compare information on balances in previous chapters. The enthalpy of the solvent vapor is the stun of the enthalpy of the liquid, the heat of evaporation, and the enthalpy according to the superheated vapor. By this way the point Gj is fixed. According to the balances of energy and mass, the point of the liquid can be found as the intersection point of the straight line through the points Gj and 1 and the isobar curve p, = const. Therefore, the relationship... 

Superheated vapor is solvent vapor heated to and beyond its normal boiling point at atmospheric pressure. Its unique capability is to heat materials to above the normal boiling point of the solvent used. 

Dodecane (NC ) is the solvent or lean oil used to recover propane and heavier components from a rich gas mixture by absorption. The initial conditions of both feed streams are fixed at 38°C and 2760 kPa. Under these conditions the lean oil is a subcooled liquid, and the rich gas is a superheated vapor. The column has ten theoretical stages and is maintained at 2760 kPa. 

Direct dryers may use air, inert gas, superheated vapor, or products of combustion as the heating medium. Combustion gases are seldom used in polymer drying because of possible product contamination. Inert gas eliminates the explosion and fire hazard and may be desirable to prevent oxidation of polymers prior to the introduction of stabilizers. Use of snperheated vapor as a heat carrier is highly desirable when solvent is vaporized in the dryer and has to be recovered. 

The vapor ascending from a solution is only made up of solvent, if the vapor pressure of the solute is negligible. With consideration of the elevation of boiling point, the vapor is superheated, so that the enthalpy of evaporation is greater than the enthalpy of vaporization at system pressure. The specific enthalpy of evaporation q... 

Fig. 2.1-9 shows the vapor pressure vs. the mole fraction (upper left) and vs. the temperature T (upper right) and a temperature-entropy diagram for the pure solvent. The superheated vapor corresponds to points with pressure pi and temperature = T b + AT b. 

If pure solvent is vaporized at system pressure pi (e.g., 1 bar), the vapor has to be supplied with additional enthalpy to reach the superheated points. The required enthalpy for superheating is equal to the area BEFG, which is adequate to the heat quantity to be supplied for isothermal expansion from p to p. Therewith q is about... 

Here, Tl = is the heat of evaporation plus an amount due to superheating when the vapor is leaving a solution according to an increase of the boiling temperature in comparison to that of the pure solvent. Now it is assumed that the same vapor mass flow is generated in all effects. The total heat transfer area of n effects is... 

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