An improved one stage, upflow process for coal gasification whereby a dry particulate carbonaceous material and an oxygen-containing gas are combusted in a vertical gasifier thereby converting the carbonaceous material (coal) into a hot gas. The hot, entrained flyslag gas is then contacted with a cooled, recycled gas in a quench zone, thus cooling the gaseous product stream and causing the molten slag particles to convert to nonsticky flyslag particles. The high level thermal energy from the flyslag-laden gaseous product stream is recovered in a fire tube heat exchanger and the flyslag particles from the gaseous product stream are separated by conventional means and recycled back to the gasifier. The product raw gas is further treated for use in a gas turbine to produce electricity.