Method for the gaseous reduction of metal ores using reducing gas produced by gasification of solid or liquid fossil fuels

A method for the gaseous reduction of particulate ores to metals in a moving bed, vertical shaft reactor using a reducing gas externally supplied from a solid or liquid fossil fuel gasification unit. The reducing gas is reformed in a reforming zone located within the reactor and treated prior to injection into the reduction zone of the reactor. A portion of the reducing gas produced in a coal gasification unit may be used to cool the metal in the cooling zone of the reactor.

BACKGROUND OF THE INVENTION 
This invention relates generally to a method for the gaseous reduction of 
particulate ores to metals in particulate form in a moving bed, vertical 
shaft reactor, and more particularly, to a method for the reduction of the 
ore and the cooling of the resulting metal particles using a reducing gas 
externally supplied from a solid or liquid fossil fuel gasification unit. 
This invention is particularly suitable to the reduction of iron ore to 
sponge iron and is illustratively described with particular reference 
thereto. 
For purposes of describing the present invention the terms "reforming," 
"reforming zone," etc., specifically refer to chemical reactions whereby 
the H.sub.2 to CO ratio of the reducing gas supplied to the moving bed, 
vertical shaft reactor is increased. 
In general, the production of sponge iron in a typical vertical shaft, 
moving bed reactor involves two principal steps, namely, reduction of the 
ore with a suitable hot reducing gas in a reduction zone of the reactor 
and then subsequent cooling of the resulting sponge iron with a gaseous 
coolant in a cooling zone of the reactor. The reducing gas is typically a 
gas largely composed of carbon monoxide and hydrogen injected into the 
reactor at temperatures in the range of 850.degree. C. to 1100.degree. C., 
preferably 900.degree. C. to 1000.degree. C. The hot reducing gas may be 
introduced into the reactor at the bottom of the reduction zone and passed 
upwardly through the reactor to flow counter-currently to the downwardly 
moving ore, or alternatively, the hot reducing gas may be introduced at 
the top of the reduction zone and caused to flow co-currently with the 
downwardly moving ore. It is well known in the art to cool the sponge iron 
by injecting a cooling gas at relatively low temperature into the cooling 
zone of the reactor and passing the cooling gas upwardly through the 
reactor whereby the cooling gas temperature is increased and the 
temperature of the sponge iron is reduced. 
In previously proposed processes, the reducing gas used in the direct 
reduction of iron ores has been derived from a number of sources, e.g., 
the catalytic reforming of hydrocarbons and steam. Systems using natural 
gas and steam to generate a reducing gas require the use of catalytic 
reforming units. In prior processes where solid or liquid fuels are used 
to generate the reducing gas as opposed to those processes which utilize 
natural gas, additional equipment has been required to enrich the gas so 
that it may be effectively used for reduction purposes. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide a metal ore 
reduction process in which a metal ore, e.g., iron ore, is reduced to 
sponge metal, e.g., sponge iron, by a reducing gas produced by the 
gasification of solid or liquid fossil fuels which is reformed within the 
reactor to increase its reducing efficiency. 
It is another object of the invention to provide a reducing gas from a 
gasification unit which is reformed within the reactor and treated prior 
to being used to reduce the metal ore. 
It is still a further object of the invention to provide a reducing gas 
with a desirable hydrogen to carbon monoxide ratio which substantially 
increases the reduction reaction rate of the metal ore and thereby 
decreases the residence time of the ore through the reactor. 
Other objects of the invention will be in part obvious and in part pointed 
out hereafter. 
GENERAL DESCRIPTION 
The objects and advantages of the present invention may be generally 
achieved by providing a reforming zone within the reactor to reform a 
reducing gas produced in a suitable gasification unit. Since the gas 
diffusion rate into the ore particles is essentially temperature 
independent and depends primarily upon the concentration of hydrogen 
present in the reducing gas, the reducing gas should desirably have a 
relatively high hydrogen content. In accordance with the invention, a 
reducing gas which may be prepared by the gasification of coal with oxygen 
and water vapor is mixed with steam and heated. The heated gas mixture is 
injected into the reactor and reformed in a reforming zone located in the 
upper portion of the reactor to produce a higher and more desirable 
H.sub.2 to CO ratio. In the reforming zone the H.sub.2 to CO ratio which 
is typically in the range of about 0.5:1 to 1:1 is raised to a suitable 
value for iron ore reduction, i.e., in the range of about 2.5:1 to 5:1 by 
means of the water-gas shift reaction: 
EQU CO+H.sub.2 O.fwdarw.H.sub.2 +CO.sub.2 
The iron-bearing material in the reactor acts as a particularly effective 
catalyst for this reaction. The composition of a typical effluent gas from 
a liquid fossil fuel gasifier unit as reported in S. C. Singer, Jr. and L. 
W. Ternhaar "Reducing Gases by Partial Oxidation of Hydrocarbons," 
Chemical Engineering Progress, Vol. 57, No. 7, (July 1961), pp. 68-74, is 
as follows: 
______________________________________ 
% Volume, Dry Basis 
______________________________________ 
H.sub.2 46.1 
CO 46.9 
CO.sub.2 4.3 
N.sub.2 1.4 
CH.sub.4 0.4 
H.sub.2 O 0.9 
100.0 
______________________________________ 
The composition of a typical effluent gas from a solid fuel gasifier unit 
as reported in the "Institute of Gas Technology Hydrogen Production From 
Coal Interim Report Project 8963" presented at N.A.S.A. Marshall Space 
Flight Center, Alabama, Apr. 24, 1975, and distributed by N.T.I.S. 
N75-24113, is as follows: 
______________________________________ 
% Volume, Dry Basis 
______________________________________ 
H.sub.2 30.4 
CO 58.3 
CO.sub.2 10.0 
N.sub.2 1.0 
CH.sub.4 0.0 
H.sub.2 O 0.3 
100.0 
______________________________________ 
This higher H.sub.2 to CO ratio is desirable because the reduction reaction 
rate using hydrogen is higher than that of carbon monoxide thereby 
decreasing the residence time of the ore in the reactor. In addition, 
since a higher amount of CO tends to deposit elemental carbon on the ore, 
the increased proportion of hydrogen will minimize such deposition. The 
change in the CO content also allows for better control of carburization. 
The reformed gas produced in the upper portion of the reactor is removed 
from the reforming zone of the reactor to an external loop wherein it is 
cooled, compressed and caused to flow through an absorption tower to 
remove carbon dioxide. The reformed and treated gas is then transferred to 
a heater in which it is heated to an elevated temperature in the range of 
about 750.degree. C. to 1000.degree. C. after which it is injected into 
the reduction zone as a reducing gas. The reducing gas passes through the 
reduction zone of the reactor in contact with the metal ore thereby 
effectuating a reduction of the ore after which it is removed from the 
reduction zone and cooled to remove water therefrom. The cooled reducing 
gas is then combined with the reformed and treated gas stream being 
recirculated to the reduction zone of the reactor. 
While it is known to use a reducing gas produced in a coal gasification 
system in the direct reduction of metal ores, reforming the gas within the 
reactor to increase the H.sub.2 to CO ratio has not been previously 
disclosed. Similarly, the method of reforming the reducing gas supplied 
from a solid or liquid fossil fuel gasification unit within the reactor 
followed by treating such gas prior to injection into the reduction zone 
of the reactor has heretofore been unknown in the prior art. The invention 
provides a method whereby a reducing gas produced in a fuel gasification 
system can be more efficiently and economically utilized for the reduction 
of metal ores. Additionally, through this invention the reducing gas is 
reformed within the reactor thereby eliminating the need for a separate 
reforming unit or reactor resulting in an energy and capital cost saving.

DETAILED DESCRIPTION OF THE DRAWING 
Referring to the drawing, numeral 10 generally designates a vertical shaft, 
moving bed reactor having a reforming zone 12 in the upper portion 
thereof, a cooling zone 16 in the lower portion, and a reduction zone 14 
located between the reforming and cooling zones. The reactor 10 is 
suitably heat-insulated and interiorly lined with a refractory material in 
a manner known in the art. 
The particulate ore which is to be treated is introduced into the reactor 
10 through a charging pipe 18. The ore charged to the reactor may be in 
the form of either lumps, pre-formed pellets, or mixtures thereof. Near 
the bottom of the reforming zone 12, the reactor is provided with an 
annular plenum chamber 38 which extends around the periphery of the 
reactor to provide a means whereby a heated gaseous mixture of reducing 
gas and steam is fed to the reactor. The vertical baffle 40 together with 
the wall of the reactor defines the annular space 38. The ore moves 
downwardly through the reforming zone wherein it is heated and partially 
reduced by the upwardly flowing reformed gas. 
The iron ore leaving the reforming zone and entering the reduction zone 14 
essentially consists of ferric oxide. Near the bottom of the reduction 
zone 14 there is a second annular plenum chamber 46, similar to plenum 
chamber 38, through which reformed and treated reducing gas may be fed 
into the reactor. A frusto-conical baffle 48 is also provided which 
together with the wall of the reactor defines the annular space 46. 
The iron ore moving downwardly through the reduction zone 14 is reduced by 
the reducing gas passing through the reduction zone. The reducing gas 
leaves the reactor through annular plenum chamber 42. The plenum chamber 
42 and the frusto-conical baffle 44 are similar to plenum chamber 46 and 
baffle 48. 
As a result of the reduction achieved in the reduction zone, the ore 
leaving this zone and entering the cooling zone 16 is highly metallized 
and of low carbon content. Near the bottom of the cooling zone 16 there is 
another annular plenum chamber 54 through which substantially inert 
cooling gas can be fed into the reactor if desired. A frusto-conical 
baffle 56 is also provided similar to baffles 44 and 48. As the sponge 
iron moves downwardly through the cooling zone 16, it is cooled by the 
cooling gas flowing therethrough and leaves through the reactor outlet 58. 
Turning now to the gas flows in the present system, the reducing gas is 
produced in a coal gasification unit 20 and flows through pipe 22 at a 
rate controlled by the flow controller 21 and into pipe 24. Steam flowing 
through pipe 28 and controlled by flow controller 26 is mixed with the gas 
from the coal gasification unit 20 and enters pipe 30. The gaseous mixture 
flows through pipe 30 to a heating coil 34 of a heater 32 wherein it is 
heated to a temperature in the range of about 300.degree. to 600.degree. 
C. The heated mixture leaves heater 32 through pipe 36 and flows into the 
plenum chamber 38. The gas flowing through plenum chamber 38 enters the 
reactor near the bottom of the reforming zone 12. Upon entering the 
reforming zone of the reactor, the heated mixture is reformed to obtain a 
higher and more desirable hydrogen to carbon monoxide ratio. The reformed 
gas flows upwardly through the reforming zone and is removed near the top 
of the reactor through an outlet connection 60 and pipe 62. 
In one modification of the invention a portion of the reducing gas produced 
in the coal gasification unit 20 is injected at low temperature into the 
cooling zone of the reactor to aid in the cooling of the sponge iron. 
However, if a low carbon content in the sponge iron is desired, a 
substantially inert gas from a suitable source may be used as the cooling 
gas. If all or part of the cooling gas supplied to the cooling zone of the 
reactor is supplied from the coal gasification system, then a portion of 
the cooling gas effluent from the cooling zone of the reactor may also be 
transferred to the reduction loop. 
The reformed gas leaving the reactor through pipe 62 enters a quench cooler 
64 into which water is introduced through pipe 66 to cool and effectuate 
the removal of water therefrom. The gas leaves cooler 64 through pipe 68 
and flows into pipe 74 which connects with the suction side of pump 76. A 
portion of the gas stream flowing through pipe 68 may flow through pipe 72 
to a suitable point of use (not shown). Pipe 72 is provided with a back 
pressure regulator 70 having an adjustable set point so that it may be 
adjusted to maintain a desired positive and constant pressure in the 
system to improve the efficiency of reactor 10. 
The gas mixture flowing to pump 76 is discharged through pipe 78 and enters 
a carbon dioxide absorber 80. The carbon dioxide in the stream entering 
the absorber 80 is removed by a method known in the art by a suitable 
absorbing medium entering the absorber 80 through pipe 82. The gas leaving 
the absorber through pipe 84 contains only small amounts of carbon 
dioxide. Gas flowing through pipe 84 enters pipe 86 and flows through pipe 
88 to the heating coil 92 of heater 90. The gas is heated in heater 90 to 
a temperature in the range of about 850.degree. to 1000.degree. C. and 
preferably in the range of 850.degree. to 900.degree. C. The heated gas 
leaves heater 90 and flows through pipe 94 into plenum chamber 46 through 
which it enters the reactor near the bottom of the reduction zone 14. 
The reducing gas passes upwardly through the reduction zone and flows into 
plenum chamber 42 through which it leaves the reactor. The reducing gas 
stream leaves the reactor through pipe 96 and enters the quench cooler 100 
into which water is introduced through pipe 98 to cool and effectuate the 
removal of water from the reformed gas. The gas leaves cooler 100 through 
pipe 102 and a portion flows through pipe 108 into the suction side of 
pump 110. A portion of the gas flowing through pipe 102 flows through pipe 
106 to a suitable point of use. Pipe 106 is provided with a back pressure 
regulator 104 having an adjustable set point so that it may be adjusted to 
maintain a desired positive and constant pressure in the system to improve 
the efficiency of reactor 10. 
The gas flows through pump 110 into the discharge pipe 112 and is mixed 
with the reformed gas leaving the carbon dioxide absorber 80 through pipe 
84. The combined gas stream then flows through pipes 86 and 88, heater 90 
and pipe 94 from which it is fed back into the bottom of the reduction 
zone 14. 
The inert make-up gas, preferably nitrogen, may be supplied from a suitable 
source (not shown) through pipe 120 at a rate controlled by the flow 
controller 122. The inert gas flowing through pipe 120 then flows through 
pipe 124 into plenum chamber 54 and into the reactor near the bottom of 
the cooling zone 16. A frusto-conical baffle 56 together with the wall of 
the reactor defines the annular chamber 54. The make-up inert gas flows 
upwardly through the cooling zone 16 of the reactor and is removed through 
annular chamber 50. The effluent cooling gas flows through pipe 126 into 
quench cooler 130 into which water is introduced through pipe 128 to cool 
and effectuate the removal of water in the effluent gas. The gas leaves 
cooler 130 through pipe 132 and flows into pipe 138 which connects with 
the suction side of pump 140. A portion of the gas stream flowing through 
pipe 132 may flow through pipe 134 to a suitable point of use not shown. 
Pipe 134 is also provided with a back pressure regulator 136 having an 
adjustable set point so that it may be adjusted to maintain a desired 
positive and constant pressure in the system to improve the efficiency of 
reactor 10. 
The gas is then discharged by pump 140 through pipe 142 where it may be 
mixed with make-up inert gas flowing through pipe 120 to enter pipe 123. 
This gas stream is then recycled back through pipe 124 and plenum chamber 
54 into the cooling zone 16 of the reactor. Alternatively, a portion of 
the gas flowing through pipe 142 is directed to the reducing loop via pipe 
150 at a rate controlled by flow controller 152 and mixed with the 
reformed and treated gas flowing through pipe 86. 
It is to be understood that the foregoing description is intended to be 
illustrative only and that the embodiments described can be modified in 
various ways within the scope of the invention. For example, a portion of 
the gas from the coal gasification unit 20 may be caused to flow through 
pipe 144 at a rate controlled by flow controller 146. The gas then flows 
through pipe 124 into plenum chamber 54 and into the bottom of the cooling 
zone 16. 
The terms and expressions which have been employed are used as terms of 
description and not of limitation, and there is no intention in the use of 
such terms and expressions of excluding any equivalents of the features 
shown and described or portions thereof, it being recognized that various 
modifications are possible within the scope of the invention.