Process of coolant feeding into bed and gas removal from a furnace is elaborated. The process essentially decreases a decarbonizing rate in a bottom roasting zone and a heat consumption. Combustion of natural gas and fuel oil in a top zone enables to intensity the roasting process without the lime overroasting. In this case, decarbonizing the lime proceeds with a maximum rate. As a result of intensive heat exchange the temperature in material bed is no higher than 1050-1150°C.