Coal mill warm milling control method for rapid peak regulation

Abstract

The invention belongs to the technical field of coal mills of coal-fired units, and particularly relates to a coal mill warm milling control method for rapid peak regulation. In order to overcome the defect that automatic control of an existing coal mill in the warm milling process is difficult to meet the rapid peak regulation requirement, the technical scheme is adopted as follows: in the warm milling process, inlet primary air flow is controlled through a cold primary air adjusting valve, and the temperature of a mill outlet is controlled through a hot primary air adjusting valve for warm milling until the temperature of an air-powder mixture at the mill outlet reaches a set value. Compared with a traditional cold air door control temperature method that the temperature rise rate is only 2-6 DEG C / min, the temperature rise rate is adjusted through a hot air door, and the method has the advantages of being fast in temperature rise and wide in adjustable range. Furthermore, according to the heat balance relation of the inlet and the outlet of the coal mill, a mathematical model between the temperature of an air-powder mixture at a mill outlet and the opening degree of a hot primary air regulating valve is obtained, the cold primary air regulating valve and the hot primary air regulating valve are operated in advance accordingly, and self-adaptive change of the temperature rise rate and temperature overshoot suppression in the warm milling process are achieved.

Description

Technical Field

[0001] This invention belongs to the technical field of coal mills in coal-fired power units, and specifically relates to a warm-up control method for coal mills for rapid peak shaving. Background Technology

[0002] In recent years, with the continuous advancement of the "dual carbon" goals, the proportion of new energy installed capacity in my country's energy structure has been continuously increasing. To cope with the high system peak-shaving pressure faced by the high proportion of new energy power grids, the role of coal-fired power units in the power grid is gradually shifting from "supporting" to "regulating," and the power grid is placing higher demands on their load change rate when undertaking rapid peak-shaving tasks.

[0003] As a crucial auxiliary machine for combustion control in coal-fired power units, the coal mill in the pulverizing system must constantly maintain a load capacity balanced with the unit load, and promptly perform warm-up and start-up operations based on increases in unit load. However, the ability to safely, quickly, flexibly, and accurately complete the warm-up of the coal mill, ensuring the outlet temperature reaches the required level within a short time, is a key challenge limiting the unit's ability to achieve rapid peak shaving.

[0004] Automatic control of the coal mill warm-up process mainly includes controlling the opening of cold and hot primary air regulating valves to ensure that parameters such as the temperature of the coal-air mixture at the mill outlet, the pressure of the inlet primary air, and the primary air flow rate meet the load-carrying capacity requirements during load increase. Traditional warm-up control methods use a cold primary air regulating valve to control the mill outlet temperature and a hot primary air regulating valve to control the primary air flow rate. This avoids the problem of increased thermal stress inside the coal mill caused by an excessively rapid rise in mill outlet temperature, which could lead to fatigue damage and improve the stability and service life of the coal mill.

[0005] However, the cold primary air regulating valve has a slow response speed to the mill outlet temperature, and can only achieve a low mill outlet temperature rise rate; in addition, the temperature rise rate in a single warm-up process under this method can only be a constant value, with a small range of possible variation, which cannot meet the requirement of flexible adjustment of the temperature rise rate when the unit is rapidly adjusting peak loads; the warm-up control adopts a constant temperature rise rate, which also cannot achieve variable temperature rise rate and overshoot suppression. Summary of the Invention

[0006] This invention addresses the shortcomings of existing automatic control methods for coal mill warm-up processes, which struggle to meet the needs of rapid peak shaving. It provides a coal mill warm-up control method for rapid peak shaving. Compared to the traditional cold air damper temperature control method (temperature rise rate 2–6℃ / min), this method, by adjusting the temperature rise rate through a hot air damper, offers advantages such as rapid temperature rise (2–10℃ / min) and a wide adjustable range. Furthermore, a simulation model (transfer function) for controlling the temperature of the coal-air mixture at the mill outlet is constructed. This model integrates the setpoints for the mill outlet temperature and temperature rise rate, the actual values ​​of the mill outlet temperature and temperature rise rate, and the actual value of the primary air temperature at the mill inlet. It then generates pre-action commands for the cold and hot primary air regulating valves, enabling adaptive changes in the temperature rise rate during the warm-up process (a faster temperature rise rate in the early stages of warm-up for rapid warm-up, and a smaller temperature rise rate in the later stages to limit overshoot).

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a coal mill warm-up control method for rapid peak shaving, comprising:

[0008] Step S1: First open the cold primary air regulating valve, then open the hot primary air regulating valve. When the opening of the cold primary air regulating valve is greater than the threshold and the hot primary air regulating valve is already open, proceed to the next step.

[0009] Step S2: Check whether the secondary air regulating valves on the A and B sides of the coal seam air box to which the mill is located are automatic. If they are both automatic, proceed to the next step.

[0010] Step S3: Check if the frequency of the dynamic separator of the coal mill is greater than the preset frequency. If it is, proceed to the next step.

[0011] Step S4: Check if the cold and hot primary air regulating valves are in the automatic position. If so, start the warm-up process. During the warm-up process, control the primary air flow rate at the mill inlet through the cold primary air regulating valve and control the temperature of the air-powder mixture at the mill outlet through the hot primary air regulating valve until the temperature of the air-powder mixture at the mill outlet reaches the set value.

[0012] As an improvement, the temperature rise rate in the early stage of the warm-up process is greater than the temperature rise rate in the later stage.

[0013] As an improvement, during the warm-up process, a transfer function is established between the temperature of the air-powder mixture at the mill outlet and the opening of the hot primary air regulating valve. By combining the set values ​​of the mill outlet temperature and temperature rise rate, the actual values ​​of the mill outlet temperature and temperature rise rate, and the actual value of the primary air temperature at the mill inlet, the action commands of the cold and hot primary air regulating valves are generated in advance, thereby realizing adaptive control of the warm-up process.

[0014] As an improvement, the temperature T of the air-powder mixture at the mill outlet is... out Variation of hot primary air regulating valve opening u h The transfer function between ' is:

[0015]

[0016] From equation (22), it is easy to see that the temperature control system for the air-powder mixture at the mill outlet is a first-order inertial element, and its gain coefficient is... The time constant is

[0017] All parameters in the gain coefficient and time constant were obtained from actual measurements at corresponding measuring points in the thermal system and at the production site.

[0018] Hot primary air regulating valve opening variation

[0019] As an improvement, based on the law of conservation of heat, a model of the heat balance of the coal mill is constructed, yielding the following formula:

[0020]

[0021] T out C is the temperature of the powder-air mixture at the mill outlet. metal and M metal These represent the specific heat capacity and total mass of the metal inside the coal mill, respectively, C. mix M is the weighted specific heat capacity of the coal-water mixture in raw coal. c and M pf For the quality of coal lumps and pulverized coal inside the coal mill, q cin and q cout Q represents the coal flow rate at the inlet and outlet of the coal mill. in and Q out The inlet and outlet heat rates of the coal mill;

[0022] This formula characterizes the difference in heat absorption rates between the inlet and outlet of the coal mill, which is equal to the sum of the heat absorption rates of the metal in the coal mill, the heat absorption rates of the coal blocks and pulverized coal inside the coal mill, and the heat absorbed by the raw coal inside the coal mill per unit time.

[0023] As an improvement, the inlet heat rate Q of the coal mill... in Write the following formula:

[0024] Q in =Q air +Q c +Q I +Q seal (2)

[0025] That is, the heat imported into the coal mill per unit time is equal to the heat of the primary air imported per unit time, Q. air Imported raw coal carries Q heat c The heat Q generated during the operation of the coal mill I Sealed air heat capacity Q seal sum.

[0026] As an improvement, the heat capacity of the primary air imported per unit time, Q air The calculation formula is:

[0027] Q air =C in T in q air (3)

[0028]

[0029] In the formula, T in C is the primary air temperature at the mill inlet. in q represents the specific heat capacity of the imported primary air. air To reduce the primary air flow rate at the grinding inlet, and These represent the maximum flow rates of the cold and hot primary air regulating valves, u c and u h These are the opening degrees of the cold and hot primary air regulating valves, respectively.

[0030] Q c =[C c_in (1-k in )+C water k in ]T env q cin (5)

[0031] In the formula, C c_in C represents the specific heat capacity of coal (dry basis) at ambient temperature. water For the specific heat capacity of water, k in T represents the moisture content of imported raw coal. env The ambient temperature;

[0032] Q I =r I I (6)

[0033] In the formula, I is the coal mill current, and r I This is the corresponding proportionality coefficient;

[0034] Q seal =C c T env q seal (7)

[0035] In the formula, the heat capacity of the sealed air is Q. seal In expression (7), C c q represents the specific heat capacity of the primary air (also the specific heat capacity of the sealing air). seal For sealing airflow.

[0036] As an improvement, the coal mill outlet heat rate Q out Write the following formula:

[0037] Q out =Q air&seal +Q cout +Q steam +Q loss (8)

[0038] That is, the heat output of the coal mill per unit time is equal to the heat Q carried out by the primary air and sealing air per unit time. air&seal Heat Q carried out by pulverized coal at the outlet cout The heat Q released by the evaporation of moisture in raw coal steam The heat loss Q of the coal mill itself loss sum.

[0039] As an improvement, the heat Q carried out by the primary air and sealed air per unit time is... air&seal The calculation formula is:

[0040] Q air&seal =C out T out (q air +q seal (9)

[0041] In the formula, C out The specific heat capacity of the primary air at the outlet;

[0042] Q cout =[C c_out (1-k out )+C water k out ]T out q cout (10)

[0043] In the formula, C c_out k is the specific heat capacity of coal (dry basis) at the mill outlet temperature. out The moisture content of pulverized coal at the mill outlet;

[0044]

[0045] In the formula, γ is the latent heat of water vaporization, and C steam The specific heat capacity of water vapor at the mill outlet temperature;

[0046] Q loss =r l Q in (12)

[0047] In the formula, r l This is the heat loss coefficient of the coal mill.

[0048] As an improvement, regarding the warm-up process of the coal mill, since the mill has not yet started and there is no raw coal input at this time, the coal quantity description M in the above formulas is different. c Mpf q cin q cout All are 0, so related terms are omitted;

[0049] Combining the above equations, we obtain the temperature T describing the mixture of air and powder at the mill outlet. out Differential equation:

[0050]

[0051] Equation (13) can be further simplified to:

[0052]

[0053] K1 = C metal M metal (15)

[0054]

[0055] K4=(1-r l (Q) I +Q seal (18)

[0056] In the simplified equation, the coefficients K1, K4, K2, and K3 are all considered constants.

[0057] The present invention provides a coal mill warm-up control method for rapid peak shaving. By adjusting the temperature rise rate through a hot air damper, it offers advantages such as rapid temperature rise (2–10°C / min) and a wide adjustable range. Furthermore, by using a hot primary air regulating valve to control the temperature of the coal-air mixture at the mill outlet and a cold primary air regulating valve to control the primary air flow rate at the mill inlet, a temperature rise rate of 2–10°C / min can be achieved. Compared to the traditional cold air damper temperature control method (temperature rise rate 2–6°C / min), this method offers advantages of rapid temperature rise and a wide adjustable range. In addition, a simulation model for controlling the temperature of the coal-air mixture at the mill outlet is constructed. This model integrates the setpoints for the mill outlet temperature and temperature rise rate, the actual values ​​of the mill outlet temperature and temperature rise rate, and the actual value of the primary air temperature at the mill inlet. This allows for the pre-generation of action commands for the hot and cold primary air regulating valves, enabling adaptive changes in the temperature rise rate during the warm-up process. Specifically, a high temperature rise rate is achieved in the early stages of the warm-up process for rapid warm-up, while a low temperature rise rate is maintained in the later stages to limit temperature overshoot and prevent the mill outlet temperature from exceeding the allowable start-up temperature (>85°C), thus preventing the mill from starting. After the warm-up grinding process is completed and the mill enters a stable state, the unit no longer requires a specific rate of temperature rise in the mill. Therefore, it switches back to the traditional mode of controlling the outlet temperature with the cold primary air regulating valve and controlling the inlet flow with the hot primary air regulating valve to stabilize the temperature of the air-powder mixture at the mill outlet and the inlet primary air flow at the set values. Attached Figure Description

[0058] Figure 1This is a structural diagram of a coal mill warming system for rapid peak shaving according to an embodiment of the present invention.

[0059] Figure 2 This is a control diagram of a coal mill warm-up system for rapid peak shaving according to an embodiment of the present invention.

[0060] Figure 3 This is a flowchart of a coal mill warm-up method for rapid peak shaving according to an embodiment of the present invention.

[0061] Figure 4 This is a graph showing the changes in various parameters during a specific implementation process of the coal mill warm-up control method for rapid peak shaving, according to an embodiment of the present invention. Detailed Implementation

[0062] The technical solutions of the embodiments of the present invention will be explained and described below. However, the following embodiments are only preferred embodiments of the present invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments in the implementation methods without creative effort are all within the protection scope of the present invention.

[0063] See Figure 1 and Figure 2 This invention relates to a coal mill warm-up system for rapid peak shaving. The system includes a coal mill, a cold primary air regulating valve, a hot primary air regulating valve, a primary air flow measurement point at the mill inlet, a primary air temperature measurement point at the mill inlet, and a coal-air mixture temperature measurement point at the mill outlet. The system also includes a temperature PID controller (for setting the outlet coal-air mixture temperature), a temperature rise rate PID controller, a hot air damper airflow PID controller, a cold air damper airflow PID controller, a temperature limit rate module, an airflow increase limit rate module, and a temperature rise rate calculation module.

[0064] See Figure 3 The warm-up control method for coal mills oriented towards rapid peak shaving according to embodiments of the present invention includes the following warm-up steps:

[0065] Step 1: Set the opening of the cold primary air regulating valve to 30%. Open the hot primary air regulating valve only after the cold primary air regulating valve opening exceeds 20%. Opening the cold primary air regulating valve to a certain opening before opening the hot primary air regulating valve prevents air leakage from the hot primary air regulating valve, which could lead to an excessively high temperature rise rate and increased thermal stress inside the coal mill. When the opening of the cold primary air regulating valve exceeds 28% and the hot primary air regulating valve is already open, proceed to the next step. Here, during the opening process of the cold primary air regulating valve, when the opening of the cold primary air regulating valve reaches 20%, open the hot primary air regulating valve, while simultaneously maintaining the cold primary air regulating valve at 30%.

[0066] Step 2: Set the secondary air regulating valves on both sides of the coal seam air box to automatic. If both valves are in the automatic position, proceed to the next step.

[0067] Step 3: Set the frequency of the coal mill dynamic separator to 30Hz. If the dynamic separator frequency is greater than 28Hz, proceed to the next step.

[0068] Step 4: Set the cold and hot primary air regulating valves to automatic, and set the target temperature of the air-powder mixture at the mill outlet to 75℃. During the warm-up process, control the primary air flow rate at the mill inlet through the cold primary air regulating valve, and control the temperature of the air-powder mixture at the mill outlet through the hot primary air regulating valve. When the cold and hot primary air regulating valves are in the automatic position and the temperature of the air-powder mixture at the mill outlet is ≥75℃, the warm-up process ends.

[0069] After the warm-up grinding process is completed and the mill enters a stable state, the unit no longer requires a specific rate of temperature rise in the mill. Therefore, it switches back to the traditional mode of controlling the outlet temperature with the cold primary air regulating valve and controlling the inlet flow with the hot primary air regulating valve to stabilize the temperature of the air-powder mixture at the mill outlet and the inlet primary air flow at the set values.

[0070] During the warm-up process, all settings can be preset before the warm-up begins.

[0071] During the warm-up grinding process, a transfer function is established between the temperature of the air-powder mixture at the mill outlet and the opening of the hot primary air regulating valve. By combining the set values ​​of the mill outlet temperature and temperature rise rate, the actual values ​​of the mill outlet temperature and temperature rise rate, and the actual value of the primary air temperature at the mill inlet, the action commands of the cold and hot primary air regulating valves are generated in advance, thereby realizing adaptive control of the warm-up grinding process.

[0072] The process of constructing the transfer function between the temperature of the air-powder mixture at the mill outlet and the opening degree of the hot primary air regulating valve is as follows.

[0073] First, based on the law of conservation of heat, a model of the heat balance of the coal mill is constructed, yielding the following formula:

[0074]

[0075] In the formula, T out C is the temperature of the powder-air mixture at the mill outlet. metal and M metal These represent the specific heat capacity and total mass of the metal inside the coal mill, respectively, C. mix M is the weighted specific heat capacity of the coal-water mixture in raw coal. c and M pf For the quality of coal lumps and pulverized coal inside the coal mill, q cin and q cout Q represents the coal flow rate at the inlet and outlet of the coal mill. in and Q out The heat absorption rate at the inlet and outlet of the coal mill is given by this formula. This formula represents the difference in heat absorption rates at the inlet and outlet of the coal mill, which is equal to the sum of the heat absorption rates of the metal in the coal mill, the heat absorption rates of the coal blocks and pulverized coal inside the coal mill, and the heat absorbed by the raw coal inside the coal mill per unit time.

[0076] Coal mill inlet heat rate Q in It can be written as the following formula:

[0077] Q in =Q air +Q c +Q I +Q seal (2)

[0078] That is, the heat imported into the coal mill per unit time is equal to the heat of the primary air imported per unit time, Q. air Imported raw coal carries Q heat c The heat Q generated during the operation of the coal mill I Sealed air heat capacity Q seal sum.

[0079] The above-mentioned heat values ​​can be further expressed as:

[0080] Q air =C in T in q air (3)

[0081]

[0082] Primary air heat Q air In expression (3), T in C is the primary air temperature at the mill inlet. in q represents the specific heat capacity of the imported primary air. air To reduce the primary air flow rate at the grinding inlet, and These represent the maximum flow rates of the cold and hot primary air regulating valves, u c and u h These are the opening degrees of the cold and hot primary air regulating valves, respectively.

[0083] Q c =[C c_in (1-k in )+C water k in ]T env q cin (5)

[0084] Imported raw coal carries Q heat c In expression (5), C c_in C represents the specific heat capacity of coal (dry basis) at ambient temperature. water For the specific heat capacity of water, k in T represents the moisture content of imported raw coal. env The ambient temperature.

[0085] Q I=r I I (6)

[0086] The heat Q generated during the operation of the coal mill I In expression (6), I is the coal mill current, r I This is the corresponding proportionality coefficient.

[0087] Q seal =C c T env q seal (7)

[0088] Sealed air heat Q seal In expression (7), C c q represents the specific heat capacity of the primary air (also the specific heat capacity of the sealing air). seal For sealing airflow.

[0089] Meanwhile, the heat rate at the outlet of the coal mill, Q out It can be written as the following formula:

[0090] Q out =Q air&seal +Q cout +Q steam +Q loss (8)

[0091] That is, the heat output of the coal mill per unit time is equal to the heat Q carried out by the primary air and sealing air per unit time. air&seal Heat Q carried out by pulverized coal at the outlet cout The heat Q released by the evaporation of moisture in raw coal steam The heat loss Q of the coal mill itself loss The sum of the above heat values ​​can be further expressed as:

[0092] Q air&seal =C out T out (q air +q seal (9)

[0093] Heat Q carried out by primary air and sealed air air&seal In expression (9), C out The specific heat capacity of the primary air at the outlet.

[0094] Q cout =[C c_out (1-k out )+C water k out ]T out q cout (10)

[0095] Heat Q carried out by pulverized coal at the outlet coutIn expression (10), C c_out k is the specific heat capacity of coal (dry basis) at the mill outlet temperature. out This refers to the moisture content of the pulverized coal at the mill outlet.

[0096]

[0097] The heat Q released by the evaporation of moisture in raw coal steam In expression (11), γ is the latent heat of water vaporization, C steam This represents the specific heat capacity of water vapor at the mill outlet temperature.

[0098] Q loss =r l Q in (12)

[0099] The heat loss Q of the coal mill itself loss In expression (12), r l This is the heat loss coefficient of the coal mill.

[0100] Regarding the warm-up process of the coal mill, since the mill has not yet started and there is no raw coal input at this time, the coal quantity description M in the above formulas is as follows: c M pf q cin q cout All are 0, and related terms can be omitted. Combining the above equations, we can obtain the temperature T describing the mixture of air and powder at the mill outlet. out Differential equation:

[0101]

[0102] Equation (13) can be further simplified to:

[0103]

[0104] K1 = C metal M metal (15)

[0105]

[0106] K4=(1-r l (Q) I +Q seal (18)

[0107] In the simplified equation, the coefficients K1 and K4 are only related to the characteristics of the coal mill itself and are independent of the inlet and outlet temperatures; therefore, they can be considered constants. The specific heat capacity of the primary air at the inlet and outlet, C... in C out The primary air temperature T at the inlet and outlet of the wearer in and T outThe impact is minimal, but the temperature variation range of the inlet and outlet primary air during the warm-up process is relatively small (only from room temperature to a maximum of 85°C). Within this small temperature range, the specific heat capacity of the hot air can be approximated as a constant. Simultaneously, the inlet primary air flow rate during the temperature rise control period... and sealing airflow q seal They can be approximated as constants, therefore K2 and K3 can also be regarded as constants.

[0108] Furthermore, considering that the primary air at the mill inlet is a mixture of hot and cold primary air, the primary air temperature T at the mill inlet can be... in The opening degree u of the primary air regulating valve for controlled heat measurement h The relationship between them is expressed as follows:

[0109]

[0110] Substituting equation (4) into equation (19), we get:

[0111]

[0112] Substituting equation (20) into equation (14) yields

[0113]

[0114] make The temperature T of the air-powder mixture at the mill outlet can be obtained. out Variation of hot primary air regulating valve opening u h The transfer function between ' is:

[0115]

[0116] From equation (22), it is easy to see that the temperature control system for the air-powder mixture at the mill outlet is a first-order inertial element, and its gain coefficient is... The time constant is

[0117] All parameters in the gain coefficient and time constant can be obtained from the corresponding measuring points in the thermal system and actual measurements at the production site.

[0118] Hot primary air regulating valve opening variation

[0119] Furthermore, according to equation (22), the exact expression of the transfer function can be conveniently given and its response simulation under various amplitude step inputs can be realized. Based on the simulation response results, the recommended setting value of the opening of the controlled calorimetric primary air regulating valve can be derived in reverse according to the desired temperature rise rate and overshoot suppression, thereby realizing the adaptive control of the warm grinding process.

[0120] Figure 4The figure illustrates the parameter variation curves of the method described in this embodiment during the warm-up grinding process of a 1,000 MW double reheat coal-fired power unit. In the figure, the average temperature rise rate during the warm-up grinding process is set to 6℃ / min, the set temperature of the air-coal mixture at the mill outlet is 75℃, the cold primary air temperature is 30℃, and the hot primary air temperature is 322℃. Starting from the warm-up mark, the opening of the cold primary air regulating valve is first slightly increased to generate a small volume of cold air, and then the hot primary air regulating valve is opened to avoid an excessively rapid temperature rise rate that could increase thermal stress in the internal metal of the coal mill. In the early stage of the warm-up grinding process, to achieve rapid warm-up, the opening of the hot primary air regulating valve is gradually opened to a larger degree, achieving a maximum temperature rise rate of 7.3℃ / min, rapidly increasing the temperature of the air-coal mixture at the mill outlet. In the later stage of the warm-up grinding process, as the temperature of the air-coal mixture at the mill outlet gradually approaches the set value of 75℃, the opening of the hot primary air regulating valve is rapidly closed to near 0 to suppress overshoot. During the entire warm grinding process, the maximum overshoot of the powder mixture temperature at the mill outlet was only 6℃, which is far lower than the overshoot of about 10℃ in the traditional method. Moreover, the actual average temperature rise rate was 5.7℃ / min, achieving adaptive temperature rise rate and overshoot suppression.

[0121] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the content described in the above specific embodiments. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A coal mill warm-up control method for rapid peak shaving, characterized in that: Coal mill warm-up control methods for rapid peak shaving include: Step S1: First open the cold primary air regulating valve, then open the hot primary air regulating valve. When the opening of the cold primary air regulating valve is greater than the threshold and the hot primary air regulating valve is already open, proceed to the next step. Step S2: Check whether the secondary air regulating valves on the A and B sides of the coal seam air box to which the mill is located are automatic. If they are both automatic, proceed to the next step. Step S3: Check if the frequency of the dynamic separator of the coal mill is greater than the preset frequency. If it is, proceed to the next step. Step S4: Check if the cold and hot primary air regulating valves are in the automatic position. If so, start the warm-up process. During the warm-up process, control the primary air flow rate at the mill inlet through the cold primary air regulating valve and control the temperature of the air-powder mixture at the mill outlet through the hot primary air regulating valve until the temperature of the air-powder mixture at the mill outlet reaches the set value.

2. The coal mill warm-up control method for rapid peak shaving according to claim 1, characterized in that: During the warm-up process, the initial temperature rise rate is greater than the later temperature rise rate.

3. The coal mill warm-up control method for rapid peak shaving according to claim 2, characterized in that: During the warm-up grinding process, a transfer function is established between the temperature of the air-powder mixture at the mill outlet and the opening of the hot primary air regulating valve. By combining the set values ​​of the mill outlet temperature and temperature rise rate, the actual values ​​of the mill outlet temperature and temperature rise rate, and the actual value of the primary air temperature at the mill inlet, the action commands of the cold and hot primary air regulating valves are generated in advance, thereby realizing adaptive control of the mill outlet temperature during the warm-up grinding process.

4. The coal mill warm-up control method for rapid peak shaving according to claim 3, characterized in that: Mill outlet air-powder mixture temperature T out Variation of hot primary air regulating valve opening u h The transfer function between ' is: From equation (22), it is easy to see that the temperature control system for the air-powder mixture at the mill outlet is a first-order inertial element, and its gain coefficient is... The time constant is All parameters in the gain coefficient and time constant were obtained from actual measurements at corresponding measuring points in the thermal system and at the production site. Hot primary air regulating valve opening variation 5. The coal mill warm-up control method for rapid peak shaving according to claim 4, characterized in that: Based on the law of conservation of heat, a model of the heat balance of the coal mill is obtained, yielding the following formula: T out C is the temperature of the powder-air mixture at the mill outlet. metal and M metal These represent the specific heat capacity and total mass of the metal inside the coal mill, respectively, C. mix M is the weighted specific heat capacity of the coal-water mixture in raw coal. c and M pf For the quality of coal lumps and pulverized coal inside the coal mill, q cin and q cout Q represents the coal flow rate at the inlet and outlet of the coal mill. in and Q out The inlet and outlet heat rates of the coal mill; This formula characterizes the difference in heat absorption rates between the inlet and outlet of the coal mill, which is equal to the sum of the heat absorption rates of the metal in the coal mill, the heat absorption rates of the coal blocks and pulverized coal inside the coal mill, and the heat absorbed by the raw coal inside the coal mill per unit time.

6. The coal mill warm-up control method for rapid peak shaving according to claim 5, characterized in that: Coal mill inlet heat rate Q in Write the following formula: Q in =Q air +Q c +Q I +Q seal (2) That is, the heat imported into the coal mill per unit time is equal to the heat of the primary air imported per unit time, Q. air Imported raw coal carries Q heat c The heat Q generated during the operation of the coal mill I Sealed air heat capacity Q seal sum.

7. The coal mill warm-up control method for rapid peak shaving according to claim 6, characterized in that: Imported primary air heat capacity Q per unit time air The calculation formula is: Q air =C in T in q air (3) In the formula, T in C is the primary air temperature at the mill inlet. in q represents the specific heat capacity of the imported primary air. air To reduce the primary air flow rate at the grinding inlet, and These represent the maximum flow rates of the cold and hot primary air regulating valves, u c and u h These are the opening degrees of the cold and hot primary air regulating valves, respectively. Q c =[C c_in (1-k in )+C water k in ]T env q cin (5) In the formula, C c_in C represents the specific heat capacity of coal (dry basis) at ambient temperature. water For the specific heat capacity of water, k in T represents the moisture content of imported raw coal. env The ambient temperature; Q I =r I I (6) In the formula, I is the coal mill current, and r I This is the corresponding proportionality coefficient; Q seal =C c T env q seal (7) In the formula, C c q represents the specific heat capacity of the primary air (also the specific heat capacity of the sealing air). seal For sealing airflow.

8. The coal mill warm-up control method for rapid peak shaving according to claim 5, characterized in that: Coal mill outlet heat rate Q out Write the following formula: Q out =Q air&seal +Q cout +Q steam +Q loss (8) That is, the heat output of the coal mill per unit time is equal to the heat Q carried out by the primary air and sealing air per unit time. air&seal Heat Q carried out by pulverized coal at the outlet cout The heat Q released by the evaporation of moisture in raw coal steam The heat loss Q of the coal mill itself loss sum.

9. The coal mill warm-up control method for rapid peak shaving according to claim 8, characterized in that: Heat Q carried out by primary air and sealed air per unit time air&seal The calculation formula is: Q air&seal =C out T out (q air +q seal ) (9) In the formula, C out The specific heat capacity of the primary air at the outlet; Q cout =[C c_out (1-k out )+C water k out ]T out q cout (10) In the formula, C c_out k is the specific heat capacity of coal (dry basis) at the mill outlet temperature. out The moisture content of pulverized coal at the mill outlet; In the formula, γ is the latent heat of water vaporization, and C steam The specific heat capacity of water vapor at the mill outlet temperature; Q loss =r l Q in (12) In the formula, r l This is the heat loss coefficient of the coal mill.

10. The coal mill warm-up control method for rapid peak shaving according to claim 5, characterized in that: Regarding the warm-up process of the coal mill, since the mill has not yet started and there is no raw coal input at this time, the coal quantity description M in the above formulas is as follows: c M pf q cin q cout All are 0, so related terms are omitted; Combining the above equations, we obtain the temperature T describing the mixture of air and powder at the mill outlet. out Differential equation: Equation (13) can be further simplified to: K1=C metal M metal (15) K4=(1-r l )(Q I +Q seal ) (18) In the simplified equation, the coefficients K1, K4, K2, and K3 are all considered constants.

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