Anti-blocking modification method for air preheater

Abstract

A method for preventing and modifying an air preheater from being blocked comprises the following steps: adding a flue gas bypass next to the air preheater, connecting one end of the flue gas bypass to a flue gas inlet pipe of the air preheater, providing a flue gas flow regulating valve at the inlet of the flue gas bypass, providing a second-stage heat pipe heater in the flue gas bypass, and providing a first-stage heat pipe heater at the flue gas outlet pipe; when the exhaust gas temperature is lower than 95°C±5°C, opening the flue gas bypass regulating valve to guide the flue gas with a higher temperature at the air preheater inlet to the second-stage heat pipe heat exchanger through the flue gas bypass; adjusting the opening of the flue gas bypass regulating valve to adjust the amount of flue gas entering the second-stage heat pipe heat exchanger, thereby achieving a second heating of the cold primary and secondary air at the air preheater inlet, and adjusting the exhaust gas temperature to not lower than 95°C±5°C; while increasing the temperatures of the primary and secondary air at the air preheater inlet, preventing the exhaust gas temperature from being excessively lowered, thereby effectively solving the problem of ammonium bisulfate accumulation in the low-temperature section of the air preheater.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal power generation, and in particular relates to an anti-blocking modification method for an air preheater. Background Art

[0002] The basic structure of a three-compartment, Junkers-type air preheater is as follows: the primary and secondary air are arranged separately, the cold section is made of enameled heat exchange elements, the rotor is composed of semi-module and module structures, and the heat exchange elements are all basket structures to facilitate maintenance and replacement. The rotor transmission device is equipped with a main drive, an auxiliary drive, an air motor and a manual turning device. To avoid air leakage in the preheater, a fully enclosed sealing system (radial, axial, annular and center sealing devices) is adopted. The seals between the fan plate, axial sealing plate and outer shell plate are made into a labyrinth type to increase leakage resistance. The radial and axial sealing plates are adjustable, and the hot section radial seal adopts an automatic tracking control system. The existing three-compartment, Junkers-type air preheaters have the following problems: after the three-compartment, Junkers-type air preheaters are put into use, the differential pressure and air leakage rate will continue to rise. Analysis shows that the reason is that the temperature of the primary and secondary air of the air preheater decreases, and ammonium bisulfate accumulates, causing the preheater to be blocked. Summary of the Invention

[0003] In view of the technical problems existing in the background technology, the air preheater anti-blocking modification method provided by the present invention increases the primary and secondary air temperatures of the air preheater, effectively utilizes the waste heat of the flue gas to increase the air temperature, solves the low-temperature condensation problem of the air preheater, and has a stable effect.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] An air preheater anti-blocking modification method comprises the following steps:

[0006] Step 1: Add a flue gas bypass next to the air preheater, connect one end of the flue gas bypass to the flue gas inlet pipe of the air preheater, and connect the other end of the flue gas bypass to the flue gas outlet pipe of the air preheater, wherein the flue gas temperature of the flue gas inlet pipe is higher than the flue gas temperature of the flue gas outlet pipe; a flue gas flow regulating valve is provided at the inlet of the flue gas bypass, and a second-stage heat pipe heater is provided in the flue gas bypass, and the second-stage heat pipe heater is used to transfer the heat in the flue gas bypass to the air preheater; a first-stage heat pipe heater is provided on the flue gas outlet pipe;

[0007] Step 2: When the exhaust gas temperature is higher than 95℃±5℃, the flue gas bypass regulating valve is closed, and the first-stage heat pipe heater uses the waste heat of the flue gas at the air preheater outlet to perform the first-stage heating of the cold primary air and secondary air at the air preheater inlet;

[0008] Step three: when the exhaust gas temperature is lower than 95℃±5℃, open the flue gas bypass regulating valve to lead the flue gas with higher temperature at the air preheater inlet to the second-stage heat pipe heat exchanger through the flue gas bypass. By adjusting the opening of the flue gas bypass regulating valve, the amount of flue gas entering the second-stage heat pipe heat exchanger is adjusted to achieve the second heating of the cold primary and secondary air at the air preheater inlet, and adjust the exhaust gas temperature to not lower than 95℃±5℃; while increasing the primary and secondary air temperatures at the air preheater inlet, it prevents the exhaust gas temperature from dropping excessively, effectively solving the problem of ammonium bisulfate accumulation in the low-temperature section of the air preheater.

[0009] Preferably, the area where the first-stage heat pipe heater is located is divided into the air preheater outlets on both sides A and B. A flue gas bypass is added to the air preheaters on both sides A and B of each furnace. The first-stage heat pipe heater uses flue gas preheating to heat the primary air and secondary air of the air preheater to 40℃±5℃; the first-stage heat pipe heater adopts a low-flow resistance and low-temperature heat pipe heater to achieve front-stage preheating and maximize the use of flue gas waste heat.

[0010] Preferably, the first-stage heat pipe heater and the second-stage heat pipe heater use corrosion-resistant ND steel pipes, and arc spray corrosion-resistant materials are used on the outer wall surface of the ND steel pipes. The cross section of the ND steel pipes is elliptical.

[0011] The second-stage heat pipe heater is preferably a three-temperature zone heat pipe, consisting of a high-temperature heat pipe bundle, a medium-temperature heat pipe bundle, and a low-temperature heat pipe bundle. The high-temperature zone heat pipe, medium-temperature zone heat pipe, and low-temperature zone heat pipe are arranged in this order along the flue gas flow. A flow-guiding, low-resistance heat pipe design is employed to achieve the most scientific flow and heat exchange. The equipment's location and layout are carefully considered, optimizing heat transfer while prioritizing wear and corrosion protection for the heat exchange equipment. To reduce unnecessary ash clogging caused by low-temperature flue gas, no fins are used on the exterior of the tubes.

[0012] An air preheater anti-blocking modification structure adds a flue gas bypass next to the air preheater. One end of the flue gas bypass is connected to the flue gas inlet pipe of the air preheater, and the other end is connected to the flue gas outlet pipe of the air preheater. The flue gas temperature of the flue gas inlet pipe is higher than that of the flue gas outlet pipe. A flue gas flow regulating valve is provided at the inlet of the flue gas bypass, and a second-stage heat pipe heater is provided in the flue gas bypass. The second-stage heat pipe heater is used to transfer the heat in the flue gas bypass to the air preheater. The "three-temperature zone heat pipe" composite heat exchange technology is adopted, and the high-temperature flue gas at the inlet side of the rotary air preheater is drawn out by the bypass as the heat source for the secondary warm air. This not only eliminates the exhaust steam heating heater, but also this technological innovation will effectively solve the stubborn problem of sticky ash blockage in the low-temperature section of the air preheater due to excessively low exhaust gas temperature during deep peak regulation of the unit. The use of a primary heat pipe heat exchanger and a secondary heat pipe heat exchanger with a bypass can heat the air temperature from 0°C to 60°C. This not only effectively improves the air inlet boundary conditions of the air preheater and solves the problem of ammonium bisulfate accumulation in the air preheater, but also reduces the exhaust gas temperature, increases the primary and secondary air temperatures, improves the boiler efficiency, and reduces the coal consumption of the unit.

[0013] This patent can achieve the following beneficial effects:

[0014] 1. Increase the primary and secondary air temperature of the air preheater, effectively utilize the waste heat of the flue gas to increase the air temperature, solve the problem of low-temperature condensation in the air preheater, and achieve stable results;

[0015] 2. Reduce the exhaust gas temperature. By recovering the waste heat of the flue gas, the exhaust gas temperature is reduced, the coal consumption of the unit is reduced, and the economic efficiency of the unit operation is improved;

[0016] 3. The steam heater system has been cancelled, which reduces steam and power loss and reduces maintenance costs;

[0017] 4. Reduce the frequency of steam soot blowing and reduce steam loss;

[0018] 5. Small wear and tear. The first and second stage heat pipe heaters are made of corrosion-resistant ND steel and arc-sprayed with corrosion-resistant materials. The elliptical heat pipe tubes effectively reduce the flow resistance and reduce the wear on the contact pipe wall.

[0019] 6. Less ash accumulation. The first and second stage heat pipe heaters use high hardness precision rolled smooth tubes to reduce ash blockage caused by low temperature flue gas. An ultrasonic soot blower is added to solve the ash accumulation problem between the heat exchange tubes.

[0020] 7. Circulation resistance is reduced. The original system is designed with a secondary air heater with a full-load pressure difference of 570 Pa. After adding the heat pipe heater and removing the original secondary air heater, the pressure difference is reduced to 100-300 Pa.

[0021] 8. The system is simpler, safer, more reliable and more economical, and can achieve extremely low maintenance rate or even maintenance-free, which greatly reduces the maintenance workload and related expenses of the staff. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0023] Figure 1 This is a schematic diagram of the structure of the existing air preheater after modification according to the present invention.

[0024] In the figure: flue gas bypass 1, flue gas flow control valve 2, first-stage heat pipe heater 3, second-stage heat pipe heater 4, blower 5, rotary air preheater 6. DETAILED DESCRIPTION

[0025] Example 1:

[0026] The present invention proposes an air preheater anti-blocking modification method, which is applied to the air preheater of Unit 5 of a power generation enterprise. The implementation method is as follows:

[0027] After the air preheater of Unit 5 of a power generation company was put into operation in 2020, the differential pressure and air leakage rate continued to rise. In particular, the differential pressure of the 5A air preheater was high and fluctuated greatly. Under rated operating conditions:

[0028] 1. The flue gas pressure drop of the air preheater on the A side is 3.01 kPa, and the flue gas pressure drop of the air preheater on the B side is 2.73 kPa. The flue gas pressure drop is much higher than the design value of about 1.083 kPa (converted to BMCR working conditions).

[0029] 2. The flue gas temperature at the outlet of the air preheater on side A is 146.24°C, and the flue gas temperature at the outlet of the air preheater on side B is 144.38°C. The flue gas temperatures at the outlet of the air preheaters on both sides are higher than the design value (127°C), which is seriously higher than the design value. The heat exchange efficiency of the air preheater is low.

[0030] Since the flue gas pressure drop of the air preheaters on the A and B sides is much higher than the design value, and the exhaust gas temperature is high, it means that the two air preheaters of boiler No. 5 are seriously clogged and the air leakage rate is relatively large, so they must be treated. After taking multiple pyrolysis and offline high-pressure water flushing measures, no significant improvement was achieved, which seriously affected the output of the unit and caused a series of problems that affect the safety and economy of the unit. The blockage of the air preheater leads to increased resistance to flue gas and air flow, increased power consumption of the six major fans, reduced heat exchange efficiency of the air preheater, increased exhaust gas temperature, and even caused adverse effects such as large wind pressure fluctuations, fan surge and stall. In severe cases, it leads to load limiting of the boiler or even forced shutdown.

[0031] In response to the above problems, the flue gas bypass of the air preheater is added as a heat source, and the direct-transfer heat pipe heater technology is used to heat the cold primary and secondary air. Specifically, an electric flue gas flow regulating valve is installed in the flue gas bypass. During high load and summer, the flue gas bypass regulating valve is closed, and the flue gas waste heat is used to perform the first-stage heating of the cold primary and secondary air at the air preheater inlet; during low load and low wind temperature in winter, the air preheater exhaust temperature is low, and the flue gas bypass regulating valve is opened to lead the flue gas with a higher air preheater inlet temperature through the flue gas bypass to the second-stage heat pipe heat exchanger. By adjusting the opening of the air preheater flue gas bypass regulating valve, the amount of flue gas entering the second-stage heat pipe heat exchanger is adjusted to achieve the purpose of adjusting the exhaust temperature, thereby increasing the exhaust temperature, realizing the second heating of the cold primary and secondary air at the air preheater inlet, and increasing the temperature of the primary and secondary air at the air preheater inlet, effectively solving the problem of ammonium bisulfate accumulation in the low-temperature section of the air preheater.

[0032] After this transformation, the following results were achieved:

[0033] 1. Reduce air leakage rate.

[0034] A 1% air leakage rate corresponds to a coal consumption of approximately 0.135g / kWh. Currently, the air leakage rate of the No. 5 furnace's air preheater is 7.6%. After the overall replacement of the heat storage elements and anti-blocking modifications, the air leakage rate can be reduced to below 5.5%, and the air leakage rate is reduced by at least 2%. Based on the annual power generation of 3 billion kWh of the No. 5 furnace, 810 tons of standard coal will be reduced each year. Based on a company's furnace input standard of 1,200 yuan / ton in the past three years, the annual fuel cost expenditure will be reduced by 972,000 yuan.

[0035] 2. Reduce the factory's electricity consumption rate.

[0036] Currently, the high pressure difference of the air preheater of No. 5 boiler causes the power consumption of the six major fans and the exhaust gas temperature to increase. The comparison under 100% working condition with the new heat storage element and No. 6 boiler is as follows:

[0037]

[0038] As shown in the table above, the exhaust gas temperature of Boiler 5 is 7.7°C higher than the design value and 6.3°C higher than that of Boiler 6. The current of the six main fans is 134A higher than that of Boiler 6 and 449A higher than when the air preheater heat storage element of Boiler 6 was replaced in 2019.

[0039] For 600MW units, every 1kPa increase in the air preheater differential pressure affects power coal consumption by approximately 1.8g / kWh. Currently, the air preheater differential pressure of Boiler 5 (average value 2.5kPa) is 1.4kPa higher than the design value (1.083kPa), and the air preheater differential pressure of Boiler 6 (average value 1.9kPa) is 0.8kPa higher than the design value (1.083kPa). Due to severe damage to the heat storage element of Boiler 5's air preheater, the differential pressure is abnormally high. Therefore, based on the development of the air preheater differential pressure of Boiler 6 over the past three years (the heat storage element of 6A was repaired and replaced on November 15, 2019):

[0040] (1) Operation status of differential pressure of air preheater of No. 6 boiler in 2020

[0041]

[0042] (2) Operation status of differential pressure of air preheater of No. 6 boiler in 2021

[0043]

[0044] (3) Operation status of differential pressure of air preheater of No. 6 boiler in 2022

[0045]

[0046] The full-load differential pressure of the No. 6 air preheater from July 2020 to July 2022 was 1.69 kPa, 1.82 kPa, and 2.07 kPa, respectively, with an average of 1.86 kPa. The pressure increased by 0.607 kPa compared to the design value in the first year, 0.13 kPa in the second year, and 0.25 kPa in the third year.

[0047] According to the above analysis, after replacing the heat storage element and implementing anti-blocking modification, the pressure difference can be reduced by 0.8kPa, which corresponds to a reduction in power supply coal consumption of 1.44g / kWh. Based on the annual power generation of 3 billion kWh of No. 5 furnace, 4,320 tons of standard coal will be reduced each year. According to a company's furnace input standard of 1,200 yuan / ton in the past three years, the annual fuel cost expenditure will be reduced by 5.184 million yuan.

[0048] 3. Eliminate the use of steam in steam heaters to save fuel.

[0049] (1) Steam saving benefits

[0050] Currently, the designed steam consumption of the third phase heater is 14.8 tons / hour. According to statistics, from July 2021 to June 2022, the No. 5 furnace heater was put into operation for a total of about 1,697 hours, of which about 785 hours were discharged, and the average steam consumption per hour was calculated at 8 tons / hour.

[0051] The discharge water quality is calculated based on 95°C, and its enthalpy value is 398kj / kg, so the corresponding heat is 8×785×398×1000=2499440000kJ.

[0052] The corresponding standard coal is: 2499440000 ÷ 29310 ÷ 1000 = 116.7 tons of standard coal

[0053] 116.7×1200=140,040 yuan.

[0054] (2) Power saving benefits

[0055] The heater drain pump current is 65.5A, the voltage level is 380V, and the power consumption is 37.07kWh per hour.

[0056] The annual power consumption of the heater drain pump is 37.07×(1697-785)=33807.8kWh.

[0057] Calculated based on the electricity price of 0.46548 yuan / kWh excluding tax, the electricity consumption cost is 33807.8×0.46548=15,700 yuan.

[0058] (3) In summary, the elimination of the steam heater system will generate a benefit of RMB 14,004 + RMB 15,700 = RMB 1,557,400 per year.

[0059] 4. Reduce soot blowing in air preheater to save fuel.

[0060] Normally, the air preheater sootblowing frequency is three times per day, with only the cold end blown for half an hour each time. Due to an abnormally high air preheater differential pressure, Boiler No. 5 has increased the sootblowing frequency to six times per day, with both the hot and cold ends blown for one hour each time. This represents an additional 4.5 hours per day compared to normal conditions. The sootblowing consumes 3.6 t / h of steam, an additional 16.2 tons of steam per day.

[0061] Unit 5 operated for 7,789.21 hours in 2021, corresponding to 324.6 days.

[0062] Steam saving: 324.6×16.2=5258.52 tons.

[0063] The load rate of Unit 5 in 2021 was 71.48%. The sootblowing steam source was low re-export steam with a steam pressure of 3.18 MPa and a temperature of 467.3°C. The corresponding enthalpy value was 3380.99 kJ / kg.

[0064] Amount of standard coal saved: 5258.52×1000×3380.99÷29310÷1000=606.7 tons

[0065] Cost: 606.7×1200=728,000 yuan / year

[0066] 5. Generate mutual benefits.

[0067] 97.2+518.4+15.574+72.8=7.03974 million yuan

[0068] In summary, the comprehensive annual economic benefits after the implementation of the direct-transfer heat pipe heater transformation can reach 7.03974 million yuan.

[0069] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention shall be the technical solutions set forth in the claims, including equivalent alternatives to the technical features of the technical solutions set forth in the claims. In other words, equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for preventing blockage of an air preheater, characterized in that The following steps are involved: Step 1: Add a flue gas bypass next to the air preheater, connect one end of the flue gas bypass to the flue gas inlet pipe of the air preheater, and connect the other end of the flue gas bypass to the flue gas outlet pipe of the air preheater, and the flue gas temperature of the flue gas inlet pipe is higher than the flue gas temperature of the flue gas outlet pipe; A flue gas flow regulating valve is provided at the inlet of the flue gas bypass, and a second-stage heat pipe heater is provided in the flue gas bypass to transfer the heat in the flue gas bypass to the air preheater; a first-stage heat pipe heater is provided at the flue gas outlet pipe; Step 2: When the exhaust gas temperature is higher than 95℃±5℃, the flue gas bypass regulating valve is closed, and the first-stage heat pipe heater uses the waste heat of the flue gas at the air preheater outlet to perform the first-stage heating of the cold primary air and secondary air at the air preheater inlet; Step 3: When the exhaust gas temperature is lower than 95°C ± 5°C, open the flue gas bypass regulating valve to guide the flue gas with a higher temperature at the air preheater inlet to the second-stage heat pipe heat exchanger through the flue gas bypass. By adjusting the opening of the flue gas bypass regulating valve, the amount of flue gas entering the second-stage heat pipe heat exchanger is adjusted to achieve a second heating of the cold primary and secondary air at the air preheater inlet, and adjust the exhaust gas temperature to no less than 95°C ± 5°C. While increasing the primary and secondary air temperatures at the air preheater inlet, it prevents the exhaust gas temperature from dropping excessively, effectively solving the problem of ammonium bisulfate accumulation in the low-temperature section of the air preheater. The second-stage heat pipe heater is a three-temperature zone heat pipe, which consists of a high-temperature heat pipe bundle, a medium-temperature heat pipe bundle and a low-temperature heat pipe bundle. Along the direction of the flue gas flow, there are high-temperature zone heat pipes, medium-temperature zone heat pipes and low-temperature zone heat pipes in turn.

2. The air preheater anti-blocking modification method according to claim 1 is characterized in that: The area where the first-stage heat pipe heater is located is divided into the air preheater outlets on both sides A and B. A flue gas bypass is added to the air preheaters on both sides A and B of each furnace. The first-stage heat pipe heater uses flue gas preheating to heat the primary air and secondary air of the air preheater to 40℃±5℃; the first-stage heat pipe heater adopts a low-flow resistance and low-temperature heat pipe heater to achieve front-stage preheating and maximize the use of flue gas waste heat.

3. The air preheater anti-blocking modification method according to claim 1, characterized in that: The first-stage heat pipe heater and the second-stage heat pipe heater adopt corrosion-resistant ND steel pipe, and the outer wall surface of the ND steel pipe is arc-sprayed with corrosion-resistant material. The cross section of the ND steel pipe is elliptical.

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