CN115974251A - Thermodynamic system water supply and ammonia addition control system and method - Google Patents

Abstract

The invention discloses a thermal system feedwater ammonia addition control system and method, which belong to the technical field of thermal system ammonia addition control. The device includes: a PLC controller, an ammonia water tank, and a first pipeline connected to the outlet of a deaerator in a boiler feedwater system. And the second pipeline connected with the inlet of the boiler feedwater economizer of the thermal system; the first pipeline connected with the outlet of the ammonia water tank and the deaerator is provided with a feedwater ammonia pump; the sampling pipeline connected with the second pipeline is connected with a pH sensor It is discharged into the recovery pool; the PLC controller is electrically connected to the feed water ammonia pump and the pH sensor at the inlet of the economizer. The PLC controller is connected to the feed water ammonia pump and the pH sensor at the inlet of the economizer, and uses the model-free adaptive control algorithm to calculate the adjustment frequency of the feed water ammonia pump at this time, and dynamically adjust the feed water ammonia addition amount. The device ensures the stability of pH at the inlet of the feedwater economizer of the thermal system, that is, meets the control requirements for adding ammonia to the feedwater of the thermal system.

Description

A thermal system water supply ammonia addition control system and method

Technical Field

The present invention relates to the technical field of thermal system ammonia addition control, and in particular to a thermal system feedwater ammonia addition control system and method.

Background Art

The technology of adding ammonia to the water supply in the thermal system is an important part of the chemical system of the power plant. A certain amount of ammonia water is added to the water supply pipeline to increase the pH value of the water supply system as a practical way to prevent metal corrosion. However, due to the large hysteresis characteristics of the water supply adding part in the thermal system and the load fluctuation, it is difficult to accurately control the pH value of the water supply manually, which increases the difficulty of operation for operators and makes the boiler water supply pipeline have a certain risk of equipment corrosion.

How to control the addition of ammonia to the water supply of the thermal system has become an urgent problem to be solved.

Summary of the invention

In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a control system and method for adding ammonia to water for a thermal system. When external factors change, the device does not need to set a large number of parameters and is easy for operators to operate, thereby ensuring the stability of the pH of the water supply to the thermal system.

In order to achieve the above purpose, the present invention adopts the following technical solutions:

A thermal system feedwater ammonia addition control system, comprising: a PLC controller, an ammonia water tank, a first pipeline connected to the outlet of a deaerator of a boiler feedwater system, and a second pipeline connected to the inlet of a feedwater economizer of a thermal system boiler;

A water supply and ammonia pump is provided on the first pipeline connecting the ammonia water tank and the outlet of the deaerator; a sampling pipeline connected to the second pipeline is connected to a pH sensor and then discharged into a recovery tank;

The PLC controller is electrically connected to the feed water ammonia pump and the economizer inlet pH sensor.

As a further improvement of the present invention, the PLC controller is connected to a touch display screen.

As a further improvement of the present invention, a manual water supply and ammonia addition door is provided on the outlet pipeline of the water supply and ammonia addition pump.

As a further improvement of the present invention, the PLC controller includes a model-free adaptive module, which is used to compare and control the actual pH value at the economizer inlet with the expected value, and utilizes its own data-driven function to dynamically adjust the frequency of the feed water ammonia pump to control the thermal system feed water pH to reach the expected value.

As a further improvement of the present invention, the control method of the model-free adaptive control module is:

或Δu(k-1)≤ε或

if

or Δu(k-1)≤ε or

In the formula, ε is a very small positive number, ρ and η represent step size factors, λ and μ are penalty factors, which are used to limit the increment of the control quantity. Among them, y ^* (k+1) is the expected value of the pH at the economizer inlet, y(k) is the sampled real-time value of the pH at the economizer inlet; u(k) is the output of the model-free adaptive control algorithm and directly acts on the feed water ammonia pump.

A method for controlling the addition of ammonia to water in a thermal system comprises the following steps:

The expected pH value at the economizer inlet is set, and the condensate ammonia pump is started; the difference between the pH sampling value at the economizer inlet and the expected value is calculated and passed through the model-free adaptive control module of the PLC controller. The model-free adaptive control module dynamically adjusts the frequency of the feed water ammonia pump, thereby controlling the feed water pH of the thermal system to reach the expected value.

As a further improvement of the present invention, the difference calculation between the pH sample value and the expected value includes:

An online pH meter is added at the economizer inlet to measure the pH of the boiler feed water online, and the pH is converted into the feed water pH value using the formula pH = 8.57 + lgSC, where SC is the online measurement value of the internal cooling water conductivity.

As a further improvement of the present invention, the control method of the model-free adaptive control module is:

或Δu(k-1)≤ε或

if

or Δu(k-1)≤ε or

In the formula, ε is a very small positive number, ρ and η represent step size factors, λ and μ are penalty factors, which are used to limit the increment of the control quantity. Among them, y ^* (k+1) is the expected value of the pH at the economizer inlet, y(k) is the sampled real-time value of the pH at the economizer inlet; u(k) is the output of the model-free adaptive control algorithm and directly acts on the feed water ammonia pump.

Compared with the prior art, the present invention has the following advantages:

The present invention uses a feed water ammonia pump at the outlet of the deaerator to add ammonia water to the boiler feed water pipeline. The sampling part is designed to add an online pH meter at the economizer inlet, and the PLC controller uses a model-free adaptive algorithm; the PLC controller is electrically connected to the feed water ammonia pump and the economizer inlet pH sensor. The PLC controller is connected to the feed water ammonia pump and the economizer inlet pH sensor, and uses a model-free adaptive control algorithm to calculate the adjustment frequency of the feed water ammonia pump at this time, and dynamically adjusts the feed water ammonia amount. The device ensures the stability of the pH at the inlet of the thermal system feed water economizer, that is, meets the control requirements of the thermal system feed water ammonia. The hysteresis of the boiler feed water ammonia system is reduced, and no manual intervention is required. The model-free adaptive algorithm can dynamically change the feed water ammonia pump frequency according to the set control parameters, thereby accurately changing the amount of ammonia added to the thermal system feed water according to the change of the working conditions of the thermal system feed water system. The device is simple and practical, and has high accuracy in controlling the pH of the thermal system feed water, thereby ensuring the stability of the pH value of the thermal system feed water and meeting the requirements of the thermal system feed water pH.

Furthermore, the method of the present invention solves the problem of large lag in the addition of ammonia to the water supply in the thermal system. The model-free adaptive control algorithm used in the PLC controller obtains the optimal output value of the model-free adaptive controller, dynamically adjusts the frequency of the water supply and ammonia addition pump, reduces the workload of the operating personnel, and ensures the safety and economy of the operation of the thermal system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a thermal system water supply and ammonia addition device provided by the present invention;

FIG. 2 is a model-free adaptive control method for adding ammonia to water in a thermal system provided by the present invention.

DETAILED DESCRIPTION

The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

As shown in FIG1 , the present invention provides a thermal system feedwater ammonia addition control system, comprising: a PLC controller 5 , a first pipeline connecting an ammonia water tank 1 to a deaerator outlet of a boiler feedwater system, and a second pipeline connecting to an economizer inlet of a boiler feedwater system of the thermal system;

The first pipeline connecting the ammonia water tank 1 and the outlet of the deaerator includes a water feed ammonia pump 2 and a water feed ammonia manual door 3 in sequence; the sampling pipeline at the economizer inlet is connected to the pH sensor 6 and then discharged into the recovery tank.

The PLC controller 5 is connected to the feed water ammonia pump 2 and the economizer inlet pH sensor 6.

The PLC controller 5 is connected to the touch screen 4. The touch screen 4 can be used for data input, data interaction, display and conventional control operations. For example, the desired pH value at the economizer inlet can be set on the touch screen 4, and the condensate ammonia pump 2 can be started.

The PLC controller includes a model-free adaptive module for comparing and controlling the actual pH value of the economizer inlet with the expected value, and using its own data-driven function to dynamically adjust the frequency of the feed water ammonia pump 2 to control the thermal system feed water pH to reach the expected value.

The core principle of the present invention is: the PLC controller is connected to the feedwater ammonia pump 2 and the economizer inlet pH sensor, and the model-free adaptive control algorithm is used to calculate the adjustment frequency of the feedwater ammonia pump 2 at this time, and dynamically adjust the feedwater ammonia amount. The device ensures the stability of the pH at the inlet of the thermal system feedwater economizer, that is, meets the control requirements of the thermal system feedwater ammonia.

The present invention also provides a method for controlling water supply and ammonia addition in a thermal system using an intelligent algorithm, comprising the following steps:

Set the expected pH value at the economizer inlet on the touch screen 4 and start the condensate ammonia pump 2. Calculate the difference between the pH sampling value at the economizer inlet and the expected value and pass it through the model-free adaptive control module to obtain the feed water ammonia pump 2 at this time, thereby controlling the pH at the feed water economizer inlet of the thermal system to reach the expected value.

The method of the present invention solves the problem of large hysteresis of water supply and ammonia addition in a thermal system. The model-free adaptive control algorithm used in the PLC controller sets parameters including a proportional coefficient P, an integral coefficient I and a differential coefficient D, thereby obtaining the optimal output value of the model-free adaptive controller, dynamically adjusting the frequency of the water supply and ammonia addition pump, reducing the workload of operating personnel, and ensuring the safety and economy of the thermal system operation.

The pH value of boiler feed water is measured online and converted to feed water pH value using the formula pH = 8.57 + lgSC.

The model-free adaptive algorithm needs to be implemented with the help of SCL programming statements in the STEP7 programming software of Siemens S7-300.

Model-free adaptive control does not rely on accurate mathematical model information of the object, and uses the online I/O data or offline I/O data of the controlled object to complete the implementation of its own controller. When the current model of the controlled object changes, the model-free adaptive controller can change its own parameters to achieve its adaptive function. MFAC is proposed on the basis of "universal model" and pseudo-partial derivatives. When the controlled object is replaced by a discretized "universal model", the online I/O data of the controlled object is used to complete the solution of the pseudo-partial derivative of the "universal model". The adaptive adjustment process of MFAC is realized through the change of pseudo-partial derivatives. MFAC only requires the I/O data of the controlled object, and does not require the internal information of the structure and order of the controlled object, which provides great convenience for the implementation of model-free adaptive controllers.

The model-free adaptive control scheme is:

或Δu(k-1)≤ε或

if

or Δu(k-1)≤ε or

In the above formula, ε is a very small positive number, ρ and η represent step size factors, λ and μ are penalty factors, which are used to limit the increment of the control quantity, where y ^* (k+1) is the expected value of the pH at the economizer inlet, and y(k) is the sampled real-time value of the pH at the economizer inlet. u(k) is the output of the model-free adaptive control algorithm and directly acts on the feedwater ammonia pump 2 to realize the automatic control of feedwater ammonia.

Through the design of the model-free adaptive controller, it can be seen from the above formula that the controller only uses the I/O data of the system and does not have any information related to the model structure. This is the characteristic of the model-free adaptive controller itself. In the control process, the adaptive change of the pseudo partial derivative plays a decisive role in the control amount of the controller.

The specific implementation of the present invention will be further described below in conjunction with Figures 1 and 2.

Example

As shown in Figure 1, when the thermal system water supply ammonia adding device is put into operation, the water supply ammonia adding manual door is opened, and the desired pH value at the economizer inlet is set on the touch display screen 4, and the condensate ammonia adding pump 2 is started, and the thermal system water supply ammonia adding device can be put into automatic operation.

As shown in Figure 2, the parameters of the model-free adaptive algorithm for adjusting the economizer inlet pH are included, where ρ and η represent the step size factors, λ and μ are the penalty factors and the expected value of the economizer inlet pH, so that the economizer inlet pH has the function of automatic control, that is, it meets the control requirements of adding ammonia to the thermal system feed water.

The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (8)

1. A thermal system feed water ammonia addition control system, characterized in that it comprises: a PLC controller (5), an ammonia water tank (1), a first pipeline connected to the outlet of a deaerator of a boiler feed water system, and a second pipeline connected to the inlet of a boiler feed water economizer of the thermal system; A water supply and ammonia pump (2) is provided on a first pipeline connecting the ammonia water tank (1) and the outlet of the deaerator; a sampling pipeline connected to the second pipeline is connected to a pH sensor (6) and then discharged into a recovery tank; The PLC controller (5) is electrically connected to the feedwater ammonia pump (2) and the economizer inlet pH sensor (6). 2. A thermal system water supply and ammonia addition control system according to claim 1, characterized in that: The PLC controller (5) is connected to the touch display screen (4). 3. A thermal system water supply and ammonia addition control system according to claim 1, characterized in that: The outlet pipeline of the water supply and ammonia addition pump (2) is provided with a water supply and ammonia addition manual door (3). 4. A thermal system water supply and ammonia addition control system according to claim 1, characterized in that: The PLC controller comprises a model-free adaptive module, which is used to compare and control the actual pH value at the economizer inlet with the expected value, and utilizes its own data-driven function to dynamically adjust the frequency of the feed water ammonia pump (2) so as to control the feed water pH of the thermal system to reach the expected value. 5. A thermal system water supply and ammonia addition control system according to claim 4, characterized in that: The control method of the model-free adaptive control module is:

if

or |Δu(k-1)|≤ε or

In the formula, ε is a very small positive number, ρ and η represent step size factors, λ and μ are penalty factors, which are used to limit the increment of the control quantity. Among them, y ^* (k+1) is the expected value of the pH at the economizer inlet, y(k) is the sampled real-time value of the pH at the economizer inlet; u(k) is the output of the model-free adaptive control algorithm and directly acts on the feed water ammonia pump. 6. A method for controlling the addition of ammonia to water in a thermal system, characterized by comprising the following steps: The expected pH value at the economizer inlet is set, and the condensate ammonia pump is started; the difference between the pH sampling value at the economizer inlet and the expected value is calculated and passed through the model-free adaptive control module of the PLC controller. The model-free adaptive control module dynamically adjusts the frequency of the feed water ammonia pump, thereby controlling the feed water pH of the thermal system to reach the expected value. 7. The method for controlling the addition of ammonia to water in a thermal system according to claim 6, characterized in that: The difference calculation between the pH sample value and the expected value includes: An online pH meter is added at the economizer inlet to measure the pH of the boiler feed water online, and the pH is converted into the feed water pH value using the formula pH = 8.57 + lgSC, where SC is the online measurement value of the internal cooling water conductivity. 8. The method for controlling the addition of ammonia to water in a thermal system according to claim 6, characterized in that: The control method of the model-free adaptive control module is:

if

or |Δu(k-1)|≤ε or

In the formula, ε is a very small positive number, ρ and η represent step size factors, λ and μ are penalty factors, which are used to limit the increment of the control quantity. Among them, y ^* (k+1) is the expected value of the pH at the economizer inlet, y(k) is the sampled real-time value of the pH at the economizer inlet; u(k) is the output of the model-free adaptive control algorithm and directly acts on the feed water ammonia pump.

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