DE19636243C2 - Process for improving the operation of wet desulphurization of fossil-fired power plants using quicklime or limestone - Google Patents

Description

The invention relates to a method for improving the operation of a Burnt lime or limestone-operated wet desulfurization of a fossil fuel power plant, especially a lignite-fired power plant.

To remove sulfur oxides from the flue gas u. a. alkali cal absorbents, such as. B. limestone flour and hydrated lime, for use com men.

With the limestone powder or hydrated lime, magnesium carbonate or Magnesium oxide / magnesium hydroxide in the washer and reacts with that Sulfur dioxide from the flue gases to easily soluble magnesium sulfate. Beson especially with high sulfur dioxide levels in the flue gas and high magnesi umcarbonate or magnesium content in limestone or quicklime comes there is a strong accumulation of magnesium sulfate in the scrubbing circuit.

An arrangement for regulating the MgSO ₄ content in flue gas desulfurization systems is known, a partial stream of the scrubber suspension being supplied to a hydrocyclone by separating the suspension into a coarse-grained solids content (gypsum) and into a water containing fine particles (DD -PS 271 848). The coarse-grained solids content is returned to a reaction tank in which the suspension is located. The water loaded with fine-grained fractions and the used suspension from the reaction basin are fed into a downstream waste-treatment plant and subjected to a further treatment. The liquid phase from the waste product plant is available for the technological process of the REA.

To control crystal growth, filterability and drainage The level of flue gas gypsum from wet flue gas desulfurization plants is high Known use of a hydrocyclone, the suspension of the hydrocyclone overflow continuously or at intervals at least part of the fine-grained To withdraw solids and only the remaining aqueous suspension in the System attributed (DE-OS 38 03 631).

All known methods have the following disadvantages:

• - Discharge from the existing separation devices (e.g. thickeners) Send constituents show insufficient solids accumulation.  
• - Too much REA water is discharged and thus ent is removed from the washing process pulled.
• - This means that an increased amount of ash must be used to incorporate the solids pension can be used to meet the required environmental requirements.
• - The ash that can be used as a building material is no longer in sufficient supply catch or not available at all.

The invention has for its object the disadvantages of the prior art avoidance by specifically influencing the REA wastewater Suspension improves the solids balance and recycling options for the previous landfill can be reached.

This is achieved in that the upper course of the first Hydrocyclones partially internal before introduction into the second hydrocyclone Precipitation stage with the addition of precipitation germs and partly the REA leads, with a partial flow in the lower reaches of the second hydrocyclone falling solids, consisting of slightly with magnesium hydroxide verses hen gypsum, as a crystal / precipitation seed of the internal precipitation stage becomes.

It is advantageous for the sludge drawn off from the thickener to Recrystallization contacted with an acid and then after separation gypsum and other calcium-insoluble products is treated with hydroxide, which then accumulates purified magnesium hydroxide after dewatering e.g. B. a thermal treatment leads and can be processed into highly refractory products.

The dewatered sludge can after the thermal treatment as well Magnesium oxide-rich product with the addition of highly concentrated magnesi Chloride solution used in construction as a building material, especially screed become.

As flocculation / precipitation aids are used to improve the sedimentation on behavior in the thickener z. B. high polymer acrylamides.  

The following advantages are achieved by the invention:

• - The solid balance is relieved, because the gypsum produced during the precipitation to separated for the most part by the hydrocyclone and over the underflow to Scrubber is returned.
• - There is a good separation of the finely divided hydrocyclone overflow in one downstream thickener in the clear phase of finely divided sludge (magnesium hydroxide and inert components).
• - This means that there is a multitude of recycling options for the residues ben.
• - The clear phase can return to the circulatory process to a greater extent leads.
• - There is no need to design a new disposal route.
• - There is far less landfill.
• - The gypsum formed during the precipitation is not disposed of with the ashes, son is available for recycling.
• - A large part of the ash is no longer used to integrate the residual REA needed and can be used as a building material.

The invention is explained in more detail using an exemplary embodiment. Here, FIG. 1 shows the process scheme.

After being discharged from the REA 8 , the REA wastewater suspension 1 reaches the hydrocyclone 2 , from the lower reaches 3 of which the gypsum obtained is fed to a mechanical separation (drainage) 4 . The overflow 5 of the hydrocyclone 2 is partly fed to the REA 8 and partly to the internal sulfate precipitation 6 with the addition of precipitation nuclei 7 and then added to another hydrocyclone 9 . The solid matter of the underflow 11 of this hydrocyclone 10 , consisting primarily of gypsum provided with magnesium hydroxide, is recycled into the REA 8 and partially supplied as the crystal / precipitation seed 7 to the internal precipitation stage 6 . The overflow 13 of the hydrocyclone 10 is added to the thickener 15 with the addition of a flocculant / precipitation aid 14 , the clear phase of which is either returned to the REA 8 and / or used for incorporation in ash. The sludge 16 to be removed from the thickener 15 is either also used for binding binding in ash and / or is used as a building material, for. B. screed, and / or after a thermal treatment, for. B. as refractory products used.

Fig. 2 shows a way to feed the sludge 16 withdrawn from the thickener 15 to a container 19 where, with the addition of an acid 18 , for. As salt acid, the magnesium hydroxide converts to magnesium chloride and the acid re-insoluble constituents, such as inert and gypsum 10 , remain and are separated from the liquid phase.

The magnesium chloride 21 is then fed to a container 22 , where calcium hydroxide 23 is added gradually, if necessary (holding heavy metals), so that ultimately pure magnesium hydroxide 24 and calcium chloride 25 are formed. The magnesium chloride 21 is particularly suitable for use in construction, for. B. as a high-quality screed and / or after a thermal treatment as refractory material with particularly good properties.

List of the reference numerals used

1

FGD waste water suspension

2

hydrocyclone

3

underflow

4

drainage

5

headwaters

6

sulfate precipitation

7

precipitation germ

8th

flue gas desulphurisation

9

precipitate

10

hydrocyclone

11

solid fuel

12

partial flow

13

headwaters

14

Flocculation / precipitation aid

15

thickener

16

mud

17

-

18

acid

19

container

20

plaster

21

magnesium chloride

22

container

23

calcium hydroxide

24

magnesium hydroxide

25

calcium chloride

Claims (4)

1. A method for improving the operation of a wet desulphurization of a fossil-fired power plant operated with quicklime or limestone, in particular a lignite-fired power plant, the residual material of the REA being a suspension which is thickened by a first hydrocyclone, the hydrocyclone underflow of a drainage Untreated in flue gas gypsum and the hydrocyclone overflow is fed to a second hydrocyclone, the lower underflow of which is introduced into the REA and the upper overflow into a thickener ( 15 ) with the addition of a flocculation / precipitation aid in thick sludge to be discharged, which can be recycled, and into one is separated into the REA clear phase to be characterized , characterized in that the upper course ( 5 ) of the first hydrocyclone ( 2 ) before introduction into the second hydrocyclone ( 10 ) partly an internal precipitation stage ( 6 ) with the addition of precipitation seeds ( 7 ) and partly the REA ( 8 ) added rt is, with a portion of the flow in the underflow ( 11 ) of the second hydrocyclone ( 10 ) resulting solids, consisting of gypsum slightly provided with magnesium hydroxide, is supplied as the crystal / precipitation seed 7 of the internal precipitation stage 6 . 2. The method according to claim 1, characterized in that from the A thicker ( 15 ) withdrawn sludge ( 16 ) for recrystallization with an acid ( 18 ) in a container ( 19 ) and then the resulting magnesium chloride ( 21 ) after separation the gypsum ( 20 ) and other products not dissolved by the acid is treated with calcium hydroxide ( 23 ) in the container ( 22 ), the resulting magnesium hydroxide ( 24 ) then being subjected to a thermal treatment after dewatering and processed into high-refractory products. 3. The method according to claim 1, characterized in that the sludge ( 16 ) is treated thermally after dewatering and the magnesium oxide-rich product with the addition of highly concentrated magnesium chloride solution in construction as a building material, in particular screed, is used. 4. The method according to claim 1, characterized in that as a flocculation / precipitation aid ( 14 ) z. B. high polymer acrylamides can be used to improve the sedimentation behavior in the thickener ( 15 ).