The high efficiency of a combined cycle and the availability of systems for deep purification of synthesis gas before combustion allow for the study of gasification-combined cycle plants as a promising solution to increase the efficiency and environmental friendliness of coal power engineering. The key element of the device is a gasifier. A Mitsubishi Heavy Industries gasifier is selected as an initial design for modernization, which consisted in heating the blast air up to 900oC and steam supply with a temperature of 900oC. The impact of modernization on the gasifier characteristics is determined by using zero-, one-, and three-dimensional models. Modernization of the gasifier allows increasing the thermal power by the synthesis gas and chemical efficiency from 77.2 to 84.9% and increasing the ratio H2/CO from 0.34 to 0.6.