Lime kiln flue gas desulfurization system and desulfurization method

The invention discloses a flue gas desulfurization system for a lime kiln. The flue gas desulfurization system comprises a cooler, a pre-dust collector, a digester, a reactor, a secondary dust collector and an induced draft fan. Flue gas from a lime kiln is cooled by a cooler and then enters a pre-dust collector, most fly ash in the flue gas is collected in the pre-dust collector, and the flue gas of the lime kiln after pre-dust collection enters a downstream reactor. Fly ash collected in the pre-dust collector is fed into the digester, the fly ash reacts with water in the digester to generate active ash, the active ash is fed into the reactor to react with SO2 in the lime kiln flue gas, then the lime kiln flue gas enters the downstream secondary dust collector, desulfurized ash in the lime kiln flue gas is collected by the secondary dust collector, and the desulfurized ash in the lime kiln flue gas is discharged into the reactor. And the desulfurized lime kiln flue gas is discharged into a chimney through an