Agglomeration by sintering

AGGLOMERATION BY SINTERING (EN: sintering, agglomeration by sintering; DE: Agglomerieren, Agglomeration, Sinterung; FR: agglomeration; ES: aglomeracion, sinterizacion; RU: агломерация) is the process of the thermal agglomeration of the powdery fine ores and concentrates, and the metal containing wastes, by the way of the sintering them together.

The starting material for the agglomeration is the mixture, which includes, besides the ores and concentrates, the coke fines (the size of the particles of less than 3 millimetres), the anthracite culm (less than 3 millimetres), the lean coal (less than 3 millimetres), the limestone (less than 3 millimetres), the lime and the return (the rejected fine agglomerate with the sizes less than 5 millimetres, which is returned to the mixture for the repeated sintering). The ore, the concentrate, the flue dust, and other additives, which do not require crushing, are delivered into the mixture section of the installation from the receiving hoppers or from the warehouse by the conveyors. The coke fines and the limestone enter into the section of the grinding, and then into the hoppers of the mixture section. The return is directed here also. Each of the components of the mixture is issued from the mixture hoppers by the metering feeders in the predetermined quantities to the combining conveyor, which transfers the material into the drums for the primary mixing. Then the mixture is transported into the special building, where it is loaded into the mixture hoppers, and then it gets into the pelletizer drums.

The sintering is performed using the conveyor sintering machines, which comprise the continuous chain of the moving carts, on which the sections of the flue grate are mounted. The vacuum chambers, which are connected to the exhausters, are placed at the bottom under the moving carts. After the placement of the mixture on the cart, it goes under the ignition hearth (the solid fuel, which is contained in the mixture, is ignited) and moves to the tail part of the machine. The vacuum up to 104 pascals is created under the flue grate with the help of the exhauster, which ensures the sucking of the air from the top down through the layer of the mixture, which is sintered, from 80 to 120 cubic metres per minute for the square metre of the surface of the layer. The time of the movement of the cart over the vacuum chambers must match the duration of the movement of the zone of the burning of the solid fuel through the layer, which is sintered. The height of the layer ranges from 180 to 550 millimetres. The gaseous products of the combustion of the fuel move between the clumps of the sintering mixture down, thus drying and heating it. The temperature of the outgoing gases before the exhauster is usually more than 100 degrees Celsius. The mixture melts in the zone of the burning of the solid fuel (the temperature of 1200-1500 degrees Celsius). After the burnup of the fuel on the horizon, the zone of the burning moves down, the melt touches the air and crystallizes, forming the so-called sinter cake. The processed sinter is thrown out from the sintering conveyor during the overturning of the cart at its tail part. Then there follow the crushing of the "cake", the separation of the fine hot return (with the sizes of less than 5 millimetres) from it, the cooling of the sinter to the temperature of 80-100 degrees Celsius, the repeated sieving out of the return from the cold sinter.

The optimal size of the sinter for the blast furnaces is 5-60 millimetres. The high quality blast furnace sinter contains the small quantity of the fines, and has the strength, which allows to transport it to the blast furnaces without breaking. The high porosity and the correctly chosen mineralogical composition of the sinter ensure the high rate of the reduction of the iron, which is contained there in the magnetite (Fe3O4), ferrites of calcium (CaO • 2 Fe2O3) and silicates (CaFeSiO4). In the USSR, the sinter is produced as the fluxed one, that is with the addition of the limestone (CaCO3) and quicklime (CaO) to the agglomerated ore, which allows to improve significantly the indicators of the performance of the blast furnaces. The average basicity of the fluxed sinter is CaO:SiO2 = 1.25.

There are working in the USSR the sintering conveyors with the area of the sintering of 50, 75, 208, and 312 square metres, and the sintering conveyor with the area of 600 square metres is designed. With the speed of the zone of the burning of the solid fuels (the vertical rate of the sintering) of 20-40 millimetres per minute, the duration of the sintering does not exceed 12-18 minutes. During the production of the blast furnace sinter, up to 99% of sulfur may be removed from the mixture. During the sintering of the sulfide ores of the nonferrous metals (ZnS, PbS, etc.), the sulfur of the sulfides is serving as the fuel, the significant part of it burns out from the mixture during the sintering process.

The agglomeration by the sintering has been proposed in the Great Britain in 1887 by F.Heberlein and T.Huntington. The conveyor sintering machine has been invented by Dwight and Lloyd (1906); the first machine of this type has been put into operation in the USA in 1911. The USSR holds the 1st place in the world in the production of the sinter for the blast furnaces (152 million tonnes in 1980).