JPS62136232A - Removal of hg in combustion exhaust gas - Google Patents

Abstract

PURPOSE:To efficiently remove Hg, by a method wherein S or a S-compound is injected in exhaust gas in a powdery form and reacted with Hg or Hg- compound in the exhaust gas to form HgS which is, in turn, removed by a filter type dust collector of which the surface temp. is 120 deg.C or more. CONSTITUTION:S or a S-compound adjusted to 10-300 mesh is injected in the exhaust gas generated from an exhaust gas generating source 1 in a powdery form from the powder supply nozzle provided to a duct 2 at 120-400 deg.C and reacted with Hg or Hg-command in the exhaust gas to form stable HgS which is, in turn, collected along with the soot in the exhaust by a bag filter 3 of which the surface temp. is 120 deg.C or more to be discharged out of the system as collection ash 11 while the gas from which Hg was removed is exhausted from a chimney 5 through a ventilation fan 4.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to the removal of mercury and mercury compounds from the exhaust gas of municipal waste incinerators, industrial waste incinerators, human waste/sewage sludge incinerators, and exhaust gas from other combustion devices. Regarding the law.

[Conventional technology]

Conventionally, there are wet removal methods and dry removal methods as methods for removing mercury and mercury compounds from combustion exhaust gas, and summaries of these methods are shown below.

(1) Wet removal method: This method uses an aqueous solution of potassium permanganate-sulfuric acid mixture, hypochlorous acid-salt solution, thiourea, di-sulfide, sodium thiosulfate, etc. as a mercury absorption liquid, and uses gas-liquid contact. The mercury in the gas is transferred to the ventral side.

(2) Dry removal method: This method uses activated carbon, sulfur or sulfur compounds on an inorganic carrier, mercury and gold vat to form an amalgam.
A or its metal halide is supported, and these adsorbing/reacting agents are brought into contact with mercury-containing exhaust gas to trap and remove mercury. These adsorbing/reacting agents are usually housed and used in a fixed bed or moving bed type reactor.

[Problem that the invention seeks to solve]

Conventional wet removal methods require treatment of mercury-containing wastewater. Further, the conventional dry removal method has the following problems.

(1) In order to increase the contact area with the gas, the device inevitably becomes larger.

(2) It is necessary to replace the adsorbent/reactant before the mercury concentration at the reactor outlet exceeds the allowable value, and to provide equipment for this purpose.

(3) Most of the components of the adsorption/reactant are carrier components;
If these are used without being recycled, it is economically disadvantageous, and even if they are recycled, equipment for desorbing and recovering mercury is required.

The present invention aims to provide a method for dry removal of mercury and mercury compounds in exhaust gas without the drawbacks of conventional dry removal methods.

[Means for solving problems]

In order to remove mercury and mercury compounds from exhaust gas as a chemically stable mercury sulfide powder, the present invention: (1) Injects an effective reactant directly into the flue.

(2) retaining unreacted reactants on a bag filter;
The solid-gas reaction on the bag filter further increases mercury removal efficiency.

(3) The mercury sulfide powder in the exhaust gas generated by the solid-gas reaction is efficiently collected and removed by the bag filter.

It is characterized by this.

That is, the present invention injects sulfur or sulfur compounds in powder form adjusted to 10 to 300 mesh into the flue of combustion exhaust gas at a temperature of 120 to 400°C, and converts mercury and mercury compounds in the exhaust gas into a chemically stable form. Mercury sulfide powder is removed from the exhaust gas together with combustion dust by installing a filtration type dust collector whose surface is maintained at a temperature of 120°C or higher on the downstream side of the injection. This is a method for removing mercury compounds.

[Effect]

Since most of the mercury and mercury compounds in the combustion exhaust gas exist in a gaseous state, it is difficult to collect them with a bag filter. However, B, Fe8. ZnEl, 0aEl, Cu
Powders like No. 8 have a strong affinity with mercury and mercury compounds, and mercury and mercury compounds are fixed on the powder side through reaction (generating mercury sulfide) or adsorption, making it easy to collect with bag filters. become.

In addition, unreacted reactants form a cake layer on the bag filter, and when the exhaust gas passes through this layer, the solid-gas reaction between mercury and mercury compounds and the reactant further progresses, reducing the mercury removal efficiency. It increases.

The reaction between sulfur or a sulfur compound used in the present invention and mercury or a mercury compound is as follows.

lit Mercury (Hg) ・B1H (5-HgS (sulfide), -Fee-)-
Hg −+ FeB−...Hg (adsorption or absorption) or Hge−)−IPaOx (oxide) II ZnS
+Hg → ZnB・-Hg or Hg8+ZnO -Oaday+Bg-1→0aS-Hg -Cue 10Hg-0uS = Hg Also, 1 phrase Mi 3.8ya. . 8 As mentioned above, KHg is adsorbed or absorbed by mercury sulfide (Hl) or a sulfur compound and is fixed in the powder.

(iil mercury compound (for example, in 111g0) Z
n8+HgO4Hgday+Zn0 OaS+HgO→1! gB 10aO Ou8+Hgo 4 HgEI + 0uOat Mercury compound (e.g., Hg0j, Te) day +Hg0
4. →HgS+04 IFe8-)-Ego/, →Hg8+I'eO/*Z
nB+T1gO114Hg8+Zn04Oaday 10Hg0
1. →HgB10aO1zOuB+T1gO1ffi
4 Hg8+0uOJF1 The reaction between the various powders (reactants) and mercury and mercury compounds is a solid-gas phase reaction (solid - reactant, gas phase - mercury and mercury compound), so in order to accelerate the reaction, It is necessary to increase the surface area of the solid or reactant. In order to increase this surface area, it is necessary to make the particles of the reactant as small as possible, and the mesh size is 10 to 300.

Further, in the method of the present invention, the reactant is injected into the exhaust gas,
In reality, it is 200~
300 mesh is preferred.

The dew point of normal combustion exhaust gas is 100 to 120℃ or higher,
If the temperature is lower than that, condensation will occur and the reactant will become wet.
1. This may cause the reactant to stick/adhere and the nozzle to become clogged.
Operation at temperatures above 20°C is required.

Furthermore, since the reactant used undergoes thermal decomposition at high temperatures, it is necessary to operate at a temperature below the thermal decomposition temperature, and the upper limit is 400°C.

From this, the reaction temperature was set at 120 to 400°C. The temperature is preferably 150 to 250°C.

One embodiment of the present invention will be described in detail with reference to FIG.

In Fig. 1, 1 is a combustion exhaust gas generation source (e.g. municipal waste incinerator, industrial waste incinerator, human waste/sewage sludge incinerator), 2 is an exhaust gas duct, 3 is a bag filter, 4 is an exhaust fan, 5
1 is a chimney, 6 is a powder supply nozzle, 7 is a powder injection duct constriction section, 8 is a powder silo, 9 is a powder quantitative feeder, 10 is a powder transport air fan, and 11 is a collected ash.

A mercury reaction occurs in the combustion exhaust gas containing mercury and mercury compounds generated in the combustion exhaust gas generation source 1 by the powder supply nozzle 6 at the powder injection duct throttle section 7 provided in the exhaust gas duct 2 in front of the gas flow of the bag filter 3. Inject the agent. The mercury reactant rapidly reacts with mercury and mercury compounds in the exhaust gas, fixing mercury from the gas side to the powder side. The mercury-fixed reactant, unreacted reactant, and combustion dust are collected on the bag filter 5 located downstream, and are brushed off by a backwashing operation and discharged to the outside of the system. The unreacted reactants together form a cake layer on the bag filter, and when the exhaust gas passes through this layer, the solid-gas reaction between mercury and mercury compounds and the reactant proceeds, increasing the mercury removal efficiency. It increases.

The combustion exhaust gas from which mercury and mercury compounds have been removed is discharged through the chimney 5 via the exhaust fan 4.

0.1 to 10 f/N- of reactant (8,
F'eS, Zn8. Up to 90% of mercury can be removed by spraying OaS (!u days) and collecting it on a bag filter. Note that the reaction temperature on the bag filter needs to be 120° C. or higher from the viewpoint of preventing low-temperature corrosion of exhaust gas (having acidity). ``Furthermore, in view of the heat resistance of the bag filter, the temperature is preferably 300° C. or lower.

Example 1 Garbage incinerator exhaust gas at 200-250°C (mercury concentration α3
ZnS with a particle size of 200 to 300 mesh
Powder 11 to 10 f/N- was injected, and fine particles were collected in a bag filter made of glass fiber (temperature: 230°C) placed downstream. As a result, the results shown in FIG. 2 were obtained.

When conducted using Fee, CaS, and OuS powders, results similar to those described above were obtained.

Example 2 Sulfur powder with a particle size of 200 to 300 mesh was added as an adsorption/reactant to exhaust gas containing mercury of a, smy/m-.
I injected f7Hms. As a result, a mercury removal rate of 50% was obtained.

〔Effect of the invention〕

(1) Mercury reactants (S, Fee, Z
nS.

Ca8,0uEl) is injected to fix mercury from the gas side to the powder side and remove mercury and mercury compounds from the combustion exhaust gas.

(2) Since the reaction between unreacted reactants and mercury and mercury compounds is promoted on the bag filter, mercury removal efficiency is increased.

(3) Mercury fixed in powder is collected in a bag filter along with combustion dust.

(4) Since the mercury in the collected ash is fixed in the form of mercury sulfide, there is almost no elution from the ash, making cement or asphalt assimilation treatment effective.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the flow of one embodiment of the present invention, and FIG.
The figure is a graph showing the results of an example of the present invention. 1 is the combustion exhaust gas generation source, 2 is the exhaust gas duct, 3 is the bag filter, 6 is the powder supply nozzle, 7 is the throttle part of the powder injection duct, and 9 is the agent for the powder metering feeder. Ryo Hagiwara − Sub-agent Atsuo Anzai Figure 1

Claims (1)

[Claims] (1) In the flue of combustion exhaust gas at 120-140℃
Sulfur or a sulfur compound adjusted to 300 mesh is injected in powder form to convert the mercury and mercury compounds in the exhaust gas into chemically stable mercury sulfide powder, and the surface is 12 mm on the downstream side of the injection.
A method for removing mercury and mercury compounds from combustion exhaust gas, which comprises removing mercury and mercury compounds from the exhaust gas together with combustion dust by installing a filtration type dust collector maintained at a temperature of 0° C. or higher.