Two-stage sludge drying system

The utility model provides a two-stage sludge drying system which comprises a preprocessor. The inlet of the preprocessor is connected with a sludge pump for conveying sludge. The outlet of the preprocessor is communicated with an anaerobic fermentation tank. The marsh gas outlet of the anaerobic fermentation tank is communicated with the inlet of a combustor after being connected with a marsh gas tank. The smoke outlet of the combustor is communicated with a waste heat boiler. The sludge outlet of the anaerobic fermentation tank is communicated with the sludge inlet of a primary dryer through a dewatering machine. The sludge outlet of the primary dryer is communicated with the sludge inlet of a secondary dryer. A crusher for crushing sludge is arranged in the primary dryer. The waste heat boiler is communicated with the primary dryer and the secondary dryer through heating pipes so as to provide heat sources for the dryers. The requirement of a sludge treatment plant for electricity of a power grid is lowered, no peculiar gas is exhausted, and energy conservation, safety and environment protection are achieved; dewatered sludge is dried at two stages, the crusher is arranged in the primary dryer to crush sludge pies in time, the drying speed is effectively improved, the drying speed is high, and space is saved.