A method for evaluating the load-carrying capacity of a coal-fired unit based on the flue gas temperature parameter

Abstract

The present invention discloses a method for evaluating the load-carrying capacity of a coal-fired unit based on the flue gas temperature parameter, belonging to the field of coal-fired power generation, and applicable to coal-fired units equipped with an electrostatic-bag / bag filter and without retrofitting a low-temperature economizer before the dust collector. Based on the reference value of the flue gas temperature parameter and the flue gas temperature influence factor, with the specified value of the flue gas temperature as the limit, and taking the direction facing the chimney of the coal-fired unit as the reference, the load-carrying capacity of the unit is evaluated respectively through the left and right sides of the boiler tail flue. The left and right sides of the boiler tail flue correspond to the A side and the B side respectively. The evaluation method mainly includes the deviation evaluation method of the representative point of the flue gas temperature, the influence evaluation method of the temperature at the inlet of the forced draft fan on the flue gas temperature, the influence evaluation method of the blockage state of the air preheater on the flue gas temperature, and the influence evaluation method of the flue gas temperature at the inlet of the air preheater on the flue gas temperature. For coal-fired units equipped with an electrostatic-bag / bag filter and without retrofitting a low-temperature economizer before the dust collector, the present invention is beneficial to improving the safe and stable operation level of the unit.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the load-carrying capacity of a coal-fired unit based on the flue gas temperature parameter, belonging to the field of coal-fired power generation. Background Art

[0002] Under the current technical conditions and installed capacity structure, coal power is the most economically feasible, safe and reliable flexible regulation energy. During the power supply guarantee and peak load period in summer, the load-carrying capacity of coal-fired units is particularly important for the safe and stable operation of the power system. The load-carrying capacity of large coal-fired generating units is affected by various factors, mainly including the reliability of the main and auxiliary equipment on the boiler side and turbine side of the generating unit and the key parameters of each subsystem. It is often difficult to monitor and evaluate the load-carrying capacity of the unit.

[0003] For the boiler side, the load-carrying capacity of the unit is mainly restricted by the coal pulverizing system and the flue gas system. When there are defects or failures in the coal mill equipment in the boiler coal pulverizing system, and the coal quality of the coal entering the furnace deviates from the design value and the calorific value is significantly low, it is easy to cause insufficient output of the coal pulverizing system, limited input heat of the boiler, and inability to meet the corresponding requirements of the unit load. The flue gas temperature parameter in the boiler flue gas system generally has little impact on the load-carrying capacity of the unit. However, during the ultra-low emission transformation of the environmental protection system of domestic coal-fired units, many coal-fired units choose to configure electric bag / bag type dust collectors and do not retrofit the low-temperature economizer before the dust collector. For this type of unit, the boiler flue gas temperature should be lower than the inlet specified temperature of the electric bag / bag type dust collector, otherwise it will pose a safety hazard and affect the service life of the electric bag / bag type dust collector, and even there is a risk of fire. If the flue gas temperature is limited, it will affect the load-carrying capacity of the unit and cannot meet the requirements of grid dispatching.

[0004] At present, the flue gas temperature in the flue gas system of many domestic coal-fired units is relatively high. The main influencing factors include three aspects. After the ultra-low emission transformation of thermal power units, ammonium bisulfate with viscosity is easily generated during the denitrification process, which acts together with fly ash and adheres to the heat exchange elements of the air preheater, easily causing the problem of blockage of the air preheater, reducing the heat exchange effect of the air preheater, and increasing the flue gas temperature. The more serious the blockage, the higher the flue gas temperature; the coal types burned by the boiler are complex, and the reduction of calorific value and the increase of moisture will both lead to an increase in the flue gas heat loss of the boiler and cause an increase in the flue gas temperature; in addition, the high ambient temperature in summer will also cause an increase in the flue gas temperature. For coal-fired units configured with electric bag / bag type dust collectors and without retrofitting the low-temperature economizer before the dust collector. For coal-fired units configured with electric bag / bag type dust collectors and without retrofitting the low-temperature economizer before the dust collector, there are few relevant literature reports on evaluating and analyzing the load-carrying capacity of the unit and the influencing factors of the flue gas temperature. Conducting research on the method for evaluating the load-carrying capacity of coal-fired units based on the flue gas temperature parameter is beneficial to improving the safe and stable operation level of the unit. Summary of the Invention

[0005] The object of the present invention is to overcome the above deficiencies existing in the prior art, and to provide a set of scientific methods for evaluating the load-carrying capacity of coal-fired power units based on the flue gas temperature parameter. The present invention is applicable to coal-fired power units equipped with electrostatic-bag / bag filters and without retrofitting low-temperature economizers before the dust collectors. Based on the reference value of the flue gas temperature parameter and the influence factors of the flue gas temperature, with the specified value of the flue gas temperature as the limit, and taking the direction facing the chimney of the coal-fired power unit as the reference, the load-carrying capacity of the unit is evaluated respectively through the left and right sides of the boiler tail flue. The left and right sides of the boiler tail flue correspond to the A side and the B side respectively. The evaluation methods mainly include the deviation evaluation method of the representative point of the flue gas temperature, the evaluation method of the influence of the inlet temperature of the forced draft fan on the flue gas temperature, the evaluation method of the influence of the blockage state of the air preheater on the flue gas temperature, and the evaluation method of the influence of the inlet flue gas temperature of the air preheater on the flue gas temperature.

[0006] The technical solution adopted by the present invention to solve the above problems is: A method for evaluating the load-carrying capacity of a coal-fired power unit based on the flue gas temperature parameter, characterized in that the specified values of the flue gas temperature on the A side and the B side of the boiler tail flue are respectively represented by T Al , T Bl , and the reference value of the flue gas temperature parameter is T As , T Bs . Among the deviation evaluation method of the representative point of the flue gas temperature, the evaluation method of the influence of the inlet temperature of the forced draft fan on the flue gas temperature, the evaluation method of the influence of the blockage state of the air preheater on the flue gas temperature, and the evaluation method of the influence of the inlet flue gas temperature of the air preheater on the flue gas temperature, the influence factors of the flue gas temperature corresponding to the A side of the boiler tail flue are respectively Z A1 , Z A2 , Z A3 , Z A4 , and the influence factors of the flue gas temperature corresponding to the B side of the boiler tail flue are respectively Z B1 , Z B2 , Z B3 , Z B4 . When the coal-fired power unit operates safely and stably and carries the rated load, the following two conditions should be met:

[0007] T As + Z A1 + Z A2 + Z A3 + ZA4 ≤ T Al

[0008] T Bs + Z B1 + Z B2 + Z B3 + Z B4 ≤ T Bl

[0009] Flue gas temperature parameter reference value T As The operating condition of the coal-fired unit is the recent rated load operating state of the unit before the time point for evaluating the unit's load-carrying capacity. Record the relevant operating parameters on the A side of the boiler tail flue of the unit in the distributed control system, including the flue gas temperature T Ai 、the flue gas temperature at the inlet of the air preheater T in-Ai and the temperature at the inlet of the A forced draft fan T e-Ai , the designed air temperature at the inlet of the air preheater is T d-Ai . The calculation formula for the flue gas temperature parameter reference value is as follows:

[0010] T As =( T d-Ai *( T in-Ai - T Ai )+ T in-Ai *( T Ai - T e-Ai )) / ( T in-Ai - T e-Ai )

[0011] Flue gas temperature parameter reference value T Bs The same calculation method as above.

[0012] In the evaluation method of the deviation of the flue gas temperature representative point, the operating condition of the coal-fired unit is the time point for evaluating the unit's load-carrying capacity, and the value of the flue gas temperature representative point on the A side T AdIt is the measured value of the flue gas temperature at the A side in the distributed control system of a coal-fired unit. If there are multiple flue gas temperature measurement points on the A side, the maximum value among the multiple flue gas temperature measurement points is taken. Conduct a deviation test on the representative point of the flue gas temperature on the A side of the boiler. Use a thermocouple to measure the temperature at intervals of 0.5 m along the depth direction of the flue at each measuring hole. The average value of the temperature test results at different depths of each measuring hole is taken, and the maximum value among the average values of the temperature tests at each measuring hole at the outlet of the air preheater on the A side measured actually T A-max is compared with the numerical value of the representative point of the flue gas temperature on the A side T Ad The calculation formula for the flue gas temperature influence factor under the deviation evaluation method of the representative point of the flue gas temperature is as follows:

[0013] Z A1 = T A-max - T Ad

[0014] The flue gas temperature influence factor under the deviation evaluation method of the representative point of the flue gas temperature Z B1 is the same as the above test and calculation method

[0015] In the evaluation method of the influence of the inlet temperature of the forced draft fan on the flue gas temperature, assume that the maximum values of the inlet temperatures of the forced draft fans on the A and B sides are represented by T e-Ai-max 、 T e-Bi-max respectively, and the corresponding flue gas temperatures are T Ai-max 、 T Bi-max respectively. The flue gas temperature at the inlet of the air preheater is taken from the flue gas temperature T in-Ai at the inlet of the air preheater. The calculation formula for the flue gas temperature on the A side corresponding to the maximum value of the inlet temperature of the forced draft fan on the A side is as follows:

[0016] T Ai-max =( T As *( T in-Ai - T e-Ai-max )- T d-Ai * T in-Ai + T in-Ai * T e-Ai-max ) / ( T in-Ai - T d-Ai )

[0017] The calculation formula for the flue gas temperature impact factor under the method of evaluating the impact of the inlet temperature of the A-side forced draft fan on the A-side flue gas temperature is as follows:

[0018] Z A2 = T Ai-max - T Ai

[0019] For the B-side forced draft fan, when the inlet temperature reaches the maximum value, the corresponding B-side flue gas temperature and the flue gas temperature impact factor are calculated using the same method as above.

[0020] In the method of evaluating the impact of the air preheater blockage state on the flue gas temperature, the air preheater blockage state is characterized by the differential pressure on the flue gas side of the air preheater. Different unit operating conditions are selected for correlation calculations. Condition 1 is the operating state of a coal-fired unit at the rated load near the time point before the evaluation of the unit's load-carrying capacity. On the A side of the boiler tail flue, the differential pressure on the flue gas side of the air preheater is P A1 , and the reference value of the flue gas temperature parameter is T As ; Condition 2 is the operating state of a coal-fired unit at the rated load after the last unit overhaul and startup before the time point of evaluating the unit's load-carrying capacity. On the A side of the boiler tail flue, the differential pressure on the flue gas side of the air preheater is P A2 , and the corrected value of the flue gas temperature parameter under Condition 2 is T As-y , T As-y The calculation method is the same as when the reference value of the flue gas temperature parameter is T As ; Assuming that at a certain time after the evaluation of the unit's load-carrying capacity, the differential pressure on the flue gas side of the air preheater is P A3 , then the calculation formula for the flue gas temperature impact factor under the method of evaluating the impact of the A-side air preheater blockage state on the A-side flue gas temperature is as follows:

[0021] Z A3 =( T As - T As-y ) / ( P A1 - P A2)* ( P A3 - P A2 )

[0022] The influence factor of the exhaust gas temperature under the evaluation method of the influence of the clogging state of the air preheater on the B side on the exhaust gas temperature of the B side is the same as the above calculation method.

[0023] In the evaluation method of the influence of the flue gas temperature at the inlet of the air preheater on the exhaust gas temperature, the selected calculation condition is the operation state of the unit at the rated load in the near future before the evaluation time point of the unit's load-carrying capacity. Assuming that the flue gas temperature at the inlet of the air preheater on the A side changes, the parameter is expressed as T in-Ai-1 Then, the calculation formula for the influence factor of the change in the flue gas temperature at the inlet of the air preheater on the A side on the exhaust gas temperature under the evaluation method of the exhaust gas temperature on the A side is as follows:

[0024] Z A4 = T in-Ai-1 - T in-Ai

[0025] Then, the influence factor of the change in the flue gas temperature at the inlet of the B side on the exhaust gas temperature under the evaluation method of the exhaust gas temperature on the B side is the same as the above calculation method.

[0026] The coal-fired unit cannot meet the operating conditions at the rated load:

[0027] T As + Z A1 + Z A2 + Z A3 + Z A4 > T Al Or T Bs + Z B1 + Z B2 + Z B3 + Z B4 > T Bl

[0028] Taking the A side of the boiler tail flue as an example, when T As + Z A1 + Z A2 + Z A3 + Z A4 > T Al At this time, the method for evaluating the load-carrying capacity of the coal-fired unit: the rated load of the unitD e The design value of the lower flue gas temperature (before correction) is T BRL-100% , and the unit load is 75% D e The design value of the lower flue gas temperature (before correction) is T BRL-75% , then when the unit is at maximum load D max it is:

[0029] D max = D e -0.25 D e / ( T BRL-100% - T BRL-75%)* ( T As + Z A1 + Z A2 + Z A3 + Z A4 - T Al )

[0030] The method for evaluating the load-carrying capacity of the coal-fired unit on the B side of the boiler's tail flue and the method for calculating the maximum load of the unit are the same as those on the A side.

[0031] Compared with the prior art, the present invention has the following advantages and effects: (1) The present invention proposes a set of scientific methods for evaluating the load-carrying capacity of coal-fired units based on flue gas temperature parameters, which is beneficial to improving the safety and stability level of unit operation for coal-fired units equipped with electric-bag / bag filters and without retrofitting low-temperature economizers before the dust collectors; (2) By selecting the key influencing factors related to the change of the boiler flue gas temperature, the influence factors of the flue gas temperature measurement point deviation, the inlet temperature of the forced draft fan, the differential pressure on the flue gas side of the air preheater, and the inlet flue gas temperature of the air preheater on the flue gas temperature are calculated. Based on the superposition of the above influencing factors, the maximum load-carrying capacity of the unit is quantitatively analyzed; (3) It can qualitatively analyze the change trend of the flue gas temperature and quantitatively analyze the change value, preventing potential safety hazards caused by the over-limit of the inlet flue gas temperature of the electric-bag / bag filter during the peak load period in summer. Brief Description of the Drawings

[0032] Figure 1 is the flow chart of the evaluation method in the embodiment of the present invention.

[0033] Figure 2It is the curve graph of the deviation test result of the representative point of the A-side flue gas discharge temperature in the embodiment of the present invention. Specific embodiments

[0034] The present invention will be further described in detail below in conjunction with the drawings and through embodiments. The following embodiments are explanations of the present invention, and the present invention is not limited to the following embodiments.

[0035] Embodiment

[0036] In this embodiment, the boiler of a 330MW unit in a certain power plant is produced by Wuhan Boiler Factory, with the model of WGZ1100 / 17.45-5, the type is subcritical parameters, natural circulation steam drum, medium-speed mill positive pressure direct-fired pulverizing system, tangential firing at four corners, Junker three-chamber rotary air preheater, burning bituminous coal, solid slag discharge. During the ultra-low emission transformation, an electric bag filter is configured and the low-temperature economizer is not transformed before the dust collector. The inlet temperature of the electric bag filter is specified not to be greater than 160°C. During the daily operation of the coal-fired unit, the flue gas discharge temperature is relatively high. Now, the load-carrying capacity of the unit is evaluated. Based on the reference value of the flue gas discharge temperature parameter and the influence factor of the flue gas discharge temperature, with the specified value of the flue gas discharge temperature as the limit, and with the direction directly facing the chimney of the coal-fired unit as the reference, the load-carrying capacity of the unit is evaluated respectively through the left and right sides of the boiler tail flue. The left and right sides of the boiler tail flue correspond to the A and B sides respectively. The evaluation methods mainly include the deviation evaluation method of the representative point of the flue gas discharge temperature, the influence evaluation method of the inlet temperature of the forced draft fan on the flue gas discharge temperature, the influence evaluation method of the blockage state of the air preheater on the flue gas discharge temperature, and the influence evaluation method of the inlet flue gas temperature of the air preheater on the flue gas discharge temperature. In the distributed control system, the flue gas discharge temperature on the A side of the boiler is higher than that on the B side. Taking the A side of the boiler tail flue as an example, the load-carrying capacity of the unit is evaluated based on the flue gas discharge temperature parameter.

[0037] Specified value of the flue gas discharge temperature on the A side of the boiler tail flue T Al Is 160°C. Reference value of the flue gas discharge temperature parameter T As The operating condition of the coal-fired unit is the recent rated load operating state of the unit before the time point of evaluating the load-carrying capacity. Record the relevant operating parameters on the A side of the boiler tail flue of the unit in the distributed control system, including the flue gas discharge temperature T Ai , the inlet flue gas temperature of the air preheater T in-Ai And the inlet temperature of the A forced draft fan T e-Ai , the designed inlet air temperature of the air preheater is T d-Ai , according to the reference value calculation formula of the flue gas discharge temperature parameter: T As =( T d-Ai *( Tin-Ai -[[]] T Ai ) + T in-Ai *([[]] T Ai -[[]] T e-Ai )) / ([[]] T in-Ai -[[]] T e-Ai ) to calculate the reference value of the flue gas temperature parameter T As is 142 °C.

[0038] In the flue gas temperature representative point deviation evaluation method, the operating condition of the coal-fired unit is the time point for evaluating the unit's load-carrying capacity. The value of the flue gas temperature representative point on the A side T Ad is the measured value of the flue gas temperature at the A side in the distributed control system of the coal-fired unit. There are 2 flue gas temperature measuring points on the A side, so the maximum value of the 2 flue gas temperature measuring points is taken. To conduct the deviation test of the flue gas temperature representative point on the A side of the boiler, a thermocouple is used to measure the temperature every 0.5 m along the depth direction of the flue at each measuring hole. The average value of the temperature test results at different depths of each measuring hole is taken, and the maximum value among the average values of the temperature tests at each measuring hole at the outlet of the air preheater on the measured A side T A-max is compared with the value of the flue gas temperature representative point on the A side T Ad According to the calculation formula of the flue gas temperature influence factor under the flue gas temperature representative point deviation evaluation method Z A1 = T A-max -[[]] T Ad , calculate to obtain Z A1 is 5 °C, as Figure 2 shown.

[0039] In the evaluation method of the influence of the inlet temperature of the forced draft fan on the flue gas temperature, assume that the maximum value of the inlet temperature of the forced draft fan on the A side T e-Ai-ma is 40 °C, and the corresponding flue gas temperature is T Ai-max , and the flue gas temperature at the inlet of the air preheater is taken from the flue gas temperature at the inlet of the air preheater T in-Ai is 370 °C. The calculation formula for the flue gas temperature on the A side corresponding to the maximum value of the inlet temperature of the forced draft fan on the A side is T Ai-max = ([[]] T As *([[]] T in-Ai -[[]] Te-Ai-max ) - T d-Ai * T in-Ai + T in-Ai * T e-Ai-max ) / ( T in-Ai - T d-Ai ) According to the calculation formula of the flue gas temperature influence factor under the evaluation method of the influence of the inlet temperature of the A - side forced draft fan on the A - side flue gas temperature Z A2 = T Ai-max - T Ai , the calculated Z A2 is 13 °C.

[0040] In the evaluation method of the influence of the air preheater blockage state on the flue gas temperature, the air preheater blockage state is characterized by the differential pressure on the flue gas side of the air preheater. Different unit operating conditions are selected for correlation calculation. Condition 1 is the operating condition of a coal - fired unit, which is the operating state of the rated load unit in the near - term before the time point for evaluating the unit's load - carrying capacity. On the A - side of the boiler tail flue, the differential pressure on the flue gas side of the air preheater is P A1 1.66 kPa, and the reference value of the flue gas temperature parameter is T As 142 °C; Condition 2 is the operating condition of a coal - fired unit, which is the operating state of the rated load after the last unit overhaul and start - up before the time point for evaluating the unit's load - carrying capacity. On the A - side of the boiler tail flue, the differential pressure on the flue gas side of the air preheater is P A2 0.97 kPa, and the corrected value of the flue gas temperature parameter under Condition 2 is 137 °C; Assume that at a certain time after the evaluation of the unit's load - carrying capacity, the differential pressure on the flue gas side of the air preheater is P A3 2.50 kPa. According to the calculation formula of the flue gas temperature influence factor under the evaluation method of the influence of the A - side air preheater blockage state on the A - side flue gas temperature Z A3 = ( T As - T As-y ) / ( P A1 - P A2 ) * ( P A3 - P A2 ), the calculated Z A3is 6°C.

[0041] In the method for evaluating the influence of the flue gas temperature at the inlet of the air preheater on the stack gas temperature, the selected calculation condition is the operating state of the unit at the rated load in the near future before the time point for evaluating the unit's load-carrying capacity. Assuming that the flue gas temperature at the inlet of the A-side air preheater changes, the parameter is T in-Ai-1 , the flue gas temperature rises by 5°C. According to the calculation formula for the influence factor of the stack gas temperature under the method for evaluating the stack gas temperature based on the change in the flue gas temperature at the inlet of the A-side air preheater Z A4 = T in-Ai-1 - T in-Ai , the calculated Z A4 is 5°C.

[0042] Based on the above analysis, T As + Z A1 + Z A2 + Z A3 + Z A4 = 171°C, T A is 160°C; T As + Z A1 + Z A2 + Z A3 + Z A4 > T A , it cannot meet the requirement of the unit to carry the rated load. T As + Z A1 + Z A2 + Z A3 + Z A4 - T A = 11°C.

[0043] Unit rated load D e The design value of the stack gas temperature (before correction) under T BRL-100% is 121°C, and the unit is at 75% load, 0.75 D eDesign value of the lower flue gas temperature (before correction) T BRL-75% is 112°C. According to the calculation formula for the unit at maximum load D max = D e -0.25 D e / ( T BRL-100% - T BRL-75% )*( T As + Z A1 + Z A2 + Z A3 + Z A4 - T Al ) = 330 - 0.25 * 330 / (121 - 112) * 11 = 229 MW.

[0044] To sum up, the deviation of the representative point of the flue gas temperature is 5°C. Assuming that the temperature at the inlet of the forced draft fan rises to 40°C, the differential pressure on the flue gas side of the air preheater rises to 2.50 kPa, and the inlet flue gas temperature of the air preheater rises by 5°C. Under the above operating conditions of the unit, the calculated maximum load-carrying capacity of the unit is 229 MW.

[0045] Contents not described in detail in this specification are all well-known prior arts to those skilled in the art.

[0046] Although the present invention has been disclosed above with embodiments, it is not intended to limit the protection scope of the present invention. Any changes and modifications made by those skilled in the art without departing from the concept and scope of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for evaluating the load-carrying capacity of a coal-fired unit based on the flue gas temperature parameter, characterized in that, Based on the reference value of the flue gas temperature parameter and the influencing factor of the flue gas temperature, with the specified value of the flue gas temperature as the limit, and taking the direction directly facing the chimney of the coal-fired unit as the reference, the load-carrying capacity of the unit is evaluated respectively through the left and right sides of the boiler tail flue. The left and right sides of the boiler tail flue correspond to side A and side B respectively. The evaluation methods include the deviation evaluation method of the representative point of the flue gas temperature, the evaluation method of the influence of the inlet temperature of the forced draft fan on the flue gas temperature, the evaluation method of the influence of the blockage state of the air preheater on the flue gas temperature, and the evaluation method of the influence of the inlet flue gas temperature of the air preheater on the flue gas temperature; The specified values of the flue gas outlet temperatures on the A side and B side of the boiler's tail flue are respectively T Al 、 T Bl , and the reference values of the flue gas outlet temperature parameters are respectively T As 、 T Bs ; In the methods for evaluating the deviation of the representative point of the flue gas outlet temperature, the influence of the temperature at the inlet of the forced draft fan on the flue gas outlet temperature, the influence of the blockage state of the air preheater on the flue gas outlet temperature, and the influence of the flue gas temperature at the inlet of the air preheater on the flue gas outlet temperature, the influence factors for the flue gas outlet temperature corresponding to the A side of the boiler's tail flue are respectively Z A1 、 Z A2 、 Z A3 、 Z A4 , and the influence factors for the flue gas outlet temperature corresponding to the B side of the boiler's tail flue are respectively Z B1 、 Z B2 、 Z B3 、 Z B4 ; When the coal-fired power unit operates safely and stably and at the rated load, the following two conditions shall be met: T As + Z A1 + Z A2 + Z A3 + Z A4 ≤ T Al T Bs + Z B1 + Z B2 + Z B3 + Z B4 ≤ T Bl Reference value of flue gas temperature parameter T As The operating condition of the coal-fired unit is the recent rated load operating state of the unit before the time point for evaluating the load-carrying capacity of the unit. Record the relevant operating parameters on the A side of the boiler tail flue of the unit in the distributed control system, including the flue gas temperature T Ai , the flue gas temperature at the inlet of the air preheater T in-Ai and the temperature at the inlet of the A forced draft fan T e-Ai . The designed air temperature at the inlet of the air preheater is T d-Ai . The calculation formula for the reference value of the flue gas temperature parameter is as follows: T As =( T d-Ai *( T in-Ai - T Ai )+ T in-Ai *( T Ai - T e-Ai )) / ( T in-Ai - T e-Ai ) Reference value of flue gas temperature parameter T Bs The calculation method is the same as T As ; When the coal-fired unit cannot meet the rated load operation conditions: T As + Z A1 + Z A2 + Z A3 + Z A4 > T Al or T Bs + Z B1 + Z B2 + Z B3 + Z B4 > T Bl On the A side of the boiler's tail flue, when T As + Z A1 + Z A2 + Z A3 + Z A4 > T Al , the method for evaluating the load-carrying capacity of the coal-fired unit is as follows: The rated load of the unit D e The design value of the flue gas temperature before correction at the rated load of the unit is T BRL-100% , and the design value of the flue gas temperature before correction at 75% load of the unit 0.75 D e The design value of the flue gas temperature before correction at the rated load of the unit is T BRL-75% , then the maximum load that the unit can carry D max is: D max = D e -0.25 D e / ( T BRL-100% - T BRL-75% )*( T As + Z A1 + Z A2 + Z A3 + Z A4 - T Al ) The evaluation method of the load-carrying capacity of the coal-fired unit on side B of the boiler tail flue and the calculation method of the maximum load of the unit are the same as those on side A.

2. The method for evaluating the load-carrying capacity of a coal-fired unit based on the flue gas temperature parameter according to claim 1, characterized in that In the method for evaluating the deviation of the representative point of the flue gas temperature, the operating condition of the coal-fired unit is the time point for evaluating the load-carrying capacity of the unit, and the value of the representative point of the flue gas temperature on the A side T Ad is the measured value of the flue gas temperature on the A side in the distributed control system of the coal-fired unit. If there are multiple flue gas temperature measuring points on the A side, the maximum value among the multiple flue gas temperature measuring points is taken; for the test of the deviation of the representative point of the flue gas temperature on the A side of the boiler, a thermocouple is used to measure the temperature at intervals of 0.5 m along the depth direction of the flue at each measuring hole, and the average value of the temperature test results at different depths of each measuring hole is taken. The maximum value among the average values of the temperature tests at each measuring hole at the outlet of the air preheater on the A side measured actually T A-max is compared with the value of the representative point of the flue gas temperature on the A side T Ad The calculation formula for the influence factor of the flue gas temperature under the method for evaluating the deviation of the representative point of the flue gas temperature is as follows: Z A1 = T A-max - T Ad Flue gas temperature influence factor in the evaluation method of flue gas temperature representative point deviation Z B1 The calculation method is the same as Z A1 .

3. The method for evaluating the load-carrying capacity of a coal-fired unit based on the flue gas temperature parameter according to claim 1, wherein In the method for evaluating the influence of the inlet temperature of the forced draft fan on the flue gas temperature, it is assumed that the maximum values of the inlet temperatures of the forced draft fans on the A side and the B side are respectively T e-Ai-max 、 T e-Bi-max , and the corresponding flue gas temperatures are respectively T Ai-max 、 T Bi-max . The inlet flue gas temperature of the air preheater is taken from the inlet flue gas temperature of the air preheater T in-Ai . The calculation formula for the flue gas temperature on the A side corresponding to the maximum value of the inlet temperature of the forced draft fan on the A side is as follows: T Ai-max =( T As *( T in-Ai - T e-Ai-max )- T d-Ai * T in-Ai + T in-Ai * T e-Ai-max ) / ( T in-Ai - T d-Ai ) The calculation formula of the influencing factor of the flue gas temperature in the evaluation method of the influence of the inlet temperature of the forced draft fan on the flue gas temperature on side A is as follows: Z A2 = T Ai-max - T Ai The calculation methods of the flue gas temperature corresponding to the maximum value of the inlet temperature of the forced draft fan on side B and the influencing factor of the flue gas temperature are the same as those on side A.

4. The method for evaluating the load-carrying capacity of a coal-fired unit based on the flue gas temperature parameter according to claim 1, wherein In the method for evaluating the influence of the air preheater clogging state on the flue gas temperature, the air preheater clogging state is characterized by the differential pressure on the flue gas side of the air preheater. Different unit operating conditions are selected for correlation calculation. Condition 1 is the operating state of a coal-fired unit at the rated load of the recent rated load unit before the time point for evaluating the unit's load-carrying capacity. On the A side of the boiler tail flue, the differential pressure on the flue gas side of the air preheater is P A1 , and the reference value of the flue gas temperature parameter is T As ; Condition 2 is the operating state of a coal-fired unit at the rated load after the last unit overhaul start before the time point for evaluating the unit's load-carrying capacity. On the A side of the boiler tail flue, the differential pressure on the flue gas side of the air preheater is P A2 , and the correction value of the flue gas temperature parameter in Condition 2 is T As-y , T As-y The calculation method of T As is the same as the reference value of the flue gas temperature parameter being P A3 ; Assuming that the differential pressure on the flue gas side of the air preheater at a certain time after the time point for evaluating the unit's load-carrying capacity is​ Z A3 =( T As - T As-y ) / ( P A1 - P A2 )*( P A3 - P A2 ) The calculation method of the influencing factor of the flue gas temperature in the evaluation method of the influence of the blockage state of the air preheater on the flue gas temperature on side B is the same as that on side A.

5. The method for evaluating the load-carrying capacity of a coal-fired unit based on the flue gas temperature parameter according to claim 1, wherein In the method for evaluating the influence of the flue gas temperature at the inlet of the air preheater on the exhaust gas temperature, the selected calculation condition is the operating state of the unit at the rated load in the near future before the time point for evaluating the load-carrying capacity of the unit. Assuming that the flue gas temperature at the inlet of the A-side air preheater changes, and the parameter is T in-Ai-1 , then the calculation formula for the influence factor of the exhaust gas temperature on the exhaust gas temperature evaluation method at the inlet of the A-side air preheater is as follows: Z A4 = T in-Ai-1 - T in-Ai Then the calculation method of the influencing factor of the flue gas temperature in the evaluation method of the influence of the change of the inlet flue gas temperature on the flue gas temperature on side B is the same as that on side A.

Images