Abstract: The invention relates to a method of improving the heat recovery in a waste head boiler, in which gas, produced in high-temperature processes and containing molten and/or solid particles and/or evaporated components, is cooled. In a waste heat boiler, a slowly cooling zone, i.e. a hot "tongue" is generally formed in the gas flow. To improve the cooling of the hot "tongue", gas and/or solid particles and/or vaporizing liquid, such as circulating gas or circulating particles separated from the process and cooled, are introduced into the hot zone or "tongue".