The invention relates to a method defined in the preamble of claim 1. The invention further relates to equipment defined in the preamble of claim 2.
Continuous strand sintering is used, after pelletizing powdery mineral material, for agglomerating pellets, which improves the strength and reactivity of the pellets. In this specification, the term ‘mineral material’ refers to a mineral that has similar crystal chemistry properties as those of the oxide group and contains the metal to be recovered, the metal being mainly present as compounds of metal and oxygen.
A strand sintering furnace is divided into several sequential zones, with different temperature conditions prevailing in each one of them. The strand sintering equipment includes a perforated conveyor belt, which is conveyed as an endless loop around two deflector rolls. At the forward end of the furnace, wet fresh pellets are fed onto the conveyor belt to form a bed with a thickness of a few decimeters. The conveyor belt conveys the bed of pellets through the drying, heating, sintering and equalizing zones of the sintering furnace, and further through sequential cooling zones. The cooling zones comprise cooling chambers that are separated by partition walls. After traveling through the cooling zones, the pellets are discharged at the tail end of the strand sintering equipment in a sintered form. To optimize the energy economy, the energy contained in the cooling gases at the tail end of the furnace is used for drying, heating and sintering at the forward end of the furnace, wherefore the strand sintering equipment includes overhead circulation gas ducts for realizing the gas circulation mentioned above. Burners are placed in the circulation gas ducts, and they are used to increase the temperature of the conducted gas up to the sintering temperature required in the sintering process. Below the conveyor belt, there are provided lower exhaust gas ducts for conducting out, through washers, the gas that exits each drying/heating/sintering zone, and has been conducted through the pellet bed and the conveyor belt. Below the conveyor belt, there are arranged lower inlet gas ducts for conducting the gas to the cooling zones. The movement of the gas in the ducts is provided by means of blowers, which are arranged in the lower exhaust and inlet gas ducts.
In a known strand sintering furnace, the partition wall between the sequential adjacent cooling chambers is placed so near to the surface of the pellet bed that any gas exchange cannot essentially take place in between the cooling chambers. Therefore the pressure prevailing in adjacent cooling chambers can be different, when a different quantity of gas is sucked from a certain cooling chamber than what is blown in from below. The drawback is that the gas quantity to be blown in from below must be accurately adjusted at each cooling chamber separately. Yet another drawback is that for each cooling chamber, it has been necessary to provide a specific blower. A large quantity of blowers in turn makes the equipment expensive.
The object of the invention is to eliminate the above mentioned drawbacks.
A particular object of the invention is to introduce a method and equipment that make it possible to reduce the number of blowers and to improve cooling, in which case the cooling section can be made shorter.
The method according to the invention is characterized by what is presented in claim 1. The strand sintering equipment according to the invention is characterized by what is presented in claim 2.
According to the invention, the method allows gas circulation on top of the pellet bed, between two adjacent cooling zones, in order to equalize pressure therebetween.
According to the invention, in a strand sintering equipment, the partition wall placed in between two adjacent cooling chambers is in the height direction placed at a distance from the pellet bed, so that between the partition wall and the pellet bed, there is left a gap for allowing gas circulation between two adjacent cooling chambers through said gap, in order to equalize the pressure between the cooling chambers.
When the partition wall of the cooling chambers is raised higher from the pellet bed than before, so that on top of the pellet bed, gas also has access to the adjacent cooling chamber when necessary, in order to equalize the pressure, there is achieved the effect that the pressure on top of the bed is equalized better than before, even if the gas quantity sucked from one of the cooling chambers was different than the quantity that is blown therein from below. Now the gas quantity to be blown in from below need not be accurately adjusted at each cooling chamber separately, which means that it is possible to combine cooling blowers and thus save expenses. Moreover, the cooling is made more effective throughout, so that the length of the cooling element can be cut shorter.
The invention is explained in more detail below with reference to exemplifying embodiments and to the appended drawings, where
As is seen in
The invention is not restricted to the above described embodiment only, but many modifications are possible within the scope of the inventive idea defined in the appended claims.
Number | Date | Country | Kind |
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20095821 | Aug 2009 | FI | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FI10/50615 | 8/3/2010 | WO | 00 | 1/27/2012 |