JPS595035B2 - Treatment method for wet denitrification and desulfurization waste liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating a wet denitrification/desulfurization waste liquid that can remove amine compound ions contained in the waste liquid discharged from a wet denitrification/desulfurization process.

In the process of wet denitrification and desulfurization, which simultaneously processes SOx and NOx, amine-based nitrogen compound ions, such as hydroxylamine-based NH (OH
)(SO2), N(OH)(803)2”.

Or sulfamine-based NH2S03″″, NH(5O
3) A considerable amount of 22- is generated, dissolved in the absorption liquid, and discharged as waste liquid.

These amine nitrogen compound ions form part of the COD component, turning the waste liquid into a liquid that does not meet the discharge standards of the Water Pollution Control Act, so it is not allowed to discharge it as it is, and therefore, it is not allowed to be discharged as it is. The waste liquid was treated and then disposed of.

The conventional method used for this treatment is to add nitrite to the waste liquid to decompose the amine compounds.

However, even when this method is applied to a waste liquid in which other ions that increase COD, such as dithionate ions, coexist, it does not produce a satisfactory effect in removing COD from the waste liquid.

An object of the present invention is to provide a method for treating a wet denitrification/desulfurization waste liquid, which allows a waste liquid containing amine compound ions or dithionate ions in addition to these to be treated as a liquid that can be disposed of.

Embodiments of the method of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a diagram showing the process of treating the raw liquid from the wet denitrification and desulfurization process by the method of the present invention.

The alkali treatment steps 2 and 3 described below perform alkali treatment and filtration of the raw liquid.

In step 2, the raw liquid from the wet denitrification and desulfurization process (step 1) is received in a preliminary coagulation sedimentation tank that also serves as a raw water storage tank.

The Suru SS, which is mainly composed of fly ash and is contained in the received raw solution, is naturally settled in the pre-coagulation sedimentation tank, and the metals such as Fe"+ and Cr3+ contained in the raw solution are The ions are precipitated and removed (filtered) by maintaining the acidic raw waste solution, which has a pH of 2 or less, at a pH of 6 to 8 with an alkaline agent such as calcium hydroxide.

By removing both of these, the load on the coagulation-sedimentation apparatus described below is reduced.

The waste liquid (clarified liquid) obtained in the pre-coagulation sedimentation tank is transferred to step 3.
The liquid is supplied to the coagulation sedimentation device.

'In this coagulation-sedimentation apparatus, the pH of the liquid is raised to around 11 using an alkaline agent such as calcium hydroxide.

As a result, most of the metal ions contained in the supplied liquid that have not yet been precipitated and separated in the pre-coagulation sedimentation tank can be precipitated and separated in the form of hydroxides in an elevated pH range.

At the same time, sulfate ions in the waste liquid that could not be removed in the treatment in step 2 can be precipitated and separated as calcium sulfate as much as possible.

The waste liquid treated in step 3 is received in an amine nitrogen compound ion coagulation and precipitation step 4, an amine nitrogen compound ion inorganic coagulation and precipitation apparatus.

By adding an inorganic flocculant containing aluminum ions and an alkaline agent to the received waste liquid to make the pH of the waste liquid around 12, the amine nitrogen compounds are reduced to 70% as shown in Table 1. ~80% was removed, and fluorine was also removed.

Along with this, dithionate ions were also efficiently removed as described below.

The inorganic flocculant containing aluminum ions used for this purpose is an inorganic flocculant whose main component is polyaluminum chloride: PAC (trade name) (hereinafter referred to as PAC).

), sodium aluminum oxide (AlNaO2), aluminum sulfate (A12(S04)3), fly ash solution, etc.

In addition, there are alkaline agents such as calcium hydroxide, sodium hydroxide, and sodium carbonate, but calcium hydroxide is the main agent, and undissolved components remain when the pH is adjusted to pH 11 or higher (optimum 12) using only calcium hydroxide. In order to prevent
Sodium hydroxide, sodium carbonate, etc. may be used to adjust H.

Adding PAC to the waste solution and reducing the pH of the waste solution with calcium hydroxide
When H is around 12, the dithionate ion concentration (pp
m) 1 to PAC (ppm as A1203) 0.
Requires 5 or more.

When sodium aluminum oxide or aluminum sulfate is used as an inorganic flocculant containing aluminum ions, and the aluminum ions in the waste liquid are kept at a constant concentration sufficient to precipitate dithionate ions, the removal rate of dithionate ions is In the former case, it reached almost 1oo%, but in the latter case, it only reached about 50%.

This means that sulfate ions act as an interfering element against the precipitation of dithionate ions.

In this way, sulfate ions prevent the precipitation of dithionate ions, but if a large amount of an inorganic flocculant containing aluminum ions, such as the above-mentioned PAC, is added, in other words, if the aluminum ion concentration is increased, the coagulation and precipitation of dithionate ions can be prevented. Processing can be carried out.

In the presence of sulfate ions, the required amount of PAC is 7 or more, which is the sum of the dithionate ion concentration (ppm) and the sulfate ion concentration (ppm).

When the process in Step 4 described above is carried out, the amine-based nitrogen compounds in the waste liquid are removed simultaneously with the removal of dithionate ions in the waste liquid.

Most of the aluminum ions attached in the process of step 4 mentioned above are consumed by removing dithionate ions, but the few aluminum ions that remain in the waste liquid react with calcium ions in the waste liquid to form calcium aluminate. It has precipitated as.

Therefore, even if the pH of the waste liquid from step 4 is returned to the neutral range in the pH adjustment tank of pH adjustment step 5, reprecipitation of aluminum ions hardly occurs.

Therefore, the load on the filtration device in the filtration step 6 can be reduced, and a simple sand filtration device can be used as the filtration device.

Waste liquid after filtration in step 6 [treated water (step 7)]
As a result of investigating the COD, the raw fabric solution with a COD of 1100 ppm was treated water with a COD of several ppm or less, which met the discharge standards set by the Water Pollution Control Act, and therefore can be discharged.

Step 8 is a heat treatment step, in which the precipitate is
By heating at 00°C, it can be turned into a precipitate that can be disposed of.

Furthermore, within this temperature range, exhaust gas can be effectively used as a heating source.

In the above example, an example of the treatment of waste liquid in which amine nitrogen compound ions, fluorine ions, and dithionate ions coexisted was explained, but amine nitrogen compound ions also existed alone in waste liquid after wet desulfurization treatment. The method of the present invention can also be applied to such cases.

As is clear from the above description, according to the present invention, 70 to 80% of the amine nitrogen compounds contained in the stock solution can be removed.

Therefore, it greatly contributes to lowering the COD of treated water to below the discharge standards set by the Water Pollution Control Law.

[Brief explanation of the drawing]

The accompanying drawings illustrate the process steps of the present invention. In the figure, 2 and 3 are alkali treatment steps, 4 is an amin nitrogen compound ion coagulation and precipitation step, 5 is a pH adjustment step, and 6 is a filtration step.

Claims (1)

[Claims] 1. A method for treating waste liquid containing amine-based nitrogen compound ions from a wet denitrification and desulfurization process, in which the waste liquid is treated with an alkali and then filtered, an inorganic flocculant containing aluminum ions is added to the filtered waste liquid, and the waste liquid is treated with an alkali and then filtered. A method for treating wet denitrification and desulfurization waste liquid, which comprises adjusting the pH of the liquid to 10 or higher using an alkaline agent to coagulate and precipitate the amine nitrogen compound ions.