Coal gasification offers a flexible and efficient conversion of the solid fuel into CO- and H2-rich synthetic gas (syngas) for production of various chemicals and energy products. Since the hot syngas leaving a gasifier contains various impurities such as acidic gases and particulates, it needs to be cooled down for cleaning prior to conversion into the final product. A dedicated heat exchanger called a syngas cooler (SGC) is used to lower the gas temperature while recovering the thermal energy. This study investigated the heat transfer characteristics in a commercial-scale SGC consisting of a series of concentric helical coil channels. First, the detailed flow and heat transfer pattern in the unique heat exchanger were analyzed using computational fluid dynamics (CFD) for various operating loads and fouling conditions. The predicted heat transfer rate was used to derive correlations for Nusselt number for the channel sections of the SGC. Second, a one-dimensional model of the equipment was proposed for fast-response process simulations. In terms of heat transfer rate and gas temperature, the process model showed a reasonable accuracy compared to the CFD results for the tested cases.