US2786082A - Dephenolization process and apparatus - Google Patents

Description

March 19, 1957 o. E. KLocKMAN DEPHENOLIZATION PROCESS AND APPARATUS 2 Sheets-Sheet l Filed March 20, 1951 t9 umm @E nfwm INVENTOR. 077'@ loc-MAN BY ww., Q/LWLMJLQQ March 19, 1957 o. E. KLocKMAN 2,785,082

DEPHENOLIZATION PRocEss AND APPARATUS Filed Maren 2o. 1951 2 sheets-sheet 2 INVENTOR. Orr@ E K/ ocgMA/v BY weit/14 @www United States Patent O DEPHENOLIZATION PRGCESS AND APPARATUS Otto E. Klockman, Arcadia, Calif., assignor to Kappers Company, Inc., a corporation of Delaware Application March 20, 1951, Serial No. 216,548

2 Claims. (Cl. 260627) This invention relates to an improved method of and apparatus `for ytreating liquors containing tar acids, Whereby substantially complete removal and recovery of the tar acids can be eiected, thereby giving not only an increased economic advantage to the process, but the solution of an acute industrial problem as well.

It further relates to a process of and apparatus for carrying out the above by removing acidic gases from the liquor containing tar acids, stripping substantially all of the tar acids from the acidic gas-free liquor with a recirculating inert vapor in a single stripping step, scrubbing substantially all of the tar acids from the recirculating inert vapor by means of contacting said vapor with a stream of alkaline solution in a bubble cap column, and recirculating the inert vapor to strip substantially all of the tar acids from another quantity of liquor in a single stripping step.

In many localities, the discharge of industrial eluents and other waste liquors contaminated with tar acids (made up primarily of phenols, cresols and their homologues) into water courses, sewers, etc., is prohibited. Consequently, many industries have been confronted with a serious problem regarding disposal of eluents contaminated with tar acids.

This problem has been especially acute in the manufactured gas industry and in the by-product coke industry where it is general practice to cool and partially condense the crude gas from coke ovens, retorts, etc. to remove tar and ammonia. During thiscondensation ammoniacal gas liquor is produced, which is contaminated with tar acids.

When gas liquor is distilled in the usual manner for recovery of ammonia, the major portion of the tar acids remains in the liquor which is discharged into streams as still waste. If this water is subsequently chlorinated in the course of purification for municipal consumption, an unpleasant taste results, and it is this nuisance that regulations prohibiting phenolic pollution of streams are intended to prevent.

To eliminate this nuisance, it is desirable to remove tar acids prior to the discharge of the still wastes.

To accomplish this removal, several processes whereby dephenolization is effected have been devised. Of these, the most successful and economical is the Shaw vapor recirculation process, disclosed in U. S. Patent 1,920,604, to Sperr and Shaw; U. S. Patent 1,957,295 to Shaw; U. S. Patent 1,928,507 to Shaw and U. S. Patent 2,127,503 to Denig.

Briey stated, such process comprises the following steps:

The gas liquor or solution, bearing tar acids, ammonia and other volatile constituents, is distilled in the manner known in the art. The free ammonia and acidic gases such as H25, CO2 and HCN are removed in the so called free ammonia section of :the still by bringing the ammonia liquor in intimate contact with a countercurrent ow of sufficient steam to volatilize and remove the free ammonia, HzS, CO2, and HCN in the steam vapor stream, but

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insutiicient vto volatilize and remove a major portion of the tar acids. The hot liquor from the bottom of the free ammonia section is then exposed in a suitable stripping tower to an ascending current of hot recirculating inert vapor which volatilizes and removes the tar acids from the liquor as it descends through the tower. The stripping tower is usually iilled with contact material such as wooden hurdles. The recirculating vapor containing the stripped volatile tar acids is subsequently scrubbed in a packed scrubbing tower by passing said vapor upwardly through the packing of the scrubbing tower countercurrently to a descending stream of an alkaline solution preferably sodium hydroxide, to eiect the removal of the volatilized tar acids before the recirculating gases are again recirculated back to the stripping tower where they are brought into contact with new quantities of hot liquor.

The gas liquor, then substantially dephenolized, is returned to the lime mixing tower of the ammonia still, where the xed ammonia is freed from its various combinations by admixture with milk of lime. The ammonia thus liberated is then removed by distillation with steam in the lixed ammonia section of the still, and the eluent still waste substantially freed of both ammonia and tar acid is discharged into the public waterways.

Usually the stripping of the tar acid from the gas liquor by the inert vapor and the scrubbing of tar acid from `the stripping inert vapor by the alkaline solution is carried out in a two-compartment packed tower, utilizing a recirculating inert vapor blower to circulate the stripping vapor through both compartments. The top compartment is usually a stripping tower where tar acid (phenols) is stripped from the ammonia liquor by countercurrent contact with upwardly flowing recirculated inert vapor and carried upwardly with said inert vapor. The tar acid-containing inert vapor is recirculated from the top of `the stripping tower to the bottom of the bottorn compartment which is an absorption or scrubbing tower, where tar acid (phenols) is absorbed from the upwardly flowing volatile tar acid-containing recirculated inert vapor by countercurrent contact with a downward Vllow of caustic soda solution with which it reacts to form tar acid salts which dissolve in and are carried down by the caustic solution.

The quantity of vapor throughput utilized in the dephenolization tower is dependent on the desired ammonia iliquor throughput. The maximum rate of vapor throughput, which depends upon the maximum rate of liquor flow required, determines the cross sectional area of the tower. The quantity of vapor required to eectively strip out the relatively small amounts of tar acids contained in the ammoniacal liquor is relatively large, resulting in a large volume of vapor emerging from the stripping tower containing minute quantities of tar acids. To convert these small quantities of tar acids to tar acid salts only a very small amount of caustic is theoretically required. Even if twice the caustic required is utilized the amount is still very small. For instance, if 14 gallons per minute of ammonia liquor containing 3 grams/liter of tar acid could be reduced, to 0 grams/liter, the amount of tar acid to be removed would be 3.00 grams/liter or a little less than 11.2 grams per gallon of liquor, making a total of about 157 grams or about 0.35 pound per minute per 14 gallons of liquor. Assuming this to be entirely phenol, the amount of caustic soda theoretically required to react with it to form phenolate is about 0.15 pound. If twice this amount is actually used to ensure thorough removal of tar acids from the vapor, the total amount of caustic soda to be supplied is about 0.30 pound/minute. If this caustic is supplied to the scrubbing section in the form of a 10 percent NaOH solution about 0.35 gallon 0f caustic solution would be required per minute. At an ammonia liquor ow of 14 gallons per minute, a conventional rate of vapor throughput would be 6,000 cubic feet/minute. Therefore 0.35 gallon of caustic must be thoroughly contacted with 6,000 cubic feet of vapor every minute in order to efficiently remove the tar iacids contained in such vapor. The problem of eiiciently contacting such a small amount of caustic with such a relatively large quantity of vapor in order to allow eicient reaction and scrubbing is a diflicult one. This problem is magnified by the fact that the scrubbing tower cross sectional area required for such a large vapor volume throughput is comparatively large. Therefore, not only must a small quantity of caustic solution be contacted with a large volume of vapor but the contact must be carried out in a comparatively large cross sectional tower area. By utilizing a larger volume of a more dilute caustic solution, better contact is made possible, but the practical limit of such dilution is a 4 percent caustic solution. Furthermore, the more dilute the caustic soda solution, the more dilute is the tar acid salt solution obtained, resulting in higher tar acid salt shipping costs.

An excess of caustic maybe utilized to obtain an added volume of liquid to facilitate contact. However, unless it is practical to recycle such unreacted excess of caustic, its use is impractical due to increased costs.

The economically feasible limit to the caustic feed rate, utilizing from 4 percent to 50 percent caustic solution and an ammonia liquor containing from 0.75 to 3.5 grams/liter of tar acids is from about 0.0033 to 0.08 times the ammonia liquor rate. Therefore, at ammonia liquor rates ranging from 12.7 to 127 gallons per minute, economically permissible caustic solution rates would range from about 0.042 to 10.0 gallons per minute. The use of ratios of caustic to liquor greater than the above economically practical limits, would make the dephenolization costs prohibitive.

The tar acid salts contained in the solution withdrawn from the scrubbing tower are made up of phenolates and cresolates and may be recovered and hydrolyzed to phenol and cresol both of which have great utility in the chemical industry. The recent war effort has greatly increased the need for these basic chemical compounds. The use of large quantities of excess caustic solution in the scrubbing tower results in dilute solutions of tar acid salts, containing large quantities of unreacted caustic. Since shipping costs of such dilute solutions of tar acid salts include the cost of shipping the useless water of solution as well as the excess caustic, such costs are prohibitively high Vunless such water and caustic are removed before shipment. However, the cost of the removal of large quantities of water and caustic from the tar acid salts is as high, if not higher, than the increased shipping costs.

Therefore, the caustic solution-ammonia liquor ratio limits above are necessitated by (l) the prohibitive cost of using excess caustic and (2) the undesirability of obtaining dilute tar acid salt solutions containing large quantities of unreacted caustic. To overcome these disadvantages, methods have been suggested wherein an excess of caustic is utilized with recycling of the caustic-containing tar acid salt solution, but these methods have not proved economically successful.

The practically permissible ratio of gallons of caustic solution to gallons of ammonia liquor for agiven tower area and vapor throughput is greater for ammonia liquor containing greater phenol concentrations. Furthermore, more dilute caustic solutions would permit higher caustic solution-ammonia liquor ratios. The concentrations of tar acids in coke oven ammonia liquor may range from 0.75 to 3.5 grams per liter. The maximum permissible caustic solution concentration is 50 percent and the minimum 4 percent. All these factors have been taken into consideration in computing 0.08 as the maximum permissible ratio of caustic solution to ammonia liquor and 0.0033 as the minimum. However, the usual 4 practical ratios are from 0.01 to 0.02 utilizing from 5-20 percent caustic solution and ammonia liquors containing from 0.75 to 3.5 grams/liter. Therefore, at ammonia liquor rates of 12.7 toV 127 gallons/minute, usual practical caustic solution rates would range from 0.127 to 2.54 gallons/minute.

As has been stated, the efcient contacting of this small quantity of caustic soda solution with the relatively large quantity of vapor required to strip the tar acids from the ammonia liquor in the relatively large scrubbing tower cross sectional area required by such a large quantity of vapor presents a diicu-lt problem. The pressure drop through the tower has to be kept to a low ligure in order to keep the cost of power for the vapor blower within reasonable limits.

The tar acid stripping capacity of the recycled inert vapor passing through the stripping tower decreases accordingly as the amount of volatile tar acid present in the vapor increases. Therefore, if the inert vapor emerging from the scrubbing tower and passing into the stripping tower has not been scrubbed thoroughly so as to remove substantially all the volatile tar acids contained therein, said vapor when recirculated through the stripping tower will not strip out as much tar acid as it would have had the recirculating vapor contained substantially no volatile tar acid.

The total amount of tar acid removed from'the liquor in the stripping tower depends then on the degree of tar acid removal in the scrubbing tower, which in turn depends on the eiiciency with which the t-ar acids are scrubbed from the vapor in said scrubbing tower. However, to obtain eicient scrubbing in the scrubbing ltower, it is essential that the caustic soda solution be thoroughly contacted with the large volume of vapor throughput in spite of the very small quantities of such solution which may be economically used. The problem was handled in the past by building the scrubbing section as well as the stripping section ofthe phenolv tower as packed towers. The ammonia liquor stripping section was packed with wood grids. The caustic soda absorbing section has been packed with spiral tile, lathe turnings and, more recently, manufactured steel spirals. The ammonia liquor rate at conventional and practical vapor rates through the packed stripping section is about the minimum liquid rate for the required tower area at which fairly good liquid-Vapor contact can be maintained in the packed tower of this type. Since the permissible rate of caustic solution utilized in the packed scrubbing tower was only a fractional part of the rate of ammonia liquor utilized in the stripping tower, which in turn was the minimum for good contact with the required tower cross sectional area and volume of vapor, and since the tower cross sectional areas and vapor volumes were required to be the same in both towers, it was evident that the caustic solution rate in the scrubbing section was much too low for etlicient continuous distribution and contact. In order to solve this problem, the caustic soda solution was sprayed onto the packing intermittently for a period of about 15 seconds once every 15 to 30 minutes. This method of operation `distributed the solution eiciently over the top of the packing since the solution was sprayed at a relatively high rate for short periods of time. Contact of the caustic soda solution and vapor depended upon the solution being held up in the packing and gradually .trickling down over a period of 15 to 30 minutes.

Utilizing this system with the economically practical amounts of caustic soda solution as defined above, the dephenolized ammonia liquor still contained 5 percent tar acids which eventually passed into the still waste. Since many state regulations forbid even this small concentration of tar acids, other expensive processes are required to reduce this 5 percent tar acid content of the still wastes.

Furthermore, even this shot system is not practical with higher concentrations of caustic. solution such as from 20 percent to 50 percent, `at which concentrations the caustic solution rate is extremely small. However the use of such higher concentrations of caustic is desired since the resulting tar acid salt solutions withdrawn are more concentrated, therefore requiring less tank cars for shipment, with a resulting savings in shipping costs.

Wi-th this system, obviously some of the soda solution trickled through the packing without contacting the vapor sufficiently to convert much of lthe caustic soda to tar acid salts. Also, with this system, the full volume of the packing was seldom thoroughly wetted with soda solution, resulting in lower efficiency of absorption of ztar acids from the vapor. This was true even when the solution was recycled. These two disadvantages resulted in a higher consumption of caustic soda and a lower eciency of tar acid removal from the ammonia liquor than could be obtained if the caustic soda solution and vapor could be contacted more eiciency.

This invention provides a process and apparatus for providing such a more efficient contact of caustic soda solution and inert vapor.

This invention further provides an improved Shaw vapor recirculation process of, and apparatus for, removing tar acids from liquids containing them, more efficiently and more economically than has heretofore been possible by means of prior vapor recirculation processes and apparatus.

This invention further provides an industrially feasible improved Shaw vapor recirculation process of, and apparatus for, removing tar `acids from ammonia liquors so as to produce a more tar acid-free still waste than has ever been produced heretofore by such process with the same amounts of caustic.

This invention further provides an industrially feasible improved Shaw vapor recirculation process of, and apparatus for, removing tar acids from ammonia liquors so as to produce a still waste as free of tar `acid as has ever been produced heretofore by such a process and `apparatus, utilizing less caustic than has ever lbeen utilized heretofore in such a process and with such an apparatus.

These advantages are effected, with the process and apparatus hereinafter described, by removing acidic gases from the liquor containing tar acids, stripping substantially all of the tar acids from the acidic gas-free liquor with a recirculating inert vapor in a single stripping step, scrubbing substantially lall of the tar acids from the recirculating inent vapor by means of contacting said vapor with a stream of alkaline solution in a bubble cap column, and recirculating the inert vapor to strip substantially all of the tar acids from another quantity of liquor in a single stripping step.

This invention further consists in such other new and useful improvements as may be found to obtain in the processes and apparatus hereafter set forth, described or claimed.

In Ithe accompanying drawings forming a part of this specification are shownV for purposes of exemplication,

a preferred form and manner in which the invention may be embodied and practiced 'but without limiting the claimed invention to such illustrative instance or instances.

Fig. l is a partially diagrammatic view of an ammonia recovery and dephenolization apparatus and system for the practice of the present invention.

Fig. 2 is a horizontal section II-Il of the dephenolization tower of Figure 1.

Fig. 3 is a vertical section III-III of the horizontal section Il--IL The present invention is carried out by utilizing a bubble cap column for the caustic soda solution absorption of phenol from the volatile tar acid-containing inert vapor coming from the phenol stripping tower rather than the intermittently sprayed packed tower of the old Shaw process. The volatile tar acid-containing inert vapor from the stripping tower is passed upwardly, serially and countercurrently to a downward flow of dilute caustic solution through a plurality of vertically superimposed bubble cap or bell trays of a multiple bubble cap column having a thin liquid head of dilute caustic solution on every tray. This inert vapor ow is serially and continuously contacted with a plurality of thin layers of the caustic solution owing continuously across the top surfaces of each of the respective trays transversely to the inert vapor ow. These thin layers of solution ow from a caustic solution inlet portion of each tray to a caustic solution overflow outlet portion of the tray, where the solution finally overows onto the inlet portion of the next lower tray. As the inert vapor `serially ascends the bell trays, its tar acid content is continuously decreased by reaction of the tar acid with the caustic in each of the thin moving layers of caustic solution retained on the trays. The caustic solution is maintained or held up on each tray until substantial equilibrium is approached or attained between the volatile tar acid contained in the inert vapor and the tar acid contained in the caustic solution on that particular tray in the form of tar acid salts, by controlling the rate of ow of the liquid layers across the trays and the depth of the lliquid head on each tray. Since there is practically no leakage off the trays, the rate of flow of the liquid across the trays is the same as the rate of overow of the liquid and the rate of introduction of the solution into the bubble cap column.

VThe caustic solution on each lower tray has a greater tar acid salt concentration and a smaller caustic concentration than the adjacent tray above it. A solution of tar acid saltsand caustic are removed from the bottom of the bubble cap column and a substantially tar acid-free inert vapor passes out of the top of the bubble cap column back to the single stripping zone for further contact with tar acid-containing ammonia liquor for removal of substantially all of the tar acids contained therein. The inert vapor containing the stripped tar acids emerges from the stripping tower and is recirculated back to the bottom of the bubble cap column where it is again scrubbed by a countercurrent ilow of caustic solution. The soda solu tion is fed continuously into the bubble cap column, at the low rate required. Each tray serves as a sort of reservoir of caustic solution providing for continuous contact of caustic solution with the upwardly rising inert vapor. The trays are made to t tightly without leaks, for a relatively small leak would permit all the soda feed to leak out of the tray and no contact would be obtained on that tray. The usual weep holes at the outlet weirs are eliminated for the same reason. Special baliles or hoods are provided over the downspouts and over part of the bubble caps or bells directly adjacent to the downspouts to prevent the solution from being thrown off the trays and into the downspouts by the agitation of the vapor passing through the bubble caps or bells. The overow area of each tray is kept at a minimum by means of dams blocking side portions of the ordinary bubble cap tray overflow area. Since there is no way for the solution to leak off the tray, the residence time of the solution on each tray and the total residence time on all the trays can be controlled perfectly by controlling the rate of introduction of caustic solution into the bubble cap column. Furthermore, since there is no tray leakage, the rate of introduction of caustic solution into the column is the same as the rate of ow of the solution across the trays and the rate of overflow from each tray. The degree of contact of solution and vapor on each tray for any rate of vapor ow depends on the rate of flow of the solution across each tray, and the height of the liquid head on each tray.

The liquid seal over the bubble caps is kept at a minimum in order to keep the pressure drop and ultimately the power requirements as low as possible. The bubble cap or bell trays are spaced widely to eliminate carryover from tray to tray due to foaming. A dry bank of steel spirals is provided above the top tray to prevent carryover of soda solution containing phenol into the stripping section of the tower.

The pressure drop through the bubble cap trays is somewhat higher than the old type packing. To partly compensate forthis .additional pressure drop, the wood grids in the ammonia liquor stripping section are spaced farther apart and the height of the grids increased to provide adequate contact surface with the wider slat spacing. The wider spacing also allows solids in the ammonia liquor to pass through the wood grids, which formerly would have lodged in the packing'eventually plugging the grids.

By the use of this bubble cap column within the limits of the economically feasible caustic flow rates al-l but 2.5 percent or l to 25 parts per millionof the tar acids in the ammonia liquor may be removed. As stated above, the best tar acidrernoval obtained with the old design tower still left 5 percent of the original tar acids in the still waste. Therefore 100 percent more tar acids were left in the ammonia liquor by the old Shaw process than by the present inventive process, utilizing the same economically feasible maximum amount of caustic. It follows that the same amounts of tar acids may be removed from ammonia liquor by the inventive process and apparatus as was removed by the old Shaw process, utilizing less caustic than in the old Shaw process.

These unusual and unexpected results are probably due to the longer contact times made-possible by this invention, between the small quantities of caustic solution and the inert vapor, and the more eicient distribution of the small amounts of available caustic solution for greater Contact of such with the inert gas. All this is brought about by maintaining a long residual time of caustic solution on the bell trays utilizing a sufficient liquid seal to assure a fairly large liquid gas contact area on each tray. By the present inventive process it is possible to contact the very small amounts of caustic required, with the large volumes of inert vapor in the large tower area required more efiiciently than has ever been done before in this type of process with a resulting greater removal of phenol from the inert vapor, and ultimately from the ammonia liquor. Y

If the number of bubble cap trays are increased, the amount of tar acids which can be removed from the arnmonia liquor is increased so that all but la fraction of a percent of the tar acids may be removed from the liquor with the same caustic ow rates. However, the greater the number of bubble cap trays, the greater the pressure drop through the tower and the higher the cost of power for operating t-he vapor blower. Furthermore, the greater the number of trays, thehigher the initial construction costs. Therefore, the number of trays used must be limited to that which will result in reasonable pressure drop and reasonable initial construction costs.

The smallest number of bubble cap trays which can eiiciently be used is dictated by ordinary bubblev cap tower design principles and the desired rate of vapor ow.

The inert vapor volume rates for any particular ammonia liquor rate are conventional and well known in the art.

To obtain suicient tar acid removal so as to leave only 5 percent tar acid in the ammonia liquor by the old Shaw process, the soda solution has to be fed intermittently for only about one minute cut of each hour. Under such conditions it is dii'licult to adjust the soda feed properly. 'i

The relatively large reservoirs of soda solution on the bubble cap trays, as compared with the small quantity of soda solution held up in the packing with the intermittent soda feed, provides a much more stable operation, allowing ample time to adjust the caustic feed rate before the phenol removal and caustic conversion efficiency are affected appreciably.

ri`h-e increasedV pressure drop through the dephenolization tower utilizing the bubble cap scrubbing tower over the packed tower is negligible.

The use of bubble cap trays in the scrubbing section of the dephenolization tower results in much better tar acid removal, greatly increased caustic conversion eiciency and more stable operation than the old Shaw process, utilizing the same economically feasible limits of caustic rate.

Furthermore, as stated above, the use of solutions of higher caustic soda concentrations such as 20-50 percent solutions is impractical in the packed tower since economically feasible caustic rates are so small at such caustic soda concentrations, that only a small portion of the packing at any one time is wet. However, this is not true utilizing the bubble cap column, since the rate of caustic ow into the tower may easily be controlled to accommodate the very small caustic solution rates required at high caustic concentrations. This is an important feature since the higher the caustic concentration used, the less dilute is the tar acid salt solution withdrawn at the bottom of the bubble cap column, necessitating less tank cars for shipment. The shortage of tank cars resulting from the present war crisis renders this an important advantage.

A preferred method of, and apparatus for practicing the present improved process is now described with reference to the accompanying drawings. Ammonia liquor from ammonia liquor storage tank 1 is pumped through conduit means 2 and an ammonia liquor filter 3 by means of pump 4 into free ammonia still 5, where it cornes into intimate contact with a countercurrent flow of hot inert vapor such as steam entering the free ammonia still through connection 6 and/or riser duct 7. The vapor volatilizes and removes free ammonia and other volatile constituents such as the acidic gases CO2, HCN and H2S from the liquor and carries them out of the free ammonia still through a vapor line 8 to an ammonia dephlegmator 9 and hence by means of vapor line 10 to the main coke oven by-product gas line before the primary coolers. Temperatures are adjusted in the free ammonia still by controlling the rate at which steam is supplied to the still from connection 6 and/or riser duct 7 so that substantially all of the free yammonia and acidic gases are removed but a major portion of the tar acids remain in the liquor which collects at the bottom of the free ammonia still, 63, from where it is pumped by means of pump 11 through acidic gas-free ammonia liquor conduit means 12 and 13 and acidic gas-free ammonia liquor sprays 14 or other suitable distributing devices into the tar acid stripping section 15 of a dephenolizing tower 16 containing a top stripping section 15 and a bottom scrubbing section 28 which is composed of a bubble cap column. The liquor is distributed by the sprays 14 over suitable contact material such as wooden hurdles or spiral tile packing with which the section 1S is packed and passes downwardly over this packing. During its downward passage, the hot liquor is intimately contacted with a countercurrent flow of hot inert vapor which volatilizes, strips out and removes tar acids from the acidic gas-free ammonia liquor, forming a Volatile tar acid-inert gas mixture which leaves section 1S as a tar acid-containing inert vapor through a downcomer 18.

The dephenolized liquor collects in a well 19 at the bottom of the stripping section 15 and is returned through a sealed and vented acidic gas-freeA and tar acid-free arnmonia liquor conduit means 20 to the lime mixing tower 21. In this tower, it is mixed with lime or other suitable alkaline material introduced through lime inlet 22 by means of steam brought in through steam inlet 23, which steam passes out of the lime mixing tower into the free ammonia still through connection 6. The lime liberates the fixed ammonia and the liquor overows from the lime mixing tower through lan acidic gas-free, tar acid-free ammonia liquor overflow conduit 24 to the xed ammonia still 25. In this still the lliquor is subjected to further distillation with hot inert vapor such as steam introduced through steam inlet 26 for removal of the previously fixed ammonia, and the vapors pass from the fixed still 25 into the free ammonia still through the riser duct 7.

The distilled liquor or still waste is discharged from the bottom of the fixed still through a still waste outlet 27 to the sewer.

The tar acid-containing inert vapor passes from the downcomer 18 into the bottom of scrubbing sectionor bubble cap column 28, by means of a vapor blower 29. The tar acid-containing inert vapor flows upwardly and serially through a plurality of risers 33 in each of a plurality of vertically superimposed bubble cap or bell trays 3i) supported on tower rings, 31, which in turn, are supported by the shell-walls 32 of the bubble cap column 28. Bubble caps or bells 34 attached to plates 30 by clamp 35, bolt 36, and nut 37, and located over each riser, direct the ow of tar acid-containing inert vapor rising through each respective riser downwardly between the outer walls of each riser and the lower inner walls of the bubble cap or bell to a point below the surface of thin layers of caustic soda solution 38 flowing slowly across the top surfaces of each tray transversely to the upward inert gas flow through the tower. The tar acidcontaining inert vapor bubbles upwardly through that part of the thin layer of solution between that point beneath the liquid layer where the vapor escapes from under the bubble cap and the top surface of the layer, through the space above the thin layer of solution and through risers 33 of the next higher tray 30, until finally a substantially tar acid-free inert gas, emerges from above the uppermost thin layer 38, passes through a dry bank of steel spirals 39, 12 inches deep, and flows upwardly through riser duct 40 into the stripping tower 15, where it again strips tar acid from the descending stream of acidic gas-free ammonia liquor in the Stripping section. The bank of steel spirals is provided above the top tray to prevent carryover of soda solution into the stripping section 15 of the tower. The thin layers of caustic solution are supplied by pumping at controlled rates, by means of pump 42, a flow of hot caustic soda from a caustic storage tank 40 to a dilution tank 41, where it is diluted with water to a desired caustic concentration while maintaining the solution hot by means of introducing steam, thence to a flowmeter 43 and then to the caustic soda inlet 44 of the scrubbing section onto vthe caustic solution inlet portion of the top tray where it flows slowly in a thin layer across the top surface of the tray over an adjustable weir at an outlet overow portion 64, of the tray. The adjustable weir comprises a fixed weir member 44 attached to the overflow outlet portion 64 of the tray and having at least one protruding threaded stud, an adjustable Weir member 45 adjustably attached to the fixed weir member by means of at least one elongated slot in said adjustable weir member through which the protruding threaded stud of said fixed weir member passes. The weir height may be adjusted by immovably fixing said threaded stud in any portion of said slot by means of at least one tightening nut applied to the threaded portion of said stud. The height of the adjustable weir may be adjusted to maintain any desired depth of the thin layer of liquid on the tray. The solution overflows over the adjustable weir of the top tray through downspout 46 onto the caustic solution inlet portion 65 of the next lower tray, and thence in a thin layer across said next lower tray to its overflow outlet portion 64 where it overflows to the inlet portion 65 of the next lower tray and so on until the solution has flowed in thin layers across all the trays to the bottom tray, where it finally passes from the downspout of such bottom tray and collects on a sloped bottom portion of the scrubbing tower 59. Each of the ascending thin caustic solution layers removes more tar acid from the ascending flow of inert vapor by reaction of said tar acid with caustic in said solution, until the inert vapor emerging from the top ythin layer of solution is substantially tar acid free. The tar acid on reaction with the caustic in the solution layers forms tar acid salts which dissolve in the caustic solution and ilow with the solution to the lower layer where more tar acid salts are picked up. Each descending layer therefore contains more tar acid salts and less caustic than its next adjacent higher layer. The tar acidcaustic solution passes from the bottom of scrubbing section 28 through a pipe 47 to a reboiler evaporator 48 where part of the water of solution is evaporated by boiling. The solution flows around a bank of tubes through which live steam from steam line 52 is passed. The heat from the steam evaporates part of the water of solution and the concentrated solution passes through a vented pipe 49 to a storage tank 50. The water of evaporation in the form of steam flows through steam line 51 back into the bottom of the bubble cap column, where it serves to maintain the bubble cap column temperature at about the boiling point of the liquid solution in the column, and as a source of inert vapor.

The amount of evaporation of the tar acid salt solution varies according to the temperature in the reboiler evaporator which is controlled by the amounts of live steam entering the bank of tubes. The reboiler may be supplied with a thermostatic device to maintain a constant desired reboiler temperature. When the temperature falls below this point a valve 65 is automatically opened allowing steam to pass through the reboiler tubes until the desiredtemperature within the reboiler is reached and the valve is then automatically closed. The scrubbing tower 28 and the free ammonia still 5 are each vented by means of respective vent lines 60 and 61 to vapor line 8. Vent line 60 has a valve 62. in the ammonia liquor which are not removed in the free ammonia still 5, and excess amounts of steam coming from reboiler 48 through line 51 tend to build up in the dephenolization tower resulting in a pressure build-up in the closed dephenolization system. Vent line 60 prevents such a build up. Valve 62 may be automatically controlled to maintain a constant desired pressure in vapor line 60 and dephenolization tower 16.

To prevent the solution on the trays from being thrown off the trays and into the downspouts by the agitation of the vapor passing through the bubble caps, special adjustable hoods are provided directly above the outlet overflow portion of each tray. Each adjustable hood is comprised of a fixed hood member S3, attached to the bubble cap column wall above the overflow outlet portion of each tray having at least one protruding threaded stud, and an adjustable hood member 54 adjustably attached to the fixed hood member by means of at least one elongated slot through which the threaded stud of the fixed hood member passes. The effective hood length may be adjusted by immovably fixing the stud in any portion of the slot by means of at least one tightening nut 55 applied to the threaded portion of the stud. To

prevent spraying close to the overflow outlets, resulting in spray being thrown off the trays into the downspout, the bubble caps or bells directly adjacent to the overflow outlet of each tray are supplied with half covers or straps 56, which circumferentially cover the half of the periphery of each bubble cap facing the overflow outlet portion of the tray. These covers prevent inert vapor from bubbling up from under the half of the bubble cap or bell facing the overflow outlet portion of the tray.

The overflow outlet portion 64 of each circular tray is formed by the chord of a cut out end segment of each circular tray 30. The weir 44 and 45 extends across the entire chord of the tray segment.

In no wise is the use of the principle limited to such single illustrative instance. For example, any type of standard bubble cap tray arrangement may be utilized wherein thin layers of liquid may be maintained on each tray for a controlled period of time and flowed across each entire tray area at a controlled rate.

For instance, the overflow outlets of all the trays may fall in the same vertical plane with downspouts carrying the Inert gases contained t l l overow liquid of each tray to the peripheral extremities of the next lower tray opposite from the peripheral vextremities at which the overflow outlet of such tray is located. However, the liquid overow and Idownspout arrangement disclosed in the drawings is preferred.

The Weir heights may be adjusted to maintain the depth of the thin liquid layers on the trays so as to give a liquid head or seal of from 1A `inch to 11/2 inches. However, a liquid head of from to 1" is preferred. The optimum liquid head is 1/2. The invention is not limited to the range of liquid heads given above. The greatest depth of liquid head which may be utilized is limited only by reasonable power costs to compensate for the increased pressure drop. Y

The rate of ammonia liquor feed into the dephenolization tower may be from 0.2 to 2.0 gallons per minute per square foot of cross-sectional area. The preferred rate is 0.5-1.0 gals./min./ft.2 of tower area, and the optimum rate is 0.9 gals./min./ft.2 of tower area. The ammonia liquor may contain .75 to 3.5 grams per liter of tar acid depending on the type of ammonia liquor utilized. However, the invention is not limited to any range of ammonia liquor feed rates; and it may be utilized with any desired rate of ammonia liquor feed, containing the various amounts of tar acids found in all types of ammonia liquor. The economically permissible limits of caustic solution rate-ammonia liquor rate ratios with from 4% to 50% caustic concentration and liquor containing from 0.75 to 3.5 grams per liter of tar acid are from 0.0033 to 0.080. The preferred ratio of caustic soda solution rate to ammonia liquor rate is from 0.01 to 0.02 utilizing from 5 to 20% caustic solution and ammonia liquors containing from 0.75-3.5 grams of tar acids per liter.

These ammonia-liquor-caustic solution ratio limits are Y applicable to any ammonia liquor feed rate containing the various amounts of tar acids found in all types of ammonia liquors. The optimum ratio is about .01 utilizing a caustic solution, with a rate of ammonia liquor feed of about 0.9 gals./min./ft.2 of tower area, and an ammonia liquor containing 0.91 grams of tar acid per liter.

From the above ratios, one may compute that the highest permissible rate of caustic solution feed at from 4% to 50% concentrationis from about .0007 to 0.16 gals./min./ft.2. However, the preferred rates are from 0.005 to .02 gals./min./ft.2 using a5 to 20% caustic solution. The optimum caustic solution rate utilizing a 10% caustic solution with a rate of ammonia liquor feed of 0.9 gaL/mirL/ft.2 of tower area is .009 gal./min./ft.2. Although caustic soda (sodium hydroxide) solution is preferred as an alkaline solution, any alkali metal hydroxide is suitable. ln fact anynmetal hydroxide which is soluble in water is satisfactory.

Although lime (calcium hydroxide) is preferred in freeing fixed ammonium compounds in the lime tower, any alkaline earth met-al hydroxide is satisfactory.

Other inert gases than steam may be utilized to strip out the ammonia from the ammonia stills including all those inert gases mentioned below as being suitable ,for stripping tar acids from the liquor.

As a specic example of the inventive process, a feed of 3600 gai/hr. of ammonia liquor containing .91 gram of tar acid per liter, after being passed through the free ammonia still where the acidic gases were removed, was introduced with 36 gallons per hour `of a 10% caustic solution into a dephenolization tower as shown in the drawings, utilizing steam as an inert vapor.

Five bubblercap trays were used each 63.5' square feet with 104 standard bubble caps and a liquid head of solution of 1/2 inch. The temperature in the stripping section of the tower was 102 C. The time of residence of the caustic solution on each tray was over 3 hours and the total time of residence Von all the 'trays was over 16 hours. Y The tar acid concentratiorgin the .dephenolized l2 liquor leaving the tower was 0.024 gram/liter. The temperature in the reboiler evaporator was C.

4 Thus, the percentage of tar acid remaining in the dephenolized ammonia liquor, and therefore in the still waste was 2.6% of the tar acid originally contained.

The term, inert vapor, utilized in this speciiication and in the claims includes inert gases such as air, nitrogen, ammonia or coke oven gas saturated with water vapor as well as inert vapors such as steam. Steam is preferred.

It is essential that the acidic gases be removed from the ammonia liquor in the free ammonia still prior to introducing the liquor into the scrubbing tower since failure to do so would result in reaction between the caustic in the scrubbing tower and the acidic gases, wherein undesirable products are formed with an increased consumption of caustic.

The temperature maintained in the dephenolizer is regulated so that the tar acid-free liquor leaves the stripping section at its boiling point. The temperature of the recirculated vapor leaving the stripping section is also at about the boiling point of the liquor.

Complete insulation ofthe tower and conduits is important in keeping this temperature approximately constant.

It is to be understood that in the foregoing description the term phenols is synonymous with tar acids and includes phenol, cresol and their homologues. Similarly, dephenolization signifies the removal of these tar acids; and dephenolization tower the apparatus in which such removalris practiced.

Furthermore, although the inventive process has been described in connection with the removal of tar acids from ammoniacal gas liquor, it is not limited to that application, but is broadly adapted to the treatment of any liquid containing tar acids or phenol or cresol.

Although an attempt has been made to explain the theoretical basis for the unexpected results obtained in the practice of the present invention, it is to be understood that the invention is not limited to any particular theory.

It will be obvious to those skilled in the art that various modifications can be made in the several parts of the present apparatus and the several steps of the present process in addition to those enumerated hereinabove without departing from the spirit of the invention, and it is intended to cover in the claims such modifications as are included within the scope thereof.

I claim:

l. An apparatus for removing tar acid from a tar acidcontaining liquid comprising: a single dephenolization tower having a single top stripping section and a single bottom scrubbing section; a volatile tar acid-containing inert vapor conduit leading from volatile tar acid-containing inert vapor outlet means at an upper portion of the stripping section to volatile tar acid-containing inert vapor inlet means at a bottom portion of said scrubbing section; tar acid-containing liquid spray inlet means at an upper portion of said stripping section; tar acid saltcontaining liquid outlet means at a lower portion of said scrubbing section; caustic solution inlet means at an upper portion of said scrubbing section; vented tar acidfree liquor outlet means at a lower portion of said stripping section; partition means separating the stripping section from the scrubbing section; riser duct means leading from said scrubbing section to said stripping section through said partition means, for owing tar acid-free inert vapor from said scrubbing section to said stripping section; steam-inlet means at a lower portion of said scrubbing portion; volatile tar acid-containing inert vapor outlet means at an upper portion of the stripping section; volatile tar acid-containing inert vapor inlet means at a lower portion of said scrubbing section; vapor vent means located at an upper portion of said-scrubbing section, for preventing inert gases and vapors from building up pressure in the dephenolization tower; a plurality of vertically spaced superimposed bubble cap trays within7 and attached to, in gas-tight relation with the surrounding shell of the scrubbing section and interposed between said volatile tar acid-containing inert vapor inlet means and said partition means that separate the sections, said caustic solution inlet means being located lat a distance above the top tray below the normal liquid level of the liquid on said top tray; means for slowly owing thin, parallel, vertically spaced, superimposed, horizontal layers of dilute caustic solution across the tops of said trays transversely and countercurrently to, and in contact relationship with, an upward ow of tar acid-containing inert gas through the scrubbing section, said lastmentioned means comprising means on each of said trays for overflowing each of said slowly moving thin liquid layers over adjustable weir means onto the adjacent next lower slowly moving layer and also adjustable Weir means attached to each bubble cap tray adjacent to said overflow means for maintaining the liquid layer thickness on top of each of the bubble cap trays; adjustable hood means located directly above the overflow means of each tray and attached to the scrubbing section, for preventing liquid on each tray from splashing over said Weir means and into said overflow means; cover means attached to each of those bubble caps directly adjacent to the overllow means of each tray and circumferentially covering the half of the periphery of each of said adjacent bubble caps facing said overow means, to prevent vapor from escaping from under said half of the peripheries of each of said adjacent bubble caps; and means located below said partititon means and above the uppermost bubble cap tray for preventing liquid from passing from the scrubbing section to the stripping section.

2. An apparatus for removing tar acid from a tar acidcontaining coke-oven ammonia gas liquor comprising: a free ammonia still for removing volatile acidic gases from said liquor; a single tar acid stripping tower for stripping tar acids from the acidic gas-free ammonia liquor; conduit means for ow of the acidic-gas-free ammonia liquor from said free ammonia still downwardly through said tar acid stripping tower; means for passing a hot inert Vapor upwardly through the downward ow of said acidic-gas-free ammonia liquor in said stripping tower to Volatilize and strip out the tar acids contained in the acidic-gas-free ammonia liquor and thereby form a volatile tar acid-inert vapor mixture and an acidic-gas-free, tar acid-free ammonia liquor; a lime mixing tower for freeing xed ammonia compounds in the acidic-gas-free and tar acid-free ammonia liquor; a conduit means for owing said acidic-gas-free and tar acid-free ammonia liquor from said stripping tower to said lime mixing tower; a flxed ammonia still for removing the ammonia set free in the lime mixing tower from the acidic-gas and tar acid-free ammonia liquor; conduit means for owing acidic-gas-free and tar acid-free ammonia liquor containing the freed ammonia from said lime mixing tower to said fixed ammonia still; a single tar acid scrubbing tower comprising an upright shell for scrubbing the volatile tar acid from said tar acid-inert vapor mixture; a plurality of vertically spaced, superimposed bubble cap trays interposed within, and attached in gas-tight relation with said shell; tar acid-inert vapor mixture inlet means to the shell below said plurality of trays; tar acid-free inert vapor outlet means from the shell above said plurality of trays, make up steam inlet means to the shell below said plurality of trays; means for slowly flowing thin, parallel, vertically spaced, superimposed horizontal layers of dilute caustic solution across said trays transversely and countercurrently to, and in contact relationship with, an upward flow of tar acid-inert vapor mixture through the shell of the scrubbing tower, said last-mentioned means comprising dilute caustic so lution inlet means to the shell above and for said plurality of trays said caustic solution inlet means being located at a distance above the top tray below the normal liquid level of the liquid on said top tray, overflow means located on each tray for overowing each of said thin liquid layers onto the next lower slowly moving layer, and adjustable weir means located on each tray adjacent to said overow means for maintaining a controlled thin depth of liquid on top of each of said trays; a tar acid salt solution outlet from the shell below said plurality of trays; conduit means for flowing tar acid-inert vapor mixture from the top of said stripping tower to said tar acid-inert vapor mixture inlet of said scrubbing tower; reboiler means for concentrating a tar acid salt solution by the evaporation of part of its water of solution; conduit means for flowing a tar acid salt solution from said tar acid salt solution outlet of said scrubbing tower to said reboiler means; conduit means for owing the water of evaporation of the tar acid salt solution produced in said reboiler means from said reboiler means to said steam inlet means of said scrubbing tower; automatic means for maintaining a constant, predetermined temperature of the tar acid salt solution in the reboiler means; and automatic means for maintaining a constant, predetermined pressure within the scrubbing tower.

References Cited in the le of this patent UNITED STATES PATENTS 1,957,295 Shaw May l, 1934 2,056,748 Taylor Oct. 6, 1936 2,127,503 Denig Aug. 23, 1938 2,263,688 Allen et al Nov. 25, 1941 2,274,041 Cook et al. Feb. 24, 1942 2,338,446 Lambert Jan. 4, 1944 2,376,940 Riemenschneider May 29, 1945 2,398,213 Dutson, Ir. et al. Apr. 9, 1946 2,520,391 Findlay Aug. 29, 1950

Claims (1)

1. AN APPARATUS FOR REMOVING TAR ACID FROM A TAR ACIDCONTAINING LIQUID COMPRISING: A SINGLE DEPHENOLIZATION TOWER HAVING A SINGLE TOP STRIPPING SECTTION AND A SINGLE BOTTOM SCRUBBING SECTION; A VOLATILE TAR ACID-CONTAINING INERT VAPOR CONDIUT LEADING FROM VOLATILE TAR ACID-CONTAINING INERT VAPOR OUTLET MEANS AT AN UPPER PORION OF THE STRIPPING SECTION TO VOLATILE TAR ACID-CONTAINING INERT VAPOR INLET MEANS AT A BOTTOM PORTION OF SAID SCRUBBING SECTION; TAR ACID-CONTAINING LIQUID SPRAY INLET MEANS AT AN UPPER PORTION OF SAID STRIPPING SECTION; TAR ACID SALTCONTAINING LIQUID OUTLET MEANS AT ALOWER PORTION OF SAID SCRUBBING SECTIONF CAUSTIC SOLUTION INLET MEANS AT AN UPPER PORTION OF SAID SCRUBBING SECTION; VENTED TAR ACIDFREE LIQUOR OUTLET MEANS AT A LOWER PORTION OF SAID STRIPPING SECTION; PARTITION MEANS SEPARATING THE STRIPPING SECTION FROM THE SCRUBBING SECTION; RISER DUCT MEANS LEADING FROM SAID SCRUBBING SECTION TO SAID STRIPPING SECTION THROUGH SAID PARTITION MEANS, FOR FLOWING TAR ACID-FREE INERT VAPOR FROM SAID SCRUBBING SECTION TO SAID STRIPPING SECTION; STEAM-INLET MEANS AT A LOWER PORTION OF SAID SCRUBBING PORTION; VOLATILE TAR ACID-CONTAINING INERT VAPOR OUTLET MEANS AT AN UPPER PORTION OF THE STRIPPING SECTION; VOLATILE TAR ACID-CONTAINING INERT VAPOR INLET MEANS AT A LOWER PORTION OF SAID SCRUBBING SECTION; VAPOR VENT MEANS LOCATED AT AN UPPER PORTION OF SAID SCRUBBING SECTION, FOR PREVENTING INERT GASES AND VAPORS FROM BUILDING UP PRESSURE IN THE DEPHENOLIZATION TOWER; A PLURALITY OF VERTICALLY SPACED SUPERIMPOSED BUBBLE CAP TRAYS WITHIN, AND ATTACHED TO, IN GAS-TIGHT RELATION WITH THE SURROUNDING SHELL OF THE SCRUBBING SECTION AND INTERPOSED BETWEEN SAID VOLATILE TAR ACID-CONTAINING INERT VAPOR INLET MEANS AND SAID PORTION MEANS THAT SEPARATE THE SECTIONS, SAID CAUSTIC SOLUTION INLET MEANS BEING LOCATED AT A DISTANCE ABOVE THE TOP TRAY BELOW THE NORMAL LIQUID LEVEL OF THE LIQUID ON SAID TOP TRAY; MEANS FOR SLOWLY FLOWING THIN, PARALLEL, VERTICALLY SPACED, SUPERIMPOSED, HORIZONTAL LAYERS OF DILUTE CAUSTIC SOLUTION ACROSS THE TOPS OF SAID TRAYS TRANSVERSELY AND COUNTERCURRENTLY TO, AND IN CONTACT RELATIONSHIP WITH, AN UPWARD FLOW OF TAR ACID-CONTAINING INERT GAS THROUGH THE SCRUBBING SECTION, SAID LASTMENTIONED MEANS COMPRISING MEANS ON EACH OF SAID TRAYS FOR OVERFLOWING EACH OF SAID SLOWLY MOVING THIN LIQUID LAYERS OVER ADJUSTABVLE WEIR MEANS ONTO THE ADJACENT NEXT LOWER SLOWLY MOVING LAYER AND ALSO ADJUSTABLE WEIR MEANS ATTACHED TO EACH BUBBLE CAP TRAY ADJACENT TO SAID OVERFLOW MEANS FOR MAINTAINING THE LIQUID LAYER THICKNESS ON TOP OF EACH OF THE BUBBLE CAP TRAYS; ADJUSTABLE HOOD MEANS LOCATED DIRECTLY ABOVE THE OPVERFLOW MEANS OF EACH TRAY AND ATTACHED TO THE SCRUBBING SECTION, FOR PREVENTING LIQUID ON EACH TRAY FRO SPLASHING OVER SAID WEIR MEANS AND INTO SAID OVERFLOW MEANS; COVER MEANS ATTACHED TO EACH OF THOSE BUBBLE CAPS DIRECTLY ADJACENT TO THE OVERFLOW MEANS OF EACH TRAY AND CIRCUMFERENTIALLY COVERING THE HALF OF THE PERIPHERY OF EACH OF SAID ADJACENT BUBBLE CAPS FACING SAID OVERFLOW MEANS, TO PREVENT VAPOR FROM ESCAPING FROM UNDER SAID HALF OF THE PERIPPHERIES OF EACH OF SAID ADJACENT BUBBLE CAPS; AND MEANS LOCATED BELOW SAID PARTITITON MEANS AND ABOVE THE UPPERMOST BUBBLE CAP TRAY FOR PREVENTING LIQUID FRO M PASSING FROM THE SCRUBBING SECTION TO THE STRIPPING SECTION.

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