JP7209533B2 - Method for treating exhaust gas containing heavy metals - Google Patents

Description

The present invention relates to a method for treating exhaust gas containing heavy metals.

A non-catalytic denitrification method is known that does not use a catalyst to decompose nitrogen oxides (NO or NO ₂ , hereinafter referred to as NO _x ) contained in flue gas generated by combustion. The non-catalytic denitration method is a method of adding (more specifically, blowing in) a reducing agent (e.g., ammonia water or urea water) to combustion exhaust gas to reduce and decompose nitrogen oxides, thereby denitrifying. (for example, Patent Documents 1 to 3).

JP 2014-74515 A JP 2006-289326 A JP 2013-94765 A

In the non-catalytic denitrification method, heavy metals such as Cu, Pb, Zn, and Fe or their compounds (especially Cu is an example, and both simple Cu and its compounds are collectively referred to as “Cu-containing”) are added to the dust in the combustion exhaust gas and The present inventors have found that their coexistence as smoke and/or smoke significantly reduces the denitrification rate or _NOx removal rate for the flue gas. Hereinafter, dust will also be referred to as dust, and smoke will also be referred to as fume. The solids content in both is simply referred to as "solids content".

SUMMARY OF THE INVENTION An object of the present invention is to effectively denitrify waste gas containing heavy metals containing copper.

A first aspect of the present invention is
Denitrification with a reducing agent for heavy metal-containing exhaust gas produced by burning a heavy metal-containing raw material and containing nitrogen oxides and having a copper concentration of 0.07 g/m ³ or more in the heavy metal-containing exhaust gas. A method for treating heavy metal-containing exhaust gas to be treated, comprising:
a combustion step of burning the heavy metal-containing raw material while adding a hydrocarbon different from the heavy metal-containing raw material;
a denitrification step of adding the reducing agent to the heavy metal-containing exhaust gas at 700 to 1000° C.;
A method for treating heavy metal-containing exhaust gas.

A second aspect of the present invention is the invention according to the first aspect,
The hydrocarbon is at least one of LNG, heavy oil, methane and propane.

A third aspect of the present invention is the invention according to the first aspect,
Said hydrocarbon is LNG.

A fourth aspect of the present invention is the invention according to any one of the first to third aspects,
The reducing agent is at least one of liquid ammonia, aqueous ammonia, and aqueous urea.

A fifth aspect of the present invention is the invention according to any one of the first to fourth aspects,
The concentration of copper in the heavy metal-containing exhaust gas is 3.0 g/m ³ or more.

A sixth aspect of the present invention is the invention according to any one of the first to fifth aspects,
the heavy metal-containing raw material includes waste electronic equipment;
The combustion step is performed in a metal smelting furnace.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to denitrify effectively with respect to the heavy metal containing waste gas containing copper.

FIG. 1 is a schematic diagram of an apparatus for performing a method for treating heavy metal-containing exhaust gas according to this embodiment. FIG. 2 is a plot showing the relationship between copper grade (horizontal axis) and denitrification rate (vertical axis) in Examples 1 to 4 and Comparative Example 3.

The present embodiment will be described below. In this specification, "-" refers to a predetermined numerical value or more and a predetermined numerical value or less. Also, the top-to-bottom direction is defined as upward, and the top-to-bottom-to-bottom direction is defined as downward.

In the method for treating heavy metal-containing exhaust gas according to the present embodiment, the heavy metal-containing exhaust gas is generated by burning a heavy metal-containing raw material, contains nitrogen oxides, and has a copper concentration of 0.07 g/m ³ or more. The heavy metal-containing exhaust gas is subjected to denitrification treatment with a reducing agent. Moreover, it has at least the following steps.
A combustion step of burning the heavy metal-containing raw material while adding a hydrocarbon different from the heavy metal-containing raw material A denitrification step of adding the reducing agent to the heavy metal-containing exhaust gas at 700 to 1000 ° C.

As long as each of the above steps can be performed, there is no particular limitation on the apparatus for performing the method for treating heavy metal-containing exhaust gas according to the present embodiment. For example, a metal smelting furnace or a heating furnace of a metal or chemical plant may be used.

Although the type of heavy metal-containing raw material varies depending on the application of the apparatus, the type of heavy metal-containing raw material is not particularly limited. For example, electronic devices that have already been discarded may be employed as heavy metal-containing raw materials. An electronic device usually has a wiring board on which electronic components using heavy metals are mounted. In one example of this embodiment, waste electronic equipment is combusted in a metal smelting furnace to form molten metal (later recovered), with which heavy metal-containing exhaust gas is generated. However, in that case, it is often called smelting instead of burning. The combustion process in the present embodiment also includes oxidative heat treatment of raw materials at 1000° C. or higher in the smelting process of non-ferrous smelting.

A heavy metal as used herein refers to a metal having a specific gravity greater than that of iron, and examples thereof include Cu, Pb, Zn, and Fe. A heavy metal-containing raw material in this specification refers to a raw material containing a heavy metal simple substance or a compound thereof (in the present embodiment, the case of containing copper (Cu) is exemplified). Heavy metal-containing exhaust gas also refers to raw materials containing heavy metal simple substances or their compounds (for example, as fine particles in dust or fume, ie, solid content).

In the present embodiment, the heavy metal-containing raw material includes waste electronic equipment, and the combustion step is performed in a metal smelting furnace, and the denitrification step is performed in a boiler communicating with the metal smelting furnace. is exemplified.

FIG. 1 is a schematic diagram of an apparatus 1 for performing a method for treating heavy metal-containing exhaust gas according to this embodiment.

Said apparatus 1 comprises a furnace 2 for burning heavy metal-containing raw materials and a boiler 3 communicating with the furnace 2 .

The furnace 2 has a raw material inlet 21 for charging heavy metal-containing raw materials into the furnace 2, and a gas addition port 22 for adding oxygen, air, fuel, etc. for combustion into the furnace 2. It's ready.

The boiler 3 includes a first boiler section 31 that communicates with the furnace 2 and extends upward, and a second boiler section 32 that communicates with the first boiler section 31 and extends downward. Prepare. A boiler 3 recovers the heat of the heavy metal-containing exhaust gas.

It should be noted that the boiler 3 does not have a function as a boiler, but may be a flue having other functions or a simple flue. Efficient to use in the process. However, while the first boiler section 31 has the function of a boiler as the first flue section, a duct or a dust chamber section may be provided instead of the second boiler section 32 to serve as the second flue section. . That is, part of the boiler 3 may be a flue having a function other than that of a boiler. The term "flue" is used herein to include boilers, ducts, dust chambers, and the like. In this embodiment, the boiler 3 is exemplified.

The heavy metal-containing exhaust gas generated by burning the heavy metal-containing raw material advances upward through the first boiler section 31 communicating with the furnace 2 (white arrow in FIG. 1). A reducing agent spraying mechanism 4 is provided in the middle of the first boiler section 31 in the longitudinal direction. Further, a water spray mechanism (not shown) for adjusting the temperature of the heavy metal-containing exhaust gas may be provided at the end of the first boiler section 31 in the longitudinal direction, that is, near the top plate.

The reducing agent spraying mechanism 4 includes a reducing agent storage unit 41 , a pump 42 that transfers the reducing agent, an air intake unit 43 that takes in the atmosphere, and a reducing agent to the heavy metal-containing exhaust gas passing through the inside of the first boiler unit 31 . and a blowing nozzle 44 . The number of nozzles 44 may be singular or plural. In FIG. 1, a plurality of nozzles 44 are provided along the longitudinal direction of the first boiler section 31, but in addition or instead of that, a plurality of nozzles 44 may be provided along the inner circumference of the first boiler section 31. good.

The nozzle 44 of the reducing agent spray mechanism 4 can be attached to the second boiler section 32, but as time passes, the nitrogen in the heavy metal-containing exhaust gas may oxidize and NO _x may increase. Therefore, it is preferable to provide the nozzle 44 in the first boiler section 31 through which heavy metal-containing exhaust gas is generated and passes first.

The boiler 3 of this embodiment includes a first boiler section 31 that communicates with the furnace 2 and extends upward, and a second boiler section that communicates with the first boiler section 31 and extends downward. 32 has been exemplified, but this need not be the case.
For example, a first boiler section communicating with the furnace 2 and extending in a horizontal direction (eg, rightward in FIG. 1) and a second boiler section extending in an opposite horizontal direction (eg, leftward in FIG. 1). A boiler section may be provided.
Alternatively, the boiler may extend upward after communicating with the furnace 2 and extending downward.

The heavy metal-containing exhaust gas that has passed through the first boiler section 31 makes a U-turn downward along the second boiler section 32 . In order to make this U-turn smoothly, a taper 33 with a gradually increasing inner diameter is provided at the transition from the first boiler section 31 to the second boiler section 32 .

From the second boiler section 32 onwards, a known exhaust gas treatment mechanism may be provided, and a known exhaust gas treatment process may be performed. Finally, the exhaust gas is discharged to the outside through a chimney (not shown).

The combustion process and the denitrification process are described in detail below.

In the combustion step, the heavy metal-containing raw material is combusted. Adding a hydrocarbon at that time is one of the major features of the present embodiment. By this operation, a high denitrification rate can be achieved even with exhaust gas containing heavy metals, as will be shown in the items of Examples described later.

The hydrocarbons added in the combustion process are separate substances from the heavy metal-containing feedstock. That is, the hydrocarbon is added from the gas addition port 22 separately from the heavy metal-containing raw material when the heavy metal-containing raw material is burned. This hydrocarbon may also serve as fuel.

The type of hydrocarbon is not particularly limited, but includes at least one of LNG, heavy oil, methane and propane (especially LNG). In addition, LNG in this specification includes ethane (C ₂ H ₅ ), propane (C ₃ H ₇ ), n _- butane (nC ₄ H ₁₀ ), isobutane (iC ₄ H ₁₀ ), 2-methylbutane (iC ₅ H ₁₂ ), and other saturated hydrocarbon components. LNG may also be referred to as a hydrocarbon gas containing methane as its main component.

By performing the combustion process, heavy metal-containing exhaust gas is generated and rises in the first boiler section 31 . The temperature of the exhaust gas containing heavy metals is measured with a thermometer provided on the side wall of the first boiler section 31 . Based on this measurement result, among the plurality of nozzles 44 provided along the longitudinal direction (vertical direction) of the first boiler part 31, the heavy metal-containing exhaust gas Operate the nozzles at the part where the temperature is 1000°C. As a result, a denitration process is performed in which a reducing agent is added to the heavy metal-containing exhaust gas.

In the denitration process, denitration is performed using a reducing agent without a catalyst. The term "catalyst-free" refers to the absence of a separate catalyst during denitrification (more specifically, when the reducing agent comes into contact with the heavy metal-containing exhaust gas to decompose _NOx ). In other words, before and after the timing at which the reducing agent comes into contact with the heavy metal-containing exhaust gas, a catalyst-containing filter or the like may be provided in at least one of the first boiler section 31 and the second boiler section 32 for purposes other than denitrification. .

A specific example of the denitrification process includes spraying the reducing agent from the nozzle 44 of the reducing agent spray mechanism 4 to the heavy metal-containing exhaust gas in the temperature range of 700 to 1000° C. (black arrow in FIG. 1).

The type of reducing agent is not particularly limited, but at least one of liquid ammonia, ammonia water and urea water (especially urea water) can be used. These compounds have a high denitrifying effect on heavy metal-containing exhaust gas in the temperature range of 700 to 1000°C.

Exemplary in this embodiment, when the heavy metal-containing feedstock includes waste electronic equipment and the combustion process is performed in a metal smelting furnace, the NO _x concentration in the heavy metal-containing exhaust gas is 50-400 ppm. The amount of the reducing agent to be added may be 1.0 times the molar amount of NO _x or more. In any case, with the method of the present embodiment, the denitrification process can be performed more effectively even for exhaust gas containing heavy metals, compared to the case where the method is not applied.

Further, as shown in the section of Examples below, when the concentration of copper in the heavy metal-containing exhaust gas generated in the combustion process is 0.07 g/m ³ or more (especially 3.0 g/m ³ or more) , the effect brought about by the present embodiment, that is, the non-catalytic denitrification treatment of the heavy metal-containing exhaust gas can be performed remarkably and effectively. The copper concentration (g/m ³ ) in the heavy metal-containing exhaust gas can be obtained by time), the weight of copper in the solid content collected by the bag filter (not shown) installed on the way to the chimney (not shown) that discharges the exhaust gas to the outside world, and the amount of copper in the exhaust gas containing heavy metals. Obtaining the concentration (g/m ³ ).

Also, as will be shown later in the section of Examples, the higher the copper grade (% by weight, the same shall apply hereinafter) in the solid content of the heavy metal-containing exhaust gas, the lower the denitrification rate. That is, when the copper content in the heavy metal-containing exhaust gas generated in the combustion process is 0.1% or more (especially 4% or more), the effect brought about by the present embodiment, that is, the non-catalytic denitrification treatment for the heavy metal-containing exhaust gas. can be performed remarkably and effectively.

The copper content in the heavy metal-containing exhaust gas may be determined by, for example, an ICP (inductively coupled plasma) emission spectrometer.

Through the above steps, it becomes possible to effectively denitrify exhaust gas containing heavy metals containing copper.

The technical scope of the present invention is not limited to the above-described embodiments, and includes various modifications and improvements within the range where specific effects obtained by the constituent elements of the invention and their combinations can be derived.

For example, if the denitration process is the first denitration process, the second denitration process may be performed in the second boiler 32 by adding alcohol. It should be noted that it is sufficient to separately prepare the reducing agent spray mechanism 4 for the second denitrification step (not shown). At that time, the temperature of the heavy metal-containing exhaust gas is preferably 300 to 700°C, more preferably 400 to 600°C. The alcohol includes at least one of methanol, ethanol, propanol, and aldehydes or carboxylic acids derived therefrom.

EXAMPLES Next, the present invention will be specifically described by showing examples. The invention is not limited to the following examples. Contents not described below are the same as those described in the present embodiment.

<Examples 1 to 4>
In Example 1, the denitrification treatment for the heavy metal-containing flue gas was performed by the apparatus 1 shown in FIG.

Waste electronic equipment was adopted as the raw material containing heavy metals, and LNG was adopted as the hydrocarbon used in the combustion process. Aqueous urea was sprayed toward the heavy metal-containing exhaust gas from a nozzle 44 arranged at a portion of the first boiler section 31 where the heavy metal-containing exhaust gas produced by the combustion process reaches 700 to 1000°C.

Then, the denitrification rate ( _NOx removal rate) was measured. In order to obtain the denitration rate, the _NOx concentration in the heavy metal-containing exhaust gas before and after the denitration process is required.
A portion of the heavy metal-containing flue gas before the denitrification step was sampled from an outlet (not shown) provided near the furnace 2 in the first boiler section 31 .
Then, the NO _x concentration and oxygen concentration of the sampled exhaust gas containing heavy metals were measured using an infrared gas analyzer (model number URA-208, manufactured by Shimadzu Corporation). A non-dispersive infrared absorption method was adopted as the method for measuring _NOx . In addition, the magnetic wind method was adopted for the measurement method of oxygen.
In addition, the quality of copper (Cu) in the sampled exhaust gas containing heavy metals was measured using an ICP emission spectrometer (model number SPS5100, manufactured by SII Nano Technology Co., Ltd., hereinafter the same). The Cu grade was obtained by measuring the solid content sampled by a bag filter (not shown) provided on the way to the chimney using an ICP emission spectrometer.
From the above measurements, the NO _x concentration and oxygen concentration before the denitrification step, the grade of copper (Cu), and the concentration of copper in the heavy metal-containing exhaust gas were obtained.
Regarding the heavy metal-containing exhaust gas after the denitrification process, a part of the exhaust gas finally discharged from the chimney was sampled, and the NO _x concentration and oxygen concentration were determined by the same method as the above method.
Since the _NOx concentration depends on the oxygen concentration, the _NOx concentration is divided by the oxygen concentration, and then the degree of decrease in the _NOx concentration is expressed as a percentage, which is the denitrification rate in this specification.

In Example 1, the copper concentration in the heavy metal-containing exhaust gas was 9.3 g/m ³ (Cu grade was 13.9%), and in Example 2, the copper concentration was 7.3 g/m ³ (Cu grade was 10.9%). 1%), in Example 3, the copper concentration is 7.8 g/m ³ (Cu grade is 9.5%), and in Example 4, the copper concentration is 3.8 g/m ³ (Cu grade is 5.5%). 1%) to obtain the denitrification rate.
In Example 1, the oxygen concentration (% by weight, the same applies hereinafter) of the heavy metal-containing exhaust gas before the denitrification step was 11.5%, the temperature was 888° C., and the amount of urea water added was 0.9 m ³ /h.
In Example 2, the NO _x concentration of the heavy metal-containing exhaust gas before the denitrification process was 1.7 times that of Example 1, the oxygen concentration was 10.5%, the temperature was 873° C., and the amount of urea water added was 0. .6 m ³ /h.
In Example 3, the _NOx concentration of the heavy metal-containing exhaust gas before the denitrification process was 1.5 times that of Example 1, the oxygen concentration was 9.5%, the temperature was 916° C., and the amount of urea water added was 1. .1 m ³ /h.
In Example 4, the _NOx concentration of the heavy metal-containing exhaust gas before the denitrification process was 1.7 times that of Example 1, the oxygen concentration was 10.3%, the temperature was 885°C, and the amount of urea water added was 0. .7 m ³ /h.

<Comparative Examples 1 and 2>
In Comparative Example 1, the same test as in Example 1 was performed except that pulverized coal was added instead of adding LNG in Example 1. The concentration of copper in the heavy metal-containing exhaust gas was 4.5 g/m ³ (Cu grade was 7.9%). In addition, the _NOx concentration of the heavy metal-containing exhaust gas before the denitrification process was 1.4 times that of Example 1, the oxygen concentration was 8.6%, the temperature was 857°C, and the amount of urea water added was 0.3 m ³ . / h.
Similarly, in Comparative Example 2, the same test as in Example 1 was performed except that pulverized coal was added instead of adding LNG in Example 1. The copper concentration in the heavy metal-containing exhaust gas was 3.8 g/m ³ (Cu grade was 6.9%). In addition, the _NOx concentration of the heavy metal-containing exhaust gas before the denitrification process was 1.9 times that of Example 1, the oxygen concentration was 4.1%, the temperature was 936°C, and the amount of urea water added was 1.9 m ³ . / h.

Table 1 below summarizes the test conditions and denitrification rates in Examples 1 to 4 and Comparative Examples 1 and 2.

<Result 1>
In Examples 1 to 4, a good denitrification rate could be achieved regardless of the value of the copper concentration. In other words, in Examples 1 to 4, a denitration rate of 49% or more could be ensured even when the Cu grade was 4% or more.
In Comparative Examples 1 and 2, pulverized coal, which is not a hydrocarbon, not only failed to achieve a good denitration rate, but ammonia leaked from the urea water, resulting in a negative denitration rate. In other words, in Comparative Examples 1 and 2, even if the urea water was sprayed, the nitrogen oxides were not removed and instead increased. The reason for this is that ammonia in urea was oxidized to produce nitrogen oxides.

<Comparative Example 3>
In Comparative Example 3, a plurality of samples with finely changed Cu grades were prepared, and the same test as in Comparative Example 1 was performed.

<Result 2>
FIG. 2 is a plot showing the relationship between copper grade (horizontal axis) and denitrification rate (vertical axis) in Examples 1 to 4 and Comparative Example 3. The results of Comparative Example 3 in this plot also include the results of Comparative Examples 1 and 2 above.

As can be seen from FIG. 2, in Comparative Example 3, in which pulverized coal was used as the fuel, the denitrification rate decreased as the dust Cu grade (and thus the copper concentration in the heavy metal-containing exhaust gas) increased. Under the condition that the denitrification rate was negative, when urea was sprayed, the nitrogen oxides were not removed and instead increased.
On the other hand, in the examples using LNG as the fuel, a high denitrification rate of 49% or more was obtained under any conditions, although the concentration of copper (Cu quality) was high.

DESCRIPTION OF SYMBOLS 1... Apparatus 2... Furnace 21... Raw material inlet 22... Gas addition port 3... Boiler 31... First boiler part 32... Second boiler part 33... Taper 4... Reducing agent spraying mechanism 41... Reducing agent storage part 42... Pump 43... Air intake part 44... Nozzle

Claims (4)

a combustion step of burning a heavy metal-containing raw material while adding LNG, which is a hydrocarbon different from the heavy metal-containing raw material ;
For the heavy metal-containing exhaust gas generated by the combustion process , which contains nitrogen oxides, has a copper concentration of 0.07 g/m ³ or more, and has a temperature of 700 to 1000 ° C. a denitration step in which denitration is performed by adding a reducing agent to the
has
A method for treating exhaust gas containing heavy metals, wherein the raw material containing heavy metals includes a wiring board on which electronic components using heavy metals are mounted . 2. The method for treating heavy metal-containing exhaust gas according to claim 1 , wherein said reducing agent is at least one of liquid ammonia, ammonia water and urea water. 3. The method for treating heavy metal-containing exhaust gas according to claim 1 , wherein the concentration of copper in said heavy metal-containing exhaust gas is 3.0 g/m< ³ > or more. The method for treating heavy metal-containing exhaust gas according to any one of claims 1 to 3 , wherein the combustion step is performed in a metal smelting furnace.

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