An acoustic system having a plurality of speakers applying acoustic energy as a series of acoustic waves to various target sites on the exterior of the reactor to vibrate and deflect the interior surfaces of the reactor structure such that the slag is dislodged from the internal surfaces of the reactor structure. Each speaker generates acoustic waves having a waveform corresponding to the resonant frequency of the ash crystallized on the reactor structures. The acoustic waves induce vibrations and/or deflections in the portion of the reactor wall to which the slag is engaged as well as the slag itself breaking the interstitial bonds of the slag deposit and bonding holding the slag to the wall. The separated or disintegrated slag can then be gravimetrically fall to the bottom of the reactor for removal from the reactor.