Synthesis gas is produced by the partial oxidation of a high silicon and sulfur-containing heavy liquid hydrocarbonaceous fuel and/or petroleum coke having a nickel and vanadium-containing ash that includes calcium and sodium, in a mixture with an iron and/or copper containing additive in a vertical free-flow reaction zone lined with refractory A or a combination of refractory A and refractory B. Refractory A lining of the reaction zone comprises in wt %: Cr.sub.2 O.sub.3 about 20 to 82, MgO about 5.0 to 45, Fe.sub.2 O.sub.3 about 0 to 10.5 Al.sub.2 O.sub.3 about 0 to 6.2, CaO about 0 to 1.0, SiO.sub.2 about 0 to 2.5, and others about 0 to 1.3. Refractory B comprises in wt. %: Cr.sub.2 O.sub.3 about 0 to 40, MgO about 20 to 85, Fe.sub.2 O.sub.3 about 0 to 16, Al.sub.2 O.sub.3 about 0 to 9.0, SiO.sub.2 about 0 to 2.7, and others about 0 to 1.1. In the reaction zone separate portions of said Fe and/or Cu containing additive: (1) combine with portions of said Fe, Ni, and S to generate a liquid phase washing agent; (ii) combine with a portion of refractory components, and V, Fe, Ni and Al to form high melting spinel and oxide lath phases which are washed by said liquid phase washing agent; and (iii) combine with a portion of said Ni, Ca, Si, Al, Mg and Na to generate a liquid oxide silicate phase that fluxes substantially all of the remaining vanadium and other ash components.