• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The subject of this invention is a method for the removal of mercury from scrubber suspensions (1) incurred in a wet flue gas scrubbing. The gypsum-containing suspension (1) is thickened by means of at least one hydrocyclone (11), the upper run (2, 4) of the hydrocyclone (11) being fed to at least one sewage cyclone (12) for solids recovery and the upper run (5) of the sewage cyclone (12 ) is subsequently treated in a wastewater treatment plant (13). According to the invention, the mercury concentration in the upper reaches (5) of the wastewater cyclone (12) is increased and only the concentrated wastewater stream 7 is fed to the wastewater treatment plant 13.
    公开号:AT516734A4
    申请号:T50298/2015
    申请日:2015-04-15
    公开日:2016-08-15
    发明作者:Michael Dipl Ing Kramer；Harald Dipl Ing Dr Reissner
    申请人:Andritz Ag Maschf；
    IPC主号:
    专利说明:

    Method for removing mercury from scrubber suspensions
    The subject of this invention is a method for the removal of mercury in the flue gas desulfurization. The resulting gypsum slurry in the scrubber, which also contains the mercury, thickened by means of at least one gypsum cyclone (hydrocyclone) and discharged the thickened gypsum suspension through the lower reaches of the hydrocyclone. The upper run of the hydrocyclone is fed to at least one sewage cyclone for solids recovery and the upper run of the sewage cyclone is then treated or purified in a wastewater treatment plant.
    Wet flue gas desulphurisation is a process for removing sulfur compounds from the exhaust gases of e.g. Power plants, waste incineration plants or large engines. The sulfur compounds are formed by the burning of sulfur-containing mostly fossil fuels. The flue gas desulphurisation plants are abbreviated to REA (flue gas desulphurisation plant). A flue gas desulphurisation plant can also be used for the production of gypsum (REA gypsum). This type of gypsum extraction has long been state of the art.
    The scrubbing suspension (gypsum suspension) used in the desulfurization is generally thickened by means of hydrocyclones and then brought to the final dry content via belt filter or centrifuge. Usually, requirements regarding the degree of purity are made of the gypsum grade. In addition to the desulphurisation in the wet scrubber, there is a separation of mercury-halogen compounds contained in the flue gas
    In the deposition of mercury
    Combustion gases, in particular in the generation of electricity from coal, are confronted with the problem of the re-emission of the already separated mercury from the wet scrubber.
    Oxidized mercury species (of the form HgXj X = C1, Br, I) behave in a water-soluble manner, and are accordingly readily separable from the flue gas with the other acidic exhaust gas constituents. Depending on the scrubber chemistry, the mercury incorporated in the wash water is dissolved (but generally not dissociated), or complexing by means of halogen salts or adsorptive bonding to, in particular, C-containing fines is also possible. Dissolved (oxidized) mercury can re-emit through the given intrinsic vapor pressure, alternatively, a reductive destruction of the compound is possible with simultaneous release of elemental (water-insoluble)
    Mercury, which reemitiert in the episode in its entirety.
    This problem can be addressed by converting the dissolved Hg species into an adsorbed form. Options for this include, for example, adsorbents based on activated carbon, or the precipitation of the relevant contaminants in the scrubber cycle (with, for example, sulfidic precipitants).
    The adsorptively bound mercury is preferably found on a fine particulate fraction, coarse-grained solids remain almost free of mercury.
    Today in the field of wet REA usual
    Gypsum drainage systems (see Fig. 1) consist mostly of a gypsum cyclone 10, a subsequent band filter (not shown in Figure 1) and a wastewater cyclone 12 for solids recovery before
    Wastewater treatment plant (ARA) 13. The hydrocyclones used in this process are characterized by the fact that they accumulate particles at high sinking rates in the underflow.
    All particles with a density above that of the fluid in the underflow are enriched, regardless of their size (except colloidal systems). Large particles are deposited almost entirely, very small accumulate only slightly.
    The result is an increased mercury entry into the cyclone underflow and thus into the product REA gypsum because the (also enriched) fine fraction fraction is the mercury. Depending on the operating condition and wastewater volume / cyclone type, up to 90% of the mercury load can land in the gypsum. The volume-related mercury contents in the upper reaches are slightly reduced via the cyclone stage. This means that after a 2-stage cyclone circuit, the discharged concentration is below that in the scrubber.
    An improvement brings the use of the
    Wash water cycle technology as described in AT 512 479 Bl. There by means of additional water metering a depletion of fines in the lower reaches instead.
    Such systems reduce the mercury load in the cyclone underflow by ~ 20 - 30%. However, the gypsum remains the main sink in the process. The cyclone overflow has slightly higher levels of mercury than when using a conventional cyclone.
    This problem becomes more topical due to the fact that a massive tightening of limits is to be expected against the background of the mercury emission limit value discussion. Including the plant circuits dominating in Europe (Boiler-SCR-ESP-WFGD), it can be assumed that the most economical separation will take place in the scrubber.
    A conceivable variant would be a 2-stage plaster drainage (gypsum wash) with intermediate dilution by process water.
    In this way, a high-purity and almost Hg free gypsum would be conceivable, but then the Hg inventory in the scrubber would rise until the registered cargo (by means of flue gas) corresponds to the discharged through the wastewater stream. This condition requires very high Hg concentrations in the scrubber, which in turn tend to increased re-emissions into the clean gas.
    The problem is that the amount of wastewater in coal-fired power plants is usually relatively small. Based on the stream supplied to the gypsum pre-dewatering, the waste water quantity is in the range <10%, often in the range between 5 - 7%. To ensure a high mercury load in the wastewater treatment plant, the concentration must therefore be high, which in turn leads to increased remissions in the scrubber.
    So if you want to reduce the Hg transfer in the gypsum, the amount of waste water must be raised. However, this means an increased investment in the wastewater treatment plant.
    Alternatively, by means of a modified plaster pre-dewatering (by means of a washing cyclone), the Hg transfer into the REA gypsum can be reduced. Without further measures, however, this means a significant Hg increase in the scrubber with an increased tendency to re-emission.
    The invention is therefore based on the object to provide a method with which mercury can be reliably separated from flue gases, but the mercury enrichment in REA gypsum and the size of the wastewater treatment plant should be limited.
    This object is achieved by a method in which the volume-based mercury concentration is increased and in which this concentrated wastewater stream is fed to the wastewater treatment plant.
    Thus, according to the invention, there is a mercury concentration level upstream of the entry into the wastewater treatment plant (ARA). As a result, on the one hand a high Hg freight of wastewater treatment is supplied, with a low volume flow. In addition, the Hg level is lowered in the scrubber.
    The essential feature of this process is a significantly lower Hg concentration in the scrubber compared to the waste water stream.
    The resulting in the concentration filtrate (accept) can be found elsewhere in the scrubber system use. The "thick matter" is fed to the ARA.
    The technology is particularly effective in combination with a washing stage for the REA gypsum. This can be done for example via a washing water cyclone or a two-stage cyclone with intermediate dilution.
    A depletion of the fines fraction in the underflow can be done by a simple intermediate dilution within a cyclone or by the displacement of the liquid phase in the lower run by targeted dosing a wash water stream. In WO 2010/089309 Al is spoken in this regard of a countercurrent classification. However, the intermediate dilution must be carried out with a fluid flow that does not include the problem fraction.
    Another useful washing water cyclone is also described in AT 512 479 Bl or in AT 511 837 Bl. In this case, the hydrocyclone is fed in addition to the gypsum suspension via its own supply water, so that it comes to a Feinstoffabreicherung, based on the suspension volume in the lower reaches.
    In this way, a discharge into the ARA of up to 90% of the total registered in the scrubber mercury is conceivable, at the same time the purity of the REA gypsum in areas of natural gypsum advance (~ 0.1 mg / kg TS, highly dependent on the operating condition) ,
    As a concentration stage, all procedural operations are conceivable that allow a solid enrichment (centrifuges, sediments, flotation, etc.).
    In summary, the invention involves a controlled influence on the liquid balance of gypsum drainage systems by discharging a thickened wastewater stream with fines containing mercury-laden activated carbon or precipitated mercury compounds to the lowest possible level
    To achieve plant sizes in the field of wastewater treatment.
    The method according to the invention will be described below with reference to a drawing. Show it:
    Fig. 1 is a schematic process diagram of the prior art;
    FIG. 2 shows a schematic process diagram for an exemplary embodiment of the method according to the invention; FIG.
    The same reference numerals in the two drawings indicate the same components or streams.
    1 shows a conventional process scheme in which a gypsum suspension 1, which also contains mercury, is obtained in the scrubber 10 of a flue gas desulphurisation plant.
    The gypsum suspension 1 is fed to a gypsum cyclone (hydrocyclone) 11 and the thickened gypsum suspension is discharged via the underflow 3. The upper reaches 2, usually often only a part 4 of the upper reaches 2, is fed to a sewage cyclone 12. In sewage cyclone 12, solids such as gypsum or residual carbonate are recovered via the underflow 6 and fed back to the scrubber 10. The upper reaches 5 of the sewage cyclone 12 is fed to a wastewater treatment plant 13, in which the mercury contained is separated from the remaining wastewater.
    FIG. 2 now shows a simple exemplary embodiment of the method according to the invention. Here, the upper reaches 5 of the wastewater cyclone 12 is fed to a concentrator 14. in the
    Concentrator 14, the upper reaches 5 "thickened." In this case, the fines to which the mercury is bound, enriched and so the
    Increases mercury concentration, this concentrated wastewater stream 7 is then fed to the wastewater treatment plant 13.
    The mercury is substantially adsorptively bound to a fines fraction. If one can enrich these mercury-laden solids in the wastewater stream by means of suitable process control, a high wastewater load is possible, while at the same time having a low volume flow. The ARA can thus be kept small.
    The concentrator 14 may be, for example, a centrifuge, a sediment, a flotation plant or the like.
    The filtrate 8, that is to say the mercury-depleted material stream, is supplied here again to the scrubber 10.
    There are also other embodiments conceivable in which, for example, the hydrocyclone 11 is designed as a washing cyclone or in which the gypsum drainage takes place in two stages with intermediate dilution.
    权利要求:
    Claims (5)
    [1]
    claims
    1. A process for the removal of mercury in the flue gas desulfurization, wherein a gypsum suspension (1), which also contains the mercury, in the scrubber (10) of a wet flue gas scrubbing obtained and the gypsum suspension (1) by means of at least one hydrocyclone (11) thickened and the thickened gypsum suspension is discharged via the underflow (3) of the hydrocyclone (11), the upper run (2, 4) of the hydrocyclone (11) being fed to at least one sewage cyclone (12) for solids recovery and the upper run (5) of the sewage cyclone (12 ) is subsequently treated in a wastewater treatment plant (13), characterized in that the mercury concentration in the upper reaches (5) of the wastewater cyclone (12) in the concentrator (14) is increased and that this concentrated wastewater stream 7 of the wastewater treatment plant (13) is supplied.
    [2]
    2. The method according to claim 1, characterized in that the obtained in the concentration filtrate (8) is fed back to the scrubber (10).
    [3]
    3. The method according to claim 1 or 2, characterized in that the hydrocyclone (11) in addition to the gypsum suspension (1) is supplied via its own supply water, thereby resulting in a Feinstoffabreicherung, based on the suspension volume in the lower reaches (3) ,
    [4]
    4. The method according to claim 1 or 2, characterized in that the gypsum wash a two-stage gypsum drainage with intermediate dilution is carried out by process water.
    [5]
    5. The method according to any one of claims 1 to 4, characterized in that the concentration of the upper reaches (5) is carried out with a centrifuge, a sediment or by flotation.
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    引用文献:
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    法律状态:
    优先权:
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