The transient performance of an integrated radiant syngas cooler (RSC) of an entrained-bed gasifier and steam methane reformer (SMR) is investigated. Base-case designs using either co-current or counter-current configurations are subjected to operating transients to evaluate the feasibility to transition to new steady states. Each system, under open loop, is subjected to changes in key variables of the SMR feed on the tube side and disturbances to variables of the coal-derived syngas on the RSC side to determine the dynamics and stability of the integrated system. The results indicate that the co-current configuration is flexible to move to new operating steady states and more safe than the countercurrent configuration, although it provides less cooling and has poorer methane conversion. The variables likely to violate the design limit in the event of a disturbance are identified. A start-up procedure is also established based on industrial practices employed for entrained-bed gasifiers and methane reformers. (C) 2017 American Institute of Chemical Engineers AIChE J