Abstract: A two-dimensional physical model of COREX melter gasifier was constructed to study experimentally the melting behavior of burden in the furnace. Paraffin was used to simulate DRI, and corn was used to simulate coke and lump coal. High-speed camera was used to record the experimental images. An image processing method was developed to characterize the cohesive zone boundary according to the color change of burden before and after the experiment. The proposed method can give the cohesive zone boundary, and thus the position and thickness can be obtained. The variation of the cohesive zone under various experimental conditions was examined. The effect of operation condition on the cohesive zone can thus be analyzed by the proposed method in the future studies.