US2036374A - Chilling - Google Patents

Description

CHILLING Filed April 26, 1930 INVENTOR W W W tb vywu W ATTORNEY jg Feed Patented Apr. 7, 1936 UNITED STATES PATENT OFFICE 6 Claims.

This invention relates to the chilling of fluids and in particular to the reduction of temperature of oil for the purpose of precipitating therefrom substances, such as wax, that may be precipitated by reduction of temperature.

It is an object of this invention to provide a method and process capable of effecting intense cooling by means which are definitely controllable to afford uniform continuous reduction of temperature and which are nevertheless simple, economical and of high efiicien'cy.

While this invention is applicable to the chilling of fluids generally, it will be described by way of illustration in connection with' the reduction of temperature of oils in connection with the dewaxing thereof. In so far as this invention is applied to the dewaxing' of oils, it is immaterial from what source the oil is derived, inasmuch as the oil may be crude petroleum oil, or a fraction, such as a distillate or residue thereof, or vegetable oil, or animal oil, or oil produced in the destructive distillation of carbonaceous material or shale. The form of apparatus and method herein set forth are particularly adapted to the de- Waxing of fractions of parafiinor mixed base crude oils at low temperatures for the production of low cold test lubricating oil.

In reducing the temperature of the oil to precipitate wax therefrom, sudden cooling or shock chilling is disadvantageous. The oil should be cooled gradually in order to have the'wax precipitate out in the physical form best suited to the'removal thereof from the oil and to produce an oil of superior cold test. Where oil is cooled by coming in contact with a chilled surface, the chilled surface with which the warmoil comes in contact should not be more than approximately F. colder than the oil in order to avoid shock chilling and to prevent accumulation of wax on the chilled surface.

According to the method and apparatus of this invention, the dewaxing of oils may be accomplished in a continuous and relatively rapid manner, and at uniform rate of cooling without shock chilling. The wax precipitated from the oil is thrown down in a form well suited for removal as by centrifugal force, and an increased yield of dewaxed oil is produced which is of improved cold test.

It has been found that the separation of wax from oil can be promoted by mixing therewith a substance which is a solvent for" both the oil and wax while the mixture is warm, but is a solvent for the oil only when the mixture is chilled. Thus, in the practice of this invention, it is desirable to mix a certain amount of solvent with the oil prior to chilling. For example, a solvent such as naphtha may be mixed with oil and a solution formed by bringing the mixture to- 100 F., and upon reducing the temperature to 40 F. wax will be precipitated from the solution. The naphtha can be recovered by distillation after separation of the wax from the solution. While it may be desirable to mix a certain .amount of solvent such as naphtha with oil in dewaxing oil according to this invention, it is to be understood that the word oil as used both in the specification and claims is regarded as covering oils either mixed or unmixed with a solvent.

Heretofore, it has been proposed to chill oil prior to treatment thereof for the removal of wax therefrom, by bringing the warm wax-containing oil into heat exchange relation with cold oil flowing from that treatment and thereby partly cool ing the wax-containing oil, and then bringing the partly cooled oil in an intermediate step and a separate final step into heat exchange relation with liquid volatile refrigerant to further cool the oil. It has also been proposed to cool the warm oil by heat exchange with cold dewaxed oil mixed with warm dewaxed oil, and then by heat exchange with cooling medium cooled by liquid volatile refrigerant, and then finally to bring the wax-containing oil so partly cooled into direct heat exchange relation with liquid volatile refrigerant. These methods involve loss of cooling effect of the dewaxed oil because, in order to secure a steady supply of cold dewaxed oil that is not subject to fluctuations which would cause shock chilling, no more cold oil flowing from the wax separation step can be safely used than that which occurs at the minimum rate of production, thus wasting about twenty per cent. of the cooling effect of the cold dewaxed oil. Moreover the wax bearing oil which has been cooled by cold dewaxed oil is not sufficiently cooled according to the above processes so that the intensely cold dewaxed oil can be brought directly from the wax separation step into heat exchange with the wax bearing oil without shock chilling, but must have its intense cold tempered either by warming it or by mixing warm dewaxed oil therewith, with resultant loss of efficiency. These methods also require an intermediate cooling step between the step in which dewaxed oil is used and the step in which liquid volatile refrigerant is brought into heat exchange relation with the wax-containing oil at the minimum pressure used.

It is a feature of this invention that the warm wax-containing oil is cooled, by being brought into heat exchange relation with cold dewaxed oil, to a temperature (e. g., 25 F.) which is within a few degrees of the lowest temperature (e. g., 40 F.) desired for the precipitation of wax, and which is sufiiciently low for the production of oil of commercially acceptable cold test, and which is so low that cooling to lower temperatures when oil of especially low cold test is desired, may be effected by direct heat exchange with liquid volatile refrigerant in a single step, all of the cooling being effected without shock chilling.

Important features of this invention are that the dewaxed oil used as a cooling medium in the cooling of wax-containing oil, is further cooled, prior to use as a cooling medium, and then it is used to reduce the temperature of the wax-containing oil to a low temperature as above stated, and that all of the cold dewaxed oil coming from the dewaxing operation may be employed in heat exchange relation with the warm wax-containing oil, and that the temperature of the cold dewaxed oil coming from the dewaxing operation need not be raised prior to such use thereof, either by mixture with warm oil or otherwise. A further feature of this invention is that the dewaxed oil used as a cooling medium may consist of oil coming directly from the dewaxing operation and further cooled, or of oil that has been passed in heat exchange relation with warm oil and so warmed and then re-cooled; or of a mixture of such further-cooled oil and such re-cooled oil.

Advantageously, in the practice of this invention, all of the dewaxed oil flowing from the wax separating operation is passed to a cooling operation preparatory to passing it in counterflow in heat-exchange relation with wax-containing oil to be chilled, and a regulated quantity of warm dewaxed oil that has passed in heatexchange relation with wax-containing oil is added to the cold dewaxed oil flowing from the separating operation to the cooling operation; and the resulting mixture of dewaxed oil is cooled to a temperature which is preferably below the temperature of the dewaxed oil flowing from the dewaxing operation. The volume of warm oil so added is so regulated as to compensate for the reduction in volume caused by the removal of the wax from the oil in the wax separating operation and for heat given off in the solidifying of the wax during cooling of the wax-containing oil. This is important because if the heat absorbed from the warm wax bearing oil not only in low ering its temperature but also in withdrawing the latent heat incident to precipitate the wax is greater than the capacity to absorb heat of the cold dewaxed oil flowing countercurrent and in heat exchange therewith, the cold dewaxed oil will be warmed more rapidly than the warm wax bearing oil is cooled, thus producing such lack of uniformity of rate of cooling and temperature gradient that shock chilling and inefficiency will result. The volume of cold dewaxed oil used as a cooling medium is thus regulated in relation to the volume of wax-bearing oil being chilled therewith, so that there will not only be suflicient volume of cold oil to lower the temperature of the wax bearing oil at approximately the same rate as cold dewaxed oil is warmed but also suflicient additional volume temperature gradient that there will be no shock chilling and maximum efiiciency will be obtained.

Important features and advantages of this invention are that the cooling of wax-containing oil by the use of dewaxed oil as a cooling medium, as above described, is capable of effective regulation whereby shock chilling is avoided, and the wax-containing oil may thereby be brought to a temperature at which it may be at once dewaxed to produce valuable oil or it may be at once, without intermediate cooling and without shock-chilling, further cooled by being brought into heat exchange relation with liquid volatile refrigerant to a temperature so low that separation of wax will produce oil of very low cold test.

The steps comprising this invention may be employed separately and when so employed constitute separate parts of this invention. They may also be employed conjointly and when so employed cooperate with one another to produce special advantages resulting from their cooperative relation.

Other and further objects, features and advantages of this invention will be apparent in consideration of the accompanying drawing which is a diagrammatic view of apparatus embodying this invention and whereby this invention may be practiced.

Warm wax bearing oil may be stored in tank it prior to chilling. Where the oil is mixed with a solvent such as naphtha prior to chilling, the solution may be blended in tank I0. Preferably, this solution is made at a temperature of approximately 100 F. in order to effect substantially complete solution. The warm wax bearing oil or solution, which latter will also be referred to as oil, may then be pumped by pump II from tank Ii] by lines l2 and I3 so as to enter a series of heat exchangers l4, l5, l6, l1, I8, [9, 20, and 2| wherein the oil is progressively chilled by heat exchange with cold dewaxed oil. The heat exchange is indirect, that is, without resultant mixing of warm wax-bearing oil with the cold dewaxed oil. The wax bearing oil flows between said heat exchangers by lines 22. From the last heat exchanger 2| in this step of the chilling process, the partially chilled wax bearing oil may pass by line 23 to heat exchanger 24 where it is subjected to a second and last step of chilling by direct heat exchange with an intense refrigerant such as ammonia vapor. Thus, for example, warm wax bearing oil may be gradually chilled to about -25 F. during the first step by heat exchanged with cold dewaxed oil and then cooled to about 40 F. by direct heat exchange with compressed ammonia released at a pressure of six pounds per square inch absolute during the second step.

The chilled wax bearing oil passes from heat exchanger 24 by line 25 through control valve 26 and supply line 21 to a wax separating device 28 which is here shown diagrammatically as a centrifuge. While the use of a centrifuge is preferable according to this invention, any other wax separating device may, of course, be used. Connected with supply line 21 is a standpipe 29 and tank 30 in which there is a float 3| for regulating the control valve 26, thus efiecting automatic control of the flow of chilled wax bearing oil into wax separator 28. Wax separated from the oil by the wax separator 28 may be discharged from separator 28 through line 32 to tank 33 Where it may be accumulated and stored. Dewaxed oil discharged from the wax separator 26 may be conducted byline 34 to tank 35.

The cold dewaxed oil in tank 35 is chilled and used as a refrigerant for the Warm wax hearing oil according to this invention as follows: Cold dewaxed oil in tank 35 passes by line 36 to pump 31 from which it is discharged through line 33 into cooler 39. In addition to cooler 39 a second cooler 4| is shown having a lower temperature than cooler 39 as it is preferable to chill the dewaxed oil in two steps. The dewaxed oil passes from cooler 39 to cooler 4| by line 49. In cooler 39 chilling may be accomplished by 2.1- lowing ammonia vapor, for example, to vaporize therein at a pressure of 15 lbs. per square inch absolute. In cooler 4| chilling may be accomplished by allowing ammonia to vaporize therein at a pressure of only 6 lbs. per square inch absolute. From cooler 4| the chilled dewaxed oil is conducted by line 42 to heat exchanger 2| and flows through the coils thereof in heat exchange relation with the wax bearing oil. From heat exchanger 2| the oil passes successively through heat exchangers 29, |9, |8, l7, |6, I5 and I4, being conducted between said exchangers by lines 43.

The dewaxed oil which has been warmed by virtue of having passed through the above mentioned heat exchangers in the counterflow with the warm wax bearing oil is discharged from heat exchanger |4 through line 44 to the tank 45. A part of this warm dewaxed oil can be rechilled according to this invention for further use as a refrigerant by pumping it by pump 48 back to the tank 35 through lines 46 and 41. The rate of return flow of this warm dewaxed oil to tank 35 may be regulated by a valve 49 which is controlled by a float 59 in tank 35. The rate of flow of chilled dewaxed oil through heat e'xchangers |4 to 2| and withdrawn from tank 35 by line 36 is greater than the flow of cold dewaxed oil from the wax separator into the tank 35 by line 34. It is thus apparent that all of the cold Wax free oil from wax separator 28 is used to chill the incoming wax bearing oil. The level of the oil in tank 35 automatically controls by float 5|] and valve 49, the amount of warm dewaxed oil that must be added to the cold dewaxed oil flowing into the tank 35 by line 34.

The rate of flow of chilled dewaxed oil through the aforesaid heat exchangers to chill the warm wax bearing oil is controlled by pump 31 which may be set to maintain the rate necessary to progressively cool the incoming warm oil at a desired temperature gradient.

The partially chilled wax bearing oil is chilled in heat exchanger 24 by intense refrigerant in the following way. Liquid volatile refrigerant such as ammonia is fed into accumulator 5| where it is allowed to vaporize at a pressure, e. g., 6 lbs. per square inch absolute. The circulation of the ammonia is caused by the rise in temperature in coils 52 of the heat exchanger 24 and by such vaporization as may occur in these coils.

Where, for example, ammonia is used as a refrigerant and is released at 6 lbs. per square inch absolute both in cooler 4| and accumulator 5|, cooler 4| and accumulator 5| may be arranged in parallel with respect to a common compressor 53. The compressed ammonia passes from compressor 53 by the line 54. It is taken by lines 55 and 56 through control valve 51 to cooler 4| where it is released. The ammonia vapor is reconveyed to the suction side of the compressor 53 from cooler 4| by lines 58 and 59. Ammonia from the compressor 53 is taken to the accumulator 5| by lines 54, 6|] and 6| through control valve 62 which releases the ammonia into the accumulator 5|. The ammonia vapor from accumulator 5| is reconveyed to the suction side of the compressor 53 by lines 63 and 69.

Ammonia which is released in cooler 39, for example at 15 lbs. per square inch absolute, is compressed by compressor 64 from which it passes by lines 55 and 66 through control valve 61 into cooler 39. From cooler 39 ammonia vapor may be reconveyed to the suction side of compressor 64 by line 68.

The ammonia compressed in compressors 53 and 64 may be condensed in condensers 69 and T0 and stored in receptacles l and 72. Valves 5'! and Bl which admit the ammonia vapor into coolers 4| and 39 respectively and valve 62 which admits vapor into accumulator 5| may be operated by float control for maintaining a constant level of ammonia in coolers 4| and 39 and in ac cumulator 5|, thus securing automatic regulation.

By the process and apparatus above described, wax bearing oil at about 1.00 F. may be gradually cooled to a temperature of -40 F. at which temperature the wax will have precipitated so that it may be readily removed as by centrifugal separation from the oil. By chilling with the apparatus above described and centrifugally separating the wax therefrom a lubricating oil hav ing a cold test of 0 F. to 5 F. may be produced; Oils having a higher cold test may be obtained by operating at higher temperatures. In some cases, on the other hand, it may be advisable to operate at lower ammonia pressures and temperatures in order to obtain a lower cold test. While the oil may contain some residual wax which has not been precipitated by the chilling and which has not been removed therefrom, it has nevertheless been freed of sufficient wax to produce an oil of desired cold test, and oil from which wax has been thus removed is in this sense wax-freed.

According to the above process and apparatus, the incoming warm oil may be chilled by the chilled dewaxed oil to a temperature which permits the partially chilled oil to be subjected directly to an intense refrigerant Without shock chilling which latter refrigerant will complete the process of chilling to the desired low temperature. By controlling the flow of chilled dewaxed oil through heat exchangers l4 to 2| by pump 31, a progressive gradual and continuous chilling of the warm oil flowing in counterfiow therewith may be accomplished without shock chilling, to precipitate the wax in the best physical state for separation from the oil.

While specific forms of apparatus and specific methods of operation have been set forth above, it is to be understood that such specific description has merely been by way of illustration of this invention and that the same may be modified in many details without departing from the scope of this invention.

I claim:

1. A process of. dewaxing oil by chilling said oil to precipitate wax and removing precipitated wax, which comprises separating wax from chilled oil by centrifugal force affording wax-freed oil separated from wax, chilling the warm waxbearing oil before and chilling the wax-freed oil after the separation of wax therefrom by heat exchange with a volatile liquid refrigerant released both before and after the'wax separation step at substantially similar pressures and compressed from said pressures by a common compresssor, and bringing said rechilled wax-freed oil into indirect counterflow heat exchange with warm wax-bearing oil while the wax-freed oil is at a lower temperature than the temperature thereof when taken from the wax separation step and while the wax-freed oil contains substantially less wax than the warm wax-bearing oil.

2. A process of dewaxing oil by chilling said oil to precipitate wax therefrom and removing precipitated wax, which comprises chilling wax bearing oil by liberating compressed volatile liquid refrigerant at a given pressure, separating dewaxed oil from the chilled wax-bearing oil, chilling the dewaxed oil by releasing a compressed volatile liquid refrigerant at a higher pressure than that used in chilling the wax bearing oil, then further chilling the dewaxed oil by releasing compressed volatile liquid refrigerant at a pressure substantially the same as that used in chilling the wax bearing oil, and then using the chilled dewaxed oil to partially chill warm wax bearing oil.

3. A process of dewaxing oil by chilling said oil to precipitate wax therefrom and removing precipitated wax, which comprises compressing a volatile liquid refrigerant with a single compressor, chilling wax bearing oil by heat exchange with said volatile liquid refrigerant upon releasing a portion of said refrigerant at a given pres sure, separating dewaxed oil from the chilled wax bearing oil, chilling said dewaxed oil by direct heat exchange with said volatile liquid refrigerant upon releasing another portion of refrigerant at a like pressure, and returning said released refrigerant to said compressor.

4. In a process of dewaxing oil wherein wax bearing oil is chilled to precipitate wax therefrom and cold dewaxed oil is separated from the precipitated Wax and comprised in a refrigerant used to chill warm wax bearing oil by heat exchange, the steps comprising adjusting the heat absorptive characteristics of. the refrigerant comprising the cold dewaxed oil in relation to the heat giving characteristics of the warm wax bear ing oil which is chilled thereby so as to cause the refrigerant comp-rising cold dewaxed oil to be warmed at substantially the same rate that the warm wax bearing oil is cooled during said heat exchange and chilling said refrigerant comprising cold dewaxed oil from the wax separation step prior to bringing said refrigerant into heat exchange with warm wax bearing oil.

5. In apparatus for dewaxing oil, means for passing dewaxed oil in indirect heat-exchange relation and out of contact with wax-containing oil, means for separating precipitated wax from wax-containing oil and adapted to receive cold wax-containing oil from said heat-exchanging means, a tank adapted to receive cold dewaxed oil from said separating means, a pipe for conducting to said tank dewaxed oil flowing from said heat-exchanging means, means dependent upon the level of oil in said tank for controlling flow through said last-named pipe to said tank, a chiller and means for passing dewaxed oil from said tank to said chiller and from said chiller to said heat-exchanging means.

6. A process of dewaxing oil by chilling said oil to precipitate wax therefrom and removing precipitated Wax, which comprises separating a cold dewaxed oil from a wax-bearing oil by a dewaxing step, adding to said dewaxed oil from said dewaxing step additional dewaxed oil to form a mixture, bringing said mixture into counterflow heat exchange with warm wax-bearing oil, vary ing the amount of dewaxed oil added to the de- Waxed oil taken from the wax separation step in accordance with variations in the amount of dewaxed oil from the wax separation step so as to maintain the amount of the mixture in counterfiow with warm wax-bearing oil substantially constant and bringing the mixture to effective chilling temperature by means of a refrigerating operation subsequent to the dewaxing step.

' MALCOLM H. TU'I'I'LE.

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