Method of improving the product properties of clinker in the firing of raw meal in a clinker or cement furnace in which at least part of the fuels used are low-heating-value or alternative fuels, waste products containing organic substances or low-heating-value or alternative fuels are subjected to thermal dissociation and reaction of the dissociation products using radiant energy. The product gas or synthesis gas formed in this way is fed to the burners of the main firing facility to increase the flame temperature.