An online monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler

Abstract

The present invention relates to an on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler. This method does not require additional boiler measurement points. In the calculation of the flue gas temperature at the furnace outlet, the soft measurement of the coal quality of the coal fed into the furnace is considered simultaneously, so that the monitoring result of the flue gas temperature at the furnace outlet can more accurately reflect the true value of the flue gas temperature at the furnace outlet in real time, and at the same time provide the flue gas temperature distribution along the width direction of the furnace. Compared with the prior art, the present invention has the advantages of solving the problems commonly existing in current power generation enterprises, such as the large variety of blended coal types and the large change in the coal quality of the coal fed into the furnace, resulting in a large change in the flue gas temperature at the furnace outlet, and enabling the measurement result to more accurately reflect the true value of the flue gas temperature at the boiler furnace outlet in real time, etc.

Description

Technical Field

[0001] The present invention relates to the field of monitoring operating parameters of power station boilers, and particularly to an online monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power station boiler. Background Art

[0002] The flue gas temperature at the furnace outlet of a coal-fired power station boiler is an important parameter during boiler operation. Achieving accurate online temperature measurement of the furnace outlet flue gas is of great significance for ensuring the safe operation of thermal power plants, improving the economy of units, and optimizing boiler design. When a power station boiler is operating, the flue gas temperature at the furnace outlet is high (900 - 1400) and the flue gas contains a large amount of fly ash, which is not conducive to long-term online monitoring. Currently, there are mainly two types of measurement methods for the flue gas temperature at the furnace outlet of power station boilers in patent literature: 1) Physical measurements based on acoustic measurement technology, optical measurement technology, etc. Such methods have defects such as troublesome installation, expensive equipment, difficult maintenance, and poor reliability; 2) Soft measurement methods that calculate the flue gas temperature based on the heat balance principle of the high-temperature heating surface of the boiler through the data of the installed operating parameter measuring points.

[0003] Chinese Patent Application No. 201110107881.3 discloses a method for measuring the flue gas temperature at the furnace outlet of a boiler. This method measures the flue gas temperature in the furnace from both the positive and negative directions of the flue gas side through the actual operating data related to the neutralization model parameters of the unit, based on the energy balance of furnace combustion and radiation, the energy balance of the flue gas side and the working medium side of the superheater, the energy balance of the flue gas side and the working medium side of the reheater, and the energy balance of the tail flue gas, and then calculates the flue gas temperature using a linear superposition formula. However, this method uses the input coal quality components to calculate the flue gas physical property parameters library, and the calculated flue gas temperature is the average value at the furnace outlet of the boiler, which cannot reflect the combustion deviation of the boiler.

[0004] Chinese Patent Application No. 201510764823.6 discloses a soft measurement method for the flue gas temperature at the furnace outlet of a power station boiler. This method establishes a real-time inference soft measurement model for the flue gas temperature at the furnace outlet by jointly calculating the heat transfer balance of the furnace and the convective heating surface and considering the real-time slagging property in the furnace, and can output the real-time value of the flue gas temperature at the furnace outlet. Similarly, this method uses the input coal quality components to calculate the flue gas physical property parameters, and the calculated flue gas temperature is the average value at the furnace outlet of the boiler.

[0005] Currently, the supply situation of coal resources is complex and its price is also changeable. It is difficult to ensure the quality and quantity of the designed coal type, and power generation enterprises generally adopt the method of blending other coal types to cope with it, resulting in large variations in the coal quality of the coal entering the furnace. During the actual operation of the unit in the power plant, the coal quality components are generally sampled and analyzed offline, which has a relatively long lag time and cannot guide the operation of the on-site unit. The change in coal quality has a great impact on the flue gas temperature at the furnace outlet of the boiler. If this factor is not considered, the monitoring result has poor accuracy and is not suitable for popularization.

[0006] Due to the existence of combustion deviation in the boiler, the flue gas temperature distribution along the width direction of the furnace is uneven. Therefore, how to obtain the flue gas temperature distribution along the width direction of the furnace, so as to analyze the current combustion condition of the boiler and guide the combustion adjustment, becomes a technical problem to be solved. Summary of the Invention

[0007] The purpose of the present invention is to provide an on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler to overcome the defects existing in the above-mentioned prior art.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] According to one aspect of the present invention, an on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler is provided. This method does not require additional boiler measurement points. When calculating the flue gas temperature at the furnace outlet, the soft measurement of the coal quality of the coal entering the furnace is considered simultaneously, so that the monitoring result of the flue gas temperature at the furnace outlet can more accurately reflect the true value of the flue gas temperature at the furnace outlet in real time, and at the same time provide the flue gas temperature distribution along the width direction of the furnace.

[0010] As a preferred technical solution, the method specifically includes the following steps:

[0011] Step S1) Establish a database of equipment structure parameters;

[0012] Step S2) Establish a data interface with the power plant distributed control system or SIS system and read in the operation data;

[0013] Step S3) Establish a neural network fly ash carbon content prediction model based on the historical fly ash carbon content test data of the power plant;

[0014] Step S4) Establish a neural network slag carbon content prediction model based on the historical slag carbon content test data of the power plant;

[0015] Step S5) Establish a calculation model for the moisture content of the coal entering the furnace according to the energy balance and mass balance principles of the coal mill system;

[0016] Step S6) Set the initial boiler efficiency;

[0017] Step S7) Calculate the lower calorific value Qar0 of the coal entering the furnace according to the total heat absorption of the working medium in the boiler;

[0018] Step S8) Establish a neural network ash content prediction model for the coal entering the furnace based on the historical coal quality data of the power plant;

[0019] Step S9) Establish a system of equations for the relationship between the combustion products of coal and the input elements according to the principles of material balance and chemical analysis of coal combustion; solve the system of equations to obtain the lower calorific value Qar of the coal entering the furnace and the coal quality elemental analysis data;

[0020] Step S10) Calculate the current boiler efficiency;

[0021] Step S11) According to the deviation between the lower calorific value Qar of the coal entering the furnace and Qar0, perform iterative calculations of steps S7 - S10;

[0022] Step S12) Divide the flue gas heat exchanger between the furnace outlet section and the low - temperature zone outlet section into four types of heat transfer modules according to the flue gas flow, namely, platen heating surface, semi - radiant heating surface, convective heating surface, and additional heating surface;

[0023] Step S13) Starting from the flue gas temperature at the outlet of the low - temperature zone heating surface, along the direction opposite to the flue gas flow, apply the principle of heat balance of the heating surface to gradually calculate the flue gas temperature between each heating surface, and finally calculate the flue gas temperature at the furnace outlet;

[0024] Step S14) According to the furnace wall temperature measurement points at the outlet of the heating surface in the furnace and the operating parameters, calculate the inter - screen thermal deviation distribution coefficient of this heating surface; according to the structure and header system layout of this heating surface, calculate the inter - screen flow deviation distribution coefficient and inter - screen area deviation distribution coefficient of this heating surface, and obtain the heat load deviation distribution coefficient of this heating surface;

[0025] Step S15) According to the heat load deviation distribution coefficient of this heating surface, the average inlet and outlet flue gas temperatures of this heating surface, the outlet wall temperatures of the monitoring tubes of each screen of this heating surface, and the average inlet and outlet steam temperatures of this heating surface, obtain the flue gas temperature distribution along the furnace width direction at the furnace outlet.

[0026] As a preferred technical solution, the step S2) of reading the operating data includes: generator power, feed water temperature, feed water flow rate, main steam flow rate, main steam temperature, reheated steam temperature, atmospheric pressure, atmospheric temperature, oxygen content, superheater desuperheating water volume, reheater desuperheating water volume, burner tilt angle, SOFA air volume, CCOFA air volume, secondary air volume, coal feeding amount of each mill, primary air volume of each mill, outlet air - powder temperature of each mill, furnace - windbox differential pressure, inlet and outlet steam temperatures of each heating surface, and flue gas temperature at the economizer outlet.

[0027] As a preferred technical solution, the step S3) is specifically as follows:

[0028] Based on the historical fly ash carbon content test data of the power plant, establish a neural network fly ash carbon content prediction model. Take the operating parameters such as boiler evaporation, burner tilt angle, oxygen content, SOFA air volume, CCOFA air volume, main characteristics of coal quality, coal feeding amount of each coal mill, furnace - windbox differential pressure, and primary air volume of each mill as the input variables of the neural network, and the fly ash carbon content as one output of the neural network. The neural network adopts the BP neural network;

[0029] The step S4) is specifically as follows:

[0030] Based on the historical test data of the carbon content in the slag of the power plant, a neural network prediction model for the carbon content in the slag is established. The operating parameters such as the boiler evaporation capacity, the burner swing angle, the oxygen content, the SOFA air volume, the CCOFA air volume, the main characteristics of the coal quality, the coal feeding amount of each coal mill, the differential pressure between the furnace and the wind box, and the primary air volume of each coal mill are used as the input variables of the neural network, and the carbon content in the slag is used as one output of the neural network. The neural network adopts the BP neural network, where the main characteristics of the coal quality include the calorific value, moisture, ash, and volatile matter of the coal entering the furnace.

[0031] As a preferred technical solution, the specific content of step S5) is as follows:

[0032] According to the principles of energy balance and mass balance of the coal mill system, that is, the total heat input at the starting section of each coal mill system is equal to the total heat carried out and consumed at the terminal section, solving this set of equations can obtain the moisture of the coal entering the furnace. The specific formula is as follows:

[0033] q gz +q rc +q nm +q mf +q lf =q sf +q fq +q jr +q sr

[0034] In the formula:

[0035] The total heat input for drying and grinding 1 kg of coal in the coal preparation system includes:

[0036] The physical heat q gz ;

[0037] The physical heat q rc of the raw coal;

[0038] The heat q nm generated by grinding during the operation of the coal mill;

[0039] The physical heat q mf of the sealing air;

[0040] The physical heat q lf of the leaked cold air;

[0041] The total heat carried out and consumed for drying and grinding 1 kg of coal in the coal preparation system includes:

[0042] The heat q sf consumed for evaporating the moisture in the raw coal;

[0043] The heat q fq carried out by the exhausted drying agent;

[0044] The heat q jr;

[0045] Equipment heat dissipation loss q sr 。

[0046] As a preferred technical solution, step S7) calculates the lower calorific value Qar0 of the coal fed into the boiler according to the total heat absorption of the working medium in the boiler, specifically as follows:

[0047] The total heat absorption Q of the working medium in the boiler boiler is:

[0048] Q boiler = G ms (h ms - h fw ) + G rc (h rh - h rc ) + G rj (h rh - h rj ) + G sj (h ms - h sj )

[0049] Where G ms is the main steam flow rate, h ms is the main steam enthalpy, h fw is the main feed water enthalpy, G rc is the cold reheat flow rate, h rh is the hot end enthalpy of the reheated steam, h rc is the cold end enthalpy of the reheated steam, G rj is the desuperheating water flow rate of the reheater, h rj is the desuperheating water enthalpy of the reheater, G sj is the desuperheating spray water flow rate of the superheater, h sj is the desuperheating spray water enthalpy of the superheater;

[0050] Calculate the lower calorific value of the coal fed into the boiler:

[0051]

[0052] Where Q ar0 is the lower calorific value per kilogram of coal fed into the boiler, η0 is the boiler efficiency, G coal is the coal feed quantity of the boiler.

[0053] As a preferred technical solution, step S9) establishes a relationship equation set between the coal combustion products and the input elements according to the material balance and the principle of coal combustion chemical analysis, specifically as follows:

[0054] According to the material balance and the principle of coal combustion chemical analysis, express the various gases generated by coal combustion as equations of the dry ash-free basis element content:

[0055] Cdaf = 53.59γ co2 (V RO2，daf + V N2，daf + V O2，daf ) + (1 - γ co2 )X cucr

[0056] S daf = 142.86γ so2 (V RO2，daf + V N2，daf + V O2，daf

[0057]

[0058] O daf = k1C daf + k2

[0059] N daf = k3N daf

[0060] C daf + H daf + O daf + N daf + S daf = 100

[0061] V RO2，daf = 0.01866(C daf + 0.375S daf ) - 0.01866X cucr

[0062]

[0063]

[0064]

[0065] V gk，daf = 0.0889(C daf + 0.375S daf ) + 0.265H ar - 0.0333O ar - 0.0889X cucr

[0066]

[0067] C cucr = α fh C fh + a lz C lz

[0068]

[0069] Q ar = 339C ar + 1028H ar - 109(O ar - S ar ) - 25M ar

[0070] where k1, k2, and k3 are correlation coefficients related to the dry ash - free basis components; C cucr is the average unburned carbon content in the ash; γ co2 , γ o2 , γ so2 are the gas volume fractions in the flue gas of the exhaust; C daf , H daf , O daf , N daf , S daf are the dry ash - free basis elemental components of the coal; C ar , H ar , O ar , N ar , S ar are the as - received basis elemental components of the coal; V RO2，daf , V N2，daf , V O2，daf are the amounts of various standard gases calculated based on the dry basis components; α is the excess air coefficient; is the volume fraction of oxygen in the air; X cucr is the correction amount for unburned carbon loss; α fh , α lz are the fractions of fly ash and slag; C fh , C lz are the carbon contents of fly ash and slag, V gk，daf is the flue gas volume calculated based on the dry basis components, M ar is the as - received basis moisture of the coal.

[0071] As an optimized technical solution, the heat balance calculation methods for various types of heating surfaces in step S13) are as follows:

[0072] a) For the platen heating surface:

[0073] Qz = Qf1 + Qf2 + Qd;

[0074] Qy = Qf2 + Qd - Qfh;

[0075] In the formula:

[0076] The heat absorbed by the heat exchanger working medium Qz;

[0077] The radiant heat received by the platen Qf1;

[0078] The radiative heat release Qf2 from the flue gas between the screens to the tube screens;

[0079] The convective heat release Qd from the flue gas between the screens to the tube screens;

[0080] The heat Qy transferred from the flue gas to the working medium;

[0081] The heat Qfh radiated by the flue gas between the screens to the heating surface behind the screens

[0082]

[0083] Where:

[0084] D is the working medium flow rate; i out is the enthalpy of the working medium at the outlet; i in is the enthalpy of the working medium at the inlet; B j is the actual fuel combustion rate;

[0085]

[0086]

[0087] Where:

[0088] is the heat preservation coefficient considering heat dissipation loss; I′ and I" are the flue gas enthalpies at the inlet and outlet of the heating surface; is the heat brought in by air leakage; α pj is the screen emissivity; T pj is the average flue gas temperature of the screen; H fc is the outlet area of the screen;

[0089]

[0090]

[0091] Where:

[0092] q fp is the furnace radiative heat load at the height where the screen is located; H fp is the screen radiation heating area; η gd is the furnace height heat load distribution coefficient; Φ is the furnace heat preservation coefficient; Q yx is the effective heat release per unit fuel in the furnace; h lcy is the flue gas enthalpy at the furnace outlet; Q fr is the radiative heat load from the furnace to the screen heating surface; F lt is the furnace wall area; B j is the actual fuel combustion rate;

[0093]

[0094] Where:

[0095] α f is the radiative heat release coefficient; T pj is the average flue gas temperature; T hw is the fouled wall temperature;

[0096]

[0097] Where:

[0098] α d is the convective heat release coefficient; D w is the outer diameter of the tube; s2 is the longitudinal pitch; x is the angle factor of the screen;

[0099] b) For the semi-radiant heating surface:

[0100] Qz = Qfq + Qf2 + Qd

[0101] Qy = Qf2 + Qd - Qfh;

[0102] Where:

[0103] The heat absorbed by the heat exchanger working medium Qz;

[0104] The radiant heat received from the furnace and the upper heating surface Qfq;

[0105] The radiant heat release from the flue gas between the screens to the tube screen Qf2;

[0106] The convective heat release from the flue gas between the screens to the tube screen Qd;

[0107]

[0108] Where:

[0109] α lpj is the emissivity of the upper screen; T lpj is the average flue gas temperature of the upper screen; H lfc is the outlet area of the upper screen; x lpj is the angle factor from the inlet cross-section to the outlet cross-section of the upper screen;

[0110] c) For the convective heating surface:

[0111] Qz = Qf2 + Qd;

[0112] Qy = Qf2 + Qd;

[0113] Where:

[0114] The heat absorbed by the heat exchanger working medium Qz;

[0115] The radiant heat release from the flue gas between the screens to the tube screen Qf2;

[0116] The convective heat release from the flue gas between the screens to the tube screen Qd;

[0117] d) For the additional heating surface:

[0118] The calculation of the additional heating surface mainly includes two parts. One part is the calculation of the additional water-cooled wall, and the other part is the calculation of the suspension pipe. The calculation process is to divide the additional heating surface into multiple segments according to the main heating surface of the boiler where it is located, and the calculation of each segment is carried out together with the main heating surface. During the calculation, the heat transfer coefficient of each segment of the additional heating surface is the same as that of the main heating surface calculation method.

[0119] As a preferred technical solution, the calculation of the inter-screen thermal deviation distribution coefficient of the heating surface in step S14) is specifically as follows:

[0120] According to the furnace outer wall temperature measurement points of the primary superheater, calculate the inter-screen thermal deviation distribution coefficient of the primary superheater, that is:

[0121]

[0122] In the formula

[0123] Δi pc is the enthalpy increase of the monitoring tube of a certain screen;

[0124] Δi pj is the average enthalpy increase of the heating surface;

[0125] The inter-screen thermal deviation distribution coefficient is respectively the ratio of the product of the heat load deviation distribution coefficient and the heating area deviation distribution coefficient to the flow rate deviation distribution coefficient, that is

[0126]

[0127] In the formula:

[0128] η r is the inter-screen heat load deviation distribution coefficient; η j is the inter-screen area deviation distribution coefficient; η l is the inter-screen flow rate deviation distribution coefficient;

[0129] The inter-screen heat load deviation distribution coefficient can be obtained:

[0130]

[0131] As a preferred technical solution, the calculation of the furnace outlet flue gas temperature distribution in step S15) is specifically as follows:

[0132] The furnace outlet flue gas temperature distribution, that is, the inlet flue gas temperature distribution of the primary superheater, is calculated according to the following formula:

[0133] TGAS i = η r (TGAS inavg + TGASoutavg -t inavg -t outavg ) + t inavg +t outi -TGAS outavg

[0134] In the formula:

[0135] TGAS inavg is the average flue gas temperature at the inlet of the primary superheater; TGAS outavg is the average flue gas temperature at the outlet of the primary superheater; t inavg is the average steam temperature at the inlet of the primary superheater; t outavg is the average steam temperature at the outlet of the primary superheater; t outi is the outlet wall temperature of the monitoring tube of the i-th screen; η r is the distribution coefficient of the heat load deviation between screens.

[0136] Compared with the prior art, the present invention has the following advantages:

[0137] 1. Compared with the existing monitoring technologies, the on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler proposed by the present invention is based on the existing DCS real-time data, has the advantages of easy data acquisition, no need to additionally increase measuring points on site, low cost, and wide applicability to various types of coal-fired power plant boilers based on the combustion mechanism.

[0138] 2. Compared with the existing monitoring technologies, the on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler proposed by the present invention adopts methods such as soft measurement of the coal quality of the coal fed into the furnace and soft measurement of the carbon content in fly ash, solves the problem that there are many types of blended coal and large changes in the coal quality of the coal fed into the furnace, which lead to large changes in the flue gas temperature at the furnace outlet in current power generation enterprises, and enables the measurement results to more accurately reflect the true value of the flue gas temperature at the boiler furnace outlet in real time. For a certain ultra-supercritical tower boiler, it is found through the monitoring by this method that the flue gas temperature at the furnace outlet of the boiler is on the high side (about 1250 - 1350 °C) at medium and high loads. According to the ash fusion temperature of the coal quality of the coal fed into the furnace at that time, it is judged that there may be coking phenomena in the primary superheater screens of the boiler. On-site manual measurement with an infrared thermometer shows that the measured flue gas temperature at the furnace outlet of the boiler is about 1250 - 1370 °C, and at the same time, the maintenance personnel feedback that there are indeed coking phenomena in the primary superheater screens of the boiler. This verifies the accuracy of the monitoring data of this method.

[0139] 3. Compared with the existing monitoring technologies, the on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler proposed by the present invention can monitor the flue gas temperature distribution along the furnace width direction, reflect the combustion heat load distribution in the boiler furnace in the form of a dynamic curve, and can diagnose and analyze the current combustion status of the boiler on line.

[0140] 4. The on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler proposed by the present invention can assist in monitoring the combustion operation of the boiler, guide the operation to adjust the boiler combustion, and prevent problems such as heating surface coking caused by too high flue gas temperature at the furnace outlet and overheating of the heating surface caused by boiler combustion deviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0141] Figure 1 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0142] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0143] Under the condition that the coal quality of the coal entering the furnace in current power plants is generally variable, the present invention proposes a method for monitoring the flue gas temperature at the furnace outlet. This method does not require additional boiler measuring points. In the calculation of the flue gas temperature at the furnace outlet, the soft measurement of the coal quality of the coal entering the furnace is considered at the same time, so that the monitoring result of the flue gas temperature at the furnace outlet can more accurately reflect the true value of the flue gas temperature at the furnace outlet in real time, and at the same time provide the flue gas temperature distribution along the width direction of the furnace.

[0144] Select a boiler for example calculation to further illustrate the specific implementation manner of the present invention. The boiler model is SG-2956 / 27.46-M534. The boiler adopts ultra-supercritical pressure parameter variable pressure operation, single furnace tower arrangement, once-through intermediate reheat, tangential firing at four corners, direct blow pulverized coal system, balanced draft, dry slag removal, all-steel suspension structure, and outdoor arrangement, and is matched with a 1000MW ultra-supercritical pressure single-shaft four-cylinder four-exhaust condensing steam turbine generator set.

[0145] As Figure 1 shown, the method of the present invention specifically includes the following steps:

[0146] 1. According to the boiler design data, establish a database of the structural parameters of the main equipment, as shown in Table 1;

[0147] Table 1

[0148]

[0149]

[0150] 2. Establish a data interface with the power plant's distributed control system (DCS) or plant-level monitoring system (SIS) to read in operating data; the data acquisition cycle is 30 seconds. The main data includes: generator power, feed water temperature, feed water flow rate, main steam flow rate, main steam temperature, reheated steam temperature, atmospheric pressure, atmospheric temperature, oxygen content, superheated desuperheating water volume, reheated desuperheating water volume, burner tilt angle, SOFA air volume, CCOFA air volume, secondary air volume, coal feed rate of each mill, primary air volume of each mill, outlet air-powder temperature of each mill, furnace-to-air box differential pressure, inlet and outlet steam temperatures of each heating surface, and economizer outlet flue gas temperature.

[0151] 3. Based on the historical fly ash carbon content test data of the power plant, establish a neural network fly ash carbon content prediction model. Use operating parameters such as boiler evaporation, burner tilt angle, oxygen content, SOFA air volume, CCOFA air volume, main coal quality characteristics, coal feed rate of each coal mill, furnace-to-air box differential pressure, and primary air volume of each mill as the input variables of the neural network, and the fly ash carbon content as one of the outputs of the neural network. The neural network can use a general BP neural network.

[0152] 4. Based on the historical slag carbon content test data of the power plant, establish a neural network slag carbon content prediction model. Use operating parameters such as boiler evaporation, burner tilt angle, oxygen content, SOFA air volume, CCOFA air volume, main coal quality characteristics, coal feed rate of each coal mill, furnace-to-air box differential pressure, and primary air volume of each mill as the input variables of the neural network, and the slag carbon content as one of the outputs of the neural network. The neural network can use a general BP neural network, where the main coal quality characteristics include calorific value, moisture, ash content, and volatile matter of the coal entering the furnace.

[0153] 5. According to the principles of energy balance and mass balance of the coal mill system, that is, the total heat input at the starting section of each coal mill system is equal to the total heat carried out and consumed at the terminal section. Solving this system of equations can obtain the moisture content of the coal entering the furnace.

[0154] Namely:

[0155] q gz +q rc +q nm +q mf +q lf =q sf +q fq +q jr +q sr

[0156] In the formula:

[0157] The total heat input for drying and grinding 1 kg of coal in the coal preparation system includes:

[0158] The physical heat q gz of the desiccant;

[0159] The physical heat qrc ;

[0160] The heat q generated by grinding during the operation of the coal mill nm ;

[0161] The physical heat q of the sealing air mf ;

[0162] The physical heat q of the leaked cold air lf ;

[0163] The total heat taken out and consumed for drying and grinding 1 kg of coal in the coal pulverizing system includes:

[0164] The heat q consumed for evaporating the moisture in the raw coal sf ;

[0165] The heat q carried out by the exhausted drying agent fq ;

[0166] The heat q consumed for heating the fuel jr ;

[0167] The heat loss q due to equipment heat dissipation sr ;

[0168] All relevant variables in the formula can refer to DL / T 5145-2012 "Design Calculation Specification for Coal Pulverizing System in Thermal Power Plants"

[0169] 6. The total heat absorption of the working medium in the boiler is:

[0170] Q boiler = G ms (h ms - h fw ) + G rc (h rh - h rc ) + G rj (h rh - h rj ) + G sj (h ms - h sj )

[0171] Where:

[0172] G ms is the main steam flow rate, h ms is the main steam enthalpy, h fw is the main feed water heat enthalpy, G rc is the cold reheat flow rate, h rh is the hot end enthalpy of the reheated steam, h rc is the cold end enthalpy of the reheated steam, G rj is the desuperheating water flow rate of the reheater, h rj is the desuperheating water enthalpy of the reheater, G sjis the desuperheating water injection volume of the superheater, h sj is the enthalpy of the desuperheating water injection of the superheater.

[0173] 7. Set the initial boiler efficiency η0;

[0174] 8. Calculate the lower calorific value of the coal entering the boiler:

[0175]

[0176] In the formula:

[0177] Q ar is the lower calorific value of the coal entering the boiler per kilogram, η0 is the boiler efficiency, and G coal is the coal input volume of the boiler. For the direct-fired pulverized coal system, it is the sum of the coal volumes of all operating coal mills.

[0178] 9. Based on the historical coal quality data of the power plant, the ash content of the coal entering the furnace can establish a neural network prediction model based on its strong correlation with the moisture and calorific value of the coal entering the furnace. The neural network can adopt the general BP neural network.

[0179] 10. According to the principle of material balance and coal combustion chemical analysis, express the various gases generated by coal combustion as equations of the dry ash-free base element content:

[0180] C daf = 53.59γ co2 (V RO2，daf + V N2，daf + V O2，daf ) + (1 - γ co2 )X cucr

[0181] S daf = 142.86γ so2 (V RO2，daf + V N2，daf + V O2，daf

[0182]

[0183] O daf = k1C daf + k2

[0184] N daf = k3N daf

[0185] C daf + H daf + O daf + N daf + S daf = 100

[0186] V RO2，daf= 0.01866(C daf + 0.375S daf ) - 0.01866X cucr

[0187]

[0188]

[0189]

[0190] V gk，daf = 0.0889(C daf + 0.375S daf ) + 0.265H ar - 0.0333O ar - 0.0889X cucr

[0191]

[0192] C cucr = α fh C fh + a lz C lz

[0193]

[0194] Q ar = 339C ar + 1028H ar - 109(O ar - S ar ) - 25M ar

[0195] where k1, k2, k3 are correlation coefficients related to dry ash-free basis components; C cucr is the average unburned carbon content in ash residue, %; γ co2 , γ o2 , γ so2 are the gas volume fractions in the flue gas; Cdaf, Hdaf, Odaf, Ndaf, Sdaf are the dry ash-free basis elemental components of coal, %; Car, Har, Oar, Nar, Sar are the as-received basis elemental components of coal, %; V RO2，daf , V N2，daf , V O2 , daf are the amounts of various standard gases calculated based on dry basis components; m3 / kg; α is the excess air coefficient; is the volume fraction of oxygen in air; X cucr is the correction amount for unburned carbon loss; α fh , αlz is the share of fly ash and slag; C fh 、C lz is the carbon content of fly ash and slag, %, V gk,daf is the flue gas volume calculated based on dry basis composition, M ar is the as-received moisture of coal. Calculated according to Article 3 and Article 4; For the calculation of relevant variables, please refer to Liu Jizhen, Liu Huanzhang, Chang Taihua, Tan Wen, Wang Yong. Boiler coal quality analysis model under partial flue gas information. Proceedings of the CSEE, 2007(14): 1-5. DOI: 10.13334 / j.0258-013.pcsee.2007.14.001.

[0196] 11. Solve the system of equations listed in Article 10 to obtain the lower calorific value Qar of the coal entering the furnace and the elemental composition of each component on the as-received basis.

[0197] 12. Calculate the boiler efficiency, refer to GB10184-2015 "Regulations for Performance Tests of Utility Boilers", where the carbon content of fly ash and the carbon content of slag are calculated according to Article 3 and Article 4. The coal quality data used for calculating the boiler efficiency are calculated from Articles 8-11.

[0198] 13. According to the calculated boiler efficiency, return to Article 8 to iteratively calculate the coal quality data until the difference between the lower calorific value Qar in the coal quality data calculated in Article 11 and the lower calorific value Qar0 calculated in Article 8 is less than a certain value:

[0199]

[0200] 14. Divide the flue gas heat exchanger between the furnace outlet section and the low-temperature zone outlet section into four types of heat transfer modules according to the flue gas flow, namely the platen heating surface, semi-radiant heating surface, convective heating surface, and additional heating surface. The convective heating surface of this boiler includes the economizer, primary reheater, and secondary superheater. The semi-radiant heating surface includes the secondary reheater. The platen heating surface includes the primary superheater and the tertiary superheater.

[0201] 15. Starting from the economizer outlet flue gas temperature with relatively accurate measurement, along the direction opposite to the flue gas flow, apply the heat balance principle of the heating surface to gradually calculate the flue gas temperature between each heating surface, and finally calculate the flue gas temperature at the inlet of the primary superheater platen, that is, the furnace outlet flue gas temperature. The heat balance calculation methods for each type of heating surface are as follows:

[0202] For the platen heating surface:

[0203] Qz = Qf1 + Qf2 + Qd;

[0204] Qy = Qf2 + Qd - Qfh;

[0205] In the formula:

[0206] Heat absorption of the working medium in the heat exchanger, Qz, kJ / kg;

[0207] Radiant heat received by the screen from the furnace, Qf1, kJ / kg;

[0208] Radiant heat release from the flue gas between the screens to the tube screens, Qf2, kJ / kg;

[0209] Convective heat release from the flue gas between the screens to the tube screens, Qd, kJ / kg;

[0210] Heat transferred from the flue gas to the working medium, Qy;

[0211] Heat radiated from the flue gas between the screens to the heating surface behind the screen, Qfh

[0212]

[0213] Where:

[0214] D: Working medium flow rate, kg / s; i out : Enthalpy of the working medium at the outlet, kJ / kg; i in : Enthalpy of the working medium at the inlet, kJ / kg;

[0215]

[0216]

[0217] Where:

[0218] Heat preservation coefficient considering heat dissipation loss; I‘ and I“: Enthalpy of the flue gas at the inlet and outlet of the heating surface, kJ / kg; Heat brought in by air leakage, kJ / kg; α pj : Screen emissivity; T pj : Average flue gas temperature of the screen, °C; H fc : Outlet area of the screen, m 2 ;

[0219]

[0220]

[0221] Where:

[0222] q fp : Radiant heat load of the furnace at the height where the screen is located; H fp : Radiant heating surface area of the screen, m 2 ; η gd : Distribution coefficient of the heat load at the furnace height; Φ: Heat preservation coefficient of the furnace; Q yx : Effective heat release per unit fuel in the furnace, kJ / kg; h lcy : Flue gas enthalpy at the furnace outlet, kJ / kg; Q fr: Radiation heat load from furnace to platen heating surface, kJ / kg; F lt : Furnace wall area, m 2 ; B j : Actual fuel combustion rate, kg / h;

[0223]

[0224] In the formula:

[0225] α f : Radiation heat release coefficient; T pj : Average flue gas temperature, °C; T hw : Ash fouling wall temperature, °C;

[0226]

[0227] In the formula:

[0228] α d : Convective heat release coefficient, kW / (m 2 °C); D w : Outer diameter of tube, m; s2: Longitudinal pitch, m; x: Angular coefficient of platen;

[0229] For semi-radiant heating surface:

[0230] Qz = Qfq + Qf2 + Qd

[0231] Qy = Qf2 + Qd - Qfh;

[0232] In the formula:

[0233] Heat absorption of heat exchanger working medium Qz, kJ / kg;

[0234] Radiant heat received from furnace and upper heating surface Qfq, kJ / kg;

[0235] Radiant heat release from flue gas between platens to tube platen Qf2, kJ / kg;

[0236] Convective heat release from flue gas between platens to tube platen Qd, kJ / kg;

[0237]

[0238] In the formula:

[0239] α lpj : Emissivity of upper platen; T lpj : Average flue gas temperature of upper platen, °C; H lfc : Outlet area of upper platen, m2; x lpj : Angular coefficient of inlet cross-section of upper platen to outlet cross-section;

[0240] For convective heating surface:

[0241] Qz = Qf2 + Qd;

[0242] Qy = Qf2 + Qd;

[0243] Where:

[0244] The heat absorption of the working medium of the heat exchanger Qz, kJ / kg;

[0245] The radiative heat release from the flue gas between the screens to the tube screens Qf2, kJ / kg;

[0246] The convective heat release from the flue gas between the screens to the tube screens Qd, kJ / kg;

[0247] For the additional heating surface:

[0248] The additional heating surface of this boiler mainly refers to the hanging tubes arranged in the boiler and the wall-type water-cooled walls above the furnace outlet. The hanging tubes start from the inlet header of the primary superheater above the furnace, pass through the upper part of the entire boiler furnace, and finally flow into the platen primary superheater directly receiving the furnace radiation; the additional wall-type water-cooled walls are arranged upward from the water-cooled walls at the furnace outlet, covering the upper part of the entire furnace, and the working medium directly flows into the outlet header of the water-cooled walls arranged in the upper part of the furnace.

[0249] The calculation of the additional heating surface mainly includes two parts. One part is the calculation of the additional water-cooled wall, and the other part is the calculation of the hanging tubes. The overall calculation idea is to divide the additional heating surface into multiple sections according to the main heating surface of the boiler where it is located, and the calculation of each section is carried out together with the main heating surface. During the calculation, the heat transfer coefficient of each section of the additional heating surface is made the same as the calculation method of the main heating surface.

[0250] 16. Calculate the distribution coefficient of the inter-screen thermal deviation of the primary superheater based on the measured temperature of the outer wall of the primary superheater furnace, that is:

[0251]

[0252] Where

[0253] Δi pc - The enthalpy increase of the monitored tube of a certain screen (kJ / kg)

[0254] Δi pj - The average enthalpy increase of the heating surface (kJ / kg)

[0255] 17. The distribution coefficient of the inter-screen thermal deviation is the ratio of the product of the distribution coefficient of the heat load deviation and the distribution coefficient of the heating surface deviation to the distribution coefficient of the flow rate deviation, that is

[0256]

[0257] Where:

[0258] η r: Distribution coefficient of heat load deviation between screens; η j : Distribution coefficient of area deviation between screens; η l : Distribution coefficient of flow deviation between screens.

[0259] The distribution coefficient of heat load deviation between screens can be obtained as follows:

[0260]

[0261] The distribution coefficient of flow deviation between screens can be calculated according to the hydrodynamic calculation standard. The distribution coefficient of area deviation between screens depends on the specific structure of the heating surface.

[0262] 18. The flue gas temperature distribution at the furnace outlet, i.e., the flue gas temperature distribution at the inlet of the primary superheater, is calculated as follows:

[0263] TGAS i = η r (TGAS inavg + TGAS outavg - t inavg - t outavg ) + t inavg + t outi - TGAS outavg

[0264] In the formula:

[0265] TGAS inavg : Average flue gas temperature at the inlet of the primary superheater; TGAS outavg : Average flue gas temperature at the outlet of the primary superheater; t inavg : Average steam temperature at the inlet of the primary superheater; t outavg : Average steam temperature at the outlet of the primary superheater; t outi : Outlet wall temperature of the monitoring tube of the i-th screen; η r is the distribution coefficient of heat load deviation between screens.

[0266] 19. The real-time calculation results can be displayed on the screen of the independent monitoring system, or the results can be uploaded to the DCS through the data communication interface and displayed on the DCS screen in the centralized control center; the power plant operators can see the on-line real-time measured values of the flue gas temperature at the furnace outlet, and display the flue gas temperature at the furnace outlet and the flue gas temperature distribution along the furnace width in the form of a trend chart or a data table in real time, so as to monitor the operation of the boiler in real time and ensure the operation safety.

[0267] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler, characterized in that, This method does not require additional boiler measurement points. When calculating the flue gas temperature at the furnace outlet, the soft measurement of the quality of the coal entering the furnace is considered simultaneously, so that the monitoring result of the flue gas temperature at the furnace outlet can more accurately reflect the true value of the flue gas temperature at the furnace outlet in real time, and at the same time provide the flue gas temperature distribution along the width direction of the furnace; This method specifically includes the following steps: Step S1) Establish a database of equipment structure parameters; Step S2) Establish a data interface with the power plant's distributed control system or SIS system and read in operation data; Step S3) According to the historical fly ash carbon content test data of the power plant, establish a neural network prediction model for fly ash carbon content; Step S4) According to the historical slag carbon content test data of the power plant, establish a neural network prediction model for slag carbon content; Step S5) According to the energy balance and mass balance principles of the coal mill system, establish a calculation model for the moisture content of the coal entering the furnace; Step S6) Set the initial boiler efficiency; Step S7) Calculate the lower calorific value Qar0 of the coal entering the furnace according to the total heat absorption of the working medium in the boiler; Step S8) According to the historical coal quality data of the power plant, establish a neural network prediction model for the ash content of the coal entering the furnace; Step S9) According to the material balance and the principle of chemical analysis of coal combustion, establish a system of equations for the relationship between coal combustion products and input elements; solve the system of equations to obtain the lower calorific value Qar of the coal entering the furnace and the coal quality elemental analysis data; Step S10) Calculate the current boiler efficiency; Step S11) According to the deviation between the lower calorific value Qar of the coal entering the furnace and Qar0, perform iterative calculations for steps S7 - S10; Step S12) Divide the flue gas heat exchanger between the furnace outlet section and the low-temperature zone outlet section into four types of heat exchange modules according to the flue gas flow, namely, platen heating surface, semi-radiant heating surface, convective heating surface, and additional heating surface; Step S13) Starting from the flue gas temperature at the outlet of the low-temperature zone heating surface, along the direction opposite to the flue gas flow, apply the principle of heat balance of the heating surface to gradually calculate the flue gas temperature between each heating surface, and finally calculate the flue gas temperature at the furnace outlet; Step S14) Calculate the inter-screen thermal deviation distribution coefficient of this heating surface according to the furnace outer wall temperature measurement points and operation parameters of the heating surface at the furnace outlet; according to the structure and header system layout of this heating surface, calculate the inter-screen flow deviation distribution coefficient and inter-screen area deviation distribution coefficient of this heating surface, and obtain the heat load deviation distribution coefficient of this heating surface; Step S15) Obtain the flue gas temperature distribution along the width direction of the furnace outlet according to the heat load deviation distribution coefficient of this heating surface, the average inlet and outlet flue gas temperature of this heating surface, the outlet wall temperature of each monitoring tube of this heating surface, and the average inlet and outlet steam temperatures of this heating surface.

2. The on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler according to claim 1, characterized in that, The operation data read in step S2) includes: generator power, feed water temperature, feed water flow rate, main steam flow rate, main steam temperature, reheated steam temperature, atmospheric pressure, atmospheric temperature, oxygen content, desuperheating water flow rate for superheated steam, desuperheating water flow rate for reheated steam, burner tilt angle, SOFA air volume, CCOFA air volume, secondary air volume, coal feeding amount of each mill, primary air volume of each mill, outlet air and powder temperature of each mill, furnace and wind box differential pressure, inlet and outlet steam temperatures of each heating surface, and flue gas temperature at the outlet of the economizer.

3. The on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler according to claim 1, characterized in that, The specific content of step S3) is: Based on the historical fly ash carbon content test data of the power plant, a neural network prediction model for fly ash carbon content is established. The operating parameters such as boiler evaporation, burner swing angle, oxygen content, SOFA air volume, CCOFA air volume, main characteristics of coal quality, coal feeding amount of each coal mill, furnace and wind box differential pressure, and primary air volume of each coal mill are used as the input variables of the neural network, and the fly ash carbon content is used as one output of the neural network. The neural network adopts the BP neural network; The specific content of step S4) is as follows: Based on the historical slag carbon content test data of the power plant, a neural network prediction model for slag carbon content is established. The operating parameters such as boiler evaporation, burner swing angle, oxygen content, SOFA air volume, CCOFA air volume, main characteristics of coal quality, coal feeding amount of each coal mill, furnace and wind box differential pressure, and primary air volume of each coal mill are used as the input variables of the neural network, and the slag carbon content is used as one output of the neural network. The neural network adopts the BP neural network, where the main characteristics of coal quality include calorific value, moisture, ash content, and volatile matter of the coal entering the furnace.

4. The on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler according to claim 1, characterized in that, The specific content of step S5) is as follows: According to the energy balance and mass balance principles of the coal mill system, that is, the total heat input at the starting section of each coal mill system is equal to the total heat carried out and consumed at the terminal section, solving this system of equations can obtain the moisture content of the coal entering the furnace. The specific formula is as follows: q gz +q rc +q nm +q mf +q lf =q sf +q fq +q jr +q sr In the formula: The total heat input for drying and grinding 1 kg of coal in the coal preparation system includes: Physical heat q of the desiccant gz ; Physical heat of raw coal q rc ; The heat q generated by grinding during the operation of the coal mill nm ; Physical heat q of the sealed air mf ; Physical heat q of the leaked-in cold air lf ; The total heat carried out and consumed for drying and grinding 1 kg of coal in the coal preparation system includes: The heat q consumed for evaporating the moisture in raw coal sf ; The heat quantity q carried out by the exhausted air of the desiccant fq ; The heat q consumed by the heating fuel jr ; Equipment heat dissipation loss q sr .

5. The on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler according to claim 1, characterized in that, The specific content of step S7) for calculating the lower calorific value Qar0 of the coal entering the furnace according to the total heat absorption of the working medium in the boiler is as follows: The total heat absorption Q of the working fluid in the boiler boiler is as follows: Q boiler = G ms (h ms - h fw ) + G rc (h rh - h rc ) + G rj (h rh - h rj ) + G sj (h ms - h sj ) Among which G ms is the main steam flow rate, h ms is the main steam enthalpy, h fw is the feed - water heat enthalpy, G rc is the cold reheat flow rate, h rh is the hot - end enthalpy of the reheated steam, h rc is the cold - end enthalpy of the reheated steam, G rj is the desuperheating water flow rate of the reheater, h rj is the desuperheating water enthalpy of the reheater, G sj is the desuperheating spray water flow rate of the superheater, h sj is the desuperheating spray water enthalpy of the superheater; Calculate the lower calorific value of the coal entering the furnace: where Q ar0 is the lower calorific value brought into the boiler per kilogram of coal fed into the furnace, η0 is the boiler efficiency, and G coal is the amount of coal fed into the boiler.

6. The on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler according to claim 1, characterized in that, The specific content of step S9) for establishing the relationship system of equations between the coal combustion products and the input elements according to the material balance and the principle of chemical analysis of coal combustion is as follows: According to the material balance and the principle of chemical analysis of coal combustion, express the various gases generated by coal combustion as equations of dry ash-free basis element content: C daf = 53.59γ co2 (V RO2,daf + V N2,daf + V O2,daf ) + (1 - γ co2 )X cucr S daf = 142.86γ so2 (V RO2,daf + V N2,daf + V O2,daf O daf = k1C daf + k2 N daf = k3H daf C daf +H daf +O daf +N daf +S daf = 100 V RO2,daf = 0.01866(C daf + 0.375S daf ) - 0.01866X cucr V gk,daf = 0.0889(C daf + 0.375S daf ) + 0.265H ar - 0.0333O ar - 0.0889X cucr C cucr = α fh C fh + a lz C lz Q ar = 339C ar + 1028H ar - 109(O ar - S ar ) - 25M ar where k1, k2, and k3 are correlation coefficients related to the dry ash-free basis composition; C cucr is the average unburned carbon content in the ash residue; γ co2 、γ o2 、γ so2 are the gas volume fractions in the flue gas; C daf 、H daf 、O daf 、N daf 、S daf are the dry ash-free basis elemental compositions of the coal; C ar 、H ar 、O ar 、N ar 、S ar are the as-received basis elemental compositions of the coal; V RO2,daf 、V N2,daf 、V O2,daf are the amounts of various standard gases calculated based on the dry basis composition; α is the excess air coefficient; is the volume fraction of oxygen in the air; X cucr is the correction amount for unburned carbon loss; α fh 、α lz are the fractions of fly ash and slag; C fh 、C lz are the carbon contents of fly ash and slag, V gk,daf is the flue gas volume calculated based on the dry basis composition, M ar is the as-received basis moisture content of the coal.

7. The on-line monitoring method for the flue gas temperature at the furnace outlet of a coal-fired power plant boiler according to claim 1, characterized in that, The heat balance calculation methods for various types of heating surfaces in step S13) are as follows: a) For the platen heating surface: Qz = Qf1 + Qf2 + Qd; Qy = Qf2 + Qd - Qfh; In the formula: The heat absorption of the working medium in the heat exchanger Qz; The radiant heat received by the platen from the furnace Qf1; The radiant heat release from the flue gas between the platens to the tube platen Qf2; The convective heat release from the flue gas between the platens to the tube platen Qd; The heat transferred from the flue gas to the working medium Qy; The radiant heat from the flue gas between the platens to the heating surface behind the platen Qfh; In the formula: D is the working fluid flow rate; i out is the enthalpy of the working fluid at the outlet; i in is the enthalpy of the working fluid at the inlet; B j is the actual fuel combustion quantity; In the formula: The heat retention coefficient considering heat dissipation loss; I′ and I" are the enthalpies of flue gas at the inlet and outlet of the heating surface; is the heat brought in by air leakage; α pj is the screen emissivity; T pj is the average flue gas temperature of the screen; H fc is the outlet area of the screen; In the formula: q fp is the furnace radiant heat load at the height where the screen is located; H fp is the radiation heating surface area of the screen; η gd is the furnace height heat load distribution coefficient; Φ is the furnace heat preservation coefficient; Q yx is the effective heat release in the furnace per unit fuel; h lcy is the flue gas enthalpy at the furnace outlet; Q fr is the radiation heat load from the furnace to the screen heating surface; F lt is the furnace wall area; B j is the actual fuel combustion amount; In the formula: α f is the radiative heat release coefficient; T pj is the average flue gas temperature; T hw is the fouled wall temperature; In the formula: α d is the convective heat transfer coefficient; D w is the outer diameter of the tube; s2 is the longitudinal pitch; x is the angle factor of the screen; b) For the semi-radiant heating surface: Qz = Qfq + Qf2 + Qd Qy = Qf2 + Qd - Qfh; In the formula: The heat absorption of the working medium in the heat exchanger Qz; The radiant heat received from the furnace and the upper-level heating surface Qfq; The radiant heat release from the flue gas between the platens to the tube platen Qf2; The convective heat release from the flue gas between the platens to the tube platen Qd; In the formula: α lpj is the blackness of the upper-level screen; T lpj is the average flue gas temperature of the upper-level screen; H lfc is the outlet area of the upper-level screen; x lpj is the angle coefficient of the inlet cross-section to the outlet cross-section of the upper-level screen; c) For the convective heating surface: Qz = Qf2 + Qd; Qy = Qf2 + Qd; In the formula: The heat absorption of the working medium in the heat exchanger Qz; The radiant heat release from the flue gas between the platens to the tube platen Qf2; The convective heat release from the flue gas between the platens to the tube platen Qd; d) For the additional heating surface: The calculation of additional heating surfaces mainly includes two parts. One is the calculation of additional water walls, and the other is the calculation of suspension tubes. In the calculation process, the additional heating surfaces are divided into multiple segments according to the main heating surfaces of the boiler where they are located, and the calculation of each segment is carried out together with the main heating surface. During the calculation, the heat transfer coefficient of each segment of the additional heating surface is calculated in the same way as that of the main heating surface.

8. A method for on-line monitoring of the flue gas temperature at the furnace outlet of a coal-fired power plant boiler, characterized in that, The calculation of the inter-screen heat deviation distribution coefficient of the heating surface in step S14) is specifically as follows: Based on the measured points of the outer wall temperature of the primary superheater, calculate the inter-screen heat deviation distribution coefficient of the primary superheater, that is: In the formula Δi pc is the enthalpy increase of a certain screen monitoring tube; Δi pj is the average enthalpy increase of the heating surface; The inter-screen heat deviation distribution coefficient is the ratio of the product of the heat load deviation distribution coefficient and the heating surface area deviation distribution coefficient to the flow rate deviation distribution coefficient, that is Where: η r is the deviation distribution coefficient of the heat load between screens; η j is the deviation distribution coefficient of the area between screens; η l is the deviation distribution coefficient of the flow rate between screens; The heat load deviation distribution coefficient between screens can be obtained:

9. A method for on-line monitoring of the flue gas temperature at the furnace outlet of a coal-fired power plant boiler, characterized in that, The calculation of the flue gas temperature distribution at the furnace outlet in step S15) is specifically as follows: The flue gas temperature distribution at the furnace outlet, that is, the flue gas temperature distribution at the inlet of the primary superheater, is calculated according to the following formula: TGAS i = η r (TGAS inavg + TGAS outavg - t inavg - t outavg ) + t inavg + t outi - TGAS outavg Where: TGAS inavg is the average flue gas temperature at the inlet of the primary superheater; TGAS outavg is the average flue gas temperature at the outlet of the primary superheater; t inavh is the average steam temperature at the inlet of the primary superheater; t outavg is the average steam temperature at the outlet of the primary superheater; t outi is the outlet wall temperature of the monitoring tube of the i-th screen; η r is the distribution coefficient of the heat load deviation between screens.

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