PROCESS FOR DEWAXING HYDROCARBONS EMPLOYING LOW-SPEED SCRAPED-SURFACE CHILLERS

Abstract: A hydrocarbon oil dewaxing process comprises passing the waxy oil through a staged vertical tower, injecting cold solvent at a plurality of stages along the vertical tower under conditions of high agitation to achieve substantially instan­ taneous mixing at each point, continuing the chilling, prefer­ ably at a rate of from 0.55 to 4.44°C (1 to 8°F) per minute, by means of cold solvent injection until a temperature above the filtering temperature but less than 22.2°C (40°F) above the filtering temperature is reached. The oil is subsequently cooled to the wax separation temperature in rotating-element scraped-surface chillers. The operating speed of the rotating elements in the scraped surface chiller is in the range of from 8 to 14% of the original design operation speed. Operation at this reduced speed improves wax separation rates by about 10 to 20% while not substantially adversely affecting the heat transfer performance of the chillers.

Description: PROCESS FOR DEWAXING HYDROCARBONS EMPLOYING LOW-SPEED SCRAPED-SURFACE CHILLERS The present invention relates to a process for dewaxing hydrocarbons employing low-speed scraped-surface chillers. More specifically, this invention relates to an improved process for dewaxing hydrocarbon oils, particularly petroleum oils, most particularly lube oils wherein said waxy oil is introduced at a temperature above its cloud point into à first chilling zone divided into a plurality of stages, passing said waxy oil from stage-to-stage of said chilling zone, introducing a cold dewaxing solvent into at least a portion of said stages, whereby a solvent-waxy oil mixture is formed, maintaining a high degree of agitation in at least a portion of the stages containing solvent and waxy oil, thereby effecting substantially instantaneous mixing of said solvent and said waxy oil while cooling said solvent-waxy oil mixture, preferably at a rate of from 0.55 to 4.44 C (1 to 8 F) per minute, as it progresses through said first chilling zone to a temperature greater than the temperature at which the wax is separated from the oil i.e., the separation temperature, but less than about 22.20C (400F), above said separation temperature, whereby a substantial portion of the wax is precipitated from said waxy oil under conditions of said high degree of agitation, and forming a solvent-oil mixture containing precipitated wax, withdrawing said mixture containing precipitated wax from said first chilling zone, and cooling the same to the separation temperature in a second chilling zone comprising scraped surface chillers, thereby precipitating a further portion of said wax from said waxy oil and separating said wax from the oil-solvent in solid-liquid separation means, the scraped surface chillers of the second chilling zone being operated at a speed of only from 5 to 20%, preferably 8 to 14%,of the original design operating speed. This approximately 10 fold decrease in scraper element speed results in obtaining wax filtration rates improved on the order of 10 to 20%, preferably 15 to 20%, while heat transfer coefficients are either uneffected or reduced by only about 15%. This loss of heat transfer efficiency is more than compensated by the improved wax filtration rates obtained. It is known in the prior art to dewax hydrocarbon oilstocks by cooling an oil-solvent solution in scraped surface heat exchangers before separating the crystallized wax from the oil by physical means. In U.S. Patent 3,775,288 it is taught that scraped surface heat exchangers can be used as a secondary cooling zone for the dewaxing of hydrocarbon oils following a primary cooling zone in which oil is cooled by contacting said oil with a cold solvent at a plurality of points along a vertical tower while maintaining a zone of intense agitation in at least a portion of the points of solvent injection, such that substantially instaneous mixing occurs at each point, i.e., within a second or less. This first cooling zone has become known as DILCHILL, a registered service mark of Exxon Research and Engineering Company. In the standard DILCHILL operation, oil is cooled by the injection of a chosen dewaxing solvent along the various stages of the DILCHILL tower with intense agitation from the cloud point to a temperature about 400F above the separation temperature of the wax-in-oil typically followed by additional cooling in scraped surface chillers to the separation temperature. It has been discovered that the above process is improved by reducing the speed of the rotating elements in the scraped surface chiller to a speed of from about 5 to 20%, preferably 8-14% of the original design operation speed of the scraped surface chiller. Operation at this reduced speed improves wax filtering rates by about 10 to 20%, preferably 15 to 20%, while not adversely affecting the heat transfer performance of the chillers. This approximately 10 fold decrease in scraper element speed resulting in improved wax separability (as by filtration) is accompanied by no more than a 15% loss of heat transfer efficiency. This loss of heat transfer efficiency is more than made up by the improved wax separation [filtration) rates obtained. Any hydrocarbon oilstock, petroleum oilstock, distillate fraction or lube oil fraction may be dewaxed by the process of this invention. In general, these stocks will have a boiling range within the broad range of about 5000F to about 13000F. The preferred oil stocks are the lubricating oil and specialty oil fractions boiling in the range of 5500F to 12000F. These fractions may come from any source such as paraffinic crudes obtained from Aramco, Kuwait, the Pan Handle, North Louisana, Western Canada, etc. The hydrocarbon oil stock may also be obtained from any of the synthetic crude processes now practiced or envisioned for the future such as coal liquefaction, tar sands extraction, shale oil recovery, etc. Any low viscosity solvent for oil may be used in the process of this invention, representative of such solvents are the ketones having 3 to 6 carbon atoms such as acetone, methylethylketone (MER) r and methylisobutyl-ketone (MIBK) and the low molecular weight hydrocarbons such as ethane, propane, butane, propylene and the like, as well as the mixtures of the foregoing ketones and mixtures of the aforesaid ketones with C6 to C10 aromatic compounds such as benzene and toluene. In addition, halogenated low molecular weight hydrocarbons such as dichloromethane and dichloroethane and mixtures thereof may be used as solvents. Specific examples of suitable solvent mixtures are methylethylketone and methylisobutylketone; methylethylketone and toluene; acetone and toluene; acetone and propylene; benzene and toluene; dichloromethane and dichloroethane. The preferred solvents are the ketones. A particularly preferred solvent mixture is a mixture of methylethylketone and methylisobutylketone or a mixture of acetone and propylene. Another preferred solvent mixture is methylethylketone and toluene. General operating conditions of the instant invention are recited and presented in detail in U.S. Patents 3,775,288 and 3,773,650, both of which are incorporated by reference. The instant application is an improvement over both of these patents by demonstrating improved dewaxing and wax filterability by reducing the speed of the scraper element in the scraped surface chilling units which follow the DILCHILL process tower. Scraped surface chillers such as those used in combination with DILCHILL towers described in U.S. Patent 3,773,650 and 3,775,288 generally operate at rotating element speeds from 14 to 30 revolutions per minute. This rotation is in response to the need to remove wax from the chiller walls since build-up of wax on the cooling surfaces results in a substantial decrease in the chilling efficiency of the units. The build-up of wax on the chilling surf aces and internals also has the effect of effectively blocking the flow paths of the precipitated wax/oil solvent slurry increasing the pressure drop through the unit. It has now been surprisingly discovered that scraped surface chillers can be run efficiently at approximately a 10 fold decrease in rotating element scraper speed, i.e., at speeds of from 1.5 to 2.4 RPM, and that such a speed reduction does not hamper the heat exchange ability of the chiller nor result in an unacceptable pressure drop across the chiller. In fact, and surprisingly, it has been found that the wax coming from such a unit wherein the rotating element is operating at the reduced speed exhibits a surprisingly increase/improvement in separability (i.e., filterability) yielding a wax cake which does not clog the filter clothes or filtering means typically employed in a solid-liquid separating means. The frequency of wax removal from the wall is sufficient to maintain adequate heat transfer rates, but significantly reduces the addition of "wall crystals" to the slurry which are responsible for reducing filtration performance. EXAMPLE A The lead and lag scraped surface chillers in a typical DILCHILL process stream had their rotating element speed reduced frp, 14 RPM to 2.3 RPM in the 6" lead chiller and from 24 RPM to 1.8 RPt5 in the 8" lag chiller. This reduction in rotating element speed resulted in an increase in laboratory measured wax filter rates by 15% on LP 150N and LP 600N oils. A base DILCHILL process stream (sequence 1-4) and a test DILCHILL process stream (monitored both before sequence (1A, 2A) and after sequence (3A, 4A) element speed reduction) were compared so as to evaluate the degree of benefit obtained by the speed reduction when handling LP 150N oil stock. Table I summarizes the results of the runs, TABLE I BAYTOWN @P 150@ TEST RESULTS EMI6.1 <SEP> <tb> <SEP> -UU- <SEP> - <SEP> o <SEP> o <SEP> = <SEP> n <SEP> e <SEP> g <tb> <SEP> oo^e <SEP> e <SEP> E) <tb> <SEP> :1 <SEP> I <tb> <SEP> Oe <SEP> %I <SEP> X <SEP> h;l <tb> <SEP> C <SEP> ¯ <SEP> ¯ <SEP> G <SEP> C <SEP> o <SEP> C <SEP> ¯- <SEP> O <SEP> s <SEP> C <SEP> G <SEP> > <SEP> O <tb> <SEP> 0 <tb> <SEP> O <SEP> O; <SEP> N <SEP> e <SEP> l <SEP> <SEP> o <SEP> D <SEP> Y > &verbar; <SEP> e <SEP> N <SEP> o <tb> <SEP> YY <SEP> i)tlutlon <SEP> CCI/ <SEP> N <SEP> Li <SEP> I <SEP> Ollutlon <SEP> NLi <SEP> ulds <SEP> tv <SEP> ¯ <SEP> N <SEP> ev <SEP> b <tb> <SEP> 1)at <SEP> f, <SEP> flatlo <SEP> r <SEP> I?at <SEP> g <SEP> iar <SEP> latlo <SEP> 0u(1 <SEP> etlinI <SEP> CL <tb> <SEP> 1 <tb> <SEP> Sequence <SEP> r <SEP> ooh <SEP> -- <SEP> wiw <SEP> !!!!nI'day <SEP> ¯¯¯¯¯¯¯ <SEP> M3/tt11 <SEP> o <SEP> ¯¯¯¯¯¯ <SEP> > <SEP> I <SEP> c <SEP> m <SEP> C' <tb> <SEP> o <SEP> cu <SEP> ;I <SEP> <tb> DI1ÙIL1. <SEP> 1 <SEP> 9,95 <SEP> 4.!?G <SEP> 2.40 <SEP> t. <SEP> tt <SEP> rt <tb> TOWJ:.R <SEP> I <tb> <SEP> u <tb> <SEP> m <tb> <SEP> UZ <SEP> W <tb> <SEP> V <SEP> 11.33 <SEP> 5.43 <SEP> 454 <SEP> 2.719.41 <SEP> m <SEP> N <SEP> t <SEP> O <SEP> 2.14 <SEP> 03.1 <tb> <SEP> cy <SEP> El <SEP> 01 <SEP> 0) <SEP> 01 <SEP> Ij <tb> <SEP> E <SEP> o <SEP> e7t <SEP> 5.22 <SEP> .2.63 <SEP> 10.99 <SEP> o <SEP> N <SEP> t <SEP> <SEP> $ <SEP> C <SEP> <tb> DIlCIlILL <SEP> IA <SEP> 10.33 <SEP> 5.17 <SEP> 2.?() <SEP> 7.9? <SEP> 4.31 <SEP> 2.10 <SEP> 11.2 <tb> <SEP> 1,, <SEP> 4.20 <SEP> 2.66 <SEP> 1(1.4 <tb> < <SEP> II <SEP> 2A <SEP> 10.11 <SEP> 4.73 <SEP> 2.0 <SEP> 12.22 <SEP> 4.10 <SEP> 2.92 <SEP> C <SEP> 2.0(1 <SEP> 03.5 <tb> <SEP> 11.69 <SEP> ¯ <SEP> 21I06SSC11,19 <SEP> 4.59 <SEP> 2738sSC916 <tb> <SEP> 0 <tb> <SEP> Ma <SEP> = <SEP> m <SEP> e <SEP> C <SEP> m <SEP> *n <SEP> w <SEP> O <tb> <SEP> Low <SEP> rw <SEP> r <SEP> ¯ <SEP> Ln <SEP> n <SEP> <tb> <SEP> > <SEP> . <SEP> . <SEP> ¯¯¯ <SEP> . <SEP> . <SEP> . <SEP> . <SEP> . <SEP> . <SEP> . <tb> I)tIÌ1ILL <SEP> 3A <SEP> 12.29 <SEP> e <SEP> 2.fl0 <SEP> 12.47 <SEP> 4.!;5 <SEP> 2.92 <SEP> 10.03 <SEP> e <SEP> e <SEP> v <SEP> X <SEP> e <tb> <SEP> r <SEP> N <SEP> o <SEP> II <SEP> 12.66 <SEP> > <SEP> 2.115 <SEP> 6"SSC <SEP> = <SEP> rX <SEP> K <SEP> n <SEP> f <tb> '' <SEP> E' <SEP> L: <SEP> 4A <SEP> 12.06 <SEP> N <SEP> 2.00 <SEP> 12.60 <SEP> 3.0 <SEP> 2.00 <SEP> 11.14 <SEP> e <SEP> 2.0? <SEP> 2.5 <tb> <SEP> 12.34 <SEP> o <SEP> | <SEP> 4.20 <SEP> 2.90 <SEP> 11.00 <SEP> 4.3(1 <SEP> 2.09 <SEP> (19.2 <tb> <SEP> ¯ <SEP> o <SEP> xi <SEP> Sn <SEP> e <SEP> m <SEP> ' <SEP> : <SEP> C <SEP> O <SEP> s <SEP> C <SEP> ;n <SEP> 2 <SEP> s <tb> <SEP> > <SEP> = <SEP> v <SEP> N <SEP> s <SEP> O <SEP> , <SEP> , <SEP> 8 <SEP> t <SEP> C <SEP> = <SEP> 2 <SEP> D <tb> <SEP> ¯w¯ <SEP> s <SEP> ev <SEP> N <SEP> N <SEP> rzl <SEP> N <SEP> N <SEP> N <SEP> N <SEP> N <SEP> N <SEP> s <SEP> N <tb> <SEP> vwl <SEP> I <tb> <SEP> ma <SEP> w <SEP> e <SEP> v <SEP> m <SEP> n <SEP> N <SEP> N <SEP> Y <SEP> ¯ <SEP> l <SEP> <SEP> N <SEP> > <SEP> <tb> <SEP> > <SEP> C <SEP> n <SEP> ¯^ <SEP> ¯ <SEP> rs <SEP> ISz <SEP> O <SEP> &verbar; <SEP> es <SEP> o <SEP> c <SEP> D <tb> <SEP> <SEP> > <SEP> v <SEP> "n <SEP> v <SEP> v <SEP> r <SEP> 1 <SEP> ¯ <SEP> e <SEP> wr <SEP> e <tb> <SEP> bb <SEP> > <SEP> o <SEP> es <SEP> m <SEP> o <SEP> x <SEP> ¯&verbar; <SEP> ¯ <SEP> D <SEP> t7 <tb> <SEP> ¯ <SEP> ¯ <SEP> o <SEP> o <SEP> ¯ <SEP> OI <SEP> O <SEP> <tb> <SEP> 1 <tb> <SEP> 1 <tb> <SEP> 1 <SEP> < , <SEP> < <SEP> < <SEP> c <tb> <SEP> 1 <tb> <SEP> tel <tb> <SEP> n <SEP> X <SEP> U <SEP> X <SEP> m <tb> <SEP> S <SEP> 3 <SEP> W <SEP> 3 <SEP> ç <SEP> 3 <SEP> ç <tb> <SEP> H <SEP> O <SEP> ux <SEP> i <SEP> O <SEP> Ei <SEP> H <SEP> O <SEP> b <tb> <SEP> n <SEP> H <SEP> ¯ <SEP> n <SEP> H <SEP> ¯ <SEP> C <SEP> Ei <SEP> w <tb> *SSC = scraped surface chiller m3 2 The outlet feed filter rate averaged 8.80 /m day on the base stream for the entire test period which represents 81.3% of the average filter rate entering the base process stream. The performance of the test stream prior to the speed reduction is similar (Sequence lA, 1B), averaging 32 8.97 m /m day or 79.7% of the filter rate entering the test process stream. When the speed of the rotating elements in the scraped surface chillers in the test process stream was reduced (Sequence 3A, 4A), the filter rate in 32 creased 23% to 11.00 m /m day; 89.2% of the entering filter rate. Comparing the outlet-inlet filter rate ratio of the test process stream before (79.7%) and after (89.2%), the speed reduction reveals a 12% increase in the throughput as the result of the slow speed scraping. A similar test was conducted employing LP 600N as the feedstock. This test differed from the previous one, however, in that the before and after data from the test process evaluation stream comes from two different runs. See Table 2. In Table 2 speed reduction is shown only for DILCHILL Tower II (Test Stream) (Sequence A3-C3). The comparison is to a separate and distinct DILCHILL Tower I (Standard stream) (Sequence Al-Cl). No direct comparison was run on the test stream with the scraped surface chillers running at normal speed. At a different time, however, DILCHILL Tower II (Test Stream) had been run with the scraped surface chillers run at normal speed (Sequence A2 D2). TABLE 2 LP 600N TEST RESULTS EMI8.1 Ratio <tb> Filter <SEP> Dilution <SEP> Filter <SEP> Dilution <SEP> Filter <SEP> Dilution <SEP> Outlet/Inlet <tb> Rate <SEP> Liquids <SEP> Ratio <SEP> Rate <SEP> Liquids <SEP> Ratio <SEP> Rate <SEP> Liquids <SEP> Ratio <SEP> Filter <SEP> Rate <tb> Sequence <SEP> m3/m2 <SEP> day <SEP> Solids <SEP> w/w <SEP> m3/m2 <SEP> day <SEP> Solids <SEP> w/w <SEP> m3/m2 <SEP> day <SEP> Solids <SEP> w/w <SEP> % <tb> DILCHILL <SEP> A1 <SEP> 4.06 <SEP> 9.37 <SEP> 2.99 <SEP> 3.76 <SEP> 7.89 <SEP> 2.80 <SEP> 3.34 <SEP> 7.79 <SEP> 2.96 <SEP> 82.3 <tb> TOWER <SEP> I <SEP> B1 <SEP> 4.00 <SEP> 9.50 <SEP> 2.77 <SEP> - <SEP> 6"SSC*- <SEP> 3.68 <SEP> 8.22 <SEP> 2.66 <SEP> -8"SSC- <SEP> 3.44 <SEP> 7.83 <SEP> 2.76 <SEP> 86.0 <tb> (STANDARD <SEP> STREAM) <SEP> C1 <SEP> 4.22 <SEP> 9.96 <SEP> 2.63 <SEP> 3.81 <SEP> 9.40 <SEP> 2.74 <SEP> 3.61 <SEP> 8.10 <SEP> 2.72 <SEP> 85.5 <tb> 4.09 <SEP> 9.61 <SEP> 2.80 <SEP> 3.75 <SEP> 8.50 <SEP> 2.73 <SEP> 3.46 <SEP> 7.91 <SEP> 7.91 <SEP> 84.6 <tb> DILCHILL <SEP> A2 <SEP> 5.25 <SEP> 7.22 <SEP> 3.18 <SEP> NOT <SEP> SAMPLED <SEP> 3.04 <SEP> 7.57 <SEP> 3.00 <SEP> 57.9 <tb> TOWER <SEP> II <SEP> B2 <SEP> 5.55 <SEP> 7.34 <SEP> 2.66 <SEP> -6"SSC*- <SEP> -8"SSC- <SEP> 3.58 <SEP> 7.50 <SEP> 2.18 <SEP> 64.5 <tb> (TEST <SEP> STREAM) <SEP> C2 <SEP> 4.87 <SEP> 8.33 <SEP> 2.08 <SEP> 3.20 <SEP> 6.76 <SEP> 2.77 <SEP> 65.7 <tb> D2 <SEP> 4.77 <SEP> 8.11 <SEP> 3.20 <SEP> 3.18 <SEP> 6.33 <SEP> 2.83 <SEP> 66.7 <tb> 5.11 <SEP> 7.75 <SEP> 2.78 <SEP> 3.25 <SEP> 7.04 <SEP> 2.70 <SEP> 63.7 <tb> DILCHILL <SEP> A3 <SEP> 5.09 <SEP> 8.60 <SEP> 3.16 <SEP> 4.24 <SEP> 8.23 <SEP> 3.19 <SEP> 3.85 <SEP> 7.29 <SEP> 3.07 <SEP> 75.6 <tb> TOWER <SEP> III <SEP> B3 <SEP> 4.77 <SEP> 8.60 <SEP> 3.11 <SEP> -6"SSC- <SEP> 4.54' <SEP> 7.42 <SEP> 2.83 <SEP> -8"SSC- <SEP> 3.86 <SEP> 7.66 <SEP> 3.08 <SEP> 80.9 <tb> (TEST <SEP> STREAM) <SEP> C3 <SEP> 5.04 <SEP> 8.93 <SEP> 2.94 <SEP> Reduced <SEP> 4.46 <SEP> 8.04 <SEP> 2.97 <SEP> Reduced <SEP> 4.06 <SEP> 7.54 <SEP> 2.91 <SEP> 80.6 <tb> Speed <SEP> Speed <tb> 4.97 <SEP> 8.71 <SEP> 3.07 <SEP> 4.41 <SEP> 7.90 <SEP> 3.00 <SEP> 3.92 <SEP> 7.50 <SEP> 3.02 <SEP> 79.0 <tb> *SSC = scraped surface chiller Comparing the absolute outlet filter rates before (3.25 m3/m2 day) (Sequence A2-D2) and after (3.92 m day) (Sequence A3-C3), the speed reduction, based on approximately equal entering filtering rates for the different runs reveals an improvement in the test process stream of about 21%. EXAMPLE B The base DILCHILL Process stream and the test process stream (before and after speed reduction) were evaluated to determine the effect of the reduction in the speed of the rotating elements on liquids/solids ratio for LP 150N, and for LP 600N. Based on approximately equal liquids/solids ratios from the DILCHILL towers, it was determined that the reduction in speed in the scraped surface chiller had little absolute effect on the liquids/ solids ratio exiting the process streams. Tables I and II present this data. EXAMPLE C The base DILCHILL process stream and the test process stream, again before and after speed reduction, were compared and evaluated to determine the effect of the speed reduction on heat transfer efficiency. Table III summarizes the results of the comparison tests. For given test sequences, as when comparing the before and after values for either LP 150N (Sequences 1A, 2A and 3A, 4A) or LP 600N (Sequences Al, B1, C1 and A3, B3, C3) the slurry flow volumes, flow velocities and chill rates are relatively equivalent. TABLE 3 HEAT TRANSFER DATA EMI10.1 <tb> <SEP> rune <tb> <SEP> ç <SEP> ¯ <SEP> G <SEP> ¯ <SEP> ,* <SEP> . <SEP> . <SEP> ¯ <SEP> ¯ <SEP> e <SEP> <tb> <SEP> Tube <SEP> Dlasotcr <SEP> 6 <SEP> 1 <SEP> In <SEP> Tube <SEP> Diatnater <SEP> c; <SEP> 6 <SEP> In <tb> <SEP> IIc.t <SEP> ;ransier <SEP> Area <SEP> 761 <SEP> rt2 <SEP> lle'L <SEP> Transrer <SEP> rea <SEP> 1005 <SEP> rt' <tb> <SEP> 1 <SEP> B" <SEP> SSC <tb> <SEP> Ie1;:P. <SEP> pr1aPne <SEP> q <SEP> U <SEP> T0ePt <SEP> T;nsi <SEP> Tenip <SEP> (1 <SEP> U <SEP> o,'Tcp <tb> <SEP> F <SEP> 111 <SEP> Pt" <SEP> lit" <SEP> 'F <SEP> Vre,ane <SEP> ill <SEP> Pt,' <SEP> IILu <SEP> 'F <tb> <SEP> Tt1 <SEP> F <SEP> 5 <SEP> ,ns <SEP> rst <SEP> zoors <tb> 1 <SEP> 26.6 <SEP> =t <SEP> c <SEP> 173.2 <SEP> 1.0 <SEP> 3.11 <SEP> 0t <SEP> <SEP> ol <SEP> w <SEP> <tb> <SEP> 2 <SEP> 25.9 <SEP> 8 <SEP> 2.12 <SEP> 125.6 <SEP> 6.6 <SEP> LP <SEP> 2 <SEP> cn <SEP> V) <tb> <SEP> 3 <SEP> 21.5 <SEP> - <SEP> 2.61 <SEP> 165.6 <SEP> 3.1 <SEP> 16rnI <SEP> 3.1 <SEP> -31.1 <SEP> 2.5 <SEP> s <tb> <SEP> &commat; <SEP> ç <SEP> ¯ <SEP> ¯ <SEP> <SEP> - <SEP> ¯ <SEP> <tb> <SEP> = <SEP> aO <SEP> e <tb> z <SEP> ¯ <SEP> :1.o <SEP> lOt <SEP> 0,5 <SEP> ;;12..; <SEP> .: <SEP> 0 <SEP> -1.;,; <tb> <SEP> 8 <tb> Cl <SEP> 15.5 <SEP> -,) <SEP> 2.29 <SEP> o <SEP> ¯ <SEP> e <tb> <SEP> 2.58 <SEP> 135.2 <SEP> 1.16 <SEP> 11.1 <tb> <SEP> Cr <tb> <SEP> g- <SEP> ssc <tb> <SEP> ¯L <SEP> 4 <SEP> \ <SEP> ¯ <SEP> I <SEP> x <tb> lA <SEP> 26.6 <SEP> -11.6 <SEP> 1.12 <SEP> 170.6 <SEP> 1.1 <SEP> 1.1 <SEP> ¯ <tb> 2A <SEP> 26.1 <SEP> -11.1 <SEP> 2.11 <SEP> 110.3 <SEP> 1.0 <SEP> O- <SEP> -----h---7 <SEP> 10.0 <SEP> -14.4 <tb> <SEP> 2.91 <SEP> 163.5 <SEP> 2.01 <SEP> 80.1 <tb> <SEP> % <SEP> Speed <SEP> Drive <SEP> ln1aI1ed <SEP> 15011 <SEP> Slow <SEP> Speed <SEP> c <SEP> e <SEP> r7 <SEP> X <tb> 3A <SEP> 26.6 <SEP> -12.9 <SEP> 2.00 <SEP> 115.1 <SEP> I <SEP> * <tb> 4A <SEP> 21.1 <SEP> -11,0 <SEP> 2.11 <SEP> 113.3 <SEP> 2.8 <SEP> 2.0 <SEP> -31.2 <SEP> ? <SEP> 1.011 <SEP> 65.0 <SEP> -12.1 <tb> <SEP> 2.00 <SEP> 111.2 <SEP> 1.91 <SEP> 66.2 <tb> A3 <SEP> 15.0 <SEP> -0.0 <SEP> 2.91 <SEP> 143.9 <SEP> 1.3 <SEP> . <SEP> 1.3 <SEP> .22.0 <SEP> 1.51 <SEP> 67.9 <SEP> -1.1 <tb> B3 <SEP> 11.1 <SEP> -6.6 <SEP> 271 <SEP> 111.1 <SEP> 8.3 <SEP> -21.1 <SEP> 1.61 <SEP> 60.7 <SEP> -6.S <tb> w <SEP> 36.8 <SEP> -6.6 <SEP> 2.99 <SEP> 112.9 <SEP> 9.6 <SEP> (;0O11 <SEP> S <SEP> -25.2 <SEP> 1.85 <SEP> o1 <SEP> -6.a <tb> <SEP> c <SEP> 112.1 <SEP> . <SEP> iffi61 <SEP> 69.1 <tb> <SEP> c <SEP> * <SEP> <SEP> 0 <SEP> rs <SEP> zal <SEP> <SEP> '1 <SEP> <SEP> o l <SEP> et <tb> <SEP> ¯ <SEP> V <SEP> O <SEP> ¯ <SEP> v <SEP> N <SEP> N <SEP> s <SEP> s <SEP> ¯ <SEP> e <SEP> <SEP> F" <SEP> w <SEP> " <SEP> ¯ <SEP> N <SEP> <SEP> <tb> <SEP> c <SEP> Z <SEP> o <SEP> o <SEP> oi <SEP> ¯ <SEP> o <SEP> o <SEP> e <SEP> o <SEP> ¯ <SEP> ¯ <SEP> > <SEP> o <SEP> o <SEP> o <SEP> o <tb> <SEP> ¯ <SEP> ¯0; <SEP> -0 <SEP> -'OVD <SEP> ¯¯ <SEP> srs <SEP> o"oO <tb> <SEP> * <SEP> a <SEP> O <SEP> O <SEP> Y <SEP> e <SEP> O <SEP> ¯ <SEP> O <SEP> ¯ <SEP> O <SEP> G <tb> <SEP> E <SEP> a <SEP> s¯ <SEP> o <SEP> ¯ <SEP> ¯ <SEP> <SEP> l <SEP> <SEP> us <SEP> e <SEP> o <tb> <SEP> z <tb> <SEP> g <SEP> H <SEP> - <SEP> < <SEP> C <SEP> n <SEP> rF <tb> <SEP> W1 <SEP> H <SEP> N <SEP> e-) <SEP> < <SEP> < <SEP> < <SEP> ° <SEP> n <tb> *SSC = Scraped Surface Chiller The heat transfer coefficients were calculated for each sequence using average throughput and temperature data for five l-hour periods during each sequence and averaging the result. For the LP 150N runs, it can be seen that very little change occurred in heat transfer performance of the 6" scraped surface chillers after the speed reduction. An 18% decrease in heat transfer coefficients was recorded for the 8" scraped surface chillers after the speed reduction. For the LP 600N runs, very little difference is seen in the heat transfer coefficients of the 6" chillers while about a 128 reduction in heat transfer coefficient was measured for the 8"chiller. Since a majority of the heat removal occurs in the 6" chiller, the overall debit in heat transfer is about 6 to 7% along the entire process stream. In this patent specification, the following approximate conversions of units apply: Temperature in F are converted to C by subtracting 32 and then dividing by 1.8. Temperature differences in OF are converted to OC by dividing by 1.3. Lengths in inches (in. or ") are converted to centimetres by multiplying by 2.54. Areas in square feet (ft2) are converted to cm2 by multiplying by 929.0. Amounts of heat in, British Thermal Units (BTU) are converted to calories by multiplying by 252.0. The feeds LP 150N and LP 600N are wax-containing hydrocarbon oils having viscosities of 150 SUS (about 32 centi-strokes) and 600 SUS (about 130 centi-strokes) respectively.

Claims: CLAIMS 1. A process for dewaxing a wax-containing hydrocarbon oil comprising introducing said oil at a temperature above its cloud point into a first chilling zone divided into a plurality of stages, passing the oil from stage-to-stage of said chilling zone, introducing a dewaxing solvent into at least a portion of said stages, whereby a solvent-oil mixture is formed, maintaining a high degree of agitation in at least a portion of the stages containing solvent and oil thereby effecting substantially instantaneous mixing of said solvent and said oil while cooling said solvent-oil mixture as it progresses through said first chilling zone to a temperature greater than the temperature at which the wax is separated from the oil, i.e., the wax separation temperature, but less than about 22.220C (400F) above said separation temperature, whereby a substantial portion of the wax is precipitated from said oil under conditions of said high agitation and forming a slurry containing the solvent-oil mixture and precipitated wax, withdrawing said slurry containing precipitated wax from said first chilling zone and cooling same to a wax separation temperature in a second chilling zone comprising scraped surface chillers thereby precipitating a further portion of said wax from said oil and separating said wax from the solvent-oil mixture in solid-liquid separation means, the process being characterized by comprising operating the scraped surface chillers of the second chilling zone at a speed of from 5 to 20% of the original design operating speed. 2. The process of claim 1 wherein the hydrocarbon oil which is dewaxed is a petroleum oil. 3. The process of claim 1 wherein the hydrocarbon oil which is dewaxed is a lube oil. 4. The process of any one of claims 1, 2 or 3 wherein the rotating element of the scraped surface chiller rotates at a speed of from 1.4 to 2.4 RPM. 5. The process of any one of claims 1, 2, 3 or 4 wherein the dewaxing solvent is selected from the group consisting of C3 to C6 ketones, low molecular weight hydrocarbons, mixtures of C3 to C6 ketones with aromatic compounds having from 6 to 10 carbon atoms, halogenated low molecular weight hydrocarbons and mixtures thereof. 6. The process of claim 5 wherein the dewaxing solvent is selected from the group consisting of C3 to C6 ketones and mixtures of C3 to C6 ketones with aromatic compounds having from 6 to 10 carbon atoms, 7. The process of claim 5 wherein the dewaxing solvent is selected from the group consisting of methylethylketone, methylisobutylketone and mixtures thereof, methylethylketone and toluene, acetone-and toluene, and acetone and propylene. 8. The process of any one of claims 1 to 7 wherein the first chilling zone is a DILCHILL tower wherein the oil is mixed with portions of cold de-waxing solvent in at least some stages thereof with a high degree of agitation in at least a portion of each stage where cold solvent is introduced. 9. The process of claim 8, wherein the wax and oil/solvent mixture are separated by filtration. 10. The process of any one of claims 1 to 9 wherein the scraped surface chiller of the second chilling zone is operated at a speed of from 8 to 14% of the original design operating speed.

Inventors: BROADHURST, THOMAS EDWIN
Applicants: EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1980
Main classification: C10G73
IPC codes: C10G73