JPH08141363A - Urea blowing method - Google Patents

Abstract

PURPOSE: To improve nitrogen oxide removing efficiency and lower the leakage of ammonia by blowing urea to a combustion furnace after urea is evaporated and hydrolyzed in a bent part of a nitrogen oxide removing agent blowing pipe installed in the wall of the combustion furnace. CONSTITUTION: Urea particles supplied to a nitrogen oxide removing agent blowing pipe 7 are blown to a leading pipe 18 in the inside of a furnace wall by a nitrogen oxide removing agent blowing medium 16 such as steam-containing air, steam, etc., and the particles are separated from the blowing medium due to the centrifugal force in a bent part of the leading pipe 18 and come into collision against the inner wall of the leading pipe. The urea particles colliding against the inner wall of the leading pipe are fused and adhere to the inner wall of the leading pipe, furthermore hydrolyzed to be converted into ammonia, and the ammonia is mixed with the blowing medium 16 and blown to the furnace while the blowing angle being altered at 90 degree. The ammonia blown to the furnace reduces NOx in a combustion gas within a short time and thus removes nitrogen oxides. As a result, the nitrogen oxide removing efficiency can be heightened and the leakage of ammonia can be lowered simultaneously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a urea blowing method, and more particularly, it can be suitably used for non-catalytic denitration such as a refuse incinerator, which is useful for simplifying the urea blowing equipment, saving energy and reducing pollution. Urea blowing method.

[0002]

BACKGROUND ART It is well known as a non-catalytic denitration method to blow nitrogen, urea, etc. into a high temperature combustion gas in the presence of oxygen to reduce nitrogen oxides (NOx). Ammonia is a gas under normal temperature and pressure, and is mixed with steam, air and combustion gas as it is, and is blown into the furnace. However, since ammonia gas is toxic to the human body, when handling a large amount, it is necessary to install a safety protection facility in accordance with legal regulations.

On the other hand, urea is a solid at room temperature and atmospheric pressure, is easy to handle, and is harmless to the human body, so that urea is more often used in small equipment such as a refuse incinerator. However, the melting temperature of urea is as low as 135 ° C., and if particles or powders are conveyed as an air stream, the problem of melting and adhering to the inner wall of the pipe near the furnace occurs. Therefore, generally, as shown in FIG. 4 (A), a method of spraying urea aqueous solution 40 as atomized urea water 43 into a furnace using a two-fluid atomizer together with atomizing medium 41 such as high-pressure air or steam, or As shown in FIG. 4 (B), a method is adopted in which pressurized urea water 44 pressurized by a pump is sprayed as atomized urea water 43 into the furnace by using a pressure spray atomizer 45.

When urea is blown into the furnace as water droplets in this way, the water droplets must first be vaporized in order for urea to react with NOx. That is, unlike the case where ammonia is blown in as a gas as it is, it takes time for the aqueous urea solution to vaporize in the furnace. Further, in order for urea to react with NOx to be reduced, it is necessary to react with steam and hydrolyze to produce ammonia as described below. H ₂ NCONH ₂ + H ₂ O → 2NH ₃ + CO ₂ (1) In order for urea to act as ammonia and act as a denitration agent, (1) vaporization of urea water droplets and (2) hydrolysis of vaporized urea are necessary. is there.

Also, depending on the size of water droplets and the temperature inside the furnace,
It takes several seconds / 10 for vaporization of water droplets. In addition, as a result of investigating an ammonia production reaction by thermal decomposition of solid urea particles in an air flow using an instantaneous heating reactor, it takes about 1 to 2 seconds at 500 to 800 ° C. to reach a maximum reaction rate. . It should be noted that in an actual furnace, the temperature is higher than this, and because radicals that promote the reaction coexist in the combustion gas, it is considered that urea is pyrolyzed faster. On the other hand, the residence time of the blown denitration agent in non-catalytic denitration in an actual furnace is as follows.

First, the residence time of the combustion gas in the furnace is about 2 to 3 seconds in the case of slow burning coal, and it is 3 to 4 seconds even in the case of burning various miscellaneous wastes such as refuse incinerators that are difficult to burn. It is a degree. However, when a denitration agent such as ammonia or urea is blown into a region where the combustion reaction is actively progressing, the nitrogen component is oxidized (combusted) rather than acting as a denitration agent, and conversely generates NOx. Therefore, in the case of non-catalytic denitration, the denitration agent must be blown near the exit of the furnace where the combustion reaction is almost completed, that is, in the length of the furnace, about a half to two-thirds of the length of the furnace. I don't get. Since the combustion gas residence time from the position where the denitration agent is blown to the furnace outlet is about 1 to 2 seconds, the residence time of the denitration agent in the actual furnace is also 1
~ 2 seconds.

As described above, in order for urea to function as a denitration agent, urea needs to be vaporized and hydrolyzed to NH _3. Therefore, when it is directly blown into the furnace as water droplets, urea is vaporized and hydrolyzed. The time until decomposition is a dead time, while the residence time in the furnace is limited, so the time spent for the denitration reaction is substantially shortened. That is, even when urea is used as a denitration agent, the residence time required for the denitration reaction is not sufficient, so the denitration rate is lower than that of ammonia, and unreacted leaked ammonia is likely to be discharged.

Therefore, if urea is vaporized and hydrolyzed in advance and then blown into the furnace, the denitration reaction time in the furnace can be increased by that much, which serves to increase the denitration rate and at the same time reduce leakage ammonia. That is clear. From such a viewpoint, a method has been proposed in which urea particles or urea water is vaporized in advance and then blown into the furnace.

FIG. 5 is an explanatory view of a conventional method of vaporizing urea particles and blowing them into a furnace. According to this method, the urea particles stored in the hopper 1 are measured by the valve 2 and the double rotary feeder 3 and supplied to the heater surface 36 of the carburetor 35, which is vaporized by the heater 28 to convey nitrogen or vapor. The medium 29 is blown into the furnace through the pipe 30 and the denitration agent blowing pipe 34. However, the pipe 30 and the denitration agent blowing pipe 34 need to be installed and heated by the heater 31 so that the urea vaporized in the vaporizer 35 does not coagulate and solidify, which increases the facility cost and the operating cost and is uneconomical. There is a drawback that. Furthermore, (1) it takes time to melt and vaporize the urea particles dropped on the heater surface 36, (2) the volume of the vaporizer 35 and the pipe volume from the vaporizer 35 into the furnace are large, and (3) liquid In comparison, a powder feeder has a problem of low control response, for example, because of its low response in principle, and it has hardly been put to practical use.

[0010]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of the prior art, and when urea is blown into the furnace as a denitration agent, the blowing equipment becomes large, and the equipment cost and operating cost increase. It is an object of the present invention to provide a urea blowing method capable of blowing urea into the furnace to improve the denitration rate and reducing the amount of leaked ammonia without causing the above.

[0011]

The inventions claimed in this application are as follows. (1) When urea is blown into a combustion furnace by a denitration agent blowing pipe to reduce and denitrate nitrogen oxides in combustion gas, a bent portion of the denitration agent blowing pipe is provided in the wall of the combustion furnace, and the urea is bent at the bending portion. A method for injecting urea, which comprises injecting into a combustion furnace after vaporizing and hydrolyzing. (2) The urea blowing method according to (1), wherein the urea supplied to the denitration agent blowing pipe is solid urea or spray urea water, and the urea is conveyed by air containing steam or a steam flow.

According to the method of the present invention, solid urea or urea water droplets carried in an air or steam stream containing water vapor comprises:
At the bent part of the conduit provided in the high temperature furnace wall, centrifugal force separates from the carrier flow, adheres to the high temperature wall, and solid urea or urea water adhering to the wall is vaporized by receiving heat from the wall, It is hydrolyzed and converted to ammonia. Ammonia is blown into the furnace together with a carrier flow such as air or steam flowing in the conduit to reduce and denitrate NOx in the combustion gas. By doing this, it is possible to convert urea into ammonia and then blow it into the furnace without adding any special large-scale equipment or heat source. Leakage ammonia is prevented from being discharged.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings.
FIG. 1 is a cross-sectional explanatory view of a urea injection part of a combustion furnace showing an embodiment of the present invention. In the figure, a fitting furnace wall 10 is fitted into the urea blowing portion of the fixed furnace wall 9 of the combustion furnace. The fitting furnace wall 10 has a bent portion, one opening is connected to the denitration agent blowing pipe 7, and the other opening is a furnace wall conduit 18 and a furnace wall conduit 18 opening into the furnace. A thermometer 17 provided at the bent portion and the furnace outlet is installed. The bent portion of the furnace wall conduit 18 has a wall temperature of about 700 to
It is bent 90 degrees at a position of 800 ° C.

A urea particle supply pipe 4 and a water injection pipe 8 for supplying urea particles are connected to the denitration agent blowing pipe 7, and urea by melting of urea particles is connected to a denitration agent blowing pipe connection portion of the urea particle supply pipe 4. A water cooling jacket 6 is installed to prevent the particles from adhering to the inside of the wall of the pipe. Further, a water injection pipe 5 is provided in the urea particle supply pipe 4, and when urea is adhered and solidified on the inner wall at the connecting portion between the denitration agent injection pipe 7 and the urea particle supply pipe 4 and clogged, water is supplied. Can be washed away.

On the other hand, the water injection pipe 8 sprays water in the vicinity of the furnace wall inlet of the denitration agent injection pipe 7 based on the signal from the thermometer 17 provided in the furnace wall conduit 18. If the temperature inside the furnace wall deviates from the proper temperature due to changes in the properties of the fuel or the operating conditions of the furnace,
This is for properly adjusting the temperature of the conduit 18 in the furnace wall. The signal from the thermometer 17 of the conduit 18 in the furnace wall is sent to the arithmetic unit, the flow meter 14 and the control valve 15 are adjusted via the controller, and the water in the water tank 11 is supplied from the injection pipe 8 by the valve 12 and the pump 13. It is supplied to the denitration agent blowing pipe 7.

Urea particles are supplied from the hopper 1 through the double rotary feeder 3 and the urea particle supply pipe 4 into the denitration agent blowing pipe 7. Double rotary feeder 3
A single rotary feeder may be used only for the purpose of quantitatively supplying urea particles, but in this embodiment, the denitration agent blowing medium 16 supplied to the denitration agent blowing pipe 7 is prevented from flowing backward to the hopper 1. Therefore, the double rotary feeder 3 is used.

The urea particles supplied to the denitration agent injection pipe 7 are
The denitration agent blowing medium 16 such as air or steam containing steam is blown into the furnace wall conduit 18, and the bent portion of the conduit 18 is separated from the blowing medium 16 by centrifugal force and collides with the conduit inner wall. Since the melting temperature of urea is 135 ° C., the urea particles that have collided with the inner wall of the conduit are melted and adhered to the inner wall of the conduit, further hydrolyzed by the above reaction formula (1) and converted into ammonia, and mixed with the blowing medium 16. It is blown into the furnace by changing its direction by 90 degrees. Ammonia blown into the furnace reduces and denitrates NOx in the combustion gas in a short time.

FIG. 2 is a cross sectional view showing a urea injection portion of a combustion furnace showing another embodiment of the present invention. In FIG. 2, FIG.
5 is different from the urea particles in that the supply amount of the urea aqueous solution is appropriately adjusted and the denitration agent injection pipe 7 is supplied from the injection nozzle 27.
I tried to blow it into. That is, urea is stored in advance in the tank 19 as an aqueous solution, and in the tank 20, water used for controlling the temperature of the furnace wall conduit 18 is stored. The urea water in the tank 19 and the water in the tank 20 are supplied to and mixed with the mixer 25 by the valves 12 and 21 and the pumps 13 and 22, respectively, reach the spray nozzle 27 through the pipe 26, and enter the denitration agent injection pipe 7. Is sprayed. The sprayed urea water becomes water droplets, and high-pressure steam, combustion air,
It is conveyed together with the denitration agent blowing medium 16 such as exhaust gas and nitrogen, and reaches the bent portion of the furnace wall conduit 18. As in the case of FIG. 1, the supply amount of urea water and water is based on the signal from the thermometer 17 in the conduit 18 in the furnace wall, the calculator, the controller, and the flowmeter 1.
4, 23, control valves 15, 24.

In the embodiments shown in FIGS. 1 and 2, in consideration of easiness of maintenance and maintenance, the in-furnace wall conduit 18 in which the furnace wall conduit 18 is made of a refractory block separate from the fixed furnace wall 9 of the furnace body is installed. Although 10 is provided, the present invention is not limited to this. Further, in the above-described embodiment, two bent portions of the furnace wall conduit 18 are provided. However, as shown in FIG. 3, the bent portions may be provided in several places as needed, and the residence time in the furnace wall conduit 18 is set. Can be increased. Note that FIG. 3A is a sectional view taken along the line AA of the urea injection part furnace wall, and FIG. 3B is a sectional view taken along the line BB.

[0020]

According to the inventions of claims 1 and 2,
Since urea can be blown into the furnace after converting urea into ammonia in the conduit in the furnace wall, a high denitration rate and low leak ammonia can be realized at the same time, which is particularly useful for reducing pollution of the combustion device.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view of a urea injection part of a combustion furnace showing an embodiment of the present invention.

FIG. 2 is an explanatory cross-sectional view of a urea injection part of a combustion furnace showing another embodiment of the present invention.

FIG. 3 is a furnace wall cross-sectional view of the urea injection part of the present invention,
(A) is a sectional view taken along the line BB, and (B) is a sectional view taken along the line AA.

FIG. 4 is an explanatory view of a urea injection method according to a conventional technique,
(A) shows a urea blowing method using a two-fluid atomizer, and (B) shows a urea blowing method using a pressure atomizing atomizer.

FIG. 5 is an explanatory view of a method of vaporizing urea particles and blowing them into a furnace according to a conventional technique.

[Explanation of symbols]

1 ... Hopper, 2 ... Valve, 3 ... Double rotary feeder,
4 ... Urea particle supply pipe, 5 ... Water injection pipe, 6 ... Water cooling jacket, 7 ... Denitration agent injection pipe, 8 ... Water injection pipe, 9 ... Fixed furnace wall, 1
0 ... Inset furnace wall, 11 ... Water tank, 12 ... Valve, 13 ...
Pump, 14 ... Flowmeter, 15 ... Control valve, 16 ... Denitration agent blowing medium, 17 ... Thermometer, 18 ... Furnace wall conduit, 19 ... Tank, 20 ... Tank, 21 ... Valve, 2 ... Pump, 23 ... Flow rate Total, 24 ... Control valve, 25 ... Mixer, 26 ... Piping, 27 ...
Spray nozzle, 28 ... Heater, 29 ... Transport medium, 30 ... Piping, 31 ... Heater, 32 ... Valve, 33 ... Air or steam,
34 ... Denitration agent blowing pipe, 35 ... Vaporizer, 36 ... Heater surface.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Sente 6-9 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Kure Factory

Claims (2)

[Claims] 1. When the urea is blown into the combustion furnace by a denitration agent blowing tube to reduce and denitrify nitrogen oxides in the combustion gas, a bent portion of the denitration agent blowing tube is provided in the wall of the combustion furnace, and the bent portion is formed. A method for injecting urea, which comprises vaporizing and hydrolyzing urea in step 1, and then injecting it into a combustion furnace. 2. The urea supplied to the denitration agent blowing pipe is solid urea or atomized urea water, and the urea is conveyed by air containing steam or steam flow.
The urea blowing method described.