US1907078A - Production of pitch - Google Patents

Description

y 1933- G. E. MCCLOSKEY 1,907,078

PRODUCTION OF PITCH Filed Oct. 19, 1928 2 Shets-Sheet l INVENTOR ATTORNEYS y 1933- G. E. MCCLOSKEY 1,907,078

PRODUCTION OF PITCH Filed Oct. 19, 1928 2 Sheets-Sheet 2 INVENTOR ATTORNEY5 Patented May 2, '1933 UNITED STATES PATENT OFFICE PENNSYLVANIA, ASSIGNOB TO THE CORPORATION OF N EW JERSEY PRODUCTION OF PITCH Application filed October 1a, 1928. serial no. 313,423

This invention relates to the construction and operation of coal distillation lants adapted for the production of dehy rated tars and pitches, and includes an electrical precipitator of new design. The invention will be described more particularly as applied to a by-product coke oven battery.

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 foul gases which leave the ovens at high temperature, e. g. 600 to 700 C. or higher, are cooled ordinarily 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 rapid cooling causes the separatiorr of heavy tar 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 uantit of tar carrying both heavier and lig ter oi s is thus separated. Light 'tar or tarry oil is thrown down in the condensing system. The collected tars are ordinarily shipped from the coke-oven plant to a tar distillation plant for distillation and separation of the oils and the production of pitches of varyin qualities. This redistillation of tar to recover pitches and oils therefrom involves considerable additional expense.

According to this invention, coal distillation may be carried on in the ordinary way and the distillation gases may be collected in the ordinary way, but they are passed through an electrical precipitator of new design in which entrained particles are thrown out of the gasses, and the heavy tar or pitch thus produced is so treated in the electrical precipitator that a dehydrated product is obtained directly. On cooling the cleaned gases-which pass through the precipitator clean oils are obtained directly from the ases. The necessity of distilling tar to pro uce such clean oils is thus avoided. By regulating the amount of cooling to which the gases are subjected in the collector main and elsewhere before they are subjected to the electric discharge in the precipitator, the amount and nature of the oils thrown down in the recipitator and the amount and nature of the clean oils obtained inthe condensers located beyond the precipitator can be controlled. The cooling of the gases in the collector main may be ac: complished by the application of sprays of ammonia liquor or ammonia liquor and tar thereto, but indiscriminate cooling as heretofore practiced is preferably avoided and the amount of the cooling,medium supplied to the collector main is regulated so as to reduce the temperature of the gases to a predetermined extent. This may be accomplished readily by varying the amount of the cooling medium supplied with reference to the temperature and volume of the gases treated so as to condense only those constituents of the gaseswhich are to be separated both in the collector main and by electrical precipitation. If the ases pass through the precipitator at a big temperature, the higher boiling constituents of the gases pass through the precipitator in vapor form and a pitch of higher or lower melting point is precipitated. When the gases are passed through the precipitator at lower temperature, lower boiling oils are also thrown down in the precipitator and tar is obtained as the product of the precipitator.

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 in the collector main, as by spraying with ammonia liquor or ammonia liquor and tar, it is possible to effect the collection of the desired pitch constituents in the collector main and in the electrical precipitator, leaving the desired oils in the vapor phase. Thus, by sufliciently lowering the temperature of the gases in the collector main all or any desired part of the heavy oil constituents can be converted into the liquid phase while the remainder of the oil constituents is still in the form of vapor. To accomplish the intended pur ose the temperature of the gases should e maintained above the dew point of the gases for all constituents which are to be retained in the gases and carried over thereby after the separation of the pitch therefrom. Some of the tarry or itch constituents do not separate readily om the gases, but as tar fog tend ordinarily to remain in the gas stream. The electrical recipitator, however, effectively removes t is"tar fog from the gases. By regulating the temperature of the gases so as to condense more or less of the heavy oil with the tarry constituents the consistency and character of the heavy tar or pitch recovered in the precipitator can be varied to produce directly commercial products of the desired character. "Part of the tarr or pitch constituents condensed by the coo ing action of the ammonia liquor or ammonia liquor and tar separate in the collector main and a part goes forward as suspended particles in the gas stream. It is that part which remains" sus ended in the gas stream which is' removed y and recovered" in the electrical precipitator.

The precipitator used may be, for example, the well known Cottrell precipitator and it should be operated at a temperature such as to avoid the condensation of the oils which are to be carried over with the gases. Consequentl the electrical precipitator should be disposed preferabl closely adjacent to the collector main an the gases carrying the pitch constituents should be delivered directly thereto. The electrical precipitator may be insulated advantageously to prevent loss of heat from the gases. This is particularly desirable if the product to be recovered is a relatively high melting point pitch requiring the maintenance of the gases at high temperature to avoid dilution of the pitch with oil constituents.

Although the temperature at which the electrical precipitator is operated is above the dew point of water, some water may nevertheless be carried over in the form of spray from the collector main and the water may be present in the form of liquid particles in the electrical precipitator because the limited time of contact with the gases prevents evaporation of the water. In this case the removal of water in the liquid phase will be efiected by the electrical discharge in the electrical precipitator and the water will be carried down therein with the heavy tar or pitch constituents, thus producing a product containing a proportion of water which is undesirable.

The gases in the electrical precipitator may also contain drops of water produced by local cooling of those gases near the walls of the mains through which the gases pass or the tubes of the precipitator. A Although the average temperature of the gases passing through the precipitator may be above the dew point of the gases for water, drops of water ma form in any portion of the gases which is cooled, e. g. by contact with a cold surface, and such drops may not have sufiicient time to blend with the hotter gases and be vaporized thereby before the uses enter the electrical precipitator. Such rop. lets of water are separated from the gases in the precipitator together with the pitch or heavy tar.

According to this invention, water from any source whatever which is present in the gases in the li uid phase and is separated from the gases 1n the electrical precipitator, is returned to the gases by dehydration of the heavy tar or pitch thrown down in the precipitator. Any gases or hydrocarbon vapors which are evolved during the dehydration of the heavy tar or pitch are added to the gases leaving the precipitator. There is no loss of hydrocarbons from the system during the dehydration.

The heat employed in the dehydration may be supplied. to the pitch or tar in various ways. Advantageously, the dehydration is effected by the provision of heating means such as a steam coil in the bottom of the precipitator through which steam under pressure and at a suitable temperature, for example, approximately 150 C. can be conducted for the purpose of heating the heavy tar or pitch in the precipitator and evaporating the water therefrom.

The amount of steam required for this purpose is relatively limited because only a small amount of water in liquid phase will normally be carried into the precipitator from the collector main. Thus, in a plant having sixty ovens and producing a total of about 10,000 gallons of tar per day by the ordinary methods of operation, the amount of pitch with a melting point of 105 F. obtained directly, may not exceed 5,000 gallons carrying approximately 0.7% of water. The operation of such a plant would require not to exceed 650 pounds of steam per day to dehydrate the pitch. The amount of steam. required would vary, of

course, depending upon the amount of pitch produced and the proportion of water normally contained therein as the pitch is separated in the precipitator.

The heating of the tar or pitch in the precipitator can be effected in other ways as by the introduction of other hot gases such as flue gases or by the use of other heating media. The apparatus employed for heating may be modified to meet the requirements of the particular heating media, but the heating should preferably be effected in the bottom of the precipitator so that the water is removed from the tar or pitch as the latter is recovered and so that the vapors, including water and volatile oil constituents, separated from the product, will be carried through the precipitator and recovered in the condensers.

The operation of an electrical precipitator as commonly used 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 delivered from the converter to the electrical precipitator at practically the potential at which it leaves the transformer.

The electrical precipitator consists commonly of a group of vertical pipes with a wire or rod in the centre of each, the pipes being connected to proper headers for the introduction and discharge of the gases. The pipes generally constitute the positive electrodes and the wires 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 with pipes 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 diiference (secondary current) between the electrodes, this maximum being just below the break-down voltage at which arcing occurs.

The eificiency of the cleaning is depend ent upon several variables. Satisfactory cleaning of the gas may be accomplished if the time of treatment is of the order of one second, although this time may be varied widely depending upon the character of the oil to be recovered from the gases leaving the precipitator. In working with tubes nine feet long and six inches in diameter, for example, an oil substantially free from all tarry constituents has been obtained with a time of treatment of from one and one-half to two seconds, that is to say, with a gas velocity of from 6 to 4.5 feet per second. This has given an efiiciency of cleaning of approximately ninetynine percent. If it is desired to collect oils containing small amounts of tar shorter treatment may be used, for example, a treatment of from 0.5 to one second, that is to say, with a velocity of from 18 to 9- feet per second.

From the electrical precipitator the gases carrying the condensable oil vapors can be conducted through suitable condensing apparatus including coolers, scrubbers, fractional condensers, fractionating columns, etc. designed to reduce the temperature of the gases and to cause the se aration of oils therefrom. One total oil action can Electrical precipitators of the type employed for the separation of the tar or pitch from the gases may be employed to separate the condensed oil vapors by passing the gases through such preci itators at predetermined temperatures. llhe condensed constituents can be separated eifectively and sharp cuts of oil can be obtained. The gases after successive condensations accompanied by separation of the oil constituents can be conducted through the usual equipment provided for the purpose of cooling the gases and of recovering other valuable constituents such as ammonia and light oils thereom. It will be understood that in the practice of the present invention the cooling of the gases in the collector main will be regulated by supplying more or less ammonia liquor or other cooling agent thereto for the purpose of determining the character of the tar or pitch which may be separated in the electrical precipitator and that by such regulation the amount of tar and oil constituents which are condensed in the collector main and separated in the electrical precipitator may be regulated to produce tar or pitch having different melting points and other characteristics. Where very close regulation is desired it may be of advantage to insulate the collector main and the cross-over main up to the electrical precipitator.

The tars and pitches recovered may be employed for the purposes for which similar products produced by the ordinary methods are used, the melting point of the particular product being adjusted by the regulation of the cooling in the collector main as hereinbefore described. The free carbon content of the products will in general be lower than that of corresponding products produced in the ordinary way. The invention may be applied to existing coke-oven plants without any considerable modification thereof except for the addition of the electrical precipitator and the provision of fractional condensing apparatus if fractional condensation rather than total condensation as ordinarily practiced is desired. Fractional condensation is particularfy desirable in the treatment of gases containing clean Vapors because the fractions recovered can be utilized for commercial purposes without further distillation or other treatment.

The present invention is applicable to the treatment of coal distillation gases at all temperatures at which water is carried into above the dewpoint of the gases for water.

5 to the accompanying drawin with reference s which show apparatus embodying the invention and a apted for the practice thereof, but it is intended and will be understood that the invention is not limited to the specific de- It will be further described .10 tails of the apparatus as illustrated in the drawings, in which Fig. 1 is a plan view of a portion of a coke-oven battery illustrating tion of the invention thereto;

Fig. through the collector main and electrical precipitator; and

Fig. '3 is a section through the precipitator.

Referring to the drawings, 5 indicates the battery of ovens which are connected through uptake pipes and goose-necks 6 to a collector main 7. Spray nozzles 8 and 9 are provided in the goose-necks and collector main and are connected by pipes 10 to a pump 11 which delivers the cooling medium, for example, ammonia liquor, to the oose-necks and collector main from a suita ble source thereof such as a tank 12. The amount of the cooling medium thus supplied is regulated as hereinbefore described to accomplish the desired reduction in temperature of the gases in the collector main, it being understood that the temperature should be maintained above the dew points of constituents of the gases which are to pass through the electrical precipitator in the vapor phase.

From the collector main the gases carrying oil vapors and the condensed tarry or pitchy constituents are delivered through a pipe 13 to the electrical precipitator. The latter comprises a casing 14 enclosing a number of tubes 15 which are supported in heads 16 and 17 within the casing. An inlet 18 near the bottom of the casing conimunicates with a chamber 19 which is partially separated from the tube section by a battle 20. An outlet 21 permits the escape of the gases from the separator after the latter have, passed through the tubes.

A plurality of electrodes 22 preferably in the form of metal rods extend through the tubes and are supported from a bus-bar 23 located near the upper ends of the tubes. The bus-bar 23 extends at both ends into casings 24 which enclose insulators 25 upon which the bus-bar is supported. The high tension current lines extend into one of the casings 24 and connect with the bus-bar 23, 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 applica- 2 is an enlarged vertical section the circuit. The casing and tubes form the positive electrode, the electrodes connected to the bus-bar being negative. The form and arrangement of the conductors in the circuit can be varied. The arrangement should be such as to supply high tension uni-directional current to the electrodes, thereb permitting a substantially continuous silent discharge between the electrodes and the tubes through which the gases pass.

The gases carrying tar in the form of globules or tar fog together with solid materials such as carbon, etc. in finely divided form, enter the electrical precipitator from the collector main and pass through tubes in the precipitator, being subjected therein to the electrical discharge which through 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 19 at the bottom of the separator. A steam coil 26 is shown disposed in the chamber 19, supplied with steam through a pipe ,27. The condensed steam may be withdrawn through a pipe 28, steam trap 29 and drip 30. The tar or pitch thrown out of the gases is thus heated to the temperature requisite to remove water therefrom and the water vapor together with other vaporizable constituents of the tar or pitch joins the gas stream and passes through the tubes of the precipitator. The product can be withdrawn through a sealed outlet 31 which maintains a suitable head in the chamber 19 surrounding the steam coil 26. r

The gases carrying the condensable vapors escape through the outlet 21 and are delivered by a pipe 32 to a condenser 33. The condenser may be of any suitable form and in the present instance I have shown a condenser of the ordinary direct 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 condensates are withdrawn through a pipe 34 to a decanter 35 wherein the oils are separated from the ammonia liquor. The gases leaving the condenser through pipe 36 are delivered toan exhauster 37 which maintains the pressure balance in the system. The gases may be conducted thence through the usual equipment for the recovery of ammonia, light oils, etc.- therefrom. The ammonia liquor which separates in the condenser can be'recirculated to effect the desired cooling therein and in the collector main and a part thereof can be treated in the usual manner for the recovery of ammonia.

The present invention permits the direct recovery of heavy tar or pitch free from water and of clean oil products from cokeoven and other coal distillation gases and thus avoids the necessity for dehydration and distillation of tar to produce these products. The desired products are recovered at a lower cost and in a condition more suitable for commercial utilization. These and other advantages of the invention may be attained by the practice of the principles as hereinbefore set forth, it being understood that various changes may be made in the details of the operation and in the apparatus as described without departing from the invention or sacrificing the advantages thereof.

I claim The method of producing dry tar or pitch which comprises cooling hot coal gasification gases resulting from the gasification of coal to form therein a suspenslon comprising suspended particles of water and of tarry constituents, subjecting the gases to electrical precipitation to remove the suspended particles from the gases, heating the precipitated material to a temperature of at least 150 C. so as to evaporate the water therefrom, and returning to the gas stream the water vapor evolved during the heating. 4 In testimony whereof I afiix my signature. GREGORY EDWARD McGLOSKEY.

Images