Resistance reducing system of flue gas shunting type air pre-heater

Abstract

The utility model discloses a resistance reducing system of a smoke flow dividing type air pre-heater. The resistance reducing system comprises a rotary air pre-heater, an inlet flue and an outlet flue, the inlet flue is connected with a flue gas inlet of the plate-type flue gas heat exchanger through a flue gas bypass pipeline, an air inlet of the plate-type flue gas heat exchanger is connected with the fan, an air outlet of the plate-type flue gas heat exchanger is communicated with the air side of the rotary air pre-heater through a warm air duct, and a flue gas outlet of the plate-type flue gas heat exchanger and the outlet flue are both connected with the dust remover; the resistance reducing device has the advantages of being low in cost and good in resistance reducing effect, improves the heat exchange efficiency of a system, avoids blocking, and improves the economical efficiency of a unit.

Description

Technical Field

[0001] The utility model relates to an air preheater resistance reduction system, in particular to a flue gas split-flow air preheater resistance reduction system. Background Art

[0002] For large coal-fired boilers, a rotary air preheater is usually arranged after the economizer and denitrification device to heat the boiler's supply air, thereby reducing the boiler's exhaust gas temperature and improving boiler efficiency. The main indicators of the rotary air preheater are heat exchange efficiency, flue gas resistance, and air leakage rate.

[0003] There's a conflicting relationship between air preheater heat transfer efficiency and flue gas resistance. High heat transfer efficiency implies a large component area, which in turn leads to high flue gas resistance. Excessive flue gas resistance can lead to insufficient fan output and boiler load reduction. Therefore, the relationship between heat transfer and resistance must be comprehensively considered, with the goal of ensuring efficient and stable operation of the unit. For early non-denitrification preheaters, the air preheaters were undersized, and clogging increased with operating time. This is primarily due to the fact that even after component modifications, heat transfer efficiency must be maintained, and component density does not decrease significantly, resulting in a high design resistance. This inadequate resistance to clogging is impaired when external conditions change (for example, increased ammonia slip promotes ammonium bisulfate formation and flue gas volumes increase). Ammonium bisulfate clogging under current ultra-low emission conditions, coupled with high flue gas volumes from burning low-quality coal, results in high air preheater resistance, insufficient fan output at full load, and impacts unit operation. Ammonium bisulfate clogging under current ultra-low emission conditions, coupled with high flue gas volumes from burning low-quality coal, results in high air preheater resistance, insufficient fan output at full load, and impacts unit operation.

[0004] There are currently two main solutions to the problem of large resistance in the air preheater of old units: 1. Expand the air preheater to reduce resistance by increasing the flow cross-section, but this requires the unit to have enough space for expansion, and often the steel structure of the unit does not have this condition; 2. Add a flue gas bypass solution in front of the air preheater to divert the flue gas entering the air preheater and reduce the flue gas flowing into the air preheater. After the flue gas flow is reduced, the flue gas resistance will naturally decrease. At the same time, the bypass flue gas is used to heat the condensate to recover the flue gas heat, and then the condensate is used to heat the air to increase the exhaust temperature of the air preheater to prevent low-temperature corrosion of the air preheater. The principle of this solution is feasible, but it requires intermediate medium water for heat absorption and heat release conversion. The system is large, complex, and costly, and the heat exchange equipment, the tubular heat exchanger, is prone to leakage and blockage, and has a short service life. Summary of the Invention

[0005] The purpose of this utility model is to address the above-mentioned deficiencies in the prior art and provide a flue gas split-flow air preheater resistance reduction system, which has the advantages of low cost and good resistance reduction effect, and improves the system heat exchange efficiency, avoids blockage, and improves the economy of the unit.

[0006] In order to achieve the above-mentioned purpose, the utility model provides a flue gas diversion air preheater resistance reduction system, including a rotary air preheater, an inlet flue and an outlet flue; its characteristics are: the inlet flue is connected to the flue gas inlet of the plate flue gas heat exchanger through a flue gas bypass pipe, the air inlet of the plate flue gas heat exchanger is connected to the fan, the air outlet of the plate flue gas heat exchanger is connected to the air side of the rotary air preheater through a warm air duct, and the flue gas outlet and the outlet flue of the plate flue gas heat exchanger are both connected to the dust collector.

[0007] The utility model divides the flue gas before the rotary air preheater into two paths by setting a flue gas bypass pipe. The main flue gas normally passes through the rotary air preheater. After the flue gas flow is reduced, the resistance reduction effect of the rotary air preheater is good; the bypass flue gas exchanges heat through the plate heat exchanger to reduce the exhaust temperature, and the cold air from the fan is first heated by the plate heat exchanger before entering the rotary preheater; compared with the tubular heat exchanger that heats the flue gas to condense water to recover the flue gas heat, this system uses a plate flue gas heat exchanger to directly exchange heat between the flue gas and the air, which has a lower cost, improves the system heat exchange efficiency, and improves the economic efficiency of the unit;

[0008] As a further improvement of the present invention, the plate-type flue gas heat exchanger includes several modules, each module includes several flue gas channels and several air channels with inlets located in different directions, the flue gas channels and the air channels are spaced apart, a flue gas damper door is provided at the flue gas inlet of each module, and an air damper door is provided at the air inlet of each module; when ammonium bisulfate is produced in a module, the air damper door of the module is closed, and only flue gas passes through the module, the metal wall temperature rises, and the ammonium bisulfate is vaporized or decomposed by the heating of the flue gas. After the ammonium bisulfate in the module is removed, the air damper door of the module is opened; and so on, each module is heated by flue gas in turn, and the ammonium bisulfate can be removed online to avoid blockage;

[0009] As a further improvement of the present invention, an air damper is provided on the flue gas bypass duct; the amount of flue gas entering the flue gas bypass duct can be adjusted, thereby adjusting the final exhaust gas temperature and the temperature of the cold air entering the air preheater, ensuring that the exhaust gas temperature is above the acid dew point temperature, thereby avoiding low-temperature corrosion;

[0010] As a further improvement of the present invention, the width of the smoke channel is greater than 12 mm; the smoke channel adopts a wide flow channel design to further avoid blockage;

[0011] In summary, the utility model has the advantages of low cost and good resistance reduction effect, and improves the heat exchange efficiency of the system, avoids blockage, and improves the economy of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a structural schematic diagram of an embodiment of the present utility model.

[0013] Figure 2 for Figure 1 A three-dimensional diagram of several modules of a medium-plate flue gas heat exchanger.

[0014] Figure 3 for Figure 2 P-direction view.

[0015] Figure 4 for Figure 2 M-direction view. DETAILED DESCRIPTION

[0016] The present invention is further described below with reference to the accompanying drawings. Taking a 600MW unit as an example, the air side resistance is about 1.6KPa, the flue gas side resistance is about 2.2KPa, and the exhaust gas temperature is about 140°C.

[0017] like Figures 1 to 4 As shown, a flue gas split air preheater resistance reduction system of this embodiment includes a rotary air preheater 1, an inlet flue duct 2 and an outlet flue duct 3; the inlet flue duct 2 is connected to the flue gas inlet of the plate type flue gas heat exchanger 5 through a flue gas bypass pipe 4, and the flue gas bypass pipe 4 is provided with an adjusting damper 14; the air inlet of the plate type flue gas heat exchanger 5 is connected to the fan 6, and the air outlet of the plate type flue gas heat exchanger 5 is connected to the air side of the rotary air preheater 1 through a warm air duct 7. The flue gas outlet 5 and the outlet flue 3 are both connected to the dust collector 8; the plate-type flue gas heat exchanger 5 includes a plurality of modules 9, each module 9 includes a plurality of flue gas channels 10 and a plurality of air channels 11 whose inlets are located in mutually perpendicular directions, the flue gas channels 10 and the air channels 11 are arranged at intervals, and the width of the flue gas channels 10 is greater than 12 mm. A flue gas damper door 12 is provided at the flue gas inlet of each module 9, and an air damper door 13 is provided at the air inlet of each module 9.

[0018] In this embodiment, the flue gas in front of the rotary air preheater is divided into two paths by setting a flue gas bypass pipe 4. The main flue gas passes through the rotary air preheater 1 normally, and the flue gas entering the flue gas bypass pipe 4 accounts for 12% (which can be adjusted according to different parameters). At this time, due to the reduction in the amount of flue gas entering the rotary air preheater, the resistance of the air preheater drops to 1.2KPa, and the resistance reduction effect is good. At the same time, the bypass flue gas passes through the plate heat exchanger 5 and exchanges heat with the cold air from the fan 6. The cold air entering the air preheater is heated to 50°C, and the comprehensive temperature of the cold end of the air preheater is greatly improved. It can prevent the ammonium bisulfate in the air preheater from being blocked, and ensure that the resistance does not increase during long-term operation; due to the addition of the plate flue gas heat exchanger 5, it is equivalent to expanding the heat exchange area, and removing The exhaust gas temperature of the dust collector 8 is reduced from the original 140°C to 125°C, and the heat exchange efficiency of the system is improved. When ammonium bisulfate is produced in a module 9, the air damper door 13 of the module is closed, and only flue gas passes through the module, which increases the metal wall temperature. The ammonium bisulfate is vaporized or decomposed by the heating of the flue gas. After the ammonium bisulfate in the module is removed, the air damper door 12 of the module is opened. Similarly, each module is heated by flue gas in turn, which can remove ammonium bisulfate online, avoid blockage and eliminate the need for flushing. The amount of flue gas entering the flue gas bypass duct 4 can be adjusted by adjusting the damper 14, thereby adjusting the final exhaust gas temperature and the cold air temperature entering the air preheater to ensure that the exhaust gas temperature is above the acid dew point temperature, thereby avoiding low-temperature corrosion.

[0019] Compared with the tubular heat exchanger that heats the flue gas to condensate and recover the flue gas heat, this system uses a plate flue gas heat exchanger 5 to directly exchange heat between the flue gas and the air, which has a lower cost. Taking a 600MW-class unit as an example, by implementing this patent, the flue gas temperature at the rotary preheater outlet is 145°C, the inlet air temperature is 50°C, the total resistance on the air side of the system is 1.3KPa, the resistance on the flue gas side is 1.2KPa, the flue gas temperature at the plate heat exchanger outlet is 80°C, and the exhaust gas temperature is about 125°C. The exhaust gas temperature in this embodiment is reduced by 1 5℃, furnace efficiency increased by 0.75%, and smoke resistance decreased by 1.3 kPa. The direct economic benefit is a savings of approximately RMB 6.41 million in coal consumption and electricity costs each year. Taking a 600MW unit as an example, eliminating the steam air heater can save RMB 600,000 per furnace annually (assuming the steam air heater is in operation for three months each year). It can also reduce the cost of downtime and flushing each year. Assuming each flush costs RMB 1 million, this saves RMB 2 million. The above economic benefits total RMB 9.01 million per year, improving the unit's economic efficiency.

[0020] The above embodiments have been used for illustration, but it should be understood that the above embodiments are only used for the purpose of example and description, and are not intended to limit the present invention to the scope of the described embodiments.

Claims

1. A flue gas split-flow air preheater resistance reduction system, comprising a rotary air preheater, an inlet flue duct, and an outlet flue duct; characterized in that: The inlet flue is connected to the flue gas inlet of the plate flue gas heat exchanger through a flue gas bypass pipe. The air inlet of the plate flue gas heat exchanger is connected to the fan. The air outlet of the plate flue gas heat exchanger is connected to the air side of the rotary air preheater through a warm air duct. The flue gas outlet and the outlet flue are both connected to the dust collector.

2. The flue gas split-flow air preheater resistance reduction system according to claim 1, characterized in that: The plate-type flue gas heat exchanger includes several modules, each module includes several flue gas channels and several air channels with inlets located in different directions, the flue gas channels and the air channels are arranged at intervals, a flue gas damper door is provided at the flue gas inlet of each module, and an air damper door is provided at the air inlet of each module.

3. A flue gas split-flow air preheater resistance reduction system according to claim 1 or 2, characterized in that: An adjusting damper is provided on the flue gas bypass duct.

4. The flue gas split-flow air preheater resistance reduction system according to claim 2, characterized in that: The width of the smoke channel is greater than 12 mm.

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