Bubble point pressures system

After the model is built, the program can be generated and compiled. At execution time, the user has considerable flexibility and we chose to predict the bubble point pressure for a fixed temperature and specified total svstem composition in order to compare some of our results with the data of Otsuku (14). Figure 3 presents the results for a system composed of 10.14 wt% CO2 and NH3 at a temperature of 80° where the %C02 in the CO2 and NH3 was varied. 

Figure 4. Comparison of predicted and experimental bubble point pressures for methanol-carbon dioxide system ((C)) (14) (A, V) (24) (---) predicted)...

COMPARISON OF PREDICTED AND EXPERIMENTAL BUBBLE POINT PRESSURE FOR THE NITROGEN-CARBON DIOXIDE, HYDROGEN SULFIDE, METHANOL SYSTEM AT -15°C (From Reference 9)... 

A liquid sample from a black oil reservoir had a volume of 227.0 cc in a laboratory cell at reservoir temperature and bubble-point pressure. The liquid was expelled through laboratory equipment which is the equivalent of the field separator-stock tank system. The oil volume collected in the stock tank was 167.4 cc. The separator produced 0.537 scf of gas, and the stock tank produced 0.059 scf of gas. Calculate the formation volume factor of the oil and the solution gas-oil ratio. 

Solution The given pressure lies between the dew- and bubble-point pressures established for this system in Example 14.3. The system therefore surely consists of two phases. The procedure is to find by trial that value of V for which Eq. (10.30) is satisfied. We recall that there is always a trivial solution for V = 1. The results of several trials are shown in the following table. The columns headed y, give values of the terms in the sum of Eq. (10.30), because each such term is in fact a y, value, as shown by Eq. (10.29). 

In the late 1970 s Knapp et al. (1982) performed a very thorough review of VLE for systems of interest in the natural gas processing industry. They summarized their results in terms of the estimate bubble point pressure (AP/P) and the estimate vapor composition (Ay). They reported other errors associated with their predictions, but these are the most significant to this discussion. 

A, B, C, and D have been calculated in the preceding example. The point A at 22.75 psia represents the computed bubble-point pressure for a solution whose mole fraction of C4H10 is 0.50. Point B represents the composition of the vapor at the bubble point. Similarly, the points C and D represent the bubble point and composition of the vapor at the bubble point for a solution whose mole fraction of C4Hio>is 0.75. The points E and jP. represent the vapor pressure of pure butane and pure propane, respectively, at 0° F. The line FACE is tile bubble-point line and the line FBDE is the dew-point line. It is obvious that a pressure-composition diagram for any ideal binary system could be calculated in this manner and would serve to describe the phase behavior quantitatively. 

Ahernate Method for Catculaling the Bubble-Point Pressure of an Ideal Two-Component System. Although Raoult s Law can be used directly to calculate the bubble-point pressure of an ideal solution, an alteiTiate method which is applicable to two-component systems will now be presented. Since equations 5 to 8 ai e applicable an3rwhere in the two-phase region they apply at the bubble point and the dew point. At the bubble point the system is essentially all liquid except for an infinitesimal amount of vapor. Consequently, the composition of the liquid will be equal to the overall composition of the system. If the overall composition is substituted for x and Xz in equations 5 and 6 then either may be solved for Pt at a given temperature. The value of Pt calculated in this manner is equal to the bubble-point pressure. The com position of tlie infinitesimal amount of vapor at the bubble point may be computed by substitution in equations 7 and 8. 

Example. A system is composed of one mole of -hutane and one mole of -pentaae. Calculate the bubble-point pressure and the composition of the vapor at 180 S using the alternate method presented above. 

Calculations Assuming Ideal Solution Behavior for Multicomponent Systems. The oaloulation of the bubble-point pressure and the composition of the vapor at the bubble point for an ideal solution consisting of more than two components involves no new principles or procedures. If Raoult s Law is applicable the partial pressure of each component in the vapor can be calculated and their sum is equal to the bubble-point pressure. Stated mathematically... 

Calculation of Bubble-Point Pressure and Dew-Point Pressure Using Equilibrium Constants. Since the total pressure P

bubble-point and dew-point pressure as was done in the case of ideal solutions. A method will now be presented for calculating the bubble-point pressure and the dew-point pressure, which is applicable to both binary and multicomponent systems which are non-ideal. At the bubble point the system is entirely in the liquid state except for an infinitesimal amount of vapor. Consequently, since ti, = 0 and n — n% equation 19 becomes... 

Two hydrocarbona, A and B, form an ideal solution. The heats of vaporization are 9630 and 11,000 Btu per pound-mole, respectively. The normal boiling points are 31° F and 97° F, respectively. For a system containing 2 pound-moles of A and 3 poimd-moles of B, calculate the bubble-point pressure at 97° F Answer 27.7 psia. 

When the wetting fluid is expelled from the largest pore, a bulk gas flow will be detected on the downstream side of the filter system (Fig. 7). The bubble point measurement determines the pore size of the filter membrane, i.e., the larger the pore the lower the bubble point pressure. Therefore, filter manufacturers specify the bubble point limits as the minimum allowable bubble point. During an integrity test, the bubble point test has to exceed the set minimum bubble point. 

Since liquids are not very compressible, at low and moderate pressures liquid-liquid equilibrium compositions are almost independent of pressure. Therefore, assuming that the liquid-liquid equilibrium of the isobutane (l)-furfural (.2) mixture at 37.8°C calculated in Illustration 11.2-2 is unaffected by pressure, compute the pr essure at which the first bubble of vapor will form (i.e., compute the bubble point pressure of this system) and the composition of the vapor that forms. Data ... 

Use the Peng-Robinson equation of state and the van der Waals one-fluid mixing rules, with 12 = 0.114, to compute the bubble point pressure and vapor composition in equilibrium with the two coexisting liquid phases in the C02-)i-decane system of Illustration 11.2-5. 

Weissenburger et al. (50) described an engineering system to predict solids production based on the Morita et al. model. It incorporates parameters such as oil type and bubble point pressure, to-... 

Figure 4 P-T crossection of isopleths showing bubble-point pressures (L+V—>L), horizontal curves, and solid-liquid (S+L—>L), vertical curves, for the binary system CO2/RP 70.

Tindy and Raynal (1966) measured the bubblepoint pressure of two reservoir crude oils in both an open space (PVT cell) and a porous medium with grain sizes in the range of 160 to 200 microns. The bubble-point pressures of those two crude oils were higher in the porous medium than in a PVT cell by 7 and 4 kg/cm, respectively. Specifically, the bubblepoint pressure of one of the two crude oils measured at 80 C in a PVT cell was 121 kg/cm and the bubblepoint pressure at the same temperature in a porous medium of 160 to 20 microns was 128 kg/cm. On the other hand, when these authors used a mixture of methane and n-heptane, they observed no differences in the saturation pressure. Sigmund et aL (1973) have also investigated the effect of the porous medium on phase behavior of model fluids. Their measurements on dewpoint and bubblepoint pressures showed no effect of the porous medium. The fluid systems used by these authors were Cj/nC. and Ci/nCs. The smallest bead size used was 30 to 40 U.S. mesh. In Example 2.3 presented at the end of this chapter, the effect of interface curvature on dewpoint pressure and equilibrium phase composition will be examined. 

Different types of equations of state have been used to model the phase behaviour of ionic liquid systems. Cubic equations of state such as the Peng-Robinson equation and the Redlich-Kwong equation have been used to describe the solubility of carbon dioxide, trifluoromethane and organics in ionic liquids. Because cubic equations of state require the critical parameters of ionic liquids, which are unknown, these have to be estimated by using group-contribution methods. Thus estimates obtained from cubic equations of state for ionic liquid systems are unreliable. Moreover, cubic equations of state can only describe the carbon dioxide solubility in ionic liquids at low concentrations, but cannot predict the dramatic increase in bubble point pressure at higher carbon dioxide concentrations. ... 

During fluid circulation for a tank internal TVS system or mixing pump, the LAD must be capable of delivering smaller flow rates despite an unknown initial position of the L/V interface within the tank. Therefore the LAD must have a high bubble point pressure, and be capable of delivering lower flows in low gravity conditions. 

Either in 1 -g or in microgravity, a LAD screen will separate liqitid and vapor phases so long as the pressure differential across the screen does not exceed the bubble point pressure of that screen. Therefore the total pressure loss in the LAD system must be less than this pressure to prevent vapor ingestion into the channel ... 

Figure 4.4 illustrates this effect for a room temperature bubble point and reseal test where the corrected reseal pressure is superimposed on the raw DPT signal. As shown, the reseal pressure is always lower than the bubble point pressure. Unlike bubble point data reduction, the DPT across the screen carmot alone be used to determine screen reseal. Rather, time synchronization with the visualization system is required to determine the exact differential pressure across the screen at reseal. Sole reliance on visualization makes reseal point data inherently noisier than bubble point data. 

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