US2934488A

US2934488A - Automatic process for treating coke oven tar

Info

Publication number: US2934488A
Application number: US699998A
Authority: US
Inventors: Harvey S Auvil; Lawrence D Schmidt
Original assignee: Allied Chemical Corp
Current assignee: Honeywell International Inc
Priority date: 1957-12-02
Filing date: 1957-12-02
Publication date: 1960-04-26
Anticipated expiration: 1977-04-26

Description

April 26, 1960 H. s. AUvn. ET AL AUTOMATIC PRocEss Foa TREATING com: ovEN TAR Filed Deo. 2. y195? Unite rates AUTOMATIC PRCESS FOR TREATING COKE v@VEN TAR Harvey S. Anvil, Ashland, Ky., and Lawrence D. Schmidt,

New York, NX., assignors to Allied Chemical Corporation, a corporation of New York Application December 2, 1957, Serial No. 699,998

6 Claims. (Cl. 20S- 45) The p-resent invention relates to an automatic, continuous process for substantially removing from coke vinvariably result in corrosion of the distillation equipment and plugging, due to ammonium chloride deposits, of the condensers associated with the distillation equipment. These difficulties are mostly attributable to the small amount of ammonium chloride invariably present in the `coke oven tar. Various proposals have been advanced for eliminating the small amount, usually of the order'of 0.2% by weight, of ammonium chloride present in coke oven tar to minimize corrosion of the distillation equipment and plugging up of the condensers when the tar is distilled, Of these proposals, one has involved the wash ing of the tar with water frequently by pumping the tar into the top of a storage tank containing a layer of water under atmospheric pressure and temperature, the -tar descending through the water layer and forming a tar layer underlying the water layer. After introduction of the desired batch of tar into the water layer, the tar and water containing the dissolved salt are separately removed from the tank. This procedure is objectionable for numerous reasons, among which may be mentioned (l) it is relatively costly to carry out since it involves vthe use of one or more large storage tanks for the water layer through which the tar is passed and, hence, is capable of handling only a limited amount of tar per unit of time; in order to handle the large volume of tar subjected to distillation in a tar distillation plant, a number 'of such tar washing units are required involving substantial plant investment, and (2) the procedure frequently results in a tar having a high water content, in excess of the water content of the tar originally processed, which tar, prior to distillation, requires al dehydration treatment materially increasing the cost of treating the tar.

In accordance with Tiddy U.S. Patent 2,440,311, substantially all of the small amount of ammonium chloride present in coke oven tars is removed by continuously mixing coke oven tar with hot water or water and steam, owing this mixture at a temperature within the range of :about 200 to about 350 F. and under superatmospheric pressure through a settling and decanting tank wherein 'the ammonium chloride solution produced separates from lthe tar, forming a supernatant ammonium chloride solution resting on a tar layer, removing the coke oven tar `substantially free of ammonium chloride from this tank land separately removing the ammonium chloride solution from the tank.

The use of a pressurized settling and decanting tank, was,

ice

in Tiddy, results in formation of an aqueous emulsion as an interphase between the layers of tar and ammonium chloride solution. This interphase which contains diculty decantable tar usually constitutes about 10 to 50% by weight of total tank contents. In the process of Tiddy, liquid level control devices are employed for determining the position of the tar-ammonium chloride solution interphase and regulating the rate of ilow of each phase from the settling and decanting tank. Such devices are not automatic and require constant supervision to avoid buildup or depletion of tar in the tank. Furthermore, process difficulties are occasioned by fouling of the devices with clots of tar normally present in the tar charge.

. The object of the present invention is to provide an automatic, continuous process of exceptional inherent controllability or stability for decantation of aqueous liquor from coke oven tar. Other objects and advantages of the invention will appear from the following detailed description thereof. i Y

In accordance with this invention, substantially all of the water-soluble salts present in the coke oven tar are removed by continuously charging streams of the coke `oven tar and aqueous solution, at approximately constant rates, into a mixing zone, continuously owing said mixture of tar and aqueous solution at temperature above C. and under superatmospheric pressure through `a pressurized settling and decanting zone wherein aqueous liquor containing water-soluble salts separates as an upper layer and tar as a lower layer, alternately and cyclically withdrawing, at substantially equal rates, material only from the top and only from the bottom, respectively, of the pressurized settling and decanting zone for predetermined portions of the cycle, so that for each cycle (1) the total withdrawal is equal to the total charge during the cycle, (2) the withdrawal from the bottom is less than the anhydrous tar content of the total charge during Vthe cycle, and (3) the withdrawal from the top is correspondingly greater than the remainder of the total charge during the cycle, whereby the material withdrawn from the .top comprises aqueous liquor containing water-soluble salts and diiicultly decantable tar, and the material withdrawn from the bottom comprises product tar relatively free of water-soluble salts and aqueous liquor.

`For the sake of eliiciency, it is generally preferred that the withdrawal from the bottom for each cycle be about 5 to 20% less than the anhydrous tar content of the total charge during the cycle. However, in treating charge which tends to form greater amounts of diicultly decantable tar, the bottom withdrawal for each cycle may be up to about 35% less than the anhydrous tar content or the total charge.

During each cycle, the proportionate time for top and bottom withdrawal from the pressurized settling and decanting zone, which is controlled by aconventional timer, will vary, depending on the relative quantities of coke oven tar and aqueous solution fed to the system. It will also vary with dierences in anhydrous tar content of total charge, as well as differences in the decanting characteristics of the tar. Ordinarily, with substantially equal withdrawal rates, the time for top withdrawal will be greater than Vthe time for bottom withdrawal per unit volume of aqueous solution charge and tar charge, respectively. For instance, when approximately equal volumes of coke oven tar charge (containing from about `5 to 20% of water) and aqueous solutioncharge are Y quality.

.A preferred aspect of this invention involves recirculatsolution are introduced thereinto.

Afrom the bottom of the atmospheric pressure settling and decanting zone, and continuously recycling all of said difcultly decantable tar, to the initial mixing zone. If desired or required, part or all of the aqueous liquor may Valso be recycled to the mixing zone.

Operation in accordance with the process of this invention -permits automatic, continuous separation of aqueous liquor from tar, requiring minimum supervision in an inherently stable system unaffected by the variations normally occurring zin the feed rates of coke oven tar and aqueous solution, as well as by variations in tar quality or moisture content.

The amount of aqueous solution mixed with the coke voven tar will ydepend on the capacity of the equipment in which the process is carried out, the water-soluble salt content of the tar, and the temperature and pressure conditions under which the settling and decanting are effected. In general, from one to three volumes of tar are mixed with each volume of aqueous solution. Preferably about -equal volumes of tar and aqueous solution are employed.

The mixture of aqueous solution and coke oven tar is maintained within the settling and decanting zone at a temperature above 90 C. and under superatmospheric pressure. Preferably the temperature utilized is within Vthe range of about 145 to 180 C., while preferable superatmospheric pressures are within the range of about '150 to 175 pounds per square inch gauge.

The rates of ilow of the tar and aqueous solution to the VVpressurized settling and decanting zone are not critical lfactors and will depend upon the specific equipment in which the process is carried out and are so chosen as to subject the tar and aqueous solution to a time of treatment in the settling and decanting zone hereinafter disclosed. However, it is essential for maintenance of an automatic, stable system that during a cyclic period the total withdrawal rate of tar and aqueous liquor from the pressurized settling and decanting zone be equal to the total chargin-g rate of tar and aqueous solution streams.

lMoreover, material must be alternately withdrawn, at

substantially equal rates, only from the top and only from the bottom, respectively, of the pressurized settling and decanting zone for predetermined portions of the cycle, so that the withdrawal from the bottom is less, preferably about 5 to 20% less, than the anhydrous tar content of the total charge during the cycle, and the withdrawal from the top is correspondingly greater than the remainder of the total charge during the cycle. As a result of this particular withdrawal system, the material withdrawn from the top of the pressurized settling and decanting zone comprises aqueous liquor containing watersoluble salts and difcultly decantable (emulsied) tar, and the material withdrawn from the bottom comprises product tar relatively freev of water-soluble salts and aqueous liquor.

The time of treatment of the tar in the pressurized settling and decanting zone will depend upon the extent of this zone and the rate at which the tar and aqueous These factors should be so correlated that the time of treatment falls within the range of about 0.25 to 1.1 hours; i.e., a time interval falling within the range of about 0.25 to 1.1 hours elapses between the time a particle of the mixture of tar and aqueous solution enters this zone and the time the `tar portion of this particle mixture is withdrawn therefrom.

p Preferably these factors are so correlated that the tar `and 4 aqueous solution require about 0.5 hour to pass through this zone.

According to a specific aspect of the present invention, the aqueous liquor containing water-soluble salts and diilcultly decantable tar withdrawn from the top of the pressurized settling and decanting zone is cooled, before being introduced into the atmospheric settling and decanting zone, to a temperature of about 80 to 98 C., preferably about 90 to 95 C.

The time of treatment of the aqueous liquor containing water-soluble salts and difcultly decantable tar inthe atmospheric pressure settling and decanting zone will depend on the extent of the zone, the rate -at which the material is introduced thereto and the rate at which the material is withdrawn therefrom, as well as the content of dicultly decantable tar in the material.

Recovery of tar values from difiicultly decantable tar Aremoved from the atmospheric settling and decanting zone `is accomplished by recycling the entire quantity Yof difficultly decantabletar to the mixing zone and again circulating it through the system. It has beenr found that when 5 to 20% of the total tar (anhydrous basis) charged to the decanter is withdrawn from the pressurized settling and decauting zone and later recycled, the quality of the product tar is improved due to a larger fraction of decanter volume being devoted to the dilcultly decantable tar. Further, no change in timer setting is necessary to produce specification tar, even though the rate of tar feed or quality of tar feed changes considerably.

If desired orrequired, part or all of the aqueous liquor.

can -be recycled from the atmospheric settling and decanting zone to the mixing zone. However, under some conditions no lliquor need be recycled. Recycle of aqueous liquor permits build-up of the ratio of wash liquor to tar to any desired ratio for efcient washing without serious dilution of the product liquor which would make subsequent recovery of ammonium chloride prohibitively expensive. Recirculation of aqueous liquor and resultant separation of components from it also prevent stream pollution that would result from complete rejection of the liquor during commercial operation.

The invention will be further described in connection with the accompanying drawing which is a ow sheet of the process and shows diagrammatically apparatus suitable for carrying out the process. l

Crude'coke oven tar, produced in coke oven batteries and containing, for example, from about 10 to 50 pounds of ammonium chloride per 1000 gallons of tar and from about 5 to 20% by volume of water, is charged through line 1 to mixing tank 2, provided with a conventional agitator 3. Aqueous solution, comprising (l) recycled aqueous liquor and (2) fresh water, is charged to tank 2 through line 4. Alternatively, the recycled aqueous liquor Y may be charged directly to the tank, alone or combined with recycled tar. In any event, the aqueous solution is charged to the mixing tankat an approximately constant predetermined rate, for example, at' the rate of about l0 gallons per .minute of each charge material or the tar is charged at the approximately constant rate at which it is produced in the coke oven plant, say at 10 gallons per minute.

The mixture of tar and aqueous solution exits mixing tank 2 via line 5 and is pumped by means of a pump 6 which raises-its pressure to that in line 7 through a heater 8 wherein the mixture is heated to a temperature above C., preferably to about 145 to 180 C.

The tar-aqueous liquor mixture is then passed through line 9 into a pressurized settling and decanting tank 10 wherein the mixture is maintained by back pressure valves, -described below, at a constant superatmospheric pressure, preferably within the range of about to 175 pounds per square inch gauge. Further, tank 10 is provided with heating coils throughY which a suitable fluid, e.g., steam, may be circulated to maintain the contents .of the tank at. the desired temperature of above y90" C.,

preferably about 145. to 180I C. VAbout 0.25 to 1.1 hours are required'for -the mixture of'tar4 and aqueous solution to pass through tank 10, during which time aqueous liquor containing water-soluble salts, chieiiy, ammonium chloride, separates as an upper layer, while tar separates as a lower layer. In addition, an aqueous interphase containing diflicultly deoantable `tar in the form of an emulsion is formed. ThisinterphasecomprisesV about 25 to 55% of total tank contents. i

The exit ow of the aqueous liquor from the top and tar from the bottom of` the tank is regulatedby a con- `ventionaltimer 11 operating on a cycle which controls the lrelative amount of top and bottom exit ilows byalternately opening and closing

outlet solenoid valves

12 and 13, according to a preset schedule. For example, timer 11 may comprise an electrical timing device which is arranged to alternately open valve 12, connected to the timing device by means of a lead 14, Yand allow aqueous liquor to be withdrawn from the top, valve 13'meanwhile being closed, and then to openvalve 13, connected to the timingV device byl means of a lead 15, to allow tar to be withdrawnfrom the bottom of the tank, valve 12 meanwhile being closed.V Alternate and cyclic withdrawal, at approximately equal rates, of aqueous liquor from the top and tar from the bottomis accomplished for predetermined portions ofthe cycle, so that for leach cycle (l) the total withdrawal is equal to `thetotal charge during the cycle, (2) the withdrawal from thebottom is less, preferably.about 5 to 20% less, than the anhydrous tar content ofv the total charge during the cycle, and (3) vthe withdrawal from the top is correspondingly greater than the remainder of the total charge during the cycle. As-a result of such withdrawal procedure, the material withdrawn from the top of tank 10 comprises aqueous liquor containing water-soluble salts and diiicultly decantable tarrand the material withdrawn from the bottom of the tank comprisesl high quality product tar relatively free of water-soluble salts and aqueous liquor. In other Words, the cyclic control, as described, enables control of the amount of tar present in the top exit ow to maintain optimum quality of bottom tar.

The aqueous liquor containing water-soluble salts and diilicultly decantable tar passes from Vthe `top of lpressurized settling and decanting tank via line 16 through a cooler'` 17 wherein the temperature of the liquor is reduced to about 80 to 98 C. From the cooler 17, the aqueous liquor passes through line 18 toa back pressure regulating valve 19 which maintains the liquor at the desired superatmospheric pressure. Then, the aqueous liquor is passed via line 21 through an atmospheric pressure settlingand decanting. tank 22 in a period of about 8 to 24 hours. In tank 22, an upper aqueous liquor layer containing water-soluble salts separates from a lower layer comprising diliicultly decantable tar. The aqueous liquor is withdrawn from ythe top of tank 22 via line 23, and a portion, to 80%, preferably about 50 to 80% by volume, of the liquor 'is recycled Via line 24 and combined inline 4 with aqueous solution entering mixing tank 2. The remainder of the aqueous liquor is rejected from the -system through line 25. The lower layer in tank22, comprising diiicultly decantable ta-r, exits the tank'via line 26 and fis recycled in toto directly to mixing tank 2 or is passed lthrough line 27 toline 1 where it is combined with feed tar entering mixing tank 2.

The product tar withdrawn from pressurized settling and decanting tank 10 is passed via line 23 through a back pressure regulating valve 29 to maintain the tar at the desired supe-ratmospheric pressure, and is then passed to storage for further processing.

The following example illustrates one manner of carrying out the process of the present invention.

4 Crude coke oven tar produced in coke oven batteries and containing about 30 pounds of ammonium chloride per 1000 gallons of tar and about 10% by volume of water is charged to mixing tank 2 at the rate of about 10 perature of about C. The tar-aqueous liquor mixture is then passed through pressurized settling and decanting tank 10 in about 0.6 hour. In tank 10, the mixture is maintained at a pressure of about pounds per square inch gauge and at the aforesaid temperature of about 165 C. Aqueous -liquor containingammonium chloride separates as an upper layer while tar separates as a lower layer in tank 10. By means of timer 11, operating on a short cycle, material is alternately withdrawn from the top and from the bottom of the tank. For each 5-minute period, material is withdrawn from the top of the tank for 3 minutes at the rate of 23.2 gallons per minute, while material is withdrawn from the bottom of the tank for 2 minutes at the same rate. Thus, during each S-minute period, a total of 116 gallons of material is withdrawn, 69.6 gallons being withdrawn from the top and 46.4 gallons from the bottom. As a result of lthe time-controlled, alternate withdrawal of materials from the top and bottom of the tank, the material withdrawn from the top of the tank comprises aqueous liquor containing ammonium chloride and diliicultly decantable tar, and the material withdrawn from the bottom of the tankV comprises high quality specication product tar relatively free of ammonium chloride and aqueous liquor, i.e., containing 0.025% by weight of ammonium chloride and about 3% by weight of aqueous liquor.

The aqueous liquor containing ammonium chloride and ditlicultly decantable tar is cooled in cooler 17 to a temperature of about 95 C. The cooled aqueous liquor is then passed through atmospheric pressure settling and decanting tank 22 in about 12 hours. In tank 22, an upper aqueous liquor layer containing ammonium chloride separates from a lower layer comprising dicultly decantable tar. The aqueous liquor is withdrawn from the top of tank 22 at about 10.7 gallons per minute. About 6.7 gallons per minute of the aqueous liquor is recycled to mixing tank 2. The remainder of the aqueous liquor is rejected from the system. The lower layer in tank 22 comprising diliicultly decantable .tar is recycled to mixing tank 2 at the rate of about 3.2 gallons per minute.

The example given above, illustrating one manner in which the invention can be carried out, is outlined as Case I in the following table. In this case the ammonium chloride content of the product tar was 0.025%, which is substantially below the accepted specification limit of 0.04%. Cases II and VI show the `effect of accidental [Conditions: Timer is set to give top flow for 60% of the time and bottom flow for 40% of the time. Constant fresh-water feed of 3.3 gallons per minute is used. Recycle tar contains about 50% wateix] Feed tar rate-gallons per minute 10. 0 10. 0 10. 0 10. 0 7. 7 12. 3 Water in feed tar-percent by volume 10. 0 25. 0 0. 0 10. O 10. 0 10. 0 Tar ln lfeed (anhydrous basis) gallons per minute 9.0 7. 5 10.0 9. 0 6. 9 11. 1 Recycle liquor-gallons Y per minute 6. 7 6. 7 6. 7 0.0 6. 7 6. 7 Recycle tar (anhydrous basisl-gallons per minute 1.6 0. 0 2.8 1. 6 0. 0 2. 7 Product Tar: Ammonium f chloride content-per Y setting the timer.

assiale@ variations inrate of tar feed and in liquor content of tar feed,'al1 other factors being thesame as in Case I. Case II shows that when the waterycontent of the feed tar accidentally increased from l to 25%, specitication product tar was still produced without any necessity for re- Case III shows that when the water content of the feed tar accidentally decreased tozero, specification tar was still produced. Case lV shows that when no aqueous liquor was recycled to the mixing tank, no substantial change in product tar occurred. Case V shows that when the rate of tar feed accidentally decreased 23%, no change in timer setting was required to maintain production of specification tar. Case Vl shows that when there was an accidental increase of 23% in tar feed rate, no change in timer Setting was required. However, in Case VI, the maximum specification chloride content of 0.04% was approached, and any larger increase in tar feed would require adjustment in timer setting. l

From the foregoing description of detailed embodiments of our invention, many advantages thereof will be apparent to those skilled in the art. The principal advantage is that high quality tar may be obtained by a continuous process which is amenable to stable automatic control. Another advantage is that'a minimum maintenance is required. Many other advantages will be apparent to those skilled in the art.

It is to be understood that this invention is not restricted to the present disclosure as variations may be made Without departing from the scope of the invention;

We claim:

l. An automatic, continuous process for treating coke oven tar containing water-soluble salts which comprises continuously charging streams of coke oven tar and aqueous solution, at approximately constant rates, into a mixing zone, continuously yliowing said mixture of tar and aqueous solution at temperature above 90 C. and under superatmospheric pressure through a pressurized settling and decanting zone wherein aqueous liquor containing water-soluble salts separates as an upper layer and tar as a lower layer, responsive to a time cycle control alternately withdrawing, at substantially equal rates, material only from the top and only from the bottom, respectively, of the pressurized settling and decanting zone for predetermined portions of the time cycle, so that for each cycle (l) the total Withdrawal is equal to the total charge during the cycle, (2) the Withdrawal from the bottom is at least about less than the anhydrous tar content of the total charge during the cycle, and (3) the Withdrawal from the top is correspondingly greater than the remainder of the total charge during the cycle, whereby the material withdrawn from the top comprises aqueous liquor containing water-soluble salts and dillicultly. decantable tar and the material withdrawn from the bottom comprises product tar relatively free of water-soluble salts and aqueous liquor. l

2. An automatic, continuous `process for treating coke oven tar containing water-soluble salts which comprises continuously charging streams of coke oven tar and' aqueous solution, at approximately constant rates, into a mixing zone, continuously flowing said mixture of tar and aqueous'solution at temperature above 90 C. and under superatmospheric pressure through a pressurized settling and decanting zone wherein aqueous liquor containing water-soluble salts separates as an upper layer and tar asa lower layer, responsive to a time cycle control alternately withdrawing, at substantially equal rates, material only from the top and only from the bottom, respectively, of the pressurized settling and decanting zone for predetermined portions of the time cycle, so that for each cycle (l) the total withdrawal is equal to the total charge during the cycle, (2) the withdrawal fromv the bottom is about 5 to 201% less than the anhydrous tar content of the total charge during the cycle, and (3) the withdrawal from the top is correspondingly greater l 8 t 4 than' the remainder of the total charge during the cycle, whereby the material withdrawn from thetop comprises aqueous liquor containingWater-soluble salts andv diticultly decantable tar'and the material withdrawn from the bottom comprises product tar-relatively free of watersolublesalts and aqueous liquor.

Y 3. An automatic, continuous process for `treating coke oven tar containing vwater-soluble salts which comprises continuously charging streams of coke oven tar and aqueousv solution, at approximately constant rates, into a mixing zone, continuously flowing said mixture of tar andV aqueous solution at temperature above C. and under superatmospheric pressure through a pressurized settling and decanting zone wherein aqueous liquor containing Water-soluble salts separates as an upper layer and tar as a lower layer, responsive to a time cycle control alternately withdrawing, at substantially equal rates, material only from the top and only from the bottom, respectively, of the pressurized settling and decanting zone for predetermined portions of the time cycle, so that for each cycle (l) the total withdrawal is equal to the total charge during the cycle, (2) the withdrawal from the bottom is at least about 5% `less than the anhydrous tar content of the total charge during the cycle, and (3) the withdrawal from the top is correspondingly greater thanV the remainder of the total charge during the cycle, whereby the material withdrawn from the top comprises aqueous liquor containing water-soluble salts and difficultly decantable tar and the material withdrawn from the bottom comprises product tar relatively free of watersoluble salts and aqueous liquor, continuously passing said withdrawn aqueous liquor containing water-soluble salts and diicultly decantable tar through a cooling zone, continuously passing said cooled aqueous liquor through an atmospheric pressure settling and decanting zone in which aqueous liquor containing water-soluble salts separates as an upper layer and diflicultly decantable tar as a lower layer, continuously withdrawing aqueous liquor from the top and diicultly decantable tar from the bottom of the atmospheric settling and decanting zone, and continuously recycling all ofsaid ditlcultly decantable tar to the aforesaid mixing zone. i

4. An automatic vcontinuous process for treating coke oven tar containing water-soluble salts which vcomprises continuously charging streams of coke oven tar and aque'- ous solution, at approximately constant rates, into a mixing zone, continuously flowing said mixture of tar and aqueous solution at temperature above 90 C. and under superatmospheric pressure through a pressurized settling and decanting zone wherein aqueous liquor containing Water-soluble salts separates as an upper layer and tar as a lower layer, responsive to a time cycle control alternately withdrawing, at substantially equal rates, material only from the top and only from the bottom, respectively, of the pressurized settling and decanting zone for predetermined portions of the Atime cycle, so that for each cycle (l) the total withdrawal is equal to the total charge during the cycle, (2) the withdrawal from the bottom is about 5 to 20% less than the anhydrous tar content of the total charge during the cycle, and (3) the withdrawal from the top is correspondingly greater than the remainder of the total charge during the cycle, whereby the material withdrawn from the top comprises aqueous liquor containing water-soluble salts and difficultly decantable tar and the material withdrawn from the bottom comprises product tar relatively free of watersoluble salts and aqueous liquor, continuously passing said withdrawn aqueous liquor containing water-soluble salts and diicultly decantable tar through a cooling zone, continuously passing said cooled liquor through an at-- mospheric pressure settling and decanting zone in which aqueous liquor containing water-soluble salts separates as an upper layer and dicultly decantable tar as a lower layer, continuously withdrawing aqueous liquor from the top and dicultl'y decantable tar' from the bottom of ii the atmospheric settling and decanting zone, and con tinuously recycling all of said dicultly decantable tar to the aforesaid mixing zone.

5. An automatic, continuous process for treating coke oven tar containing water-soluble salts which comprises continuously charging streams of coke oven tar and aqueous solution, at approximately constant rates, into a mixing zone, continuously flowing said mixture of tar and aqueous solution at temperature of about 145 to 180 C. and under pressure of about 150 to 175 pounds per square inch gauge through a pressurized settling and decanting zone wherein aqueous liquor containing watersoluble salts separates as an upper layer and tar as a lower layer, responsive to a time cycle control, alternately withdrawing, at substantially equal rates, material only from the top and only from the bottom, respectively, of the pressurized settling and decanting zone for predetermined portions of the time cycle, so that for each cycle (1) the total withdrawal is equal to the total charge during the cycle, (2) the withdrawal from the bottom is at least about 5% less than the anhydrous tar content of the total charge during the cycle, and (3) the withdrawal from the top is correspondingly greater than the remainder of the total charge during the cycle, whereby the material withdrawn from the top comprises aqueous liquor containing water-soluble salts and diiiicultly decantable tar and the material withdrawn from the bottom comprises product tar relatively free of water-soluble salts and aqueous liquor, continuously passing said withdrawn aqueous liquor containing water-soluble salts and diliicultly decantable tar through a cooling zone, continuously passing said cooled aqueous liquor through an atmospheric pressure settling and decanting zone in which aqueous liquor containing water-soluble salts separates as an upper layer and dilicultly decantable tar as a lower layer, continuously withdrawing aqueous liquor from the top and dicultly decantable tar from the bottom of the atmospheric settling and decanting zone, and continuously recycling all of said diicultly decantable tar to the aforesaid mixing zone.

6. An automatic, continuous process for treating coke oven tar containing water-soluble salts which comprises continuously charging streams or" coke oven tar and aquous solution, at approximately constant rates, into a mixing zone, continuously llowing said mixture of tar and aqueous solution at temperature of about to 180 C. and under pressure of about to 175 pounds per square inch gauge through a pressurized settling and decanting zone wherein aqueous liquor containing water-soluble salts separates as an upper layer and tar as a lower layer, responsive to a time cycle control alternately withdrawing, at substantially equal rates, material only from the top and only from the bottom, respectively, of the pressurized settling and decanting zone for predetermined por. tions of the time cycle, so that for each cycle l) the total withdrawal is equal to the total charge during the cycle, (2) the withdrawal from the bottom is about 5 to 20%V less than the anhydrous tar content of the total charge during the cycle, and 3) the withdrawal from the top is correspondingly greater than the remainder of the total charge during the cycle, whereby the material withdrawn from the top comprises aqueous liquor containing watersoluble salts and diftcultly decantable tar and the material withdrawn from the bottom comprises product tar relatively free of water-soluble salts and aqueous liquor, continuously passing said withdrawn aqueous liquor containing water-soluble salts and ditlicultly decantable tar through a cooling zone, continuously passing said cooled aqueous liquor through an atmospheric pressure settling and Adecanting zone in which aqueous liquor containing water-soluble salts separates as an upper layer and diflcultly decantable tar as a lower layer, continuously withdrawing aqueous liquor from the top and diicultly decantable tar from the bottom of the atmospheric settling and decanting zone, and continuously recycling all of said dilcultly decantable tar to the aforesaid mixing zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,104,310 Roelfsema Jan. 4, 1938 2,440,311 Tiddy Apr. 27, 1948 2,599,133 Schilling Jan. 3, 1952 2,753,292 Porter et al. July 3, 1956`

Claims

1. AN AUTOMATIC, CONTINUOUS PROCESS FOR TREATING COKE OVEN TAR CONTAINING WATER-SOLUBLE SALTS WHICH COMPRISES CONTINUOUSLY CHARGING STREAMS OF COKE OVEN TAR AND AQUEOUS SOLUTION, AT APPROXIMATELY CONSTANT RATES, INTO A MIXING ZONE, CONTINUOUSLY FLOWING SAID MISTURE OF TAR AND AQUEOUS SOLUTION AT TEMPERATURE ABOVE 90*C. AND UNDER SUPERATMOSPHERIC PRESSURE THROUGH A PRESSURIZED SETTLING AND DECANTING ZONE WHEREIN AQUEOUS LIQUOR CONTAINING WATER-SOLUBLE SALTS SEPARATES AS AN UPPER LAYER AND TAR AS A LOWER LAYER, RESPONSIVE TO A TIME CYCLE CONTROL ALTERNATELY WITHDRAWING, AT SUBSTANTIALLY EQUAL RATES, MATERIAL ONLY FROM THE TOP AND ONLY FROM THE BOTTOM, RESPECTIVELY, OF THE PRESSURIZED SETTLING AND DECANTING ZONE OR PREDETERMINED PORTIONS OF THE TIME CYCLE, SO THAT FOR EACH CYCLE (1) THE TOTAL WITHDRAWAL IS EQUAL TO THE TOTAL CHARGE DURING THE CYCLE, (2) THE WITHDRAWAL FROM THE BOTTOM IS AT LEAST ABOUT 5% LESS THAN THE ANHYDROUS TAR CONTENT OF THE TOTAL CHARGE DURING THE CYCLE, AND (3) THE WITHDRAWAL FROM THE TOP IS CORRESPONDINGLY GREATER THAN THE REMAINDER OF THE TOTAL CHARGE DURING THE CYCLE, WHEREBY THE MATERIAL WITHDRAWN FROM THE TOP COMPRISES AQUEOUS LIQUOR CONTAINING WATER-SOLUBLE SALTS AND DIFFICULTLY DECANTABLE TAR AND THE MATERIAL WITHDRAWN FROM THE BOTTOM COMPRISES PRODUCT TAR RELATIVELY FREE OF WATER-SOLUBLE SALTS AND AWUEOUS LIQUOR.