Coal-fired unit main steam temperature control method based on feed water flow asynchronous adjustment

Abstract

The invention discloses a coal-fired unit main steam temperature control method based on feed water flow asynchronous regulation, which comprises the following steps of: firstly, calculating the variation of total heat carried by a boiler drum inlet working medium corresponding to unit feed water flow change, and further calculating the variation of saturated steam flow generated by a drum according to energy balance; therefore, the main steam temperature change value corresponding to the change of the unit feed water flow is obtained, then the feed-forward quantity of the main steam temperature deviation on the regulation of the feed water flow of the boiler system is obtained in combination with the real-time deviation of the main steam temperature, and asynchronous regulation of the feed water flow is realized. According to the method, the control effect of the main steam temperature can be greatly improved, and the method is of great significance to improvement of the rapid load changing capacity of the coal-fired unit.

Description

Technical Field

[0001] The invention belongs to the technical field of coal-fired unit control optimization, and in particular relates to a main steam temperature control method of a coal-fired unit based on asynchronous regulation of feed water flow. Background Art

[0002] Since the beginning of the 21st century, the world's energy structure has continued to develop and transform in the direction of clean, low-carbon, high-efficiency and diversified. However, due to the strong time-varying characteristics of renewable energy such as wind energy and solar energy, it is difficult to absorb renewable energy power generation in my country, and the problems of wind and solar power abandonment are serious. Improving the operating flexibility of conventional coal-fired units and providing absorption services for renewable energy power generation are important technical directions. Coal-fired power generation will shift from the main energy source to the basic energy source, and the load variation amplitude and load variation frequency of coal-fired power generation units will gradually increase. Therefore, coal-fired units will be in a transient operating condition with frequent load changes for a long time.

[0003] As an important part of the power system, coal-fired units will take on more and more important peak-shaving tasks, and the requirements for their rapid load-changing capabilities are getting higher and higher. In model simulation and actual power plant operation, it is found that the control quality of the main steam temperature has become an important bottleneck restricting the coal-fired units from further improving their load-changing capabilities. When the unit changes load rapidly, the main steam temperature is very likely to exceed the limit, which limits the improvement of the unit's flexibility. How to quickly and effectively suppress the over-limit problem of the main steam temperature during rapid load changes is an important part of the optimization of the coal-fired unit boiler coordinated control system.

[0004] The steam drum, an important working fluid and energy storage device, enables the coal-fired unit to partially decouple the feedwater flow and the saturated steam flow, which means that the regulation of the feedwater flow does not rely heavily on the load increase or decrease and the amount of coal fed, but can be adjusted asynchronously in a certain range. The main steam temperature is related to the coal feed of the coal-fired unit, the superheater water spray flow and other parameters. The control of the coal feed is mainly related to the boiler master control signal. The superheater water spray cooling is the original main steam temperature control strategy in the coal-fired unit boiler coordination system. Therefore, how to quickly and effectively adjust the saturated steam flow and the main steam flow in the process of rapid load changes becomes the key to effectively control the main steam temperature. Therefore, the present invention proposes a main steam temperature control method for a coal-fired unit with asynchronous feedwater flow regulation. Summary of the invention

[0005] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a main steam temperature control method for a coal-fired unit with asynchronous feed water flow regulation. By means of asynchronous feed water flow regulation, the total heat entering the boiler system is changed, thereby affecting the saturated steam flow. When the spray water flow remains unchanged, the main steam temperature is finally adjusted. The present invention can greatly improve the main steam temperature overheating problem occurring during rapid load changes of the coal-fired unit.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for controlling the main steam temperature of a coal-fired unit based on asynchronous regulation of feedwater flow, characterized in that: asynchronous regulation of feedwater flow is used to assist in controlling the main steam temperature, and the feedforward amount of feedwater flow regulation is obtained by calculating the main steam temperature deviation and the main steam temperature change value corresponding to the unit feedwater flow change based on the collected and processed coal-fired unit operation measurement data:

[0008] The feedforward quantity for water flow regulation is:

[0009]

[0010] Where: Δm ls,fwr The feedforward value of boiler feedwater regulation used to control the main steam temperature, kg / s; k is the feedforward regulation coefficient of feedwater flow rate regulation. The specific value is determined in the actual application of the method according to the response characteristics of asynchronous regulation of feedwater flow rate to the main steam temperature of different coal-fired units; ΔT ls,dev Main steam temperature deviation, °C; ΔT ls is the change in main steam temperature corresponding to a unit change in feed water flow rate, °C;

[0011] Among them, the main steam temperature deviation is:

[0012] ΔT ls,dev =T ls,set -T ls,rt

[0013] Where: T ls,set is the main steam temperature setting value, °C; T ls,rt Real-time value of main steam temperature, ℃.

[0014] The feedwater flow rate is asynchronously regulated to assist in controlling the feedwater flow rate of the main steam temperature, and the feedwater control logic of the coal-fired unit cooperates with the original feedwater control logic of the coal-fired unit to control the feedwater flow rate of the coal-fired unit;

[0015] The auxiliary control of the main steam temperature by asynchronous regulation of feed water flow and the original main steam temperature control of the coal-fired unit coordinately regulate the main steam temperature of the coal-fired unit;

[0016] The feedwater control logic of asynchronous regulation of feedwater flow to assist in controlling the main steam temperature ultimately needs to rely on the regulation of the feedwater pump to achieve real-time asynchronous regulation of feedwater flow.

[0017] The main steam temperature change ΔT corresponding to the unit feed water flow change ls The calculation method is:

[0018]

[0019] Where: T ls ′ is the main steam temperature after the unit feed water flow rate changes, °C; T ls is the main steam temperature before the unit feedwater flow rate changes, °C; Δh ls is the change in main steam enthalpy caused by a unit change in feed water flow, kJ / kg; c ls is the specific heat capacity of the main steam, obtained from the main steam temperature and pressure with the help of thermophysical property relations, kJ / (kg·K);

[0020] Among them, the change in main steam enthalpy caused by the change in unit feed water flow rate is calculated using the following formula:

[0021]

[0022] Where: m spwi is the mass of desuperheating water in the boiler system, kg / s; h ssmf is the enthalpy of saturated steam generated by the drum in the boiler system, kJ / kg; h spw is the desuperheating water enthalpy of the boiler system, kJ / kg; Q sh is the total heat absorbed by the working fluid inside the superheater in the boiler system, kJ / s; m ls It is the main steam flow rate before the unit feed water flow rate changes. The flow rate is collected from the data in the DCS system of the coal-fired unit. If the data is unreliable, the main steam flow rate is calculated using the Flugel formula, kg / s; Δm ssmf It is the change in saturated steam flow rate generated by the drum in the boiler system when the unit feed water flow rate changes, kg / s.

[0023] The change in the saturated steam flow rate generated by the boiler drum when the unit feed water flow rate changes Δm ssmf The specific calculation method is as follows:

[0024] According to the mass balance and energy balance in the drum of the boiler system, ignoring the change in the working pressure of the drum during the change of the unit feed water flow rate, the change in the saturated steam flow rate generated by the drum in the boiler system when the unit feed water flow rate changes is obtained as follows:

[0025]

[0026] Where: ΔQ eco is the change in the total heat absorption of the working medium in the economizer when the unit feed water flow changes, kJ / s; Δm fw is the change in water flow rate, kg / s; h sw is the enthalpy of saturated water in the drum of the boiler system, kJ / kg; h eco,in is the feed water enthalpy at the economizer inlet of the boiler system, kJ / kg; h ssmfIt is the enthalpy of saturated steam generated by the drum in the boiler system, kJ / kg.

[0027] About the total heat absorption Q of the working fluid inside the superheater in the boiler system sh The specific calculation method is as follows:

[0028] According to the energy balance of the superheater system, calculate the total heat absorption of the working fluid inside the superheater system:

[0029] Q sh =m ssmf (h ls -h ssmf )+∑m spwi (h ls -h spw )

[0030] m ssmf =m ls -∑m spwi

[0031] Where: m ssmf is the saturated steam flow rate generated by the drum in the boiler system before the unit feed water flow rate changes, kg / s; h ls It is the main steam enthalpy before the unit feed water flow rate changes, kJ / kg.

[0032] About using Flugel's formula to calculate the main steam flow rate m before the unit feed water flow rate changes ls The specific method is as follows:

[0033] Use the regulating stage pressure, temperature and high-pressure cylinder exhaust pressure combined with the Flugel formula to calculate the main steam flow rate m before the unit feed water flow rate changes ls :

[0034]

[0035] Where: m ls0 is the main steam flow rate under design conditions, kg / s; p tj and p tj0 They are real-time regulating stage pressure and design operating condition regulating stage pressure; p ehp and p ehp0 are the real-time high-pressure cylinder exhaust pressure and the design high-pressure cylinder exhaust pressure; T tj and T tj0 They are the real-time regulating stage pressure and the design operating condition regulating stage pressure respectively.

[0036] The change in the total heat absorption of the working medium in the economizer when the unit feed water flow changes ΔQ eco The specific calculation method is as follows:

[0037] When the unit feed water flow rate changes, the flow rate of the working medium flowing through the economizer in the boiler system changes, and its heat absorption will also change to a certain extent. However, there are no measurement points for the flue gas temperature before and after the flue gas side of each heating surface in the boiler system, so it is impossible to measure it. Therefore, it is impossible to use an accurate method to predict the change in heat absorption. Here, a simple method is used to estimate the change in heat absorption of the working medium in the economizer:

[0038] Define two limit boundaries of heat absorption of working fluid in economizer;

[0039] First, the increase in the total heat absorption of the working fluid in the economizer is proportional to the increase in the working fluid flow rate.

[0040] ΔQ eco,max =Δm fw (h eco,out -h eco,in )

[0041] Where: ΔQ eco,max is the maximum value of the total heat absorption of the working fluid in the economizer, kJ / s; h eco,out is the enthalpy of the working fluid at the economizer outlet in the boiler system, kJ / kg;

[0042] Second, the total heat absorption remains unchanged

[0043] ΔQ eco,min =0

[0044] Where: ΔQ eco,min is the minimum value of the total heat absorption of the working fluid in the economizer, kJ / s;

[0045] In fact, the change in the total heat absorption of the working fluid in the economizer when the unit feed water flow changes should be between the above two limits:

[0046] ΔQ eco =k eco ΔQ eco,max =k eco Δm fw (h eco,out -h eco,in )

[0047] Where: k eco is the correction coefficient of the total heat absorption of the working fluid in the economizer, 0<k eco <1.

[0048] The specific processing process of the collected coal-fired unit operation measurement data is as follows:

[0049] The collected data needs to be cleaned;

[0050] (1) First, the collected raw measurement data is subjected to noise reduction, and the Kalman filter method is used to perform noise reduction and filtering on the raw measurement data;

[0051] (2) Then, the noise-reduced measurement data set is analyzed to screen missing values, abnormal values, and erroneous values ​​in the measurement data, fill in the missing values, correct the abnormal values, and remove the erroneous values;

[0052] (3) Analyze the size and change trend of important basic parameters that are indispensable for coal-fired units, mainly the unit load W p , main steam pressure p out,1 and water flow rate m fw According to the changing trend of basic parameters, combined with the physical mechanism and changing law of the actual operation of the coal-fired unit, it is judged whether the size and changing trend of the measured values ​​of other parameters except the unit load, main steam pressure and feed water flow parameters collected are inconsistent with the changes in the basic parameters of the coal-fired unit, and more accurate measuring points are selected for the data of multiple measuring points. For the data points that are inconsistent with the changes in the basic data of the coal-fired unit, the data are corrected or discarded, and finally the cleaning of the collected measurement data is completed.

[0053] The specific coordinated control method of the feedwater control logic for asynchronous regulation of feedwater flow to assist in controlling the main steam temperature and the original feedwater control logic of the coal-fired unit is as follows:

[0054] The original control method for feedwater flow in the coordinated control system of coal-fired units is mainly achieved by means of the deviation between the real-time water level of the drum and the set water level, and at the same time, the feedforward control of the main steam flow is superimposed. When the coal-fired unit increases or decreases the load, the feedwater flow will show the characteristics of synchronous regulation with the coal supply; the feedforward regulation of the main steam temperature deviation is introduced into the feedwater flow control logic. With the help of the real-time deviation of the main steam temperature of the coal-fired unit, the main steam temperature change value when the unit feedwater flow changes is calculated, combined with the feedforward regulation coefficient of the main steam temperature deviation on the feedwater flow, the feedforward amount of the main steam temperature deviation of the coal-fired unit on the feedwater flow regulation is finally obtained, thereby forming an optimized control logic for auxiliary control of the main steam temperature through feedwater flow feedforward regulation; the final feedwater flow instruction calculation formula is:

[0055] m fwc =f PID (ΔH drum )+k ls m ls +Δm ls,fwr

[0056] Where: m fwc is the final water supply flow instruction, kg / s; ΔH drum is the drum water level deviation, mm; k ls is the main steam flow feedforward coefficient; m lsIt is the main steam flow rate before the unit feed water flow rate changes; the PID algorithm for generating control instructions adopts the incremental PID algorithm;

[0057] The main purpose of the original feed water flow control method of coal-fired units is to maintain the stability of the steam drum water level and ensure the reliability of steam-water separation; after adding the main steam temperature feed forward to the feed water, the influence of the total heat change of the feed water flow on the boiler system drum is used to assist in controlling the main steam temperature.

[0058] The specific coordinated control method of the main steam temperature of the coal-fired unit by the auxiliary control of the main steam temperature by asynchronous regulation of the feed water flow and the original main steam temperature control of the coal-fired unit is as follows:

[0059] The original main steam temperature control of coal-fired units relies on two-stage water spray to control the screen superheater outlet temperature and the high-temperature superheater outlet temperature respectively, thereby ultimately achieving control of the main steam temperature. The original control plays a major role in control. The main steam temperature control method of coal-fired units with asynchronous feed water regulation plays an auxiliary role in controlling the main steam temperature by calculating the feedforward regulation amount of the feed water flow rate by the real-time deviation of the main steam temperature.

[0060] The formula that reflects the coordination of the original water spray cooling main steam temperature control loop and feed water asynchronous regulation of the coal-fired unit is as follows:

[0061] m spw1 =f(ΔT PLS,out )

[0062] m spw2 =f(ΔT HTS,out )

[0063]

[0064] Where: m spw1 and m spw2 are the first and second stage desuperheating water volumes, kg / s; ΔT PLS,out and ΔT HTS,out are the outlet temperature deviation of the platen superheater and the outlet temperature deviation of the high temperature superheater, ℃; ΔT ls,cc The predicted value of the main steam temperature change of the superheater spray cooling and feed water flow asynchronous regulation coordinated control, ℃; ∑m spwi is the total amount of superheater desuperheating water, kg / s; ∑Δm spwi is the total change of superheater desuperheating water, kg / s; Q sh is the total heat absorbed by the working fluid inside the superheater in the boiler system, kJ / s; m ssmf is the saturated steam flow rate generated by the drum in the boiler system before the unit feed water flow rate changes, kg / s; Δm ssmfIt is the change in the saturated steam flow rate generated by the drum in the boiler system when the unit feed water flow rate changes, kg / s; h ssmf is the enthalpy of saturated steam generated by the drum in the boiler system, kJ / kg; h spw is the enthalpy of superheater desuperheating water, kJ / kg; m ls is the main steam flow rate before the unit feedwater flow rate changes, kg / s; c p is the specific heat capacity of main steam, kJ / (kg·K);

[0065] The original water spray cooling regulation of the coal-fired unit works together with the asynchronous water feed regulation to adjust the main steam temperature. The water spray cooling effect of the original main steam temperature control is faster, but when the water spray flow reaches the minimum or maximum limit, it will be difficult to regulate the main steam temperature. At this time, the asynchronous water feed regulation can still play a role in regulating the main steam temperature.

[0066] The specific implementation method of feedwater control logic with feedwater flow asynchronous regulation to assist in controlling the main steam temperature with the help of feedwater pump regulation is as follows:

[0067] When the feedforward regulation amount of the feedwater flow rate changes due to the main steam temperature deviation, the feedwater pump working medium flow rate needs to be controlled accordingly; for a fixed speed pump, the feedwater pump flow rate is controlled by controlling the outlet valve opening:

[0068] m fw,dp =f(kv pump )

[0069] Where: m fw,dp is the feed water flow rate of the fixed speed pump, kg / s; f represents the characteristic curve between the opening of the outlet valve of the feed water pump and the feed water pump flow rate; kv pump is the outlet valve opening of the water pump;

[0070] For variable speed pumps, the flow rate of the water pump is adjusted by changing the speed of the pump:

[0071] m fw,bp =f(N pump )

[0072] Where: m fw,bp is the feed water flow rate of the variable speed pump, kg / s; f represents the characteristic curve between the feed water pump speed and the feed water pump flow rate; N pump is the speed of the water feed pump, r / min.

[0073] The beneficial effect of the present invention is that: by using the important energy storage medium and energy storage equipment of the coal-fired unit drum, the adjustment range of the feed water flow is liberated, and the asynchronous adjustment of the feed water flow when the load is raised or lowered can be realized. By supplementing and optimizing the automatic control logic of the main steam temperature of the coal-fired unit through asynchronous adjustment of the feed water flow, the main steam temperature can be effectively prevented from exceeding the limit when the coal-fired unit changes load rapidly, and the main steam temperature exceeding the limit, which is the bottleneck that limits the further increase of the unit's load change rate, can be suppressed, thereby improving the unit's operating flexibility.

[0074] Advantages of the present invention

[0075] 1) The present invention provides a main steam temperature control method for a coal-fired unit based on asynchronous regulation of feedwater flow, and its advantages are embodied in the specific auxiliary control method of the main steam temperature of the coal-fired unit by asynchronous regulation of feedwater flow: the present invention uses the calculated main steam temperature deviation and the main steam temperature change value corresponding to the unit feedwater flow change to calculate the feedforward amount of feedwater flow regulation required to eliminate the deviation when the main steam temperature deviation increases, and organically combines the feedwater control logic of the auxiliary control of the main steam temperature by asynchronous regulation of feedwater flow with the original feedwater control logic of the coal-fired unit, organically combines the auxiliary control of the main steam temperature by asynchronous regulation of feedwater flow with the original main steam temperature control loop of the coal-fired unit, and finally transmits the feedwater flow regulation instruction to the feedwater pump control system to realize the change of feedwater flow, and finally realizes the auxiliary control of the main steam temperature by asynchronous regulation of feedwater flow;

[0076] 2) The present invention provides a main steam temperature control method for a coal-fired unit based on asynchronous regulation of feed water flow, and its advantages are specifically reflected in the method for calculating the main steam temperature change value corresponding to a unit feed water flow change: the present invention calculates the flow change of the main steam when the unit feed water flow changes through the mass balance and energy balance of the boiler evaporation system, and calculates the influence of the main steam flow change on the main steam temperature with the help of the boiler superheater energy balance, and finally calculates the main steam temperature change value corresponding to the unit feed water flow regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 This is a control effect diagram of a 330MW subcritical coal-fired unit using a main steam temperature control method for a coal-fired generator set based on asynchronous regulation of feedwater flow to quickly reduce the load from 75% to 50%. DETAILED DESCRIPTION

[0078] In order to make the purpose, technical solution and advantages of the present invention more clear, the method of the present invention is further described in detail below in conjunction with specific implementation cases. It should be understood that the specific implementation cases described herein are only used to explain the present invention and are not used to limit the present invention.

[0079] The present invention discloses a main steam temperature control method for a coal-fired unit based on asynchronous regulation of feedwater flow, which is characterized in that: asynchronous regulation of feedwater flow is used to assist in controlling the main steam temperature, and the feedforward amount of feedwater flow regulation is obtained by calculating the main steam temperature deviation and the main steam temperature change value corresponding to the unit feedwater flow change based on the collected and processed coal-fired unit operation measurement data:

[0080] The feedforward quantity for water flow regulation is:

[0081]

[0082] Where: Δm ls,fwr The feedforward value of boiler feedwater regulation used to control the main steam temperature, kg / s; k is the feedforward regulation coefficient of feedwater flow rate regulation. The specific value is determined in the actual application of the method according to the response characteristics of asynchronous regulation of feedwater flow rate to the main steam temperature of different coal-fired units; ΔT ls,dev Main steam temperature deviation, °C; ΔT ls is the change in main steam temperature corresponding to a unit change in feed water flow rate, °C;

[0083] Among them, the main steam temperature deviation is:

[0084] ΔT ls,dev =T ls,set -T ls,rt

[0085] Where: T ls,set is the main steam temperature setting value, ℃; T ls,rt Real-time value of main steam temperature, ℃.

[0086] The feedwater flow rate is asynchronously regulated to assist in controlling the feedwater flow rate of the main steam temperature, and the feedwater control logic of the coal-fired unit cooperates with the original feedwater control logic of the coal-fired unit to control the feedwater flow rate of the coal-fired unit;

[0087] The auxiliary control of the main steam temperature by asynchronous regulation of feed water flow and the original main steam temperature control of the coal-fired unit coordinately regulate the main steam temperature of the coal-fired unit;

[0088] The feedwater control logic of asynchronous regulation of feedwater flow to assist in controlling the main steam temperature ultimately needs to rely on the regulation of the feedwater pump to achieve real-time asynchronous regulation of feedwater flow.

[0089] Preferably, the main steam temperature change value ΔT corresponding to the unit feed water flow change ls The calculation method is:

[0090]

[0091] Where: T ls ′ is the main steam temperature after the unit feed water flow rate changes, °C; Tls is the main steam temperature before the unit feedwater flow rate changes, °C; Δh ls is the change in main steam enthalpy caused by a unit change in feed water flow, kJ / kg; c ls is the specific heat capacity of the main steam, obtained from the main steam temperature and pressure with the help of thermophysical property relations, kJ / (kg·K);

[0092] Among them, the change in main steam enthalpy caused by the change in unit feed water flow rate is calculated using the following formula:

[0093]

[0094] Where: m spwi is the mass of desuperheating water in the boiler system, kg / s; h ssmf is the enthalpy of saturated steam generated by the drum in the boiler system, kJ / kg; h spw is the desuperheating water enthalpy of the boiler system, kJ / kg; Q sh is the total heat absorbed by the working fluid inside the superheater in the boiler system, kJ / s; m ls It is the main steam flow rate before the unit feed water flow rate changes. The flow rate is collected from the data in the DCS system of the coal-fired unit. If the data is unreliable, the main steam flow rate is calculated using the Flugel formula, kg / s; Δm ssmf It is the change in saturated steam flow rate generated by the drum in the boiler system when the unit feed water flow rate changes, kg / s.

[0095] Preferably, the change in the saturated steam flow rate generated by the drum of the boiler system when the unit feed water flow rate changes Δm ssmf The specific calculation method is as follows:

[0096] According to the mass balance and energy balance in the drum of the boiler system, ignoring the change in the working pressure of the drum during the change of the unit feed water flow rate, the change in the saturated steam flow rate generated by the drum in the boiler system when the unit feed water flow rate changes is obtained as follows:

[0097]

[0098] Where: ΔQ eco is the change in the total heat absorption of the working medium in the economizer when the unit feed water flow changes, kJ / s; Δm fw is the change in water flow rate, kg / s; h sw is the enthalpy of saturated water in the drum of the boiler system, kJ / kg; h eco,in is the feed water enthalpy at the economizer inlet of the boiler system, kJ / kg; h ssmf It is the enthalpy of saturated steam generated by the drum in the boiler system, kJ / kg.

[0099] Preferably, the total heat absorption Q of the working fluid inside the superheater in the boiler system sh The specific calculation method is as follows:

[0100] According to the energy balance of the superheater system, calculate the total heat absorption of the working fluid inside the superheater system:

[0101] Q sh =m ssmf (h ls -h ssmf )+∑m spwi (h ls -h spw )

[0102] m ssmf =m ls -∑m spwi

[0103] Where: m ssmf is the saturated steam flow rate generated by the drum in the boiler system before the unit feed water flow rate changes, kg / s; h ls It is the main steam enthalpy before the unit feed water flow rate changes, kJ / kg.

[0104] Preferably, regarding the calculation of the main steam flow rate m before the unit feed water flow rate changes using the Flugel formula ls The specific method is as follows:

[0105] Use the regulating stage pressure, temperature and high-pressure cylinder exhaust pressure combined with the Flugel formula to calculate the main steam flow rate m before the unit feed water flow rate changes ls :

[0106]

[0107] Where: m ls0 is the main steam flow rate under design conditions, kg / s; p tj and p tj0 They are real-time regulating stage pressure and design operating condition regulating stage pressure; p ehp and p ehp0 are the real-time high-pressure cylinder exhaust pressure and the design high-pressure cylinder exhaust pressure; T tj and T tj0 They are the real-time regulating stage pressure and the design operating condition regulating stage pressure respectively.

[0108] Preferably, the change in the total heat absorption of the working medium in the economizer when the unit feed water flow changes ΔQ eco The specific calculation method is as follows:

[0109] When the unit feed water flow rate changes, the flow rate of the working medium flowing through the economizer in the boiler system changes, and its heat absorption will also change to a certain extent. However, there are no measurement points for the flue gas temperature before and after the flue gas side of each heating surface in the boiler system, so it is impossible to measure it. Therefore, it is impossible to use an accurate method to predict the change in heat absorption. Here, a simple method is used to estimate the change in heat absorption of the working medium in the economizer:

[0110] Define two limit boundaries of heat absorption of working fluid in economizer;

[0111] First, the increase in the total heat absorption of the working fluid in the economizer is proportional to the increase in the working fluid flow rate.

[0112] ΔQ eco,max =Δm fw (h eco,out -h eco,in )

[0113] Where: ΔQ eco,max is the maximum value of the total heat absorption of the working fluid in the economizer, kJ / s; h eco,out is the enthalpy of the working fluid at the economizer outlet in the boiler system, kJ / kg;

[0114] Second, the total heat absorption remains unchanged

[0115] ΔQ eco,min =0

[0116] Where: ΔQ eco,min is the minimum value of the total heat absorption of the working fluid in the economizer, kJ / s;

[0117] In fact, the change in the total heat absorption of the working fluid in the economizer when the unit feed water flow changes should be between the above two limits:

[0118] ΔQ eco =k eco ΔQ eco,max =k eco Δm fw (h eco,out -h eco,in )

[0119] Where: k eco is the correction coefficient of the total heat absorption of the working fluid in the economizer, 0<k eco <1.

[0120] Preferably, the specific processing process of the collected coal-fired unit operation measurement data is as follows:

[0121] The collected data needs to be cleaned;

[0122] (1) First, the collected raw measurement data is subjected to noise reduction, and the Kalman filter method is used to perform noise reduction and filtering on the raw measurement data;

[0123] (2) Then, the noise-reduced measurement data set is analyzed to screen missing values, abnormal values, and erroneous values ​​in the measurement data, fill in the missing values, correct the abnormal values, and remove the erroneous values;

[0124] (3) Analyze the size and change trend of important basic parameters that are indispensable for coal-fired units, mainly the unit load W p , main steam pressure p out,1 and water flow rate m fw According to the changing trend of basic parameters, combined with the physical mechanism and changing law of the actual operation of the coal-fired unit, it is judged whether the size and changing trend of the measured values ​​of other parameters except the unit load, main steam pressure and feed water flow parameters collected are inconsistent with the changes in the basic parameters of the coal-fired unit, and more accurate measuring points are selected for the data of multiple measuring points. For the data points that are inconsistent with the changes in the basic data of the coal-fired unit, the data are corrected or discarded, and finally the cleaning of the collected measurement data is completed.

[0125] Preferably, the specific coordinated control method of the feedwater control logic for auxiliary control of the main steam temperature by asynchronous regulation of the feedwater flow rate and the original feedwater control logic of the coal-fired unit is as follows:

[0126] The original control method for feedwater flow in the coordinated control system of coal-fired units is mainly achieved by means of the deviation between the real-time water level of the drum and the set water level, and at the same time, the feedforward control of the main steam flow is superimposed. When the coal-fired unit increases or decreases the load, the feedwater flow will show the characteristics of synchronous regulation with the coal supply; the feedforward regulation of the main steam temperature deviation is introduced into the feedwater flow control logic. With the help of the real-time deviation of the main steam temperature of the coal-fired unit, the main steam temperature change value when the unit feedwater flow changes is calculated, combined with the feedforward regulation coefficient of the main steam temperature deviation on the feedwater flow, the feedforward amount of the main steam temperature deviation of the coal-fired unit on the feedwater flow regulation is finally obtained, thereby forming an optimized control logic for auxiliary control of the main steam temperature through feedwater flow feedforward regulation; the final feedwater flow instruction calculation formula is:

[0127] m fwc =f PID (ΔH drum )+k ls m ls +Δm ls,fwr

[0128] Where: m fwc is the final water supply flow instruction, kg / s; ΔH drum is the drum water level deviation, mm; k lsis the main steam flow feedforward coefficient; m ls It is the main steam flow rate before the unit feed water flow rate changes; the PID algorithm for generating control instructions adopts the incremental PID algorithm;

[0129] The main purpose of the original feed water flow control method of coal-fired units is to maintain the stability of the steam drum water level and ensure the reliability of steam-water separation; after adding the main steam temperature feed forward to the feed water, the influence of the total heat change of the feed water flow on the boiler system drum is used to assist in controlling the main steam temperature.

[0130] Preferably, the specific coordinated control method for the auxiliary control of the main steam temperature by asynchronous regulation of the feed water flow and the original main steam temperature control of the coal-fired unit for coordinated control of the main steam temperature of the coal-fired unit is as follows:

[0131] The original main steam temperature control of coal-fired units relies on two-stage water spray to control the screen superheater outlet temperature and the high-temperature superheater outlet temperature respectively, thereby ultimately achieving control of the main steam temperature. The original control plays a major role in control. The main steam temperature control method of coal-fired units with asynchronous feed water regulation plays an auxiliary role in controlling the main steam temperature by calculating the feedforward regulation amount of the feed water flow rate by the real-time deviation of the main steam temperature.

[0132] The formula that reflects the coordination of the original water spray cooling main steam temperature control loop and feed water asynchronous regulation of the coal-fired unit is as follows:

[0133] m spw1 =f(ΔT PLS,out )

[0134] m spw2 =f(ΔT HTS,out )

[0135]

[0136] Where: m spw1 and m spw2 are the first and second stage desuperheating water volumes, kg / s; ΔT PLS,out and ΔT HTS,out are the outlet temperature deviation of the platen superheater and the outlet temperature deviation of the high temperature superheater, ℃; ΔT ls,cc The predicted value of the main steam temperature change of the superheater spray cooling and feed water flow asynchronous regulation coordinated control, ℃; ∑m spwi is the total amount of superheater desuperheating water, kg / s; ∑Δm spwi is the total change of superheater desuperheating water, kg / s; Q sh is the total heat absorbed by the working fluid inside the superheater in the boiler system, kJ / s; m ssmf is the saturated steam flow rate generated by the drum in the boiler system before the unit feed water flow rate changes, kg / s; Δmssmf It is the change in the saturated steam flow rate generated by the drum in the boiler system when the unit feed water flow rate changes, kg / s; h ssmf is the enthalpy of saturated steam generated by the drum in the boiler system, kJ / kg; h spw is the enthalpy of superheater desuperheating water, kJ / kg; m ls is the main steam flow rate before the unit feedwater flow rate changes, kg / s; c p is the specific heat capacity of main steam, kJ / (kg·K);

[0137] The original water spray cooling regulation of the coal-fired unit works together with the asynchronous water feed regulation to adjust the main steam temperature. The water spray cooling effect of the original main steam temperature control is faster, but when the water spray flow reaches the minimum or maximum limit, it will be difficult to regulate the main steam temperature. At this time, the asynchronous water feed regulation can still play a role in regulating the main steam temperature.

[0138] Preferably, the specific implementation method of feedwater control logic for asynchronously regulating feedwater flow to assist in controlling main steam temperature by means of feedwater pump regulation is as follows:

[0139] When the feedforward regulation amount of the feedwater flow rate changes due to the main steam temperature deviation, the feedwater pump working medium flow rate needs to be controlled accordingly; for a fixed speed pump, the feedwater pump flow rate is controlled by controlling the outlet valve opening:

[0140] m fw,dp =f(kv pump )

[0141] Where: m fw,dp is the feed water flow rate of the fixed speed pump, kg / s; f represents the characteristic curve between the opening of the outlet valve of the feed water pump and the feed water pump flow rate; kv pump is the outlet valve opening of the water pump;

[0142] For variable speed pumps, the flow rate of the water pump is adjusted by changing the speed of the pump:

[0143] m fw,bp =f(N pump )

[0144] Where: m fw,bp is the feed water flow rate of the variable speed pump, kg / s; f represents the characteristic curve between the feed water pump speed and the feed water pump flow rate; N pump is the speed of the water feed pump, r / min.

[0145] Figure 1The control effect of the main steam temperature of a 330MW subcritical coal-fired unit during 75%-50% rapid load reduction using the original main steam temperature adjustment method and the main steam temperature adjustment method of the present invention was compared. Under the original control strategy, when the load reduction rate was 2.5%Pe / min, the main steam temperature deviation exceeded the maximum allowable limit of 8°C, so the maximum load reduction rate of the unit was 2.0%Pe / min.

[0146] By using the main steam temperature regulation method of the present invention, the maximum deviation of the main steam temperature of the coal-fired unit is reduced from 8.72°C to 7.39°C at a load reduction rate of 2.5%Pe / min, and the load reduction rate of the unit is finally increased from 2.0%Pe / min to 3.0%Pe / min. The main steam temperature control method of the coal-fired unit with asynchronous feedwater flow regulation significantly enhances the main steam temperature control effect.

[0147] Table 1 shows in detail the changes in the main steam temperature control effect of the coal-fired unit before and after the main steam temperature control method using asynchronous adjustment of feed water flow, mainly including three indicators: the maximum deviation of the main steam temperature, the cumulative deviation of the main steam temperature and the maximum load reduction rate of the unit.

[0148] Table 1 Control effect of main steam temperature regulation method of coal-fired unit with asynchronous feedwater regulation

[0149]

[0150] It can be seen from Table 1 that after using the main steam temperature control method of the coal-fired unit with asynchronous adjustment of the feed water flow rate of the present invention, the maximum deviation and cumulative deviation of the main steam temperature at a variable load rate of 2.5% Pe / min decreased by 15.3% and 21.1% respectively, and the maximum variable load rate increased by 1.0% Pe / min, which significantly improved the operating flexibility of the coal-fired unit.

Claims

1. A method for controlling the main steam temperature of a coal-fired unit based on asynchronous regulation of feedwater flow, characterized in that: The feedwater flow rate is asynchronously regulated to assist in controlling the main steam temperature. The feedforward amount of the feedwater flow rate regulation is obtained by calculating the main steam temperature deviation and the main steam temperature change corresponding to the unit feedwater flow rate change based on the collected and processed coal-fired unit operation measurement data: The feedforward quantity for water flow regulation is: Where: Δm ls,fwr The feedforward value of boiler feedwater regulation used to control the main steam temperature, kg / s; k is the feedforward regulation coefficient of feedwater flow rate regulation. The specific value is determined in the actual application of the method according to the response characteristics of asynchronous regulation of feedwater flow rate to the main steam temperature of different coal-fired units; ΔT ls,dev Main steam temperature deviation, °C; ΔT ls is the change in main steam temperature corresponding to a unit change in feed water flow rate, °C; Among them, the main steam temperature deviation is: ΔT ls,dev =T ls,set -T ls,rt Where: T ls,set is the main steam temperature setting value, ℃; T ls,rt Real-time value of main steam temperature, ℃. The feedwater flow rate is asynchronously regulated to assist in controlling the feedwater flow rate of the main steam temperature, and the feedwater control logic of the coal-fired unit cooperates with the original feedwater control logic of the coal-fired unit to control the feedwater flow rate of the coal-fired unit; The auxiliary control of the main steam temperature by asynchronous regulation of feed water flow and the original main steam temperature control of the coal-fired unit coordinately regulate the main steam temperature of the coal-fired unit; The feedwater control logic of asynchronous regulation of feedwater flow to assist in controlling the main steam temperature ultimately needs to rely on the regulation of the feedwater pump to achieve real-time asynchronous regulation of feedwater flow.

2. The main steam temperature control method of a coal-fired unit based on asynchronous regulation of feedwater flow according to claim 1 is characterized in that: The main steam temperature change corresponding to the unit feed water flow change ΔT ls The calculation method is: Where: T ls ′ is the main steam temperature after the unit feed water flow rate changes, °C; T ls is the main steam temperature before the unit feedwater flow rate changes, °C; Δh ls is the change in main steam enthalpy caused by a unit change in feed water flow, kJ / kg; c ls is the specific heat capacity of the main steam, obtained from the main steam temperature and pressure with the help of thermophysical property relations, kJ / (kg·K); Among them, the change in main steam enthalpy caused by the change in unit feed water flow rate is calculated using the following formula: Where: m spwi is the mass of desuperheating water in the boiler system, kg / s; h ssmf is the enthalpy of saturated steam generated by the drum in the boiler system, kJ / kg; h spw is the desuperheating water enthalpy of the boiler system, kJ / kg; Q sh is the total heat absorbed by the working fluid inside the superheater in the boiler system, kJ / s; m ls It is the main steam flow rate before the unit feed water flow rate changes. The flow rate is collected from the data in the DCS system of the coal-fired unit. If the data is unreliable, the main steam flow rate is calculated using the Flugel formula, kg / s; Δm ssmf It is the change in saturated steam flow rate generated by the drum in the boiler system when the unit feed water flow rate changes, kg / s.

3. The main steam temperature control method of a coal-fired unit based on asynchronous regulation of feedwater flow according to claim 2 is characterized in that: The change in saturated steam flow rate generated by the boiler drum when the unit feed water flow rate changes Δm ssmf The specific calculation method is as follows: According to the mass balance and energy balance in the drum of the boiler system, ignoring the change in the working pressure of the drum during the change of the unit feed water flow rate, the change in the saturated steam flow rate generated by the drum in the boiler system when the unit feed water flow rate changes is obtained as follows: Where: ΔQ eco is the change in the total heat absorption of the working medium in the economizer when the unit feed water flow changes, kJ / s; Δm fw is the change in water flow rate, kg / s; h sw is the enthalpy of saturated water in the drum of the boiler system, kJ / kg; h eco,in is the feed water enthalpy at the economizer inlet of the boiler system, kJ / kg; h ssmf It is the enthalpy of saturated steam generated by the drum in the boiler system, kJ / kg.

4. The main steam temperature control method of a coal-fired unit based on asynchronous regulation of feedwater flow according to claim 2 is characterized in that: Total heat absorption Q of the working fluid inside the superheater in the boiler system sh The specific calculation method is as follows: According to the energy balance of the superheater system, calculate the total heat absorption of the working fluid inside the superheater system: Q sh =m ssmf (h ls -h ssmf )+∑m spwi (h ls -h spw ) m ssmf =m ls -∑m spwi Where: m ssmf is the saturated steam flow rate generated by the drum in the boiler system before the unit feed water flow rate changes, kg / s; h ls It is the main steam enthalpy before the unit feed water flow rate changes, kJ / kg.

5. The main steam temperature control method of a coal-fired unit based on asynchronous regulation of feedwater flow according to claim 2, characterized in that: Use Flugel's formula to calculate the main steam flow rate m before the unit feed water flow rate changes ls The specific method is as follows: Use the regulating stage pressure, temperature and high-pressure cylinder exhaust pressure combined with the Flugel formula to calculate the main steam flow rate m before the unit feed water flow rate changes ls : Where: m ls0 is the main steam flow rate under design conditions, kg / s; p tj and p tj0 They are real-time regulating stage pressure and design operating condition regulating stage pressure; p ehp and p ehp0 are the real-time high-pressure cylinder exhaust steam pressure and the design high-pressure cylinder exhaust steam pressure; T tj and T tj0 They are the real-time regulating stage pressure and the design operating condition regulating stage pressure respectively.

6. The main steam temperature control method of a coal-fired unit based on asynchronous regulation of feedwater flow according to claim 3, characterized in that: The change in total heat absorption of the working fluid in the economizer when the unit feed water flow changes ΔQ eco The specific calculation method is as follows: When the unit feed water flow rate changes, the flow rate of the working medium flowing through the economizer in the boiler system changes, and its heat absorption will also change to a certain extent. However, there are no measurement points for the flue gas temperature before and after the flue gas side of each heating surface in the boiler system, so it is impossible to measure it. Therefore, it is impossible to use an accurate method to predict the change in heat absorption. Here, a simple method is used to estimate the change in heat absorption of the working medium in the economizer: Define two limit boundaries of heat absorption of working fluid in economizer; First, the increase in the total heat absorption of the working fluid in the economizer is proportional to the increase in the working fluid flow rate. ΔQ eco,max =Δm fw (h eco,out -h eco,in ) Where: ΔQ eco,max is the maximum value of the total heat absorption of the working fluid in the economizer, kJ / s; h eco,out is the enthalpy of the working fluid at the economizer outlet in the boiler system, kJ / kg; Second, the total heat absorption remains unchanged ΔQ eco,min =0 Where: ΔQ eco,min is the minimum value of the total heat absorption of the working fluid in the economizer, kJ / s; In fact, the change in the total heat absorption of the working fluid in the economizer when the unit feed water flow changes should be between the above two limits: ΔQ eco =k eco ΔQ eco,max =k eco Δm fw (h eco,out -h eco,in ) Where: k eco is the correction coefficient of the total heat absorption of the working fluid in the economizer, 0<k eco <1.

7. The main steam temperature control method of a coal-fired unit based on asynchronous regulation of feedwater flow according to claim 1, characterized in that: The specific processing process of the collected coal-fired unit operation measurement data is as follows: The collected data needs to be cleaned; (1) First, the collected raw measurement data is subjected to noise reduction, and the Kalman filter method is used to perform noise reduction and filtering on the raw measurement data; (2) Then, the noise-reduced measurement data set is analyzed to screen missing values, abnormal values, and erroneous values ​​in the measurement data, fill in the missing values, correct the abnormal values, and remove the erroneous values; (3) Analyze the size and change trend of important basic parameters that are indispensable for coal-fired units, mainly the unit load W p , main steam pressure p out,1 and water flow rate m fw ; According to the changing trend of basic parameters, combined with the physical mechanism and changing law during the actual operation of the coal-fired unit, it is judged whether the size and changing trend of the measured values ​​of other parameters except the unit load, main steam pressure and feed water flow parameters are inconsistent with the changes in the basic parameters of the coal-fired unit, and more accurate measuring points are selected for the data of multiple measuring points. For the data points that are inconsistent with the changes in the basic data of the coal-fired unit, the data are corrected or discarded, and finally the cleaning of the collected measurement data is completed.

8. The main steam temperature control method of a coal-fired unit based on asynchronous regulation of feedwater flow according to claim 1, characterized in that: The specific coordinated control method of the feedwater control logic of the feedwater flow asynchronous regulation to assist in controlling the main steam temperature and the original feedwater control logic of the coal-fired unit is as follows: The original control method for feedwater flow in the coordinated control system of coal-fired units is mainly achieved by means of the deviation between the real-time water level of the drum and the set water level, and at the same time, the feedforward control of the main steam flow is superimposed. When the coal-fired unit increases or decreases the load, the feedwater flow will show the characteristics of synchronous regulation with the coal supply; the feedforward regulation of the main steam temperature deviation is introduced into the feedwater flow control logic. With the help of the real-time deviation of the main steam temperature of the coal-fired unit, the main steam temperature change value when the unit feedwater flow changes is calculated, combined with the feedforward regulation coefficient of the main steam temperature deviation on the feedwater flow, the feedforward amount of the main steam temperature deviation of the coal-fired unit on the feedwater flow regulation is finally obtained, thereby forming an optimized control logic for auxiliary control of the main steam temperature through feedwater flow feedforward regulation; the final feedwater flow instruction calculation formula is: m fwc =f PID (ΔH drum )+k ls m ls +Δm ls,fwr Where: m fwc is the final water supply flow instruction, kg / s; ΔH drum is the drum water level deviation, mm; k ls is the main steam flow feedforward coefficient; m ls It is the main steam flow rate before the unit feed water flow rate changes; the PID algorithm for generating control instructions adopts the incremental PID algorithm; The main purpose of the original feed water flow control method of coal-fired units is to maintain the stability of the steam drum water level and ensure the reliability of steam-water separation; after adding the main steam temperature feed forward to the feed water, the influence of the total heat change of the feed water flow on the boiler system drum is used to assist in controlling the main steam temperature.

9. The main steam temperature control method of a coal-fired unit based on asynchronous regulation of feedwater flow according to claim 1, characterized in that: The specific coordinated control method of the main steam temperature of the coal-fired unit by the auxiliary control of the main steam temperature by asynchronous regulation of the feed water flow and the original main steam temperature control of the coal-fired unit is as follows: The original main steam temperature control of coal-fired units relies on two-stage water spray to control the screen superheater outlet temperature and the high-temperature superheater outlet temperature respectively, thereby ultimately achieving control of the main steam temperature. The original control plays a major role in control. The main steam temperature control method of coal-fired units with asynchronous feed water regulation plays an auxiliary role in controlling the main steam temperature by calculating the feedforward regulation amount of the feed water flow rate by the real-time deviation of the main steam temperature. The formula that reflects the coordination of the original water spray cooling main steam temperature control loop and feed water asynchronous regulation of the coal-fired unit is as follows: m spw1 =f(ΔT PLS,out ) m spw2 =f(ΔT HTS,out ) Where: m spw1 and m spw2 are the first and second stage desuperheating water volumes, kg / s; ΔT PLS,out and ΔT HTS,out are the outlet temperature deviation of the platen superheater and the outlet temperature deviation of the high temperature superheater, ℃; ΔT ls,cc The predicted value of the main steam temperature change of the superheater spray cooling and feed water flow asynchronous regulation coordinated control, ℃; ∑m spwi is the total amount of superheater desuperheating water, kg / s; ∑Δm spwi is the total change of superheater desuperheating water, kg / s; Q sh is the total heat absorbed by the working fluid inside the superheater in the boiler system, kJ / s; m ssmf is the saturated steam flow rate generated by the drum in the boiler system before the unit feed water flow rate changes, kg / s; Δm ssmf It is the change in the saturated steam flow rate generated by the drum in the boiler system when the unit feed water flow rate changes, kg / s; h ssmf is the enthalpy of saturated steam generated by the drum in the boiler system, kJ / kg; h spw is the enthalpy of superheater desuperheating water, kJ / kg; m ls is the main steam flow rate before the unit feedwater flow rate changes, kg / s; c p is the specific heat capacity of main steam, kJ / (kg·K); The original water spray cooling regulation of the coal-fired unit works together with the asynchronous water feed regulation to adjust the main steam temperature. The water spray cooling effect of the original main steam temperature control is faster, but when the water spray flow reaches the minimum or maximum limit, it will be difficult to regulate the main steam temperature. At this time, the asynchronous water feed regulation can still play a role in regulating the main steam temperature.

10. The main steam temperature control method of a coal-fired unit based on asynchronous regulation of feedwater flow according to claim 1, characterized in that: The specific implementation method of feedwater control logic of asynchronous regulation of feedwater flow to assist in controlling the main steam temperature with the help of feedwater pump regulation is as follows: When the feedforward regulation amount of the feedwater flow rate changes due to the main steam temperature deviation, the feedwater pump working medium flow rate needs to be controlled accordingly; for a fixed speed pump, the feedwater pump flow rate is controlled by controlling the outlet valve opening: m fw,dp =f(kv pump ) Where: m fw,dp is the feed water flow rate of the fixed speed pump, kg / s; f represents the characteristic curve between the opening of the outlet valve of the feed water pump and the feed water pump flow rate; kv pump is the outlet valve opening of the water pump; For variable speed pumps, the water supply pump flow rate is adjusted by changing the pump speed: m fw,bp =f(N pump ) Where: m fw,bp is the feed water flow rate of the variable speed pump, kg / s; f represents the characteristic curve between the feed water pump speed and the feed water pump flow rate; N pump is the speed of the water feed pump, r / min.

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