Online biuret cleaning system and method for urea hydrolysis system

Abstract

The invention provides an online biuret cleaning system and method for a urea hydrolysis system. The online biuret cleaning system comprises a first dilution fan, a second dilution fan, a first flue gas heater, a second flue gas heater, an ammonia-air mixer and an ammonia spraying branch pipe. The blocked branch pipe is positioned through temperature monitoring, the bypass is used for heating air to decompose biuret, the clearing effect is enhanced in combination with the standby fan, and continuous and efficient operation of the urea hydrolysis system is achieved. The system has the functions of blockage early warning and online cleaning, the running temperature of the ammonia spraying branch pipe is monitored in real time, the blockage condition in the pipeline is pre-judged in advance, the system is suitable for urea hydrolysis ammonia production, events such as unit shutdown caused by blockage are reduced, and the economical efficiency and safety of unit running are improved; the problem of blockage of biuret can be treated on line during operation, shutdown treatment is not needed, the problem of out-of-control ammonia spraying is avoided, the amount of ammonia escape is reduced, and the problem of blockage of downstream equipment is relieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of flue gas denitrification treatment, and relates to a cleaning method for an online cleaning system of biuret in a urea hydrolysis system Background Art The SCR technology is widely used in industries such as thermal power, iron and steel, and coking to remove nitrogen oxides in flue gas. Its principle is to introduce the reducing agent NH3 into the flue gas, and react with NO in the flue gas under the action of a catalyst x to generate N2 and H2O

[0002] The commonly used reducing agents are mainly liquid ammonia and urea. Since liquid ammonia is a major hazard source, there are relatively large hidden dangers in transportation, storage and use. In this regard, coal-fired power plants are classified according to the hazard source level. By the end of 2024, the vast majority of thermal power units have completed the transformation project of replacing liquid ammonia with urea. Among them, the power plants using the urea hydrolysis ammonia production process account for the vast majority

[0003] To prepare NH by using the urea hydrolysis process 3， It is necessary to first dissolve urea particles in water to prepare a urea solution of about 50%, and then the urea solution is in the hydrolysis reactor at 140 - 160°C and 0.6Mp to produce a mixture of NH3, CO2 and H2O. The reason for choosing these reactor parameters is that corrosion will intensify when the temperature is too high, and a large amount of by-products of urea hydrolysis such as biuret and cyanuric acid will be produced when the temperature is too low. In addition, a certain amount of biuret is also produced during the urea production process. Biuret is commonly used in the industry as a foaming and sponging production promoter, has strong binding and foaming abilities, and its decomposition temperature is 190°C. In actual engineering, there have been many cases where biuret enters the ammonia injection pipeline with the product gas, combines with the dust in the dilution air or the hot primary air, forms a large amount of bubbly substances in the local low-speed areas such as the valves and elbows of the ammonia injection branch pipes, and then gradually blocks the ammonia injection branch pipes, resulting in the inability of the ammonia-air mixture to pass. This causes the loss of control of ammonia injection, a sharp increase in ammonia escape, and in severe cases, the occurrence of events such as unit shutdown

[0004] Since biuret is an intermediate product of hydrolysis, it cannot be cleaned in the intermediate link, and there is currently no early warning for biuret blockage and treatment method during online operation. Usually, after the blockage occurs, the ammonia injection branch pipe is cut open manually during the temporary shutdown of the unit for cleaning Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide an online cleaning system and cleaning method for biuret in a urea hydrolysis system. This system has the functions of blockage early warning and online cleaning, is applicable to the urea hydrolysis ammonia production system, reduces the occurrence of events such as unit shutdown caused by blockage, and improves the economy and safety of unit operation

[0006] The present invention is realized through the following technical solutions An on-line cleaning system for biuret in a urea hydrolysis system, comprising a first dilution blower, a second dilution blower, a first flue gas heater, a second flue gas heater, an ammonia-air mixer and an ammonia injection branch pipe; The inlet of the first flue gas heater is connected to the second dilution blower, and the inlet of the second flue gas heater is connected to the first dilution blower; after the outlets of the first flue gas heater and the second flue gas heater are aggregated, they are connected to the ammonia injection branch pipe through the ammonia-air mixer; temperature monitoring devices are provided at the inlet and outlet of the ammonia injection branch pipe, and the temperature monitoring device interlock control module is used to compare the temperature difference or temperature change trend between the inlet end and the outlet end of the ammonia injection branch pipe; when the detected temperature is lower than the preset threshold and the temperature does not rise significantly after adjusting the valve opening of the corresponding branch pipe, a biuret blockage warning signal is triggered.

[0007] Preferably, the temperature monitoring device includes a first bimetallic thermometer and a second bimetallic thermometer; the first bimetallic thermometer is arranged at the inlet of the ammonia injection branch pipe, and the second bimetallic thermometer is arranged at the outlet of the ammonia injection branch pipe.

[0008] Preferably, both the first flue gas heater and the second flue gas heater are arranged at the outlet of the denitration reactor.

[0009] Preferably, the ammonia injection branch pipe is composed of multiple parallel pipes, and the ammonia injection branch pipe is a pipe with a single inlet and multiple outlets.

[0010] Preferably, a manual butterfly valve and a metal expansion joint are arranged on the pipe.

[0011] Preferably, a first electric switch valve is arranged on the bypass air duct between the inlet of the second flue gas heater and the first dilution blower, and a second electric switch valve is arranged on the outlet pipe of the second flue gas heater.

[0012] Preferably, the second flue gas heater adopts a multi-stage countercurrent heat exchange structure, its heat exchange area is increased by 30%-50% compared with the first flue gas heater, and the medium is completely cut off by adjusting the first electric switch valve and the second electric switch valve in the non-working state to avoid waste heat loss of the flue gas.

[0013] Preferably, the first flue gas heater and the second flue gas heater are arranged in parallel, and the second flue gas heater serves as a standby heater for the first flue gas heater.

[0014] Preferably, the first dilution blower and the second dilution blower are arranged in parallel, and the first dilution blower serves as a backup for the second dilution blower.

[0015] A cleaning method for an on-line cleaning system for biuret in a urea hydrolysis system, comprising: Obtain the temperature field data at the inlet and outlet of the ammonia injection branch pipe through the temperature monitoring device; Analyze the relationship between the temperature distribution and flow rate balance at the inlet and outlet of the ammonia injection branch pipe, and locate the blocked risk area; Through the first dilution fan and the second flue gas heater, control the dilution air volume to remain unchanged, increase the heat exchange area, and use the incremental heat exchange to raise the air temperature to the biuret decomposition threshold; Through the scouring action of hot air, biuret is decomposed into gaseous products, which are carried by the ammonia-air mixture into the downstream flue, and the blockage is removed.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: An on-line cleaning system for biuret in a urea hydrolysis system of the present invention locates the blocked branch pipe through temperature monitoring, decomposes biuret by heating air through a bypass, and combines a spare fan to enhance the cleaning effect, realizing the continuous and efficient operation of the urea hydrolysis system. This system has the functions of blockage warning and on-line cleaning. By real-time monitoring the operating temperature of the ammonia injection branch pipe, it can predict the internal blockage situation of the pipeline in advance, is applicable to the urea hydrolysis to ammonia system, reduces the occurrence of events such as unit shutdown caused by blockage, and improves the economy and safety of unit operation; it can on-line handle the biuret blockage problem during operation without shutdown, avoid the problem of out-of-control ammonia injection, reduce the amount of ammonia escape, and slow down the blockage problem of downstream equipment. The present invention effectively solves the problems of frequent shutdowns, high energy consumption, and high maintenance costs caused by biuret blockage in the traditional urea hydrolysis system, realizes the composite benefits of high-efficiency continuous operation, energy conservation and consumption reduction, intelligent control, and environmental friendliness, and is applicable to scenarios with strict requirements for the reliability of the denitration system such as large coal-fired power plants and chemical plants.

[0017] Furthermore, the on-line cleaning system for biuret of the present invention has a simple structure, and on-line cleaning does not consume additional energy.

[0018] Furthermore, in an on-line cleaning system for biuret of the present invention, by raising the temperature of the mixed gas to above 200°C and combining with a catalytic coating to accelerate decomposition, the blockage is converted into gaseous products and directly enters the flue without physical disassembly; by dynamically adjusting the total pressure and flow rate of the mixed gas through a booster fan, the scouring effect on the remaining blockage is enhanced. Description of the Drawings

[0019] Figure 1 It is a flow chart of an on-line cleaning system for biuret in a urea hydrolysis system; In the figure: the first dilution fan 1, the second dilution fan 2, the first flue gas heater 3, the first electric switch valve 4, the second flue gas heater 5, the second electric switch valve 6, the ammonia-air mixer 7, the ammonia injection branch pipe 8, the first bimetal thermometer 9, the second bimetal thermometer 10. Detailed Embodiments

[0020] The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations of the present invention rather than limitations.

[0021] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the scope of protection of the present invention.

[0022] The object of the present invention is to provide a biuret on-line cleaning system, which has the functions of blockage warning and on-line cleaning, and is applicable to the urea hydrolysis to ammonia system. In the usual urea hydrolysis process system of the invention, a spare flue gas heater, bypass inlet and outlet electric switch doors, double-metal thermometers at the inlet and outlet of the ammonia injection branch pipe, etc. are added. It has reduced the occurrence of events such as unit shutdown caused by blockage, and improved the economy and safety of unit operation.

[0023] A biuret on-line cleaning system for a urea hydrolysis system, as Figure 1 shown, The first dilution fan 1, the second dilution fan 2, the first flue gas heater 3, the second flue gas heater 5, the ammonia-air mixer 7, the ammonia injection branch pipe 8; The inlet of the first flue gas heater 3 is connected to the second dilution fan 2, and the inlet of the second flue gas heater 5 is connected to the first dilution fan 1; after the outlets of the first flue gas heater 3 and the second flue gas heater 5 are aggregated, they are connected to the ammonia injection branch pipe 8 through the ammonia-air mixer 7; temperature monitoring devices are provided at the inlet and outlet of the ammonia injection branch pipe 8, and the temperature monitoring device interlock control module is used to compare the temperature difference or temperature change trend between the inlet end and the outlet end of the ammonia injection branch pipe 8; when the detected temperature is lower than the preset threshold and the temperature does not rise significantly after adjusting the valve opening of the corresponding branch pipe, a biuret blockage warning signal is triggered.

[0024] The cleaning method of the biuret on-line cleaning system for a urea hydrolysis system described above includes: Obtaining the temperature field data at the inlet and outlet of the ammonia injection branch pipe 8 through the temperature monitoring device; Analyzing the relationship between the temperature distribution and flow balance at the inlet and outlet of the ammonia injection branch pipe 8 to locate the blockage risk area; Controlling the dilution air volume to remain unchanged through the first dilution fan 1 and the second flue gas heater 5, increasing the heat exchange area, and using incremental heat exchange to raise the air temperature to the biuret decomposition threshold; Making the biuret decompose into gaseous products through the hot air scouring effect, and being carried by the ammonia-air mixture into the downstream flue, so that the blockage is removed.

[0025] The temperature monitoring device includes a first bimetallic thermometer 9 and a second bimetallic thermometer 10; the first bimetallic thermometer 9 is arranged at the inlet of the ammonia injection branch pipe 8, and the second bimetallic thermometer 10 is arranged at the outlet of the ammonia injection branch pipe 8.

[0026] Both the first flue gas heater 3 and the second flue gas heater 5 are arranged at the outlet of the denitration reactor.

[0027] The ammonia injection branch pipe 8 is composed of multiple parallel pipes, and the ammonia injection branch pipe 8 is a pipe with a single inlet and multiple outlets. A manual butterfly valve and a metal expansion joint are arranged on the pipe.

[0028] A first electric switch valve 4 is arranged on the bypass air duct between the inlet of the second flue gas heater 5 and the first dilution fan 1, and a second electric switch valve 6 is arranged on the outlet pipe of the second flue gas heater 5. The first electric switch valve 4 and the second electric switch valve 6 adopt electric actuators and are connected to the DCS system to form a timing control logic, and different flue gas heaters are alternately enabled during the cleaning period to balance equipment losses.

[0029] The second flue gas heater 5 adopts a multi-stage countercurrent heat exchange structure, and its heat exchange area is 30%-50% larger than that of the first flue gas heater 3. And in the non-working state, the medium is completely cut off by adjusting the first electric switch valve 4 and the second electric switch valve 6 to avoid waste heat loss of the flue gas.

[0030] The bypass channel includes a standby flue gas heater 5, whose heat exchange area is larger than that of the main heating device. By opening the bypass switch door, a dilution air shunt is formed to make the temperature of the heated air reach above the melting point of biuret. The inlet end of the bypass air duct is connected to the outlets of the first dilution fan 1 and the second dilution fan 2, and the outlet end is connected to the upstream of the ammonia-air mixer to form a switchable multi-stage heating channel.

[0031] The first flue gas heater 3 and the second flue gas heater 5 are arranged in parallel, and the second flue gas heater 5 serves as a standby heater for the first flue gas heater 3. The first dilution fan 1 and the second dilution fan 2 are arranged in parallel, and the first dilution fan 1 serves as a standby for the second dilution fan 2. The first dilution fan 1 serves as a booster fan, and the booster fan is configured to increase the total pressure of the mixed gas during the cleaning process. Its start-stop logic is dynamically associated with the temperature control unit. The air volume adjustment of the first dilution fan 1 is based on the real-time detected temperature value of the mixed gas. When the temperature is lower than 200°C, the rotation speed is automatically increased, and a negative feedback control loop for preventing flue gas heat loss is provided.

[0032] The inlet end of the bypass air duct is provided with a flow distributor, which is used to balance the main / bypass air volume ratio when switching to the standby heating module, ensuring that the total dilution air volume fluctuation does not exceed ±5%.

[0033] An auxiliary ash cleaning structure is provided at the elbow and valve of the ammonia injection branch pipe. The auxiliary ash cleaning structure includes a high-frequency vibration generator or an ultrasonic vibrator, whose excitation frequency matches the natural frequency of the branch pipe, and is used to superimpose mechanical vibration during the thermal decomposition stage to accelerate the stripping of blockages. This device generates high-frequency mechanical vibration waves synchronously during the thermal decomposition cleaning stage. The excitation frequency of the vibration ash cleaning device forms a resonance relationship of 1.2 - 1.5 times with the natural frequency of the branch pipe. The high-frequency vibration generator is interlocked with the temperature monitoring device and is only activated after detecting abnormal temperature and starting the standby heating module, and the vibration intensity is adjusted in grades according to the degree of blockage.

[0034] The control module integrates a temperature difference gradient analysis algorithm. When the temperature difference of a single branch pipe exceeds 15% - 25% of the average temperature difference of adjacent branch pipes, it is determined as an abnormal blockage condition. The control module has a built-in temperature difference threshold determination algorithm. When the inlet and outlet temperature difference of a single ammonia injection branch pipe exceeds 20% of the average temperature difference of adjacent branch pipes and the temperature difference does not recover after manual adjustment of the valve, a blockage warning signal is automatically triggered, and the corresponding branch pipe positioning information is generated.

[0035] The control unit executes the following control logic: Real-time monitor the temperature distribution of each ammonia injection branch pipe and generate a flow balance index; When an abnormal temperature area is detected, execute the valve opening adjustment - temperature response test cycle; If the temperature does not recover and the abnormal area continues to expand, automatically open the bypass channel and adjust the heating parameters; In the enhanced mode, dynamically match the air volume and temperature parameters according to the preset algorithm.

[0036] During the decomposition process, increase the system total pressure by linking the standby fan, so that the flow velocity of the mixed gas in the branch pipe increases by 20% - 50%, enhancing the heat and mass transfer efficiency.

[0037] The temperature threshold is dynamically adjusted according to the phase change characteristics of biuret, and the control range is 195°C - 230°C, preferably 200°C - 220°C.

[0038] The system maintains the flow balance degree of the ammonia injection branch pipe group ≥85%, so that the fluctuation coefficient of the ammonia concentration at the inlet of the denitration reactor ≤0.15, and improves the denitration efficiency by 1.2% - 2.5%.

[0039] The heat exchange tube surfaces of the first flue gas heater 3 and the second flue gas heater 5 are coated with a catalytic decomposition coating, and the coating contains transition metal oxides, which is used to promote the reaction rate of biuret decomposition into NH3 and cyanuric acid at temperatures above 200°C.

[0040] The specific implementation process is as follows: The present invention relates to an on-line cleaning system for biuret in a urea hydrolysis system. The technological process during normal operation is as follows: Air enters the flue gas heater 3 arranged at the outlet of the denitration reactor through the second dilution blower 2 and is heated to about 180°C. It is mixed with the hydrolysis product gas through the ammonia-air mixer 7, and the temperature of the hydrolysis product gas is about 150°C. The mixed ammonia-air mixture enters the flue through the ammonia injection branch pipe 8. The ammonia injection branch pipe 8 is usually composed of dozens of parallel pipes, and is equipped with devices such as manual butterfly valves and metal expansion joints.

[0041] Biuret enters the ammonia injection branch pipe 8 together with the hydrolysis product gas. Since the ammonia injection branch pipe is a pipe with a single inlet and multiple outlets, and there are differences in the flow rate of each ammonia injection branch pipe due to different pipe system resistances, in the ammonia injection branch pipe with a low flow rate, biuret is likely to accumulate and block at the valves, elbows, etc. on the pipe. As the amount of blockage increases, the flow rate of this ammonia injection branch pipe further decreases. For this reason, two local bimetal thermometers are respectively set at the inlet and outlet of each ammonia injection branch pipe, and the flow rate of the branch pipe is indirectly monitored by monitoring the temperature.

[0042] Blockage warning function: During operation, if it is found that the values of the first bimetal thermometer 9 and the second bimetal thermometer 10 set on some ammonia injection branch pipes are lower than the normal temperature of the ammonia-air mixture, and after appropriately increasing the opening degree of the manual regulating valve on this branch pipe, the thermometer value still does not increase significantly, it indicates that there is a biuret blockage inside this ammonia injection branch pipe.

[0043] On-line treatment during operation: The first electric switch valve 4 and the second electric switch valve 6 are in a normally closed state. When on-line cleaning is required, open the first electric switch valve 4 and the second electric switch valve 6, and part of the dilution air enters the standby flue gas heater. This process is equivalent to keeping the dilution air volume unchanged and increasing the heat exchange area, and the temperature after passing through the flue gas heater rises above 200°C. Through the hot air heating reaching the melting point, the biuret blockage is gradually melted and decomposed into substances such as NH3 and cyanuric acid, and the decomposed products are carried by the ammonia-air mixture into the downstream flue, and the blockage is removed.

[0044] As a strengthening measure, the first dilution blower 1 can be started in parallel. While ensuring that the temperature after passing through the flue gas heater is not lower than 200°C, by appropriately increasing the dilution air volume, the total pressure and flow velocity of the ammonia-air mixture in the ammonia injection branch pipe are increased to strengthen the cleaning function of biuret.

[0045] During the purging process, the heat for heating the dilution air comes from the heat of the flue gas without additional energy. When the purging system is not working, close the first electric switch valve 4 and the second electric switch valve 6, and there is no medium flowing inside the standby heater, and there is no heat loss of the flue gas.

[0046] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0047] It should be noted that when a component is referred to as "fixed to" another component, it can be directly on the other component or there may also be an intermediate component. When a component is considered to be "connected to" another component, it can be directly connected to the other component or there may be an intermediate component at the same time. When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be an intermediate component at the same time.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0049] As described above, it is only the preferred embodiment of the present invention, and there is no restriction in any form to the present invention; any person skilled in the art of this industry can smoothly implement the present invention according to what is shown in the drawings of the specification and the above description; however, any equivalent changes made by those skilled in the art in the technical field without departing from the technical solution of the present invention, using the technical content disclosed above and making some modifications, decorations and evolutions, are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments according to the essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A urea hydrolysis system biuret online cleaning system, characterized in that: include, A first dilution fan (1), a second dilution fan (2), a first flue gas heater (3), a second flue gas heater (5), an ammonia-air mixer (7), and an ammonia injection branch pipe (8); The inlet of the first flue gas heater (3) is connected to the second dilution fan (2), and the inlet of the second flue gas heater (5) is connected to the first dilution fan (1); the outlets of the first flue gas heater (3) and the second flue gas heater (5) are combined and connected to the ammonia injection branch pipe (8) through an ammonia-air mixer (7); the inlet and outlet of the ammonia injection branch pipe (8) are provided with a temperature monitoring device, and the temperature monitoring device is interlocked with a control module to compare the temperature difference or temperature change trend between the inlet and outlet ends of the ammonia injection branch pipe (8); when it is detected that the temperature is lower than a preset threshold and the temperature does not rise after adjusting the opening of the corresponding branch pipe valve, a biuret blockage warning signal is triggered.

2. The urea hydrolysis system biuret online cleaning system according to claim 1, characterized in that: The temperature monitoring device comprises a first bimetallic thermometer (9) and a second bimetallic thermometer (10); the first bimetallic thermometer (9) is arranged at the inlet of the ammonia injection branch pipe (8), and the second bimetallic thermometer (10) is arranged at the outlet of the ammonia injection branch pipe (8).

3. The urea hydrolysis system biuret online cleaning system according to claim 1, characterized in that: The first flue gas heater (3) and the second flue gas heater (5) are both arranged at the outlet of the denitration reactor.

4. The urea hydrolysis system biuret online cleaning system according to claim 1, characterized in that: The ammonia injection branch pipe (8) is composed of a plurality of pipes arranged in parallel, and the ammonia injection branch pipe (8) is a pipe with a single inlet and multiple outlets.

5. The urea hydrolysis system biuret online cleaning system according to claim 4, characterized in that: A manual butterfly valve and a metal expansion joint are arranged on the pipeline.

6. The urea hydrolysis system biuret online cleaning system according to claim 1, characterized in that: A first electric switch valve (4) is provided on the bypass air duct between the inlet of the second flue gas heater (5) and the first dilution fan (1), and a second electric switch valve (6) is provided on the outlet pipe of the second flue gas heater (5).

7. The urea hydrolysis system biuret online cleaning system according to claim 6, characterized in that: The second flue gas heater (5) adopts a multi-stage countercurrent heat exchange structure, and its heat exchange area is increased by 30%-50% compared with the first flue gas heater (3). In a non-operating state, the medium is completely cut off by adjusting the first electric switch valve (4) and the second electric switch valve (6), thereby avoiding the loss of flue gas waste heat.

8. The urea hydrolysis system biuret online cleaning system according to claim 1, characterized in that: The first flue gas heater (3) and the second flue gas heater (5) are arranged in parallel, and the second flue gas heater (5) serves as a backup heater for the first flue gas heater (3).

9. The urea hydrolysis system biuret online cleaning system according to claim 1, characterized in that: The first dilution fan (1) and the second dilution fan (2) are arranged in parallel, and the first dilution fan (1) serves as a backup for the second dilution fan (2).

10. A cleaning method for a urea hydrolysis system biuret online cleaning system according to any one of claims 1 to 9, characterized in that: include: Acquiring temperature field data at the inlet and outlet of the ammonia injection branch pipe (8) through a temperature monitoring device; Analyze the relationship between the temperature distribution and flow balance of the inlet and outlet of the ammonia injection branch pipe (8) to locate the blockage risk area; The first dilution fan (1) and the second flue gas heater (5) are used to control the dilution air volume to remain unchanged, thereby increasing the heat exchange area and utilizing incremental heat exchange to raise the air temperature to a biuret decomposition threshold; The hot air flushing action causes biuret to decompose into gaseous products, which are carried into the downstream flue by the ammonia-air mixture, and the blockage is cleared.

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