Online monitoring and analyzing method for performance parameters of air preheater

Abstract

The invention discloses an on-line monitoring and analyzing method for performance parameters of an air preheater, which comprises the following steps of: firstly, setting performance monitoring conditions, and extracting flue gas samples at a flue gas inlet and a flue gas outlet for component analysis; secondly, monitoring parameters are collected, temperature, pressure, flow and gas component collecting devices are installed according to preset positions, and temperature, static pressure, mass flow, the percentage content of O and CO in dry flue gas, atmospheric pressure and relative humidity parameters are collected; next, calculating performance parameters, and respectively calculating air leakage, non-diluted flue gas outlet temperature, energy balance, mixed air temperature, temperature difference, thermal efficiency, pressure drop and average pressure difference based on the collected parameters; and finally, comparing a test value with a design value: calculating a thermal operation margin according to an ASME equation and the correction curve, correcting air leakage and pressure drop, comparing with the design value, and evaluating the performance state of the air preheater. The problems that traditional offline monitoring is discontinuous and existing online monitoring is incomplete are solved, and data support is provided for equipment operation and maintenance.

Description

A method for online monitoring and analysis of air preheater performance parameters Technical Field

[0001] This invention relates to the field of industrial thermal system equipment monitoring technology, specifically to an online monitoring and analysis method for the performance parameters of an air preheater. Background Technology

[0002] As a core energy-saving device in industrial thermal systems, the air preheater utilizes the heat from the high-temperature flue gas at the boiler's tail end to preheat the cold air entering the boiler, thereby reducing exhaust gas temperature, improving boiler thermal efficiency, and reducing energy consumption and carbon emissions. With increasing industrial energy efficiency requirements and stricter environmental regulations, the operating performance of the air preheater directly impacts the economy, safety, and environmental friendliness of the thermal system, making real-time and accurate monitoring and analysis of its performance parameters a critical need. Traditional offline monitoring has limitations: it relies on periodic shutdowns for manual sampling and testing, requiring interruptions to the production process, affecting continuity and causing economic losses, and is particularly unsuitable for continuous operation scenarios such as large thermal power generating units; furthermore, the test results only reflect the instantaneous state and cannot capture the dynamic changes in equipment performance under different operating conditions such as load fluctuations, fuel changes, and seasonal temperature differences. It is difficult to detect early performance degradation problems such as ash accumulation and blockage, and seal wear in a timely manner, which can easily exacerbate increased equipment energy consumption, the risk of localized overheating damage, and even system failure. The shortcomings of existing online monitoring technologies: Some companies' online monitoring devices only collect basic parameters such as temperature, pressure, and flow rate through sensors at key points. This results in insufficient rationality in sensor layout and a lack of parameter correlation analysis, making it impossible to accurately determine the root cause of performance abnormalities. At the same time, the data processing methods are simple, only enabling real-time display and over-limit alarms. They cannot combine historical operating data, design parameters, and operating conditions for in-depth analysis, making it difficult to quantify the degree of performance degradation, predict fault development trends, and provide accurate decision support for operation and maintenance.

[0003] In summary, developing an online monitoring and analysis method for air preheater performance parameters that enables real-time acquisition of multiple parameters, in-depth data analysis, and accurate performance status assessment has become an urgent need in the current industrial field. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an online monitoring and analysis method for air preheater performance parameters. This method enables real-time monitoring and accurate calculation of air leakage from the air to the flue gas side, pressure drop between flue gas and air, and thermal performance of the air preheater. It solves the problems of discontinuous traditional offline monitoring and incomplete existing online monitoring, providing data support for equipment operation and maintenance.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for online monitoring and analysis of air preheater performance parameters includes the following steps:

[0007] S1. Set performance monitoring conditions: Take flue gas samples at the flue gas inlet and outlet for component analysis; keep the air and flue gas flow rates of the air preheater constant and the O2 content stable during the monitoring period, keep the steam generator load close to the design value, and run stably for at least 30 minutes before the monitoring test begins; the monitoring duration is at least 15 minutes, and at least two sets of consistent data are obtained;

[0008] S2. Collect and monitor parameters: Install temperature, pressure, flow rate, and gas composition acquisition devices at preset locations to collect parameters such as temperature, static pressure, mass flow rate, percentage of O2 and CO in dry flue gas, atmospheric pressure, and relative humidity. When acquiring temperature, a probe and thermocouple are used to form a grid covering the cross-section of the duct. Static pressure acquisition is achieved through a fixed measuring hole in the pipe wall. When acquiring gas composition, the sampling probe is kept to extract the same volume of flue gas.

[0009] S3. Calculate performance parameters: Based on the parameters collected in step S2, calculate air leakage, non-diluted flue gas outlet temperature, energy balance, mixed air temperature, temperature difference, thermal efficiency, pressure drop and average pressure difference respectively.

[0010] S4. Compare test values ​​with design values: Calculate the thermal operating margin based on the ASME equations and correction curves, correct for air leakage and pressure drop, and compare with the design values ​​to evaluate the performance status of the air preheater; the air leakage in step S3 is calculated using the following formula:

[0011] Where the coefficient

[0012]

[0013] ρ g The density of the flue gas under standard conditions is given by k, where k is the percentage of moisture content at the flue gas inlet; the outlet temperature of the non-dilutable flue gas is calculated as follows:

[0014] Tg 2NL =L×(Tg2-Ta1)+Tg2

[0015] Calculate where L is the decimal leakage value, Tg2 is the flue gas outlet temperature, and Ta1 is the air inlet temperature.

[0016] Furthermore, the temperature acquisition locations in step S2 include: secondary air inlet, secondary air outlet, primary air inlet, flue gas inlet, and flue gas outlet; the thermocouples have independent correction coefficients and are marked on the calibration certificate.

[0017] The flow rate acquisition in step S2 includes: the flue gas inlet velocity is preferentially measured by crossing the inlet plane with a Pitot tube; the portion that cannot be directly measured is estimated by CO and O2 content and combustion calculation values; the secondary air outlet flow rate is measured by lateral movement of the Pitot tube, and the flow rate of the blower is compared to confirm the balance; the primary air flow rate is calculated by energy balance or measured by the Pitot tube, and cross-verified by the blower current and coal mill parameters.

[0018] In step S3, the mass flow rate of the flue gas at the inlet of the two-compartment air preheater is calculated according to...

[0019] Mg1×ΔT g ×Cp g =Ma×ΔT a ×Cp a

[0020] Calculation; flue gas mass of the three-compartment air preheater according to

[0021] Mg×ΔT g ×Cp g =Ma1×ΔT a1 ×Cp a1 +Ma2×ΔT a2 ×Cp a2

[0022] Calculate, and assume that heat loss is negligible.

[0023] In step S3, the inlet temperature of the mixed air is as follows:

[0024] Calculation, outlet temperature according to

[0025]

[0026] Calculate the temperature difference on the flue gas side.

[0027] ΔT g =Tg1-Tg 2NL

[0028] Air-side temperature difference

[0029] ΔT a =Ta2-Ta1.

[0030] In step S3, the flue gas side thermal efficiency is calculated according to...

[0031]

[0032] Calculate the flue gas side pressure drop.

[0033] ΔP g =Psg1-Psg2,

[0034] Secondary wind side pressure drop

[0035] ΔP as =Psa 1s -Psa 2s ,

[0036] Primary wind side pressure drop

[0037] ΔP ap =Psa 1p -Psa 2p .

[0038] In step S4, the air leakage correction is performed.

[0039]

[0040] Calculation, LR represents design-related air leakage, ρ gD ρ gT The respective flue gas densities under design and test conditions, ΔP gD ΔP gT These represent the flue gas side pressure drop under design and test conditions, T a1D T a1T These refer to the air inlet temperature for design and test operating conditions, respectively.

[0041] The instruments used in step S2 meet the following requirements: thermocouple tolerance ±1.5℃, temperature measuring instrument error ±1.0℃, oxygen analyzer error ±0.1% O2, pressure measuring instrument error ±4%, flue gas side efficiency retest deviation ±5%, and inlet oxygen retest deviation from design value ±1% O2.

[0042] If the flue gas flow is stratified in step S2, the velocity is measured separately at each position of the cross-section of the airway and is proportional to the corresponding flue gas flow rate. The average value is then taken. Furthermore, the dynamic pressure is measured at the same position and moment as the flue gas sampling and temperature measurement.

[0043] Compared with the existing technology, the beneficial effects of the present invention are: (1) Real-time continuous monitoring: The core performance parameters of the air preheater can be collected and analyzed without shutdown, avoiding the impact of traditional offline monitoring on production continuity and reducing economic losses. It is especially suitable for continuous operation scenarios such as large thermal power generating units. (2) Comprehensive monitoring: By scientifically arranging multiple types of sensors such as temperature, pressure, flow, and gas composition, the entire process of the air preheater on both the air side and the flue gas side is covered. Combined with multi-parameter correlation analysis, the root cause of performance abnormalities can be accurately located. (3) Optimized analysis depth: A multi-dimensional calculation model for air leakage, temperature, energy balance, efficiency, and pressure drop is established. Combined with equipment design parameters and operating conditions, the degree of performance degradation and the prediction of fault development trends are realized, providing accurate decision support for equipment operation and maintenance. (4) Data accuracy assurance: The instrument accuracy requirements and parameter collection specifications are clearly defined. Through measures such as correction coefficients, air intrusion prevention, and layered measurement, measurement errors are reduced, ensuring the reliability of monitoring and analysis results. Detailed Implementation

[0044] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments.

[0045] A method for online monitoring and analysis of air preheater performance parameters includes the following steps:

[0046] S1. Set performance monitoring conditions: Take flue gas samples at the flue gas inlet and outlet for component analysis; keep the air and flue gas flow rates of the air preheater constant and the O2 content stable during the monitoring period, keep the steam generator load close to the design value, and run stably for at least 30 minutes before the monitoring test begins; the monitoring duration is at least 15 minutes, and at least two sets of consistent data are obtained;

[0047] S2. Collect and monitor parameters: Install temperature, pressure, flow rate, and gas composition acquisition devices at preset locations to collect parameters such as temperature, static pressure, mass flow rate, percentage of O2 and CO in dry flue gas, atmospheric pressure, and relative humidity. When acquiring temperature, a probe and thermocouple are used to form a grid covering the cross-section of the duct. Static pressure acquisition is achieved through a fixed measuring hole in the pipe wall. When acquiring gas composition, the sampling probe is kept to extract the same volume of flue gas.

[0048] S3. Calculate performance parameters: Based on the parameters collected in step S2, calculate air leakage, non-diluted flue gas outlet temperature, energy balance, mixed air temperature, temperature difference, thermal efficiency, pressure drop and average pressure difference respectively.

[0049] S4. Compare test values ​​with design values: Calculate the thermal operating margin based on the ASME equations and correction curves, correct for air leakage and pressure drop, and compare with the design values ​​to evaluate the performance status of the air preheater; the air leakage in step S3 is calculated using the following formula:

[0050] Where the coefficient

[0051]

[0052] ρ g The density of the flue gas under standard conditions is given by k, where k is the percentage of moisture content at the flue gas inlet; the outlet temperature of the non-dilutable flue gas is calculated as follows:

[0053] Tg 2NL =L×(Tg2-Ta1)+Tg2

[0054] Calculate where L is the decimal leakage value, Tg2 is the flue gas outlet temperature, and Ta1 is the air inlet temperature.

[0055] The temperature acquisition locations in step S2 include: secondary air inlet, secondary air outlet, primary air inlet, flue gas inlet, and flue gas outlet; the thermocouples have independent correction coefficients and are marked on the calibration certificate.

[0056] The flow rate acquisition in step S2 includes: the flue gas inlet velocity is preferentially measured by crossing the inlet plane with a Pitot tube; the portion that cannot be directly measured is estimated by CO and O2 content and combustion calculation values; the secondary air outlet flow rate is measured by lateral movement of the Pitot tube, and the flow rate of the blower is compared to confirm the balance; the primary air flow rate is calculated by energy balance or measured by the Pitot tube, and cross-verified by the blower current and coal mill parameters.

[0057] In step S3, the mass flow rate of the flue gas at the inlet of the two-compartment air preheater is calculated according to...

[0058] Mg1×ΔT g ×Cp g =Ma×ΔT a ×Cp a

[0059] Calculation; flue gas mass of the three-compartment air preheater is calculated as Mg×ΔT g ×Cp g =Ma1×ΔT a1 ×Cp a1 +Ma2×ΔT a2 ×Cp a2 Calculate, and assume that heat loss is negligible.

[0060] In step S3, the inlet temperature of the mixed air is as follows:

[0061]

[0062] Calculation, outlet temperature according to

[0063]

[0064] Calculate the temperature difference ΔT on the flue gas side. g =Tg1-Tg 2NL

[0065] Air-side temperature difference ΔT a =Ta2-Ta1.

[0066] In step S3, the flue gas side thermal efficiency is calculated according to...

[0067]

[0068] Calculate the flue gas side pressure drop ΔP. g =Psg1-Psg2,

[0069] Secondary wind side pressure drop ΔP as =Psa 1s -Psa 2s Primary wind side pressure drop ΔP ap =Psa 1p -Psa 2p .

[0070] In step S4, the air leakage correction is performed.

[0071]

[0072] Calculation, LR represents design-related air leakage, ρ gD ρ gT The respective flue gas densities under design and test conditions, ΔP gD ΔP gT These represent the flue gas side pressure drop under design and test conditions, T a1D T a1T These refer to the air inlet temperature for design and test operating conditions, respectively.

[0073] The instruments used in step S2 meet the following requirements: thermocouple tolerance ±1.5℃, temperature measuring instrument error ±1.0℃, oxygen analyzer error ±0.1% O2, pressure measuring instrument error ±4%, flue gas side efficiency retest deviation ±5%, and inlet oxygen retest deviation from design value ±1% O2.

[0074] If the flue gas flow is stratified in step S2, the velocity is measured separately at each position of the airway cross section and is proportional to the corresponding flue gas flow rate. The average value is then taken. Furthermore, the dynamic pressure is measured at the same position and moment as the flue gas sampling and temperature measurement. In cases of severe stratification, the dynamic pressure must be measured.

[0075] When collecting gas components in step S2, measures must be taken to prevent air intrusion in the sampling pipeline and the analytical instrument, and the instrument must be kept clean. When collecting flow rate, air leakage from the bypass and recirculation baffle, as well as the mutual influence between hot and cold pipelines, must be considered.

[0076] Performance monitoring conditions settings:

[0077] During the monitoring of the performance parameters of the air preheater, each flue gas sample must be taken from the flue gas inlet and outlet for composition analysis to determine the parameters related to air leakage. At the same time, the air and flue gas flow rates of the air preheater must be kept constant during the monitoring period to ensure stable O2 content. The steam generator load should be as close as possible to the design value and stabilized for at least 30 minutes before each monitoring test. The monitoring duration should be stable for at least 15 minutes, and at least two sets of completely consistent monitoring data should be obtained from one air preheater.

[0078] Core detection parameters:

[0079] The key parameters that need to be collected, such as temperature, pressure, flow rate, and gas composition, are shown in the table below:

[0080]

[0081]

[0082]

[0083] Parameter acquisition requirements:

[0084] (1) Temperature Acquisition: The fixed probe and thermocouples are installed together to form a grid covering the entire cross-section of the air duct; a fast-scanning digital recorder output can be used to track the measured values ​​of all thermocouples as they change over time and space; each thermocouple must have its own correction factor, which must be clearly marked on the calibration certificate. The temperature acquisition location must meet the following requirements:

[0085] Secondary air inlet: Blower outlet (after primary air and soot blower sealing air are stopped)

[0086] Secondary air outlet: At the inlet of the bellows (before other gases are added)

[0087] Primary air inlet: Primary air fan outlet (after bypass shutdown)

[0088] Flue gas inlet: behind the ash hopper at the economizer outlet (on the horizontal section).

[0089] Flue gas outlet: behind the ash hopper and before the bend of the dust collector.

[0090] (2) Static pressure acquisition: Connect the pressure gauge to the pressure measuring hole on the transition pipe wall of the air preheater, and measure the average static pressure through the fixed measuring hole on the pipe wall to ensure that the measurement accuracy is higher than that of the transverse moving method.

[0091] (3) Gas composition sampling: A single-point sampling probe is used to move comprehensively in the air duct, or a multi-point sampling probe is used to extract flue gas samples from the entire air duct, and each sampling probe extracts the same volume of flue gas (the sampling tube length must be consistent); measures are taken to prevent air intrusion in the flue gas analysis instrument and sampling pipeline, the instrument must be kept clean, and human error should be reduced.

[0092] (4) Flow and velocity data acquisition:

[0093] The flue gas inlet velocity is initially determined by using a pitot tube to cross the flue gas inlet plane; for the portion that cannot be directly measured, the flue gas composition is determined by measuring the CO and O2 content in the pipe, combining the combustion calculation value and the flue gas recirculation value, and then estimating the flow rate based on the unit weight of the fuel burned.

[0094] The secondary air outlet flow rate is measured by moving a Pitot tube across the air outlet duct, and the flow rates of the two supply fans (taken from the axial flow fan mounting components) are compared to determine the flow balance of each air preheater.

[0095] The primary air flow rate can be calculated by combining the flue gas inlet flow rate, the secondary air outlet flow rate, and the energy balance of the air preheater (including the measured temperature and calculated specific heat); it can also be directly measured by the lateral movement of the Pitot tube, while comparing the primary air fan current to check the flow balance, and cross-checking the coal mill inlet flow rate and temperature.

[0096] If the flue gas flow exhibits stratification, the velocity should be measured individually at each location on the cross-section of the airway, and the velocity should be proportional to the flue gas flow rate at the corresponding location. The average value should represent the measured value at that cross-section. The velocity pressure (dynamic pressure) should be measured at the same location and at the same time as the flue gas sampling and temperature measurement. In cases of severe stratification, dynamic pressure measurement is mandatory.

[0097] Performance parameter calculation method:

[0098] (1) The percentage of air leakage at the flue gas inlet flow rate is calculated using the following formula:

[0099]

[0100] Among them, coefficient

[0101]

[0102] This coefficient is used to convert a dry basis to an aqueous basis, ρ g Flue gas density under standard conditions (kg / m³) 3 ), where k is the percentage of moisture at the flue gas inlet (%), and the density and humidity percentage in the flue gas can be obtained through combustion analysis.

[0103] (2) Calculation of non-dilution flue gas outlet temperature:

[0104] Tg 2NL =L×(Tg2-Ta1)+Tg2

[0105] Where L represents air leakage (expressed in decimal), Tg2 represents the measured flue gas outlet temperature (°C), and Ta1 represents the air inlet temperature (°C).

[0106] (3) Two-compartment air preheater: Measure the inlet flow rate of the air preheater from the test point at the outlet of the blower, and calculate the inlet mass flow rate of the flue gas using the following heat balance equation:

[0107] Mg1×ΔT g ×Cp g =Ma×ΔT a ×Cp a

[0108] Where Mg1 is the flue gas inlet mass flow rate (kg / s), and ΔT g Cp represents the temperature difference on the flue gas side (°C). g Ma is the average specific heat of the flue gas (J / kg·℃), Ma is the air mass flow rate (kg / s), and ΔT is the average specific heat of the flue gas (J / kg·℃). a Cp represents the air-side temperature difference (°C). a The average specific heat of air is (J / kg·℃).

[0109] (4) Three-compartment air preheater: Since there are two independent air flows through the rotor, the air leakage is the total air leakage from the primary air and secondary air to the flue gas. It is necessary to measure the mass flow rate of the air outlet and calculate the flue gas mass using the following equation:

[0110] Mg×ΔT g ×Cp g =Ma1×ΔT a1 ×Cp a1 +Ma2×ΔT a2 ×Cp a2

[0111] Where Ma1 is the primary air mass flow rate (kg / s), and ΔT a1 Cp represents the primary wind-side temperature difference (°C). a1 Ma2 is the average specific heat of primary air (J / kg·℃), Ma2 is the mass flow rate of secondary air (kg / s), and ΔT is the average specific heat of primary air (J / kg·℃). a2 The secondary wind side temperature difference (°C), Cp a2 The average specific heat of the secondary air is (J / kg·℃); heat loss is assumed to be negligible in the calculation.

[0112] (5) Calculation of mixed air temperature (for thermal analysis)

[0113] Air inlet temperature:

[0114] Air outlet temperature:

[0115] Among them, Ta 1p Ma represents the primary air inlet temperature (°C). 1p Ta is the primary air inlet mass flow rate (kg / s). 1s Ma represents the secondary air inlet temperature (°C). 1s Ta is the secondary air inlet mass flow rate (kg / s). 2p Ma represents the primary air outlet temperature (°C). 2p Ta is the primary air outlet mass flow rate (kg / s). 2s Ma represents the secondary air outlet temperature (°C). 2s The mass flow rate at the secondary air outlet is (kg / s).

[0116] (6) Temperature difference calculation

[0117] Flue gas side temperature difference: ΔT g =Tg1-Tg 2NL

[0118] Air-side temperature difference: ΔT a =Ta2-Ta1

[0119] Where Tg1 is the flue gas inlet temperature (°C), Tg 2NL Ta1 is the outlet temperature of the non-diluted flue gas (°C), Ta2 is the outlet temperature of the mixed air (°C), and Ta1 is the inlet temperature of the mixed air (°C).

[0120] (7) Thermal efficiency calculation

[0121] Flue gas side thermal efficiency:

[0122] Where, η g The thermal efficiency (%) is the flue gas side efficiency.

[0123] (8) Pressure drop calculation

[0124] Flue gas side pressure drop: ΔP g =Psg1-Psg2

[0125] Secondary wind side pressure drop: ΔP as =Psa 1s -Psa 2s

[0126] Primary wind side pressure drop: ΔP ap =Psa 1p -Psa 2p

[0127] Where Psg1 is the static pressure at the flue gas inlet (kPa), Psg2 is the static pressure at the flue gas outlet (kPa), and Psa 1s The static pressure at the secondary air inlet (kPa), Psa 2s The static pressure at the secondary air side outlet (kPa), Psa 1p The primary air side inlet static pressure (kPa), Psa 2p The static pressure at the primary air side outlet (kPa).

[0128] (9) Calculation of mean pressure difference

[0129] Average pressure difference at the hot end:

[0130] Average pressure difference at the cold end:

[0131] (10) Calculation of average specific heat

[0132]

[0133] Where Cp is the average specific heat of flue gas or air within the relevant temperature range (J / kg·℃), T1 is the inlet temperature (℃), T2 is the outlet temperature (℃), and Cp(T) is the instantaneous specific heat at temperature T (J / kg·℃).

[0134] (11) Air leakage analysis

[0135] Before comparing the calculated air leakage value with the design value, corrections need to be made based on the differences between the flow rate and cold-end pressure difference and the "design value". The correction uses the ASME equation and the weighted average air inlet temperature, and the correction formula is as follows:

[0136]

[0137] Where L is the corrected leakage rate (%), LR is the leakage rate (%) related to the design flow rate and cold junction pressure difference, and ρ g D is the flue gas density under design conditions (kg / m³). 3 ), ρ g T is the flue gas density (kg / m³) under the test conditions. 3 ), ΔP g D represents the flue gas side pressure drop (kPa) under design conditions, ΔP gT T represents the flue gas side pressure drop (kPa) under test conditions. a1D T represents the air inlet temperature (K) under design operating conditions. a1T The air inlet temperature (K) is the air inlet temperature under test conditions.

[0138] (12) Pressure drop analysis

[0139] The pressure drop under design conditions is calculated using the following standard equation:

[0140]

[0141] For a typical heat transfer element, β = -0.32, the equation can be simplified to:

[0142]

[0143] Wherein, ΔP D ΔP is the pressure drop (kPa) under design operating conditions. T The pressure drop (kPa) under test conditions, μ g D represents the flue gas viscosity (Pa·s) under design conditions, μ g T is the flue gas viscosity (Pa·s) under the test conditions, Q gD Flue gas flow rate (m³) under design conditions 3 / s), Q gT The flue gas flow rate (m³) under test conditions 3 / s).

[0144] Accuracy requirements for monitoring instruments:

[0145] To ensure the accuracy of monitoring data, the instruments used must meet the following accuracy requirements:

[0146]

[0147]

[0148] Example:

[0149] Taking the three-compartment air preheater of a 300MW unit in a thermal power plant as an example, the performance parameters are monitored and analyzed online using the method of this invention. The specific steps are as follows:

[0150] 1. Monitoring Preparation

[0151] Thermocouples and temperature probes are installed at the secondary air inlet (blower outlet, primary air and soot blower sealing air stop), secondary air outlet (air box inlet), primary air inlet (primary air fan outlet, bypass stop), flue gas inlet (horizontal section after ash hopper at economizer outlet), and flue gas outlet (before bend in dust collector after ash hopper) of the air preheater to form a grid covering the cross-section of the air duct; pressure measuring holes and pressure gauges are installed on the wall of the transition pipe; multi-point sampling probes (sampling tubes of consistent length) are installed at the flue gas inlet and outlet, and connected to the oxygen analyzer and CO analyzer.

[0152] Check the load of the steam generator, adjust it to the design value (300MW), and run it stably for 30 minutes; ensure that the air and flue gas flow rates are constant and the O2 content is stable.

[0153] 2. Parameter Acquisition

[0154] Start the fast scan digital recorder output and continuously acquire data for 20 minutes (meeting the requirement of "at least 15 minutes of stable data acquisition and two sets of consistent data"), recording the temperature (Ta). 1s Ta 1p Ta 2s Ta 2p (Tg1, etc.) and pressure (Psa) 1s Psa 2s Psg1, Psg2, etc.), flow rate (Ma 2s The system records parameters such as Mg1, gas composition (O2 inlet, O2 outlet, CO inlet, CO outlet, etc.), and simultaneously records the fan current and the position of the control baffle.

[0155] The secondary air outlet flow rate was measured by transverse displacement of a Pitot tube. The flow rates of the two blowers (taken from the axial flow fan components) were compared to confirm flow balance. The flue gas inlet flow rate was estimated by combining the CO and O2 contents at the flue gas inlet and outlet with combustion calculations. Since there was no obvious stratification of the flue gas flow, the average velocity of the cross-section of the air duct was taken as the measured value.

[0156] 3. Performance Parameter Calculation

[0157] Air leakage calculation: Given O2 inlet = 5.2% and O2 outlet = 7.8%, ρ is obtained through combustion analysis. g =1.35kg / m 3 k = 8.5%, calculate the coefficients.

[0158]

[0159] Substitute into the air leakage formula:

[0160] Calculation of undiluted flue gas outlet temperature: Given Tg2 = 135℃, Ta1 = 25℃,

[0161] Tg 2NL =0.152×(135-25)+135≈151.7℃.

[0162] Energy balance calculation: Given Ma1 = 28 kg / s, ΔT a1 =180℃

[0163] Cp a1 =1010J / kg·℃, Ma2=42kg / s, ΔT a2 =175℃

[0164] Cp a2 =1005 J / kg·℃, ΔT g =320℃, Cp g =1050J / kg·℃,

[0165] Substituting into the three-part energy balance formula:

[0166] Mg×320×1050=[28×180×1010]+[42×175×1005], solving for Mg≈68.5kg / s.

[0167] Thermal efficiency calculation:

[0168] Flue gas side thermal efficiency

[0169] (Tg1=481.7℃=Tg 2NL +ΔT g ).

[0170] Pressure drop calculation: Given Psg1 = 3.2 kPa, Psg2 = 1.8 kPa, the flue gas side pressure drop ΔP g =3.2-1.8=1.4kPa; Psa 1s =2.5kPa, Psa 2s =1.1 kPa, secondary wind side pressure drop ΔP as =2.5-1.1=1.4kPa.

[0171] 4. Results Comparison and Analysis

[0172] The air preheater was designed to have a leakage rate of 10%, but the corrected leakage rate was 15.2%, which is higher than the design value, indicating that the seals may be worn. The measured thermal efficiency on the flue gas side was 72.3%, which is lower than the design value (75%), suggesting that there may be slight ash accumulation and blockage. The designed flue gas side pressure drop was 1.2 kPa, but the measured value was 1.4 kPa, which is slightly higher than the design value, so the air passage patency needs to be checked.

[0173] Based on the analysis results, the following maintenance recommendations are made: inspect and adjust the seals, and remove dust from the air passages to reduce air leakage and improve thermal efficiency.

Claims

1. A method for online monitoring and analysis of performance parameters of an air preheater, characterized in that, Includes the following steps: S1. Set performance monitoring conditions: Extract flue gas samples at the flue gas inlet and outlet for component analysis; maintain constant air and flue gas flow rates and stable O2 content in the air preheater during the monitoring period, ensure the steam generator load is close to the design value, and ensure stable operation for at least 30 minutes before the monitoring test begins; the monitoring duration should be at least 15 minutes, and at least two sets of consistent data should be obtained; S2. Collect monitoring parameters: Install temperature, pressure, flow rate, and gas composition acquisition devices at preset locations, and collect parameters such as temperature, static pressure, mass flow rate, percentage of O2 and CO in dry flue gas, atmospheric pressure, and relative humidity; for temperature acquisition, use a probe and thermocouple to form a grid covering the cross-section of the duct; for static pressure acquisition, use a fixed measuring hole in the pipe wall; for gas composition acquisition, ensure that the volume of flue gas extracted by the sampling probe is the same; S3. Calculate performance parameters: Based on the parameters collected in step S2, calculate air leakage, non-diluted flue gas outlet temperature, energy balance, mixed air temperature, temperature difference, thermal efficiency, pressure drop, and average pressure difference, respectively; S4. Compare test values ​​with design values: Calculate the thermal operating margin based on the ASME equations and correction curves, correct for air leakage and pressure drop, and compare with the design values ​​to evaluate the performance status of the air preheater; the air leakage in step S3 is calculated using the following formula: Where the coefficient ρ g The density of the flue gas under standard conditions is given by , and k is the percentage of moisture content at the flue gas inlet; the outlet temperature of the non-dilutable flue gas is calculated according to Tg. 2NL =L×(Tg2-Ta1)+Tg2, calculate, where L is the decimal leakage value, Tg2 is the flue gas outlet temperature, and Ta1 is the air inlet temperature.

2. The method according to claim 1, characterized in that, The temperature acquisition locations in step S2 include: secondary air inlet, secondary air outlet, primary air inlet, flue gas inlet, and flue gas outlet; the thermocouples have independent correction coefficients and are marked on the calibration certificate.

3. The method according to claim 1, characterized in that, The traffic collection in step S2 includes: The flue gas inlet velocity is first measured by a Pitot tube traversing the inlet plane. For the portion that cannot be directly measured, it is estimated by CO and O2 content and combustion calculations. The secondary air outlet flow rate is measured by the lateral movement of the Pitot tube, and the balance is confirmed by comparing the blower flow rate; the primary air flow rate is verified by energy balance calculation or Pitot tube measurement, combined with cross-verification of blower current and coal mill parameters.

4. The method according to claim 1, characterized in that, In step S3, the inlet mass flow rate of the flue gas in the two-compartment air preheater is calculated as Mg1×ΔT. g ×Cp g =Ma×ΔT a ×Cp a Calculation; flue gas mass of the three-compartment air preheater is calculated as Mg×ΔT g ×Cp g =Ma1×ΔT a1 ×Cp a1 +Ma2×ΔT a2 ×Cp a2 Calculate, and assume that heat loss is negligible.

5. The method according to claim 4, characterized in that, In step S3, the inlet temperature of the mixed air is as follows: Calculation, outlet temperature according to Calculate the temperature difference ΔT on the flue gas side. g =Tg1-Tg 2NL Air-side temperature difference ΔT a =Ta2-Ta1.

6. The method according to claim 5, characterized in that, In step S3, the flue gas side thermal efficiency is calculated according to... Calculate the flue gas side pressure drop ΔP. g =Psg1-Psg2, Secondary wind side pressure drop ΔP as =Psa 1s -Psa 2s Primary wind side pressure drop ΔP ap =Psa 1p -Psa 2p .

7. The method according to claim 1, characterized in that, In step S4, the air leakage correction is performed according to... Calculation, LR represents design-related air leakage, ρ gD ρ gT The respective flue gas densities under design and test conditions, ΔP gD ΔP gT These represent the flue gas side pressure drop under design and test conditions, T a1D T a1T These refer to the air inlet temperature for design and test operating conditions, respectively.

8. The method according to claim 1, characterized in that, The instruments used in step S2 shall meet the following requirements: thermocouple tolerance ±1.5℃, temperature measuring instrument error ±1.0℃, oxygen analyzer error ±0.1%O2, pressure measuring instrument error ±4%, flue gas side efficiency retest deviation ±5%, and inlet oxygen retest deviation from design value ±1%O2.

9. The method according to claim 1, characterized in that, If the flue gas flow is stratified in step S2, the velocity is measured separately at each position of the cross-section of the airway and is proportional to the corresponding flue gas flow rate. The average value is then taken. Furthermore, the dynamic pressure is measured at the same position and moment as the flue gas sampling and temperature measurement.

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