Abstract: By a method for heat treatment of pulverous material, e.g. burning of lime, the lime is first preheated by means of exit gas in a preheater (1, 2, 3) and subsequently burnt in a calciner (4, 14), after which the burnt lime is cooled in a cooler (6, 7).In order to be able to alter the reactivity of the finish-burnt lime, the calciner is divided into two chambers, namely a first chamber (4) in which the lime is burnt at, e.g. 1050.degree. C. and a second chamber (14) in which a larger or smaller portion of the lime is further burnt at a higher temperature, e.g. 1300.degree. C.By means of a splitting gate (16) in the outlet from a separation cyclone (5) for the calciner (4, 14), it is possible to determine the size of the portion of lime which should be exposed to the higher burning temperature in the second calciner chamber (14) and consequently to predetermine the reactivity of the finish-burnt lime.