Combined heating method of electric heating and flue gas heat exchange in urea pyrolysis ammonia production system

Abstract

The application discloses a combined heating method of electric heating and flue gas heat exchange in a urea pyrolysis ammonia production system, comprising the following steps: S1, system starting and basic heating establishment; S2, flue gas heat exchange dominant heating and temperature monitoring; S3, electric heating auxiliary temperature adjustment and compensation; S4, load fluctuation response and heat source switching; S5, operation maintenance and safety control. In the implementation of the application, the waste heat of the boiler tail flue gas is recovered and utilized by the flue gas heat exchanger as a basic heat source, which greatly reduces the energy consumption of direct electric heating and has significant energy-saving benefits; the electric heater arranged in parallel as an adjusting and standby heat source can quickly and accurately compensate for the insufficient heating caused by the flue gas parameter fluctuation or system load change, so that the pyrolysis chamber temperature is always maintained within the set range, and the continuity and stability of ammonia production are ensured.

Description

Technical Field

[0001] This invention relates to the field of urea pyrolysis ammonia production technology, specifically to a combined heating method of electric heating and flue gas heat exchange in a urea pyrolysis ammonia production system. Background Technology

[0002] In flue gas denitrification systems of industrial facilities such as coal-fired power plants, urea pyrolysis to produce ammonia is a commonly used ammonia preparation technology. When implementing this method, urea solution needs to be pyrolyzed at high temperature to generate ammonia.

[0003] Traditional heating methods are mainly divided into two categories: one is to use electric heaters to provide the heat required for pyrolysis. This method is simple to operate but consumes a lot of energy, resulting in a significant increase in plant power consumption and high operating costs; the other is to use the flue gas at the tail end of the boiler for heating through a heat exchanger. Although this method is energy-saving, it is greatly affected by fluctuations in boiler load and flue gas parameters (such as temperature and flow rate). When the load is low or the flue gas temperature is insufficient, it is difficult to maintain a stable temperature in the pyrolysis chamber, affecting the reliable supply of ammonia production, and thus threatening the overall operational stability and denitrification efficiency of the denitrification system. Summary of the Invention

[0004] To address this issue, the present invention provides a combined heating method of electric heating and flue gas heat exchange in a urea pyrolysis ammonia production system. This method solves the problem in the prior art where the pyrolysis chamber temperature is difficult to maintain under low load or insufficient flue gas temperature due to fluctuations in boiler load and flue gas parameters (such as temperature and flow rate), which affects the reliable supply of ammonia production and thus threatens the overall operational stability and denitrification efficiency of the denitrification system.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A combined heating method using electric heating and flue gas heat exchange in a urea pyrolysis ammonia production system, wherein the urea pyrolysis ammonia production system includes a pyrolysis chamber, a blower connected to the air inlet of the pyrolysis chamber, a flue gas heat exchanger and an electric heater installed in the duct between the blower and the pyrolysis chamber, and the hot-side medium channel of the flue gas heat exchanger is connected to the boiler tail flue; the method includes the following steps:

[0007] S1. System startup and basic heating establishment steps: Start the air supply fan to send ambient air or preheated air into the air duct; at the same time, draw out a portion of high-temperature flue gas from the tail flue of the boiler and let it flow through the hot side medium channel of the flue gas heat exchanger to indirectly exchange heat with the combustion air flowing through the cold side medium channel of the flue gas heat exchanger.

[0008] S2. Flue gas heat exchange as the main heating and temperature monitoring steps: When the boiler is running at medium to high load, the air is heated by the heat provided by the flue gas heat exchanger; the heated air enters the pyrolysis chamber to provide the required heat for the pyrolysis reaction of the urea solution; during this process, the reaction temperature in the pyrolysis chamber or the air temperature at the outlet of the electric heater is monitored in real time.

[0009] S3, Electric heating assisted temperature adjustment and compensation step: Compare the real-time temperature value in the pyrolysis chamber monitored in step S2 with the preset target temperature range; when the real-time temperature value in the pyrolysis chamber is lower than the lower limit of the target temperature range, start the electric heater or increase its operating power to supplement the heating of the air after the initial heating by the flue gas heat exchanger, so that the temperature of the air entering the pyrolysis chamber rises to the target range.

[0010] S4. Load fluctuation response and heat source switching steps: When the boiler load decreases, causing the temperature of the flue gas at the tail of the boiler or the flow rate of the flue gas to decrease, making it impossible for the flue gas heat exchanger alone to maintain the temperature required for the pyrolysis chamber, the output power of the electric heater is automatically increased; conversely, when the boiler load increases and the flue gas heat exchange capacity is enhanced, the output power of the electric heater is automatically reduced or it is turned off.

[0011] S5. Operation, maintenance and safety control steps: Periodically or according to the differential pressure signal, purge the flue gas heat exchanger; install an over-temperature protection sensor in the duct section where the electric heater is located, and immediately cut off the power supply to the electric heater when the temperature exceeds the safety threshold.

[0012] Preferably, in step S1, the pipeline from which the high-temperature flue gas is drawn out of the boiler tail flue is equipped with a regulating valve, and the flow rate of the flue gas introduced into the flue gas heat exchanger is controlled by adjusting the opening degree of the valve.

[0013] Preferably, the opening control of the regulating valve is linked to the boiler load signal or the urea solution injection quantity signal of the pyrolysis chamber; when the boiler load increases or the demand for urea solution injection increases, the opening of the regulating valve is automatically increased to introduce more high-temperature flue gas.

[0014] Preferably, in step S3, the power regulation of the electric heater adopts a PID control algorithm, which dynamically calculates and outputs a corresponding power control signal based on the deviation between the real-time temperature value and the target set value and its rate of change.

[0015] Preferably, the electric heater adopts a multi-stage group arrangement or a multi-level power adjustment design; in steps S3 and S4, the heating groups are started or stopped step by step, or switched to different power levels, according to the required amount of compensation heat.

[0016] Preferably, in step S2, the parameters monitored in real time also include the air temperature at the cold side outlet of the flue gas heat exchanger; in step S4, when the boiler load decreases, it is first determined whether the cold side outlet temperature of the flue gas heat exchanger is lower than a first set value. If so, the electric heater is activated for compensation; when the boiler load increases, it is first determined whether the cold side outlet temperature of the flue gas heat exchanger is higher than a second set value. If so, the power of the electric heater is reduced.

[0017] Preferably, the system also includes a rapid heating step during initial startup or restart after a long period of shutdown: in this stage, the electric heater is first started at full power or simultaneously, so that the pyrolysis chamber reaches the minimum reaction temperature required for urea pyrolysis in the shortest possible time; after the temperature of the pyrolysis chamber stabilizes and the boiler flue gas conditions allow, the power of the electric heater is gradually reduced and the system switches to an operation mode that mainly uses flue gas heat exchange.

[0018] Preferably, in the rapid heating step, if the flue gas heat exchanger cannot provide effective heat in the initial stage of startup due to the low flue gas temperature, then by closing its cold side bypass or minimizing the bypass opening, all or most of the combustion air can flow through the electric heater for heating.

[0019] Preferably, the flue gas heat exchanger is a partitioned heat exchanger, and its hot-side medium channel has an anti-wear and anti-clogging design; the electric heater is a high-temperature resistant resistance heater, and its heating element surface is provided with heat-expanding fins to enhance heat exchange.

[0020] The present invention has the following advantages: When the present invention is implemented, the waste heat of the flue gas at the tail end of the boiler is recovered and utilized as the basic heat source by the flue gas heat exchanger, which greatly reduces the energy consumption of direct electric heating and has significant energy-saving benefits.

[0021] By using parallel electric heaters as regulating and backup heat sources, insufficient heating caused by fluctuations in flue gas parameters or changes in system load can be quickly and accurately compensated, thereby ensuring that the temperature of the pyrolysis chamber is always maintained within the set range, thus ensuring the continuity and stability of ammonia production.

[0022] The intelligent coordination and switching between the two heat sources achieves the best balance between energy saving and reliability, and is particularly suitable for the complex variable load operation conditions of power plants, thus improving the adaptability and economy of the entire denitrification system. Attached Figure Description

[0023] To more intuitively illustrate the prior art and this application, exemplary drawings are provided below. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing this application; for example, based on the technical concept disclosed in this application and the exemplary drawings, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, size ratios, etc. of certain units (components).

[0024] Figure 1 A flowchart illustrating the combined heating method of electric heating and flue gas heat exchange in the urea pyrolysis ammonia production system provided in this application embodiment. Detailed Implementation

[0025] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. It should be understood that these embodiments are merely for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Technical engineers in the field can make some non-essential improvements and adjustments to the present invention based on the above-described content. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Please see Figure 1 A combined heating method using electric heating and flue gas heat exchange in a urea pyrolysis ammonia production system, wherein the urea pyrolysis ammonia production system includes a pyrolysis chamber, a blower connected to the air inlet of the pyrolysis chamber, a flue gas heat exchanger and an electric heater installed in the duct between the blower and the pyrolysis chamber, and the hot-side medium channel of the flue gas heat exchanger is connected to the boiler tail flue; the method includes the following steps:

[0027] S1. System startup and basic heating establishment steps: Start the air supply fan to send ambient air or preheated air into the air duct; at the same time, a portion of high-temperature flue gas is drawn out from the boiler tail flue and flows through the hot side medium channel of the flue gas heat exchanger to indirectly exchange heat with the combustion air flowing through the cold side medium channel of the heat exchanger, thereby initially heating the air and establishing a basic heat source supply.

[0028] S2. Flue gas heat exchange as the main heating and temperature monitoring step: When the boiler is running at medium to high load, it mainly relies on the heat provided by the flue gas heat exchanger to heat the air; the heated air enters the pyrolysis chamber, providing most of the required heat for the pyrolysis reaction of the urea solution; during this process, the reaction temperature in the pyrolysis chamber or the air temperature at the outlet of the electric heater is monitored in real time.

[0029] S3, Electric heating assisted temperature adjustment and compensation step: Compare the real-time temperature value monitored in step S2 with the preset target temperature range; when the real-time temperature value is lower than the lower limit of the target temperature range, start the electric heater or increase its operating power to supplement the heating of the air after the initial heating by the flue gas heat exchanger, so that the temperature of the air entering the pyrolysis chamber rises to the target range.

[0030] S4. Load Fluctuation Response and Heat Source Switching Steps: When the boiler load decreases, causing a drop in the temperature of the flue gas at the boiler tail or a decrease in the flow rate of the flue gas, making it impossible for the flue gas heat exchanger alone to maintain the temperature required for the pyrolysis chamber, the output power of the electric heater is automatically increased to share more of the heating load; conversely, when the boiler load increases and the flue gas heat exchange capacity is enhanced, the output power of the electric heater is automatically reduced or it is turned off to save energy.

[0031] S5. Operation, maintenance and safety control steps: Periodically or according to the differential pressure signal, purge the flue gas heat exchanger to prevent ash accumulation from affecting the heat exchange efficiency; install an over-temperature protection sensor in the duct section where the electric heater is located, and immediately cut off the power supply to the electric heater when the temperature exceeds the safety threshold.

[0032] In this system, the blower delivers air into the duct, while high-temperature flue gas is introduced from the boiler's tail flue to the flue gas heat exchanger. The two fluids exchange heat indirectly within the heat exchanger, and the waste heat from the flue gas is recovered to heat the air, thus establishing a stable and economical basic heat source. In this state, most of the heat is provided by the free waste heat from the flue gas, and the electric heater is in standby or low-power mode. The system monitors key temperature points in real time, providing a basis for subsequent control. When changes in boiler operating conditions lead to insufficient flue gas heating, the electric heating auxiliary temperature adjustment and compensation mechanism is immediately activated. The control system compares the real-time temperature with the set value; if the temperature is too low, it automatically starts or increases the power of the electric heater to supplement the air heating, ensuring that the air temperature entering the pyrolysis chamber accurately meets the standard. Load fluctuation response and heat source switching dynamically adjust the output ratio of the two heat sources according to changes in boiler load (which directly affects flue gas temperature and flow): when the load decreases, the electric heating power is increased to maintain total heat; when the load increases, the electric power is reduced, prioritizing the use of waste heat from the flue gas, thereby achieving the optimal balance between energy saving and stability. Finally, operation, maintenance, and safety control ensure the long-term, safe, and efficient operation of the system through regular heat exchanger purging and the installation of over-temperature protection.

[0033] In step S1, a regulating valve is provided on the pipeline from the tail flue of the boiler to draw high-temperature flue gas. The flow rate of flue gas introduced into the flue gas heat exchanger is controlled by adjusting the opening of the valve, thereby initially adjusting the amount of basic heat supply.

[0034] By adjusting the valves to control the flow rate of flue gas introduced into the flue gas heat exchanger, a means of preliminary and active adjustment of the heat supply from the basic heat source is provided. Operators or the control system can precisely control the amount of flue gas entering the heat exchanger according to the initial needs of pyrolysis, thereby avoiding energy waste or equipment overheating that may be caused by excessive introduction of waste heat from flue gas when the boiler is under high load. It can also extract as much usable waste heat as possible when the boiler is under low load, reducing the load on the subsequent electric heating compensation stage and further optimizing the overall energy efficiency of the system.

[0035] The opening of the regulating valve is linked to the boiler load signal or the urea solution injection signal in the pyrolysis chamber; when the boiler load increases or the demand for urea solution injection increases, the opening of the regulating valve is automatically increased to introduce more high-temperature flue gas.

[0036] Linking the control of the regulating valves to boiler load or urea demand signals improves the timeliness and intelligence of the system response, reduces the delay caused by relying solely on temperature feedback, and makes the system heating more stable with less fluctuation, further enhancing the stability and automation of the entire ammonia production process. When the boiler load increases (indicating a potential need for more ammonia) or the actual urea injection command increases, the valves automatically open wider to increase the basic flue gas heat supply in advance, preparing for the pyrolysis reaction.

[0037] In step S3, the power regulation of the electric heater adopts a PID control algorithm. Based on the deviation between the real-time temperature value and the target set value and its rate of change, the corresponding power control signal is dynamically calculated and output to achieve precise and stable temperature control.

[0038] The PID algorithm comprehensively considers the magnitude of the deviation between the real-time temperature and the set target, the duration of the deviation, and the trend of the deviation change, thereby calculating the most suitable heating power. This avoids temperature overshoot or oscillation caused by simple on / off or step temperature control, and enables the temperature of the pyrolysis chamber to be maintained extremely stably near the center point of the set range, improving the quality of ammonia generation and the quality of system control.

[0039] The electric heater employs a multi-stage grouping arrangement or a multi-level power adjustment design. In steps S3 and S4, heating groups are started or stopped step by step, or different power levels are switched, according to the required amount of heat compensation, to improve adjustment accuracy and equipment lifespan. When the required heat compensation is small, only some heating groups are started or a low power level is used, which avoids energy waste and reduces frequent impacts on the heating elements, extending their lifespan. When a large amount of heat compensation is needed, more power units are gradually added. This design allows the electric heater to more precisely match actual needs, improves energy utilization efficiency, and reduces equipment maintenance costs.

[0040] In step S2, the parameters monitored in real time also include the air temperature at the cold side outlet of the flue gas heat exchanger; in step S4, when the boiler load decreases, it is first determined whether the cold side outlet temperature of the flue gas heat exchanger is lower than the first set value. If so, the electric heater compensation is started; when the boiler load increases, it is first determined whether the cold side outlet temperature of the flue gas heat exchanger is higher than the second set value. If so, the power of the electric heater is reduced.

[0041] By monitoring the outlet air temperature of the flue gas heat exchanger, changes in the flue gas heat source capacity can be detected earlier and more directly, before significant fluctuations occur in the pyrolysis chamber temperature. Based on this temperature value, judgments can be made and interventions made in advance in the electric heater, resulting in a smoother heat source transition. This effectively prevents large fluctuations in the pyrolysis chamber temperature due to flue gas-side disturbances, improving the system's anti-interference capability and control stability.

[0042] It also includes a rapid heating step during system initial startup or restart after a long period of shutdown: In this stage, the electric heater is first started at full power or simultaneously, so that the pyrolysis chamber reaches the minimum reaction temperature required for urea pyrolysis in the shortest possible time; after the temperature of the pyrolysis chamber stabilizes and the boiler flue gas conditions allow, the power of the electric heater is gradually reduced and the system switches to an operation mode that mainly uses flue gas heat exchange.

[0043] After power plant units are started up or systems are under maintenance, boiler flue gas temperatures are typically low and cannot immediately provide sufficient heat. In this case, prioritizing full-power electric heating ensures that the urea pyrolysis ammonia production system is activated independently and quickly, enabling the denitrification system to be put into operation as soon as possible and meet immediate environmental emission requirements.

[0044] In the rapid heating step, if the flue gas heat exchanger cannot provide effective heat in the initial stage of startup due to the low flue gas temperature, the heating process is accelerated by closing its cold side bypass or minimizing the bypass opening, so that all or most of the combustion air flows through the electric heater for heating.

[0045] Closing the bypass ensures that all combustion air flows through the electric heater and is fully heated, avoiding heat loss. This allows all the limited electrical energy to be used to raise the air temperature, thus heating the pyrolysis chamber to the operating temperature in the shortest time and with the least energy consumption, further optimizing the economy and timeliness of the rapid start-up mode.

[0046] The flue gas heat exchanger is a partitioned heat exchanger with anti-wear and anti-clogging design for its hot-side medium channel; the electric heater is a high-temperature resistant resistance heater with heat-expanding fins on the surface of its heating element to enhance heat exchange.

[0047] It also includes a control unit that receives data from the pyrolysis chamber temperature sensor, the electric heater outlet temperature sensor, the flue gas temperature sensor, the flow meter, and the boiler load signal. The control unit is configured to perform the above steps and output control signals to the regulating valve, the blower frequency converter, the electric heater power controller, and the purging device to achieve automated operation and optimized management of the entire heating process. The control unit has multiple preset composite heating strategies corresponding to different boiler loads and different urea requirements, and can automatically select or smoothly switch to the most economical and stable strategy based on real-time operating data.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A combined heating method using electric heating and flue gas heat exchange in a urea pyrolysis ammonia production system, characterized in that, The urea pyrolysis ammonia production system includes a pyrolysis chamber, a blower connected to the air inlet of the pyrolysis chamber, a flue gas heat exchanger and an electric heater installed in the duct between the blower and the pyrolysis chamber, wherein the hot-side medium channel of the flue gas heat exchanger is connected to the boiler tail flue; the method includes the following steps: S1. System startup and basic heating establishment steps: Start the air supply fan to send ambient air or preheated air into the air duct; at the same time, draw out a portion of high-temperature flue gas from the tail flue of the boiler and let it flow through the hot side medium channel of the flue gas heat exchanger to indirectly exchange heat with the combustion air flowing through the cold side medium channel of the flue gas heat exchanger. S2. Flue gas heat exchange as the main heating and temperature monitoring steps: When the boiler is running at medium to high load, the air is heated by the heat provided by the flue gas heat exchanger; the heated air enters the pyrolysis chamber to provide the required heat for the pyrolysis reaction of the urea solution; during this process, the reaction temperature in the pyrolysis chamber or the air temperature at the outlet of the electric heater is monitored in real time. S3, Electric heating assisted temperature adjustment and compensation step: Compare the real-time temperature value in the pyrolysis chamber monitored in step S2 with the preset target temperature range; when the real-time temperature value in the pyrolysis chamber is lower than the lower limit of the target temperature range, start the electric heater or increase its operating power to supplement the heating of the air after the initial heating by the flue gas heat exchanger, so that the temperature of the air entering the pyrolysis chamber rises to the target range. S4. Load fluctuation response and heat source switching steps: When the boiler load decreases, causing the temperature of the flue gas at the tail of the boiler or the flow rate of the flue gas to decrease, making it impossible for the flue gas heat exchanger alone to maintain the temperature required for the pyrolysis chamber, the output power of the electric heater is automatically increased; conversely, when the boiler load increases and the flue gas heat exchange capacity is enhanced, the output power of the electric heater is automatically reduced or it is turned off. S5. Operation, maintenance and safety control steps: Periodically or according to the differential pressure signal, purge the flue gas heat exchanger; install an over-temperature protection sensor in the duct section where the electric heater is located, and immediately cut off the power supply to the electric heater when the temperature exceeds the safety threshold.

2. The combined heating method of electric heating and flue gas heat exchange in the urea pyrolysis ammonia production system according to claim 1, characterized in that, In step S1, the pipeline from which the high-temperature flue gas is drawn out of the boiler tail flue is equipped with a regulating valve. The flow rate of the flue gas introduced into the flue gas heat exchanger is controlled by adjusting the opening of the valve.

3. The combined heating method of electric heating and flue gas heat exchange in the urea pyrolysis ammonia production system according to claim 2, characterized in that, The opening of the regulating valve is linked to the boiler load signal or the urea solution injection signal in the pyrolysis chamber; when the boiler load increases or the demand for urea solution injection increases, the opening of the regulating valve is automatically increased to introduce more high-temperature flue gas.

4. The combined heating method of electric heating and flue gas heat exchange in the urea pyrolysis ammonia production system according to claim 1, characterized in that, In step S3, the power regulation of the electric heater adopts a PID control algorithm. Based on the deviation between the real-time temperature value and the target set value and its rate of change, the corresponding power control signal is dynamically calculated and output.

5. The combined heating method of electric heating and flue gas heat exchange in the urea pyrolysis ammonia production system according to claim 4, characterized in that, The electric heater adopts a multi-level group arrangement or a multi-level power adjustment design; in steps S3 and S4, the heating group is started or turned off step by step, or switched to different power levels, according to the required amount of compensation heat.

6. The combined heating method of electric heating and flue gas heat exchange in the urea pyrolysis ammonia production system according to claim 1, characterized in that, In step S2, the parameters monitored in real time also include the air temperature at the cold side outlet of the flue gas heat exchanger; in step S4, when the boiler load decreases, it is first determined whether the cold side outlet temperature of the flue gas heat exchanger is lower than the first set value. If so, the electric heater compensation is started; when the boiler load increases, it is first determined whether the cold side outlet temperature of the flue gas heat exchanger is higher than the second set value. If so, the power of the electric heater is reduced.

7. The combined heating method of electric heating and flue gas heat exchange in the urea pyrolysis ammonia production system according to claim 1, characterized in that, It also includes a rapid heating step during system initial startup or restart after a long period of shutdown: In this stage, the electric heater is first started at full power or simultaneously, so that the pyrolysis chamber reaches the minimum reaction temperature required for urea pyrolysis in the shortest possible time; after the temperature of the pyrolysis chamber stabilizes and the boiler flue gas conditions allow, the power of the electric heater is gradually reduced and the system switches to an operation mode that mainly uses flue gas heat exchange.

8. The combined heating method of electric heating and flue gas heat exchange in the urea pyrolysis ammonia production system according to claim 7, characterized in that, In the rapid heating step, if the flue gas heat exchanger cannot provide effective heat in the initial stage of startup due to the low flue gas temperature, then by closing its cold side bypass or minimizing the bypass opening, all or most of the combustion air can flow through the electric heater for heating.

9. The combined heating method of electric heating and flue gas heat exchange in the urea pyrolysis ammonia production system according to claim 1, characterized in that, The flue gas heat exchanger is a partitioned heat exchanger with anti-wear and anti-clogging design for its hot-side medium channel; the electric heater is a high-temperature resistant resistance heater with heat-expanding fins on the surface of its heating element to enhance heat exchange.

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