Ammonia supply system and method for preparing sodium carbonate

The invention provides an ammonia supply system for preparing sodium carbonate. The ammonia supply system comprises a heat exchange unit, a distillation unit, an ammonium chloride preparation unit anda calcium hydroxide preparation unit; the ammonium chloride preparation unit comprises an ammonium chloride dissolving tank, a cyclone separator and a tail gas washing tower; the distillation unit comprises a distillation tower, a reaction barrel and a flash evaporator, the distillation tower is provided with an ammonia outlet, and a raw material inlet of the distillation tower is communicated with the ammonium chloride dissolving tank through a pipeline; the heat exchange unit comprises a heat exchanger, the heat exchanger is provided with a refrigerant inlet, a heating medium inlet, a refrigerant outlet and a heating medium outlet, the heating medium inlet of the heat exchanger is communicated with the flash evaporator through a pipeline, and the refrigerant outlet of the heat exchangeris communicated with the