US1817250A - Process of steam distillation - Google Patents

Description

4, 1931- J. G. GLASGOW PROCESS OF STEAM DISTILLATION Filed May 11, 1926 gvwe'ntoz day/ 6. 52,45 flW, W01; "5& 61mm;

Patented Aug. 4, 1931 UNITED STATES JOHN G. GLASGOW, OF PORT ARTHUR, TEXAS,

PANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF TEXAS PROCESS OF STEAM DISTILLATION Application filed May 11,

This invention relates to processes of steam distillation; and it comprises steam distillation of organic liquids under partial reflux conditions with the degree of preheat of the ingoing charge sufficient to furnish all or most of the heat required for vaporization, whereby any great amount of condensation of water in the still is prevented; the injected steam used acting primarily to reduce the boiling point of the material undergoing distillation, rather than to introduce into the still suflicient available heat to provide for the vaporization of the distillate; all as more fully hereinafter set forth and as claimed.

In petroleum refining and in other industries which practice the process of distillation, it is customary to run various materials through steam stills to separate them into fractions with a definite range of boiling points, the distillate being exposed to the action of open steam in a suitable still which is not usually heated by any additional means. For example, in refining pe troleum, crude naphtha distillate produced in various ways of distilling the crude petroleum is rerun in a steam still to produce gasoline, etc., as distillates, and higher boiling residues. In this operation it is desirable to avoid any localized high temperature; that is temperatures materially higher than the distillation temperature. For this reason outside firing and the use of high temperature steam coils in the still are both considered undesirable. No very high temperature is required in the operation of steam stills but the .number of heat units required for the vaporization is very great. lVhere the heat necessary for vaporization is furnished by steam and results in the condensation of water, the hot condensed Water formed in the still cannot be conveniently returned to the boilers or otherwise used; and to this extent the contained heat is wasted. In many cases where closed steam coils are used there is some decomposition of the material charged, due to local overheating; and the distillate from a steam still so heated may be off test. In the distilling of light petroleum fractions 1926. Serial No. ioaaw.

any local overheating will always give a product having bad doctor test. In steam stilling with all the heat required for vaporization furnished by condensation of an equivalent amount of steam the accumulation of water in the still is a nuisance and the production of the steam which furnishes this water is relatively expensive. For reasons stated, this hot water is a waste product.

It the object of the present invention to furnish all or substantially all of the heat needed for the distillation to the incoming charge before it reaches the still so that distillation can be carried on by means of open steam without any great condensation of water, such as occurs where the latent heat of steam is relied on for vaporizing the distillate. In the present process, low pressure open steam is employed, this being usually exhaust steam, and suflicient additional heat over and above that carried with the steam is supplied as pro-heat to the charge entering the still so raising its temperature to a point sufficient as to provide for the vaporization of at least 25% of the charge. In the steam stilling of a crude naphtha distillate the temperature may be so raised to about 310 F., this usually being a safe temperature.

According to my invention, pro-heat may be delivered to the ingoing charge in a number of ways and in practice I often use more than one, bearing in mind always, however, the desirability of avoiding localized. high temperatures at any point in the system. Some of the heat may be derived by methodical use of heat in the steam still hot toms or in the condensed water or in high pressure steam. In distillation I ordinarily use partial refluxing conditions, that is I employ a dephlegmating tower and I may effect some supply of heat in this tower to offset the heat losses there occurring. It

is often desirable to deliver the incoming charge into this tower whereby it is in part vaporized at the expense of the heat units of outgoing vapors of higher boiling point: in other words, I may effect part of the distillation in the reflux tower. The exhaust SSIGNOR- TO GULF REFINING COM- steam introduced into the still may be some what super-heated prior to its entry. The outgoing still bottoms and the condensation water (if any) may flow through a heat interchanger and deliver heat to inflowing colder charge in fore-warmers; the material thus warmed then being brought to a higher temperature by another supply of heat prior to its entry into the still. The

charge is thus introduced to the still. and

distillationcarried on at a higher temperature than usual with steam stills. In the practice of this invention there may be considerable vapor formedin the heating ele mentssometimes as high as 25%-but' the vapors so formed go forward to the still together with the unvaporized portion, separation of vapor upon introduction to the still or tower being effected. If some ofthe extra heat is furnished by superheating the exhaust steam on its way to the still, the temperature of the incoming charge may be somewhat lower than otherwise, the reduction corresponding to the amount of heat so supplied. One characteristic of this invention is the maintenance oi": still temperatures somewhat higher than usual in a steam still, resulting in lower steam consumption.

In the accompanying drawing I have shown more or less diagrammatically one form of apparatus capable of use in the perifoi'mance of my process in several alterna, tive ways.

In the drawing, reference numeral 1 designates the steam still which maybe of any usual type and 2 designates perforated steam coil or spider, supplied with open steam through line 3. The still bottoms are removed through line 5 and by means of pump 6 are sent through pipe 30 to heat.- interchanger 7 and thence out of the system, or pump ,6 may discharge them directly out of the system through lines 19 and 29, or pump 6 may discharge them through lines 19, 20 and 33 into the heat-interchanger 12. In practice, a part of the material may be discharged through more than one of these outlets simultaneously. The material to be distilled comes by way of pump 9, going thence through various p e-heaters to the still, either directly or by of a refiUX tower, later described. Two such preheaters, 7 and 12, are shown, by-pass 32 being provided so that pro-heater 7 may be cut out if desired. Pre-heater 12 is heated by means of exhaust steam or, live steam, the heating medium entering through line 27 and leaving through line 28.- The preheater 7 is always heated by a part of the residue from the still, which enters by line 30 and leaves by line 8. Part of the unvaporizedresidue removed from the still 1 is discharged by pump 6. through lines 19 and 20 where it joins the fresh charge from line 11 or line 32 and continues with this new charge through pre-heater 12 and line 14 from which it may be dispatched directly into the still through line 15 or may enter the still indirectly through line 16, the tower 20 and run-back-line 17, valves being provided for this control. Such unvaporized residue is preferably so proportioned in quantity that together with the preheated charge oil there is conveyed to the still sufficient available heatlfor the vaporization of the fractions to be distilled without necessi-tating theheating or" the charge so high as to injuriously affect the desired fractions. In the operation of one 01 these stills, internal conditions change during the distillation, so that the provision of various alternative ways of heating is desirable. Reflux from the tower 20 goes back to the still through line 17, and the vapors "from the still enter the tower through line 18. The tower may or may not be provided with a covering of heat insulating material on the outside, and itsinterior may. be. provided with the usual packing materials (broken stone, tile, etc). Uncondensed steam and unrefluxed vapors; leave the reflux. tower through line 23 and are. condensed in the final condenser 24, disposed in watertank 25, and withdrawn for storage through outlet 34,

Theapparatus described is susceptible of use in a number of ways. EXhaust steam, at or slightly above atmospheric pressure, may be supplied to the still through line 3 and; spider 2. This steam is sometimes super-heated in super-heater 26.

In the steam distillation oflight petroleum fractions inone form of my invention, the fractionto bedistilled comes from astorage tank, not shown, is pumped by piunp 9 through lines 10 and 31 into heat-interchanger 7 where it. is heated somewhat by heat xtracted thereinfrom a portion of the unvaporized residue from steam still 1, which residueenters this pre-heater by line 30 andleaves by line 8. This pre-heated charge proceeds by line 11 and is joined here by stream of unvaporized residue from the steam still issuing from line 20. Tl'iesetwo streams, upon uniting, now proceed through line 33'and. enter pre-heater 12 wherein they are further heated by steam which may be either exhaust, live, or super-heated; this heating medium entering pre-heater 12 through line 27 and leaving through line 28. The charge, together with its accompanying liquid, has now beenheated to a temperature sufficient to conduct into the still the approximate number of heat units requireclfor the vaporization of the material which it is intended to vaporize. In the steam distillation of the light petroleum fraction which we are describing, the charge may be heated from 200 F. to 400 F., but with many naphthas a preheat temperature of 810 F. and a still temperature of about 275 F. are satisfactory.

IVith one particular charging stock having a temperature of 92 F. as it enters the pre-heater 7, with a temperature of about 126 F. as it leaves the pre-heater 7, with a temperature of 302 F. upon leaving the pre-heater-12, and with a temperature in the still of 212 F., I obtained a yield of gasoline of very good gravity and color and with a satisfactory doctor test. In this instance live steam was used for heating the 7 pre-heater 12 and exhaust steam was used in the coil or spider 2 in the still. In this run no steam still bottoms ware added to the charging stock. There was substantially no water in the bottom.

Either of the pre-heaters 7 or 12 may be used singly or the two may be used in series. Ordinarly I furnish exhaust steam to the still through spider 2 by line 3, but this steam may be super-heated in super-heater 26 if desired. In the preferred performance of the process, the steam is introduced into the charge in a proportion and at such a rate as to reduce the boiling point of the material being distilled but not at such a proportion and rate as to supply heat for substantial vaporization.

It is quite essential that the material being heated on its way to the still should be heated in a manner precluding any local over-heating of the freshly charged material. In order that there may be conveyed to the still a number of heat units sufiicient to effect the required vaporization in the still, the fresh charge is accompanied by residual material withdrawn from the still or another liquid of higher boiling point than that to be vaporized, both the fresh charge and this accompanying liquid being heated to the same temperature in the event it becomes desirable to add another liquid to the fresh charge other than simply the residual material withdrawn from the still or in place of the residual material withdrawn from the still, this additional liquid may be introduced through pipe 36, and may be directed by means of valves 38 and 37 into the stream of fresh charging stock as it enters preheater 7 or in case preheater 7 is not being used it may be introduced into the stream of charging stock and delivered to preheater 12. The added liquid serves as a heat storing means and should be one miscible with the liquid to be distilled. In distilling naphtha the residual oil in the still itself is well adapted for that purpose.

What I claim is 1. In the steam distillation of light fractions of petroleum the process which comprises preheating the said fractions by admixing therewith hot residual oil, stepping introducing into the still steam under conditions whereby it acts to reduce the boiling point of the material undergoing distillation but not to primarily supply the heat units for such distillation, removing vapors from the still, subjecting them to partial condensation, returning condensate to the still, finally condensing the remaining vapors, and controlling the temperature of the material delivered to the still for distillation to a point below that which will injuriousy affect the products of the distillation.

2. A process in accordance with claim 1 in which the hot residual oil used is the residual oil from the steam distillation of the light fractions forming the charge to the steam still.

3. A process in accordance with claim 1 in which the preheating of the light fractions by the residual oil is accomplished by passing the charge oil in heat exchange but out of contact with a portion of the hot residual oil and in mixing such preheated charge with another portion of the hot residual oil.

4. In the steam distillation of petroleum crude naphtha distillates the process which comprises preheating them by admixing therewith hot residual oil, stepping up the temperature of such mixture to a point below that which will injuriously affect the products of distillation but sufiiciently to supply heat units necessary for the vaporization of the fractions to be distilled therefrom, delivering such heated mixture to a steam still, supplying steam to such still under conditions whereby it acts to reduce the boiling point of the mixture undergoing distillation but not to primarily supply the heat units for such distillation, whereby substantial condensation of steam is avoided, and finally condensing the desired fractions from such distillation.

5. In the distillation of light fractions of petroleum of the nature of crude naphtha distillates the process which comprises passing such fractions through a heat exchanger, heating such exchanger by means of residual oil from the process itself but out of contact with such fractions, then mixing with such fractions another portion of the residual oil from the process itself to further raise the temperature, heating such mixture to a temperature to supply substantially all the heat units needed for distillation, delivering such mixture to a still, introducing into the still steam in sufficient quantity and under suflicient heat to reduce the boiling point of the material but not to primarily supply the heat units for distillation and removing from the steam still andifinal- 1y condensing the vapors produced.

6. A ;process in kaccordailee with Claim '1 in which the mixture of theffractions to 'be distilled and .theresidual oil, on the way 'to the steamstill, is used .to dephlegmate the vapors from said steam still.

In ltestimony whereof, I have hereunto afiixed my signature. 7 r V JOHN GLASGOW.

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