The best way to clean the off-gas flow and a device for its implementation
(57) Abstract:The invention relates to a method of cleaning exhaust gas containing hydrogen chloride and sulphur dioxide, and ustroystvo for its implementation. The inventive method for purification of exhaust gas flow containing hydrogen chloride and sulphur dioxide, is that the gas stream is treated in a device for wet cleaning (5), then add the lime (9) and the flow passes through the filter (13). The method and apparatus are characterized in that the portion of the gas flow bypass bypass device for wet cleaning (5) through a pipeline (15) and connects with the rest of the gas stream upstream of the filter (13). Thus, the hydrogen chloride from the bypass flow reacts supplied with lime, resulting in the formation of calcium chloride, which enables separation of the sulfur dioxide when entering lime. 2 C. and 8 C.p. f-crystals, 1 Il. The invention relates to a method for purification of exhaust gas flow containing hydrogen chloride and sulphur dioxide, and device for its implementation.At the present time drastically increase costs for cleaning exhaust gases, since this treatment includes not only the separation of dust, for example, ash-onoguria and hydrogen chloride, contained in the gas stream, which is formed, for example, by burning garbage. Sulfur dioxide may be separated, for example by wet cleaning in the scrubber, where the gas stream is in contact with the aqueous alkali solution, which absorbs sulfur dioxide. Hydrogen chloride is separated by treatment in a wet scrubber, where the gas stream is in contact with the aqueous solution, which absorbs hydrogen chloride. The separation of hydrogen chloride and sulfur dioxide is usually performed in a combined device for wet treatment, in this case, the hydrogen chloride is absorbed in the first stage, and sulfur dioxide on the second. The flow of gases coming out of such a combined device for wet cleaning, contains almost no particulate matter, hydrogen chloride and sulfur dioxide and, thus, can be considered clean enough to discharge into the atmosphere. As the requirements to the environment increase, the pollution that need to be removed, as well as oxides of nitrogen (NOX), and therefore the flow of gases must be subjected to further purification, and to the maximum extent possible should be removed particles of heavy metals and sulfur dioxide. Thus, when catalic the IDA in the flow of gases did not exceed 5 mg and sulfur trioxide 0,1 per nm3.In order to produce additional cleaning of the exhaust gases flow after conventional wet cleaning, the gas stream is injected lime, and it is appropriate to introduce it in conjunction with activated carbon. To ensure that the remaining contamination was also subjected to the reaction, the resulting reaction products are collected in the filter. Lime is introduced into the gas stream in the form of a powder, but can also be entered in the form of sludge. Final separation of the sludge lime and water is at its introduction into the gas stream, while the water is in contact with the stream of hot gas evaporates. The remaining particles of lime react with the impurities of the gas stream mainly with sulphurous anhydride, and then is collected in the filter. For this purpose, bag filters, which consist of filter bags made of textile materials, installed in the filter chamber. Enter lime, usually in conjunction with activated carbon is collected in the filter bags, and the flow of purified gas comes out of the bag filter. Containing lime residue in the bag filter reacts with the impurities remaining in the gas flow type sulphurous anhydride, before the rest of UDA the measures for subsequent discharge into the garbage.An example of the above process can serve as cited in Warner Bulletin", February 1, 1993, an improved installation for the incineration of garbage - contamination below the detection level.Further it is known, for example, from the article by Hans T. Karlsson, Jonas Klingspor, Marita Lynn and Ingemar Berle "Activated process wet and dry cleaning SO2"published in the journal of the Association of pollution control of air,
so 33, No. 1, January 1983, S. 23-28 that the separation of the sulfur dioxide with the help of lime filter, as described above, is significantly activated in the presence of calcium chloride (CaCl2). If calcium chloride is not present, the flow of gas to contact with a large quantity of lime, i.e. the process should be used much more because of the appreciation of the process. Naturally, the increase in the consumption of lime also increases the duration of the discharge of the filter bag, which is a big drawback. In order to reduce the consumption of lime and duration of discharge, it is advisable that the separation of the sulfur dioxide with the help of lime filter took place in the presence of calcium chloride.The purpose of izobretalnosti after the device for wet treatment in the presence of calcium chloride.To achieve this goal, part of the gas stream containing hydrogen chloride, bypasses bypass device for wet cleaning, which is separated from the stream of hydrogen chloride, and then both streams are connected after the device for wet cleaning before filter for lime.Additional features of the invention are given in the following paragraphs of the application.It should be noted that in U.S. patent N 2078702 described purification process gas flow through the jet absorption drying process, which includes the introduction in the process of lime, and subsequent filtration in the filtration chamber, and a portion of the gas flow bypasses the stage of jet absorption drying, and then comes together with a part of the gas flow past the stage of jet absorption drying, in a special section of the filter chamber. The remainder of the gas stream, which has passed the stage of jet absorption drying, passes through another part of the filter chamber and both streams are connected after the filter chamber. The purpose of this bypass is re-heated gas stream.The figure schematically shows the equipment in accordance with the invention.The flow of gases, which contain chlorite is Azov enters the dust separator 3, for example, the electrostatic precipitator, which separates the particles of hard material such as fly ash. Then the gas stream is fed via line 4 into the device for wet cleaning 5 for separating hydrogen chloride, and the main part of the sulfur dioxide. Thus purified gas stream exits the device for wet cleaning through an outlet pipe 6. The stream leaving gas typically has a relatively low temperature, for example 50-80oC and in order to avoid corrosion installed next equipment provided by the heaters 7 type heat exchangers, which provide heating temperature of the effluent gases to 80-120oC.After wet cleaning and heating the stream of gas passes through the pipe 8 to station 9, where the input of lime. In this case, the term "lime" includes limestone (CaCO3), as well as burnt lime (CaO) and slaked lime (Ca(OH)2). The pipeline 11 lime served at station 9 of the feeder 10.It is advisable to coordinate the supply of lime feeding activated charcoal, which is served by the feeder 12.As mentioned above, the lime is fed into the gas stream in the form of powder or, if required, in such so that the water separated from the sludge at its input and evaporated, and the solid particles were entrained by the gas stream and collected in the bag bag filter 13. The lime particles and other solid particles are separated in a bag filter 13, and the gas flow goes through the pipeline 14.In order to improve the separation efficiency of the sulfur dioxide when entering lime reaction between sulfur dioxide and lime should, as mentioned above, take place in the presence of calcium chloride. To this end, the portion of the stream of gas is supplied by pipeline 15 from the inlet pipe 4 devices for wet cleaning, is a device for the wet treatment and is removed through outlet piping 8 devices for wet cleaning the area prior to the filter 13, the input of lime occurs in front of the station 9, as shown in the drawing.As part of the gas flow bypasses the device for wet cleaning 5, this flow is not separated hydrogen chloride, as is the device for wet cleaning. As a result of this hydrogen chloride, which is present in the bypass gas stream reacts with the injected lime, forming chloride of calcium, which increases the separation efficiency of the sulfur dioxide. the total volume a greater effect is obtained by 2-5% of the volume. In order to get the proper ratio of the bypass flow and gas flow, which passes through the device for wet cleaning 5, the pipe 15 is embedded regulating device 16. Regulating device 16 to control the flow of gas that passes through the bypass (Obvodny pipeline) in accordance with the gas flow through the inlet pipe 4 and/or the content of hydrogen chloride in the gas stream that is included in the pipeline 4.As described above and shown in the drawing, the bypass gas flow (bypass) 15 is connected with the main stream, passed through the device for wet cleaning 5 in front of the station 9, in which the input of lime. However, the bypass gas stream 15 may be connected with the main gas stream which has passed through the device for wet cleaning alternative 5 - after station 9 to enter the lime. It is necessary to ensure that two threads were merged upstream of the filter 13.Shown are a few examples to illustrate the invention. Devices used in these examples, a similar type as described above.Example 1. By burning household garbage is formed a gas flow, which contains the 250 mg SO21 nm3. About 5% of the total amount of gas passes on Obvodny pipeline by a wet scrubber and connects with the stream of gas leaving the wet scrubber station before entering the lime.The flow of gases entering the station to enter lime contains about 50 mg HCl, and approximately 250 mg of SO21 m3. Lime is introduced in the amount of five times the stoichiometric ratio. After entering to exhaust the gas flow is directed in a bag filter, after which the gas stream contains less than 2.5 mg HCl and less than 25 mg SO2at nm3. It denotes the 95% efficiency of separation of HCl and 90% efficiency Department SO2. The chlorine content of the dust collected in the bag filter, about 2 - 3%.Example 2. The same gas flow as in example 1, is introduced through a wet scrubber, which was separated not only HCl, but SO2. After mornago scrubber in the gas stream contained less than 5 mg HCl and less than 50 mg SO2. About 2% of the gas flow was directed to bypass the wet scrubber and connected with the gas flow after the wet scrubber station before entering the lime. In the flow of gases introduced to the station for supply of lime, in this case contained about 20 mg of HCl and approximately the solution. After entering to exhaust the gas flow was directed into the bag filter to separate the lime and any other solids. Analyses of the gas stream emerging from the bag filter, to determine the content of HCl and SO2showed that the HCl content is less than 1 mg, and the content of SO2- less than 5 mg / nm3that means more than 90% efficiency in the separation SO2. The chlorine content of the dust collected in the bag filter was approximately 2%. 1. The purification method of the flow of exhaust gas, which contains hydrogen chloride and sulphur dioxide, including processing and device for wet cleaning (5), the subsequent introduction of lime (9) and the outlet in the filter (13), characterized in that the part of the flow of exhaust gas through the bypass device for wet cleaning (5), and then connect with a part of the gas flow that passes through a device for wet cleaning, before the filter (13).2. The method according to p. 1, characterized in that the volume flow of the exhaust gas flowing in the bypass device for wet cleaning, is approximately 1 to 8% vol.3. The method according to p. 2, characterized in that the amount of exhaust gas flowing in the bypass device for wet cleaning, is approximately 2 - 5 vol.% of the for wet cleaning (5), heated to a temperature of about 80 - 120oWith before it is combined with the gas stream, which bypasses the device for wet cleaning.5. The method according to any of paragraphs.1 to 4, characterized in that the lime is injected into the flow of exhaust gas in the form of powder.6. The method according to any of paragraphs.1 to 5, characterized in that the lime, which is injected into the process gas cleaning, is a slaked lime (CA(Oh)2), calcined lime (Cao) or calcium carbonate (caso3).7. A device for cleaning the flow of exhaust gas, which contains hydrogen chloride and sulfur dioxide, comprising the inlet pipe (4) through which the gas stream fed into the device for wet cleaning (5), the output pipe (6) through which the gas stream exits the device for wet cleaning (5), station (9) for the supply of lime in the off-gas flow after the device for wet cleaning (5) and the filter (13) for the Department of lime, characterized in that it comprises a pipe (15), which passes from the inlet pipe (4) device for wet cleaning (5) to the outlet pipe (8) device for wet cleaning (5) before the filter (13), through which a portion of the gas flow bypasses the device for wet treatment (5).9. The device under item 7 or 8, characterized in that the device (16) for controlling the flow of gas is controlled depending on the gas flow in the inlet piping (4) and/or content of hydrogen chloride in the gas in the inlet piping (4).10. Device according to any one of paragraphs.7 to 9, characterized in that the outlet pipe (6) device for wet cleaning (5) fitted with devices for heating.
FIELD: production of aluminum in cells with self-fired anodes, possibly processes for cleaning anode gases.
SUBSTANCE: method comprises steps of accumulating anode gases, preliminarily combusting them together with air in burner devices mounted in cells; supplying gas-air mixture after preliminary combustion of anode gases along gas duct to stage of dust and gas trapping and blowing out to atmosphere. Before supplying gas-air mixture from burner devices to stage of dust and gas trapping, it is fed to process for oxidizing roasting; heated up to temperature 800-1100°C and then it is cooled until 230-290°C and heat is used for production needs.
EFFECT: lowered content of carbon, resin and CO in exhaust gases.