US2439434A - Method and apparatus for dewaxing oils - Google Patents

Description

April 13, 1948. H. o. LINDGREN METHOD AND APPARATUS FORA DEWAXING OILS Filed April 26, 1946 Ofi-Wax Y r-l W/fA/ESS.'

Patented Apr. 13, 1948 Ariflrrii DEWAXING o s` iran-secar Lindgren. .smeasiiie ortica signor to Aktiebolaget SeparatonNsDela-'stckholm, Sweden, a corporation of Sweden reclaim? This invention relates and transformation 'produets'thereoi' and vsimilar products. From the wax-bearing stock so much wax is removed by centrifuging,flte`ring or grav-'- ity-settling'that the pour point of theoil' is lowered' tothe point desired. i Thewax is precipitated 'by chilling lthe oil, usually'mined` with a In order 'to reduce theieXpense of Achille ing, the cold dewaxed oil or oil solutionis vused` solvent.

as a chilling 'medium' in' a regenerative installation wherein the' wax-heairing stock is chilled;

As adiluent or' solvent;v a'liquidis used which hasa higher solubilityfor oil than for wax; at low temperature. It may bea"solvent lighter than the oil and thus adapted'to `maintain the' specific gravity of thesolution:substantiallyblow that' ofthe wax," examples of whieh'are any iight' hydrocarbon' liquid; such "as 'i nahtha; i or it' "may bea solvent somuch heavier thantheoil that" theV speciiic vgravity fof thesolution will` loe sub 1 stantialiy alcove that of Ithe "waxg ,examples of" which" are ihalogenated-hydrocarbons su'ch as ethylene dich'loride," trichl'orethylene, acetone," butanone (methyiethylketone; or 'mixtures in i' cludingsuch solvents. 2 T1ie""solvent 4*not fonlyf' brings about thenec'e'ss'ary 'specificgravity'dif= ferential between the oil so1ution"an2i"tl'iewax` cipitation of thewaxf'and 'lowers the Vviscosity 'of the chilled" liquidi` The"wa`x"'may"be' removed either as the lheavier component, -e..g."when Vusing naphtha as a diluent; or asth'e lightercompen'ent,T e. g. when using'ethylene 'dichlorid'e as *at diluent'."v

Oil and diluentA in` suitable proportions," ehg."

1:3 byvolumefare usuallyrstmixed at a temperature sufficiently high 'tor bring` 'about "coml- `45 bearing stock is chilled by means of the wax-free plete solution-of the oil-in 'thediluent."` The'sollrtionis `then' Achilledfand the 'precipitated wax is removed.

Some light and thin oilsysuch `as' gas oil, spindle i oil and transformer oilymay sometinies'be del waxed withoutusing a solvent'. (For the sakeof simplicity both undiluted oir andloilplus vsolvent;l that is oilsolutiom'will be'referred 'to hereinafter to installations orxde WaXIIg mineral oils; tars, distillation products 3 (o1. s-iti the maximum allowable temperature`4 differential vary," for diffeient stcksand diluerits.l

For practical ,reasons a :xdewaxing plant will y havev tojoe .usedxforsdi-ffcrent ikinds of stock, and

theiregeneratiye ,"Chllng:@installation Lshould loe arrangedsoi-thatthefichillngssurface canpbe fully utilizedfunder:alleonltonszby; maintaining. the

maximum allowable .temperature differentiatb e..

1o tween the .oir-.and thegchllingsmedium.. When using ya 1 sim'plje `-regrenerative.. installation this .ish eenerallyi not; possible, ssine.; the.; cold dewaxed;` cii nowinggthrough. .the` .regenerative system will.. be; or sxnailen volume l(because `vof 4the removalof Y 15m/Jax andloffsome oiLandLdiluent therefromlthan ie flow of wax-bearing stock. When theseY tivoV liquid .streams-are simplyjpassed .in counterfiow throughtheiresenerativc systsmthetemnerature i A differential;willtthusbegsmaller at the beginning 261 ithan `at' the end I;o f the; chilling. .,CQriSequelltly,

theV greaterjpartot. tlflehllngxsurfac otithe regenerativesystemisbadlyntilized. But;` even if z'iithe stream of4 cold, dewaxed oil. through the re.- y

obtained.:hy'using--the '-process accordingto this inventiom.. i

"Iheppresentginven 'onrelates toa methodof dewaxing oils and oil-'solutlons.. of4 the kind Lmeni. tioned,;abve,;,using i. ga. V.regenerative installation -for chilling the wax-bearing stock indirect heat c gravity settlement), but also"facilitates`th"e 'pree i exchangarelaton in .counter-,current to cold, de,-

emitting 4andthe heatlabsorbing liquid, consistent 40 withthe precipitationzof-.the waxin a `form fVlf ableior its. remgceilal.;J is maintained. in different s partsnf thereeeneratve system; by chilling the Chilling@medinmpxitselfi. rJIhis; chilling f advantageously, takes` .place wat the same time ,the Y.wax-

oil.

In theacompa'nying drawings: s Figure 1 isaadiagrammatic view of a dewaxing plantinwhichthe improved process is adapted 4to behpractnied.

oil; f .t

diagrams how the plant nasa-raarste h chinery forkeepingthe chilling surfaces'free of ,Figure his Riddell., arrarigement` inggthechilling 'by the 'latterof the wax-bearing maybema'de; toz.work ;under different conditions.`

Thecilio beLdewa-xedis fedthrough the piping` precipitated wax and thus ensuring a high heat transfer coecient. During its passage through the system the stock is chilled (for example) from +50 C. to 15 C., according to the diagram in Figure 3. From the last heat exchanger chiller 2 removed and discharged through the piping 5.-

The dewaxed oil iiows through the piping 6 to the v amount of heat can be transmitted in the rtank 1, and by means of the pump 8 it is taken through the piping 9 into the coldest regenerative apparatus 2 and is passed through the whole regenerative system, in counter-current ow with the wax-bearing stock. Y

The number of the chillers 2 and 3 and of the centrifuges can of course be varied.

From the warmest regenerative apparatus 2, the dewaxed oil is discharged through the piping iii. The dewaxed oil used as the chilling medium iiows in an annular channel I I, whereas the waxbearing stock passes in counter-current flow through the central channel I2 (Figure 2). The channel II is surrounded byva jacket I3 with eX- panding ammonia introduced through the pipe line I4. Alternatively, another chilling medium than ammonia may be used, and the jacket I3 may be replaced by a cooling coil inserted in the intervening space.

Cooling jackets according to Figure 2 can be inserted at suitable places in one or more or all of the chillers 2 so as to obtain the desired temperature curve of the chilled wax-bearing oil. It

is, for instance, possible to t all the dewaxedoil pipes with a jacket over theirvwhole length, thereby obtaining a chilling 'as per diagram in Figure 3, if the chilling mediumris introduced at a suitable rate. According to the diagram the wax-bearing stock introduced through the piping I gives oil 286,000 kg.cal./hr. in the regenerative system, and the same amount of heat is of course absorbed per hour by the dewaxed oil passing in counter-flow through the heat exchangers. However, the liquid entering through the piping 9 can absorb only 190,000 kg.cal./hr. The remaining 96,000 kg.cal./hr. are absorbed through the dewaxed oil by the chilling medium circulating in the jacket I3.

In the diagram, Figure 3, a is the temperature curve for the wax-bearing stock, b the temperature curve for the dewaxed oil at a constant temperature differential throughout the whole regenerative system, c a temperature curve for a temperature diierential increasing at higher in order to obtain a Vchilling as per the diagram.

The chilling surface will thus be less utilized than if the chilling is carried out according to the invention (the curves b and c) If the dewaxed oil is then chilled to such an extent that the curve c applies, a still larger generative system, the chilling surface of which is thus still better utilized. This is conditional, however, on an increase of the temperature ,dif-

`ferential above 15 C'. being permitted.`

The curves e and f indicate the drop in temperature of the oil-wax in the chillers 3 in Figure l, which are loperating at ammonia evaporating temperatures of 33 C. and 40 C., respectively.

As `already mentioned, the heat exchanger chillers of the regenerative system must be provided with scraping machinery. The price of such chillers per square metre of chilling surface is about 4 to 5 times higher than the cost of ordinary tube and shell chillers. This less expensive type of chiller can be advantageously used for chilling the chilling oil, bearing in mind that the latter is de-waxed and no accumulation of wax on the chilling surfaces need therefore be feared. Furthermore, there is no limitation of the temperature differential between the oil solution and the medium (e. g. ammonia) for chilling it and consequently only a relatively small chilling surface is necessary.

By thus utilizing as far as possible, according to the present invention, the surface of the relatively expensive heat exchanger chillers, the plant investment costs are considerably reduced.

In certain cases it may 4be advantageous for economical reasons to t chilling jackets I3 or corresponding chilling coils in the channel II or to introduce the chilling medium in such a manner that the temperature curve differs from that raccording to Figure 3, the minimum or maximum vertical distance between the curves beinglocated somewhere between their extreme ends.

In Figure 4 the curves g and h, represent cases in which the dewaxed oil used as the chilling medium vis chilled in the last and the two iirst chillers 2, respectively, the temperature differential between the two counterow oil streams thus having a minimum and maximum, respectively, in the piping between the second and the third chillers 2. The best mode of operation will, of course, depend on the temperature diierentials which can be allowed at diierent stages of the chilling, consistently with-the precipitation of the wax in the desired form.

The curves a, g and h in Figure 3 will not in reality be straight lines.

As will be seen from Figure 3, the temperature of the dewaxed oil solution conducted to the regenerative system is somewhat (2 C.) higher, due to thermal losses in the centrifuges, pipe lines, etc., than the temperature to which the Waxbearing oil is chilled (in this case 32 C.).

Summarizing.-The essential feature of the invention consists in chilling the dewaxed oil in the course of its flow, in heat exchange relation with the wax-bearing oil, either through the entire course of its ow preceding the ammonia chillers, or through a part of the course of such flow. Further, the amount of heat abstracted from the dewaxed flow in a plurality of loci in which the chilling of the heat absorbing dewaxed oil occurs may be so varied that the lowing dewaxed oil may have any predetermined temperature at each locus so as to maintain at each locus approximately the ideal temperature differential between the direct heat-absorbing medium-the dewaxed oil-and the oil-bearing wax, such ideal Y. temperature difference being as high as is permis- What I claim and desire to protect by Letters Patent is:

1. In the process oi dewaxing mineral oils, tars, distillation and transformation products thereof and similar products, in which the wax-bearing oil is chilled in countercurrent heat exchange relation to a flowing heat absorbing liquid and in which wax and substantially wax-free oil are separated from the chilled wax-bearing oil and in which the separated dewaxed oil is utilized as the heat absorbing liquid, the improvement which comprises maintaining throughout the heat exchange system a predetermined temperature differential between the heat-absorbing dewaxed oil and the wax-bearing oil by chilling with a chilling medium the dewaxed oil in the course of its now in heat exchange relation with the waxbearing oil.

2. The process defined in claim 1 in which the dewaxed oil is chilled in the course of its flow to the extent required to maintain throughout the heat-exchange system a substantially constant temperature differential between wax-bearing oil and the dewaxed oil.

3. The process defined in claim 1 in which the dewaxed oil is chilled in the course of its flow to the extent required to maintain a temperature differential between the wax-bearing oil and the dewaxed oil that progressively decreases in the course of the iiow of the wax-bearing oil,

4. The process dened in claim 1 in whichthe dewaxed oil is chilled in the course of its flow to the extent required to maintain a temperature differential between the Wax-bearing oil and the dewaxed oil that progressively increases in the course of the flow of the wax-bearing oil.

5. The process defined in claim 1 in which the chilling medium for the heat-absorbing dewaxed oil is regulated to absorb different amounts of heat from the dewaxed oil at different loci in the course of the flow of the dewaxed oil in said heat exchange relation with the wax-bearing oil, so as to maintain predetermined temperature differentials between the dewaxed oil and the wax-bearing oil at such different loci.

6. The process defined in claim 1 in which the chilling medium for the heat-absorbing dewaxed oil is regulated to absorb different amounts of heat from the dewaxed oil at diierent loci in the course of the ow of the dewaxed oil in said heat exchange relation with the wax-bearing oil, so as to maintain approximately the predetermined maximum temperature difference between the dewaxed oil and the wax-bearing oil consistent with the precipitation of the Wax in a form favorable to its subsequent removal.

7. The process defined in claim 1 in which the dewaxed oil is chilled during only that part of the course of its o-w wherein the desired temperature differential between the unchilled dewaxed oil and the wax-bearing oil is outside a predetermined temperature range.

8. The process defined in claim 1 in which the double chilling, consisting of said chilling of the wax-bearing oil and said chilling of the dewaxed oil, is effected by flowing the dewaxed oil in an annular stream surrounding the flowing waxbearing oil and by cooling said annular stream with said chilling medium.

9. The process defined in claim 1 in which the double chilling, consisting of said chilling of the wax-bearing oil and said chilling of the dewaxed oil, is elected by flowing the dewaxed oil in an annular stream surrounding the flowing waxbearing oil and in which the annular stream of dewaxed oil is cooled by surrounding it with said chilling medium.

10. In the process of dewaxing mineral oils, tars, distillation and transformation products thereof and similar products, in which the waxbearing oil is chilled in countercurrent heat exchange relation to a owing heat absorbing liquid and in which wax and substantially wax-free oil are separated from the chilled wax-bearing oil and in which the separated dewaxed oil is utilized as the heat absorbing liquid, the improvement which comprises cooling dewaxed oil during its flow through the heat exchange system but after it has passed through part of the system and before it has completed its flow therethrough to thereby, in the earlier part of the heat-exchange between the wax-bearing oil and the dewaxed oil reckoned in the direction of flow of the waxbearing oil, increase the temperature differential between them above what it would be without such cooling, thereby maintaining a desired temperature differential between the wax-bearing oil and the dewaxed oil through substantially the entire system.

11. The process dened in claim 1 in which the double chilling, consisting of said chilling'of the wax-bearing oil and said chilling of the dewaxed oil, is effected by flowing the dewaxed oil in an annular stream surrounding the flowing waxbearing oil and in countercurrent thereto, and by surrounding said annular stream with an annular stream of said chilling medium flowing in countercurrent to said first annular stream.

12. In an oil dewaxing plant having a device for chilling the wax-bearing oil to a temperature at which the wax precipitates in a form suitable for separation of the wax from the oil, a separator connected to the outlet of said device and operable to separate the chilled product there- `from into wax and dewaxed oil, and a heat eX- changer having a duct connected to the inlet of the chilling device for delivering the wax-bearing oil thereto, the exchanger also being connected to the dewaxed oil outlet of the separator, the improvement which comprises two additional ducts in substantially concentric relation to said wax-bearing oil duct, the three ducts defining a central passage, an intermediate annular passage and an outer annular passage, said intermediate passage being connected to flow the dewaxed oil from the separator in countercurrent relation to` the wax-bearing oil in one of said central and outer passages, and inlet and outlet connections to the other of said central and outer passages for owingtherethrough a cooling medium in countercurrent relation to the dewaxed oil flow in the intermediate passage.

13. The improvement defined in claim 12, in which said central passage is connected to deliver the wax-bearing oil to the chilling device, the outer passage having said inlet and outlet connections.

HANS OLOF LINDGREN.

REFERENCES CITED The following references are of record ln the file of this patent:

UNITED STATES PATENTS Number Name Date 1,748,295 Kelley Feb. 25, 1930 2,036,374 Tuttle Apr. 7, 1936 2,085,521 Anderson et al June 29, 1937

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