Desalted water replenishing and ammonia adding control method and system for waste incineration power plant

Abstract

The invention discloses a demineralized water replenishing and ammonification control method and system for a waste incineration power plant. The method comprises the steps that S1, the target conductivity in a demineralized water pipeline is preset; s2, supplementing water to a boiler system through a desalting water pump; s3, ammonia water is added into the demineralized water pipeline through an ammonia adding pump; s4, the real-time conductivity and the demineralized water flow value in the demineralized water pipeline are collected through the control device for PID calculation, the control device controls the output frequency of the frequency converter according to the PID calculation result so as to adjust the output of the ammonia adding pump, the PID calculation formula is # imgabs0 #, Q is the demineralized water flow value, Ti is an integral time constant, Td is a differential time constant, and the control device controls the output frequency of the frequency converter according to the PID calculation result so as to adjust the output of the ammonia adding pump. E (t) is the difference between the expected value and the sampling value of the conductivity, and u (t) is the control quantity of the frequency converter. The system has the advantages of being simple in structure, low in cost, capable of enabling a control system to be more stable, higher in anti-interference capacity and the like.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of adding ammonia to desalted water in a waste incineration boiler, and in particular to a method and system for controlling the addition of ammonia to desalted water in a waste incineration power plant. Background Art

[0002] The boiler feed water of waste incineration power plants is usually weakly acidic or close to neutral. Under certain conditions, metal ions such as iron ions in the water will undergo hydrolysis reactions to generate precipitation such as iron hydroxide and release hydrogen ions, which will increase the acidity of the water. Steel is prone to corrosion in an acidic environment. Ammonia is a weak base. When added to water, it will react with water to generate monohydrated ammonia. Monohydrated ammonia partially ionizes hydroxide ions, thereby increasing the pH value of the water and making the feed water weakly alkaline. Generally, the pH value is controlled between 8.5 and 9.2, which helps to form a stable protective film on the metal surface and slow down the corrosion rate. The main purpose of adding ammonia to desalted water is to adjust the pH value of boiler feed water. Specifically, it is to keep the pH value of boiler condensate and feed water between 8.5-9.2. The principle is to use the alkalinity of ammonia water to neutralize carbon dioxide in water, generate bicarbonate and water, and then adjust the pH value to slow down the acid corrosion of equipment. Since there is a certain correlation between the conductivity and pH value of the desalinated water solution, controlling the conductivity of the feed water can effectively prevent the corrosion of the water supply pipeline and the damage of the metal surface protective film. In actual production, manual ammonia addition or common DCS-controlled automatic ammonia addition system is currently used, which has the following problems: 1. During the manual ammonia addition process, the operator's experience affects the control accuracy of the ammonia addition and the continuity is poor, which can easily lead to large fluctuations in the pH value of the boiler feed water and even cause the boiler pH value to exceed the standard, causing adverse effects on the boiler equipment.

[0003] 2. The pH meter used to monitor boiler feed water in the ammonia addition system has a high failure rate and is prone to inaccurate measurements, resulting in unstable control of the ammonia addition pump.

[0004] 3. In the common DCS control ammonia adding control system, the conductivity target value is realized through the PID control module. The calculation formula in PID is: , where Kp is the proportional coefficient, Ti is the integral time constant, Td is the differential time constant, e(t) is the difference between the expected value and the sampled value, and u(t) is the control amount; the influence of the proportional Kp control part on the anti-interference ability of the system is mainly reflected in that when the interference causes the system output to deviate from the set value, the proportional control part will immediately produce a control effect proportional to the deviation. For example, in a conductivity control system, if the set conductivity is 4, and the actual conductivity drops to 3 due to interference, the deviation e(t) = 1. If Kp is 5, the proportional control part will produce a control action Kpe(t)=1*5=5, which will drive the system control conductivity to change in the direction of reducing the deviation; In the conventional setting of the existing DCS control ammonia control system, Kp is usually a fixed value. When this control system is applied to the ammonia control of the waste incineration boiler, the desalted water replenishment amount of the waste incineration power plant is affected by many factors, resulting in discontinuous replenishment and non-fixed replenishment flow, which affects the unstable regulation of the ammonia control system, large fluctuations in the regulation system, and finally the pH value of the boiler feed water also fluctuates greatly. Due to the sudden change of the desalted water flow, the PID control module cannot respond to the changes of the system in time, resulting in unstable regulation; Although increasing the proportional coefficient Kp can enhance the anti-interference ability, if the proportional coefficient Kp is too large, it may cause the system to overshoot, that is, the system output exceeds the set value and then oscillates back. At the same time, an excessively large proportional coefficient Kp may also make the system unstable and produce continuous oscillations. Therefore, how to reasonably adjust the Kp value in practical applications to achieve the best control effect and anti-interference performance is a technical problem that needs to be solved by technicians in this field. Summary of the invention

[0005] In view of the technical problems existing in the prior art, the present invention provides a method and system for controlling the addition of desalted water and ammonia in a waste incineration power plant, which has a simple structure, low cost, and can make the control system more stable and have stronger anti-interference ability.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for controlling the addition of ammonia to desalted water in a waste incineration power plant, comprising: Step S1: presetting the target conductivity in the desalted water pipeline; Step S2: replenishing water to the boiler system through a desalted water pump; Step S3: adding ammonia water into the demineralized water pipeline through an ammonia adding pump; Step S4: The control device collects the real-time conductivity and the flow rate of the desalted water in the desalted water pipeline for PID calculation. The control device controls the output frequency of the inverter according to the PID calculation result to adjust the output of the ammonia pump. The PID calculation formula is as follows: , where Q is the desalted water flow rate, Ti is the integral time constant, Td is the differential time constant, e(t) is the difference between the expected value and the sampled value of conductivity, and u(t) is the control quantity of the inverter.

[0007] As a further improvement of the present invention: the function is any one of a linear function, a nonlinear function or a piecewise function.

[0008] As a further improvement of the present invention: , where K is the proportional coefficient and M is the compensation constant.

[0009] As a further improvement of the present invention: the step S3 is specifically as follows: the desalted water flow value is collected by the control device, and when the desalted water flow value Q>4t / h, the control device sends a start signal to start the ammonia adding pump.

[0010] As a further improvement of the present invention, it also includes step S5: collecting the flow value of desalted water through the control device, when Q<2t / h, the control device sends a stop signal to stop the ammonia adding pump.

[0011] The present invention discloses a system based on the above-mentioned desalted water replenishment and ammonia addition control method for a waste incineration power plant, comprising a desalted water pipeline connected to a desalted water tank, an ammonia water pipeline connected to an ammonia solution tank, and a control device, wherein the water outlet end of the ammonia water pipeline is connected to the desalted water pipeline, and a desalted water pump inlet valve, a desalted water pump, a desalted water flowmeter and a conductivity detector are arranged on the desalted water pipeline; an ammonia addition pump and an ammonia addition pump inlet valve are arranged on the ammonia water pipeline, the control device is connected to the desalted water flowmeter and the conductivity detector, and the control device is connected to the ammonia addition pump via a frequency converter.

[0012] As a further improvement of the present invention: a first check valve is provided at the outlet end of the desalted water pump.

[0013] As a further improvement of the present invention: a second check valve is provided at the outlet end of the ammonia adding pump.

[0014] Compared with the prior art, the advantages of the present invention are: The desalted water replenishment and ammonia addition control method and system for a waste incineration power plant of the present invention innovatively introduces a dynamically variable Kp value in the PID module of the DCS ammonia addition control system. Specifically, by accurately importing the real-time dynamic change data of the desalted water flow rate into the PID control module, the synchronous linkage change of the proportional coefficient Kp and the desalted water flow rate is achieved. When the desalted water flow rate rises, the Kp value increases accordingly. This design enables the control system to obtain the changing trend of the desalted water flow rate in a timely manner, and increase the adjustment amount in a timely manner, so as to implement precise control in advance. This dynamic control strategy not only significantly enhances the stability of the control system, but also enables it to have excellent anti-interference ability, effectively ensuring the efficient and stable operation of the desalted water replenishment and ammonia addition link of the waste incineration power plant, and ensuring the reliable operation of the entire power generation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of a basic flow chart of a control method according to an embodiment of the present invention.

[0016] Figure 2 1 is a comparison diagram of the effects before and after optimization in the embodiments of the present invention, wherein (a) is a curve diagram of the conductivity obtained by using the original DCS control system versus the flow rate of desalted water; wherein (b) is a curve diagram of the conductivity obtained by using the control method of the present invention versus the flow rate of desalted water.

[0017] Figure 3 Schematic diagram of a control system according to an embodiment of the present invention.

[0018] Legend: 1. Ammonia solution tank; 2. Ammonia pump inlet valve; 3. Frequency converter; 4. Control device; 5. Ammonia pump; 6. Second check valve; 7. Desalted water tank; 8. Desalted water pump inlet valve; 9. Desalted water pump; 10. First check valve; 11. Conductivity detector; 12. Desalted water flowmeter; 13. Desalted water pipeline; 14. Ammonia water pipeline. DETAILED DESCRIPTION

[0019] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0020] In the description of the present invention, it should be understood that the terms "side", "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0021] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or suggesting relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1 As shown, this embodiment discloses a method for controlling the addition of ammonia to desalted water in a waste incineration power plant, comprising: Step S1: presetting the target conductivity in the desalted water pipeline 13; Step S2: replenishing water to the boiler system through the desalted water pump 9; Step S3: adding ammonia water into the demineralized water pipeline 13 through the ammonia adding pump 5; Step S4: The control device 4 collects the real-time conductivity and the desalted water flow value in the desalted water pipeline 13 to perform PID calculation. The control device 4 controls the output frequency of the inverter 3 according to the PID calculation result to adjust the output of the ammonia pump 5. The PID calculation formula is as follows:

[0024] Wherein Q is the desalted water flow value, Ti is the integral time constant, Td is the differential time constant, e(t) is the difference between the expected value and the sampled value of conductivity, and u(t) is the control quantity of the frequency converter 3.

[0025] Since there is a correlation between the conductivity and pH value of the desalinated water solution, the following formula is obtained based on the data relationship between conductivity and pH value: pH= +11; V is the measured conductivity, and pH is the pH value converted according to the conductivity, that is, the pH value of the desalinated water solution can be obtained through the conductivity.

[0026] The desalted water replenishment and ammonia addition control method for the waste incineration power plant in this embodiment innovatively introduces a dynamically variable Kp value in the PID module of the DCS ammonia addition control system. Specifically, by accurately importing the real-time dynamic change data of the desalted water flow rate into the PID control module, the proportional coefficient Kp and the desalted water flow rate are synchronously linked to each other. When the desalted water flow rate rises, the Kp value increases accordingly. This design enables the control system to obtain the changing trend of the desalted water flow rate in a timely manner and increase the adjustment amount in a timely manner, so as to implement precise control in advance. This dynamic control strategy not only significantly enhances the stability of the control system, but also enables it to have excellent anti-interference ability, effectively ensuring the efficient and stable operation of the desalted water replenishment and ammonia addition link of the waste incineration power plant, and ensuring the reliable operation of the entire power generation system.

[0027] like Figure 2 As shown in (a) and 2 (b), curve 1 represents the desalted water flow rate, curve 2 represents the conductivity curve, and curve 3 represents the output frequency change curve of the ammonia pump 5; Figure 2 As shown in (a), with the existing DSC ammonia control system, when the desalted water flow rate does not change, the conductivity curve can be well controlled. However, when the desalted water flow rate suddenly changes, the control system becomes oscillating and unstable, and the conductivity curve shows obvious fluctuations. Figure 2 As shown in (b), using the control method in this embodiment, when the desalted water flow rate changes twice in succession, the system can still stably adjust the conductivity of the desalted water, and the conductivity curve does not show obvious fluctuations. The control method in this embodiment can make the control system better adapt to the changes in the desalted water flow rate, making the control system more stable. In this embodiment, The function may be a linear function, a nonlinear function, or a piecewise function, which may be any one of a linear function, a nonlinear function, or a piecewise function. Further, in a preferred embodiment, , where K is the proportional coefficient and M is the compensation constant. It should be noted that the values ​​of the proportional coefficient K and the compensation constant M can be determined according to the system characteristics. For example, when the desalted water flow rate is 10t / h, K is 0.05, and M is 0.3, then the PID control module is 0.8, when the desalted water flow is 30t / h, the PID control module It is 1.8, which means that the proportional coefficient Kp and the desalted water flow rate are synchronously linked.

[0028] In this embodiment, step S3 specifically includes: collecting the desalted water flow value through the control device 4, and when the desalted water flow value Q>4t / h, the control device 4 sends a start signal to start the ammonia pump 5; and also includes step S5: collecting the desalted water flow value through the control device 4, and when Q<2t / h, the control device 4 sends a stop signal to stop the ammonia pump 5. In this embodiment, not only the proportional coefficient Kp and the desalted water flow rate are synchronously linked, but also the desalted water flow rate is introduced into the desalted water flow signal of the control device 4 to start and stop the ammonia pump 5, which can protect the ammonia pump 5.

[0029] like Figure 3 As shown, the present embodiment also discloses a system based on the above-mentioned desalted water replenishment and ammonia addition control method for a waste incineration power plant, comprising a desalted water pipeline 13 connected to a desalted water tank 7, an ammonia water pipeline 14 connected to an ammonia solution tank 1, and a control device 4, the outlet end of the ammonia water pipeline 14 is connected to the desalted water pipeline 13, and the desalted water pipeline 13 is provided with a desalted water pump inlet valve 8, a desalted water pump 9, a desalted water flowmeter 12 and a conductivity detector 11; the ammonia water pipeline 14 is provided with an ammonia addition pump 5 and an ammonia addition pump inlet valve 2, the control device 4 is connected to the desalted water flowmeter 12 and the conductivity detector 11, and the control device 4 is connected to the ammonia addition pump 5 through a frequency converter 3.

[0030] In this embodiment, the outlet end of the desalted water pump 9 is provided with a first check valve 10, and the outlet end of the ammonia pump 5 is provided with a second check valve 6. The first check valve 10 can prevent the solution in the pipeline from flowing back to the desalted water tank 7, and the second check valve 6 can prevent the solution in the pipeline from flowing back to the ammonia solution tank 1. The ammonia addition control system in this embodiment has a simple structure and low cost. By introducing the desalted water flow into the DCS control module to adjust the parameters of the PID control module, the control system is made more stable and has stronger anti-interference ability.

[0031] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for controlling the addition of ammonia to desalted water in a waste incineration power plant, characterized in that: include: Step S1: presetting a target conductivity in the desalted water pipeline (13); Step S2: replenishing water to the boiler system through the desalted water pump (9); Step S3: adding ammonia water into the demineralized water pipeline (13) via the ammonia adding pump (5); Step S4: The control device (4) collects the real-time conductivity and the flow rate value of the desalted water in the desalted water pipeline (13) to perform PID calculation. The control device (4) controls the output frequency of the frequency converter (3) according to the PID calculation result to adjust the output of the ammonia adding pump (5). The PID calculation formula is as follows: , where Q is the desalted water flow rate, Ti is the integral time constant, Td is the differential time constant, e(t) is the difference between the expected value and the sampled value of conductivity, and u(t) is the control variable of the frequency converter (3).

2. The method for controlling the addition of ammonia to desalted water in a waste incineration power plant according to claim 1, characterized in that: The function is any one of a linear function, a nonlinear function or a piecewise function.

3. The method for controlling the addition of ammonia to desalted water in a waste incineration power plant according to claim 2, characterized in that: , where K is the proportional coefficient and M is the compensation constant.

4. The method for controlling the addition of ammonia to desalted water in a waste incineration power plant according to claim 1, characterized in that: The step S3 specifically comprises: collecting the desalted water flow value through the control device (4); when the desalted water flow value Q>4 t / h, the control device (4) sends a start signal to start the ammonia adding pump (5).

5. The method for controlling the addition of ammonia to desalted water in a waste incineration power plant according to claim 1, characterized in that: The method further comprises step S5: collecting the flow value of desalted water through the control device (4); when Q<2 t / h, the control device (4) sends a stop signal to stop the ammonia adding pump (5).

6. A system based on the desalted water replenishment and ammonia addition control method for a waste incineration power plant according to any one of claims 1 to 5, characterized in that: The invention comprises a desalted water pipeline (13) connected to a desalted water tank (7), an ammonia water pipeline (14) connected to an ammonia solution tank (1), and a control device (4); the water outlet end of the ammonia water pipeline (14) is connected to the desalted water pipeline (13); the desalted water pipeline (13) is provided with a desalted water pump inlet valve (8), a desalted water pump (9), a desalted water flow meter (12), and a conductivity detector (11); the ammonia water pipeline (14) is provided with an ammonia pump (5) and an ammonia pump inlet valve (2); the control device (4) is connected to the desalted water flow meter (12) and the conductivity detector (11); and the control device (4) is connected to the ammonia pump (5) via a frequency converter (3).

7. The system according to claim 6, characterized in that A first check valve (10) is provided at the outlet end of the desalted water pump (9).

8. The system according to claim 6, characterized in that A second check valve (6) is provided at the outlet end of the ammonia addition pump (5).

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