Bypass flue for inlet and outlet of air pre-heater of unit

The utility model discloses a bypass flue for an inlet and an outlet of a unit air pre-heater, which comprises a machine body component, and the machine body component comprises a smoke inlet pipe, an air pre-heater, a low-temperature economizer, an electric dust remover and a gas guide pipe. The auxiliary heating mechanism comprises a bypass branch pipe, a temperature sensor, a display screen, a PLC (Programmable Logic Controller), a relay and an electric heating ring; and the bottom of the smoke inlet pipe is communicated with the inlet smoke of the air preheater. High-temperature gas in the smoke inlet pipe is guided out through the bypass branch pipe and then conveyed into the gas guide pipe, smoke exhausted by a low-temperature economizer in the gas guide pipe is heated, then the temperature of the gas guide pipe is detected through the temperature sensor, and then the smoke in the gas guide pipe is subjected to auxiliary heating work through the electric heating ring. Therefore, the temperature of the a