Bubble point adjustment

Either the temperatures or flows could be adjusted first. The common choice is to correct the temperature. Correction of temperatures is usually done through either bubble-point or dew-point determinations on the calculated stage compositions. After correcting the stage temperatures, the liquid and vapor enthalpies may be obtained from the calculated compositions, and the flows corrected by solution of the now linear heat balance equations of Table I. 

This chapter begins with bubble-point pressure and solution gas-oil ratio, and then explains methods of estimating the density of reservoir liquids. The results of the density calculations are used to estimate oil formation volume factors. A technique for adjusting the results of the correlations to fit field derived bubble-point pressure is presented. 

Figure 11-1 gives a correlation for bubble-point pressure.1 3 The correlation is entered with solution gas-oil ratio derived from early production history. If the information is based on gas sales, the gas-oil ratio must be adjusted for stock-tank vent gas and for any gas lost or used in surface operations. 

Now we will examine the methods of estimating the density of a reservoir liquid at reservoir conditions. First, we will consider liquids at their bubble points or liquids in contact with gas in either case, we will call these saturated liquids. The first step in the calculation procedure is to determine the density of the liquid at standard condition. The next step is to adjust this density to reser >oir conditions. 

The calculation of liquid density at pressures above the bubble point is a two-step procedure. First, the density at the bubble point must be computed using one of the methods previously described. Then this density must be adjusted to take into account the compression due to the increase in pressure from bubble-point pressure to the pressure of interest. 

The normal procedure for estimating formation volume factor at pressures above the bubble point is first to estimate the factor at bubble-point pressure and reservoir temperature using one of the methods just described. Then, adjust the factor to higher pressure through the use of the coefficient of isothermal compressibility. The equation used for this adjustment follows directly from the definition of the compressibility coefficient at pressures above the bubble point. 

Adjustment of Formation Volume Factor of Oil and Solution Gas-Oil Ratio for Field Derived Bubble-Point Pressure... 

Tables of oil formation volume factor and solution gas-oil ratio tabulated against pressure are adjusted by changing the values of pressure. A delta pressure is calculated as the difference between field derived bubble-point pressure and bubble-point pressure from correlation.

EXAMPLE 11—13 Examination of reservoir pressure measurements shows that the bubble-point pressure of the reservoir oil of Example 11-1 is 2635 psia and 220°F. The table below gives results of Examples 11-1, 11-2, and 11-11. Adjust the table to agree with the field derived bubble-point pressure. 

Field data indicate the bubble-point pressure to be 2265 psia. Adjust the table above to the field bubble point. 

Six pound moles of ethane, three lb moles of propane and one lb mole of n-butane are mixed in a closed container and the temperature is adjusted to 75°F. What is the bubble-point pressure What is the dew-point pressure Calculate the composi-... 

Estimation of Formation Volume Factor of Oil at Saturation Pressure Using Ideal-Solution Principles—Estimation of Formation Volume Factor of Oil at Saturation Pressure by Correlation—Estimation of Formation Volume Factor of Oil at Pressures Above the Bubble-Point Pressure Adjustment of Formation Volume Factor of Oil and Solution Gas- Oil Ratio for Field Derived Bubble-Point Pressure Total Formation Volume Factor The Coefficient of Isothermal Compressibility of Oil... 

Depending on the initial guesses, the calculated value of B may not equal the specified B. A calculated B higher than specified indicates that tm and are too low, and that the bottom product contains excessive lights. An additional trial is then needed, at higher t and/or t . Usually, the estimated fasd temperature is raised this raises both tn and tm. Since the top and bottom temperatures are fixed by the products dew and bubble points, they are best maintained constant until Bxb edds up to the specified amount. Conversely, if the calculated Bxb is lower than specified, the estimated feed temperature should be lowered, The above is analogous to an operator adjusting the control temperature to obtain a desired split. 

The theta method. This method has been primarily applied to the Thiele-Geddes equations but a form of the theta method equation has also been applied to the equations of the Lewis-Matheson method. The main independent variable of the method is a convergence promoter, theta (or 6). The convergence promoter 0 is used to force an overall component and total material balance and to adjust the compositions on each stage. These new compositions are then used to calculate new stage temperatures by an approximation of the dew- or bubble-point equation called the Kb method. The power of the Kb method is that it directly calculates a new temperature without the sort of failures that occur when iteratively solving the bubble- or dew-point equations. 

I used the bubble point option of program VLMU treating the liquid mole fraction of C02 as an adjustable parameter, until a C02 partial pressure of 1.013 bar in the vapor phase was obtained. The results appear below ... 

The manufacturers early recognized the discrepancy between theoretical and experimental bubble points. They introduced an experimental constant into equation (1) called a "shape-factor" which supposedly took into account the fact that tortuous pores are not cylindrical in shape. However, a shape factor of 0.25 cannot be justified from the capillary rise equations, as any good textbook on surface chemistry will attest. Indeed, for noncircular pores, equation (1) is adjusted to ... 

The timers functioning entirely on electronic principles allow take-off and reflux periods of 0.1 sec to 20 min. to be adjusted with an accuracy of 1% [56]. For an alteration of the reflux ratio they require a change to be made in both the take-off and reflux times. A number of electronic devices are commercially available most of which are provided with bubble-point control. The column head is set at infinite reflux ratio as soon as the pre-set temperature of the contact thermometer placed in the column head is reached. When the temperature falls below this threshold the preselected reflux ratio is automatically switched on again. As an example. Fig. 386... 

Pump manufacturers have established guidelines to ensure each pump they supply is not exposed to conditions that result in cavitation. The design standard is called NPSHR or net positive suction head required. The NPSHR takes into account any potential head losses that might occur between the pump s suction nozzle and impeller thereby ensuring the liquid does not drop below its vapour pressure (bubble point). The NPSH is a measure of the proximity of a liquid to its vapour pressure, and must exceed the pump manufacturer s pump NPSHR. There are two process variables that can be adjusted, in case the available NPSH is less than the NPSHR raise the static head and lower friction losses. Conversely, the NPSHR can be reduced by using a larger, slower speed pump, a double suction impeller, a larger impeller inlet area, an oversized pump and a secondary impeller placed ahead of the primary impeller. 

Condensate subcooling occurs when the distillation tower overhead product is all liquid. This means the contents of the reflux drum must be at or below its bubble point. The condenser operation will automatically adjust itself to satisfy this condition. 

We have seen that pressure affects bubble points and relative volatility any disturbance to pressure will therefore disturb product composition. While we will show later that there can be advantages in adjusting pressure, we want to do this in managed way, making the changes slowly and taking compensating action to maintain constant composition. We want to avoid deviations from the pressure controller SR... 

Static methods. In which the system of interest is enclosed in a magnetically stirred variable volume cell [64, 76] which in some cases contains a window. The temperature and pressure within the cell are accurately metered. The cell volume may be changed either using a mercury piston or a mechanical piston and samples of the fluid phases present may be obtained, if required, under conditions of constant temperature and pressure by suitably reducing the cell volume. In the windowed cell version [76] sampling is unnecessary for binary systems since the cell may be charged with known amounts of the two components and conditions adjusted to obtain trace presence only of one of the phases. In this way the dew- and bubble-point curves for binary systems may be established and similarly the solubilities of solids in compressed fluids may be determined. 

The old must be reduced by multiplying by 1 0.000 194 0.00615. The adjusted values together with those above constitute the new X7 s. The new bubble point is 94 C. 

The introduction of more liquid feed means that more liquid benzene is cascading down the trays. As liquid reaches the bottom tray, the bubble point of the liquid on that tray decreases. The temperature controller reduces the valve opening on the bottoms stream to conqtensate. The reboiler level rises, resulting in more steam being introduced by the action of the level controller. The benzene and pentane are vaporized and move back up the column. As the column adjusts to the increased feed flow rate, the temperature profile in the column rises. The bottoms flow rate is then increased and settles back down to its new steady-state value. 

Adjust the pressure till the bubble point is reached. In simulation packages, the pressure is estimated using vapor fraction as 0.0. The estimafed pressure is saturation pressure P. Because this calculation is based on the subcooled liquid at tire PRV inlet, the saturation pressure (PJ will always be less than tire relieving pressure (P ). Perform a flash calculation using a small vapor fraction, say, 0.01, keeping pressure as P the temperature will change slightly. 

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