CN1483506A

CN1483506A - Method for recovering waste liquid produced in process of chemical cleaning for intlustrial boiler

Info

Publication number: CN1483506A
Application number: CNA031277845A
Authority: CN
Inventors: 林瀚贵; 李胜珉; 崔美花
Original assignee: Korea Electric Power Corp
Current assignee: Korea Electric Power Corp
Priority date: 2002-07-18
Filing date: 2003-07-18
Publication date: 2004-03-24
Anticipated expiration: 2023-07-18
Also published as: KR20040008342A; CN1241673C

Abstract

Provided is a method for recycling waste liquid generated from chemical cleaning process of industrial boiler by adding additives of 20 to 30 wt.% of ammonium salts and 10 to 15 wt.% of iron to the waste liquid, thereby recycling the waste liquid to remove NOx and SOx in flue gas. The method comprises the steps of (a) adding additives of 20 to 30 wt.% of ammonium salts and 10 to 15 wt.% of iron to the waste chemical cleaning water of industrial boiler, (b) heating the waste chemical cleaning water at temperature in range of 50 to 70 deg.C to obtain ferric, (c) passing flue gas through the heated waste chemical cleaning water to remove NOx and SOx in the flue gas.

Description

Method for recovering waste liquid generated in chemical cleaning process of industrial boiler

Technical Field

The present invention relates to a waste liquid generated in a chemical cleaning process of an industrial boiler, and more particularly, to a method for recovering a waste liquid generated in a chemical cleaning process of an industrial boiler, which can remove flue gas by mixing an additive with the cleaning waste liquid.

Background

Generally, industrial boilers rely on the heat of combustion of fossil fuels such as coal, oil, natural gas, and the like. Metal oxides (hereinafter referred to as scale) produced during the combustion of fossil fuels can form on the inner surfaces of industrial boiler tubes. The scale thus formed should be removed quickly using a cleaning solution.

In this case, the chemical cleaning solution is ammonium EDTA (ethylene diamine tetraacetic acid). This ammonium EDTA reacts with the scale formed on the inner wall of the pipe, producing iron (II) EDTA (Fe (II) EDTA, hereinafter referred to as ferrous iron). This ferrous iron reacts with oxygen or an oxidizing agent, so that ammonium EDTA is discharged as iron (III) EDTA type (fe (III) EDTA, hereinafter referred to as washing waste liquid).

In addition, flue gases are generated during the combustion process of industrial boilers. In particular, in the case where Nox and Sox in the flue gas are directly discharged to the air, air pollution is increased. Therefore, a flue gas denitrification apparatus or a flue gas desulfurization apparatus is installed in the discharge pipe to remove the harmful substances.

However, maintenance of the desulfurization apparatus and the denitrification apparatus for removing harmful gases from flue gas is expensive, and if the desulfurization apparatus and the denitrification apparatus are used together, denitrification efficiency is lowered. Because of the high cost of the chemical treatment, the overall processing costs are increased.

Summary of The Invention

It is therefore an object of the present invention to overcome the problems encountered in the conventional processes.

It is another object of the present invention to provide a method for recovering spent liquor generated in a chemical cleaning process of an industrial boiler by mixing an additive into the spent liquor generated in the chemical cleaning operation stage of the industrial boiler to remove harmful gases in flue gas.

To achieve the above object, there is provided a method for recovering waste liquid generated in a chemical cleaning process of an industrial boiler, characterized in that flue gas is introduced into a cleaning waste liquid discharged in the type of ferric EDTA (III) by injecting ammonium EDTA into a pipe cleaning liquid of the industrial boiler, and ferric EDTA is generated by reacting ammonium EDTA with attached scale in a pipe, and then reacted with oxygen, thereby removing harmful substances.

In addition, in order to achieve the above object, there is provided a method for recovering waste liquid generated in a chemical cleaning process of an industrial boiler, characterized in that 20 to 30% by weight of ammonium EDTA and 10 to 15% by weight of iron powder are added to the waste cleaning liquid of the industrial boiler, heated at a temperature of 50 to 70 ℃ for 30 to 60 minutes to generate divalent iron, and the resultant is introduced into flue gas to remove harmful substances.

Further, in order to achieve the above object, there is provided a method for recovering waste liquid generated in a chemical cleaning process of an industrial boiler, characterized in that 15 to 25% by weight of calcium carbonate, 20 to 30% by weight of ammonium EDTA and 10 to 15% by weightof iron powder are added to the waste cleaning liquid of the industrial boiler, the resultant is heated at a temperature of 50 to 70 ℃ for 30 to 60 minutes to prepare an aqueous solution of calcium carbonate, and the resultant is introduced into a flue gas to remove harmful substances

Detailed description of the drawings

The invention may be better understood by reference to the accompanying drawings, which are illustrative only and not limiting of the invention, and in which:

FIG. 1 is a graph showing the denitrification efficiency of a cleaning waste liquid according to a first embodiment of the present invention;

FIG. 2 is a graph showing the denitrification efficiency of a cleaning waste liquid according to a second embodiment of the present invention;

FIG. 3 is a graph showing the change of the concentration based on denitrification and desulfurization of a washing waste liquid according to a second embodiment of the present invention;

FIG. 4 is a graph showing the change in the efficiency of denitrification and desulfurization based on a washing waste liquid according to the second embodiment of the present invention; and

FIG. 5 is a graph showing the change of concentration and efficiency based on denitrification and desulfurization of a washing waste liquid according to the second embodiment of the present invention.

Detailed description of the preferred embodiments

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

Ammonium EDTA, whichis a chemical cleaning solution according to the present invention, penetrates the inner wall of the pipe and reacts with scale to generate an Intermediate Iron (II) EDTA, which reacts with oxygen or an oxidizing agent discharged along the inner wall of the pipe and is discharged in the form of iron (III) EDTA.

At this time, the scale adhered to the inner wall of the pipe contained the components shown in Table 1. As shown in the table, since at least 90% of iron oxide is contained in the scale, it is known that the waste liquid generated in the tube cleaning stage of the industrial boiler is more than 90% of the cleaning waste liquid.

Therefore, the main component of the cleaning waste liquid is ferric oxide, the pH value is 5.0-9.7, and the concentration of iron ions is 50000-15,000 ppm. Including small amounts of other metallic species.

TABLE 1

Components	Content (weight/weight%)
Components	Content (weight/weight%)	Fe₂O₃	55～99％
Cu	Less than 40%	Fe₂O₃	55～99％
Cu	Less than 40%	Al₂O₃，ZnO，NiO	Less than 10%
Cr₂O₃，MnO₃	Small amount of	Al₂O₃，ZnO，NiO	Less than 10%
Cr₂O₃，MnO₃	Small amount of	SiO₂，Mg，CaO，SO₂	5.0% or less
P₂O₅	Less than 10%	SiO₂，Mg，CaO，SO₂	5.0% or less

Example 1

First, ammonium supplied as a chemical cleaning solution to the inner wall of the industrial boiler pipe reacts with scale attached to the inner wall of the pipe to produce ferrous iron. The ferrous iron produced reacts with air or an oxidizing agent to produce a washing waste liquor of the type iron (III) EDTA. Nitrogen oxides and sulfur oxides are removed from the flue gas by passing through the flue gas.

FIG. 1 is a graph showing the denitrification efficiency of a cleaning waste liquid. As shown in the figure, the denitrification effect was achieved by injecting harmful gas containing 1750ppm of nitrogen oxide into the washing waste liquid containing 4100ppm of iron ions at a rate of 2.50 ml per minute. In this case, as shown in fig. 1, the denitrification efficiency of the cleaning waste liquid was about 95% or more, and remained 65% after about 50 minutes. From this, it was found that the denitrification efficiency was excellent.

Example 2

Firstly, 20-30 wt% of ammonium EDTA and 10-15 wt% of iron powder are added into a cleaning waste liquid generated by an industrial boiler. Heating the obtained mixture at the temperature of 50-70 ℃ for 30-60minutes to convert the mixture into ferrous iron. The flue gas is fed with the reduced material to remove nitrogen oxides and sulfur oxides.

That is, fig. 2 is a graph showing the denitrification efficiency using the cleaning waste liquid (ammonium + iron powder). As shown in the figure, 20-30 wt% of ammonium EDTA and 10-15 wt% of iron powder are added into the cleaning waste liquid containing 8200ppm of iron ions, the obtained substance is heated at 50 ℃, and is reduced into ferrous iron based on the chemical structural formula I, and the iron powder is dissolved. The resulting material was then diluted with a solution containing 4500ppm of iron ions. The flue gas is then passed through the resultant mass to remove the hazardous substances.

--------------------(I)

At this time, as shown in FIG. 2, the denitrification efficiency was maintained at about 95% or more in the initial stage and at 90% or more after 60 minutes. Then, the denitrification efficiency decreased, and remained at 60% after 170 minutes.

In addition, fig. 3 is a graph showing the change in concentration and the change in efficiency based on the denitrification and desulfurization of the cleaning waste liquid (ammonium EDTA + iron powder). As shown in the figure, 20-30 wt% of ammonium EDTA and 10-15 wt% of iron powder are added to a cleaning waste liquid containing 8200ppm of iron ions, the resultant is heated at 70 ℃, and reduced to ferrous iron based on chemical structural formula I, and the iron powder is dissolved. The resulting material was diluted with a solution containing 4500ppm of iron ions. The flue gas is then passed into the resultant mass.

At this time, as shown in FIG. 3, the initial concentration of nitrogen oxide (nitrile oxide) was maintained at 210ppm, and the initialconcentration of sulfur oxide was maintained at 1100 ppm.

As shown in fig. 4, the cleaning waste liquid (ammonium EDTA + iron powder) was used to remove harmful substances. The desulfurization/denitrification efficiency was maintained at about 95% in the initial stage and at about 80% after 60 minutes. Then, the efficiency gradually decreased, remaining at about 50% after 170 minutes.

Example 3

Adding 15-25 wt% of carbonic acid, 20-30 wt% of ammonium EDTA and 10-15 wt% of iron powder into cleaning waste liquid discharged from an industrial pot, heating the obtained substance at 50-70 ℃ for 30-60 minutes to generate a calcium carbonate aqueous solution, introducing flue gas into the obtained substance, and removing nitrogen oxide and sulfur oxide.

Fig. 5 is a graph showing the change of concentration and efficiency based on desulfurization and denitrification of the washing waste liquid (ammonium EDTA + calcium carbonate + iron powder). Adding 15-25 wt% of calcium carbonate into a cleaning waste liquid which contains 4500ppm of iron ions and is used as a desulfurizing agent, and then adding 20-30 wt% of ammonium EDTA and 10-15 wt% of iron powder.

And then heating the obtained product of the cleaning waste liquid at 50-70 ℃ for 30-60 minutes to generate a final product. The flue gas is then passed into the resultant mass. The denitrification/desulfurization efficiency remained at about 80% at all times within 50 minutes. From this, it was found that the removal efficiency of the harmful substances was excellent.

As described above, according to the method for recovering a waste liquid generated in the chemical cleaning stage of an industrial boiler of the present invention, ammonium EDTA, iron powder or a desulfurizing agent is added to a cleaning waste liquid discharged from the industrial boiler as a waste liquid, thereby removing harmful substances in a flue gas. Therefore, in the present invention, the recovery of the washing waste liquid is carried out so that the industrial cost of recovering the waste liquid can be reduced and the process can be reduced. In addition to this, various associated costs based on the removal of harmful substances from the flue gas can be reduced.

As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within, or equivalence to, the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.

Claims

1. A method for recovering waste liquid generated in a chemical cleaning process of an industrial boiler, characterized in that flue gas is introduced into a cleaning waste liquid discharged in the type of ferric EDTA (III) obtained by injecting ammonium EDTA into a tube cleaning liquid of the industrial boiler and reacting with adhered scale in a tube, and then reacting the generated ferrous iron with oxygen, thereby removing harmful substances.

2. A method for recovering waste liquid generated in a chemical cleaning process of an industrial boiler, characterized in that 20-30 wt% of ammonium EDTA and 10-15 wt% of iron powder are added to the waste liquid of the industrial boiler, heated at a temperature of 50-70 ℃ for 30-60 minutes to generate divalent iron, and the resulting substance is introduced into flue gas to remove harmful substances.

3. A method for recovering waste liquid generated in a chemical cleaning process of an industrial boiler, characterized in that 15 to 25% by weight of calcium carbonate, 20 to 30% by weight of ammonium EDTA and 10 to 15% by weight of iron powder are added to the waste cleaning liquid of the industrial boiler, the resultant is heated at a temperature of 50 to 70 ℃ for 30 to 60 minutes to prepare an aqueous solution of calcium carbonate, and the resultant is introduced with flue gas to remove harmful substances.