US1977054A - Dewaxing system - Google Patents

Description

R. N. GILES DEWAXING SYSTEM Oct. 16, 1934.

Filed Dec. 27, 1952 ATTORNEY N-Gz'les S Q B EE N \mbubonuww INVENTOR SN B B090 mm as 3 L S QQ Q L E QN kw Patented Oct. 16,1934 I 1 UNITED STATES DEWAXING SYSTEM Roy N. Giles, Casper, Wyo., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application December 27, 1932, Serial No. 648,846

3 Claims.

This invention relates to a dewaxing system and it pertains more particularly to a system for the separation of wax from petroleum lubricating oilsby means of liquefied normally gase- 5 one diluent-refrigerants such as propane.

The latest improved method of separating wax from petroleum lubricating oils, particularly from heavy distillate stocks, is the. so-called process of propane dewaxing. The waxy oil is completely dissolved in a large excess of propane so that both oil and wax are in solution; the solution is then cooled by the vaporization of. a part of the diluent, thereby causing the wax to solidify or crystallize in readily separable form, the solidified wax is mechanically separated from the diluted oil by means of filtration, settling, etc., and finally, the propane is recovered from both the wax and the wax-free oil, condensed, and returned to storage tanks for reuse.

The object of my invention is to provide a method and means of cooling the diluted lubricating stock so that the wax will crystallize out in readily filterable or separable form and to thereby increase the yield of finished oil, provide a finished oil of low pour point, and expedite the mechanical separatiorf of wax from the diluted oil. A'further object is to minimize compressor costs and toutilize more effectively the refrigeration which is available in the system. In other words, the object isto effect a saving of steam, a saving of condenser water, a saving of compressor costs, etc., and at the same time to effect the crystallization of wax in readily separable form (avoiding shock chilling).

, I have discovered that .if a solution of oil and wax in propane comes in contact with a metal surface or a body of liquid which is at a considerably lower temperature, the wax will solidify 40, ahnost instantaneously in the form of almost imperceptible fine crystals. Ihave found that the formation of such crystals is very undesirable-particularly where the separation of wax from diluted oil is effected by filtration, and I have found that once these undesirable small crystals are formed it is practically impossible to remedy the situation. It might be supposed that these crystals would subsequently dissolve, or act as nuclei for the formation of larger crystals, or coalesce, or in some other way .be transformed into a more desirable structure.

-Experience has shown, however, that such a reformation of crystal structure is ractically impossible andthat from a commercial standpoint it is necessary to avoid what may be called shock chilling".

When oil is diluted with naphtha or other liquid solvents and chilled by means of the brine coils of an ammonia refrigeration plant, 0 the temperature must be lowered very slowly, only a few degrees an hour; otherwise the temperature differential between the diluted oil and the brine coil will be too great and there will be shock chilling at the surface of the brine coil. 5 When propane is used as a refrigerant and is evaporated directly from the diluted oil, the cooling may be about fifty or sixty times as fast aswas possible with brine coolers-it may be from about one-half to eight degrees per minute, preferably about three degrees per minute. However, when a solution of waxy oil in propane hits a cold metal surface or any cold body, there is an instantaneous cooling of the mixture at a theoretically infinite rate or, in other words, for an extremely small fraction of a second the cooling rate may be several hundred degrees per minute. This results in shock chilling and it causes the formation of wax crystals which are so fine that they can- 30 not be readily removed from diluted oil by filtration and/or other mechanical means. The object of my invention is to prevent this shock chilling in a propane dewaxing system.

In practicing my "inventionl prefer to obtain complete solution of both oil and wax in propane before I: begin the chilling step. Thereafter I am careful in transferring the diluted oil-wax mixture to see that it does not come in contact with any metal surface or any body of liquid which is at an appreciably lower temperature and which would therefore cause shock chilling.

In a preferred embodiment of my invention I heat chill chambers and conduits by condensation of propane therein between the cooling of successive batches. When a cold wax slurry has been withdrawn from a chill chamber, that chamber is necessarily cold,I warm it up prior to the introduction of a fresh charge by merely allowing Warm propane vapors to condense 1 therein, the condensed propane remaining to serve as additional diluent and refrigerant for the next batch to be cooled.

I may, in fact, employ a plurality of chill chambers arranged so that the first may be dis- 1 5 charged by gravity into the second, etc. When the second chiller has been cooled by evaporative refrigeration and the charge has been removed to the third chiller, the top ofthe second chiller is connected to the vapor space of the first chiller so that the vapors leaving the first chiller to effect the cooling thereof are condensed in the second chiller and thereby heated to the same temperature as that to which the first chiller is cooled. When equilibrium is reached the slurry is passed from the first chiller into the second chiller, and the next step of cooling is effected by vaporizing propane from thesecond chiller and condensing it in the third chiller which is quite cold due to the previous charge which was just removed therefrom. By operating in this manner shock chilling is avoided, compressor costs are reduced to a minimum, and a marked saving in steam and condenser water is effected. Furthermore, this type of cooling obviates the necessity of using an expensive variable compressor which has heretofore been required to reduce the pressure in a chill chamber from about 170 pounds/square inch to 0 pounds gauge.

The invention will be more fully understood from the following detailed description and from the accompanying drawing which forms a part of this specification and which diagrammatically represents my improved system.

In describing myinvention I will refer to the separation of wax from'a heavy lubricating distillate from Mid-Continent crude, the distillate having been acid treated and neutralized but not clayed, and having a viscosity of about seconds Sa'ybolt at 210 F. It should be understood, however, that the invention is equally applicable to the separation of wax from any overhead or residual lubricating stock from any other type of crude, treated or untreated.

Propane that is used in this specification is illustrative only of normally gaseous substances which may be liquefied to serve as diluent-refrigerants in this type of a dewaxing process. I prefer to use ordinary commercial propane which may contain ,a' fraction of a percent of ethane and 8% or 10% of isobutane and/or normal butane. The propane may contain larger amounts of butane, and it may contain unsaturateds such as ethylene and propylene. Also, I may use liquefied normally gaseous substituted hydrocarbons, such as methyl chloride, dichlor difiuor methane, etc., or I may use normally gaseous ethers such as methyl ether or amines such as dimethylamine. The word propane as .used throughout this specification should not be limited to that particular compound but should be understood broadly to include the equivalents thereof. In other words, propane will be'considered to mean a liquefied normally gaseous diluent-refrigerant compound" or mixtures of compounds.

Referring to the drawing, propane in storage tanks 10 may be transferred through pipes 11 by means of pump 12 to mixer 13, which may be provided with steam coil 14 for effecting complete solution of both oil and waxin the propane. The waxy oil stock from storage tank 15 is withdrawn through discharge heater 16 in pipe 17 and then forced by pump 18 through pipe 19 to the mixer 13. From mixer 13 the solution of oil and wax in propane is discharged through pipe 20 and valve 21 into the first chill chamber 22 ( valves 23, 24 and 26 being closed), which has been previously heated in a manner which will be hereinafter described.

When the first chill chamber is about threefourths filled valve 21 is closed, valves 24 and 25 are opened and valves 26, 27 and 28 are "Wash propane collector 58.

closed, thereby allowing propane vapors to pass through pipes 29 and 30 to second chiller 31. This second chiller is at a low temperature because of the chilled mixture which has just been removed therefrom. Consequently, propane vapors condense in this chamber very rapidly, and in ten or fifteen minutes the first chamber has been cooled about thirty degrees and is exactly at the same temperature as that of chiller 31 and conduit 32, which may be considered as a part of the second chiller.

When equilibrium has thus been established, valve 23 is opened thereby allowing the slurry from the first chiller to pass by gravity through pipe 32 to the second chiller. When the transferis complete valves 23, 24, 25, 28, 34 and 35 are closed and valves 27 and 33 are opened. It should be understood that the third chiller which has been emptied of a previously cooled batch, is cooled to about -40 F.

The second and third chillers, being thus connected through vapor line 3'7, rapidly reach equilibrium, propanevaporizing from the second chiller to lower the temperature thereof and condensing in the third chiller to raise its temperature. When equilibrium is finally reached, valve 28 is openedso that the chilledslurry may pass through pipe 38 to third chiller 36. Valves 2'7, 28 and 33 are then closed and valve 34 is opened so that the fin'al chilling in the third chiller may be effected by the removal of propane vapors through pipe 39 and low pressure gas line 40. This low pressure gas line is connected to the inlet side of compressor 41, which compresses the propane and forces it through pipe 42, condenser 43 and pipe 44, which leads back to propane storage tanks 10.

When the slurry in the third chill chamber has reached about 40 F., valve 34 is closed, valve 35 is opened and the slurry is dropped into mix tank 45. From the mix tank the cold slurry is forced by pump 46 through pipe 47 and open valve 48 into closed filter 50. .The pressure is rapidly increased in the closed filter until it reaches about 40 pounds/square inch, after which time it gradually tapers off to about 65 pounds/square inch. The filter element 51 may be the usual canvas cloth supported by suitable screens and firmly clamped around its edges. The filtrate passes through pipe 52 and valve 53 to filtrate collector 54.

When a sufficient cake is built up on the filter element, the slurry in the closed filter is displaced by means of wash propane introduced through pipe 55, valve 48, pipe 47, and valve 56 baclcto mix tank 45. Valve 48 is then closed, the first propane wash which carries large amounts of oil is sent to the filtrate collector through valve 53, and subsequent quantities. of used wash propane are conveyed through pipe 57 to used After the washing step the valve in pipe 55 is closed and propane in the filter is displaced by gas pressure or otherwise through pipe 47, valve 59 and pipe 60 to used wash propane collector 58 (valve 56 being closed) After the wash propane has been displaced from filter 50 the Wax cake is discharged from filter element 51 by means of blowing back or any other suitable means, and it is discharged through valve 49 to conduit 61, which may contain a screw conveyor or other suitable transfer means for conveying the wax slurry to a suitable stripper for removing diluent and returning it to the system.

The filtrate from collector 54 may be forced bypump 62 through pipe 63 and heat exchanger 64 to cool the wash propane, after which it is passed through pipe 65 to high pressure stripper 66 which is heated by steam coil 6'1. Propane is removed throughpipe' 68 and the oil passes through pipe 69 and reducing valve 70 to low pressure stripper '11 which is heated by steam coil 67. Some direct steam or other stripping medium may be used to insure the removal of propane .trom the oil in the low pressure stripper. The dewaxed oil is finally removed through pipe 72 to suitable storage tanks not shown.

Propane from the top of low pressure stripper 71 is removed through pipe 73 to low pressure gas line 44. Likewise, propane from the top of filtrate collector 54 is conducted by pipe 74' to low pressure gas line $0, and propane from used wash propane collector 58 is conducted thereto by means of pipe 75. In short, low pressure gas line' 40 is connected-to all of the equipment which must be maintained at about 35 F. or 40 F}, or from, which all propane should be removed. Q

The used wash propane from collector 58 may be returned by pump 76 through pipe '17 and valve '78 to pipe 20, through pipe 77 and valve '79 to pipe 32, or through pipe 80 and valve 81 to pipe 38. In other words, this used wash propane may be added to the propane-oil mixture at any stage of the cooling, and I prefer to add this propane at the stage at which its temperature is the same as that of the slurry undergoing cooling.

It will be observed that the second and third chillers are heated by propane vapors from the first and second chillers respectively, but, that no means has so far been described for heating the first chiller. heated by steam. I may,-however, close valves 21, 23, 24 and.82, and open valves 26 and 83 so that propane from the high pressure stripper perature up to that of the incoming solution of oil and wax in-propane. I may also, of course, close valve 85 and open valve 86 and pass propane directly from the compressor to the first chill chamber 'or I may simply open valve 87 and conduct propane vapors from the top of the storage tank 10 through conduit 88. In any case, it will be observed that I heat up the first chiller by condensing the propane directly therein, and this is particularly effective when the propane is from the high pressure stripper 66.

It 'may be that the heat capacityof the chill chambers is not enough to condense the requisite amount of propane or to efiect the desired amount of chilling in three stages, and it should be understood that any number of cooling stages may be used. Usually the mass of iron in the chiller is greater than that of the propane-oil mixture and two to four stages of cooling are suficient. Also, I may supplement the chilling by removing some vapors through pipe 89in amounts regulated by valve 90.

The operation of my invention will be apparent from the description of the apparatus. I may introduce about three parts by volume of propane with about one part by volume of oil into the first chill chamber at a temperature of about90 F. (the chill chamber having been previously warmed by the condensation of propane vapors therein). The condensed propane in the first chill chamber may increase the rela- This chiller may, of course, be

tive volume of propane to oil to about four or five to, one. The emptied second chiller may be at a temperature of about 20 F., and when the first and second chillers are connected through conduit 30, both of these chillers may reach a temperature of about 60 F., at which temperature the slurry may be transferred from the, first chiller to the second chiller. In the meantime, the batch in the third chiller has been cooled by withdrawal of vapors through conduit 39 to a temperature of about 40 and emptied, and when the second chiller is connected to the third through conduit 37, equilibrium is reached at a temperature of 20, at which temperature the slurry is transferred from the second chiller to the third chiller. The temperature of the slurry in the third chiller is finally lowered to about 40 by withdrawal of vapors through pipe 39 by compressor 41,and the second'chiller, which is now back to- 20, isready to be used once more to condense propane from the first chiller, the first chiller having been warmed up before the introduction of the charge by warm high pressure propane vapors from stripper 6B.

A most important featureof the invention "is the method of avo'ding shock chilling without excessive loss of re rigeration, thereby. efiecting a very great saving in compressor costs; The metal in each chill chamber will probably weigh more than all of the propane and oil which it contains, and by this systemb! warming up the chill chambers by condensing propane vapors therein I may raise and lower the temperature of this enormous mass of metal at practically no cost and without great heat losses.

Another very important feature is that I maintain my diluent ratio substantially constant throughout the several chilling stages. In other words, the diluent-evaporated from the first chiller and condensed in the second chiller is reunited with the slurrybefore the cooling in the second chiller is initiated.

By connecting thevapor spaces 0 successive chilling tanks, as hereinabove desc ibed, I insure absolute equilibrium of both temperature I and pressure and Iiind that this equilibrium is established in 'a small time interval, usually about tento fifteen minutes. The balancing of temperatures and pressures is automatic and tool-proof, and besides the substantial savings in compressor costs and in steam and condenser water requirements, I- positively avoid shock chilling and am enabled to carry out the entire process rapidly and smoothly without interruption. l 1

Whi e I have described in detail a preferred embodi ent of my invention it should be under stood that I do not limit myself to the details hereinabove set forth except as defined by the following claims which should be construed as broadly as the prior art will permit. It may be necessary, for instance, to regulate the flow of gas from one chill chamber to thenext so that,

a desired cooling rate of about 3? per minute may be obtained. Two or more chillers may be employed and I may use any number of stages. Filters, filtrate collectors, etc. may be replaced by any equivalent means, and any of these elements may be modified in accordance with engineering practice familiar to those skilled in the art.

that the description of the invention might be clearly and concisely stated.

I claim:

1. The method of preventing shock chilling in a propane dewaxing system wherein a diluted oil-wax mixture is chilled in a plurality of stages which comprises connecting the vapor space of one stage to a following stage whereby propane vapors from the first stage are condensed in the said following stage to bring about equalization of both pressure and temperature, and subsequently transferring the cooled slurry from the first stage to said following stage wherein it is re-combined with the condensed propane.

2. In a propane dewaxing system wherein chilling of a diluted oil-wax mixture is effected in a plurality of stages, the method of chilling which comprises removing chilled slurry from a latter stage, connecting said stage with the top of a prior stage whereby propane vapors from the prior stage may be removed and condensed in the latter stage, allowing the two stages substantially to come to equilibrium and thereafter transferring the slurry from the prior stage to the latter stage.

3. In a propane dewaxing system, the method of chilling a diluted oil-wax slurry which comprises a plurality of transfers between stages in the manner set forth in claim 2.

ROY N. GILES.

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