Optimal waste heat utilization set for use at cold end of boiler of thermal power generating unit

Abstract

The invention discloses an optimal waste heat utilization set for use at the cold end of a boiler of a thermal power generating unit. An air-oil heat exchanger and a flue gas-oil heat exchanger are provided behind an air preheater; the air-oil heat exchanger is connected with the flue gas-oil heat exchanger through a circulating pipeline; the circulating pipeline is filled with heat transfer medium, heat transfer oil; the circulating pipeline is provided with an expansion tank and a circulating pump. One end of the flue gas-oil heat exchanger is connected with a flue gas outlet of the air preheater; the other end of the flue gas-oil heat exchanger is provided with another flue gas outlet. One end of the air-oil heat exchanger is connected with an air inlet of the air preheater; the other end of the air-oil heat exchanger is provided with another air inlet. The optimal waste heat utilization set has the advantages that smoke emission temperature can be greatly lowered, utilization of flue gas waste heat is achieved, load of the air preheater is reduced, thermal deformation and air leakage are reduced for the air preheater, and energy consumption of the thermal power generating unit is reduced.

Description

technical field [0001] The invention relates to an optimized waste heat utilization device at the cold end of a thermal power unit boiler, which belongs to a method and a device for utilizing boiler flue gas waste heat and reducing the exhaust gas temperature of a thermal power unit. Background technique [0002] In the boiler heat loss, the power plant exhaust heat loss accounts for a large proportion. For every 10~15°C reduction in exhaust gas temperature, the boiler efficiency can be increased by 1%. At present, the design exhaust gas temperature of large-scale units is generally 120~130°C. With the continuous improvement of flue gas desulfurization and denitrification technology, the acid dew point of flue gas is around 90°C, so there is still a lot of room for the exhaust gas temperature to decrease. At the same time, the exhaust gas temperature of supercritical and ultra-supercritical unit boilers is generally higher than the design value, and the temperature of the f...

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Problems solved by technology

However, there is a limit to reducing the exhaust gas temperature. On the one hand, when the exhaust gas temperature is relatively low, as the temperature of the flue gas further decreases, the temperature difference with the air decreases, that is, the heat transfer area of ​​the air preheater increases a lot, and the temperature of the flue gas decreases. On the other hand, when the exhaust gas temperature is low and the wall temperature of the preheater tube is lower than the dew point of the flue gas, low-temperature corrosion will occur, and the preheater will need to be replaced after one or two years of operation, and in severe cases, it will need to be replaced within half a year

Another way is to add a low-pressure economizer at the tail of the flue, appropriately increase the heating surface of the economizer, impose waste heat utilization of the flue gas, and increase the temperature of the feed water. The coal burner utilizes the waste heat of the flue gas, which contributes little to the power generation of the unit and has a great loss of useful energy

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