A waste heat recovery unit (WHRU) is an energy recovery heat exchanger that recovers heat from hot streams with potential high-energy content. There are sources like heat in flue gases, heat in Vapour streams, convective and radiant heat that is lost from exterior of equipment. Heat losses from cooling water, and losses while providing chilled water, or for that matter in the disposed of chilled water, also heat stored in products that leave the process which finally losses heat in gaseous and liquid effluents leaving the process. Flue gas leaving de-carb annealing furnace to stack ranges from more than 350˚ C. At present, this gas is directly going to atmosphere and causes thermal pollution as well as loss of valuable energy. The target is to reduce thermal pollution and reuse this waste energy again in furnace.