In a coal gasifier and heat exchanger, adhered and deposited ash and char inhibit heat transfer making the stable operation of the gasifier difficult. Since heat transfer performance of the heat exchanger directly affects the output of Integrated Coal Gasification Combined Cycle plants, it is important to understand the effect of char on the characteristics of adhesion and deposition on the heat exchanger tube beforehand. However, very few studies have been conducted concerning the relationship between char's property and its adherability, which varies depending on the coal type and the operating conditions. In this study, we first conducted an analysis of the characteristics of heat transfer in the heat exchanger of the pilot plant gasifier to understand the effects of the properties of the char on the heat transfer in the heat exchanger. Using a bench-scale gasifier at CRIEPI, a transformation of the char morphology took place as the gasification reaction progressed. In the experiment, char from three distinct coal types was made to adhere on a plate and then allowed to re-entrain, so that the inter-particle adhesion strength of the char could be measured. Using the char from the same coals, deposition experiments on a horizontal tube placed in a drop tube furnace were also conducted to examine the mechanism of char adhesion on the heat exchanger tube. (C) 2003 Elsevier Ltd. All rights reserved.