CZ177093A3 - Process of treating combustion products based on wet absorption - Google Patents

Abstract

This process of purifying combustion products based on wet absorption, in particular combustion products from the pyrolytic combustion of domestic, industrial and special wastes by washing acid gases and the prevailing part of the insoluble substances, during which the used washing water from the washing is filtered and part of the filtered water is sprayed on the surface of the burnt waste and the remaining part of the filtered water is returned, whereas the technological water is added at a volume corresponding to the volume of filtered washing water sprayed on the surface of the burnt waste. It is preferable to keep the pH value of the washing water under the value of NaHCO3 and Na2CO3, preferably between 6.0 and 7.0.

Description

METHOD OF CLEANING WATER ABSORPTION

Technical field

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning flue gases based on wet absorption, in particular flue gases from pyrolytic waste incineration, e.g.

BACKGROUND OF THE INVENTION

Techniques and apparatuses for flue gas cleaning are known which differ from one another depending on the concentration of individual pollutants in the flue gas. For high concentrations of dusts with heavy metals, halides, sulfur dioxide and nitrogen oxides, three-stage absorption systems of flue gas cleaning with fully separated circuits on both sides are used, for less demanding cases the system is simplified up to a one-stage absorption system. In principle, the flue gas cleaning methods are based on two processes, dry and wet absorption.

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The wet absorption scrubbing process, a wet scrubber scrubber, is constructed according to the pollutant content of the flue gas as a one-stage to four-stage scrubber. After the first removal of the dust in the filter, the flue gas flows to the pre-stage. Here, the two-stage wet scrubbing liquid, which contains salts and solids, is injected by means of a spraying device into the flue gas stream and evaporated. The solids in the flue gas are dried to form, together with the crystalline salts, a fine-grained loose residue which is conveyed to the silo of the residual material. A large part of the finest solid particles still contained in the flue gas is filtered off in a subsequent fabric filter from which it is conveyed to the same silo of residual material. The flue gas then flows into the first scrubbing stage, i.e. the pre-scrubber, in which the acidic reactants, hydrogen chloride, hydrogen fluoride, are washed. Saturated flue gas flows into the main scrubber where the remnants of hydrogen chloride, hydrogen fluoride and sulfur dioxide are washed. The saturated wash suspension is partially discharged to the pre-stage through a neutralization tank. Addition of a precipitate separates the rtulf j contained in the wash suspension. The washed flue gas is passed through a droplet eliminator, then reheated and passed through a DENOx catalyst operating on the principle of selective catalytic reduction, and finally conveyed through a dioxin trap to a stack.

Existing wet flue gas scrubbers from pyrolytic furnaces produce waste water containing dissolved substances, especially inorganic salts and insoluble substances including heavy metal hydroxides. The concentration of dissolved inorganic salts depends on the amount and quality of the waste to be burned, the flow of process water into the flue gas scrubber and the pH maintained in the scrubbing water in the flue gas scrubber. In existing washing machines, the flue gas from the pyrolysis furnace is maintained at a pH between 8.0 and 10.0, which, together with hydrogen chloride and sulfur dioxide HC1 S0 ₂ scrubbed carbon dioxide C0 _second The HCO, 'and CO ₃ ² ' concentration resulting from CO ₂ scrubbing is conditioned by the pH value in the above interval.

In order to comply with the limits of solutes in the waste water discharged from the flue gas scrubber into the sewer or watercourses, it is necessary to dilute the resulting soluble inorganic salts by a corresponding flow of process water into the flue gas scrubber. A two-stage neutralization station must be used to reduce the concentration of heavy metals in the discharged water from the flue gas scrubber. There is no technology for removing or reducing the concentration of dissolved inorganic substances in the waste water beyond evaporation where no concentrate is formed outside the diluate.

The existing closed scrubbing circuits in the flue gas scrubbers from the pyrolytic furnaces represent a complex and costly technological device consisting mainly of a scrubbing member, a neutralization station for the disposal of part of the waste water discharged from the closed circuit and a cyclone to remove large particulate insoluble matter. drawn from the member to evaporate the proportion of wash water.

The disadvantages of the flue gas cleaning methods mentioned above are, in particular, the unwanted scrubbing of CO ₂ from the flue gas, the formation of HCO ₃ 'and CO ₃ ² ' in CO ₂ scrubbing. waste water into the sewer or watercourse or the use of a two-stage neutralization station. Another disadvantage is the considerable consumption of NaOH and process water.

SUMMARY OF THE INVENTION

The disadvantages of the aforementioned disadvantages are solved by a method for cleaning exhaust gases based on wet absorption, in which acid gases and most of the insoluble substances are scrubbed with water, in the embodiment according to the invention which consists in filtering the used scrubbing liquid. the surface of the incinerated waste and the remainder of the filtered water are returned, filling the process water in an amount corresponding to the volume of filtered wash water sprayed onto the surface of the incinerated waste. The effect is further increased by spraying the filtered workpiece periodically on the surface of the incinerated waste. It is further advantageous to spray filtered wash water onto the surface of the incinerated waste in an amount such that the concentration of dissolved inorganic salts in the wash water does not exceed the limit value above which the inorganic salts are deposited on the moving components of the respective technological machinery. It is also advantageous according to the invention to keep the pH of the washing water below the existence of NaHCO ₃ qJNa ₂ CO ₃ by means known per se, preferably in the range 6.0 <7.0.

An advantage of a method of operating a wet scrubber flue gas according to the invention is particularly considerable saving of water and sodium hydroxide in scrubbing carbon dioxide CO ₂ from flue gas. Due to the creation of a closed wash water circuit, the waste water from the flue gas scrubber is not discharged into the sewer or watercourse. By the mode of spraying the filtered washing water into the pyrolysis chamber of the pyrolysis furnace, a gradual deposition of substances dissolved in the sprayed washing water in the incinerated waste is ensured. This eliminates the need to dilute the resulting soluble inorganic salts with a corresponding flow of fresh process water into the flue gas scrubber, which represents a considerable saving of process water, and no need to use a two-stage neutralization station to reduce the concentration of heavy metals in the waste water. The importance of the process according to the invention is therefore also to protect the environment from pollution.

Overview of the drawings

The flue gas cleaning method according to the invention is explained in more detail by means of the accompanying drawing, in which a schematic diagram of a flue gas cleaning apparatus from a pyrolytic furnace with a closed wash water circuit is shown.

EXAMPLES vtjrt & leZU

The method for cleaning flue gases, in particular flue gases from the pyrolytic incineration of waste, for example household, industrial and special waste according to the invention, consists in washing water in which the acid gases and most of the insoluble inorganic substances are scrubbed ^{from the} flue gas scrubber. is passed through a filter press to the filtered water tank 1, where a portion of the filtered water is conveyed to the pyrolysis chamber of the pyrolysis furnace 5, where it is sprayed onto the surface of the incinerated waste and the remaining portion of filtered water is returned to the wash water tank 2. Preferably, the scrubbing water from the filtered water reservoir 1 is injected periodically into the pyrolysis chamber, wherein the feed mode, i.e. the ratio between the feed time and the pause before the next feed, is selected to ensure the deposition of solutes from the sprayed wash water in the incinerated waste. The quantity of sprayed water in one period must be such that it does not penetrate the incinerated waste under the pyrolysis chamber. Furthermore, the amount of wash water to be sprayed is controlled by the concentration of dissolved inorganic salts in the wash water in the wet scrubber 3. This concentration must not exceed the limit value above which the inorganic salts are deposited on the moving components of the respective process equipment. wet fan. Therefore, the pH of the scrubbing water in the wet scrubber is continuously maintained below the existence of NaHCO ₃ and Na ₂ CO ₃ in this water, preferably in the range of 6.0 to 7.0. The value is monitored by a microprocessor-controlled measuring device 6. The amount of wash water which can be sprayed on the waste to be burned depends on the type of waste and the criteria mentioned above, but its determination is solved by means known per se and is not the subject of the present invention.

The loss of scrubbing water caused by spraying a portion of it into the pyrolysis furnace 5 is compensated for by inlet of fresh process water into the scrubbing tank 2 in a corresponding volume.

Industrial applicability

The method according to the invention can also be successfully applied to other types and types of pyrolysis incinerators, including grate burning ovens, rotary and muffle furnaces, as well as combinations and assemblies for incineration lines.

Claims (5)

Process for the purification of flue gases based on wet absorption, in particular flue gases from the pyrolytic incineration of domestic, industrial and special waste, in which acid gases and the bulk of insoluble matter are scrubbed from the flue gases, characterized in that the washing water used is filtered, water is sprayed onto the surface of the waste to be incinerated and the remainder of the filtered water is returned for reuse; Wr ' replenishes the process water in an amount corresponding to the volume of filtered wash water sprayed onto the surface of the incinerated waste. 2. The flue gas cleaning method according to claim 1, characterized in that it is filtered through a scrubbing cycle of the waste to be burned periodically. Marking Sprays on Marking Surface 3. A method for cleaning flue gases according to claim 1, characterized in that the filtered scrubbing water is sprayed onto the surface of the incinerated waste in an amount such that the concentration of dissolved inorganic salts in the scrubbing water does not exceed the limit value above which inorganic salts are deposited on the moving process components. a wet scrubber, especially a wet fan. I 9 4. A method according FGT HAF "(« l, 2,3, characterized in that the pH of the wash water is maintained below the existence of NaHCO ₃ and Na ₃ C0 _third 5. The flue gas cleaning method according to Π4ΓίΊ (Μ4), characterized in that the pH value of the washing water is maintained in the range 6.0 to 7.0.