A system and method for quickly judging the blockage of urea spray gun in denitrification system and a treatment method

Abstract

The present disclosure relates to a system and method for quickly judging the blockage of a urea spray gun of a denitration system, and a treatment method. The flow rate of hot primary air entering the pyrolysis furnace is obtained according to a first flow meter on the inlet pipeline of the pyrolysis furnace, and the blockage caused by crystallization of the pyrolysis furnace can be eliminated according to the flow rate of hot primary air. In addition, according to a second flow meter on the inlet pipeline of the urea spray gun and the opening of the urea spray gun, it is possible to quickly and accurately judge whether the urea spray gun is blocked.

Description

Technical Field

[0001] The present disclosure relates to the field of flue gas denitration, and in particular, to a system and method for quickly determining blockage of a urea spray gun in a denitration system, and a treatment method. Background Art

[0002] The system of SCR denitrification process mainly includes: SCR catalytic reactor and catalytic components, ammonia preparation, ammonia injection system, denitrification utility system, etc. Among them, ammonia preparation mainly adopts urea pyrolysis ammonia production process.

[0003] Urea pyrolysis is a decomposition reaction of urea at high temperature. The urea solution prepared in the urea dissolving tank is transported to the urea solution storage tank. The urea solution in the urea solution storage tank is pumped to the urea metering module of each furnace by a high-flow circulation pump. After passing through the metering module, the urea solution is sprayed into the pyrolysis furnace by a spray gun and decomposed into ammonia and water at high temperature. However, urea crystallization often occurs during the operation of the urea pyrolysis furnace, blocking the pyrolysis furnace outlet and spray gun, resulting in abnormal denitrification treatment. In addition, there is no method to quickly determine the blockage of the spray gun and post-processing method. Summary of the invention

[0004] The purpose of the present disclosure is to provide a system and method and a treatment method for quickly judging the blockage of a urea spray gun in a denitrification system, so as to solve the problem of low judgment efficiency in the prior art.

[0005] In order to achieve the above-mentioned object, the first aspect of the present disclosure provides a system for quickly judging the blockage of a urea spray gun of a denitration system, the system comprising a pyrolysis furnace, a urea spray gun arranged inside the pyrolysis furnace, and a detection unit; The inlet of the pyrolysis furnace is used to communicate with a hot primary air source, and the outlet of the pyrolysis furnace is used to communicate with a boiler flue; the inlet of the urea spray gun is used to communicate with a urea solution source; A first flow meter is provided on the inlet pipeline of the pyrolysis furnace; A second flow meter is provided on the inlet pipeline of the urea spray gun; The detection unit is electrically connected to the first flow meter, the second flow meter and the urea spray gun, and is used to receive a first flow signal from the first flow meter, a second flow signal from the second flow meter and an opening signal from the urea spray gun, and to determine a blockage state of the urea spray gun.

[0006] Optionally, a nitrogen oxide detector is provided on the boiler flue to detect the nitrogen oxide concentration of the flue gas inside the boiler flue; The nitrogen oxide detector is electrically connected to the detection unit; The system further comprises a control unit, wherein the control unit is electrically connected to the urea spray gun and the detection unit; The detection unit is used to receive the nitrogen oxide concentration signal from the nitrogen oxide detector and send a signal to the control unit; the control unit is used to receive the signal sent by the detection unit and adjust the opening of the urea spray gun.

[0007] Optionally, the number N of the urea spray guns is a positive integer, and N≥2.

[0008] A second aspect of the present disclosure provides a method for quickly determining whether a urea spray gun of a denitration system is blocked by using the system described in the first aspect of the present disclosure, the method comprising: The urea solution is allowed to enter the pyrolysis furnace through the urea spray gun and contact with the hot primary air for atomization treatment to obtain atomized urea; the detection unit is allowed to obtain the flow signal of the hot primary air, the flow signal of the urea spray gun, and the opening signal of the urea spray gun; When the flow signal of the hot primary air decreases to less than a first threshold, it indicates that the pyrolysis furnace is blocked; When the flow signal of the hot primary air is above the first threshold and the flow signal of the urea spray gun decreases to be less than the second threshold, it indicates that the urea spray gun is in a blocked state; When the flow signal of the hot primary air is above the first threshold, the flow signal of the urea spray gun is above the second threshold, and the opening signal of the urea spray gun increases to above the third threshold, it indicates that the urea spray gun is in a blocked state; The first threshold is selected from 4000~5900Nm 3 / h; the second threshold is selected from 0~0.03m 3 / h; the third threshold is selected from any value between 50% and 100%.

[0009] Optionally, the method further comprises, before performing the atomization treatment, heating the hot primary air to 340-650°C.

[0010] Optionally, the concentration of the urea solution is 40-60% by weight; and the crystallization temperature of the urea solution is 15-25°C.

[0011] Optionally, the flow ratio of the urea solution to the hot primary air is 1:(1115~1125).

[0012] Optionally, when the number of the urea spray guns N is greater than or equal to 2, the urea solution is allowed to pass through each urea spray gun and enter the pyrolysis furnace; the detection unit is allowed to obtain a flow signal of the hot primary air, a flow signal of each urea spray gun, and an opening signal of each urea spray gun; When the flow signal of the hot primary air decreases to less than the first threshold, it indicates that the pyrolysis furnace is blocked; When the flow signal of the hot primary air is above the first threshold and the flow signal of any urea spray gun decreases to be less than the second threshold, it indicates that the urea spray gun is in a blocked state; When the flow signal of the hot primary air is above the first threshold, the flow signal of any urea spray gun is above the second threshold, and the automatic valve opening signal of the urea spray gun increases to above the third threshold, it indicates that the urea spray gun is in a blocked state.

[0013] A third aspect of the present disclosure provides a method for treating a urea spray gun blockage, the method comprising: The method according to the second aspect of the present disclosure is used to judge the working state of the urea spray gun. When the urea spray gun is in a blocked state, the detection unit is enabled to obtain the nitrogen oxide concentration of the boiler flue and send a signal to the control unit; If the nitrogen oxide concentration increases to above a fourth threshold, the control unit increases the opening of the urea spray gun until the nitrogen oxide concentration decreases to below a fifth threshold, and the control unit decreases the opening of the urea spray gun; The fourth threshold is selected from any value between 40 and 45 weight %; and the fifth threshold is selected from any value between 25 and 30 weight %.

[0014] Optionally, when the nitrogen oxide concentration increases to above a sixth threshold, the urea spray gun is closed and flushed with water; the sixth threshold is selected from any one value between 50 and 55 weight %.

[0015] Through the above technical solution, the flow rate of the hot primary air entering the pyrolysis furnace is obtained according to the first flow meter on the inlet pipeline of the pyrolysis furnace, and the blockage caused by crystallization of the pyrolysis furnace can be eliminated according to the flow rate of the hot primary air. In addition, according to the second flow meter on the inlet pipeline of the urea spray gun and the opening of the urea spray gun, it is possible to quickly and accurately determine whether the urea spray gun is blocked.

[0016] Other features and advantages of the present disclosure will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0017] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0018] The first aspect of the present disclosure provides a system for quickly judging whether a urea spray gun of a denitration system is blocked, the system comprising a pyrolysis furnace, a urea spray gun arranged inside the pyrolysis furnace, and a detection unit; the inlet of the pyrolysis furnace is used to communicate with a hot primary air source, and the outlet of the pyrolysis furnace is used to communicate with a boiler flue; the inlet of the urea spray gun is used to communicate with a urea solution source; A first flow meter is provided on the inlet pipeline of the pyrolysis furnace; A second flow meter is provided on the inlet pipeline of the urea spray gun; The detection unit is electrically connected to the first flow meter, the second flow meter and the urea spray gun, and is used to receive a first flow signal from the first flow meter, a second flow signal from the second flow meter and an opening signal from the urea spray gun, and to determine a blockage state of the urea spray gun.

[0019] Through the above technical solution, the flow rate of the hot primary air entering the pyrolysis furnace is obtained according to the first flow meter on the inlet pipeline of the pyrolysis furnace, and the blockage caused by crystallization of the pyrolysis furnace can be eliminated according to the flow rate of the hot primary air. In addition, according to the second flow meter on the inlet pipeline of the urea spray gun and the opening of the urea spray gun, it is possible to quickly and accurately determine whether the urea spray gun is blocked.

[0020] In one embodiment, the urea spray gun described in the present disclosure is a conventional choice in the art and is not required by this application; the setting of the urea spray gun may also include embedding the urea spray gun in a pyrolysis furnace, wherein the nozzle of the urea spray gun is inside the pyrolysis furnace, and the remaining part of the urea spray gun is arranged outside the pyrolysis furnace.

[0021] In one embodiment, each pyrolysis furnace of the present disclosure may include a plurality of spray guns, wherein the number N of the urea spray guns is a positive integer, and N≥2, and the preferred number of the urea spray guns is preferably 4.

[0022] In one embodiment, a nitrogen oxide detector is provided on the boiler flue to detect the nitrogen oxide concentration of the flue gas inside the boiler flue; The nitrogen oxide detector is electrically connected to the detection unit; The system further comprises a control unit, wherein the control unit is electrically connected to the urea spray gun and the detection unit; The detection unit is used to receive the nitrogen oxide concentration signal from the nitrogen oxide detector and send a signal to the control unit; the control unit is used to receive the signal sent by the detection unit and adjust the opening of the urea spray gun.

[0023] A second aspect of the present disclosure provides a method for quickly determining whether a urea spray gun of a denitration system is blocked by using the system described in the first aspect of the present disclosure, the method comprising: The urea solution is allowed to enter the pyrolysis furnace through the urea spray gun and contact with the hot primary air for atomization treatment to obtain atomized urea; the detection unit is allowed to obtain the flow signal of the hot primary air, the flow signal of the urea spray gun, and the opening signal of the urea spray gun; When the flow signal of the hot primary air decreases to less than a first threshold, it indicates that the pyrolysis furnace is blocked; When the flow signal of the hot primary air is above the first threshold and the flow signal of the urea spray gun decreases to be less than the second threshold, it indicates that the urea spray gun is in a blocked state; When the flow signal of the hot primary air is above the first threshold, the flow signal of the urea spray gun is above the second threshold, and the opening signal of the urea spray gun increases to above the third threshold, it indicates that the urea spray gun is in a blocked state; The first threshold is selected from 4000~5900Nm 3 / h; the second threshold is selected from 0~0.03m 3 / h; the third threshold is selected from any value between 50% and 100%.

[0024] In this embodiment, the method disclosed in the present invention can not only quickly eliminate the blockage of the pyrolysis furnace, but also quickly and accurately determine whether the urea spray gun is blocked. The judgment process disclosed in the present invention mainly includes: S1, judging whether the pyrolysis furnace is blocked by the flow rate of the hot primary air; S2, judging whether the urea spray gun is blocked by the flow rate of the urea spray gun; S3, judging whether the urea spray gun is blocked by the opening of the urea spray gun.

[0025] The specific method of judging step S1 is as follows: when the flow signal of the hot primary air is above the first threshold, it indicates that the pyrolysis furnace is not blocked; when the flow signal of the boiler exhaust gas decreases to less than the first threshold, it indicates that the pyrolysis furnace is blocked.

[0026] Among them, the specific method of judging in step S2 is: when the flow signal of the hot primary air is above the first threshold and the flow signal of the urea spray gun is reduced to less than the second threshold, it indicates that the urea spray gun is in a blocked state; when the flow signal of the hot primary air is above the first threshold and the flow signal of the urea spray gun is above the second threshold, it indicates that the urea spray gun is not blocked.

[0027] Wherein, the specific method of judging in step S3 is: when the flow signal of the hot primary air is above the first threshold, the flow signal of the urea spray gun is above the second threshold, and the opening signal of the urea spray gun increases to above the third threshold, it indicates that the urea spray gun is in a blocked state; when the flow signal of the hot primary air is above the first threshold, the flow signal of the urea spray gun is above the second threshold, and the opening signal of the urea spray gun is below the third threshold, it indicates that the urea spray gun is not blocked.

[0028] In a preferred embodiment, the first threshold is selected from 4000 Nm 3 / h; the second threshold is selected from 0.02m 3 / h; the third threshold is selected from any value of 50%. In this embodiment, by optimizing the first threshold, the second threshold and the third threshold, the sensitivity and accuracy of the judgment method can be further enhanced.

[0029] In one embodiment, the method further comprises, before the atomization treatment, heating the hot primary air to 340-650° C. In this embodiment, the hot primary air enters the pyrolysis furnace to atomize the urea solution and then enters the boiler flue to react with the boiler exhaust gas to undergo a denitration reaction, which can effectively remove a large amount of nitrogen oxides in the boiler exhaust gas.

[0030] In one embodiment, the concentration of the urea solution is 45-60% by weight, preferably 50-55% by weight, and the crystallization temperature of the urea solution is 15-25° C., preferably 18-20° C. In this embodiment, the urea solution used in the present disclosure is completely atomized in a pyrolysis furnace by a urea spray gun, and the completely atomized urea droplets are decomposed into ammonia and water by high temperature, which can improve the performance of the denitration reaction.

[0031] In one embodiment, the temperature of the urea solution used in the present disclosure is 50-60°C.

[0032] In one embodiment, in order to further improve the performance of the denitration reaction, the flow ratio of the urea solution to the boiler exhaust gas is limited. Specifically, the flow ratio of the urea solution to the boiler exhaust gas is 1: (1115-1125). In this embodiment, when the urea solution and the boiler exhaust gas are in a suitable ratio, not only the performance of the denitration reaction can be guaranteed, but also the denitration temperature can be maintained at a higher level, further ensuring the performance of the denitration reaction.

[0033] In one embodiment, when the number of the urea spray guns N is greater than or equal to 2, the urea solution is allowed to pass through each urea spray gun and enter the pyrolysis furnace; the detection unit is allowed to obtain the flow signal of the hot primary air, the flow signal of each urea spray gun, and the opening signal of each urea spray gun; When the flow signal of the hot primary air decreases to less than the first threshold, it indicates that the pyrolysis furnace is blocked; When the flow signal of the hot primary air is above the first threshold and the flow signal of any urea spray gun decreases to less than the second threshold, it indicates that the urea spray gun is in a blocked state; When the flow signal of the hot primary air is above the first threshold, the flow signal of any urea spray gun is above the second threshold, and the automatic valve opening signal of the urea spray gun increases to above the third threshold, it indicates that the urea spray gun is in a blocked state.

[0034] In this embodiment, through the above technical solution, it is possible to accurately and quickly determine that a certain urea spray gun has an abnormality, and to perform post-processing in a targeted manner.

[0035] In one embodiment, a method for quickly determining whether a urea spray gun of a denitrification system is blocked includes: Whether the pyrolysis furnace is blocked is judged by the flow rate of the hot primary air. The specific method is: when the flow signal of the hot primary air is above the first threshold, it indicates that the pyrolysis furnace is not blocked; when the flow signal of the hot primary air decreases to less than the first threshold, it indicates that the pyrolysis furnace is blocked.

[0036] Whether a certain urea spray gun is blocked is judged by the flow rate of the urea spray gun; the specific method is: when the flow signal of the hot primary air is above the first threshold and the flow signal of any one of the urea spray guns is reduced to less than the second threshold, it indicates that the urea spray gun is in a blocked state; when the flow signal of the hot primary air is above the first threshold and the flow signal of any one of the urea spray guns is above the second threshold, it indicates that the urea spray gun is not blocked.

[0037] Whether the urea spray gun is blocked is judged by the flow rate of the urea spray gun and the opening of the urea spray gun. The specific method is: when the flow signal of the hot primary air is above the first threshold, the flow signal of the urea spray gun is above the second threshold, and the opening signal of any one of the urea spray guns increases to above the third threshold, it indicates that the urea spray gun is in a blocked state; when the flow signal of the hot primary air is above the first threshold, the flow signal of the urea spray gun is above the second threshold, and the opening signal of any one of the urea spray guns is less than the third threshold, it indicates that the urea spray gun is not blocked.

[0038] A third aspect of the present disclosure provides a method for treating a urea spray gun blockage, the method comprising: The method according to the second aspect of the present disclosure is used to judge the working state of the urea spray gun. When the urea spray gun is in a blocked state, the detection unit is enabled to obtain the nitrogen oxide concentration of the boiler flue and send a signal to the control unit; If the nitrogen oxide concentration increases to above a fourth threshold, the control unit increases the opening of the urea spray gun until the nitrogen oxide concentration decreases to below a fifth threshold, and the control unit reduces the opening of the urea spray gun; the fourth threshold is selected from any one of 40 to 45 weight %; the fifth threshold is selected from any one of 25 to 30 weight %.

[0039] In this embodiment, when the pyrolysis furnace is blocked, the amount of hot primary air entering will decrease, and the amount of urea solution added will remain unchanged, so the content of nitrogen oxides will decrease. At this time, the control unit reduces the opening of the urea spray gun to keep the urea solution and the hot primary air in a suitable ratio. When the urea spray gun is in a blocked state, the amount of urea added will decrease, so the concentration of nitrogen oxides will increase. At this time, the control unit increases the opening of the urea spray gun, which can ensure that the urea solution and the boiler exhaust are in a suitable ratio on the one hand, and on the other hand, it can flush away the blocking material to solve the problem of urea spray gun blockage.

[0040] In one implementation manner, when the number N of the urea spray guns is greater than or equal to 2, when the urea spray gun is in a blocked state, when the nitrogen oxide concentration increases to above a fourth threshold value, the detection unit detects that one or several urea spray guns are in an abnormal state through the judgment method of the second aspect, and sends an adjustment signal to the corresponding control unit so that the control unit increases the opening of the urea spray gun in the abnormal state.

[0041] In a specific implementation, when one of the urea spray guns is abnormal and the nitrogen oxide content of the denitrification exhaust gas increases to above a fourth threshold, the detection unit sends a signal to the control unit so that the control unit increases the opening of the urea spray gun until the nitrogen oxide concentration decreases to below a fifth threshold, and then gradually reduces the opening of the urea spray gun.

[0042] In another specific embodiment, when all urea spray guns are abnormal and the nitrogen oxide content of the denitrification exhaust gas increases to above a fourth threshold, the detection unit sends a signal to the control unit so that the control unit increases the opening of each urea spray gun until the nitrogen oxide concentration decreases to below a fifth threshold, and then gradually reduces the opening of each urea spray gun.

[0043] In one embodiment, when the nitrogen oxide concentration increases to above a sixth threshold, the urea spray gun is closed and flushed with water; the sixth threshold is selected from any one value between 50 and 55 weight %.

[0044] In one embodiment, the first threshold, the second threshold, the third threshold, the fourth threshold, the fifth threshold and the sixth threshold described in the present disclosure are all obtained based on a summary of previous data.

[0045] The present disclosure is further illustrated below by way of examples, but the present disclosure is not limited thereby.

[0046] Example 1 Quickly determine that the urea spray gun of the denitrification system is blocked. There are 4 urea spray guns in the system; Methods for judging the blockage of the four urea spray guns include: The flow rate of boiler tail gas is used to determine whether the pyrolysis furnace is blocked. The specific method is as follows: when the flow signal of the hot primary air is 4000Nm 3 / h or more, indicating that the pyrolysis furnace is not blocked; when the flow signal of the hot primary air decreases to less than 4000Nm 3 / h, it indicates that the pyrolysis furnace is blocked.

[0047] The flow rate of the urea spray gun is used to determine whether a urea spray gun is blocked; the specific method is: when the flow signal of the hot primary air is 4000Nm 3 / h or more and the flow rate signal of any one of the urea spray guns is reduced to less than 0.02m 3 / h, it indicates that the urea spray gun is in a blocked state.

[0048] The urea spray gun is blocked by the flow rate and opening of the urea spray gun. The specific method is as follows: when the flow rate signal of the hot primary air is 4000Nm 3 / h or more, the flow signal of any urea spray gun is 0.02m 3 / h or more and the opening signal of the urea spray gun increases to more than 50%, indicating that the urea spray gun is in a blocked state; when the flow signal of the hot primary air is 4000Nm 3 / h or more, the flow signal of any one of the urea spray guns is 0.02m 3 / h or more and the opening signal of the urea spray gun is less than 50%, it indicates that the urea spray gun is not blocked.

[0049] Methods for dealing with urea spray gun blockage include: When the urea spray gun is completely blocked, the detection unit acquires the nitrogen oxide concentration in the boiler flue and sends a signal to the control unit; If the nitrogen oxide concentration increases to more than 45% by weight, the control unit increases the opening of the abnormal urea spray gun until the nitrogen oxide concentration drops to less than 25% by weight, and then the control unit gradually decreases the opening of the urea spray gun; If the nitrogen oxide concentration increases to more than 55 wt %, the urea spray gun in the abnormal state is closed and flushed with water.

[0050] The total amount of nitrogen oxides in the denitrification exhaust gas generated within 1 hour of operation of the denitrification system is 45 mg.

[0051] The actual judgment result of the method of this embodiment is: after 100 tests of judging whether the spray gun is blocked, the accuracy is 100% and the average judgment time is 60 seconds.

[0052] The method disclosed in the present invention is used to judge the blockage of the urea spray gun, and can accurately and quickly judge the blockage of the pyrolysis furnace and the urea spray gun and the degree of the blockage of the urea spray gun; the judgment method is simple and intuitive, and does not require a large number of modifications to the existing equipment; in addition, the present invention can quickly deal with the problem of urea spray gun blockage.

[0053] The preferred embodiments of the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0054] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0055] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A system for quickly determining the blockage of a urea spray gun in a denitrification system, characterized in that: The system includes a pyrolysis furnace, a urea spray gun arranged inside the pyrolysis furnace, and a detection unit; The inlet of the pyrolysis furnace is used to communicate with a hot primary air source, and the outlet of the pyrolysis furnace is used to communicate with a boiler flue; the inlet of the urea spray gun is used to communicate with a urea solution source; A first flow meter is provided on the inlet pipeline of the pyrolysis furnace; A second flow meter is provided on the inlet pipeline of the urea spray gun; The detection unit is electrically connected to the first flow meter, the second flow meter and the urea spray gun, and is used to receive a first flow signal from the first flow meter, a second flow signal from the second flow meter and an opening signal from the urea spray gun, and to determine a blockage state of the urea spray gun.

2. The system according to claim 1, characterized in that A nitrogen oxide detector is provided on the boiler flue to detect the nitrogen oxide concentration of the flue gas inside the boiler flue; The nitrogen oxide detector is electrically connected to the detection unit; The system further comprises a control unit, wherein the control unit is electrically connected to the urea spray gun and the detection unit; The detection unit is used to receive the nitrogen oxide concentration signal from the nitrogen oxide detector and send a signal to the control unit; the control unit is used to receive the signal sent by the detection unit and adjust the opening of the urea spray gun.

3. The system according to claim 1, characterized in that The number N of the urea spray guns is a positive integer, and N≥2.

4. A method for quickly determining whether a urea spray gun of a denitrification system is blocked by using the system described in any one of claims 1 to 3, characterized in that: The method includes: The urea solution is allowed to enter the pyrolysis furnace through the urea spray gun and contact with the hot primary air for atomization treatment to obtain atomized urea; the detection unit is allowed to obtain the flow signal of the hot primary air, the flow signal of the urea spray gun, and the opening signal of the urea spray gun; When the flow signal of the hot primary air decreases to less than a first threshold, it indicates that the pyrolysis furnace is blocked; When the flow signal of the hot primary air is above the first threshold and the flow signal of the urea spray gun decreases to be less than the second threshold, it indicates that the urea spray gun is in a blocked state; When the flow signal of the hot primary air is above the first threshold, the flow signal of the urea spray gun is above the second threshold, and the opening signal of the urea spray gun increases to above the third threshold, it indicates that the urea spray gun is in a blocked state; The first threshold is selected from 4000~5900Nm 3 / h; the second threshold is selected from 0~0.03m 3 / h; the third threshold is selected from any value between 50% and 100%.

5. The method according to claim 4, characterized in that The method also includes, before the atomization treatment, heating the hot primary air to 340-650° C.

6. The method according to claim 4, characterized in that The concentration of the urea solution is 40-60% by weight; the crystallization temperature of the urea solution is 15-25°C.

7. The method according to claim 4, characterized in that The flow ratio of the urea solution to the hot primary air is 1:(1115~1125).

8. The method according to claim 4, characterized in that When the number of the urea spray guns N is greater than or equal to 2, the urea solution is allowed to pass through each urea spray gun and enter the pyrolysis furnace; The detection unit is enabled to obtain a flow signal of the hot primary air, a flow signal of each urea spray gun, and an opening signal of each urea spray gun; When the flow signal of the hot primary air decreases to less than the first threshold, it indicates that the pyrolysis furnace is blocked; When the flow signal of the hot primary air is above the first threshold and the flow signal of any urea spray gun decreases to be less than the second threshold, it indicates that the urea spray gun is in a blocked state; When the flow signal of the hot primary air is above the first threshold, the flow signal of any urea spray gun is above the second threshold, and the automatic valve opening signal of the urea spray gun increases to above the third threshold, it indicates that the urea spray gun is in a blocked state.

9. A method for treating urea spray gun blockage, characterized in that: The treatment method includes: The working state of the urea spray gun is judged by the method described in any one of claims 4 to 8. When the urea spray gun is in a blocked state, the detection unit obtains the nitrogen oxide concentration of the boiler flue and sends a signal to the control unit; If the nitrogen oxide concentration increases to above a fourth threshold, the control unit increases the opening of the urea spray gun until the nitrogen oxide concentration decreases to below a fifth threshold, and the control unit decreases the opening of the urea spray gun; The fourth threshold is selected from any value between 40 and 45 weight %; and the fifth threshold is selected from any value between 25 and 30 weight %.

10. The processing method according to claim 9, characterized in that: When the nitrogen oxide concentration increases to above a sixth threshold, closing the urea spray gun and flushing the urea spray gun with water; The sixth threshold value is selected from any value between 50 and 55 weight %.