JPH0470352B2 - - Google Patents

Description

Claim 1: A desired liquid product in a product removal line at the bottom of the first distillation column in which the distillation process is carried out, having an introduction line, a stripping vapor introduction line, a plurality of trays and an overhead vapor removal line. A method for controlling the composition of a column, the method comprising: measuring the partial pressure of a component vaporized from a liquid at the bottom of the column; monitoring the temperature of the liquid at the bottom of the column; using the partial pressure and temperature to control the composition of the column. Obtain the initial boiling point (IBP) of the liquid at the bottom of the column; compare the IBP with the desired composition;
and a control method characterized by adjusting the distillation process so as to approach a target composition.

2. The first distillation column is a stripper column having an inlet line for receiving a draw from the second distillation column, and the second distillation column is a multi-draw column, and the evaporated components are removed from the overhead vapor. 2. The method of claim 1, wherein the method is returned to the multi-draw column in a line.

3. The method of claim 1, wherein the IBP is an equilibrium flash evaporation (EFV) curve IBP.

4. The IBP of the EFV is the IBP at atmospheric pressure,
The method according to claim 3.

5. The method of claim 1, wherein said adjustment comprises adjusting the flow in said various lines.

6. further comprising a plurality of stripper columns having inlet lines for receiving the draw liquid from the multi-draw column, and a step of obtaining similar measuring steps, monitoring steps, and IBPs in the additional stripper columns;
By further carrying out the comparison process and adjustment process,
A method according to claim 2, comprising:

7. The method of claim 6, wherein the adjustment comprises adjusting the flow in the various lines.

8. The method of claim 2, wherein the multi-draw tower receives crude oil.

FIELD OF THE INVENTION This invention relates to the removal of distillate fractions from liquid mixtures, and more particularly to the control of cut points in petroleum crude towers.

BACKGROUND OF THE INVENTION It is already known to correlate the temperature of a side draw with cut points by simultaneously monitoring a number of column parameters (e.g. McGraw-Hill, Inc.). McGraw-Hill), Nelson.
Author, “Petroleum Refinery Engineering”
4th edition, pp. 473 et seq. (1958)].

SUMMARY OF THE INVENTION The inventor has discovered that the cut point between any heavy fraction and light material to be withdrawn can be controlled simply based on parameters around the bottom tray of the heavy fraction stripper.

In particular, the inventor has discovered that the distillation point can be controlled by using the properties of the liquid in the bottom tray.

In a preferred embodiment, the characteristic is the partial pressure of the liquid.

In a further preferred embodiment, the property is based on the equilibrium flash evaporation curve of the liquid.
vaporization curve) at atmospheric pressure (IBP/EFV).

The “cut point” is the true boiling point (“TBP”) curve (i.e., the
refluxed tower), the mixture being removed;
For example, it means its initial boiling point temperature (〓) on a batch process curve of the percentage of crude oil versus the temperature reached at which a predetermined degree of separation is achieved, achieving its removal.

Preferred Embodiments Next, drawings and descriptions of preferred embodiments of the invention will be provided.

Drawings FIG. 1 is a schematic diagram relating to the implementation of the method.

FIG. 2 shows a pair of intersecting curves that provide cut points.

Process The conventional crude oil tower arrangement is shown in Figure 1. In FIG. 1, column 10 is a second distillation column and includes approximately 50 shelves. Column 10 was continuously fed with heated crude oil through line 12. Tower 10 is a multidraw tower.
column), and the draw-out line 14 (atmospheric light oil) in order in the height direction.
gas oil), 16 (for diesel oil), 18
(for kerosene) and 20 (for heavy naphtha).
These withdrawal lines each led to the top plate of each of the first distillation columns, strippers 22, 24, 26, and 28 (each stripper had approximately six shelves, and the evaporated components were (with an overhead vapor removal line returning the water to the multi-draw column). In addition, in Figure 1, Q _BPA represents the heat flow around the bottom pump.
Q _TPA refers to the heat flow around the top pump, Q _OVHD refers to the heat flow to the overhead condenser, and COND refers to the steam condensate drawn from the overhead condenser.

The target composition range to be manufactured is the cut point between atmospheric gas oil and diesel oil.
It was previously determined to require 704°, 492° as the cut point between diesel oil and kerosene, and 322° as the cut point between kerosene and heavy naphtha. The present invention was used to maintain and control at each of these three predetermined cut points (all temperatures herein indicated in degrees Fahrenheit).

The invention will be described in particular detail with respect to the cut point between diesel oil and kerosene.

Initially, the temperature within the drawer tray from which the drawer line 16 exited was monitored until approximately the temperature appeared to be associated with the desired cut point of approximately 515°.

Next, the precise cut point was adjusted using the control method of the present invention.

The following measurements were taken every minute: (1) Steam flow rate into stripper 24 (lbs/hour), (2) Diesel oil flow rate exiting the bottom of stripper 24 (barrels/day), (3 ) Temperature in the diesel oil drawing line 16, (4) Temperature of the diesel oil flowing out from the bottom of the stripper 24, (5) Pressure in the stripper 24 (drawing line 1
(6) the temperature of the steam entering the stripper 24; and (7) the temperature of the steam entering the stripper 24. Steam pressure entering 24.

Using these seven measurements, along with constants giving the specific heat obtained from experimental data, the stripper 2
Obtain the partial pressure of the diesel oil (“liquid”) in the vapor above the bottom shelf of step 4. Next, use this partial pressure to determine the atmospheric pressure IBP/EFV of diesel oil. In making this determination, we obtain EFV values for various vaporization rates from the most recent experimental data (usually taken daily).
API Technical Data Book (AIP
Technical Data Book) (August 1963)
It is preferable to use constants that update the vertices of the two-phase region triangle defined by plotting as shown in 3B3.1. In this triangle, the pressure versus temperature graph for each proportion of the mixture is a straight line. (The partial pressure and temperature of the diesel oil on the bottom tray of stripper 24 define the initial boiling point...i.e., 100% liquid "IBP"... line and a point on the other vertex.Atmospheric pressure IBP/ EFV is easily determined.) ASTM curves of temperature versus vaporization rate were obtained for both diesel oil and kerosene by conducting experiments once a day.

A true boiling point curve was established for each using normal conversions. These were plotted over a range reflecting their relative capacity (barrels/day) and a curve was drawn for kerosene. Everything is as shown in FIG. The intersection of the curves is the cut point temperature.

The difference between this temperature and the IBP/EFV temperature is
Provides a correction factor that can be used in conjunction with EFV temperature to obtain a running (minute by minute) cut point.

If the measured cut point is not exactly as desired, the flow rates in withdrawal lines 16 and 18 are varied appropriately by equal but opposite amounts.

In the same way, the cut point between normal pressure light oil and diesel oil is also set to stripper 2 in the above control.
Control was performed in the same manner as in 4 using the stripper 22 as the control focus. The cut point between kerosene and heavy naphtha was similarly controlled using stripper 26 as the control focus. The cut point between heavy naphtha and light naphtha was controlled by the conventional method. However, the method of the present invention can of course also be used.