Bubble-point performance

Differences in bubble point performance are also attributable to differences in evaporation rates of the LCH4 away from the interface (Pong and Moses, 1986). The non- condensable gas with the higher atomic mass may cause a larger decrease in the condensation rate because... 

This new correlation works very well at explaining bubble point performance of other LAD meshes as well. For example, similar results are seen by comparing the performance of the 200 X 1400 and the 250 x 1370. These two weaves have nearly the same number of wires per inch in both directions, yet the 250 x 1370 outperforms the 200 x 1400 with a lower Dp. The big difference between the two meshes is in comparing /"d values. The 250 x 1370 has a higher ratio of 0.68 while the 200 x 1400 has a lower ratio of 0.57 Therefore, the 250 x 1370 has a larger value of X. This matches with the trend that larger values of X correspond to lower values of Dp. 

Sampling saturated reservoirs with this technique requires special care to attempt to obtain a representative sample, and in any case when the flowing bottom hole pressure is lower than the bubble point, the validity of the sample remains doubtful. Multiple subsurface samples are usually taken by running sample bombs in tandem or performing repeat runs. The samples are checked for consistency by measuring their bubble point pressure at surface temperature. Samples whose bubble point lie within 2% of each other may be sent to the laboratory for PVT analysis. 

The oil and gas samples are taken from the appropriate flowlines of the same separator, whose pressure, temperature and flowrate must be carefully recorded to allow the recombination ratios to be calculated. In addition the pressure and temperature of the stock tank must be recorded to be able to later calculate the shrinkage of oil from the point at which it is sampled and the stock tank. The oil and gas samples are sent separately to the laboratory where they are recombined before PVT analysis is performed. A quality check on the sampling technique is that the bubble point of the recombined sample at the temperature of the separator from which the samples were taken should be equal to the separator pressure. 

A third fundamental type of laboratory distillation, which is the most tedious to perform of the three types of laboratory distillations, is equilibrium-flash distillation (EFV), for which no standard test exists. The sample is heated in such a manner that the total vapor produced remains in contact with the total remaining liquid until the desired temperature is reached at a set pressure. The volume percent vaporized at these conditions is recorded. To determine the complete flash curve, a series of runs at a fixed pressure is conducted over a range of temperature sufficient to cover the range of vaporization from 0 to 100 percent. As seen in Fig. 13-84, the component separation achieved by an EFV distillation is much less than by the ASTM or TBP distillation tests. The initial and final EFN- points are the bubble point and the dew point respectively of the sample. If desired, EFN- curves can be established at a series of pressures. 

The calculation of y and P in Equation 14.16a is achieved by bubble point pressure-type calculations whereas that of x and y in Equation 14.16b is by isothermal-isobaric //cm-/(-type calculations. These calculations have to be performed during each iteration of the minimization procedure using the current estimates of the parameters. Given that both the bubble point and the flash calculations are iterative in nature the overall computational requirements are significant. Furthermore, convergence problems in the thermodynamic calculations could also be encountered when the parameter values are away from their optimal values. 

If the K-value requires the composition of both phases to be known, then this introduces additional complications into the calculations. For example, suppose a bubble-point calculation is to be performed on a liquid of known composition using an equation of state for the vapor-liquid equilibrium. To start the calculation, a temperature is assumed. Then, calculation of K-values requires knowledge of the vapor composition to calculate the vapor-phase fugacity coefficient, and that of the liquid composition to calculate the liquid-phase fugacity coefficient. While the liquid composition is known, the vapor composition is unknown and an initial estimate is required for the calculation to proceed. Once the K-value has been estimated from an initial estimate of the vapor composition, the composition of the vapor can be reestimated, and so on. 

Solution To determine the location of the azeotrope for a specified pressure, the liquid composition has to be varied and a bubble-point calculation performed at each liquid composition until a composition is identified, whereby X = y,-. Alternatively, the vapor composition could be varied and a dew-point calculation performed at each vapor composition. Either way, this requires iteration. Figure 4.5 shows the x—y diagram for the 2-propanol-water system. This was obtained by carrying out a bubble-point calculation at different values of the liquid composition. The point where the x—y plot crosses the diagonal line gives the azeotropic composition. A more direct search for the azeotropic composition can be carried out for such a binary system in a spreadsheet by varying T and x simultaneously and by solving the objective function (see Section 3.9) ... 

Perform a pressure hold test with the sterilized filter. Perform the filtration of the product to be sterile filtered using normal production conditions. After the filtration step, the filter should be tested again with the bubble point test. 

At the end of filling the product solution, perform a bubble point integrity test of the final filter. 

Again, this seems to be a rather nice application for computer technology. Even a good-quality programmable calculator can store a number of vapor-pressure curves. At least for hydrocarbons, equations for these curves can be extracted from the API (American Petroleum Institute) data book. Also, a programmable calculator can perform bubble-point and dew-point calculations, with over 10 components, without difficulty. 

The point e to the left on Figure 15-3A is the position of the bubble point at the temperature of the isotherm, and the point e to the right is the position of the dew point. If the above analysis were performed at various temperatures below the critical temperature, the phase envelope would be defined. Figure 15-4 shows the position of the phase envelope along with three isotherms. 

Related Calculations. The convergence-pressure K -value charts provide a useful andrapid graphical approach for phase-equilibrium calculations. The Natural Gas Processors Suppliers Association has published a very extensive set of charts showing the vapor-liquid equilibrium K values of each of the components methane to n-decane as functions of pressure, temperature, and convergence pressure. These charts are widely used in the petroleum industry. The procedure shown in this illustration can be used to perform similar calculations. See Examples 3.10 and 3.11 for straightforward calculation of dew points and bubble points, respectively. 

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. 

In general the PR and SRK equation perform equally well for these mixtures with errors in the bubble point pressure typically less than 3% and errors in the vapor composition typically less than 2 mol%. A notable exception to this is the binary H2S + N2, which has significantly larger errors. The authors of the original study do not provide an explanation for this result and none is present here. 

The more complex BWRS equation performs worse than the two cubic equations (the errors are consistently higher for both the bubble point and the vapor composition) and consistently had more rejected points (i.e is less robust). 

This would correspond to the bubble-point calculation as performed for vapor-liquid equilibrium, the object being to determine the temperature at a given pressure, or vice versa, whereby the first drop of vapor ensues from the vaporization of the liquid phase. That is, it would correspond to a point or locus of points on the saturated liquid curve. 

The calculation is readily performed for the condition F/F — 0, analogous to the bubble-point type determination. If, however, F/F — 1, then the dew-point type determination must be used, such that... 

It is essential that the microbiological particle passage test is performed as part of the development of new sterile formulations. Because of its very specialized nature, the test is normally performed only by the filter manufacturers, who then provide limits for secondary physical tests (e.g., bubble point, pressure decay, forward flow, etc.), which can be applied to verify the pore size rating and integrity of the membrane filters. 

We can predict azeotropic behavior as follows from infinite-dilution /T-values. Using a flowsheeting system, we perform a bubble-point calculation for each species in the mixture. Assuming a mixture contains the species A, B, C, and D, we wish to compute the infinite-dilution L-values for three of the species in the remaining one. For example, we perform a flash calculation where A is dominant and B, C, and D are in trace amounts, using something like a feed composition of 0.99999, 0.000003333, 0.000003333, 0.000003334. It does not... 

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