System and method for preparing nitric acid by circulating pyrolysis of nitrate gas

The invention relates to a system for preparing nitric acid by circulating pyrolysis of nitrate gas. The system comprises a melting tank, a spray drying device, a thermal decomposition device, a dust collector, a heat compensation system and a nitric acid absorption device. The heating and melting tank is used for heating and melting nitrate to obtain nitrate hot fluid; the spray drying device is used for completely evaporating moisture in the nitrate hot fluid for spray drying; the thermal decomposition device is used for thermally decomposing the dried nitrate; the dust collector is used for separating dust entrained in the mixed nitrogen oxide gas; and the nitric acid recovery device is used for absorbing the oxynitride gas after dust collection to generate new nitric acid. The nitric oxide gas obtained by utilizing the system is high in concentration, nitric acid absorption is facilitated, meanwhile, the heat energy utilization efficiency is high, the thermal decomposition cost is reduced, the investment