US2031118A - Process and apparatus for dewaxing oils - Google Patents

Process and apparatus for dewaxing oils Download PDF

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US2031118A
US2031118A US726968A US72696834A US2031118A US 2031118 A US2031118 A US 2031118A US 726968 A US726968 A US 726968A US 72696834 A US72696834 A US 72696834A US 2031118 A US2031118 A US 2031118A
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chiller
wax
line
oil
propane
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David R Merrill
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Union Oil Co of California
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    • CCHEMISTRY; METALLURGY
    • C10PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10GCRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G73/00Recovery or refining of mineral waxes, e.g. montan wax
    • C10G73/02Recovery of petroleum waxes from hydrocarbon oils; Dewaxing of hydrocarbon oils
    • C10G73/06Recovery of petroleum waxes from hydrocarbon oils; Dewaxing of hydrocarbon oils with the use of solvents

Description

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- .UNITEDL STATES] I PATENT OFFICE Pnocns's AND APPAIgUs non nEwAxmG David R. Merrill, Long Beach, Calif.,

assigner to Union Oil Company of California, Los Angeles, vCali1?.,a corporation'of California Application May `22, 1934. serial No. 'izasss '2a claims. (c1. s2-17o) trolled precipitation of the wax from the waxcontaining stocks.

` In lubricating stocks, especially those of considerable Viscosity range or boiling range, there will normally be present waxes varying widely in characteristics comprising at, the one extreme,

hard waxes of relatively high melting point, such as, for example, 150 F. and at the other extreme,

' p soft waxes of relatively low melting point, such to dilute the oiL as, for example, 110 F. Although ordinarily only a small proportion of the total wax content in .the lubrica'tingkoil stock will consist of hard waxes, their presence in the waxy stock is very limportant since they have such a. low solubility in the solution Vof waxy oil and diluent and are usually the iirst type of wax to separate onl gradual cooling.

- Also because of the low initial concentration in the solution such hard waxes are precipitated in a very nely divided form on excessively rapid show little tendency towards resolution of these iine particles and crystal growth. -It'is, therefore, evident that the most critical temperature range is that in which the initial separation of wax occurs because if an excessivel number of nuclei are formed at this time there is little possibility of correcting this situation by subsequent digesting operations. It is an object of my invention to control the formation of nuclei during the initial stages of wax separation so as to prevent formation of an excessive number of such nuclei and to permit further crystal growth on nuclei formed in the. early stages of chilling.

In general, crystallization of wax is accomplished by inducing a supersaturated condition in the solution of waxy oil and solvent employed This is accomplished either by increasing the concentration ofthe solute by vaporization orseparation of solvent, or by reduc-A ing vthe solubility by cooling, or both. Some investigators have shown there is a narrow range of concentration and a corresponding range of temperature of supersaturation within which free formation of new crystal nuclei will not'occurv. In this range of supersaturation, crystallization will occur on nuclei already present but formation of new nuclei will 'occur toonly a very lim-,-

. range of supersaturation is the production of lubricating oils pane.

phase.

ited extent, if at all. This range `o supersaturation is commonly referred to as the metastable range. For purposes of deiinition,` the metastable that range of supersaturation within which' crystallization occurs on 5 the surfaces of crystals already present and spontaneous formation of new crystal nuclei in large amount does not occur.

As soon as'the metastable range of supersaturation is exceeded, however, a so-called labile range of supersaturation is reached in which rapid formation of new crystal nuclei will occur. Thus, the labile range of supersaturation denotes" a degrec of supersaturation inV which spontaneous formation of lnew large extent. With a slow rate of chilling, the rate of crystallization upon'the wax nuclei already present is suiciently rapid to -relieve the supersaturation and permit crystallization to occur within the metastable range so that uncontrolled formation of new nuclei does not occur. With an excessively rapid rate of chilling, however, the degree of supersaturation exceeds the metastable range and this results in the formation of large numbers of new nucleiand conse- 25.

quent reduction in the average particle size due to the production of a large amount of ne particles which are of a gelatinous or slimy character. A wax slurry of this characteris diicult to separate from the oil solvent solution by either settling or filtering. The permissible rate of chilling will, of course, depend not only on the extent of the metastable range but also upon the rate at which supersaturation is relieved by crystallization upon particles of wax .already present. It is another object of my invention to control conditions and rate of chilling in dewaxing operations within the metastable range of supersaturation and to relieve supersaturation by crys-. tallization of wax on wax particles already present in the solution.

In. one of the known methods fonseparating' wax from oils, the oil is mixed with a hydrocarbon solvent, more particularly-a. liquefied normally gaseous hydrocarbon solvent, such as liquid pro- The admixture is eected under a pressure suilicient to maintain the solvent in the liquid Thereafter, a portion of the solvent is` vaporized under reduced pressure inorder to eiect chilling and precipitation of wax from solution. In the case of propane, by reducing the vpressure down to atmospheric, a temperature of approximately 40 F. may be obtained in the remaining oil and solvent solution. The wax which precipitated during the chilling operation crystal nuclei occurs to avery 15` is then removed by settling, ltering or centrifuging. The remaining propane may then be removed from the dewaxed oil by distillation.

In dewaxing lubricating oils by the use of.

liquefied normally gaseous hydrocarbons such as propane', it has been found that in batch operation the rate of chilling must be very carefully controlled because when the chilling is accomplished at an excessive rate, a wax slurry is formed which is very diiiicult to separate from the oil and remaining solvent by such means as settling or filtering. It is usually found undesirable to exceed a chilling rate of about .3 F. per minute in the temperature range from about the temperature at which wax begins to precipitate from solution or the cloud point of the oil solution down to the final dewaxing temperature. However, more rapid chilling may more often be carried out between the temperature ranges of 0 F. and the usual final temperature of about 40 F. Preferably, however, the rate of chilling should not be more than 3 F. per minute from the cloud Y point of the solution down to the final temperature of 40 F. While such control of chilling rate in bath operations is relatively simple and can b'e accomplished readily in chilling by internal refrigeration merely by drawing oif the propane vapor at a suitably controlled rate so that the pressure of the vapor above the liquid falls at a rate corresponding with the desired rate of reduction of temperature, controlled chilling under the conditions of continuous flow is more diiiicult to accomplish because it has usually been necessary in the past to employ a definite number of stages with definite pressure differences between each stage. 'I'hese pressure differences correspond with definite differences in temperature and the tendency is for the temperature of the stream to drop immediately, due to flash vaporization, as soon as the pressure is reduced on passage through the control Valve in the line connecting the stages. It is thus another object of my invention to accomplish controlled chilling under conditions of continuous ow and to obtain results similar to controlled vaporization of solvent in batch chilling operations.

' Various other objects and features of my invention will become apparent to those skilled in the art from the following description of my invention taken from the drawings.

I have discovered that controlled chilling within the metastable range of supersaturation in'a continuous system may be effectively accomplished by employing a plurality of chilling chambers operating at succeedingly lower temperatures and in which the stream of entering solution of waxy oil and solvent to the first chiller and from one chiller to the next succeeding chiller is commingled with a considerable amount of colder recirculated solution from the chiller to which the entering stream is passed. The mixing is, for example, in the ratio of 9 volumes of recirculated solution to one of the entering stream. By rapid mixing and thorough agitation of the entering stream and the recirculated stream, cooling of the entering stream is accomplished by mixing with concurrent reduction of the wax content by dilution rather than by vaporization of propane under reduced pressure, so that the metastable range of supersaturation is not exceeded at any time. Of course, the chillers in the series are maintained at successively lower temperatures by vaporizat-ion of propane at successively lower pressures but the actual chilling of the entering stream is accomplished by mixing with colder recirculated solution.

The combined streams are introduced into the bottom of the respective chillers and as the mixture flows up the chiller, the temperature is reduced by lessening of hydrostatic head at a rate not in excess of about 3 per minute.

The process will be more readily understood by the following description taken from the drawings in which:

Fig. 1 represents a general flow diagram of arrangement of apparatus adapted to carry out my process;

Fig. 2 represents a modification of arrangement of chillers adapted to carry out the process, and

Fig. 3 represents another .modification of a series of 'chillers provided with a schedule of differentpumps to prevent breakingV down of wax crystals by attrition as will be set forth in detail.

`Referring to Fig. l, a wax-containing oil such as an S. A. E. i0 waxy distillate produced from Santa Fe Springs crude oil is taken from tank I and is passed Via line 2 to pump 3 which forces the oil through line 4 and heater 5 and then via line 6 into line 1 where it meets a stream of liquefied normally gaseous hydrocarbon solvent such as liquid propane which has been Withdrawn from tank 8 via lines 9 and I0 and pump Il. Approximatelyv4 to 6 volumes of propane are mixed with one volume of the waxy oil. The waxy oil and liquid propane brought together by means of separate pumps 'are passed through mixer I2 and thence through heat interchanger I4, line I5, and heater I6 where the temperature of the solution is raised to that at which the wax is completely in solution as, for example, F.' The mixture then passes via line I1 through heat interchanger I8, line I9 and cooler 20 where the solution is cooled down to a temperature which is definitely above the temperature of the initial separation of wax although preferably the temperature may be reduced to approximately a few degrees above the cloud point of the oil-diluent mixture. Pressure is controlled by means of relief valve 22 on line 2|. This valve is employed for the purpose of maintaining suflicient pressure in the heater I6 to prevent flashing in the heater.

The combined stream of oil and propane is then led into the bottom of the first of the series of chillers 23, 23a, 23h and 23o operating at successively lower temperatures. Prior to the introduction of the mixture into the first of the series of chillers, it is commingled with recirculated chilled oil and propane from the top of chiller 23 which is circulated via line 24 by pump 25. The resultant mixture then flows through 26 into the bottom of chiller 23. upper part of this chiller as well as in the succeeding chillers operating at successively lower temperatures is maintained constant by maintaining a constant pressure in the propane vapor leaving them. Recirculation from the chiller is desirably accomplished in the ratio of about 9 volumes of recirculated 'solution to one volume of the entering solution so that the wax concentration in the mixture entering the chiller does not exceed the metastable range of supersaturation. It will be observed that the combined stream is introduced into the chiller at or near the bottom so that there is little or no evolutionof vapor or flashing on entrance of the mixture into the chiller. The height of liquid at the point of introduction will preferably be such that its hydrostatic head is equal to the difference in the vvapor pressure of the solution at the temperature of the entering The temperature in the mixture. and at the top when the solution at the top is in equilibrium with propane at the pressure normally maintained in the chiller. On continued circulation, the warm entering mixture will be -gradually cooled as it rises in the chiller due to the reduction in hydrostatic head and consequent evolution of vapor in conjunction with a certain amount oi mixing by eddy currents. 'The chiller will be preferably of such size thatthe volume of the up-iiowing stream will be suiiicient so that the desired cooling rate of for example, about 3 F.

per minute, will not be exceeded.. I

Upon reaching the top of the ilrst chiller, the

Y solution ows down through line 39 and valve 3| which is actuated by a float control 32 in the first chamber. It will be noted ,that this valve is located at a low level so that the distance from the valve to the mixer is very short and ashing upon passage through the valve is reduced to a minimum by immediate mixing and consequent cooling of the stream. Upon passage through valve 3| the partially chilled solution-is immediately commingled with colder solution from the top of the second chiller' 23a circulated via line 24 and pump 25 in exactly the same manneras in the iirst chilling chamber. 'I'he mixture is then introduced into the bottom of the second chiller vla line 26. Chilling in chiller 23a is exactly-the same as in chiller 23 except that temperature and pressure conditions are lower. Likewise, the operationin the subsequent lchillers 23h and 23e is similar to that in the previous chillers. It is apparent that the number of chilling stages provided should be sufllcleutrthat the chilled salu-f tion leaving the top of the last chiller will be.; at the desired dewaxing temperature as, for example, 40 F. When the oil being chilled does not contain suiiicie'nt propane to accomplish' the desired chilling, further quantities may be `introduced through lines 38a controlled by valves y The pressure at the top of each chiller 23, 23a, 23h and 23e is controlled by compressors 35, 35a, 35h and 35e. The propane vapors from the various chillers are removed from the chillers via line 33 which pass to compressors 35, 35a, 35h

and 35e where the vapors are compressed'and trolled by float control valve 4| by means of pump 42 which forces the mixture towax separating devices such` as settlers, illters, centrifuges or other mechanical wax separating units. In the drawings, the chilled mass is passed into the vapor tight wax separator or settler 43. Make-up propane at 49 F. may be introduced into the chilled oil via line controlled by valve 45 in order to provide ior adequate settling or iltration of the precipitated wax. In order to prevent ebullition or boiling in the wax separator during the wax settling operation, pressure is imposed upon the solution of oil. This is accom- .plished by maintaining pressure within the separator by pump 42. As the chilled mass in the wax separator remains in a non-ebullient state, the wax settles out and is collected yby vanes 46 on shaft 41 which is operated by belt 48 connected to a suitable source of power not shown. The

`ferred temperature of 40 F. via line 49 containing the remaining vpropane is collecting tank A59. The precipitated wax slurry containing propane settling at the bottom of the wax separator 43 isremoved through line 5| and pumpedby pump 52 into line 53'where it meets a'stream of chilled recovered oil and propane from surge tank 54 via line 55 and pump.56: The

two streams then pass through line 53 and mixer x 51 into settlerV 58 which is constructed Similarly to vsettler- 43 and in which the wax i'rom settler 43 is washed -with the lilute'oil-propane solution from surge tank 54. Oil and propane separated from thev wax slurry is withdrawn via line 59 and passed into collecting tank 59.

The once washed wax slurry is withdrawn from the bottom of settler 59 vialine 69 by pump 6| which forces the wax slurry through line 62 where 'it meets a stream oi' chilled propane at 49 F.

coming from chilled propane storage tank 93 via line 64, pump 65, line 61 and valve 68. The mixturethen flows through mixing coil' 69 into another rsettler 19 constructed similarly to settlers 43 and 58. In settler 19 the wax from settler 59 is washer withV fresh chilled propane and. any oil separated is withdrawn together with the chilled propane via line 1| and passed into surge tank 54. As stated previously, this solution containing a small amount of recovered oil is employed to wash the wax slurry from the` rst settler 43. The countercurrent Washing 'steps may be carried on in as many stages as desired. The chilled propane in tank 6 3 is produced bywithdrawing a portion of the'propane under pressure from tank 8 via lines 9 and 12, cooling it in heat interchang ers 13 and 14 and passing it into tank 63. The

vpropane m sa ls chilled to 40 ruby vaporizlng a portion through line 15 and compressor 19 which forces the vaporized propane through line 11coo1er 36, line 31 into propane storage .tank l.

The substantially oil-free wax is 'withdrawn' from the bottom of settler 19 via line 99 by pumpl 8| which forces the wax through line 32, heat in-A terchanger 83. line 94 into high. pressure exhauster where vaporized propane under high pressure is Withdrawn via line 86 into line 81. Wax in exhauster 85 is continuously recirculated, from the bottom into the top of the exhauster via line 99, pump 89, line 99, heater 9| and line 92. 'I'he Wax or a portion thereof is then passed through valvey 3" .wax-free oil dissolved in propane` is withdrawn 4from'separator 43 via line 49 and is passed into 93, line 94, heater 95, line 96 into the'low pressure exhauster 91. `Vaporiaed propane under low pressure is withdrawn via line 98, compressed in compressor 99 and passed into line 91. Wax in low pressure exhauster 91 is recirculated via line |99,-

pump |9 I, valve |92, line 94, heater 95 and line 96. Substantially propane-free wax is withdrawn through valve |93 and passed through.coo.er..|94, line |95 into waxstorage tank |96where it is maintained melted by steam circulatedv through coil |91.

The substantially wax-free oil and propaneV from collectingtank 59 is withdrawn via line ||9 f and'pumped by pump through line ||2, heat interchanger ||4, line ||5, valve ||6'into high vpressure exhauster 1 wherevaporirled propane underhigh pressure is withdrawn via line. H9. The oil in high pressure exhauster |'|1'is continuouslyrecirculated through line I9, pump 29, line |2|, heater |22 and linev |23. 'gde oil conen passed through valve'l24, line |25, heater |29, line |21 into low pressure exhauster |29. Propane and oil from the low pressure exhauster is continuously relrculdted through une m. pump m.valve nl,

line |25, heater |26, line |21 into exhauster |28. Vaporized propane under low pressure is withdrawn from low pressure exhauster via line |32 and passed into line 98, compressed in 99 and passed into line 81. Substantially propane-free oil is withdrawn from the low pressure exhauster vla line |29, pump |30, valve |33, line |34 and passed into storage tank |35 which is cooled by cooling coil |36. The propane Vaporized from the low and high pressure exhausters and passing through lines 81 and I8 is passed into lines |31, 11, cooler 36, line 31 into propane storage tank 8.

In the foregoing disclosure, I have described a method for chilling oil to precipitate wax wherein the stream of waxy oil and propane solution after cooling to a temperature slightly above that of initial separation of wax is introduced under conditions of thorough mixing into a much larger stream of propane-oil solution at a considerably lower temperature at which temperature it is saturated but not appreciably supersaturated with wax and carries in suspension wax particles. The relation between the temperatures and Volumes of the two streams is preferably such that the increase in temperature of the circulated stream and consequent increase in solubility of wax in the propane solution is substantially sumcient to hold in solution the quantity ofv wax brought in by the entering stream. In other Words, operating conditions will preferably be chosen so that the wax concentration in solution in the combined stream corresponds approximately with the solubility of wax in the solution at the temperature of the combined stream and will certainly be chosen so that any supersaturation will be very minor in extent and within the metastable range.

'I'he amount of recirculation required in each stage for production of avwax slurry containing the wax in coarse crystals so as to be readily removable by settling or filtration will depend primarily upon the number of stages of chilling provided or, in other words, upon the difference in temperature between stages. With a larger number of stages or smaller difference in temperature, less recirculation of liquid will be required. Other factors which influence the amount of recirculation required in any particular case are the extent to which supersaturation is reduced in the circulating stream prior to mixing with the incoming solution and the concentration of wax in the incoming solution as influenced by the amount of dilution of the waxy oil with propane or other diluent. In general, it is necessary in the practice of my invention to choose such conditions of recirculation as will result in the wax' concentration in the mixed stream not exceeding the metastable range of supersaturation of wax at the temperature of the stream. The extent of this metastable range of supersaturation will in turn depend upon such factors as the character and quantity of wax in the waxy oil, the concentration of oil in the solution as influencing the solvent power of the propane for wax, and the presence in the solution of colloidalimpurities which ordinarily tend to reduce the crystallization rate or modify the crystal habit. Such impurities may be asphaltic y metastable range may be determined by chillingv the solution at Ivarying rates and determining the rate at which uncontrolled formation of new nuclei occurs and hence at that rate of chilling, the degree of supersaturation exceeds the metastable range. At some lower rate of chilling' where large crystals of wax are formed, the supersaturation will be found not to exceed the metastable range.

The four steps shown to chill the oil are possibly not the minimum permissible in all cases but should be suiiicient for most cases. For example, when it is desired to chill the oil-propane solution from 90 down to 40 F., the oil-propane solution in line 2| at a temperature of 90 F. and under a pressure of 153 lbs. gauge is mixed with 9 volumes of colder solution at 60 F. recirculated from the ilrst chilling column. The combined mixture will have a temperature of 63 F. when introduced into the bottom of the chiller 23. As the combined stream flows up through the chiller, the lessening of the hydrostatic head permits vaporiz-ationof a portion of the propane which cools the oil from 63 F. at the bottom to 60 F. at the top.

The chiller is preferably of such size that the volume of the up-flowing stream will be suflicient so that the desired cooling rate, for example 3 F. per minute, will not be exceeded. It is evident that with a recirculation of 9 volumes of recirculated material to one volume of entering stream and with a temperature differential of 3 F. between the bottom and the top of the chiller, the volume of up-ilow should approximately correspond to ten minutes ,flow of the entering stream. Pressure is maintained at the top of the chiller at about 97 lbs. gauge by operation of compressor 35. 'I'he operation of chiller 23a is exactly the same as that in chiller 23 except that it is maint-aimed at a lower temperature level, for example, the mixture withdrawn from the top of the chiller 23 at a temperature oi 63 F. is commingled with 9 volumes of recirculated material from chiller 23a at a temperature 'ot 30 F. The combined stream will havea temperature corresponding to 33 F. As the hydrostatic head on the mixture in 23a is reduced, vaporization of propane will gradually reduce the temperature to 30 F. at the top of the chiller.

Pressure is controlled in 23a by compressor 35a which maintains a pressure in the chiller at about 55 lbs. gauge. In chiller 23h material from the top of chiller 23a at 30 F. is commingled with 9 volumes of recirculated material from the top Aof chiller 23b at a temperature of 0 F. to produce a combined stream at a temperature of 3 F. which is reduced by flowing up through the chiller 23h to 0 F. A pressure of about 27 lbs. gauge is imposed on chiller 23h by means of compressor 35h. In the next chiller, 23e, one volume of 0 F. material from the top of chiller 23h is commingled with 9 volumes of F. material from the top of chiller 23e, producing a combined stream having a temperature of 36 F. which is reduced at the tcp of the chiller to approximately -40 F. by vaporization of propane at the reduced hydrostatic head. The pressure maintained at the top of gauge with theentering stream. In Fig. 2, I have shown a modiiication for accomplishing the aboveresulta It will be observed that Fig. 2 merely represents a series of chilling. chambers. However, it'will be understood that apparatus for propane with waxy oil vand for preparing the mixture prior ,to introduction into the chilling chambers is similar to that described ,in Fig. l. Likewise, the apparatus-for separating vpropane from. the separated oil and wax fractions and for recovering propane may be carried-on similarly to that described 'for Fig. l. l

Referring to Fig. 2, it will be observed that each 'chiller comprises a vertical column as the chillers shown in Fig.. 1, except that it iscenn trally divided by a vertical partition or baille 21 extending almost to the top of the column which dividesv the chiller intotwo sections 28 and 29. At the lower portion of the partition, an injector 38 is provided which permits iiuid iromsection-28 and line 2| to passh into section 29. Injector 38 is provided with bailies 38 in section 29 so that 'mixing of the two streams' is promotedbefore discharge into section 29.

must be so' thorough and the The enterlngstreamcf propane and waxy oil i'rom line 2| `passing through relief valve 22 passes through the entrance nozzle 39 which is lprovided with insulating sleeve `39 in order to` prevent appreciable cooling of the entering stream by surrounding-cold solution. and accom- 'panying deposition ofwaxonthe walls of the nozzle. 'I'he entering stream is injected into the injector 38 and is commlugledl with approximately 9 volumes'of chilled solution drawn into the injector from Asection 28. The mixture passing through'the injector 38 and bailles A38' is lintroduced. into the lower portion of sectionl 29. As the combined stream ows up section 29, the temperature is lowered approximately 3 by vaporization of propane due to the reduction in hydrostatic head. The mixture overows overV4 partition wall 21 into chamber 28 where it is recirculated to the injector, part o1' the solution bein withdrawn via'line 30. Thus,'by providing. an injector I may produce circulation of the mixture within the chiller. The agitation mixing so rapid that no vopportunity is aiorded for cooling of the incoming stream by conduction-of .heat to the circulating stream but the cooling. should take place only by actual mixing ci.' the two streams, since otherwise, the supersaturation may readily exceed the-metastable range'. In practice this mixing may be accomplished more readily lay-employing multiple iets rather than the simple jet injec rshown.

fThe Vrtially chilled mixture is withdrawn from thebottom of'section 28v vialine 30 and lower temperatures.- sure conditions inthe chiller will be exactly the pump 25 and passes through float control valve 3| into the `next chiller. The operation in chiller 23a and in vsubsequent stages 23h and 23el is exthesame asin' the rst chiller 2 3 except that the chillersare maintained at' successively f The temperature and pressame "as in the .case of .external recirculation xample,`if it is dsil'edl'to' the top of 'the chamber. A pressure of 97 f solution in the iirst chiller, for tain a relatively limited number o1' nuclei and the chill oil from .90 F. to 40 F., the entering stream at 90 F. under pressure of 153 lbs. gauge is commingled with 9- volumes ofV 60 .material in inJector 38, the-combined stream having a temperature of 63 which is reduced to 601b s. gauge ismaintained in 'chiller '23 by compressor 35. Material withdrawn from the bottom of section- 28 of. chiller 23 at 60 F. is commingled with 9 volumes of v30 F. material in the injector 10 of chiller 23a to produce a combined mixture of 23 F. material which is reduced at the top of the chiller to 30 F. A pressure of 55 lbs. gauge'is maintained in chiller v23a by compressor a. Likewise, material at 30 the bottom of the chiller 23a is commingledl with 9 volumes -of 0 F. material .at the bottom o! section 28 of chiller 23h to produce a mixture of 3 F. material in section 29 which is reduced to 0 F. at the top of the of 27 lbs. gauge is maintained in chiller 23h by compressor 35h. 0 F.materlal withdrawn from the bottom of chiller 23h is commlngled with 9 volumes of F. material at the bottom of F. withdrawn from l5 chiller. A pressure 20 section 28 of chiller 23e to produce a mixture 25 or 36 F.' which is reducedat the tcp of the chiller 23cto 40 F. A `pressure of 0 lbs. gauge vis maintained in chiller 23e by compressor 35e.

The chilled solution containing precipitated cipitated wax is separated from the oil and remaining propane.

Operation oi the chillers is best started by lling all or thechillers with the propane-waxyoil solution at a temperaturev above the temperature of initial separation of wax and then cooling each wax is withdrawn from section 28 oi' the last 80 Achiller very slowly by drawing'off propane vapors o at a controlled rate so that crystallization will occur slowly and relatively large crystals will be l formed. After proper temperatures are attained in each chiller, the continuousv flow may be started. Under these conditions,

example, will contendency will be for crystallization to occur on these nuclei already present ratherthan for new the circulating nuclei to be formed. On continued operation, the

nuclei will tend'to be carried on in the succeedlng chillers and the number of nuclei in suspensionin the rst chiller will be reduced. However, fortuitous formation of nuclei by local excess chilling or by attrition will keep the proportion 58 oi.' nuclei in suspe on at a suitable point. This tends to be self-re ating'since if the proportion oi nuclei is unduly decreased, the rate at which supersaturation will be relieved will be reduced and there will be a greater tendency for the super- .60

saturation to enter the labile range with formation oiadditional nuclei. The reduction in the number of nuclei by flowing into succeeding stages is very` desirable, las it will tend to promote the formation of larger crystals the subsequent settling or ltering operation.

'One V of the most essential points for successi'ul operation is the immediate and complete mixing of the two streams, that is, the entering stream and the colder recirculating and 70 the avoidance of any appreciable cooling of the entering stream in any manner except by mixing with the circulating stream. cooling or the en# .l tering 'streamby conduction oi 'heat' to the ciri' 'culating stream or by partial vaporization is par- 7l which will facilitate ticularly to be avoided. While it is possible that by the use of injector types of mixing devices, 'mixing can be accomplished so quickly as to prevent appreciable iiashing of the entering stream on release of pressure at the entering nozzle or orifice, such avoidance of fiashing may at times be diflicult to `accomplish in practice and in this latter case it is proposed to prevent flashing by maintaining a sufiicient pressure upon the combined streams during the mixing operation so that any possibility of iiashing is obviated.

The maintenance of a higher pressure at the point of mixing will, of course, necessitate the release of the pressure at a later point in order that vaporization may take place in the chiller at the desired temperature. The release of the pressure by passage through a relief valve or orifice will result in the setting up of shearing stresses in the iiowing liquid which may cause appreciable attrition of the wax particles in suspension with consequent formation of additional nuclei and general reduction of particle size of wax. Moreover, the release of the pressure through a valve or orifice will result in dissipation of the energy corresponding with the pressure differential in the form of heat. With ,the recirculation of, for example, 9 volumes for one volume 'of entering solution, the energy so dissipated would be appreciable and the heat generated would increase the load on the refrigerating system. In Fig. 3 I have disclosed an arrangement of apparatus wherein the energy corresponding with the pressure drop may be converted back into mechanical energy as by -passage, of the solution through a positive displacement pump, such as a gear, Kinney, Waterous or reciprocating pump. I f desired, the mechanical energy may be converted into electrical energy and the electrical energy may be returned to the line. In this way any undue increase in the refrigeration load is avoided. Moreover, by suitable choice of the type of pump, the breaking down of the wax crystals by attrition is reduced to a minimum.

Referring more particularly to Fig. 3, .the waxy oil solution in propane prepared in they manner disclosed in Fig. 1 and passing through line 2| is introduced into injector |50 where it is commingled with colder solution from chiller 23, for example, in the ratio of 9 volumes of recirculated solution to one volume of' the entering solution and circulated from chiller 23 via line 24 and circulating pump 25. The mixture then flows through mixing coil |5|, and passes through a positive displacement pump |52 from which the combined streams fiow through line |53 into section 29 of chiller 23. Chiller 23 is preferably divided into two sections `28 and 29 by' vertical baffle 21, theupper portion of the chiller being open to permit flow of'v liquid from section 29 into section 28. 'I'he operation and flow of liquid in chiller 23 is exactly the same as that in the chillers disclosed in Fig. 2 except that the injector in the interior of the chiller is omitted, circulation being accomplished externally in. the manner up by pump |55 which comprises a positive displacement pump, the speed of which is controlled by float control 32. The solution picked up by pump |55 is passed by line 2|a into injector lilla where it is commingled with colder solution from section 28a circulating via'line 24a andpump 25a. Combined streams pass through mixer I5 a, pump |520, line |53a into section 29a of chiller 23a.

" scribed for Fig. 1.

A portion of the chilled solution` from section 23a passing through line 24a is by-passed through line |54a to pump |55a controlled by iioat control 32a which is forced through line 2lb to further chilling in a manner similar to that described for chillers 23 and 23a, or it may be passed to wax settling or filtration in order to separate precipitated wax from solution in the manner dethe chillers 23 and 23a is controlled by compressors 35 and 35a. Propane vaporized from the chillers is withdrawn via lines 33 and 33a, compressed in compressors 35 andv 35a and passed into manifold 34 from which it may be passed to the propane condenserand recovered in a manner described in Fig. 1.

Thus, in Fig. 3, I have described the method of operation by which all valves with accompanying possibility of attrition of wax crystals is avoided and the flow is controlled by speed control of positive displacement pumps. As stated above, pumps |55 and |55a comprise positive displacement pumps with speed control by a float control device. Pumps 25 and 25a comprise constantspeed centrifugal pumps, preferably of slow speed type and pumps |52 and 52a comprise positive displacement pumps such as gear, Kinney, Waterous or reciprocating pumps which are connected to induction motors which, when over-driven, will return power to the line.

In the above schedule of pump types, instead of employing a constant-speed centrifugal pump in the position indicated, for pumps 25 and 25a, a positive displacement pump with speed control to maintain; constant pressure may be substituted therefor, pumps |52, |52a and |55, |55a remaining the same as in the above schedule. It is obvious to those skilled in the art that further modi-.

cations could be made in the types of pumps and methods of control without departing from the spirit of the invention.

While I have described the use of liquid propane as the internal refrigerant-diluent, itl may be observed that I may 'employ other liquefied normally gaseous hydrocarbons for. this purpose. vSuch hydrocarbons include methane, ethane, propane, iso-butane, butane or mixtures thereof. These hydrocarbons may be obtained by rectification of casinghead gasoline by the so-called0 stabilizing method. They are the overhead thus obtained. They are liquefied by compression and cooling in the conventional manner and are drawn off into pressure chambers where they are maintained in the liquid state until they are used.

It is to be understood that the above description is merely illustrative of preferred embodiments of my invention of which many variations may be made by those skilled in the art without departing from theA spirit thereof.

I claim: v

1`. An apparatus for separating wax from oils which 'comprises means for mixing waxy oil with a liquefied normally gaseous solvent, a plurality of chillers, means connecting said Chillers to permit passage of solution from the top to the bot- The pressure at the top of y tom of successive chillers and.means for recirl Imaintaining said chillers at successively lower means for' mixing waxy oil circulating to the bottom of said other compartment with oil entering said chiller and means for withdrawing oil containing precipitated wax from `the bottom of said other compartment.

5. An apparatus as in claim 4 in` which said means for circulating oil and for mixing entering oil with oil at the bottom of said other compartment comprises an injector.

6. An apparatus for separating wax from oils which comprises a plurality of chillers, a partition dividing the lower portion of each of said chillersinto 'two compartments, an injector positioned at the bottom of said chillers and compartition in said chiller,

municating from one compartment to th other,

means for passing oil from said chiller into said injector, means connecting the bottom of said chillers with successive chillef and means for maintaining said successive chillers at successively lower temperatures.

7. An apparatus for separating wax from oil which comprises a vertical chiller, means in said chiller to divide thelower portion of said vertical chiller into two vertical compartments, a mixer, means for passing oil from the bottom vof one of said compartments to said mixer, means for passing oil to be chilled to said mixer, means' for passing the combined streams from said mixer to the bottom of said other compartment and a pump positioned on said last mentioned means.

8.` An apparatus for separating wax from oil which vcomprises a .vertical vchiller,- a vertical said partition dividing the lower portion of said chiller into two'compertinents, a mixer, 'a conduit connecting the bottom of one compartment with said mixer,l a

i conduit connecting said mixer with the bottom of said other compartment, means for passing oil from the bottom of said rst mentionedcompartment to said mixer and from said mixer to the bottom of said other compartment, said means comprising a pump-positioned intermediate said conduit connecting the bottom of `said first mentioned compartment with said mixer,` means.

for passing oil to bechilled into said'mixer and means on said conduit from said mixerto. the

l bottom of said other compartment to vreduce the pressure of the combined stream passing tosaid other compartment.`

9. A process for chilling liquids-which'comprises mixing'the liquid to be vchilled with a volatile liquid refrigerant under superatmos?.

pheric pressure, commingling said mixture with a sulcient quantity of to reduce the temperature o1' the mixture to be chilled to substantially that oflthe previously chilled liquid and removingvaporized liquid re' frigerant. from the-combined mixtures 9 in which .the voladrant is a liquefied normally gaseous hydrocarbon.

10. A process asin claim s 11. A process as in claim -9 in which the `vola tile liquid refrigerant is liquid propane. chilling liquids which com- 12. A process for prises mixing the liquid to bechilled* with a volatile liquid ,refrigerantv under superatmosof the previously chilled s ing a portion of the volatile liquid refrigerant passing the mixture previously chilled liquid chamber connected in series 'to be chilled in suflcient quantities to reduce the temperature of the mixture to be chilled to substantially that of the chilled mixture withdrawn from the chilling chamber and 'vaporiz'lng a portion of the volatile liquid refrigerant from 10 the chilling chamber' to chill the combined mixture.

13. A process as in claim 12 in which the temperature of the combined mixture of liquid to be chilled, volatile liquid refrigerant and chilled 15 liquid withdrawn from the chilling chamber is reduced tothe temperatureA of the withdrawn chilled liquid by lessening the hydrostatic head on said mixture.

14. In aV process for dewaxing oils the steps 20 comprising-mixing waxy oil with a volatile liquid y refrigerant under. supsratmospheric pressure, A commingling said mixture with a'suftlcient quantity of previously chilled waxy oil to reduce the temperature of the'waxy oil to be chilled to sub- 26 stantially that of the previously chilled waxy oil, and vaporizing a portion of the volatile liquid refrigerant from the combined mixtures.

15. In a process for dewaxing oils the steps comprising mixing waxy oil with a. volatile liquid. 80 refrigerant under superatmospheric pressure, commingling said mixture with a suilicient quantity of previously chilled wainr oil to reduce the/ temperature of the waxy oil to be chilled to approximately 3 F. higher waxy oil, and Vaporizfrom the combined mixtures.; 16. A process as in claim 14 in which the volatile liquid refrigerant is a. liquefied normally 40 gaseous hydrocarbon.

17. A process as in claim 14 1in which the volatile liquid refrigerant is liquid propane.

18. In a process for d'ewaxing oils the steps comprising mixing waxy'oiPwith a volatile liquid refrigerant under superatmospheric pressure. into the bottom of a chilling chamber which is maintained at 'a lower pressure and at a lower 'temperature than said mixture, withdrawing chilled waxy oil and volatile liquid 50 refrigerant from the top of the chilling chamber and mixing said withdrawn mixture with the waxy oil and volatile liquid refrigerant to be s chilled in a suiil'cient quantity to reduce-'the tem.-

perature of the mixture to be chilled to substan- 66 tially the temperature of the withdrawn chilled mixture and vaporizing al 'portion of the volatile liquid refrigerant from the combined mixtures.

19. A process as in claim 18 in which'the temperaturewf the combined mixtures is reduced 60 to the temperature of the chilled waxy oil and volatile liquid refrigerant withdrawn top of the chilling chamber.

2 0. In a process for dewaxing' oils the steps comprising mixing waxy oil with a volatile liquid refrigerant under superatmospheric pr'eure.

passing said mixture into thev bottom of chilling s and maintained at successively y'lower temperature and pressure levels by vaporization of said volatile liquid refrigerant under reduced pressure, withdrawing chilled mixture from' the top of said chilling chambers and commingling said withdrawn mix- .ture with the 'mixture to be chilled entering` the bottom of said chilling chamber. said admix- 16 than the temperature 8 6 from the l ture being in quantities suiicient tovreduce the .temperature of the combined mixture to subxels by vaporizationof said volatile liquid. refrigerant under reduced pressure, withdrawing chilled mixture from the top of said chilling chambers and commingling said withdrawn mixture with the mixture to be chilled entering the bottom of said chilling chambers said admixture being in quantities suicient to reduce the temperature of the combined mixture to substantially the temperature of the chilled mixture withdrawn from the top of the chilling chambers, and lowering the temperature of the combined mixture to substantially the temperature oi the Withdrawn chilled mixtlre from the top of the chilling chambers by reducing the hydrostatic head on the mixture.

^ 23. In a process for dewaxing oils the steps comprising mixing waxy oil with a. volatile liquid refrigerant under superatmospheric pressure, passing said mixture into the bottom of chilling chambers connected in series and maintained at successively lower temperature and pressure levels by vaporization of said volatile liquid refrigerant under reduced pressure, withdrawing chilled mixture from the top of said chilling chambers and commingling said withdrawn mixture with the mixture to be chilled entering the bottom of said chilling chambers, said admixture being in quantities suilicient to reduce the temperature of the combined mixture to approximately 3 F. higher than the temperature of the chilled mixture withdrawn from the top of the chilling chambers and reducing the temperature of the combined mixture to substantially the temperature of the chilled mixture withdrawn from the top of the chilling chambers by lessening the hydrostatic head on the 'mixture and. vaporizing a portion of the volatile liquid refrigerant.

DAVID R. MERRIIL.

US726968A 1934-05-22 1934-05-22 Process and apparatus for dewaxing oils Expired - Lifetime US2031118A (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2486014A (en) * 1945-07-06 1949-10-25 Atlantic Refining Co Hydrocarbon oil dewaxing
US2530976A (en) * 1947-09-12 1950-11-21 Standard Oil Dev Co Method of chilling mixtures
US3747358A (en) * 1968-05-01 1973-07-24 J Swearingen Cryogenic process
US3859811A (en) * 1970-10-21 1975-01-14 Atomic Energy Authority Uk Dewaxing of a hydrocarbon feedstock by direct contact with a refrigerant

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2486014A (en) * 1945-07-06 1949-10-25 Atlantic Refining Co Hydrocarbon oil dewaxing
US2530976A (en) * 1947-09-12 1950-11-21 Standard Oil Dev Co Method of chilling mixtures
US3747358A (en) * 1968-05-01 1973-07-24 J Swearingen Cryogenic process
US3859811A (en) * 1970-10-21 1975-01-14 Atomic Energy Authority Uk Dewaxing of a hydrocarbon feedstock by direct contact with a refrigerant

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