JP5517460B2 - Denitration equipment - Google Patents

Description

  The present invention relates to a denitration apparatus, and more particularly to a denitration apparatus that reduces nitrogen oxides in exhaust gas and oxidizes mercury in the exhaust gas.

  Exhaust gas generated by burning coal, oil, etc. in boilers contains harmful substances such as nitrogen oxides and trace amounts of mercury. It is known to do.

  For example, Patent Document 1 discloses a denitration apparatus that injects ammonia into a flue through which exhaust gas discharged from a boiler flows, introduces exhaust gas containing ammonia into a catalyst layer, and reduces nitrogen oxides in the exhaust gas with ammonia. There has been proposed an exhaust gas treatment apparatus including In addition, the same catalyst layer promotes the oxidation reaction of mercury and hydrogen chloride in the exhaust gas to produce mercury chloride, and the generated mercury chloride is dissolved in the absorption liquid of the subsequent wet desulfurization device to remove mercury from the exhaust gas. I have to. In particular, according to this document, if the chlorine content in the fuel is small, hydrogen chloride in the exhaust gas decreases and the oxidation rate of mercury decreases, so that chlorine, hydrogen chloride, ammonium chloride, etc. Chlorine compound is injected to improve mercury oxidation rate.

JP-A-10-230137

  However, Patent Document 1 does not consider that mercury is oxidized with a substance other than chlorine or a chlorine compound.

  The problem to be solved by the present invention is to realize a denitration apparatus that can oxidize mercury in exhaust gas with a catalyst for denitration even with substances other than chlorine and chlorine compounds.

  In order to solve the above problems, a denitration apparatus according to a first aspect of the present invention includes a denitration agent injection means for injecting a denitration agent into a flue through which exhaust gas containing at least nitrogen oxides and mercury flows, A chemical injection means for injecting a chemical containing at least one of bromine and iodine, a denitration agent and an exhaust gas containing the chemical are introduced, a reaction of reducing nitrogen oxides with the denitration agent, and mercury being oxidized with the chemical, It is characterized by comprising a catalyst layer that promotes a reaction for producing at least one of mercury iodide.

  According to this, mercury in exhaust gas can be reacted with bromine or iodine to oxidize mercury to mercury bromide or mercury iodide, so that mercury can be oxidized without using chlorine or chlorine compounds. In particular, the reaction between mercury and bromine has a high reaction rate, and mercury can be oxidized while suppressing the amount of bromine injected.

  Also, bromine or iodine compounds can be injected into the flue instead of bromine or iodine alone. In particular, the ammonium salt of bromine and iodine is dissociated into bromine, iodine and ammonia at a high temperature in the flue, for example, 350 ° C. to 500 ° C., and bromine and iodine oxidize mercury, and the dissociated ammonia serves as a denitration agent. Therefore, the amount of the denitration agent injected into the flue can be reduced.

  On the other hand, the denitration apparatus according to the second aspect of the present invention is an injection means for injecting at least one of bromine, chlorine or iodine ammonium salt as a denitration agent into a flue through which exhaust gas containing at least nitrogen oxides and mercury flows. In addition, exhaust gas containing denitration agent is introduced to promote reaction to reduce nitrogen oxide with denitration agent and oxidation of mercury with denitration agent to produce at least one of mercury bromide, mercury chloride or mercury iodide. The catalyst layer is provided.

  According to this, the ammonium salt of bromine, chlorine or iodine can reduce the nitrogen oxides in the exhaust gas to nitrogen, and the mercury in the exhaust gas can be oxidized to mercury bromide, mercury chloride or mercury iodide. That is, bromine, chlorine or iodine ammonium salt dissociates into ammonia and bromine, chlorine or iodine at a high temperature in the flue, for example, 350 ° C to 500 ° C, ammonia becomes a denitration agent, and bromine, chlorine or iodine oxidizes mercury. Therefore, the chemical supply system of the denitration apparatus can be made into one system. Since the reaction rate between bromine and mercury is high, bromine may become excessive depending on the amount of mercury in the exhaust gas. In this case, ammonia or urea can be added to ammonium bromide.

On the other hand, the denitration device of the third aspect of the present invention includes a two-fluid nozzle inserted into a flue through which an exhaust gas containing at least nitrogen oxides and mercury flows, and a catalyst layer on the downstream side of the two-fluid nozzle. The two-fluid nozzle includes an inert diluting gas added to a gaseous denitration agent and infuses the diluted gas with an aqueous solution of a chemical containing at least one of a halogen or a halogen compound into the flue. , and the catalyst layer, the exhaust gas is introduced comprising a denitrating agent and the drug, forming a reaction and mercury reducing nitrogen oxides in the denitration agent with a catalyst to promote the reaction of the mercury halide is oxidized with drug It is characterized by being.

  According to this, since the exhaust gas can be denitrated and the mercury in the exhaust gas can be oxidized without providing a denitration agent and a chemical injection means for converting mercury into mercury halide, the supply system of the denitration agent and the chemical is 1 System can be made, and denitration equipment can be simplified.

  ADVANTAGE OF THE INVENTION According to this invention, the denitration apparatus which can oxidize mercury in waste gas with the catalyst for denitration also with substances other than chlorine and a chlorine compound is realizable.

It is the schematic of the boiler plant of Embodiment 1 of this invention. It is the schematic of the boiler plant of the reference example 1 of this invention. It is the schematic of the boiler plant of the reference example 2 of this invention.

Hereinafter, the present invention will be described based on embodiments.
(Embodiment 1)
FIG. 1 shows a schematic diagram of a boiler plant including the denitration apparatus of the first embodiment. The boiler plant of this embodiment is provided in, for example, a thermal power plant. The boiler 1 is configured to burn fossil fuel, for example, pulverized coal. The boiler 1 is provided with a heat transfer tube (not shown) so that water flowing through the heat transfer tube can be evaporated by the heat of the exhaust gas generated in the boiler 1, and steam can be supplied to a steam turbine (not shown) to generate electricity. It has become. The exhaust gas discharged from the boiler 1 is introduced into the economizer 3 and exchanges heat with a heat medium flowing through a heat transfer pipe (not shown) provided in the economizer 3. The exhaust gas discharged from the economizer 3 is introduced into the denitration device 5.

  The denitration device 5 includes a two-fluid nozzle 9 inserted in the flue 7 and a denitration catalyst layer 11 formed on the downstream side of the two-fluid nozzle 9. The two-fluid nozzle 9 is connected to a denitrating agent container 13 for storing ammonia, for example, and an oxidizing agent container 14 for storing an agent for oxidizing mercury, for example, an aqueous solution of ammonium bromide, through a pipe. Yes. The two-fluid nozzle 9 is supplied with ammonia gas and an aqueous solution of ammonium bromide, and the aqueous solution of ammonium bromide can be injected into the flue 7 using the ammonia gas as an injection gas. A gas mixing adjuster 15 is provided in the middle of the pipeline between the two-fluid nozzle 9 and the denitration agent container 13. The gas mixing controller 15 can adjust the ammonia gas supplied from the denitration agent container 13 and the dilution gas 17 such as air to a predetermined flow rate ratio. A pump 19 capable of adjusting the discharge amount is provided in the middle of the pipeline between the two-fluid nozzle 9 and the oxidant container 14. The pump 19 supplies an aqueous ammonium bromide solution from the oxidant container 14 to the two-fluid nozzle 9.

  The denitration catalyst layer 11 is formed of a known catalyst such as a three-way catalyst that promotes a reaction of reducing nitrogen oxides in exhaust gas with ammonia and a reaction of oxidizing metal mercury in the exhaust gas with bromine to generate mercury bromide. Has been. On the outlet side of the denitration catalyst layer 11, a NOx monitor 21 for detecting the nitrogen oxide concentration in the exhaust gas discharged from the denitration catalyst layer 11 and an Hg monitor 23 for detecting metallic mercury are provided. The NOx monitor 21 is connected to the gas mixing adjuster 15, and the Hg monitor 23 is connected to a discharge amount adjusting means (not shown) of the pump 19.

  An exhaust gas purifying device 25 including a dust collecting device and a wet desulfurization device is provided on the downstream side of the denitration device 5. The exhaust gas purification device 25 is configured to remove dust, sulfur oxide, mercury bromide, and the like in the exhaust gas from the exhaust gas. The exhaust gas purified by the exhaust gas purification device 25 is discharged from a chimney (not shown).

  Next, operation | movement of the boiler plant of Embodiment 1 is demonstrated. The exhaust gas generated in the boiler 1 is adjusted to a temperature of, for example, 350 ° C. to 500 ° C. by the economizer 3. Ammonia gas and aqueous ammonium bromide solution are added from the two-fluid nozzle 9 to the temperature-controlled exhaust gas. The added aqueous solution of ammonium bromide is vaporized by the heat of the exhaust gas in the process of flowing through the flue 7, and dissociates into bromine and ammonia. An exhaust gas accompanied by ammonia and bromine is introduced into the denitration catalyst layer 11. The denitration catalyst layer 11 promotes a reaction in which nitrogen oxides in the exhaust gas are reduced to nitrogen by ammonia, and promotes a reaction in which metallic mercury in the exhaust gas is oxidized to water-soluble mercury bromide by bromine. Thereby, the exhaust gas is denitrated and the metal mercury is oxidized.

  The NOx monitor 21 and the Hg monitor 23 on the outlet side of the denitration catalyst layer 11 measure the nitrogen oxide concentration and the metal mercury concentration in the exhaust gas. In accordance with the indicated value of the NOx monitor 21, the gas mixing adjuster 15 adjusts the flow rate ratio of the ammonia gas and the dilution gas 17 so that the molar ratio of ammonia / nitrogen oxide is 0.8 to 0.9, for example. .

  On the other hand, according to the indication value of the Hg monitor 23, the pump 19 adjusts the injection amount of the ammonium bromide aqueous solution in the range of 100 to 5000, preferably 300 to 2000, for example, in the molar ratio of bromine / metal mercury.

  According to this, mercury in exhaust gas can be reacted with bromine to oxidize mercury to mercury bromide, so that mercury can be oxidized without using chlorine or chlorine compounds. Furthermore, even when using a fuel with low chlorine content, the amount of water-soluble mercury compound can be increased, so that the amount of mercury that can be removed from the exhaust gas by the exhaust gas purification device 25 including a wet desulfurization device can be increased, and the mercury in the exhaust gas. The removal rate can be improved.

  Further, by providing a NOx monitor 21 and a Hg monitor 23 and measuring the nitrogen oxide concentration and the metal mercury concentration in the exhaust gas, ammonia gas or bromide can be produced according to the load fluctuation of the boiler 1 or the fuel quality fluctuation. The injection amount of the aqueous ammonium solution can be controlled. That is, even if the nitrogen oxide concentration or mercury concentration of the exhaust gas discharged from the boiler 1 fluctuates, the injection amount of ammonia gas and aqueous ammonium bromide solution is adjusted according to the fluctuation, so that excess ammonia or bromine Generation can be reduced.

  In this embodiment, ammonium bromide is injected into the flue 7. However, bromine alone or a compound such as sodium bromide, potassium bromide, or hydrogen bromide can be used. However, sodium acts as a binder in the exhaust gas, which may increase the amount of ash attached to the flue and equipment on the downstream side. Further, sodium or potassium becomes a poisoning component of the denitration catalyst, and the catalytic performance of the denitration catalyst layer 11 may be lowered. On the other hand, hydrogen bromide is very corrosive and difficult to handle. Therefore, it is preferable to use an ammonium salt that does not contain poisoning components of the denitration catalyst and is easy to handle. Furthermore, when an ammonium salt is used, ammonia generated by dissociation of ammonium bromide in the flue 7 acts as a denitration agent. Therefore, the use amount of the denitration agent can be reduced by using the ammonium salt.

  In this embodiment, bromine alone or a bromine compound is used as an agent for oxidizing mercury because the reaction rate of bromine and mercury is fast, so by using bromine or a bromine compound, This is because mercury can be oxidized while suppressing the amount of use. However, instead of this, a simple substance of iodine or a compound of iodine can be injected. In this case, the injection amount of iodine or an iodine compound is adjusted so that the molar ratio of iodine / metal mercury is, for example, 10,000 to 150,000, preferably 10,000 to 50,000.

  Further, in this embodiment, the ammonia bromide aqueous solution is injected into the flue 7 by the two-fluid nozzle 9 using ammonia gas as the injection gas. However, the ammonia gas and the ammonium bromide aqueous solution can be injected from separate nozzles. it can. However, by using ammonia gas as the injection gas, it is not necessary to separately provide a nozzle for injecting the denitration agent, and the configuration of the denitration device 5 can be simplified.

  The dilution gas 17 may be any inert gas such as air, oxygen, nitrogen, and argon that does not interfere with the denitration reaction or the mercury oxidation reaction. However, the denitration reaction or the mercury oxidation reaction is performed in the presence of oxygen. Since activity improves, it is preferable to use air or oxygen as the dilution gas 17.

( Reference Example 1 )
FIG. 2 shows a schematic diagram of a boiler plant including the denitration apparatus of Reference Example 1 . Reference Example 1 is different from Embodiment 1 in that an ammonium chloride aqueous solution is stored in the denitration agent container 13 instead of ammonia. Furthermore, a pump 19 capable of adjusting the discharge amount is provided in place of the gas mixing adjuster 15, and the NOx monitor 21 and the Hg monitor 23 are connected to a discharge amount adjusting means (not shown) of the pump 19. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  The pump 19 can adjust the injection amount of the ammonium chloride aqueous solution according to the nitrogen oxide concentration and the metal mercury concentration on the outlet side of the denitration catalyst layer 11. The aqueous ammonium chloride solution sucked up by the pump 19 is entrained by the dilution gas 17 introduced into the pump 19 and conveyed to the two-fluid nozzle 9 by airflow. The aqueous ammonium chloride solution conveyed to the two-fluid nozzle 9 is injected into the flue 7 at 350 ° C. to 500 ° C., for example, using the dilution gas 17 as an injection gas. The ammonium chloride aqueous solution injected into the flue 7 is vaporized by heat in the flue 7 and dissociates into ammonia and chlorine. The ammonia generated by dissociation promotes a reaction for reducing nitrogen oxides in the exhaust gas by the denitration catalyst layer 11. On the other hand, chlorine generated by dissociation promotes a reaction for oxidizing metallic mercury in the exhaust gas to mercury chloride by the denitration catalyst layer 11. That is, ammonium chloride acts as a denitrating agent and an oxidizing agent that oxidizes mercury.

  According to this, by injecting only the ammonium chloride aqueous solution into the flue 7, the exhaust gas can be denitrated, and the mercury in the exhaust gas can be oxidized to mercury chloride. Therefore, a facility for separately supplying the denitration agent into the flue 7 can be omitted, and the chemical supply system of the denitration device 5 can be made into one system, so that the denitration device 5 can be configured simply.

  Instead of ammonium chloride, ammonium iodide can be injected into the flue 7. Also by this, the exhaust gas can be denitrated, and the metal mercury in the exhaust gas can be oxidized to mercury iodide.

  On the other hand, when ammonium bromide is injected into the flue 7, bromine may be excessively large due to the high reaction rate of bromine and mercury. In this case, a denitration agent such as ammonia or urea can be separately injected.

In this reference example , the injection amount of the ammonium chloride aqueous solution is adjusted according to the instruction values of the NOx monitor 21 and the Hg monitor 23. However, the injection amount of the ammonium chloride aqueous solution is adjusted only by the instruction value of the NOx monitor 21. be able to. In other words, since the nitrogen oxide concentration in the exhaust gas is as high as 10000 times the mercury concentration, the amount of chlorine required for the oxidation reaction of mercury can be reduced by adjusting the amount of ammonium chloride according to the nitrogen oxide concentration. Can be added. The injection amount of ammonium chloride or ammonium iodide can be adjusted so that the ammonia / nitrogen oxide molar ratio is in the range of 0.8 to 0.9.

  When mercury is oxidized to mercury chloride, the injection amount of the ammonium chloride aqueous solution is adjusted to be, for example, 10,000 to 150,000, preferably 10,000 to 50,000, for example, in a molar ratio of chlorine / metal mercury. Can do.

( Reference Example 2 )
FIG. 3 shows a schematic diagram of a boiler plant including the denitration apparatus of Reference Example 2 . Reference Example 2 is different from the first embodiment in that a liquid denitration agent, for example, a liquid denitration agent such as ammonia water or urea water, is stored in the denitration agent container 13 and the discharge amount of the denitration agent can be adjusted. This is that the water is sucked up by 31 and joined to a pipe through which an aqueous solution of ammonium bromide flows. Furthermore, a gas regulator 29 for adjusting the flow rate and pressure of the dilution gas 17 is arranged, and a denitration agent and an aqueous solution of ammonium bromide are injected into the flue 7 from the two-fluid nozzle 9 using the dilution gas 17 as an injection gas. It is. Since other configurations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  A NOx monitor 21 is connected to a discharge amount adjusting means (not shown) of the pump 31. The pump 31 adjusts the supply amount of the denitration agent, for example, so that the molar ratio of ammonia / nitrogen oxide is in the range of 0.8 to 0.9 according to the indicated value of the NOx monitor 21 and the like. ing. The gas regulator 29 adjusts the supply amount and pressure of the dilution gas 17, and can uniformly inject a liquid denitration agent and an aqueous ammonium chloride solution from the two-fluid nozzle 9 using the dilution gas 17 as an injection gas.

  This also allows mercury in exhaust gas to react with bromine and be oxidized to mercury bromide, so that mercury can be oxidized without using chlorine or chlorine compounds. Even when the amount of chlorine in the fuel is small and the amount of hydrogen chloride in the exhaust gas is insufficient, the amount of mercury oxidation can be increased. Therefore, it is removed from the exhaust gas by the exhaust gas purification device 25 including a wet desulfurization device. The amount of mercury can be increased. Furthermore, since the denitration agent and the ammonium chloride aqueous solution are injected from the same two-fluid nozzle 9, the denitration agent and the agent that oxidizes mercury can be injected with one system of injection equipment, and the configuration of the denitration device 5 can be simplified.

  In addition, the NOx monitor 21 and the Hg monitor 23 can measure changes in nitrogen oxide concentration and metal mercury concentration in the exhaust gas, and control the pumps 19 and 31. The flow rate ratio of the aqueous ammonium solution can be adjusted, and the drug can be used efficiently.

  Further, a means for adjusting the concentration ratio of the denitration agent and the ammonium bromide aqueous solution is provided by making the flow rate ratio of the denitration agent and the ammonium bromide aqueous solution constant, and according to the indicated value of the NOx monitor 21 and the Hg monitor 23, the ammonia / The molar ratio of nitrogen oxides and the molar ratio of bromine / metal mercury can be adjusted within a predetermined range.

  The agent that oxidizes mercury is not limited to ammonium bromide. Mercury can be oxidized by injecting a simple substance of halogen such as bromine, chlorine or iodine or a halogen compound into the flue 7.

In addition, a gaseous denitration agent such as ammonia gas can be introduced into a pipe through which the ammonium bromide aqueous solution flows in place of the liquid denitration agent, and the ammonium bromide aqueous solution can be conveyed by airflow. In this case, instead of the pump 31, means for adjusting the flow rate and pressure of gas such as a gas regulator is provided, and the NOx monitor 21 is connected to the gas regulator or the like. And according to the instruction | indication value of NOx monitor 21, gaseous denitration agent is introduce | transduced into the piping through which ammonium bromide aqueous solution flows, and ammonium bromide aqueous solution is carried by airflow. For example, under the condition where the amount of exhaust gas is about 1000 m ³ N / h and the concentration of nitrogen oxides is 100 ppm, the flow rate of ammonia gas is 1.5 L / min (molar ratio of ammonia / nitrogen oxide is 0.9). As a result, the aqueous ammonium bromide solution can be conveyed and air-jetted from the two-fluid nozzle 9. On the other hand, when the amount of exhaust gas is large and the large-capacity two-fluid nozzle 9 is used, there is a possibility that the amount of ammonia gas becomes excessive if the ammonium bromide aqueous solution is jetted by air flow only with ammonia gas. In this case, the diluent gas 17 can be mixed with the ammonia gas, and the aqueous ammonium bromide solution can be conveyed by airflow using the mixed gas and injected from the two-fluid nozzle 9. When a chemical agent that oxidizes mercury with a gaseous denitration agent is carried by airflow, the chemical agent that oxidizes mercury is not limited to ammonium bromide, and a halogen simple substance or a compound can be used.

DESCRIPTION OF SYMBOLS 1 Boiler 5 Denitration apparatus 7 Flue 9 Two-fluid nozzle 11 Denitration catalyst layer 13 Denitration agent container 14 Oxidant container

Claims (1)

A two-fluid nozzle inserted in a flue through which exhaust gas containing at least nitrogen oxides and mercury flows, and a catalyst layer on the downstream side of the two-fluid nozzle,
The two-fluid nozzle is a gas denitration agent added with an inert diluting gas, and the diluted gas is accompanied by an aqueous solution of a chemical containing at least one of halogen alone or a halogen compound, and injected into the flue. Yes,
The catalyst layer, said exhaust gas containing said and said denitration agent agent is introduced, facilitates the reaction of the reaction and the mercury reducing the nitrogen oxides in the denitration agent is oxidized with the agents to mercury halide A denitration device formed by a catalyst that performs

Images