LU81802A1 - PROCESS FOR PURIFYING WASTEWATER - Google Patents

Description

"* 4 *

I BL — 2740 / EM / BM

c-Js ^ Bevendiaation of the priority of a patent application ß * ~ - filed in Belgium on 20 oetobre 1978 under J No 871.436 C 1907/7810.

METALLURGICAL RESEARCH CENTER -CENTRUM V00R RESEARCH IN DE METALLURGIE,

Nonprofit organization -

Vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Process for purifying waste water.

4 t

The present invention relates to improvements to the methods for purifying waste water, applicable in particular to the purification of coke oven waste water.

It is known that the most widespread treatment method currently used to purify coke oven waste water consists first of all in removing volatile mineral elements (NH3, HCN, H2S, C02) and a small fraction of the phenol compounds by distillation or by Steam stripping with simultaneous treatment with lime or soda, to liberate am-I moniac from its fixed salts. The waters are then freed from / t 2.- residual phenols and non-volatile elements such as sulfo-cyanides, etc., by biological oxidation; ammonia vapors are either destroyed in suitable incinerators with controlled formation of nitrogen oxides, or treated with sulfuric acid for the production of ammonium sulfate.

We also know the importance that this desorption operation has in the purification cycle of coke oven wastewater. An insufficiency in this operation leads notably to the following well-known drawbacks: * a) the overload of biological basins where certain inhibition effects can jeopardize the very effectiveness of the treatment, b) the need for additional finishing treatment = -> ant rejection of water in the natural environment (for example will treat with activated carbon, ...), c) the risk of atmospheric pollution above the basirr <3 'aeration, by entrainment of residual volatile matter, • it as a result, it is quite obvious that the desorption operation, whether it has been carried out by distillation or by stripping, must be pushed until it is practically carried out: - encroachment, to be considered as fully effective.

To carry out such a purification, one. a dice; - -ro_ * m posed a process in which one makes use of a fall of Stripping containing in particular a number of plateatrx, substantially horizontal, arranged one above the other, £ l ~ entée at its upper part by the waste water to be puoifier has its lower part by steam and laterally, â. an r. Several levels, strong base. According to this process, the ammor salts. ^; AuX / whether volatile or not, are eliminated almost o-omplèr-s ^ t des! - waste water, while other compounds such as ^ bhenols, sulfocyanides, complex cyanides, etc: ..., î.-r removed from these waters by a process of biological oxidation, Λ i 3.- Unlike the process recalled above, the object of the present invention is to reveal a process for the purification of waste water, such as coke oven water, according to which not only is it rid of the ammoniacal elements in the co-; lonne of stripping, but they also get rid of most of the other pollutants such as phenols, sulfocyanides; and complex cyanides.

| With this in mind, the same applicant has already proposed a method according to which, in a stripping column comprising a number of substantially horizontal plates, arranged one above the other, said column being supplied at its upper part by the waste water to be purified and at its lower part by a stripping fluid, a strong base is introduced laterally, at least at one level of the column, into the zone of decomposition of fixed ammonium salts and, at least at another level of this same column, in the phenol elimination zone, an injection of acids such as for example HCl or ^ SO ^.

Departing from the latter process, that described in the invention, implemented in a stripping column for waste water comprising the two usual zones for removing volatile and fixed ammoniacal compounds, is characterized by the fact that, 4 in addition to the introduction of basic elements at a certain level of the column to allow the stripping of fixed ammoniacal salts, there is also introduced into this same column, in one or more levels, one or more agents of oxidizing nature, alone or mixed.

The method of the invention can be implemented regardless of the type of stripping columns used, for example columns of trays of all kinds, columns with packing, stacking, spraying, etc.

It has indeed been observed that in these columns, the. phenols and similar compounds could undergo sufficient degradation by oxidation to be removed from water during stripping, preferably under special pH conditions, most often different from those which allowed their removal without oxidation phenomenon .

It is not excluded, according to the invention, to use catalysts for phenol oxidation reactions or the like, which facilitates the start of the process and increases the yield. It is possible at this rate, in the case of an oxidation by H2 ° 2 '^ a ^ re ^ used ^ for example of ferrous iron salts or metallic copper, preferably finely divided.

According to a first variant of the process of the invention, the oxidizing agent (s) added in addition to the stripping column have their degrading nature, especially in basic medium. Such are for example the cases of monopersulfuric acid (^ SO ^) effective at pH ~ 10, ammonium dipersulfate (NH.) „. S „0o, also effective at pH ~ 10, as well as potassium iron ferrate VI (K2Fe04) and ozone (03) effective at pH ^ 8.

According to this first variant, the oxidizing agents are preferably introduced into the stripping column, whatever its type, in two very specific ways: 1. simultaneously, with one or more basic agents such as Ca (OH) or NaOH; alkaline agents have their own action for the elimination of fixed ammonia, while oxidants exert their degrading power, in this basic medium, on phenol compounds or the like.

2. after prior alkalization and elimination of fixed ammonia.

In the case mentioned under 1., the stripping column essentially comprises two regions, namely ï from top to bottom, a region where the elimination of the free ammonia takes place and a region where the elimination takes place simultaneously. fixed ammonia and the oxidation of phenol compounds.

t On the other hand, in the case listed under 2, the case column. stripping essentially comprises three superimposed regions, at i j- j! Cx _! * i,. .

j know from top to bottom, successively an area where one eliminates the free ammonia, an area where one eliminates fixed ammonia and one area where one oxidizes the phenol compounds.

According to a second variant of the process of the invention, the oxidizing agent or agents added in addition to the stripping column have their degrading nature, essentially in an acid medium, such as for example hydrogen peroxide (^ C ^) which exerts its oxidizing action in an area where the pH is around 3 to 4.

>. According to this second variant, it is possible, with advantage, to introduce the oxidizing agents in the following ways: a) simultaneous introduction with one or more acid agents (such as for example HNO3, HCl, H2SC> 4); these exert their own action of elimination of phenols, essentially by deionization and hydrolysis, whereas the oxidizing agents exert, in the same place, their oxidizing action on these same phenols. A stripping column operating according to this process essentially comprises, from top to bottom, 3 successive regions, namely the region where the elimination of volatile ammonia takes place, a region where s1 simultaneously effect elimination by deionization and hydrolysis and the oxidation of phenol compounds or the like in an acid medium, the region where the elimination of fixed ammonia takes place.

b) introduction of the oxidizing agents, after the acidification of one of the regions of the column and the elimination of a significant part of the phenols, essentially by deionization and hydrolysis. In this case, the stripping column successively comprises 4 regions, namely, from top to bottom, a region where the elimination of free ammonia is carried out, a region at acidic pH, where the elimination of phenols is carried out. , essentially by deionization and hydrolysis, a region where the oxidation of com-. posed remaining phenolics, and a region where the elimination of fixed ammonia takes place.

6.-% c) in the case. · Where in the stripping column a region of acid character is naturally created between the two usual regions of basic character, the oxidizing agents are introduced into this region at the place where the pH corresponds to the efficiency range of the oxidant (s). Such a stripping column has only two regions, namely, from top to bottom, that of the elimination of free ammonia, where the pH drops progressively and naturally, to values allowing the introduction, with effective action, of the oxidizing agent (s) considered and that in which the fixed ammonia is eliminated.

,. d) in the case where the degradation of phenols and similar elements is carried out on waste water already rid of its volatile and fixed ammoniacal elements, the column will comprise three regions, namely, from top to bottom, the region where the the free ammonia is eliminated, the region where the fixed ammonia is eliminated and the region where the phenols and the like are degraded. The introduction of the acid elements and of the oxidizing elements effective in an acid medium then takes place at the upper part of the lower region.

It does not, however, depart from the field of the invention to practice, at the top of the column, the elimination and / or degradation (by oxidation), of phenols and of similar elements, in which case, substantially at the level of the introduction. water to be stripped, acid elements are also introduced into the column (for example H2SO4, HCl, HN03), whether or not accompanied by oxidizing agents effective in acidic medium, these however being able to be introduced into the column to somewhat lower, but still in the acidic region. The same remark is made with respect to injections of oxidizing agents, effective either in basic medium or in medium at any pH, which can also be introduced at the head of the column.

7.-

According to a third variant of the process of the invention, use is made of an oxidizing agent such as, for example, chlorine dioxide (CIO), oxygen-enriched air, pure oxygen I ^ I '( under appropriate pressure in the column), the introduction of which can! take place in any region of the stripping column, its action on the phenols being exerted whatever the pH of the water to be stripped, at the site of the injection. We can therefore use this CK ^ in any of the columns provided above, where in a usual co-'j lonne comprising only the two regions where the free ammonia and fixed ammonia, the place of l 'introduction of CK ^' in this column being indifferent for its oxidizing action on phenol compounds and the like.

According to a fourth variant of the process of the invention, use is made of one or more oxidizing agents, having their zone of activity in a region where the pH is between 6.5 and 7.5. This category includes, in particular, chlorine (C ^) or sodium hypochlorite (NaOCl) which are to be introduced into the stripping column after elimination of the free ammonia in the appropriate pH zone, but before the basic treatment of elimination of fixed ammonia. According to this variant, there is a real advantage in carrying out this introduction in a place where the pH is indeed very close to 7.

The diagrams below, given by way of nonlimiting example and not to scale, make it possible to better understand how it is possible to design a stripping column of the * plate type allowing the implementation of the process of invention, in its different variants. These diagrams all relate to columns of the type with perforated plates, but it is repeated here that the method applies to all kinds of columns, in which case the diagrams could be modified (in particular as regards the circuit water to be stripped), without the principles implemented being al-J tered.

r 8.-

Figures la and Ib relate to the introduction of an effective oxidizing agent in basic medium, Figures 11a, Ilb, Ile and Ild relate to the introduction of an oxidizing agent, effective in acid medium. Figure III relates to the introduction of an oxidizing agent, effective in acidic and basic medium, Figure IV relates to the introduction of an effective oxidizing agent in the pH range between 6.5 and 7.5 .

In FIG. 1a, the column of the tray type / is composed of two regions, namely that 1 where the elimination of free ammonia is carried out and that 2 where one eliminates. 1 fixed ammonia * as well as phenols and the like. The water to be stripped is introduced at 3 to the upper part of region 1, the stripping fluid is introduced at 4 to the lower part of region 2. At the top of the column escapes at 5 the charged stripping fluid ammonia and other volatile pollutants, as well as degradation products of phenols by oxidation, while in 6, the stripped water is discharged, also accompanied by degradation products of phenols. The two regions 1 and 2 are separated by a partition 7 allowing only elements of vapor or gas to pass, in the direction 2 - * - l. The waters being stripped are evacuated from region 1 by its base (at 8) and introduced to the upper part of region 2 at 9 with a supply of lime milk at 10. Oxidizing agents, effective in basic medium are introduced in 11 at the top of region 2, they can be through the same conduits as milk of lime. Such a device has the advantage of a smaller number of plates, and therefore of lesser investment.

In FIG. 1b, the stripping column, of the plate type, is composed of three superimposed regions, namely from top to bottom, in 1 the region where the free ammonia is eliminated, in 2 the region where is eliminated ammonia fixes, in 3 the region where the phenol elements and the like are oxidized. The stripper waters are introduced in 4 to the upper part of region 1, the fluid of! stripping is introduced at 5 at the bottom of region 3. At the upper part of the column, the stripping fluid is discharged at 6 - charged with ammonia and other volatile pollutants, as well as pro-! phenol degradation products; in 7, the water stripped off with phenol degradation products is discharged. Regions 1 and 2 are separated by a wall 8 allowing only vapor or gaseous elements to pass, in the direction 2 - * - 1; regions 2 and 3 are separated by a wall 9 allowing the vapor or gaseous elements to pass, in the direction 3 - 2 and the liquid in the direction 2 - ► 3.

Leaving region 1, the waters being stripped are directed by 10 and 11 towards the upper part of region 2. The introduc- | lime milk from 12 can be made in the region! 2, by this same line 11. The oxidizing agents, effective in • basic medium are introduced at 13 at the upper part of [region 3, where they can oxidize phenols and the like. A stripping column of the kind shown in the diagram in FIG. 1b has the advantage of requiring only a lower consumption of oxidizing reagent and stripping fluid.

In FIG. 11a, a stripping column, of the plate type, is schematically represented, in which use is made of oxidizing agents, effective in an acid medium. This column has three regions, namely from top to bottom, region 1 where the elimination of free ammonia takes place, at 2 the region where the oxidation of phenols takes place at the same time as their elimination by vapor in an acid medium, in 3 the region where the elimination of fixed ammonia takes place. The column is supplied with water to be stripped at 4 at the top of region 1, the column is supplied with stripping fluid on the one hand, at 5 at the base of the region 3 and on the other hand in 6, at the base of region 2; in 7, the stripped water is discharged, with phenol degradation products, while at the top of the column, the discharge of the stripping fluid loaded with ammonia and other volatile pollutants as well as phenol degradation products s 'performs in 8.

Regions 1 and 2 are separated by a partition 9 allowing in the direction 2 - 1, the passage of the vapor / or gaseous elements and in the direction 1 - ► 2, the passage of the liquid.

10.-.

Regions 2 and 3 are separated at 10 by a sealed wall preventing any communication between them. The acid agents are introduced at 11 at the top of the region 2 / - as is the introduction at 12 of the oxidizing agents effective in acid medium. The waters being stripped cross the wall 9 to go from region 1 to region 2, they arrive in region 3 via the outlet pipe 13 located at the bottom of region 2 and the reentry pipe 14 at the top of region 3; the supply of lime milk 15 to the column can be done by the same pipe as 14. The fixed ammonia released in 3 is driven into region 1, • without possible contact with region 2, for example by means of a pipe 16 crossing the latter from side to side. It should be understood that in region 2, the action of acid agents and that of oxidizing agents, effective in acid medium are cumulative on phenols and the like. Such a column has the advantage of a lower number of plates, and therefore of a lower investment.

The diagram of FIG. 1b shows a stripping column of the plate type, into which oxidizing agents are introduced, effective in acid medium, in a place where a significant part of the phenols and the like has already been eliminated by the vapor, in an acidic region of the column, character obtained by injection, into it, of acid elements such as for example HCl, ^ SO ^.

"

Such a column presents, from top to bottom, four regions, namely at 1, the region where is eliminated. · - the free ammonia at 2, the region where phenols and the like are subjected to the action of acidic agents , in 3 the region where the phenols and the like are subjected to the action of oxidizing agents, effective in an acid medium, in 4 the region where the fixed ammonia is eliminated.

The water to be stripped is introduced at 5 at the top of region 1, the stripping fluid is introduced at 6 at the base of region 4 and in 7 at the base of region 3. The evacuation of stripped water and products. degradation of phenols is carried out in 8 at the bottom of the column, I while that of the stripping fluid loaded with ammonia or other 11.- volatile pollutants and products of degradation of phenols is carried out in 9 at the top of the column . Regions 1 and 2 are separated by a wall 10 allowing the vapor and gaseous elements to pass from bottom to top and the liquid from top to bottom. It is the same for the wall 11 separating region 2 from region 3. The wall 12 separating regions 3 and 4 is impermeable, the fixed ammonia eliminated in region 4 is led directly to region 1, for example by a pipe 13 crossing regions 3 and 2 and without | 'possible contact with them. The acid elements are introduced at 14 at the top of region 2, while the agents j. oxidants effective in acidic medium are introduced at 18 into · the column at the top of region 3. The waters being stripped leave region 3 through its bottom at 15! j and enter the upper part of region 4, par 16. The i! supply of lime milk in 17 can be made by the same conduit 16 d in this region 4. This type of column also has the advantage of reduced consumption of oxidizing reagent and of stripping fluid.

FIG. 11 schematically represents a stripping column of the plate type, in which the acid character of the water is obtained naturally at a certain level, by progressive reduction of the pH from plate to plate.

Such a column has two regions, namely region 1 where the elimination of free ammonia takes place on the one hand and, in its lower part, elimination by steam and oxidation , phenols and the like in an acid medium; region 2 where the elimination of fixed ammonia takes place. The column is supplied with stripper water at 3 at the top of region 1, the stripping fluid supply. takes place at the bottom of region 2, at 4. The evacuation of the stripped water and of phenol degradation products is carried out at 5, at the bottom of the column, while the evacuation of the stripping fluid loaded with ammonia , other volatile pollutants and degradation products of phenols is carried out in 6 at the top of the column. Regions 1 and 2 are separated by a partition 7 fl allowing the vapor and gaseous elements to pass from bottom to top.

H T.1 ϊηίτηΛηρΗ nn rlpq anonfs OTOrlanl-q pf f ΐ rapp “; An acid medium is 12.- carried out at 11 in region 1, at a level where the pH has naturally dropped to a value of the order of 4 to 5. The waters being stripped leave this region 1 at its lower part / by the conduit 8 to enter by 9 in the upper part of the region 2. The addition of lime by 10 can be done in the said region 2, by this same conduit 9. This type of column has the advantage of a moderate investment.

. FIG. 11d schematically represents a stripping column of the plate type, in which the elimination and the degradation of the phenols are carried out on waters already freed of their free and fixed ammonia.

Such a column has three regions, namely ï from top to bottom, region 1 where the elimination of free ammonia takes place, region 2 where the elimination of fixed ammonia takes place, region 3 where the elimination and degradation of phenols take place. The stripping water is introduced at 4 at the top of region 1, the stripping fluid is introduced at 5 at the bottom of region 3. The stripped water is discharged at 6, at the bottom of the column, with degradation products from the phenols; the free and fixed ammonia, as well as the degradation products of the phenols are removed, at 7 at the top of the column. Regions 1 and 2 are separated by a wall 8 letting in the direction 2 - * - l the vapor and gaseous elements. Regions 2 and 3 are separated by a wall 9 letting through, in the direction 3 - * ~ 2, the vapor and gaseous elements and in the direction 2 - * - 3, the liquid. The waters being stripped leave the lower part of region 1 through line 10 and enter the upper part of region 2 through line 11, the lime milk 12 to be introduced into this same region can be through this same conduit 11. The introduction of the acid elements is carried out in the upper part of the region 3, by the conduit 13, while the oxidizing elements are introduced by 14 in this same region, ie substantially at the same level as the conduit 13 , which is somewhat below this level. This type of column has the advantage of a relatively moderate consumption of oxidizing reagent.

13.- i.

i! j Figure III relates to a stripping column I of the plate type, in which an oxidizing agent is used.

I being able to degrade phenols and the like, as well in acid medium as in basic medium. The scheme is then as follows.

The column is made up of two regions, namely 1 where free ammonia is removed and where phenols can be degraded, region 2 where fixed ammonia is removed and where one can also degrade phenols. The column is supplied with water to be stripped at 3, at the top of region 1, the column is supplied with stripping fluid at 4 at the bottom of the column at the bottom from region 2, the removal of stripped water and phenol degradation products is at 5 at the bottom of the column, while the stripping fluid laden with ammonia, other volatile pollutants and phenol degradation products are evacuated in 6 at the top of the column. Regions 1 and 2 are separated by a partition 7 allowing the passage of vapors and gaseous elements from bottom to top. The waters in the process of stripping leave region 1 in its lower part via conduit 8 | and enter by 9 in the upper part of region 2. The contribution. of lime in 10, also intended for the upper part of region 2 can be carried out by the same conduit 9. The introduction of the oxidizing elements, effective as well in acid medium as in basic medium, can be carried out in one or more levels of any one of regions 1 and 2. The introductions are shown diagrammatically by the arrows in dashed lines 11, 12, 13 and 14.

Figure IV also relates to a stripping column of the plate type, in which the oxidizing agents used are effective in a narrow range, of pH between 6.5 and 7.5 and at values as close as possible to 7 .

The scheme used is then as follows in the column; has two regions: namely region 1 where - is removed, ·. · 1 free ammonia and where the phenols are degraded, region 2 where is removed fixed ammonia. The column 1 is supplied with waste water at 3 at the top of region ^ # 14.- the stripping fluid is supplied at 4 at the base of region 2, evacuation stripped water as well as phenol degradation products is done at the base of the column, at 5, the stripping fluid laden with ammonia, other volatile pollutants and phenol degradation products is evacuated 6, at the top of the column. The two regions 1 and 2 are separated by a wall 7, which * allows vapors and gaseous elements to pass from bottom to top. The waters being stripped leave, via line 8, the lower part of region 1, and enter via line 9 in the upper part of region 2, the supply of lime milk 10 in this region can be carried out by this same procedure 9.

The introduction of the effective oxidizing agent into the 6.5 - 7.5 pH zone is carried out in region 1, at a level where from plateau to plateau, the pH naturally descends to a value included in this region.

Claims (16)

1. Method for purifying waste water, such as coke oven water, according to which use is made of a stripping column supplied in its upper part with the water to be stripped, and in its lower part by a stripping fluid, and in which volatile pollutants and in particular free ammonia and fixed ammonia are eliminated, the latter being freed from its salts by the introduction of a strong base at a determined level of the column, characterized in that in addition, there is also introduced into this same column, at one or more levels, one or more agents of oxidizing nature, individually or as a mixture, the said oxidizing nature having in particular a degrading action on the phenols and elements analogues, sulfocyanides, complex cyanides ... 2. Method according to claim 1, characterized in that the oxidizing agents have their degrading character, especially in basic medium. 3. Method according to claim 2, characterized in that as oxidizing agents, use is made of an or. ^. . . several of the following compounds: E ^ SO,., (NH ^) ^ ^ 2 ° 8 'I ^ FeO ^, ° 3 * 4. Method according to either of claims 2 and 3, characterized in that the oxidizing agents are introduced into the column, substantially at the same level as that of the introduction of the basic elements. P ”16.- 5. Method according to either of Claims 2 and 3, characterized in that the introduction of the oxidizing agents is carried out in the column at a place where the waste waters have already been freed from their volatile and fixed ammoniacal compounds . 6. Method according to claim 1, characterized in that the oxidizing agents have their degrading nature, especially in an acid medium. 7. Process according to claim 6, characterized in that, as oxidizing agent, use is made of I ^ C ^. 8. Process according to one or other of the dreams dations 6 and 7, characterized in that the introduction of the oxidizing agents, as well as an introduction of acid elements are carried out between the region where one eliminates the free ammonia and that in which the fixed ammonia is eliminated, the vapors or gases charged with ammonia coming from the fixed ammonia elimination zone, being led directly to the region where the free ammonia, without any contact with the region where the phenols are eliminated and degraded. . 9. Method according to claim 8, characterized in that the introduction of the oxidizing agents takes place at a level lower than that of the introduction of the acid elements. 10. Process according to either of Claims 6 and 7, characterized in that the introduction of the oxidizing agents is carried out in the region where the free ammonia is eliminated to a level, where by natural decay, the pH of the water is below. | cended to values of the order of 5. X I * 17.- IX. Process according to either of Claims 6 and 7 / characterized in that the introduction of the agents is carried out on water already free of its free and fixed ammoniacal elements, said introduction being accompanied by an introduction of acid elements in the same region. 12. Method according to claim 1, characterized in that the oxidizing agents have their degrading efficiency in acid medium and in basic medium. * 13. The method of claim 12, character ized in that as an oxidizing agent, use is made of ClC ^ and / or air enriched in oxygen, and / or pure oxygen. 14. Method according to either of claims 12 and 13, characterized in that the introduction of the oxidizing agents is carried out at one or more places in the region where the elimination of the free ammonia is effected and / or the region where the elimination of fixed ammonia takes place. 15. The method of claim 1, characterized in that the oxidizing agents used have their degradation efficiency in an area where the pH is between 6.5 and 7.5. 16. The method of claim 15, characterized in that the oxidizing agent used is NaOCl. 17. Process according to either of claims 15 and 16, characterized in that the introduction of the oxidizing agents is carried out in the region where the free ammonia is eliminated, at a level where the pH has dropped naturally, has reached. values between 6.5 and 7.5. r- 18.- '♦ t 18. Process according to either of Claims 1 to 17, characterized in that use is made, in addition to a catalyst, of reactions for the elimination of phenols and the like. 19. The method of claim 18, characterized in that use is made as catalyst, of "ferrous or metallic copper salts, preferably finely divided. 20. Processes as described above. ".