Double wall temperature composite phase change heat exchanger

Abstract

The invention discloses a composite phase change heat exchanger with double wall temperatures. A phase change section is divided into a high-temperature phase change section and a low-temperature phase change section that are serially connected in a flue gas channel, a descending pipe and an ascending pipe of the high-temperature phase change section are communicated with a steam header of the high-temperature section, a descending pipe and an ascending pipe of the low-temperature phase change section are communicated with a steam header of the low-temperature section, and a desalted water pipeline used for heat exchange is respectively connected in the steam header of the high-temperature section and the steam header of the low-temperature section; an automatic control device adjusts and controls the flow of desalted water in the high-temperature section and wall surface temperature of the high-temperature phase change section, and simultaneously adjusts and controls the flow of the desalted water in steam header of the low-temperature section and wall surface temperature of the low-temperature phase change section. Temperature control of different wall surfaces of the two phase change sections separates flue gas into two temperature decreasing sections, reduces the temperature decreasing difference between each temperature decreasing section, reasonably distributes the heat flow density between heated surface tube banks of each phase change section, and can not only ensure good global heat conductivity with temperature decreasing value of the flue gas larger than 60 DEG C and improve the afterheat utilization rate, but also can satisfy the higher output temperature requirement of the heated desalted water by setting proper wall temperature of the high-temperature section.

Description

[technical field] [0001] The invention relates to a device for recovering and utilizing boiler flue gas waste heat, specifically a double-wall temperature composite phase-change heat exchanger that connects two phase-change heat exchangers in series in the flue gas duct and controls different wall temperatures to recover flue gas waste heat device. [Background technique] [0002] Economizers and air preheaters are usually installed in the exhaust duct of power plant boilers, which absorb part of the waste heat of the flue gas. 3 Existence of 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, so the boiler The design exhaust gas temperature is usually 140°C to 160°C or higher. The composite phase change heat exchanger ca...

AI Technical Summary

Problems solved by technology

But on the one hand, when the temperature drop of the flue gas is greater than 60, the temperature and pressure of the first row of finned tubes are too large, often exceeding the limit value of the phase change heat, resulting in a sharp deterioration of the heat transfer, and the increase of the wall temperature destroys the overall integrity of the phase change section. Under normal working conditions, the overall heat transfer performance of the device will eventually decrease, and the waste heat utilization rate will not reach the design index; on the other hand, when the user needs the heated desalted water to have a higher outlet temperature, even exceeding the minimum When the wall temperature is low, the composite phase change heat exchanger with single wall temperature control cannot meet the requirements

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