System and method for preparing ultra-pure coal from low-ash-content coal

The invention discloses a system and a method for preparing ultra-pure coal from low-ash-content coal. According to the method, the pulverized coal is subjected to microwave pretreatment before being fed into the molten alkali leaching tank, part of structures in the coal are fractured to form cracks through microwave pretreatment, the contact area of reactants and the coal is increased, and the follow-up acid pickling and leaching speed is increased. According to the invention, acid washing is not directly used when the leached coal is treated, but water washing is carried out firstly and then acid washing is carried out, so that the steps of acid and alkali recovery are simplified, and the economical efficiency of the system is improved. The main energy source of the system comes from the high-temperature flue gas, energy in the high-temperature flue gas is used for supplying energy to the system through gradient utilization, the energy utilization efficiency is improved, in addition, the flue gas finally p