Abstract: A method of cooling hot bulk material using a reactor comprises passing a cooling gas in heat exchange relationship with the bulk material, contacting the cooling gas and the bulk material with a water vaporizing heat exchanger surface to remove a part of the heat content of the bulk material and the cooling gases which are heated by the bulk material, and directing the cooling gases after the contact, to an additional water vaporizing heat exchange surface to cool the contacted gases for reuse. The cooling gases after they are heated are directed preferably to a waste heat boiler where they are cooled and after separation returned back to be again circulated to the reacting vessel for cooling the bulk material. The cooling reactor for cooling the hot bulk material comprises a vertically elongated vessel defining a cooling chamber which has a top charging inlet for the bulk material and a bottom charge discharge for the cooled bulk material.