Temperature control method of coal mill system

Abstract

The present invention discloses a method for controlling the temperature of a coal mill system, which is used for controlling the hot air valve of the coal mill system, and includes the following steps: step 1, establishing a coal mill temperature state space model; step 2, realizing hot air valve optimization control based on the coal mill temperature state space model. In addition, the method of the present invention also performs hot air valve optimization control based on the coal mill system inlet air temperature, and controls the hot air valve and cold air valve based on the abnormal working conditions of the coal mill system. The present invention does not rely on manual experience, has the advantages of high control accuracy and easy adjustment, and can realize the advantages of automatic operation.

Description

Technical Field

[0001] The invention relates to the field of coal mill system control methods, in particular to a coal mill system temperature control method. Background Art

[0002] As a relatively independent system, the task of the coal powder preparation system in the production process is to safely process the raw coal into coal powder that meets the requirements, and transport the prepared coal powder to the coal powder warehouse for storage, so as to provide fuel for the subsequent cement production process. Therefore, the quality of coal powder directly determines the final quality of the product. Therefore, the coal powder preparation system occupies a very important position in the entire cement production process.

[0003] The pulverized coal preparation system includes a coal mill system for grinding coal raw materials into components, a hot air valve for introducing hot air into the coal mill system, and a cold air valve for introducing cold air. The gas entering the mill is heated by the hot air valve and then sent to the coal mill system for heating. The gas entering the mill can also be directly used as cold air to enter the coal mill system through the cold air valve for cooling. At present, in the control of pulverized coal preparation, the hot air valve and the cold air valve are mainly manually controlled by the operator's production experience. This can neither fully understand the operating status of the system as a whole, nor is it convenient to automatically adjust the operating parameters in time, which seriously affects product quality and production efficiency. Summary of the invention

[0004] The object of the present invention is to provide a method for controlling the temperature of a coal mill system, so as to solve the problem that the temperature of a coal mill system in a coal powder preparation system in the prior art relies on empirical control.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for controlling the temperature of a coal mill system, used for controlling a hot air valve of a coal mill system, comprises the following steps:

[0007] Step 1: Establish the coal mill temperature state space model:

[0008] The on-site outlet gas temperature data and hot air valve opening data of the coal mill system are obtained; then the outlet gas temperature data and the hot air valve opening data of the coal mill system are preprocessed in turn; then, based on the preprocessed outlet gas temperature data and the hot air valve opening data of the coal mill system, a subspace identification method is used to establish a coal mill temperature state space model;

[0009] Step 2: Optimize the hot air valve control based on the coal mill temperature state space model:

[0010] Predict the future output curve of the temperature of the gas at the outlet of the coal mill system using the state space model of the coal mill temperature established in Step 1, compare it with the set value of the desired temperature of the gas at the outlet of the coal mill, and optimize the predictive control based on the comparison result to obtain the first optimized control value of the opening of the hot air valve. Finally, control the opening of the hot air valve with the first optimized control value of the opening of the hot air valve.

[0011] Further, it also includes: Step 3, further optimize the control of the opening of the hot air valve based on the temperature of the gas entering the mill. The process is as follows:

[0012] Obtain the temperature data of the gas entering the coal mill at the site of the coal mill system, then calculate the deviation value of the temperature data of the gas entering the mill at adjacent times, then set the weight coefficient, and calculate the second optimized control value of the opening of the hot air valve based on the calculated deviation value and the weight coefficient. Finally, control the opening of the hot air valve with the second optimized control value of the opening of the hot air valve combined with the first optimized control value.

[0013] Further, it also includes: Step 4, control the hot and cold air valves based on the abnormal working conditions of the coal mill system. The process is as follows:

[0014] Step 4.1, obtain the temperature at the outlet of the coal mill, the running signal of the main motor of the coal mill, the running signal of the weighing scale of the coal mill, and the material quantity signal of the weighing scale in the coal mill system;

[0015] Step 4.2, set two levels of temperature T1 and T2, where T1 < T2, and make a judgment based on the temperature at the outlet of the coal mill in Step 4.1. When the temperature at the outlet of the coal mill exceeds T1 °C for a continuous time S1, fully open the cold air valve and fully close the hot air valve; when the temperature at the outlet of the coal mill exceeds T2 °C for a continuous time S2, fully open the cold air valve and fully close the hot air valve;

[0016] Step 4.3, make a judgment based on the running signal of the main motor of the coal mill. When a falling edge appears in the running signal of the main motor of the coal mill, fully open the cold air valve and fully close the hot air valve;

[0017] Step 4.4, make a judgment based on the running signal of the weighing scale of the coal mill. When the running signal of the weighing scale of the coal mill is 0 for a continuous time S3, fully open the cold air valve and fully close the hot air valve;

[0018] Step 4.5, when the material quantity of the weighing scale is less than G1 tons for a continuous time S4, display that the material of the weighing scale is abnormally low, and fully open the cold air valve and fully close the hot air valve.

[0019] Further, the preprocessing in Step 1 includes filtering processing and normalization processing in sequence.

[0020] Furthermore, in step 1, a moving average filter is first used to filter and preprocess the coal mill system outlet gas temperature data and the hot air valve opening data respectively; then a min-max normalization algorithm is used to normalize and preprocess the coal mill system outlet gas temperature data and the hot air valve opening data after filtering and preprocessing.

[0021] Furthermore, in step 1, the average correlation variance method is used to obtain the accuracy of the established coal mill temperature state space model.

[0022] In the present invention, by constructing a coal mill temperature state space model, and obtaining the first opening control optimization value of the hot air valve based on the coal mill temperature state space model, and then combining the second opening control optimization value of the hot air valve obtained based on the inlet gas temperature, the hot air valve is optimized and controlled, thereby realizing the temperature control of the coal mill system. At the same time, the present invention also uses a conditional judgment method based on the abnormal working conditions of the coal mill system to further realize the control of the hot and cold air valves of the coal mill system.

[0023] Compared with the prior art, the present invention does not rely on manual experience in controlling the hot and cold air valves of the coal mill system. The entire control method is based on a comprehensive understanding of the data of the coal mill system. It has the advantages of high control accuracy and easy adjustment, and can achieve automatic operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the method of an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0026] like Figure 1 As shown, the coal mill system temperature control method of this embodiment is used to control the hot air valve and cold air valve before the coal mill system. Specifically, the corresponding control is achieved by constructing a prediction controller, an inlet gas temperature feedforward controller, and an abnormal operating condition controller. The method process of this embodiment is as follows:

[0027] Step 1: Establish a coal mill temperature state space model as a predictive controller.

[0028] Get real-time data of coal mill system MM (k),u FM (k)}, k represents time, k = 1, ..., N, where T MM (k) is the real-time coal mill outlet gas temperature, u FM (k) is the opening degree of the hot air valve obtained in real time.

[0029] Using moving average filter to preprocess real-time data of coal mill system MM (k),uFM (k)}, get the filtered data in: Corresponding to T MM (k) and u FM (k) Filtered data.

[0030] Then the min-max normalization algorithm is used to normalize the filtered data to obtain the normalized data in:

[0031] Corresponding to Normalized data.

[0032] Next, the normalized data obtained As input and output data, the matrix A is identified using the subspace identification method. m , B m , C m , the coal mill temperature state space model is obtained, as shown in formulas (1) and (2):

[0033] x m (k+1)=A m x m (k)+B m u(k) (1),

[0034] y(k)=C m x m (k) (2),

[0035] In formulas (1) and (2), x m (k) represents the state of the coal mill temperature state space model; u(k) represents the input of the coal mill temperature state space model, y(k) represents the input of the coal mill temperature state space model,

[0036] Finally, the average correlated variance method is used to determine the accuracy of the established coal mill temperature state space model.

[0037] Step 2: Use the predictive controller to control the hot air valve opening.

[0038] According to the coal mill temperature state space model, the future output curve of the coal mill system outlet gas temperature is predicted and compared with the expected coal mill system outlet gas temperature setting value. Based on the comparison result, predictive control optimization is performed to obtain the first opening control optimization value u of the hot air valve. FMpre (k) to control the temperature of the actual coal mill system. The process is as follows:

[0039] First, combine formulas (1) and (2) to obtain formula (3) as follows:

[0040]

[0041] From formula (3), we can get:

[0042] Δx m (k+1)=x m (k+1)-x m (k)

[0043] =A m (x m (k)-x m (k-1))+B m (u(k)-u(k-1)) = A m Δx m (k)+B m Δu(k) (4),

[0044] y(k+1)-y(k)=C m (x m (k+1)-x m (k)) = C m Δx m (k+1)

[0045] =C m A m Δx m (k)C m B m Δu(k) (5),

[0046] According to (4) and (5), the state space equation is shown in formula (6):

[0047]

[0048] in:

[0049] C=[0 m 1],0 m =[0, ..., 0].

[0050] Assume that the current time is k i ,x(k i ) is the system state variable, then N c The future control variable sequence is expressed as Δu(k i ), Δu(k i +1),…,Δu(k i +N c +1), N p The predicted state variable is represented as x(ki +1|k i ), x(k i +2|k i ), …, x(k i +m|k i ), …, x(k i +N p |k i ). Based on the state space equation of formula (6), the future state variables are calculated using the future control parameters as shown in formula (7):

[0051]

[0052] The output variable for calculation prediction is shown in formula (8):

[0053]

[0054] Combining (7) and (8), we get formula (9) as follows:

[0055] Y=Fx(k i )+ΦΔU (9),

[0056] in:

[0057]

[0058] The performance function is defined as shown in formula (10):

[0059]

[0060] in:

[0061] r(k i ) is k i The set value at the moment;

[0062]

[0063] r ω To control the weight of the quantity, it is an adjustable constant.

[0064] Substitute formula (9) into formula (10), find the partial derivative of J, set the partial derivative to 0, and finally obtain formula (11) as shown below:

[0065]

[0066] The first opening control optimization value u of the hot air valve FMpre (k) = u FMpre (k-1)+ΔU.

[0067] Step 3: Establish a feedforward controller for the temperature of the gas entering the mill based on the temperature deviation of the gas entering the mill to control the opening of the hot air valve.

[0068] Obtain real-time coal mill system inlet gas temperature data {T RMM (k)}, calculate the deviation Error of the gas temperature entering the mill at adjacent times RMM (k) = T RMM (k)-T RMM (k-1), according to this deviation Error RMM (k) Establish a feedforward controller for the inlet gas temperature, the formula is as follows:

[0069] U RMM (k) = K RMM *Error RMM (k) (12),

[0070] Among them, U RMM (k) is the feedforward controller output of the inlet gas temperature; K RMM (k) is the controller weight coefficient, K RMM (k) is an adjustable parameter, which can be adjusted manually according to the actual situation.

[0071] Take U RMM (k) The second opening control optimization value of the hot air valve is used to further adjust the opening of the hot air valve. Specifically, the second opening control optimization value is added to the first opening control optimization value obtained in the previous step 2 as the control optimization amount to realize compensatory control of the coal mill outlet temperature.

[0072] Step 4: Establish an abnormal operating condition controller based on the abnormal operating condition of the coal mill system to control the hot air valve and the cold air valve.

[0073] First, obtain the coal mill outlet temperature, coal mill main motor operation signal, coal mill metering scale operation signal, and four abnormal operating conditions in the coal mill system. If an abnormal operating condition occurs, the abnormal operating condition controller will perform corresponding control on the hot air valve and cold air valve.

[0074] The four abnormal conditions have different priorities. The abnormal condition controller first executes the corresponding control process under the abnormal condition with the highest priority based on the priority. The priorities are shown in Table 1:

[0075] Table 1 Abnormal working condition priority table

[0076] Abnormal working conditions Priority (the smaller the number, the higher the priority) Two-stage temperature abnormal conditions 1 Abnormal operation of coal mill tripping 2 Abnormal working condition of weighing scale tripping and stopping 3 Abnormal working condition of low material on weighing scale 4

[0077] The control process of the abnormal condition controller is as follows:

[0078] 4.1. Two-stage temperature abnormality

[0079] When the temperature at the outlet of the coal mill exceeds T1℃ for a duration of S1, it indicates an abnormal high temperature at the outlet of the coal mill. The abnormal condition controller fully opens the cold air valve and fully closes the hot air valve.

[0080] When the temperature at the outlet of the coal mill exceeds T2℃ for a duration of S2, it indicates an extremely high abnormal temperature at the outlet of the coal mill. The abnormal condition controller fully opens the cold air valve and fully closes the hot air valve.

[0081] Among them, S1, T1, S2, and T2 are all configurable. Generally, S1 > S2 and T1 < T2. If the temperature at the outlet of the coal mill remains high for a long time, an explosion may occur. The higher the temperature, the shorter the duration for which an explosion can occur. In a certain cement plant, the set parameters are S1 = 5s, T1 = 75℃, S2 = 3s, and T2 = 85℃. The set parameters of other cement plants can be modified according to the actual situation.

[0082] 4.2 Abnormal condition of coal mill trip

[0083] When the falling edge of the running signal of the main motor of the coal mill appears, it indicates an abnormal coal mill trip. The abnormal condition controller fully opens the cold air valve and fully closes the hot air valve.

[0084] 4.3 Abnormal condition of weighing scale trip

[0085] When the running signal of the coal mill weighing scale is 0 for a duration of S3, it indicates an abnormal weighing scale trip. The abnormal condition controller fully opens the cold air valve and fully closes the hot air valve. Among them, S3 is configurable.

[0086] 4.4 Abnormal condition of low material level on weighing scale

[0087] When the material quantity on the weighing scale is less than G1 tons for a duration of S4, it indicates an abnormal low material level on the weighing scale. The abnormal condition controller fully opens the cold air valve and fully closes the hot air valve. Among them, S4 and G1 are both configurable. If the material quantity in the coal powder silo is too low, it will lead to insufficient material supply to the coal mill system, and it is very easy for the coal mill system to experience a material cutoff phenomenon. In a certain cement plant, the set parameters are S4 = 5s and G1 = 1t. The set parameters of other cement plants can be modified according to the actual situation.

[0088] The embodiments described in the present invention are only descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various variations and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope of the present invention. The technical content claimed by the present invention has been fully recorded in the claims.

Claims

1. A method for controlling the temperature of a coal mill system, used for controlling the hot air valve of a coal mill system, characterized in that: It includes the following steps: Step 1: Establish a coal mill temperature state space model: Obtain the on-site outlet gas temperature data and hot air valve opening data of the coal mill system; then preprocess the outlet gas temperature data and hot air valve opening data of the coal mill system in sequence; then, based on the preprocessed outlet gas temperature data and hot air valve opening data of the coal mill system, use the subspace identification method to establish a coal mill temperature state space model; Specifically as follows: First, obtain the real-time data of the coal mill system {T MM (k),u FM (k)}, k represents time, k = 1, ..., N, where T MM (k) is the real-time coal mill outlet gas temperature, u FM (k) is the opening of the hot air valve obtained in real time; Using moving average filter to preprocess real-time data of coal mill system MM (k),u FM (k)}, get the filtered data in: Corresponding to T MM (k),u FM (k) filtered data; Then the min-max normalization algorithm is used to normalize the filtered data to obtain the normalized data in: Corresponding to Normalized data; Next, the normalized data obtained As input and output data, the matrix A is identified using the subspace identification method. m , B m , C m , the coal mill temperature state space model is obtained, as shown in formulas (1) and (2): x m (k+1)=A m x m (k)+B m u(k) (1), y(k)=C m x m (k) (2), In formulas (1) and (2), x m (k) represents the state of the coal mill temperature state space model; u(k) represents the input of the coal mill temperature state space model, y(k) represents the input of the coal mill temperature state space model, Finally, use the average correlation variance method to judge the accuracy of the established coal mill temperature state space model; Step 2: Realize the optimization control of the hot air valve based on the coal mill temperature state space model: Use the coal mill temperature state space model established in Step 1 to predict the future output curve of the outlet gas temperature of the coal mill system, and compare it with the expected set value of the coal mill outlet gas temperature, and perform predictive control optimization based on the comparison result to obtain the first opening control optimization value of the hot air valve, and finally control the opening of the hot air valve through the first opening control optimization value of the hot air valve.

2. The method for controlling the temperature of a coal mill system according to claim 1, characterized in that: It also includes: Step 3: Further optimize the control of the hot air valve opening based on the inlet mill gas temperature. The process is as follows: Obtain the on-site inlet mill gas temperature data of the coal mill system, then calculate the deviation value of the inlet mill gas temperature data at adjacent times, then set the weight coefficient, and calculate the second opening control optimization value of the hot air valve based on the calculated deviation value and weight coefficient, and finally control the opening of the hot air valve through the combination of the second opening control optimization value and the first opening control optimization value of the hot air valve.

3. The method for controlling the temperature of a coal mill system according to claim 2, characterized in that: It also includes: Step 4: Control the hot and cold air valves based on the abnormal conditions of the coal mill system. The process is as follows: Step 4.1: Obtain the coal mill outlet temperature, coal mill main motor operation signal, coal mill weighing scale operation signal, and weighing scale material quantity signal of the coal mill system; Step 4.2: Set two levels of temperature T1 and T2, where T1 < T2, and make a judgment based on the coal mill outlet temperature in Step 4.

1. When the coal mill outlet temperature exceeds T1 °C for a continuous time S1, fully open the cold air valve and fully close the hot air valve; when the coal mill outlet temperature exceeds T2 °C for a continuous time S2, fully open the cold air valve and fully close the hot air valve; Step 4.3: Make a judgment based on the coal mill main motor operation signal. When there is a falling edge in the coal mill main motor operation signal, fully open the cold air valve and fully close the hot air valve; Step 4.4: Make a judgment based on the coal mill weighing scale operation signal. When the coal mill weighing scale operation signal is 0 for a continuous time S3, fully open the cold air valve and fully close the hot air valve; Step 4.5: When the material quantity of the weighing scale is less than G1 tons for a continuous time S4, display that the weighing scale material is abnormally low, and fully open the cold air valve and fully close the hot air valve.

4. The method for controlling the temperature of a coal mill system according to any one of claims 1 to 3, characterized in that: The preprocessing in Step 1 includes filtering processing and normalization processing in sequence.

5. The method for controlling the temperature of a coal mill system according to claim 4, characterized in that: In Step 1, first use a moving average filter to perform filtering preprocessing on the outlet gas temperature data and hot air valve opening data of the coal mill system respectively; then use the min-max normalization algorithm to perform normalization preprocessing on the filtered preprocessed outlet gas temperature data and hot air valve opening data of the coal mill system respectively.

6. The method for controlling the temperature of a coal mill system according to any one of claims 1 to 3, characterized in that: In Step 1, use the average correlation variance method to obtain the accuracy of the established coal mill temperature state space model.

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