Smelting reduction method with high productivity

The invention relates to a method for smelting reduction of metal ores involving a combination process wherein the metal ores are partly reduced in one or more stages and then completely reduced to metal in a melt-down reactor. The combination process comprises at least three process units, and the melt-down reactor forms one process unit. The partial reduction of the metal ores is performed in at least two further process units. A different waste gas is produced in each of these at least three process units.

FIELD OF THE INVENTION 
The present invention relates to a method for smelting reduction of metal 
ores involving a combination process wherein the metal ores are partly 
reduced in one or more stages and then completely reduced to metal in a 
smelting reactor. 
BACKGROUND OF THE INVENTION 
It is not new to reduce metal-oxygen compounds, preferably metal ores, in a 
molten bath and to supply the necessary energy to the smelt by 
carbonaceous fuels and oxygenous gases, and there are a number of 
protective rights and prior publications which deal with smelting 
reduction. 
In steelmaking by the various air refining methods there were already 
efforts to reduce ores with carbon in a converter. The oxygen content of 
the blowing medium serves, among other things, to produce the necessary 
heat by oxidizing part of the carbon. German patent no. 605 975, from 
1932, describes a method wherein the blowing medium and the carbon are 
separated from each other and supplied alternatingly to the smelt and, 
interestingly, the carbon was added in the form of a carbonaceous gas. 
This is also indicated by the claim with the following wording: "A method 
for making steel in converters or in air furnaces provided with tuyeres 
wherein ores are reduced in an iron sump and the carbon is added, carried 
by an oxygenous blowing medium, characterized in that air or 
oxygen-enriched air or pure oxygen and neutral gases or gases which 
release carbon themselves or have a reducing effect are alternatingly used 
as a blowing medium and carbon carrier." 
An essential contribution to economical operation of the reduction of metal 
ores in a molten metal bath was made by afterburning the reaction gases, 
mainly CO and H.sub.2, in the gas space above the molten bath and 
recycling the resulting heat to the molten bath. The teachings on this 
afterburning of the reaction gases and the successful retransfer of the 
heat to the molten bath are described for the first time by the worldwide 
protected method for improving the thermal balance during steel finery, 
for instance U.S. Pat. No. 4,195,985. This patent print also states in 
col. 14, line 39, the use of iron ore instead of scrap as a coolant during 
steelmaking. A particularly advantageous form of this method and its 
further development to achieve higher afterburning rates and a special 
apparatus are set down in the internationally protected method and the 
apparatus for afterburning reaction gases, for instance in U.S. Pat. No. 
5,052,918. 
A well thought-out method for making iron/crude steel with a carbon content 
of 2 to 3% is described in German patent no. 33 18 005. In this process 
approx. 70 t crude steel are produced per hour in a melt-down vessel 
containing an iron smelt of approx. 120 t. The method is a combination 
system involving a melt-down reactor, a gas conditioning vessel and a 
shaft furnace for prereducing the ores. This method for making iron from 
ore is characterized in that the reaction gases emerging from the iron 
smelt are partly afterburned in the melt-down vessel whereby the resulting 
heat is largely transferred to the smelt and the reaction gases are cooled 
and reduced with reduction agents on the way to the ore reduction vessel. 
This process is characterized not only by the stated productivity but also 
by a comparatively small amount of recycle gas of 80,000 Nm.sup.3 /h with 
which 110 t iron ore are reduced to a degree of metalization of approx. 
75%, and the gas then leaves the shaft furnace with a composition of 
approx CO 41 %, CO.sub.2 30%, H.sub.2 23%, H.sub.2 O 1%, N.sub.2 4%, to be 
subsequently used as a service gas, for example for heating purposes. 
The hitherto described prior art clearly indicates steps which 
substantially contribute to an economical operation of a smelting 
reduction method. For example, whereas the basic considerations on the 
reduction of iron ores in steelmaking were set forth a relatively long 
time ago, the last-mentioned process describes in its examples the 
practical application of smelting reduction with production data and gas 
compositions and amounts. By contrast, many newly granted protective 
rights for smelting reduction contain only a row of known steps and no 
quantitative data on the quantity and materials balance of these 
processes. A random example of this is U.S. Pat. No. 4,985,068 whose main 
claim reads as follows: "A method for smelting reduction of iron oxide, 
comprising (a) feeding prereduced iron oxide into an enclosed smelter; (b) 
heating, melting and reducing said iron oxide to molten metal by 
combusting a surplus of natural gas with oxygen, carburizing the molten 
metal by dissolving dissociated carbon in the metal, and forming a reacted 
off-gas; (c) introducing hot air into the enclosed smelter above the 
molten bath and oxidizing a portion of the off-gas to produce a flue gas; 
(d) cleaning and cooling flue gas to a temperature of from about 
800.degree. C. to 950.degree. C.; (e) contacting said iron oxide with said 
cleaned flue gas to perform the prereducing function; and (f) drawing off 
molten iron product." 
At the European Ironmaking Conference in Glasgow in September 1991 the 
authors Cusack/Hardie/Burke presented an extensive report on the 
development of smelting reduction in their contribution "HIsmelt--Second 
Generation Direct Smelting," and this publication indicates a number of 
important process parameters and their mutual relations. It deals with the 
degree of prereduction of the ores as a function of the degree of 
afterburning of the reaction gases and the resulting coal required for 
ironmaking, as well as the stages of development of the smelting reduction 
methods known from industry and their essential characteristics. It states 
a simplified materials and thermal balance for the HIsmelt process, and 
mentions for the demonstration plant under construction a production 
capacity of 14 t pig iron per hour or 100,000 t per year. 
Some common disadvantages are also indicated by the many prior publications 
on smelting reduction of metal ores and the combination of an ore 
prereduction stage with a melt-down vessel, and by the details known about 
the pilot plants and production facilities on this basis. The known 
production capacity, i.e. the metal production per unit of time, is 
relatively low. Limits probably result from the high energy turnovers in 
the melt-down reactor. It is also striking that, although there are 
differences in the amounts of gas to be removed from the process and their 
residual energy contents, considerable amounts of gas with relatively high 
thermal values must in any case be removed from the process. This even 
holds for methods wherein the partly afterburned gases from the melt-down 
vessel are utilized for prereducing ore with a relatively low degree of 
metalization. The economy of this processes remains contingent on the 
profits made in selling the surplus amounts of gas. 
SUMMARY OF THE INVENTION 
The present invention is accordingly based on the problem of providing a 
method which makes it possible in an economical way to clearly increase 
productivity in the melt-down vessel of a smelting reduction plant, i.e. 
to produce a very much greater amount of liquid metal per unit of time, 
based on the weight of the molten bath in the melt-down reactor, in 
comparison to known methods and to improve the utilization of the gas in 
the total process. The inventive problem is thus aimed at improving the 
economy in metal production by the smelting reduction method. 
This problem is solved according to the invention if the combination 
process comprises at least three process units and the melt-down reactor 
forms one process unit while the partial reduction of the metal ores is 
performed in at least two further process units, a different waste gas is 
produced in each of these at least three process units, and the waste gas 
from the melt-down reactor is guided only through one process unit for 
partial reduction. 
The object of the invention is accordingly a method for smelting reduction 
of metal ores involving a combination process wherein the metal ores are 
partly reduced in several stages and then completely reduced to metal in a 
melt-down reactor, the combination process comprising at least three 
process units and the melt-down reactor forming one process unit while the 
partial reduction of the metal ores is performed in at least two further 
process units, and a different waste gas being produced in each of these 
at least three process units, characterized in that partly reduced ore 
from the partial reduction facility, process unit C, is passed into the 
smelt of the melt-down reactor, process unit A, and the afterburned waste 
gas from process unit A is passed into the initial reduction facility of 
process unit B where it is fully burned and removed from the combination 
process. 
The inventive method has made it possible in an unforeseeable way to 
increase the production of molten bath in the melt-down reactor of a 
smelting reduction plant constructed as a combination process from several 
process units to approximately twice that in smelting reduction plants. 
Furthermore, the inventive method has made it possible to reduce the coal 
consumption for the production of 1 t molten bath by more than 10% 
compared to known processes. This fuel saving is probably due to the 
surprisingly high degree of afterburning of the reaction gases in the 
melt-down reactor and the simultaneous good heat retransfer of the energy 
arising during gas afterburning to the molten metal bath. 
In all hitherto known smelting reduction methods in combination with ore 
prereduction, the reaction gases from the melt-down vessel are used to 
prereduce the metal ores. One can work either with or without a relatively 
low after-burning of the reaction gases in the melt-down vessel in order 
to provide an applicable reducing gas for the metal ores during their 
prereduction. At a higher degree of afterburning in the melt-down vessel 
the waste gases must be conditioned suitably to improve their reduction 
potential. The gas conditioning facilities used for this purpose are 
elaborate and require the gases to be cooled for CO.sub.2 washing. The 
purified gas must then be heated again to the favorable reduction 
temperature for the metal ores. As for the also known, direct reduction of 
the waste gases from the melt-down reactor on the way to the ore reduction 
vessel with corresponding reduction agents, such as carbon and natural 
gas, there are also hitherto difficulties with the operating reliability 
and reproducibility of this method step. 
The method according to the invention opens up a completely new way here, 
which ultimately leads to the surprisingly favorable results. The starting 
point is a combination process for smelting reduction of metal ores which 
consists of a plurality, but at least three, process units. The term 
"process unit" is deliberately selected here as opposed to a customary 
method step in order to make it clear that these units constitute 
relatively independent facilities, which can be of varying design, in the 
total combination process. One must merely coordinate the process 
engineering design data of the individual process units to ensure a 
uniform flow of material for the inventive combination process. For 
example, each of the at least two partial reduction units can be of 
multistage design. One can use, among other things, a multistage 
circulating fluid bed for one or both of the process units for the partial 
reduction of the metal ores. 
The inventive method is particularly suitable for reducing iron ore and 
iron-containing ores. But it is suitable in general for ores, dusts and 
similar materials containing oxides of one or more transition metals, in 
particular those of vanadium, chromium, manganese, iron, cobalt, nickel, 
copper, zinc and lead, preferably those with mainly iron. 
An advantageous design of the inventive combination process for smelting 
reduction of metal ores can consist of three process units, whereby 
process unit A is the melt-down reactor. The waste gases from the 
melt-down reactor have a high degree of afterburning and directly reach 
process unit B, a preheating and initial reduction facility for the metal 
ores. The waste gases from this process unit B are fully burned, and their 
physical residual heat can be utilized for example directly or via a heat 
exchanger for heating purposes. The metal ores heated and possibly 
somewhat reduced in process unit B are supplied to the third process unit 
C, the actual partial reduction facility, and prereduced there to a 
clearly higher degree of metalization and then supplied to process unit A, 
the melt-down reactor. 
With the method according to the invention, waste-gas streams differing in 
their amounts, their gas compositions and their thermal values arise in 
the three different process units. In the following the gas composition 
will be expressed by the degree of afterburning, which is an important 
characteristic for the assessment of the overall method, the combination 
process, and the individual process units. The degree of afterburning in 
percent is defined as follows: 
##EQU1## 
Gas constituents [vol. %] AB=degree of afterburning [%] 
Since virtually only CO and H.sub.2 emerge from the molten metal bath as 
reaction gases in the melt-down reactor and are then afterburned with 
oxygen or air in the gas space thereabove, the waste gas for each process 
unit is composed only (apart from small impurities) of the components CO, 
H.sub.2, CO.sub.2, H.sub.2 O and the constituent N.sub.2 from the 
afterburning air. For example, the gas composition 16.3% CO, 10.0% 
CO.sub.2, 3.59% H.sub.2, 9.89% H.sub.2 O and 60.23% N.sub.2 has a degree 
of afterburning of 50% according to the definition. In the further 
description this statement on the degree of afterburning will also hold as 
the implicit quantity for the gas composition. 
With the stated advantageous design of the inventive combination process 
for smelting reduction of metal ores, approximately the following 
waste-gas streams arise in the individual process units for the production 
of 1 t iron smelt with approx. 3.5% carbon from a high-quality iron ore. 
From the melt-down reactor, process unit A, approx. 2000 Nm.sup.3 with a 
temperature of 1680.degree. C. and a degree of afterburning of 60% flow 
into the preheating and initial reduction facility, process unit B. The 
waste-gas stream from this process unit is approx. 2600 Nm.sup.3 with a 
temperature of approx. 900.degree. C. and is fully burned, i.e. the degree 
of afterburning is 100%. In process unit C, i.e. the partial reduction 
facility, a reducing gas is selectively produced from coal and an 
oxidizing gas, mainly hot air, and what leaves this facility is approx. 
825 Nm.sup.3 of a high-quality combustion gas with a temperature of 
950.degree. C., a degree of afterburning of 30% and a thermal value of 1.2 
Mcal/Nm.sup.3. This gas can be utilized in any way, e.g. for producing hot 
air. 
The individual facilities or process units in the combination of which the 
inventive smelting reduction method takes place can be built and designed, 
for example, as follows. The melt-down reactor, process unit A, can be an 
inclined drum vessel having feed tuyeres encased with protective medium 
below the bath surface, supply means for various solids and one or more 
top blowing tuyeres for oxygen or oxygenous gases for afterburning the 
reaction gases in the upper reactor space. Proven underbath tuyeres are 
the customary constructions consisting of two concentric pipes, and 
circular slot tuyeres, as described for example by German patent no. 24 38 
142, as well as simple pipes for supplying additional circulation gas, for 
example to increase the bath motion in limited areas of the melt-down 
reactor. It is also within the scope of the invention to supply 
circulation and reaction gases to the slag zone of the vessel. The tuyeres 
are of course then installed higher in the side wall or in a corresponding 
supply level of the vessel or its lining. To supply the afterburning 
oxygen in the gas space of the melt-down reactor one can use, firstly, 
several simple pipes or, secondly, so-called block tuyeres wherein 
shower-like gas jets emerge from a metal block having several channels, 
or, preferably, top blowing tuyeres according to U.S. Pat. No. 5,051,127. 
The oxygenous gases used for afterburning may be pure oxygen, air or 
oxygen-enriched air and preferably hot air, i.e. preheated air, with or 
without added oxygen. 
All solids can be introduced both below the bath surface and onto the bath 
surface. It is preferable to introduce the solids, depending on their 
composition, grain size and temperature, into the smelt both below the 
bath surface and through the top blowing tuyeres or special supply pipes 
within the top blowing tuyeres. For example, it is frequently the case 
that the separated dust from the various parts of the plant is 
recirculated into the smelt through bottom tuyeres. Coal, usually only 
partial amounts of the total amount required, and ore, in some cases also 
the preheated, partly reduced ores, are simultaneously blown through the 
bottom tuyeres into the melt-down reactor. However, the prereduced hot ore 
is usually guided directly from process unit C into the melt-down reactor 
from above. 
In the method according to the invention the waste gas from the melt-down 
reactor, process unit A, flows into the preheating facility, process unit 
B. The plant type of this process unit is not fixed. For example, it can 
be a rotary tubular furnace, a shaft furnace or a normal fluid bed. A 
circulating fluid bed has proved to be advantageous. In this circulating 
fluid bed the waste gases from the melt-down reactor are fully burned with 
oxygen or air, but preferably with hot air. Beforehand, however, the 
reduction potential of the waste gases is utilized to prereduce the metal 
ores, and the latter are furthermore dried and heated by the introduced 
heat. Limestone can be additionally deacidified in this circulating fluid 
bed in order to use the resulting quicklime for instance as a slag forming 
agent in the melt-down gasifier. Further loading materials, in particular 
the slag forming agents, can also be heated and possibly calcined here. 
The further surplus energy from the afterburning of the waste gases serves 
to generate steam in the known cooling elements of a circulating fluid 
bed. The waste gas leaves this process unit B fully burned and with a 
temperature of approx. 900.degree. C. The preheated ores normally leave 
the circulating fluid bed with a degree of prereduction of 10 to 30%, but 
it is also within the scope of the invention only to dry and heat the ores 
in process unit B, to supply them to the actual partial reduction 
facility, process unit C, with a very low degree of prereduction or even 
no prereduction at all. 
According to the invention the partial reduction facility, process unit C, 
is a circulating fluid bed. As is generally known, a circulating fluid bed 
substantially comprises, regarded downstream, a mixing chamber, a riser 
pipe and a cyclone with a solids return pipe to the mixing chamber. With 
such a fluid bed reactor, for example of the Fluxflow type, the charge is 
fed to the mixing chamber, and the riser pipe contains the cooling 
systems, mainly heat exchangers, in which steam can also be produced. 
Along with the slightly prereduced ores with a temperature of about 
900.degree. C. and the slag forming agents from the preheating and initial 
reduction facility, process unit C is also charged with coal and the 
oxygen necessary for combustion, preferably in the form of hot air. The 
solids, preferably in a grained or ground form, are supplied to the 
partial reduction facility pneumatically together with the customary 
amount of carrier gas. 
According to the invention, the amount of supplied coal is greater than can 
be burned in process unit C by the amount of introduced oxidizing gas in 
order to produce the desired high-quality reducing gas. This surplus coal 
is liberated from its volatile components in the partial reduction 
facility, and the thus produced coke passes together with the prereduced 
ore, which usually has a degree of metalization in the range of about 50%, 
and the slag forming agents from process unit C into the melt-down 
reactor, process unit A, thereby closing the circulation of material in 
this combination process. 
The circulating fluid bed and its operation with the selective partial 
reduction of the metal ores and the controlled production of a valuable 
waste gas with a high energy content constitutes an essential feature of 
the inventive method for smelting reduction of metal ores. This process 
unit offers the possibility of optimally adjusting both the reducing gas 
itself and the degree of prereduction of the ores independently of the 
degree of afterburning of the reaction gases in the melt-down reactor and 
the further utilization of its waste gases. Not only the quantitative 
proportion of coal and combustion oxygen but also the sojourn time of the 
ores in this circulating fluid bed and the amount of the pneumatic 
conveying gas or an additional inert gas can be used to adjust the degree 
of metalization of the metal ores from 30% to 70%, preferably from 35% to 
65%. 
Due to the additional production of coke via the liberation of the 
introduced coal from its volatile components in the circulating fluid bed, 
the inventive method also offers a particularly economical supply of the 
melt-down reactor with carbon as a heating medium. For example, 
approximately half the added amount of coal in the partial reduction 
facility is supplied to the melt-down reactor as coke together with the 
partly reduced metal ore having a degree of metalization of approx. 55% 
and a temperature of 950.degree. C. Under these conditions it is possible, 
surprisingly, to approximately double the pig iron production in the same 
melt-down reactor, i.e. with the same weight of charge and the same 
geometrical dimensions, over known methods. This increase in productivity 
in a melt-down reactor offers not only the economic advantages already 
shown, e.g. the calcination of the slag forming agents and coke 
production, but also other economic improvements mainly because the costs 
for the refractory vessel lining, thermal losses of the facilities and 
general operating and staff costs do not increase in proportion with the 
pig iron production. 
With the hitherto known methods for smelting reduction of iron ores the 
production rate in tons per hour, based on the average weight of charge in 
the melt-down vessel--referred to in the following as the production 
index--is no more than 0.6. For example, 70 t pig iron are produced per 
hour in the melt-down vessel with an average weight of the iron smelt of 
120 t described in German patent no. 33 18 005. This results in a 
production index of 0.58. The "average weight of the iron smelt in the 
melt-down reactor" refers here to the arithmetic mean of the weight of the 
smelt in the melt-down vessel before and after the tapping of a batch or 
partial amount. With the method according to the invention one can attain 
production indices of more than 0.8, preferably of more than 1.0. 
Although the method according to the invention already has a surprisingly 
high productivity and considerable economic advantages in the described 
combination with three process units, it is within the scope of the 
invention to add further process units, possibly including existing 
facilities and external utilization of the gas, to the combination 
process. Thus, process unit B can be designed as a multistage fluid bed or 
comprise two separate facilities of the same or a different type. For 
example, it is possible to combine a rotary tubular furnace with a 
circulating fluid bed. It may be advantageous to operate process unit C, 
not with one circulating fluid bed, but with two circulating fluid bed 
facilities which largely work separately. It is then possible to adjust a 
higher afterburning rate in the first circulating fluid bed, i.e. to 
exploit the chemical energy of the added coal further. The high degree of 
metalization of the ore can then be reached in the second circulating 
fluid bed. With this additional process unit, namely the second 
circulating fluid bed following the actual process unit C, advantages 
result for the energy balance of the combination process since the coal 
consumption is about 20% lower. 
A recommendable form of the inventive method intended to increase the 
productivity and, if possible, to lower the energy required, i.e. the coal 
consumption, results from a temperature increase of the hot air both for 
the coal combustion and for the afterburning of the reaction gases. Hot 
air is normally produced with a temperature of at most 1200.degree. C. 
With the waste gases from known smelting reduction processes which are 
customarily utilized as fuel for preheating the air it is not possible to 
increase the hot air temperature further without adding high-energy gas. 
The use of the high-energy waste gas from process unit C readily permits 
hot air temperatures up to approx. 1400.degree. C. to be obtained. The 
heater assembly for the air can be, for example, a so-called pebble heater 
as described by German patent no. 38 41 708. 
A further advantageous form of the inventive method with the same objective 
as stated above is achieved by oxygen enrichment of the hot air. The 
oxygen enrichment of the hot air can take place up to oxygen contents of 
50%. However, very much lower oxygen enrichments, for example up to oxygen 
contents of 25%, have also proved to be surprisingly favorable. 
A particularly advantageous form of the inventive method can be obtained 
with the combination the two lastmentioned improvements, i.e. the 
temperature increase of the hot air with a simultaneous increase in its 
oxygen content. For example, with hot air temperatures of 1350.degree. C. 
and an additional increase in the oxygen content to approx. 25%, approx. 
50 kg coal were saved when producing 1 t liquid pig iron, and the 
productivity in the melt-down reactor increased in an unforeseeable way by 
approx. 40%. 
Finally, it is within the scope of the invention to meet the energy 
requirements in the individual process units partly by supplying physical 
heat, for example by introducing highly heated, inertly behaving gases. 
One can use different gases with temperatures from 900.degree. to 
1600.degree. C., preferably from 1200.degree. to 1400.degree. C. For 
example, the recycled, fully burned waste gas from process unit B, carbon 
dioxide and nitrogen, has proved to be useful. The application of these 
hot gases to supply heat is of course not limited to the stated types of 
gas; one can use comparable gases and any mixtures thereof. 
The method according to the invention is extremely flexible in the 
selection of fuels. Solid, liquid and gaseous fuels can be processed 
singly or in mixtures. Any coal qualities, from gas flame coals to 
anthracite, can be used as well as problematic burnable residues from 
graphite and aluminum production. One can also use refinery residues, all 
heavy oil qualities, any types of oil including diesel oil and domestic 
fuel. Of the gaseous fuels, natural gas, methane, ethane, propane, butane 
and mixtures thereof have proved to be suitable.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Process unit A comprises the melt-down reactor, which has a refractory 
lining (not shown) and contains molten bath 2. The reacting agents are 
blown into gas space 6 of meltdown reactor 1 through bottom tuyeres 3, 
supply means 4 above the bath surface and top blowing tuyere 5 for the 
oxygenous gas, preferably hot air. The reaction gases emerging from smelt 
2 react in gas space 6 with the oxygen of the hot air from tuyere 5, and 
the thereby liberated heat is transferred to smelt 2 with an efficiency of 
over 80%. The resulting waste gas leaves melt-down reactor 1 through the 
waste-gas opening symbolized by arrow 7. The produced molten bath and the 
slag leave melt-down reactor 1 through outlet 8. 
Process unit B, or the preheating and initial reduction facility, comprises 
a circulating fluid bed with mixing chamber 10, riser pipe 11 containing 
heat exchanger 12 for the steam generation, and cyclone 13 with solids 
return pipe 14 and discharge 15. Via inlet 17 the waste gas passes from 
process unit A into mixing chamber 10 of process unit B. The hot air for 
afterburning the introduced gases and for the ores and the slag forming 
agents to be calcined is introduced into mixing chamber 10 via opening 18. 
The waste gas leaves this process unit via opening 16. Outlet 19 is 
intended for the preheated solids which are conveyed pneumatically from 
there to process unit C. 
Through injection port 20 all solids pass into mixing chamber 21 of process 
unit C. These solids are the heated and initially reduced metal ores, the 
calcined and heated slag forming agents, the coal and the conveying gas 
required for the pneumatic transport. Via injection port 22 in mixing 
chamber 21 the oxygenous gases, usually hot air, is supplied for 
combustion, preferably partial combustion, of the coal introduced into 
mixing chamber 21. Through outlet 23 the solids from process unit C, i.e. 
mainly the metal ores selectively reduced to a high degree of metalization 
as well as the slag forming agents and the coke, pass into the melt-down 
reactor, i.e. process unit A. The relatively high-energy waste gas from 
process unit C is supplied via waste-gas opening 24 to the consumers, for 
example the burners of the pebble heater for the hot air production. 
The operation of process unit C and analogously of process unit B, since in 
this example this is also a circulating fluid bed, is basically as 
follows. The solids are supplied to mixing chamber 21 through opening 20 
and solids return pipe 29 and partly burned therein by the oxygenous gases 
flowing in through injection port 22. A fluid bed is produced from the gas 
and the solids, which rises in riser pipe 30 containing cooler 25. Cooler 
25 is fed with water via inlet 26 and the resulting steam escapes via 
outlet 27. The fluid bed then enters cyclone 28 tangentially, and the 
waste gas largely liberated from the solids here in cyclone 28 leaves the 
latter via waste-gas opening 24. One part of the solids passes via solids 
pipe 31 and outlet 23 to the melt-down reactor and another part flows via 
solids return pipe 29 back into mixing chamber 21. The solids stream is 
divided by control valves (not shown), for example slides or discharge 
means such as cellular wheel sluices. From the mixing chamber the solids 
stream recirculates through the facility as described. 
Here are several examples to explain the inventive method in more detail. 
All numerical data stated in the examples relate to the production of one 
metric ton of liquid pig iron from a high-quality iron ore, e.g. a typical 
Australian ore. The melt-down reactor and thus also the pig iron 
production are selected so as to be relatively small in the examples and 
correspond approximately to a pilot plant in which the weight of the smelt 
in the melt-down reactor is about 15 t on the average. The ore 
prereduction, i.e. process units B and C, are designed as circulating 
fluid bed facilities, for example of the Fluxflow type. 
The first example is for the sake of comparison and describes the known 
method comprising a smelting reduction vessel with an ore prereduction 
stage, as published e.g. for the HIsmelt process. 
Approx. 700 kg coal and approx. 150 kg recycled dust are supplied to the 
smelting reduction vessel via the bottom tuyeres and 1700 kg ore with a 
degree of prereduction of 20% and a temperature of 900.degree. C. above 
the bath surface. For afterburning, approx. 2800 Nm.sup.3 hot air with a 
temperature of 1200.degree. C. is blown into the gas space above the 
smelt. From the smelting reduction vessel, 3700 Nm.sup.3 waste gas with a 
temperature of 1700.degree. C. and a degree of afterburning of 50% flows 
into the ore prereduction stage, a circulating fluid bed, which is charged 
with 350 kg slag forming agents and 1600 kg ore. The amount of waste gas 
from this facility is 2300 Nm.sup.3 with a temperature of 900.degree. C. 
and a degree of afterburning of 70%. The thermal value is approx. 0.35 
Mcal. With this known process one can obtain a maximum production rate of 
7 t per hour, corresponding to a production index of 0.47, the resulting 
amount of slag being approx. 400 kg/t pig iron. 
With the inventive method, by contrast, one can obtain in the same 
melt-down reactor a production of approx. 13 t per hour and thus a 
production index of 0.87. Via bottom tuyeres 3 encased with protective 
medium one introduces into melt-down reactor 1 approx. 100 kg coal and the 
recycled dust from the total plant of approx. 250 kg together with the 
necessary carrier gas. Via supply means 4, 250 kg coke, approx. 1300 kg 
prereduced ore with a degree of prereduction of 65% and a temperature of 
950.degree. C. pass into smelt 2 of melt-down reactor 1. For afterburning 
the reaction gases from smelt 2, approx. 1550 Nm.sup.3 hot air with a 
temperature of 1200.degree. C. is blown into gas space 6 through 
afterburning tuyere 5. Through waste-gas opening 7 approx. 2000 Nm.sup.3 
waste gas with a temperature of approx. 1700.degree. C. and a degree of 
afterburning of approx. 60% passes via inlet 17 into mixing chamber 10 of 
the preheating and initial reduction facility. This process unit B is 
additionally supplied via the inlet port with 350 kg slag forming agent, 
1500 kg ore and approx. 450 Nm.sup.3 hot air. The amount of waste gas from 
this process unit B is 2500 Nm.sup.3 with a temperature of 900.degree. C., 
and it is fully burned, i.e. it has a degree of afterburning of 100%. This 
waste gas flows out of opening 16 to the end-users which utilize the 
physical heat of the gas. 
From this process unit B, 1600 kg slightly prereduced ore with a degree of 
prereduction of 11% and a temperature of 900.degree. C. passes via outlet 
19 into the circulating fluid bed of process unit C. One additionally 
supplies facility C with 500 kg coal and 300 Nm.sup.3 hot air. The amount 
of waste gas from this facility is 800 Nm.sup.3 with a temperature of 
950.degree. C., a degree of afterburning of 30% and a thermal value of 1.2 
Mcal/Nm.sup.3. From this partial reduction facility the amounts of ore 
and slag forming agent stated at the beginning of the example are supplied 
to the melt-down reactor. 
In a typical example of the inventive method the production is approx. 15 
t/h, corresponding to a production index of 1.0. Passing from the partial 
reduction facility (process unit C) into the melt-down reactor are 250 kg 
coke, 1300 kg prereduced ore with a degree of prereduction of 65%, a 
temperature of 950.degree. C. and a proportion of carrier gas of 60 
Nm.sup.3. In addition, 90 kg coal and about 250 kg recycled dust flow 
through the bottom tuyeres. For afterburning the reaction gas one uses 
1500 Nm.sup.3 hot air with a temperature of 1200.degree. C. in the 
melt-down reactor. The amount of waste gas of about 1800 Nm.sup.3 with a 
degree of afterburning of 70% and a temperature of 1700.degree. C. flows 
into the fluid bed of the preheating and initial reduction facility 
(process unit B). This facility is also charged with 340 kg slag forming 
agents, 1540 kg ore and 270 Nm.sup.3 hot air. Escaping from process unit B 
is 2300 Nm.sup.3 fully burned waste gas (degree of afterburning 100%) with 
a temperature of 900.degree. C. As already explained, this waste gas is 
supplied to any desired end consumer to utilize the physical heat. 
In the partial reduction facility (process unit C) a high-quality reducing 
gas is produced from 540 kg coal and 660 Nm.sup.3 hot air to reduce the 
1600 kg ore with a temperature of 900.degree. C. and a degree of 
prereduction of 11%, which has been transferred from process unit B to 
process unit C, to the aforesaid degree of prereduction (65%). Escaping 
from process unit C is 1200 Nm.sup.3 high-energy waste gas with a 
temperature of 950.degree. C., a degree of afterburning of 38% and a 
thermal value of 0.9 Mcal/Nm.sup.3. This gas can be utilized for example 
to heat the amount of hot air for the inventive combination process in a 
pebble heater. 
Finally, a third example which utilizes the particularly advantageous form 
of the inventive method, namely an elevated hot air temperature with 
simultaneous oxygen enrichment of the hot air, shows the following thermal 
and quantity balance. The smelt in the melt-down reactor is supplied below 
the bath surface with approx. 50 kg coal and approx. 100 kg recycled dust 
with the customary amounts of carrier gas. Above the bath surface, 1400 kg 
partly reduced ore with a degree of prereduction of 65% and 900.degree. C. 
passes into the smelt. For afterburning one uses approx. 1000 Nm.sup.3 hot 
air with a temperature of 1350.degree. C. and an oxygen content of 24.5%. 
The amount of waste gas from process unit A which is supplied to process 
unit B is 1260 Nm.sup.3 with a temperature of 1720.degree. C. and a degree 
of afterburning of 66%. Process unit B is charged with approx. 1540 kg 
ore, 330 kg slag forming agent and approx. 190 Nm.sup.3 hot air, likewise 
with 1350.degree. C. and 24.5% oxygen. From process unit B, 1680 Nm.sup.3 
fully burned waste gas with a temperature of 900.degree. C. escapes. From 
this preheating and initial reduction facility, 1640 kg ore with a degree 
of prereduction of 11% and a temperature of 900.degree. C. passes into the 
circulating fluid bed of process unit C together with 530 kg coal and 530 
Nm.sup.3 hot air. The amount of waste gas from this partial reduction 
facility is 1100 Nm.sup.3, and the waste gas has a temperature of 
950.degree. C., a degree of afterburning of 40% and a thermal value of 0.9 
Mcal/Nm.sup.3. 
In this example there was an extremely high production rate of approx. 20 t 
per hour operating time, corresponding to a production index of 1.33. 
The method according to the invention, which makes it possible to partly 
reduce metal ores selectively to a certain degree of metalization in a 
combination process comprising at least three process units and to reduce 
them completely to metal in a melt-down reactor with unprecedented 
productivity, is characterized by high flexibility. It can be integrated 
advantageously into existing metallurgical factories, e.g. a steel mill, 
and adapted in a favorable way to the various production conditions. As 
already explained above, both the preheating and initial reduction 
facility and the actual partial reduction facility can be of one- or 
multistage construction. A fourth process unit, for example for 
simultaneously supplying an accordingly designed melt-down reactor, can 
also be added to the combination process along with the three process 
units mainly described. 
Due to the separate waste-gas streams from process units B and C according 
to the invention it may also prove expedient for certain applications to 
interrupt the flow of material between these two process units wholly or 
partly. It is conceivable to put part, or the total amount, of the dried 
and initially reduced metal ores produced in intermediate storage for a 
certain time. This procedure is unfavorable in terms of the energy balance 
but may be useful for adapting the combination process to existing ways of 
production and is therefore within the scope of the invention. 
It is also within the customary framework of expedient reorganization of 
the combination process to modify and vary the flow of material in the 
individual process units in accordance with operational experiences. These 
practical adaptations and advantageous developments are likewise within 
the scope of the method according to the invention.