JPS60232235A - Treatment of exhaust gas - Google Patents

Abstract

PURPOSE:To make exhaust gas causing public nuisance innoxious by efficiently collecting and recovering a low b.p. heavy metal such as Hg, by cooling exhaust has generated by treating low b.p. heavy metal-containing waste with a direct current supply type melting treatment furnace in a moisture-containing state. CONSTITUTION:Dust 11 containing low b.p. heavy metals collected at the time of the incineration of urban garbage is moistened by a humidifier 23 while the moistended dust 11 receives melting treatment in a direct current supply type melting treatment furnace 12. The generated exhaust gas 13 is forcibly cooled by a cooler 14 and a mixture 16 of condensed Hg and soot is guided to a mercury refining press 17 to extract and recover metal Hg. The press residue 18 is returned to the melting treatment furnace 12. The exhaust gas 15 issued from the cooler 14 is guided to an adsorbing tower 20 and Hg is adsorbed and removed by Hg adsorbing activated carbon or a chelate resin to discharge the exhaust gas to the open air in a state generating no public nuisance. When moisture is imparted to dust in the humidifier 23, moisture in the exhaust gas becomes high and the dew point of said gas is raised and the precipitation effect of Hg in the cooler 14 increases.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for treating exhaust gas.

In particular, when processing waste such as low boiling point heavy metals, such as dust collected at municipal waste incineration facilities containing mercury, and wastewater sludge from washing smoke, in a direct current melting furnace,
This relates to an exhaust gas treatment method that captures mercury from the generated exhaust gas and makes it pollution-free.

[Prior Art] Various wastes such as municipal garbage, sewage sludge, and treated wastewater discharged from mines and factories are incinerated in incinerators, and the resulting incinerated ash has conventionally been disposed of in landfills. However, due to the difficulty of securing land for a landfill -2- and the risk that the harmful heavy metals contained in the landfill may leach into the ground and contaminate the area around the landfill site, causing secondary pollution, for example, Methods have been proposed in which base metals are melted and solidified using an electric arc furnace or a direct current melting furnace. When waste is incinerated in the above-mentioned incinerator, the generated dust pollutes the atmosphere, so it is captured by various types of dust collectors such as wet dust collectors, electric dust collectors, bag filters, etc.
The dust captured by the electrostatic precipitator contains Na0, KC,
Water-soluble salts such as Qa Q, Si 02, ΔFun2
0B, poorly soluble oxides in water such as Fe2Og, and A
Heavy metals such as sXCr, Zn1Cd, pl], and 11g are contained, and these heavy metals are generally in water-soluble forms such as halides or sulfates. Therefore, if this dust 1 is buried in a landfill as it is, there is a risk that heavy metals will be leached into the ground, so the same method as incineration ash is used, in which it is melted and solidified. The present inventors have conducted various studies on the melting treatment of dust generated during the incineration of waste in an incinerator, and found that when dust is melted in a direct energized slag furnace, the slag generated is in the upper layer. They discovered that the slag and the lower layer have different compositions, and that by extracting the slag separately, it is possible to use each slag effectively according to its characteristics, while also rendering heavy metals harmless. Showa 56-128637>.

FIG. 5 is a schematic cross-sectional view showing an example of the above-mentioned directly energized melting furnace for treating dust generated from the incinerator. That is, the furnace body is hermetically constructed of SiC2A, ZOs-Zro2 system refractory material 1 with a high content of 7rQ2, and includes an inlet 2 for dust generated during waste incineration and an exhaust port 2 for gas generated. A pipe 3, a horizontally retractable electrode 5.5, an upper slag discharge port 6, a lower slag discharge lower, etc. are provided. Then, an alternating current is passed through the voltage regulating power source 1 to the lance 8 to generate Joule heat in the melting initiator, and the electrode 5.5 functions to maintain the melted state by internal heating.

Typical examples of the material include molybdenum electrodes, and other examples include graphite, iron, tin oxide, and tungsten electrodes.

In order to treat dust generated in a waste incinerator using such a direct current melting furnace, the dust is introduced into the furnace main body through the guest inlet 2 and into the molten pool formed by the melting initiator. This causes a slag 9 to be formed. The temperature of the slag 9 in this case is in the range of about 1200 to 1350°C, although it depends on the grade of the dust introduced. At that time, an electrode 5.5 attached to the furnace body is immersed in the slag in advance and an alternating current is passed through it, and the molten state is maintained by the Joule heat generated by using this as a conductor. The current at this point is approximately 700 to 1200K, depending on the properties of the Das I- applied.
W/l (workpiece) range. Note that 10 is a covering layer of unmelted dust which is successively introduced.

Next, the upper layer of the generated slag 9 is discharged from the discharge port 6 which is located at a higher position of the two discharge ports provided in the furnace body, and is discharged into the pit 1 filled with water (not shown). released into the

As a result, the main components, alkali metal salts such as NaC-5- and KC-5, are eluted into water. In addition, slag 9 CaOz A l 20 s, S j
The lower layer, which mainly contains components that are poorly soluble in water such as O2 and Fe20a, is installed at the lower position of the two exhaust ports provided in the furnace body (the slag is discharged from the lower part of the first outlet, making it harmless). It is transported and solidified together with the heavy metals.

By the way, waste (captured dust, smoke washing factory drainage sludge, etc.) usually contains 7N, C at a concentration of several tens to several thousand ppm.
d, mercury (hereinafter referred to as 1-1 ci), and other low-boiling point heavy metals. At the beginning of supply, 14. An unmolten covering layer 10 is formed on the molten slag 9 heated to 00 to 1500°C. and,
The thickness of the covering layer 10 is kept at about 300,000 m, and the temperature from the interface with the slag 9 to the surface is 1200°C.
A temperature gradient of ~100°C is generated, making it possible to suppress the temperature of the exhaust gas generated from the furnace at around 100°C.

Therefore, some of the low boiling point heavy metals contained in the waste, such as Zn 1Cd, 1-1 (), are partially turned into steam and are discharged into the atmosphere from the exhaust pipe 3 along with the 11 gases. % migrates into the slag 9.These include Zn%Cd%
The boiling point of low-boiling heavy metals such as 1" 0 under normal pressure,
Also, the transfer rate to the exhaust gas and slag 9 side (when the surface temperature of the J-burring layer is controlled to about 100° C.) is approximately as shown in the following table.

As is clear from this table, in the treatment using a direct current melting furnace, 7n and Cd are captured in the covering layer 10 (J) in the parts below their respective boiling points, and the molten slag 9
Although the proportion of l-1 g transferred to the inside is high at 70 to 95%, even under wet conditions where the exhaust gas temperature is about 100° C. on average, the vapor pressure is high and as much as 95% of l-1 g transfers to the exhaust gas side.

-7- [Problems to be Solved by the Invention] In the treatment of waste containing low-811-point heavy metals that is sent to the direct current melting furnace, the exhaust gas generated from the furnace contains low-boiling-point heavy metals. It contains HO vapor, especially HO vapor, which pollutes the atmosphere and causes serious damage to the living environment, so it is necessary to capture it by some means and make it pollution-free. It is also known that the purpose of removing only HO from waste is to use a paddle dryer to heat the waste using steam as a heat source, and to expel and capture Hg as steam. , which requires a large amount of heat source and is not necessarily an efficient method.

E Means for Solving the Problems The present invention aims to solve the above-mentioned problems in the treatment of low-boiling point heavy metal-containing wastes using a direct energized melting furnace. This method traps and precipitates heavy metals, in particular, 10 vapor, and recovers them in a non-polluting manner.It also treats the waste in a moist state, making it easier to trap low-boiling point heavy metals. By the method of the present invention, the waste containing low boiling point heavy metals to be fed into the direct energization type melting furnace is directly humidified or mixed with other high moisture content waste to increase the moisture content of the untreated material. It is possible to increase the moisture content in the exhaust gas generated from the furnace, raising the dew point and promoting the condensation effect within the cooler.

In addition, by mixing waste with a high Hg concentration and increasing the Hg concentration in the exhaust gas, it is possible to increase the recovery rate of H(+ in the cooler. In other words, the present invention Processing of waste gas generated from a direct energized melting furnace for waste containing low boiling point heavy metals. The gist is the method.

[Operation: When waste containing low-boiling point heavy metals is processed in a direct current melting furnace, the generated exhaust gas is cooled to precipitate small vaporized metals that come out along with it, and capture and recover them. and remove it. In particular, if the waste is put into a processing furnace in a moist state, heavy metals in the form of vapor can be more easily entrained, allowing efficient capture and recovery.

[Example] Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a flowchart when dust containing low boiling point heavy metals collected during municipal waste incineration is treated alone.

Dust 11 is directly energized in a conventional melting furnace 12.J:
Melt treatment. The direct current type melting furnace 12 has a structure as shown in FIG. 5, for example, and slag 9 and exhaust gas 13 are generated during the melting process. dust 1
Among the low-boiling heavy metals such as Zn, Cd, and 1-IQ contained in 1, 7n and cd account for 70% to 95% in slag 9.
Approximately 95% of H(I) is discharged out of the furnace along with the exhaust gas 13. For example, in the case of a direct current melting furnace with a processing capacity of 6 tons/day, the amount of exhaust gas 13 is 12
．． 5N/min, discharge temperature 100℃,
0mo/nfN. The exhaust gas 13 is led by piping to a cooler 14 where brine brings the outlet temperature to about 10
Forced cooling down to ℃.

= 10 - The saturation HQ depth in the exhaust gas 15 after cooling is 61110/n
fN, and about 110 m (1/mN) of condensed HO and soot 16 are generated in the cooler 14. The press residue 18 contains 20 to 30% Hg, so it is directly returned to the energized melting furnace 12 and treated together with the dust 11. The exhaust gas 15 exiting the cooler 14 is led to the adsorption tower 20, where the Hg)IA polishing is reduced to 0.1111(]/rrrN or less, and the exhaust gas 15 is made non-polluting and released into the atmosphere.

Examples of the H(+ adsorbent filled in the adsorption tower 20 include activated carbon for Hq adsorption, chelate resin for H(l adsorption, etc.). 21 is led to a normal water treatment device 22 for purification, and then water is discharged.

FIG. 2 shows another example of the present invention, and is a flowchart in which dust containing low-boiling heavy metals collected during municipal waste incineration is pre-humidified and melted. In this case, a humidifier 23 is installed in front of the direct current type melting furnace in the embodiment shown in FIG. As a humidifier 23, as a result of mixing live steam or atomizing water in an atomizer (spray) to give moisture to the Begitast being processed, the moisture content in the exhaust gas increases as described above. This has the advantage of increasing the dew point and increasing the precipitation effect of l-1a within the cooler 14.

FIG. 3 shows yet another example of the invention. That is, the wastewater sludge 11 generated when cleaning smoke during municipal waste incineration is added to the dust containing low-boiling point heavy metals collected during municipal waste incineration.
A is added and melted according to the flow shown in Figure 1. Unlike the process shown in Figure 2, the process is carried out in the presence of moisture contained in the untreated material itself, without using a humidifier. , the processing effect itself is no different from the case shown in FIG. Washing smoke wastewater sludge contains 11 g of about 500 () it'a 10, which is contained in the collected dust, and when it is mixed with dust, it is more effective than when it is treated with dust alone. The Hc+1 degree in the exhaust gas discharged from the direct current melting furnace is about 17 times higher.

-12= Therefore, there is an advantage that the recovery rate of 119 in the cooler 14 becomes high.

FIG. 4 shows yet another example of the present invention. That is, wastewater sludge generated when cleaning smoke during municipal waste incineration is added to dust containing low-boiling heavy metals collected during municipal waste incineration, and the mixture is melted according to the flow shown in Figure 2.
Unlike the method shown in FIG. 3, this method uses a humidifier 23 to add water to the water contained in the wastewater sludge as necessary, and the treatment effect itself is not much different from that shown in FIG.

[Effects of the present invention] As described above, the present invention provides forcible cooling of the exhaust gas generated when the collected dust during municipal waste incineration and/or smoke washing wastewater sludge is processed in a direct energized melting furnace. This method efficiently captures and recovers low-boiling point heavy metals, makes exhaust gas pollution-free, and prevents environmental pollution, and has great industrial applicability.

[Brief explanation of drawings]

1 to 4 are flowcharts of an example of the present invention, and FIG. 5 is a schematic cross-sectional view of a direct current type melting I41 processing furnace. 1... Fireproof material 2... Inlet 3... Exhaust pipe 5... Electrode 6.7... Slag discharge port 8... Voltage adjustment power supply 1 to lance 9... Slag DESCRIPTION OF SYMBOLS 10... Covering layer 11... Dust 12... Directly energized melting furnace 13... Exhaust gas 14... Cooler 15... Exhaust gas 16... Condensed Hg and soot mixture 17... Soot processing press 18...Press residue 19...Metal HO20...Adsorption tower 21...Condensed water 22...Water treatment equipment 23...Humidifier agent Patent attorney Tsutomu Setate and 1 other person -14-

Claims (1)

[Scope of Claims] 1. Waste containing low-boiling point heavy metals is directly charged into an electrified melting furnace in a moist state, and the generated exhaust gas is cooled to recover the precipitated low-boiling point heavy metals and render them harmless. A method for treating exhaust gas generated from a directly energized melting furnace for waste containing low boiling point heavy metals, characterized by: 2. The exhaust gas treatment method according to claims 1 and 2, wherein the precipitated low-boiling heavy metals are adsorbed on activated carbon or recovered using an adsorption chelate resin. 3. The method for treating exhaust gas according to any one of claims 1 to 3, wherein the precipitated low-boiling heavy metal is mercury. 4. A patent claim for obtaining a moist state by passing waste containing low boiling point heavy metals through a humidifier or mixing it with high water content waste before feeding it into a direct energized melting furnace. The exhaust gas treatment method according to any one of items 1 to 4. 5. The exhaust gas treatment method according to claim 5, wherein the soot residue deposited in the cooler during exhaust gas cooling is directly re-injected into the energized melting furnace together with waste containing low boiling point heavy metals.