Gradient utilization method and device of boiler flue gas waste heat

Abstract

The invention discloses a gradient utilization method and device of boiler flue gas waste heat. An additional heating face is added to an economizer segment of a boiler of a thermal power generating unit; a bypass pipe is provided at a water feed main arranged at an inlet of a steam turbine side high-pressure heater and leads to another water feed main arranged at an outlet of the steam turbine side high-pressure heater; the bypass pipe is provided with a flow regulating valve; a flue gas-oil heat exchanger and an air-oil heat changer are added to the cold end of an air preheater; a circulating pipeline is provided between the flue gas-oil heat exchanger and the air-oil heat changer; 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; a low-pressure heat exchanger is disposed between the air preheater and the flue gas-oil heat exchanger; the inflow side of a low-pressure heater is provided a guide pipe leading to the low-pressure heat exchanger; an inflow pipe from the low-pressure heat exchanger is added to the inflow side of an oxygen extractor. The gradient utilization method and device of boiler flue gas waste heat has the advantages that suited gradient utilization of flue gas waste heat is achieved, boiler efficiency and generating efficiency of the thermal power generating unit are improved, energy consumption of the thermal power generating unit is lowered, and emission of carbon dioxide is reduced.

Description

technical field [0001] The invention relates to a method and a device for cascaded utilization of waste heat of boiler flue gas, which can reduce the exhaust gas temperature of a thermal power unit, improve the thermal efficiency of the boiler and the power generation efficiency of the unit, reduce coal consumption for power generation, and reduce pollution discharge. 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-supercritica...

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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 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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