US2675215A

US2675215A - Benzol spray scrubber

Info

Publication number: US2675215A
Application number: US34515A
Authority: US
Inventors: Otto Carl
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-06-22
Filing date: 1948-06-22
Publication date: 1954-04-13
Anticipated expiration: 1971-04-13

Description

April 13, 1954 c. OTTO BENZOL SPRAY SCRUBBER 3 Sheets-Sheet 1 Filed June 22, 1948 .RO. Y m m0 .m

April 13, 1954 I c, QTTQ BENZOL SPRAY SCRUBBER 3 Sheets-Sheet 2 Filed June 22, 1948 INVENTOR 6446 1 0770 BY *0 l 6 ATTORNEY April 13, 1954 OTTO BENZOL SPRAY SCRUBBER Filed June 22, 1948 3 Sheets-Sheet 3 Patented Apr. 13, 1954 UNITED STATES PATENT OFFICE BENZOLSPRAY SCRUBBER Carl Otto, Manhasset, N. Y. ApplicationJune22, 1948; Serial No. 34,515

14 Claims. 1

The general object of the present invention is to provide an improved method of, and improved apparatus for separating vapor constituents from a gas by passing the gas through a scrubbing chamber in which the gas is brought into intimate contact with a liquid scrubbing agent adapted to absorb said vapors.

The invention was devised for use, and is of special utility in separating benzol or light oil vapors from distillation gas. and particularly coke oven gas, by scrubbing the latter with. a vapor absorbing liquid. The latter may Well be, and in this country ordinarily is, the petroleum product known as straw oil, though other wash oils may be used, and in- Europe the scrubbing agent usually employed to recover benzol vapors is the tar oil known as creosote oil. The word benzol is used generically herein to apply to substances known as lightoils including benzene, toluene, xylenes and solvent. naphtha in their liquid and gaseous phases. In the ordinary use of the present invention,.benzol vapors are separated from coke gas after the latter has been treated in accordance. with the usual prior practice in the operation of by-product coke o ven plants to eliminate-tar and tar oils from the gas, and to recover the gaseous ammonia content of the coke oven gas by converting it into ammonium sulphate. The present invention differs substantially from prior practice in respect to the manner in which benzol is scrubbed. out of the gas.

It is theoretically possible to separate benzol vapors from cokeovengas in scrubbing towers of various known types through which the coke oven gas moves upward from the bottom to the top of the tower and through which the scrubbing liquid moves downward from top to the bottom of the tower. For example, the scrubbing towers heretofore theoretically available for use in separating benzol vapors from coke oven gas include towers of bubble still type, and. towers of a spray type. However, prior to the present invention it had long been substantially universal practice in "by-product. coke oven plants in this country to separate benzol vapors from coke oven gas in scrubbing towers, each filled with a pervious mass of liquid. and gas distributing. material, except for a relatively short liquid distributing space adjacent the upper end of the tower into which the scrubbing liquid is usually sprayed and from which the gasis withdrawn.

Formerly the mass of pervious distributing material usually consisted of a multiplicity of wooden grids stacked or piled inthe tower. In

recent years, expanded metal, and sometimes. metal: shavings or turnings, have been largely used as the gridmaterials stacked or piled up in benzol scrubbing towers. As the scrubbing. oil moves downward. through the scrubbing tower, the grids, Whether of wooden or metallic material, divide and. redivide the oil into films. and finely divided and. broken. streams. The grids thus provide a large amount .of oil surface dis,- tributed throughout the tower, with which the gas moving upwardly through the tower isconstantly coming into close contact.

The separation of benzolv vapors from coke oven gas presents special problems because of; the large volume of gas to be: scrubbed in a modern by-product coke .oven plant of customary capacity. Such a. plant may include several grid filled. benzol scrubbing towers, each. having; a height of from ninety to one hundred ten :feet and a diameter of from thirteen to fifteen feet. Customarily, the: maximum rate at which. gas is passed through sucha tower is about thirty-five million cubic feet per twenty-four hours; In some of those plants; gas is passed successively in one direction through two such towers while wash oil is. passed in the opposite direction through said. towers, so that part of the benzol content or the gasstream may be eliminatedin each tower.

Agrid filledxbenzol scrubbing toweris relativelyinexpensive to construct, and under favorable conditions its action approximates the practically desirable, true counter-flow action .in which the benzol vapor contentof. thegas and benzol liquid content of the scrubbing liquid so progressively diminish from the bottom. to the top of the-tower that the driving. force tending to transfer the bGHZOlI from the gaseous phase into the liquid phase need not become undesirably low at any level. Metal grids in the form of expandedimetal or lathe turnings or shavings ofier' less resistance to the gas now upward through. the towerrthan do Wooden grids. It has long been recognized, however, that any grid filled benzol scrubbing tower hasthe inherent and practically important disadvantage of offering considerable resistance to gas flow through the tower at an economically adequate velocity, and thus entails a substantial installation and operating cost for gas pumping machinery. The grid resistanceto the upfiow of gasthrough the grid filled tower is due in part to the reduction of the free flow area through the tower by the grids, in part to the relatively small and tortuous character of the gas flow passages through the mass of grids, and in part to a channeling tendency resulting in unequal fiow rates in difierent portions of the grid mass. Another disadvantageous characteristic of the customary grid filled benzol scrubber, is the need for frequently cleaning and replacing the grids. In operation, there is a tendency for clogging material to accumulate in the flow passages through the grid stack and thereby reduce the perviosity of the grid stack or mass. Dimculty due to such clogging actionis especially pronounced because of the formation and accumulation in the scrubbing oil of a gummy substance having a tendency to adhere to the grid surfaces. The removal of the gummy material adhering to the grid is an especially troublesome but necessary procedure.

A specific object of the present invention is to provide a method of and apparatus for separating benzol vapor from coke oven gas which makes it possible to recover a suitably large percentage of the benzol vapor content of coke oven gasmoving upward through a scrubbing tower of given horizontal and vertical dimensions, while maintaining a greater volumetric rate of gas flow upward through the tower than is practically possible with tower constructed and used in the manner heretofore customary. Further specific objects of the invention are to provide a benzol scrubbing tower containing no grids, and oiiering substantially less resistance to the upiiow of gas T at a given volumetric rate through a tower of the dimensions heretofore customary, than is practically possible with the benzol scrubbing towers heretofore in general use in this country.

The improved benzol scrubbing tower constructed in accordance with the present invention, is of a novel spray type and is particularly characterized by its provisions for continuously spraying finely subdivided absorbing oil into substantially all portions of the gas space in the tower and thereby maintaining an aggregate interfacial surface of gas and liquid contact in the tower which is substantially larger than can be maintained in a grid filled tower of the same dimensions. In a preferred form of the present invention, an upper group or set of spray nozzles are arranged to spray scrubbing oil into the upper portion or section of the tower and a separate group or set of spray nozzles is located in each of a plurality of tower portions or sections at respectively diiferent distances below the upper group of nozzles. In accordance with the present invention, all of the scrubbing oil sprayed into each of the superposed tower sections below the uppermost section, is oil previously sprayed into a tower section at a higher level and subsequently collected by liquid collecting means adjacent the lower end of each said upper section. Associated with the difierent liquid collecting spaces are pipes and pumping means for passing liquid from each such collecting space to the spray nozzles in which the liquid is to be again sprayed into the tower.

In the ordinary use of the invention, I now contemplate that there will be some two or three scrubbing sections beneath the top section of each tower. I also contemplate that more oil will be sprayed into each lower section than is sprayed into the top section. This means that, some of the oil sprayed into each lower section will be oil previously sprayed into that section and collected at the bottom or the latter. In consequence, each particle of scrubbing oil initially sprayed into the top section of the tower, is resprayed into the tower morethan as many times as there are spray sections below the top section before that particle reaches the final oil outlet from the bottom of the tower from which the oil is passed to th apparatus in which the absorbed benzol is stripped from the wash oil.

In the prefer-red form of the present invention, I spray the scrubbing oil into some, at least, of the tower sections in such manner that the oil sprayed into the lower portion of the section is more finely subdivided than the oil sprayed into the upper portion of the section. In such case the nozzles used to spray the oil into the lower portion of the spray section may be atomizing nozzles of such character that the average diameter of the oil particles discharged by those nozzles may be of the order of. one-half millimeter, whereas the nozzle or nozzles spraying liquid into the upper portion of the section may be arranged to discharg a relatively coarse spray comprising particles having an average diameter of the order of two millimeters. The fine subdivision of the oil sprayed into the lower portion of the spray section greatly increases the interfacial surface of gas and liquor contact, and insures a desirably high gas absorption factor in the lower portion of the section. The coarser spray discharged into the upper portion of the section makes the fine subdivision of the oil sprayed into the lower portion of the section practically feasible, by substantially reducing the amount of oil entrained by the gas passing away from the section at the upper end of the latter.

Preferably, the upfiow of gas in the improved tower is substantially unobstructed except to the relatively small extent to which it is obstructed by the spray nozzles, associated piping and collecting devices. Each of the collecting devices advantageously comprises an annular liquid receiving space and louvre-like means for deflecting into said space the scrubbing oil sprayed into and passing downward through the portion of the tower immediately abov the collecting device.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages, and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

Of the drawings:

Fig. 1 is a diagrammatic elevation of a scrubbing tower;

Fig. 2 is an elevation, partly in section, of a portion of the scrubbing tower shown diagrammatically in Fig. 1;

Fig. 3 is a plan section on the line 33 of Fig. 2;

Fig. 3a is a diagrammatic plan section showing the arrangement of spray nozzles shown in Figs. 1 and 2;

Fig. 4 is a partial section on the line 4-4 of Fig. 3;

Fig. 5 is a diagrammatic elevation of a second scrubbing tower embodiment of the present invention;

Fig. 6 is an elevation of a portion of another tower structure;

Fig. 7 is a plan section of the apparatus shown in Fig. 6; and

Fig. 8 is a diagrammatic elevation of a portion of a third form of tower.

The embodiment of the invention shown diagrammatically by way of example in Fig. 1, com- .upperportion of each bracket I llaeengage and-are secured to the cor-respondingraften part [0. The

. portion ofthe scrubbingstage a by a plurality of.

cam-ms zzprises. ascrubbing tower I'which is:provided :wvith .arciateralt gas:.inlet :2 .adjacent its lower end; and alateral gas outlet.3Jadjacent its'upperendu Z'Ihe scitubbingrichamber in the E'lJGWBI' I iSiIdiVidedI into rupper, intermediate; and lower: stages: OIJSBCfiOIlS .a, b and c, ..respeotively. Theas'e'ctions' atand b .areseparated by a liquid collectingdevice' a..=,.- and the sections In and care separated by a liduid'xcollecting device b which may-J be,=.1and ESZLShOWnliS -z=substantially similar; to the device a.

The liquid collectingzdevice bfishown diagramdistances from the member 5- and aztopsmember fi which may comprise a hollow conewbdyspor-x etion. Each of the members 6, I- and fl isiin the form .of a section of a hollow cone. Theupper Hand lower edges of member I respectively overlap -thelower-edge of the member S-and'the upper edge ofthe member 6. .The' lower :edge ofsthe ...member fi'overlaps the upper edge 'of: the sub- :jacent member ,and the lower or outer edge of .the top member fl overl'aps'the inner upperi'edge of the member 8. Theimembers 5;.6; 'I.-,8 and 9 arev vertically displaced. to provide an annular gas outlet, or louvre opening beneath each .ofnsaid members .6, I, 8 and 9.

The collecting device a shownin Fig. l may be structurally: identical tothe collectingdevice b except in certain respects hereinafter. mentioned,

E but for convenient identification the: annular liquid receivingspace of .the device a is designated 4a. The

members

6, 1,18 and 19- of each collecting device a. may :be supported .inzanytconvenient 1 manner. As shownin Fig. 4, each ofithemembers 5, I, and 8 is directly .supportedby'dour.bracket tlikeparts- Ifia spaced. about thetowera-xis, and

each of the brackets isdirectlysupported-by one or another of fourinclined rafterparts IIL: Each L bracket part -.I ta: may be a strip of -meta-l plate.

comprising an upper portion; di-rectlybeneath and wsecured to the corresponding member. 6, 'I,-;or. 8,

and a transverse lower portion. The loweraend of the lower portion. and the {upper end ofr the lower end of eachrafterpart I9 is securedto't-he tower shell through th corresponding. trough part 5 and its upper end is secured. to and assists vin supporting thecorrespondingmember 9. The. parts- In andlila may be'attached totthe correu-

spondingparts

5,5, I, 8 and S'by rivets or-we-lding.

Scrubbing oil. is sprayed intothe upper end spray nozzles I I. .As shown, the spraynozzles I I are all. located at the. same level though this is .not essential, and .arearranged .to: discharge downwardly directed jets into the'subjaoent portion of the scrubbing chamber. The scrubbing'oilv is supplied to the nozzle II bybranch pipes from a scrubbing oil supply pipe I Inordinary practice,.oil.wi1lbepassed into thepipe II by pumping 'wmeans not. shown, which may. receiveloilzdirectly or: indirectly .from the .outletsofwithe. associated 6 u'debenzolizing:zapparatus;.i.not ShOWILLt tort-which :3. he-zoi'kpassin'g through: the tower ;I:-isa passed',-for iitherrseparatiom from the scrubbing oil -of-.r.those benzoleconstituents: absorbed from the gas; pass- 5.1;inghthrough the f-scrubbing :tower. 1 1 A; suitable .t'iarnount of ffresh .makeeup rscrubbing oilwmay. "be dded: to thersscrubbingzoil returned 'to the tower iriron'r:the'rdebenzolizing apparatus.

. .1 :Snrubbingeoilis sprayed into :the upper portion lofrthescrubbingrstage b: by nozzlesshown ascom- .zaprising. azxcentral'xuppernozzle 13, a plurality of a. intermediateinozzles I4 and a1 pluralityof lower nozzles I5. As shown, the nozzle I3 is centrally -.cdisposed in the domeshap'ed'louvre. structure of fizitheudevice aybeneath and .in close proximity to thetop member 9" of thatv structure. .Theinter- -lrmediate nozzles I4" are shownas located at alevel 1-::slightlyczbelowathebottomafof the liquid. receiving chamber 4. wThewspraywnozzlesI5of theistage b 0 are-located: at .a :levelbelow that of the nozzles I4 andraboverthat of the-top member of thelouvre zzrstructure b. The arrangement ofthe nozzles: I3, i rand: I 5-relativeto'the vertical axis of the tower Ii is shown diagrammatically in Fig.3a. 1 In Fig. 1, :=each or the: nozzles. I3, I4Jand IBsprayingliquid intothescrubbingstage 11, receives liquid through wan individual branchlsupplypipe I6 from atbus .pipe I'II extending-circularly about the tower I l at a'level which advantageously; and. as shown, is intermediate the levels'ofthe nozzles I3 and' I 5 r discharging intoratheucscrubbing stage 12. Spray liquid is supplied under pressure to the bus pipe I through 'theoutlet pipe l8+of awpump I9 which I has its inlet Iconnectedby apipeiiifi tosthe annular & receiving space lbv of-thecollectingdevice b.

The-collectingr-device b" receivesthe. liquid sprayed into the stage I) through the nozzles I3, I 4 .and 'l 5 discharging directly: into that space,

and also-receives liquid dromthe annular-receiv- 405 ing .space: 4a: of..the. upper collecting device a through andrainpipe 2|. The trough shaped wreceivingispace 4b--of.-the. co1lecting device I),

- thus receives.all.of thescrubbing oilsprayed into each of the upper'scrubbing stages aand b. The 4;, oil received in therecei-v-ingspa ce 4110f the collecting'device' b- :and not withdrawn/therefrom by the pump l 9,3-passesflthrough an overflow drain-apipe 'fl :into ailiquid holding space 23in :the-lowenend portionof the tower I. The space 23 also-received oilsprayed into the stage 0. and

-vaccumulating in the lower end of the latter. The :pump- I-Ba draws scrubbing oil from'thespaceZS through a pipe =24 and discharges itathrough a pipe 25 into a bus pipe I 1a, which may be exactly .-::like the bus pipe-l1,-.and--which supplies scrubbing loil wtlrroughdndividualbranch pipes. to. the

I and l5'= are shown'as-tsimilar'in arrangement to, and they may be identical in construction with '.the previously mentioned nozzles I3, I4 and I5, respectively. A pump: 26 draws the enriched =scrubbing oil away from the :lower end :portion of.-.the tower I; and passes it directly or indi- I 65. :rectly -to. the-associated debenzolizing apparatus,

: not shown.

*Figs. .2 and 3 collectively illustrate onewform vof means which may be employed to prevent the oilv passedwbycthe'pump. I9. to spray nozzles' l3,

* -I45J.3Ild I5: fromuentraining an objectionable iamQUIIt-"Of gasg'and for insuring that the oil r'xpassedrto .the nozzles "by the pump I9 includes r zsubstantiallyfall ofthe oil coming-to the liquid receiving spacr'flb fromsthe liquid receiving space ;:4a xthrougluthe: pipe 2 I 1 To this end-i thepipes and 2| each communicate with a compartment 2'! which may be regarded as a segregated portion of the space 412. The compartment 4?) receives oil sprayed into the tower section I) only through the remainder of the space lb. As shown, the compartment 21 is separated from the remainder of the space db by radially extending

partitions

28 and 29. The partition is shaped to provide a relatively restricted port 30 through which the compartment 2'! is in restricted communication with the body portion of the space 4b. The partition 29 may or may not be provided with a similar port 30.

A plate 3! extends over the top of the compartment 21 and has depending end portions 31' which overlap the upper portions of the

partitions

28 and 29. As shown, the portion of the louvre member 6 immediately adjacent the compartment 2'! is provided with an uprising lip 32 to divert the oil flowing'downward over the member 6 into the portions of the space db at the opposite ends of the compartment 21. The rapid separation of entrained gas from the oil passed into the compartment 2'! by the pipe 21, is [facilitated by displacing the ends of the pipes 20 and 2i communicating with compartment 21, angularly from one another about the vertical axis of the tower, as is shown in Fig. 3, and by providing a curved oil guide 33 in the compartment arranged to give a circular motion to the stream of oil passing into the compartment 27 through the pipe 2!. The hoodmember 30 has its body portion at a level above the tops of the partitions 2B and 29 and above the trough wall member 5, so as to permit the ready escape of the gas separating from the oil in'the compartment 21.

In the preferred form of the present invention, the spray nozzles l4 and Ill are of the type commonly referred to" as atomizing nozzles, and are adapted to discharge thescrubbing oil in particles or droplets so small that the portion of the spray discharged adjacent each nozzle comprises particles, the average diameter of the bulk of which is of the order of 0.5 millimeter. The upflowing gas stream would entrain and carry out of the scrubbing stages 12 and c a substantial portion of the oil respectivelysprayed into the stages b and c by the corresponding nozzlesl5 and if the entraining action were not wholly or large prevented by scrubbing liquid sprayed into the extreme upper end portions of the stages 2; and c by the corresponding spray nozzles l3 and 13.

In practice, each of the nozzles 13 and I3 is arranged to discharge a coarse spray of a volume substantially greater than the volume of liquid discharged by each of the nozzles ldand M. Preferably, the amount of liquid discharged by the intermediate group of nozzlesof each stage is some greater than the amount of scrubbing oil sprayed into the stage by the corresponding upper nozzle or nozzles l3 and I3. In practice, the coarse spray nozzles l3 and i3'discharge oil in the form of drops having an average diameter of not less than about two millimeters. The lowermost nozzles i5 and 55 of the scrubbing stations I) and 0 may be atomizing nozzles discharging oil having the same fineness of subdivision as the oil discharged by the nozzles M and Hi. In most cases, I consider it preferable, however, to employ nozzles l5 and 15, which discharge a spray somewhat coarser thanthe spray discharged by the nozzles l4 and i4,

7 though finer than the spray discharged bythe 8 nozzles I3 and I3. When the spray discharged by the nozzles l5 and I5 is as fine as that desirably discharged by the nozzles l4 and I4, there is a tendency for the gas to move an objectionably large portion of the oil discharged'by the lowermost nozzle l5 and [5 to upper levels and with the result that more of the oil in spray form is in portions of the scrubbing chamber above the levels of the nozzles l5 and i5, and less of it below the respective levels of the nozzles l5 and I5 than is desirable.

The operation of the tower l is highly eilicient, and the tower is adapted in regular operation to recover the available light oil Vapors in a volume of coke oven gas substantially larger than the volume of gas from which the available light oil vapors can be recovered in a tower of similar dimensions containing the mass of grids heretofore customarily employed in benzol scrubbers. The benzol scrubbin tower illustrated diagram- 'matically in Fig. 1 is of a design adapted for use in the conversion of an existing grid filled tower of conventional type into a tower having special features, and the mode of operation, characteristic of the present invention. In essence, such a conversion requires the removal of the grids from the old tower shell and the addition to the latter of the liquid collecting devices a and b and the associated spray nozzles and piping below the nozzles l I of Fig. 1. In its original condition, the normal average gas upilow velocity across the tower cross-section is about 1 feet per second. With the tower shown in Fig. 1, the average gas upflow velocity'acr'oss the tower cross section may be in excess of three feet per second in regular operation.

The general operation of the tower l in its converted form shown in Fig. 1, is generally like that of the tower in its original grid filled condition, in that as the gas ascends and the wash oil descends through the tower, the transfer of benzol from the gas to the wash oil similarly diminishes the benzol content of the gas and increases the .benzol content of the wash oil. Under similar operating conditions, the rate at which the benzol content of the gas is being transferred to the wash i oil at any one tower level of any particular tower,

is dependent on the difference between the partial pressure of the benzol in the gas and the partial pressure of the benzol in the wash oil, and is also dependent upon the aggregate interracial surface of gas and liquid contact per unit of tower volume.

In the practical operation of a benzol scrubbing tower, the pressure of the benzol in the gas and the benzol in the wash oil must be so related that the actual benzol partial pressure in the gas is appreciably in excess of the partial benzol pressure in the gas under the equilibrium condition in which there is no net transfer of benzol between the gas and wash oil. The difference between the actual and equilibrium partial benzol pressures in the gas provides the driving force or partial pressure head necessary to effect the transfer of benzol from the gas to the oil. The necessity for such a driving force or partial pressure head explains why it is not practically possible in the operation of a scrubbing tower, to remove all of the benzol content of the gas entering the tower. Under any given set of operating conditions, the benzol content of the gas entering the scrubbing tower available for recovery therein, is the portion of the initial benzol content of the gas in excess of the benzol content which must be left in the gas leaving the tower aevaars to maintain an adequate driving force diiferential between the actual and equilibrium partial pressures of the gas at the top of the tower. The aggregate interfacial surface of the gas and liquid contact per unit of the tower volume depends upon the tower construction and mode of operation.

The efiiciency of a benzol scrubbing tower is indicated by its H. T. U. characteristic, i. e., by the average height of its transfer units. The tower has as'many transfer units as it has superposed sections in each of which the amount of benzol vapor transferred from the gas to the scrubbing oil is that required to make the resultant change in the benzol content of the gas equal to the arithmetical average of the differences between the actual partial pressure of the benzol in the gas and its equilibrium pressure at the upper and lower ends of the section. The eificiency of a tower of given height operating under given conditions, is thus directly indicated by the number of its transfer units, and the relative efficiencies of two benzol scrubbing towers of the same height and operating under the same conditions, is thus directly expressed by the ratio of the transferunits of the two towers. In a scrubbingtower usedto scrub benzol Vapor out of coke oven gas, the number of transfer units of the tower is approximately inversely proportional to the amount of gas upflow through the tower per unit of tower cross-sectional area, e. g., cubic feet of gas per hour per square foot of tower cross-sectional area.

The described provisions in the apparatus shown in Fig. 1 for spraying the wash oil into contact with the gas passing upward. through the tower makes possible a substantially greater aggregate interfacial surface of gas and oil contact per unit of tower volume than is practically attainable with the customary grid filled tower, or other benzol scrubbing tower of which I have knowledge.

Under normal operatin conditions in an ordinary by-product coke oven plant, a tower constructed in accordanc with the present invention may be expected to have not less than twice as many transfer units as the ordinary grid filled benzol scrubbing tower of the type heretofore in general use in this country, whenthe two towers are of the same height. In consequence, for the usual percentage reduction in the benzol content of the coke oven gas passing through the two towers, twice as many cubic feet of gas per hour may be passed through the tower constructed in accordance with the present invena tion as can be passed through the prior grid filled tower when the two towers are of equal height and have the same internal diameters.

The apparatus used in the practice of the present invention may include other forms'than that shown inFigs. 1 to 4. Thus, the tower Ia shown in Fig. 5, differs from the tower I in having a section d interposedbetween its sections 2) and c. The tower shown in Fig. also difiers from the tower shown in Figs. 1-4 in the arrangement of the spray nozzles I4 and I5 and piping through which those nozzles are supplied with wash oil. The additional tower section (1 shown in Fig. 5 may be a counterpart of the other intermediate tower section 1). Thus, the section at has a pump I9 and conduits 28 and BI associated therewith which are counterparts of thepump I9 and pipes and '2 I, respectively associated with the section b. The nozzles I4 and I5 of Fig. 5-are connected to-pipe rings 34 and'35 within and coaxial tothe tower la. The outlet pipe gIB from the pump I9 of Fig. :5 is directly connected by pipe 36'to the nozzle I 3 and is directly connected by

pipes

31 and 38 to the pipe rings 34 and 35, respectively. As shown, each of the

pipes

36, 3! and 38 includes an individual throttling valve 39. By adjustments of the different valves 39, the pressures, and therefore the amounts of oil supplied to the nozzles I3, I4 and it may be proportioned. Similar pipe connections are provided for connecting each of the pumps I9 and l9a of Fig. 5 to the nozzles I 3, I4 and I5, respectively associated with those pumps. Whenaproportioning adjustment in a scrubbing section increases or decreases the amountof oii discharged at the level of the nozzles 15, for example, of one scrubbing section, relative to the amounts of oil discharged at the levels of the nozzles I3 and M of the same scrubbing section, the rate at which the adjacent upfiowing gas gives up benzol respectively increases or decreases, and thus varies the differential in said scrubbing section between the benzol in the gas and the benzol in the oil at the levels of the nozzles I3. and I4, as well as at the levels of the nozzles I5.

The number of nozzles associated with each tower sectionand the sizes of the different nozzles may vary with conditions. Thus, for example, in the particular tower design illustrated in Figs. 2, 3 and 4, there are nine nozzles I 4 and six nozzles E5 in each of the sections b andc. In the particular design shown in Fig. 5 eighteen 1 inch nozzles I4 and twelve 1 inch nozzles 15 areprovided for each of the sections b, c and d. When the number of nozzles are increased, the sizes of the various nozzles may be diminished. In the particular design shown diagrammatically in Fig. 5, there are twelve 2 inch nozzles II. The nozzles I3 of Fig. 5 are .2 inch nozzles. It will be understood, of course, that. the nozzle numbers andsizes stated above are given by way of illustration and example andnot by way of limitation. As previously stated, the vertical extent of a benzol scrubbing tower is ordinarily not less than feet and not more than 110 feet. With a tower height of the intermediate value of feet and four sections as shown in ,Fig. 5, the average height of each of the three vertically elongated

subjacent sections

12,13 and 6! will be of the order of 25 feet. With the'majorportion of the scrubbing oil sprayedinto the vertically elongated section b, for example, partly through the intermedjate nozzles I4 and partly through the lower nozzles I5, there is no such reduction in the absorption of benzol in the lower portion of the section as there would be if all of the scrubbing oil were sprayed into the uppermost portion of the section through the top spray nozzle i3. Such reduction would result in part, from the rapid absorption of benzol by .the spray oil passing down through the upper portion of the section, and in part from the coalescence and enlargement of the spray oil particles or droplets moving from the top of the section down to and through the lower portion of the section, and in part, also, from the deposit of spray oilon the exposed internal portions of the tank structure.

With a substantial portion of the scrubbing oil sprayed into and dispersed in the lower half of the section b by the nozzles I5 which are about half way between the top of the section b and the liquid'level in the collecting trough at the bottom of the section, and with the intermediate nozzles I4 at alevel nearer the levelofthe nozzles I 5 than the level of thenozzle I3, it is practically possible to avoid objectionably large variations at different levels between the benzol in the scrubbing oil and the benzol in the gas. As will be apparent, what has just been said with respect to section 1), applies also to the sections at and c of Fig. 5. The vertical and horizontal distribution of the spray points shown in Fig. 1 and in Fig. 5, permits of the effective use of benzol scrubbing towers of large diameters and vertical extents without an unduly large number of superposed sections. Any reduction in the number of sections of a tower of given height appreciably reduces the inherent construction cost of the tower.

Each of the liquid collecting devices of such a tower as is shown in Figs. 1, 2 and 5, may have an external reservoir and overflow box 40, associated with each of its liquid collecting spaces a, 1) etc. in the general'manner shown in Figs. 6 and '7. As there shown, the box 40 receives oil from the trough space 42 of a collecting device b generally like the device I) of Fig. 1 through a' pipe 4!, and returns gas separating from the oil" through a pipe 43, and also receives and discharges oil through

pipes

21a and 26, respectively corresponding to the pipes 2| and 20 of Fig. 1. The pipe 44 is adapted to serve the purpose of the-pipe 22 of Fig. l. The pipe 21a is connected to the reservoir 40 through a congential inlet 45.

In normal operation, the reservoir Ml acts as a'cyclone separator to liberate and return to the tower gas entrained in the oil entering the reservoir through its congential inlets 4| and 45. It also contributes to a simple and effective design having the special advantage of reducing the required capacity of the associated oil receiving space '42. The reduction in said space "permits of a relative increase in the diameter of the'upper end of the conical member 45 which forms the inner wall of the trough space 42. 'The restriction of the path of upfiow of the gas moving through the tower may thus be inherently smaller with the arrangement shown in Figs. 6 and 7 than with the form of apparatus illustrated in Figs. 1-4.

The arrangement shown in Figs. 6 and '7 thus permits of an operation with a smaller gas pressure drop 'in the tower than is possible with the tower construction shown in Figs. 1-4, as-

suming similar tower diameters and heights and the same volumetric rates of gas flow through the two towers. As will be apparent, the set of superposed

conical louvre members

6, 1, 8 and 9 of Figs. 1, 2, and or of Figs. 6 and 7, may be so proportioned and disposed that said members will restrict the cross-section of the gas flow path less than it is restricted by the inner wall of the space 4a or 4b of Fig. 1, or by the inner wall of the space 42 of Fig. 6. It is practically possible with the arrangement shown in Fig. 1 to keep the cross-section of the upper end of the space surrounded by the wall 5 of the receiving space 4a or 41) in excess of one-half the cross-sectional area of the tower.

The spray nozzles and piping employed in any of'the forms of the invention illustrated, oiier relatively insignificant resistance to the upflow of the gas, and the provision of the two collecting devices 'a and b shown in Fig. l, or the three collecting devices shown in Fig. 5, offer vmuch less resistance to the upflowing gas than is offered by the grids of a grid filled tower of similar dimensions. The gas pressure drop in a tower having each collecting device associated with an external reservoir like the reservoir 49 shown in Figs. 6 and 7, need not be as great as it would need to be if the tower were not provided with external reservoirs analogous in purpose to the reservoir 48 of Figs. 6 and 7. s

Fig. 8 illustrates a modified arrangement of the piping supplying wash oil to the spray nozzles associated with each section of a scrubbing tower constructed in accordance with the present invention. In that figure each of the nozzles l4 and I5 and each of a plurality of nozzles 13 are connected to the discharge ends of a corresponding branch 50 from a supply pipe 51. The latter as shown, comprises a vertical portion to which the branch pipes 5c are connected, and a horizontal portion extending through a nozzle part 52 through which the tower shell supports the pipe 5!. As will be apparent, the piping arrangement shown in Fig. 8 is of simple and relatively inexpensive construction.

This application is a continuation in part of my prior application Serial No. 724,874, filed J anuary 28, 1947, which became abandoned after the instant application was filed.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims, and that in some cases certain features of my invention may be -usedto advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is: i r

1. In separating benzol vapors from coke oven gas, the method which consists in passing the gas upward through substantially unobstructed superposed sections of a vertically elongated scrubbing path, spraying an absorbing oil into the uppermost of said sections and respraying said oil in each of a major number of subjacent sections at a plurality of spray points distributed both vertically and horizontally throughout a major portion of each of said subjacent sections and collecting the oil sprayed into each upper section and spraying it into: the immediate subjacent section at the said vertically and horizontally distributed spray points.

2. A method as specified in claim 1, in which the'wash oil sprayed into eachsection is collected at the bottom of said section and in which the wash oil sprayed into each subjacent section consists in part of wash oil collected at the bottom of the section above said subjacent section, and in part of wash oil collected at the bottom of said subjacent section.

3'. A method as specified in claim 1, in which the oil being redistributed is degasified prior to its redistribution. v

4. Apparatus for separating benzol vapors from coke oven gas comprising in combination a vertically elongated scrubbing tower shell with a gas inlet and a gas outlet at its lower and upper ends respectively, and providing a continuousgas flow path betweensaid inlet and outlet, and meansfor passing an absorbing oil into the portion of said path in each of a plurality of superposed tower sections comprising means for passing oil into and distributing it in the upper portion of the uppermost of said sections, and a plurality of spray nozzles distributed vertically section, and oilpumping means for passing the oil collected in each collectingdevice under pressure to the diiierent spray nozzles in the subjacent section, each of said subjacent sections having an average vertical extent which is greater than fifteen feet and is substantially unobstructed.

5. Apparatus as specified in claim 4, in which theheight of each of said subjacent sections is substantially greater than fifteen feet.

6. Apparatus as specified in claim 4, in which said gas flow path is substantially unobstructed except by said collecting devices.

7. Apparatus as specified in claim 4, in which each collecting device comprises an annular trough space adjacent said shell and surrounding a portion of said gas flow path having a minimum cross-sectional area not less than. about one-half of the cross-sectional area of said shell, and in which said device comprises a hood shaped louver structure above said trough and smaller in diameter at its upper end than the internal diameter of said trough path and formed with horizontal gas outlet spaces collectively forming a portion of the gas flow path of greater cross-sectional area than the minimum cross-section of the portion of said path surrounded by said trough.

8. Apparatus as specified in claim 4, in which the means for spraying oil into the lower portion of each subjacent section are arranged to sub divide the oil sprayed by them into particles so fine that the upflowing gas tends to move a substantial portion of said particles up out of said section, and the oil sprayed into the upper portion of the section comprises particles too coarse to be substantially entrained by the Lip-moving as, and is so distributed as to coalesce with said fine particles and thereby substantially prevent the latter from being carried out of the section by the gas.

9. Apparatus as specified in claim 4, in which the spray nozzles in each of said subjacent sections include one or more upper nozzles arranged to subdivide the oil into particles having an average diameter of the order of two millimeters, and

in which at least some of the lower nozzles are atomizing nozzles adapted to subdivide the oil into particles having an average diameter or the order of one-half millimeter.

10. In separating benzol vapors from coke oven gas, the method which consists in passing the gas upward through substantially unobstructed superposed sections of a vertically elongated scrubbing path, spraying an absorbing oil into the uppermost of said sections and re-spraying said oil in each of a plurality of subjacent sections at a plurality of spray points distributed both vertically and horizontally in each of said subjacent sections and collecting the oil sprayed into each upper section and spraying it into the immediate subjacent section at the said vertically and horizontally distributed spray points, the wash oil sprayed into the upper portion of each subjacent section being in the form of a relatively coarse spray while the oil sprayed into the lower portion of the section is in the form of a relatively fine spray.

11. In separating benzol vapors from coke oven gas, the method which consists in passing the gas upward through substantially,unobstructed superposed: sections of a vertically elongated scrubbing path, spraying an absorbing oil into the uppermost of said sections and re-spraying said oil in each of a plurality of subjacent sections .at a plurality of spray points distributed both verti- 'cally and horizontallythrough a major portion of each ofsaid subjacent sections and collecting the oil sprayed into each upper section and spraying it into the immediate subjacent section at the said vertically and horizontally distributed spray points therein, the vertical extent of each subjacent section being great enough to substantially reduce the interfacial surface of contact of the gas and the portion of the scrubbing liquid passing into the lower portion of the last mentioned section from the uppermost of said spray points, and a substantial portion of the scrubbing oil being initially dispersed in the lower half of the section.

12. Apparatus for separating benzol vapors from coke oven gas comprising in combination a vertically elongated scrubbing tower shell with a gas inlet and a gas outlet at its lower and upper ends respectively, and providing a continuous gas flow path between said inlet and outlet, and means for passing an absorbing oil into the portion of said path in each of a plurality of superposed tower sections comprising means for passing oil into and distributing it in the upper portion of the uppermost of said sections, and a plurality of spray nozzles distributed vertically and horizontally in each of the subjacent sections, a wash oil collecting device at the upper end of each of said subjacent sections arranged to collect the oil sprayed into the section immediately above said subl'acent section, and oil pumping means for passing the oil collected in each collecting device under pressure to the different spray nozzles in the subjacent section, each of said tower sections having an average vertical extent which is greater than the tower diameter, and is substantially unobstructed, the nozzles spraying oil into each subjacent section being arranged to discharge oil into an upper portion of the section which is less finely divided than the oil sprayed into a lower portion of the section.

13. In separating benzol vapors from coke oven gas, the method which consists in passing the gas upward through substantially unobstructed superposed sections of a vertically elongated scrubbing path, spraying an absorbing oil into the uppermost of said sections and re-spraying said oil in each of a major number of subjacent sections at a plurality of spray points distributed both vertically and horizontally throughout a major portion of each of said subjacent sections, the vertical extent of each of said subjacent sections being more than 15 feet and some of the spray points in each of the last mentioned sections being located not higher than about midway between the upper and lower ends of the corresponding subjacent section and collecting the oil sprayed into each upper section and spraying it into the immediate subjacent section at the said vertically and horizontally distributed spray points.

14. In separating benzol vapors from coke oven gas, the method which consists in passing the gas upward through substantially unobstructed superposed sections of a vertically elongated scrubbing path, spraying an absorbing oil into the uppermost of said sections and re-spraying said oil in each of a major number of subjacent sections at a plurality of spray points distributed major portion of each of said subjacent sections,

whereby the benzol content of the gas decreases and the benzol content of the oil increases as the oil moves downward and the gas moves upward past the various spray points, regulating the difference between the partial pressure of the benzol in the gas relative to the benzol in the oil at different levels in one of said subjacent sections by varying the relative rates at which oil is supplied to the different spray points in that section and collecting the oil sprayed into each upper section and spraying it into the immediate subjacent section at the said vertically and horizontally distributed spray points.

References Cited in the file of this patent UNITED STATES PATENTS Number 5 1,169,764 1,655,171 1,868,886 1,934,600 1,985,010 10 1,989,033 2,277,651 2,413,238

Numb er Name Date Brassert Feb. 1, 1916 Wagner Jan. 3, 1928 Collins July 26, 1932 Coubrough Feb, 6, 1934 Berkhuljsen Dec. 18, 1934 Weir Jan. 22, 1935 Steele Mar. 24, 1942 Liptak Dec. 24, 1946 FOREIGN PATENTS Country Date Great Britain Nov. 7, 1918