Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1998-11-17
2001-06-05
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S444000, C075S446000, C266S172000
Reexamination Certificate
active
06241801
ABSTRACT:
The invention relates to a method for treating, preferably reducing, particulate material in the fluidized bed method, in particular for reducing fine ore, wherein said particulate material is maintained in a fluidized bed by a treating gas flowing from bottom to top and thereby is treated, and a vessel for carrying out the method.
A method of this kind is known f.i. from U.S. Pat. No. 2,909,423, WO 92/02458 and EP-A -0 571 358. In this method, oxide-containing material, f.i. fine ore, is reduced in a fluidized bed maintained by a reducing gas inside a fluidized-bed reduction reactor, with the reducing gas, which via a nozzle grate is fed into the fluidized-bed reduction reactor, flowing through the reduction reactor from the bottom toward the top, whereas the oxide-containing material permeates the reduction reactor roughly cross-current to the reducing-gas stream. In order to maintain the fluidized bed, a specific velocity of the reducing gas inside the fluidized bed zone is required which is a function of the particle size of the charged material.
Due to the relatively high velocity of the reducing gas which is necessary with the known methods there is a substantial discharge of superfines of the oxide-containing material as well as at an advanced stage of the reduction process a discharge of already reduced oxide-containing material from the fluidized bed, said superfines being then contained in the reducing gas. To remove said superfines from the reducing gas—on the one hand in order to be able to further utilize the partially oxidized reducing gas, f.i. for precedingly arranged reduction reactors, or for the recovery of the oxide-containing material or the already reduced material which otherwise would be lost—the reducing gas containing the superfines is conducted through dust separators, such as cyclones, and the separated dust is recycled back into the fluidized bed. The dust separators or cyclones respectively are preferably arranged inside the reactors (cf. U.S. Pat. No. 2,909,423); but they can also be installed outside of the reactors.
In practice it has emerged that partially reduced or completely reduced fine-grained particles of the oxide-containing material tend to stick or cake to each other and/or to the walls of the reactors or cyclones and to the connection ducts or conveying ducts. This phenomenon is referred to as “sticking” or “fouling”. Sticking or fouling are functions of the temperature and the degree of reduction of the oxide-containing material. Such sticking or attachment of the partly or completely reduced oxide-containing material to the walls of the reduction reactors or to other parts of the plant may cause failures, so that it is not feasible to operate the plant continuously over a prolonged time period without any shut-down. It has been found that continuous operation for more than a year is hardly possible.
Removal of the attachments or cakings requires a huge amount of work and entrains substantial costs, namely labor costs and costs arising due to the production loss of the plant. Often, these attachments will detach spontaneously, as a result of which they either drop into the fluidized bed and thus lead to a disturbance of the reduction process, or—if the attachments detach themselves from the cyclone—cause the dust recycling channels that lead from the cyclone to the fluidized bed to become plugged, so that further separation of dust from the reducing gas will be completely impossible.
In practice, one disadvantage with the known fluidized bed methods resides in the inflexibility and difficulties encountered in splitting up and feeding in the treating-gas stream, i.e. with the above-described prior-art processes this would be the splitting up and feeding in of the reducing-gas stream. A further disadvantage associated with the prior art is that in each process stage, that is in pre-heating, pre-reduction and final reduction, in most cases two or several product streams leaving the apparatuses allocated to the process stages have to be sluiced out, thus causing substantial expenses in terms of conveying and sluice means. Moreover, two gas supply systems have to be adjusted in each process stage, which in practice presents major difficulties in the case of hot dust-containing gases.
In addition to this, due to the relatively high velocity of the reducing gas there is a substantial consumption of reducing gas. Considerably more reducing gas is consumed than would be necessary for the reduction process as such, with the excess consumption merely serving to keep up the fluidized bed.
A process for reducing metal ores by a fluidized bed method is also known from GB-A -1 101 199. Here, the process conditions have been chosen such that the material will cake together in the course of the reduction process, whereby agglomerates are formed which, due to their size, are not fluidized. Thereby it is feasible to separate the completely reduced material, which is discharged from the fluidized bed reactor in the downward direction, from the not completely reduced material, which remains fluidized. Smaller product particles are withdrawn at the upper end of the fluidized bed. Thus with this process there likewise result two product streams, necessitating considerable expenses in terms of apparatus.
The invention aims at avoiding these disadvantages and difficulties and has as its object to provide a method of the initially described kind and a vessel for carrying out the method, which enable treatment of particulate oxide-containing material at minimum consumption of treating gas over a substantial tine period without the danger of failures caused by sticking or fouling. In particular, it is to be feasible to reduce both the amount of the treating gas required for maintaining the fluidized bed and the flow rate of the same, so that there will only be a minimum discharge of fine particles.
In accordance with the invention, this object is achieved in that a particulate material having a wide grain distribution containing a relatively high portion of fines and a portion of larger particles is used for treatment and that the superficial velocity of the treating gas in the fluidized bed is kept to be smaller than the velocity required for fluidizing the portion of larger particles of said particulate material, wherein all of the larger particles together with the fines are moved upward and discharged from the upper region of the fluidized bed.
It has become apparent that in case of a wide even grain distribution the superficial velocity in the fluidized bed is maintained within a range of 0.25 to 0.75 of the velocity required for fluidizing the largest particles of said particulate material.
Preferably, a particulate material with a grain having a medium grain diameter of the grain band of 0.02 to 0.15, preferably 0.05 to 0.10, of the largest grain diameter of said particulate material is used.
Herein, suitably, for the treating gas above the fluidized bed a superficial velocity relative to the largest diameter of a vessel designated for receiving the fluidized bed is adjusted for a theoretic cut grain size of 50 to 150 &mgr;m, preferably 60 to 100 &mgr;m, wherein advantageously in the fluidized bed a superficial velocity ranging between 0.3 m/s and 2.0 m/s is adjusted for reducing run-of-mine fine ores.
A method for producing molten pig iron or liquid steel pre-products from charging substances formed of iron ores and fluxes and at least partially comprising fines utilizing the treating method according to the invention is characterized in that the charging substances are directly reduced to sponge iron in at least one reduction zone by the fluidized bed method, the sponge iron is melted in a melting-gasifying zone under the supply of carbon carriers and oxygen-containing gas, and a CO and H
2
-containing reducing gas is produced which is injected into the reduction zone, is reacted there, is withdrawn as an export gas and is supplied to a consumer.
A vessel for carrying out the method in accordance with the invention is characterized by the combination
Hauzenberger Franz
Kepplinger Werner Leopold
Lee Il-Ock
Schenk Johannes-Leopold
Wallner Felix
Andrews Melvyn
Ostrolenk Faber Gerb & Soffen, LLP
Voest-Alpine Industriean-lagenbau GmbH
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