CH633726A5 - METHOD FOR REMOVING ACID POLLUTANTS AND HOVING SUBSTANCES FROM EXHAUST GASES FROM INDUSTRIAL OVENS, ESPECIALLY FROM WASTE COMBUSTION PLANTS, AND SLUDGE SEPARATORS FOR THE EXECUTION THEREOF. - Google Patents

Description

The invention relates to a method for removing acidic pollutants and suspended matter from exhaust gases from industrial furnaces, in particular from waste incineration plants, in which the exhaust gases are first passed through an indirect heat exchanger for the purpose of dissipating thermal energy, then an evaporative cooler and then via a dry cleaner of a wet wash with at least one Gas washing stage are supplied and the washing water of the wet scrubber is also circulated via a sludge separator and is removed from the sludge separator via a return line pollutant suspension and fed to the evaporative cooler, the pollutant suspension being introduced into the exhaust gases in a mixing room of the evaporative cooler.

A system of the above type for carrying out the cleaning of exhaust gases from industrial furnaces for the treatment of non-ferrous metal melts, in particular aluminum melts, is described in DE-OS 2 408 222 by Gottfried Bi-schofFBau compl. Gasreinigungs- und Wasserkückkühlanlagen KG, Essen, Germany.

When this known system is operated, exhaust gases, in particular from an aluminum melt covered with salts such as sodium chloride or potassium chloride, are introduced directly into an evaporative cooler at temperatures well above 400 ° C., normally from 800 to 1000 ° C. In the evaporative cooler, the hot exhaust gases from the aqueous pollutant suspension injected there, which is taken from a later stage of the process, absorb very large amounts of water, which are further increased by further water absorption in the subsequent wet scrubbing. The sum of the total amount of water absorbed by the exhaust gas flow now leads firstly to a considerable increase in the gas volume to be cleaned and thus to a substantial, costly enlargement of the wet-washing apparatus, and secondly to the formation of an undesirably intensive water vapor condensation plume at the outlet of the Ka2

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mins, from which the cleaned exhaust gases are released into the ambient air.

In the course of intensified efforts to keep the ambient air clean, wet washing is also required in several countries in addition to dry flue gas cleaning of incineration plants. The purpose of this wet scrubbing is to remove gaseous pollutants such as HCl, H2F2 and S02 from the exhaust gas. However, an important function of wet scrubbing is also to cool the gases, as a result of which tar-like, initially gaseous substances and also salt-like substances can be condensed and then separated.

This cleaning effect cannot be achieved with only dry gas cleaning, which is usually carried out at temperatures above 200 ° C.

A major disadvantage of wet washing, however, is that heavily polluted waste water is produced, the removal of which is associated with considerable costs.

As mentioned at the beginning, it is known per se to remove the sludge-containing waste water from wet scrubbing scrubbers by spraying them into an evaporative cooler upstream of the wet scrubbing process and producing a dry crystal slurry there.

However, this process means that the exhaust gases introduced into the system are very hot, which is not the case with the exhaust gases from waste incineration, apart from the fact that a large part of the heat content of the still unpurified gases from waste incineration is obtained beforehand through indirect heat exchange should be withdrawn, e.g. by indirect heating of a steam boiler, whereby hot steam for industrial purposes, e.g. for heating or for generating electrical energy.

The pre-cooled exhaust gases from modern waste incineration plants are therefore only at a temperature below 400 ° C, and usually in the range of 150 to 400 ° C, before being subjected to a cleaning process.

While waste gases from aluminum and the like non-ferrous metal melts contain small amounts of hydrofluoric acid and hydrochloric acid, these amounts produce wastewater with a pH value above 4 and often above 6.5 in wet scrubbing, in contrast, the waste gases from waste incineration plants have a strong one Content of hydrogen chloride, especially from the incineration of polyvinyl chloride waste, and above all, that of S02. In addition, their primary dust content is usually significantly higher than that of the fumes from aluminum melting furnaces.

Therefore, the choice between an electrostatic cleaner (electrostatic filter) and a mechanical cleaner (cyclone dust) is optional in the Bischoff plant (DE-OS 2 408 222) as a dry cleaner, in known processes for cleaning exhaust gases with a high content of acid components, such as e.g. that in DE-OS 2 431 130 of Walther and Cie. AG, Cologne, Germany, however, the use of an electrostatic dry cleaner, which is more expensive per se, is always required. Before the exhaust gases are cleaned in an electrostatic precipitator, in this known method the flue gases are first mixed with a salt solution that has been extracted from the method itself and is concentrated as much as possible, in particular by injection into an injection evaporator (evaporative cooler) charged with the flue gases, and the flue gas / salt solution mixture obtained is evaporated . Only then is the dust content separated in the electrostatic filter.

In the case of wet washing, the Walther process basically works with alkaline washing liquids, especially those containing sodium and ammonium ions, and thus achieves this

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concentrated salt solutions in wet washing, which are returned to the evaporative cooler (injection evaporator).

In relation to these known methods, the object of the invention is to implement a method for purifying exhaust gases in the system described at the outset, which utilizes the preceding part of the energy content of the exhaust gases in the usual way, e.g. by indirect heat emission in a steam boiler, also permitted, nevertheless producing clear, little polluted and easy to remove waste water (e.g. in the gas cleaning system itself by spraying it into the evaporative cooler), and which can be implemented in a system that uses a Makes electrostatic filters unnecessary, and their total space requirement is also not greater than that which an electrostatic filter would require approximately the same useful power.

This object is achieved and the objectives mentioned are achieved by a method of the type described at the outset, which is characterized in that the method simultaneously

(a) the proportion of acidic pollutants in the exhaust gases to be cleaned is kept so high that in wet scrubbing the pH of the washing liquid and pollutant suspension occurring there is below 4 and the exhaust gases have a non-water-soluble primary dust content of at least 500 mg per Nm3,

(b) the pH of the liquid phase is kept below 4 in the sludge separator and in each gas scrubbing stage upstream of it, and

(c) the vaporizable portion of the liquid phase of the pollutant suspension to be introduced into the evaporation cooler is kept at a value of at least 90% by weight and the injected amount of this pollutant suspension is only measured taking into account its pH value in such a way that the treated with it Exhaust gases passing through the dry cleaner still have such a high content of acidic pollutants that a pollutant suspension with a pH below 4 is formed in the subsequent wet washing.

By injecting the pollutant suspension into the evaporative cooler, the separation of the water-insoluble primary dust from the exhaust gases by agglomeration of fine dust particles and their subsequent separation in the dry cleaner can be increased so that the washing liquid of the wet laundry remains exceptionally clean. In addition, a very thin sludge phase (pollutant suspension) with a low pollutant content usually arises in the sludge separator.

The "pollutant suspensions" mentioned are also referred to in industry as "slurry". These are aqueous suspensions of solid pollutants described in detail below or else aqueous emulsions of liquid water-insoluble pollutants or aqueous mixtures consisting of such a suspension and emulsion, the viscosity of which is relatively low, and the density of which is preferably increased by 1 to can be about 1.3 g / ml.

Insofar as the pollutants are water-soluble, they are in solution in the aqueous phase of the "pollutant suspensions"; when saturated, the excess of water-soluble pollutants is suspended.

Pollutants from which industrial exhaust gases are to be cleaned with the aid of the inventive method are not only the pollutants which can be detected by the usual dry flue gas cleaning by means of an electrostatic precipitator, which condense to sufficiently large dust or fog particles at the temperatures prevailing in the electrostatic precipitator, but also

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Oils or tar-like substances and also some of the metal oxides or salts contained in the flue gas, which only form an aerosol when the exhaust gases cool down after they have left the chimney and thus lead to air pollution, and above all harmful gases such as HCl, H2F2 or S02, all of which cannot be separated by an electrostatic filter.

Atomizing dryers are used as evaporative coolers (or injection evaporators, as they are e.g. by NIRO Atomizer Ltd., Copenhagen, Denmark, and as described in "Food Engineering" February 1966, pages 83-86. They contain a mixing chamber or similar space in which pollutant suspension is injected into the exhaust gases flowing through it.

A mechanical deduster, e.g. a cyclone dust collector of known design can be used. In contrast to the known methods, no electrostatic filter (electrostatic deduster) is required here.

For wet scrubbing, devices with at least one of the flue gas scrubbing towers, such as those used by Fattinger, Schmitz and Schneider in publication no. 107 “Technique of exhaust gas cleaning” of the conference “Air hygiene 1976” of December 3, 1976 of the publisher, are preferably used VFWL (Association for Water and Air Hygiene), Huttenstrasse 36,8006 Zurich, Switzerland (see Figures 1 to 4).

Such a tower is preferably used with the X separator described there.

The water to be added to wet scrubbing as a replacement for the water discharged from the system with the cleaned exhaust gases can consist of fresh water or wastewater, and can therefore be used at various points in wet scrubbing on the one hand as fresh water, on the other hand as wastewater or as an aqueous suspension of solid pollutants and / or as an aqueous emulsion of liquid pollutants of the type mentioned above.

The pollutant suspension is separated from the washing liquid in a separating apparatus, which for the sake of brevity is referred to herein as “sludge separator”. It replaces the apparatus referred to in DE-OS 2 408 222 as “thickener”. A new type of sludge separator, constructed by Jürg Schneider, is advantageously used, the construction and mode of operation of which is described in more detail below.

The residence time of the exhaust gases in the mixing chamber of the evaporative cooler with the pollutant suspension is preferably at least 2 seconds.

With a dwell time of less than 2 seconds i.e. If the mixing space is too small, the finer pollutant particles are no longer sufficiently agglomerated into larger ones, but this is necessary for satisfactory separation in the dry cleaner. In the evaporative cooler, the injected pollutant suspension (sludge) must have enough time to absorb the finer dust content from the exhaust gases. If the dwell time is too short, salts and crystal formation can occur on the lower wall parts of the mixing chamber of the evaporative cooler, because moist particles can still reach the wall of the mixing chamber.

On the other hand, the evaporative cooler must be designed larger and more expensive for the same amount of exhaust gas if longer residence times are to be achieved without the process being improved to a corresponding extent. Evaporative coolers that are too large therefore work less economically.

The temperature of the exhaust gases in the dry cleaner should preferably be kept below 170 ° C. by using an appropriate amount of pollutant suspension in the evaporative cooler.

If the temperature of the exhaust gases in the dry cleaner exceeds 170 ° C, the condensation of the solid particles or liquid droplets of the pollutants to be separated out is not sufficient. If the exhaust gas leaves the dry cleaner too hot, too much water is evaporated from the washing liquid in the subsequent wet washing and carried away by the exhaust gas and led out of the system, and the pollutant concentration in the pollutant suspension becomes too high, and therefore the washing liquid is too dirty, which in the case of whose return in the circuit through the wet wash leads to an inadequate cleaning effect. The washing liquid can even be oversaturated with salts, so that crystallization of salt in the scrubber can possibly lead to its constipation.

When they are introduced into the mixing zone of the evaporative cooler, the exhaust gases to be cleaned preferably have a temperature in the range from 150 to 400 ° C.

If the exhaust gas introduced into the evaporative cooler has a temperature below 150 ° C, the energy consumption for heating the above-mentioned mixing chamber of the evaporative cooler is too high in order to maintain a temperature above the water dew point, i.e. to avoid condensation of harmful substances and harmful deposits on the evaporative cooler walls. to allow the plant to operate economically.

At temperatures of the exhaust gases introduced into the evaporative cooler above 400 ° C, the cooling limit temperature at the outlet of the system becomes too high for the cleaned exhaust gases, because a higher exhaust gas temperature means the absorption of larger quantities of water, which means that the internal heat exchange system of the system has to be designed too large. With an upper temperature limit of 400 ° C for the exhaust gases to be treated in the evaporative cooler, the heat exchange system coupled with the washing liquid circuit of wet scrubbing already works at 70-80 ° C, i.e. quite close to the theoretical limit given by the boiling point of the washing liquid for systems operating without overpressure .

Due to the aforementioned minimum residence time of the exhaust gases in the mixing chamber of the evaporative cooler (2 see) and by keeping the temperature of the exhaust gases in the dry cleaner below 170 ° C, a particularly satisfactory cleaning of the exhaust gases is achieved with inlet temperatures in the range from 150 to 400 ° C specified above.

The combination of the features listed under (a), (b) and (c) now requires, when carrying out the process according to the invention, the pH value of the liquid in the sludge separator and in or in the gas washing stages upstream of it for wet washing 4, ie no or only very small amounts of basic neutralizing agents, such as sodium hydroxide solution, the washing liquids or, for example Lime milk to add to the pollutant suspensions, while in known processes e.g. that in DE-OS 2 431 130 of Walther and Cie. AG,

Cologne, Germany, the acidic components of the exhaust gases, especially S02, must be converted into the corresponding, preferably water-soluble salts by chemical reaction with an alkaline solution. In this known process, the pH of the liquid circulated should be between 4.0 and 7.8, but in practice below pH 6.5, probably only with very small proportions of acidic components, but usually between 6.5 and 7 , 5 can be carried out, that is, with a considerable outlay on basic substances. When working at a pH above 4

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However, in the method according to the invention, precipitation would occur to such an extent, particularly in the wet-washing installation, that the entire installation would become blocked.

The process of the present invention is preferably carried out with a strongly acidic washing liquid with a pH below 2, in the sludge separator and in each washing step directly upstream thereof, thereby saving costs for alkaline chemicals.

Only if the HCl and S02 content of the exhaust gases to be cleaned is particularly high (above 2 g / Nm3 HCl + S02) is it advisable to concentrate the pollutants, which are completely returned from the sludge to the injection nozzle of the evaporative cooler, before entering the latter partially neutralize. The suspension can become alkaline, but then becomes acidic again in the wash due to the acidity of the exhaust gases (HCl) (pH less than 4).

The temperature of the inner walls of the mixing zone of the evaporative cooler (injection evaporator) coming into contact with the exhaust gases to be cleaned can be kept in such a temperature range in a preferred own construction of the latter by heating the outer sides of these inner walls by means of the hot exhaust gases running along these outer sides that No condensation of pollutants takes place on the walls mentioned, which above all creates corrosion problems and forces the use of special, corrosion-resistant materials and also impairs the production of the most dry possible pollutant granules in the evaporative cooler and dry cleaner.

This temperature control can also be achieved by indirect heating of the walls of the mixing room by means of hot steam. The jacket of the dry cleaner, for which a mechanical deduster, in particular a cyclone, is preferably used, is advantageously also indirectly heated, so that condensation of corrosive pollutants, in particular hydrochloric acid or sulfuric acid, is also prevented there.

The exhaust gas temperature in the cyclone dust collector should preferably be kept below 170 ° C.

Preferably, the walls of the evaporative cooler and the dry cleaner in contact with the exhaust gases are heated to such an extent that they are kept at or above the temperature which adiabatically arises in the exhaust gas after the inlet gas has been mixed with the injected pollutant suspension.

It is advantageous to increase the temperature of the walls of the mixing chamber in the evaporative cooler in contact with the exhaust gas to be cleaned and also the corresponding walls of the mechanical dedusting device by more than 5 degrees Celsius above the dew point of the acid in the exhaust gas and the injected pollutant suspension (sludge ) to keep the mixture formed.

Particularly good results are obtained here if, on the one hand, the residence time of the exhaust gases in the evaporative cooler is from 3 to 7 seconds and, on the other hand, the exhaust gas temperature in the mechanical deduster (cyclone) is kept at 140 to 150 ° C.

At speeds of the gas flowing through the wet scrubber above 1 m / sec, a wash tower loaded with a packing layer is advantageously used in the wet scrubbing, the packing layer preferably consisting of hedgehog packing bodies (see FIG. 7 of the above-mentioned publication by the Association for Water and Air Hygiene, Zurich) consists. The free cross-section of the scrubber through which the exhaust gas flows is advantageously selected so that the gas velocity is above 1 m / sec.

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Furthermore, the wet scrubber can advantageously contain a wet mechanical aerosol separator with a gas resistance of 5 to 60 and preferably 10 to 30 mbar. An X-separator is preferably used as the aerosol separator, which is also described in the aforementioned publication by the VFWL Zurich (FIGS. 2 and 3).

Preferably more than 50% by volume of the circulating liquid which flows through the first gas scrubbing stage downstream of the mechanical deduster is passed through the settling tank of the sludge separator (thickener), but particularly advantageously from 70 to 100%, the residence time of the liquid in the settling tank of the sludge separator preferably, depending on the size of the latter, between 1 and 8 minutes, but particularly advantageously 3 to 5 minutes.

Slag extinguishing water from a waste incineration plant is preferably used as the wastewater used to replace water discharged from the plant with the exhaust gases. This waste water can be introduced into the washing liquid circuit, but preferably into the sludge separator.

Finally, a heat exchanger can be used in the washing liquid circuit of the wet laundry, which cools the washing liquid, and which releases heat extracted from it, preferably in a heat pump system, via a second heat exchanger to supply air, which is thereby heated and then mixed with the cleaned exhaust gases in the chimney of the system for dilution .

A binder and / or a chemical which binds the salts present in the solid phase of the pollutants and, above all, reduces their solubility in rainwater, may also be metered into the partially neutralized pollutant suspension to be supplied to the evaporative cooler from the sludge separator, e.g. a silicate like water glass.

Embodiments of the invention are apparent from the following description in conjunction with the accompanying drawings, in which

1 schematically shows a first embodiment of a plant for carrying out the method of the invention,

2 schematically shows a practical arrangement of the embodiment of FIG. 1 in side view,

3 shows the arrangement according to FIG. 2 in plan view, FIG. 4 shows a perspective, partially cut-open representation of the system according to FIGS. 2 and 3

5 shows a schematic illustration of a longitudinal section through a preferred embodiment of the sludge separator in the system according to FIGS. 1 to 3, and

Fig. 6 shows a schematic representation of a second embodiment of the system, which is particularly suitable for those cases in which the lowest possible water vapor plume is required at the chimney outlet when discharging the cleaned exhaust gases into the environment.

The system shown in FIG. I comprises an evaporative cooler 1, the outer wall of which is surrounded by an insulation jacket 17. The evaporative cooler 1 has in its interior a cylindrical partition wall 18 which separates a mixing and reactor space 100 from an outer annular chamber 101 surrounding it. An exhaust gas supply line 11 opens into the outer annular chamber 101 for the supply of exhaust gas to be cleaned into the system. At its upper end, the cylindrical partition 18 has passages through which the mixing chamber 100 is freely connected to the outer annular chamber 101. At the upper end of the mixing chamber 100, an atomizing nozzle 19 is provided, from which liquid can be sprayed into the interior of the mixing chamber 100. An exhaust pipe 12 leads from the lower region of the mixing chamber 100 into a cylinder.

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Cloning dust 2. The wall of the exhaust pipe 12 and the outer wall of the cyclone dust collector 2 are surrounded by a heating jacket 20, in which turns of half-tubes 23 are provided for heating the cyclone dust collector and the exhaust pipe 12. At the lower end of the mixing chamber 100 there is a discharge line 15, at the lower end of the annular chamber 101 there are discharge lines 14 and at the lower end of the cyclone dust collector 2 there is a discharge line 24 through which separations from the exhaust gas in solid or liquid concentrated form from the evaporative cooler or the cyclone dust collector 2 can be drained into a dust collector 9.

The draining is preferably carried out intermittently and is controlled via valves 71, 72, 74, which are provided in lines 14, 15, and 24, respectively. The half-tubes 23 are heated with hot steam, which is introduced via a steam feed line 231. Condensate forming in the half-pipes is continuously drained into a condensate pot 233 via a condensate drain 232.

A gas transfer line 22 leads from the upper area of the cyclone dust collector 2 into the central area of a washing tower 3 of a wet wash.

The middle area of the tower 3 is filled with a packing layer 31 which rests on a cross grate 34.

Above the packing layer 31 there is an injection nozzle 131 in the washing tower 3, which serves to spray the packing layer with washing liquid from a liquid run-off line 33. In the upper part of the washing tower 3, an aerosol separator 35 is placed thereon, preferably an X separator, the diaphragm wall 135 of which is sprayed with washing liquid via a spray nozzle 133, which is fed to the nozzle 133 from the circuit line 33 via the branch line 133a. The aerosol separator 35 is in free connection on the one hand with the interior of the washing tower 3 and through the diaphragm wall 135 with a droplet separator 36. A spray nozzle 136 is arranged in front of the droplet separator, in which a fresh water supply line 90 with a shut-off valve 91 opens. The fresh water sprayed in from the spray nozzle 136 rinses the walls of the droplet separator 36 and collects in a collecting tank 92 from which it flows into the washing tower 3 above the packing layer 31 via the line 192. From the droplet separator 36, a gas line 32 for the cleaned exhaust gas leads via a fan 5 into a gas outlet line 52, which opens into a chimney 6. At the lower end of the washroom 3 there is a sludge separator 4, the construction of which is described in more detail below in connection with FIG. 5. Washing liquid is pumped out of the sludge separator 4 by means of a pump 81 through the circuit line 33 to the nozzles 131 and 133.

The settling tank 41 of the sludge separator 4, which is filled with washing liquid, has at its upper end a conical dividing wall 44 which is designed to be pointed upwards and towards the center.

The washing liquid trickling downward in the tower 30 from the nozzle 131 collects on the bottom 134 of the washing tower 3, which is inclined conically downwards towards the center and flows from there through a drain line 42, which extends downward through the opening in the middle of the partition 44 into the Settling tank 41. From the annular space 144, which is located above the dividing wall 44 and below the bottom 134, a floating sludge discharge line 43 leads downward via a shut-off valve 87 and merges with a sludge line 13 which extends from the lower end of the settling container 41 of the sludge separator 4 Check valve 86 leads.

After the union with the line 43, the line 13 leads via a circulating pump 82, which leads via a sieve or filter 213 to the upper end of the evaporative cooler 1, where it is connected to the injection nozzle 19. The injection nozzle 19 is designed as a two-substance nozzle, air or steam being able to be blown in as atomizing medium via a feed line 89 and a shut-off valve 88.

In FIGS. 2 to 6, parts corresponding to the apparatus elements in FIG. 1 are identified by the same reference numerals as in FIG. 1.

The evaporative cooler 1 is designed in the embodiment according to FIGS. 2 to 4 as a cylindrical container. The supply line 11 for the exhaust gases to be cleaned opens here into the upper end of the evaporative cooler 1, while a plurality of nozzles 19 each in a lower position through the branch line 13a branched off from the liquid line 13 via a ring line 113a, and in a higher position of the branch line 13b branched off from line 13 is supplied via a ring line 113b.

In this embodiment, the nozzles 19 direct the liquid cones upwards, that is to say against the exhaust gas flowing in through line 11.

Arranged around the lower area of the evaporative cooler 1 are ten cyclone dusts 2, into which the exhaust gas leaving the evaporative cooler 1 in its lower area is introduced via ten lines 12. The exhaust gas which has been dedusted dry in the ten cyclone sprinklers 2 passes via a ring line 112 from a cross-section which gradually widens after the gas transfer line 12 into the latter line, the flow cross-section of the ring line 112 preventing throttling of the gas flow into line 12. At the lower end of the evaporative cooler 1, as in the embodiment according to FIG. 1, there is a discharge line 15 for pollutant agglomerations, which is provided with a shut-off valve 72.

The lower ends of the cyclone duster 2 are connected to discharge lines 114, which end together with the line 15 in a collecting vessel 115, which can be emptied through a line 116 provided with a shut-off valve 70.

The exhaust gas transfer line 22 is connected in the same way as in the system according to FIG. 1 to a washing tower 3 of wet scrubbing, which is equipped in the same way as that in FIG. 1.

The preferred embodiment of the sludge separator 4 shown in FIG. 5 also comprises a settling container 41, a liquid inflow line 42, which projects through the central opening 244 of a partition 44 tapering to a point and upwards towards the center and comes into contact with its upper end the outlet opening 234 of the bottom 134 of the washing tower 3, which slopes conically inwards and downwards, is connected.

At its lower end, the line 42 carries a mouth funnel 142 which widens conically downwards and outwards and is open at the bottom, in the interior of which a baffle plate 45 is fastened opposite the line 42 by struts 46 perpendicular to the end of the line 42.

A vent pipe 47 is inserted in the center of the inflow line 42 by means of struts, the upper ends of which open above the floor 134 and the lower end just above the baffle plate 45.

In the middle region of the container 41, just above the mouth funnel 142, there is the inlet opening 48 of an outlet pipe socket 49, to which the circuit line 33 for washing liquid is connected outside the sludge separator 4.

The partition wall 44 projects into the lower open end of the washing tower 3, which is the ring 5 and is placed on the upper area of the separator 4 surrounding the opening 244

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room 134 forms. A two-point level controller 75 is connected to the sludge separator 4, of whose two measuring heads or sensors 76 and 77 the lower measuring head 76 responds when the liquid in the container 41 has dropped to the level Ni while the upper sensor 77 responds,

when the liquid in the container 41 has risen to the upper limit level denoted by N2.

The operation of the sludge separator 4 is such that washing water from the washing tower 3 first flows through the inflow line 42 into the container 41 and fills it with the pump 81 at a standstill and with the valve 86 closed until the upper level N2 is reached. The pump 81 is then started and the valve 86 is opened.

The sludge separator 4 is now operated continuously. The outflow rate (volume per unit time) of the washing liquid from the low-pollutant central region of the container 41 via the line 33 and that of the sinking sludge, i.e. Sludge with a density above 1, enriched pollutant suspension through line 13 together slightly exceed the inflow rate of washing liquid into container 41 through line 42.

As a result of this and due to the evaporation of part of the washing water which is carried away from the exhaust gases in the washing tower 3, the liquid level in the container drops from the upper level N2 to the lower level Nt. If this level is reached, the sensor 76 of the level controller 75 responds and opens the valve 91, whereby fresh water enters the washing tower 3 through the line 90, and a shut-off valve 79 of a waste water feed line 78, through which waste water now flows directly through the opening 244 in flows into the container 41. The slag extinguishing water from a waste incineration plant is advantageously used as waste water.

The liquid level now rises again in the container 41 until it has reached the upper level N2, whereupon the sensor 77 responds and the level controller 75 closes the valves 79 and 91 again.

When the liquid level rises to level N2, a layer of floating sludge (density below 1) accumulated on the liquid surface is pushed up out of the opening 244 and runs downwards on the top of the conical partition 44 and through the floating sludge discharge line 43 to itself to combine with the sinking sludge in line 13. The combined pollutant suspension formed from floating sludge and sinking sludge is now pumped up into the nozzles 19 of the evaporative cooler 1 by means of the pump 81.

The flow cross sections of the lines 42 and 33 are preferably designed such that when the valve 86 is closed in the main discharge line 13 for sinking sludge, the same amount of washing liquid flows to the container 41 through line 42 as flows out of it via line 33. The removal of pollutant suspension via line 13, and from time to time via line 43, as well as the evaporation from wash tower 3, which reduces the amount of liquid flowing through line 42, thus causes the liquid level to drop from the level N2 to the level Nt and this decrease can therefore be influenced primarily by means of valve 86.

While in a previously known separator (DE-OS 2 408 222) only a part of the pollutants, namely the sludge portion is conveyed into the evaporative cooler and the floating sludge portion is pumped back into the washing liquid, both sludge and floating sludge are separated in the sludge separator according to the invention and circulate back in the washing liquid to a minimum (suspension of pollutant particles with density 1).

A special flushing water line (not shown) can also be provided in the annular space 144 in the event of a particularly high accumulation of floating sludge, from which water is sprayed onto the outer surface of the partition 44 and flushes the floating sludge deposited there into the line 43.

The settling of sinking sludge from the liquid flowing through the inflow line 42 into the container 41 is promoted by firstly breaking and distributing this liquid flow on the baffle plate 45 and secondly by the liquid flowing off here on the inner wall of the mouth funnel 142 through which it flows inward expanding scope is further slowed down.

The throughput rate through the container 41 is very favorable, in practical operation of the separator 4 about eight container contents are circulated per hour, in contrast to previously known systems in which only a small liquid flow flows into a large-volume settling container and a correspondingly small outflow of liquid is provided, so that for each circulation of the contents of a container with the same cleaning effect, a ten times larger volume of the container, or approximately one or an hour and a half for each circulation, is required.

The embodiment of a system according to Fig. 6 is particularly suitable on the one hand for cleaning exhaust gases with a particularly high content of acidic pollutant components, especially S02 gas, and on the other hand for those cases in which the water vapor condensation plume, which is regularly at the outlet of the fireplace 6 forms, should be suppressed as much as possible.

In contrast to the previously described embodiments of the exhaust gas purification system, the wet scrubbing in the system according to FIG. 6 comprises two towers connected in series in the gas flow direction, the exhaust gas from the cyclone sprayer 2, into which it passes through the inlet openings 21 from the evaporative cooler 1, initially via the gas transfer line 22 in the washing tower 30 and from this through the gas line 122 into a second washing tower 103 and from this exclusively as in the systems described above via lines 32 and 52 into the chimney 6.

Wash tower 30 has a sump 30a, a grate 34,

a packing layer 31 and in its upper part an aerosol separator 35 and a droplet separator 36; Wash tower 103 also a sump 103a, a packing layer 39 with grate and a droplet separator 37. The washing liquid is pumped out of the sludge separator 4 by means of a pump 81 through line 33 to the aerosol separator 35 and there with it the packing layer 31 and nozzle 133 from nozzle 131 the diaphragm wall 135 is sprayed, as is also the case in the embodiment according to FIG. 1.

Washing liquid from the packing layer 31 flows loaded with pollutant into the sump 30a and out of this through the inflow line 42 to the settling tank 41 of the sludge separator 4.

Sink sludge from sludge separator 4 passes via line 13 and floating sludge via line 43 into a neutralizing tank 7, in which the pollutant suspension can be at least partially neutralized by means of lime milk. The containers 7 and 41 behave like communicating tubes and a level regulator 175 opens a valve 38 when the liquid level in the container 7 drops to a lower level and closes the valve 38 when the liquid level rises to an upper level.

The container 7 is also equipped with a stirrer 80 and a motor.

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When the valve 38 is opened, washing liquid, which is less loaded with pollutant than that circulating through lines 33 and 42, is pumped from the sump 103a of the washing tower 103 by means of the pump 83 through the line 84 into the droplet separator 36 of the washing tower 30 and sprayed through the nozzle 136, while a part of the washing liquid from line 84 reaches the nozzle 139 through a branch line 84a and is sprayed from there onto the packing layer 39 of the washing tower 103.

The sprayed-in washing liquid finally arrives from the droplet separator 36 via collecting vessel 92 and line 192 into the washing liquid circuit of the washing tower 30.

The liquid level in the sump 103a of the washing tower 103 is controlled by a two-point level regulator 275, which opens a valve 88 when the level drops to a lower level, as a result of which fresh water or, if the SO2 content in the exhaust gases is high, a dilute sodium hydroxide solution through line 85 is introduced into the washing liquid circuit in line 85. When an upper level in the sump 103a is reached, the level controller 275 then closes the valve 88 again.

Finally, the formation of a water vapor condensation plume at the outlet of the chimney 6 can be reduced by blowing air into the chimney by means of a fan 50, which is preferably heated to over 100 ° C. in a heat exchanger 110.

The heat is supplied in the heat exchanger by means of a heating fluid pumped in a line 106 by means of a pump 60 in the circuit. The heating liquid takes its heat content in the heat exchanger 10 from the washing liquid flowing through it and heated by the exhaust gases in the washing tower 30 from the line 33 and optionally an additional heater 107.

As can be seen from the figures of the drawing, the sludge obtained in the gas scrubbing is sprayed into a reactor (evaporative cooler) after the addition of lime milk and is dried in such a way that it comes into contact with the flue gases at over 200 ° C which leave the steam boiler , in which they share a large part of their

Have to give up thermal energy. The finely sprayed sludge binds most of the dust content of the raw gases, which means that at the outlet of the downstream cyclone 2 there is only a little dust in the gas. The circulating liquid of the subsequent wet washing remains relatively pure, because an optimal separation of the sludge in the sedimentation apparatus io (sludge separator) 4 is made possible by optimal temperature setting in the reactor 1 and by appropriate control of the composition of the washing liquid.

When operating for several months, no disturbing incrustations in the washing system or caking of dust in the dry pre-cleaning (Cyclone 2) are observed.

15 When cleaning the flue gases of a municipal waste incineration plant, the following advantageous results were achieved without the need for an expensive electrostatic precipitator:

Pollutant content of the cleaned exhaust gas to be discharged into the environment:

20th

- Reduction of the dust content below 50 mg / Nm3 (measured after gas cooling)

- Free hydrochloric acid below 5 mg / Nm3.

- Total chloride content (as Cl ~) below 15 mg / Nm3 25 - Sö2 below 100 mg / Nm3

- nitrogen oxides below 100 ppm

The following advantages were also achieved:

- Utilization of the flue gas temperature (after the steam boiler) to dry the sludge generated in the gas scrubber

30 me and to remove the slag extinguishing water from the incinerator

- Conversion of all separated pollutants into free-flowing ashes

- low water consumption (less than 50 kg / 1000 Nm3 smoke-35 gas)

- very low consumption of lime milk (less than 50 g Ca (OH) i / 1000 Nm3 flue gas)

- Low energy consumption thanks to the use of an X separator to separate the aerosols (below 360 mm water column

40 fan differential pressure).

s

3 sheets of drawings

Claims (10)

633726 PATENT CLAIMS 1.Procedure for removing acidic pollutants and suspended matter from exhaust gases from industrial furnaces, in particular from waste incineration plants, in which the exhaust gases are first passed through an indirect heat exchanger (101) for the purpose of dissipating thermal energy, then an evaporative cooler (1) and then via a dry cleaner ( 2) a wet wash in a wash tower (3) with at least one gas washing stage, and wherein the wash water of the wet wash is also circulated via a sludge separator (4) and is removed from the sludge separator (4) via a return line (13) and pollutant suspension and is fed to the evaporative cooler (1), the pollutant suspension being introduced into the exhaust gases in a mixing chamber (100) of the latter, characterized in that in the method at the same time (a) the proportion of acidic pollutants in the exhaust gases to be cleaned is kept so high that in wet scrubbing the pH value of the washing liquid and pollutant suspension occurring there is below 4 and the exhaust gases have a non-water-soluble primary dust content of at least 500 mg per Nm3 exhaust gas , (b) the pH of the liquid phase is kept below 4 in the sludge separator (4) and in each gas scrubbing stage upstream of this, and (c) the vaporizable portion of the liquid phase of the pollutant suspension to be introduced into the evaporation cooler (1) is kept at a value of at least 90% by weight and the injected amount of this pollutant suspension, taking into account its pH value, is only measured so that in the with it treated exhaust gases passing through the dry cleaner (2), such a high content of acidic pollutants remains that a pollutant suspension with a pH below 4 is formed in the subsequent wet washing. 2. The method according to claim 1, characterized in that the exhaust gases are kept at a temperature in the range of 150 to 400 ° C when entering the evaporative cooler (1). 3. The method according to claim 1, characterized in that the residence time of the exhaust gases in the mixing chamber (100) of the evaporative cooler (1) with the pollutant suspension is at least 2 seconds. 4. The method according to claim 1, characterized in that the temperature of the exhaust gases in the dry cleaner (2) is kept below 170 ° C by using an appropriate amount of pollutant suspension in the evaporative cooler (1). 5. The method according to claim 1, characterized in that the walls in contact with the exhaust gases of the evaporative cooler (1) and the dry cleaner (2) are heated so high that they are kept at or above that temperature which is adiabatic in the Exhaust gas sets after the inlet gas has been mixed with the injected pollutant suspension. 6. The method according to claim 1, characterized in that the walls of the evaporative cooler (1) with which the mixture of exhaust gas and injected pollutant suspension comes into contact are kept at a temperature which is 5 degrees Celsius above that at which acids in mentioned mixture would condense. 7. The method according to claim 1, characterized in that the gas scrubbing stage of the wet scrubbing is formed by a scrubbing tower (3) with a packing layer (31). 8. The method according to claim 7, characterized in that the speed at which the exhaust gas flows through the packing layer (31), kept above 1 m / sec, based on the free cross section of the washing tower (3) before filling the packing, and the Packing layer (31) is formed from hedgehog packing. 9. The method according to claim 1, characterized in that the sludge separator (4) comprises a settling tank (41), at the upper end of which the liquid flowing out of the directly connected washing tower (3) of the gas washing stage is introduced and washing liquid is discharged from the central region thereof, while pollutant suspension containing sinking sludge is discharged at the lower end and floating sludge overflows upwards from the sedimentation tank at the upper end. 10. sludge separator for performing the method according to claim 1, characterized in that it has a settling tank (41) which in its upper region an inlet (42) for liquid loaded with sludge, in its bottom region an outlet (13) for sediment sludge has loaded liquid and an upper partition (44) with a central opening (244) tapering upwards towards the center, through which a tube forming said inlet (42) leads into the interior of the settling container (41), and furthermore one above the the lower end of this tube laterally from the central region of the settling tank (41) outflow pipe (49) is present for liquid substantially free of sludge.