DE102013006289A1 - Process for the improved purification of waste water from a coke oven plant - Google Patents

Abstract

The invention relates to a process for the improved purification of effluents from a coke oven plant, which carries out a purification of wastewater by a biological detoxification stage, and the wastewater obtained, which contains only ammonia as Hauptabbauprodukt, passes without subsequent nitrification and denitrification in an intermediate column of where the desorbed ammonia is fed into a desorption column, which serves to degas the wastewater before the biological purification, so that a disposal of the ammonia from the biological detoxification stage is possible, and according to the invention the gas, which serves to desorb the ammonia in the intermediate column, can also be used for the purification of waste water in the desorption by degassing. In a preferred embodiment, the gas for desorption of the ammonia is steam.

Description

The invention relates to a process for the improved purification of effluents from a coke oven plant, which carries out a purification of wastewater by a biological detoxification stage, and the wastewater obtained, which contains only ammonia as Hauptabbauprodukt, passes without subsequent nitrification and denitrification in an intermediate column of where the desorbed ammonia is fed into a desorption column, which serves to degas the wastewater before the biological purification, so that a disposal of the ammonia from the biological detoxification stage is possible, and according to the invention the gas, which serves to desorb the ammonia in the intermediate column, can also be used for the purification of waste water in the desorption by degassing. In a preferred embodiment, the gas for desorption of the ammonia is steam.

In coking plants are often wastewater, which contain due to the previous use pollutants, which must be converted before the environmentally friendly disposal of wastewater in an environmentally safe form. Such effluents come from process steps which serve for cleaning and cooling of fabrics and objects in a coking plant. Examples of such process steps are gas scrubbing processes for coke oven gas, which is washed by an aqueous liquid, extinguishing processes for coke or process steps for pressure control with aqueous control liquids. The water streams used absorb pollutants that can not easily be released into the environment. Examples of such pollutants are nitrogen compounds, cyanides, phenols, organic compounds and sulfur compounds.

In order to remove these pollutants before the discharge of the wastewater into the environment, or to convert it into a harmless form, these are transferred in the prior art in a wastewater treatment. Since recovery of these pollutants is generally not economical, prior art wastewater is purified from said pollutants by first outgassing them by desorption process and converting the remaining pollutants into a harmless form. The desorption process takes place in a desorption column into which the unpurified effluents are first added, and in which all foreign substances which can be converted into gaseous or gaseous form are expelled by the use of a spewing gas.

Such flue gas is in most cases hot steam. This is usually present in large quantities in a coking plant and is an effective flue gas for many compounds. This is also able to thermally split thermally labile pollutants, and then expel the resulting gases. The collected vapor already contains a large part of the pollutants and can be condensed out for the separation of pollutants or be given for disposal, for example in a Claus reactor. The Austriebsvorgang to expel the gaseous substances from the wastewater takes place in a desorption, which is often called Kokereikolonne.

Desorption processes for purifying a wastewater by desorption with the aid of a flash gas are known in the art. The US4311597A describes a process for removing ammonia from a waste water containing free and bound ammonia, the process comprising the steps of distilling the wastewater to remove the free ammonia, treating the distilled waste water with soda ash to release the bound ammonia, and distilling the treated waste water Removal of released ammonia contains. In one embodiment of the invention, low pressure steam is passed through the column to aid the expulsion of both the free ammonia and the liberated ammonia. In this way, the ammonia can be recovered as valuable material.

The effluent obtained after desorption by a gas still contains the non-expansible substances, so that this wastewater can not be readily discharged into the environment. This requires a new wastewater treatment. In most cases, this is done by biological wastewater treatment in a detoxification reactor in which the pollutants are metabolically converted to metabolites by anaerobic or aerobic conversion. Such metabolites are, for example, ammonium compounds and carbon dioxide, and sulfates at low sulfur concentration by sulfation.

Also, since ammonium compounds can not readily be discharged into the environment, they can be converted to nitrogen by the prior art biological processes with the subsequent steps of nitrification and denitrification. In nitrification, the ammonium compounds are converted into nitrates, and in the subsequent denitrification, the nitrates are converted into nitrogen. This is then released into the atmosphere.

An example of a purification process with the steps of detoxification and nitrification with subsequent denitrification describes the DE 10 2011 001 962 A1 , The teaching describes a process for the biological purification of coke oven wastewater, which is loaded with nitrogen compounds, cyanides, phenols, and sulfides, and which is supplied together with a biomass-containing material stream to a detoxification reactor, which is a gassing zone to remove pollutants that inhibit nitrification and a reaction zone, wherein the feed mixture fed to the detoxification reactor is subjected to a gaseous oxidant in the gassing zone and an oxidant-enriched stream is fed to the reaction zone where cyanides and other nitrification-inhibiting contaminants are biodegraded and out of the reaction zone the detoxification reactor is withdrawn a stream and recycled to the detoxification reactor, and a wastewater stream from the detoxification reactor by means of membrane filtration in a retentate stream containing biomass and a purified Pe Rmeatstrom is separated, and from the retentate a partial stream entrains excess sludge, is discharged, and the retentate is recycled after separation of the partial stream in the detoxification reactor, and the permeate stream is purified by nitrification with subsequent denitrification.

However, setting up a series of biological purification steps is quite expensive and must be accompanied by filtration after the individual biological purification steps. In addition, the ammonium compounds, which are added with the wastewater in the biological treatment stage, are lost unused by the stages of nitrification and denitrification. It would therefore be of advantage if the ammonium compounds which are still present in the waste water after the flash-out in the coking column can at least be used as valuable substances.

It has been found in the present invention by measuring the effluent from the detoxification stage that the nitrogen compounds in the effluent from this stage are converted into free ammonia with appropriate handling of the detoxification stage. The subsequent reaction steps of nitrification and denitrification can be omitted thereby.

The free ammonia, which is still contained in the wastewater in the reaction stage of the detoxification, can then be made by expulsion with a gas. This is advantageously carried out in an intermediate column, so that the wastewater from the desorption column, which is passed into the detoxification stage, does not have to be returned to the desorption column. In order to continue to use the gas, which is used for the expulsion of the free ammonia in the intermediate column, this can be returned to the desorption column. Thereby, it is not necessary to provide two different gas supply systems with a corresponding consumption of desorption gas. At the same time, the ammonia can be carried out in the same way as the expelled foreign gas from the desorption column. If the desorption gas is steam, steam is saved.

There is therefore the object to provide a method which makes the purification of a coking plant after a first degassing by a detoxification from the prior art without subsequent nitrification and denitrification, the ammonia-containing wastewater degassed by a desorbing gas from the entrained ammonia , and the desorbing gas thereby utilizes, by this is returned to the desorption column for the first degassing of the foreign-gas-containing wastewater.

The present invention solves this problem by a method which carries out the purification of the wastewater from a coking plant, in which this is first cleaned in a desorption with a desorption of entrained foreign gases, the so purified by foreign gases then wastewater from the desorption in a detoxification stage in which a microbiological wastewater treatment of the previously degasified wastewater is carried out by a biomass, and the wastewater is purified by filtration of the biomass, and the resulting purified wastewater is then passed into an intermediate column in which the ammonia-containing wastewater by a desorbing Gas is freed from the entrained residual ammonia from the detoxification stage, and the desorbing gas is then returned according to the invention with the desorbed ammonia from the intermediate column in the desorption column.

Steam is preferably used as desorption gas. This has a sufficient desorption effect for ammonia and can be provided in a coking plant without great technical effort. In principle, however, any desorption gas can be used which is suitable for the desorption of foreign gases from waste water. These are known to those skilled in the purification of wastewater, and are described by way of example in the US2777815A ,

• • in einer Kokerei ein schwefel- und stickstoffhaltiges Abwasser anfällt, welches in einer Desorptionskolonne unter Durchleitung von einem Gas von den mitgeführten gelösten Fremdgasen gereinigt wird, so dass mit dem Gas die desorbierten Fremdgase und ein von gelösten Gasen gereinigtes Abwasser erhalten wird, und
• • die desorbierten Fremdgase aus der Desorptionskolonne ausgeführt werden, und
• • das von Fremdgasen gereinigte Abwasser, welches mit Verunreinigungen aus Stickstoffverbindungen, Cyaniden, Phenolen, organischen Verbindungen und Schwefelverbindungen beladen ist, in einen Entgiftungsreaktor gegeben wird, wo das gereinigte Abwasser mit einer mikroorganismenhaltigen Biomasse, welche einen aeroben oder anaeroben Abbau der Stickstoffverbindungen, Cyanide, Phenole, organischen Verbindungen und Schwefelverbindungen durchführt, und Luftsauerstoff zur Reaktion gebracht wird, so dass ein von Verunreinigungen gereinigtes ammoniakhaltiges Abwasser erhalten wird, und
• • das so erhaltene Abwasser durch eine Ultrafiltration von der Biomasse gereinigt wird, und welches dadurch gekennzeichnet ist, dass
• • das gereinigte ammoniakhaltige Abwasser, welches nach der Ultrafiltration aus dem Entgiftungsreaktor ausgeführt wird, ohne weitere Nitrifikation und Denitrifikation in eine Zwischenkolonne geführt wird, welche zur Desorption des darin enthaltenen Ammoniaks mit Desorptionsgas beaufschlagt wird, und
• • das Desorptionsgas nach der Durchleitung durch die Zwischenkolonne im Gemisch mit dem desorbierten Ammoniak in die Desorptionskolonne zurückgeführt wird, so dass das Ammoniak mit den in der Desorptionskolonne desorbierten Fremdgasen aus der Desorptionskolonne ausgeführt wird, und aus der Zwischenkolonne ein gereinigtes Abwasser erhalten wird, welches frei von gelösten Gasen und Fremdstoffen ist, und in die Umgebung abgegeben werden kann.

Claimed is in particular a process for the treatment of waste water in a coking plant by a microbiological detoxification, wherein

• • In a coking plant a sulfur and nitrogen-containing wastewater is obtained, which is purified in a desorption column while passing through a gas from the entrained dissolved foreign gases, so that the desorbed with the gas Foreign gases and a purified of dissolved gases wastewater is obtained, and
• • the desorbed foreign gases are carried out from the desorption column, and
• The wastewater purified from foreign gases, which is loaded with impurities from nitrogen compounds, cyanides, phenols, organic compounds and sulfur compounds, is placed in a detoxification reactor where the treated wastewater is treated with a microorganism-containing biomass which aerobic or anaerobic degradation of the nitrogen compounds, cyanides, Phenols, organic compounds and sulfur compounds is carried out, and atmospheric oxygen is reacted so that an impurities purified ammonia-containing wastewater is obtained, and
• The wastewater thus obtained is purified from the biomass by ultrafiltration and which is characterized in that
• • the purified ammonia-containing waste water, which is carried out after ultrafiltration from the detoxification reactor, is passed without further nitrification and denitrification in an intermediate column, which is acted upon for desorption of the ammonia contained therein with desorption gas, and
• • The desorption gas is recycled after passing through the intermediate column in a mixture with the desorbed ammonia in the desorption, so that the ammonia is carried out with the desorbed in the desorption column foreign gases from the desorption column, and from the intermediate column, a purified wastewater is obtained, which is free of dissolved gases and foreign matter, and can be released into the environment.

In carrying out the process, it has been found that ultrafiltration can not be dispensed with, since the microbial wastewater from the detoxification stage still contains activated sludge, which is harmful in the desorption process and pollutes the columns. However, the ultrafiltration is compared to the subsequent nitrification and denitrification stage, which then omitted, a relatively low cost.

In one embodiment of the invention, the desorbed foreign gases are carried out from the desorption and introduced after the execution in the sulfur-containing acid gas for a Claus plant, which consists of a Claus furnace for combustion of a substream of sulfur-containing acid gases in sulfur dioxide, and a Claus reactor for Conversion of sulfur dioxide with the second partial stream of sulfur-containing acid gas in elemental sulfur. However, the desorbed foreign gases may be carried out after execution from the desorption column and fed to the execution of any further use. This can also be, for example, a process for producing sulfuric acid.

In a further embodiment of the invention, the desorption gas is steam. This can be provided as required. The steam which is provided as desorption gas and which is used for introduction into the intermediate column may be, for example, a steam which is steam from the steam system of the coking plant. The steam which is used to introduce into the intermediate column, but may also be a vapor which is generated in a separate steam boiler.

Instead of steam, any other desorption gas can be used in principle, which is suitable for the desorption of ammonia from wastewater. Instead of steam, for example, carbon dioxide, nitrogen, helium, hydrogen, ethane, propane or mixtures thereof can be used. In practice, however, it has been found that steam is the most suitable desorption gas because steam desorbs the ammonia well and also thermally splits ammonium compounds still present in the wastewater.

The vapor, which is returned from the intermediate column in the Kokereikolonne, can be further treated, as is customary in the prior art. This can be condensed out, for example, after execution from the Kokereikolonne, and the foreign gases or foreign substances are recovered. It is also possible within the scope of the invention to pass the steam from the coker column into the Claus process. In many coking plants, a Claus plant is also operated to convert the sulfur-containing foreign substances into elemental sulfur. Claus plants for the conversion of hydrogen sulfide or organosulfur compounds into elemental sulfur are known in the art. Embodiments of a Claus process teach the patents WO2004014792A1 and WO2004014791A1 ,

The wastewater, which is taken from the detoxification stage without further nitrification and denitrification, after ultrafiltration to filter off the biomass usually has a residual content of foreign substances, which is below the permissible limits for release to the environment. However, it is often still necessary to carry out a post-purification in order to achieve optimum water quality for delivery to the aquiferous environment. A post-purification may consist, for example, in a particle filtration or in an oxygen enrichment. In a further embodiment of the invention, it is therefore possible to pass the waste water from the intermediate column into a container in which it is cached before execution from the process. This allows the wastewater to be treated if necessary before it is released to the water-bearing environment. It is also possible to at least partially recycle the wastewater into the desorption column. The wastewater can be passed from the intermediate column in a container in which this is temporarily stored before the execution in the desorption. The wastewater treatment by the detoxification reactor is usually carried out in cycles and can therefore be arranged several times.

Also claimed is a plant for carrying out a process for improved purification of effluents from a coke oven plant, said plant comprising a desorption column for the purification of waste water from a coking plant and a detoxification reactor with subsequent ultrafiltration, in which the loaded wastewater from the desorption is performed, and which is characterized in that the detoxification reactor has no downstream nitrification and denitrification, and the apparatus comprises an intermediate column into which the purified wastewater is passed after the ultrafiltration, which is equipped with a steam supply line, and with an execution line for the steam, which in the desorption column is guided.

The process described above has the advantage of enabling wastewater treatment in a coke production plant, dispensing with the expensive steps of nitrification and denitrification required in the prior art after detoxification to convert the ammonium compounds into elemental nitrogen can, and wherein the wastewater contains only ammonia, which can be readily expelled in a subsequent intermediate column, and the desorption used in this case can be used without further energy saving in the Kokereikolonne. This achieves an improved economy of the entire process.

The invention will be further explained by a drawing, this drawing is only an exemplary embodiment and is not limited thereto.

In a desorption column ( 1 ) is a polluted wastewater ( 2 ) introduced therein dissolved foreign gases from a coking plant. At the same time, the desorption column ( 1 ), which are used for improved mass transfer with mass transfer elements ( 1a ), hot steam ( 3 ) introduced in countercurrent. In the wastewater ( 2 ) contained foreign gases ( 4 ) are expelled or, if they are present as thermally labile solids, thermally decomposed and then expelled. The expelled foreign gases ( 4 ) and the steam ( 3 ) are removed from the desorption column ( 1 ) ( 4 ). The wastewater purified by the foreign gases ( 4a ) is then pumped ( 2a ) into the detoxification reactor ( 5 ), which consists of a ventilated basin with air supply ( 5a ), in which the wastewater ( 6 ) over a biomass ( 7 ) is purified by aerobic and anaerobic metabolism. The cleaning process can also be achieved by a stirring process ( 5b ) get supported. The purified wastewater ( 8th ) is removed from the detoxification reactor ( 5 ) into an ultrafiltration ( 9 ). The wastewater ( 8th ) is determined by the biomass ( 7 ) and contains as foreign substances still carbon dioxide and ammonia as metabolized foreign substances. The purified filtered wastewater ( 10 ) is then an intermediate column ( 11 ), in which the purified wastewater ( 10 ) with hot steam ( 12 ). This steam ( 12 ) is stored in a separate steam boiler ( 12a ) generated. This expels the carbon dioxide and ammonia. The carbon dioxide and the ammonia, which are expelled, according to the invention with the steam ( 12b ) in the desorption column ( 1 ), whereby the desorption process in the desorption column ( 1 ) is supported. The from the desorption column ( 1 ) expelled foreign gas ( 13 ) is mixed with the steam ( 4 ) from the desorption column ( 1 ), and can be connected via a valve ( 13a ) in the Claus process. This consists of a Claus oven ( 14 ) for the combustion of a partial flow ( 14a ) of the hydrogen sulphide and a Claus reactor ( 15 ) for the reaction of the residual hydrogen sulfide ( 14b ) with the one from the Claus oven ( 14 ) sulfur dioxide ( 16 ). The ammonia, which from the purified wastewater ( 10 ) in the intermediate column ( 11 ) was expelled, is thus in the Claus furnace ( 14 ) and there at least partially burned to nitrogen. This gives after passing through the Claus reactor ( 15 ) a nitrogen-containing exhaust gas ( 15a ). The wastewater ( 17 ) from the intermediate column ( 11 ) is via a valve ( 11a ) and stored in a storage tank ( 18 ). After storage, it is discharged into the environment ( 18a ).

LIST OF REFERENCE NUMBERS

1

desorption column

1a

Mass transfer elements

2

sewage

3

steam

4

Prescribed foreign gases

4a

Wastewater purified by foreign gases

5

detoxification reactor

5a

air supply

5b

stirring

6

sewage

7

biomass

8th

Purified wastewater

9

ultrafiltration

10

Filtered wastewater

11

between column

11a

Valve for draining the purified wastewater

12

steam

12a

steam boiler

12b

Steam returned to the desorption column

13

foreign gas

13a

Valve

14

Claus furnace

14a

First partial flow of hydrogen sulphide

14b

Second substream hydrogen sulfide

15

Claus reactor

15a

Nitrogen-containing exhaust gas

16

sulfur dioxide

17

sewage

18

storage tank

18a

Drained water

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 4311597 A [0005]
• DE 102011001962 A1 [0008]
• US 2777815 A [0014]
• WO 2004014792 A1 [0020]
• WO 2004014791 A1 [0020]

Claims (8)

Process for the treatment of waste water in a coking plant by a microbiological detoxification, wherein • in a coking plant a sulfur and nitrogenous wastewater obtained, which is purified in a desorption column while passing gas from the entrained dissolved foreign gases, so that with the gas desorbed foreign gases and waste water purified from dissolved gases is obtained, and • the desorbed foreign gases are discharged from the desorption column, and • the waste gas-cleaned waste water loaded with impurities of nitrogen compounds, cyanides, phenols, organic compounds and sulfur compounds is put in a detoxification reactor where the purified wastewater is reacted with a microorganism-containing biomass which performs an aerobic or anaerobic digestion of the nitrogen compounds, cyanides, phenols, organic compounds and sulfur compounds, and atmospheric oxygen, i an ammonia-containing wastewater purified from impurities is obtained, and the wastewater thus obtained is purified from the biomass by ultrafiltration, characterized in that the purified ammonia-containing waste water which is discharged from the detoxification reactor after the ultrafiltration, without further nitrification and denitrification is passed into an intermediate column, which is acted upon for desorption of the ammonia contained therein with desorption gas, and • the desorption is returned after passing through the intermediate column in admixture with the desorbed ammonia in the desorption, so that the ammonia desorbed with those in the desorption Foreign gases from the desorption is carried out, and from the intermediate column, a purified wastewater is obtained, which is free of dissolved gases and foreign substances, and can be discharged into the environment. A method according to claim 1, characterized in that the desorbed foreign gases are carried out from the desorption column and are introduced after the execution in the sulfur-containing acid gas for a Claus plant, which consists of a Claus furnace for burning a partial stream of the sulfur-containing acid gases in sulfur dioxide, and a Claus reactor for converting the sulfur dioxide with the second substream of the sulfur-containing acid gas into elemental sulfur. Method according to one of claims 1 or 2, characterized in that it is the desorption gas is steam. A method according to claim 3, characterized in that the steam which is used for introduction into the intermediate column, steam from the steam system of the coking plant. A method according to claim 3, characterized in that the steam which is used for introduction into the intermediate column, is generated in a separate steam boiler. Method according to one of claims 1 to 5, characterized in that the waste water from the intermediate column is fed into a container in which this is temporarily stored before the execution of the process. Method according to one of claims 1 to 5, characterized in that the waste water from the intermediate column is passed into a container in which this is temporarily stored before the execution in the desorption column. Plant for carrying out a process according to one of claims 1 to 7, wherein it comprises a desorption column for the purification of waste water from a coking plant and a detoxification reactor with subsequent ultrafiltration, in which the loaded waste water is led out of the desorption column, characterized in that the detoxification reactor has no downstream nitrification and denitrification, and the device comprises an intermediate column, in which the purified wastewater is passed after the ultrafiltration, which is equipped with a steam supply line, and with a feed line for the steam, which is fed into the desorption.

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