US2640013A - Distillation of tars and like liquid hydrocarbons - Google Patents

Description

y 6, 1953 T. o. WILTON 2,640,013

DISTILLATION OF TARS AND LIKE LIQUID HYDROCARBONS Filed June 7, 1950 Nil W W Patented May 26, 1953 DISTILLATION OF TABS AND LIKE LIQUID DROCARBONS Thomas O. Wilton, Worthing, England; Winifred Louise Wilton and Leonard Vivian Russell, executors of said Thomas O. Wilton, deceased, assignors to Chemical Engineering, Wiltons Limited, Horsham, England, a British company Application June '7, 1950, SerialNo. 166,580

In Great Britain April 30, 1943 '7 Claims.

A process for the distillation and fractionation of a mixture comprising hydrocarbon compounds, including volatile and non-volatile constituents, is known, which consists in continually circulating a mixture of non-volatile constituents, partly treated stock and added increments of new stock through apparatus including heating means adapted to'raise the said mixture to and maintain it at a predetermined temperature such as to vaporize all of the compounds which it is desired to separate from the residue of non-volatile constituents, dividing the stream of materials issuing from the heating means into two streams, maintaining in the lower portion of a mixing column a pool consisting of the mixture aforesaid, sending the materials of one of the said two streams directly into the said pool, sending the materials of the other of the said two streams into the upper part of said mixing column, feeding a fresh charge of new stock into the upper part of said mixing column, mixing and flowing the materials of the said other stream and the new stock downwardly in said column into the said. pool in the lower part of the column, re-circulating the materials of the said pool through the heating means, releasing vapours from the materials issuing from the heating means before dividing them into two streams, releasing vapours from themixed materials during said downwards flow, combining all the vapours so released and fractionating the combined vapours.

I According to this invention, instead of a process of the kind just described, in which the stream of materials issuing from the heating means is divided into two streams one of which proceeds directly to the pool in the lower part of the mixing column and the other is mixed with fresh stock, I provide a process of this kind in which the stream of materials issuing from the heating means is divided into at least two subsidiary streams; in the case of two streams only, the first stream'enters a first mixing chamber of a mixing-dehydrating column, where it is mixed with fresh stock, dehydration taking place in this chamber and vapours of low boiling point being also liberated, the second stream enters a second mixing chamber of the said column, where it is mixed with the mixed materials discharged from the first mixing chamber and where the distillation of the volatile constituents of the fresh stock is completed; the mixed material in this second mixing chamber proceeds to form a pool in the lower part ofthe mixing column, and are recirculated through the heating means to be raised to the predetermined required temperaturefor 2 eifecting a complete distillation, the materials issuing from the heating means, before being divided into two substreams, passing through a flash chamber where any vaporizable materials still remaining in these materials are vaporized, and vapours of high boiling point are released; the latter vapours are combined with those released in the first and in the second mixing chambers and the combined vapours are fractionated. I

After passing through the flash chamber, th stream issuing from the heating means may be subdivided into more than two subsidiary streams, that is, into four or more streams, one stream is mixed with fresh stock in a first mix ing chamber, a second stream is mixed, in a second mixing chamber, with the mixed materials discharged from the firs-t mixing chamber, a third stream is mixed, in a third mixing chamber, with the mixed materials discharged from the second mixing chamber, a fourth stream is mixed, in a fourth mixing chamber, with the mixed materials discharged from the third mixing chamber, and so on, the mixed materials discharged from the last mixing chamber proceed to form a pool in the lower portion of the mixing-distilling column and are re-circulated through the heating means, vapours being released in every mixing chamber, all the vapours so released being combined'with the vapours released in the flash chamber and the combined vapours being fractionated.

Referring to the drawing, the figure is a diagrammatic view illustrating, as an example, a preferred arrangement of plant suitable for carrying out the process according to the invention, which, for the sake of illustration, will be supposed to -be used for distilling tar completely by dividing the main stream issuing from the heat---' ing means into four subsidiary streams.

The crude stock, which may be pre-heate'd, partly dehydrated and partly freed from its volatile constituents of lowest boiling point, is pumped from a storage tank (not shown) by a pump I, is preliminarily heated to as high a temperature as -maybe attained by a heat-exchanger i, a waste steam heater 2 and a waste heat coil 3, and proceeds by the pipe 5 to the uppermost chamber 7 of a mixing-distilling column, which it enters at 6 at a temperature of about C. and where it is partly dehydrated and partly stripped of some light oils, the mixed vapours escaping by pipe 27. The materials hereafter referred to as "residues, discharged from the last (here the fourth) mixing-distilling chamber and having collected to form a pool in the lower part I! of the mixing-distilling column are pumped at 18 along the pipe 19 by the circulating pump 20 and forced through a heating coil 2| disposed in a furnace 22, where they are re-heated to a temperature of about 350 0.; these residues proceed by the pipe 23 and enter at 24 a flash chamber 25 near the top of the mixing-distilling column. This flash chamber may be provided with a steam coil (not shown) and is preferably disposed immediately under the chamber 1, to which it imparts some of its heat. In the chamber 25, the residues are stripped of the vaporizable constituents they still contain, the vapours escaping by pipe 38; a portion of the non-vaporizable residue, which in this case is pitch, is discharged as finished product at 26, while the remaining pitch flows down a pipe 33, heavily lagged to minimise heat losses, from which pipe the hot pitch, at a temperature of about 350 C. is tapped at points 34, 35, 36 and 31 under control of valves, so that the pitch leaving the flash chamber 25 is subdivided into four subsidiary streams, the said streams entering corresponding mixing chambers 9, ll, l3 and [5, respectively.

The crude stock in chamber l, partly dehya drated and partly stripped of light oils, flows down pipe 8 into the mixing chamber 9, where it mixes over trays with pitch of the first subsidiary stream entering at 34, the temperature at the bottom of chamber 9 being about 180 C. The

mixed materials from this chamber 9 flow by pipe In into the mixing chamber H where they mix over trays with pitch of the second subsidiary stream entering at 35, the temperature at the bottom of the chamber ll being about C. The mixed materials from this chamber ll flow by pipe [2 into the mixing chamber [3 where they mix over trays with pitch of the third subsidiary stream entering at 36, the temperature at the bottom of the chamber l3 being about 280 C. The mixed materials from this chamber l3 flow by pipe l4 into the mixing chamber l5 Where they mix over trays with pitch of the fourth subsidiary stream entering at 31, and the mixed materials from this chamber I5, at a temperature of about 300 C. flow down by pipe 16 to form a pool in chamber I1, and are sent again through the heating means 2| to repeat the cycle of operations.

The vapours of lowest boiling point, including water vapour, released in chambers l and 9, are led by pipes 21 and 28 to a condenser 29 and a separator 30, the light oils condensates being returned to the chamber H by pipe 3|. The vapours released in the flash chamber and in the three mixing chambers II, I3 and I5 are led by pipes 38, 4|, 42 and 43, respectively, into a manifold 39 where they are combined and the whole of the deyhdrated vapours proceed by pipe 44 to the fractionation column 45 where they are fractionated. Such condensates as may form in the manifold 39 are returned to the chamber 15 at 40.

It will be understood that the temperatures mentioned above are only for the sake of illustration and that, in practice, difierent temperatures may be obtained actually.

The return of the light oils condensates back to the distillation column-Dean and Start method-has for its purpose to prevent frothing in the distilling column. It has besides the advantage that the combined vapours entering the fractionation column are free from water vapour, the result being a higher efiiciency of working of the fractionation column and closer cuts.

In order to further improve the fractions produced and minimize cracking, a vacuum may be applied to the whole plant or to a portion thereof.

Processes for the distillation of tars and like liquid hydrocarbons have been worked in connection with the re-circulation principle on an ever increasing scale with plants of increased dimensions in an endeavour to cope with the increasing outputs necessary to meet the ever growing demands for the finished products of the distillation and fractionation. With plants of over tons per day capacity, however, the increasing size of the pipe still and of the mixingdistilling column begins to present a serious problem. Pipes of from 6 to 7 in. diameter must be used in the construction of the pipe still in order to obtain the necessary area of heating surface and sections of as much as 6 feet diameter become necessary for constructing the mixing-distilling column. To attain an output of 300-400 tons daily, it would therefore be necessary to construct a mixing-distilling column with sections of such a large diameter as to become altogether too expensive and unwieldly to manufacture while pipe stills would have to be constructed with pipes of such diameter as to be impracticable.

As far as the pipe still is concerned, a solution of the problem is described in my specification No. 2,266,698.

The present invention provides a solution of the problem presented by the mixing-distilling column for large outputs. By tapping the stream of hot residues issuing from the heating means and therefore at their highest temperature, at a '1 plurality of points along its path towards the pool through which series of chambers the materials undergoing the heat treatment are flowing by gravitation, receiving, as they enter each successive chamber, a fresh addition of hot residues, the temperature of the mixture of fresh stock and 7 residues, as it leaves one chamber to flow into the next one underneath, increases progressively from the temperature of the in-coming fresh stock, preheated by'heat exchange, up to a temperature which is not much below that of the hot residues leaving the heating means, so that vaporizable constituents of progressively higher boiling points are vaporized in each chamber in a quantity depending on the range of temperature between the in-flowing and the out-flowing mixture of materials in each chamber. As this range can be made as small as may be desired by increasing the number of superposed mixing chambers, their size, that is, the diameter of the mixing-distilling column, can be kept of such dimensions as to be economical and convenient.

A further advantage is that, by releasing in this way a limited quantity of vapours at each step, the danger of a too violent reaction, which might take place where large quantities of high temperature residues and relatively cool vaporizable materials are brought in presence, is avoided.

The two streams of hot residues and fresh or partly distilled stock, admitted in each chamber, are brought into intimate contact by flowing over mixing trays, baffles or like devices adapted to effect a thorough mixing of the materials, so as to perform as complete a distillation as possible of the constituents whose boiling points are ture during themixing.

ace-epic It will be seen that, instead of having one pair of paths running in the same general direction, one conveying only heat-carrying residues and one conveying a mixture of heat-carrying residues and fresh stock subject .to distillation while flowing down a single mixing column, the first stream of residues flowing directly. into a pool at the bottom of the mixing column without contacting any materials under treatment and therefore without causing any distillation whatsoever, so that itsheat is entirely wasted; the present invention consists in providing at least two pairs of paths running in the same general direction, said pairs of paths being connected in series, one of the paths of each pair being common to an pairs and conveying only heat-carry ing residues while the other path of said pair conveys a mixture of heat-carrying residues and of fresh stock or'partly distilledstock, each flowing through a separate mixing chamber, to which a mixture of fresh heat-carrying residues is added at each point where two adjacent pairs of paths are connected in series, the final mixture formed in the last mixing chamber providing a pool, so that every portion of the stream of heatcarrying residues in ultimately finding its way to the said pool is contacting on its way to said pool with some crude or partly distilled stock, the materials in said pool being recirculated through a heating zone and a flash chamber before being again caused to flow along the said pairs of paths, vapor being released in the said flash chamber and in each mixing chamber, all of said vapors being combined and the combined vapors sub jected to fractionation.

What I claim is:

1. Apparatus for the complete distillation down to non-vaporizable residues and fractionation of mixtures of hydrocarbon compounds containing distillable constituents and residues, comprising a mixture-distilling column having a plurality of superposed separate distilling chambers, a flash chamber near the top of the column and a receiving chamber at the bottom of the column, a fractionating column, an inlet for'crude stock at the top of the uppermost distilling chamber, fluid-conducting means leading from the bottom of each distilling chamber to the top of the next lower distilling chamber and from the bottom of the lowest distilling chamber to the top of the receiving chamber, residue conducting means from the bottom of the receiving chamber to the top of the flash chamber, means for heating the residue before it reaches the flash chamber, conducting means for heat-carrying residues from the bottom of the flash chamber to the top of each of the distilling chambers below the flash chamber, an outlet at the bottom of the flash chamber for residues discharged as finished products, vapor conducting means from the top of each of the two uppermost distilling chambers, a condenser and separator to which said vapor conducting means lead, condensate conducting means from the separator to the top of the next lower distilling chamber and a vapor manifold connected to the tops of the flash chamber and the distilling chambers below the two uppermost ones and to the fractionating column.

2. Apparatus for the complete distillation down to non-vaporizable residues and fractionation of mixtures of hydrocarbon compounds containing distillable constituents and residues, comprising a mixing-distilling column having a plurality of superposed separate distilling chambers, and a receiving chamberat the bottom of the column, a fractionating column, an inlet for crude stock at the top of the uppermost distilling chamber, fluid-conducting means leading from the bottom of each distilling chamber to the top of the next lower distilling chamber and from the bottom of the lowest distilling chamber to the top of the receiving chamber, vapor-conducting means from the top of at least the uppermost distilling chamber, a condenser and separator'to which saidvapor-conducting mean lead, condensateconducting means from the separator to the top of the next lower distilling chamber, a vapor manifold connected to the top of said next lower distilling chamber and to the tops of those below it and to the fractionating column, and a recir-'- culating system comprising an outlet from the receiving chamber, means for heating the recirculated material, a downtake pipe for the heated recirculated material disposed alongside of the distilling column, and separate tap-off conne'c tions between the downtakepipe and the top of each of the distilling chambers below the uppermost one for admitting heated recirculated 'material to-said chambers.

' 3. A process for the complete distillation down to non-vaporizable residues and fractionation of mixtures of hydrocarbon compounds containing distillable constituents and residues, comprising feeding crude stock to the first of a series of distillation zones, allowing material to flow from each zone to the next and from the last zone to a residue receiver, extracting residue from the receiver, heating it and dividing it into a number of streams, one of which is passed to each of the second, and subsequent distillation zones and therein mixed with the material being distilled so as to heat same, collecting vapors liberated in the distillation zones and fractionating the collected vapors.

i. A process for the complete distillation down to non-vaporizable residues and fractionation of mixtures of hydrocarbon compounds containing distillable constituents and residues, comprising feeding crude stock to the first of a series of distillation zones, allowing material to flow from each distillation zone to the next zone and from the last zone to a residue receiver, extracting residue from the receiver, heating it and dividing it into a number of streams, one of which is passed to each of the second and subsequent distillation zones and therein mixed with the material being distilled so as to heat same, collecting vapors liberated in the first and second distillation zones, condensing same, separating aqueous condensate therefrom and feeding hydrocarbon condensate to the third distillation zone, collecting vapors liberated in the third and subsequent distillation zones, and fractionating the collected vapors.

5. A process for the complete distillation down to non-vaporizable residues and fractionation of mixtures of hydrocarbon compounds containing distill-able constituents and residues, comprising feeding crude stock to the first of a series of distillation zones, allowing material to flow from each zone to the next and from the last zone to a residue receiver, extracting residue from the receiver, heating it and dividing it into a number of streams, one of which is passed to each of the second and subsequent distillation zones and therein mixed with the material being distilled so as to heat same, the proportion of heated residue passed to each zone being adjusted so that in each zone a higher temperature is reached than in'the preceding zone, collecting vapors liberated in the distillation zones and fractionating the collected vapors.

6. A process for thecomplete distillation down to non-vaporizable residues and fractionation of mixtures of hydrocarbon compounds containing distillable constituents and residues, comprising feeding crude stock to the first of a series of distillation zones, allowing material to flow from each zone to the next and from the last zone to a residue receiver, extracting residue from the receiver, heating it and dividing it into a number of streams, one of which is passed to each of the second and subsequent distillation zones and therein mixed with the material being distilled so as to heat same, collecting vapors liberated from the heated residue and vapors liberated in the distillation zones, and fractionating the collected vapors.-

7. A process for the complete distillation down to non-vaporizable residues and fractionation of mixtures of hydrocarbon compounds, containing distillable constituents and residues, comprising feeding crude stock to the first of a series of distillation zones, allowing material to flow from each zone to the next and from the last zone toa residue receiver, extracting residue from the receiver, heating it and dividing it into a number of streams, one of which is passed to each of the second and subsequent distillation zones and therein mixed with the material being distilled so as to heat same, the proportion of heated residue passed to each zone being adjusted so that in each zone a higher temperature is reached than in the preceding zone, collecting vapors liberated in the first and second distillation zones, condensing same, separating aqueous condensate therefrom and feeding hydrocarbon condensate to the third distillation zone, collecting vapors liberated from the heated residue and vapors liberated in the third and subsequent distillation zones, and fractionating the collected vapors.

THOMAS O. WILTON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,260,072 Wilton Get. 21, 1941 2,292,256 Wilton Aug. 4, 1942 2,322,652 McClintock June 22, 1943 2,343,646 Dinley Mar. '7, 1944

Claims (1)

1. 3. A PROCESS FOR THE COMPLETE DISTILLATION DOWN TO NON-VAPORIZABLE RESIDUES AND FRACTIONATION OF MIXTURES OF HYDROCARBON COMPOUNDS CONTAINING DISTILLABLE CONSTITUENTS AND RESIDUES, COMPRISING FEEDING CRUDE STOCK TO THE FIRST OF A SERIES OF DISTILLATION ZONES, ALLOWING MATERIAL TO FLOW FROM EACH ZONE TO THE NEXT AND FROM THE LAST ZONE TO A RESIDUE RECEIVER, EXTRACTING RESIDUE FROM THE RECEIVER, HEATING IT AND DIVIDING IT INTO A NUMBER OF STREAMS, ONE OF WHICH IS PASSED TO EACH OF THE SECOND, AND SUBSEQUENT DISTILLATION ZONES AND THEREIN MIXED WITH THE MATERIAL BEING DISTILLED SO AS TO HEAT SAME, COLLECTING VAPORS LIBERATED IN THE DISTILLATION ZONES AND FRACTIONATING THE COLLECTED VAPORS.

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