WO1985003455A1

WO1985003455A1 - Method for stripping noxious gas substances contained in flue gas

Info

Publication number: WO1985003455A1
Application number: PCT/EP1985/000029
Authority: WO
Inventors: Urban Cleve
Original assignee: Hugo Petersen, Gesellschaft Für Verfahrenstechnisc
Priority date: 1984-02-06
Filing date: 1985-02-06
Publication date: 1985-08-15
Also published as: EP0170689A1; ZA85887B; DE3403995A1

Abstract

Method for stripping by dry process noxious susbstances contained in flue gas or other exhaust gas, particularly SO2 and NOx, and simultaneously all noxious gases, such as fluorine and chlorine compounds, as well as heavy metals. For stripping the noxious substances, there are added to the firing flue gas, and preferably to flue gas in the medium temperature range (300-500oC) and/or in the lower temperature range (150-300oC), fly ashes, after their stripping in a filter either alone or mixed with known additives for the stripping of noxious substances, the noxious substances being first bound on the basis of the fluorine and/or chlorine compounds as well as part of the sulphur-containing noxious substances. Finally, the flue gas are treated, after stripping of the fly ashes and/or the mixture of fly ashes and additives, with a reducing gas, preferably ammonia, and the mixture of flue gas and ammonia is passed through a layer of active charcoal or coke while removing nitrogen oxides, residual SO2 and finally heavy metal and residual fly dust.

Description

- / -

A method for depositing in Rauchg ^* aS 'gaseous pollutants contained ^•

The invention relates to a dry process for the multi-stage separation of pollutants contained in flue gases or in other exhaust gases, in particular S0 ₂ and NO, wherein at the same time all other harmful gases such as fluorine and / or chlorine compounds and heavy metals are also separated.

The subject of German patent application P 33 08 927.2-43 is a process for binding gaseous pollutants, such as sulfur oxides, fluorine, which are contained in flue gases from the combustion of fossil fuels containing minerals, in particular lignite and hard coal as well as oil and gas firing. and chlorine compounds, which is characterized in that the fly ash with the mineral substances contained therein, such as calcium oxide and / or magnesium oxide, after separation in a filter in a dry and / or Suspended form, optionally with the addition of additives such as lime, magnesium oxide and / or limestone, the flue gases coming from the furnace, preferably flue gases in the medium (300 - 500 ° C) or lower 5 (80 - 300 ° C) temperature range are mixed again .

In this process, the fly ash itself and the minerals it contains are used to bind harmful substances. With this method, the pollutants based on fluorine and / or chlorine compounds can go almost completely, sulfur dioxide largely, that is to say about 50-75%, but nitrogen oxides are practically not.

The invention aims to improve the method described above, namely that the sulfur dioxide 5 should be removed practically completely and also the nitrogen oxides as well as remaining heavy metals and flying dust from the smoke or exhaust gases.

The invention therefore relates to a process for the dry separation of gaseous pollutants contained in flue gases by admixing the fly ash with the minerals contained therein after separation in a filter in dry and / or suspended form, optionally with the addition of known additi ¬ ven to the flue gases coming from the furnace, preferably the flue gases of the medium (300 - 500 ° C) and / or the lower (150 - 300 ° C) temperature range, which is characterized in that the flue gas after separation of the Fly ash or the mixture of fly ash and additives treated with a reducing gas, preferably ammonia, and the mixture of flue gas and reducing gas through a layer of A-coal or A-coke with removal of the nitrogen oxides, the remaining SO and so the Heavy metals and the dust is directed.

According to the invention, the fly ash with the minerals it contains, such as calcium oxide and / or magnesium oxide, is then firstly separated in a filter in a dry and / or suspended form, if appropriate with addition, in a first cleaning stage or a first cleaning cycle of additives, such as lime, magnesium oxide and / or limestone, again mixed with the flue gases coming from the furnace, preferably flue gases in the medium (300 - 500 ° C) and / or low (150-30O ° C) temperature ranges.

Since the minerals contained in the fly ash generally develop their optimum reaction in the medium or low temperature range, the process is limited to these temperature ranges. When using fly ash returned to the flue gases to increase the degree of binding of the pollutants, additional additives can be used, either together with the fly ash as a mixture or separated from the fly ash at different locations in the above-mentioned temperature ranges for the flue gas be added.

When the method according to the invention is applied to steam generators with lignite or hard coal firing, oil or gas firing, the places of addition for the fly ash or the fly ash and the additive are in the area before the end of the boiler heating surface downstream of the firing, before entering the air warmer or in the area between the air warmer and the filter inlet.

To fully utilize the binding capacity of pollutants, fly ash or fly ash and additives can be added to the flue gas not just once but several times. For this it is of course necessary that on a or several specific points of the flue gas stream fly ash or fly ash and additive are separated and returned.

Alternatively, the method according to the invention can also be carried out in such a way that fly ash or fly ash and additives from the various separation systems are mixed in terms of quantity in accordance with their loading capacity, and are wholly or partially fed back or discharged to the various addition sites.

The loading capacity which has not yet been exhausted, particularly in the case of dry processes. According to a preferred embodiment, the fly ash or the fly ash and additive can be further improved according to the invention by using a bag filter of known construction as a second cleaning stage for separating fly ash or fly ash and additive. The deposition of the fly ash and / or the additives on the surface of the filter causes further contact between the harmful gases and additives which are still absorbent, so that the degree of separation of the pollutants increases further and the filter thus simultaneously with the fly ash additive-harmful gas and heavy metal separation serves. Instead of a bag filter, an electrical filter can also be used. Optimal integration of the pollutants contained in the flue gases by the fly ash or fly ash and additives can be supported by adding fly ash or fly ash and additives at different locations in the medium and / or low temperature range. This addition, which is graded in the direction of flow of the flue gases, increases the action of the agents which trigger the integration. This action can in turn ^' by the consistency of the fly ash or fly ash and Additives, namely in suspended and / or dry form can be further influenced.

According to the invention, the nitrogen oxides not yet separated out as well as the remaining SO are removed in a third cleaning stage after the separation of the fly ash or of fly ash and additives.

. In this further cleaning stage, the flue gas is passed over or through a layer of a catalyst, preferably activated carbon or activated coke,

10 headed. The flue gas is expediently forced through a filter loaded with activated carbon or activated coke. The nitrogen oxides react with a reducing gas under the influence of the catalyst to form nitrogen. Ammonia is primarily used as the reducing gas for practical purposes. When using ammonia, the following reactions occur simultaneously in the filter made of activated carbon / activated coke:

6 NO + 4 H ₃ -5 ** - 5 N ₂ + 6 H ₂ 0 2 S0 ₂ + 0 ₂ + 2 H ₂ 0 -s- 2 H ₂ S0 ₄

0 2 S0 ₂ + 4 NH ₃ + 0 ₂ + 2 H ₂ 0 → 2 (NH4) _. S0 ₄ -

The catalyst made from activated carbon / activated coke preferably operates in a temperature range from 100 to 150 ° C., that is to say in a range which corresponds to the exhaust gas temperatures customary today for large boiler systems.

In this activated carbon / activated coke filter, the residual separation, in particular of the heavy metals and the flying dust, also takes place at the same time, so that the flue gas is thus almost completely cleaned.

If ammonia is used as the reducing gas, this is preferably used as an aqueous solution in the flue gas stream injected.

The advantages of the method according to the invention are that the method steps described above complement each other in a particularly effective and economical manner.

For example, the disadvantage of the activated carbon / coke adsorber is that the activated carbon / coke layer, which is highly loaded with all pollutants, can be desorbed, ie cleaned, only with considerable effort, and the losses or the consumption of activated carbon / activated coke, the economy of the process as a single process considered, significantly reduces. As a result of the method according to the invention, wherein a large part of the pollutants are removed before they enter the activated carbon filter, the latter is subjected to far less stress. Thereby, the __ increase in tool life of ^{Aktivkohleabsσrbers'?} it can be carried out at the same time with considerably less effort.

The invention is explained below on the basis of the exemplary embodiments illustrated in the drawings:

FIG. 1 shows a diagram of a steam generator in which only fly ash is used for the binding of pollutants ^{in the} medium temperature range.

FIG. 2 shows the diagram of FIG. 1, in which fly ash and additives for the binding of harmful substances in the low temperature range are used.

Figure 3 shows the scheme of Figure 1, in the fly ash and additive in suspended form in Medium temperature range and fly ash and ^• additive can be used in dry form in the low temperature range.

FIG. 4 shows an embodiment in which additives and fly ash are added in the medium-temperature range, no pre-separation of fly ash and / or additives takes place, but rather flue gas and fly ash or, fly ash and additives flow through the air preheater. The separation takes place in the main separator designed as a fabric filter.

In FIG. 1, fly ash is added to the flue gases from any combustion system 1 of the steam generator 2 immediately behind or in front of the last heating surface. The furnace system can be a coal-fired furnace, a furnace with dry ash extraction, a traveling grate or a fluidized bed boiler, but it can also be a furnace or another furnace system. In the radiant heating surfaces 2a and the overheating heating surfaces 2b and the contact heating surfaces 2c, the flue gases are cooled to a temperature level of approximately 300 to approximately 500 ° C. The fly ash originates from a pre-separator 3 and a main separator 4. The fly ash is transported via lines 5, 6 and 7. In the flue gas path of the steam generator 2, a fly ash addition device 8 is installed behind or in front of the last heating surface, which performs a first uniform distribution of the fly ash in the flue gas. Downstream, a further mixing device 9, which can also be configured as a post-heating section, is provided, in which, in addition to the continued mixing, a substantial proportion of the pollutant incorporation takes place. The fly ash that is not required for the inclusion of pollutants is fed via the line lo withdrawn from the pre-separator 3. The flue gas then flows through the air preheater 12.

"In order to have a sufficient amount of fly ash available for the inclusion of pollutants in the areas 8.9, the amount of pollutant still contained in the flue gas is measured at 11 and the amount of the added fly ash, including the flue gases, is measured via this measured value controlled at 8. In the flow direction behind the measuring point 11 there is a suction fan 20, by means of which the flue gases are pressed through an activated carbon / activated coke filter 22. In front of this filter, ammonia is injected evenly into the flue gas stream at 24 Filter 22 enters the flue gas into chimney 26.

5 In FIG. 2, fly ash and additive are added, specifically behind the air preheater 12 via a device 8a. The intensive mixing between fly ash and fly ash and additive with simultaneous extensive incorporation of pollutants takes place in the mixing device 9a installed downstream. The preparation of Flug¬ ash and additive is done in a mixer 14. In this case, ^'the additive through line 13, and fly ash are conveyed through the line 7a. The control of the amount of fly ash and additive entered at 8a is carried out like 5 in the embodiment according to FIG. 1 by a pollutant measurement of the flue gas at 11a.

In the exemplary embodiment according to FIG. 3, fly ash and additive in suspended and in dry form are added to bind the pollutants in the flue gases. o In this case, fly ash and additive are added in suspended form at 8b with subsequent device 9b for intensive mixing -with the flue gases, and fly ash and additive are added in dry form at 8c with subsequent mixing device 9c. The suspen- dated fly ash and additive are produced in a mixer, fly ash being fed via line 7b, additive via line 13a and water via line 16. From the mixer 15, the suspension is fed via line 17 with pump 18 to the input point 8b. This. Addition location is characterized by a medium temperature range. The place of addition for the fly ash and additive in dry form is 8c and is characterized by a low temperature range. The type of addition takes place in the same way as in the exemplary embodiment in FIG. 2. Fly ash is discharged from the pre-separator 3b via line 10b. The amount of the agents added to the flue gases at the various addition sites 8b and 8c - fly ash and additi in suspended form or fly ash and additive in dry form - is, as in the processes described in FIGS controlled in the flue gases measured at 11b pollutant content.

FIG. 4 shows an embodiment in which the flue gases flow through the air preheater. 12, in which the mixture is thoroughly mixed again, through the flue gas duct to the filter system. -4 flow, which is either designed as an electrostatic filter, but preferably as a bag filter. The separated fly ash and / or additives are withdrawn from the filter 4 and to

Injection point 8 of the boiler returned. At 28 fresh additives are added, at lo a corresponding amount of fly ash and / or additives from the. Circuit ejected.

Claims

Patent claims

1. Process for the dry separation of gaseous pollutants contained in flue gases by mixing the fly ash with the minerals contained therein after separation in a filter in dry and / or suspended form, optionally with the addition of known additives to those from the Combustion coming flue gases, preferably flue gases of the medium (300-500 ° C) and / or the lower (150 - 300 ° C) temperature range, characterized in that the flue gas after separation of the fly ash or the mixture of fly ash and additives treated with a reducing gas, preferably ammonia, and the mixture of flue gas and reducing gas through a layer of charcoal or coke with removal. tion of the nitrogen oxides, the remaining SO, as well as the heavy metals and the airborne dust.

2. The method according to claim 1, characterized in that ^* the fly ash or the mixture of fly ash and additives is separated in a bag filter.

3. The method according to any one of claims 1-2, characterized ge indicates that in a steam generator, the fly ash or fly ash and additives are added in the region between the end of the heating surface and the inlet air preheater and / or in the region between the air preheater and the filter inlet.

4. The method according to any one of claims 1-3, characterized ge indicates that additives and / or fly ash are injected in cross-flow, counter-current or cocurrent into the flue gas. 5. The method according to any one of claims 1-4, characterized ge indicates that the fly ash or fly ash and additives are added to the flue gases at various points between the medium and low temperature range.

6. The method according to claim 5, characterized in that fly ash or fly ash and additives in suspended form in the medium temperature range and fly ash or fly ash and additives in dry form are added in the low temperature range.

I ^{■ •}

• j ^ 7. The method according to any one of claims 1-6, characterized in that the amount of fly ash or additives and fly ash added to the flue gases is selected as a function of the remaining harmful gases in the flue gas before entering the chimney.

15. The method according to any one of claims 1-7, characterized in that fly ash or fly ash and additives are added to the flue gas several times.

9. The method according to any one of claims 1-8, characterized ge indicates that in the middle and low temperature

20 area in p _. direction of flow behind the point of addition for fly ash or fly ash and additives, flue gases with fly ash or fly ash and additives are mixed thoroughly.

10. The method according to claim 9, characterized in that at the end ²⁵ of the mixing zone of flue gases with fly ash or fly ash and additive, a pre-separation is effected by Flug¬ bzw..Flugasche ash and additive.

11. The method according to any one of claims 1-10, characterized in that the fly ash or fly ash and additives from the various separating systems accordingly, their loading capacity mixed with pollutants in quantities and the whole or part of the different addition sites are supplied or discharged again.

12. The method according to any one of claims 1-11, characterized in that the flue gas is passed at temperatures of about 100 - 150 ° C over the activated carbon / activated coke catalyst.

13. The method according to any one of claims 1-12, characterized in that ammonia is injected as an aqueous solution into the flue gas.