Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1997-10-14
2001-09-11
Kastler, Scott (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C266S142000
Reexamination Certificate
active
06287363
ABSTRACT:
The invention relates to a method of utilizing dusts incurring in the reduction of iron ore by means of a reducing gas and separated on that occasion in a scrubber in the form of sludges.
In a process of that kind, known for instance from AT-B-376.241, the reducing gas after the separation of solids as well as the top gas emerging from the direct reduction zone are subjected to gas scrubbing in cyclones. In order to efficiently utilize the sludges separated by gas scrubbing, the sludges are mixed with binders composed of iron oxide dust, solid pitch, bitumen or bituminous brown coal, are hot-briquetted and are supplied to the melting gasifying zone, the iron oxide dust coming from a blast furnace gas purification plant.
Nearly all of the solids incurring in solids separation—dust coal in the first place—are recycled into the lower region of the melting gasifying zone; a slight portion of the dust coal is admixed to the sludges mixed with binder and is briquetted together with the same.
In doing so, it is however disadvantageous that, due to the elevated amount of iron oxides charged, reduction work must be done within the melter gasifier in order to reduce the iron oxide, thereby withdrawing energy required for the meltdown procedure from the latter and disturbing the process occurring in the melting gasifying zone. Furthermore, said hot briquetting constitutes an expensive solution in terms of investment and operational costs.
From DE-A-41 23 626 it is known to agglomerate metallurgical recyclings by aid of binders, slag formers and reducing agents, and to introduce the agglomerates into the upper charging region of a melting aggregate, preheating and drying of the agglomerates being effected in said charging region of the melting aggregate. The charge passes through the melting aggregate according to the counterflow principle by initially getting into a reduction zone provided in the interior of the melting aggregate and subsequently being melted in the lower region of the melting aggregate. That known method requires much energy inasmuch as the waste and residual substances must be dried and sintered in the melting aggregate, thus adversely affecting the process occurring within the melting aggregate.
Also there, reduction work must be done in the melter gasifier due to the introduction of iron oxides (such as, e.g., scales), which additionally involves a considerable consumption of energy. Furthermore, it has been proposed to use as binders, e.g., waste sulfite lyes, thereby, however, causing sulfur to be introduced into the process, which is undesired.
The invention aims at avoiding these drawbacks and has as its object to utilize the sludges incurring in the reduction of iron ore in an efficient manner without disturbing the process course of the reduction, with any additional energy consumption being kept as low as possible. Moreover, effective utilization is to be feasible even if heavy metal compounds are contained in the sludges, thereby being able to avoid dumping, which has been necessary so far with the utilization of such sludges in the production of iron melts for the purpose of preventing a build-up of the contents of such heavy metal compounds.
In accordance with the invention, this object is achieved in that the sludges are dehydrated and used as starting materials for the production of cement.
From EP-A-0 124 038 it is known to produce cement material from industrial sludges of primarily organic or inorganic composition. In doing so, the sludges having compositions not defined in detail (including domestic sewage) are mixed with cement material in powdery form, subsequently are granulated or pelletized. The cement components that are essential to the cement composition are added only with a view to their future use in the cement industry. Thus, the admixture of substances that appear suitable as cement components, to the various sludges used as cement substitutes or additives is realized with a view to obtaining a clinker product that is suitable for the cement industry. This is subsequently granulated while adding calcium carbonate.
By contrast, the invention substantially facilitates the course of production, since the sludges employed according to the invention for the production of cement do already contain the four basic components of the cement material, namely iron oxides, silicon oxide, aluminum oxide and calcium oxide, which need not be added separately.
It is particularly advantageous if the sludges are dehydrated to a residual moisture content of 25 to 50%, preferably 35 to 40%, prior to further processing. As a result, the sludges are more readily manipulatable for further processing.
A preferred embodiment of the invention is characterized in that
the sludges at first are dehydrated to a residual moisture content,
the sludges subsequently are granulated and
the thus formed granulated material is used as a starting material for the production of cement.
Therein, advantageously quick lime as a binder as well as optionally coal dust are added to the sludges after dehydration and granulation is effected afterwards. Preferably, the sludges are dehydrated to a residual moisture content of 25 to 50%, preferably 35 to 40%, prior to further processing. As a result, a sludge having such a residual moisture content may be directly charged into a mixer granulator. The preferred range of the residual moisture content allows for a quantitatively favourable consumption of quick lime. Without such dehydration a substantially higher consumption of quick lime would be necessary to obtain a sufficient strength of the granulated material.
The method according to the invention is suitable, in particular, for processing sludges incurring in the reduction of iron ore by aid of a reducing gas produced by a coal gasification process. When treating the coal used in coal gasification coal filter dusts will incur, which may then be added to the sludges along with the binder quick lime such that the addition of the coal dust does not involve any additional costs, but, by contrast, allows for the cheap utilization of the coal dust, which otherwise would have to be used elsewhere. In this respect, the method according to the invention in a particularly advantageous manner lends itself to the utilization of sludges as they incur, for instance, in the processes according to AT-B-376.241 and AT-B-370.134, in which coal gasification is provided.
According to the invention, the granulated material suitably is ground to raw meal used for the production of cement, is dried and subsequently is burnt.
In doing so, it is advantageous to mix the granulated material with mineral substances required for the production of cement, such as limestone, clay, etc. and to grind, dry and subsequently burn the thus prepared clinker formulation.
Suitably, coal dust is added to the dehydrated sludges in amounts of up to 30%, preferably up to 25%, of the amount of dehydrated sludge. Coal dust in the amounts mentioned positively influences the strength of the granulated material. The use of coal dust derived from dedusting means of a coal drying plant, which has been integrated in the present concept for producing an iron melt or pig iron and/or steel preproducts, is of particular advantage for reasons of environmental protection and with a view to avoiding transportation and dumping costs for the coal dust. Furthermore, the addition of coal dust to the dehydrated sludge has the advantage that the granulates subsequently formed in the mixer granulator comprise considerable carbon contents, the coal dust contributing its valuable energetic share in the burning of the granulates.
According to a preferred variant of operation, the sludges, after dehydration, with their residual moisture are used as starting materials for the production of cement and are mixed with raw meal serving for the production of cement. This variant is of particular interest if the sludges used according to the invention only make up a slight percentage of the amount of the raw meal additionally serving for the production of ceme
Grunbacher Herbert
Schrey Gunter
Zettl Franz
Zettl Stefan
Deutsche Voest-Alpine Industrienalagenbau GmbH
Kastler Scott
Ostrolenk Faber Gerb & Soffen, LLP
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