JPS63270594A - Treatment of fluorine in flue gas desulfurization waste water - Google Patents

Abstract

PURPOSE:To stabilize the fluorine treating capability and to control the corrosion of the material for a device by adding the dust collected by an electrostatic precipitator in the cooling stage of a desulfurizer to adjust the concn. ratio of the aluminum to fluorine in the cooling stage waste water. CONSTITUTION:The dust 31 collected by the electrostatic precipitator 1 preceding the cooling stage is previously supplied into the cooling stage 2 as powder or the material classified by a liq. such as waste water. The dust 31 contains 15-30% aluminum compd., expressed in terms of Al2O3, a part of the dust is converted into dissolved aluminum in the cooling stage 2, and a fluorine- aluminum complex is formed. The cooling stage waste water 21 contg. the fluorine-aluminum complex is introduced into a first pH adjusting stage 7, a calcium compd. such as slaked lime 34 is added to adjust the pH to 7-11, and hence the fluorine-aluminum complex is decomposed and deposited as hardly soluble calcium fluoride.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for treating fluorine in flue gas desulfurization wastewater in a coal-fired boiler.

[Conventional technology]

Combustion exhaust gas from coal as fuel is collected using an electrostatic precipitator.
Treated with desulfurization equipment using the plaster method.

To explain this using Figure 2, 'dust is collected in an electrostatic precipitator 1, then cooled, humidified, and dust removed in a cooling process 2, and then led to an absorption process 3 where sulfur oxides are absorbed and removed by an absorption liquid. It is then released as clean gas.

At this time, the cooling process wastewater 21 containing chlorine, fluorine, boron, heavy metal S, etc. caused by the fuel is discharged from the cooling plant @ 2 after solid-liquid separation of the fly ash or as it is.

In addition, the absorption liquid from the absorption process 5 is sent directly or through the oxidation process 84 to the gypsum separation process 5, where the by-product gypsum 23 is recovered, and COD components such as persistent nitionates caused by the flue gas treatment system. Supernatant water 22 containing water is discharged.

The supernatant water 22 from this gypsum separation process 5 is led to the COD acid decomposition process a6, where #32k of sulfuric acid is added and heated with water vapor 33 to decompose the nitionate in the waste water, followed by cooling process 2
The water is collected and reused as make-up water for the cooling process.

Exhausted from the cooling step 2, chlorine, heptadium, boron,
The cooling process wastewater 21 containing heavy metals, etc. is led to the first adjustment step 7, where slaked lime 34 is added to adjust the pH to 7 to 11, and fluorine and heavy metals in the wastewater are precipitated as poorly soluble calcium fluoride and hydroxide, respectively. Then, the mixture is led to a solid-liquid separation step 8, where a polymer flocculant 35 is added to form coarse flocs of the calcium heptadide, hydroxide, etc., and then separated by precipitation. The separated slurry 24 from the solid-liquid separation step 8 that has been precipitated and separated is led to a dewatering step 1o where it is dehydrated and then extracted as sludge 25 and disposed of.

The waste water from the solid-liquid separation process 8 from which fluorine, heavy metals, etc. have been removed is led to the second voice adjustment process 9, and mineral acid 52 is added as necessary.
, preferably by adding hydrochloric acid to adjust - to within the discharge regulation range and discharge as treated water 26.

Here, in flue gas desulfurization wastewater from coal-fired boilers, especially in cooling process wastewater, in addition to fluorine and heavy metals, boron exists in the form of boron heptides, etc., which has an adverse effect on fluorine treatment performance8. Since water quality varies greatly depending on fuel conditions (coal type, coal co-combustion rate), exhaust gas treatment system configuration, operating conditions, etc. It was difficult to stably process the following.

Therefore, the Ministry of the Invention has already proposed in Japanese Patent Application Laid-Open No. 59-39385 to deal with the above-mentioned problems, by fully injecting aluminum compounds such as polyaluminum chloride (PAC) into the cooling process wastewater. It is proposed in all the headings that by decomposing the recalcitrant borofluoride contained in wastewater to produce a heptadium-aluminum complex, and then adding the calcium compound kfiS, it is possible to separate the heptadium in wastewater as calcium heptadide. ing.

That is, as shown in Fig. 5g2, from the aluminum compound 41 from the aluminum compound 41, aluminum hydroxide, salt (sulfate, hydrochloride), aluminate compound such as aluminum hydroxide, aluminum sulfate, polyalbanium chloride This is a method in which one or more types of aluminate powder are directly mixed with gold or mixed into the waste water from the COD acid decomposition step 6 to flow into the cooling step 2, and the subsequent treatment methods are as described above. be.

[Problem that the invention seeks to solve]

This method makes it possible to stabilize the treatment performance of 7-wire ropes without making any changes to the process by simply allowing the aluminum compound to act on fluorine in waste water, which has traditionally been considered difficult to treat. Aluminum compounds have unique effects such as inhibiting corrosion of equipment materials during the cooling process by masking fluorine, but they have the following problems.

fil The content of aluminum dissolved in cooling process wastewater and resulting from 97 lithium fuel varies greatly depending on the brand of coal used as fuel, combustion conditions, and the configuration and operating conditions of the exhaust gas treatment system. If the concentration is strictly limited, is there a constant and sufficient concentration of aluminum? 9. It is difficult to secure.

(2) Therefore, the molar ratio of soluble aluminum to fluorine (
In order to make A//F ) 0.4 or more, preferably 0.5 or more, it was necessary to add expensive aluminum compounds such as polyaluminum chloride and aluminum sulfate from the outside.

The present invention solves these problems and instead of using expensive aluminum compounds such as polyaluminum chloride, all aluminum is recovered from dust collected by an electrostatic precipitator in the same plant, and used as flue gas desulfurization wastewater. The purpose is to provide a method for processing seven processes in a weighted manner.

[Means for resolving the problem] The present invention provides a desulfurization device for a method in which fluorine in the waste water of a coal-fired boiler exhaust gas removed from a lime-gypsum method is neutralized with slaked lime and precipitated and separated as calcium fluoride. This special smoke is characterized by adding nine particulates collected by an electric precipitator to the cooling process, adjusting the concentration ratio of aluminum and fluorine in the cooling process wastewater, and stabilizing the fluorine treatment performance. This is a method for treating fluorine in desulfurization wastewater.

It is preferable to elute all the aluminum from the dust so that the aluminum concentration (t) molar ratio of the cooling process wastewater is 0.4 or more, preferably 0.5 or more of fluorine. Alternatively, the method of adding dust can be selected from among pneumatic transportation, slurry transportation using cooling process wastewater, mineral acid, or industrial water.

[Effect]

Next, the operation of the present invention will be explained with reference to FIG.

Did I mention it above? From the cooling process 2, the cooling process wastewater 2 contains chlorine, chlorine, boron, heavy metals, etc. caused by the fuel.
1 is ejected.

At this time, during the exhaust gas treatment process, soot dust 31 (fly ash) collected by the electrostatic precipitator 1 before the main cooling process 2 is dispersed in gold powder or liquid such as waste water. It is supplied in advance during the cooling process 2.This dust 51 contains 15 to 30% in terms of aluminized metal 7/203, although it varies depending on the brand of coal used as fuel. A part of the circulating fluid melts in the acidic atmosphere to produce molten aluminum.In the cooling step 2, borofluoride, which is contained in the waste water along with 7-fluoride and is treatable, is converted into a It reacts as shown in Figure 2 and forms on a fluorine-aluminum complex.

At +BFn(OHΣa −, 7n −1)H20
#A/F,'-” +B (OH) s + (
n-ri cod...Equation 1 This reaction is carried out under 20 conditions of the cooling step (temperature 50-60°C, p
Since this reaction can be carried out using H0.5-2.0 and a residence time of 10 to 20 hours, no step is required for this reaction.

In addition, the addition t of particulate matter 31 is such that the molar ratio to the 7 parts of soluble aluminum in the cooling process waste water 21 after adding particulate matter 31 is 0.4 or more, preferably 0.5 or more. do it like this. The rate of aluminum elution from the dust 31 varies depending on the brand of coal, but can be roughly estimated from the composition of the dust 31.

That is, the elution of aluminum from the dust 31 in the cooling step 2 depends on the composition of the dust, especially At203. Na2
It is controlled by the content of O, K2O, CaO and MgO. There is a strong correlation between the value X of the equivalents of Na2O, K2O, C1aO, and MgO in dust divided by the equivalent of At205, and the elution rate of aluminum, Y, in that the larger X becomes, the larger Y becomes. , Y naturally varies depending on the type of coal, but is in the range of 5S50%. Therefore, the amount of dust added can be easily set based on the correlation based on the analysis value of the ash content of the dust or the coal used.

Regarding the addition of acetic acid to the dust 31 in the cooling process 2, as mentioned above, when treating the exhaust gas, the concentration of dust at the outlet of the electrostatic precipitator 1 is adjusted appropriately, and the dust 31 is cooled through the exhaust gas line. Although it is conceivable that the dust 51 may arrive directly in the step 2, in this method of supplying the dust 51, heat exchange is performed in the intermediate gas-gas heater process from the electrostatic precipitator 1 to the cooling step. Particulate matter may be mixed into the treated exhaust gas, making it impossible to meet the regulation concentration of particulate matter in the discharged exhaust gas.

On the other hand, according to the present invention, which supplies the dust once collected by the electrostatic precipitator 1, there is no such adverse effect on the emitted exhaust gas.

Next, the cooling process wastewater 21i containing the 7-wire-aluminum complex is led to the 1st p) 1 adjustment step 7, and a calcium compound ka such as slaked lime 54 is added to adjust the pH to 311, preferably 7 to 9, as shown in the second formula. In this way, the fluorine-aluminum complex is completely decomposed and precipitated as poorly soluble calcium heptafluoride.

AtF, “-hFca”+50H-# At (OH)
a + , Ca F 2 . . . At the same time, the heptadium ions present in the cooling process wastewater 21 react as shown in Equation 5 and are precipitated as poorly soluble calcium heptadide.

2F''''+0a(OH)2#0aF2+OH-...3rd formula contains aluminum hydroxide, heavy metal hydroxide, etc. in addition to the reaction product calcium heptadide 1st≠Adjustment step 7
The wastewater is led to a solid-liquid separation step 8, where a polymer flocculant 35 is added to form a suspension of calcium fluoride, etc. into coarse flocs, and then separated by sedimentation. At this time, since the aluminum hydroxide produced by the reaction shown in the second equation acts as a flocculant, it has the effect of accelerating the precipitation.

The precipitated solid-liquid separation step separated slurry 24 is led to a dehydration step 10, dehydrated, and then disposed of as sludge 25.

After removing fluorine, the wastewater from the solid-liquid separation process 8 is adjusted to within the total discharge regulation range by adding sulfuric acid 52 to the second regulator A9, and the cumulative concentration is 1519/A or less ( The treated water is discharged as treated water 26, which meets the national standards.

〔Example〕

Fluorine in the cooling process wastewater generated when exhaust gas discharged from a coal-fired power generation facility with an output of 150 MW was desulfurized by the total lime-gypsum method - treated according to the flow shown in Figure 1.

The conditions and results are as shown in Table 1. In the table, Comparative Example 1 was treated with 70- as shown in FIG. Comparative Example 2 is an example in which wastewater treatment was performed without actively cooling the aluminum source.

As is clear from the comparison of the seven-point yield of the treated water, the concentration of the Example of the present invention can be reduced to nearly half that of Comparative Example 2, and is almost the same as that of Comparative Example 1 in which aluminum sulfate is added heavily. It can be seen that processing has been carried out.

〔Effect of the invention〕

The present invention achieves the following effects by employing the above configuration.

(1) In the cooling process, by adding soot and dust collected by an air dust collector, it is possible to stabilize the 7-wire treatment performance without adding expensive aluminum compounds such as polyaluminum chloride. It became.

(2) The soot and dust that has been collected by an electrostatic precipitator and disposed of is used as a waste material, and aluminum compounds that become a source of sludge are not brought in from the outside of the thread. The reduction of waste has become a gT function.

(3) In addition to the above-mentioned cumulative treatment properties, since fluorine was masked by aluminum in the dust, a corrosion inhibiting effect on equipment materials during the cooling process was obtained.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing an embodiment of the flue gas desulfurization wastewater treatment method of the present invention, and FIG. 2 is a 70-sheet of the conventional method. 1 Electrostatic precipitator 21 Cooling process wastewater 2 Cooling process 22 Gypsum separation process supernatant water 3 Absorption process
25 By-product gypsum 4 Oxidation process 24 Solid-liquid separation process Separated slurry 5 Stone/U separation process 25 Sludge 6 COD acid decomposition process 26 Treated water 7 1st-adjustment process 31 Dust 8 Slag separation process @ 32 Sulfuric acid 9 2nd- Straightening process 66 Steam 10 Dehydration process 54 Slaked lime 11 Aluminum rA conditioning process 65 Polymer flocculant 41 Aluminum compound

Claims (1)

[Claims] In a method in which fluorine in the waste water of a desulfurization device using the lime-gypsum method for coal-fired boiler exhaust gas is neutralized with slaked lime and precipitated and separated as calcium fluoride, soot dust collected by an electrostatic precipitator is used in the cooling process of the desulfurization device. A method for treating fluorine in flue gas desulfurization wastewater, the method comprising adding fluorine to the wastewater from a cooling process, adjusting the concentration ratio of aluminum to fluorine in the wastewater from the cooling process, and stabilizing the treatment performance of fluorine.