a continuous process for the combustion of solid fuels in the presence of an aqueous liquid phase under conditions such that oxides of nitrogen are not formed and oxides of sulfur and particles of ash are effectively prevented from contaminating the gaseous products released to the atmosphere . fuel is charged as a slurry in alkaline aqueous solution and contacted with combustion air so that the catalytic properties of both water and alkali operate to permit rapid and complete combustion at comparatively low temperatures . temperatures in the adiabatic reactor are , however , permitted to exceed the critical temperature of the liquid phase . under the conditions of the process , formation of nitrogen oxides is negligible , sulfur in the fuel goes to sulfur trioxide which dissolves completely in the alkaline liquid phase which also retains particles of ash and unburned fuel . the resulting flue gas is essentially free from objectionable pollutants . heat is made available at a temperature high enough to generate and superheat steam .