Process and apparatus for purifying waste gases.

The invention relates to a method for cleaning exhaust gases from combustion plants that arise during the combustion process and to a device for carrying out this method.

In the course of ever increasing efforts to reduce the environmental pollution caused by the exhaust gases from combustion plants, many measures have been taken which, at least on the combustion plant side, ensure that the primary energy sources are optimally burned.

Even if combustion plants are operated in an optimized manner with regard to the combustion process that takes place in them, the problem of the emission of sulfur and nitrogen oxides, which is extremely harmful to the environment, does not take a back seat, since these pollutant components are still present in the exhaust gases due to the primary energy sources used. In large combustion plants, for example in power plants, extensive filter devices or Plants have been installed that filter this polluting pollutant from the exhaust gases, but these measures cannot be transferred directly to small combustion systems, such as those used in building heating systems.

On the other hand, the problem of retrofitting arises in the case of building heating or firing systems which are already installed, as a result of the increasing requirements imposed by the legislator in relation to the degree of environmental pollution which such firing systems are likely to pose in the future.

It is an object of the present invention to provide a method and an apparatus with which existing firing systems can also be operated and retrofitted, which can be carried out simply and inexpensively and can be installed easily with respect to the apparatus, and the pollutant content of the firing system operated or equipped therewith drastically reduced. In addition, the method and the device should be inexpensive to use or be producible, so that there is an increased incentive to use this method and this device in the operation of a furnace.

The object is achieved according to the invention in that the highly heated exhaust gases leaving the firing area are cooled by coolant to such an extent that the dew point of the exhaust gases is undershot and, as a result, the water content of the exhaust gases fails, while at the same time binding the pollutant component, that the pollutant-reduced exhaust gases are subsequently sprayed with water for subsequent cleaning and then the coolant cools the superheated exhaust gases and is released to the environment by the heat exchange.

The flue gases from the combustion plant are, as it were, guided in a circular process using this method, in which the cooled, cleaned flue gases, before being released into the environment, pre-cool the high-temperature primary flue gases coming from the combustion plant in order to reach their dew point. In this way, the cleaned exhaust gases to be released into the ambient air form part of the coolant in order to reach the dew point of the pollutant-enriched, highly heated exhaust gases of the combustion system.

Advantageously, the water that has been collected and freed from the pollutant content is at least partially used as spray water in the post-cleaning process, so that the method according to the invention can in principle be operated without extraneous water, with the result that costs due to extraneous water for spraying the exhaust gases are not required for the post-cleaning process .

In a further embodiment of the method, ambient air is admixed with the exhaust gases after the post-cleaning process, so that the coolant property of the cleaned exhaust gases for cooling the primary, highly heated exhaust gases is further improved and, moreover, the pollutant concentration in the exhaust gas volume expelled is reduced. In addition, the quantity-controlled admixture of the ambient air enables the throughput of the exhaust gases to be controlled when this method is carried out.

In a further advantageous embodiment of the method, the portion of the water that is not used for the post-purification process of the exhaust gases is collected and fed to a separate pollutant disposal device. Basically, the water that falls out of the exhaust gases after falling below their dew point is in a cyclic process, because after it has been precipitated and cleaned, it is then used for the post-cleaning process and in turn falls back into a reservoir into which it already is previously fell at the time of failure after the condensation process.

To achieve the object, the device has a heat exchanger in the exhaust gas flow of the combustion system for cooling the exhaust gases and a condenser arranged behind it on the exhaust gas flow side that cools the exhaust gases below the dew point, a container arranged under the condenser for collecting the pollutants of the exhaust gases, and a water condensate device downstream of the exhaust gas downstream of the condenser for subsequently spraying the exhaust gases with water, the cleaned exhaust gases serve as coolant for the heat exchanger. All individual elements of the device can be accommodated in a single housing and can therefore be arranged in a simple manner as an additional device in series with the firing system, that is to say, in existing firing systems, the device only needs to be used in the exhaust line or in the exhaust gas flow path between the firing system and the chimney device . This also enables highly efficient cleaning of the exhaust gases from already installed combustion systems without great effort.

The heat exchanger is advantageously designed as a so-called cross-flow heat exchanger, ie the highly heated exhaust gases coming from the combustion system flow through a first path of the heat exchanger, while the cleaned and cooled exhaust gases flow through the second path running transversely to this path and are then subsequently released to the environment . Both paths of the heat exchanger are thus flowed through by the same exhaust gases, but connected in the respective path with significantly below with a container for the pollutant disposal of the water condensate, i.e. when the pollutant concentration in the purified water is so large that it is no longer useful for post-cleaning purposes can be used, the water is drained from the collection container or activated by appropriate actuation of the valves pumped off by a pump in the line and then subjected to a separate pollutant disposal.

Ambient air can advantageously be fed into the flow path of the cleaned exhaust gases between the spraying device and the heat exchange, with this valve device on the one hand adjusting the throughput of the exhaust gases to be cleaned through the device and on the other hand thereby reducing the concentration of pollutants per exhaust gas volume exiting the device is adjustable so that premixing with the ambient air can already take place in this way.

Finally, it is advantageous that a fan device for conveying the exhaust gases into the ambient air is arranged in the exhaust gas flow path of the cleaned exhaust gases after they have passed the heat exchanger as a coolant for the highly heated exhaust gases. Such a configuration of the device may be necessary if, for example, long exhaust ducts have to be connected. This fan device can also preferably be used to adjust the throughput of the exhaust gases to be cleaned through the device in such a way that the exhaust gases are actually cleaned with an optimized throughput quantity.

The invention will now be described in detail with reference to the following schematic single drawing using an exemplary embodiment.

The single figure shows a device in section, which is inserted into the exhaust pipe of a furnace.

The device 10 is essentially formed from a housing 101 of any suitable shape, which has an exhaust gas inlet 102 and an exhaust gas outlet 103. In the exhaust gas inlet 102, the highly heated exhaust gas stream 111, which comes from the combustion system, not shown here, is introduced into the device 10. The cleaned exhaust gas 17 goes from the exhaust gas outlet 103, possibly via exhaust gas lines not shown separately here, into a chimney or directly into the environment.

The exhaust gas flow path running in the device 10 from the exhaust gas inlet 102 to the exhaust gas outlet 103 is symbolically represented in the figure by a dashed line. In the following illustration of the individual device components, reference is made to their relative arrangement with respect to the exhaust gas flow path 110 shown in dashed lines.

A heat exchanger 12 is arranged downstream of the exhaust gas inlet 102 in the device 10 in the exhaust gas flow path 110 and is described in detail below. A condenser 13 is arranged downstream of the heat exchanger 12, the heat exchanger 12 and the condenser 13 being connected via a suitable pipe connection 104. The condenser 13 can in principle be designed in any suitable manner and serves the purpose of cooling the exhaust gas 17 which has already been pre-cooled in the heat exchanger 12 in such a way that the dew point of the exhaust gases 17 is not reached.

Below the condenser 13 is a collecting container 14 in the device housing 101 for collecting the water condensate 15 different pollutant content.

According to an advantageous embodiment, a collecting device for the water condensate is arranged in the vertical direction below the condenser and below the spraying device, from which the water condensate is placed in a collecting container. The collecting container is preferably formed by a plurality of chambers, which, depending on the type of training, can comprise any suitable number of chambers, and which are each filled with a reactant. whereby the water condensate can be passed alternately from a first chamber to a last chamber below and above the chamber walls. With the aid of the reactant, the polluted water condensate is chemically cleaned and emerges from the last chamber in a highly purified state and can then be fed to the spray device, through which the exhaust gases are subjected to a further purification.

The collecting device is advantageously designed so that it opens into the first chamber with its outlet, so that it is ensured that the entire cleaning chain formed from the individual chambers filled with reactant is completely flowed through, that is, the existing cleaning possibility is fully exhausted.

The collecting container is preferably connected to the spraying device via a line provided with valve devices, which line can be partially or completely remote-controlled, so that these systems can be fully remote-controlled in connection with the automatic control of a connected firing system, and can thus be operated automatically. According to an advantageous other embodiment, the collecting container is arranged via a line provided with a valve device, which drops out of the exhaust gas 17 in the condenser 13. The collecting container 14 consists of a plurality of chambers 22, 23, 24, 25, 26, 27, which are separated from one another by corresponding chamber partition walls 28, 29, 30, 31, 32. The chamber partitions 28 to 32 are designed such that they are alternately closed at the bottom and open at the bottom from the first chamber 22 to the last chamber 27. The chambers 22 to 27 are filled with a reactant, and the chemical reaction by means of which the polluted water condensate 15 is cleaned is described in more detail below. The pollutant-free water emerging from the collecting container 14 opens into a container part 105 in the bottom region of the device 10.

Adjacent to the device area in which the water condensate 15 precipitates from the condenser 13, but separated by a wall 106 into the area of ​​a collecting device 21 by a wall 106, there is a zone in the exhaust gas flow path 110 downstream of the condenser 13 in which one Spraying device 16 is arranged transversely to the exhaust gas flow path 110 of the exhaust gases 17. The spraying device 16 in the exhaust gas flow path 110 subsequently passes through the exhaust gas 17 through a suitably designed pipe connection 107, subsequently the heat exchanger 12.

After the exhaust gas 17 has left the heat exchanger 12, it is released to the environment by a fan device 44 arranged downstream of the heat exchanger 12 in the exhaust gas flow path 110, ie either via a chimney or similar device (not shown here) or directly to the environment.

Arranged essentially in the vertical direction below the spraying device 16 and essentially in the vertical direction below the condenser 13 is a collecting device 21 which on the one hand collects the water condensate precipitating from the condenser 13 and on the other hand the water 18 emerging from the spraying device 16 and to an outlet 33 of the fall arrester.

The collecting device 21 is slightly inclined with respect to the horizontal, so that the water 18 or the water condensate emerging from the condenser 13 automatically flows to the outlet 33, the outlet being arranged directly above the first chamber 22 of the collecting container 14.

As already described above, the individual chambers are filled with a reactant, so that the highly polluted water flowing into the chamber 22 flows into the container part 105 free of pollutants after flowing through the chambers, which is symbolically represented by the arrow 108. At the lower end of the container part 105, an outlet port 109 is attached, which is connected to a line 38. The line 38 leads via a valve 34 connected in series, a pump 37, a valve 35 and a further valve 36 to the spraying device 16, which, as already shown, is arranged essentially below the heat exchanger 12.

In addition, the line 38 between the valve 35 and valve 36 is connected in the form of a T-piece to a further valve 40, which is connected on the outlet side via a line 48 to a container, not shown here, and into which the water accumulating in the container part 105 is then pumped when the degree of pollutant enrichment has become so great despite cleaning that it can no longer be used in the spraying device 16 for the purpose of subsequent cleaning. The water, which is enriched with pollutants and is located in the container (not shown), can then be cleaned by means of an associated pollutant disposal device, to an extent that complies with the legal requirements. It can then be drained into the sewage system.

The valves 34, 35, 36, 40, like the pump 37, can be remote-controlled, so that the flow path of the water 18 within the pipes 38, 41 can be controlled completely automatically.

The valve device 42 arranged in the pipe connector 107 above the spraying device 16, which controls the supply of ambient air 43 into the pipe connector 107 for mixing with the exhaust gas 17, can also be actuated or regulated automatically.

When the method is carried out, the exhaust gas stream 11 coming from a combustion system (not shown here) enters the device 10 via the exhaust gas inlet 102. The exhaust gas stream 11 has a temperature of plus 170 ° C. to plus 240 ° C. Downstream of the exhaust gas flow path 110, the exhaust gas represented by the arrows 17 enters a first path 19 of the heat exchanger 12 designed as a cross-flow heat exchanger and is cooled to approximately 60 ° C. by the exhaust gas 17, which flows around the second path 20 that runs transversely to the first path 19. Subsequently, the exhaust gas 17 cooled to 60 ° C. enters the condenser 13, in which it is cooled in such a way that the dew point of the exhaust gas 17 falls below and consequently that in the exhaust gas 17 occurs and binds the pollutants of the exhaust gas in the form of water condensate 15 the collecting device 21 drips. The exhaust gas 17 then, after having flowed longitudinally below the partition wall, which is arranged between the condenser 13 and the spraying device 16, reaches the region below the spraying device 16, where it is sprayed with water 18 in a post-cleaning process, the flowing water 18 is also collected in the collecting device 21 and flows together with the water condensate 15, as described above, into the first chamber 22 of the collecting container 14. The exhaust gas 17 leaving the spray device 16 essentially in the vertical direction then has a temperature of approximately 30 ° C.

Subsequently, the exhaust gas 17 flows through the pipe connector 107 and is optionally enriched or mixed with ambient air 43 there via the valve device 42. Subsequently, the exhaust gas 17 flows through the vertically extending second path 20 of the heat exchanger 12 and, in the process, extracts heat from the highly heated and contaminated exhaust gas 17 coming from the furnace, as described above, flowing in the first path 19. The cleaned exhaust gas 17 emerging from the second path 20 of the heat exchanger 12 in turn heats up to approximately 80 ° C. and is either discharged into the environment via the outlet 103 of the device 10 or, insofar as the exhaust gas 17 draws its own is sufficient within the device 10, released directly to the environment. The water emerging from the collecting container 14 according to the arrow 108 into the container part 105 is subjected to a complete purification by the reactant, ie the sulfur and nitrogen oxide portions of the exhaust gas 11 of the furnace are bound to such an extent that a degree of purification of the exhaust gases after these leave the device 10 is reached by more than 80%.

In principle, any suitable agent can be used as the reaction agent 45. Calcium carbonate (limestone, marble) in granulate form is particularly suitable for this, since it is inexpensive to provide and can neutralize both the sulfur oxide content SO₂, SO₃ and the nitrogen oxide content NO, NO₂. The reaction of such a reagent 45 proceeds, for example, as follows.<chemistry id="chem0001" num="0001"><img file="EP0243778A2_D0001.tif" /></chemistry>

In principle, Mg CO₃ (magnesium carbonate) and Mg (OH) ₂ (magnesium hydroxide) are also suitable as reactants 45.

Reference list

<ul id="ul0001" list-style="none"><li>10th contraption</li><li>101 casing</li><li>102 Exhaust gas inlet</li><li>103 Exhaust outlet</li><li>104 Pipe connection</li><li>105 Container part g</li><li>106 wall</li><li>107 Pipe connection</li><li>108 arrow</li><li>109 Outlet connector</li><li>110 Exhaust gas flow path</li><li>11 Exhaust gas flow</li><li>12th Heat exchanger</li><li>13 capacitor</li><li>14 Collecting container</li><li>15 Water condensate</li><li>16 Spraying device</li><li>17th Exhaust gas</li><li>18th water</li><li>19th first path</li><li>20 second path</li><li>21 Fall arrester</li><li>22 chamber</li><li>23 chamber</li><li>24th chamber</li><li>25th chamber</li><li>26 chamber</li><li>27 chamber</li><li>28 chamber</li><li>29 Chamber partition</li><li>30th Chamber partition</li><li>31 Chamber partition</li><li>32 Chamber partition</li><li>33 Outlet</li><li>34 Valve</li><li>35 Valve</li><li>36 Valve</li><li>37 pump</li><li>38 management</li><li>39</li><li>40 Valve</li><li>41 management</li><li>42 Valve device</li><li>43 Ambient air</li><li>44 Fan device</li><li>45 Reactants</li></ul>