A method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary

Abstract

The present invention provides a method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary, comprising the following steps: under a stable load of the unit, the flue gas recirculation device maintains normal operation at a stable speed according to the load of the unit; measuring the flue gas parameters at the outlet of the flue gas recirculation device, synchronously testing the atmospheric pressure and ambient dry-bulb temperature near the flue gas recirculation device, and calculating the volume flow, temperature and oxygen content of the recirculated flue gas; synchronously testing the flue gas composition and flue gas temperature at the boiler boundary; calculating the heat difference between the recirculated flue gas entering and leaving the system boundary, and then obtaining the percentage of heat increase brought by the recirculated flue gas entering the system boundary; finally calculating the accurate boiler efficiency by calculating various conventional heat losses of the boiler; improving the accuracy of the efficiency calculation of the boiler with the flue gas recirculation device outside the system boundary, and providing guidance for energy conservation and emission reduction of power station boilers.

Description

Technical Field

[0001] The present invention relates to the technical field of energy conservation and emission reduction of power station boilers, and in particular to a method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary. Background Art

[0002] To reduce NOx emissions at the boiler outlet and increase main steam and reheat steam temperatures, flue gas recirculation technology has been effectively applied in double-reheat boilers and circulating fluidized bed boilers. A portion of the flue gas in the tail duct, which is cooler, is recirculated into the furnace or combustion air through the flue gas recirculation device. This heat enters the system as heat outside the system boundary, and its impact on boiler efficiency cannot be ignored.

[0003] Unlike conventional boilers with system boundaries, the GB / T10184-2015 "Standard for Performance Tests of Power Plant Boilers" (GB / T10184-2015) is unable to accurately measure boiler efficiency, a key indicator, for boilers with flue gas recirculation outside the system boundary. If the impact of recirculated flue gas on boiler efficiency is not considered, or if an estimate is used, power plant technicians will be unable to accurately assess the impact of recirculated flue gas regulation on boiler efficiency, making it difficult to determine the unit's true coal consumption. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary, which improves the accuracy of the efficiency calculation of a boiler with a flue gas recirculation device outside the system boundary, accurately grasps the impact of recirculating flue gas regulation on boiler efficiency, and then accurately grasps the actual coal consumption level of the unit, providing guidance for energy conservation and emission reduction of power plant boilers.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] The present invention provides a method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary, comprising the following steps: under a stable load of the unit,

[0007] S1: When the unit is under stable load, the flue gas recirculation device maintains normal operation at a stable speed according to the unit load;

[0008] S2 measures the flue gas parameters at the outlet of the flue gas recirculation device, and simultaneously tests the atmospheric pressure and ambient dry-bulb temperature near the flue gas recirculation device, and calculates the volume flow rate, temperature and oxygen content of the recirculated flue gas;

[0009] S3 simultaneously tests the flue gas composition and temperature at the boiler boundary;

[0010] S4 calculates the heat difference between the recirculated flue gas entering and leaving the boiler system boundary, and then obtains the heat increment percentage caused by the recirculated flue gas entering the boiler system boundary;

[0011] S5 calculates the conventional heat loss of the boiler and finally calculates the accurate boiler efficiency.

[0012] The present invention proposes a method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary, which improves the accuracy of the efficiency calculation of a boiler with a flue gas recirculation device outside the system boundary, accurately grasps the impact of recirculating flue gas regulation on boiler efficiency, and further accurately grasps the actual coal consumption level of the unit, providing guidance for energy conservation and emission reduction of power plant boilers.

[0013] As a preferred technical solution, step S2 measures the flue gas parameters at the outlet of the flue gas recirculation device, and simultaneously measures the atmospheric pressure and ambient dry-bulb temperature near the flue gas recirculation device to calculate the volume flow rate, temperature and oxygen content of the recirculated flue gas. Specifically, the following steps are included: using the equal-section grid method to measure the flue gas dynamic pressure P at the outlet of the flue gas recirculation device. di , oxygen content O 2,re and temperature t fg,re , and the flue gas static pressure P at the measurement section s , and simultaneously test the atmospheric pressure P near the flue gas recirculation device A and ambient dry bulb temperature t A , calculate the recirculating flue gas volume flow V fg,re , Recirculated flue gas temperature t fg,re and the recirculated flue gas oxygen content O 2,re .

[0014] As a preferred technical solution, step S4 calculates the heat difference between the recirculated flue gas entering and leaving the boiler system boundary, and then obtains the heat increment percentage caused by the recirculated flue gas entering the boiler system boundary, which specifically includes the following steps:

[0015] S401 corrects the recirculating flue gas volume flow rate to the recirculating flue gas volume flow rate under the oxygen content at the boiler system boundary, and obtains the recirculating flue gas volume flow rate V corrected to the oxygen content at the boiler system boundary. fg,re,cr ;

[0016] S402 records the total coal volume of the unit DCS during the test period, and divides the recirculating flue gas volume flow rate corrected to the oxygen content at the boiler system boundary by the total coal volume during the test period to obtain the recirculating flue gas flow rate v corresponding to unit mass of fuel. fg,re According to the national standard of power plant boiler performance test procedures, the dry flue gas volume v corresponding to unit mass of fuel is calculated fg,d,re The amount of water vapor v corresponding to unit mass of fuel wv,re Two parts;

[0017] S403 obtains the average constant pressure specific heat capacity c of the dry flue gas in the recycled flue gas by checking the original data. p,fg,d,reand the average constant-pressure specific heat capacity of water vapor c p,wv,re , and the average constant pressure specific heat capacity c of dry flue gas at the boundary of the boiler system p,fg,d,AHlv and the average constant-pressure specific heat capacity of water vapor c p,wv,AHlv , calculate the heat Q of the recirculated flue gas entering the boiler system boundary fg,re and the heat Q leaving the boiler system boundary fg,AHlv ;

[0018] S404 calculates the heat difference between the recirculated flue gas entering and leaving the boiler system boundary, and then compares it with the lower calorific value of the fuel to obtain the heat increment percentage q brought by the recirculated flue gas into the boiler system boundary. re .

[0019] As a preferred technical solution, step S5 calculates various conventional heat losses of the boiler and finally calculates the accurate boiler efficiency, which specifically includes the following steps: according to the national standard of the power plant boiler performance test procedure, calculate various conventional heat losses: exhaust heat loss q2, gas incomplete combustion heat loss q3, solid incomplete combustion heat loss q4, boiler heat loss q5, ash physical sensible heat loss q6, circulating fluidized bed boiler desulfurization heat loss q7, other heat losses q oth , the percentage of external heat to fuel low calorific value q ex , combined with the percentage of heat gain from the recirculated flue gas q re , and finally the boiler efficiency η is calculated.

[0020] As a preferred technical solution, the volume flow rate of the recirculated flue gas V in step S2 fg,re Calculated according to the following formula:

[0021]

[0022]

[0023]

[0024] Among them, V fg,re is the volume flow rate of recirculated flue gas, in Nm 3 / h; A is the area of the measurement cross section at the outlet of the recirculation device, in m 2 ; K is the flow coefficient of the velocity tube; P d is the average dynamic pressure of the measuring section, in Pa; P di is the dynamic pressure at each measuring point, in Pa; ρ is the flue gas density at the measuring section, in kg / m 3 ; n is the total number of measuring points; ρ a is the standard flue gas density, in kg / m 3 ;P Ais the measured atmospheric pressure, in kPa; P s is the static pressure at the measurement section; t fg,re The actual measured recirculating flue gas temperature, in °C.

[0025] As a preferred technical solution, the recirculated flue gas volume flow rate V is corrected to the oxygen content at the boiler system boundary in step S401. fg,re,cr Calculated according to the following formula:

[0026]

[0027] Among them, V fg,re,cr The volume flow of recirculated flue gas corrected to the oxygen content at the system boundary, in m 3 / h; V fg,re is the measured recirculation flue gas volume flow rate, in m 3 / h; O 2,AHlv is the oxygen content in the flue gas at the boundary of the boiler system, in %; O 2,re is the oxygen content in the recycled flue gas, in %.

[0028] As a preferred technical solution, the recirculated flue gas flow rate v corresponding to the unit mass of fuel in step S402 fg,re Calculated according to the following formula:

[0029]

[0030] v fg，rg =v fg，d，re +v wv，re

[0031] Among them, v fg,re is the recirculated flue gas flow rate corresponding to unit mass of fuel, in m 3 / kg;D rl is the total coal volume during the test, in t / h; v fg,d,re The dry flue gas volume in the recirculated flue gas corresponding to unit mass of fuel, in m 3 / kg; V fg,re,cr The volume flow rate of recirculated flue gas corrected to the oxygen content at the boiler system boundary, in m 3 / h;v wv,re is the amount of water vapor in the recycled flue gas corresponding to unit mass of fuel, in m 3 / kg.

[0032] As a preferred technical solution, the heat Q of the recirculated flue gas entering the boiler system boundary in step S403 fg,re and the heat Q of the recirculated flue gas leaving the boiler system boundary fg,AHlv Calculated according to the following formula:

[0033] Q fg,re =v fg,d,re ×c p,fg,d,re ×(t fg,re -t fg,AHlv )+v wv,re ×c p,mv,re ×(t fg,re -t fg,AHlv )

[0034] Q fg,AHlv =v fg,d,AHlv ×c p,fg,d,AHlv ×(t fg,AHlv -t0)+v wv,AHlv ×c p,mv,AHlv ×(t fg,AHlv -t0)

[0035] Among them, Q fg,re is the heat of the recirculated flue gas entering the boiler system boundary, in kJ / kg; v fg,d,re The dry flue gas volume corresponding to unit mass of fuel, in m 3 / kg;c p,fg,d,re is the average constant pressure specific heat capacity of dry flue gas in the recycled flue gas, in kJ / (m 3 ·K); t fg,re is the recirculating flue gas temperature, in °C; t fg,AHlv is the flue gas temperature at the boundary of the boiler system, in °C; v wv,re is the amount of water vapor in the recycled flue gas corresponding to unit mass of fuel, in m 3 / kg;c p,mv,re is the average constant-pressure specific heat capacity of water vapor in the recycled flue gas, in kJ / (m3·K); v fg,d,AHlv The dry flue gas volume at the boiler system boundary corresponding to unit mass of fuel, in m 3 / kg;v mv,AHlv is the amount of water vapor in the flue gas at the boiler system boundary corresponding to unit mass of fuel, in m 3 / kg;c p,fg,d,AHlv is the average constant pressure specific heat capacity of dry flue gas at the boundary of the boiler system, in kJ / (m 3 ·K);c p,mv,AHlv is the average constant pressure specific heat capacity of water vapor in the flue gas at the boundary of the boiler system, kJ / (m 3 ·K); t 0 is the reference temperature, in °C, Q fg,AHlv is the heat leaving the boiler system boundary, in kJ / kg.

[0036] As a preferred technical solution, the percentage of heat gain q brought into the boiler system by the recycled flue gas in step S404 isre Calculated according to the following formula:

[0037]

[0038] Among them, Q fg,re is the heat of the recirculated flue gas entering the boiler system boundary, in kJ / kg; q re Q is the percentage of heat gain brought into the boiler system by the recycled flue gas, in %; net,ar is the low calorific value of the fuel entering the furnace, in kJ / kg; Q fg,AHlv is the heat leaving the boiler system boundary, in kJ / kg.

[0039] As a preferred technical solution, the boiler efficiency η in step S5 is calculated according to the following formula:

[0040] η=100-(q2+q3+q4+q5+q6+q7+q oth -q ex )+q re

[0041] Wherein, η is the boiler efficiency, in %; q2 is the exhaust heat loss, in %; q3 is the heat loss of incomplete combustion of gas, in %; q4 is the heat loss of incomplete combustion of solid, in %; q5 is the heat loss of boiler, in %; q6 is the physical sensible heat loss of ash, in %; q7 is the desulfurization heat loss of circulating fluidized bed boiler, in %; q oth is other heat loss, in %; q ex It is the percentage of external heat to the low calorific value of fuel, in %; q re It is the percentage of heat gain brought into the boiler system by the recirculated flue gas, in %.

[0042] The present invention proposes a method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary, which improves the accuracy of the efficiency calculation of a boiler with a flue gas recirculation device outside the system boundary, accurately grasps the impact of recirculating flue gas regulation on boiler efficiency, and further accurately grasps the actual coal consumption level of the unit, providing guidance for energy conservation and emission reduction of power plant boilers. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A flow chart of a method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary provided by the present invention;

[0044] Figure 2 A schematic structural diagram of a boiler with a flue gas recirculation device outside the system boundary provided by the present invention;

[0045] Among them, 1-flue gas recirculation device, 2-recirculating flue gas test position, 3-economizer, 4-SCR denitrification device, 5-air preheater, 6-dust collector, 7-induced draft fan, 8-desulfurization tower, 9-chimney, 10-primary fan, 11-forced draft fan, 12-wind box and burner, 13-boiler system boundary; 14-raw coal; 15-slag. DETAILED DESCRIPTION

[0046] Preferred embodiments of the present invention are described in detail below.

[0047] It can be understood that the present invention achieves the purpose of the present invention through some embodiments. Figure 1 As shown, the present invention provides a method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary, comprising the following steps: under a stable load of the unit,

[0048] The S1 unit exits AGC mode and completes furnace soot blowing before the test. No soot blowing or blowdown is performed during the test, and the load is maintained stable for at least 2 hours. The operating oxygen level is switched to manual mode and remains unchanged, and the furnace pressure is in automatic mode. The flue gas recirculation device 1 operates normally at a stable speed according to the unit load.

[0049] S2 measures the flue gas parameters at the outlet of the flue gas recirculation device 1, and simultaneously measures the atmospheric pressure and ambient dry bulb temperature near the flue gas recirculation device 1, and calculates the volume flow rate, temperature and oxygen content of the recirculated flue gas. Specifically, the following steps are included: Using the equal-section grid method to measure the flue gas dynamic pressure P at the outlet of the flue gas recirculation device 1 di , oxygen content O 2,re and temperature t fg,re , and the flue gas static pressure P at the measurement section s , and simultaneously test the atmospheric pressure P near the flue gas recirculation device 1 A and ambient dry bulb temperature t A , calculate the recirculating flue gas volume flow V fg,re , Recirculated flue gas temperature t fg,re and the recirculated flue gas oxygen content O 2,re , where the recirculated flue gas volume flow V fg,re Calculated according to the following formula:

[0050]

[0051]

[0052]

[0053] Among them, V fg,re is the volume flow rate of recirculated flue gas, in Nm 3 / h; A is the area of the measurement cross section at the outlet of the recirculation device, in m 2 ; K is the flow coefficient of the velocity tube; P d is the average dynamic pressure of the measuring section, in Pa; P di is the dynamic pressure at each measuring point, in Pa; ρ is the flue gas density at the measuring section, in kg / m 3 ; n is the total number of measuring points; ρ a is the standard flue gas density, in kg / m 3 ;P A is the measured atmospheric pressure, in kPa; P s is the static pressure at the measurement section; t fg,re is the measured recirculation flue gas temperature, in °C;

[0054] S3 is tested synchronously with step S2 to obtain the flue gas composition (O) at the boiler system boundary 13 (air preheater outlet) 2,AHlv 、CO 2,AHlv and CO AHlv etc.) and flue gas temperature t fg,AHlv ;

[0055] S4 calculates the heat difference between the recirculated flue gas entering and leaving the boiler system boundary 13, and then obtains the heat increment percentage caused by the recirculated flue gas entering the boiler system boundary 13, which specifically includes the following steps:

[0056] S401 corrects the recirculating flue gas volume flow rate to the recirculating flue gas volume flow rate under the oxygen content at the boiler system boundary 13, and obtains the recirculating flue gas volume flow rate V corrected to the oxygen content at the boiler system boundary 13. fg,re,cr , corrected to the recirculated flue gas volume flow V under the oxygen content at the boiler system boundary 13 fg,re,cr Calculated according to the following formula:

[0057]

[0058] Among them, V fg,re,cr The volume flow rate of recirculated flue gas corrected to the oxygen content at the boiler system boundary 13, in m 3 / h; V fg,re is the measured recirculation flue gas volume flow rate, in m 3 / h; O 2,AHlv is the oxygen content in the flue gas at the boundary of the boiler system, in %; O 2,re is the oxygen content in the recirculated flue gas, in %;

[0059] S402 records the total coal volume of the unit DCS during the test period, and divides the recirculating flue gas volume flow rate corrected to the oxygen content at the boiler system boundary 13 by the total coal volume during the test period to obtain the recirculating flue gas flow rate v corresponding to unit mass of fuel.fg,re , the recirculated flue gas flow rate v corresponding to unit mass of fuel fg,re Calculated according to the following formula:

[0060]

[0061] Among them, v fg,re is the recirculated flue gas flow rate corresponding to unit mass of fuel, in m 3 / kg;D rl is the total coal volume during the test, in t / h; v fg,d,re The dry flue gas volume in the recirculated flue gas corresponding to unit mass of fuel, in m 3 / kg; V fg,re,cr The volume flow rate of recirculated flue gas corrected to the oxygen content at the boiler system boundary, in m 3 / h;v wv,re is the amount of water vapor in the recycled flue gas corresponding to unit mass of fuel, in m 3 / kg; According to the national standard of power plant boiler performance test procedures, the dry flue gas volume v corresponding to unit mass of fuel is calculated fg,d,re The amount of water vapor v corresponding to unit mass of fuel wv,re Two parts;

[0062] S403 obtains the average constant pressure specific heat capacity c of the dry flue gas in the recycled flue gas by checking the original data. p,fg,d,re and the average constant-pressure specific heat capacity of water vapor c p,wv,re , and the average constant pressure specific heat capacity c of dry flue gas at the boundary of the boiler system p,fg,d,AHlv and the average constant-pressure specific heat capacity of water vapor c p,wv,AHlv , calculate the heat Q of the recirculated flue gas entering the boiler system boundary fg,re and the heat Q leaving the boiler system boundary fg,AHlv , the heat Q of the recirculated flue gas entering the boiler system boundary fg,re and the heat Q of the recirculated flue gas leaving the boiler system boundary fg,AHlv Calculated according to the following formula:

[0063] Q fg,re =v fg,d,re ×c p,fg,d,re ×(t fg,re -t fg,AHlv )+v wv,re ×c p,mv,re ×(t fg,re -t fg,AHlv )

[0064] Q fg,AHlv =v fg,d,AHlv ×c p,fg,d,AHlv ×(tfg,AHlv -t0)+v wv,AHlv ×c p,mv,AHlv ×(t fg,AHlv -t0)

[0065] Among them, Q fg,re is the heat of the recirculated flue gas entering the boiler system boundary 13, in kJ / kg; v fg,d,re The dry flue gas volume corresponding to unit mass of fuel, in m 3 / kg;c p,fg,d,re is the average constant pressure specific heat capacity of dry flue gas in the recycled flue gas, in kJ / (m 3 ·K); t fg,re is the recirculating flue gas temperature, in °C; t fg,AHlv is the flue gas temperature at 13 points on the boiler system boundary, in °C; v wv,re is the amount of water vapor in the recycled flue gas corresponding to unit mass of fuel, in m 3 / kg;c p,mv,re is the average constant-pressure specific heat capacity of water vapor in the recycled flue gas, in kJ / (m3·K); v fg,d,AHlv The dry flue gas volume at the boiler system boundary corresponding to unit mass of fuel, in m 3 / kg;v mv,AHlv is the amount of water vapor in the flue gas at the boiler system boundary corresponding to unit mass of fuel, in m 3 / kg;c p,fg,d,AHlv is the average constant pressure specific heat capacity of dry flue gas at 13 locations on the boiler system boundary, in kJ / (m 3 ·K);c p,mv,AHlv is the average constant pressure specific heat capacity of water vapor in the flue gas at 13 points on the boiler system boundary, kJ / (m 3 ·K); t 0 is the reference temperature, in °C, Q fg,AHlv is the heat leaving the boiler system boundary, in kJ / kg;

[0066] S404 calculates the heat difference between the recirculated flue gas entering and leaving the boiler system boundary 13, and then compares it with the lower calorific value of the fuel to obtain the heat increment percentage q brought by the recirculated flue gas into the boiler system boundary 13. re , the percentage of heat gain brought into the boiler system by the recycled flue gas q re Calculated according to the following formula:

[0067]

[0068] Among them, Q fg,re is the heat of the recirculated flue gas entering the boiler system boundary, in kJ / kg; q reQ is the percentage of heat gain brought into the boiler system by the recycled flue gas, in %; net,ar is the low calorific value of the fuel entering the furnace, in kJ / kg; Q fg,AHlv is the heat leaving the boiler system boundary, in kJ / kg;

[0069] S5 calculates the conventional heat loss of the boiler and finally calculates the accurate boiler efficiency. The specific steps include: According to the national standard of the power plant boiler performance test procedure, calculate the conventional heat loss: exhaust heat loss q2, gas incomplete combustion heat loss q3, solid incomplete combustion heat loss q4, boiler heat loss q5, ash physical sensible heat loss q6, circulating fluidized bed boiler desulfurization heat loss q7, other heat losses q oth , the percentage of external heat to fuel low calorific value q ex , combined with the percentage of heat gain from the recirculated flue gas q re , and finally the boiler efficiency η is calculated. The boiler efficiency η is calculated according to the following formula:

[0070] η=100-(q2+q3+q4+q5+q6+q7+q oth -q ex )+q re

[0071] Wherein, η is the boiler efficiency, in %; q2 is the exhaust heat loss, in %; q3 is the heat loss of incomplete combustion of gas, in %; q4 is the heat loss of incomplete combustion of solid, in %; q5 is the heat loss of boiler, in %; q6 is the physical sensible heat loss of ash, in %; q7 is the desulfurization heat loss of circulating fluidized bed boiler, in %; q oth is other heat loss, in %; q ex It is the percentage of external heat to the low calorific value of fuel, in %; q re It is the percentage of heat gain brought into the boiler system by the recirculated flue gas, in %.

[0072] The present invention proposes a method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary, which improves the accuracy of the efficiency calculation of a boiler with a flue gas recirculation device outside the system boundary, accurately grasps the impact of recirculating flue gas regulation on boiler efficiency, and further accurately grasps the actual coal consumption level of the unit, providing guidance for energy conservation and emission reduction of power plant boilers.

[0073] like Figure 2 As shown, the present invention takes a 150MW circulating fluidized bed boiler of a power plant as an example;

[0074] The tests were conducted under three load conditions (T-01, T-02, and T-03): 140MW, 120MW, and 90MW. The unit exited AGC mode and completed furnace soot blowing before the test. No soot blowing or blowdown was performed during the test, and the load was maintained stable for approximately two hours. The operating oxygen level was switched to manual mode and remained constant, while the furnace pressure was in automatic mode. The flue gas recirculation system operated stably at different speeds. The boiler efficiency test results for the 140MW, 120MW, and 90MW load conditions are shown in Table 1 below.

[0075] Table 1 Boiler efficiency test results

[0076]

[0077]

[0078] It can be seen from Table 1 above that according to the method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary provided by the present invention, the recirculated flue gas flow rate v corresponding to the unit mass of fuel under the load conditions of 140MW, 120MW and 90MW is: fg,re Calculated according to the following formula: The calculated recirculating flue gas flow rates are 32049.02m 3 / kg、41191.75m 3 / kg and 35095.02m 3 / kg; the measured recirculated flue gas temperatures were 162.1°C, 164.9°C and 158.1°C, and the measured recirculated flue gas oxygen contents were 6.14%, 5.68% and 6.50%; the measured air preheater outlet flue gas temperatures were 147.1°C, 144.9°C and 140.1°C, and the measured air preheater outlet flue gas oxygen contents were 5.63%, 5.49% and 6.55%; the percentage of heat gain brought into the boiler system by the recirculated flue gas q re Calculated according to the following formula: The calculated percentages of heat gain brought into the system by the recirculated flue gas are 0.07%, 0.10% and 0.11% respectively. Considering the influence of other heat losses and external heat, the boiler efficiency η is calculated according to the following formula: η=100-(q2+q3+q4+q5+q6+q7+q oth -q ex )+q re The calculated boiler efficiencies are 89.81%, 90.55% and 89.54% respectively; under each load condition, the percentage of heat gain brought into the boiler system by the recirculated flue gas is q re Calculated according to the following formula: The calculated percentage of heat gain brought into the system by the recirculated flue gas is 0.07% to 0.11%, which affects the unit's power supply coal consumption by about 0.3g / kWh to 0.4g / kWh. This improves the accuracy of efficiency calculations for boilers with flue gas recirculation devices outside the system boundary, accurately grasps the impact of recirculated flue gas regulation on boiler efficiency, and thus accurately grasps the unit's actual coal consumption level, providing guidance for energy conservation and emission reduction of power plant boilers.

[0079] It will be appreciated that the present invention is described through some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are subject to various changes or equivalent substitutions. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope protected by the present invention.

Claims

1. A method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary, characterized in that: The following steps are included: Under stable load of the unit, S1: When the unit is under stable load, the flue gas recirculation device maintains normal operation at a stable speed according to the unit load; S2 measures the flue gas parameters at the outlet of the flue gas recirculation device, and simultaneously measures the atmospheric pressure and ambient dry-bulb temperature near the flue gas recirculation device, and calculates the volume flow rate, temperature and oxygen content of the recirculating flue gas. The recirculating flue gas volume flow rate V fg,re Calculated according to the following formula: Among them, V fg,re is the volume flow rate of recirculated flue gas, in Nm 3 / h; A is the area of the measurement cross section at the outlet of the recirculation device, in m 2 ; K is the flow coefficient of the velocity tube; P d is the average dynamic pressure of the measuring section, in Pa; P di is the dynamic pressure at each measuring point, in Pa; ρ is the flue gas density at the measuring section, in kg / m 3 ; n is the total number of measuring points; ρ a is the standard flue gas density, in kg / m 3 ;P A is the measured atmospheric pressure, in kPa; P s is the static pressure at the measurement section; t fg,re is the measured recirculation flue gas temperature, in °C; S3 simultaneously tests the flue gas composition and temperature at the boiler boundary; S4 calculates the heat difference between the recirculated flue gas entering and leaving the boiler system boundary, and then obtains the heat increment percentage caused by the recirculated flue gas entering the boiler system boundary; The recirculated flue gas volume flow rate V corrected to the oxygen content at the boiler system boundary fg,re,cr Calculated according to the following formula: Among them, V fg,re,cr The volume flow of recirculated flue gas corrected to the oxygen content at the system boundary, in m 3 / h; V fg,re is the measured recirculation flue gas volume flow rate, in m 3 / h; O 2,AHlv is the oxygen content in the flue gas at the boundary of the boiler system, in %; O 2,re is the oxygen content in the recirculated flue gas, in %; Recirculated flue gas flow rate v corresponding to unit mass of fuel fg,re Calculated according to the following formula: v fg,re =v fg,d,re +v wv,re Among them, v fg,re is the recirculated flue gas flow rate corresponding to unit mass of fuel, in m 3 / kg;D rl is the total coal volume during the test, in t / h; v fg,d,re The dry flue gas volume in the recirculated flue gas corresponding to unit mass of fuel, in m 3 / kg; V fg,re,cr The volume flow rate of recirculated flue gas corrected to the oxygen content at the boiler system boundary, in m 3 / h;v wv,re is the amount of water vapor in the recycled flue gas corresponding to unit mass of fuel, in m 3 / kg; The heat Q of the recirculated flue gas entering the boiler system boundary fg,re and the heat Q of the recirculated flue gas leaving the boiler system boundary fg,AHlv Calculated according to the following formula: Q fg,re =v fg,d,re ×c p,fg,d,re ×(t fg,re -t fg,AHlv )+v wv,re ×c p,mv,re ×(t fg,re -t fg,AHlv ) Q fg,AHlv =v fg,d,AHlv ×c p,fg,d,AHlv ×(t fg,AHlv -t0)+v wv,AHlv ×c p,mv,AHlv ×(t fg,AHlv -t0) Among them, Q fg,re is the heat of the recirculated flue gas entering the boiler system boundary, in kJ / kg; v fg,d,re The dry flue gas volume corresponding to unit mass of fuel, in m 3 / kg;c p,fg,d,re is the average constant pressure specific heat capacity of dry flue gas in the recycled flue gas, in kJ / (m 3 ·K); t fg,re is the recirculating flue gas temperature, in °C; t fg,AHlv is the flue gas temperature at the boundary of the boiler system, in °C; v wv,re is the amount of water vapor in the recycled flue gas corresponding to unit mass of fuel, in m 3 / kg;c p,mv,re is the average constant-pressure specific heat capacity of water vapor in the recycled flue gas, in kJ / (m3·K); v fg,d,AHlv The dry flue gas volume at the boiler system boundary corresponding to unit mass of fuel, in m 3 / kg;v mv,AHlv is the amount of water vapor in the flue gas at the boiler system boundary corresponding to unit mass of fuel, in m 3 / kg;c p,fg,d,AHlv is the average constant pressure specific heat capacity of dry flue gas at the boundary of the boiler system, in kJ / (m 3 ·K);c p,mv,AHlv is the average constant pressure specific heat capacity of water vapor in the flue gas at the boundary of the boiler system, kJ / (m 3 ·K); t 0 is the reference temperature, in °C, Q fg,AHlv is the heat leaving the boiler system boundary, in kJ / kg; The percentage of heat gain brought into the boiler system by the recirculated flue gas q re Calculated according to the following formula: Among them, Q fg,re is the heat of the recirculated flue gas entering the boiler system boundary, in kJ / kg; q re Q is the percentage of heat gain brought into the boiler system by the recycled flue gas, in %; net,ar is the low calorific value of the fuel entering the furnace, in kJ / kg; Q fg,AHlv is the heat leaving the boiler system boundary, in kJ / kg; S5 calculates the conventional heat loss of the boiler and finally calculates the accurate boiler efficiency; the boiler efficiency η is calculated according to the following formula: η=100-(q2+q3+q4+q5+q6+q7+q oth -q ex )+q re Wherein, η is the boiler efficiency, in %; q2 is the exhaust heat loss, in %; q3 is the heat loss of incomplete combustion of gas, in %; q4 is the heat loss of incomplete combustion of solid, in %; q5 is the heat loss of boiler, in %; q6 is the physical sensible heat loss of ash, in %; q7 is the desulfurization heat loss of circulating fluidized bed boiler, in %; q oth is other heat loss, in %; q ex It is the percentage of external heat to the low calorific value of fuel, in %; q re It is the percentage of heat gain brought into the boiler system by the recirculated flue gas, in %.

2. The method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary according to claim 1, characterized in that: Step S2 measures the flue gas parameters at the outlet of the flue gas recirculation device, and simultaneously measures the atmospheric pressure and ambient dry-bulb temperature near the flue gas recirculation device, and calculates the volume flow rate, temperature, and oxygen content of the recirculated flue gas. Specifically, the following steps are included: using the equal-section grid method to measure the flue gas dynamic pressure P at the outlet of the flue gas recirculation device di , oxygen content O 2,re and temperature t fg,re , and the flue gas static pressure P at the measurement section s , and simultaneously test the atmospheric pressure P near the flue gas recirculation device A and ambient dry bulb temperature t A , calculate the recirculating flue gas volume flow V fg,re , Recirculated flue gas temperature t fg,re and the recirculated flue gas oxygen content O 2,re .

3. The method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary according to claim 1, characterized in that: Step S4 calculates the heat difference between the recirculated flue gas entering and leaving the boiler system boundary, and then obtains the heat increment percentage caused by the recirculated flue gas entering the boiler system boundary, which specifically includes the following steps: S401 corrects the recirculating flue gas volume flow rate to the recirculating flue gas volume flow rate under the oxygen content at the boiler system boundary, and obtains the recirculating flue gas volume flow rate V corrected to the oxygen content at the boiler system boundary. fg,re,cr ; S402 records the total coal volume of the unit DCS during the test period, and divides the recirculating flue gas volume flow rate corrected to the oxygen content at the boiler system boundary by the total coal volume during the test period to obtain the recirculating flue gas flow rate v corresponding to unit mass of fuel. fg,re According to the national standard of power plant boiler performance test procedures, the dry flue gas volume v corresponding to unit mass of fuel is calculated fg,d,re The amount of water vapor v corresponding to unit mass of fuel wv,re Two parts; S403 obtains the average constant pressure specific heat capacity c of the dry flue gas in the recycled flue gas by checking the original data. p,fg,d,re and the average constant-pressure specific heat capacity of water vapor c p,wv,re , and the average constant pressure specific heat capacity c of dry flue gas at the boundary of the boiler system p,fg,d,AHlv and the average constant-pressure specific heat capacity of water vapor c p,wv,AHlv , calculate the heat Q of the recirculated flue gas entering the boiler system boundary fg,re and the heat Q leaving the boiler system boundary fg,AHlv ; S404 calculates the heat difference between the recirculated flue gas entering and leaving the boiler system boundary, and then compares it with the lower calorific value of the fuel to obtain the heat increment percentage q brought by the recirculated flue gas into the boiler system boundary. re .

4. The method for calculating the efficiency of a boiler with a flue gas recirculation device outside the system boundary according to claim 1, characterized in that: Step S5 calculates various conventional heat losses of the boiler and finally calculates the accurate boiler efficiency. Specifically, it includes the following steps: According to the national standard of the power plant boiler performance test procedure, calculate various conventional heat losses: exhaust heat loss q2, gas incomplete combustion heat loss q3, solid incomplete combustion heat loss q4, boiler heat loss q5, ash physical sensible heat loss q6, circulating fluidized bed boiler desulfurization heat loss q7, other heat losses q oth , the percentage of external heat to fuel low calorific value q ex , combined with the percentage of heat gain from the recirculated flue gas q re , and finally the boiler efficiency η is calculated.

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