CH619864A5 - Process and device for treating flue gases - Google Patents

Description

The present invention relates to a method and a device for treating flue gases before expelling them into the atmosphere, consisting of dedusting, cooling to about room temperature and removal of pollutants which are still gaseous at room temperature.

This includes primarily the flue gases generated in combustion plants, steam boilers, heating systems, incineration plants or the like, but also other exhaust gases, such as e.g. B. from roasting plants, cement kilns or the like., And generally exhaust gases which, in addition to nitrogen and carbon dioxide, share of carbon monoxide. Hydrogen chloride, hydrogen sulfide, hydrocarbon, water vapor and the like. Like. Have, which are to be regarded as pollutants or their release into the atmosphere is disadvantageous.

It is known and customary to dedust dust from flue gases by cyclones, electrostatic filters or the like, and also to cool them for partial use of the heat contained in them by heat exchange with a cooler medium, for. B.

by preheating the combustion air and / or the fuel. Known, but only common in special cases in the case of particularly dangerous exhaust gases, is furthermore a partial separation of the gaseous pollutants by gas scrubbing with subsequent neutralization of the washed-out pollutants. The invention is therefore based on a method of the type specified in claim 1.

Basically, the partially cooled and significant pollutant smoke gases are emitted into the atmosphere by high chimneys. The associated disadvantages are: air pollution, waste of the thermal energy contained in the flue gases and the construction and operating costs of high chimneys.

A loss of recoverable energy is inevitable because the temperature of the gases that are blown off by a chimney must be significantly higher than the ambient temperature in order to create the necessary draft in the chimney5

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ken, and should preferably be above the temperature of the dew point to avoid condensation in the chimney.

This means not only a loss of sensible heat, but also the latent heat of the water vapor contained in the flue gas cannot be recovered, because otherwise the condensation would cause corrosion damage.

In practice, these heat losses are already considered to be so inevitable that the designer of boiler systems usually uses the lower calorific value as the basis for the calculation of the energy yield, but this is in principle misleading. The upper and lower calorific values (also referred to as calorific value and calorific value) of the individual fuels can be viewed in relevant specialist books. So z. For example, the upper calorific value of hydrogen is 18 '(above the lower one. This difference is 11% for methane and 13% for methyl alcohol. Although the hydrogen content in coal is relatively low (on average 4-5%), the difference between the upper ones and the lower calorific value is also small, the moisture content of the coal, which is normally between 3 and 15%, is significant, so the energy loss due to the fact that water vapor escapes unused can be considerable disguised that the lower calorific value was used as a basis.

With increasing concern about air pollution, higher chimneys were built to provide better gas distribution. Higher chimneys, however, only increase the cost of building and maintaining them, but do not guarantee that the problem of environmental pollution caused by pollutants such as sulfur dioxide, chlorine gases, phosphorus oxides etc. will be solved. Particularly unpleasant pollutants are carbon dioxide, sulfur dioxide as well as chlorine and fluorine gases, which form acids with the moisture in the air. The carbon dioxide content in some industrial areas has already increased to 1 times the normal concentration. Acid-producing components have brought the acidity of the rainwater from the normal 6.9 pH to 4.0 pH. Already at pH 5.5 of the rainwater, life in the water is killed and buildings and monuments are seriously damaged.

One way to remove acid-forming components from flue gases is to send the entire amount of gas through a wash before letting the gas escape through the chimney. Such washes require large amounts of water that are not available everywhere. They also require expensive and large devices. So you need at least half a m3 of water per ton of waste in waste incineration plants. Such large quantities for water washing cost a lot and are also not practical.

Smoke delivery has become a serious problem for industry all over the world, especially since the dispersion of exhaust gases through high chimneys is not a solution to the problem.

The invention has for its object to provide a method of the type mentioned, in which the energy losses and pollutant emissions associated with the usual flue gas treatment are avoided and the use of a chimney is basically superfluous.

This object is achieved by the characterizing features of claim 1. A device for carrying out the method according to the invention is specified in claim 10. The subclaims relate to advantageous refinements of the invention.

The advantages achieved with the invention consist essentially in the fact that the thermal energy contained in the flue gas, including the latent heat of the water vapor,

can be used to a large extent that the pollutants can be substantially completely removed, as a result of which cool and completely inert gas is expelled into the atmosphere, as a result of which a chimney with its high construction and operating costs can be saved, and that the separated pollutants are small Have volumes so that only a small amount of liquid is required to neutralize them, in contrast to gas washing. This liquid can be obtained from the condensate of the flue gases, so that the system even works with excess liquid without the need for liquid. The neutralization device can be kept small in terms of apparatus. Since the cleaned outlet gas is cool and absolutely dry, it can be used even further, e.g. B. for water cooling in evaporative cooling towers. Since the energy content of the fuel is better utilized overall by converting the heat content of the flue gases into work output, cheaper fuel, and in particular fuel with a high sulfur content, can be used. A system according to the invention also has the advantage that additional harmful or exhaust gases from other sources, eg. B. Exhaust gases from petroleum refineries or the like, with abandoned and can be cleaned.

Furthermore, in the method according to the invention, it is possible to process the pollutants which are separated off in a purely physical manner, instead of neutralizing them, into useful products, for example by extracting elementary sulfur if the flue gases have a high sulfur content.

The savings that are achieved through the use of cheap fuels, as well as through the replacement of chimneys, through the additional generation of energy, the savings in water consumption and the reduced design of a neutralization system, result in a high economic benefit in a wide range from the method according to the invention Possible uses.

An embodiment of the invention is explained in more detail below with reference to the drawing, which represents a diagram of a flue gas treatment system according to the invention.

The combustion site is generally designated 10 in the process diagram. It can have one or more furnaces or also roasting plants, cement ovens etc. which emit hot exhaust gases by combustion, these gases being components such as nitrogen, carbon dioxide, sulfur dioxide, hydrogen chloride, hydrogen sulfide. Carb monoxide, nitrogen oxides, hydrogen cyanide and hydrocarbons, etc. may contain.

Fuel is supplied to combustion chamber 10 through line 11. In particular, cheap fuel, whether solid, liquid or gaseous, can be used, which has a higher sulfur content and is therefore not permitted in normal combustion plants.

Air or oxygen or air enriched with oxygen is supplied to the combustion chamber 10 through the line 12. The combustion air is preferably compressed by a compressor 13, so that the combustion chamber works under pressure. Depending on the pressure level in the combustion chamber 10, compression in the exhaust gas treatment can be dispensed with in whole or in part, as will be explained below.

The combustion gases from the combustion chamber, as indicated by arrows 15, 16, 17, are passed through a series of dust separators 20, 21, 22, in which solid parts are retained. The separator 20 is preferably a cyclone in which particles up to 50 µm are separated, as indicated by arrow 24. The separators 21 and 22 are e.g. B. bag filters that separate even smaller particles (see arrows 25, 26). The separators 20, 21, 22 should be insulated in order to largely avoid heat losses.

The flue gases, which are now freed from solid particles, are conveyed by a blower 30 (arrow 17), which passes the gas through the separators 20, 21, 22 and into the line 31

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promotes. If an air compressor 13 is connected upstream of the combustion chamber and keeps the combustion chamber under an overpressure, the fan 30 can also be omitted, an overpressure of 0.5 to 0.7 atm would be sufficient for this.

The pipe 31 leads to a heat exchanger 35, which is carried out in two stages 36 and 37. The flue gases then continue into line 38. As the gases flow through heat exchangers 36 and 37, the sensible and latent heat is released to a working medium which is warmed up in coils 39, 40. While the gases are cooled below the dew point (35), the latent heat of the steam is recovered and thus part of the upper calorific value is used in contrast to conventional systems, in which only the lower calorific value is expected from the start. In the first stage of the heat exchanger 36, the gases are cooled almost to the dew point, and only in the second stage (37) does the temperature drop below the dew point and the steam is condensed out. The condensate is withdrawn from the second stage (37), as indicated by arrow 41, and is then preferably used in the neutralization system for the separated gaseous pollutants, whereby on the one hand the liquid requirement for these can be covered and on the other hand the pollutants dissolved in the condensate are also neutralized .

The flue gases enter the first stage at a temperature of 150-180 ° C, are cooled there to 100-120 ° C and cooled down to 10-40 ° C in the second stage.

The line 38 brings the cooled gas into a compressor 45, which conveys the gas through the exchangers 35 and brings the gases into the line 49 at a pressure of about 3 atm. An aftercooler 50 serves to cool the gas to ambient temperature, and then the gas is forced through line 53. Line 53 brings the gas to the cleaning and separation system, as indicated by arrow 58. The compressor 45 can also be omitted if the pressure in the combustion chamber 10 by means of the upstream compressor 13 is sufficiently high, e.g. B. is held over 2 atm.

The separation system 58 consists of at least three identical regenerators 59, 61, 63. Each of these regenerators 59, 61, 63 contains loose solids, such as, for. B. ceramic balls, quartz stones, steel balls or other bodies that have large surfaces and serve as heat transfer and do not corrode. It is heat insulated at least in its lower part.

Automatic switching valves 64a, 64b, 64c and 65a, 65b and 65c are connected at both ends of each of the regenerators 59, 61, 63 via pipe connections 67, 68.

The feed line 53 leads to the valves 64a. An exhaust line 70 for acid gas extends from valves 64b, while the cleaned gas is withdrawn through line 71 from valves 64c.

An expansion turbine 75, which drives a power generator 76, is connected to the valves 65a and 65c via lines 73, 74.

The acid gas, i.e. H. the pollutants are sucked out of the discharge line 70 by a vacuum pump 79 and reaches the compressor 81 via a line 80, which compresses them as necessary and brings them via line 82 for further processing, in particular for neutralizing gas scrubbing.

The gas resulting from the burning of fuels in the boiler room 10 is processed cyclically in the regenerator system 58. In each period, each of the regenerators 59, 61, 63 operates in a different phase. While a regenerator cools the inflowing gas and the filling mass is slightly warmed up, in the second regenerator, which is shut off from the gas supply, the separated heavier components are sucked off by vacuum and in the third regenerator, the filling mass is fed from the first regenerator by supplying the clean gas, which is further cooled by expansion recently cooled down. The first period is initiated by opening valves 64a, 65a at the top and bottom of regenerator 59 and valves 64c, 65c at the top and bottom of regenerator 63. Gas flows through tank 59, drives turbine 67, and is swept away by the Container 63 returned. The expanding gases in the turbine 67 are thereby cooled and give off the cold in the regenerator 63. Of course, it is assumed that the system has already been pre-cooled and that the regenerators at the cold end maintain the appropriate temperature. The less volatile components are frozen out during the charging of the regenerators with the flue gas. The regenerators are switched every 6 to 10 minutes. A sufficient pressure ratio between the inlet and outlet of the expansion turbine 67 is important for the functioning of the system. This pressure ratio must be large enough to cool the recirculated clean gas and thus the regenerator 63 accordingly. The less volatile components of the gas are condensed or sublimed during cooling in the regenerator 59, while the “clean gas” is reheated to the ambient temperature via the regenerator 63. The connections or switching valves 65b are not required here, but can be useful if, for. B. a fourth regenerator is to be connected.

Another phase that occurs simultaneously with the loading of the first and cooling of the third regenerator is the evaporation of the frozen components in the second regenerator 61. This step is carried out by closing the valves 65a, 65b and 65c and the warm end of the regenerator 61 is connected to the pump 79 and the compressor 81 through the valve 64b. The vacuum pump works at a pressure ratio of 1:10. At this pressure ratio, the frozen components are evaporated again and drawn off from the regenerator 61 in the form of acid gas. The gas extracted in this way is compressed in the compressor 81 and pressed into the pipeline 81. The acid gas will normally consist of C02 with relatively small amounts of H2S, S02, S03, HCN, NOx and other pollutants. Depending on how low the temperature at the lower end of the regenerators 59, 61, 63 is set, any unburned hydrocarbons present in the flue gas, such as e.g. B. C2H4 and C2H6 as well as C3 and C4 fractions. The pollutants in the acid gas are neutralized in an alkali wash, and the water which has been discharged from the exchanger 35 can be used. The hydrocarbons mentioned can then be separated off for further use.

The successive phases, as just described, are then shifted so that the regenerator 63 is fed through line 53 and valve 64, the harmful components in turn being excreted, while the clean gas, after being expanded into turbine 72, is discharged through the Regenerator 61 is returned. At the same time, the sublimed or frozen-out components that were held in the regenerator 59 evaporate. The next switching phase is similar to the previous ones, with the gas being fed through line 53 into the regenerator 61 and the regenerator 59 being cooled by clean gas and the acid gas being sucked out of the regenerator 63 by pump 79 and being pressurized in the compressor 81. The cleaned gases are released into the atmosphere at 71 without the need for a chimney. Since these exhaust gases are dry, they can possibly be used in an evaporative cooler.

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The gas that is sent through line 82 to a neutralization system passes through a lye wash, for which the water from exchanger 35 is also used for the treatment. Pollutants from chemical processes that do not originate from the combustion at 10 can be treated with the 5 gases in line 53. The addition of such gases is indicated by arrow 90 in the process diagram.

A discharge system similar to a sewage system 101 can be provided to purify all kinds of exhaust gases. A corresponding compression can be provided in line 101 in order to be able to feed the collected gases into line 53. If more valuable components, such as hydrogen or hydrocarbons, also get into the collection system 101, they can be separated beforehand and sent for recycling.

The working medium, which is heated by hot flue gases and is intended to pass through the exchanger 35, is used to gain work performance. In the embodiment, the coils 39, 40 belong to a circuit system with an expansion turbine 91, a condenser 92, a liquid pump 93, all of which are connected by pipes 94, 95, 96, 97. The working medium that is heated during the passage in 39, 40 is expanded in an expansion turbine 91 that drives a generator 99 25. This working medium is then passed back through the condenser 92 and a pump 93 and to the heating coils 39, 40.

Various types of working media can be used in such a system, e.g. As water, ammonia, 30 propane, butane, pentane, hexane and halogenated hydrocarbons and lithium bromide, etc. Halogenated benzenes are preferred because they are non-toxic and can be used over a wide temperature range without risk of decomposition. In addition, the halogenated benzenes 35 have the advantage of high molecular weight and are relatively fire-proof and hardly corrosive.

The working energy that can be obtained in the circulation of the working medium can be read from the Mollier diagram (pressure-enthalpy diagram) of the respective working medium when one considers the area within which the relaxation in the turbine 91, the isobaric condensation in the condenser 92, and the isothermal pressure increase the pump 93 and the isobaric heating and evaporation lies in the lines representing heat exchanger 35.

It is also possible to use the heat given off in the cooling of the flue gases in the heat exchanger 35 for purposes other than work, e.g. B. for district heating purposes. A particularly advantageous embodiment results if the condenser and heat exchanger 92 can be connected to a district heating system and the expansion turbine 91 is connected, for. B. can be bridged by means of a bypass. Since the amount of heat that can be used by means of a district heating system is subject to seasonal fluctuations, it is possible in this way to use the heat obtained from the flue gases either for work in the turbine or for district heating purposes.

The already mentioned use of oxygen-enriched combustion air in the combustion chamber 10 has the advantage that the total amount of combustion gases produced is significantly reduced and that therefore all subsequent treatment stages, in particular the regenerator system, have to process significantly smaller amounts of gas and can therefore be made smaller in terms of apparatus. In addition, the containers for pure oxygen are under pressure anyway, so that a certain pressure level can be maintained in the combustion chamber 10 even without using the compressor 13, as may be sufficient to e.g. B. omit the downstream fan 30. The oxygen supplied to the combustion chamber 10 can also be replaced with air using a z. B. from the line 49 branched part of the combustion gases or with a part of the pure gas drawn off at 71, which results in a recycle.

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1 sheet of drawings

Claims (16)

mm 1. A method for treating flue gases before expelling them into the atmosphere, consisting of dedusting, cooling to about room temperature, and separating pollutants which are still gaseous at room temperature, characterized in that for separating the gaseous pollutants, the flue gases are compressed by a with a Filling material filled regenerator are routed, which is pre-cooled to a temperature drop below the condensation point of the gaseous pollutants and on the cooling surfaces of which the pollutants condense as condensate, and that the flue gases are cooled further after leaving the regenerator by relaxing and in the opposite direction by the regenerator for pre-cooling conducted and reheated to about ambient temperature. 2. The method according to claim 1, characterized in that the compression of the flue gases takes place at least in part by the fact that the combustion producing the flue gases takes place in the combustion chamber under pressure. 2nd PATENT CLAIMS 3. The method according to claim 1, characterized in that the flue gases are cooled to about room temperature before being introduced into the regenerator by heat exchange with a working medium, which evaporates and is performed for work by a working machine. 4. The method according to claim 3, characterized in that the condensed water obtained when the flue gases cool to room temperature is separated from the flue gases before they are introduced into the regenerator. 5. The method according to claim 4, characterized in that the cooling to room temperature is carried out in two stages, the falling below the dew point of the water vapor and collecting the condensed water only in the second stage. 6. The method according to claim 3, characterized in that the evaporating during the cooling of the flue gases working medium is passed through a circuit consisting of expansion machine, condensation and compression. 7. The method according to claim 1, characterized in that the flue gases are fed to the regenerator periodically and the regenerator in succession with the working phases a) passing the compressed flue gases through the regenerator with pre-cooled cooling surfaces, b) vacuum suction of the deposited pollutants from the regenerator, c) passing the cleaned flue gases, which are further cooled by expansion, in the opposite direction through the regenerator to cool the cooling surfaces again, is operated cyclically. 8. The method according to claim 7, characterized in that at least three regenerators are operated simultaneously with mutually offset working phases. 9. The method according to any one of claims 1 to 7, characterized in that additional flue gas to be cleaned is added to the flue gases before dedusting or before cooling or in particular before the separation of the pollutants. 10. Device for carrying out the method according to claim 1, with a dedusting stage, a cooling stage with indirect heat exchanger, one side of which the flue gases flow through and the other side of which is flowed by a liquid heat exchange medium, and a body with a large surface area for separating gaseous pollutants, characterized in that a working machine (91) for the working medium is connected to the heat exchanger and that the separating device (58) has a regenerator (59, 61, 63) with cooling surfaces for thawing out the separated pollutants. 11. The device according to claim 10, characterized in that the heat exchanger (35) is designed in two stages and a collecting device (41) for condensate in the second stage (37) is provided. 12. The device according to claim 10, characterized in that a from the heat exchanger (35), an expansion turbine (91), a condenser (92) and a pump (93) existing circuit for the working medium is provided. 13. The device according to claim 10, characterized in that a compressor (13 or 45) is provided for compressing the flue gases. 14. Device according to claim 13, characterized in that the compressor (13) upstream of the combustion chamber in which the flue gases are generated for compressing the combustion air and / or the fuel and the combustion chamber is under pressure. 15. The device according to claim 13, characterized in that the compressor (45) downstream of the furnace and either the dedusting stage (20, 21, 22) or the cooling stage (35) or the separation stage (58) is connected upstream. 16. The device according to claim 11, characterized in that the condensate drain (41) of the heat exchanger (35) is connected to a neutralization device for the separated pollutants.