Process for roasting by fluidization, more particularly for magnetizing roasting

摘要

A process for roasting ores, especially magnetizing roasting, by fluidization in a number of steps, each step being carried out in a separate fluidization bed, comprises a first series of steps consisting of roasting of the ore, preceded if necessary by a dehydrating heating, the ore being fluidized by a stream of fumes or hot gases, followed by a second series of steps consisting of reduction of the ore in a fluidized bed into which reducing agents are introduced, and then a cooling step during which at least part of the sensible heat of the ore is transferred to the second stream of fluidization gas for the second series of steps, which stream is formed by at least part of the gases derived from the first series of steps, while the rate of flow, temperature and chemical composition of the two fluidization streams are adjusted separately. Four steps may be employed for the fluidization, namely: (a) dehydrating heating process, (b) roasting process, the ore being fluidized by a stream of hot gases which circulate from the second to the first bed, (c) reduction of the ore and (d) cooling treatment the ore being fluidized by a stream of gas which circulates from the fourth to the third bed. The reducing agents which are injected into the third fluidized bed may be a low-boiling gasoline or its decomposition products. Part of the sensible heat which passes out in the cooling step may be used to heat fresh ore which is supplied to the first bed. At least part of the gases which pass out may be used for heating the air and fuel which are employed in a furnace for generating hot gases for the first fluidization stream. Oxidation of the ore may be completed during the roasting stage by ensuring the presence of oxygen in the gases which fluidize the bed in which roasting occurs. With reference to the drawing, iron ore from hopper 5 passes to the roasting reactor 1 and partial dehydration and roasting of the ore is carried out in beds F1 and F2, respectively. The ore in chambers 3 and 2 is fluidized by the stream of hot gases C, C1 and C2. The ore then passes to reduction reactor 13 via 11, and magnetizing reduction and recovery of the sensible heat of the ore is carried out in beds F3 and F4 respectively The ore in chambers 14 and 15 is fluidized by the stream of hot gases C4, C5 and C6. Low-boiling gasoline is fed in at 17. Fresh ore from hopper 23 is pneumatically transported through 25 into 21 wherein it is heated, and thence to hopper 5 for storage. Fuel and combustion air are admitted at B1 and B2 respectively, and are heated, by means of heat-exchangers, by the stream of hot gases C6. The stream of gases C2 is subdivided into streams E3 and C3 for discharge and re-use, respectively, and valves V1 and V2 adjust the respective flow rates. The stream C3 forms the fluidization stream for the reduction and cooling steps. The successive processing temperatures are: 300 DEG C. in the partial heating and dehydration bed F1, 900 DEG C. in the roasting bed F2, 760 DEG C. in the reduction bed F3, and about 300 DEG C. in the heat recovery bed F4.