JPH10211417A - Method and apparatus for injecting into two-stage boiler to reduce nitrogen oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove nitrogen dioxide effectively from a flue gas by a method wherein after injecting NHi precursor into the flue gas in a first injection zone having a comparatively high temperature of a specific gas, peroxyl initiator is injected into the flue gas in a second injection zone at a lower temperature than the specific gas temperature. SOLUTION: In the case where NOx in flue gas is reduced in a two stage boiler, NO is reduced to nitrogen by injecting firstly NHi precursor such as liquid phase urea or ammonium hydroxide into a flue gas in a first injection zone 12 at a temperature higher than 1400 deg.F (760 deg.C). Then, by injecting a hydrocarbon material such as methanol, and peroxyl initiator such as hydrogen and hydrogen peroxide into the flue gas in the second injection zone 14 at a temperature lower than 1400 deg.F (760 deg.C), NO is further reduced to nitrogen, the residual NO is oxidized into NO2 , and leak of ammonia is reduced. As the NHi precursor, cyanuric acid, biuret, triuret, ammelide, ammonia, etc., are used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for removing nitrogen oxides from a combustion emission gas. More specifically, the present invention converts nitric oxide (NO) to both nitrogen (N ₂ ) and nitrogen dioxide (NO ₂ ) and releases this flue gas from the flue gas prior to release into the atmosphere. The present invention relates to a technique for removing nitrogen dioxide.

[0002]

2. Description of the Related Art Coal-fired boilers use NOx and sulfur.
This produces O ₂ emissions and causes acid rain. Since the NOx-related part of the acid rain component causes significant damage to trees and forests, in addition to the NOx regulations currently required in Japan and West Germany, NOx for coal-fired boilers
x Control technology is becoming necessary for many industrialized countries. Although NOx control is also an important requirement for incineration systems, no NOx control technology capable of removing 70% or more of NOx has been disclosed to date.

[0003] Existing lime-fired boilers or solid waste incinerators have already installed wet scrubbers to control SO ₂ or HCl emissions. In particular, wet scrubbers are installed in the United States when the coal-fired power output is about 60,000 MWe or more, and in West Germany about 40,000 MWe.
It is installed in the above cases.

[0004] Many other countries now require the installation of wet scrubbers for coal-fired boilers and solid waste incinerators.

[0005] The NOx control technology currently industrialized includes:
Mainly selective catalytic reduction method (Selective Catalytic Redu
In this case, ammonia gas is injected into the flue gas and reacted with NOx on the catalyst at about 700 ° F. (371 ° C.) to produce nitrogen gas and water. A typical NOx reduction rate is 80%. The catalyst bed is
It is usually designed to be large enough to reduce ammonia leakage and avoid fly ash contamination by ammonia salt precipitates. Here, the term "ammonia leak" or "ammonia slip" refers to the concentration of ammonia gas contained in the flue gas leaving the NOx controller. The cost of SCR technology is reportedly around $ 60.
/ Kw to $ 120 / Kw, depending on location. The operating costs of the SCR process include the cost of expensive catalyst replacement about once every two years. The SCR method is considered to be inapplicable to incinerators, because of catalyst contamination and poisoning by the catalyst.

An NHi precursor, such as gaseous ammonia or liquid urea, is injected into the flue gas at about 1400 ° F. (760
Other NOx control methods for reducing NO to nitrogen at (.degree. C.) are known. These methods are based on the selective non-catalytic reduction method (Se
lective Non-Catalytic Reduction (SNCR), but with sufficient NHi precursor material injected, high NOx
Achieving the removal efficiency has the disadvantage that unacceptable ammonia leakage occurs. This ammonia slip combines with SO ₂ , SO ₃ , HCl and HF,
Form ammonia salts below 500 ° F (260 ° C). As such salts condense, solid particles form and precipitate in critical zones, such as air preheating systems associated with conventional boilers.
In order to avoid this problem, the injection amount of the NHi precursor material is reduced, so that the total NOx by the “SNCR method” is reduced.
The reduction ability is generally limited to 30 to 60%.
This level of removal is too low to compete with the SCR method.

A typical SNCR method is described in Kei. U.S. Patent No. 3,90 in the invention of Lion (RKLyon)
No. 0,554 discloses a technique disclosed in US Pat. M.
No. 4,624,840 to AMDean et al. (Exxon-type thermal DeNox method using gaseous ammonia); Kei.
Nos. 4,208,386 and 4,325,924 of JKArand et al. (EPRI / Fuel Tec using liquid urea)
h (Fuel utilization technology) NOx removal method). The Exxon method and the Fuel Tech (fuel utilization technology) method are 1700-1900 ° F (927-1038).
C)), the operation can be performed smoothly only within a narrow temperature range, but at a slightly lower temperature, operation is possible only by adding hydrogen or a hydrocarbon material to the combustion gas. Usually, hydrogen is added in the Exxon method, and methanol is added in the Fuel Tech (fuel utilization technology) method. The actual NO reduction mechanism is thought to involve a number of radical reactions, but the most important reaction is:

NH ₂ + NO = N ₂ + H ₂ O

[0009]

SUMMARY OF THE INVENTION The present invention provides a very high level NOx removal method with a NOx removal rate of 70% or more, especially when a coal-fired boiler or incinerator is already equipped with a wet scrubber. What you want to do. The present invention seeks to achieve such high levels of NOx removal without the use of expensive catalytic NOx reduction technology.

It is an object of the present invention to provide a similar high level of NOx removal performance without requiring the use of SCR technology. This seeks to achieve significant savings in fixed and operating costs.

[0011]

SUMMARY OF THE INVENTION The addition of hydrogen or hydrocarbons to nitrogen oxides results in the normal temperature range (ie, 1800 ° F.).
± 100 ° F (982 ± 56 ° C), for example, 1500 ° F ± 100
° F (816 ± 56 ° C). In this case, a sufficient amount of hydrocarbon is added to increase the hydroxyl (OH) radical concentration to increase the NH ₂ radical concentration at a low temperature, and to reduce ammonia leakage by the following equation.

NH ₃ + OH = NH ₂ + H ₂ O However, the method of adding hydrogen, hydrogen peroxide, or hydrocarbon to lower the optimum temperature in the “SNCR method” is about 1500 ° F. (816 ° C.). Is the limit, 1400 ° F
Below (760 ° C.), the NO reduction efficiency of the SNCR method is extremely reduced, and below about 1300 ° F. (704 ° C.), the reduction reaction substantially no longer occurs.

Here, the term “temperature range” refers to SNCR
It means the temperature range over which the process is effective in reducing NO to nitrogen. Normally, NO reduction does not occur at very high temperatures. As the temperature decreases, the NO reduction capacity continues to increase until the NO reduction capacity becomes the highest at the "optimum temperature". As the temperature of the flue gas further decreases, the ammonia leakage increases rapidly and at the same time the NO reduction capacity decreases until it reaches the lower end of the temperature range, below which NO reduction no longer occurs. As used herein, the term "optimal temperature" refers to the flue gas temperature at which the NO reduction capability of the SNCR process is at its highest. The term "SNCR process" refers to a process in which NO is selectively and non-catalytically reduced to nitrogen using a single or complex NHi precursor injected into the flue gas within the above temperature range. . "Single NH
The term "i-precursor" refers to ammonia or other compounds, such as ammonium hydroxide, or ammonium carbonate, or mixtures thereof, wherein these compounds are:
Releases ammonia (NH ₃ ) upon thermal decomposition. The term "complex NHi precursor" urea (NH _{2) 2} CO, cyanuric acid, biuret, triuret, ammelide (ammelide), other amide, or a mixture thereof, first NH ₂ radical when pyrolysis Means that liberates

[0014] Other types of flue gas NOx control method for oxidizing NO to NO _2, the inventors according entitled "Apparatus and method for removing nitrogen and sulfur oxides from the combustion gas" U.S. Patent Application Serial No. 734,393 Is disclosed. In this method (hereinafter sometimes referred to as the Jones method), operating at 800-1400 ° F. (427-760 ° C.), a hydrocarbon material such as methanol (a type of peroxyl initiator) is air NO is efficiently oxidized to NO ₂ by being dispersed in the carrier gas. The preferred temperature range is 800 to 140
0 ° F (427-760 ° C). This method is a different type of boiler injection method that uses peroxyl radicals (HO ₂ ) instead of hydroxyl radicals (OH). NO is oxidized according to the following equation.

NO + HO ₂ = NO ₂ + OH Here, an appropriate temperature, for example, 1400 ° F. (760 ° C.), is determined by the NO reduction method of the SNCR type (ie, 1400 ° C.).
This creates a separation line between F.sub.oF (760.degree. C.) and Jones type NO oxidation (i.e., below 1400.degree. F. (760.degree. C.)). In the method of the present invention, NH3 is added to the flue gas above about 1400 ° F. (760 ° C.) in the first stage injection zone.
by injecting i precursor includes the step of reducing NO to N _2. In the second step, about 1400 ° in the second stage injection zone
The peroxyl initiator is injected into the flue gas at a temperature lower than F (760 ° C.), and the remaining NO is oxidized to N ₂ .

The features, aspects and advantages of the present invention may be better understood with reference to the following embodiments, the accompanying detailed description, and the accompanying drawings.

FIG. 1 shows a two-stage boiler 1 useful for implementing the method of the present invention for reducing NOx in flue gas.
FIG. In this method, a 1400 ° F. (760
NO) is reduced to nitrogen by injecting a liquid phase urea or NHi precursor, such as ammonium hydroxide, into the flue gas of the first injection zone 12 at a higher temperature, and in a second stage 1400 °
NO is further reduced to nitrogen by injecting a hydrocarbon material such as methanol or a peroxyl initiator such as hydrogen or hydrogen peroxide into the flue gas in the second injection zone 14 at a temperature lower than F (760 ° C.). Then, the remaining NO is oxidized to NO ₂ to reduce ammonia leakage. Additional NHi precursors include:
More complex compounds than ammonia, such as cyanuric acid, biuret, triuret, ammelide, or mixtures thereof, and ammonia are included. If the flue gas temperature in the first zone 12 falls below an optimal level, a hydrocarbon material such as hydrogen, hydrogen peroxide or methanol is injected with the NHi precursor to reduce the optimal temperature for the NO reduction reaction, In addition, the degree of ammonia leakage can be reduced. The injection point of the NHi precursor may be one or more points or a position of the boiler which offsets the temperature change. As seen in FIG. 1, the injection manifold 16 is connected to a compressor 18 from which air is supplied to an injection nozzle 20. The detailed structure of the injection nozzle 20 is shown in FIGS. 2 and 3, where the compressed air enters the injection nozzle 20 from the air inlet 22 and is discharged from the outlet 24. The NHi precursor enters the injection nozzle 20 through an inlet 26, mixes with air in a mixing section 28 via a nozzle 30, and exits through an outlet 24.

Automatically controlling the injection amount of the co-injection, such as hydrogen, hydrogen peroxide or hydrocarbon, and / or the injection point based on a flue gas temperature sensor located in the first injection zone 12. Is preferred. Preferred injection materials are aqueous urea, methanol, or both.

As discussed earlier, the optimum temperature for the SNCR method lies within a narrow range. A list of known documents
The optimum temperature is 1825 ± 75 ° F (996 ± 42 ° C), or 17
It is between 50 ° F (954 ° C) and 1900 ° F (1038 ° C). The reason for the uncertainty is that temperatures measured at these high levels are detected as low as 50-150 ° F (28-83 ° C) due to radiant heat loss from the sensor member itself. True gas temperature can be measured by applying convective heat using a suction pyrometer.
All temperatures described herein refer to the true gas temperature as measured by a suction pyrometer. According to U.S. Pat. No. 4,208,386 to Arand et al., The temperature range for urea is shown in Example I, but Table 1 shows the NO reduction capacity plotted against temperature. The optimum temperature here is clearly shown to be about 1850 ° F (1010 ° C) based on

One surprising result that forms part of the present invention is that the optimum temperature for urea is clearly 1670 ° F. (9
10 ° C.), most preferably 1605 ° F. (874
° C). It is clear that the optimum temperature taught by U.S. Pat. No. 4,208,386 to Arand et al. Is incorrect. This amazing discovery,
Conventionally, a method of processing in a relatively narrow temperature range is known as SNC.
It implies that it was believed to be applicable to the R method. In one embodiment, the single NHi precursor is
The composite NHi precursor is injected into the hotter flue gas upstream of the R process, and subsequently into the cooler flue gas downstream of the SNCR process. In another embodiment, the single NHi precursor is from about 1900 ° F. (1038 ° C.) to about 17 ° C.
Inject at a temperature of 50 ° F (954 ° C) followed by about
The composite NHi is injected at a temperature from 1750 ° F (954 ° C) to about 1550 ° F (843 ° C). The optimal temperature for the composite NHi precursor is about
It is 175 ° F. (97 ° C.) lower, indicating a much wider temperature range than the known literature teaches. In yet another embodiment, based on inputs from a flue gas temperature sensor, an automatic injection of single or complex NHi precursors into the flue gas from one or several locations of the injection nozzle. Adopt control system. In another embodiment suitable for automatic control, a mixture of single and composite precursors is injected into the flue gas from one or several injection nozzles and based on the measured flue gas temperature at each location. Automatically control the ratio of single and composite NHi precursors delivered to each injection location.

When there are two or more injection points in the SNCR method, one of the other preferable embodiments is to (1) simultaneously inject dilution water together with an aqueous urea solution or an NHi precursor such as ammonium hydroxide. Moving the injection position towards a cooler downstream nozzle or increasing the use of a single NHi precursor using automatic control if the flue gas temperature becomes too high, The other is (2) N
Reduce the amount of diluent water injected with the Hi precursor and move the injection position upstream towards a hotter nozzle, or if the flue gas temperature is too low, use automatic control to control the combined NHi. Increase the amount of precursor material.

Such automatic control includes a flue gas temperature sensor,
It can be based on input from a flue gas NO analyzer, or both.

A suitable method of injecting the injection material is provided by the present invention. While many different techniques are available, such as injecting a liquid or gas directly into the flue gas, it is preferred to premix the chemical with air, steam, circulating flue gas, or a mixture thereof. Premixing is carried out in a suitable device outside the boiler, and the resulting infusate consists of a premix of carrier gas and infused chemical. One suitable device for preparing a premixed injection is a carrier gas venturi, such as the injection nozzle 20 described above.
Thereby, the aqueous solution of the injected chemical is atomized and dispersed in the carrier gas. The infusate is injected at high speed into the flue gas using external forces such as air or flue gas from the compressor 18.

If desired, steam from a boiler may be used instead of air. Pressure loss between the mixing steps can be minimized by careful design of the atomizing nozzle or dispersive injection nozzle 20.
This injection is then placed in the flue gas or in the injection nozzle 20.
The injection nozzle 20 is located only on the wall 32 of the boiler, or is actually located inside the flue gas zone by the cooling action of the carrier gas, by means of an internal injection grid tube. You can also support it. The actual design and location of the nozzle and injection system will depend on boiler constraints, the desired NOx removal rate, and other parameters such as flue gas temperature and composition and dispersion rate.

The two-stage boiler injection method of the present invention provides unexpected and significant benefits of increased total NO conversion and reduced ammonia leakage as compared to the SNCR method operating at similar conditions. Even if the SNCR method is operated under different conditions, an ammonia leak that can be achieved by the two-stage boiler injection method of the present invention operating under similar conditions is achieved at a NO conversion rate higher than the present invention. Is impossible. As far Conversely, Jones for oxidation of NO to NO ₂ (Jones) method, for NO conversion, might be achieved a much higher level, for example, the reduction to nitrogen of small amounts of NO Even if it is performed upstream of the SNCR process, the overall NO conversion efficiency of the two-stage process of the present invention is higher than that of the SNCR process if the Jones process is operated as it is. The surprising benefits of significant reduction in ammonia leakage as provided by the present invention are not disclosed in the known literature. Another advantage of this two-stage boiler injection method is that the residual NO, which is converted to NO ₂ in the second stage, is wet scrubber or Jones.
)), Which can be removed by other techniques disclosed in the known literature, thereby providing high levels of NO without the difficulty of high levels of ammonia leakage as would occur in operation of the SNCR itself.
x removal rates (ie, greater than 80%) can be achieved.
Other advantages of the present invention will become apparent from an understanding of the particular embodiment described below.

This two-stage boiler injection method for NOx control is of great interest for industrial applications, including both coal-fired boilers and solid waste incinerators. In general, application to coal fired boilers has been found to be easier than application to solid waste incinerators. The reason is that, for the same performance, the molar ratio of the chemical to NOx is small and the utilization efficiency of methanol in the second stage is good, so that the carbon content in the produced fly ash is slightly small. Next, the application of this two-stage boiler injection method to a solid waste incinerator will be described with reference to an example. The NOx removal rate is 72 without a wet scrubber.
%, And the adoption of a wet scrubber of downstream flue gas can achieve an NOx removal rate of 81%.

Example I The conditions of a municipal solid waste incinerator with a capacity of 300 tons per day, which is actually being treated, were directly applied to a combustion tunnel for confirming the efficiency of a two-stage boiler injection method for removing NOx. . These tests include the injection of fly ash from an electrostatic precipitator installed in the incinerator to determine the effect of the ash on the process chemistry. The ash injection rate was about 3.0 grains / SCF, or about 7,000 mg / Nm ³ .

In the boiler of FIG. 1, the initial typical flue gas composition in zone 34 (Band A) prior to injection is as follows (% by volume, dry basis):

NO 125 ppm HCl 840 ppm NO ₂ 5 ppm SO ₂ 60 ppm NOx 130 ppm SO ₃ 3 ppm CO 30 ppm HF 15 ppm O ₂ 12% ash 7,000 mg / Nm ³ CO ₂ 10% The water vapor content of the flue gas is typically 9 % By volume.

In the first injection zone 12, an aqueous solution of urea or ammonium hydroxide is injected into the flue gas flowing across using an apparatus as shown in FIGS. And a carrier gas such as air or steam. As shown in FIG. 1, compressed air as a carrier gas was supplied to the injection nozzle 20 via the manifold 16 using the rotary blower 18. The amount of carrier gas was about 6% by weight of the total flue gas from the incinerator. The injection chemical was mixed with the carrier gas in the injection nozzle 20. The injection nozzle 20 penetrates the wall 32 of the boiler, and has an air inlet 22 as a connecting pipe between the carrier gas and the injection chemical, an injection pipe 26, and a chemical outside the two-stage boiler 10 for holding and checking. A device 38 for moving the nozzle 30 for injection, a chemical as a device for atomizing and / or dispersing and premixing the carrier gas and the injection chemical in the venturi section 40 of the injection nozzle 20 located upstream of the outlet 24 Injection nozzle 3
0 is included. The outlet 24 is designed so that a premixed amount of the carrier gas and the injection chemical (NHi precursor or peroxyl initiator) can be injected at high speed. In a preferred embodiment, as seen in FIG.
Operating at sonic or subsonic speed and utilizing a wall jet by a tangential sidewall injector 42 to form a tangential flow pattern to promote rapid mixing, as shown in FIG. Inducing a helical flow pattern in the bulk flue gas. If necessary, convergent-divergent nozzles can be used to promote supersonic injection, or internal injection pipes and manifold nozzles located throughout the flue gas cross-section to facilitate good mixing. Of course, it is possible to promote good sectional effective use. In this embodiment, the diluted aqueous urea solution is used in the first stage of the two-stage injection method, but an aqueous ammonium hydroxide solution may be used instead of urea. When this ammonium hydroxide is heated in the flue gas zone, it immediately releases NH ₃ vapor, but NH ₂ liberated by the decomposition of urea contains enough water to evaporate, and It is not released until the urea is saturated and / or crystallization occurs. Therefore, by increasing or enhancing the dilution ratio, or the droplet size, with some degree delay release of NH ₂ to flue gases from the urea solution, a more intimate mixing of the flue gas As a result, the effective area utilization rate can be improved. This has advantages over ammonium hydroxide in boiler size, desired NOx removal rates, and the degree of temperature and incomplete distribution rate, injection nozzle location and residence time constraints.

As can be seen from the graph of FIG. 5, when the molar ratio of urea to NO is 1.4, the initial NO 125 ppm
NO conversion to nitrogen at 1670 ° F (910 ° C) is 72%
Is obtained. As can be seen in FIG. 5, when the urea / NO molar ratio is 1.4, the ammonia slip is 35 ppm. In FIG. 6, the injection temperature is 1760 ° F (960 ° C) and urea /
At a 1.4 molar NO ratio, the corresponding increase in CO emissions is:
It was 13 ppm. The change in the flue gas composition at this point was as follows.

Band A (FIG. 1) Band B (FIG. 1) Before first stage injection After first stage injection NO 125 ppm 35 ppm NO ₂ 5 ppm 5 ppm NOx 130 ppm 40 ppm CO 30 ppm 43 ppm NH ₃ zero 35 ppm The temperature of the first injection zone 12 When the temperature deviates from the optimum temperature, the NOx removal efficiency is fatally reduced unless a correction operation is performed. The correction operation is based on the temperature sensor input.
Further, as shown in FIG. 1, one or more injection positions are provided to automatically control the boiler position for injecting urea. Alternatively, the hydrocarbon material may be co-injected with the NHi precursor chemical to cause a reduction reaction at the optimum temperature. This method is shown schematically in FIG. 7, where the temperature drops below the optimal range, the NH ₃ leakage increases significantly when no hydrocarbons are injected together, and the NO removal efficiency also increases. Is fatally reduced. These two adverse effects are between 1400 and 1800
Co-injection of hydrocarbons in the range of ° F (760 to 982 ° C) can be counteracted. If CO emission is the limiting factor, the same effect can be obtained by injection of hydrogen or hydrogen peroxide. In a preferred embodiment of this embodiment, for the co-injection of hydrocarbon, methanol is mixed with an aqueous urea solution, and the amount of methanol is automatically controlled based on an input signal from a temperature sensor.

Referring to the examples and FIG. 8, when the molar ratio of methanol to NO is 0.5 in the second injection zone 14, the conversion of NO to NO ₂ is 30% and 7,000 mg /
In the presence of Nm ³ incinerator fly ash and 25 ppm ammonia, an additional 5% NO conversion to nitrogen at 1328 ° F (720 ° C) is added. Fly ash containing unburned carbon tends to slightly hinder the second stage NO conversion efficiency. As seen in FIG. 8, when ash is not present (or the ash has a very low carbon content),
About 45 percent conversion of NO with respect to NO ₂ in methanol in the same molar ratio obtained for NO, further in the presence of ammonia 22 ppm, 1328 ° F to about 7% NO conversion to nitrogen at (720 ° C.) is can get. This ammonia is present in the second stage due to the ammonia slip from the first stage.

According to FIG. 10, the ammonia slip is
It decreased in the second injection zone 14, where a 40% reduction could be recorded in the combustion tunnel field test. In this case, fly ash injection was also used. In FIG. 9, CO emission is 28 ppm
, Where the effect of fly ash is a significant increase in CO emissions compared to ash-free (or low carbon ash) conditions. At this point, the change in flue gas composition is as follows. In this case, the urea / NO molar ratio in the first stage was 1.4, and the methanol / NO molar ratio was 0.5.

[0035]

[Table 1]

At this time, the NOx removal rate is 72%. Assuming that 80% of the NO ₂ is removed by a downstream wet scrubber or spray dryer, the overall removal rate is:
It changes from 130 ppm to 25 ppm, which is 81%. This degree of NOx removal is competitive with the catalyst-based SCR method and corresponds to the expected operating performance of the SNCR method under similar conditions in the high temperature first injection zone 12 (i.e., a 13% NOx removal rate of 13%).
Much higher than 0 ppm to 40 ppm).

EXAMPLE II The test was performed in a quartz-coated combustion tunnel with a capacity of 0.5 MMBTU / hr at a flue gas flow rate of about 25 SCFM. Nitrogen oxide was injected with the main combustion air, ammonia was injected with the dilution air at the throat (chimney inlet), and methanol was injected 11 inches (28 cm) downstream using the carrier gas. The test was performed at a flue gas temperature of 1200 ° F (649 ° C) at the methanol injection point. Samples were taken at the tunnel exit using two water-cooled probes. One of the probes is a continuous gas analyzer and the other is an ammonia sampling system. The gas residence time was about 1 second in the combustion tunnel. The combustion products are passed through a dilute sulfuric acid-containing impinger solution, and ion-specific electrodes are used.
The ammonia in the impinger solution was analyzed using a ctrode). The ammonia concentration was determined by averaging three results. Table 1 shows the results.

[0038]

[Table 2]

The temperature of 1200 ° F. (649 ° C.) is too low for the reduction of NO to nitrogen by injection of ammonia, and in fact only about 2% was obtained. With the Jones method of methanol-only injection, reduction of NO to nitrogen could be achieved at 22%. Summarizing these two independent results, the overall two-stage method provided by the practice of the principles of the present invention provides NO
Is expected to be reduced to 23.6%. As a matter of fact,
Beyond all expectations at 1200 ° F (649 ° C)
A reduction rate of NO to nitrogen of 29% was obtained. The known technique does not disclose a boiler injection method that achieves a 29% reduction of NO to nitrogen at such a low molar ratio or low temperature. In addition, a 54% ammonia reduction rate was simultaneously observed. During the operation of the two-stage injection system, when the addition of NO was stopped, the degree of NH ₃ reduction dropped from 54% to 10%. It is believed that the presence of NO ₂ is important in significantly reducing ammonia leakage.

Example III Additional tests were performed using a crude oil fired boiler (10 MMBTU / hr). Crude oil containing 1.2% sulfur was burned using a steam atomizing burner gun. About 1550 ° F urea aqueous solution
(843 ° C) and injected upstream of the furnace. As seen in FIG. 1, methanol was injected near the boiler tube where the temperature of the flue gas flowing across was 1180 ° F. (638 ° C.). The molar ratio of urea to NOx is about 0.3, NO
The methanol molar ratio to x was about 1.7. Samples were taken at the boiler outlet using an ice-cooled impinger and a continuous chemiluminescent NO-NOx analyzer. The result is
It is shown in the table.

[0041]

[Table 3]

The temperature of 1550 ° F. (843 ° C.)
Very low for the R method, and the urea injector uses only urea in the first injection zone 12 to reduce the NO reduction to nitrogen to 13 despite the low effective cross-sectional utilization of the flue gas.
% Has been reached. In the injection of only methanol in the second injection zone 14, the reduction ratio of NO to nitrogen was 21%. The calculated NOx reduction expected value is 30%. The measured reduction rate of NOx using the two-stage injection method of the present invention was 32%.
This temperature of 1180 ° F which can achieve 32% NO conversion to nitrogen
(638 ° C) is well below the temperature of SNCR technology where 1300 ° F (704 ° C) is the lowest temperature limit so far. A boiler injection method of 32% NO reduction to nitrogen at 1180 ° F. (638 ° C.) has never been disclosed.

The above-described preferred embodiment for removing NOx from flue gas is exemplary only;
The present invention is not limited to these embodiments, and those skilled in the art can make various modifications. The invention is limited only by the recitation of the claims at the beginning.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a two-stage boiler illustrating a preferred embodiment of a two-stage injection method provided by practicing the principles of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating one preferred embodiment of an injection nozzle provided by practicing the principles of the present invention. The NHi precursor and / or peroxyl initiator is injected through this nozzle.

FIG. 3 is a schematic diagram illustrating one preferred embodiment of an injection system for injecting NHi precursors and / or peroxyl initiators provided by practicing the principles of the present invention.

FIG. 4 is an illustration showing a preferred process pattern for the NHi precursor and peroxyl initiator introduced by the injection nozzle assembly provided in accordance with the practice of the present invention.

FIG. 5 shows the NO concentration as a function of the molar ratio of urea injected into the flue gas to the NO concentration in the flue gas at both 1670 ° F. (910 ° C.) and 1760 ° F. (960 ° C.). It is a graph which shows a change.

FIG. 6: N in flue gas at 1760 ° F. (960 ° C.)
3 is a graph showing the change in ppm of CO as a function of the molar ratio of urea injected into the flue gas to the Ox concentration.

FIG. 7 is a graph showing optimal temperatures for NO reduction and ammonia slip when urea is injected by implementing the principles of the present invention, with and without hydrocarbons.

FIG. 8: NO% to N ₂ and N as a function of the molar ratio of methanol injected into the flue gas to the NOi concentration in the flue gas at an injection temperature of 1328 ° F. (720 ° C.)
Is a graph showing the NO% for O _2.

FIG. 9 is a graph showing the change in CO concentration as a function of the molar ratio of methanol injected into the flue gas to the NO concentration in the flue gas at an injection temperature of 1720 ° F. (938 ° C.).

FIG. 10 is a graph showing ppm ammonia slip at 1328 ° F. (720 ° C.) as a function of the molar ratio of methanol injected into the flue gas to the NOi concentration in the flue gas.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Two-stage boiler 12 ... 1st injection zone 14 ... 2nd injection zone 20 ... Injection nozzle 22 ... Air inlet 24 ... Outlet 26 ... Injection pipe 28 ... Mixing part 30 ... Nozzle 32 ... Wall

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[Procedure amendment]

[Submission date] April 15, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Claims (20)

[Claims] 1. A method for reducing a part of NO to N ₂ in the flue gas of the first injection zone having a gas temperature higher than 1400 ° F. (760 ° C.). of injecting NHi precursors, further, in order to oxidize the (b) residual NO to NO _2, gas temperature 14
Injecting one or more peroxyl initiator materials into the flue gas of the second injection zone at a temperature lower than 00 ° F. (760 ° C.) for the purpose of reducing nitrogen oxides in the combustion emission gas. A two-stage boiler injection method. 2. A via a wet scrubber located downstream of the second injection zone, by passing the NO ₂ containing gas stream, further comprising Claim removing the NO ₂ exiting the second injection zone 2. A two-stage boiler injection method for the purpose of reducing nitrogen oxides in a combustion emission gas according to item 1. By introducing wherein NO ₂ containing gas stream into a spray dryer, nitrogen oxides in the combustion discharge gas of the further encompasses claim 1, wherein the step of removing NO ₂ exiting the second injection zone Two-stage boiler injection method for the purpose of reducing methane. 4. The nitrogen oxides of claim 1, wherein said NHi precursor is selected from ammonia, urea, cyanuric acid, biuret, triuret, ammelide, and mixtures thereof. Two-stage boiler injection method for the purpose of reducing methane. 5. The method according to claim 1, wherein hydrogen, hydrogen peroxide or a hydrocarbon material is co-injected with the NHi precursor into the first injection zone. A two-stage boiler injection method. 6. The peroxyl initiator material is propane, benzene, ethane, ethylene, n-butane, n-octane, methane, hydrogen, methanol, isobutane, pentane, acetylene, methyl alcohol, ethyl alcohol, acetone, glacial acetic acid. , Ethyl ether, propyl alcohol, nitrobenzyl alcohol, methyl ethyl ketone, propylene, toluene, formaldehyde, camphor,
The two-stage boiler injection method for reducing nitrogen oxides in a combustion emission gas according to claim 1, wherein the method is selected from ether and glycol, and a mixture thereof. 7. The method of claim 1, wherein the peroxyl initiator material injected into the second zone is injected in the form of an injection fluid comprising a peroxyl initiator and air. A two-stage boiler injection method for the purpose of reducing substances. 8. A method for mixing a precursor material with a carrier gas prior to introducing the NHi precursor into the first injection zone, and mixing a peroxyl initiator with the peroxyl initiator prior to introducing the peroxyl initiator material into the second injection zone. 2. The method for injecting a two-stage boiler for reducing nitrogen oxides in a combustion gas according to claim 1, wherein the carrier gas is mixed with the carrier gas, and the premixing is performed outside the injection zone. 9. The flue gas produced in a boiler,
Both the mixture of the NHi precursor material and the carrier gas and the mixture of the peroxyl initiator material and the carrier gas are provided by a wall jet disposed on a boiler wall.
9. The method according to claim 8, wherein the gas is injected into cross-flow flue gas.
A two-stage boiler injection method for reducing nitrogen oxides in a combustion gas as described in the above. 10. The introduction of the mixture of the NHi precursor material and the carrier gas and the mixture of the peroxyl initiator material and the carrier gas, wherein the wall jet is configured to generate a tangential vortex in the flue gas. 9. The two-stage boiler injection method for reducing nitrogen oxides in a combustion gas according to claim 8, comprising a step of providing a tangential orientation. 11. The flue gas is generated in a boiler,
The method of claim 1 wherein both the mixture of the NHi precursor material and the carrier gas and the mixture of the peroxyl initiator material and the carrier gas are injected into the cross-flow flue gas via an internal injection grid tube and nozzle. Item 8. A two-stage boiler injection method for the purpose of reducing nitrogen oxides in combustion gas. 12. In an SNCR process for removing NOx from combustion emissions, a single NHi precursor is injected upstream of a relatively high flue gas temperature and a complex NHi precursor is injected downstream of a relatively low temperature. Reducing the nitrogen oxides in the flue gas by controlling the optimum temperature in the downstream section by about 175 ° F. (97 ° C.) below the optimum temperature in the upstream section. 2 for the purpose
Step boiler injection method. 13. A temperature of about 1750 ° F. to 1900 ° F. (954 to 10
In the upstream where flue gas in the range of 38 ° C) exists, a single N
Implanting a Hi precursor, and from about 1550 ° F. to about 1750 ° F.
13. The method according to claim 12, wherein the composite NHi precursor is injected into a downstream portion where flue gas at a temperature of about 843 to about 954 ° C. is present. A two-stage boiler injection method. 14. An S for removing NOx from the combustion emission gas.
In the NCR method, a mixture of single and composite NHi precursors is injected into the flue gas via one or two injection nozzles and fed to a predetermined location.
The flue gas temperature, flue gas NO analyzer signal,
Alternatively, a two-stage boiler injection method for reducing nitrogen oxides in a combustion emission gas, which is automatically controlled based on both of them. 15. The reduction of nitrogen oxides in a combustion effluent gas according to claim 14, wherein the single NHi precursor material is ammonium hydroxide and the composite NHi precursor material is an aqueous urea solution. A two-stage boiler injection method for the purpose. 16. The flue gas of claim 14, wherein the hydrogen, hydrogen peroxide or hydrocarbon material is co-injected with the NHi precursor into the flue gas at one or several injection nozzles. A two-stage boiler injection method for the purpose of reducing nitrogen oxides therein. 17. A method for premixing an NHi precursor and a peroxyl initiator material with a carrier gas, the NHi precursor or peroxyl initiator material mixed with a carrier gas including means disposed externally to the boiler. Device for injecting into gas. 18. A mixture of the NHi precursor and a carrier gas or a mixture of the peroxyl initiator material and a carrier gas injected into a flue gas flowing therethrough by a wall jet disposed on a boiler wall. 18. An apparatus for injecting NHi precursor or peroxyl initiator material mixed with a carrier gas according to claim 17 into the flue gas of a boiler. 19. A mixture of the NHi precursor and a carrier gas or a mixture of the peroxyl initiator material and a carrier gas is injected into the flue gas flowing therethrough by an internal injection grid tube and nozzle. Item 17
Apparatus for injecting NHi precursor or peroxyl initiator material mixed with the described carrier gas into the boiler flue gas. 20. The NHi mixed with a carrier gas according to claim 18, wherein said wall jets are provided tangentially oriented to generate tangential vortices to the flue gas. A device for injecting precursor or peroxyl initiator material into the boiler flue gas.