DE19636243A1 - Improving operation of wet desulphurisation process - Google Patents

Abstract

Improving the operation of a wet desulphurisation process of a fossil-fired power station, especially a brown coal power station comprises producing a suspension as residue of the REA (waste gas desulphurisation plant), the suspension being separated by mechanical separation into a clear phase and a solids-enriched slurry. The clear phase is either recycled to the REA or disposed of, and the solids-enriched slurry is disposed of as waste product. The novelty is that the REA suspension (1) is fed to a cyclone (2), the lower course (3) of a dewatering device (4) and the upper course (5) of a precipitator (6). The precipitation product (9) is fed to a hydrocyclone (10) and the solids (11) produced in the lower course (3) consisting of small amounts of gypsum with Mg(OH)2, are fed as partial stream (12) directly to the REA (8) and/or as crystal/precipitation core (7) of the precipitation step (6). The upper course (13) consisting of Mg(OH)2 contaminated with finely divided gypsum and inert materials is added to a thickener (15) together with a flocculating/precipitating aid (14), where the clear phase is fed to the REA (8) and/or after ash binding of the waste and the slurry produced in the thickener is utilised and/or disposed of.

Description

The invention relates to a method for improving the Operation of one with quicklime or limestone Wet desulfurization of a fossil-fired power plant, esp special of a brown coal power plant.

To remove sulfur oxides from the flue gas u. a. alkaline absorbents, such as. B. limestone flour and Hydrated lime.

Magnesium also comes with the limestone powder or hydrated lime carbonate or magnesium oxide / magnesium hydroxide in the washer and reacts too easily with the sulfur dioxide in the flue gases soluble magnesium sulfate. Especially with high sulfur dioxide levels in the flue gas and high magnesium carbonate or Magnesium levels in limestone or quicklime may occur a strong accumulation of magnesium sulfate in the washer cycle.

An arrangement for regulating the MgSO₄ content is known in flue gas desulfurization plants, with a partial flow of Laundry suspension is fed to a hydrocyclone by separation of the suspension into a coarse-grained solid portion of the material (plaster) and one loaded with a fine grain portion Water takes place (DD-PS 2 71 848). The coarse-grained solid part is returned to a reaction tank in which the suspension is located. The one loaded with fine grain fractions Water and the used suspension from the reaction tank are directed into a downstream waste product plant and subjected to further treatment. The liquid phase out The waste production plant stands for the technological process available to the REA.  

To control crystal growth, filterability and the drainability of flue gas gypsum from wet flue gas it is sulfurization plants when using a hydrocyclone known, the suspension of the hydrocyclone overflow continuously or at least part of the fine-grained at intervals To withdraw solids and only the remaining aqueous Sus pension in the system (DE-OS 38 03 631).

All known methods have the following disadvantages:

• - The from the existing separating devices (e.g. indent components to be discharged are too small Solid enrichment on.
• - Too much REA water is discharged and therefore the Washing process withdrawn.
• - This means that an increased amount of ash must be used to incorporate the Solid suspension can be used to meet the required To meet environmental requirements.
• - The ash that can be used as a building material is no longer pending sufficient scope or not available at all.

The invention has for its object the disadvantages of Avoid prior art by using a targeted Influencing the REA wastewater suspension the solids balance improved and recycling options for the previous Landfill goods can be reached.  

This is achieved in that the REA-Sus a cyclone, the sub course of a drainage and the upper course partially one in ternal precipitation stage if necessary with the addition of precipitation seeds and / or the REA is supplied, the precipitate fed to a hydrocyclone and those in the lower reaches Solids consisting of slightly with magnesium hydroxide provided plaster, as a partial stream directly to the REA tet and / or fed to the precipitation stage as a crystal nucleus and the upper course, consisting of finely divided gypsum and inert contaminated magnesium hydroxide, with the addition of a Flocculant / precipitant added to a thickener is, the clear phase of the REA and / or after a Ashes are added to the landfill and to the thickener resulting sludge is recycled and / or after ashes of the landfill is abandoned.

It is advantageous that the one withdrawn from the thickener Sludge if necessary after mechanical dewatering for recirculation stallization with an acid, e.g. B. hydrochloric acid contacted and then after separating the plaster and others products not dissolved by the acid with calcium hydroxide is treated in stages, if necessary, whereby the accruing cleaned magnesium hydroxide after dewatering e.g. B. subjected to a thermal treatment and to highly refractory Products can be processed.

The dewatered sludge can after the thermal treatment as well as the magnesium oxide-rich product with the addition of high Concentrated magnesium chloride solution in construction as a building fabric, especially screed, can be used.  

As flocculation / precipitation aids are used for improvement the sedimentation behavior in the thickener z. B. high polymer Acrylamides used.

The following advantages are achieved by the invention:

• - The solid balance is relieved, since the ent during precipitation standing gypsum removed for the most part by the hydrocyclone separates and returned to the washer via the lower reaches becomes.
• - The finely divided hydrocyclone is separated well in a downstream thickener in
• - Clear phase
• - finely divided sludge (magnesium hydroxide and inert Components)
• - This means there are a multitude of recycling options for given the residues.
• - The clear phase can to a greater extent in the Kreislaufpro zeß be returned.
• - There is no need to design a new disposal route.
• - There is far less landfill material.
• - The gypsum formed during the precipitation is not with the Ash disposed of, but is available for recycling Available.  
• - A large part of the ashes are no longer used for integration the REA residues are needed and can be used as building materials will.

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 mechanically separated (dewatering) 4 . The overflow 5 of the hydrocyclone 2 is fed to the internal sulfate precipitation 6 with the addition of precipitation germs 7 and then another hydrocyclone 9 is added . The solid matter of the underflow 11 of this hydrocyclone 10 , consisting mainly of gypsum provided with magnesium hydroxide, is returned to the REA 8 . 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 recycled into the REA 8 and / or used for incorporation in ash. The sludge 16 to be deducted from the thickener 15 is either also used for binding in ashes and / or is used as a construction material, for. B. screed, and / or after a thermal treatment's, z. B. used as refractory products.

Fig. 2 shows a way to feed the sludge 16 drawn from the thickener 15 to a container 19 , where with the addition of an acid 18 , for. As hydrochloric acid, the magnesium hydroxide converts to magnesium chloride and the acid-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 carbonate 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, z. B. as a high-quality screed and / or after a thermal treatment as a refractory material with particularly good properties.

Reference list

1 REA wastewater suspension
2 hydrocyclone
3 underflow
4 drainage
5 upper reaches
6 sulfate precipitation
7 precipitation bacteria
8 flue gas desulfurization system
9 precipitation product
10 hydrocyclone
11 solid
12 partial flow
13 upper reaches
14 flocculants / precipitants
15 thickeners
16 mud
17th
18 acid
19 containers
20 plaster
21 magnesium chloride
22 containers
23 calcium hydroxide
24 magnesium hydroxide
25 calcium chloride

Claims (4)

1. A method for improving the operation of a wet desulfurization operated with quicklime or limestone of a fossil-fired power plant, in particular a lignite-fired power plant, whereby as a residue of the REA, among other things, a sus pension arises, which is divided into a clear phase and a solids-enriched sludge by mechanical separation processes the clear phase is either returned to the REA or disposed of and the solids-enriched sludge is disposed of as an off-product, characterized in that the REA suspension ( 1 ) is a cyclone ( 2 ), the underflow ( 3 ) of a drainage ( 4 ) in a manner known per se. and the overflow ( 5 ) is partly fed to an internal precipitation stage ( 6 ), possibly with the addition of precipitation nuclei ( 7 ) and / or the REA ( 8 ), the precipitation product ( 9 ) being fed to a hydrocyclone ( 10 ) and that in the underflow ( 3 ) accumulating solids ( 11 ) consisting of gypsum slightly provided with magnesium hydroxide , Directly to the REA (8) is derived as a partial flow (12) supplied and / or as crystal / precipitate nucleation (7) of the precipitation stage (6) is fed and the top run (13), consisting hydroxide from contaminated with finely divided gypsum and inert substances magnesium, a thickener ( 15 ) is added with the addition of a flocculation / precipitation aid ( 14 ), the clear phase of which is fed to the REA ( 8 ) and / or after incorporation of ash into the landfill, and the sludge ( 16 ) formed in the thickener is recycled and / or is abandoned after the landfill is ash-bound. 2. The method according to claim 1, characterized in that the sludge ( 16 ) drawn off from the thickener ( 15 ) optionally after egg ner mechanical dewatering for recrystallization with an acid ( 18 ), for. B. hydrochloric acid, contacted in a container ( 19 ) and then the resulting magnesium chloride ( 21 ) after separation of the gypsum ( 20 ) and other products not dissolved by the acid is treated with calcium hydroxide ( 23 ) in the container ( 22 ), if necessary in stages, the purified magnesium hydroxide ( 24 ) which is then produced is dehydrated and subjected to a thermal treatment and processed into refractory solid 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. highly polymeric acrylic lamides can be used to improve the sedimentation behavior in a thicker ( 15 ).