DE10306722A1 - Reverse osmosis process and assembly to render a spent dilute etching agent from a boiler pipe system fit for disposal - Google Patents

Abstract

Process for treating a pickling / cleaning agent after cleaning or pickling a piping system,
wherein an aqueous 3 to 5% pickling / cleaning agent solution with a high COD value is used as the pickling / cleaning agent and the method comprises the following steps,
Collecting the pickling / cleaning agent solution after the pickling or cleaning process in a container or tank,
and then lowering the COD value of the pickling / cleaning agent solution to <100 mg / 1 by filtering it in a reverse osmosis system, the reverse osmosis system being at least one-stage and in a multi-stage reverse osmosis system the stages are connected in series (FIG. 1).

Description

The invention relates to a Method and device for treating a pickling / cleaning agent after cleaning or pickling piping systems.

It is known piping systems of steam generator systems, for example, before they are used or cleaning their start-up with a pickling / cleaning agent or pickling before they are exposed to a working medium or a working medium is passed through the piping system becomes.

• – Salzsäure,
• – Citronensäure,
• – Flusssäure.

A large number of inorganic and organic acids and also complicated mixtures of different acids have been investigated in the literature and proposed for pickling purposes of piping systems or heat exchanger tubes. Nevertheless, in the course of time essentially only three acids have become widespread:

• - hydrochloric acid,
• - citric acid,
• - hydrofluoric acid.

• – höheres Lösevermögen gegenüber Eisenoxiden sowie die Möglichkeit zum Lösen von Silikaten,
• – kürzere Kontaktzeiten der Beizflüssigkeit mit den Materialien und letztendlich geringere Abtragsraten des Grundmetalls,
• – niedrigere Konzentrationen und niedrigere Temperaturen ermöglichen ein wirtschaftlicheres Verfahren.

In the modern pickling technology of large plants, hydrochloric acid no longer played the major role of earlier decades. By using new pipe materials, other acids such as citric acid and hydrofluoric acid were used. Hydrofluoric acid, which has become known, for example, from the publication "The use of hydrofluoric acid in the chemical-technical cleaning of plants", VGB KRAFTWERKSTECHNIK 58, Issue 12, December 1978, pages 927 to 930, offers a number of advantages over citric acid:

• - higher dissolving power compared to iron oxides and the possibility of dissolving silicates,
• - shorter contact times of the pickling liquid with the materials and ultimately lower removal rates of the base metal,
• - lower concentrations and lower temperatures enable a more economical process.

While according to chapter 5: "Pickling of steam boiler systems / chemical cleaning ", page 18 to 33, especially page 20 from the publication “Innere Cleaning of water pipe steam generator systems and pipes ", VGB guideline R 513 H, in the European Room the hydrofluoric acid treatment prevailed has, is the pickling with organic acids (citric acid) and Complexing agents (EDTA / NTA) in the Asian and Anglo-American region still important. When using organic acids Working temperatures of approx. 90 ° C and required for complexing agents from 120 - 180 ° C.

In the course of an ever increasing ecological Awareness also in emerging countries or emerging industrial countries the wastewater problem plays an increasingly important role in the Selection of the acids using ro or pickling / cleaning agents.

Form both citric acid and hydrofluoric acid slightly soluble Calcium salts, but only hydrofluoric acid let yourself practically quantitative with the help of lime milk as calcium fluoride, i.e. to below the concentration prescribed by law.

Additional problems arise disposal of organic acids (Citric acid) due to a high COD value (COD = chemical oxygen demand) in Wastewater, which usually only involves high financial expenses solved can be.

• – Bei einer Entsorgung über eine biologische Kläranlage zeigt sich nachteilig, dass die Kläranlage sehr teuer ist. Da diese meistens an der oberen Auslastungsgrenze arbeitet, können nur geringe Mengen darüber entsorgt werden. Dadurch dauert das Reinigungsverfahren sehr lange. Eine derartige Anlage ist auch nicht immer vorhanden.
• – Die Eindüsung der Abwässer in die Brennkammer der Dampferzeugeranlage ist nicht immer zulässig.
• – Das Abpumpen der Abwässer auf Kohlehalden und anschließend gemeinsames Verbrennen mit der Kohle ist nur in speziellen Fällen zulässig.
• – Das Abpumpen der Abwässer auf die Aschedeponie ist ebenfalls nur in speziellen Fällen zulässig.
• – Durch eine mehrstufige Oxidation und Fällung der Beiz-/Reinigungslösung können die geforderten Grenzwerte meistens nicht erreicht werden und das Verfahren ist außerdem sehr teuer.
• – Eine Oxidation mit Ozon und alkalische Fällung kommt sehr teuer.
• – Eine Eindickung des Beiz-/Reinigungsmittels über eine Verdampfung mittels speziellem Hilfsdampferzeuger erfordert einen erheblichen Investitionsaufwand.

The previously used, known and below-mentioned methods for cleaning citric acid-containing pickling / cleaning agents cannot achieve a COD value of <100 mg / l or only achieve it with extremely high financial expenditure or are not permitted in the respective country:

• - When disposed of via a biological sewage treatment plant, it is disadvantageous that the sewage treatment plant is very expensive. Since this mostly works at the upper utilization limit, only small amounts can be disposed of above it. As a result, the cleaning process takes a very long time. Such a system is also not always available.
• - The injection of waste water into the combustion chamber of the steam generator system is not always permitted.
• - Pumping the waste water onto coal dumps and then burning them together with the coal is only permitted in special cases.
• - The pumping of waste water to the ash dump is also only permitted in special cases.
• - A multi-stage oxidation and precipitation of the pickling / cleaning solution usually means that the required limit values cannot be reached and the process is also very expensive.
• - Oxidation with ozone and alkaline precipitation is very expensive.
• - A thickening of the pickling / cleaning agent via evaporation using a special auxiliary steam generator requires a considerable investment.

It is therefore an object of the present invention to propose a method for treating a pickling / cleaning agent in which the aforementioned disadvantages are avoided and in which environmentally friendly waste water is disposed of into the environment and an apparatus for carrying out this method. It is a further object of the invention to provide a method and a device for treating a pickling / cleaning agent with which a wastewater quality of the pickling / cleaning agent is achieved, the COD value (chemical Oxygen demand) is <100 mg / l, as required, for example, by the Chinese standard "Disposal of waste solution".

The above task will with regard to the procedure by all the characteristics of the Claim 1 and with regard to the device by the whole of the features of claim 8 solved.

Advantageous embodiments of the Invention are the dependent claims refer to.

• – Gegenüber den bekannten Verfahren wird eine wesentlich geringere Menge an Chemikalien benötigt (wenigstens 90 % der Chemikalien können gegenüber den bekannten Verfahren eingespart werden). Dadurch kann das Behandlungsverfahren zum einen wesentlich preisgünstiger durchgeführt werden (die hohen Chemikalienkosten treiben ansonsten die Betriebskosten in die Höhe) und zum anderen kann ein ökologisch unbedenkliches Abwasserprodukt an die Umwelt abgegeben werden.
• – Durch Einsatz einer transportablen Umkehrosmoseanlage für den benötigten Zeitraum der Beiz-/Reinigungsmittelaufbereitung können weitere Investitionskosten gespart werden.
• – Durch das erfindungsgemäße Verfahren lässt sich die Menge der Beiz-/Reinigungsmittellösung und somit die ökologisch bedenklichen Stoffe durch Aufkonzentration auf weniger als 10 % der Ursprungsmenge reduzieren. Die Restmenge kann dann anschließend in einer biologischen Kläranlage ökologisch abgebaut oder in einer Verbrennungsanlage verbrannt werden und somit umweltfreundlich entsorgt werden.

The solution according to the invention creates a method and a device for treating a pickling / cleaning agent which has the following advantages:

• Compared to the known methods, a significantly smaller amount of chemicals is required (at least 90% of the chemicals can be saved compared to the known methods). On the one hand, this enables the treatment process to be carried out much more cheaply (otherwise the high chemical costs drive up the operating costs) and, on the other hand, an ecologically harmless wastewater product can be released into the environment.
• - By using a portable reverse osmosis system for the required period of pickling / cleaning agent preparation, further investment costs can be saved.
• - By the method according to the invention, the amount of the pickling / cleaning agent solution and thus the ecologically questionable substances can be reduced by concentration to less than 10% of the original amount. The remaining amount can then be biodegraded in a biological sewage treatment plant or burned in an incineration plant and thus disposed of in an environmentally friendly manner.

It is advantageous to use it as a pickling / cleaning agent solution citric acid use, as these are easy to use and handle and harmless is for people.

By setting a pH> 10 by adding of lime milk in the pickling / cleaning agent solution collected in a container high COD value, a pre-reduction of the COD value can be achieved and at the same time a partial precipitation of the iron dissolved in the pickling / cleaning agent solution be achieved.

An advantageous embodiment of the Invention provides for the COD value of the collected in a container Pickling / detergent solution additionally to reduce and still solved Oxidize iron by adding the pickling / cleaning solution Oxidizing agent, usually air, is supplied.

It is advantageous to use an activated carbon filter for filtering out an inhibitor from the pickling / cleaning agent solution before feeding in to provide the reverse osmosis system. This measure will allows, a pickling / cleaning agent solution use with inhibitor for the pickling / cleaning process is an important component, since it removes the base material of the piping system to be cleaned prevented.

In an advantageous embodiment of the Invention, the reverse osmosis system is designed in several stages, because thereby opposite a higher throughput is possible in a single-stage reverse osmosis system and more effective filtration takes place.

The method and device according to the invention is used in a particularly advantageous manner in pipeline systems, whose pipes as heat exchanger pipes be used, d. H. a working medium flows in the pipes, which through a heat source heated becomes.

In appropriate training of the procedure or In the device, the reverse osmosis system has at least one pressure tube on that with flat modules arranged in disc technology for filtering the solution is trained. Flat modules are very easy to clean and lose thus their filter effect is only insignificant even after very long operation.

Below are exemplary embodiments the invention with reference to the drawing and the description explained in more detail.

It shows:

1 a process diagram of the inventive method

1 shows schematically the method according to the invention, from which the device for carrying out the method according to the invention can also be derived. The piping system of a steam generator or a steam generator system, not shown, is internally coated with a pickling / cleaning agent after it has been created or before it is commissioned 2 cleaned or stained. The cleaning or pickling of the piping system 1 can refer to the pipes 1 in parallel or in succession or in a combination of both. In the piping system 1 A steam generator is a heat exchanger tube through which a water / steam working medium flows when the steam generator is in operation.

The method according to the invention provides for pickling or cleaning the piping system 1 an aqueous 3 to 5% pickling / cleaning agent solution 2 with a high COD value (COD = chemical oxygen demand), advantageously to use a citric acid solution which is uncomplicated to use and safe for humans and which is subjected to the subsequent treatment steps.

After the cleaning process or the introduction and single or repeated passage (depending on the acid concentration values and which are known to be measured during cleaning) Iron quantity values) of the pickling / cleaning agent solution 2 through the piping system 1 becomes the pickling / cleaning agent solution 2 in a suitable container or tank 3 collected and in an advantageous embodiment of the invention by adding lime milk 4 pre-neutralized and adjusted to a pH value> 10. Furthermore, the pickling / cleaning agent solution 2 in the container or tank 3 air for post-oxidation 5 are supplied or injected. This can reduce the COD value in the container 3 collected pickling / cleaning agent solution 2 additionally reduced and dissolved iron can be oxidized.

Then you can in the pickling / cleaning agent solution 2 any inhibitor contained by means of an activated carbon filter 6 from the pickling / cleaning agent solution 2 be filtered out and finally the pickling / cleaning agent solution 2 in an at least one-stage, preferably multi-stage, reverse osmosis system 7 filtered and the COD value reduced to <100 mg / l. After passing through and filtering the pickling / cleaning agent solution 2 through the reverse osmosis system 7 a purified permeate is formed 8th and a low volume of concentrate 9 , The permeate 8th is discharged into the environment and the filtered concentrate 8th can like in 1 shown back in the container 3 managed, but it can also be disposed of separately. The level (s) of the reverse osmosis system 7 are each designed with membrane modules.

To over the life of the reverse osmosis system 7 To achieve a high filtering efficiency, it has proven to be advantageous to use the pickling / cleaning agent solution 2 to filter in one or more reverse osmosis system stages, each of which has at least one pressure tube which is formed with flat membrane modules arranged in disc technology or cushion technology. The arrangement of flat membrane modules ensures that they can be cleaned very well and thus ensures high filter performance. Instead of the flat membrane modules, disc modules or winding modules can also be used. The characteristic structure of a flat module membrane is such that in each case one membrane is arranged on two sides (front and rear) of a pane, while in the case of a pane module a membrane is characteristically arranged between two panes.

Thanks to the advantageous addition mentioned above 4 of milk of lime (with pH adjustment> 10) in a container 3 collected pickling / cleaning agent solution 2 With a high COD value, a pre-reduction of the COD value can be achieved and at the same time a partial precipitation of the iron dissolved in the pickling / cleaning agent solution 2 can be achieved.

For filtering out a possibly in the pickling / cleaning agent solution 2 In the present inhibitor, the pickling / cleaning agent solution 2 is, in an advantageous embodiment of the invention, before it is fed into the reverse osmosis system 7 through an activated carbon filter 6 directed. This measure enables a pickling / cleaning agent solution 2 use with inhibitor, which is an important component for the pickling / cleaning process, since it removes the base material of the piping system 1 prevented.

A multi-stage reverse osmosis system 7 has the advantage that this increases the throughput of the pickling / cleaning agent solution 2 is possible and more effective filtration takes place. According to the invention, the pickling / cleaning agent solution is filtered 2 in a multi-stage reverse osmosis system 7 in series, ie connected in series to increase the cleaning effect.

The method and device according to the invention can advantageously be used in pipeline systems 1 are used, the tubes of which are used as heat exchanger tubes of steam generator heating surfaces, bundle heating surfaces or the like, ie in whose tubes a working medium flows which is heated by a heat source, for example a furnace heated with fossil fuels.

The method according to the invention can also be used for any piping system 1 of chemical plants, process plants and the like are used.

1

Piping or heat exchanger tubes

2

Pickling / detergent (3 - 5% Citric acid solution)

3

container

4

Lime milk feed

5

Supply of oxidizing agent

6

Activated carbon filter

7

Reverse osmosis system

8th

permeate

9

concentrate

Claims (15)

Process for treating a pickling / cleaning agent after cleaning or pickling a piping system, - in which An aqueous 3 to 5% pickling / cleaning agent solution with a high COD value is used as the pickling / cleaning agent and the process comprises the following steps - field the pickling / cleaning agent solution after the pickling or cleaning process in a container or Tank, - and subsequent The COD value of the pickling / cleaning agent solution is reduced to <100 mg / l by filtering them in a reverse osmosis system, the reverse osmosis system is at least one-stage and in a multi-stage Reverse osmosis system the stages are connected in series. A method according to claim 1, characterized in that as a pickling / cleaning agent solution with high COD value an aqueous 3 to 5% Citric acid solution used becomes. A method according to claim 1 or 2, characterized in that that a setting of the in the container or tank collected pickling / cleaning agent solution to a pH of> 10 with the addition of milk of lime he follows. Method according to one of claims 1 to 3, characterized in that that post-oxidation of the collected in the container or tank Pickling / detergent solution through air injection he follows. Method according to one of claims 1 to 4, characterized in that that before the pickling / cleaning agent solution is introduced into the reverse osmosis system filters out the contained in the pickling / cleaning agent solution Inhibitors using an activated carbon filter. Method according to one of claims 1 to 5, characterized in that that the filtering of the pickling / cleaning agent solution in a multi-stage reverse osmosis system he follows. Method according to one of claims 1 to 6, characterized in that that the filtering of the pickling / cleaning agent solution within the reverse osmosis system stage is accomplished by flat membrane modules. Device for carrying out the method according to one of the preceding claims, wherein a pickling / cleaning agent solution ( 2 ) flow through successive device components - the piping system to be cleaned ( 1 ), - a container or tank ( 3 ) to collect the pickling / cleaning agent solution ( 2 ), - and an at least one-stage reverse osmosis system ( 7 ) to reduce the COD value of the pickling / cleaning agent solution ( 2 ) to <100 mg / l by filtering and in a multi-stage reverse osmosis system ( 7 ) the stages are connected in series. Apparatus according to claim 8, characterized in that the container ( 3 ) with a supply line ( 4 ) for milk of lime to adjust the pickling / cleaning agent solution ( 2 ) is designed for a pH value> 10. Apparatus according to claim 8 or 9, characterized in that the container ( 3 ) with center for injection ( 5 ) of oxidizing agent for post-oxidation of the pickling / cleaning agent solution ( 2 ) is trained. Device according to one of claims 8 to 10, characterized in that upstream of the reverse osmosis system ( 7 ) an activated carbon filter ( 6 ) for filtering out the in the pickling / cleaning agent solution ( 2 ) contained inhibitor is arranged. Device according to one of claims 8 to 11, characterized in that the piping system ( 1 ) is formed from heat exchanger tubes. Device according to one of claims 8 to 12, characterized in that that the reverse osmosis system stage has at least one pressure tube which is formed with flat modules arranged in disk technology. Device according to one of claims 8 to 12, characterized in that that the reverse osmosis system stage has at least one pressure tube which with disc modules arranged in disc technology (DT modules) is trained. Device according to one of claims 8 to 12, characterized in that that the reverse osmosis system stage has at least one pressure tube which is designed with winding modules.