DE19514135A1 - Desulphurisation and denitrification of flue gas by dry additive process - Google Patents

Abstract

Multistage redn. of gaseous air pollutants formed during combustion of fossil fuel contg. S, without waste liquor prodn., involves supplying air and/or fuel in stages to the combustion chamber of a boiler or fire and adding alkaline earth-rich additive (I) to the flue gas. (I) is used in an upper temp. window of ca. 800-1000 deg C in a small amts., just sufficient to bind SO3 already formed and prevent re-formation of SO3; and more (I) is added in a second lower temp. window of ca. 80-120 deg C where the SO2 content is such that, in addn. to the other air pollutants, NOx is also bound by a highly effective quasi-dry process.

Description

The present invention relates to a multi-stage process to reduce pollutant emissions, in particular from Sulfur and nitrogen oxides as well as hydrogen chloride and hydrogen fluoride, according to the preamble of claim 1.

For the reduction of emissions from the aforementioned Air pollutants are already numerous different ver drive known and in large-scale application.

Most of it is based on the total performance of the furnaces equipped with it, with regard to the Desulphurization plants using so-called wet processes (flue gas Washes), which usually also include dry end products (Ab sorpte) or by further treatment solid or liquid value substances (such as technical anhydrite / gypsum or fertilizers or Sulfuric acid).

The wet processes for flue gas desulfurization work at the adiabatic water vapor saturation temperature. That requires egg complex corrosion protection of the entire washing section and  also a re-heating of those exiting from it Flue gases before they enter the chimney to values that prevent corrosion caused by residual emissions and also there such a great boost under unfavorable outside air conditions The flue gases cause it to be a cheap pollutant spread comes with which the permissible immission limit values do not be crossed, be exceeded, be passed. German regulations currently require for these reasons a chimney inlet temperature of the Rauchga at least 72 ° C. In addition, these procedures require one in-process or external wash water treatment. You are therefore comparatively in terms of investment and operating costs very expensive.

In addition to the wet processes, there are also different ones dry and quasi-dry flue gas desulfurization processes known, where no waste water is produced. To the so-called dry process belongs to the dry additive process (TAV). In this process, alkaline or alkaline earth are rich Absorbents (dry additives), in particular limestone powder or Lime hydrate with high mixing intensity in the combustion chamber a furnace was introduced. Although strong with these procedures superstoichiometric additive mass flows (e.g. with (Ca / S) mol ratios of up to 3-5) are only maximum Sulfur integration levels between approx. 60 and 85% can be achieved. The relatively large additive mass flows also cause a heating surface pollution and corrosion. In addition, because of the fall only moderate degrees of implementation (especially during the sulfati sation) with disposal-problematic calcium oxides and Cal ciumsulfite highly contaminated waste.

Examples of dry additive processes are given in the following published or patent documents:
NL 74 14 617, DE 28 22 086, US 41 78 349, DE 30 20 016 A1, JP 56 126 429 A2, AT 82-3632, JP 600 22 920 A2 and JP 0 621 0128 A2.

The quasi dry processes include the spray absorption process. These are based on the known process principle of spray drying, in which the pumpable particle suspension sprayed in a sorption reactor (spray absorber) by means of nozzles or rotary atomizers through sufficiently hot drying gases with high drying speed down to the equilibrium moisture dependent on the partial pressure of the gas phase of the suspending agent and the drying gases (Sorption equilibrium according to sorption isotherm) is dried. The high drying speeds result from the fine atomization of the suspension and at the same time thorough mixing of the fine suspension droplets with the drying gases, from which large mass and heat exchange surfaces result. Added to this are the very high mass and heat transfer coefficients associated with the phase change (evaporation of the liquid droplets). These very good material and heat exchange ratios also ensure very good levels of integration of various air pollutants from the flue gases used for drying (such as sulfur oxides, chlorine and hydrogen fluoride) into the solid particles of the additive suspension. As with the dry processes, the quasi-dry spray absorption process also uses alkali-rich or earth-alkali-rich absorbents. Examples of spray absorption processes are given in the following published or patent specifications:
DE 22 24 224, GB 20 78 702 A, DE 30 17 835 A1, DE 30 34 822 A1, EP 0 112 101 A1, DD 2 79 184 A1, JP 92-20 002, US 52 84 637 A, CA 20 99 796 A1 and EP 0 128 589 A2.

A major disadvantage of the known dry or quasi-dry processes is the fact that they often require the addition of an additional separate flue gas denitrification system in addition to combustion-technical measures (such as staggered air and / or fuel supply, flue gas recirculation) so that the required by law or the stricter NO _x limit values agreed between the manufacturer and the operator of a boiler or other combustion systems are adhered to or fallen below.

The object of the present invention is therefore a gat to provide appropriate procedure with which not only excellent levels of integration of sulfur and nitrogen oxides den, as well as of chlorine and hydrogen fluoride, son which at the same time also adds smoke Gas denitrification plants can be dispensed with in many applications power.

This object is achieved by means of a genus resolved according to the multi-stage process, as it from the license plate of claim 1 emerges.

According to the invention, the additive is supplied in a boiler rich, in which the flue gas temperatures between about 800-1000 ° C lie. It has been found that in this temperature range the greatest sales rates can be achieved after sulfation. According to the invention, the additive is added compared to the known dry additive process (TAV) with a very never third specific (based on the fuel mass flow) Addi active mass flow. This is dimensioned so that a safe one binding of formed sulfur trioxide or a suppression of whose new formation is guaranteed. This succeeds when used of limestone flour or hydrated lime as an additive even with one (Ca / S) molar ratio of about 0.5-1.0 (here S is the total sulfur content of the fuel). The attainable  Inclusion of sulfur dioxide is between 10-40%. The According to the invention, flue gas occurs with a high sulfur dioxide concentration in a second additive addition. About It has surprisingly been found that this Emission reduction level thanks to the quasi-dry, highly effective Chemisorption of the gaseous air pollutants to the suspensier not only a large part of the gas still in the flue gases air pollutants containing sulfur dioxide and chlorine and hydrogen fluoride into the dry, free-flowing sorption pro product, but also in the flue gas a significant reduction in the nitrogen oxide concentration from to 15-30% of the entrance concentration takes place. This ef fect allows in most applications to a downstream separate denitrification plant.

The comparatively low specific already explained Additive mass flow in the first addition point also causes advantageously also a comparatively lower additional heating surface contamination and corrosion. This will decrease the pollution-related influences of adding dry additives on the exhaust gas and superheated steam outlet temperature rature or on the injection quantity. The same goes for through the additive supply due to the endothermic calcination and the exothermic sulfation caused changes in the total heat balance of fuel conversion and heat transfer process.

Known to suppress sulfuric acid corrosion Lich the sulfuric acid dew point on the entire flue gas path in at no point within the boiler. Here are in particular the walls of the components in contact with the flue gas in which the work equipment (feed water, combustion air) enters the boiler at the cold end of the boiler. All in one the lower the entry of work equipment, the greater the extent  temperature is. Otherwise, the affected components corresponding effective secondary corrosion protection measures ge be hit. The sub caused with the first additive Pressing the sulfuric acid dew point enables without any special secondary corrosion protection measures a significant reduction the exhaust gas temperatures that can be driven without sulfuric acid corrosion up to near the water vapor dew point. This adiabatic water vapor saturation temperature is, for example, that for Incineration of raw lignite in atmospheric furnaces water vapor partial pressures between about 45 and 55 ° C.

Because of the dew point suppression according to the invention, the proposed method in both the second additive distribution point as well as in the downstream fabric filter in one optimal temperature range between 80-120 ° C without any special Sulfuric acid corrosion protection measures are being worked on. There are relatively low in the second additive addition point very high air pollutant due to specific additive mass flows Integration levels achievable. So when using Lime hydrate as an additive in this addition point already at (Ca / S) - Molar ratios of 1.0-2.0 additional desulfurization levels achieve about 45-75%.

It is also in the filter in the downstream fabric filter cake, the greater the density, the greater the density the flue gas temperature at the adiabatic water vapor saturation temperature is. Because of the work in the lower temperature furnace Additional desulphurization levels of approx. 10-25% reached.

Because of the sulfuric acid dew point according to the invention pressure could further lower the lower temperature window shifted below and thus the pollution rate as well the boiler efficiency can be increased. From macroeconomic  Considerations are made taking into account the minimum temperature of the flue gases at the chimney entrance waived these advantages. But also with this waiver depending on the application, exhaust gas temperature reductions of approx. Realize 10-50 K, which increases the boiler efficiency by up to 0.5-2.5 percentage points is increased.

Further advantageous refinements of the present invention result from the subclaims.

In addition to the air pollutants already mentioned above through the application of the proposed method also a highly effective integration of further gaseous air pollutants such as polycyclic aromatic hydrocarbons, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzo-fura ne in the additive / sorbent particles.

To further explain the invention is in the accompanying Drawing one by restricting it to the essential one directions simplified procedural scheme of an execution game of the proposed wastewater-free multi-stage process to reduce the combustion of fossil sulfur air pollutant emissions poses.

This embodiment relates to the combustion of Lignite dry dust - hereinafter referred to as "fuel" - in a dust burner operated at low furnace pressure with dry ash extraction. This fuel has one Water content of around 10%, an ash content of 5-10%, one Total sulfur content of around 1%, a nitrogen content of 0.6-0.8% has a lower calorific value of around 21 MJ / kg. His grind is due to residues on the 0.2 mm sieve of less than 15 Mass% and on the 0.09mm sieve of less than 45 mass% draws.  

The fuel is drawn off from a storage silo 2 that can be shut off by means of a shut-off valve 3 via a discharge line 4 with a controllable metering device 5 with a mass flow required to meet the respective operating requirements. For this purpose, the speed of the fuel metering device 5 (here, for example, a rotary valve) is regulated according to the measured values of the working fluid parameters, mass flow, temperature and pressure, which are just emerging at the outlet from the boiler or possibly the turbine. At the same time, the corresponding controlled system is used to implement a change in the working fluid entry and / or exit parameters by a corresponding change in speed.

The fuel mass flow 1 drawn off in a controlled manner from the fuel silo 2 is conveyed by means of the carrier air 7 conveyed by a speed and / or swirl flap-controlled delivery fan 6 and a fuel entry device (not shown in the drawing) (e.g. via an injector / Ejector) entered in a pneumatic delivery line / dust line 8 .

This initially common line 8 for the entire fuel mass flow branches into the dust lines 11 and 12 . These are installed in the combustion chamber front wall 9 of a boiler 10 in two stacked burner levels 13 , 14 instal lated dust burner with fuel.

At the same time, the burners are supplied with a certain part of the combustion air 15 conveyed by a fresh fan 16 , which is also speed-controlled and / or swirl-flap-controlled, as further primary air 18 a or 18 b.

The fresh air supply to the burners is dimensioned so that an air ratio of about 0.80-0.85 is realized together with the conveying air 7 on the burners. In this thus reducing flue gas atmosphere, in addition to relatively low combustion temperatures, not only is there a relatively low NO _x formation, but at the same time, compared to an over-stoichiometric, unstaged air and fuel supply, there is in particular less sulfur dioxide formation a suppression of sulfur trioxide formation. In addition, a significant proportion of the fuel particles involved in the inclusion of pollutants only degasses the volatile constituents (with their immediate combustion).

The degassed fuel particles are very pore-rich and therefore have very large inner surfaces (with BET values of <100-300 m² / 8), on which the air pollutants contained in the flue gas 21 are integrated to a similar extent as to separately produced brown coal activated coke.

Despite the subsequent supply of further combustion air who which these degassed fuel particles do not completely ver burns so that a certain portion of the free upon combustion air pollutants in the fly ash adsorptively bound remains.

The known process principle of the staged fuel and air supply used here thus represents a first in-situ / online cleaning step of the flue gases 21 with regard to the reduction of air pollutant emissions.

Depending on the overall combustion boundary conditions (reaction kinetic fuel parameters, particle size distribution and speed of the fuel particles, in the interaction of heat release and heat dissipation, particle and flue gas temperatures, ...), with regard to the realization of a combustion temperature as low as possible and thus as possible Low nitrogen oxide formation favorable Ab stood above the upper burner level 14 with sufficient mixing energy, the first branched off from the air line 17 is blown out of fire air 19 a (ABL 1). The mass flow of this first burnout air 19 a is dimensioned such that an air ratio of approximately 1.05 to 1.15 (preferably 1.10) is present after mixing with the flue gases 21 .

The distribution of the fuel mass flows and the combustion air volume flows is carried out by means of control or trim flaps (with electric motor drive) 20 so that the highest possible quality of combustion (low NO _x formation with largely perfect and complete combustion) is realized. The drawing shows where such flaps 20 are installed in the air or solids delivery lines.

Above the supply of the burnout air 19 a (ABL 1) in a flue gas temperature range of 800-1000 ° C as a sorbent for the integration of gaseous air pollutants (sulfur oxides, nitrogen oxides as well as chlorine and fluoride), hydrated lime (calcium hydroxide) in fine-grained dry form entered in the boiler 10 . This implements the second stage of the proposed multi-stage emission reduction process as a dry additive process (TAV). The specified flue gas temperature range is technically and economically optimal for the calcination / dehydration of the calcium hydroxide as well as for the sulfation of the calcium oxide formed (upper optimal temperature window).

To implement the TAV, hydrated lime 22 is fed from a pre-silo 23 via a discharge line 24, which can be shut off by means of a shut-off valve 3, to a rotary valve 25 . Their speed is adjusted via a control so that the additive mass flow required for sufficient emission reduction in the just driven operation is withdrawn from the silo 23 . This total additive mass flow is composed of the mass flow for the TAV and the mass flow for the third emission reduction stage (spray absorption), which is described below.

The guide values for adjusting the speed of the rotary valve 25 are the emissions in the chimney 44 at the point 45 at the air pollutants mentioned and the total flue gas volume flow measured before the suction 42 . The total additive mass flow is split at a branch 26 in two sub-flows. The first partial stream is branched off via line 27 for the TAV. The size of this partial flow is adjusted by the speed-controllable rotary valve 30 via a separate control loop in such a way that no (detectable) sulfur trioxide formation occurs within the boiler 10 along the entire flue gas path.

As a guide for this measure to suppress the sulfuric acid dew point of the flue gases 21 , the SO 3 measured value to be kept at the end of the boiler below the detection limit and the total flue gas volume flow measured before the suction draft 42 are used.

The additive mass flow required for the TAV is entered into the boiler 10 by means of pneumatic conveying. The required dry conveying air 28 is promoted by a conveying fan 29 via a suction line into the heated conveying line 27 .

The actual entry of the lime hydrate-laden flow into the boiler 10 takes place via a multi-nozzle entry system, not shown. This entry system is designed in terms of the number, the geometric design and arrangement of the nozzles in a known manner so that it is as complete as possible mixing of the additive solid particles with the Rauchga sen 21 . To suppress the sulfuric acid dew point, a relatively low additive mass flow is required under the given conditions of use. It is generally sufficient here to achieve a (Ca / S) molar ratio of around 0.5.

Is in the present embodiment above the dry additive supply, a second combustion air (ABL 2) via the line 19 b in the boiler 10 with sufficient mixing energy in such a volume flow blown, that thereafter the air aspect ratio in a range from 1.15 1.20. With these air ratios, experience has shown that both complete and complete combustion and substantial oxidation of the (relatively easily leachable) calcium sulfite (CaSO₃) that is primarily formed when sulfur is incorporated into the calcined additive can be achieved for more stable and therefore easier to deposit calcium sulfate (CaSO₄). On the other hand, higher air ratios would unnecessarily reduce the efficiency of the overall system.

Alternatively, in other applications it can be more economical to implement the above-mentioned favorable air ratio figures with the ABL1 and the additive conveying air 28 .

With the mentioned boundary conditions regarding the flue gas temperature temperature range, the air ratio and the (Ca / S) molver ratios are in the embodiment in the second emis sion reduction level (TAV level) reached about 10-20%. The integration size that occurs here de for hydrogen chloride and hydrogen fluoride are somewhat higher (at at least 15-25%).

The fly ash portion separated into the combustion chamber funnel in the combustion chamber or in the first draft of the boiler 10 reaches a fly ash silo 48 via a lockable discharge line 46 . The fly ash portion separated in the ash hopper of the boiler cross train is also introduced into this silo 48 via a lockable discharge line 47 . To a small extent, this fly ash (due to adsorptive / adhesive binding to the fly ash particles) also contains hydrated lime particles.

By suppressing the The sulfuric acid dew point of the flue gases is without any special Corrosion protection measures on the endangered smoke gas Components of the minimum boiler exhaust gas temperatures that can be moved now initially only from the much lower water vapor dew point the flue gases determined.

For the fuel used in the embodiment lies the sulfuric acid dew point, for example, for an air ratio nis number of 1.2 in full load operation at around 120 ° C, the water steam dew point, however, only at around 50 ° C.

The lowest exhaust gas temperature is usually certain for the sake of safety so determined that the surface temperature of the components in contact with smoke gas at least 5-15 at each point K is warmer than the flue gas dew point temperature. This waiter surface temperature is both from the flue gas temperature as well from the lowest temperature of the work equipment (air, water) as well as the local heat transfer conditions. For the assessment of the economic benefits of the described Procedure for reducing the flue gas dew point temperature significant that the reduction in exhaust gas temperature by 10 K in an increase in the boiler within the stated value range efficiency by approx. 0.5 percentage points. About in the ver ratio of the relative improvement in efficiency are reduced then the fuel and addi with the same boiler output tiv mass flow and all emission values, in particular also the CO₂ emission values.  

With the proposed multi-stage emission reduction scheme will drive this savings potential for the following reasons overall advantageously not fully used.

So it is initially advantageous to set the flue gas temperature in the ge whole process not below the required chimney minimum lower the temperature of 72 ° C. Otherwise - as with the wet desulfurization process - required re-start heating the flue gases is expensive in terms of total costs diger than the compensation of the corresponding Efficiency ver wrestling.

In the exemplary embodiment, therefore, the flue gas temperature becomes so regulated that they the above mentioned at the chimney entrance Demand value does not fall below and therefore on a renewed heating the flue gases can be dispensed with.

This results in a lower reaction temperature (smoke gas temperature at the outlet from the spray absorber 37 ) of around 80 ° C. for the third emission reduction stage realized in a spray absorber 37 , which connects to the transverse pull of the boiler 10. Furthermore, to achieve high conversion speeds and consequently higher ones Desulfurization levels with the lowest possible additive mass flows limit the flue gas temperature in the spray absorber 37 in the exemplary embodiment to approximately 105 ° C.

By observing this "lower optimal temperature window", which is effected by means of a conventional, after the flue gas outlet temperature from the spray absorber 37 controlled water injection 37 a, at (Ca / S) molar ratio of the lime hydrate of 1.5-2 , 0 depending on the reactivity and the BET surface area of the hydrated lime used, sulfur levels of 55 to 75% achieved. For the chlorine and hydrogen fluoride, the levels of integration under the conditions mentioned are high at around 30-50%.

In particular, with your proposed special multi-stage emission reduction process, the presence of a still sufficiently high sulfur dioxide entry concentration in the spray absorber 37 enables a further reduction of the nitrogen oxide concentration of the flue gases 21, which is very significant with values of approximately 15-30%. The maximum NO _x reduction values occur at a reaction temperature of approx. 100 ° C.

The hydrated lime required for the spray absorption is deducted as part of the total additive mass flow with the rotary valve 25 via the discharge line 24 from the additive silo 23 in a controlled manner. After the partial flow required for the TAV has already been branched off at the branch 26 , the remaining (larger) additive partial flow passes via a shut-off, heated line 31 into a suspension 33 equipped with an agitator.

For suspension 32 water is introduced into the Sus pensator 33 in a quantity such as it is required for suspension up to perfect conveyability by means of a pump 35 via a line. The suspending device 33 is equipped with a filling level, measuring and regulating device which ensures that the filling level does not exceed an upper limit value and does not fall below a lower limit value.

The well-mixed lime hydrate suspension is conveyed by the pump 35 via a lockable and equipped with a control flap made of a suspension outlet line (suction line) 34 and a suspension delivery line (pressure line) 36 to the head of the spray absorber 37 . There it is finely atomized using a conventional rotary atomizer operating at high speeds (e.g. at 5000-10,000 rpm) (average droplet diameter approximately (15-25) × 10 ^-6 m). The drive shaft of the Rotationszer atomizer is arranged vertically, so that the main direction of flight of the suspension droplets is horizontal. This results in a very good mixing of the hydrated lime suspension with the smoke gases 21 , which are also known to be tangential to the head of the spray absorber 37 and are swirled by baffles (not shown).

It is also possible to achieve the thorough mixing of the lime hydrate suspension with the flue gases 21 required for a high level of pollutant incorporation with one of the likewise known atomizing nozzle systems.

The spray absorber 37 is designed in terms of the material and heat balances in a known manner so that it contains pollutants for the air, sulfur and nitrogen oxides as well as chlorine and fluorofluoride for all boiler loads, the emission reduction share required to meet the overall required emission reduction ( by realizing a corresponding (Ca / S) molar ratio). It is also designed so that the absorptive / fly ash mixture obtained in its discharge hopper is dry and free-flowing.

The emission values measured in the chimney 44 (in comparison to the corresponding demand values) and the flue gas volume flow measured in front of the suction draft 42 are used as reference values for the control of the hydrated lime mass flow to the suspending device 33 or the suspension mass flow to the spray absorber 37 . The emission reduction already achieved with the TAV is subtracted from the total required emission reduction.

From the discharge funnel of the spray absorber, the mixture which has fallen there is introduced via a lockable line 49 into a sorpt / fly ash silo 50 . The flue gases 21 pass through a flue gas duct 39 to a fabric / bag filter 40 .

In this filter 40 , which is known per se, the fourth emission reduction stage of the proposed multi-stage method is implemented. In addition to the primarily intended highly effective dust separation, an additional substantial reduction in the sulfur oxide, chlorine and hydrogen fluoride concentration is achieved in a manner known per se when the flue gases 21 flow through the solid particles already deposited on or in the tissue. This emission reduction is brought about by the very intimate contact that the above-mentioned (as well as other gaseous) air pollutants have when flowing through the so-called filter cake, in that a significant proportion of unreacted calcium hydroxide or calcium oxide or Particles are included. For example, in the exemplary embodiment for the flue gas components mentioned in the case of the process example in the lower optimal temperature window, filter reductions of around 20-30% are achieved.

The introduced into the silos 48 , 50 and 52 fly ash / from sorpt mixture can on the one hand via the lines 53 and 55 , or 59 and 61 , or 62 and 64 by means of not shown entry devices, such as injectors / ejectors in a pneumatic För derleitung / pressure line 58 are abandoned. Through this För derleitung 58 , it can be disposed of by means of the carrier air sucked in by a conveying fan 57 via a suction line 56 from the actual multi-stage flue gas cleaning process or can be fed to a further processing process. On the other hand, it is also possible in an analogous manner to enter the fly ash / absorpt mixture from the silos 58 , 50 and 52 via the lines 53 , 59 and 62 into a pneumatic delivery line / pressure line 67 . Through this conveying line 67 , part of this mixture can be recirculated by means of the carrier air sucked in by a conveying fan 66 via a suction line 65 for better utilization of its sorption capacity and entered at the entry point 68 in the sus pensator 33 . This entry point 68 is carried out in a manner not shown here according to known process techniques so that there is no entry of significant portions of the conveyed air volume flow into the suspension 33 .

The degree of sorption of the additive that has already been achieved, as well as the technical and economic objective of achieving the pollutant emission limit values to be observed with the lowest possible use of additive, determine the size of the fly ash / absorber mass flow components to be recirculated from the silos. For the realization of these recirculation parts 53 , 59 and 62 branch pieces 54 , 60 and 63 are installed in the shut-off lines. Each of these branches to one of the outgoing lines in the delivery lines 58 or 67 , also lockable lines make it possible to realize the most appropriate recirculation portion by closing or opening the corresponding shut-off valve.

In addition to the recirculation of the absorber / fly ash mixture shown in the drawing from the silos 48 , 50 and 52 to the Sus pensator 33 , it is also possible to return this mixture to the dry additive mass flow, which is entered dry into the boiler 10 .

In addition, all solid-state silos 21 , 2 , 48 , 50 and 52 and the suspensor 33 are equipped with level measuring devices of known design which trigger an alarm signal when the permissible upper level is exceeded. In the silos for the fuel 2 and for the additive 23 , such a message is also given for the suspending device 33, even when the minimum required level is undershot.

All lines through which additive and / or absorpt are promoted for the safe conveyance of these solids sufficiently heated or insulated.  

Overall, the multi-stage process according to the invention succeeds Emission reduction method in the above-described embodiment Example of using commercially available lime hydrate already at a total (Ca / S) molar ratio of 2.0-2.5 one Emission reduction rate for sulfur oxides of around 90% to reach. For all other air pollutants, the ge legally required emission limit values.

Claims (12)

1. Multi-stage process for wastewater-free reduction of air pollutants released in the combustion of fossil sulfur-containing fuels, a staged air and / or fuel supply into the combustion chamber of a boiler or a combustion system and an addition of alkaline earth-rich additives to the flue gases, characterized in that the Add the alkaline earth-rich additive ( 22 ) in an upper temperature window of approx. 800-1000 ° C in an additive-fuel-mass flow ratio that is only as low as it is for the integration of already formed sulfur trioxide and for avoiding the formation of new sulfur trioxide is just necessary, so that the flue gases ( 21 ) in a second, in a lower temperature window of about 80-120 ° C working additive addition point ( 37 ) with such a high sulfur dioxide content that besides the other air pollutants also nitrogen oxide highly effectively quasi dry in in the Flue gases ( 21 ) registered earth alkaline additive ( 22 ) is incorporated. 2. The method according to claim 1, characterized in that in one of the second additive downstream process step for further incorporation of the gaseous air pollutants in the lower temperature window, primarily serving the dust separation fabric filter ( 40 ) is used. 3. The method according to any one of the preceding claims, characterized in that lime hydrate is used as an alkaline earth additive ( 22 ). 4. The method according to any one of the preceding claims, characterized in that the alkaline earth metal additive ( 22 ) at the second addition point by means of a conventional spray absorber ( 37 ) is sprayed as an aqueous suspension into the flue gases ( 21 ) and is mixed with these as completely as possible . 5. The method according to any one of claims 1-3, characterized in that the alkaline earth metal additive ( 22 ) is introduced dry in the second addition point and then sufficiently humidified by water or steam-conditioned flue gases ( 21 ) to achieve a high reactivity. 6. The method according to claim 5, characterized in that the quasi-dry incorporation of the air pollutants into the alkaline earth-rich additive ( 22 ) in a preferably circulating operated solid / gas fluidized bed reactor is realized, the flue gases ( 21 ) as the fluidizing agent and Additive fly ash particles are used as a solid. 7. The method according to any one of the preceding claims, characterized in that the lower temperature window is set by injecting a corresponding water or steam mass flow ( 37 a) at the entrance of the spray absorber ( 37 ) or the fluidized bed reactor, raw water as injection water / Process water can be used. 8. The method according to any one of the preceding claims, characterized net by adding on the inclusion of the gaseous air pollutants in the alkaline earth additive highly catalytic acting additives, such as sodium chloride, sodium hydroxide, Sodium sulfite and calcium fluoride. 9. The method according to claim 8, characterized in that the addition of the additives in a mass fraction of 1-10% of the main additive ( 22 ). 10. The method according to any one of the preceding claims, characterized in that for better utilization of the additive ( 22 ) in the boiler ( 10 ) and / or spray absorber ( 37 ) or in the vortex layer reactor and / or in the fabric filter ( 40 ) accumulated absorpt - / fly ash mixture is completely or partially recirculated. 11. The method according to any one of the preceding claims, characterized in that to further reduce the gaseous air pollutant emissions, in particular the nitrogen oxide emissions, a partial recirculation of cooled flue gases ( 21 ) from the rear part of the boiler ( 10 ) in the Brennkam mer is made. 12. The method according to claim 11, characterized in that a part of the recirculated flue gases ( 21 ) is used to adjust the upper temperature window and a further proportion of these flue gases ( 21 ) is used as the conveying medium for the dry additive ( 22 ).