Multi-unit urea water hydrolysis ammonia production system collaborative control method and system

Abstract

The application provides a kind of multi-unit urea hydrolysis ammonia production system coordinated control method and system, method includes the following steps: with the DCS system linkage of unit control, real-time acquisition each unit key operating parameter and hydrolysis ammonia production system key parameter;According to the key operating parameter of each unit and the key parameter of hydrolysis ammonia production system, dynamic load distribution model, steam consumption model and economic operation model are established;According to the output / ammonia consumption of hydrolysis reactor of dynamic load distribution model, the opening of urea solution feed valve of hydrolysis reactor and operating temperature are controlled according to the output / ammonia consumption of hydrolysis reactor;According to steam consumption model, obtain the steam consumption, and control the opening of steam regulating valve according to the steam consumption;According to economic operation model, obtain the optimal solution of the lowest total cost between the number of hydrolysis reactor operation and start-stop times.The technical effect of the application is that the hydrolysis reactor can be safely operated to meet the ammonia supply demand of the unit, and the economic operation can be realized.

Description

Technical Field

[0001] This invention belongs to the field of multi-unit urea hydrolysis ammonia production technology, specifically relating to a collaborative control method and system for a multi-unit urea hydrolysis ammonia production system. Background Technology

[0002] In recent years, coal-fired power plants have upgraded their reducing agent supply systems for flue gas denitrification by replacing liquid ammonia with urea. After the upgrade, urea becomes the reducing agent in the SCR denitrification unit, with urea hydrolysis being a common technology. For coal-fired power plants with 4-8 units, 3-6 hydrolyzers are typically installed. The current operation of these hydrolyzers faces the following two problems: (1) The overall operation is relatively rough. For a single hydrolyzer, its output cannot always operate within the design range. Generally speaking, the output of the hydrolyzer should not be lower than 20% of the full output. If the hydrolyzer operates under low output conditions for a long time, the reaction temperature of the hydrolyzer will be low, the urea reaction will be incomplete, and it will be easy to clog. Under high output conditions, the reaction temperature of the hydrolyzer is high and the reaction efficiency is high. However, when the hydrolyzer is close to the design output (that is, the critical point), false liquid level and boiling phenomena will occur, which will affect the safe operation of the hydrolyzer. Studies have shown that the economical operating output period of the hydrolyzer is 60%~85%, while the existing fixed main standby or average distribution mode leads to frequent start-stop or long-term inefficient operation of the hydrolyzer under low load.

[0003] (2) The switching of the hydrolyzer takes a period of time. When the unit requires a large amount of ammonia, the standby hydrolyzer needs to be turned on. However, because thermal power units are currently facing deep peak shaving and need to respond to changes in power plant load in a timely manner, the power generation of coal-fired power plant units fluctuates greatly over a period of time. Some units often shut down after running for a few days. This requires improving the hydrolyzer's response to load.

[0004] (3) Poor economic efficiency. The hydrolysis reaction requires continuous steam heating (accounting for more than 60% of the operating cost). The existing control mode cannot adjust the steam supply as needed, resulting in energy waste. In addition, the redundant hydrolyzers have a high standby rate all year round, resulting in high maintenance costs and low equipment utilization.

[0005] Therefore, there is an urgent need for a collaborative control method and system for multi-unit urea hydrolysis ammonia production systems, which can ensure the safe operation of the hydrolyzer, meet the ammonia supply requirements of the units, and operate economically. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art, and to provide a new technical solution for a collaborative control method and system for a multi-unit urea hydrolysis ammonia production system.

[0007] According to a first aspect of the present invention, a method for coordinated control of a multi-unit urea hydrolysis ammonia production system is provided, comprising the following steps: Step S1: Link with the DCS system of the unit control to obtain key operating parameters of each unit and key parameters of the hydrolysis ammonia production system in real time. Step S2: Establish dynamic load distribution model, steam consumption model and economic operation model based on the key operating parameters of each unit and the key parameters of the hydrolysis ammonia production system; Step S3: Obtain the output / ammonia consumption of the hydrolyzer according to the dynamic load distribution model, and control the opening degree of the urea solution feed valve and the operating temperature of the hydrolyzer according to the output / ammonia consumption of the hydrolyzer; obtain the steam consumption according to the steam consumption model, and control the opening degree of the steam regulating valve according to the steam consumption; obtain the optimal solution with the lowest total cost between the number of hydrolyzers in operation and the number of start-ups and shutdowns according to the economic operation model.

[0008] Optionally, the calculation formula for the dynamic load allocation model is as follows: ; In the above formula, This represents the hydrolyzer's output / ammonia consumption, expressed in kg / h. Flue gas volume, unit: m³ 3 / h; The inlet NOx concentration is expressed in mg / m³. 3 ; The ammonia-nitrogen molar ratio; Let be a constant, taken as 0.37 × 10⁻⁶. -6 ; The target value for NOx concentration at the inlet is expressed in mg / m³. 3 ; This represents the ammonia slip concentration, typically taken as 3, with units of µL / L.

[0009] Optionally, the calculation formula for the steam consumption model is as follows: ; In the above formula, Steam consumption, expressed in kg / h; The steam coefficient for ammonia production; This is the temperature regulation coefficient; The optimal target reaction temperature is calculated based on the current operating conditions, and the unit is °C. The actual operating temperature of the hydrolyzer is shown in °C.

[0010] Optionally, the calculation formula for the economic operation model is as follows: ; In the above formula, The amount of steam consumed / saved under the current mode, in kg; 150 represents the cost price of steam, expressed in yuan / kg. This represents the number of times the hydrolyzer has been started and stopped in the current mode. The equipment cost of the hydrolyzer; The number of fatigue cycles required for the design of the hydrolyzer equipment.

[0011] Optionally, the steam consumption model is dynamically corrected through a self-learning mode. as well as .

[0012] Optionally, when obtaining the optimal solution with the lowest total cost, the output of the hydrolyzer is greater than 20% and less than 85%.

[0013] Optionally, the key operating parameters of each unit include the daily load curve of each unit, the NOx concentration at the SCR inlet, the NOx concentration at the outlet, and the flue gas flow rate.

[0014] Optionally, the key parameters of the hydrolysis ammonia production system include the ammonia pressure / temperature at the hydrolyzer outlet and the steam flow rate.

[0015] According to a second aspect of the present invention, a collaborative control system for a multi-unit urea hydrolysis ammonia production system is provided, comprising: The acquisition module is used to link with the DCS system for unit control to acquire key operating parameters of each unit and key parameters of the hydrolysis ammonia production system in real time. The model building module is used to establish dynamic load allocation models, steam consumption models, and economic operation models based on the key operating parameters of each unit and the key parameters of the hydrolysis ammonia production system. The control module is used to obtain the output / ammonia consumption of the hydrolyzer according to the dynamic load distribution model, and control the opening degree of the urea solution feed valve and the operating temperature of the hydrolyzer according to the output / ammonia consumption; obtain the steam consumption according to the steam consumption model, and control the opening degree of the steam regulating valve according to the steam consumption; and obtain the optimal solution with the lowest total cost between the number of hydrolyzers in operation and the number of start-ups and shutdowns according to the economic operation model.

[0016] Optionally, the multi-unit urea hydrolysis ammonia production system collaborative control system also includes a model optimization module, which is used to optimize the dynamic load allocation model, steam consumption model, and economic operation model.

[0017] One technical advantage of this invention is that: In this embodiment, the coal-fired power plant can obtain the predicted load curve for the day. Combined with the dynamic load allocation model, steam consumption model and economic operation model in this embodiment, it can predict the daily ammonia demand and the total output of the hydrolyzer in advance, realizing timely response of the hydrolyzer and precise control of the steam consumption of the hydrolysis reaction. At the same time, it can find the optimal solution with the lowest total cost among the number of hydrolyzers in operation and the number of start-ups and shutdowns.

[0018] Therefore, the collaborative control method and system for the multi-unit urea hydrolysis ammonia production system can ensure the safe operation of the hydrolyzer, meet the ammonia supply requirements of the units, and operate economically. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart of a collaborative control method for a multi-unit urea hydrolysis ammonia production system according to another embodiment of the present invention. Detailed Implementation

[0020] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present application.

[0021] The embodiments of this application will now be described in detail. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0022] According to a first aspect of the invention, see Figure 1 A collaborative control method for a multi-unit urea hydrolysis ammonia production system is provided, comprising the following steps: Step S1: Link with the DCS system of the unit control to obtain key operating parameters of each unit and key parameters of the hydrolysis ammonia production system in real time. Step S2: Establish dynamic load distribution model, steam consumption model and economic operation model based on the key operating parameters of each unit and the key parameters of the hydrolysis ammonia production system; Step S3: Obtain the output / ammonia consumption of the hydrolyzer according to the dynamic load distribution model, and control the opening degree of the urea solution feed valve and the operating temperature of the hydrolyzer according to the output / ammonia consumption of the hydrolyzer; obtain the steam consumption according to the steam consumption model, and control the opening degree of the steam regulating valve according to the steam consumption; obtain the optimal solution with the lowest total cost between the number of hydrolyzers in operation and the number of start-ups and shutdowns according to the economic operation model.

[0023] In this embodiment, the coal-fired power plant can obtain the predicted load curve for the day. Combined with the dynamic load allocation model, steam consumption model and economic operation model in this embodiment, it can predict the daily ammonia demand and the total output of the hydrolyzer in advance, realizing timely response of the hydrolyzer and precise control of the steam consumption of the hydrolysis reaction. At the same time, it can find the optimal solution with the lowest total cost among the number of hydrolyzers in operation and the number of start-ups and shutdowns.

[0024] Therefore, the collaborative control method and system for the multi-unit urea hydrolysis ammonia production system can ensure the safe operation of the hydrolyzer, meet the ammonia supply requirements of the units, and operate economically.

[0025] Optionally, the calculation formula for the dynamic load allocation model is as follows: ; In the above formula, This represents the hydrolyzer's output / ammonia consumption, expressed in kg / h. Flue gas volume, unit: m³ 3 / h; The inlet NOx concentration is expressed in mg / m³. 3 ; The ammonia-nitrogen molar ratio; Let be a constant, taken as 0.37 × 10⁻⁶. -6 ; The target value for NOx concentration at the inlet is expressed in mg / m³. 3 ; This represents the ammonia slip concentration, typically taken as 3, with units of µL / L.

[0026] In the above implementation, the real-time ammonia demand of the computer group can be accurately and quickly calculated, thereby obtaining the output of the hydrolyzer. The output of the hydrolyzer can be adjusted by regulating the urea solution feed valve and the operating temperature, thereby improving the hydrolyzer's response to load.

[0027] Optionally, the calculation formula for the steam consumption model is as follows: ; In the above formula, Steam consumption, expressed in kg / h; The steam coefficient for ammonia production (dynamic correction) represents the theoretical minimum steam consumption required to produce a unit mass of ammonia. This is the temperature regulation coefficient (dynamic correction), which represents the additional amount of steam required to raise or maintain the reactants to the target temperature. This primarily compensates for system heat losses (such as equipment heat dissipation) and the temperature rise requirements of the materials. The optimal target reaction temperature is calculated based on the current operating conditions, and the unit is °C. The actual operating temperature of the hydrolyzer is shown in °C.

[0028] It should be noted that the steam consumption prediction model is based on the premise that steam is a key factor in the urea hydrolysis reaction and a major component of energy consumption. However, in traditional operating modes, steam supply is often disconnected from ammonia production demand. For example, when the unit load decreases, ammonia production decreases, but traditional systems may still inject a large amount of steam to maintain a fixed high-temperature and high-pressure state. In other words, traditional systems typically set a fixed, high target temperature (e.g., always 140°C) to ensure ammonia supply capacity under the worst operating conditions. However, this represents a huge waste of energy during most off-load operations. Furthermore, as unit operating time increases, when heat exchangers scale and efficiency decreases, the controller with fixed parameters cannot detect this. To achieve the same ammonia production effect, operators can only manually and empirically increase the steam valve opening, which is a passive, lagging, and inefficient operating method.

[0029] In the above implementation method, based on the steam consumption model, the following functions can be achieved: (1) Since steam consumption is directly linked to ammonia production and has a linear relationship, when the demand for ammonia decreases, the basic steam consumption calculated by the steam consumption model can immediately decrease synchronously, and the calculation results are relatively accurate.

[0030] (2) Since steam is used not only for the basic hydrolysis reaction, it also needs to provide just enough heat to compensate for the temperature difference between the current temperature and the target temperature and the heat loss, the steam consumption model will be based on... Lower the target temperature For example, at low loads, the heat loss to the environment is significantly reduced due to the lower reaction temperature, and the energy required to maintain the liquid phase is also reduced, so there is no need for high temperature compensation, thus saving steam significantly.

[0031] (3) Self-learning mode: In this embodiment , These are all dynamically adjusted, not fixed, for various reasons. For example, fouling in the heat exchanger can lead to a decrease in thermal efficiency. , The value will automatically increase, meaning that more steam is needed to produce the same amount of ammonia or reach the same temperature; the heat loss of the equipment differs between winter and summer, and the required steam compensation also differs. However, this is a fuzzy relationship that is difficult to express with a mathematical model. This is where a self-learning steam consumption model is needed. The steam consumption model continuously collects historical operating data (e.g., past...). , , (such as ambient temperature), and learns a complex, non-linear mapping relationship from this data. That is, under certain equipment conditions and environments, it can capture exactly how much steam is needed to achieve a specific ammonia production rate and temperature. , A pattern that changes slowly over time. And the latest predictions. , By substituting the values ​​into the above formula of the steam consumption model, real-time and accurate prediction of steam demand can be achieved. As operating time increases, the amount of basic data grows larger and larger. , It will become increasingly accurate.

[0032] Optionally, the calculation formula for the economic operation model is as follows: ; In the above formula, The amount of steam consumed / saved under the current mode, in kg; 150 represents the cost price of steam, expressed in yuan / kg. This represents the number of times the hydrolyzer has been started and stopped in the current mode. The equipment cost of the hydrolyzer; The number of fatigue cycles required for the design of the hydrolyzer equipment.

[0033] In the above implementation, this embodiment has achieved timely response of the hydrolyzer and precise control of the hydrolysis reaction. However, for coal-fired power plants with 4 to 8 units, 3 to 6 hydrolyzers are usually equipped. Under a certain ammonia production, how many hydrolyzers should be selected to operate, and within what output range should each hydrolyzer operate, to achieve the most economical overall operation? This requires setting an economical operation mode.

[0034] The operating cost of a hydrolyzer consists of two parts: steam consumption and start-up / shutdown losses. Assuming a decrease in load necessitates a reduction in ammonia demand, the following operating mode can be considered: (1) First operating mode: If one hydrolyzer is reduced from operation and the output of each hydrolyzer is increased, then there will be equipment start-up and shutdown losses due to the shutdown of one hydrolyzer. This is because the hydrolyzer is a pressure vessel subjected to cyclic thermal stress. During the start-up and shutdown process, its core components will generate alternating stress due to drastic changes in temperature and internal pressure, leading to low-cycle fatigue damage. The manufacturer will provide a key guarantee value based on the materials - the design fatigue cycle count. This value directly reflects the number of start-up and shutdown cycles that the equipment can withstand before failure. Dividing the total cost of the equipment by the number of cycles represents the equipment life loss caused by a single start-up and shutdown.

[0035] At this point, n=1, the cost of equipment loss can be determined. Meanwhile, due to the reduction in the number of hydrolyzers, the amount of heat preservation steam decreases, and the reduction in the number of hydrolyzers increases the output of a single hydrolyzer. Within a more economical range, the steam loss decreases. The cost calculated for the first operating mode is M1.

[0036] (2) Second operating mode: Multiple hydrolyzers are still in operation, reducing the output of each hydrolyzer. This mode avoids frequent start-up and shutdown of the hydrolyzers. Since the start-up and shutdown of the hydrolyzers are not required, the equipment will not suffer losses due to start-up and shutdown. n=0, the latter term is 0, but the former term, because multiple hydrolyzers are in operation, increases the steam consumption for hydrolyzer insulation. Therefore, the cost is mainly the cost of insulation steam. Thus, the cost calculated for the second operating mode is M2.

[0037] Comparing M1 and M2 yields the economically optimal solution. These two schemes are merely examples; in reality, the economic operation model also needs to be linked to the safe operation mode of the hydrolyzer, i.e., the hydrolyzer's output cannot be lower than 20% or higher than 85% to avoid safety issues. Under this premise, economic calculations and strategy selection are conducted.

[0038] Optionally, the steam consumption model is dynamically corrected through a self-learning mode. as well as This helps to ensure as well as This ensures the accuracy of the steam consumption model calculations.

[0039] Optionally, when obtaining the optimal solution with the lowest total cost, the output of the hydrolyzer is greater than 20% and less than 85%, which helps to ensure the safe and stable operation of the hydrolyzer.

[0040] Optionally, the key operating parameters of each unit include the daily load curve of each unit, the NOx concentration at the SCR inlet, the NOx concentration at the outlet, and the flue gas flow rate. These key operating parameters help to effectively establish dynamic load allocation models, steam consumption models, and economic operation models.

[0041] Optionally, the key parameters of the hydrolysis ammonia production system include the ammonia pressure / temperature at the hydrolyzer outlet and the steam flow rate. Understanding these key parameters helps in effectively establishing dynamic load allocation models, steam consumption models, and economic operation models.

[0042] According to a second aspect of the present invention, a collaborative control system for a multi-unit urea hydrolysis ammonia production system is provided, comprising: The acquisition module is used to link with the DCS system for unit control to acquire key operating parameters of each unit and key parameters of the hydrolysis ammonia production system in real time. The model building module is used to establish dynamic load allocation models, steam consumption models, and economic operation models based on the key operating parameters of each unit and the key parameters of the hydrolysis ammonia production system. The control module is used to obtain the output / ammonia consumption of the hydrolyzer according to the dynamic load distribution model, and control the opening degree of the urea solution feed valve and the operating temperature of the hydrolyzer according to the output / ammonia consumption; obtain the steam consumption according to the steam consumption model, and control the opening degree of the steam regulating valve according to the steam consumption; and obtain the optimal solution with the lowest total cost between the number of hydrolyzers in operation and the number of start-ups and shutdowns according to the economic operation model.

[0043] In the above embodiments, the collaborative control system of the multi-unit urea hydrolysis ammonia production system is reasonably designed, which can not only ensure the safe operation of the hydrolyzer and meet the ammonia supply requirements of the unit, but also ensure economic operation.

[0044] Optionally, the multi-unit urea hydrolysis ammonia production system collaborative control system also includes a model optimization module, which is used to optimize the dynamic load allocation model, steam consumption model, and economic operation model.

[0045] In the above embodiments, the optimization of the dynamic load distribution model, steam consumption model and economic operation model by the model optimization module helps to accurately control the regulating devices of key equipment such as the urea solution feed valve, steam regulating valve and circulating pump of the hydrolyzer, thereby realizing the regulation and control of key parameters of the hydrolyzer.

[0046] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for coordinated control of a multi-unit urea hydrolysis ammonia production system, characterized in that, Includes the following steps: Step S1: Link with the DCS system of the unit control to obtain key operating parameters of each unit and key parameters of the hydrolysis ammonia production system in real time. Step S2: Establish dynamic load distribution model, steam consumption model and economic operation model based on the key operating parameters of each unit and the key parameters of the hydrolysis ammonia production system; Step S3: Obtain the output / ammonia consumption of the hydrolyzer according to the dynamic load distribution model, and control the opening degree of the urea solution feed valve and the operating temperature of the hydrolyzer according to the output / ammonia consumption of the hydrolyzer; obtain the steam consumption according to the steam consumption model, and control the opening degree of the steam regulating valve according to the steam consumption; obtain the optimal solution with the lowest total cost between the number of hydrolyzers in operation and the number of start-ups and shutdowns according to the economic operation model.

2. The method for coordinated control of a multi-unit urea hydrolysis ammonia production system according to claim 1, characterized in that, The calculation formula for the dynamic load allocation model is as follows: ； In the above formula, This represents the hydrolyzer's output / ammonia consumption, expressed in kg / h. Flue gas volume, unit: m³ 3 / h; The inlet NOx concentration is expressed in mg / m³. 3 ; The ammonia-nitrogen molar ratio; Let be a constant, taken as 0.37 × 10⁻⁶. -6 ; The target value for NOx concentration at the inlet is expressed in mg / m³. 3 ; This represents the ammonia slip concentration, typically taken as 3, with units of µL / L.

3. The method for coordinated control of a multi-unit urea hydrolysis ammonia production system according to claim 1, characterized in that, The calculation formula for the steam consumption model is as follows: ； In the above formula, Steam consumption, expressed in kg / h; The steam coefficient for ammonia production; This is the temperature regulation coefficient; The optimal target reaction temperature is calculated based on the current operating conditions, and the unit is °C. The actual operating temperature of the hydrolyzer is shown in °C.

4. The method for coordinated control of a multi-unit urea hydrolysis ammonia production system according to claim 3, characterized in that, The calculation formula for the economic operation model is as follows: ； In the above formula, The amount of steam consumed / saved under the current mode, in kg; 150 represents the cost price of steam, expressed in yuan / kg. This represents the number of times the hydrolyzer has been started and stopped in the current mode. The equipment cost of the hydrolyzer; The number of fatigue cycles required for the design of the hydrolyzer equipment.

5. The method for coordinated control of a multi-unit urea hydrolysis ammonia production system according to claim 4, characterized in that, In the steam consumption model, dynamic corrections are made through a self-learning mode. as well as .

6. The method for coordinated control of a multi-unit urea hydrolysis ammonia production system according to claim 5, characterized in that, When obtaining the optimal solution with the lowest total cost, the output of the hydrolyzer is greater than 20% and less than 85%.

7. The method for coordinated control of a multi-unit urea hydrolysis ammonia production system according to claim 6, characterized in that, The key operating parameters for each unit include the daily load curve, SCR inlet NOx concentration, outlet NOx concentration, and flue gas flow rate.

8. The method for coordinated control of a multi-unit urea hydrolysis ammonia production system according to claim 7, characterized in that, The key parameters of the hydrolysis ammonia production system include the ammonia pressure / temperature at the hydrolyzer outlet and the steam flow rate.

9. A collaborative control system for a multi-unit urea hydrolysis ammonia production system, characterized in that, include: The acquisition module is used to link with the DCS system for unit control to acquire key operating parameters of each unit and key parameters of the hydrolysis ammonia production system in real time. The model building module is used to establish dynamic load allocation models, steam consumption models, and economic operation models based on the key operating parameters of each unit and the key parameters of the hydrolysis ammonia production system. The control module is used to obtain the output / ammonia consumption of the hydrolyzer according to the dynamic load distribution model, and control the opening degree of the urea solution feed valve and the operating temperature of the hydrolyzer according to the output / ammonia consumption; obtain the steam consumption according to the steam consumption model, and control the opening degree of the steam regulating valve according to the steam consumption; and obtain the optimal solution with the lowest total cost between the number of hydrolyzers in operation and the number of start-ups and shutdowns according to the economic operation model.

10. The collaborative control system for a multi-unit urea hydrolysis ammonia production system according to claim 9, characterized in that, It also includes a model optimization module, which is used to optimize the dynamic load allocation model, steam consumption model and economic operation model.

Images