KR101491497B1 - Method for Removing Elemental Mercury in the Flue Gas - Google Patents

Abstract

The present invention relates to a method for converting elemental mercury into mercury oxide by an oxidant formed by injecting NaClO into an exhaust gas. According to the present invention, an elemental mercury oxidizing agent is formed in an exhaust gas by injecting an aqueous solution of NaClO into an exhaust gas containing elemental mercury, and the elemental mercury is oxidized to mercury oxide by the oxidizing agent formed; And removing the mercury oxide from the flue-gas. According to the method of the present invention, the elemental mercury in the exhaust gas is converted into mercury oxide and effectively removed. Further, since a strong oxidizing agent is formed by the heat of the exhaust gas itself and moisture in the exhaust gas, nitrogen oxides (NOx) and sulfur oxides (SOx), it is not necessary to input a separate substance other than NaClO. Not only elemental mercury is oxidized to mercury oxide in a gaseous state but also forms mercury oxide at a wide range of temperatures from room temperature (about 20 ° C.) to 500 ° C., and the reaction is limited by the reaction temperature or side effects such as clogging of pipes due to precipitation are accompanied It does not. Furthermore, trace elemental mercury in the exhaust gas can be effectively removed without additional equipment such as a wet scrubber used for elemental mercury removal in the conventional exhaust gas and operation of facilities.

Flue gas, elemental mercury removal, oxidized mercury, sodium hypochlorite (NaClO), nitrogen oxides, sulfur oxides

Description

[0001] The present invention relates to a method for removing elemental mercury from flue gas,

The present invention relates to a method for converting mercury into elemental mercury by converting it into mercury oxide with an oxidant formed by NaClO injection in an exhaust gas .

In general, mercury is present in the form of an alloy (amalgam) with other metals in nature, or in the form of HgS, which is in the form of reaction with sulfur, which are harmless. However, HgS and the like are reduced to elemental mercury by high temperature in various combustion processes (for example, steelmaking process, sintering process, coal-fired power generation, and incineration process).

As the temperature decreases after combustion, elemental mercury reacts with the various chemical species contained in the flue-gas and is released to the atmosphere as elemental mercury, mercury oxide and particulate mercury. The composition ratio of the mercury compounds contained in the exhaust gas after the combustion chamber depends on the composition of the halogen compound and sulfur contained in the raw material and the combustion temperature. Generally, when a raw material contains a large amount of a halogen compound and a sulfur component, the ratio of mercury oxide increases. The flue-gas stream discharged from the combustion process is generally scrubbed, i.e., contacted with water or an aqueous solution to dissolve the contaminants in water. However, among the mercury compounds in the flue gas produced after combustion, elemental mercury is less reactive than mercury oxide and has a very low solubility in water. Therefore, attempts have been made to oxidize and remove elemental mercury by mercury oxide.

Among the methods of converting elemental mercury to mercuric oxide, one that can be easily applied is to inject a chemical substance capable of oxidizing elemental mercury into a high-temperature flue-gas. US Patent Application Publication Nos. 2005/0255022, 2008/0060520 and 2007-40752 disclose a method for removing elemental mercury using hydrogen peroxide water. US Patent Application Publication No. 2003/0161771 discloses a method of oxidizing elemental mercury by injecting Ca (OCl) ₂ , MgBr ₂ , and KI ₃ into a flue gas as a halogen molecule or a thermolabile molecular halogen precursor that generates halogen molecules by thermal decomposition Lt; / RTI >

United States Patent Publication 2005/0147549 and Korea Patent Publication 2005-0004807 and by injecting the ammonium salts such as NH ₄ Cl, NH ₄ Br, NH ₄ I in a high temperature exhaust gas of the combustion chamber rear end, and U.S. Patent Publication 2007/0202020 is a NH ₄ Cl , HCl and Cl ₂ are injected into the exhaust gas to oxidize the elemental mercury. U.S. Patent No. 6,294,139 and Korean Patent No. 367140 disclose a method for oxidizing elemental mercury in a wet scrubber, which reacts NaClO ₂ and HCl contained in a scrubbing solution to generate a substance capable of oxidizing elemental mercury. Also, an aqueous solution of oxi-acids of chlorine used as a process for oxidizing elemental mercury using a wet scrubber can be prepared by reacting HClOx (x = 1,2, < RTI ID = 0.0 > 3,4) and a solution of the salt were used. However, the methods disclosed in the above document must be used with a wet scrubber, or the generated HX (X = Cl, Br, I) and mercury react at 180 ° C or higher, so that when the temperature of the exhaust gas is lowered, It has the disadvantage that not only decrease the reactive HX and unreacted NH ₃ (in particular, the injection for removing NOx in the exhaust gas of the power plant, unreacted NH ₃₎ to stop the pipe by forming a salt with the reaction again. Also, HX and X ₂ (X = Cl, Br, I) injected with a mercury oxidizing agent are caustic gases.

An object of the present invention is to provide a method for removing elemental mercury in an exhaust gas which oxidizes and removes elemental mercury in an exhaust gas by forming a strong elemental mercury oxidizing agent.

Another embodiment of the present invention is to provide a method for removing elemental mercury in an exhaust gas that does not require the addition of a separate substance for forming a wet scrubber and an elemental mercury oxidizer, as in the method for removing elemental mercury in a conventional exhaust gas.

Another embodiment of the present invention is to provide a method for removing elemental mercury in flue-gas using an oxidant formed by heat of water, nitrogen oxides (NOx) and sulfur oxides (SOx) in flue-gas and heat of flue-gas itself.

According to the present invention,

An elemental mercury oxidizing agent in the exhaust gas is formed by injecting NaClO 3 aqueous solution into the exhaust gas containing mercury oxide, and the elemental mercury is oxidized to mercury oxide by the oxidizing agent formed; And

There is provided a method for removing elemental mercury in an exhaust gas, comprising the step of removing the mercury oxide from the exhaust gas.

The elemental mercury in the flue gas is converted into mercury oxide by the method according to one embodiment of the present invention and is effectively removed. Further, since a strong oxidizing agent is formed by the heat of the exhaust gas itself and moisture in the exhaust gas, nitrogen oxides (NOx) and sulfur oxides (SOx), no separate substance other than NaClO is required. In addition, not only elemental mercury is oxidized to mercury oxide in a gaseous state, but mercury oxide is formed at a wide temperature range of room temperature (about 20 ° C) to 500 ° C, and the reaction is limited by the reaction temperature, . Furthermore, trace amounts of elemental mercury in the exhaust gas can be effectively removed without operating any equipment or equipment such as a wet scrubber used for removing elemental mercury in the conventional exhaust gas.

As described above, the present invention has been proposed in order to remove elemental mercury contained in an exhaust gas, which is difficult to remove by a conventional method, without any problems of existing patents. The method according to one embodiment of the present invention includes (Hereinafter referred to as " NaClO aqueous solution ") is injected into an exhaust gas containing elemental mercury to effectively oxidize and remove the elemental mercury by mercury oxide.

The flue gas includes moisture, nitrogen oxides (NOx) and sulfur oxides (SOx), as well as harmful substances of the elemental mercury lamps to be removed in the present invention, and is a high temperature of about 500 ° C. at the maximum. Therefore, in the present invention, the oxidizing agent effective for oxidation of elemental mercury is formed in the exhaust gas by using the characteristics of the exhaust gas, so that the elemental mercury in the exhaust gas is oxidized and removed by mercury oxide. Aqueous NaClO 2 is injected into the flue gas so that an oxidant is formed in the flue gas.

The aqueous NaClO 2 solution injected into the exhaust gas containing elemental mercury is decomposed by the heat of the exhaust gas itself and chemically reacts with moisture, nitrogen oxides and sulfur oxides (especially SO ₂ ) in the exhaust gas to effectively oxidize the elemental mercury in the exhaust gas Form a strong oxidizing agent. Specifically, when an aqueous solution of NaClO is injected into the exhaust gas, moisture contained in the NaClO mist is evaporated by the heat in the exhaust gas, and minute micro-sized NaClO particles are present in the exhaust gas. NaClO particles are very unstable and can be decomposed into a gas phase reaction and / or a gas-solid phase reaction with the exhaust gas components, specifically moisture contained in the exhaust gas, nitrogen oxides and sulfur dioxide. To form ClOH, ClOO, ClO, Cl and Cl ₂ , powerful oxidizing agents capable of oxidizing elemental mercury.

Oxidation of the elemental mercury in the exhaust gas by the oxidant and reaction of water, nitrogen oxide, sulfur dioxide and the like in the aqueous NaClO solution according to the present invention with the oxidizing agent is carried out at a temperature of about room temperature (about 20 ° C) to 500 ° C, It can be effectively conducted at 300 ° C. Such a reaction proceeds with excellent efficiency even at a low temperature such as room temperature and does not involve problems such as clogging of piping due to side reaction. The temperature of the flue gas is at most about 500 ° C, and thus the method for removing elemental mercury in the flue gas according to the embodiment of the present invention can be carried out in the flue gas without special temperature control.

In the method according to the present invention, since the oxidant is formed in a gas-phase or gas-solid-phase reaction, there is no need for a separate facility such as a wet scrubber which is essentially used in the prior art.

It said oxidizing agent is formed by oxidizing the elemental mercury to form a mercury oxide, such as HgO, HgCl _2, and HgOCl. Specifically, the oxidation of elemental mercury by reaction with elemental mercury and oxidizing agent is as follows.

Hg ⁰ + ClOH HgO + OH (1)

Hg ⁰ + ClO - > HgO + Cl (2)

Hg ⁰ + ClO - > HgCl + O (3)

Hg ⁰ + ClO + M? HgOCl + M (M: N ₂ , CO ₂ , O ₂ etc.) (4)

_{HgOCl + O 2 → HgO + ClOO} (5)

Hg⁰ + ClOO - > HgCl + O₂ (6)

Hg ⁰ + ClOO HgO + ClO (7)

Hg ⁰ + Cl + M? HgCl + M (M: N ₂ , CO ₂ , O ₂ etc.) (8)

Hg ⁰ + Cl _{2 -} > HgCl + Cl (9)

HgCl + Cl to HgCl₂ (10)

HgCl + Cl _{2 -} > HgCl ₂ + Cl (11)

Hg ⁰ + Cl ₂ + M? HgCl ₂ (M: N ₂ , CO ₂ , O _2, etc.) (12)

As shown in the following Table 1, the mercury oxide formed by the reaction of the elemental mercury with the strong oxidizing agent formed of NaClO and the components of the exhaust gas is superior to the elemental mercury in the solubility in water. Among the above reaction schemes, Cl ₂ is not harmful due to the formation of trace amounts of Cl ₂ in the method of the present invention in relation to the oxidation of elemental mercury in the conventional exhaust gas, and OClO is not reactive with elemental mercury. However, ClOO formed in the reaction of elemental mercury to oxidize elemental mercury.

 [Table 1]

characteristic  Hg HgO HgCl ₂ Solubility in water
(20 < 0 > C, 1 atm)
(Μl / l) 20 69,000,000 53,000

As can be seen from Table 1, mercury oxide (for example, HgO ₂ , HgCl _2, etc.) is significantly more soluble in water than elemental mercury, and therefore mercury oxide converted into an oxidized form is electrodeposited ), Filter dust collector (wet, dry) and wet scrubber. Further, mercury oxide is adsorbed on the mercury oxide particles, and the removal efficiency of the elemental mercury is further increased.

Hereinafter, the present invention will be described in more detail by way of examples. The following examples are intended to illustrate the invention and are not intended to limit the invention.

≪ Example 1 >

A 0.1 M NaClO aqueous solution was sprayed at a flow rate of 1 in a flue gas (gas flow rate: 1000 L / min) at 100 DEG C containing elemental mercury at 260 mu g / m <

Silver (mercury oxide). Thereafter, the mercury oxide formed by using the dry filter dust collector was removed. Before the removal of mercury oxide by filtration dust collection, the degree of oxidation of mercury oxide was measured. On the other hand, since the oxidized mercury is completely removed by the filter, the degree of oxidation of the elemental mercury is shown in FIG. 1 as the elemental mercury removal efficiency. As can be seen from the graph of FIG. 1, elemental mercury can be removed by oxidizing up to about 90% by weight of the exhaust gas at 100 ° C.

FIG. 1 is a graph showing the removal efficiency of elemental mercury according to the NaOCl flow rate change in Example 1. FIG.

Claims (5)

(NO _x ) and sulfur oxides (SO _x ) contained in the exhaust gas by introducing an aqueous solution of NaClO into the exhaust gas containing elemental mercury, thereby producing ClOH, ClO, ClOO, Cl and < RTI ID = 0.0 &_gt; Cl2 < / RTI > in a gaseous or gas-solid reaction; Oxidizing the elemental mercury to mercury oxide by the elemental mercury oxidizing agent; And And removing the mercury oxide from the flue gas. The method of claim 1, wherein the exhaust gas has a temperature ranging from room temperature to 500 ° C. delete The method of claim 1, wherein the oxidized mercury is removed method elemental mercury in the exhaust gas, characterized in that the at least one kinds selected from the group consisting of HgO, HgCl _2, and HgOCl. The method of claim 1, wherein the mercury oxide is removed by an electrostatic precipitator, a filter or a wet scrubber.

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