Process for the production of molten pig iron and steel pre-products

A process and an arrangement for the production of molten pig iron or steel pre-products from particulate ferrous material as well as for the production of reducing gas in a meltdown gasifier. A fluidized bed of coke particles is formed by the addition of coal and the injection of oxygen-containing gas. In order to ensure a satisfactory mode of operation of the meltdown gasifier even if coal of inferior quality with a high moisture content and a high portion of volatile matter is used, additional heat is supplied to the meltdown gasifier above the feed lines for the fluidized-bed-forming oxygen-containing gas by burning and/or degassing coal particles separated from the reducing gas.

The invention relates to a process for the production of molten pig iron or 
steel pre-products from particulate ferrous material, in particular from 
pre-reduced iron sponge, as well as for the production of reducing gas in 
a meltdown gasifier, wherein a fluidized bed of coke particles is formed 
by the addition of coal and the injection of oxygen-containing gas, as 
well as to an arrangement for carrying out the process. 
A process of the defined kind is described in U.S. Pat. No. 4,317,677. 
There, the oxygen-containing gas or pure oxygen is blown into the lower 
region of the meltdown gasifier, thus producing a fluidized bed of coke 
particles. The particulate ferrous material, in particular prereduced iron 
sponge, and the lumpy coal are top-supplied through charging apertures 
provided in the hood of the meltdown gasifier, the falling particles are 
braked in the fluidized bed and the ferrous particles are reduced and 
melted as they are falling through the fluidized bed of coke. The melted 
metal covered by slag collects on the bottom of the meltdown gasifier. 
Metal and slag are drawn off through separate tap holes. 
The temperature of the gas produced in the fluidized bed decreases upwardly 
on account of the heat required for heating and melting the iron sponge 
particles and on account of various endothermic reactions occurring during 
heating, dehydration, degasification and gasification of the charged coal. 
The thermal loss due to the endothermic reactions is the higher the lower 
the carbon content C.sub.fix of the carbon used, i.e., the higher its 
moisture content and portion of volatile matter. If the temperatures on 
top of the meltdown gasifier fall to below 1,000.degree. C., the gas 
temperature will no longer suffice to completely decompose the volatile 
matter contained in the gas so that a condensation of tar-containing 
components takes place in the regions of low gas temperatures. The 
separation of tar, however, involves considerable difficulties in terms of 
plant technology and with respect to the treatment of the water required 
for the purification of gas. 
The invention aims at avoiding these difficulties and has as its object to 
ensure a satisfactory mode of operation of the meltdown gasifier even if 
coal of inferior quality with a high moisture content and a high portion 
of volatile matter is used, such as, e.g., brown coal, which is cheap and 
available in large amounts. 
In accordance with the invention, this object is achieved with a process of 
the initially defined kind in that, when using coal having a C.sub.fix 
content of less than 80%, additional heat is supplied to the meltdown 
gasifier above the feed lines for the fluidized-bed-forming 
oxygen-containing gas by burning and/or degassing coal particles separated 
from the reducing gas. 
Advantageously, the additional heat supply is effected by burners coronally 
arranged in at least two horizontal planes and penetrating the side wall 
of the meltdown gasifier, i.e., by burners arranged in a plane in the 
lower region of the fluidized bed and by burners arranged in a plane 
closely above the fluidized bed. In between, i.e., in the intermediate 
plane, it is also possible to supply additional heat. 
Preferably, the additional heat supply is controlled in dependence on the 
temperature measured in the reducing crude gas, wherein heating by burners 
in the upper heat supply plane is effected to relatively increase the 
temperature of the reducing crude gas and heating by burners in the lower 
heat supply plane takes place to relatively lower the temperature of the 
reducing crude gas. 
The invention, furthermore, relates to an arrangement for carrying out the 
process, which arrangement comprises a refractorily lined meltdown 
gasifier including apertures for charging coal and ferrous material as 
well as a discharge duct for the reducing gas produced, furthermore, a 
slag and melt tap hole, a lower section of the meltdown gasifier being 
provided to collect molten material and liquid slag, a central section 
including feed lines for oxygen-containing gas and provided to accommodate 
a coke fluidized bed, and an upper section being provided as killing 
space, which arrangement is characterized in that burners are arranged 
above the feed lines, which burners penetrate the side wall of the 
meltdown gasifier and are equipped with supply ducts for dusty fuel and 
for oxygen. 
Such burners may be operated as gasification burners, i.e., the fuel 
gasification under an excess of oxygen merely exclusively produces CO as 
the product of combustion. 
Suitably, the burners are coronally arranged in at least two superposed 
horizontal planes. 
According to an advantageous embodiment, the fuel supply ducts of the 
burners are connected with a dust storage container and with propellant 
lines. Suitable propellants include reducing gas freed from fine dust, top 
gas, any other burnable gas or even inert gas. 
The burners also may be designed as plasma or other electric burners in 
order to introduce particularly high energy amounts. 
According to a further suitable embodiment, the dust storage container is 
aligned in duct-like manner with a hot cyclone, which serves to separate 
fine dust substantially comprised of coal from the reducing crude gas. 
Preferably, the burners of the superposed burner rings are connected with a 
temperature measuring means provided in the reducing crude gas and with a 
control loop.

A refractorily lined meltdown gasifier 1 comprises a lower section 1', a 
central section 1" and a widening upper section 1"'. The lower section 1' 
is destined to receive molten metal and slag and is equipped with a melt 
and slag tap hole. In the central section 1", feed lines 2 for oxygen are 
provided, by means of which a fluidized bed 3 of coke particles is formed, 
which is maintained above a solid bed 4. The widening upper section 1"' is 
provided with supply ducts for lumpy coal 5 and for iron sponge 6. Heat is 
generated in the fluidized bed and reducing gas is produced. A discharge 
duct 7 is provided in the upper part for the reducing gas. 
Above the oxygen feed lines 2, there are provided, according to the 
invention, gasification burners in two superposed horizontal planes, which 
burners each are arranged so as to be coronally distributed over the 
periphery of the meltdown gasifier. There is illustrated only one burner 
each. The individual burners 8 of the lower plane are arranged in the 
lower region of the fluidized bed, the upper plane being closely above the 
fluidized bed, with its burners being denoted by 9. Each gasification 
burner includes supply ducts for dusty fuel 10 and 11, respectively, and 
for oxygen 12 and 13, respectively. 
The fuel supplies 10 and 11 are in connection with a storage container 14 
with the dusty fuel being conveyed by means of a propellant supplied from 
line 15. The storage container 14 is charged via a hot cyclone 16; into 
this hot cyclone, reducing crude gas is injected from discharge duct 7 
and, there, is freed from solids substantially consisting of coal 
particles 17. The purified reducing gas is discharged via conduit 18 and 
fed to a direct reduction shaft furnace. 
For the purpose of controlling the operation of the burners 8 and 9, a 
temperature measuring device 19 is linked with the discharge duct 7 for 
the reducing crude gas, which is electrically connected with a control 
loop 20, 21. By the aid of this control loop, valves 22, 23 are actuated 
in dependence on the temperature measured wherein, with the temperature 
being too low, the burners 9 of the upper plane and, with the temperature 
being too high, the burners 8 of the lower plane, are actuated. Thus, the 
upper burners, when activated, serve to achieve a relatively higher 
reducing crude gas temperature and the lower burners, when activated, 
serve to achieve a relatively lower reducing crude gas temperature. 
In FIG. 2, the temperature profile over the height of the meltdown gasifier 
is illustrated, the height meters being plotted on the ordinate and the 
temperatures being entered on the abscissa. The full lines indicate the 
temperature course of the coal added and of the gas formed when 
high-quality coal having a C.sub.fix content of about 80%, a content of 
volatile matter of 10%, of ash of 5%, and of water of 5% is used, the 
broken-line curves reflect the course when using inferior-quality coal 
having a C.sub.fix content of 50%, a content of volatile matter of 25%, of 
ash of 20% and of water of 5%. The coal charging temperature is 
illustrated by vertical line 24, the temperature after effected 
dehydration by vertical line 25, the temperature at the start of degassing 
by vertical line 26, and the final temperature by vertical line 27. 
It is apparent that, due to the process according to the invention, the 
temperature courses of low-quality carbon carriers and of the gas produced 
may be adapted to the temperature courses of coal and gas, respectively, 
as they are attained when using high-quality coal.