US1976356A - Distillation of tar - Google Patents

Description

Oct. 9, 1934. s. P. MILLER DIST ILLATION OF TAR Filed Sept. 25, 1929 3 Sheets-Sheer?l l INVENTOR MM M EY ATTCRNEY @Stzw Oct. 9, 1934. s. P. MILLER DISTILLATION OF TAR 5 Sheets-Sheet 2 Filed Sept, 25j 1929 DOCID INVENTOR WMM BY f?! ama /awgrg ATTORNEYS Filed Sept. 25, 1929 3 Sheets-Sheet 3 ATTORNEYS? @atented @et 9, 1934 PATENT OFFICE DISTILLATION F TAR Stuart Parmelee Miller, Englewood, N. J., assignor to The Barrett Company, New York, N. Y., a corporation of New Jersey Application September 25, 1929, Serial No. 395,117

9 Claims.

This invention relates to improvements in the distillation of tar and the production of pitches and distillate oils therefrom and includes a method of tar distillation and improved apparatus therefor. More particularly the invention relates to the recovery of desirable products from coal distillation plants such, for example, as by-product coke ovens.

In the ordinary operation of by-product coke l0 ovens, gases produced by the coking operation pass fromthe individual ovens through uptake pipes and goosenecks t0 a collector main common to the ovens of the battery. The coke oven gases which leave the ovens at temperatures from 600 l5 to 700 C. or higher are cooled in the collector main and in condensers connected therewith to separate tar constituents therefrom. The separated coal tar is commonly shipped to tar distillation plants where it is subjected to distillation to produce pitches and various other products. Owing to the high temperature of the gases from the coke ovens and particularly because of the enormous amount of heat carried thereby, the successful operation of the collector main in connection with these ovens has always been a serious problem. .The heat carried by the gases is many times that required for the distillation of all of the tar content in the gases. A certain amount of heavy tar or pitch may separate in the collector main, and if such tar or pitch, while in the main, is subjected to the distilling eect of the high temprature gases passing thru the main, formation of solid, hard pitch or coke in the main may result. Such hard pitch or coke can in some cases be removed only by shutting down the plant and scraping or digging it out. It is customary to liush the collector main with a mixture of tar and ammonia liquorA or with ammonia liquor alone, but this practice does not always avoid the diiculty. In fact the use of water or ammonia liquor aggravates the trouble in some cases because the pitches formed in the main are insoluble in water or ammonia liquor and hence are not flushed out unless an extremely large amount of the liquor is employed.

The use of a large amount of ammonia liquor to iush the collector main is disadvantageous because of the. resulting lowered temperature of the gases. Thus by spraying ammonia liquor into the collector main in suflicient quantity to prevent accumulations of pitch therein, the temperature of the gases may be so reduced that a considerable proportion of the valuable oil constituents which are present in the gases is condensed and thrown down with the tar and can be removed therefrom only by subsequent distillation.

It is the object of the present invention to provide an improved method and apparatus for tar distillation directly at acoal distillation plant such as a by-product coke oven plant, and especially an improvement in the operation of the collector main whereby advantage can be taken of the heat carried by the hot coke oven gases to distill tar and oils and to produce pitch therefrom.

A further object of the invention is to provide a method of operating the collector main of a coke oven plant or other coal distillation plant so that the hot gases passing into the main may be maintained at a high temperature within the main and will leave the main at a suiciently` high temperature to retain valuable constituents thereof in the Vapor state. These gases leaving the collector main carrying a high percentage of oil vapors which comprise vapors of high boil- "i5 ing constituents may be treated in diferent ways. They may be carried over into the ordinary condensers employed with such plants and there cooled to condense tarry oils which may be similar to the tarry oils ordinarily produced at such plants but will contain additional constituents which comprise higher boiling compounds condensed from vapors carried over from the' collector main, which vapors are ordinarily condensed within the collector main according to the usual methods of operation. Where clean oil products are desired the hot gases carrying vapors of higher boiling constituents, are subjected to a cleaning operation at a high temperature, preferably directly after the gases leave the collector main, and entrained impurities are removed from the gases while allowing the vapors of constituents desired as clean oils to pass over through the cleaning apparatus to suitable condensers. An electrical precipitator adapted for cleaning hot gases may be employed for the cleaning operation, or a suitable scrubber or a mechanical detarring device may be used. The gases may be cooled to produce a total condensate which, where complete cleaning of the gases nas been effected, may be a clean oil condensate, or a tarry oil condensate where cleaning has not been employed or has been only partially complete; fractional condensers may be employed to obtain fractional condensates. Y

It is a further object of the invention to provide for collecting the gases from the various units of a coke oven plant or other coal distillation plant while maintaining the gases at a high temperature within the gas collecting means and 110 thereafter employing the gases for the distillation of tar, which distillation may take place in a scrubber or suitable still preferably located in close proximity to the collector main.

'Ihe present invention provides an improved process of operating a coke oven plant, whereby tar is flushed through the collector main as a flowing stream or river, whereby the diiiculty of pitch accumulation is obviated, valuable oil constituents are retained in the hot coke oven gas and the tar is partly distilled to yield further quantities of desirable distillates, which are added to those retained in the hot gas and are recovered in the subsequent cooling operations. A continuous river of fresh tar may be employed but in the preferred form of the invention the tar is recirculated and may be distilled to yield pitches of various melting point characteristics depending upon the extent of recirculation and the extent of distillation of the recirculated material.

It is a feature of the invention that the walls of the main are flushed with tar as the gases pass through the main, in order to prevent the accumulation of hard pitch or coke upon the Walls as a result of distillation of tar which might otherwise collect on these walls. The gases pass through the main at a high temperature, and the bottom of the main is flushed with tar and the walls are ushed with tar so undesirable coking on the bottom and walls of the main is prevented and the hot gases are not. sprayed with the tar except as the walls are sprayed, so that as a result the gases are maintained at a high temperature throughout their passage thru the main. The gases in passing through the main are enriched in condensable constituents volatilized from the tar employed for flushing the bottom of the main and washing the walls of the main. The pitch resulting from the distillation may be withdrawn from the main and then recirculated therethrough for further heating and distillation. The amount of distillation may be regulated by the extent to which the tar and pitch are subjected to the heating effect of the gases, and consequently the character of the pitch produced can be modified as desired to produce saleable pitch products.

'I'he tar and pitch flowing through the collector main will be heated by the hot gases, and their temperature may be raised considerably. Part ofthe heat is employed, however, in vaporizing oil constituents of the tar without increasing the temperature of the unvaporized portion of the tar so that the maximum temperature of the tar and of the resulting pitch may be considerably below that of the gases. To avoid pitching of the main. it is important that a relatively large amount of tar or pitch iiow through the main and that this tar or pitch be circulated actively Within the main so as to prevent any accumulation of hard solid pitchV therein. According to this invention, the walls of the main are also sprayed with tar or pitch to prevent the accumulation of solid pitch or coke thereon. The heat available in the gases is such as to ensure the heating of the tar or pitch to a temperature at which it is thinly fluid, so that it can be circulated easily. Moreover, the hot tar or pitch readily dissolves any deposits of the solid hard pitch in the main land accumulation thereof is thus avoided. I

In thus giving off heat to the tar or pitch in the collector main and in coming in Contact with the walls of the main the gases are cooled, and

the cooling of the gases results in a tendency toward condensation of pitchy or tarry constituents therein, and some condensed pitch or tar may separate at what is still a relatively high temperature upon the exposed internal surface of the main. Such pitch if not removed is subjected to the gradual distilling and coking effect of the gases, which may result in the accumulation of solid hard pitch or coke on the exposed internal surface of the main. To avoid this difliculty, the exposed surface is washed with tar or pitch in a quantity suihcient to dissolve any accumulation of solid hard pitch from the wall and to wash anyaccumulation that may form into the bottom of the main where it will join the stream of tar or pitch owing therethrough and be carried from ,the main. This flushing of the walls of the main may be readily accomplished by the provision of suitable spraying devices arranged to direct the pitch or tar upon the exposed surfaces. The spraying device can be supplied with tar from a suitable source thereof under suiiicient pressure to ensure distribution of the tar or oil over the exposed surface in quantity sufficient to accomplish the purpose indicated.

The tar or pitch employed for washing the walls of thecollector main may be the same as that used to flush the bottom of the main. It may be partially distilled tar which hasbeen drawn olf from the main, or it may be fresh tar. Tar from the collector main of an ordinary coke oven battery, tarry oils from the condensers of such a battery, or tar or pitch from another source, such as gas retort tar may be employed. The tar or pitch employed for washing the walls of the main may be a blend of fresh tar or pitch and partially distilled tar recirculated from the collector main.

Although indiscriminate cooling of the gases in the collector main as heretofore practised is to be avoided, it may be desirable to introduce water or ammonia liquor with the tar or pitch for the purpose of cooling the 'gases to a predetermined and regulated extent. The regulation of the cooling effect can be accomplished more readily with water or ammonia liquor because of the higher specific and latent heats of water as compared with those of tar. It is possible, therefore, to add water or ammonia liquor in the proportion required to remove substantially all heat from the gases except that needed for the distillation of the tar. When harder pitches are desired, less water may be added. Cooling of the gases to a regulated extent can be accomplished also by the introduction of relatively light oil with the tar. Thus a proportion of the lighter oil recovered from the gases can be returned to the collector main and mingled with the tar or pitch therein. The distillation of this oil in the collector main will absorb heat from the gases and thus permit the maintenance of the desired temperature therein.

The hot gases flowing through the collector main will be cooled partially by transfer of heat to the tar or pitch undergoing distillation, and the gases will be enriched in oil constituents derived from the distillation of the tar or pitch. The gases will, however, leave the collector main still at relatively high temperature and will carry in addition to the oil vapors a certain proportion of l tar or pitch in the form of tar fog", together with solid particles of coal, coke, etc., which are carried over from thecoke ovens. The dew points of the gases for the several constituents carried therein as vapor are lower than the normal boiling points of these constituents, and by suitable regulation of the temperature of the gases during distillation and during the subsequent treatment of the gases, as where the gases are subjected to cleaning or other subsequent treatment, it is possible to retain the desired oils therein. The temperature of the gases leaving the main will be such that although higher boiling pitchy constituents of the gases and some of the higher boiling oils may collect in the collector main, the latter is preferably operated at such high temperatures that a substantial amount of higher boiling oils will be carried over from the collector main to the condensers by the gases leaving the collector main. VThe temperature of the gases leaving the main should be maintained above the dewpoint of the gases for those condensable constituents desired in the products obtained beyond the collector main. The gases leaving the main may be cooled in suitable condensers to produce one or more condensate fractions.

Substantially all of the entrained impurities, that is, tar fog and solid particles, can be separated from the gases by passing them through an electrical precipitator such, for example, as the well-known Cottrell precipitator, the precipitator being operated at substantially the temperature required to maintain the desired oil constituents in the vapor phase, that is to say, at a temperature higher than the dew point of the gases `for the constituents desired in the clean oil product or products.

By passing the gases which leave the main at a high temperature through a suitable scrubber, entrained impurities may be washed from the gases. By employing in the scrubber as a scrubbing medium pitchy material of the same composition and temperature as that suspended in the gases, entrained pitchy .nipurities can be removed Without altering the composition of the gases. On the other hand, where a scrubbing medium which contains lower boiling constituents is employed, these lower boiling constituents may be volatilized during the scrubbing operation, so that the gases leaving the scrubber will contain vapors of these lower boiling constituents which, on cooling, will be removed from the gases together with the vapors contained in the gases as they leave the collector main.

The invention can be applied to ordinary coke oven plants such as Semet-Solvay plants, Koppers plants, etc., without substantial modification thereof, the usual standard equipment being employed with the addition of means for flushing the inner walls of the collector main and means for providing a stream of tar in the bottom of the collector main Where such latter means does not already exist, and with the omission of the usual spraying means in the collector main and preferably also in the uptake pipes. Where aprecipitator or scrubber is to be employed, this additional equipment may readily be added in the usual cross-over main. The gases will leave the collector main at a higher temperature than at present so additional cooling means must be provided in the cross-over main or the condensers. Additional ammonia liquor sprays may be provided in the cross-over main for this purpose.

As a modification of the apparatus above described, the hot-tar-enriched gases may be Withdrawn from the collector main through different gas mains and may be differently treated. For example, the greater part of the gases may be Withdrawn from the collector main through a center-box and cross-over main, or other means of the type `usually employed for removing the gases from a gas collector main. Another gas main may lead from another portion of the collector main as, for example, from one end of the main for conveying a portion of the gases to different treating means, as for example through an electrical precipitator when it is desired to produce clean oils from a portion of the hot gases. In this Way a portion of the gases may be cooled to produce tarry oils and another portion cleaned and cooled to produce clean oils. The proportion of the gases subjected to each treatment can be regulated by means of suitable Valves in the corresponding gas conduit. The precipitator may be located on the usual crossn over main when desired, and a portion of the oils withdrawn thru another gas main may be cooled to produce tarry oils directly. Instead of an electrical precipitator a scrubber in which the gases are enriched and partly or wholly cleaned may be thus-employed.

The present invention is of more or less general application to the distillation of tar and the recovery of clean oils therefrom, and it will be further'illustrated by the following more detailed description taken with the accompanying drawings which show apparatus embodying the invention and adapted for the practice thereof. It is intended and will be understood that the invention is not limited to the specific details of the apparatus as illustrated in the drawings, in which Fig. 1 is a plan view of a portion of a coke oven plant illustrating the application Vof the invention thereto;

Fig. 2 is an enlarged sectional view thru the cross-over main;

Figs. 3 and 4 are different views showing one type of precipitator which may be employed for cleaning the gases;

Figs. 5 `and 6 show an enlarged detail of the nozzle shown in Figs. 2 and 3 for washing the Walls of the collector main;

Figs. 7 and 8 show details of another type of nozzle which may be employed, and

Figs. 9 and l0 show means for scrubbing the hot gases to give clean oils, which means may be employed for distilling tar in the hot gases.

Referring to the drawings, 5 indicates a coke oven battery which is equipped in the usual way with uptake pipes 6 and a collector main '7. Gases from the collector main pass through the centerbox 8 into the cross-over main 9 and are cooled in the condensers 10. An exhauster l1 is pro- 'vided for drawing the gases through the system and carrying them over to means for the recovery of ammonia and light oils.

At one end of the main a pipe 12 is shown for carrying a portion of the gases from the collector main over to the electrical precipitator 13 where the gases are cleaned. Form the precipitator the ,cleaned gases pass to the condensers 14 where clean oils are separated from the gases. The clean oils are drawn oi from the condensers to a decanter and thence to the storage tank 14. By fractional cooling of the gases two or more clean oil fractions may be obtained. An exhauster l5 is provided beyond the condensers 14. The gases passing thru this exhauster may advantageous'y be treated for the recovery of ammonia and light oils together with the gases from the condensers 10.

A valve 15 is provided for shutting off the pipe 'l2 when it is not to be used. If desired, by proper manipulation of the valves shown, all of the gases lil() from the collector main may pass thru pipe 12 to the electrical precipitator 13 and the con densers 14. This method may commonly be the practice at a plant having several collector mains, but may also be practiced even if only one co1- lector main is in use for distillation.

When the valve 15 is closed, or where the collector main is connected with the condensers by only one gas main, as in the ordinary by-product recovery systems, the operation of the collector main is as follows:

Tar from a source 16 which may be ordinary coal tar or heavy coal tar from the collector main of an ordinary coke oven plant or tarry oils from the condensers of an ordinary coke oven plant or tar from another source such as water gas tar or gas retort tar, etc. is supplied to the main in a suflicient quantity to flush the bottom of the main and prevent the accumulation of tar or pitch therein. In the drawing, the tar is shown as pumped thru the lines 1 7 and v18 by means of the pump 19 into the opposite ends of the collector main. The stream or river of tar which flows through the collector main is withdrawn from the center-box 8 through the line 20 into the receiver 21. The tar or pitch which collects in this receiver comprises the distillation residue of the tar circulated by pump 19 as well as the tarry or pitchy constituents thrown down out of the gases from the coke ovens as these gases pass from the coke ovens to the cross-over main 9. Tar or pitch from the receiver 21 may be withdrawn to the storage tank 22, or a portion of it may be recirculated by means of the pump 23 through the line 24 into the ends of the main, together with fresh tar from the container 16.

In addition to providing for a river of tar thru the bottom of the collector main, means is also provided for spraying the walls of the collector main with tar or pitch. This may be fresh tar fromf the receiver 16, or fresh tar fromlanother source, or it may comprise both fresh tar and tar or pitch from the receiver 21. According to the drawings, the tar is sprayed onto the walls of the collector main through spray nozzles 25 from the pipes 26 fed by the line 2'7 which branches from the line 17. The vspray is directed onto the walls in such a way as to prevent unnecessary spraying of the hot gases with the tar, which would result in unnecessary cooling of the gases, b`ut is supplied in suflicient quantity and so directed as to adequately flush the surfaces of the main to prevent accumulation of pitch on them.

According to this embodiment of the invention, fresh tar is employed in the collector main, either for `flushing out the bottom of the main, or for washing down the walls of the main, or both, and lower boiling constituents of the fresh tar thus employed are distilled by the hot gases and the resulting vapors pass from the collector main with the -gases to the condensing means. A portion of the tar or pitch drawn off of the collector main may be blended with the fresh tar thus employed.

The tar fed to the bottom of the collector main and the tar sprayed onto the walls of the collector main may be preheated, and where a portion of the partly distilled tar or pitch withdrawn from'the. center-box is recirculated through the collector main, it is preferably recirculated at a somewhat elevated temperature before it has had time to cool.4 A small amount of water or ammonia liquor may be admixed with the tar supplied to the collector main, but such aqueous solutions Will be present in small quantity sufficient only to regulate the temperature of the gases and will not be present in such quantity that any appreciable amount of aqueous solution is withdrawn from the collector main with the tar or pitch.

By replacing the collector main sprays of the usual type through which large quantities of cooling medium are ordinarily sprayed into the gases in the main by sprays of the type described, the usual sharp reduction of temperature of the gases is avoided, and the gases pass through the main at a relatively high temperature and are withdrawn through the cross-over main at such high temperature that the pitch or tar removed from the gases in the collector main is considerably less in amount than the tar normally recovered from the gases, and the tarry oils obtained in the condensers 10 comprise a correspondingly larger percentage of the vapor constituents carried by the gases leaving the ovens than is ordinarily collected in the condensers, and these oils comprise 'a higher percentage than usual of high boiling oils.

Where desired, the valve 15 may be opened so that a portion of the high temperature gases from the collector main may be withdrawn from the end of the main in addition to the gases leaving the center-box, and the gases passing from the end of the main may be subjected to different treatment from that to which the gases passing through the cross-over main through the center-box are subjected. Fig. 1 shows means whereby the gases passing through the pipe 12 from the end of the collector main are cleaned in an electrical precipitator 13 in which pitch is removed from the gases. The pitch is collected in the receiver 28. The cleaned gases passing from the precipitator are cooled in the condenser 14, and clean oils are obtained therein. The collector main, the precipitator and the main 12 connecting the collector main with the precipitator may be insulated to prevent loss of heat and the gases are advantageously passed over into the condensers 14 at a relatively high temperature, so that higher boiling oils ordinarily removed in the collector main may be carried over through the precipitator in the vapor state and collected in the condensers 14.

The precipitator 13 is shown in more or less detail in Figs. 3 and 4. 'I'he gases from the short main 12 enter the bottom of the precipitator and leave the precipitator through the main 30. Rods or wires 31 are suspended through the tubes from the bus-bar 32. This busfbar is in turn supported from the insulators 33 within the chambers 34. 'I'he current employed is ordinarily high tension uni-directional current which is supplied through conductor 32' and bus-bar 32 v to the discharge electrodes 31; the collecting electrodes 29 are ordinarily grounded. In passing up through the electrodes or tubes 29 the gases are subjected to a silent electrical discharge, at high potential, and entrained impurities are thrown out of the gases onto the tubes and drain from the tubes into the bottom of the precipitator. The precipitator tubes may be jacketed with a heating jacket as shown.

As an alternative arrangement, the precipitator may be located in the cross-over main 9, preferably close to the collector main, and the main 12 leading from the end of the collector main 7 may be omitted entirely. According to this arrangement, all of the gases leaving the collector main pass thru the precipitator on the way to the condensers and are subjected to cleaning therein.

Diderent forms of nozzles may be employed for washing the walls of the main. Figs. 5 and 6 show details of one type of nozzle which may be employed. The tar fed thru the passage 28 ows out thru the openings 29 between the lateral supports 30 and is directed by the plate 31 against the walls of the main. 'I'he plate 31 is supported by the lateral supports 30. These supports prevent undue spraying of the gases and direct the tar thru the openings 29 against the walls of the main.

Fish tail or ian tail nozzles, such as that shown in Figs. 'l and 8, may be employed for washing the walls of the main. They are advantageously located adjacent to the walls to ,be washed, each nozzle being employed to wash only a single wall. Nozzles should be positioned at intervals along the wall so that the whole wall is flushed to prevent the formation of pitch and coke on the walls. The mouth of the nozzle is ared so that each nozzle will wash a considerable portion of the wall. Other types of nozzles which concentrate the tar sprays on th walls of the collector main and reduce to a minimum any spraying of the gases passing thru the main can be used. By spraying the walls of the co1- lectorl main the formation of coke or pitch on the walls of the main is prevented, and the gases pass thru the main at a higher temperature than when the gases are subjected to any considerable spraying in the main.

Figs. 9 and 10 show a modified arrangement by which all or a part of the hot gases leaving the collector main may be cleaned by scrubbing them with an intense spray of tar or pitch. The main 'l is shown equipped with sprays 25 for spraying the walls of the main without any substantial spraying of thev gases passing thru the main, as already described. The gases leave the main at a relatively ligh temperature and the tar employed for scrubbing the gases may be distilled simultaneously with the scrubbing operation.

The arrangement in Fig. 9 is quite similar to the arrangement described in connection with Fig. 1. Fig. 9 shows a coke oven 5 equipped with a collector main '7 provided with sprays 25 for spraying the walls of the main with minimum spraying of the gases in the main similar to the arrangement shown in Fig. 1. The gases may pass thru the usual cross-over main to condensing means, or they may be diverted thru the main 12 to the scrubber 40 and there scrubbed. The tar employed as the scrubbing medium may be distilled. The scrubbed gases pass to condensers where vclean oils are separated from the gases. Where the scrubbing is accompanied by distillation, the oils which are separated from the gases in the condenser will comprise constituents distilled from the tar in the scrubbing device in addition tooils present in the gases as they leave the collector main. The gases leaving the collector main comprise vapors originally present in the gases as they leave the ovens and'also vapors resulting from the distillation of tar in the collector main. i .l

The scrubber 40 contains apparatus for producing an intense spray of tar or pitch in the gases. Taror pitch is contained in the bottom of the scrubber and means is provided for spraying the tar or pitch into the gases. The amount of tar or pitch in thescrubber is controlled by the adjustable levelling arm 41 thru which residue from the scrubbing operation is withdrawn from the be employed for this purpose.

scrubber thru the trap 42 into the trough 43. 'I'he tar or pitch from the bottom of the scrubber is thrown up into the gases by the roll 44. Motor 45 is provided for rotating this roll at a high rate of sped, for example, 90o-1200 R. P. M.

'Ihe scrubber is advantageously provided with a tower 46 thru which the gases pass on their way to the condensers 47. The tower acts as a settling chamber in which entrained spray settles out of the gases, and the particles of spray which separate from the gases are returned to the scrubber. The scrubber may be provided with baiiles such as the bailles 48 and 49. Raschig rings or other bailling means are advantageously employed in the settling tower to remove entrained particles of spray.

The scrubbing medium may be heavy tar or pitch which is removed from the gases. In this case suicient tar or pitch is added to the scrubber to provide the necessary spray to start the scrubbing operation and after the scrubber has been put in operation the tar or pitch removed from the gases collects in the bottom` of the scrubber and is sprayed up into the gases by the roll so that it is unnecessary to add additional scrubbing medium to the scrubber. Excess tar or pitch is drawn oi thru the levelling arm as it is removed from the gases.

The roll maintains such an intense spray of the tar or pitch in the gases that the gases are substantiallydetarreddue to the removal of entrained matter by the intense tar spray. The gases leaving the scrubber thru the tower 46 are substantially free from entrained matter except that any particles of the spray carried forward by the gases may be removed in the settling tower.

Instead of scrubbing the gases with tar or pitch of the same composition as that contained in the gases, tar or pitch of a different composition may Such tar or pitch is advantageously fed to the scrubber thru the spray 50 in the tower 46 and supplied to the spray by the line 51. In passing over the baiiles 49 a large surface of the spray comes in contact with the gases passing up thru the tower and the removal of entrained particles of spray is thus aided and distillation of the spray by the hot gases and vapors leaving the scrubber results where the tar contains lower boiling ingredients which are volatile under the conditions there obtaining. Higher boiling constituents not volatilized in the tower may be distilled from the tar within the body of the scrubber. The heavy tar or pitch resulting from the scrubbing operation, and the distillation where any occurs, is drawn off vthru the adjustable levelling arm 41 and the trough 43 into the tank 52. A portion of this residue may be recirculate'd thru the scrubber by means of the pump 53 and the line 54.

The drawings show means for the counter-current ilow of the gases and scrubbing medium thru the scrubber. Concurrent flow of the gases and scrubbing medium may be provided by introducing the partially distilled tar from the bottom of 'the tower 46 into the scrubber 40 at the gas-inlet end of the scrubber thru a pipe, not shown, and removing the pitch formed in the scrubber atvthe gas outlet end thru anadjustable levelling arm 4l, placed at the end of scrubber 40 opposite to that shown in the drawings.

The gases and vapors leaving the tower 46 are free from entrained impurities and on cooling in the condensers 47 clean oils will separate from the gases. Where there has been no substantial enrichment of the gases by distillation during the scrubbing operation, the oils recovered in the condenser will be oils present in the gases in vapor form as the gases leave the collector main. The boiling range of such oils will depend upon the temperature of the gases in the scrubber which in turn is dependent upon the cooling effected in the collector main. By controlling the operation of the collector main so that the gases pass thru the scrubber at a higher or lower temperature, oils of higher or lower boiling range will be separated from the gases in the condenser.

Where tar is distilled during the scrubbing operation, the distillation may be controlled so as to enrich the gases in oils of any desired boiling range in order to control the composition of the oils recovered in the condensers; or the distillation can be regulated to control the composition of the pitch obtained from the scrubber. This pitch will comprise impurities removed from the gases in addition to any residue from the distillation.

In the drawings condensers of the direct type are indicated at 47 and means for drawing off two separate fractions into the decanters 55 and 56 and thence to the storage tanks 57 and 58 are shown. From the condensers the `gases pass thru an eXhauster to means for the recovery of ammonia and light oils.

The composition of the clean oils in the condensers depends upon the temperature at which the gases leave the scrubber and the temperature to which they are cooled as well as the amount of enrichment resulting from any distillation of tar which may take place in the scrubber. The gas main connecting the collector main with the scrubber and the scrubber may advantageously be insulated to prevent loss of heat thru radiation.

Although the invention has been described more particularly as applied to the operation of a coke oven battery, it is to be understood that it may also be applied to other coal distillation plants such as horizontal gas retort plants, etc.

I claim:

1. The process of operating the gas collector main of a coal distillation plant whereby the gases leave the main at a high temperature and tar and pitch are employed for preventing the accumulation of pitch or coke within the main, which comprises ilushing the bottom of the main with tar and pitch resulting from the distillation of the tar and spraying the walls of the main with tar or pitch whereby the gases within the main are enriched in vapors distilled from the tar employed, the said spraying of the walls being effected without substantial spraying of the gases passing thru the main, and removing the coal distillation gases from the' gas collector main at a temperature sufciently high so that the gases leaving the main retain in vapor form high boiling oil constituents originally present in` the gases, and also retain in vapor form the constituents distilled from the tar within the main.

2. The improved operation of the by-product recovery system of a` coke oven battery, which comprises collecting the gases from a plurality of the ovens in a gas collector main, flushing the bottom of the collector main with tar and pitch resulting from the distillation of the tar and spraying the walls of the main with tar or pitch whereby the gases are enriched in vapors by distillation of the tar therein, said spraying of the walls being conducted in such a way as to avoid any substantial spraying of the gases passing thru the main whereby the gases leave the collector main at a high temperature, and then cooling the gases leaving the main to recover oils comprising constituents present in the gases coming from the ovens and constituents originally present in the tar employed within the co1- lector main.

3. The improved operation of the by-product recovery system of a coke oven battery, which comprises collecting the gases from a plurality of the coke ovens in a gas collector main, flushing the bottom of the collector main with tar and pitch resulting from the distillation of the tar and spraying the Walls of the main with tar or pitch without substantial spraying of the gases passing thru the main, whereby the gases are allowed to leave the main at a high temperature and the gases are enriched in vapor content by distillation of the tar within the main, cleaning the gases leaving the main while still at a high temperature, and cooling the resulting clean gases to recover clean oils comprising constituents originally present in the gases leaving the ovens and constituents originally present in the tar employed within the main.

4. The improved operation of the by-product recovery system of a coke oven battery, which comprises collecting the gases from a plurality of the coke ovens ina gas collector main, flushing the bottom of the collector main with tar and pitch resulting from the distillation of 'the tar and spraying the walls of the main with tar or pitch without substantial spraying of the gases passing thru the main whereby the tar is distilled within the main and the gases leave the main at a high temperature, and cleaning the gases leaving the main in an electrical precipitator while still at a high temperature.

5. The improved operation of the by-product 115 recovery system of a coke oven battery, which comprises collecting the gases from a plurality of the coke ovens in a gas collector main, ushing the bottom of the collector main with tar and pitch resulting from the distillation of the tar and spraying the walls of the main with tar or pitch without substantial spraying of the gases passing thru the main whereby the tar is distilled within the main and the gases leave the main at a high temperature, and subjecting the 125 gases leaving the main to a cleaning operation by scrubbing them with tar or pitch of the same composition as that carried in suspension in the gases.

6. The improved operation of the by-product 130 recovery system of a coke oven battery, which comprises collecting the gases from a plurality of the coke ovens in a gas collector main, flushing the bottom ofthe collector main with tar and pitch resulting from the distillation of the tar and spraying the walls of the main with tar or pitch without'substantial spraying of the gases passing thru the -main whereby the tar is distilled within the main and the gases leave the main at a high temperature, bringing the gases leaving the main into direct contact with tar whereby the tar is distilled and the gases are enriched in condensable constituents, and cooling the enriched gases to recover oils therefrom.

7. The improved operation of the by-product 145 recovery system of a coke oven battery, which comprises collecting the gases from a plurality of the lcoke ovens in a gas collector main, ushing the bottom of the collector main with tar or pitch and spraying the walls of the main with 150 tar or pitch without substantial spraying of the gases passing thru the main whereby tar or pitch is distilled within the main and the gases leave the main at a sufficiently high temperature to retain in vapor form high boiling oils originally present therein, scrubbing the gases leaving the main with tar at a high temperature whereby entrained impurities are removed from the gases and the tar is distilled and the gases are thereby enriched in condensable constituents, and thereafter coolingthe enriched gases to separate oils therefrom.

8. The method of operating the collector main of a coal distillation plant connected with a plurality of the ovens or retorts of the plant which comprises passing the gases through the main at a high temperature so as to retain high boiling oil constituents in vapor form in the gases leave ing the main, spraying the walls of the main with tar or pitch without substantial spraying of the gases passing through the main, to prevent the formation of deposits of hard pitch on the Walls.

9. The method of operating the collector main of a coal distillation plant connected with a plurality of the ovens or retorts of the plant which comprises passing the gases through the collector main at a high temperature so as to retain high boiling oil constituents in vapor form in the gases leaving the main, spraying the walls of the main with tar or pitch Without substantial spraying of the gases passing through the main, to prevent deposits of hard pitch on the walls, and causing tar to flow through the bottom of the main in surface contact with the hot gases so as to distill the tar to pitch and enrich the gases in volatile constituents.

STUART PARMELEE MILLER.

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