A method for rapid load adjustment using superheated steam energy storage in front of the machine

Abstract

The present invention discloses a method for rapid load adjustment using superheated steam energy storage in front of the unit. The method obtains the superheated steam energy storage at the real-time load point and the target load point respectively through a new calculation method, and calculates the steam energy storage deviation; then, the energy storage deviation is equivalently converted into the load deviation and the pressure deviation, and the deviation is introduced into the coordinated control system feedforward, thereby achieving the purpose of rapid load adjustment using superheated steam energy storage. The present invention avoids the experiment of the on-site unit, calculates the energy storage coefficient of the typical load point by equivalently calculating the historical data, designs the steam turbine feedforward control on this basis, and improves the rapidity of the unit load adjustment by making full use of the energy storage of the superheated steam section in front of the unit.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal power plant control, and relates to a method for optimizing the control of a CCS system of a thermal power unit, and in particular to a method for rapid load adjustment by utilizing superheated steam energy storage in front of the unit. Background Art

[0002] With the in-depth study of the dynamic performance of thermal power units, the control strategy based on boiler energy storage utilization has become a more effective coordinated control system optimization method. This method uses the unit's own energy reserves for rapid load regulation, which can improve the peak-shaving and frequency-regulating capabilities of the entire power supply side under new energy disturbances and reduce the wind and solar power abandonment rate. It is one of the main research topics for my country's thermal power units to adapt to the "carbon peak and carbon neutrality" policy in the future. In response to this problem, the current research focus is mainly on the accurate calculation of the boiler energy storage coefficient, because how to determine the accurate energy storage capacity of the unit is an important prerequisite for the coordinated optimization design of the unit. The existing traditional method for calculating the boiler energy storage coefficient is the disturbance experiment of the high-pressure regulating valve of the unit's steam turbine. Through this method, the energy storage coefficient of the unit under a specific load can be obtained; similar to this method, there are also studies that only study the two steady-state objects before and after the main steam valve action during the primary frequency regulation of the unit without considering the dynamic model, and then obtain the boiler heat storage; in order to avoid a large number of experiments, similar disturbance experiments can also be carried out in the constructed simulation model, and the ideal energy storage coefficient can also be obtained. Therefore, a nonlinear model of the unit is first established, and the dynamic energy storage coefficient of the unit is calculated based on the simplified model. Adding this coefficient to the coordinated control optimization becomes a more realistic boiler energy storage calculation method.

[0003] In the traditional method of calculating boiler heat storage, the step increment of steam flow is related to the heat storage of the boiler. The high-pressure valve disturbance experiment is usually used. The basic theoretical basis of this experimental process is that the water supply system, combustion system and other systems can maintain the basic stable operation of the unit under the premise of keeping the unit main control under manual control. Under the above state, the high-pressure valve opening on the turbine side is adjusted in steps to obtain the change in the load and pressure of the unit, and the energy storage coefficient of the boiler under this load condition is calculated by the following formula:

[0004]

[0005] In the above formula, the unit starts the step action at t0 and ends the step action at t1. b (t0) is the boiler energy storage coefficient at time t0, N E (t0), N E (t1) are the load values ​​of the unit at t0 and t1, respectively, p d (t0), p d (t1) are the pressure values ​​before the unit at t0 and t1 respectively.

[0006] The calculation of the above formula is based on an ideal state experiment, which mainly has the following problems:

[0007] (1) The problem of obtaining the ideal state. Before this experiment, the unit needs to adjust the pressure and temperature of the unit according to the load at that time to reach the corresponding value of the rated load. However, in the actual operation process, the pressure and temperature under a specific load are not fixed values, but a range. Taking the 300MW unit as an example, the temperature value is within a reasonable range as long as it is between 535℃ and 545℃. Under the operation state of large flow superheated steam, a temperature difference of 10℃ will inevitably lead to a large energy storage deviation.

[0008] (2) The cost of disturbance testing of the unit is high, and the performance of the unit will change during operation. Under the current thermal power operation conditions, it is difficult to conduct disturbance testing on each unit under each operating condition.

[0009] (3) The traditional energy storage coefficient is the sum of all the steam, water and metal energy storage in the water-cooled wall section, the steam drum section and the superheated steam section. Since the biggest driving force for the energy change of the steam drum and the water-cooled wall comes from the furnace combustion, the lag is large and the actual effect is not good during the rapid adjustment process. Summary of the invention

[0010] Based on the above reasons, the present invention provides a method for rapid load adjustment using superheated steam energy storage in front of the machine. This method obtains the superheated steam energy storage at the real-time load point and the target load point respectively through a new calculation method, and calculates the steam energy storage deviation; then, this energy storage deviation is equivalently converted into a load deviation and a pressure deviation, and this deviation is introduced into the coordinated control system feedforward, thereby achieving the purpose of rapid load adjustment using superheated steam energy storage. The present invention avoids the experiment of the on-site unit, and calculates the energy storage coefficient of the typical load point through historical data. On this basis, the turbine feedforward control is designed, and the rapidity of the unit load adjustment is improved by making full use of the energy storage of the superheated steam section in front of the unit.

[0011] The objective of the present invention is achieved through the following technical solutions:

[0012] A method for rapid load adjustment using superheated steam energy storage in front of a machine comprises the following steps:

[0013] Step 1: Collect historical data of the unit under stable operation and superheated steam parameters before the unit under continuously variable load, and use a large amount of data to average to obtain the main steam pressure, main steam flow, and main steam temperature parameters corresponding to the typical load point;

[0014] Step 2: Process the data collected in step 1 and use the segmented and working medium calculation method to calculate the effective energy of the steam in the superheated steam section before the machine under the steady state of each typical load point. The specific steps are as follows:

[0015] Step 21: Load from N i Change to N s When the main steam flow rate q i Change to q s , the change Δq is:

[0016] Δq=q s -q i ;

[0017] Step 22: Calculate the effective energy E of superheated steam si (N i ,P i ), which is calculated as follows:

[0018] E si (N i ,P i )=(H i -H0)-T0(S i -S0);

[0019] In the formula, H i is the enthalpy value in the initial state, H0 is the ground state enthalpy value, S i is the entropy value of the initial state, S0 is the entropy value of the ground state, and T0 is the ground state temperature;

[0020] Step 2 and 3: Combine load point N i The flow rate q i , obtain steam working energy Q ssi :

[0021] Q ssi =q i ·E si (N i ,P i );

[0022] Step 24: Follow the method of steps 22 and 23, combined with the load point N s The flow rate q s , obtain steam working energy Q sss ;

[0023] Step 25: Calculate the change in superheated steam energy storage capacity ΔQ between two points based on Δq SS (N i ,N s ):

[0024] ΔQ ss (N i ,Ns )=Q sss -Q ssi ;

[0025] Step 3: Based on step 2, convert the effective energy of superheated steam into instantaneous equivalent load. The specific steps are as follows:

[0026] Step 3: After obtaining the target load, during the process of adding or reducing the load of the unit, the difference in the total energy of the superheated steam is approximately converted into the instantaneous equivalent load difference, the difference in the effective energy of the two load points is calculated, and the two load differences are converted into energy at the same time to obtain the energy difference between the two load points. The calculation is as follows:

[0027] ΔQ(N i ,N s )=ΔQ N (N i ,N s )+ΔQ ss (N i ,N s )

[0028] In the formula, ΔQ(N i ,N s ) is the load from N i To N s The energy required for the load increase ΔQ N (N i ,N s ) and the change in superheated steam energy ΔQ SS (N i ,N s );

[0029] Step 3.2: Change the main steam energy by ΔQ SS (N i ,N s ) According to the following formula, the equivalent load value ΔN is obtained ss Then it is used to correct the load deviation ΔN:

[0030] Q ss (t)-Q ss (t-Δt)=N ss (t)-N ss (t-Δt);

[0031] In the formula, Q ss (t) is the energy storage capacity of the superheating section before the machine at time t; N ss (t) is the change in load;

[0032] Step 4: Get the load point N based on step 3 iThe load deviation optimization value of the coordinated control system (based on the BF state) under different adjustment states is added to the coordinated control system as feedforward to achieve rapid load response.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1) Without conducting field experiments, the instantaneous energy storage of superheated steam in front of each load section of the unit can be obtained based on historical data;

[0035] 2) The instantaneous energy storage of superheated steam in front of the machine can adjust the load more quickly, reducing the impact of the combustion lag on the coordination system regulation performance;

[0036] 3) It does not rely on proprietary disturbance experiments, but uses conventional historical data to obtain the dynamic energy storage of steam. The method is low-cost, accurate in data, and has good practical and promotion value;

[0037] 4) According to the existing energy storage calculations, the energy storage in the superheating section accounts for more than 50% of the total energy storage. By studying the actual operation curve, it can be found that the instantaneous rapid adjustment of the load is essentially to quickly convert the energy of the superheated steam in front of the machine into power generation. The present invention uses this feature to optimize the unit control and can achieve rapid and accurate adjustment of the unit load. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart for calculating the dynamic heat storage coefficient of the unit based on historical data;

[0039] Figure 2 For steam energy calculation and energy signal application. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0041] The present invention provides a method for rapid load adjustment by utilizing the energy storage of superheated steam in front of the unit. The method is to study the energy storage change of the superheated section steam when the unit load changes. The microelement time analysis method is introduced, and Δt is taken as the instantaneous time of the pulse level. At the same time, it can be known from the relationship between the unit load change and the energy in front of the unit that:

[0042] Q ss (t)-Q ss (t-Δt)=N ss (t)-N ss (t-Δt) (1);

[0043] In the formula, Q ss (t) is the energy storage capacity of the superheating section before the machine at time t; N ss (t) is the change in load. The above formula is valid in the instant of dynamic process, that is, the energy of load change in Δt time is equal to the change in energy storage of superheated steam section before the machine.

[0044] The above-mentioned design concept is carried out in a coordinated manner between the furnace and the machine. When the load is adjusted quickly, the unit valve directly adjusts the superheated steam in front of the machine. The combustion (radiation and convection) is delayed by the fuel supply, so the instantaneous impact of the combustion disturbance on the superheated steam in front of the machine is not considered at the moment of valve adjustment. The present invention first designs a superheated steam section energy storage calculation method, and fits the steam energy storage at each point on the basis of the above data, thereby correcting the load deviation setting value at different load points. By accurately setting the load deviation, not only can the superheated steam energy storage in front of the machine be fully utilized, but the energy demand of the load change can also be quickly reflected to the boiler side. Specifically including the following steps:

[0045] Step 1: Collect the historical data of the unit under stable operation and the superheated steam parameters before the unit under continuously variable load, and use the method of averaging a large amount of data to obtain the main steam pressure, main steam flow, and main steam temperature parameters corresponding to the typical load point.

[0046] In this step, a large amount of data is analyzed based on the basic historical data of each load stage of the unit, with the purpose of analyzing the correlation between system steam parameters, unit adjustment mechanism and unit load changes.

[0047] In this step, the data processing process is mainly reflected in: first, data selection is performed under the stable operation state of the unit, because when stable, the unit's fuel quantity, valve opening and combustion state have a high degree of uniformity, which can be regarded as invariants to facilitate the statistical analysis of other variables in big data, and obtain the more accurate pre-machine superheated steam parameters of the unit under steady state, which is used as a reference point to calculate the change in steam energy storage during load changes. Then, the pre-machine superheated steam parameters are collected when the unit continuously increases or decreases load.

[0048] Step 2: Process the data collected in step 1, and use the segmented and working medium calculation method to calculate the effective energy of the steam in the superheated steam section before the machine under the steady state of each typical load point.

[0049] In this step, the calculation method for the change of superheated steam storage energy before the machine is as follows:

[0050] According to the steam-water characteristics of the 300MW drum boiler, based on step 1, the corresponding load N is calculated using the superheated steam temperature, pressure and flow rate. i 、N s Energy change of superheated steam under .

[0051] Load from N i Change to N s When the main steam flow rate q i Change to q s , the change Δq is:

[0052] Δq=q s -q i (2);

[0053] To calculate the change of steam energy, the energy per kilogram of steam before the machine is E. si (N i ,P i ), which is the effective energy of superheated steam, is calculated as follows:

[0054] E si (N i ,P i )=(H i -H0)-T0(S i -S0) (3);

[0055] In the formula, H i is the enthalpy value at the initial state, KJ / kg; H0 is the ground state enthalpy value, KJ / kg; S i is the entropy value of the initial state, KJ / (kg·K); S0 is the entropy value of the ground state, kJ / (kg·K); T0 is the ground state temperature, K. The initial enthalpy value takes the steam enthalpy and entropy value at (450℃, 10Mpa) as the initial value, and the calculation results are H0=192.4346KJ / (kg·K), S0=0.3806KJ / (kg·K).

[0056] The calculation of the above enthalpy value can be obtained by the calculation method of steam parameters, that is, when the easily measurable pressure p and temperature t are selected as independent variables, the following formula (4) is obtained. The calculation method is shown in the international general enthalpy entropy table in the reference:

[0057] H=f0(p,t) (4).

[0058] Similarly, the entropy calculation model used in the mathematical model of superheated steam parameter entropy proposed by Zhou Zemin for the calculation of the entropy of superheated steam at the above temperature and pressure is as follows:

[0059]

[0060] Where t is Kelvin temperature (K), p is standard atmospheric pressure (atm), and s is in KJ / (KG·K). The conversion relationship is:

[0061] 1*P=101.325Kpa (6).

[0062] The calculation of superheated steam enthalpy value refers to the method of calculating the enthalpy value by dividing the area into sections adopted in the literature Tang Qingsheng's practical calculation formula for superheated steam enthalpy, which is expressed as follows:

[0063]

[0064] The above-mentioned steam pressure range is 80 to 180 absolute atmospheres, the temperature range is 450 to 570°C, and the unit of H is KJ / KG.

[0065] E in formula (3) can be calculated by formulas (4), (5), (6), and (7). si (N i ,P i ), combined with the load point N i The flow rate q i , steam working energy Q can be obtained ssi (Similarly, load point N s ):

[0066] Q ssi =q i ·E si (N i ,P i ) (8).

[0067] The change in superheated steam energy storage between two points can be calculated from Δq in formula (3), that is, from the load N s To load N i Steam energy deviation ΔQ SS (N i ,N s )for:

[0068] ΔQ ss (N i ,N s )=Q sss -Q ssi (9).

[0069] Based on the above related theories, it can be calculated that at the load point N i The dynamic energy required for the superheated steam in front of the machine.

[0070] Step 3: Based on step 2, convert the effective energy of superheated steam into instantaneous equivalent load.

[0071] For the same unit, the effective energy of superheated steam at the same load point is relatively unchanged (with a small error) under stable operation at different times; however, during the addition and subtraction process, the effective energy of steam is higher, whether the load is added or reduced. During the process of adding and subtracting loads, the effective energy of superheated steam corresponding to each load point changes (relative to the stable state), so the trend of steam effective energy changes during dynamic changes does not follow the trend of unit load changes. However, the energy change represented by the overall superheated steam is consistent with the load change, because the change in steam flow corrects the fluctuation of superheated steam effective energy.

[0072] Therefore, after obtaining the target load, during the process of adding or reducing the load of the unit, the difference in the total energy of the superheated steam can be approximately converted into the instantaneous equivalent load difference, and the difference in the effective energy of the two load points can be calculated. At the same time, the two load differences can be converted into energy to obtain the energy difference between the two load points. The calculation is as follows:

[0073] ΔQ(N i ,N s )=ΔQ N (N i ,N s )+ΔQ ss (N i ,N s ) (10);

[0074] In the formula, ΔQ(N i ,N s ) is the load from N i To N s The energy required for the load increase ΔQ N (N i ,N s ) and the change in superheated steam energy ΔQ ss (N i ,N s ) and the main steam energy change ΔQ ss (N i ,N s ) According to formula (1), the equivalent load value ΔN is obtained ss It is then used to correct the load deviation ΔN.

[0075] Step 4: Get the load point N based on step 3 i The load deviation optimization value of the coordinated control system (based on the BF state) under different adjustment states is added to the coordinated control system as feedforward to achieve rapid load response.

[0076] N i To N s The superheated steam energy change under the load deviation ΔN is equivalent to ssAfter that, the deviation is used as feedforward, and the load deviation value is corrected in real time. At the same time, the load signal is converted into a pressure deviation signal as feedforward on the boiler side. Figure 1 As shown in the figure, steam energy calculation and energy signal application are as follows Figure 2 shown.

Claims

1. A method for rapid load adjustment using superheated steam energy storage in front of the machine, characterized in that The method comprises the following steps: Step 1: Collect historical data of the unit under stable operation and superheated steam parameters before the unit under continuously variable load, and use a large amount of data to average to obtain the main steam pressure, main steam flow, and main steam temperature parameters corresponding to the typical load point; Step 2: Process the data collected in step 1 and use the segmented and working medium calculation method to calculate the effective energy of the steam in the superheated steam section before the machine under the steady state of each typical load point. The specific steps are as follows: Step 21: Load from N i Change to N s When the main steam flow rate q i Change to q s , the change Δq is: Δq=q s -q i ; Step 22: Calculate the effective energy E of superheated steam si (N i ,P i ), which is calculated as follows: E si (N i ,P i )=(H i -H0)-T0(S i -S0); In the formula, H i is the enthalpy value in the initial state, H0 is the ground state enthalpy value, S i is the entropy value of the initial state, S0 is the entropy value of the ground state, and T0 is the ground state temperature; Step 2 and 3: Combine load point N i The flow rate q i , obtain steam working energy Q ssi : Q ssi =q i ·E si (N i ,P i ); Step 24: Follow the method of steps 22 and 23, combined with the load point N s The flow rate q s , obtain steam working energy Q sss ; Step 25: Calculate the change in superheated steam energy storage capacity ΔQ between two points based on Δq SS (N i ,N s ): ΔQ ss (N i ,N s )=Q sss -Q ssi ; Step 3: Based on step 2, convert the effective energy of superheated steam into instantaneous equivalent load. The specific steps are as follows: Step 3: After obtaining the target load, during the process of adding or reducing the load of the unit, the difference in the total energy of the superheated steam is approximately converted into the instantaneous equivalent load difference, the difference in the effective energy of the two load points is calculated, and the two load differences are converted into energy at the same time to obtain the energy difference between the two load points. The calculation is as follows: ΔQ(N i ,N s )=ΔQ N (N i ,N s )+ΔQ ss (N i ,N s ); In the formula, ΔQ(N i ,N s ) is the load from N i To N s The energy required for the load increase ΔQ N (N i ,N s ) and the change in superheated steam energy ΔQ SS (N i ,N s ); Step 3.2: Change the main steam energy by ΔQ SS (N i ,N s ) According to the following formula, the equivalent load value ΔN is obtained ss Then it is used to correct the load deviation ΔN: Q ss (t)-Q ss (t-Δt)=N ss (t)-N ss (t-Δt); In the formula, Q ss (t) is the energy storage capacity of the superheating section before the machine at time t; N ss (t) is the change in load; Step 4: Get the load point N based on step 3 i The load deviation optimization value of the coordinated control system is obtained under different adjustment states, and this optimization value is added into the coordinated control system as feedforward to achieve rapid load response.

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