Exhaust gas temperature correction method based on different air leakage positions of air pre-heater

Abstract

The invention discloses an exhaust gas temperature correction method based on different air leakage positions of an air pre-heater. The exhaust gas temperature correction method comprises the steps that the exhaust gas temperature is corrected through air leakage at the hot end of the air pre-heater, the exhaust gas temperature is corrected through air leakage at the cold end of the air pre-heater, and the exhaust gas temperature is corrected through the air leakage rate of the air pre-heater. According to the exhaust gas temperature correction method based on the different air leakage positions of the air pre-heater, exhaust gas temperature correction is conducted on the basis that it is clear that the air leakage rate of the air pre-heater is only cold and hot end air leakage, and a calculation formula of the influence of the air leakage rate deviation of the hot end and the cold end of the air pre-heater on the exhaust gas temperature is deduced based on the energy balance principle; and the calculation accuracy of the exhaust gas temperature is improved.

Description

Technical Field

[0001] The invention relates to the technical field of air preheaters, and more specifically to a method for correcting exhaust gas temperature based on different air leakage positions of an air preheater. Background Art

[0002] The "Power Plant Boiler Performance Test Procedure" (GB / T 10184-2015) provides a calculation method for exhaust temperature correction when the inlet air temperature deviates from the design value, but does not provide a correction for the exhaust temperature when the air preheater leakage deviates from the design.

[0003] Air preheater leakage has a great influence on boiler exhaust temperature and boiler thermal efficiency. Accurately and quantitatively reflecting the influence of air leakage changes in different parts of the air preheater on exhaust temperature is not only beneficial to the daily operation, maintenance and overhaul of the air preheater, but also related to whether the boiler thermal efficiency can be accurately calculated and the energy-saving potential of the boiler unit can be tapped. Therefore, studying the correction calculation of exhaust temperature caused by air preheater leakage has important practical significance. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for correcting the exhaust gas temperature based on different air leakage positions of an air preheater, so as to solve the problems in the background technology.

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows.

[0006] A method for correcting exhaust gas temperature based on different air leakage positions of an air preheater, comprising:

[0007] Correction of exhaust temperature due to air leakage at the hot end of air preheater: Air leakage at the hot end of air preheater is the leakage of heated hot air into the flue gas at the inlet of air preheater. According to the heat exchange mechanism of air leakage at the hot end, the correction calculation of the influence of the change of air leakage at the hot end on the exhaust temperature is classified as the correction of the exhaust temperature due to the change of the flue gas temperature at the inlet of air preheater. The exhaust temperature is corrected according to the energy balance principle.

[0008] Correction of exhaust gas temperature by air leakage at the cold end of air preheater: Since the travel distance of flue gas and air at the lower end of the cold end of air preheater is relatively short, the air leakage at the cold end simply cools the flue gas and does not participate in the heat exchange of air preheater. Through energy heat exchange, the correction component of exhaust gas temperature at the outlet of air preheater after the air leakage rate at the cold end of air preheater changes is derived;

[0009] Correction of exhaust temperature by air preheater leakage rate: After the total air leakage rate of the air preheater changes, the sum of the correction components of the hot end leakage and the cold end leakage on the exhaust temperature is the correction of the exhaust temperature.

[0010] To further optimize the technical solution, the correction method for the exhaust gas temperature caused by the air leakage at the hot end of the air preheater is: based on the energy balance principle, it is expressed as:

[0011] (m rout -m rin )c rlk (t ky -t k )=m rin c ryq (t ky -t ky(wl) ) (1)

[0012] Where: m rout - Flue gas volume at the hot end outlet of the air preheater per unit mass of fuel, kg / kg;

[0013] m rin - Flue gas volume at the hot end of the air preheater under unit fuel mass, kg / kg;

[0014] t ky —Temperature of air leakage at hot end, °C;

[0015] t ky —Flue gas temperature when there is air leakage at the hot end of the air preheater, °C;

[0016] t ky(wl) —Inlet flue gas temperature at the hot end of the air preheater without air leakage, °C;

[0017] c rlk —Average constant pressure specific heat capacity of air from tk to tky, kJ / (kg.℃);

[0018] c ryq —Air from tky to t ky(wl) Average specific heat capacity at constant pressure, kJ / (kg.℃);

[0019] Formula (1) is transformed into

[0020]

[0021] Where: A rl —Air leakage rate at hot end of air preheater, %;

[0022] Among them: A rl =A l ·a rl (3)

[0023] Where: a rl —Ratio of air leakage at hot end;

[0024] Assuming that the hot air temperature at the air preheater outlet remains unchanged, when the air leakage rate at the hot end of the air preheater changes, equation (2) can be changed to:

[0025]

[0026] For the correction of the air preheater inlet flue gas temperature, when only the inlet flue gas temperature changes, it is assumed that the flue gas side efficiency of the air preheater before and after the correction remains unchanged, so there is

[0027]

[0028] Where: t0—air preheater inlet cold air temperature, °C;

[0029] t' ky(wl) —The actual exhaust gas temperature at the heat exchange outlet of the air preheater after correction or conversion to the change of the hot end leakage rate, °C;

[0030] Combining formulas (2), (3) and (4) and ignoring the difference in specific heat between flue gas and air, we can get

[0031] Quantity, that is:

[0032]

[0033] Where: Δt py(rlf) —Correction component of exhaust gas temperature caused by change of air leakage rate at hot end of air preheater, ℃;

[0034] a ll —Ratio of air leakage at the hot end;

[0035] The correction component of the flue gas temperature at the air preheater outlet after the air leakage rate at the hot end of the air preheater changes can be calculated through formula (6).

[0036] To further optimize the technical solution, the correction method for the exhaust gas temperature caused by the air leakage at the cold end of the air preheater is: deriving the correction component through energy heat exchange:

[0037]

[0038] Where: Δt py(llf) —Correction component of the exhaust gas temperature at the air preheater outlet taking into account the change in the air leakage rate at the cold end of the air preheater.

[0039] To further optimize the technical solution, the correction method of the air preheater leakage rate to the exhaust gas temperature is: firstly agree on the proportion of hot end air leakage and cold end air leakage in advance, and then calculate the correction component of the leakage rate to the exhaust gas temperature:

[0040]

[0041] Due to the adoption of the above technical scheme, the technical progress achieved by the present invention is as follows.

[0042] The present invention provides a method for correcting exhaust temperature based on different leakage positions of an air preheater. The exhaust temperature is corrected on the basis that it is clear that the leakage rate of the air preheater is only the leakage at the cold and hot ends, and a calculation formula for the influence of the leakage rate deviation at the hot and cold ends of the air preheater on the exhaust temperature is derived based on the energy balance principle, thereby improving the accuracy of the exhaust temperature calculation. DETAILED DESCRIPTION

[0043] The present invention will be further described in detail below with reference to specific embodiments.

[0044] A method for correcting exhaust temperature based on different air leakage positions of an air preheater includes corrections of exhaust temperature due to air leakage at the hot end of the air preheater, corrections of exhaust temperature due to air leakage at the cold end of the air preheater, and corrections of exhaust temperature due to air leakage rate of the air preheater.

[0045] (1) Correction of exhaust gas temperature due to air leakage at the hot end of air preheater

[0046] The air leakage at the hot end of the air preheater is mainly the heated hot air, which leaks into the flue gas at the inlet of the air preheater, reducing the flue gas temperature at the inlet of the air preheater and affecting the heat transfer characteristics and heat transfer effect of the air preheater. Therefore, from the heat exchange mechanism of the hot end leakage, the air leakage at the hot end of the air preheater reduces the inlet flue gas temperature, and the correction calculation of the impact of the hot end leakage change on the exhaust temperature is approximately attributed to the correction of the exhaust temperature due to the change of the air preheater inlet flue gas temperature.

[0047] For the hot end leakage, according to the energy balance principle, it can be expressed as:

[0048] (m rout -m rin )c rlk (t ky -t k )=m rin c ryq (t ky -t ky(wl) ) (1)

[0049] Where: m rout - Flue gas volume at the hot end outlet of the air preheater per unit mass of fuel, kg / kg;

[0050] m rin - Flue gas volume at the hot end of the air preheater under unit fuel mass, kg / kg;

[0051] t ky —Temperature of air leakage at hot end, °C;

[0052] t ky —Flue gas temperature when there is air leakage at the hot end of the air preheater, °C;

[0053] t ky(wl)—Inlet flue gas temperature at the hot end of the air preheater without air leakage, °C;

[0054] c rlk —Average constant pressure specific heat capacity of air from tk to tky, kJ / (kg.℃);

[0055] c ryq —Air from tky to t ky(wl) Average specific heat capacity at constant pressure, kJ / (kg.℃);

[0056] Formula (1) is transformed into

[0057]

[0058] Where: A rl —Air leakage rate at hot end of air preheater, %;

[0059] Among them: A rl =A l ·a rl (3)

[0060] Where: a rl —Ratio of air leakage at hot end;

[0061] Assuming that the hot air temperature at the air preheater outlet remains unchanged, when the air leakage rate at the hot end of the air preheater changes, equation (2) can be changed to:

[0062]

[0063] For the correction of the air preheater inlet flue gas temperature, when only the inlet flue gas temperature changes, it is assumed that the flue gas side efficiency of the air preheater before and after the correction remains unchanged, so there is

[0064]

[0065] Where: t0—air preheater inlet cold air temperature, °C;

[0066] t' ky(wl) —The actual exhaust gas temperature at the heat exchange outlet of the air preheater after correction or conversion to the change of the hot end leakage rate, °C;

[0067] Combining formulas (2), (3) and (4) and ignoring the difference in specific heat between flue gas and air, we can get

[0068] Quantity, that is:

[0069]

[0070] Where: Δt py(rlf) —Correction component of exhaust gas temperature caused by change of air leakage rate at hot end of air preheater, ℃;

[0071] a ll —Ratio of air leakage at hot end;

[0072] The correction component of the flue gas temperature at the air preheater outlet after the air leakage rate at the hot end of the air preheater changes can be calculated through formula (6).

[0073] (2) Correction of exhaust gas temperature due to air leakage at the cold end of air preheater

[0074] Since the travel distance of the flue gas and air at the lower end of the cold end of the air preheater is relatively short, the air leakage at the cold end simply cools the flue gas and does not participate in the heat exchange of the air preheater. It is just a simple energy heat exchange. By the same token, the correction component of the exhaust gas temperature at the air preheater outlet after the air leakage rate at the cold end of the air preheater changes is derived.

[0075] The correction component is derived through energy heat exchange:

[0076]

[0077] Where: Δt py(llf) —Correction component of the exhaust gas temperature at the air preheater outlet taking into account the change in the air leakage rate at the cold end of the air preheater.

[0078] (3) Correction of air preheater leakage rate on exhaust gas temperature

[0079] After the total air leakage rate of the air preheater changes, the sum of the correction components of the hot end leakage and the cold end leakage on the exhaust temperature is the correction of the exhaust temperature.

[0080] First, agree in advance on the ratio of hot-end airflow and cold-end air leakage, and then calculate the correction component of the air leakage rate on the exhaust temperature:

[0081]

[0082] In the calculation of the exhaust temperature correction due to the deviation of air preheater leakage from the design value, the radial leakage at the hot and cold ends of the air preheater accounts for a large proportion of the total leakage of the air preheater, accounting for more than 2 / 3 of the total leakage. Therefore, by deriving the influence formula of the air preheater cold and hot end leakage on the exhaust temperature, the accuracy of the exhaust temperature calculation is improved.

Claims

1. A method for correcting exhaust gas temperature based on different air leakage positions of an air preheater, characterized in that: include: Correction of exhaust temperature due to air leakage at the hot end of air preheater: Air leakage at the hot end of air preheater is the leakage of heated hot air into the flue gas at the inlet of air preheater. According to the heat exchange mechanism of air leakage at the hot end, the correction calculation of the influence of the change of air leakage at the hot end on the exhaust temperature is classified as the correction of the exhaust temperature due to the change of the flue gas temperature at the inlet of air preheater. The exhaust temperature is corrected according to the energy balance principle. Correction of exhaust gas temperature by air leakage at the cold end of air preheater: Since the travel distance of flue gas and air at the lower end of the cold end of air preheater is relatively short, the air leakage at the cold end simply cools the flue gas and does not participate in the heat exchange of air preheater. Through energy heat exchange, the correction component of exhaust gas temperature at the outlet of air preheater after the air leakage rate at the cold end of air preheater changes is derived; Correction of exhaust temperature by air preheater leakage rate: After the total air leakage rate of the air preheater changes, the sum of the correction components of the hot end leakage and the cold end leakage on the exhaust temperature is the correction of the exhaust temperature.

2. The method for correcting exhaust gas temperature based on different air leakage positions of an air preheater according to claim 1 is characterized in that: The correction method for the exhaust gas temperature caused by air leakage at the hot end of the air preheater is: based on the energy balance principle, it is expressed as: (m rout -m rin )c rlk (t ky -t k )=m rin c ryq (t ky -t ky(wl) ) (1) Where: m rou t - Flue gas volume at the hot end outlet of the air preheater per unit mass of fuel, kg / kg; m r i n - Flue gas volume at the hot end of the air preheater under unit fuel mass, kg / kg; t ky —Temperature of air leakage at hot end, °C; t ky —Flue gas temperature when there is air leakage at the hot end of the air preheater, °C; t ky(wl) —Inlet flue gas temperature at the hot end of the air preheater without air leakage, °C; c rlk —Average constant pressure specific heat capacity of air from tk to tky, kJ / (kg.℃); c ryq —Air from tky to t ky(wl) Average specific heat capacity at constant pressure, kJ / (kg.℃); Formula (1) is transformed into Where: A rl —Air leakage rate at hot end of air preheater, %; Among them: A rl = A l a rl (3) Where: a rl —Ratio of air leakage at hot end; Assuming that the hot air temperature at the air preheater outlet remains unchanged, when the air leakage rate at the hot end of the air preheater changes, equation (2) can be changed to: For the correction of the air preheater inlet flue gas temperature, when only the inlet flue gas temperature changes, it is assumed that the flue gas side efficiency of the air preheater before and after the correction remains unchanged, so there is Where: t0—air preheater inlet cold air temperature, °C; t′ ky(wl) —The actual exhaust gas temperature at the heat exchange outlet of the air preheater after correction or conversion to the change of the hot end leakage rate, °C; Combining formulas (2), (3) and (4) and ignoring the difference in specific heat between flue gas and air, we can get Quantity, that is: Where: Δt py(rlf) —Correction component of exhaust gas temperature caused by change of air leakage rate at hot end of air preheater, ℃; a ll —Ratio of air leakage at hot end; The correction component of the flue gas temperature at the air preheater outlet after the air leakage rate at the hot end of the air preheater changes can be calculated through formula (6).

3. The method for correcting exhaust gas temperature based on different air leakage positions of an air preheater according to claim 1 is characterized in that: The correction method for the exhaust gas temperature caused by the air leakage at the cold end of the air preheater is: deriving the correction component through energy heat exchange: Where: Δt py(llf) —Correction component of the exhaust gas temperature at the air preheater outlet taking into account the change in the air leakage rate at the cold end of the air preheater.

4. The method for correcting exhaust gas temperature based on different air leakage positions of an air preheater according to claim 1 is characterized in that: The correction method of the air preheater leakage rate to the exhaust gas temperature is as follows: firstly, the proportion of the hot end leakage and the cold end leakage is agreed in advance, and then the correction component of the leakage rate to the exhaust gas temperature is calculated:

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