Composite phase change heat exchanger with medium and low pressure

Abstract

The invention discloses a composite phase change heat exchanger with a medium-pressure and low-pressure evaporator, which comprises the medium-pressure and low-pressure evaporator and a steam header which are communicated by an ascending pipe and a descending pipe, a water feeding pipe and a steam outputting pipe are arranged on the steam header, an upper section of the composite phase change heat exchanger is positioned in a wind channel of an original air preheater, and a lower section of the composite phase change heat exchanger is positioned in a back flue channel of the air preheater; an automatic control device of the composite phase change heat exchanger adjusts and controls the heat exchange volume of the evaporator and the wall temperature of the lower section of the composite phase change heat exchanger. The composite phase change heat exchanger not only directly produces low-pressure or medium-pressure steam by using the recycled heat through a steam generating device and provides heat usage as a heat supply, but also controls the thermal equilibrium among the heat exchange volumes of the flue gas, the medium-pressure and low-pressure evaporator, a coal economizer and the wall of the air preheater by adjusting the steam flow of the steam outputting pipe of the steam header through the automatic control device, and consequently leads the flue gas temperature at the outlet to be higher than a flue gas acid dew point on the lower section wall surface of the composite phase change heat exchanger, avoids moisture condensation and achieves the purpose of utilizing waste heat of the flue gas to the utmost degree.

Description

[technical field] [0001] The invention relates to a device for recovering and utilizing waste heat of boiler flue gas, in particular to a composite phase change heat exchanger with a medium and low pressure evaporator combined with an economizer and an air preheater in a flue. [Background technique] [0002] There are usually economizers and air preheaters in the exhaust flue of power plant boilers, which absorb part of the waste heat of the flue gas, but the exhaust gas temperature is usually 140°C to 160°C or higher, and there is still waste heat that can be used. Due to the SO in the boiler flue gas 3 Existence of the flue gas outlet temperature of the heating surface at the tail of the air preheater is limited, and the exhaust gas temperature is too low will cause the wall temperature of the heating surface to be lower than the acid dew point of the flue gas, resulting in serious condensation corrosion and ash blocking. It is a difficult problem to use waste heat and re...

AI Technical Summary

Problems solved by technology

Due to the SO in the boiler flue gas 3 Existence of the flue gas outlet temperature of the heating surface at the tail of the air preheater is limited, and the exhaust gas temperature is too low will cause the wall temperature of the heating surface to be lower than the acid dew point of the flue gas, resulting in serious condensation corrosion and ash blocking. Difficulties that must be faced by utilizing waste heat and reducing exhaust gas temperature

[0003] The composite phase change heat exchanger can recycle waste heat while maintaining a high minimum wall temperature, greatly reduce the exhaust gas temperature, and control the exhaust gas temperature to only about 15°C higher than the minimum wall temperature, which can usually control the wall temperature At 100 °C, the exhaust gas temperature is about 115 °C, but in practical applications, the thermal balance must also be dealt with in order to achieve the effect of avoiding condensation and reducing the exhaust gas temperature

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