US1909978A - Distillation of tar - Google Patents

Description

May 23, 1933. s p MlLLER 1,909,978

DISTILLATION OF TAR Filed May 5. 1927 2 Sheets-Shet 1 I f/ecfr/ ca INVENTOR ATTORNEYS DISTILLATION OF TAR Filed May 3, 1927 2 Sheets-Sheet 2 I 5 "f, //7 INVEN R /6 W v- BY 24 25 MMr ATTORNEYS Patented May 23, 1933 UNITED STATES PATENT OFFICE s'rnm'r rammmm KILLER, or menu, NEW JERSEY, ASSIGNOB To run nannn'r'r column, on NEW YORK. 11.1, a CORPORATION on NEW msm' DISTILLATION F TAR This invention relates to improvements in the distillation of tar, and particularly to the utilization of the heat available in the gases produced in coal-carbonization plants 5 to distill tar and to. produce clean oils and pitches by such distillation. The invention will be described especially with reference to its application to coke ovens.

In the ordinary operation of by-product coke ovens the gases produced .by the coking operation pass from the individual ovens through uptake pipes and goose-necks to a collector main common to the ovens of the battery. The gases, commonly known as foul gases, leave the ovens at high temperature, e. g., 600 to 700 C. or higher, and carry a considerable proportion of volutilized tars and oils as well as solid particles of coke, coal and carbon and other impurities. Ordinarily the gases are cooled as rapidly as possible by the application of sprays of ammonia liquor or ammonia liquor and tar in the goose-necks and collector main, the heat in the gases being thereby dissipated and lost. The rapid cooling causes separation of tar containing heavier oils in the collector main.- Further cooling is effected in the cross-over main which connects the collector main to the condensing system and an additional quantity of tar carrying both heavier and lighter oils is separated. The collected tar is shipped ordinarily from the coke-oven plant to a tardistillation plant for distillation and separation of the oils and the production of pitches of varying qualities. Handling losses, freight charges and distillation costs, including fuel and capital and maintenance expenses for the special equipment required for distillation, adds to the cost of production of the tar-distillation products.

It is the object of the present invention to provide a method and apparatus which permit the distillation of tar at a coke-oven plant, the utilization of the heat of the cokeoven gases for that purpose, and particularly the production of clean oils directl by such distillation, together with pitches haw ing the various qualities and characteristics required by the trade.

1927. seal No. 188,438.

According to the present invention the heat of the coke-oven gases as they come from the coke ovens is utilized to distill tar and to separate vaporizable oils therefrom by spraying or otherwise bringing the tar into intimate contact with the hot coke-oven gases from selected ovens while the gases are at a temperature sufiiciently, high to accomplish the desired distillation and the gases and vapors resulting from the distillation are subjected to cleaning by electrical precipitation to remove solid and liquid particles therefrom, leaving the clean vapors for subsequent condensation. The gases from the remaining ovens are subjected to regulated cooling and thereafter to cleaning by electrical precipitation to separate liquid and solid particles therefrom, the clean gases being then cooled to condense volatile con,-

stituents therein. The tar which is separated in the electrical precipitators may be returned to the still or stills for further distillation and separation of the volatile constituents therefrom, the oil constituents being thereby separated and recovered .from the clean gases. The invention permits the direct recovery of clean oils from all of the coke-oven gases and the separation of valuable oil constituents from the tar produced by the battery.

The distillation of the tar by means Off the hot coke-oven gases can be conducted in uptake stills formed, for example, by providing enlarged casings surrounding the usual uptake pipes. The tar to be distilled can bev introduced to the stills through spray nozzles which atomize or otherwise reduce the tar to a form which permits the exposure of the maximum surface thereof to the effect of the heated gases rising from the coke oven. An apron or similar device may be provided to deflect the tar spray and to prevent the tar from passing into the oven. In falling through the space within the casing surrounding the uptake pipe, the tar. spray is subjected to sufiicient heat to vaporize the more volatile portions thereof and the residue or pitch collects in the bottom of the still and can be withdrawn therefrom. A single tar spray can be used for each of the individual stills or a plurality or series of such stills can be employed and the rate at which the tar is'sprayed as well as its temperature can be regulated and controlled to obtain a greater or less degree of distillation of the tar and the product-ion of distillates having desired characteristics and harder or softer pitches or pitch-like products In a coke-oven plant having a small battery of ovens, for example, a twenty-oven battery, one or two uptake stills may be sufficient to distill the tar from the remaining ovens of the battery. In a larger cokeoven plant having a larger number of ovens in the same or separate battery, alarger number of uptake stills may be required to distill the tar produced by the remaining ovens of the battery or batteries. Tar from outside sources such as gas-retort tar, watergas tar, etc., may also be distilled and the number of uptake stills provided may be such as to permit the distillation of the normally available supply of tar.

The present invention contemplates more particularly a coke-oven battery in which the gases from a certain number of the ovens are employed for distillation of tar in the manner described while the remaining ovens of the battery discharge gases to a collector main of the usual type in which the gases are mingled with a cooling medium such as ammonia liquor or ammonia liquorand tar which is sprayed into the collector main in regulated amount for the purpose of reducing the temperature of the gases to the desired extent. The gases thus delivered to the collector main carry solid particles of coal and coke and globules of tar as well as tar fog. The cooling of the gases effects a further condensation of the tar which, however, does not separate easily from the gases. To avoid the contamination of the condensate in the coolers or condensers the gases are subjected as hereinbefore stated to electrical precipitation.

The dew points of the gases for the several constituents carried thereby as vapor are lower than the normal boiling. points of these constituents and by suitable regulation of the temperature of the gases during the distillation and especially during the subsequent treatment of the gases in the collector main, it is possible to retain the desired oils therein while the tarry constituents are condensed. Thus, by sufficiently lowering the temperature of the gases in the collector main all or substantially all of the tarry constituents can be converted into the liquid phase while the oils remain as vapors therein. The temperature of the gases should, to accomplish the intended purpose, be maintained above the dew point of the gases for the most readily condensable oil constituent desired so that substantially all of the oils will be retained and will be carried over with the gases from the collector main.

Substantially all of the undesirable constituents 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 gas for the most readily condensable oil constituent therein. The gases freed from tarry constituents will, upon cooling, yield clean oils substantiallv free from contamination by tar.

The gases which are thus cleaned will upon total condensation yield a mixture of oil constituents. The dew points of the gases for these several constituents are different and it is possible by fractional condensation to recover oils having varying characteristics. These oils, being substantially free from tarry constituents and other impurities, are in condition for immediate utilization for the purposes to which oils commonly obtained by distillation of tar are ada ted.

T e operation of the electrical precipitator consists in passing the gas to be treated between electrodes whose difference in electrical potential is very great. Experience has shown that it is best to use a rectified alternating current. The alternating current (the'primary) is sent through a step-up transformer to produce a high potential current (the secondary) which is then rectified to an intermittent uni-directional current, for example, by means of a rotary converter. The rectified current is dehvered from the converter to the electrical precipitator at practically the potential at which it leaves the transformer.

The electrical precipitator consists essentially of a group of vertical pipes with a wire or rod in the centre of each, the pipes being connected to roper headers for the introduction and dlscharge of the gases.

The pipes generally constitute the positive electrodes and the wire or rods the negative electrodes. The size of the pipes may vary but in general pipes of less than six inches in diameter are not used. Electrical precipitators withtubes six inches in diameter using secondary voltages from 35,000 to 50,- 000 volts are satisfactory for the purposes of this invention. It is generally best to operate with maximum potential difference (secondary current) between electrodes, this maximum being just below the break-down voltage at which arcing occurs.

The efficiency of the cleaning is dependent upon several variables. Satisfactory Cleaning of the gas maybe accomplished if the time of treatment is of the order of one second although this time maybe varied widely depending upon the character of the tar to be recovered from the gases passing through the precipitator. In working with tubes nine feet long, for example, substantially all of the tar has been separated with a time of treatment of from one and one-half to two seconds, that is, with a. gas velocity of from six to 4.5 feet per second. This gives an efiiciency of cleaning of approximately ninety-nine per cent. Somewhat less efi'ective cleaning can be accomplished with a time of treatment of from 0.5 to one second, that is, with a velocity of from eighteen to nine feet per second.

From the electrical precipitator the gases carrying condensable vapors can be conducted through suitable condensing appara tus including coolers, scrubbers, fractional condensers, fractionating columns, etc., designed to reduce the temperature of the gases and to cause the separation of oils therefrom. One total oil fraction may be collection if the gases are cooled in the one step to the lowest desired temperature. Several oil fractions can be recovered if the signed for separate collection of oils corresponding to the individual cooling steps.

Electrical precipitators of the type employed for the initial cleaning of the gases may be used to separate the condensed vapors. By passing the gases through such precipitators at predetermined temperatures the condensed constituents may be separated effectively and sharp cuts of oil can be obtained. The gases, after the successive condensations accompanied by separation of the oil constituents, can be conducted through the usual equipment provided forthe purpose of cooling the gases and recovering other valuable constituents such as ammonia and light oil therefrom-.

In subjecting the gases to electrical precipitation in the manner described a considerable quantity of tar is recovered from the bottom of the precipitator and in accordance with the present invention this tar is subjected, together with tar which separates in the collector main, to distillation by contact with the hot coke-oven gases in the uptake stills. The collected tar can be delivered to the stills by pumps under suitable pressure in regulated amounts calculated to effect the desired amount of distillation and to produce pitches having desiredcharacteristics. The pitches produced can be withdrawn and utilized as such-or recirculated for further distillation, or the pitches may be subsequently distilled in other apparatus.

The gases from the uptake stills carrying the vapors produced by distillation of the tar also carry a certain amount of solid particles of coke, coal, etc., derived from the coke ovens, together with globules of tar and tar fog. The direct condensation of the volatile constituents in these gases would result in the production of oils contaminated with tar and other impurities.- The gases are, therefore, delivered from the uptake still or stills to an electrical precipitator of the kind previously described, a short collector main being interposed between the stills and the precipitator if a number of the stills are operated. In passing through the electrical precipitator the gases are cleaned thoroughly, the tarry constituents being separated together with any solid particles while the gases enriched in the vapors produced by distillation are carried over into the condensing system which may be a total condenser or a fractional condenser such as has been previously described. The tar separated from the gases in the precipitator may be mixed with the tar from other parts of the recovery system and returned to the uptake stills for further 'distillation therein.

As in the case of gases from the remaining ovens of the battery, it is important to gases are cooled by stages in coolers de-' regulate the temperature at which the gases are delivered from the uptake stills to the electrical precipitator in order to avoid the condensation and separation of any considerable proportion of oils with the tar.

The regulation may be accomplished by varying the rate of the tar supply to the uptake stills and by subjecting the gascs in the short collector main to regulated cooling with ammonia liquor or ammonia liquor and tar supplied thereto through spray nozzles from a suitable source.

The present invention includes not only the distillation of tar for the production of distillate oils therefrom but also the production of pitches of varying properties and characteristics. By limiting the time of contact of the tar with the hot gases and the temperature to which the tar or pitch is raised during distillation pitches of low free carbon content and oils having defiriite characteristics can be roduced readily. When the pitch'first prod iiced is recirculated a further heating thereof will result in the separation of additional quantities of oil con,- stituents therefrom and the production of a harder pitch. Thus, by suitable regulation of the operation it is possible to recover the valuable constituents of the tar and at the same time to separate pitches having characteristics required for commercial purposes.

Itis also possible to utilize the invention for the distillation of oils, particularly dirty oils containing more or less tarry material, as a contamination or lighter oils contaminated with heavy oils. Such oils .can be introduced to the uptake stills either alone or mingled with tar or pitch which is supi ner described, can be condensed to plied thereto for the purpose of distillation and the distillate, when treated in the manproduce clean oil fractions.

The present invention is of more or less general application to the distillation of tar and oils and the recovery of clean oils therefrom. The invention involves utilization of the hot gases from coal-carbonization plants for the distillation of tar or oil by bringing the tar or oil into direct contact therewith and the condensation of the resulting vapors after separation of the tar and other impurities from the gases at relatively high temperature in an electrical precipitator.

The invention will be further illustrated bythe following more detailed description in connection with theaccompanying drawings which show apparatusembodylng the invention and adapted forthe practice thereof. It is intended and will beunderstood that the invention is not limited to the specific details of the apparatus as illustrated in thedrawings, in which Fig.1 is a plan view of a portion of a coke oven plant illustrating the application of the invention thereto; 1

Fig. 2 is an enlarged sectional view of the uptake still;

Fig. 3 is an enlarged sectional view of the electrical precipitator; and

Fig. 4 is a section of the structure illus trated in Fig. 3.

Referring to Fig. 1 of the drawings,-5 indicates a battery of coke ovens in which the individual ovens are connected by uptake pipes and goose-necks 6 to a collector main 7 having a centre box 8. The collector main is connected by a pipe 9'to the electrical precipitator 10 disposed closely adjacent thereto.

The electrical precipitator may be of any suitable form or construction. Preferably it consists of a shell 11 enclosing a number of tubes 12 supported in heads 13 and 14 within the shell. An inlet 15 near the bottom of the shell communicates with a chamber 16 which is partially separated from the tube section by a baflie 17. An outlet 18 per-.

mits the escape of gases from the separator after the latter have passed through the tubes.

p -A plurality of electrodes 19, preferabl in the form of metal rods, extend throu'g the tubes and are supported on bus-bars 21 near the upper ends of the tubes. The busbar 21 at the top of the separator extends at both ends into casings 22 which enclose insulators 23 upon which the bus-bar is supported. The high tension current lines extend into one of the casings 22 and connect with the bus-bar, thus supplying the necessary current from any suitable source of uni-directional current under high tension.

The casing of the separator is grounded or otherwise connected to the source of current to complete the circuit. The casings and tubes form the positive electrode, the electrodes connected to the bus-bar being negavided form, enter the electrical precipitator from the collector main and pass through the tubes in the precipitator, belng subjected therein to an electrical discharge which, throu h ionization of the solid and liquid partic es, causes them to separate from the gases and condensable vapors. The separated liquids, together with the solid particles, run down the inner walls of the tubes into the chamber at the bottom of the separator and can be withdrawn through a pipe 24: and delivered to a suitable storage receptacle 25. The gases carrying condensable vapors escape through the outlet 18 and are delivered through a pipe 26 to a condenser 27. This condenser may be of any suitable form and in the present instance I have shown a condenser of the ordinary or wet type which is employed frequently in byproduct recovery systems. The gases and vapors are cooled therein by contact with grid surfaces wet by sprays of ammonia liquor, for example, and the resulting condensate is withdrawn through pipe 28 to a decanter 29 wherein the oil is separated from the ammonia liquor. The gases from the condensers pass to an exhauster 30 which maintains the pressure balance in the system. The gases may be conducted thence through the usual equipment for the further recovery of ammonia liquor, light oils, etc.

The ammonia liquor from the decanter can be returned through a pipe 31 to the spray nozzles 32 in the collector main by means of a pump 33, thus supplying the cooling medium to the gases in the collector main. The amount of ammonia liquor thus returned may be regulated to ensure the requisite reduction of temperature of the gases flowing through the collector main to permit operation of the electrical precipitator with maximum efiiciency for the separation of tar from the coke-oven gases and the recovery of the oil content from such gases. The ammonia liquor and the tar separated in the collector main can be withdrawn from the centre box through a pipe 35 and de livered to a suitable storage receptacle 36.

The tar accumulated from the operation of the precipitator and. in the collector sirability of retainin posed closely adjacent thereto.

main, together with tar from other sources, are distilled in accordancewith the present invention by supplying it to one or more uptake stills connected to selected ovens of the battery. Each uptake still may comprise a casing 37 communicating withthe usual uptake pipe and provided at its top with one or more spray, nozzles 37 which is supplied with tar by a pipe 38 and pump 39 from any suitable source such as the storage rece tacle hereinbefore mentioned. A bafile 40 a ove the end of the uptake pi e prevents the descent of tar into the colic oven. The tar spray is intimately mingled with the hot coke-oven gases directly as the latter are discharged from the oven and is subjected thus to the heat of these gases with the result that the tar is heated and distilled. The residue or pitch falls to the bottom of the still and can be withdrawn therefrom either continuously or intermittently through a pipe 41. It may be recirculated if desired for distillatiton in the same or another uptake still or in a different distilling apparatus.

The gases escapin from the still with the vapors produced by distillation are carried through a goose-neck 42 to a separate collector main 43, it being understood that in ordinary practice two or more uptake stills will be provided so that the separate collector main permits the bringing together of the gases and the vapors produced by distillation in the several stills. In the separate collector main the gases may be partially cooled by the application of sprays of ammonia liquor or ammonia liquor and tar, the amount of cooling being regulated in view of the conditions hereinbefore specified with reference to the dethe oil constituents in the vapor phase. rom the separate collector main the gases and vapors are conducted to an electrical precipitator 44 dis- The structure of the electrical precipitator may be substantially identical with that previously. described. It will ordinarily be somewhat smaller in dimensions, particularly if there are only a few uptake stills. In the electrical precipitator the solid and liquid particles are separated from the gases leavin clean gases which upon condensation yiel clean oils. The separated tar can be withdrawn through an outlet pipe 45 and delivered to a suitable storage receptacle 46 from which it can be withdrawn for further distillation.

The clean gases escaping through the outlet pipe 46' are delivered to a suitable condensing apparatus, for example, condensers 47 of the usual type in which the gases are subjected to contact with ammonia liquor for the purpose of reducing the temperature thereof. The condensate, comprising oil and ammonia liquor, can be withdrawn from the condensers through pipes 48 and delivered to decanter 49 wherein the oils are separated from the ammonia liquor. The oils thus recovered are clean oils which can be utilized directly for commercial purposes. The ammonia liquor may' be utilized for further cooling or treated for the recovery of ammonia therefrom. The gases from the condensers may be delivered through a pipe 49 to the exhauster 30 and thence carried with the remaining gases from the system through the apparatus for the recovery of ammonia and light oils- .directly therefrom. The invention permits, therefore, the direct recovery of clean oils from all of the gases and the distillation of the tar produced by the battery or' tar from other sources to recover additionah quantities 'of clean oils therefrom and to produce pitches by utilizing the heat of the coke-oven gases. These and other advantages of the invention can be attained by the practice of the method and by the use of the apparatus as described. It is to be understood, however, that the description is illustrative and that various changes may be made in the form and arrangement. of the apparatus and in the operation thereof without departing from the invention 0 sacrificing any of its advantages.

I claim 1. The method of treating coke oven gases, which comprises subjecting hot fresh coke oven gases from a portion of the ovens of a coke oven battery to electrical precipitation at a high temperature to separate solid and liquid particles therefrom while retaining oils in the gases in vapor form, distilling the separated material by direct contact with hot distillation gases from other ovens of the battery, and cleaning the resulting enriched gases in an electrical precipitator at a high temperature while retaining oils in the gases in vapor form.

2. The method of producing clean oils at a coke oven battery, which comprises subjecting hot fresh coke oven gases from a portion of the ovens to electrical precipitation at a high temperature to separate solid and liquid particles" therefrom while retain ing oils in the gases in vapor form, distilling the separated material by direct contact with hot distillation gases from other ovens of the battery, cleaning the resulting 7 in the gases in vapor form, and cooling the means and means for condensing the vapors cleaned gases from both precipitation operain the gases leaving the electrical pre tions so as to condense clean oils. cipitators.

3. The method of treating the coal dis- In testimony whereof Iaflix my signature. tillation gases from a coke oven battery, STUART PARMELEE MILLER. 7;)!

which comprises subjecting hot fresh coke oven gases from a portion of the ovens to electrical precipitation at ahigh temperature to separate solid and liquid particles I 1 19 from the gases while retaining oils in the i 7 gases in vapor form, subjecting the sepa-a v rated material to distillation by direct contact with hot distillation gases from other I 5" ovens of. the battery, subjecting the resultl, r i ing enriched gases to electrical precipita- '0 tion atla high temperature to separate solid and liqhid particles from the gases while retaining oils in the gases in vapor form, and distilling this separated material in hot 20 coal distillatlon gases from the battery. 85

4. The method of treating the coal distillation gases from a coke oven battery, which comprises subjecting hot fresh coke oven gases from a portion of the ovens to a electrical precipitatlon at a high tempera- 90 ture to separate solid and liquid particles from the gases while retaining oils in the gases in vapor form, subjecting the separated material to distillation by direct contact with hot distillation gases from other 95 ovens of the battery, subjecting the resulting enriched gases to electrical precipitation at a high temperature to separate solid and liqui particles from the gases while retaming oils in the gases in vapor form, disa 1 tillin this separated material inhot coal distil ation gases from the batterly simultaneously with the material separated from the first-mentioned ases-which' are not en- 40 riched by the disti ation of tar or pitch therein.

5.- The method of producing clean oils at a coke oven battery, which comprises collecting hot fresh coal distillation gases 45 from one portion of the ovens, cleanin them in an electrical precipitator at a hig temperature to separate solid and liquid particles, subjecting all of theseparated material to distillation inthe distillation gases.

from the other ovens in the battery,'cleaning the resulting enriched gases in an electrical precipitator at a high temperature, and cooling the cleaned gases from each electrical 55 precipitation operation to separate clean oils therefrom. I a 6. In combination with a plurality of ovens at a coke oven plant, a collector main connected thereto, an electrical precipitator 00 adapted to receive the gases from the col- .lector main, a tar still, means for passing coal distillation gases from the ovens thereto, means for conveying precipitates from the precipitator to the tar still, an electrical precipitator connected to the distilling 1 13

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