JPS62140629A - Method for removing mercury contained in combustion exhaust gas - Google Patents

Abstract

PURPOSE:To increase removal efficiency of mercury and mercuric compd. even for exhaust gas contg. high-concn. mercury by spraying aq. slurry or an aq. soln. of a reactant into exhaust gas and furthermore injecting powder of the reactant and thereafter collecting a mercuric reaction product by a bag filter. CONSTITUTION:1-15wt% slurry of sulfur, FeS or the like regulated to 10-300 mesh, or 1-15wt% aq. soln. of sulfur sol and dithiocarbamic acid or the like is used as a reactant and sprayed to combustion exhaust gas at 120-600 deg.C contg. Hg and HgCl2, etc., sent from a combustion exhaust gas generating source 1 in a reaction tower 2 to bring it into gas-liquid contact with exhaust gas and also to evaporate water content. Furthermore the reactant of powder of sulfur and FeS or the like is injected from a feed installation 9 of the reactant and powder of both the reactant fixed with mercury and the nonreacted reacted and combustion soot and dust are collected on the following bag filter 3 and shaken down by backwash operation to discharge these to the outside of the system.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention removes 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 how to.

[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, sodium sulfide, sodium thiosulfate, etc. as a mercury absorption liquid, and gas is removed by gas-liquid contact. It moves the mercury inside to the source side.

(2) Dry removal method: This method supports activated carbon or an inorganic carrier with sulfur or sulfur compounds, metals that form amalgams with mercury, or halides of these metals, etc. It captures and removes mercury by bringing it into contact with exhaust gas. 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. The conventional dry removal method still 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 an allowable value, and to provide storage equipment.

(3) Most of the components of the adsorption/reactant are carrier components,
It is economically disadvantageous to use these without recirculating them, and even in the case of recycling, equipment for desorbing and recovering mercury is required.

The present invention aims to provide a method for removing mercury and mercury compounds from exhaust gas that overcomes the drawbacks of conventional removal methods.

[Means for solving problems]

In the present invention, in order to remove mercury and mercury compounds from exhaust gas as chemically stable mercury sulfide powder, (1) an effective reactant is sprayed into a reaction tower in the form of an aqueous solution or slurry;

(2) At the rear of the reaction tower, a reactant is further sprayed in powder form.

(3) The unreacted reactant is retained on the bag filter, and the mercury removal efficiency is further increased by solid-gas reaction on the bag filter.

(4) Mercury sulfide powder in the exhaust gas generated by the reaction is efficiently collected and removed by a bag filter.

It is characterized by this.

That is, the present invention installs a reaction tower in the flue gas flue,
1 to 15 wt of sulfur or a water-insoluble sulfur compound adjusted to 10 to 300 mesh is added to the exhaust gas containing mercury and mercury compounds at 120 to 600°C passing through this reaction tower.
Mercury and mercury compounds are removed from the exhaust gas by spraying a 1-15 wt% aqueous solution of sulfur sol or a water-soluble sulfur compound, and then the sulfur is added to the downstream combustion exhaust gas. Alternatively, a water-insoluble sulfur compound is injected as a powder, and a large filtration device with a surface temperature of 120°C or higher is installed on the downstream side to discharge mercury from the exhaust gas out of the system together with combustion dust. This is a method to remove mercury from combustion exhaust gas.

[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, S, FeS, ZnF2゜CaS, CuS, sulfur sol, thiourea, thiosulfate, and dithiocarbamic acid have a strong affinity with mercury and mercury compounds, and by reaction (mainly producing mercury sulfide) or adsorption, Since mercury and mercury compounds can be fixed in a powder form that can be collected by bag filters, collection by bag filters becomes easy.

In addition, since the unreacted reactant forms a cake layer on the bag filter, when the exhaust gas passes through this layer, the solid-gas reaction with mercury and mercury compounds further progresses, increasing the mercury removal efficiency.

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 (usually acidic). Further, from the viewpoint of heat resistance of the bag filter, the temperature is preferably 600° C. or lower.

FeS, which is sulfur or a water-insoluble sulfur compound.

ZnS, CaS, and Cue are prepared as a 1-15 wt% water slurry, and sulfur sol or water-soluble sulfur compounds such as thiourea, thiosulfate, and dithiocarpanic acid are prepared as a 1-15 wt% water slurry.
Used as a t% aqueous solution.

For the above reasons, the concentration of the reactant in the slurry and aqueous solution is limited, so if the mercury concentration in the exhaust gas is high,
As a two-stage process, a powdered reactant is injected downstream from the spray of a slurry or aqueous reactant to enhance the mercury removal effect.

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

(i) Mercury (Hg) S + Hg 4 HgS (Sulfide) As mentioned above, Hg is fixed in the powder by being adsorbed or absorbed by mercury sulfide (HgS) or a sulfur compound.

(11) Mercury compounds (for example, in HgO) S + Hg
O4HgS + y20g102 FeS + HgO- + HgS + FeOxZnS
+HgO-+ HgS-)-Zn0CaE3-)
HgO4HgS + C! a.

CuS+'Hg0-+HgS+Cu0(iii)
Mercury compounds (e.g. Hgct) S-1-Hg
C/4 → HgS+C! 4FeS + HgCl4
−+ HgB + FeOxZnS + HgC4−*
HgS + ZnC4C! as + HgCII
→ HgS + Ca0QOu8 + HgCl2
→ HgS + CuC/4 The reaction between the slurry of the various powders and mercury and mercury compounds is mainly gas-liquid absorption and formation reaction, and after the water in the slurry evaporates, a solid-gas reaction occurs. Therefore, in order to promote the reaction, K needs to increase the surface area of the powder. In order to increase this surface area, it is necessary to make the powder particles as small as possible, so the size was set to 10 to 300 meshes. In the present invention, since it is necessary to spray the powder slurry into the reaction tower and carry it in the air stream, 200 to 300 mesh is actually suitable. The slurry concentration is preferably 1 to 15 wt%.

Further, the reaction with the sulfur sol or water-soluble sulfur compound used in the present invention is as follows.

6v) Mercury (Eg) S (sol) + Hg-+HgS (sulfide) (horse N
), as + Hg → (H surprise N) IC! S...Hg(
adsorption or absorption) (NHa)zstos + Hg −
+ (NH4)2EJzO1-=Hg (same as above) (■
)Mercury compound (e.g. HgC1,)S(zo#)+Hg
Ck −+ HgS + 04 (HzN) gc8
+ HgCk → (JN)z (Ji +++ Hg+
Cl4(NH4)zszos + HgC14→(NH
4) zB203-1hL + C1z The reaction between the sulfur sol or water-soluble sulfur compound and mercury or a mercury compound involves gas-liquid absorption, and after water evaporates in a liquid-liquid reaction, a solid-gas reaction occurs. The sulfur sol or water-soluble sulfur compound is preferably used as an aqueous solution with a concentration of 1 to 15 wt%.

Normally, the dew point of combustion exhaust gas is 100 to 120 t: or higher, and if it is lower than that, condensation will occur and the reactant will be mowed down, causing the reactant to stick or stick and the nozzle to become clogged.
Operation at 120°C or higher 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.

The upper limit of the temperature at which the reactant can be used is 400°C, but in the present invention, the reactant is sprayed as a slurry or an aqueous solution.
Since the exhaust gas temperature decreases, the upper limit is 600°C.

From this, the reaction temperature was set at 120 to 600°C. The temperature is preferably 300 to 400°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 a reaction tower, 3 is a bag filter, 4 is an exhaust fan, 5 is a chimney, 6 7 is a supply pump, 8 is compressed air for spraying, 9 is reactant powder supply equipment, 1
゜ is collected ash.

The flue gas containing mercury and mercury compounds generated in the flue gas generation source 1 is first passed to the reaction tower 2 . In this reaction tower 2, an aqueous reactant solution or slurry sent from a reactant aqueous solution or slurry tank 6 is sprayed by a supply pump 7 to achieve anti-contact with the combustion exhaust gas and evaporate the aqueous solution or slurry. is being carried out. When the flue gas and the aqueous solution or slurry come into contact, mercury and mercury compounds in the flue gas react with the mercury reactant and migrate to the side of the reactant. At the same time, evaporation of water progresses, and the reactant remains as a powder), which flows along with the flow of combustion exhaust gas to the downstream bag filter 3 with mercury contained and fixed therein. Since the reactant which has become a powder after water has evaporated still has an unreacted portion, it further reacts with mercury and mercury compounds before leaving the reaction tower 2 and reaching the bag filter 3.

Further, a powdered reactant is injected from the reactant supply equipment 9 in front of the bag filter. The reactant with fixed mercury, unreacted reactant, and combustion dust are removed from the bag filter 3 located in the downstream.
It is collected on the top, brushed off by backwashing, and discharged from the system.

The unreacted reactants together form a cake layer on the bag filter, and when the exhaust gas passes through that layer, an additional layer of cake is formed on the bag filter.
A solid-gas reaction between mercury and mercury compounds and the reactant progresses, increasing mercury removal efficiency.

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

〔Effect of the invention〕

(1) In the reaction tower, an aqueous solution or slurry of a mercury reactant is sprayed into the combustion exhaust gas, the reactant is reacted with mercury and mercury compounds, mercury is fixed from the gas side to the powder side, and then combusted. Removes mercury and mercury compounds from flue gas.

(2) When dealing with exhaust gas containing a large amount of soluble mercury compounds (for example, Hg0t), K is used as a slurry or aqueous solution of the adsorbent/reactant, since the absorption of mercury compounds is significant.
Compared to the case where the adsorption/reaction agent is supplied as a powder, the amount of reaction between the adsorption/reaction agent and the mercury compound increases.

(3) Since the powder reactant is further injected at the rear to promote the reaction, the effect on gas containing high concentration mercury is improved.

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

(5) The mercury fixed in the powder is collected together with the combustion dust by a Bug 74 Luther.

(6) 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 solidification treatment effective.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the flow of one embodiment of the present invention. Sub-agent: 1) Akira Sub-agent Ryo Hagi Hara - Sub-agent Atsuo Yasunishi

Claims (1)

[Claims] A reaction tower is installed in the flue gas flue, and sulfur or water-insoluble sulfur compounds adjusted to 10 to 300 mesh are added to the flue gas containing mercury and mercury compounds at 120 to 600°C passing through the reaction tower. 15 wt% water slurry, or sulfur sol, or one of water-soluble sulfur compounds
Mercury and mercury compounds are removed from the exhaust gas by spraying a ~15 wt% aqueous solution, and the above-mentioned sulfur or water-insoluble sulfur compound is injected as a powder into the downstream combustion exhaust gas, and the surface is heated to 120°C or higher on the downstream side. A method for removing mercury from combustion exhaust gas, which is characterized by installing a filtration type dust collector with a temperature controlled temperature and discharging mercury from the exhaust gas to the outside of the system together with combustion dust.