Process and apparatus for purifying waste gases

0001The invention relates to a method for cleaning exhaust gases from combustion systems that arise during the combustion process, in which the highly heated exhaust gases leaving the combustion area are cooled by coolants to such an extent that the dew point of the exhaust gases is undershot and, as a result, the water content of these exhaust gases is lost while simultaneously binding the pollutant content. the pollutant-reduced exhaust gases are subsequently sprayed with water for final cleaning and are finally released to the environment in a heated state, and a device for carrying out this method.

0002A method and a device of this type are known (DE-B-12 71 296). According to this known method, pre-cleaned combustion exhaust gases are cooled in heat exchangers and treated with atomized water in single- or multi-stage sprinkling chambers, the cold exhaust gases being heated up again by the heat removed before washing out. With the known method and the known device, the disadvantage observed up to that point is that the absorption of sulfur dioxide in combustion gases proceeds extremely slowly and the sprinkler systems known up to then were not sufficient to be able to separate the sulfur dioxide completely. It has therefore been proposed to provide the cooling temperatures for the combustion exhaust gases in such a way that sufficient absorption of sulfur dioxide can be achieved with the smallest possible amounts of water. An attempt was made to achieve this by extremely cooling the exhaust gases in two targeted steps in order to increase the water solubility of sulfur dioxide very much by lowering the wash water temperatures. For this purpose, wash water was fed in, both for the lowering of the temperature of a first heat exchanger and for a sprinkler chamber downstream of this heat exchanger, which was removed from a source of external water.

0003A disadvantage of the known method and the known device is that the washing water available as a coolant from an external water source is supplied to a heat exchanger via which the exhaust gases are cooled. Furthermore, it is disadvantageous that the wastewater enriched with pollutants, which naturally occurs in large quantities there, is not used for any other purpose, but rather leaves the process process as dilute sulfuric acid and has to be disposed of separately or is released to the environment in a non-disposed state. Under today's environmental impact criteria, dealing with highly polluted water in this way, especially with regard to the constantly increasing acidification of water, is completely unthinkable and inadmissible.

0004It is an object of the present invention to provide a method and a device with which existing firing systems can also be operated and retrofitted, that the method can be carried out simply and inexpensively, and that the device is easy to install and that it can be operated largely without external energy in order to To be able to drastically reduce the amount of pollutants in the exhaust gases, whereby, as in large-scale industrial exhaust systems, the pollutants and the coolants contaminated with pollutants are not released into the environment, but can continue to be used in a cyclical process or method in the device over an almost unlimited number of operating cycles.

0005The object is achieved according to the inventive method in that the post-purification of the exhaust gases takes place in countercurrent and these pre-cool the highly heated exhaust gases before being released to the environment and are thereby heated by the heat exchange, and in that the precipitated, collected water is removed from the pollutant content in a multi-chamber process a reactant is freed and at least partially used as water spray in the post-cleaning process.

0006A major advantage of the method according to the invention is that the cooled, cleaned exhaust gases cool the high-temperature exhaust gases from the combustion system in the sense of pre-cooling. The heat exchange in the heat exchanger thus advantageously took place almost completely free of external energy, in contrast to the known heat exchanger operated with external energy, namely with separately supplied cooling water.

0007It is also advantageous that the precipitated, collected water, after being freed from the pollutant content, is at least partially used as spray water in the post-cleaning process, so that expensive cleaning water need not be provided. Even if the water can no longer be used in full for the cleaning process after a predetermined number of operating cycles, it does not automatically get into the environment in an uncontrolled manner or into the sewage system, rather, since it is continuously collected by the cycle, it can be collected, transported away and disposed of in a controlled manner in a controlled manner.

0008In 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.

0009The portion of the water that is not used for the cleaning process of the exhaust gases is collected in a further advantageous embodiment of the method and fed to a separate pollutant disposal device. Basically, the water that precipitates from 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.

0010To achieve the object, the device with which the method can be carried out is characterized in that in a condenser which is arranged behind the heat exchanger on the exhaust gas flow side, the exhaust gases are cooled below their dew point, the container being passed through a plurality of each is formed with chambers filled with a reagent, is arranged under the condenser and is connected to the spraying device, and that the device for spraying the exhaust gases with water in countercurrent to the exhaust gases is provided downstream of the condenser, the cleaned exhaust gases serving as coolant of the heat exchanger.

0011The advantages achieved by the device are essentially the same as those listed above in connection with the advantages of the method. In addition, it is advantageous in the device that all the 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 existing combustion plants. In existing combustion plants, the device only needs to be used in the exhaust pipe or in the exhaust gas flow path between the combustion plant and the chimney device. This enables highly efficient cleaning of the exhaust gases, even from combustion systems that have already been installed, without great effort.

0012The 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 in the respective path with a significantly different proportion of pollutants.

0013According 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 water condensate is advantageously conducted from a first chamber to a last chamber alternately below and above the chamber walls. With the help of the reagent, the polluted water condensate is cleaned chemically and emerges from the last chamber in a highly purified state and can be fed to the spraying device, through which the exhaust gases are subjected to a further purification.

0014The 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.

0015The 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.

0016According to an advantageous other embodiment, the collecting container is connected via a line provided with a valve device to a container for the pollutant disposal of the water condensate, ie when the pollutant concentration in the purified water is so great that it can no longer be used sensibly for post-cleaning purposes the water is drained from the collecting container by operating the valves accordingly or pumped off by a pump in the line and then subjected to a separate pollutant disposal.

0017Ambient 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.

0018Finally, 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.

0019DE-A-35 21 725 discloses a heat exchanger which, unlike the method and the device, is not intended to remove pollutants from the exhaust gases, but rather to neutralize the pollutants in the exhaust gases. According to the known previously published document, such neutralization systems or processes are to be assumed, the neutralization of the exhaust gases, for example by spraying in sodium hydroxide solution or the like, to be further improved.

0020The invention will now be described in detail with reference to the following schematic single drawing using an exemplary embodiment.

0021The single figure shows a device in section, which is inserted into the exhaust pipe of a furnace.

0022The 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 11, which comes from the furnace, 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.

0023The 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.

0024A 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.

0025Arranged below the condenser 13 in the device housing 101 is a collecting container 14 for collecting the water condensate 15, which precipitates 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.

0026Adjacent 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.

0027After 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.

0028Arranged 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.

0029As 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.

0030In 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 41 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.

0031The 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.

0032The 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.

0033When 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.

0034Subsequently, 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%.

0035In 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="EP0243778B1_D0001.tif" /></chemistry>

0036In principle, Mg CO₃ (magnesium carbonate) and Mg (OH) ₂ (magnesium hydroxide) are also suitable as reactants 45.

Reference list

0037<dl id="dl0001"><dt>10</dt><dd>contraption</dd><dt>101</dt><dd>casing</dd><dt>102</dt><dd>Exhaust gas inlet</dd><dt>103</dt><dd>Exhaust outlet</dd><dt>104</dt><dd>Pipe connection</dd><dt>105</dt><dd>Container part g</dd><dt>106</dt><dd>wall</dd><dt>107</dt><dd>Pipe connection</dd><dt>108</dt><dd>arrow</dd><dt>109</dt><dd>Outlet connector</dd><dt>110</dt><dd>Exhaust gas flow path</dd><dt>11</dt><dd>Exhaust gas flow</dd><dt>12</dt><dd>Heat exchanger</dd><dt>13</dt><dd>capacitor</dd><dt>14</dt><dd>Collecting container</dd><dt>15</dt><dd>Water condensate</dd><dt>16</dt><dd>Spraying device</dd><dt>17</dt><dd>Exhaust gas</dd><dt>18</dt><dd>water</dd><dt>19</dt><dd>first path</dd><dt>20</dt><dd>second path</dd><dt>21</dt><dd>Fall arrester</dd><dt>22</dt><dd>chamber</dd><dt>23</dt><dd>chamber</dd><dt>24</dt><dd>chamber</dd><dt>25</dt><dd>chamber</dd><dt>26</dt><dd>chamber</dd><dt>27</dt><dd>chamber</dd><dt>28</dt><dd>chamber</dd><dt>29</dt><dd>Chamber partition</dd><dt>30</dt><dd>Chamber partition</dd><dt>31</dt><dd>Chamber partition</dd><dt>32</dt><dd>Chamber partition</dd><dt>33</dt><dd>Outlet</dd><dt>34</dt><dd>Valve</dd><dt>35</dt><dd>Valve</dd><dt>36</dt><dd>Valve</dd><dt>37</dt><dd>pump</dd><dt>38</dt><dd>management</dd><dt>40</dt><dd>Valve</dd><dt>41</dt><dd>management</dd><dt>42</dt><dd>Valve device</dd><dt>43</dt><dd>Ambient air</dd><dt>44</dt><dd>Fan device</dd><dt>45</dt><dd>Reactants</dd></dl>