Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a method of continuously
rnel-ting down scrap, iron sponge and the like, in a vertically
arranged shaft furnace of substantially constant cross section,
using a count~r-flow principle in which a flame, produced by
fuel-oxygen combustion, is applied to the bottom of a colwnn of
charge material in the furnace.
This co~mterflow melting method wi~ll fuel-oxygen burners
involves the ris~ of an undesirably high oxidation of the
charge. Such oxi~ation may be influenced by various provisi.ons.
10. One possibility resides in ad~ixing coal to the charge, thereby
lowering the degree of oxidation and favouring carburisation.
However~ norma].ly this method has the disadvantage that a lar~e
proportion of the admixed coal tends to burn up in the
combustion gases within the furnace shaft and is correspondingly
less effective in the melting-down region of the furnace. The
coal which is admixed in this way and burns up in the combustion
gases has a-similar action to that involved in melting-down by
hypo-stoi.chiometric combustion which is~ howQver, much easier
to achieve by appropriate fuel-oxygcn ratios in the burner
devices. Moreover~ the pieces of coal which descen~ ~radually
with the charge material into the lower region of the shaft
furnace are already largely consumed at this point so that in
view of their small size they tend to pass out ~ith the
continuous molten outflow through the tap hole at the bottom of
the furnace.
It has further been suggested to achi.cve recarburisation
at the bottolr! of the ~elting~ vessel by blowing in coal, or by
inductively heating the bottom of the melting ve3sel~ ei-ther so
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as to reduce the liquidity point of the molten metal or to raise
the temperature of the meltS since generally the temperature of
the molten metal is only slightly above the liquidity point.
However, these provisions are complicated and expensive.
It is, therefore, the aim of the present invention to
achieve an effective improvement in the recarburisation of the
molten metal. ~
According to this invention this aim is achieved by the
creation of a reducing zone beneath the oxidising melting zone
10. in the furnace by admixing slow-reacting large pieces of coal to
the charge material, said coal pieces being of appropriate
dimensions to pass through the said oxidising melting zone and
collect at the bottom of the furnace.
For preference the coal pieces used for this purpose weigh
between 2kgs. and lO kgs. per plece with a small surface area and
a comparatively large diameter, e.g. around 200 mms. A
suitably slow-reacting type of coal is, for example, anthracite.
In addition to this~ the coal pieces may be provided with a
reaction-inhibiting coating, for example of milk of lime or a
20. similar substance which protects the coal lumps from combllstion
in the oxidising gaseous atmosphere which reigns in the melting
down zone of the furnace. The coal lumps are usually added ir
the proportion of 2% to 60/o br weight of the charge material.
By using coal lumps of such comparatively small specific
surface area and slow combustibility it is possible to cause
these ]umps to descend progressively in the shaf~ ~urnacc
together ~rith the charg~ materiQl to be l~leltod l~ithout sufferin~ j
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any significarlt degrec of combustion. The coal pieces wili then
settle at the bottom of the melting vessel in the form of a
layer of coal and no individual pieces or lumps will pass out
through the outflow in the bottom of the meltlng pot. In this
way, a strongly reducing zone is maintained beneath the
oxidisin~ melting zone of the furnace wherein the slag which is
formed as well as the molten metal triclcling through this zone
react optimally with the coal to allow favourable adjustments
to be made with regard to the fluxing or slàgging of the iron
10. and its recarburisation. T`he layer of coal is gradually
consumed as the carbon is dissolved by the metal trickling
therethrough. There is also a corresponding reduction in the
FeO content of the slag passing through this layer. Moreover,
comparatively small quantities of coal lumps are quite sufficient
for this purpose.
One example of a method according to the present invention
will now be described with reference to the accompanying drawing
which illustrates a shaft furnace 1 with an outflow 3 in the
bottom 2 thereof and a column of charge material 4, consisting
20. of scrap metal~ iron sponge or the lllce, within the furnace.
This charge column 4 ls melted down from beneath by means Or
burners 5 which extend through the lateral walls of the furnace
1, said walls having a cross sectional configuration which tapers
slightly outwardly in the downward directioIl to produce flames
in the melting region 7 beneath the charge column 4~ Large,
510w reactin~ lumps of cc,al 8 are added to the charge material
and descend contimlous]y with the charge column 4. ~hey pass
throllgh the o~idising melting zone in the region of the flames 6
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and collect at the bottom 2 of the shaft furnace 1. The molten
charge material (comprising metal and slag) flows over the coal
lumps 8 at the bottom and thereby dissolves the coal. In this
way a reducing, recarburising zone is created beneath the oxidis-
ing melting zone in the region of the flames 6. Preferably, the
aforesaid coal pieces each weigh between 2 kgs. and 10 kgs. per
piece, each piece having a small surface area and a comparatively
large diameter - e.g. around 200 mms. Conveniently, the coal
pieces are added in the proportion of 2% to 6% by weight of the-
charge material. Furthermore, the coal pieces may each be pro-
vided with a reaction - inhibiting coating (for example milk of
lime) which protects the coal from combustion in oxidising melting
zone.
The charge column 4 which descends continuously in the
course of the melting down process is preferably supported on
wall-like accretions which form around the burners 5 as a result
of using burners which are each designed in such a way that the
oxygen outlet is situated within, or surrounded by, a fuel outlet
opening, or, in the case of annular slit burners, within two
slit-like fuel outlet openings. Owing to the expansion of the
fuel emerging from the burners a comparatively cool region is
produced adjacent to the burner outlets with the result that wall-
like accretions of molten material will be formed around the
burners to provide support for the column of charge material
thereabove. Alternatively the charge column may be supported in
conventional manner from the bottom 2 of the shaft furnace 1.
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Furthermore, if the charge material is compressed into
packets or parcels it is possible to add coal, or a carbonaceous
material, to these parcels or packets in order to ensure a
reducing atmosphere w.ithin such parcels right up to the melting
down zone so as to reduce slagging of the charge material duri.ng
the melting process.
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