Step recycling method and device of boiler flue gas waste heat

Abstract

The invention discloses a step recycling method of boiler flue gas waste heat. The method is used for a steam turbine generator unit, and comprises temperature rise generated by multistage heat exchange and work of parts in a flue gas passage in an energy step reclamation mode. The invention also discloses a boiler flue gas waste heat recycling device for implementing the method. The device comprises multistage heat exchangers, wherein the flue gas sides of the heat exchangers are arranged at different positions in the flue gas passage, and the water sides of the heat exchangers are connected with a low-pressure water supply system of the steam turbine generator unit. According to the method and the device, work energy of equipment such as a draught fan, a booster fan and the like in a flue gas system can be optimally utilized and absorbed, the arrangement is more flexible, and the conventional equipment and the conventional system are affected and changed little.

Description

technical field [0001] The invention relates to a method and a device for cascade recovery and utilization of waste heat of boiler flue gas, which are used for steam turbine generator sets. Background technique [0002] The traditional low-pressure economizer is an energy-saving measure that utilizes waste heat from boiler exhaust. like figure 1 As shown, the low-pressure economizer is a heat exchanger 30, the flue gas side is installed in the tail flue of the boiler 10, and its water side is connected to the low-pressure water supply system part (A, B) of the steam turbine, and the low-pressure water supply is in the low-pressure economizer It absorbs the heat of the exhaust smoke, reduces the temperature of the exhaust smoke, and returns to the low-pressure water supply system of the steam turbine after being heated and raised in temperature to replace part of the low-pressure heater. It is an integral part of the thermal system of the steam turbine. The low-pressure eco...

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Problems solved by technology

[0005] 1. The area between the air preheater and the precipitator is a high dust content area with high fly ash content. Taking the electrostatic precipitator as an example, the dust removal efficiency is calculated according to 99.8%. , high fly ash content will aggravate the wear of the heating surface of the pipe, shorten the service life of the heat transfer pipe, and reduce the safety factor of the equipment

[0006] 2. With this arrangement, the low-temperature section of the low-pressure economizer is arranged in the high-dust area of ​​the boiler, and the risk of soot sticking due to low-temperature dew condensation in the tube row will increase greatly. Once this happens, it will cause the tube row The sticking and clogging of soot greatly increases the resistance of the flue, causing the boiler to drop the load or even force the shutdown

[0007] 3. If there is low-temperature condensation in the low-temperature section of the low-pressure economizer, acid corrosion will inevitably occur. Once the pipeline is corroded and perforated to leak, the condensed water sprayed out will become a disaster for the electrostatic precipitator, bag filter and fan

Moreover, the design of the boiler flue usually does not consider setting up a bypass. Once the system leaks, it will directly lead to the forced shutdown of the unit, and the economic loss is very large.

[0008] 4. The low-pressure economizer arranged in the tail flue of the boiler cannot make use of the work temperature rise of the induced draft fan, booster fan and other equipment in the downstream of the flue gas, resulting in waste of heat

However, for the transformation of the old unit, there are great difficulties. Due to the lack of sufficient installation positions and insufficient fan margin, it is necessary to spend a high cost to modify the original flue, steel structure and fan equipment.

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