Deep recycling and gradient utilizing system and method for low-temperature flue gas waste heat of coal-fired unit

Abstract

The invention relates to deep recycling and gradient utilizing system and method for low-temperature flue gas waste heat of a coal-fired unit. A first stage is gas-gas heat exchange; cold air is heated by utilizing an outlet flue gas of an air preheater; the flue gas waste heat is recycled, so that the temperature of an inlet flue gas of a deduster is reduced, and the dedusting efficiency is improved; and the inlet flue gas temperature of a desulfurizing tower is reduced, so that the water evaporation amount of the desulfurizing tower is reduced, and the consumption of process water is reduced. A second stage is gas-water heat exchange; hot air in the last stage is utilized for heating condensed water, so that the temperature of the condensed water is improved; and heat enters a steam turbine system, so that the heat consumption of the steam turbine is reduced. A third stage is gas-gas direct heat exchange; one path of the last-stage hot air is sent to a boiler air feeder inlet so as to be mixed with the cold air, so that secondary air is preheated; recycled heat enters a boiler system, so that the gross coal consumption rate is reduced, the boiler efficiency is improved, the cold-end temperature is improved, and the cold end of an air preheater is prevented from being corroded; and the other path of the last-stage hot air is sent to a low-temperature air feeder inlet so as tobe converged with the cold air, so that the cold end of a heat exchanger is prevented from being corroded through the low-temperature environment temperature. The system provided by the invention is simple in structure and reasonable in design, and provides a new idea for flue gas waste heat gradient utilization.

Description

technical field [0001] The invention belongs to the technical field of flue gas energy-saving and efficiency-improving transformation, and relates to a coal-fired unit waste heat recovery cascade utilization technology, in particular to a coal-fired unit low-temperature flue gas deep recovery cascade utilization system and method. Background technique [0002] The exhaust gas loss of coal-fired units is the most important heat loss in boiler operation. The exhaust gas temperature of coal-fired unit boilers is usually 110-130°C, and the corresponding heat loss is equivalent to 5%-12% of the fuel heat, accounting for 60% to 70% of boiler heat loss. The main factor affecting the heat loss of the exhaust gas is the exhaust gas temperature. In general, for every 10°C increase in the exhaust gas temperature, the heat loss of the exhaust gas will increase by 0.6% to 1%, and the corresponding increase in coal consumption will be 1.2% to 2.4%. [0003] The exhaust gas temperature of...

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Problems solved by technology

[0005] The purpose of the present invention is to provide a cascaded utilization system and method for deep recovery of low-temperature flue gas waste heat of coal-fired units, to solve the technical problem that the heat recovered by the low-temperature economizer in the prior art cannot enter the boiler system, resulting in no improvement in the actual efficiency of the boiler system, and The technical problem of equipment plugging and corrosion is easy to occur in the existing preheating recovery technology

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