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Papuna Natalya

Theme of master's work:

"Waste heaps processing by agglomeration method"

E-mail: Natalya_Papuna@mail.ru

Library

MODERN AGGLOMERATION PRACTICE

Aglomeration of iron ores/D.F. Ball, J. Dartnell, A. Grieve, R. Wild. – New York: American Elsivier Publishing Company, 1973 – 388.

Sintering

General plant layout

The plant may conveniently by divided into the following sections:

Proportioning of raw materials

Mixing

Loading the mix on to the strand

Igniting

Sintering

Sinter treatment

Waste gas system

Figure - General arrangement of a sinter plant

Proportioning of raw materials

The raw materials may be blended by laying them down and reclaiming them from beds outside the sinter plant proper, or the individual components may be stored separately and conveyed to separate bunkers in the sinter plant/ From these bunkers the various materials are withdrawn via feeders, often associated with devices to ensure that the feed rate is maintained constant, and collected on a gathering belt. Sometimes all the raw materials, including flue dust and fuel, are collected on the same belt, and sometimes the ore fines, flue dust, and coke breeze are collected separately.

Mixing

The proportioned raw materials are next mixed and moistened. This is usually done by passing them through a drum fitter with paddles, water being added to impart permeability to the mixed materials. After this initial mixing, the moist mix may be rolled in a drum to give increased permeability.

Loading the mix on to the strand

The mix is now ready to be loaded on to the strand. The aim is to lay down the material evenly across the width of the strand with the minimum of compacting. A number of means have been devised for effecting this, for example a swinging spout, a roll feeder and a vibrating-tray feeder. In some sinter plants a thin layer of inert material, such as sized sinter, is first laid on the grate bars and the sinter mix is loaded on top of this hearth layer. Immediately after loading the surface of the mix is leveled by passing it under a plate, the ‘cut-off-plate’, which is set so as to give the desired thickness of mix on the strand. Normally this is between 12 and 18 in. (300-450 mm).

Igniting

Next the mix is ignited by means of gas or oil burners. Normally the burners are set in a brick-lined hood which covers a length of strand, but vertical burners which impinge directly on to the mix are sometimes used.

Sintering

Thereafter sintering proceeds, air being sucked through the bed into the windboxes situated under the grate. The grate consists of a number of individual pallets. These pallets travel forward on wheels running on a track beside the strand, and the system is sealed as far as possible against leakage of air in at the rate edge. The strand moves forward at about 10 feet (3 m) per minute so that the mix taxes about 15 minutes to travel from the igniter to the end of the strand. During this time the combustion zone ravels through the bed, the strand speed normally being adjusted so that combustion of the fuel at the bottom of the bed is complete just before the sinter reaches the end of the strand.

Sinter treatment

At this point the finished sinter is tipped from the strand as the pallets turn for their journey back to the loading end. The sinter falls on to a crash deck and the large lumps are broken up by toothed wheels. The discharged sinter is hot, but varying in temperature according to its previous position in the bed; the sinter from the top of the bed has already been cooled to ambient temperature, whereas that from the bottom of bed is over 1850° F (1000° C).

From the crash deck the sinter moves to a vibration screen, normally set at about 3/8 in/ (9 mm). The undersize, the return fines, goes back to join the stream of raw materials and the oversize goes forward to the sinter cooler.

Various types of cooler are used, but in all cases the principle is the same. The screened sinter is laid down in a bed and air is sucked or blown through it. Since the sinter is now free of fines, the bed permeability is high and the power required is comparatively low. After cooling, it is normal to rescreen the sinter and return the undersize (typically – 5/16 in., 8 mm) to the raw material system.

Waste gas system

Suction up to about 50 in. water gauge (12 kN/m²) is applied to the bottom of the sinter bed by means of a series of windboxes. These are connected to a wind main by means of a series of downcomers. The gas issuing from the bed has a high dust content. The coarse dust settles out and is removed from the main by means of counter-weighted dust valves, while the fine dust is removed by mechanical means or by electrostatic precipitators. The main sintering fan handles the clean gas, which is finally discharged to the atmosphere through a stack.