Anti-crystallization control system for urea injection system

Abstract

The utility model provides a kind of for urea injection system's anti-crystallization control system, the system configuration is by one-way valve and compressed air source connection's purging gas storage tank, when air source unexpected gas break or gear pump power off, utilize the pre-stored compressed air in purging gas storage tank purging urea spray gun and pipeline, even in upstream air pressure station failure or power off scene, can pass pre-stored compressed air clean up stagnate urea solution, avoid crystallization problem.Simultaneously control pulse purging mode and purging flow, in the case where the pre-stored compressed air in gas storage tank is limited, both can effectively clean up pipeline residual solution, utilize air hammer effect break pipeline possibly from microcrystalline, also can reduce compressed air consumption, realize the balance guarantee purging effect of purging required resource and anti-crystallization effect, inhibit crystallization to occur.

Description

Technical Field

[0001] This utility model relates to the field of industrial waste gas treatment technology, and in particular to the treatment of nitrogen oxides in industrial waste gas. Specifically, it relates to an anti-crystallization control system for urea injection systems. Background Technology

[0002] Industrial waste gas treatment is a key aspect of air pollution prevention and control. It includes the purification of exhaust gases from industrial boilers (coal-fired, gas-fired, and oil-fired) and generator sets (fueled by diesel or natural gas). Through SCR denitrification treatment, nitrogen oxide emissions in industrial waste gases can be effectively controlled.

[0003] SCR denitrification technology reduces ammonia oxide (NOx) emissions through catalytic reduction reactions. It uses selective catalysts, typically ammonia-to-iron (NH3-Fe) or ammonia-to-vanadium (NH3-V), to catalytically react NOx with ammonia (NH3) on the catalyst surface, converting nitrogen oxides in industrial exhaust gas into environmentally harmless nitrogen and water vapor, thus reducing negative environmental impacts.

[0004] SCR denitrification technology constructs a complete treatment system consisting of a catalytic reaction core unit, a reducing agent supply system, a reaction vessel, and a catalyst regeneration module. Its key treatment 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 to react with NOx in the exhaust gas. Passing through the catalyst bed, NOx and NH3 undergo a catalytic reduction reaction to produce N2 and H2O. Catalyst regeneration removes reaction products adhering to the catalyst to maintain its activity.

[0005] In actual industrial operation scenarios, the precise and stable control of the urea injection system, as the hub for reducing agent supply, is crucial to the entire system. Stable operation of urea injection relies on both gas-driven and urea solution-driven processes, namely, a continuous supply of gas power and reliable gear pump operation. When a sudden mechanical failure at the upstream air compressor station causes a sharp drop in gas pressure or a momentary power outage causes the gear pump to stop pumping urea, the atomizing airflow from the gear pump and nozzles will simultaneously cease. This sudden interruption will cause a chain reaction throughout the entire urea supply system within a short period. The remaining urea solution in the pipeline loses its flow momentum and stagnates in the urea spray gun and pipeline section. As the system downtime extends (recovery time plays out), the stagnant solution faces two physicochemical changes: on the one hand, the temperature inside the flue gradually drops from the normal operating temperature of 320-400℃, while the urea solubility decreases exponentially with decreasing temperature, and supersaturated solutions begin to precipitate white crystals; on the other hand, the stagnant liquid accumulates in low-lying areas of the pipeline under gravity, forming a liquid film. Evaporation on its surface further increases the local concentration, accelerating crystal nucleation. Especially during winter shutdowns, the temperature difference between the ambient temperature and the flue gas exacerbates this supersaturation state. According to on-site monitoring data, the crystallization thickness at pipe bends can reach 2-3 mm after 3-4 hours of shutdown. In severe cases, it can block 20%-50% of the flow cross-sectional area, causing a sharp increase in pressure drop and uneven distribution of reducing agent when the system restarts. Utility Model Content

[0006] In view of the technical problems existing in the prior art, the first aspect of the purpose of this utility model is to provide an anti-crystallization control system for a urea injection system, characterized in that it includes a urea solution storage tank, a gear pump, a urea spray gun, a compressed air source, a purging air tank, a compressed air pipeline, a urea pipeline, and a control system.

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

[0008] The gear pump is installed in the 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 spraying.

[0009] The compressed air source enters the purge air tank via a one-way valve; a pressure detection sensor is installed inside the purge air tank to monitor the internal pressure of the purge air tank in real time.

[0010] The purge air tank and the urea spray gun are connected via a compressed air pipeline and are equipped with a pressure reducing valve to control the supply of compressed air from the purge air tank to the urea spray gun; a compressed air pressure sensor is installed in the compressed air pipeline to monitor the pressure of the supplied compressed air in real time.

[0011] The urea spray gun is configured to mix the delivered urea solution with compressed air inside the spray gun and then spray it onto the SCR reaction carrier.

[0012] The control system is connected to the pressure detection sensor, compressed air pressure sensor, gear pump, urea spray gun, and pressure reducing valve, and controls the operation of the gear pump, urea spray gun, and pressure reducing valve.

[0013] Furthermore, in the event of an unexpected interruption of the compressed air source and / or an unexpected power failure of the urea pump, the control system controls the compressed air in the purging tank to perform pulse purging of the urea spray gun according to a preset purging air flow rate and at a set cycle to prevent crystallization.

[0014] As an optional implementation, a first temperature sensor is provided inside the urea solution storage tank to detect the temperature of the urea solution contained in the storage tank.

[0015] As an optional implementation, a urea level sensor is provided inside the urea solution storage tank to detect the remaining capacity of the urea solution in the storage tank.

[0016] As an optional implementation, a first pressure sensor is provided between the gear pump and the urea spray gun to detect the pressure of the pumped urea solution.

[0017] 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 can only be sprayed from the urea spray gun after a pressure of 4 bar is established in the urea solution pipeline.

[0018] As an optional implementation, a filter is provided between the urea solution storage tank and the gear pump.

[0019] As an optional implementation, the purge air flow rate is set to be 1.2 to 1.5 times the injection compressed air flow rate.

[0020] As an optional implementation, the control system is set to perform pulse purging at a cycle of 5 to 30 minutes, with a pulse purging duration of 500 ms.

[0021] As an optional implementation, the purging gas tank is also equipped with a safety valve for depressurizing when the internal pressure of the purging gas tank exceeds the limit.

[0022] As an optional implementation, the anti-crystallization control system is also equipped with a human-machine interface (HMI) connected to the control system to provide an interface for information input and display.

[0023] As an optional implementation, the control system employs a PLC controller.

[0024] The anti-crystallization control system for urea injection systems described in the above embodiments of this utility model is equipped with a purging air tank, which is connected to a compressed air source via a one-way valve. In the event of an unexpected interruption of the air source or a power failure of the gear pump, the pre-stored compressed air in the air tank purges the urea spray gun and pipeline. Even in the event of an upstream air compressor station failure or power failure, the pre-stored compressed air can still remove residual urea solution, preventing crystallization caused by power interruption and preventing solution stagnation in the pipeline due to loss of power, thus inhibiting the formation of crystallization conditions. Simultaneously, the pre-stored compressed air in the air tank is used in a pulse purging mode (e.g., 500ms duration, 5-30min cycle) at 1.2-1.5 times the flow rate of the injected compressed air. Since the pre-stored compressed air in the air tank is limited (and cannot be replenished), it effectively removes residual solution from the pipeline and utilizes the air hammer effect to break up potential micro-crystallization in the pipeline, while also reducing compressed air consumption. This achieves a balance between the resources required for purging and the anti-crystallization effect, ensuring the purging effect and inhibiting crystallization. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of an anti-crystallization control system for a urea injection system according to an embodiment of the present invention.

[0026] Figure 2 This is a control flowchart of an SCR system for purifying exhaust gas from industrial source equipment according to an embodiment of the present invention. Detailed Implementation

[0027] To better understand the technical content of this utility model, specific embodiments are provided below in conjunction with the accompanying drawings.

[0028] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, which illustrate numerous illustrative embodiments. The embodiments disclosed herein are not necessarily intended to include all aspects of the present invention. It should be understood that the various concepts and embodiments described 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 particular implementation. Furthermore, some aspects of the present invention can be used alone or in any suitable combination with other aspects disclosed herein.

[0029] {Example 1}

[0030] Combination Figure 1 As shown, the anti-crystallization control system for a urea injection system according to this embodiment is characterized by comprising a urea solution storage tank, a gear pump, a urea spray gun, a compressed air source, a purging air tank, a compressed air pipeline, a urea pipeline, and a control system.

[0031] In this embodiment, the control system is described using a PLC controller as an example.

[0032] As shown in the figure, the PLC controller is also equipped with a human-machine interface (HMI), which is electrically connected to the control system and is used to provide an interface for information input and display.

[0033] A urea solution storage tank is used to hold urea solution.

[0034] A gear pump is installed in the 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 spraying.

[0035] As an optional embodiment, a filter is provided between the urea solution storage tank and the gear pump.

[0036] like Figure 1 As shown, a first temperature sensor T1 is installed inside the urea solution storage tank to detect the temperature of the urea solution contained in the storage tank.

[0037] A urea level sensor L1 is installed inside the urea solution storage tank to detect the remaining capacity of the urea solution contained in the storage tank.

[0038] A first pressure sensor P1 is installed between the gear pump and the urea spray gun to detect the pressure of the pumped urea solution.

[0039] When the temperature of the urea solution is maintained within a preset range (to prevent crystallization), the control system drives the gear pump to pump the urea solution. Urea can only be sprayed from the urea spray gun after a pressure of 4 bar is established in the urea solution pipeline.

[0040] like Figure 1 As shown, the compressed air source enters the purge air tank via a one-way valve.

[0041] The purging air tank and the urea spray gun are connected by a compressed air pipeline and are equipped with a pressure reducing valve to control the supply of compressed air from the purging air tank to the urea spray gun.

[0042] like Figure 1 A compressed air pressure sensor P2 is installed inside the compressed air pipeline to monitor the pressure of the delivered compressed air in real time.

[0043] A pressure sensor P3 is installed inside the purging gas tank to monitor the internal pressure of the purging gas tank in real time.

[0044] like Figure 1 As shown, the purging gas tank is also equipped with a safety valve, which is used to release pressure when the internal pressure of the purging gas tank exceeds the standard.

[0045] Furthermore, the urea spray gun is configured to mix the delivered urea solution with compressed air inside the spray gun before spraying it onto the SCR reaction carrier.

[0046] The control system is connected to a pressure detection sensor, a compressed air pressure sensor, a gear pump, a urea spray gun, and a pressure reducing valve, and controls the operation of the gear pump, urea spray gun, and pressure reducing valve. Furthermore, in the event of an unexpected interruption of the compressed air supply and / or an unexpected power failure of the urea pump, the control system controls the compressed air from the purging tank to perform pulse purging of the urea spray gun at a preset purging air flow rate and at a set cycle to prevent crystallization.

[0047] As an optional implementation, a filter is provided between the urea solution storage tank and the gear pump.

[0048] As an optional implementation, the purge air flow rate is set to be 1.2 to 1.5 times the injection compressed air flow rate.

[0049] As an optional implementation, the control system is set to perform pulse purging at a cycle of 5 to 30 minutes, with a pulse purging duration of 500 ms.

[0050] {Example 2}

[0051] Figure 2 An example is shown of the control process of an SCR system for purifying exhaust gas from industrial source equipment.

[0052] like Figure 2 As shown, after the system is running, the urea solution system is pressurized (4 bar) by the gear pump, and the compressed air pressure is monitored. The compressed air pressure is then built up (3 bar), and the system enters the pre-injection state.

[0053] Users can select manual / automatic injection mode through HMI. When automatic injection mode is selected, the injection control method of the existing design is used to calculate the urea injection amount based on the exhaust gas flow and upstream nitrogen and oxygen concentration and execute injection control accordingly. The downstream nitrogen and oxygen concentration is further monitored for feedback control to correct the urea injection amount.

[0054] When the user selects the manual injection mode, they can manually input the urea injection volume and execute the urea injection according to the set injection volume.

[0055] In automatic or manual spraying mode, if there is an unexpected shutdown (including gear pump shutdown or compressed air supply stoppage) or the user presses the stop button, the PLC controller will switch to purging mode, using compressed air from the purging tank to purge the urea solution in the urea spray gun to prevent crystallization.

[0056] Specifically, the PLC controller controls the compressed air in the purging air tank to perform pulse purging according to the preset purging air flow rate and at a set cycle.

[0057] As an optional embodiment, the PLC controller controls the compressed air in the purging air tank to be purging air at a flow rate of 1.2 to 1.5 times that of the compressed air used for injection, and performs pulse purging at a cycle of 5 to 30 minutes, with a pulse purging duration of 500 ms.

[0058] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Those skilled in the art to which this invention pertains can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of this invention shall be determined by the claims.

Claims

1. A crystallization prevention control system for a urea injection system, characterized in that, Includes a urea solution storage tank, gear pump, urea spray gun, compressed air source, purging air tank, compressed air pipeline, urea pipeline, and control system; The urea solution storage tank is used to contain urea solution; The gear pump is installed in the 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 spraying. The compressed air source enters the purge air tank via a one-way valve; a pressure detection sensor is installed inside the purge air tank to monitor the internal pressure of the purge air tank in real time. The purge air tank and the urea spray gun are connected via a compressed air pipeline and are equipped with a pressure reducing valve to control the supply of compressed air from the purge air tank to the urea spray gun; a compressed air pressure sensor is installed in the compressed air pipeline to monitor the pressure of the supplied compressed air in real time. The urea spray gun is configured to mix the delivered urea solution with compressed air inside the spray gun and then spray it onto the SCR reaction carrier. The control system is connected to the pressure detection sensor, compressed air pressure sensor, gear pump, urea spray gun, and pressure reducing valve, and controls the operation of the gear pump, urea spray gun, and pressure reducing valve. Furthermore, in the event of an unexpected interruption of the compressed air source and / or an unexpected power failure of the urea pump, the control system controls the compressed air in the purging tank to perform pulse purging of the urea spray gun according to a preset purging air flow rate and at a set cycle to prevent crystallization.

2. The anti-crystallization control system for a urea injection system according to claim 1, characterized in that, The urea solution storage tank is equipped with a first temperature sensor to detect the temperature of the urea solution contained in the storage tank.

3. The anti-crystallization control system for a urea injection system according to claim 1, characterized in that, The urea solution storage tank is equipped with a urea level sensor to detect the remaining capacity of the urea solution in the tank.

4. The anti-crystallization control system for a urea injection system according to claim 1, characterized in that, A first pressure sensor is installed between the gear pump and the urea spray gun to detect 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 can only be sprayed from the urea spray gun after a pressure of 4 bar is established in the urea solution pipeline.

5. The anti-crystallization control system for a urea injection system according to claim 1, characterized in that, A filter is installed between the urea solution storage tank and the gear pump.

6. The anti-crystallization control system for a urea injection system according to claim 1, characterized in that, The purge air flow rate is set to be 1.2 to 1.5 times the jet compressed air flow rate.

7. The anti-crystallization control system for a urea injection system according to claim 1, characterized in that, The control system is set to perform pulse purging at a cycle of 5 to 30 minutes, with a pulse purging duration of 500 ms.

8. The anti-crystallization control system for a urea injection system according to claim 1, characterized in that, The purging gas storage tank is also equipped with a safety valve for releasing pressure when the internal pressure of the purging gas storage tank exceeds the standard.

9. The anti-crystallization control system for a urea injection system according to claim 1, characterized in that, The anti-crystallization control system is also equipped with a human-machine interface (HMI), which is connected to the control system and provides an interface for information input and display.

10. The anti-crystallization control system for a urea injection system according to claim 1, characterized in that, The control system uses a PLC controller.

Images