US1988767A - Method and apparatus for dewaxing oils - Google Patents

Description

Jan. 22, 1935. B. G. ALDRIDGE El AL 1,988,767

METHOD AND APPARATUS FOR DEWAXING OILS Filed July 25, 1933 v wzzi INVENTORS A BAA/f? G. ALDR/DGE ND B/IS/L HOPPER ATTORNEY,

. Patented Jan. 22, 1935 UNITED STATES PATENT OFFICE 1,988,767 METHOD AND APPAgIAL'IUS FOR DEWAXING Blair G; Aldridge, Los Angeles, and Basil Hopper,

San Pedro, Calif., assignors to Union Oil Com- -pany of-California, Los Angeles, Calif., a corporation of California Application July 25, 1933, Serial No. 682,072

13 Claims. (Cl. 62-170) The present invention relates to the art of separating wax from wax-containing substances, and more particularly it relates to a method and apparatus used in conjunction with the separation of wax from lubricating oil fractions wherein liquefied but normally gaseous hydrocarbons are employed both as a diluent for the oil and as -a. refrigerating medium.

Quite recently a method has been developed for the separation of wax from the oil to be treated by using liquefied normally gaseous hydrocarbons such as liquefied ethane, propane, butane, ethers, light chlorinated hydrocarbons, or mixtures thereof, as diluents for the oil as well as refrigerants for the mixture being treated. Briefly stated this previously developed method consists in diluting the waxy. oil, or fractions thereof, in one or more of the above enumerated normally gaseous hydrocarbons which have been liquefied by raising the pressure and maintained in such a liquefied state. The mixing is made approximately in the proportion of about one part of the waxy oil to from one to nine or even ten parts of the diluent, depending on the character of the oil being treated. The diluted waxy oil is then introduced under pressure into a chilling chamber, whereupon the mixture is chilled by vaporizing a portion of the liquefied normally gaseous hydrocarbons used as the diluent. This chilling is carried down to temperature sufiicient to precipitate the wax from the oil, this temperature ranging from +10 F. to 40 F. depending upon the character of the oil being dewaxed, the ratio or proportionof waxy oil to diluent, and the quantity of wax present in the oil being treated. After the chilling of the diluted oil by such a vaporization of a portion of the diluent, the chilled mass or mixture, consisting of oil, diluent-refrigerant and precipitated wax, is conveyed to some mechanical or other means, such as filters, centrifuges, or settling chambers, for the separation of the thus precipitated wax from the oil and diluent, the thus dewaxed diluted oil being then distilled to remove therefrom the remaining portion of the liquefied but normally gaseous hydrocarbons used as a diluent and refrigrant.

As stated above the refrigeration or chilling of the diluted waxy oil in the chilling towers is carried out by a regulated reduction of pressure in the towers. This pressure reduction causes a vaporization of a portion of the liquefied diluent which in turn creates a'chilling of the oil mixture and a resultant precipitation of the wax dissolved therein. However it has been found that such a procedure is accompanied by certain disadvantages. Thus, since the towers used for this chilling step are usually tall in comparison to the diameter of the towers, and since the vapor lines used to lower the pressure therein lead substantially from the upper ends of these towers, the vaporization of the normally gaseous hydrocarbons used as a diluent and refrigerant is unequal in the different parts of the tower. Thus, obviously the vaporization of the diluent-refrigerant is substantially completely from the surface of the mixture. Such an unequal chilling of the diluted oil produces bumping, flashing and violent boiling of the diluted mixture. This is highly undesirable because it causes the diluted waxy oil to be forced from the upper portion of the chilling. tower into the vapor line, with the re sult that said line is clogged and that a portion of the oil being treated is lost.

It is therefore the main object of the present invention to provide a process and apparatus whereby the above disadvantages are removed. It is another object of the invention to provide a method and means to dewax the oil without permitting any flashing or violent boiling of the diluted oil in the chilling step. It is still another object of the invention to provide a method and apparatus whereby the whole mass of the oil being treated is maintained at substantially a uniform temperature during the chilling step.

As mentioned above the diluted waxy oil, after it had been chilled to a temperature sufilcient to precipitate the wax, is removed from the chilling tower and conveyed to filters, centrifuges or settling chambers, wherein the wax is extracted. This conveyance of the chilled waxy oil to the wax extracting means has been carried out usually by means of ordinary pumps which sucked the mixture from the discharge line leading from the chilling chamber through suction ports of the pumps, and discharged said chilled mixture through their discharge ports. However such a procedure has many disadvantages. Thus, the discharge of the chilled mass through the various ports in the pumps creates a disturbance of the precipitated wax structure, disseminating it and breaking it into fine wax particles which are difficult to settle. Wax crystals separated from solution by chilling diluted oils containing the same are likewise rendered less filtrable after the chilled mixture has been passed through conventional centrifugal or gear pumps. This is because the crystals or crystal aggregations are disrupted and broken so that they cannot be removed efiectively by filtration, the fine crystalline particles plugging the filters and preventing further flow of oil therethrough. Also, the usual type of pumps become vapor locked", thus preventing an efllcient removal of the chilled diluted oil from the chilling chamber. Furthermore, the precipitated wax often plugs the suction lines of the pumps and holds the valves thereof open, thus further preventing any discharge of the chilled mass.

It is therefore a still further object of the present invention to provide a pump structure for discharging the chilled mixture from the tower. said pump structure being of such construction that it obviates all of the above described disadvantages. It is still another object of the present invention to provide the chilling chamber with a pump structure which will prevent the breaking up of the wax structure in the oil, which will avoid vapor locking, and which is positive in its action.

Although the proportion of liquefied but normally gaseous hydrocarbons and of the waxy oil being treated varies within comparatively large limits, depending on the character of the oil being treated, etc., it has been found that the separation or extraction of the wax from the waxy oil is obtained most favorably when the ratio of the oil to the diluent-refrigerant is maintained constant for the specific oil. It is therefore a still further object of the present invention to provide a method and means to maintain the ratio of the diluent to the oil constant by introducing automatically into the chilling chamber a quantity of a liquefied but normally gaseous hydrocarbon equal to the quantity thereof which has been evaporated during the chilling step.

The above and other objects may be realized by withdrawing a portion of the diluted oil from the lower portion of the chilling chamber and returning it back into the upper portion of the chamber. The invention therefore broadly stated resides in a method and apparatus whereby the waxy oil and the diluent-refrigerant are withdrawn from the lower portion of the chilling chamber and returned into the upper portion thereof, thus agitating the diluted oil during the chilling step and providing a more uniform chilling of the mixture. The invention further resides in providing a method and means for main--.

taining the ratio of the diluent-refrigerant to the oil constant by introducing the former automatically into the mixture to compensate for the quantity of said diluent-refrigerant evaporated from the mixture during the chilling step. The invention further resides in providing the discharge end of the chilling chamber with a pump structure having no valves or valve seats in the suction port.

In its preferred form the invention further resides in a chilling chamber, means for introducing thereinto a mixture of waxy oil and of a liquefied but normally gaseous hydrocarbon, such as liquid propane, means for chilling the chamber by evaporating a portion of said hydrocarbon diluent, means for introducing the same or another liquefied diluent-refrigerant to compensate automatically for the evaporated portion, and a pump structure associated with the discharge end of the chamber and adapted to discharge the mixture from the chilling chamber and/or circulate a portion thereof back into the upper portion of the chamber to agitate the mixture therein. Preferably, the pump structure of the present invention comprises a cylindrical chamber communicating with the lower end of the chilling tower, a piston reciprocating within said cylinder and two discharge openings at the opposite ends of said cylinder. The lines leading from the discharge ends of the chamber are provided with check valves, while the suction end is valveless, thus reducing to a minimum the disturbance of the structure of the wax in the chilled oil being pumped. It is to be noted that the positioning of' the pump cylinder at the lower end of the chilling tower prevents a vapor lock and thus permits an eflicient operation of the pump.

For a better understanding of the above described principles reference is now made to the accompanying drawing, the sole figure of which shows diagrammatically a vertical section through a preferred embodiment of the present invention. In this figure a chilling chamber is provided with line 12 leading thereinto and adapted to conduct the mixture of waxy oil and liquefied normally gaseous hydrocarbons. This line is provided with a manually operable valve 13. and with an automatic valve 14 actuable automatically by a fioat 15 within chamber 10, the float 15 being connected to the valve stem of valve 14 by means of levers 16 and 17. Another line 18 leads into the chamber 10 and is adapted to conduct thereinto a liquefied but normally gaseous hydrocarbon such as liquid propane. This line is also provided with a manually operable valve 19 and with an automatic valve 20 actuable through a lever system by a float 21 within chamber 10. It is of course obviousthat both automaticvalves 14 and 20 in lines 12 and 18 respectively may be actuated by a single float and lever control. A vapor line 22 leads from the upper end of chamber 10 and is provided with a valve 23. The lower portion of chamber 10 is preferably in the form of an inverted truncated cone 25, the lower end 26 of which opens into a short pipe 27 leading into the middle portion of a horizontally disposed pump cylinder 28. The cylinder is closed at both ends by plates 29 and 30, respectively. A piston 32 is disposed within the cylinder 28 and is adapted to be actuated therein by a piston rod 33 attached to piston 32 and passing out of the cylinder through a packing gland 34 in plate 30. Pipes 35 and 36 lead from the opposite ends of a cylinder 28, said pipes being provided with check valves 38 and 39, respectively. These pipes 35 and 36 open into a discharge line 40 provided with valve 41 andleading to any wax separating means, such as a filter, not shown in the drawing. A branch pipe 42 provided with valve 43 leads from line 40 (upstream of valve 41) and opens at 45 into the upper portion of chamber 19. It is obvious that the lack of valves in the suction end 27 of the pump minimizes the disturbance of the structure of the wax in the diluted oil. Also, the positioning of the pump directly below the chilling tower 10 prevents any gas lock in cylinder 28. Furthermore, it is also clear that the reciprocal movement of piston 32 in cylinder 28 will cause a surging action through suction line 27 thus further assisting to maintain this line free from any wax plugs.

In operation, the waxy oil and a liquefied but normally gaseous hydrocarbon, such as liquid propane, are mixed in the desired proportions and are introduced through line 12 into chamber 10, the mixture being maintained under a pressure sufficient to keep the diluent in a liquid state. This introduction of the diluted waxy oil is continued until the mixture reaches the desaid liquefied hydrocarbon to chill the diluted sired level in chamberlO at whichtime valve 14 in line 12 is closed automatically by an upward movement of fioat 15. Thereupon valve 13 is manually closed and valve 23 in vapor line 22 is opened to release partially the pressure in chamber 10. The degree of opening of .valve 23depends on the character of the diluted waxy oil and the rate of chilling desired. The drop in pressure in the upper portion of chamber 10 above the liquid level causes the evaporation of a portion of the diluent, this evaporation in turn resulting in the chilling of the liquid mixture.

The evaporation of a portion of the diluentrefrigerant during the chilling step naturally decreases the proportion of the diluent to the waxy oil being treated. This is frequently undesirable. This is especially true in the subsequent wax separating step when it is desired to have a predetermined and constant ratio of oil to diluent. Therefore, to offset this evaporation, valve 19 in line 18 is maintained open, so that valve 20 may be actuated by fioat 21 and introduce through line 18 and into the mixture in chamber 10 an amount of the same or like diluent-refrigerant equal to the amount of it being evaporated through line 22.

The uneven evaporation of the diluent in the various parts of the chilling chamber 10 also causes the undesirable bumping, flashing, etc., described above. To prevent this, the mixture being chilled is preferably circulated by actuating the pump located under the chamber, such a circulation naturally tending to equalize the temperature of the mixture. For this purpose valve 41 in line 40 is closed, valve 43 in line 42 is opened, and piston 32 is reciprocated within cylinder 28. Obviously, such a movement of piston 32 will 'withdraw successive charges of the mixture through port 27 from the lower portion of the chilling chamber, and force them alternatingly into the discharge lines 35 and 36. The check valves 38 and 39 in these lines will prevent the back-flow of the liquid on the return strokes. The diluted oil thus withdrawn from the lower portion of the chilling chamber is then returned throughpipe 42 and opening 45 into the colder upper portion of the chamber, thus tending to equalize the temperatures therein and preventing the undesirable flashing, etc.

It is clearly obvious that the actuation of piston 32 in cylinder 28 causes a surging of the diluted oil in chamber 10 until the piston passes port 27. Such a surging further aids the prevention of flashing, and also prevents the formation of wax plugs in the suction. port 27.

When the mixture-in chamber 10 has been chilled to the temperature at which the desired precipitation of the wax occurs, valves 23, 19 and 43 in lines 22, 18, and 42, respectively, are closed, and valve 41 in line 40 is opened. The mixture is then pumped out by the above described pump to any wax separatingmeans, such as a filter, centrifuge, or the like, this pumping not being accompanied by the usual disadvantages, such as the dissemination of the waxy particles, gas locks in the pumps, etc.

It is to be understood that the above disclosures are not to be considered as limiting but merely as illustrative of the generic invention and that many variations may be made within the scope of the appended claims by those skilled in the art.

We claim: l

1. In a method for dewaxing oil, the steps of diluting the waxy oil in a liquefied but normally gaseous hydrocarbon, evaporating a portion of oil, withdrawing a portion of said chilled mixture and returning the thus withdrawn portion into another portion of the mixture being chilled, thus v obtaining a more uniform chilling of the waxy oil.

2. In a method according to claim 1, the additional step of maintaining constant the proportion of waxy oil to the liquefied but normally gaseous hydrocarbon by inJecting automatically into the mixture being chilled additional quantities of such liquefied hydrocarbon to compensate for the evaporated portion thereof.

3. In a method for removing wax from waxcontaining oil, the steps of diluting the waxy oil in a liquefied but normally gaseous hydrocarbon maintaining the mixture under pressure sufilcient to keep said normally gaseous hydrocarbon in a liquid state in said mixture, lowering the pressure of said mixture to evaporate a portion of the liquefied hydrocarbon and thus chill the mixture, withdrawing a portion of said mixture, and returning it into another portion of said mixture being chilled, thus obtaining a more uniform chilling of the waxy oil.

4. In a method for removing wax from a waxcontaining oil, the steps of diluting the waxy oil in a liquefied but normally gaseous hydrocarbon, maintaining the mixture under a pressure sufficient to keep said normally gaseous hydrocarbons in a liquid state, chilling the mixture by lowering the pressurethereof to evaporate a portion of the liquefied hydrocarbon, automatically injecting into the mixture additional quantities of a liquefied but normally gaseous hydrocarbon to compensate for the evaporated portion thereof, and maintaining the temperature of the mixture being chilled uniform by circulating a portion of said mixture.

5. In a method for dewaxing oil, the steps of chilling said waxy oil and simultaneously circulating it from and to the chilling zone to obtain a uniform chilling.

6. In a method for removing wax from a waxcontaining oil, the steps of diluting said oil in a liquefied but normally gaseous hydrocarbon,

chilling said mixture by evaporating a portion of said liquefied hydrocarbon, and maintaining a constant proportion of diluent by simultaneously and automatically injecting into said mixture additional quantities of such liquefied hydrocarbon to compensate for the evaporated portion thereof.

7. In a method for dewaxing oil, the steps of diluting the waxy oil in a liquefied but normally gaseous hydrocarbon such as propane, introducing said diluted mixture under pressure into a chilling chamber, lowering the pressure of said mixture to evaporate a portion of the liquefied hydrocarbon and thus chill the mixture, withdrawing a portion of said mixture from the lower part of said chamber, and returning the thus withdrawn portion into the upper part of the chamber, thus obtaining a more uniform chilling of the waxy oil. I

8. Ina method according to claim '7, the additional step of maintaining constant the proportion of waxy oil to liquefied but normally gaseous hydrocarbon by injecting automatically into the mixture being chilled additional quantities of such liquefied hydrocarbon to compensate for the evaporated portion thereof.

9. In a method for dewaxing oil, the steps of diluting the waxy oil in a liquefied but normally gaseous hydrocarbon, chilling said 'mixture by evaporating a .portion thereof in the chilling chamber, withdrawing a portion of said mixture from the lower part of said chamber, agitating the mixture in said lower part of the chamber, and returning the withdrawn portion of the mixture into the upper part of the chamber to maintain a more uniform temperature of said mixture.

10. In a structure for dewaxing oil, a chilling chamber, means associated with said chamber and adapted to introduce thereinto a mixture of waxy oil and of a diluent, means adapted to chill the diluted oil in said chamber by evaporating a portion of the diluent, and means associated with said chamber to maintain a constant ratio of diluent to oil by introducing thereinto automatically additional quantities of a diluent.

11. An apparatus for dewaxing oil comprising a chilling chamber, means-for introducing the oil to be treated into said chamber, means associated with said chamber and adapted to chill the waxy oil therein, a pump communicating with the lower portion of said chamber and adapted to withdraw the oil from said chamber and to return said oil into the lower portion of said chamber, and means communicating with said pump and adapted to convey said 011 from said pump into the upper portion of said chamber.

12. An apparatus for dewaxing oil comprising a chilling chamber, means for introducing thereinto a mixture of waxy oil and of a liquefied but normally gaseous hydrocarbon, means associated with said chamber and adapted to chill the mixture therein by evaporating a portion of the liquefied hydrocarbon, means for introducing automatically into said chamber additional quantities of such liquefied hydrocarbon to maintain constant the ratio of the oil to said liquefied'hydrocarbon, a pump communicating with the lower portion of the chamber and adapted to withdraw the mixture therefrom and to agitate said mixture in the lower portion of said chamber, and means communicating with said pump and with the upper portion of said chamber and adapted to return the thus withdrawn mixture back into the chamber.

13. In an apparatus for dewaxing oil, a chilling chamber, a short valveless pipe leading from the lower end of said chamber, a pump cylinder communicating directly with said pipe, a piston within said cylinder and adapted to withdraw the liquid from the chilling chamber through said short pipe, discharge openings in said cylinder, and means associated with said discharge openings and adapted to conduct the liquid withdrawn by said pump and to convey a portion thereof back into the upper part of the chilling chamber.

BLAIR G. ALDRIDGE. BASIL HOPPER.

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