Method and device for carrying out gradient utilization on boiler flue gas waste heat to improve efficiency of thermal power unit

Abstract

The invention relates to the technical field of thermal power unit energy saving, in particular to a method and device for carrying out gradient utilization on boiler flue gas waste heat to improve efficiency of a thermal power unit. The device for carrying out gradient utilization on the boiler flue gas waste heat to improve the efficiency of the thermal power unit comprises an economizer of a boiler of the thermal power unit, an air pre-heater communicated with the economizer, and a main water feed pipe of a high-pressure heater. The device for carrying out gradient utilization on the boiler flue gas waste heat to improve the efficiency of the thermal power unit is characterized in that an additional heated surface is added to the economizer, an air-and-oil heat exchanger and a flue-gas-and-oil heat exchanger are additionally arranged on the cold side of the air pre-heater, the air-and-oil heat exchanger and the flue-gas-and-oil heat exchanger are connected through a circulation pipeline, heat-transfer medium conduction oil is injected into the circulation pipeline, and a bypass pipe is arranged on the main water feed pipe of the high-pressure heater. Due to the fact that the additional heated surface of the economizer, the flue-gas-and-oil heat exchanger and the air-and-oil heat exchanger are arranged, gradient utilization corresponding to the temperature of the flue gas waste heat is achieved, boiler efficiency and generating efficiency of the thermal power unit are improved, energy consumption of the thermal power unit is reduced, and emission of carbon dioxide is reduced.

Description

(1) Technical field [0001] The invention relates to the technical field of energy saving of thermal power units, in particular to a method and a device for improving the efficiency of thermal power units by cascading the waste heat of boiler flue gas. (2) Background technology [0002] The exhaust heat loss of power plants is the largest part of boiler heat loss. For every 10~15°C reduction in exhaust gas temperature, the boiler efficiency can be increased by 1%. At present, the design exhaust 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 flue gas entering the air preheater at the ...

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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 economizer uses the waste heat of the flue gas, which makes little contribution to the power generation of the unit, and the utilization of heat energy fails to achieve temperature matching and cascade utilization, resulting in a great loss of useful energy

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