Online calculation method for stimulating heat storage capacity by adjusting deaerator water flow of power plant boiler

Abstract

The application is applied to the technical field of thermal automation, and discloses an online calculation method for exciting heat storage capacity of power station boiler adjustment desuperheating water flow. The method comprises the following steps: obtaining a lead compensation steam temperature, a desuperheating water gain, a pulse amplitude gain and a steam power coefficient; the lead compensation steam temperature is a steam temperature after lead compensation of a pipeline outlet steam temperature; obtaining a first small temperature difference correction steam temperature between a preset steam temperature upper limit and the lead compensation steam temperature; obtaining a second small temperature difference correction steam temperature between the lead compensation steam temperature and a preset steam temperature lower limit; obtaining a temperature difference capacity gain according to the desuperheating water gain, the pulse amplitude gain and the steam power coefficient; calculating a product of the first small temperature difference correction steam temperature and the temperature difference capacity gain to obtain a storable heat capacity; and calculating a product of the second small temperature difference correction steam temperature and the temperature difference capacity gain to obtain a releasable heat capacity. In this way, the accurate calculation of the storable heat capacity and the releasable heat capacity is realized.

Description

Technical Field

[0001] This invention relates to the field of thermal automation technology, specifically to an online calculation method for stimulating heat storage capacity by adjusting the desuperheating water flow rate in a power plant boiler. Background Technology

[0002] Currently, the "Implementation Plan for the Special Action to Upgrade New Generation Coal-fired Power Plants (2024-2027)" requires that, under operating conditions above 50% load, the load change rate of existing pulverized coal boilers should reach at least 2.2%Pe / min, and the load change rate of circulating fluidized bed boilers should reach at least 1.2%Pe / min. The main factor limiting the improvement of the load change rate of coal-fired power units is the large inertia and large delay characteristics of the pulverized coal boiler's pulverizing system or the coal feeding-combustion-heat transfer link of the circulating fluidized bed boiler. When the automatic power generation control commands from the power grid increase, the steam inlet regulating valve of the turbine high-pressure cylinder acts quickly, adjusting the steam inlet flow to make the unit's power generation rapidly follow the changes in automatic power generation control commands. However, due to the large inertia and large delay on the boiler side, its heat absorption and evaporation cannot keep up with the rapid changes in the steam inlet flow of the turbine. This leads to a rapid decrease in the steam pressure before the turbine, thus limiting the load change rate.

[0003] Existing technologies can fully utilize the heat storage at various stages of the power generation process as a buffer against the dynamic differences between turbine energy demand and boiler energy supply, thereby improving load response rate. The most common method is boiler steam-water heat storage, where changes in steam pressure lead to corresponding changes in the specific volume, specific enthalpy, and corresponding metal temperature of the heating surfaces of the steam and water working fluids. With a fixed total volume, this allows for the release / storage of some working fluid and energy, thus compensating for the difference between energy demand and supply during load changes. However, the heat storage capacity of the steam-water system can only support a load change rate of approximately 1.5% Pe / min for pulverized coal boilers and 1.0% Pe / min for circulating fluidized bed boilers. Further increasing the load rate will cause excessive deviations in the steam pressure before the turbine, exceeding operating limits.

[0004] However, boilers are equipped with desuperheating water for primary and secondary superheaters and reheaters. By adjusting the flow rate of the desuperheating water, the temperatures of the superheated steam and reheated steam can be controlled. Therefore, the temperature of these metal pipes can also be indirectly changed by the flow rate of the desuperheating water, thereby activating and utilizing this portion of heat storage, i.e., desuperheating water heat storage. However, the activation of heat storage by desuperheating water is constrained by various operating conditions of the coal-fired power unit, and its usable heat storage capacity is not stable and exhibits great randomness, making it impossible to accurately calculate the heat storage capacity of desuperheating water.

[0005] Therefore, in order to overcome the above-mentioned technical problems, the present invention provides an online calculation method for stimulating the thermal storage capacity of a power plant boiler by adjusting the desuperheating water flow. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to improve the accuracy of obtaining the heat storage capacity of desuperheating water. The purpose is to provide an online calculation method for adjusting the flow rate of desuperheating water in a power plant boiler to stimulate the heat storage capacity, so as to improve the accuracy of obtaining the heat storage capacity of desuperheating water.

[0007] This invention is achieved through the following technical solution:

[0008] In a first aspect, an online calculation method for stimulating heat storage capacity by adjusting the desuperheating water flow rate in a power plant boiler is provided. This method involves obtaining the advanced compensation steam temperature, desuperheating water gain, pulse amplitude gain, and steam power coefficient. The advanced compensation steam temperature is the steam temperature after advanced compensation of the pipe outlet steam temperature. When the desuperheating water is superheater desuperheating water, the pipe outlet steam temperature is the outlet steam temperature of the first-stage superheater pipe. When the desuperheating water is reheater desuperheating water, the pipe outlet steam temperature is the outlet steam temperature of the first-stage reheater pipe. A first small temperature difference correction steam temperature is obtained between a preset upper limit steam temperature and the advanced compensation steam temperature. A second small temperature difference correction steam temperature is obtained between the advanced compensation steam temperature and a preset lower limit steam temperature. A temperature difference capacity gain is obtained based on the desuperheating water gain, the pulse amplitude gain, and the steam power coefficient. The product of the first small temperature difference correction steam temperature and the temperature difference capacity gain is calculated to obtain the storable heat storage capacity. The product of the second small temperature difference correction steam temperature and the temperature difference capacity gain is calculated to obtain the releasable heat storage capacity.

[0009] In some embodiments, the advanced compensation steam temperature is obtained by: obtaining the lag time corresponding to the desuperheating water and the steam temperature at the pipeline outlet; filtering the steam temperature at the pipeline outlet using the lag time to obtain the filtered steam temperature at the pipeline outlet; obtaining the difference between the steam temperature at the pipeline outlet and the filtered steam temperature at the pipeline outlet to obtain an advanced compensation value; limiting the amplitude of the advanced compensation value to obtain an advanced compensation limit value; and summing the advanced compensation limit value with the steam temperature at the pipeline outlet to obtain the advanced compensation steam temperature.

[0010] In some embodiments, the desuperheating water gain is obtained by: obtaining the pipe heat absorption gain and the desuperheater gain; when the desuperheating water is superheater desuperheating water, the pipe heat absorption gain is the heat absorption gain of the pipe of the first-stage superheater; when the desuperheating water is reheater desuperheating water, the pipe heat absorption gain is the heat absorption gain of the pipe of the first-stage reheater; multiplying the pipe heat absorption gain by the desuperheater gain to obtain the desuperheating water gain.

[0011] In some embodiments, the heat absorption gain of the pipeline is obtained by: acquiring the measured steam temperature at the desuperheater outlet, the steam temperature at the pipeline outlet, and the steam pressure; calculating the difference between the measured steam temperature at the desuperheater outlet and a preset small temperature difference threshold to obtain a first small temperature difference correction value corresponding to the measured steam temperature at the desuperheater outlet; calculating the difference between the steam temperature at the pipeline outlet and the preset small temperature difference threshold to obtain a second small temperature difference correction value corresponding to the steam temperature at the pipeline outlet; obtaining the measured specific enthalpy of the steam at the desuperheater outlet based on the steam pressure and the measured steam temperature at the desuperheater outlet; and obtaining the relative specific enthalpy of the measured steam temperature at the desuperheater outlet based on the steam pressure and the first small temperature difference correction value. The method involves: obtaining the first corrected steam measurement enthalpy; obtaining the pipe outlet steam measurement enthalpy based on the steam pressure and the pipe outlet steam temperature; obtaining the second corrected steam measurement enthalpy corresponding to the pipe outlet steam temperature based on the steam pressure and the second small temperature difference correction value; calculating the difference between the desuperheater outlet steam measurement enthalpy and the first corrected steam measurement enthalpy to obtain the desuperheater outlet enthalpy difference; calculating the difference between the pipe outlet steam measurement enthalpy and the second corrected steam measurement enthalpy to obtain the pipe outlet enthalpy difference; and calculating the ratio between the desuperheater outlet enthalpy difference and the pipe outlet enthalpy difference to obtain the pipe heat absorption gain.

[0012] In some embodiments, the desuperheater gain is obtained by: obtaining the desuperheater outlet calculated specific enthalpy, the desuperheater outlet small temperature difference calculated specific enthalpy, steam pressure, and steam flow rate; obtaining the desuperheater outlet calculated temperature based on the desuperheater outlet calculated specific enthalpy and the steam pressure; obtaining the desuperheater outlet small deviation temperature based on the desuperheater outlet small temperature difference calculated specific enthalpy and the steam pressure; calculating the difference between the desuperheater outlet calculated temperature and the desuperheater outlet small deviation temperature to obtain the desuperheater calculated temperature difference; calculating the product of the steam flow rate and a preset flow rate unit coefficient to obtain the standard steam flow rate; and calculating the ratio between the desuperheater calculated temperature difference and the standard steam flow rate to obtain the desuperheater gain.

[0013] In some embodiments, the calculated specific enthalpy at the desuperheater outlet is obtained by: obtaining the desuperheater inlet steam temperature, desuperheating water flow rate, desuperheating water temperature, and desuperheating water pressure; obtaining the total enthalpy of the desuperheater inlet steam based on the desuperheater inlet steam temperature, the steam pressure, and the steam flow rate; calculating the sum of the steam flow rate and the desuperheating water flow rate to obtain the total flow rate; obtaining the total enthalpy of the desuperheating water based on the desuperheating water flow rate, the desuperheating water temperature, and the desuperheating water pressure; and obtaining the calculated specific enthalpy at the desuperheater outlet based on the total enthalpy of the desuperheater inlet steam, the total flow rate, and the total enthalpy of the desuperheating water.

[0014] In some embodiments, the specific enthalpy for calculating the small temperature difference at the desuperheater outlet is obtained by: obtaining the desuperheater inlet steam temperature, desuperheating water flow rate, steam flow rate, desuperheating water temperature, and desuperheating water pressure; obtaining the total enthalpy of the desuperheater inlet steam based on the desuperheater inlet steam temperature, the steam pressure, and the steam flow rate; and obtaining the specific enthalpy of the desuperheating water based on the desuperheating water temperature and desuperheating water pressure.

[0015] The product of the steam flow rate and the preset desuperheating water small deviation flow coefficient is used to obtain the desuperheating water small deviation flow rate.

[0016] The corrected desuperheating water flow rate is obtained based on the small deviation flow rate of the desuperheating water and the flow rate of the desuperheating water.

[0017] The corrected total enthalpy of the desuperheating water is obtained based on the corrected desuperheating water flow rate and the specific enthalpy of the desuperheating water;

[0018] The total outlet flow of the desuperheater is obtained based on the corrected desuperheating water flow and steam flow.

[0019] The specific enthalpy at the desuperheater outlet is calculated based on the total enthalpy of the steam at the desuperheater inlet, the total flow rate at the desuperheater outlet, and the corrected total enthalpy of the desuperheating water.

[0020] In some embodiments, the pulse amplitude gain is obtained by: obtaining the rated load object order inertia product, the rated main steam flow rate, and the boiler main steam flow rate corresponding to the desuperheating water; obtaining the ratio between the rated main steam flow rate and the boiler main steam flow rate; multiplying the ratio between the rated main steam flow rate and the boiler main steam flow rate by the rated load object order inertia product to obtain the actual load order inertia product; and determining the pulse amplitude gain by multiplying the actual load order inertia product by a preset pulse gain coefficient.

[0021] In some embodiments, the lag time is obtained by: obtaining the rated load object order inertia product, the rated main steam flow rate, and the boiler main steam flow rate corresponding to the desuperheating water; obtaining the ratio between the rated main steam flow rate and the boiler main steam flow rate; multiplying the ratio between the rated main steam flow rate and the boiler main steam flow rate by the rated load object order inertia product to obtain the actual load order inertia product; and determining the lag time by multiplying the actual load order inertia product by a preset delay time coefficient.

[0022] In some embodiments, the steam power coefficient is obtained by: obtaining the unit type corresponding to the power plant boiler; and obtaining the steam power coefficient based on the unit type.

[0023] Compared with the prior art, this invention utilizes the rapid steam pressure transmission speed and the huge thermal inertia in the pipes of the boiler superheater or reheater to instantly and dynamically adjust the flow rate of the primary superheating desuperheating water or the primary reheating desuperheating water. It can also utilize the heat storage of the pipe metal to quickly change the steam pressure without significantly affecting the outlet steam, thereby reducing the pressure deviation during the rapid load change of the boiler. By obtaining the first small temperature difference correction steam temperature between the preset upper limit of steam temperature and the advanced compensation steam temperature, and the second small temperature difference correction steam temperature between the advanced compensation steam temperature and the preset lower limit of steam temperature, the temperature difference capacity gain is obtained based on the desuperheating water gain, pulse amplitude gain, and steam power coefficient. Then, the product of the first small temperature difference correction steam temperature and the temperature difference capacity gain is calculated to obtain the storable heat capacity. The product of the second small temperature difference correction steam temperature and the temperature difference capacity gain is calculated to obtain the releasable heat storage capacity. This method enables the accurate calculation of the storable heat capacity and releasable heat storage capacity by instantaneous changes in the desuperheating water flow rate, provided that the outlet steam temperature does not exceed the equipment safety upper limit corresponding to the upper limit of steam temperature and the equipment safety lower limit corresponding to the lower limit of steam temperature. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0025] Figure 1 This is an environmental schematic diagram provided by an embodiment of the present disclosure;

[0026] Figure 2 This is a flowchart illustrating an online calculation method for stimulating thermal storage capacity by adjusting the desuperheating water flow rate in a power plant boiler, as provided in an embodiment of this disclosure.

[0027] Figure 3 This is a response characteristic curve of a pulse input signal and output signal corresponding to a fifth-order inertial object provided in an embodiment of this disclosure;

[0028] Figure 4 This is a schematic diagram of an electronic device provided in an embodiment of this disclosure. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0030] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0031] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0032] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0033] In this application, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0034] It should be noted that subcritical, supercritical, and ultra-supercritical single-stage reheat coal-fired power generating units employ a two-stage superheating and desuperheating system with a single-stage reheating system. Ultra-supercritical double-stage reheat units also include a secondary reheater. Since the second-stage superheating desuperheating water directly controls the superheated steam temperature, and its corresponding high-temperature superheater has relatively small heat storage capacity, it is not suitable to use desuperheating water to initiate heat storage. Furthermore, the secondary reheat steam temperature is difficult to control, and adjusting the steam temperature through secondary reheating desuperheating water would significantly reduce boiler efficiency; therefore, it is also unsuitable to use desuperheating water to initiate heat storage.

[0035] Therefore, the calculation method for heat storage induced by desuperheating water in this application is applicable to desuperheating water in superheaters with primary superheating and desuperheating water in reheaters with primary reheating.

[0036] In addition, the following conditions shall also be met: under normal conditions, there are no over-temperature points on the metal tube walls of the platen superheater and high-temperature superheater of the boiler, and there are no over-temperature points on the metal tube walls of the low-temperature reheater and high-temperature reheater; the primary superheat desuperheating water regulating valve, secondary superheat desuperheating water regulating valve, and reheat desuperheating water regulating valve of the boiler are all put into automatic control, and the performance of the control system meets the requirements for normal operation; the flow rate of primary superheat desuperheating water is within 30% to 70% of the rated flow rate, and it has two-way regulating capability.

[0037] It should be noted that for various types of boilers matched with coal-fired power generating units, in each boiler, the structure of the steam spray desuperheating system for utility boilers corresponding to the superheater desuperheating water and the reheater desuperheating water is the same.

[0038] Please refer to Figure 1 , Figure 1 is an environment schematic diagram shown according to an exemplary embodiment of the present application.

[0039] As shown in Figure 1 , the environment schematic diagram includes a steam spray desuperheating system of a utility boiler. The steam spray desuperheating system of the utility boiler comprises a desuperheating water flow regulating valve 101, a spray desuperheater 102 and a pipeline 103.

[0040] The steam spray desuperheating system of the utility boiler can be for a reheater or a superheater.

[0041] In the steam spray desuperheating system of the utility boiler, the desuperheating water flow regulating valve 101 is configured to regulate the flow rate of desuperheating water sprayed into the spray desuperheater; the spray desuperheater 102 is configured to use the desuperheating water to cool the steam flowing through it. The pipeline 103 is configured to allow the steam output from the spray desuperheater 102 to absorb heat generated by fuel combustion.

[0042] The pipeline 103 is a superheater heating surface pipeline or a reheater heating surface pipeline, which is a metal pipeline. In some embodiments, for a superheater, the desuperheating water is superheater desuperheating water, and the pipeline 103 is a superheater heating surface pipeline; for a reheater, the desuperheating water is reheater desuperheating water, and the pipeline 103 is a reheater heating surface pipeline.

[0043] The pipeline outlet is the outlet of the pipeline of the superheater or the reheater.

[0044] It should be noted that after the flow rate of desuperheating water is regulated by the desuperheating water flow regulating valve 101, it is sprayed in from the spray desuperheater 102 to cool the steam flowing through the spray desuperheater 102, and the steam cooled by the desuperheating water enters the pipeline 103 to absorb the heat generated by fuel combustion and then flows out from the outlet of the pipeline.

[0045] In the steam spray desuperheating system of a power plant boiler, the principle of heat storage induced by desuperheating water is as follows: whether it is superheater desuperheating water or reheater desuperheating water, the steam entering the spray desuperheater 102 has a high degree of superheat. Since the pipe 103 is a metal pipe, the pipe 103 also has a certain amount of heat storage. Therefore, after the desuperheating water is sprayed in, it will be heated and vaporized immediately, expand in volume, and push the downstream steam to enter the turbine together to do work.

[0046] Under transient operating conditions, the effect of injecting desuperheating water to increase steam flow is equivalent to increasing the steam flow generated by the same amount of water absorbing the heat produced by the combustion of boiler fuel. The steam temperature signal at the outlet of pipe 103 exhibits high-order inertia and large delay characteristics in response to changes in desuperheating water flow. This means that the steam flow signal changes immediately after the desuperheating water is injected, while the steam temperature signal does not change immediately; that is, energy changes rapidly while temperature changes slowly. Therefore, when the desuperheating water flow changes in the form of a single pulse, due to the filtering effect of high-order inertia, the unit's power generation can be changed instantaneously without significantly affecting the steam temperature. Therefore, essentially, desuperheating water-induced heat storage utilizes the dynamic time difference between the boiler's energy response and the steam temperature response after the desuperheating water is injected.

[0047] Please see Figure 2 , Figure 2 This is a schematic flowchart illustrating an exemplary embodiment of the present application of an online calculation method for adjusting the desuperheating water flow rate to activate the thermal storage capacity of a power plant boiler. It should be noted that desuperheating water is injected into a water-spray desuperheater to cool and vaporize the steam flowing through it. The steam output from the water-spray desuperheater enters a pipeline, absorbs heat, and then flows out from the pipeline outlet. The steam output from the water-spray desuperheater consists of both cooled steam and steam vaporized by the desuperheating water.

[0048] like Figure 2 As shown in the embodiments of this disclosure, an online calculation method for activating thermal storage capacity by adjusting the desuperheating water flow rate in a power plant boiler is provided. The method includes:

[0049] Step S201: Obtain the advanced compensation steam temperature, desuperheating water gain, pulse amplitude gain, and steam power coefficient; the advanced compensation steam temperature is the steam temperature after advanced compensation of the pipeline outlet steam temperature; when the desuperheating water is superheater desuperheating water, the pipeline outlet steam temperature is the outlet steam temperature of the first-stage superheater pipeline; when the desuperheating water is reheater desuperheating water, the pipeline outlet steam temperature is the outlet steam temperature of the first-stage reheater pipeline.

[0050] Step S202: Obtain the first small temperature difference correction steam temperature between the preset upper limit of steam temperature and the advanced compensation steam temperature; obtain the second small temperature difference correction steam temperature between the advanced compensation steam temperature and the preset lower limit of steam temperature.

[0051] Step S203: Obtain the temperature difference capacity gain based on the desuperheating water gain, pulse amplitude gain, and steam power coefficient.

[0052] Step S204: Calculate the product of the first small temperature difference correction steam temperature and the temperature difference capacity gain to obtain the storable heat capacity.

[0053] Step S205: Calculate the product of the second small temperature difference corrected steam temperature and the temperature difference capacity gain to obtain the releasable heat storage capacity.

[0054] In this embodiment, due to the fast steam pressure transmission speed and the huge thermal inertia in the pipes of the boiler superheater or reheater, the flow rate of the first-stage superheating desuperheating water or the first-stage reheating desuperheating water can be adjusted instantaneously and dynamically. This feature allows for rapid changes in steam pressure by utilizing the heat storage of the pipe metal without significantly affecting the outlet steam, thereby reducing the pressure deviation during the rapid load change process of the boiler. By obtaining the first small temperature difference correction steam temperature between the preset upper limit of steam temperature and the advanced compensation steam temperature, and the second small temperature difference correction steam temperature between the advanced compensation steam temperature and the preset lower limit of steam temperature, the temperature difference capacity gain is obtained based on the desuperheating water gain, pulse amplitude gain, and steam power coefficient. Then, the product of the first small temperature difference correction steam temperature and the temperature difference capacity gain is calculated to obtain the storable heat capacity. The product of the second small temperature difference correction steam temperature and the temperature difference capacity gain is calculated to obtain the releasable heat storage capacity. This method enables the accurate calculation of the storable heat capacity and releasable heat storage capacity by instantaneous changes in the desuperheating water flow rate, provided that the outlet steam temperature does not exceed the equipment safety upper limit corresponding to the upper limit of steam temperature and the equipment safety lower limit corresponding to the lower limit of steam temperature.

[0055] Furthermore, in step S201, the advanced compensation steam temperature is obtained as follows: the lag time corresponding to the desuperheating water and the steam temperature at the pipeline outlet are obtained; the lag time is used to filter the steam temperature at the pipeline outlet to obtain the filtered steam temperature at the pipeline outlet; the difference between the steam temperature at the pipeline outlet and the filtered steam temperature at the pipeline outlet is obtained to obtain the advanced compensation value; the amplitude of the advanced compensation value is limited to obtain the advanced compensation limit value; the advanced compensation limit value is summed with the steam temperature at the pipeline outlet to obtain the advanced compensation steam temperature.

[0056] In this way, by using the lag time as the inertial filtering time to filter the pipeline outlet steam temperature, high-frequency noise and rapid fluctuations are eliminated. The filtered pipeline outlet steam temperature, which characterizes the changing trend of the pipeline outlet steam temperature within the lag time period, is extracted. Then, the difference between the pipeline outlet steam temperature and the filtered pipeline outlet steam temperature is obtained, yielding a lead compensation value characterizing the rate of temperature change. The magnitude of the lead compensation value is then limited, and the limited lead compensation value is used to compensate for the pipeline outlet steam temperature, resulting in a lead compensation steam temperature. This lead compensation steam temperature is a predicted steam temperature at the pipeline outlet, essentially constructing a temperature prediction mechanism within the controller to offset the physical lag caused by pipeline transmission. This effectively reduces the control lag problem of large lag systems, thereby improving the accuracy of the heat storage capacity calculation based on the lead compensation steam temperature.

[0057] It should be noted that the pipeline outlet steam temperature is filtered by using the lag time to obtain the filtered pipeline outlet steam temperature. That is, the lag time is determined as the inertial filtering time, and then the pipeline outlet steam temperature is controlled to be filtered by the first-order inertial element corresponding to the inertial filtering time to obtain the filtered pipeline outlet steam temperature.

[0058] It should be noted that the advance compensation value is subject to a range limit to obtain the advance compensation limit value. That is, if the advance compensation value is greater than the preset compensation upper limit, the compensation upper limit is determined as the advance compensation limit value; if the advance compensation value is less than the preset compensation lower limit, the compensation lower limit is determined as the advance compensation limit value; if the advance compensation value is less than or equal to the preset compensation upper limit and greater than or equal to the compensation lower limit, the advance compensation value is determined as the advance compensation limit value.

[0059] Furthermore, the advanced compensation steam temperature is obtained by summing the advanced compensation limit value and the pipeline outlet steam temperature. This involves adding the advanced compensation limit value and the pipeline outlet steam temperature together. The sum of these two values ​​is then determined as the advanced compensation steam temperature.

[0060] Furthermore, the lag time is obtained as follows: obtain the order inertia product of the rated load object corresponding to the desuperheating water, the rated flow rate of the main steam, and the main steam flow rate of the boiler; obtain the ratio between the rated flow rate of the main steam and the main steam flow rate of the boiler; multiply the ratio between the rated flow rate of the main steam and the main steam flow rate of the boiler by the order inertia product of the rated load object to obtain the actual load order inertia product; and determine the lag time by multiplying the actual load order inertia product by the preset delay time coefficient.

[0061] In this way, by multiplying the ratio between the rated main steam flow rate and the boiler main steam flow rate by the order inertia product of the rated load object, the actual load order inertia product is obtained. This realizes the correction of the rated load object order inertia product using the ratio between the rated main steam flow rate and the boiler main steam flow rate to obtain the actual load order inertia product. Then, the product of the actual load order inertia product and the preset delay time coefficient is determined as the lag time. This adapts to the inherent characteristic that the lower the load of the desuperheating water and the steam temperature object, the greater the lag. It reduces the problem of mismatch in all operating conditions caused by the use of a fixed lag time in the existing technology, accurately matches the delay law of steam temperature dynamics, improves the accuracy of steam temperature advance compensation, and thus improves the accuracy of online calculation of desuperheating water heat storage capacity and adaptability to all operating conditions.

[0062] It should be noted that the preset delay time coefficient is... .

[0063] It should be noted that the response of desuperheating water flow rate to steam temperature changes exhibits high-order inertial characteristics. Based on this, the dynamic response characteristics of steam temperature under desuperheating water disturbance can be analyzed. The controlled object of the desuperheating water is a high-order inertial object, and high-order inertial objects have a significant filtering effect.

[0064] In some embodiments, for satisfying A fifth-order inertial object. Among them, Let be the transfer function of a fifth-order inertial object; s is a complex variable with Laplace transform.

[0065] The output response of the fifth-order inertial object under different pulse input signals is as follows: Figure 3 As shown, Figure 3 The response characteristic curves of the pulse input signal and output signal corresponding to the fifth-order inertial object are shown.

[0066] like Figure 3 As shown, Figure 3 The graph above shows the pulse input signal curve corresponding to a fifth-order inertial object; Figure 3 The graph below shows the output curves for a fifth-order inertial object. Input and output signals of the same color correspond to each other.

[0067] pass Figure 3 It can be seen that for the red curve, when the pulse amplitude of the input signal for the fifth-order inertial object is 2 and the pulse duration is 20s, the maximum amplitude of the corresponding output signal is 0.156, and the lag time from the center point of the input pulse signal to the point of maximum output amplitude is 200s.

[0068] For the green curve, when the pulse amplitude of the input signal for the fifth-order inertial object is 1 and the pulse duration is 40s, the maximum amplitude of the corresponding output signal is 0.156, and the lag time from the center point of the input pulse signal to the point of maximum output amplitude is 200s.

[0069] For the black curve, when the pulse amplitude of the input signal for the fifth-order inertial object is 0.5 and the pulse duration is 80s, the maximum amplitude of the corresponding output signal is 0.153, and the lag time from the center point of the input pulse signal to the point of maximum output amplitude is 202s.

[0070] It can be seen that although the pulse amplitudes of the signals are different, as long as the product of the pulse amplitude and the pulse duration of the input signal is the same, the maximum change amplitude of the output signal and the lag time from the center point of the input pulse signal to the point of maximum output amplitude can also be regarded as the same.

[0071] Based on extensive experimental fitting, it can be determined that for a high-order inertial object with unity gain, the order of the high-order inertial object... And is the pulse duration of the input signal. In this case, the peak amplitude of its corresponding output signal ;in, This represents the peak amplitude of the output signal corresponding to a higher-order inertial object. The integral of the input signal pulse; For higher-order inertial objects; The fundamental inertial time for a higher-order inertial object; The pulse duration of the input signal; The first coefficient obtained from the fitting is the pulse gain coefficient. The time lag between the center point of the input pulse signal and the point of maximum output amplitude is the delay time of the output signal pulse peak. ;in, The delay time of the peak value of the output signal pulse; The second coefficient obtained from the fitting is the delay time coefficient.

[0072] It should be noted that the actual desuperheating water systems on-site often employ automatic control schemes such as cascaded PID (Proportional-Integral-Derivative Controller) and predictive control. This is limited by the characteristics of the controlled object and combined with... Figure 3The analysis results show that, under normal operating conditions of the control system, even if the control schemes differ and the waveforms of the controller output (i.e., the desuperheating water flow rate signal) vary, the changing trends of the regulated quantity (i.e., the steam temperature signal at the outlet of the first-stage superheater or the first-stage reheater) will be very similar under the high-order inertial filtering effect of the controlled object. Thus, whether in open-loop or closed-loop mode, under the action of the desuperheating water flow rate signal in an approximately single-pulse form, the maximum amplitude and lag time of the steam temperature signal fluctuation are only proportional to the product of the amplitude and duration of the pulse signal, i.e., only proportional to the integral of the desuperheating water flow rate signal pulse, which is the desuperheating water quality signal.

[0073] For desuperheating water, the product of its corresponding order and fundamental inertia time increases as the boiler load decreases. Therefore, it satisfies... ;in, The rated flow rate of the main steam is the rated load main steam flow rate of the boiler. This represents the main steam flow rate of the boiler, which is the actual main steam flow rate of the boiler. The order of the steam temperature signal at the outlet of the primary superheater or the outlet of the primary reheater at the preset rated load. The basic inertia time of the steam-temperature object under rated load. The product of inertia of the rated load object.

[0074] Based on the above, through calculation Can obtain This refers to the actual load order inertia product, which is the product of the boiler's order under actual load and the fundamental inertia time; it is calculated... The product of the actual load order inertia product and the preset pulse gain coefficient is obtained, and this product is determined as the pulse amplitude gain; through calculation... The product of the actual load order inertia product and the preset delay time coefficient is obtained, and this product is determined as the lag time.

[0075] It should be noted that obtaining and There are many methods, such as: directly calculating from boiler design parameters like pipe length, pipe wall thickness, and steam flow rate; back-calculating from the master PID parameters of the cascade PID control system; or identifying through on-site disturbance experiments. No restrictions are imposed here.

[0076] Furthermore, in step S201, the desuperheating water gain is obtained as follows: the pipe heat absorption gain and the desuperheater gain are obtained; when the desuperheating water is superheater desuperheating water, the pipe heat absorption gain is the heat absorption gain of the pipe of the first-stage superheater; when the desuperheating water is reheater desuperheating water, the pipe heat absorption gain is the heat absorption gain of the pipe of the first-stage reheater; the pipe heat absorption gain and the desuperheater gain are multiplied to obtain the desuperheating water gain.

[0077] It should be noted that the desuperheater gain reflects the desuperheater's cooling capacity for steam. The pipe heat absorption gain reflects the environment's ability to heat the steam.

[0078] In this way, since the desuperheater gain reflects the desuperheater's cooling capacity for steam, and the pipe heat absorption gain reflects the environment's heating capacity for steam, the two are multiplied to obtain the desuperheating water gain. This achieves separate modeling and combination of the desuperheater cooling process and the pipe heat absorption process, closely matching the actual physical process of boiler steam desuperheating and heat absorption. It also enables precise quantification of the gain of the desuperheating water's influence on the outlet steam temperature of the pipe, improving the accuracy of obtaining the desuperheating water gain.

[0079] Furthermore, the heat absorption gain of the pipeline is obtained as follows: The measured steam temperature at the desuperheater outlet, the steam temperature at the pipeline outlet, and the steam pressure are obtained; the difference between the measured steam temperature at the desuperheater outlet and a preset small temperature difference threshold is calculated to obtain the first small temperature difference correction value corresponding to the measured steam temperature at the desuperheater outlet; the difference between the steam temperature at the pipeline outlet and the preset small temperature difference threshold is calculated to obtain the second small temperature difference correction value corresponding to the steam temperature at the pipeline outlet; the measured specific enthalpy of the steam at the desuperheater outlet is obtained based on the steam pressure and the measured steam temperature at the desuperheater outlet; the gain relative to the measured steam temperature at the desuperheater outlet is obtained based on the steam pressure and the first small temperature difference correction value. The following steps are performed: First, obtain the first corrected steam measurement enthalpy; second, obtain the pipe outlet steam measurement enthalpy based on steam pressure and pipe outlet steam temperature; third, obtain the second corrected steam measurement enthalpy corresponding to the pipe outlet steam temperature based on steam pressure and the second minimum temperature difference correction value; fourth, calculate the difference between the desuperheater outlet steam measurement enthalpy and the first corrected steam measurement enthalpy to obtain the desuperheater outlet enthalpy difference; fifth, calculate the difference between the pipe outlet steam measurement enthalpy and the second corrected steam measurement enthalpy to obtain the pipe outlet enthalpy difference; sixth, calculate the ratio between the desuperheater outlet enthalpy difference and the pipe outlet enthalpy difference to obtain the pipe heat absorption gain.

[0080] Thus, by acquiring the first small temperature difference correction value between the measured steam temperature at the desuperheater outlet and the preset small temperature difference threshold, and the second small temperature difference correction value between the steam temperature at the pipeline outlet and the preset small temperature difference threshold, the enthalpy of the steam measured at the desuperheater outlet is obtained based on the steam pressure and the measured steam temperature at the desuperheater outlet; the first corrected enthalpy of the steam measured at the desuperheater outlet is obtained based on the steam pressure and the first small temperature difference correction value; the enthalpy of the steam measured at the pipeline outlet is obtained based on the steam pressure and the steam temperature at the pipeline outlet; and the enthalpy of the steam measured at the pipeline outlet is obtained based on the steam pressure and the second small temperature difference correction value. Take the second corrected steam measurement specific enthalpy corresponding to the steam temperature at the pipeline outlet; calculate the difference between the steam measurement specific enthalpy at the desuperheater outlet and the first corrected steam measurement specific enthalpy corresponding to the steam temperature at the desuperheater outlet to obtain the desuperheater outlet specific enthalpy difference; calculate the difference between the steam measurement specific enthalpy at the pipeline outlet and the second corrected steam measurement specific enthalpy corresponding to the steam temperature at the pipeline outlet to obtain the pipeline outlet specific enthalpy difference; calculate the ratio between the desuperheater outlet specific enthalpy difference and the pipeline outlet specific enthalpy difference to obtain an accurate calculation of the pipeline heat absorption gain that reflects the heating capacity of the environment for steam.

[0081] Meanwhile, a small temperature difference threshold was introduced to determine two temperature difference corrections, namely the first small temperature difference correction value and the second small temperature difference correction value. Then, the steam specific enthalpy corresponding to each temperature condition was obtained by combining the same steam pressure. Then, by calculating the difference in steam specific enthalpy changes on the desuperheater side and the pipe outlet side and performing ratio calculation, the steam temperature change was converted into an enthalpy energy change to characterize the pipe's heat absorption amplification capability. This reduced the direct temperature change ratio error caused by steam thermodynamic nonlinearity and accurately quantified the heat absorption and temperature transfer gain from the desuperheater outlet to the pipe outlet, i.e., the pipe heat absorption gain. This is consistent with the actual heat transfer characteristics of the boiler and provides more accurate and reliable parameters for the synthesis of desuperheating water gain and subsequent precise online calculation of heat storage capacity.

[0082] It should be noted that the steam temperature measured at the desuperheater outlet is the steam temperature measured at the desuperheater outlet.

[0083] In some embodiments, the preset minimum temperature difference threshold is 3 degrees Celsius. Other values ​​may also be set, and are not limited here.

[0084] It should be noted that the measured specific enthalpy of the steam at the desuperheater outlet is obtained based on the steam pressure and the measured steam temperature at the desuperheater outlet, i.e., by calculation. The specific enthalpy of the steam at the desuperheater outlet was obtained. Specific enthalpy of steam at the desuperheater outlet; Measure the steam temperature at the desuperheater outlet; It is the steam pressure; This is a function used to calculate the specific enthalpy of water and steam using their thermodynamic properties. It should be noted that... It is a function used in the IAPWS IF97 formula, which characterizes the thermodynamic properties of water and steam, to calculate the specific enthalpy of water and steam. It is an internationally recognized formula and will not be elaborated upon here.

[0085] Furthermore, based on the steam pressure and the first small temperature difference correction value, the first corrected steam measurement enthalpy corresponding to the measured steam temperature at the desuperheater outlet is obtained, including: by calculating... The first corrected steam measurement enthalpy corresponding to the measured steam temperature at the desuperheater outlet is obtained; whereby, The first corrected steam measurement specific enthalpy corresponding to the measured steam temperature at the desuperheater outlet; This is the first small temperature difference correction value; This is the threshold for small temperature differences.

[0086] Furthermore, the enthalpy of the steam at the pipeline outlet is obtained based on the steam pressure and the steam temperature at the pipeline outlet, including: by calculation The specific enthalpy of the steam at the pipeline outlet was obtained. Specific enthalpy of steam at pipeline outlet; This refers to the steam temperature at the pipeline outlet.

[0087] Furthermore, based on the steam pressure and the second minimum temperature difference correction value, the second corrected steam measurement enthalpy corresponding to the pipeline outlet steam temperature is obtained, including: by calculating... The second corrected steam measurement enthalpy corresponding to the pipeline outlet steam temperature is obtained. Specific enthalpy of steam at pipeline outlet; This is the second smallest temperature difference correction value.

[0088] It should be noted that due to the nonlinear thermodynamic properties of water and steam, the temperature change at the desuperheater outlet is not the same as the temperature change at the pipe outlet. The pipe heat absorption gain is the gain between the measured temperature change at the desuperheater outlet and the change in the pipe outlet temperature, reflecting the environment's heating capacity for the steam. In some embodiments, the pipe heat absorption gain can be directly calculated using the formula... Obtained. Among them, This is the gain from heat absorption in the pipeline.

[0089] In some embodiments, the heat absorption gain of the pipeline, i.e., the gain of the temperature change of the measured steam temperature at the desuperheater outlet to the change of the steam temperature at the pipeline outlet, can be directly calculated using the formula. Obtained. Among them, This is the gain from heat absorption in the pipeline.

[0090] Then the gain of the desuperheated water It represents the gain of the change in desuperheating water flow rate on the change in steam temperature at the pipe outlet.

[0091] Furthermore, the desuperheater gain is obtained as follows: The calculated specific enthalpy at the desuperheater outlet, the calculated specific enthalpy at the small temperature difference at the desuperheater outlet, the steam pressure, and the steam flow rate are obtained; the calculated temperature at the desuperheater outlet is obtained based on the calculated specific enthalpy at the desuperheater outlet and the steam pressure; the small deviation temperature at the desuperheater outlet is obtained based on the calculated specific enthalpy at the small temperature difference at the desuperheater outlet and the steam pressure; the difference between the calculated temperature at the desuperheater outlet and the small deviation temperature at the desuperheater outlet is calculated to obtain the calculated temperature difference of the desuperheater; the product of the steam flow rate and a preset flow rate unit coefficient is calculated to obtain the standard steam flow rate; and the ratio between the calculated temperature difference of the desuperheater and the standard steam flow rate is calculated to obtain the desuperheater gain.

[0092] In this way, the calculated specific enthalpy at the desuperheater outlet, steam pressure, and the calculated specific enthalpy at the small temperature difference at the desuperheater outlet are used to calculate the desuperheater outlet temperature and the small deviation temperature at the desuperheater outlet, respectively. Then, by calculating the difference between the calculated temperature at the desuperheater outlet and the small deviation temperature at the desuperheater outlet, the obtained calculated temperature difference of the desuperheater can reflect the temperature change response of the desuperheater. Then, a small disturbance of the desuperheating water flow rate is constructed by introducing a standard steam flow rate. The desuperheater gain is obtained by comparing the calculated temperature difference of the desuperheater with the standard steam flow rate that represents the disturbance. This reflects the amplitude of the change in steam temperature at the desuperheater outlet caused by a unit change in the desuperheating water flow rate, reduces the influence of steam thermodynamic nonlinearity and direct temperature measurement error, and quantifies the spray cooling capacity of the desuperheater from the perspective of energy balance and thermodynamic characteristics, thus realizing the accurate calculation of the desuperheater gain.

[0093] It should be noted that the steam flow rate refers to the steam flow rate at the inlet of the desuperheater.

[0094] Furthermore, the calculated temperature at the desuperheater outlet is obtained based on the calculated specific enthalpy and steam pressure at the desuperheater outlet, including: by calculating... The calculated outlet temperature of the desuperheater is obtained. Calculate the outlet temperature of the desuperheater; Calculate the specific enthalpy at the outlet of the desuperheater; This is a function used to calculate the temperature of water and steam using the thermodynamic properties of water and steam. It is the function used in the IAPWS IF97 formula for calculating the temperature of water and steam in engineering thermodynamics, which is an international characterization formula and will not be elaborated here.

[0095] Furthermore, the specific enthalpy and steam pressure are calculated based on the small temperature difference at the desuperheater outlet to obtain the small deviation temperature at the desuperheater outlet, including: by calculating... This yields the desuperheater outlet temperature with a small deviation. This refers to the small deviation temperature at the outlet of the desuperheater.

[0096] Furthermore, the difference between the desuperheater outlet calculated temperature and the desuperheater outlet small deviation temperature is calculated to obtain the desuperheater calculated temperature difference, including: by calculating... The temperature difference calculated by the desuperheater is obtained; among which, The temperature difference is calculated for the desuperheater, which is the change in the steam temperature at the desuperheater outlet.

[0097] It should be noted that the energy balance equation on the water spray desuperheater side is: ,in, Steam flow rate, in t / h; Enthalpy of the steam at the desuperheater inlet, in kJ / kg; ; This refers to the steam temperature at the inlet of the desuperheater, expressed in °C. This is the steam pressure, expressed in MPa. The flow rate of the cooling water is expressed in t / h. The specific enthalpy of desuperheated water is expressed in kJ / kg. ; The temperature of the cooling water is expressed in °C. The pressure of the cooling water is measured in MPa. The specific enthalpy at the desuperheater outlet is calculated, with units of kJ / kg. Its physical meaning is that the energy of the steam at the desuperheater inlet plus the energy of the desuperheating water equals the total energy at the desuperheater outlet.

[0098] Based on the above, the calculated specific enthalpy at the desuperheater outlet can be derived. Furthermore, the calculated outlet temperature of the desuperheater can be calculated using the specific enthalpy of steam and pressure, through formulas relating the thermodynamic properties of water and steam. .

[0099] Let the standard steam flow rate be the change in the desuperheating water flow rate. The value is 0.001 of the cooling water flow rate, but it can also be set to other values; there are no restrictions here.

[0100] When the flow rate of the desuperheating water changes, the specific enthalpy at the desuperheater outlet also changes. The amount of this change is the specific enthalpy calculated based on the small temperature difference at the desuperheater outlet. The steam temperature at the desuperheater outlet will also change; this changed steam temperature at the desuperheater outlet is the small deviation temperature at the desuperheater outlet. The change in desuperheater outlet steam temperature corresponding to the standard steam flow rate. Therefore, the gain of the depressurizer can be obtained. .

[0101] Furthermore, the calculated specific enthalpy at the desuperheater outlet is obtained as follows: The desuperheater inlet steam temperature, desuperheating water flow rate, desuperheating water temperature, and desuperheating water pressure are obtained; the total enthalpy of the desuperheater inlet steam is obtained based on the desuperheater inlet steam temperature, steam pressure, and steam flow rate; the sum of the steam flow rate and the desuperheating water flow rate is calculated to obtain the total flow rate; the total enthalpy of the desuperheating water is obtained based on the desuperheating water flow rate, desuperheating water temperature, and desuperheating water pressure; and the calculated specific enthalpy at the desuperheater outlet is obtained based on the total enthalpy of the desuperheater inlet steam, the total flow rate, and the total enthalpy of the desuperheating water.

[0102] In this way, the total enthalpy of the desuperheater inlet steam is obtained based on the desuperheater inlet steam temperature, steam pressure, and steam flow rate. Then, the total flow rate is obtained by calculating the sum of the steam flow rate and the desuperheating water flow rate. The total enthalpy of the desuperheating water is obtained based on the desuperheating water flow rate, desuperheating water temperature, and desuperheating water pressure. Finally, the calculated specific enthalpy of the desuperheater outlet is obtained based on the total enthalpy of the desuperheater inlet steam, the total flow rate, and the total enthalpy of the desuperheating water. This achieves the accurate calculation of the calculated specific enthalpy of the desuperheater outlet.

[0103] Furthermore, the total enthalpy of the desuperheater inlet steam is obtained based on the desuperheater inlet steam temperature, steam pressure, and steam flow rate, including: through calculation. The specific enthalpy of the desuperheater inlet steam is obtained; among which, Specific enthalpy of the steam at the desuperheater inlet; This refers to the steam temperature at the desuperheater inlet, i.e., the temperature of the steam at the desuperheater inlet. The steam pressure is given. The product of the specific enthalpy of the steam at the desuperheater inlet and the steam flow rate is determined as the total enthalpy of the steam at the desuperheater inlet.

[0104] Furthermore, the total enthalpy of the desuperheating water is obtained based on the desuperheating water flow rate, desuperheating water temperature, and desuperheating water pressure, including by calculation. To obtain the specific enthalpy of desuperheated water; among which, The specific enthalpy of the desuperheating water is the specific enthalpy of the steam at the inlet of the desuperheater. To reduce the temperature of the cooling water; To reduce the pressure of the desuperheating water, the product of the specific enthalpy of the desuperheating water and the flow rate of the desuperheating water is determined as the total enthalpy of the desuperheating water.

[0105] Furthermore, the calculated specific enthalpy at the desuperheater outlet is obtained based on the total enthalpy of the steam at the desuperheater inlet, the total flow rate, and the total enthalpy of the desuperheating water, including: through calculation The calculated specific enthalpy of the desuperheater outlet is obtained, which is the specific enthalpy of the steam at the desuperheater outlet; where, Calculate the specific enthalpy at the outlet of the desuperheater; The total enthalpy of the steam at the desuperheater inlet; Steam flow rate; To reduce the total enthalpy of the water; To reduce the flow rate of the heated water; This represents the total flow rate.

[0106] Furthermore, the specific enthalpy for calculating the small temperature difference at the desuperheater outlet is obtained as follows: The desuperheater inlet steam temperature, desuperheating water flow rate, steam flow rate, desuperheating water temperature, and desuperheating water pressure are obtained; the total enthalpy of the desuperheater inlet steam is obtained based on the desuperheater inlet steam temperature, steam pressure, and steam flow rate; the specific enthalpy of the desuperheating water is obtained based on the desuperheating water temperature and pressure; the small deviation flow rate of the desuperheating water is obtained by multiplying the steam flow rate by the preset small deviation flow rate coefficient of the desuperheating water; the corrected desuperheating water flow rate is obtained based on the small deviation flow rate and the desuperheating water flow rate; the corrected total enthalpy of the desuperheating water is obtained based on the corrected desuperheating water flow rate and the specific enthalpy of the desuperheating water; the total flow rate at the desuperheater outlet is obtained based on the corrected desuperheating water flow rate and the steam flow rate; and the specific enthalpy for calculating the small temperature difference at the desuperheater outlet is obtained based on the total enthalpy of the desuperheater inlet steam, the total flow rate at the desuperheater outlet, and the corrected total enthalpy of the desuperheating water.

[0107] In this way, the total enthalpy of the desuperheater inlet steam is obtained based on the inlet steam temperature, steam pressure, and steam flow rate. Then, the specific enthalpy of the desuperheating water is obtained based on the desuperheating water temperature and pressure. The product of the steam flow rate and the preset small deviation flow coefficient of the desuperheating water is calculated to obtain the small deviation flow rate of the desuperheating water. A small disturbance in the desuperheating water flow rate is introduced, and the corrected desuperheating water flow rate and the corrected total enthalpy of the desuperheating water are calculated based on this small disturbance. Thus, the specific enthalpy of the small temperature difference at the desuperheater outlet is obtained, simulating the deviation of the outlet enthalpy value caused by a small change in the desuperheating water flow rate. No actual on-site disturbance test is required. Under the condition of reducing the interference of operating condition fluctuations, it conforms to the actual mixing heat exchange characteristics of the desuperheater and realizes the accurate calculation of the specific enthalpy of the small temperature difference at the desuperheater outlet.

[0108] Furthermore, the specific enthalpy of the desuperheating water is obtained based on the temperature and pressure of the desuperheating water, including by calculation. , thus obtaining the specific enthalpy of the desuperheated water.

[0109] It should be noted that the preset desuperheating water small deviation flow coefficient can be 0.001.

[0110] It should be noted that the total outlet flow rate of the desuperheater is the sum of the corrected desuperheating water flow rate and the steam flow rate. The corrected desuperheating water flow rate is the sum of the small deviation desuperheating water flow rate and the desuperheating water flow rate.

[0111] Furthermore, the corrected total enthalpy of the desuperheating water is obtained based on the corrected desuperheating water flow rate and the specific enthalpy of the desuperheating water, including: by calculating... The corrected total enthalpy of the desuperheated water was obtained; among which, This is the corrected total enthalpy of the desuperheated water; The small deviation flow rate of the desuperheating water is the change in the flow rate of the desuperheating water. This is the corrected flow rate of the desuperheated water.

[0112] Furthermore, the calculated specific enthalpy of the small temperature difference at the desuperheater outlet is obtained based on the total enthalpy of the steam at the desuperheater inlet, the total flow rate at the desuperheater outlet, and the corrected total enthalpy of the desuperheating water. This includes: obtaining the sum of the total enthalpy of the steam at the desuperheater inlet and the corrected total enthalpy of the desuperheating water; and determining the ratio of this value to the total flow rate at the desuperheater outlet as the calculated specific enthalpy of the small temperature difference at the desuperheater outlet.

[0113] It should be noted that the calculated specific enthalpy of the desuperheater outlet at the small temperature difference has the following relationship with the calculated specific enthalpy of the desuperheater outlet: The specific enthalpy at the small temperature difference at the desuperheater outlet is calculated; among which, Calculate the specific enthalpy for a small temperature difference at the desuperheater outlet; This represents the change in specific enthalpy of the desuperheater outlet steam corresponding to the standard steam flow rate.

[0114] Furthermore, in step S201, the pulse amplitude gain is obtained as follows: the rated load object order inertia product, the rated main steam flow rate, and the boiler main steam flow rate corresponding to the desuperheating water are obtained; the ratio between the rated main steam flow rate and the boiler main steam flow rate is obtained; the ratio between the rated main steam flow rate and the boiler main steam flow rate is multiplied by the rated load object order inertia product to obtain the actual load order inertia product; the product of the actual load order inertia product and the preset pulse gain coefficient is determined as the pulse amplitude gain.

[0115] In this way, by multiplying the ratio between the rated main steam flow rate and the boiler main steam flow rate by the rated load object order inertia product, the actual load order inertia product is obtained. This realizes the use of the ratio between the rated main steam flow rate and the boiler main steam flow rate to correct the rated load object order inertia product to obtain the actual load order inertia product. Then, the product of the actual load order inertia product and the preset pulse gain coefficient is determined as the pulse amplitude gain. This reduces the problem of mismatch in all operating conditions caused by the use of a fixed pulse amplitude gain in the prior art. It enables the pulse amplitude gain to accurately characterize the amplitude characteristics of the steam temperature response under the pulse disturbance of the desuperheating water, thereby improving the accuracy of online calculation of the desuperheating water heat storage capacity and the adaptability to all operating conditions.

[0116] Based on the foregoing, the preset pulse gain coefficient can be 1.026.

[0117] Furthermore, in step S201, the steam power coefficient is obtained as follows: the unit type corresponding to the power plant boiler is obtained; the steam power coefficient is obtained based on the unit type.

[0118] In this way, by obtaining the unit type corresponding to the power plant boiler and then obtaining the steam power coefficient based on the unit type, it is possible to match the differences in the work capacity per unit flow of superheated steam and reheat steam in different unit types, avoid the calculation deviation caused by uniform coefficients, and thus improve the accuracy and adaptability of online calculation of desuperheating water heat storage capacity under all operating conditions.

[0119] Optionally, the steam power coefficient is obtained based on the unit type, including: for superheater desuperheating water, performing a search operation in a preset superheated steam coefficient database using the unit type to obtain the superheated steam power reference coefficient corresponding to the unit type; and determining the superheated steam power reference coefficient as the steam power coefficient.

[0120] Optionally, the steam power coefficient is obtained based on the unit type, including: for reheater desuperheating water, performing a search operation in a preset superheated steam coefficient database using the unit type to obtain the superheated steam power reference coefficient corresponding to the unit type; performing a search operation in a preset work percentage database using the unit type to obtain the reheated steam work percentage corresponding to the unit type; and determining the steam power coefficient by multiplying the reheated steam work percentage by the superheated steam power reference coefficient.

[0121] Optionally, the steam power coefficient is obtained based on the unit type, including: for reheater desuperheating water, performing a search operation in a preset reheat steam coefficient database using the unit type to obtain the reheat steam power reference coefficient corresponding to the unit type; and determining the reheat steam power reference coefficient as the steam power coefficient.

[0122] It should be noted that the temperature of the steam on the desuperheater side is much higher than the saturation temperature at the corresponding steam pressure, and the pipeline has a large heat storage capacity. This means that the desuperheating water will absorb heat and vaporize instantly after being injected. The dynamic time of this process can be ignored. Therefore, from a transient perspective, the impact of changes in desuperheating water flow rate on boiler steam flow rate is the same as that of changes in feedwater flow rate. The static correspondence between boiler steam flow rate and power generation can be used to analyze the impact of desuperheating water on power generation. For units of the same type, although the capacity may differ, the steam pressure and temperature parameters are basically the same, so the work capacity per unit flow of superheated steam, i.e., the power coefficient, is also basically the same.

[0123] In some embodiments, please refer to Table 1, which is an example table of a preset superheated steam coefficient database.

[0124] Table 1

[0125] Ultra-supercritical double reheat unit 0.394 Ultra-supercritical single reheat unit 0.351 Supercritical once-through reheat unit 0.325 Subcritical once-reheat unit 0.371

[0126] In some embodiments, when the unit type is an ultra-supercritical double reheat unit, the superheated steam power reference factor is 0.394 MW / t / h. When the unit type is an ultra-supercritical single reheat unit, the superheated steam power reference factor is 0.351 MW / t / h. When the unit type is a supercritical single reheat unit, the superheated steam power reference factor is 0.325 MW / t / h. When the unit type is a subcritical single reheat unit, the superheated steam power reference factor is 0.371 MW / t / h.

[0127] The physical meaning of the superheated steam power reference coefficient corresponding to the superheater desuperheating water is: the change in power generation corresponding to a unit change in superheated steam flow rate. It can also be considered as: the change in power generation corresponding to a unit change in superheated desuperheating water flow rate under transient conditions. Therefore, the superheated steam power reference coefficient is 0.371 MW / t / h, indicating that under transient operating conditions, an instantaneous increase of 1 t / h in the superheated desuperheating water flow rate can increase the power generation by 0.371 MW, and the duration of this state is such that the superheated steam temperature does not change significantly.

[0128] For the reheat steam corresponding to the desuperheating water in the reheater, it is necessary to measure the work capacity of the reheat steam per unit flow rate. Superheated steam in the boiler performs work in the high-pressure, intermediate-pressure, and low-pressure cylinders of the turbine, while reheat steam only performs work in the intermediate-pressure and low-pressure cylinders. Therefore, the reheat steam power coefficient can be obtained by multiplying the superheated steam power coefficient by the ratio of the work done by the reheat steam to that done by the superheated steam. Since the secondary reheat steam temperature control in ultra-supercritical double reheat units is relatively difficult, only the primary reheat system can be used for heat storage in engineering projects. Therefore, the steam work ratio and reheat steam power coefficient for ultra-supercritical double reheat units only apply to the primary reheat system.

[0129] In some embodiments, please refer to Table 2, which is an example table of a preset work percentage database.

[0130] Table 2

[0131]

[0132] In some embodiments, when the unit type is an ultra-supercritical double reheat unit, the reheat steam work contribution ratio is 0.798 MW / t / h. When the unit type is an ultra-supercritical single reheat unit, the reheat steam work contribution ratio is 0.702 MW / t / h. When the unit type is a supercritical single reheat unit, the reheat steam work contribution ratio is 0.685%. When the unit type is a subcritical single reheat unit, the reheat steam work contribution ratio is 0.678%.

[0133] In some embodiments, please refer to Table 3, which is an example table of a preset reheat steam coefficient database.

[0134] Table 3

[0135] Ultra-supercritical double reheat unit 0.314 Ultra-supercritical single reheat unit 0.246 Supercritical once-through reheat unit 0.223 Subcritical once-reheat unit 0.252

[0136] In some embodiments, when the unit type is an ultra-supercritical double reheat unit, the reheat steam power reference factor is 0.314 MW / t / h, which is the product of the superheated steam power reference factor of 0.394 and the reheat steam work ratio of 0.798 for an ultra-supercritical double reheat unit; when the unit type is an ultra-supercritical single reheat unit, the reheat steam power reference factor is 0.246 MW / t / h, which is the product of the superheated steam power reference factor of 0.351 and the reheat steam work ratio of 0.7 for an ultra-supercritical single reheat unit. The product of 0 and 2; when the unit type is a supercritical single reheat unit, the reheat steam power reference factor is 0.223 MW / t / h, which is the product of the superheat steam power reference factor of 0.325 and the reheat steam work ratio of 0.685 when it is a supercritical single reheat unit; when the unit type is a subcritical single reheat unit, the reheat steam power reference factor is 0.252 MW / t / h, which is the product of the superheat steam power reference factor of 0.371 and the reheat steam work ratio of 0.678 when it is a subcritical single reheat unit.

[0137] It should be noted that in step S202, the first small temperature difference correction steam temperature between the preset upper limit of steam temperature and the advanced compensation steam temperature is obtained, that is, the difference between the preset upper limit of steam temperature and the advanced compensation steam temperature is determined as the first small temperature difference correction steam temperature. The second small temperature difference correction steam temperature between the advanced compensation steam temperature and the preset lower limit of steam temperature is obtained, that is, the difference between the advanced compensation steam temperature and the preset lower limit of steam temperature is determined as the second small temperature difference correction steam temperature.

[0138] Furthermore, the temperature difference capacity gain is obtained based on the desuperheating water gain, pulse amplitude gain, and steam power coefficient, including: calculating the product of the desuperheating water gain and the pulse amplitude gain; calculating the ratio between this product and the steam power coefficient to obtain the temperature difference capacity gain.

[0139] It should be noted that the temperature difference capacity gain is the gain of the heat storage capacity due to the temperature difference.

[0140] It should be noted that, due to the rapid steam pressure transfer speed and significant thermal inertia in the pipes of the boiler superheater or reheater, instantaneous dynamic adjustment of the flow rate of the primary superheater desuperheating water or the primary reheater desuperheating water can rapidly change the steam pressure without significantly affecting the outlet steam by utilizing the heat storage capacity of the pipe metal. This reduces pressure deviation during rapid load changes in the boiler. Furthermore, while ensuring that the outlet steam temperature does not exceed the upper and lower safety limits of the equipment, the instantaneous change in the desuperheating water flow rate can activate the stored heat capacity and the released heat storage capacity, thus enabling accurate calculation of the stored heat capacity and the released heat storage capacity.

[0141] It should be noted that the steam temperature at the pipeline outlet, the measured steam temperature at the desuperheater outlet, the steam temperature at the desuperheater inlet, the steam parameters, and the desuperheating water parameters can all be obtained by sensors, which will not be elaborated here.

[0142] Combination Figure 4 As shown, this embodiment of the disclosure provides an electronic device 400, including a processor 401 and a memory 402. Optionally, the device may further include a communication interface 403 and a bus 404. The processor 401, communication interface 403, and memory 402 can communicate with each other via the bus 404. The communication interface 403 can be used for information transmission. The processor 401 can call logical instructions in the memory 402 to execute the online calculation method for adjusting the desuperheating water flow to activate the thermal storage capacity of a power plant boiler, as described in the above embodiment.

[0143] Furthermore, the logical instructions in the aforementioned memory 402 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium.

[0144] The memory 402, as a storage medium, can be used to store software programs and computer-executable programs, such as the program instructions / modules corresponding to the methods in the embodiments of this disclosure. The processor 401 executes functional applications and data processing by running the program instructions / modules stored in the memory 402, that is, it implements the online calculation method for adjusting the desuperheating water flow to stimulate the thermal storage capacity of the power plant boiler in the above embodiments.

[0145] The memory 402 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the terminal device. Furthermore, the memory 402 may include high-speed random access memory and may also include non-volatile memory.

[0146] This disclosure provides a storage medium storing computer-executable instructions, which are configured to execute the above-described online calculation method for adjusting the desuperheating water flow rate of a power plant boiler to stimulate thermal storage capacity.

[0147] The aforementioned storage media can be either transient computer-readable storage media or non-transitory computer-readable storage media. Non-transitory storage media include various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks, and can also be transient storage media.

[0148] The foregoing description and accompanying drawings fully illustrate embodiments of this disclosure to enable those skilled in the art to practice them. Other embodiments may include structural, logical, electrical, procedural, and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. Moreover, the terminology used in this application is for describing embodiments only and is not intended to limit the claims. As used in the description of embodiments and claims, the singular forms “a,” “an,” and “the” are intended to equally include the plural forms unless the context clearly indicates otherwise. Similarly, the term “and / or” as used in this application means including one or more of the associated listed items and all possible combinations thereof. Additionally, when used in this application, the term "comprise" and its variations "comprises" and / or "comprising" refer to the presence of stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof. Without further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the process, method, or apparatus that includes said element. In this document, each embodiment may focus on the differences from other embodiments, and similar or identical parts between embodiments can be referred to mutually. For methods, products, etc., disclosed in the embodiments, if they correspond to the method section disclosed in the embodiments, the relevant parts can be referred to the description of the method section.

[0149] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the embodiments of this disclosure. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0150] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to embodiments of this disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than that shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. In the descriptions corresponding to the flowcharts and block diagrams in the accompanying drawings, the operations or steps corresponding to different blocks may also occur in a different order than disclosed in the description, and sometimes there is no specific order between different operations or steps. For example, two consecutive operations or steps may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. Each block in a block diagram and / or flowchart, and combinations of blocks in a block diagram and / or flowchart, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

Claims

1. An online calculation method for stimulating thermal storage capacity by adjusting the desuperheating water flow rate in a power plant boiler, characterized in that, The method includes: The system obtains the advanced compensation steam temperature, desuperheating water gain, pulse amplitude gain, and steam power coefficient; the advanced compensation steam temperature is the steam temperature after advanced compensation of the pipeline outlet steam temperature; when the desuperheating water is superheater desuperheating water, the pipeline outlet steam temperature is the outlet steam temperature of the first-stage superheater pipeline; when the desuperheating water is reheater desuperheating water, the pipeline outlet steam temperature is the outlet steam temperature of the first-stage reheater pipeline. Obtain the first small temperature difference correction steam temperature between the preset upper limit of steam temperature and the advanced compensation steam temperature; obtain the second small temperature difference correction steam temperature between the advanced compensation steam temperature and the preset lower limit of steam temperature; The temperature difference capacity gain is obtained based on the desuperheating water gain, the pulse amplitude gain, and the steam power coefficient. Calculate the product of the first small temperature difference corrected steam temperature and the temperature difference capacity gain to obtain the storable heat capacity; The product of the second small temperature difference corrected steam temperature and the temperature difference capacity gain is calculated to obtain the releasable heat storage capacity.

2. The method according to claim 1, characterized in that, The advanced compensation steam temperature is obtained through the following method: Obtain the lag time corresponding to the desuperheating water and the steam temperature at the pipeline outlet; The lag time is used to filter the steam temperature at the pipeline outlet to obtain the filtered steam temperature at the pipeline outlet. The difference between the steam temperature at the pipeline outlet and the filtered steam temperature at the pipeline outlet is obtained to obtain the advance compensation value; The magnitude of the advance compensation value is limited to obtain the advance compensation limit value; The advanced compensation steam temperature is obtained by summing the advanced compensation limit value with the steam temperature at the pipeline outlet.

3. The method according to claim 1, characterized in that, The gain of the desuperheating water is obtained in the following way: Obtain the heat absorption gain of the pipeline and the gain of the desuperheater; when the desuperheating water is superheater desuperheating water, the heat absorption gain of the pipeline is the heat absorption gain of the pipeline of the first-stage superheater; when the desuperheating water is reheater desuperheating water, the heat absorption gain of the pipeline is the heat absorption gain of the pipeline of the first-stage reheater. The gain of the desuperheating water is obtained by multiplying the heat absorption gain of the pipeline by the gain of the desuperheater.

4. The method according to claim 3, characterized in that, The heat absorption gain of the pipeline is obtained in the following way: Obtain the measured steam temperature at the desuperheater outlet, the steam temperature at the pipeline outlet, and the steam pressure. Calculate the difference between the measured steam temperature at the desuperheater outlet and the preset small temperature difference threshold to obtain the first small temperature difference correction value corresponding to the measured steam temperature at the desuperheater outlet; calculate the difference between the steam temperature at the pipeline outlet and the preset small temperature difference threshold to obtain the second small temperature difference correction value corresponding to the steam temperature at the pipeline outlet. The steam enthalpy at the desuperheater outlet is obtained based on the steam pressure and the measured steam temperature at the desuperheater outlet; the first corrected steam enthalpy at the measured steam temperature at the desuperheater outlet is obtained based on the steam pressure and the first small temperature difference correction value; the steam enthalpy at the pipeline outlet is obtained based on the steam pressure and the measured steam temperature at the pipeline outlet; the second corrected steam enthalpy at the pipeline outlet is obtained based on the steam pressure and the second small temperature difference correction value. Calculate the difference between the measured specific enthalpy of the steam at the desuperheater outlet and the first corrected measured specific enthalpy of the steam to obtain the specific enthalpy difference at the desuperheater outlet; calculate the difference between the measured specific enthalpy of the steam at the pipeline outlet and the second corrected measured specific enthalpy of the steam to obtain the specific enthalpy difference at the pipeline outlet. Calculate the ratio between the specific enthalpy difference at the outlet of the desuperheater and the specific enthalpy difference at the outlet of the pipe to obtain the heat absorption gain of the pipe.

5. The method according to claim 3, characterized in that, The gain of the desuperheater is obtained in the following way: Obtain the calculated specific enthalpy at the desuperheater outlet, the calculated specific enthalpy at the small temperature difference at the desuperheater outlet, the steam pressure, and the steam flow rate; The calculated temperature at the desuperheater outlet is obtained based on the specific enthalpy at the desuperheater outlet and the steam pressure. The specific enthalpy and the steam pressure are used to obtain the small deviation temperature at the outlet of the desuperheater; Calculate the difference between the calculated outlet temperature of the desuperheater and the small deviation outlet temperature of the desuperheater to obtain the calculated temperature difference of the desuperheater; Calculate the product of the steam flow rate and the preset flow rate unit coefficient to obtain the standard steam flow rate; The ratio between the calculated temperature difference of the desuperheater and the standard steam flow rate is calculated to obtain the gain of the desuperheater.

6. The method according to claim 5, characterized in that, The calculated specific enthalpy at the outlet of the desuperheater is obtained in the following manner: Obtain the desuperheater inlet steam temperature, desuperheating water flow rate, desuperheating water temperature, and desuperheating water pressure; The total enthalpy of the desuperheater inlet steam is obtained based on the desuperheater inlet steam temperature, the steam pressure, and the steam flow rate. Calculate the sum of the steam flow rate and the desuperheating water flow rate to obtain the total flow rate; The total enthalpy of the desuperheating water is obtained based on the desuperheating water flow rate, the desuperheating water temperature, and the desuperheating water pressure. The specific enthalpy at the desuperheater outlet is calculated based on the total enthalpy of the steam at the desuperheater inlet, the total flow rate, and the total enthalpy of the desuperheating water.

7. The method according to claim 5, characterized in that, The specific enthalpy of the desuperheater outlet with a small temperature difference is obtained through the following method: Obtain the desuperheater inlet steam temperature, desuperheating water flow rate, steam flow rate, desuperheating water temperature, and desuperheating water pressure; The total enthalpy of the desuperheater inlet steam is obtained based on the desuperheater inlet steam temperature, the steam pressure, and the steam flow rate. The specific enthalpy of the desuperheating water is obtained based on the temperature and pressure of the desuperheating water. The product of the steam flow rate and the preset desuperheating water small deviation flow coefficient is used to obtain the desuperheating water small deviation flow rate. The corrected desuperheating water flow rate is obtained based on the small deviation flow rate of the desuperheating water and the flow rate of the desuperheating water. The corrected total enthalpy of the desuperheating water is obtained based on the corrected desuperheating water flow rate and the specific enthalpy of the desuperheating water; The total outlet flow of the desuperheater is obtained based on the corrected desuperheating water flow and steam flow. The specific enthalpy at the desuperheater outlet is calculated based on the total enthalpy of the steam at the desuperheater inlet, the total flow rate at the desuperheater outlet, and the corrected total enthalpy of the desuperheating water.

8. The method according to claim 1, characterized in that, The pulse amplitude gain is obtained in the following way: Obtain the order inertia product of the rated load object corresponding to the desuperheating water, the rated flow rate of the main steam, and the main steam flow rate of the boiler; Obtain the ratio of the rated flow rate of the main steam to the main steam flow rate of the boiler; Multiply the ratio between the rated flow rate of the main steam and the main steam flow rate of the boiler by the order inertia product of the rated load object to obtain the order inertia product of the actual load object. The product of the order inertia product of the actual load object and the preset pulse gain coefficient is determined as the pulse amplitude gain.

9. The method according to claim 2, characterized in that, The lag time is obtained in the following way: Obtain the order inertia product of the rated load object corresponding to the desuperheating water, the rated flow rate of the main steam, and the main steam flow rate of the boiler; Obtain the ratio of the rated flow rate of the main steam to the main steam flow rate of the boiler; Multiply the ratio between the rated flow rate of the main steam and the main steam flow rate of the boiler by the order inertia product of the rated load object to obtain the order inertia product of the actual load object. The lag time is determined by multiplying the actual load order inertia product with a preset delay time coefficient.

10. The method according to claim 1, characterized in that, The steam power coefficient is obtained in the following manner: Obtain the unit type corresponding to the power plant boiler; The steam power coefficient is obtained based on the unit type.

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