DD267620A3 - WASHING PROCEDURE FOR CLEANING EXHAUST GASES - Google Patents

Abstract

The invention relates to a washing process for purifying exhaust gases from industrial plants, in particular from small and medium-sized coal-fired power plants. The object of the invention is to realize a method taking into account economic profitability through minimal additive use. According to the invention, this object is achieved in that a classification is switched into the laundry cycle and the Klassierergrobgut is subjected together with coarse bags and the additive of a wet grinding and the ground Good the Waescher is fed again, while the Klassierfeingut is introduced into a second separation stage, where a Duenntruebe, who returns to the laundry, and a thickened product is produced, which is Entwaessert and discharged.

Description

Title of the invention Washing process for cleaning exhaust gases Field of application of the invention

The invention relates to a process for the removal of pollutants, preferably of SO ₂ and fly ash, from flue gases or exhaust gases from industrial plants, in particular) of small and medium-sized coal-fired power plants.

Characteristic of the known state of the art

For the purification of exhaust gases, in particular of flue gases from power plants, Trooken-, semi-wet and wet processes and regenerative processes are known

 The wet process (washing process) in addition to the regenerative process has the advantage of good efficiency. They work with a low erosion excess of absorbent. "In these processes, the costs for the pollutant-absorbing additives are cost-determining.

In a variety of internationally developed wet process used for absorptive SOp removal from a flue gas stream calcium-containing products such as lime or limestone (additives), but auschen and Sohlaoken from the combustion process in aqueous suspension as Absorptionsmit tel. (DD-PS 213 357, DE-OS 3232 077, DE-PS 3001 258, DE-OS 3308 927, DD-PS 213 358, US-PS 4173 619, OB-PS 1496 936, JP-PS 58-150417) A series of washing processes for flue gas cleaning works with different recycling of the scrubber suspension.

In particular, the design of the crayfish is considered

1 (, 1 (, ZO 2

in multistage washing processes hydrocyclones for use. (US Pat. No. 4,267,155, DE-PS 3305 120) It is also known that in the case of wet processes in front of the scrubber, the additive or the scrubber can be subjected to the total amount of solids of comminution (milling). (DD-PS 2230 74> DD-PS 85 821, DE-OS 2224 224, SU-PS 1193 377, US-PS 4244 930) A disadvantage of the wet process is that with coarser grains of the additive or the coarse ash, the solution and reaction rates in the aqueous phase are low and the chemical conversion is not complete. By milling the additive in front of the scrubber, the free surface necessary for the reaction is initially produced, but it is blocked by moisture in the scrubber. These suede coatings can not be eliminated by the known solutions of hydrocyclone classification and subsequent recirculation of classifier fines, so that these processes do not create free surfaces of the adsorbents (ash-gypsum particles) and thus block the reaction surfaces. (US-PS 4,267,155, DE-PS 3305 120)

Sine crushing of the total amount of solids obtained after the scrubber in thin suspension is complex and ineffective, since by over-grinding on too fine grain sizes no

2+ more Ca released and at the same time the desired

Growth of gypsum crystals is prevented ·

A sufficient chemical conversion and increased 'utilization of the lime content of the absorbent can be achieved under these conditions only at higher residence times or with large equipment volumes.

Object of the invention

The object of the invention is to realize a method for purifying exhaust gases, in particular of flue gases, taking into account economic profitability by minimizing additive use and making maximum use of the lime content of the additive and the coarse ash.

Explanation of the essence of the invention

The invention has for its object to develop a process for the purification of exhaust gases, in which the solution and reaction rates of the additive or the coarse ash in the aqueous phase are large.

According to the invention, this object is achieved in that in the Wäschcrkreislauf as a first separation stage, a classification of Wäsoher Suepension, preferably with hydrocyclones, turned on and the Klassierergrobgut is subjected together with the coarse ash and the additive of a wet grinding, and the milled material is fed to the scrubber while the classifier fines are introduced into a second separation stage where a slurry is created which returns to the water and a thickened product is formed which is dewatered and discharged.

By classifying the scrubber suspension, the fine particles, in which the Ga constituents have already been largely dissolved out, are kept away from comminution. The comminution of the classifier material creates new reaction surfaces and eliminates blockages due to sulphite coatings. By classifying the scrubber suspension with subsequent comminution of the classifier coarse material, the rate of dissolution and reaction in the aqueous phase increases. This has the consequence that a faster chemical conversion or a more complete utilization of the lime content of the additive and the coarse ash is achieved. This eliminates the need for large suspension stack volumes for reaction, oxidation and neutralization. High residence times are no longer required within the process.

Erfindungswesentlioh is that used as an absorbent in the dedusting or in the wet ash and in the classifying coarse ash and / or additives, preferably finely broken, bunkerfähiger limestone, are used. For small boiler units or low dust contents in the raw gas, the dedusting can be omitted. Dia required clean gas levels are then reached in the scrubber. Furthermore, it is essential to the invention that in the task of coating the quantity ratio of granular additive and classifier material depends on the pH value of the scrubber sump.

elon is regulated "Thus, the stabilization of the pH value can only be achieved by adding broken additive in the mill.

This eliminates the very expensive ancillary equipment for the discharge, bunkering and dosing of powdered additives.

In contrast to known methods does not get the Klassierergrobgut, but the Klassieredingutut for disposal.

Furthermore, it is essential to the invention that the Klassierfeingut the first separation stage is subjected to flocculation, and that in the second separation stage a thickening apparatus, preferably a round thickener, is used. In the thickening apparatus, crystal growth or the named flocculation is sought. This results in better material properties of the thickened sludge for the subsequent sludge dewatering, for example on filter apparatuses

 The advantages of the invention are that the solution and reaction rates of the additive or the coarse ash in the aqueous phase due to the integrated classification and grinding are large "It comes to a maximum utilization of the lime content of the additive and the coarse ash and to low residence times by the permanent elimination of blocked reaction surfaces caused by sulfite coatings on the additive or ash cores. The high solution and reaction rates have the consequence that with relatively small scrubbers high SOg integration degrees can be achieved.

Another advantage of the method is that auszuschleusendes water is separated exclusively with the moisture of the dewatered solid from the process.

embodiment

The invention will be explained below with reference to an embodiment according to the attached process scheme.

The flue gas stream 9 is first fed to a pre-deduster 1 and then to a water blower 4 after it has been pre-cooled by injecting Wa ¹ eohersuspension 14 in a precooler 3. The required reheating of the clean gas 11 behind the scrubber 4 takes place by means of a crude gas stream 10 which is withdrawn before the economizer of the steam generator and which is passed through a hot gas cyclone 2. By turning on the Heißgaszyklons 2 and a Vorentstaubers 1, the coarse ash 12 of the crude gas streams 9, 10 largely recovered and fed together with the ash of the wet ash 13 through the mill 6 to the scrubber 4, and then performed as a scrubber suspension 14 in the circuit. The scrubber 4 also serves as a pen duster and as a pump sump of the naohgeschalteten hydrocyclones 5, which represent the first separation stage. Likewise, the oxidation is carried out in the pump sump of the scrubber 4. The scrubber suspension 14 is removed from the scrubber 4. abandoned and hydro hydrocyclones 5 and fed back a partial flow to the precooler 3.

The Klassierergrobgut 15 is milled together with the coarse ash 12 dee the dedusting 1 and the hot gas cyclone 2 and the ash of the wet ash 13 and the additive 17 in der.Mühle 6 and returned to the scrubber 4.

By pH control 24, the additive addition is performed so that in the scrubber 4, a pH of 4.8 to 5.5 is maintained.

The Klassierfeingut 16 is fed to a round thickener 7, which represents the second separation stage. In this case, an addition of flocculant 23 takes place.

The lap thickener overflow 18 is recirculated to the scrubber 4, including additional water 22, while the lap thickener underflow 19 reaches the vacuum filter 8. The resulting Piltrat 21 is abandoned together with the Rundeindioker overflow 18 and the Zusatzwaoser 22 the scrubber 4.

The filter cake 20 can be fed to a landfill. About the residual moisture of the filter cake 20 is the Ausschleusun & dissolved components and the stabilization of the salt load in WUscherkreislauf.

Claims (5)

zaczo? claim 1 · Washing process for the purification of exhaust gases, in particular for simultaneous dusting and flue gas desulfurization using calcareous Grobasohen and additives, characterized in that in the water cycle as the first separation stage a classification, preferably with hydrocyclones, the scrubber suspension eInge is maintained and the Klassierergrobgut is subjected to wet grinding together with the Grobasohe '& Α , and the ground material is fed to the scrubber while the classifier fines are fed to a second separation stage where a slurry is produced which returns to the scrubber to form a thickened product which dehydrates and is discharged. 2 * A process according to claim 1, characterized in that coarse ash and / or additives, preferably finely broken, bunker-limestone deposited as absorbent in the preliminary deduster or wet scrubber and in the hot gas cyclone are used. 3 * Process according to claims 1 and 2, characterized in that in the Mlihlenaufgabe the quantitative ratio of additive and Klassierergrobgut depending on the pH of the scrubber suspension is regulated · 4. The method according to claim 1, characterized in that the Classifier fines of the first separation stage of a flocculation is subjected.
30 Method according to claim 1, characterized in that in the second separation stage a thickening apparatus, preferably a lap thickener, is used. For this i page drawing