DD239128A5 - PROCESS FOR DISPERSING CONTAMINANTS FROM COMBUSTION GASES - Google Patents

Abstract

From the knowledge of the sorption chemistry and the behavior of the sorbents, a mixture of sorbents depending on the flue gas composition is given for the final purification of the flue gas after incinerators in the temperature range of about 400C, which significantly reduces the consumption of sorbents and thus mitigates the landfill problem and / or the workup loaded sorbents. In addition, the production of the sorbent from NH3 and the constituents of the flue gas is also indicated. By this method, old plants can be retrofitted, the emitted to the atmosphere flue gases meet the environmental requirements for new plants. Also, the use of new plants is advantageous because the laden sorbents incurred in great purity and are suitable as a raw material for building materials and / or Duengemittelfabriken.

Description

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a) Title of the invention

Process for the separation of pollutants from combustion exhaust gases

b) Field of application of the invention

The invention relates to a method for the separation of pollutants, such as SO2, HCl and NO _x , from combustion exhaust gases by means of dry sorbents based on hydrated oxides / hydroxides or oxides such as Ca (OH) 2, AlOOH, Al (OH) 3, Al2O3XH2O, Bauxite, CaO, NaOH and / or carbonates / hydrogen carbonates, especially with high combustion chamber temperature, such as coal firing, in which the dust-like sorbents blown at below 400 ° C flue gas temperature in at least a partial stream of the flue gas stream to bind the possibly existing chlorides and the flue gases then after a deposit of the solid constituents are discharged via a chimney into the free atmosphere, and a device for carrying out the method.

c) Characteristics of the known solutions

From DE-OS 31 39 080 it is known for chlorine and / or fluorine deposition from the flue gases of a waste incineration plant in the waste boiler at a flue gas temperature of 400 to 350 ° C to inject Ca (OH) 2 as sorbent and the pollutant

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tie. Then the exhaust gases are cleaned and released into the atmosphere. The disadvantage is that the dust and sorbent-containing exhaust gases are passed over the last heating surfaces, so that they quickly pollute. The common deposition of dust and chlorides or fluorides leads to an intimate mixing of the three components, so that a separation and further processing is virtually impossible. A simultaneous sorption of SO2 and / or reduction of NO _x or sulfate formation is not suggested. ,

It is known that in the deposition of S02 ~ containing noxious gases from flue gases on wet way, the absorption at higher efficiency than in the dry state and that in the dry separation of noxious gases at superficially same boundary conditions, but different exhaust gases, the separation is subject to large fluctuations , where in refuse incinerators generally a better degree of separation than in coal furnaces is achieved.

d) Object of the invention

The invention has set itself the task of bringing the degree of separation from the knowledge of the chemical relationships despite entering dry additive dusts in the wet deposition, the greater than three times the stoichiometry of known systems is brought into the range of simple stoichiometry. The invention uses the physically and / or chemically induced release of fission and / or reaction products during the introduction of the sorbent in the partially cooled exhaust gas flow, so that the Schadgasmole-

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On the well-dispersed sorbent, wet conditions are found in the molecular region and, instead of a gas-solid reaction, a gas-liquid reaction is carried out. As an essential parameter hiebei the "in situ" water adsorption on sorbent particles is considered, the process is controlled so that, for example, despite water accumulation on the sulfate molecule always enough water for the gas-liquid reaction at the sorbent grain is present.

the essence of the invention

The inventive method is characterized in that at least a portion of the dust generated in the combustion chamber is removed before the blowing of the sorbents in the exhaust stream to be cleaned and that at least a portion of the sorbents due to temperature in the task area E ^ D and / or NH3 and / or CO2 in molecular sizes and thus activates the entered sorbent, such compounds or sorbents may consist of one or more of the following compounds, for example: NaHCC> 3, NH4HCO3, Al (OH) 3, silica gel, Ca (OH) 2 1 salts with water of crystallization such as CaCl2f Al2O3, whereby not only SO2 (via formation of a sulphite or sulphate) is bound to form this entered sorbent, but the sorbent is particularly active over the change of the crystal structure in the status nascendi and thus also the integration resp Conversion of nitrogen oxides to nitrogen is accomplished, Essential Ausgestaltun gene of the method according to the invention are given in the dependent claims 2 to 9.

1349

The inventive device for carrying out the method is characterized in that in the flue gas stream after a combustion plant, in particular before a last heat recovery surface, after the last Rohrheizflache a supply for a sorbent or sorbent mixture is provided, a dry filter system, in particular cloth filter, and a Saugzugebläse is downstream. Essential embodiments of the device according to the invention are specified in the dependent claims 11, to 14.

In carrying out the method according to the invention, it has surprisingly been found that the conversion of NO _x -schadgasen is improved by the invention to harmless ingredients.

The formation of cleavage and / or reaction products takes place, for example, according to the following equations:

1) water of reaction: CaO + 2 HCl = CaCl2 + H? 0

2) Constitutional water: 2NaHCO3 at temperatures

above 100 ° C - Na2CO3 + _H2O + CO2 or NH4HCO3 splits at temperatures of 35 ° C in NH 3 + H ₂ O + CO 2 or Al (OH) 3 splits into AlOOH + H ₂ O

3) Crystal water: CaCl ₂ x 6H ₂ O splits at tempera

Above 30 ° C 4H ₂ O and especially at greater than 200 ° C and the remaining (2H ₂ O) crystal water from. Similarly FeCl3 and Al ₂ O ₃ react

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4) Adhesion water: in the pores of dry dusts

(Salts) can condense water from the atmosphere (capillary condensation) so in molecular sizes. These water molecules can often evaporate above 500 ° C only at high temperatures.

In addition, in the conversion of NO _x , it is still of importance that NH 3 is also provided in small (molecular) quantities to a sufficient extent in order, on the one hand, to break down the NO _x or to bind it in nitrates. Hiebei ammonia compounds, such as NH4CI, which decomposes at 300 ⁰ C in NH3 and HCl, and NH4HCO3, which already decomposes at about 60 ° C in NH3 + H? O + CO2, can be used.

The operation of concurrent desulfurization and denitrification is explained as follows: It is known that Na 2 CO 3 (soda) hardly binds sulfur efficiently, the addition of NaHCO 3, e.g. in the form of addition of edible soda or as mineral (Nahcolite) but to a significantly greater extent, the addition being carried out at temperatures above the release of H2O and CO2 (above 60 ° C). Here, H2O and CO2 leave the crystal and Na2CO3 remains, which is in a particularly active form, since it is in the "state nascendi = just formed" and thus still has the lattice structure of the feed scale, but chemically only more than Na2CX> 3 (soda) is present. At the same time there is water in the pores, which is at the

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Exit from the crystal formed, which promotes the incorporation of SO2. The active crystal: Na2CÜ3, on the other hand, is active because the lattice defects release unsatisfied electrons, which in turn cause the incorporation or conversion of NO into N2 and / or NO2, and also the specific surface area of the freshly formed or reshaping crystals is very large is. It is essential that at least partially unstable compounds are created, which reduce the NO _x in N, so that N2 can form, which can not be converted back into NO _x due to the low temperature levels. The NO 2 represented in this way is further transformed into N 2 by the concurrently provided NH 3 (either as NH 3 or NH 4 OH, or else by the decomposition of a NH 3 salt). It forms from 3NO2 + 4NH3 in the end 3'5N2 + 6H2O. For simultaneous desulfurization and denitrification, the following criteria therefore apply to the selection of the active ingredients for mixing the sorbent. In the individual groups, the selection is made according to availability or economic efficiency and / or further processing of the used sorbents. For desulfurization, it should be compounds which split off the H2O, which on the surface for incorporation into the sulfite / late sulfate creates more favorable initial conditions for the otherwise quite slow reaction gas / solid (SO2 to alkaline substance), which is kinetically favored in the presence of water, So for example, NaOH (solid or liquid), NaH (X ^, NH4HCO3, Ca (OH) 2 / Al (OH) 3, AlO (OH), compounds with water of crystallization, CaO + 2HCl = water of reaction, NaHS03, BOH, solid or liquid organic compounds such as organic acids: formic acid, acetic acid.

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For the denitrification, it should additionally or simultaneously be a compound, which accomplishes a sudden crystal or Gi tterumbau, the newly created connection (by heat, by mechanical force such as grinding possibly) in statu nascendi (the bursting, the conversion to the new Compound) is particularly active and has unsaturated surface valences and this can be used to convert from NO to N2 and / or NO2, as for example by addition of NaHCO3 (conversion to Na2C £> 3) and forms a particularly active Na2C £> 3 * in statu nascendi.

The NO2 (from the former NO) which has not been converted to N2 at the same time, must now in further, simultaneously or later, by addition of NH3 or such! ^ - compounds or solutions, which release NH3 with the supply of heat, possibly also NH3 *, ' to react converted to N2.

In the context of the invention, it is possible to increase the dry absorption efficiency. This is particularly important at high combustor temperatures, such as those found in hard coal firing where the addition of lime additive in the combustor is of little effect.

Since today the chemical industry has to change over to the needs of the flue gas cleaning (cheap sorbent of not too high purity but in large quantities), it is of great importance that the operator of the firing systems can easily produce the sorbent himself and he only the abundant chemical raw NH3 needed, whose procurement is not too great burden. In this sense, the subclaims concerning the sorbent production form a unit with the sorption process.

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f) embodiment

The invention is shown in the accompanying figure, for example and schematically. The figure shows the circuit of a thermal power plant with the flue gas cleaning and absorbent generator according to the invention. The cooled flue gas stream 1 from an incinerator 13 flows at about 200 ° C ⁴ through a cloth filter 2 in which the particulate impurities are deposited via a stack 14 to the outside. At the exit from the incinerator 13, the fly ash is separated in a dry separator, such as electrostatic precipitator 16. The purified flue gas, which is now cooled to below 400 ° C, is mixed in an absorption stage with a dry sorbent such as Ca (OH) 2 , which absorbs the noxious gases, such as SO2 and / or HCl, wherein the loaded sorbent is then deposited in a cloth filter 2. Here now the difficulty arises that at low chloride content in the exhaust gas, the sorbent reacts only superficially with SO2, so that only a very slight involvement of SO2 and then only with high stoichiometry 2 to 3, can take place. This disadvantage can be overcome by adding chlorides such as CaCl 2 or FeCl 3 to the sorbent in the order of 2 to 5%, so that the Ca (OH) 2 is mixed with chlorides. This mixture is particularly effective if the two sorbents were already produced together during the production (extinguishment of the quick lime with addition of hydrochloric acid). The main advantage of CaCl2 is that this salt can contain a relatively large amount of water of crystallization and this at room temperature.

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At temperatures exceeding 200 ° C, it releases all of these water particles in molecular sizes, in a kind of status nascendi. Due to this moisture, which not only on the surface of the dust grain but also from the interior thereof, instead of the usual insufficiently fast and insufficient gas-solid reaction takes place practically a gas-liquid reaction, which proceeds with very high efficiency , Hiebei it is essential that the liquid practically arises on the grain and is not brought by the water vapor content of the exhaust gas. This was by hitherto known, wet method, eg scrubber, spray method, dew point undershooting with wet method of cloth filter, injection of H2O before a filter and still others, tried with the unfavorable result that particular cloth filter are tainted with an uneconomically high pressure loss since the water outside of the dust particles leads to a sticking of the dust particles, while the water on the so-called inner surface of the dust particles thus on the sorbent does not have this disadvantage. Due to the Ca (OH) 2 and CaCl2 addition, the NO _x can not be degraded in larger quantities. In order to get a grip on this noxious gas as well, according to the invention Ca (OH) 2, which may also contain CaCl2, staghorn salt, essentially NH4HCO3 and / or edible soda (NaHCO3) and / or similar compounds, is added or replaced by said bicarbonates, which in the temperature range used between 30 ⁰ C and 400 ° C are not resistant and fall into their constituents. As far as these components have a great reactivity, the noxious gases can be reduced in stoichiometric ratio with high efficiency.

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Hirschhornsalz and Soda are relatively expensive absorbents, but can be in a downstream system from the CO2 of the flue gas stream and water, NH3 (and sodium chloride) produce or recover. For this purpose, the flue gas stream 1 is branched off about 5% of the flue gas and passed through a flue gas cooler 3. This substream I ^f is then fed to one or more solution reactors 10, 10 'where it is contacted with water or NH 3 -saturated water and the CQ 2 of the purified flue gas is partially dissolved. For this purpose, flue gas tapping points 4, 4 ¹ and 4 "are provided in the partial flow I ^{1 of} the flue gas The solution of the three chemicals mentioned (NH 3, NaCl and CO 2) is cooled both in solution reactors 10 'and in a downstream condenser 9 that the staghorn salt or edible soda precipitates, which is centrifuged in a centrifuge 5 and fed via a dryer 7 a crystal crushing device 8, such as mill, the sorbent feeder 6. The depleted of crystals mother liquor is fed to the NH3_Aufsättiger 12 via the recirculation line 11 or, mixed with the mother liquor saturated with NH 3, is supplied to the flue gas removal points 4 so that they again come into contact with CO 2 and generate new sorbent crystals about 200 ° C and discharged via the fan 15 in the fireplace 14 s.

To achieve a pure loaded sorbent, it is advantageous, the flue gases before the feed point 6 of the sorbent preferably

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dry dry in an electrostatic precipitator 16 and remove the ash particles according to arrow 17 so that as little as possible ash particles from the incinerator 13 get into the cloth filter 2, and this must be cleaned less often. Thus, the pressure loss is kept within limits. Other reasons are:

A) The product obtained in the sorption stage by reaction with the noxious gases has sales value or is reusable in operation, but is reduced or rendered unusable by the high crude gas dust content. The reaction of SO2 with deer horn salt produces ammonium sulfate or ammonium bisulfate, which could be used relatively pure as a fertilizer.

B) If it makes sense for the binding of the noxious gas, the reaction of the sorbent on the cloth filter should be carried out as completely as possible (additive utilization). .This means that the cloth filter has the longest possible interval between the cleaning pulses. The dust occupancy with non-reactive dust from the combustion chamber but requires a shorter cleaning interval and still reactive sorbent was prematurely removed from the reaction surface on the filter cake of the cloth filter.

C) If, in an existing plant, a (used, but by and large, or partially usable) filter, e.g. E-filter is present, the addition of this e-filter, the following cloth filter smaller and thus the overall system can be designed more cost-effective.

"Fr-w -" .. _L "-WI" - * ^ '!,'! W » -mm 'JiW IWII * V ¹ WlI Il ^ TtT'V

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This can be connected as completely as possible cleaning of the exhaust gases before the task of sorbents behind the incinerator, a fertilizer factory or a stone or plate production plant, which refines the generated laden "sorbents and benefits from the environmental protection system or at least reduces the landfill amounts.

In the context of the invention, it is possible already in the combustion chamber of the Verbrennungsanlge or in about 1000 ° C exhaust stream, so shortly thereafter, abandon a sorbent, which binds SO2 and thus creates better conditions for the downstream SO2 / NO _x -Abscheidung invention, so that, for example, the amount ratio SO2 / f0O _{x is} influenced and is present in the optimum ratio 2: 1 or even the SC> 2 partial pressure is lowered in order to reduce the correspondingly expensive sorbent expenditure in the low-temperature stage.

Claims (1)

1349 - 13- claims: 1) Process for the separation of pollutants, such as e.g. SO "HCl and NO, from combustion gases by means of dry ner sorbents based on hydrated oxides / hydroxides or oxides such as Ca (OH) _2, AlO (OH)., Al (OH) _3, Al ₂ O ₃ XH ₂ O, Bauxite, CaO, NaOH and / or carbonates / bicarbonates, such as NaHCO- or NH.HGO ", in power plants. O 4W conditions, in particular with high combustion chamber temperature, such as 10_ eg hard coal firing, in which the dust-like sorbents blown at below 400 ° C flue gas temperature in at least a partial flow of the flue gas stream with binding of any existing chlorides and the flue gases are then discharged after separation of the solid components via a fireplace in the free atmosphere, characterized in that at least a portion of the dust generated in the combustion chamber is removed from the exhaust gas stream to be cleaned before it is injected into the combustion chamber and that at least some of the sorbents are exposed to the action of temperature in the feed area H_0 and / or NH ₃ and / or C0 "in molecular sizes and thus activate the entered sorbent, wherein such compounds or sorbents may consist of one or more of the following compounds given by way of example: NaHCO 3, NH 3 HCO, Al (OH) silica gel, Ca (OH), salts with water of crystallization such as CaCl_, Al Oo, taking under education this entered n concern not only SO (via the formation of a sulfite or sulfite) but, through the change of the crystal structure in the status nascendi, the sorbent is particularly active and thus the incorporation or conversion of nitrogen oxides to nitrogen is accomplished. 1349 -41 - 2) Method according to claim 1, characterized in that in the deposition of SO _? , in particular in the absence of HCl in the flue gas, together with the sorbent, in solid or liquid form, HCl or as sorbent, a mixture with 0.5-50%, in particular 2 to 10%, of a halide, in particular chloride such as NaCl and / or an ammoniacal or alkaline compound such as NH Cl, (NH ₄ J ₂ CO ₃ or Ca (OH) is injected with a decomposition or sublimation temperature of .- 400 ° C in the exhaust stream. 3) Method according to claim 1 or 2, characterized in that as sorbent dusty over-erased Ca (OH) in a hydration stage, in particular in a mixture with CaCl 2 and / or FeCl_ with water of crystallization, is blown into the exhaust gas stream, wherein the chlorides by treatment of the Ca (OH) and its impurities are made with HCl. 4) Method according to claim 1 or 2, characterized in that in the deposition of S0_ in the absence of HCl, in particular in the additional deposition of NO, in the flue gas stream as sorbent Ca (OH) ₂ and / or bicarbonates such as NaHCO »and / or NH ₄ HCO ₃ or NH ₄ OH or NH ₃ or NH ₃ ~ compounds are blown into the flue gas stream. 5) Method according to claim 2 or 4, characterized in that the required sorbent based on ammonia and / or soda from the purified flue gas after the dry separator by introducing ammonia. is prepared in aqueous solution and with heat removal. 1349 -45 6) Method according to claim 5, characterized in that is introduced for the production of sorbents based on soda in the aqueous solution of ammonia NaCl. 7) Method according to claim 1, characterized in that the flue gases are dry-cleaned before the blowing of the sorbents in an electrostatic precipitator. 8) Method according to claim 1, characterized in that the sorbents ground, in particular immediate. milled before the task in the exhaust stream, be added to the exhaust stream. 9) Method according to claim 5 or 6, characterized in that the production of the required sorbent is preferably carried out in a Teiistrom of acidic pollutants such as SO-, HCl and NO purified flue gas stream, which is passed after a cooling at flue gas sampling points, in which the still CO.sub.2-containing flue gas is sucked in and, in particular after hydraulic compression in cooled, preferably NH.sub.2-containing liquid, is dissolved to form crystals and then the crystals are spun off and blown into the pre-cleaned flue gas stream before a cloth filter after at least superficial drying and, in particular, grinding Crystals depleted liquid is returned to the centrifuge in a NH_-Aufsättiger and fed back from this to the flue gas sampling points. 10) device for carrying out the method; according to at least one of claims 1 to 9, characterized in that in the flue gas stream after an incinerator (13),. in particular before a last heat recovery surface, after the last tube heating surface, a feed for a sorbent or sorbent mixture is provided, which is a dry filter system, 1349 in particular cloth filter, and a Saugzuggebläse is connected downstream. 11) Device according to claim 10, characterized in that, preferably in a partial flow of the flue gas stream (1) after the cloth filter (2), a flue gas cooler (3) and flue gas sampling points (4,4 ', 4 ^(l ) are provided, through which The flue gas is sucked in and is brought into contact with liquid and dissolved in it, whereby, after flowing through a cooler (9), crystals crystallize out, which are separated from the recirculated solution in a centrifuge (5) and fed through a feed device (6) in front of the cloth filter (2) in the purified of solids flue gas stream (1) are aufbar. i2) Device according to claim 11, characterized in that between the centrifuge (5) and feeding device (6), a dryer (7) and a crystal crushing device (8) are provided. 13) Device according to claim 11, characterized in that the flue gas extraction points (4,4 ', 4 ·') parts of Solution reactors (10, 10 '), which are cooled and connected in series and designed for the solution of CO ₂ in NH-containing water. 14) Device according to claim 13, characterized in that between the last solution reactor (10 ') and the centrifuge (5), a cooler (9) is provided and that at the centrifuge (5) a recirculation line (11) depleted of crystals Liquid is provided, which via a NH -Aufsättiger (12) and.the flue gas removal points (4,4 ') in the solution reactors (10 ¹ ) leads. h'zrzu ί