In a method for treating alternative, carbon-containing, low-caloric waste materials for use in furnace systems, in particular rotary tubular kilns for the production of clinker, the carbon-containing, alternative fuels are subjected to high-temperature gasification under anoxic conditions at temperatures above 1000° C., wherein water, water vapor or CO2 is injected to ensure a reaction forming CO and H2. The waste heat from a clinker cooler is used for the high-temperature gasification.