The invention relates to a method for waste-heat recovery comprising the following steps: providing a first process unit (10), which requires thermal energy, wherein the first process unit (10) comprises a heating burner (15, 16), which is fluidly connected to a fuel supply line (100, 101, 102) and to a combustion-air supply line (112, 113); providing a second process unit (20), in which thermal energy is generated, wherein the second process unit (20) comprises a combustion furnace (21), which is designed to burn waste materials (201) containing sulfur compounds; burning waste materials (201) containing sulfur compounds to generate hot combustion exhaust gas (210) which contains sulfur compounds; discharging the hot combustion exhaust gas (210) from the second process unit (20) and introducing the combustion exhaust gas (310) into a waste-heat recovery device (3) comprising a waste-heat exchanger (31, 32); transferring thermal energy from the combustion waste gas (310) by the waste-heat exchanger (31, 32) to a fluid which is used as an energy source in the first process unit (10), wherein a gas temperature (36, 37) of the combustion exhaust gas (311, 312) downstream of the waste-heat exchanger (31, 32) is set so as not to be below a dew-point temperature of the sulfur compounds in the combustion waste gas (311, 312).

The present invention provides a drying apparatus. The apparatus includes a first, upper chamber comprising a freezing section; and a second, lower chamber comprising a thawing section and a drying section. The first, upper chamber further includes an inlet and first conveying means arranged to convey material through and within the freezing section. The second lower chamber includes second conveying means arranged to convey material through and within the thawing section, and third conveying means arranged to convey material through and within the drying section. A first outlet is provided in the drying section through which dried material exits the apparatus. Generally, the material provided to be dried by the drying apparatus is alum sludge.