US2649405A - Method for coke-oven by-product recovery - Google Patents

Description

Aug- 18, 1953 G. EATON METHOD FOR COKE-OVEN lay-PRODUCT 'RECOVERY Filed Sept. 19, 1950 Patenteci ug. 18,

METHOD Foa COKE-OVEN Bri-PRODUCT RECOVERY Gerald L. Eaton, Lansdowne, Pa., assignor to United Engineers & lConstructors Inc., Philadelphia, Pa., a. corporation of Delaware Application September 19, 1950,v Serial No. 185,665

6 Claims.

This invention pertains to an improved method for the recovery of by-products from hot coke oven gases and in particular to a method and apparatus for the recovery of light oils therefrom.

In the production of coke, hot carbonaceous materials such as coal, lignite, peat or the like are heated in the absence of air with the production of cert-ain gaseous Icy-products. Among these are tars, hydrocarbons such as light oils, naphthalene, various lower parafns and oleflns, and nitrogenous compounds such as ammonia and hydrogen cyanide, as well as hydrogen and oxides of carbon.

The recovery of many of these materials, especially the light oils which contain valuable aromatic compounds such as benzene, toluene and xylenes, is economically desirable.

In the processes generally used for the recovery of the` light oils, tar and ammonia, and a least to a certain extent, naphthalene, are rst separated from the gases. The gases are then scrubbed with a wash oil, usually of petroleum origin, which absorbs the light oils. The pressures at which such scrubbing is generally carried out range from about 0.5 to about 1.5 p. s. i. g. With relation to the quantity of wash oil used, in normal practice from about to about 55 gallons of Wash oil ow through a normal scrubber per gallon of light oil recovered.

To separate the light oils from their absorber oil, general practice calls for a steam stripping operation. This involves the use of considerable quantities of steam and is expensive. In the past, suggestions have been made that the separation be carried out by distillation, but in the ordinary process, with its relatively high ratio of wash oils to light oils, such an expedient has been even more expensive than steam stripping, in most instances.

It is an object of the present invention to provide a process whereby light oils can be recovered from coke oven gases with less expense than has been possible hitherto. Y

It is another object of the present invention to provide a process for the separation of light oils from coke oven gases wherein steam stripping is eliminated.

It is another object of the present invention to provide a process for the recovery of light oils from coke oven gases by scrubbing with an Vabsorber oil wherein the separation of light oils from the mixture of absorber oil and light oil by distillation is made practical.

yIt is a further object of the invention to provide a method for the recovery of by-products from hot coke oven gases wherein the gases are scrubbed with an absorber oil to separate naphthalene therefrom and in a second treatment are scrubbed with an absorber oil to remove light oils therefrom and characterized in that the separation of the light oils from their absorber oil and naphthalene from its absorber oil may be carried out by codistillation.

Other objects of the invention will appear from a consideration of the following specification and claims.

According to the invention, the above objects are attained by compressing the gases, after they have been cleansed of tar and naphthalene and before treatment to remove light oils, to above about 5 p. s. i. g., preferably above about 30 p. s. i. g., and advantageously from about 50 p. s. i. g. to about p. s. i. g. At this pressure, and usually at a temperature of from about 20 to about 40 C., the gases are scrubbed with an absorber oil for the removal of their light oil content.

By the term absorber oil, I mean an oil having an initial point (atmospheric distillation) above about 225 C. and an end point not higher than about 400 C. which will take up light oils from the coke oven gases. Preferably the absorber oil will have an initial point of about 230 C. and end point of about 300 C. Such absorber oils may, for example, be of petroleum origin or may be creosote oils derived from the distillation of coal tar itself.

The invention is particularly useful in a process such as that disclosed and claimed in my copending application Serial No. 161,325, iiled May 1l, 1950, for Method and lApparatus for Coke Oven By-Product Recovery, where the coke oven gases having been cooled and cleansed of tar are first treated with an :absorber oil which is continuously revivii'led by distillation for the absorption of naphthalene therefrom and where the resulting mixture of naphthalene and absorber oil is combined with a heavy carrier and distilled t0 produce the naphthalene and the purified absorber oil.

VWhen the present invention is used in such :a process, the mixture of light oil and absorber oil may be combined directly with the naphthaleneabsorber oil-heavy carrier mixture and the combined streams distilled in one operation with the production of naphthalene, light oils and a reviviied absorber oil. The cooperative relationship between such process and the present invention is particularly close because whenv a continuously revivied absorber oil is used, it is possible to employ a bubble plate scrubbing column for the separation of the light oils from the gases without fear of the plates clogging up with polymerized absorber oil or sludge. The use of bubble pla-te scrubbing columns is more adaptable to relatively high pressure operation than spray or packed type apparatus which ordinarily must be used because of the sludge problem and because the lower pressure drop of spray or packed type columns is more suitable for low pressure systems. In turn, the use of pressures in excessofp. s. i. g. enables the amount of scrubbing oijl to be reduced to the point where the quantity of material which must be handled in the distillation column is suiiciently small that the heat requirements Will be less than those necessary to carry out steam stripping.

As pointed out in my said copending application Ser. No. 161,325, by the term heavy 'carrier is meant a liquid hydrocarbon carrier having an end point above the end point of the absorber oi-l and one, at least a portion of which will remain liquid when theA absorber oil is vaporiz'ed. The carrier may be of petroleum origin or may be acoal tar. Examples of suitable carriers are coke oven by-product tar, and Bunker C fuel oil of petroleum origin.

The proportion of carrier in the distilland should generally be not less than about 2% by Weight. One function of the carrier is to insure that no particles of tar or pitch carried into subsequent distillation equipment will remain on any hotsurface and therel polymerize to coke. The minimum percent specified is considered the least quantity which will perform this function.

Where theY boiling point range of the carrier issuch that a partY of it is vaporized with the absorberoil, the total quantity of carrier added must be such thatA the fraction which will remain liquid upon vaporization of the absorber oil constitutes not less than 2% of the distilland.

There is no upper, limit to the quantity of carrier-which mayV be added, but if the carrier is added solely fory the purpose off preventing the coking of entrained tar and pitch, in general no more than t-he amount required for thatV purpose will beadded.

1t-Will be understood that the boilingpoint of the absorber oill is dependent on the nature of the carrierusedl and the one must be chosen with dueY regard to the other. Thus, if'by-product tar is used asY a carrier, the boilingu range of' the absorber oil must be suchl that its endpoint is below about 335 C., inv ord-er that Vthe absorber oil may-beV readily puri-fied` of the phenanthrene and anthracene normally present inrcoal tars by distillation.

The exact pressure which is used in the light' oilV scrubbing tower is subject toy considerable variation. The stated lower limit-of 5 p. s. i. g. has been found to be approximately the lowest'v pressure at which a bubble plate scrubbing column may be used to advantage.` Where distillation rather than steam stripping is to be use'd to separate the light oil from its absorber oil, apressure of. above about 3D p. si. g. will generally be necessary for economic operation. VAs mayA Theoretically it isdesirable to conductthe ab-V inl sorption.- at. the lowest temperature possible.

4 practice, the scrubbing tower is usually operated at between 20 C. and 40 C.

The quantity of absorber oil used in the light oil scrubbing will depend on operating pressures and temperatures. By way of example, however, at a pressure of 50 p. s. i. g. and a temperature of 30 C. about 10 gallons of wash oil are necessary, per gallon of light oils recovered.

In the preferred embodiment of the invention, the absorber oil used is a creosote oil having a boiling point range (atmospheric distillation) of from about 230 C. to about 300 C. and produced from the coke oyen gases themselves. Moreover, in the preferred embodiment, the gases are rst contactedwith water to remove tar and then with a creosote absorber oil to remove naphthalene. The tar removed from the gases is used as the heavy carrier and is combined with the naphthalene rich absorber oil and the light oil rich absorber oil. This mixture is then fractionated into its variousr components.

In the drawings, the gure is a iioW-r diagram of a coke oven by-product recovery system according to the preferred embodiment of thev inven-tion.

Referring to the figure, the hot gases issuing fromv coke oven I are at a temperature of about 800 C. They pass into a collecting-main 2 Where they are met with a spray of aqueous flushing liquor introduced through an injector 3. Bycontact with this liquor, their temperature is` reduced to from about 60 C. to about 100 C., a portion of the ammonia in the gases is absorbed and some of the tar and naphthalene is condensed. The foul flushing liquor together with its tar' and naphthalene` and the absorbed ainmonia passes through a downcomer i into a decanter S. In the decanter, it separates into a tar layer and a water layer, the water layer being reused as flushing liquor in the' collecting main 2';

The gases move from downcomer 4^ to a primary cooler 5 where they are again contacted with an aqueous spray. The liquid for the pri' mary cooler sprays may also be drawn from decanter 4and` may be cooled as by passage through coolers As` they einer-ge from the top of the primaryY cooler; the gases pass, through` an entr-animent removal device 5a. provided` at. the topl of the primary cooler; AtV this point, the gases are at a temperature of from about 20" C. toabout 40 C. Their naphthalene contentmay be from about'50 to about250g'rains per hundred cubicfeet.

From the primary cooler, the gases are sent"- through a naphthalene scrubber 8' where they are met with a stream of creosote absorber oil p r'o.- duced from the bye-products themselves. Details. of operation of a preferred type of naphthalene. scrubber are described in my copendingfapplication'Serial No. 161,325.

Moving out ofthe 'naphthalene scrubber 8', the. gases whose naphthalene content is now reduced; to from about 1 to about 5 grainsperhundred cubic feet pass through an entrainment removal. device B'b'and' are delivered to the suction side of ay systemY of'bcos'ters and int'ercoolers designated'. as 9l in Fig. 1. The boosters may be drivenby, a steam turbine 9a. In the booster system, the pressure of' the gases is raised Ato above about', 30 p; s; i. gf., usuallyto from about 50 to about' k p. s. i. g. As a result' of this compression, the. temperature of the gas is raised: From the; booster system, the gas is deliveredJ to an intermediate cooler le where its temperatureis 'reduced to-fromabout 50A toabout 80 C. At this* temperature, the gas is delivered to a conventional ammonia saturator I I where the ammonia is removed. Leaving the ammonia saturator, the

temperature of the gases is stillv from about 50 to about 80 C. They are therefore passed to a final cooler I 2 wherein their temperature is again reduced to from about 20to about 40 C. At this temperature and at a pressure which is still above about 50 p. s. i. g., the gases are passed upwardly through a light oil or benzol scrubber I3 where they are contacted with a creosote Wash oil of the same nature as that used in the naphthalene scrubber 8. The benzol scrubber I3 preferably contains a number of bubble plates I3b, since, as pointed out above, the use of a bubble plate scrubbing tower is particularly adapted for pressure operations. At the exit from the benzol scrubber, the gases are run through an entrainment removal device I3@ and emerge clean and dry and ready to pass directly to the fuel mains and burners or to further processing systems.

As pointed out above, the decanter 6 contains a Water layer and a tar layer. The tar layer is drawn off and charged to a wet tar storage tank III. Emerging from storage tank I4, the

tar passes through a centrifugal separator Iv where it is cleansed of water and solid impurities. The clean tar is charged to a dry tar storage tank I6. From there, it is combined with the naphthalene rich absorber oil drawn from the bottom of naphthalene scrubber 8 and the light oil rich absorber oil drawn from the bottom of light oil scrubber I3 and charged to a red pipe still heater I9. There, the temperature of the combined streams is raised and they are delivered to an evaporator 20 for the separation of pitch. Details of evaporator 20 may be found in my said copending application Ser. No. 161,325. The bottoms from the evaporator 20 are drawn off and may be sent to pitch storage, not shown.

The overhead from the evaporator 20 may be charged to a fractionator 2| for the separation of the absorber oil from the lower boiling components.

A portion of the bottoms from the fractionator 2l consisting of a creosote oil Which should contain less than 1% of naphthalene may be reluxed to the evaporator 20. A second bottoms stream from the fractionator 2| may be passed through a reboiler 22 and recharged to the bottom of fractionator 2I. A third bottoms stream from fractionator 2l may be charged to a, creosote oil storage tank 23 for further use in scrubbers 8 and I3.

The overhead from fractionator 2| may be charged to further distillation equipment for separation into its components in any convenient manner, as for example in a system similar to that shown in my said copending application Ser. No. 161,325.

It will be understood that the mixture of light oil and absorber oil need not be delivered to distillation apparatus as in the process described, but may be steam stripped. In such case the pressure in scrubber I3 need be maintained only above about 5 p. s. i. g.

.As pointed out, the system described, wherein the light oil is removed from the gases under a pressure of above about 30 p. s. i. g., results in many savings where considered by itself. The benets to be obtained from the invention are increased, however, when the gases are further processed at high pressure after leaving the light oil scrubber. For example, the gases leaving the light oil scrubber may be subjected to hyper- CJD Cil

sorption with activated carbon at elevated presi sures for the recovery of ethylene, hydrogen cy-.r anide and other light components. such processes are not usually economical where the gas' leaving the light oil scrubber is boosted to processing pressure for this purpose alone. On the other hand, where the gases have already been compressed prior to light oil absorption, the cost, of the compression is borne partly by thev in creased efficiency of the light oil absorption, and in part by the additional materials subsequently recovered, with the result that the process as a whole becomes economically practicable.

Although the recovery system described above is, in my opinion, the most eiicient method ofA employing my invention, it is to be understood that the invention is not limited to use in such a system. Thus, for example, it is not necessary, that the light oil rich absorber oil from thelight oil scrubber be combined and, codistilled along With a naphthalene rich absorber oil and a heavy carrier.v Moreover, it is not necessary that Ithe. absorber oil used bea creosoteV oil or that, ifa: heavy carrier is usedy it be a coke oven by-product tar. Similarly, while it isrconsidered that a bub, ble plate scrubbing tower Will be most elective; at the pressures involved, it is obvious that other types of apparatus may be used with varying;

degrees of eifectiveness, Without departingfrom the invention.

What I claim is: 1. In a process for the recovery of by-,products from hot coke oven gases, a combination of stepsV which comprises removing tar from the gases, subsequently compressing the gases, vcontacting the gases at a pressure of above about 30 p. s. i. g. with a substantially naphthalene and light oil free absorber oil having an initial point above about 225 C. and an end point not higher than about 400 C. to remove light oils therefrom with consequent enrichment of said absorber oil and distilling at least a portion of the light oil rich absorber oil to separate light oils therefrom, said distillation being conducted solely by indirectly heating said light oil rich absorber oil.

2. In a process for the recovery of by-products from hot coke oven gases, a combination of steps which comprises removing tar from the gases, contacting the gases with a substantially naphthalene-free absorber oil having an initial point of above about 225 C. and an end point not higher than about 400 C. for the removal of naphthalene therefrom, subsequently compressing the gases, contacting the gases at a pressure of above about 30 p. s. i. g. with a substantially naphthalene and light oil free absorber oil hav'- ing an initial point of above about 225 C. and an end point not higher than about 400 C. to remove light oils therefrom with consequent enrichment of said absorber oil and distilling at least a portion of the light oil rich absorber oil to separate the light oil therefrom, said distillation being conducted solely by indirectly heating said light oil rich absorber oil.

3. In a process for the recovery of by-products from hot coke oven gases, a combination of steps which comprises removing tar from said gases, contacting the gases With a substantially naphthalene-free absorber oil having an initial point above about 225 C. and an end point not higher than about 400 C. for the removal of naphthalene therefrom with consequent enrichment of said absorber oil, contacting the gases at a pressure of above about 30 p. s. i. g. with a substantially light oil and naphthalene free absorber oil having an initial point above about 225 C. and

an end point not higher than about 400? C.`to removevv light oils therefrom withy consequent en-V richment of said absorber oil; and distilling said light oil rich absorber oiland said naphthalene rich absorberoi-l admi'xture' with a liquid hy drocarbon carrier having an end point greater than the end point of the absorber'oil, at least a portion ofwhich carrier will remainliqui-'d wheny the absorber oil is vaporized, said distillation being conducted. solely by indirectly heatingy saidf mixturei 4. a process forv the recovery of by-products from hotco-kev oven gases, a combination ofsteps which comprises. removing tar from the gases, subsequently compressing the gases, contacting the` gases at a pressure aboveabout 30- p; s. i; g. with a substantially naphthalene and light oil reecreosote absorber oil havingarr initial point above about 225l C. and an end point not higher than about 400* C. to remove light oils therefrom with consequent. enrichment of the absorberV eil and distillingy the light eil rich absorber oil tol separate light oils therefrom and to reviv-i'fyfsaid absorber oil, said= distillation being conductedsol'ely byv indirectly heating said light oil rich absorber oil'.

In a process for the recovery of Icy-products from hot coke oven gases, a combination of steps which comprises removing tar from said gases, contacting the gases With a substantially naphthalene-free creosote absorber oilhaving an initial point above about 225 C, and an end point not higher than: about 400 C. for the removal ofv naphthalene therefrom, subsequently compressingV the' gases, vcontacting the: gases at a pressure of above about 30 p. s. g. with a sub'- stantial'ly naphthalene and 'light oiI free creo.- sote absorber oil having an initial point above about 22 5 C and an end point, not higher than about 400 C. to, remove the light oils therefrom 8 with consequent enrichment of' the absorber oil and distilling the light oil rich absorber oil to separate light oils therefrom and to revivify said absorber oil, said distillation beingl conducted solely by indirectly heating said light oil rich absorberV oil.

6. In a process for the recovery of by-products from hot coke oven gases, a combination of' steps which comprises removing tar from said? gases, contacting the gases with a substantially naphthal'ene and light oil. free creosote absorber oil having an initial point above aboutu 225 C; and an end point not higher than about 335` C. for the removal of naphthalene therefrom With con-- sequent enrichment of said absorber oil, contacting the gases at a pressure-above about 30 p. s. i'. g. with a substantially naphthalene and light oil freecreosote absorber oil having an initial` point above about 225 C. and an end point not higher than about 335 C. to remove light oils there from with consequent enrichment of said' absorber oil and distilling the tar previouslyseparated in admixture With the naphthalene richv absorber oil and the light oil rich absorber oil to. recover the naphthalene and` light oit therefrom and to revivify the absorber oil, saidv distillation being conducted solely by: indirectly heating said mixture.

L'. EATON.,

References Cited in the. le of patent UNITED STATES PATENTS' Number Name Date 1,993,344 Jacobson e .5. 1-935` 2,198,743 Schufta-ns. Apr.. 30,1940- OTHER REFERENCES* Wilson, Renner and Natural Gasoline. Manufacturer, vol.. 21 No. 6,. pp. 176-181,. .lune 11942.

Claims (1)

1. IN A PROCESS FOR THE RECOVERY OF BY-PRODUCTS FROM HOT COKE OVEN GASES, A COMBINATION OF STEPS WHICH COMPRISES REMOVING TAR FROM THE GASES, SUBSEQUENTLY COMPRESSING THE GASES, CONTACTING THE GASES AT A PRESSURE OF ABOVE ABOUT 30 P.S.I.G. WITH A SUBSTANTIALLY NAPHTHALENE AND LIGHT OIL FREE ABSORBER OIL HAVING AN INITIAL POINT ABOVE ABOUT 225* C. AND AN END POINT NOT HIGHER THAN ABOUT 400* C. TO REMOVE LIGHT OILS THEREFROM WITH CONSEQUENT ENRICHMENT OF SAID ABSORBER OIL AND DISTILLING AT LEAST A PORTION OF THE LIGHT OIL RICH ABSORBER OIL TO SEPARATE LIGHT OILS THEREFROM, SAID DISTILLATION BEING CONDUCTED SOLELY BY INDIRECTLY HEATING SAID LIGHT OIL RICH ABSORBER OIL.

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