Air-assisted urea injection system crystallization prevention control system and control method for industrial source equipment waste gas purification

Abstract

The invention provides a control system and a control method for preventing crystallization of an air-assisted urea injection system for purifying tail gas of industrial source equipment, the system is provided with a purging air storage tank connected with a compressed air source through a one-way valve, and when the air source is accidentally cut off or a gear pump is powered off, a urea spray gun and a pipeline are purged by using pre-stored compressed air, so that the crystallization of the urea injection system is prevented. Even if the upstream air compression station breaks down or is powered off, the retained urea solution can be removed through the pre-stored compressed air, and the crystallization problem is avoided. Meanwhile, the pulse purging mode and the purging flow are controlled, the compressed air pre-stored in the air storage tank is limited, the residual solution in the pipeline can be effectively removed, possible micro-crystallization of the pipeline can be broken through the air hammer effect, and the consumption of the compressed air can be reduced. The flow and frequency of pulse purging are adaptively adjusted in real time in combination with dynamic evaluation of crystallization risks, so that resource waste caused by excessive purging is avoided, the purging effect is ensured, and crystallization is inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial waste gas treatment, in particular to the treatment of nitrogen oxides in industrial waste gas. Specifically, it relates to a control system and method for preventing crystallization of an air-assisted urea injection system for purifying waste gas from industrial equipment. Background Art

[0002] Industrial waste gas treatment is the focus of air pollution prevention and control, including the purification of waste gas emitted by industrial boilers (fired by coal, gas, or oil) and generator sets (fueled by diesel or natural gas), and the effective control of nitrogen oxide emissions in industrial waste gas through SCR denitrification treatment.

[0003] SCR denitrification technology reduces ammonia oxide (NOx) emissions through catalytic reduction reactions. It uses a selective catalyst, usually ammonia-to-iron (NH3-Fe) or ammonia-to-vanadium (NH3-V), to catalyze the reaction of NOx with ammonia (NH3) on the catalyst surface, converting nitrogen oxides in industrial exhaust gas into nitrogen and water vapor that are harmless to the environment, reducing negative impacts on the environment.

[0004] SCR denitrification technology utilizes a complete treatment system consisting of a catalytic reaction core unit, a reductant supply system, a reaction vessel, and a catalyst regeneration module. Key steps include exhaust gas pretreatment (such as particulate matter capture), urea solution injection, catalytic reduction, and catalyst regeneration. Urea solution is injected into the denitrification unit through the system, where it reacts with NOx in the exhaust gas. Passing through the catalyst layer, NOx and NH3 undergo a catalytic reduction reaction, producing N2 and H20. Catalyst regeneration removes reaction products adhering to the catalyst to maintain catalyst activity.

[0005] In actual industrial operations, the precise and stable control of the urea injection system, the reductant supply hub, is crucial for the entire system. Stable urea injection relies on both the air supply and the urea solution—consistent air power and reliable gear pump operation. If a sudden mechanical failure at the upstream air compressor station causes a sudden drop in air pressure, or a momentary power outage halts the gear pump's urea delivery, the atomizing airflow to the gear pump and nozzle simultaneously ceases. This sudden interruption can quickly trigger a chain reaction throughout the urea supply system, causing the remaining urea solution in the pipeline to lose its flow momentum and become trapped within the urea spray gun and other sections of the pipeline. As system downtime increases (and recovery time increases), the trapped solution undergoes dual physical and chemical changes: First, the flue gas temperature gradually drops from its normal operating range of 320-400°C. Concurrently, urea solubility decreases exponentially with temperature, causing the supersaturated solution to begin to precipitate white crystals. Second, the stagnant liquid, under the influence of gravity, gathers in low-lying areas of the pipeline, forming a liquid film. Evaporation from its surface further increases the local concentration, accelerating crystal nucleation. This oversaturation is particularly exacerbated during winter shutdowns, where the temperature difference between the ambient and flue gases exacerbates the problem. Field monitoring data shows that crystals can reach a thickness of 2-3mm at pipe elbows after 3-4 hours of downtime. In severe cases, this can block 20%-50% of the flow area, causing a sudden increase in pressure drop and uneven distribution of reducing agent upon system restart. Summary of the Invention

[0006] In view of the technical problems existing in the prior art, the first aspect of the present invention provides an air-assisted urea injection system for preventing crystallization control system for exhaust gas purification of industrial source equipment, comprising a urea solution storage tank, a gear pump, a urea spray gun, a compressed air source, a purge air storage tank, a compressed air pipeline, a urea pipeline and a control system;

[0007] The urea solution storage tank is used to contain the urea solution;

[0008] The gear pump is arranged in a urea pipeline extending from the urea solution storage tank to the urea spray gun, and is used to pump the urea solution from the urea solution storage tank to the urea spray gun for injection;

[0009] The compressed air source enters the purge air storage tank through a one-way valve; a pressure detection sensor is provided in the purge air storage tank for real-time monitoring of the internal pressure of the purge air storage tank;

[0010] The purge air storage tank is connected to the urea spray gun via a compressed air pipeline, and a pressure reducing valve is provided to control the delivery of compressed air from the purge air storage tank to the urea spray gun; a compressed air pressure sensor is provided in the compressed air pipeline to monitor the pressure of the delivered compressed air in real time;

[0011] The urea spray gun is configured to mix the delivered urea solution with compressed air in the spray gun and then spray the mixture onto the SCR reaction carrier;

[0012] The control system is configured to control the operation of the gear pump, the urea spray gun, and the pressure reducing valve, and when the compressed air source is accidentally cut off and / or the urea pump is accidentally powered off, the control system controls the compressed air from the purge air tank to purge the urea solution in the urea spray gun to prevent crystallization;

[0013] Among them, the control system controls the compressed air for purging the air tank according to the preset purging air flow rate, and performs pulse purging at a set period, and calculates the real-time crystallization risk value RI based on the crystallization risk index model. When the real-time crystallization risk value RI exceeds the warning value, the pulse purging frequency and / or purging air flow rate are adaptively updated, and an early warning is issued through the HMI interface.

[0014] As an optional embodiment, the control system controls the compressed air for purging the air storage tank according to a preset purge air flow rate and performs pulse purging at a set period, including:

[0015] The compressed air for purging the air storage tank is controlled to be 1.2 to 1.5 times the compressed air flow rate for injection as the purging air flow rate, and pulse purging is performed with a cycle of 5 to 30 minutes, and the duration of the pulse purging is 500ms.

[0016] As an optional embodiment, the calculating of the real-time crystallization risk value RI based on the crystallization risk index model includes:

[0017] A crystallization risk index model was established based on the temperature, concentration, and residence time of the urea solution:

[0018] RI=((35-T)*(C-32.5)) / τ+t / 60

[0019] Wherein, T represents the temperature of the urea solution in the urea spray gun, in °C; C represents the concentration percentage of the urea solution in the urea spray gun, in %, t represents the residence time, in min; τ represents the dimension scaling factor, which is determined by orthogonal test;

[0020] Through the thermodynamic coupling of urea solution concentration and temperature as well as the coupling of residence time, the risk of urea crystallization is comprehensively evaluated, and the pulse purge frequency and / or purge air flow rate are adaptively updated accordingly.

[0021] As an optional embodiment, when the real-time crystallization risk value RI exceeds the warning value, adaptively updating the pulse purge frequency and / or the purge air flow rate includes:

[0022] The real-time crystallization risk value RI calculated based on the crystallization risk index model satisfies:

[0023] RI = 0 to 3: Low crystallization risk, pulse purge is performed according to the preset purge air flow rate and set cycle;

[0024] RI=4-5: Medium crystallization risk, adaptively increase the pulse purge frequency or purge air flow for pulse purge;

[0025] RI greater than 5: High crystallization risk. Adaptively increase the pulse purge frequency and purge air flow for pulse purge.

[0026] A second aspect of the present invention further provides a method for preventing crystallization of an air-assisted urea injection system, comprising the following steps:

[0027] When the compressed air source is accidentally cut off and / or the urea pump is accidentally powered off, the control system controls the compressed air from the purge air tank to purge the urea solution in the urea spray gun to prevent crystallization;

[0028] The compressed air used to purge the air storage tank is controlled to be 1.2 to 1.5 times the compressed air flow rate for injection as the purge air flow rate, and pulse purge is performed in a cycle of 5 to 30 minutes, with a pulse purge duration of 500ms; and

[0029] Based on the temperature, concentration and residence time of the urea solution, a crystallization risk index model is established to calculate the real-time crystallization risk value RI:

[0030] RI=((35-T)*(C-32.5)) / τ+t / 60

[0031] Wherein, T represents the temperature of the urea solution in the urea spray gun, in °C; C represents the concentration percentage of the urea solution in the urea spray gun, in %, t represents the residence time, in min; τ represents the dimension scaling factor, which is determined by orthogonal test;

[0032] Comprehensively assess urea crystallization risk through urea solution concentration-temperature thermodynamic coupling and residence time coupling;

[0033] When the real-time crystallization risk value RI exceeds the warning value, the pulse purge frequency and / or purge air flow rate are adaptively updated, and an early warning is issued through the HMI interface.

[0034] In a further embodiment, the real-time crystallization risk value RI is calculated based on the crystallization risk index model and satisfies:

[0035] RI = 0 to 3: Low crystallization risk, pulse purge is performed according to the preset purge air flow rate and set cycle;

[0036] RI=4-5: Medium crystallization risk, adaptively increase the pulse purge frequency or purge air flow for pulse purge;

[0037] RI greater than 5: High crystallization risk. Adaptively increase the pulse purge frequency and purge air flow for pulse purge.

[0038] The air-assisted urea injection system for industrial source equipment exhaust gas purification according to the above embodiment of the present invention is used to prevent crystallization control system. The system is equipped with a purge gas storage tank, which is connected to the compressed air source through a one-way valve. When the gas source is accidentally cut off or the gear pump is powered off, the compressed air pre-stored in the gas storage tank is used to purge the urea spray gun and pipeline. Even in the case of a failure or power outage in the upstream air compressor station, the pre-stored compressed air can still be used to clear the retained urea solution, avoid the crystallization problem caused by power interruption, prevent the solution in the pipeline from being retained due to loss of power, and inhibit the formation of crystallization conditions. At the same time, the compressed air pre-stored in the gas storage tank is used in a pulse purge mode (such as 500ms duration and 5-30min cycle) to purge at 1.2-1.5 times the compressed air flow rate used for injection. When the compressed air pre-stored in the gas storage tank is limited (cannot be replenished), it can effectively clear the residual solution in the pipeline, and use the air hammer effect to break the possible micro-crystallization in the pipeline, and reduce the compressed air consumption. Combined with dynamic assessment of crystallization risk, the flow rate and frequency of pulse purge are adaptively adjusted in real time to avoid resource waste caused by excessive purge, while ensuring the purge effect and inhibiting crystallization.

[0039] Compared with the prior art, the air-assisted urea injection system for preventing crystallization control system for industrial source equipment exhaust gas purification of the present invention has the following significant advantages:

[0040] 1. By setting up a purge air tank, when the gas source is accidentally cut off or the gear pump is powered off, the compressed air stored in the air tank is used to continuously purge the urea spray gun and pipeline in a pulse purge mode, thereby suppressing the risk of crystallization caused by residual urea solution. Pulse purge saves compressed air and reduces compressed air consumption. In the case of uncertainty in downtime (long recovery time), the crystallization suppression action can be extended as much as possible to reduce the risk and impact of crystallization.

[0041] 2. A quantitative model is established based on the temperature, concentration, and residence time of the urea solution. The crystallization risk is comprehensively evaluated through thermodynamic coupling and time factors. The purge strategy can be dynamically adjusted according to real-time operating conditions (such as low temperatures in winter and extended downtime). Closed-loop control of the purge control is achieved through dynamic perception and evaluation. Accurate adaptive control is carried out according to actual risks to improve anti-crystallization efficiency.

[0042] It should be understood that all combinations of the foregoing concepts and the additional concepts described in more detail below, as long as such concepts are not mutually inconsistent, can be considered part of the inventive subject matter of this disclosure. In addition, all combinations of the claimed subject matter are considered part of the inventive subject matter of this disclosure.

[0043] The foregoing and other aspects, embodiments, and features of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as features and / or beneficial effects of the exemplary embodiments, will become apparent from the following description or through practice of specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings are not intended to be drawn to scale. In the accompanying drawings, each identical or nearly identical component shown in various figures may be represented by the same reference numeral. For clarity, not every component is labeled in every figure. Embodiments of various aspects of the present invention will now be described by way of example and with reference to the accompanying drawings.

[0045] Figure 1 Schematic diagram of a crystallization prevention control system of an air-assisted urea injection system for exhaust gas purification of industrial source equipment according to an embodiment of the present invention.

[0046] Figure 2 The figure is a control flow chart of an SCR system for purifying exhaust gas from industrial source equipment according to an embodiment of the present invention.

[0047] Figure 3 This is a schematic diagram of an actual product of a gas-assisted urea injection system for preventing crystallization control system for exhaust gas purification of industrial source equipment according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to better understand the technical content of the present invention, specific embodiments are given and described below with reference to the accompanying drawings.

[0049] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to include all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those described in more detail below, can be implemented in any of many ways, because the concepts and embodiments disclosed herein are not limited to any embodiment. In addition, some aspects of the present disclosure may be used alone or in any appropriate combination with other aspects disclosed herein.

[0050] {Example 1}

[0051] Combine Figure 1 As shown, an air-assisted urea injection system for preventing crystallization of exhaust gas from industrial source equipment according to an embodiment of the present invention includes a urea solution storage tank, a gear pump, a urea spray gun, a compressed air source, a purge air storage tank, a compressed air pipeline, a urea pipeline and a control system.

[0052] In this embodiment, the control system is described by taking a PLC controller as an example.

[0053] As shown in the figure, the PLC controller is also equipped with a human-machine interface HMI, which is used to provide an interface for information input and display.

[0054] The urea solution storage tank is used to contain urea solution.

[0055] The gear pump is provided in a urea pipeline extending from the urea solution storage tank to the urea spray gun, and is used for pumping the urea solution from the urea solution storage tank to the urea spray gun for injection.

[0056] As an optional embodiment, a filter is provided between the urea solution storage tank and the gear pump.

[0057] like Figure 1 As shown, a first temperature sensor T1 and a urea liquid level sensor L1 are provided in the urea solution storage tank, for detecting the temperature of the urea solution contained in the urea solution storage tank and the remaining capacity of the urea solution, respectively.

[0058] A first pressure sensor P1 is provided between the gear pump and the urea spray gun for detecting the pressure of the pumped urea solution.

[0059] When the temperature of the urea solution is kept in the preset range (to prevent crystallization), the control system drives the gear pump to pump the urea solution. Urea injection can only be carried out at the urea spray gun after a pressure of 4 bar is established in the urea solution pipeline.

[0060] like Figure 1 As shown, the compressed air source enters the purge air tank through a one-way valve.

[0061] The purge air storage tank and the urea spray gun are connected via a compressed air pipeline, and a pressure reducing valve is provided to control the delivery of compressed air from the purge air storage tank to the urea spray gun.

[0062] like Figure 1 A compressed air pressure sensor P2 is installed in the compressed air pipeline to monitor the pressure of the compressed air in real time.

[0063] A pressure detection sensor P3 is provided in the purge gas storage tank for real-time monitoring of the internal pressure of the purge gas storage tank.

[0064] like Figure 1 As shown, the purge gas storage tank is also equipped with a safety valve for relieving pressure when the internal pressure of the purge gas storage tank exceeds the standard.

[0065] Furthermore, the urea spray gun is configured to mix the delivered urea solution with compressed air in the spray gun and then spray the mixture onto the SCR reaction carrier.

[0066] The control system is configured to control the operation of the gear pump, urea spray gun, and pressure reducing valve. When the compressed air source is accidentally cut off and / or the urea pump is accidentally powered off, the control system controls the compressed air from the purge air tank to purge the urea solution in the urea spray gun to prevent crystallization.

[0067] In an embodiment of the present invention, the control system controls the compressed air for purging the air tank according to a preset purging air flow rate, and performs pulse purging at a set period, and calculates the real-time crystallization risk value RI based on the crystallization risk index model. When the real-time crystallization risk value RI exceeds the warning value, the pulse purging frequency and / or purging air flow rate are adaptively updated, and an early warning is issued through the HMI interface.

[0068] In an embodiment of the present invention, the control system controls the compressed air for purging the air storage tank according to a preset purge air flow rate and performs pulse purge at a set period, including:

[0069] The compressed air for purging the air storage tank is controlled to be 1.2 to 1.5 times the compressed air flow rate for injection as the purging air flow rate, and pulse purging is performed with a cycle of 5 to 30 minutes, and the duration of the pulse purging is 500ms.

[0070] In an embodiment of the present invention, calculating the real-time crystallization risk value RI based on the crystallization risk index model includes:

[0071] A crystallization risk index model was established based on the temperature, concentration, and residence time of the urea solution:

[0072] RI=((35-T)*(C-32.5)) / τ+t / 60

[0073] Wherein, T represents the temperature of the urea solution in the urea spray gun, in °C; C represents the concentration percentage of the urea solution in the urea spray gun, in %, and t represents the residence time, in min, which is converted into hours to reflect the time cumulative effect of solute deposition;

[0074] where τ represents the dimension scaling factor, which is determined by orthogonality test.

[0075] It should be understood that in this embodiment, the dimension scaling factor τ is used to scale the dimension of the temperature-concentration product term so that it is on the same order of magnitude as the residence time term (e.g., a typical residence time of 30 minutes corresponds to a term value of 0.5, which matches the product term value for the low temperature and high concentration scenario).

[0076] In this embodiment, the dimension scaling coefficient τ can be determined based on an orthogonal test: the crystallization rate is tested at different temperatures (5-30°C), concentrations (30%-35%), and residence times (10-120 minutes), and the coefficient is determined using linear regression so that the RI value and the crystallization probability (P) satisfy: P = 1-e -k*RI,k≈0.5, the value is an empirical value.

[0077] Therefore, the temperature term (35-T) represents the difference between the current temperature and the "safety temperature limit." 35°C was chosen as the benchmark because urea has a stable solubility between 30 and 40°C (approximately 105 g / 100 mL). Temperatures above this threshold may trigger thermal decomposition (forming biuret), making the risk of low-temperature crystallization more significant. When T is less than 35°C, the difference is positive, and the lower the temperature, the greater the term's value. When T is ≥ 35°C, the term's value is ≤ 0, negating the effect of temperature on crystallization (the primary risk is thermal decomposition). The concentration term (C-32.5) represents the degree to which the concentration deviates from the reference value (32.5%). When C is greater than 32.5%, the term is positive; higher concentrations indicate greater supersaturation. When C is 32.5%, the term's value is 0, corresponding to equilibrium. When C is less than 32.5%, the term's value is negative. Through the synergistic effect of the two factors, the risk increase at low temperatures and high concentrations is far greater than that of any single factor.

[0078] Therefore, the urea crystallization risk is comprehensively evaluated through the urea solution concentration-temperature thermodynamic coupling and residence time coupling, and the pulse purge frequency and / or purge air flow rate are adaptively updated accordingly.

[0079] In an embodiment of the present invention, when the real-time crystallization risk value RI exceeds the warning value, adaptively updating the pulse purge frequency and / or the purge air flow rate includes:

[0080] The real-time crystallization risk value RI calculated based on the crystallization risk index model satisfies:

[0081] RI = 0 to 3: Low crystallization risk, pulse purge is performed according to the preset purge air flow rate and set cycle;

[0082] RI=4-5: Medium crystallization risk, adaptively increase the pulse purge frequency or purge air flow for pulse purge;

[0083] RI greater than 5: High crystallization risk. Adaptively increase the pulse purge frequency and purge air flow for pulse purge.

[0084] In an embodiment of the present invention, when the internal pressure of the purge gas storage tank monitored in real time by the pressure detection sensor is lower than a preset standard, the control system issues an early warning, such as a red early warning, through the HMI interface.

[0085] {Example 2}

[0086] Figure 2 The SCR system control process for exhaust gas purification of industrial source equipment is shown as an example.

[0087] like Figure 2As shown, after the system is running, the urea solution system is pressurized (4 bar) through the gear pump, and the compressed air pressure is monitored and the compressed air pressure is built up (3 bar) to enter the pre-injection state.

[0088] The user can select manual or automatic injection mode through the HMI. When automatic injection mode is selected, the urea injection amount is calculated according to the exhaust gas flow rate and upstream nitrogen and oxygen concentration according to the existing injection control method, and injection control is performed accordingly. The downstream nitrogen and oxygen concentration is further monitored for feedback control to correct the urea injection amount.

[0089] When the user selects the manual injection mode, the user can manually input the urea injection amount and perform urea injection according to the set injection amount.

[0090] In automatic injection mode or manual injection mode, when an unexpected shutdown occurs (including gear pump shutdown or compressed air supply stoppage) or the user presses the stop button, the PLC controller controls the system to enter the purge mode, using the compressed air in the purge air tank to purge the urea solution in the urea spray gun to prevent crystallization.

[0091] Specifically, the PLC controller controls the compressed air for purging the air storage tank according to a preset purge air flow rate and performs pulse purging at a set period.

[0092] At the same time, the PLC controller calculates the real-time crystallization risk index (RI) based on the crystallization risk index model (calculation model) built into the controller. When the real-time crystallization risk index (RI) exceeds the warning value, the pulse purge frequency and / or purge air flow rate are adaptively updated, and an early warning is issued through the HMI interface.

[0093] As an optional embodiment, the compressed air for purging the air storage tank is controlled to be 1.2 to 1.5 times the compressed air flow rate for injection as the purge air flow rate, and pulse purge is performed in a cycle of 5 to 30 minutes, and the pulse purge duration is 500ms; and

[0094] The real-time crystallization risk value RI is calculated based on the temperature, concentration and residence time of the urea solution:

[0095] RI=((35-T)*(C-32.5)) / τ+t / 60

[0096] Wherein, T represents the temperature of the urea solution in the urea spray gun, in °C; C represents the concentration percentage of the urea solution in the urea spray gun, in %, t represents the residence time, in min; τ represents the dimension scaling factor, which is determined by orthogonal test;

[0097] Comprehensively assess urea crystallization risk through urea solution concentration-temperature thermodynamic coupling and residence time coupling;

[0098] When the real-time crystallization risk value RI exceeds the warning value, the pulse purge frequency and / or purge air flow rate are adaptively updated, and an early warning is issued through the HMI interface.

[0099] Furthermore, the real-time crystallization risk value RI is calculated based on the crystallization risk index model to satisfy:

[0100] RI = 0 to 3: Low crystallization risk, pulse purge is performed according to the preset purge air flow rate and set cycle;

[0101] RI=4-5: Medium crystallization risk, adaptively increase the pulse purge frequency or purge air flow for pulse purge;

[0102] RI greater than 5: High crystallization risk. Adaptively increase the pulse purge frequency and purge air flow for pulse purge.

[0103] While the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Persons skilled in the art will readily appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims.

Claims

1. A gas-assisted urea injection system for preventing crystallization control system for industrial source equipment exhaust gas purification, characterized in that: It includes urea solution storage tank, gear pump, urea spray gun, compressed air source, purge air tank, compressed air pipeline, urea pipeline and control system; The urea solution storage tank is used to contain the urea solution; The gear pump is arranged in a urea pipeline extending from the urea solution storage tank to the urea spray gun, and is used to pump the urea solution from the urea solution storage tank to the urea spray gun for injection; The compressed air source enters the purge air storage tank through a one-way valve; a pressure detection sensor is provided in the purge air storage tank for real-time monitoring of the internal pressure of the purge air storage tank; The purge air storage tank is connected to the urea spray gun via a compressed air pipeline, and a pressure reducing valve is provided to control the delivery of compressed air from the purge air storage tank to the urea spray gun; a compressed air pressure sensor is provided in the compressed air pipeline to monitor the pressure of the delivered compressed air in real time; The urea spray gun is configured to mix the delivered urea solution with compressed air in the spray gun and then spray the mixture onto the SCR reaction carrier; The control system is configured to control the operation of the gear pump, the urea spray gun, and the pressure reducing valve, and when the compressed air source is accidentally cut off and / or the urea pump is accidentally powered off, the control system controls the compressed air from the purge air tank to purge the urea solution in the urea spray gun to prevent crystallization; Among them, the control system controls the compressed air for purging the air tank according to the preset purging air flow rate, and performs pulse purging at a set period, and calculates the real-time crystallization risk value RI based on the crystallization risk index model. When the real-time crystallization risk value RI exceeds the warning value, the pulse purging frequency and / or purging air flow rate are adaptively updated, and an early warning is issued through the HMI interface.

2. The air-assisted urea injection system for preventing crystallization of industrial source equipment exhaust gas purification according to claim 1 is characterized in that: A first temperature sensor and a urea liquid level sensor are provided in the urea solution storage tank, for detecting the temperature of the urea solution contained in the urea solution storage tank and the remaining capacity of the urea solution respectively; A first pressure sensor is provided between the gear pump and the urea spray gun for detecting the pressure of the pumped urea solution; When the temperature of the urea solution is maintained within a preset range, the control system drives the gear pump to pump the urea solution. Urea injection can only be performed at the urea spray gun after a pressure of 4 bar is established in the urea solution pipeline.

3. The air-assisted urea injection system for preventing crystallization of industrial source equipment exhaust gas purification according to claim 1 is characterized in that: A filter is provided between the urea solution storage tank and the gear pump.

4. The air-assisted urea injection system for preventing crystallization control system for industrial source equipment exhaust gas purification according to claim 1 is characterized in that: The control system controls the compressed air for purging the air storage tank according to a preset purge air flow rate and performs pulse purging at a set period, including: The compressed air for purging the air storage tank is controlled to be 1.2 to 1.5 times the compressed air flow rate for injection as the purging air flow rate, and pulse purging is performed with a cycle of 5 to 30 minutes, and the duration of the pulse purging is 500ms.

5. The air-assisted urea injection system for preventing crystallization control system for industrial source equipment exhaust gas purification according to claim 1 is characterized in that: The calculation of the real-time crystallization risk value RI based on the crystallization risk index model includes: A crystallization risk index model was established based on the temperature, concentration, and residence time of the urea solution: RI=((35-T)*(C-32.5)) / τ+t / 60 Wherein, T represents the temperature of the urea solution in the urea spray gun, in °C; C represents the concentration percentage of the urea solution in the urea spray gun, in %, t represents the residence time, in min; τ represents the dimension scaling factor, which is determined by orthogonal test; Through the thermodynamic coupling of urea solution concentration and temperature as well as the coupling of residence time, the risk of urea crystallization is comprehensively evaluated, and the pulse purge frequency and / or purge air flow rate are adaptively updated accordingly.

6. The air-assisted urea injection system for preventing crystallization control system for industrial source equipment exhaust gas purification according to claim 5, characterized in that: When the real-time crystallization risk value RI exceeds the warning value, adaptively updating the pulse purge frequency and / or the purge air flow rate includes: The real-time crystallization risk value RI calculated based on the crystallization risk index model satisfies: RI = 0 to 3: Low crystallization risk, pulse purge is performed according to the preset purge air flow rate and set cycle; RI=4-5: Medium crystallization risk, adaptively increase the pulse purge frequency or purge air flow for pulse purge; RI greater than 5: High crystallization risk. Adaptively increase the pulse purge frequency and purge air flow for pulse purge.

7. The air-assisted urea injection system for preventing crystallization control system for industrial source equipment exhaust gas purification according to claim 1, characterized in that: When the internal pressure of the purge gas storage tank monitored in real time by the pressure detection sensor is lower than a preset standard, the control system issues an early warning through the HMI interface.

8. The air-assisted urea injection system for preventing crystallization control system for industrial source equipment exhaust gas purification according to claim 1, characterized in that: The purge gas storage tank is also equipped with a safety valve for relieving pressure when the internal pressure of the purge gas storage tank exceeds the standard.

9. A method for preventing crystallization of an air-assisted urea injection system based on the air-assisted urea injection system for preventing crystallization of an industrial source equipment exhaust gas purification control system according to any one of claims 1 to 8, characterized in that: The following steps are involved: When the compressed air source is accidentally cut off and / or the urea pump is accidentally powered off, the control system controls the compressed air from the purge air tank to purge the urea solution in the urea spray gun to prevent crystallization; The compressed air used to purge the air storage tank is controlled to be 1.2 to 1.5 times the compressed air flow rate for injection as the purge air flow rate, and pulse purge is performed in a cycle of 5 to 30 minutes, with a pulse purge duration of 500ms; and Based on the temperature, concentration and residence time of the urea solution, a crystallization risk index model is established to calculate the real-time crystallization risk value RI: RI=((35-T)*(C-32.5)) / τ+t / 60 Wherein, T represents the temperature of the urea solution in the urea spray gun, in °C; C represents the concentration percentage of the urea solution in the urea spray gun, in %, t represents the residence time, in min; τ represents the dimension scaling factor, which is determined by orthogonal test; Comprehensively assess urea crystallization risk through urea solution concentration-temperature thermodynamic coupling and residence time coupling; When the real-time crystallization risk value RI exceeds the warning value, the pulse purge frequency and / or purge air flow rate are adaptively updated, and an early warning is issued through the HMI interface.

10. The method for preventing crystallization of an air-assisted urea injection system according to claim 9, characterized in that: The real-time crystallization risk value RI calculated based on the crystallization risk index model satisfies: RI = 0 to 3: Low crystallization risk, pulse purge is performed according to the preset purge air flow rate and set cycle; RI=4-5: Medium crystallization risk, adaptively increase the pulse purge frequency or purge air flow for pulse purge; RI greater than 5: High crystallization risk. Adaptively increase the pulse purge frequency and purge air flow for pulse purge.

Images