JP2013238349A - Method and apparatus for treating exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for treating exhaust gas and an apparatus for treating exhaust gas, capable of blowing, at a high speed, ammonia gas obtained by preliminarily pyrolyzing urea, even when there is no power for a pump or a blower.SOLUTION: An apparatus for treating exhaust gas includes: a steam pipe 10 for guiding steam generated in a boiler 2 to a combustion furnace 1; a urea water injection pipe 11 for injecting urea water to the steam in the steam pipe 10; and a steam spray nozzle 12 connected to an end of the steam pipe 10 for spraying steam into the furnace. The steam to be sprayed from the steam spray nozzle 12 is controlled to a pressure of 1 MPa or more in order to be ejected at a high speed, and also controlled to 350°C or higher to hydrolyze urea water.

Description

  The present invention relates to an exhaust gas treatment method and an exhaust gas treatment device that reduce the concentration of nitrogen oxides in combustion exhaust gas such as a waste incinerator and a biomass combustion boiler.

  Conventionally, a non-catalytic denitration method that decomposes nitrogen oxides by spraying ammonia water or urea water into the combustion atmosphere of a waste incinerator, or nitrogen oxides in combustion exhaust gas in the presence of ammonia using a catalyst table Catalytic denitration methods that decompose into nitrogen gas are known (Patent Documents 1 to 5).

  In these denitration methods, urea water is used more frequently than ammonia water because of its ease of use. Urea generates ammonia by hydrolysis. The decomposition point of urea is defined as the melting point (132.7 ° C.) or higher, and the exact temperature is unknown, but it is considered that 300 to 450 ° C. is necessary for the efficient decomposition reaction, It is said that the decomposition reaction proceeds rapidly even under low temperature conditions of 200 to 250 ° C. by contacting with an appropriate catalyst (Patent Documents 6 and 7, Non-Patent Document 1, etc.).

JP-A-53-62772 JP-A-6-269634 JP 2009-103381 A JP 2010-48456 A JP 2010-99603 A JP 11-171535 A JP-A-10-244131

Peter M. Peter M. Schaber et al., “Study of the urea thermal decomposition (pyrolysis) reaction and importance to cyanuric acid production, American Laboratory, Vol. 31, No. 16, pp. 13-21, 1999

  Conventionally, urea water is sprayed into the furnace or flue, or urea water is mixed with high-temperature exhaust gas and decomposed before being blown into a gaseous state.

  In order to improve the NOx removal rate, it is necessary to contact urea water and ammonia gas evenly with the combustion exhaust gas. However, if the blowing speed is low, the contact becomes insufficient, and if it is attempted to increase the blowing speed There is a problem that pumps and blowers are enlarged.

  When spraying a liquid such as urea water or ammonia water, when the droplet size is large, the droplet collides with the wall on the opposite side, or dripping from the nozzle occurs, especially when controlling the flow rate. In all the control widths, it was difficult to optimally control the particle size.

  SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide an exhaust gas treatment method and an exhaust gas treatment apparatus that can inject ammonia gas obtained by thermally decomposing urea in advance at high speed without the power of a pump or a blower. And

  In order to achieve the above object, an exhaust gas treatment method according to the present invention comprises hydrolyzing urea water into ammonia-containing steam by mixing urea water with steam generated in a boiler, and converting the ammonia-containing steam into combustion exhaust gas. By blowing, the nitrogen oxide concentration in the combustion exhaust gas is reduced.

  Non-catalytic denitration can be performed by blowing the ammonia-containing steam into the combustion furnace.

  Alternatively, catalytic denitration can be performed by injecting the ammonia-containing vapor into flue combustion exhaust gas and bringing the combustion exhaust gas into contact with a denitration catalyst.

  The temperature of the steam for hydrolyzing the urea water is preferably 350 ° C. or higher.

  The pressure of the steam for mixing the urea water is preferably 1 MPa or more.

  The exhaust gas treatment apparatus according to the present invention is connected to a steam pipe for guiding steam generated in a boiler to a combustion furnace, a urea water injection pipe for injecting urea water into the steam in the steam pipe, and an end of the steam pipe And a steam spray nozzle for spraying steam into the furnace.

  Further, the exhaust gas treatment apparatus according to the present invention includes, as other means, a steam pipe that guides steam generated in a boiler to a flue, a urea water injection pipe that injects urea water into the steam in the steam pipe, and the steam pipe A steam spray nozzle connected to the end of the steam sprayer for spraying steam into the flue, and a catalyst denitration device interposed in the flue downstream of the steam spray nozzle.

  It is preferable that a mixing reactor for mixing and reacting steam and urea water is interposed in the steam pipe.

  Further, it is preferable that one or more hydrolysis catalysts selected from the group consisting of silica, alumina, titania, and zeolite are incorporated in the mixing reactor.

  A first steam pipe and a second steam pipe that are branched and connected in parallel; and a steam pipe on-off valve that opens and closes each of the first steam pipe and the second steam pipe on the upstream side and the downstream side; The urea water injection pipe connected to each of the first steam pipe and the second steam pipe, and urea water is supplied from the urea water injection pipe to either the first steam pipe or the second steam pipe. A supply switching valve, a purge gas supply pipe for supplying a purge gas to the urea water injection pipe, a purge gas discharge pipe for discharging the purge gas supplied to the urea water injection pipe, and the urea water injection pipe by heating the urea water injection pipe And a heating device for thermally decomposing solid matter deposited in the water injection tube.

  According to the present invention, by using high-temperature and high-pressure steam generated in a boiler as a carrier gas, ammonia-containing steam obtained by hydrolyzing urea water in advance in a combustion furnace at a high flow rate without using a pump or a blower. Mixing and stirring with combustion exhaust gas can be promoted by blowing into the flue.

1 is a system diagram showing a first embodiment of an exhaust gas treatment apparatus according to the present invention. It is a systematic diagram which shows the principal part of 2nd Embodiment of the waste gas processing apparatus which concerns on this invention. It is a systematic diagram which shows the principal part of 3rd Embodiment of the waste gas processing apparatus which concerns on this invention. It is a systematic diagram which shows 4th Embodiment of the waste gas processing apparatus which concerns on this invention.

  Embodiments of an exhaust gas treatment method and an exhaust gas treatment apparatus according to the present invention will be described below with reference to FIGS. In addition, the same code | symbol was attached | subjected to the same or similar component through all the figures and all the embodiment.

  FIG. 1 is a system diagram showing a first embodiment of an exhaust gas treatment apparatus according to the present invention. The exhaust gas treatment apparatus includes an incinerator 1, a boiler 2, a economizer 3, a temperature reducing tower 4, a bag filter 5, an induction blower 6, a chimney 7, and the like, as in the past.

  1 further includes a steam pipe 10 that guides steam generated in the boiler 2 to the combustion furnace 1, a urea water injection pipe 11 that injects urea water into the steam in the steam pipe 10, and a steam pipe 10. A steam spray nozzle 12 connected to the end and spraying steam into the incinerator 1.

  In the boiler 2 attached to a garbage incinerator or the like, steam having a pressure of 3 MPa to 4 MPa and a temperature of 300 to 400 ° C. is usually generated. A part of such high-temperature and high-pressure steam is supplied to the steam pipe 10, pumped through the steam pipe 10, and guided to the steam spray nozzle 12. Conventionally, 3 MPa, 300 ° C. class boilers have been mainstream, but due to recent improvements, 4 MPa, 400 ° C. class boilers are becoming mainstream.

  The urea water is injected into the steam pipe 10 through the urea water injection pipe 11, and the urea water is mixed with the high-temperature / high-pressure steam pumped through the steam pipe 10. Since the steam temperature is 300 to 400 ° C., the hydrolysis of urea proceeds efficiently and becomes an ammonia-containing steam containing ammonia, isocyanic acid as an intermediate product, and the like. The mixing part of the steam and the urea water, that is, the connection part between the steam pipe 10 and the urea water injection pipe 11 may be an ejector that sucks the urea water with the kinetic energy of the steam.

  The urea water injection pipe 11 is connected to a urea water tank 13 that stores urea water. The supply of urea water from the urea water tank 13 to the urea water injection pipe 11 can also be performed by a pump (not shown).

  The ammonia-containing steam in the steam pipe 10 is sprayed at high speed from the steam spray nozzle 12 into the combustion furnace 1 using steam pressure. Since the vapor pressure is used, a high-pressure pump or blower for spraying is not necessary. Ammonia-containing steam is sprayed in a combustion atmosphere of 800 to 1000 ° C. in the combustion furnace 1, and non-catalytic denitration proceeds by decomposing nitrogen oxides in the combustion exhaust gas.

  In addition, by using excessive steam conditions, the generation of decomposition by-products such as biuret and cyanuric acid is reduced, the hydrolysis of urea water is promoted with simple equipment consisting of only piping, and since it is high-pressure steam, it enters the furnace. The injection speed is high, mixing and stirring with the combustion gas is promoted, and high denitration efficiency is obtained. Naturally, since urea water is used, expensive and complicated equipment is not required when ammonia water or ammonia gas is used.

  Cyanuric acid, which is a by-product produced when decomposing urea, is a very hard, hardly decomposable and hardly soluble solid, and once produced in a reaction vessel, it is difficult to remove by means other than high-temperature heating. As for this cyanuric acid, when it exceeds 350 degreeC, it is known that a production | generation ratio will reduce rapidly (the said nonpatent literature 1). Therefore, if the steam temperature in the steam pipe 10 is 350 ° C. or higher, the generation of cyanuric acid can be reduced.

  The steam pressure in the steam pipe 10 is preferably 1 MPa or more in order to inject ammonia-containing steam from the steam injection nozzle 12 at a high speed and promote mixing and stirring with the combustion gas.

  When using high-concentration urea water, piping clogging is likely to occur due to solid matter (cyanuric acid or the like) adhering at the junction of urea water and steam (particularly on the urea water injection pipe 11 side).

  The urea water is supplied at normal temperature, but the temperature is raised from normal temperature to high temperature in the process of reaching the steam pipe 10. At this time, since solids such as cyanuric acid are easily generated, the solids are precipitated when the concentration in urea water is high or when the residence time (passage time) in the temperature range is short. It's easy to do. Therefore, instead of preventing the solid matter from precipitating, the precipitated solid matter can be removed by the system shown in FIG.

FIG. 2 shows a solid matter removal system that is a main part of a second embodiment of the exhaust gas treatment apparatus according to the present invention. Solids removal system shown in Figure 2, the first steam pipe 10 ₁ and the second steam pipe 10 ₂ connected in parallel by branching the steam pipe 10, the first steam pipe 10 ₁ and the second steam pipe 10 ₂ steam pipe on-off valve ₁₅ for opening and closing each at the upstream side and the downstream side _first, 15 _2, 15 3, 15 ₄ and the first steam is connected to the first respective steam pipe 10 ₁ and the second steam pipe 10 ₂ and switchably configured aqueous urea injection tube 11 _1, 11 ₂ so as to supply the urea water to either one of the tube 10 ₁ and the second steam pipe, a purge gas to the urea solution injection tube 11 _1, 11 ₂ heating the purge gas supply pipe ₁₆ 1, 16 ₂ for supplying a purge gas discharge pipe ₁₇ 1, 17 ₂ for discharging the purge gas supplied to the urea water injection tube ₁₁ 1, 11 _2, urea water injection tube ₁₁ 1, 11 ₂ Urea water injection tube 1 _1, 11 The solid precipitated in ₂ and the heating device ₁₈ 1, 18 ₂ for thermally decomposing, and a.

In the illustrated example, is connected to the urea water injection tube 11 ₁ and the purge gas outlet 17 ₁ between the steam pipe 10 steam pipe on-off valve 15 ₁ of ₁ and steam pipe on-off valve 15 _2, steam pipes of the steam pipe 10 ₂ urea water injection pipe 11 ₂ and a purge gas outlet 17 ₂ are connected between the on-off valve 15 ₃ and the steam pipe on-off valve 15 _4. In the illustrated example, on-off valves 19 ₁ and 19 ₂ are interposed in the urea water injection pipes 11 ₁ and 11 ₂ , respectively, and either _{one of} the on-off valve 19 ₁ and the on-off valve 19 ₂ is closed to thereby form urea. The urea water can be injected from only _{one of} the water injection pipes 11 ₁ and 11 ₂ .

Further, between the opening and closing valve 19 ₁ and the steam pipe 10 ₁ of the urea water injection tube 11 _1, and between the opening and closing valve 19 ₂ and the steam pipe 10 ₂ of the urea water injection tube 11 _2,其s, purge gas supply Tubes 16 ₁ and 16 ₂ are connected.

Then, the opening and closing valve ₂₀ 1, 20 ₂ is interposed purge gas supply pipe ₁₆ 1, 16 ₂ of其s, on-off valve ₂₁ 1, 21 ₂ are also interposed其people of the purge gas exhaust pipe 17 ₁ and 17 ₂ The heating devices 18 ₁ , 18 ₂ are urea in the vicinity of the connection between the urea water injection pipes 11 ₁ , 11 _{2 and} the steam pipes 10 ₁ , 10 ₂ where solids are likely to precipitate, that is, at the junction of urea water and steam. It can be arranged on the side of the water injection tubes 11 ₁ , 11 ₂ . Each of the heating devices 18 ₁ and 18 ₂ includes a heater capable of raising the temperature to 600 ° C.

  The example of the solid substance removal procedure by the solid substance removal system of the said structure is demonstrated.

First, close the steam pipe on-off valve ₁₅ 1, 15 _2, closes the on-off valve 19 ₁ of the urea water injection tube 11 _1. Then, with opening the on-off valve 20 ₁ of the purge gas supply pipe 16 _1, open the closing valve 21 ₁ of the purge gas exhaust pipe 17 _1, it flows a small amount of purge gas (air). The purge gas through the purge gas discharge pipe 17 ₁ is discharged to the outside of such systems outside the drawing furnace. In this state, when starting the heating of the heating device 18 ₁ to ON, the solids such as precipitated biuret and cyanuric acid is thermally decomposed, is discharged out of the system by the purge gas is removed. During this time, while the opening and closing valve 19 ₂ of the urea water injection tube 11 ₂ together with steam pipe on-off valve ₁₅ 3, 15 ₄ is opened is opened, the purge gas supply pipe 16 _{and second} opening and closing valve 20 ₂ and the purge gas exhaust pipe 17 ₂ off valve 21 ₂ are closed, steam urea water is injected therein flows through the second steam pipe 10 _2. In this case the heating device 18 ₂ is turned OFF.

Then open the steam on-off valve ₁₅ 1, 15 _2, the steam-off valve ₁₅ 3, 15 ₄ closed, the on-off valve 19 ₂ of the urea water injection tube 11 ₁ of the opening and closing valve 19 ₁ by opening urea water injection pipe 11 ₂ closed, closes the open-close valve 20 ₁ and the opening and closing valve 21 ₁ of the purge gas exhaust pipe 17 ₁ of the purge gas supply pipe 16 _1, the purge gas supply pipe 16 _2-off valve 20 ₂ and the on-off valve 21 _second purge gas exhaust pipe 17 ₂ opening, turns OFF the heater 18 ₁ of the heating device 18 ₂ and to oN. Thereby, while the steam urea water is injected therein flows through the first steam pipe 10 _1, solids deposited on the urea water injection tube 11 ₂ is removed by a purge gas is decomposed by the heating device 18 ₂ The

As described above, to remove solids precipitated urea water injection tube 11 ₁ and the urea water injection tube 11 ₂ alternately. This alternating switching can be performed periodically by manual or automatic control.

  In the example shown in FIG. 2, four steam opening / closing valves are provided, but instead, one direction switching valve may be provided at each of two branch points of the steam pipe. In the example shown in FIG. 2, the purge gas supply pipe is connected to the urea water injection pipe and the purge gas discharge pipe is connected to the steam pipe. Conversely, the purge gas supply pipe is connected to the steam pipe and the purge gas discharge pipe is connected. It may be connected to a urea water injection pipe.

  Next, a third embodiment of the exhaust gas treatment apparatus according to the present invention will be described with reference to FIG. FIG. 3 is a system diagram showing a main part of the exhaust gas treatment apparatus of the third embodiment.

  When the distance from the urea water / steam junction to the steam injection nozzle 12 is short and the reaction time of hydrolysis (and thermal decomposition) of urea is not sufficient, as shown in FIG. 30 is interposed in the steam pipe 10, the urea water injection pipe 11 is connected to the mixing reactor 30, and a residence time for mixing the steam and the urea water in the mixing reactor 30 is taken to secure the reaction time. Anyway. The residence time in the mixing reactor 30 is preferably 0.1 seconds or longer.

  In addition, one or two or more hydrolysis catalysts selected from the group consisting of silica, alumina, titania, and zeolite can be incorporated in the mixing reactor 30. When urea contacts with a hydrolysis catalyst, hydrolysis proceeds at a lower temperature. Therefore, a hydrolysis catalyst may be introduced into the mixed reactor 30 to accelerate the reaction. In this case, since the reaction proceeds at a lower temperature, the vapor temperature (for example, 250 ° C.) corresponding to the hydrolysis catalyst can be set. Note that when the steam temperature is lowered to 200 to 300 ° C., solids such as cyanuric acid are likely to be precipitated, and in particular, easily precipitated in the vicinity of the connection portion of the urea water injection pipe 11 with the steam pipe 10. You may attach the solid substance removal system as shown.

  Next, a fourth embodiment of the exhaust gas treatment apparatus according to the present invention will be described with reference to FIG. FIG. 4 shows an example of catalytic denitration.

  The exhaust gas treatment device shown in FIG. 4 is different from the first embodiment in that the steam pipe 10 and the steam spray nozzle 12 are connected to the flue 40 on the upstream side of the catalyst denitration device 9. The fourth embodiment is also different from the first embodiment in that the flue 40 is provided with the reheater 8 and the catalyst denitration device 9, but the reheater 8 and the catalyst denitration device are also provided in the first embodiment. 9 can be provided.

  The catalyst denitration device 9 decomposes nitrogen oxides in exhaust gas on the catalyst surface in the presence of ammonia. Since a low temperature catalyst of about 200 ° C. is often used as the catalyst, steam having a temperature corresponding to the low temperature catalyst can be blown from the steam spray nozzle 12 into the flue 40 through the steam pipe 10. In this case, similarly to the mixing reactor described in the third embodiment, a mixing reactor containing a hydrolysis catalyst can be interposed in the steam pipe 10.

  INDUSTRIAL APPLICABILITY The present invention can be used for non-catalytic denitration and catalytic denitration of combustion exhaust gas generated in a waste incinerator equipped with a boiler, a boiler burning such as biomass, and the like.

DESCRIPTION OF SYMBOLS 1 Incinerator 2 Boiler 9 Catalytic denitration apparatus 10, 10 ₁ , 10 ₂ Steam pipes 11, 11 ₁ , 11 ₂ Urea water injection pipes 15 ₁ , 15 ₂ , 15 ₃ , 15 ₄ Steam pipe on-off valves 16 ₁ , 16 ₂ Purge gas Supply pipes 17 ₁ and 17 ₂ Purge gas discharge pipes 18 ₁ and 18 ₂

Claims (10)

  By mixing urea water with the steam generated in the boiler, the urea water is hydrolyzed into ammonia-containing steam, and the ammonia-containing steam is blown into the combustion exhaust gas, thereby reducing the nitrogen oxide concentration in the combustion exhaust gas. An exhaust gas treatment method characterized by that.   The exhaust gas treatment method according to claim 1, wherein the ammonia-containing steam is blown into a combustion furnace.   The exhaust gas treatment method according to claim 1, wherein the ammonia-containing vapor is blown into flue combustion exhaust gas, and the combustion exhaust gas is brought into contact with a denitration catalyst.   The exhaust gas treatment method according to any one of claims 1 to 3, wherein a temperature of the steam for hydrolyzing the urea water is 350 ° C or higher.   The exhaust gas treatment method according to any one of claims 1 to 4, wherein a pressure of the steam for hydrolyzing the urea water is 1 MPa or more.   A steam pipe for introducing steam generated in the boiler to the combustion furnace, a urea water injection pipe for injecting urea water into the steam in the steam pipe, and a steam spray for connecting the end of the steam pipe to spray the steam into the furnace An exhaust gas treatment apparatus comprising: a nozzle.   A steam pipe that guides steam generated in the boiler to the flue, a urea water injection pipe that injects urea water into the steam in the steam pipe, and a steam spray that is connected to the end of the steam pipe and sprays the steam into the flue An exhaust gas treatment apparatus comprising: a nozzle; and a catalyst denitration device interposed in a downstream flue of the vapor spray nozzle.   The exhaust gas treatment apparatus according to claim 6 or 7, wherein a mixing reactor for mixing and reacting steam and urea water is interposed in the steam pipe.   The exhaust gas treatment apparatus according to claim 8, wherein the mixed reactor contains one or more hydrolysis catalysts selected from the group consisting of silica, alumina, titania, and zeolite. . A first steam pipe and a second steam pipe branched and connected in parallel; a steam pipe on-off valve for opening and closing each of the first steam pipe and the second steam pipe on the upstream side and the downstream side; The urea water injection connected to each of the first steam pipe and the second steam pipe and configured to be switchable to supply urea water to either the first steam pipe or the second steam pipe A purge gas supply pipe for supplying a purge gas to the urea water injection pipe, a purge gas discharge pipe for discharging the purge gas supplied to the urea water injection pipe, and the urea water injection pipe by heating the urea water injection pipe An exhaust gas treatment apparatus according to any one of claims 6 to 9, further comprising: a heating device for thermally decomposing solid matter deposited on the surface.

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