US1958585A - Distillation of tar - Google Patents

Description

VMilly 15, 1934- s. P. MILLER DISTILLTION OFTAR Filed May 3, 1929 5 Sheets-Sheet l MMM ATTORN EYS May 15, 1934 s. P. MILLER DISTILLTION OF TAR Filed May 3, 1929 5 Sheets-Sheet 2 lNvl-:N'r'oR B 7), -l MVM ATTORNEYS May 15 1934 s. P. MILLER DISTILLTION OF TAR Filed May 3. 1929 5 Sheets-Sheet 3 buf- Lw; im

ATTORNEYS May 15, 1934. s. P. MILLER DISTILLATION OF TAR 5 Sheets-Sheet 4 Filed May 3, 1929 ...l mw

ATTORNEYS f Annv Puk 5% 5 #su May 15, 1934. s, P. MILLER DISTILLATION OF TAR Filed May s. 1929 INVENTR BY f v /f-, 'l )l1-ano: rw

ATTORNEYS Patented May 15, 1934 msfrnlLA'rloN or TAR Stuart Parmelee Miller, Englewood, N. J., assignmto The Barrett Company, New York, N. Y., a. corporation of New Jersey Application May 3, 1929, Serial No. 360,019

14 Claims. (Cl. 20230) This invention relates to improvements in the distillation of tar, and includes an improved process and an improved apparatus. More particularly, the invention relates to a process and apparatus in which tar is heated by indirect contact with hot coke oven or other coal distillation gases. The invention also includes an improved method and apparatus in which tar is heated and distilled in part by indirect contact with hot coke oven or other gases and in part by direct contact therewith. The present invention also includes an improved process and apparatus in which tar is heated by indirect contact with hot coke oven gases, and the heating surfaces are kept liiushed with pitch to prevent deposits and accumulations of hard pitch thereon. The present invention also includes a process and apparatus in whichtar is preheated by indirect contact with hot coke oven gases and is subsequently brought into direct contact with such gases and further. distilled'thereby, and in which the pitch undergoing distillation serves to flush the surfaces of the indirect heat interchanger to keep them free from accumulated deposits of pitch.

According to the present invention, tar is heated by passing it through a pipe coil or other suitable apparatus in indirect contact with hot coke oven gases or other coal distillation or coal carbonization gases, and the tar is thereby heated to a temperature sufficient tov effect distillation thereof.

Hot coke oven gases and similar coal distillation gases are laden with pitch particles at a high temperature, and, when hot coke oven gases are brought into direct contact with pipes through which tar is being passed at a lower temperature, the coke oven gases are locally cooled and condensation of tar or pitch tends to take place. The further contact of hot coke Oven gases with the condensed tar or pitch may effect distillation thereof with tendency to produce a layer of hard pitch or coke on vthe heating surfaces. The present invention provides a process in which accumulation of objectionable deposits of pitch or coke on the heating surfaces is avoided by flushing these surfaces with hot pitch at a sufficiently high temperature so that it does not interfere with the heating of the tar .it in the pipe coils. This improved process accordingly involves the preheating and distillation of tar by indirect heat contact with hot coke oven gases and the flushing of the heating surfaces with pitch to keep such surfaces clean,

."5 from pitch or coke accumulations. 'I'his flushing operation may be continuous, or it may be periodic and intermittent.

The present invention also provides a process and apparatus in which there is combined an indirect and a direct heating of the tar by hot coke oven or other coal distillation gases, with preheating, or preheating and partial distillation, of the tar by indirect heating with the coke oven gases, and with subsequent discharge of the preheated, or preheated and partly distilled,

tar, into direct Contact with the same hot gases toeiect further distillation thereof and the production of additional distillates and a-pitch of higher melting point. The preheated tar, preheated by indirect contact with the hot coke v oven gases, may be discharged directly intothe gases, so that all of the vapors produced by the indirect heating will mix with `the coke oven gases and with the heavier oil vapors produced by the subsequent distillation by such gases. A more advantageous method, in some cases, is to discharge the tar from the indirect preheater into a vapor separating chamber or box and to take off separately and condense the distillate from the indirect distillation, and to introduce only the residue from the indirect heating and distillation into direct contact with the hot coke oven gases. In this way, the hot gases are ernployed for direct distillation of heavier oil constituents which can be readily removed at temperatures which need not greatly exceed the temperatures to which the tar is heated by indirect contact for the removal of lighter oils.

Hot coke oven gases leave the individual ovens at high temperatures, for example, at temperatures around 450 to 850 C. or higher, depending upon the type of ovens, the method of operation, etc. The heat contained in hot coke oven gases is commonly dissipated and wasted. Similar high temperature gases containing waste heat are produced at gas retort plants, gas producer plants, and water gas plants, etc. These hot gases are employed in the process and apparatus of the present invention partly for heating by indirect contact with the tar and partly for heating by direct contact with the tar or pitch to be distilled.

Hot coke oven gases, and similar coal distillation gases, are laden with tar which is commonly separated therefrom by cooling the gases. The tar is made up in part of oils which, at a high temperature, are carried by the gases in the form of vapors, and in part of heavier constituents of the nature of pitch, or particles of carbon, which are carried in suspension in the gases at d volume of tar.

produced this will present no difficulty for it will readily flow off of the tubes or other heated surfaces. However, When tar is heated by indirect contact with the gases to a high temperature,I the gases are only partially cooled, and pitch tends to separate on the heated surfaces and to be further distilled to produce coke vor hard nonfluid 'pitch which interferes with further heating of the tar. According to the present invention I provide'for the removal of such deposits of pitch or coke, either periodically or continuously, by flushing the surfaces with hot fluid pitch or tar which serves as a solvent of the deposited- Ditch.

The continuous flushing of the heated surfaces is particularly advantageous, because, in that way, the gases can be employed at a high temperature, and effective distillation accomplished, without danger or interference from deposited pitch and coke on the heated surfaces, and Without interference with the heating of the tar. When the heated surfaces are kept flushed with hot pitch, the pitch will itself be distilled by direct contact with the hot gases, and the process in this case will be a combined process of indirect and direct heating and distillation in which the waste heat of the hot coke oven gases is em ployed.

The indirect heating of the tar by the hot gases can be carried out in different types of apparatus which provides for heat interchange of the tar and hot gases. A pipe coil still through which the tar is pumped in a continuous manner is an advantageous form of apparatus, since, by a general countercurrent ilow of the tar and gases, the tar can be preheatedtoa high temperature, and the gases can be cooled to a low temperature.

` vSuch a pipe coil may discharge into a vapor box or chamber from which the vapors are drawn off vand separately condensed, and yfrom which the pitch produced may also be drawn off as a separate product. However, the pitch produced by indirect heating with the hot gases can be further distilled with particular advantage by bringing it into direct contact with the gases and using it for ilushing the heated surfaces. When this pitch is used to flush the surfaces of the pipe coil still to keep them free from hard pitch or coke formations, the heat of the gases will act upon and through the pitch to distill it and to transmit heat through it to the pipes containing the tar.

When the tar preheated by indirect contact with the hot coke oven gases is discharged into a vapor box and the koils separately drawn off and condensed, and only the pitch from such indirect distillation is brought into direct contact with the hot gases, the further distillation of the pitch will give a relatively heavy distillate which can be readily condensed from the inert gases with which the heavy oil vapors are admixed, thus greatly facilitating the recovery of the oils from the admixed gases. Y

The present invention is of special value for the production of a low melting point pitch by indirect heating or the tar with the hot coke oven gases and simultaneous production of a high melting point pitch by direct contact of the hot gases with the tar or pitch. A much higher temperature is required for distillation of tar by indirect contact with the heated gases than is required for distilling tar by direct contact with hot coke oven gases, to produce pitch of the same melting point and the same percentage of distillates. Accordingly, when the tar is heated in a pipe coil still by indirect contact with the hot coke oven gases, the only oils which are vaporized are those which distill up to the temperature to which the tar is heated. When, however, tar is heated to the same temperature by direct contact with hot coke oven gases, a much greater distillation of oils can be eected and a much higher melting point pitch produced, since in the presence of the large quantity of inert gases the oils are distilled from the tar or pitch at a temperature considerably below their normal distillation temperature. Accordingly, when tar is heater by indirect contact with hot coke oven gases to effect partial distillation, and when the resulting preheated tar or partially distilled tar or pitch is then introduced into direct contact with the gases at the temperature to which it has been preheated, such preheated tar or pitch will be in a superheated condition as roo compared with pitch of similar melting point produced by direct distillation of tar with the hot gases. Its further distillation can therefore. be readily and advantageously effected by direct and intimate contact with the hot coke oven or other coal distillation or gasification gases.

The preliminary and partial distillation of the tar by indirect contact with the hot coke Ioven gases can be further promoted by the use of a vacuum upon the vapor box of a pipe coil still so heated, thereby increasing the percentage distillate of oils and the melting point of the pitch, and cooling the pitch before it is discharged from the vapor box to a temperature lower than if no vacuum be employed.

The type of still employed in carrying out the present process can, as above stated, be varied. A pipe coil still is an advantageous still, since it enables tar to be heated continuously and the 'heating surfaces can be readily kept clean by a pipe coil still, a tubular boiler type of still can be employed, with the tar circulating through the tubes and the hot coke oven gases around the tubes, or with tubes of the fire tube boiler type Where the hot coke oven gases pass through the tubes and the tar is around the tubes. By collecting coke oven gases from a number yof ovens in a heavily insulated header or pipe, a large volume of hot coke oven gases can be made available at a high temperature for operating a tubular boiler for the distillation of tar. objectionable accumulations of pitch or coke on the heating tubes can be taken care of by keeping the tubes clean, for example, by flushing them continuouslyor periodically with hot pitch. In the case ofa iire tube boiler, any deposit of pitch or carbon on the tube can be removed by suitable cleaning devices. By carrying out the heating ina countercurrent manner the hot coke oven gases can be cooled to a relatively low temperature and their heat largely utilized for the indirect heating of tar, while the tar can be heated to a relatively high in stages, with a general countercurrent flow of the tar and pitch and of the gases so that the hottest gases are employed, for further distillation of pitch to produce higher melting point pitch, and the cooler gases are employed for preheating the gases and distilling lighter oils therefrom. A series of indirectly heated stills can thus be employed for producing a plurality of successively higher boiling distillates and higher melting point pitches, and the gases will be progressively cooled and tar constituents separated therefrom. Such parts of the apparatus asmay tend to have hard pitch or coke formed on the heated surfaces may be kept clean by ushing with hot pitch or by otherwise cleaning the surfaces.

The invention will' be further described in connection with the accompanying drawings which illustrate different types of apparatus embodying the invention and adapted for the practice of the process of the invention, but it is intended and will be understood that the invention is illustrated thereby but is not limited thereto.

Figure l is a plan view of a coke oven equipped according to this invention.

Figure 2 is an elevation partly in cross-section of the apparatus of Figure l.

Figure 3 is a cross-section on the line 3 3 of Figure 2.

Figure 4 is a detail of the coil shown in Figures 2 and 3.

Figure 5 is a modified form of apparatus employing vacuum. f

Figure 6 is a modified form of apparatus employing another type of distilling means.

Figure 7 is a section on the line 7--7 of Figure 6.

Figure 8 shows still another type of distilling means, and

Figure 9 is a detail of part of the apparatu of Figure 8.

In the drawings, 5 indicates a coke oven battery the ovens of which are connected with the collector main 6 through the uptake pipes 7.

The gases pass through the collector main to the center box 8 and thencev through the cross-over main 9 to the condensers 10. An exhauster is shown at 11. This apparatus is of the usual type and is shown more or less diagrammatically.

At the rear of the coke oven block certain 0f the ovens are provided with uptake pipes 12.

These pipes connect these ovens with the still 13.

By proper manipulation of the valves in the uptake pipes 12 and the corresponding uptake pipes 7, the gases from the ovens connected with the` still may be sent either to the still 13 or to the 'collector main 6. The gases passing up through the uptake pipes 12 linto a still 13 are employed I, for the distillation of tar, according to this invention.

The still shown in Figures 1 3 comprises. a

l chamber 14 through which the gases pass to the tower 15. A body of tar is maintained vin the bottom of the chamber 14 and the amount of 22. This tar circulates through the coil in indirect contact with the hot coke oven gases passing through the vapor space of the still 13, and is thus heated. The coil 21 may be provided with fins 23 to provide more eicient heat interchange between the gases around the coil and the tar flowing through the coil. In passing through the coil th'e tar is preheated. This, tar is passed through the line 24 to the vapor chamber 25 in which the constituents of the tar volatile at the temperature in effect are vaporized and are separated from the residue of the tar. This residue is run off through the line 26 to the storage-tank 27 and comprises a heavy tar or a pitch, depending upon the temperature of preheat, the type of tar, etc.

The vapors from the chamber 25 pass through the condenser 28 which isv here shown as an indirect condenser. The clean distillate condensed within 28 is withdrawn through the line 29 to the storage tank 30. This comprises a clean distillate of relatively low boiling range.

The hot coke oven gases as they come from the ovens carry vapors of high boiling oil constituents as well as entrained pitch and particles of dust and coke, etc. on exposed surfaces, and, Where cooling occurs, vapors -of higher boiling resinous vconstituents are condensed. In order to prevent the accumulation of deposits of such material upon the exterior of the pipe coil 21 within the chamber 14, means for thoroughly washing the exposed surfaces of the coil are provided, according to this invention. The means here shown comprises a roll 3l which dips to a slight extent into the body of tar or pitch maintained within the bottom of the chamber 14. The roll 31 is rotated at high speed, for example 900-1200 R. P. M., lby the motor 32. side of the still 13 and is rotated in such away that the tar is washed up between the roll 31 and the still, and the chamber 14 is iilled with an intense spray of tar particles. The tar washes up over the inner surface of the still and prevents the accumulation of deposits on this inner surface and the intense spray of tar particles thoroughly washes the outer surfaces of the coil 21 so as to prevent the accumulation of hard pitch or coke on the exterior of the coil.

This spray of tar or partially distilled tar or pitch thrown up by the gases passing through the still 13 is distilled by the hot coke oven gases. The distillation is by direct contact of the tar with the hot gases. The preheating which occurs within the coil is byindirect contact of the tar with the hot gases. The tar distilled within the still 13 by direct contact with the hot gases may be the residue from the vapor chamber 25 which has been collected in the tank 26 which may be supplied to the still through the line 33 by the pump 34, or tar or low melting pitch from any other source may be supplied to the still through the line 35.

The hot gases enriched in condensable oonsttuents by distillation of the tar within the still 13 pass through the chamber 15 which is of relatively large diameter and entrained particles of the spray which may be carried over from the still are allowed to settle out of the gases within this chamber and return to the still 13. The resulting gases andvapors pass through themain 36 to the condensers 37. The condensers are These tend to settle out` The roll is situated near one here shown as the ordinary direct type of con- Y densers in which the gases are sprayed with ammonia liquor. The ammonia liquor and condensate from the gases is withdrawn into decanter 38 from which the ammonia liquor is separated into an ammonia liquor storage tank, not shown, and the distillate is collected in a tank, not shown.

Where the tar distilled by direct contact with the hot coke oven gases is the residue of the tar preheated and partially distilled by indirect Contact with these gases, the coke oven gases passing from 4the still 13 are enriched in higher boiling oils. The lower boiling constituents of the tar have been separated in the vapor box 15 and collected in the clean low boiling distillate storage 30. When the gases passing into the condensers 37` are enriched only in such v higher boiling constituents, the cooling within the condensers necessary to condense these oils is not as great as the cooling necessary to relcover the oils of lower boiling constituents present in the gases such as vapors resulting from the distillation of tar which has not previously been topped, as in the vapor box 25.

From the condensers 37 the gases pass through an exhauster which may advantageously be the exhauster l1 employed for drawing the gases through the ordinary cross-over main and condensers 10.

The'apparatus in Figure 5 is similar in some respects to the apparatus shown in Figures 1-3.

1n Figure 5, a number of the ovens of a coke oven battery 5 arel connected with a still 13 through the uptake pipes 12. The gases from the still pass through the tower 15 to condensing means. Within the still 13 -is a coil 21 for preheating and partially distilling tar by indirect contact with the hot gases. The still also contains a roller 31 driven by the motor 32. This roller is rotated at high speed land generates a-spray of tar or pitch which washes the exposed surfaces of the coil 21 within the still. The pitch resulting from distillation of the tar by direct contact with the hot gases is withdrawn through the levelling arm 16 and trough 18 to the pitch storage 20. lThis apparatus may all be as described in connection with the preceding gures.

The preheated and partially distilled tar from denser 28 collects in the storage tank 30.

Partially distilled tar from the tank 27 may be supplied to the 'still lthrough the line 33 or tar `from an outside source may be supplied through 'the line 35. The vapors and gases resulting from the distillation of the tar bydirect contact with the hot gases pass from the still 13 through the tower 15 to the condensing system which comprises an indirect condenser 42 and a direct condenser 43. 'Ihe indirect .condenser comprises a coil 44 through which tar is passed and preheated by indirect contact with the hot gases andv vapors passing through the condenser 42. This tar which is admitted through the pipe 45 passes through the line 46 into the pipe coil 21 located within the still 13. This allows the tar to be preheated before entering the coil 21. Inv

the coil 21 it is further preheated and partially distilled.

The gases and vapors passing from the still are partially cooled by indirect contact with the tar in the coil 44 andA higher boiling constituents carried by the gases are separated from the gases and collected in the distillate storage tank 47. The resulting gases and vapors pass from the condenser 42 through the main 48 to the condensers 43 Awhich are here shown as direct condensers in which the gases and vapors are sprayed with water or ammonia liquor. The condensate together with ammonia liquor passes to a decanter in which the aqueous solution and oily condensate are separated and from which they are run to separate storage tanks.

The tar which is partially preheated within the preheater 42 by indirect contact with the hot gases and vapors passing from the still is further preheated and partially distilled in the coil 21 within the still 13. This preheated and partially distilled tar is passed to the vapor box 25 which is maintained under vacuum and lower boiling constituents of the tar are volatilized and separated from the residue. The partially distilled tar or pitch coming fromk the vapor box may then be further distilled by direct contact with the hot gases, or tar from another source admitted through the line 35 may be brought into direct contact with the hot gases and thus distilled. The distillation by direct contact takes place within the still 13 and the tar being distilled is sprayed and iinely atomized into the gases vby the rapidly rotating roll 31 and the spray washes the exterior of the coil 21 and prevents the formation of hard pitch or coke upon this coil.

' Figures 6 and 7 show still other means for simultaneously heating and distilling tar by direct contact with hot coke oven gases and also by indirect contact `with hot coke oven gases within the same distilling chamber. Hot coke oven gases from the coke oven battery 5 are collected in the hot gas header 50 which is connected to the ovens of the battery through the uptake pipes 12 which are similar in construction to the uptake pipes 12 of Figure 1 and similarly operated. The hot coke oven gases pass through the hot gas header 50 into the distilling chamber 51. Within the chamber is a coil 52 through which tar admitted at 53 circulates, and after being preheated and partially distilled within this coil the tar passes through the line 54 to the vapor box 55. The vaporsresulting from the distillation within the coil `52 arev separated from the'undistilled residue within this vapor box and pass to the condenser 56 which is here shown as the usual indirect type of condenser. The clean distillate resulting from the condensation is collected in the storage tank 57.

`Undistilled residue from the vapor box is collected in the storage tank 58. This may be heavy tar or low melting pointpitch. Where desirable, the vapor box 55 and condenser 56 may be maintained under a vacuum by means such as that de To prevent the accumulation of high melting point a pitch and the formation of coke on the coil 52, it is sprayed with tar from the lnozzle 59. Heavy tar or low melting point pitch from the storage Atank 58 may be used for this purpose, in which case it will be pumped through the line 60 bylthe pump 61 to the spray nozzle 59. Tar from another source may be supplied through 62. The tar sprayed down over the coil is brought into direct contact with the hot coke oven gases and a large surface of the tar is thus exposed to the hot gases and the tar is distilled to produce a pitch which may be a pitch of medium or relatively high melting point, The pitch is Withdrawn from the bottom of the distilling chamber 51 preferably through a levelling arm 63 and after being sprayed with Water from the line 64, is collected in the pitch storage bin'65.

The gases and vapors pass from the distilling chamber 51 through the main 66 to the condensers 67 which are here shown as the direct type of condensers in which the gases lare sprayed with water or ammonia liquor. A decanter 68 is shown for separate collection of the cooling liquor in the tank 69 and the condensed distillate in the tank 70.

The stills shown in Figures 1-5 inclusive are better adapted for distillation with gases at very much higher temperature than is the still shown in Figure 6.

Figures 8 and 9 show still another type of apparatus in which the hot gases are passed through pipes or tubes which are surrounded with a body of tar. The gases from the coke oven battery 5 pass through the uptake pipes 12 into a hot gas header 50 as described in connection with Figures 6 and 7. The hot gases pass into the chamber 75 of the distilling means 76 and pass up through the tubes 77 into the gas collecting chamber 78,

and pass thence through the main 79 to condensing means which may be of any suitable type; The tubes are surrounded by`a jacket which is formed by the heads 80 and 81 in which the tubes are fastened and the shell 76'. Tar is admitted to this jacket through line 82 and passes up around the tubes and is withdrawn through the line 83. Baiing means may be provided Within the jacket to insure thorough circulation of the tar around the tubes and uniform ow of tar throughout the jacket.

This tar which is preheated and partially distilled by indirect Contact with the hot gases which pass through the tubes 77 may be divided, and a part withdrawn through the line 84- to a vapor chamber or used for any purpose. The balance of this preheated and partially distilled tar is passed through the line 85 into the chamber 78 of the-distilling means 76. The `preheated tar is brought into contact with the hot gases and is distilled to a greater or less degree, depending upon the temperature of the gases, the tempera-.- ture of preheat of the tar, the quantity of the gas and of tar, etc. The volatilized oils pass with the gases through the main 79 to the condensers. The residual pitch flows down through the tubes and ushes the walls of the tubes 77. The flushing of the walls prevents the accumulation of hard pitch or coke thereon, in addition to providing for further distillation of the tar.

Any suitable means for ushing the walls of the tubes with tar may be provided. The means here shown provides for the tubes 77 extending a short distance above the head 81, and the tops of these tubes are serrated, as shown at 86 in Fig- -ure 9. The tar which is to be brought into direct contact with the hot gases is owed onto the head 81 and flows down over the walls of the tubes 77. The tar is supplied to the tubes in suilcient quantity to prevent accumulation of hard pitch or coke on the inner surfaces of the tubes. This tar is distilled and the gases and vapors resulting from the distillation pass through the main 79 to the condenser 88. The undistilled residue which co1- lects in the bottom ofthe distilling means is withdrawn through any suitable outlet which is here shown as the levelling arm 89 and is run to the storage tank 90. Where very hot gases, e. g. gases at 500 C. upwards are used for distillation, it may be necessary to flush the walls of the chamber with pitch to prevent accumulation of hard pitch and coke. In such a case spray means such as indicated at 31 of Figure 3 may be satisfactorily employed. The walls of the chamber 75 will then be sprayed and flushed intensively with pitch and will be kept free of accumulations.

The` tar which circulates through the jacket of the distilling means 76 is preheated and may be ,partially distilled. As here shown this same tar, or a portion of it, is further distilled by direct contact with the hot gases. By supplying an additional tar inlet to the chamber 78 at the top of the still 76, other tar may be supplied for. distillation by direct ContactV with the hot gases. AThe indirect preheating and distillation and the direct distillation are conducted simultaneously within the same distilling unit and the heat employed is that of the hot gases from the coke ovens.

The tar distilled by direct .contact may be the same tar as that which is'preheated by indirect contact or diierent tars may be simultaneously distilled, one by direct Contact with the gases and the other by indirect contact with the gases. When tar other than that preheated by indirect contact with the hot gases, is distilled by direct contact, the tar which has been distilled by indirect contact may be run to separate storage means, after 'first passing to a vapor box for the separation and'separate collection of distillate. The vapor box may be maintained under vacuum. l I claim:

1. The method of distilling tar which comprises bringing the tar into heat exchange relation with hot coal carbonization gases but separated from the gases by a heat conductive wall, one side of the wall contacting with the tar and the other side being exposed' to the hot gases, flushing the surface of the Wall exposed to the gases and so controlling the quantity and temperature of ushing liquid that the Wall and tar on the other side thereof are heated to distillation temperature of the tar by the heat of the gases. v

2. The method ofv using hot fresh coal carbonization gasesto effect simultaneously distillation of a liquid by indirect heat exchange and distillation of tar by direct contact with the gases, which comprises bringing the liquid into heat exchange relation with the hot fresh coal carbonization gases but separated from the gases by a heat conductive wall, one side of the wall contacting with the liquid and the other side being exposed to the hot gases, flushing the surface of the wall exposed to the gases with tar and so controlling the quantity and temperature of the tar that the tar is distilled and the wall and liquid on the other side thereof are heated/to distillation temperature of the liquid by the heat of the gases.

3. The method of distilling tar, which,com prises passing hot tar laden gases from coal distillation plants in countercurrent relation and indirect heat exchange relation with tar in such manner that heating and .distillation of the tar and cooling of the gases and condensation of tar therefrom are simultaneously eiected, and presimultaneously bringing tar venting accumulation of hard pitch or coke on the heated surfaces exposed to the tar-laden gases by flushing the same with hot pitch or tar.

4. The method of distilling tar, which comprises passing hot coal distillation gases through a distilling zone in indirect heat exchange relation with tar to effect preheating of the same and thus preheated into direct heat exchange relation with the hot gases in the said zone to eect distillation thereof.

5. The method of distilling tar, which comprises passing hot coal distillation gases through a distilling zone, circulating tar through a tubular boiler or heater in said zone, heating the tar 4during such circulation by indirect heat exchange' with the hot coal distillation gases passing through said zone, and simultaneously effecting distillation of tar by direct heat exchange with such gases by introducing it into direct contact with the gases passing throughsaid zone.

6. The method of distilling tarwhich comprises bringing tar into direct and intimate contact with hot coal distillation gases by spraying 'it into such gases, and simultaneously cooling Athe gases and heating tar therewith by passing tar into indirect heat exchange relation with the hot gases, and keeping the surfaces of the indirect heater flushed with the tar undergoing direct distillation.

7. The method of distilling tar which comprises bringing the tar into heat exchange relation with hot tar laden coal carbonization gases but separated from the gases by a heat conductive wall one side of the wall contacting with the tar and the other side being exposed to the hot gases, flushing the surface of the wall exposed to the hot gases with hot liquid tar or pitch, and so controlling the quantity and temperature of flushing liquid that the wall and tar on the other side thereof are heated to distillation temperature of the tar by the gases.

8. The methodof distilling tar, which comprises preheating the tar by indirect heat exchange with hot coal distillation gases to a' temperature sufficient to distill part of the oil contained in the tar, removing the distillate from the thus preheated tar and condensing the same, and discharging the preheated residue into direct contact with the Ahot coal distillation gases to effect further distillation thereof by direct heat exchange with'the gases.

9. The method of distilling tar, which comprises supplying to a still hot coal distillation gases, spraying tar into the gases in the still with such thoroughness and intensity that the gases are rapidly cooled to a temperature approximating that to which the tar is heated, distilling it thereby, and passing tar into indirect h eat exchange relation with the gases and spray in the still to effect heating thereof simultaneously with the distillation of tar by hot gases.

direct contact with the 10.In combination with a plant for the distillation of coal, a tar still, means for introducing tar into the still, said tar still being provided with a tar retaining wall one side of which confines a body of tar and the other side of which is exposed to direct contact with hot coal distillation gases from the plant, and means for flushing said exposed side of the retaining wall whereby pitch and coke accumulations thereon are prevented.

11. The method of distilling tar containing low boiling constituents, which comprises passing the tar into indirect heat exchange relation with hot coal distillation gases to eiect preheating of the tar to a temperature above the boiling point of the low boiling constituents, passing the heated tar into a vaporizing zone in which the low boiling constituents are varibrized and separated from the tar, passing the tar residue into direct contact With the hot coal distillation gases in the preheating zone, thereby distilling said tar residue to form pitch, and agitating the tar residue in said last mentioned zone.

12. The method of distilling tar which comprises passing hot tar-laden coal distillation gases through a distilling zone in indirect heat exchange relation with tar to preheat the tar, and flushing the surfaces exposed to the tar-laden gases in said distilling zone with hot tar or pitch to distill the tar or pitch and prevent accumulation of hard pitch or coke on said surfaces.

13. The method of distilling tar which comprises bringing the tar into heat exchange relation with hot tar-laden coal carbonization gases but separated from thegases by a heat conductive wall, one side of the wall contacting with the tar and the other side being exposed to the hot gases, flushing the surface of the ,wall exposed t0 the hot gases with hot liquid tar or pitch and controlling the quantity and temperature of ushing liquid so that oils are distilled therefrom and so that the wall and tar on the other side thereof are heated to distillation temperature of the tar by the gases.

14. The method of distilling tar which comprises bringing the tar into heat exchange relation with hot tar-laden coal distillation gases but separated from the 'gases by a heat conductive wall one side of the Wall contacting with tar and the other side being exposed to the hot gases whereby the tar is preheated `to atemperature sufficient to effect partial distillation of the tar to low melting point pitch, flushing the surfaces of the wall exposed to the hot ses with said low melting point pitch and contr ing the quantity and temperature of the ushing liquid so that the pitch is further distilled and so that the wall and tar on heated to distillation STUART Pam/rama Minna.

temperature by the gases.

roo

.the other side thereof are r

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