Note: Descriptions are shown in the official language in which they were submitted.
lZQ42~'7
This invention concerns ~ method and
apparatus for generating a low-sul~ur reducing gas by
the gasification of carbonaceous fuel in a molten iron
bath. Fuel oxygen and a slag former are injected into
the molten metal bath through the bottom of the bath-
containing vessel. The reaction within the vessel is
cooled by the injection of a gaseous coolant which is
recycled, spent top gas from a direct reduction furnace,
steam or a mixture thereof.
The present invention is an improvement to
German OLS 27 50 725, which teaches the generation of
a reducing gas in a molten metal bath. The known
gasifier is noted for its refractory wear. The present
invention alleviates the refractor~ wear problem by
maintaining the bath temperature OL the gasifier at a
lower level. This is achieved by lnjecting a coolant
into the molten metal bath to cool the reaction.
The present invention also provides a well-
balanced reducing gas for the direct reduction of iron.
This is achieved by maintaining the operating tempera-
ture of the molten bath gasifier above the iron-car~on
eutectic point.
In the direct reduction of iron oxide to
metallized iron in a shaft furnace, the reacted top gas
is superheated and must be cooled immediately upon
removal from the furnace. The present invention
utilizes this superheat to calcine lime for sulfur
removal from the shaft furnace.
According to a method aspect of the invention
there is provided a method for generating a reducing
gas wherein sulfur-containing fuel, ox~gen and a flu~
are injected into a molten metal bath within a pressure-
3~ :
12~)4287
tight vessel beneath the surface of the bath to produce
a partially-desulfurized par-tial-oxidation gas having
a h~drogen and carbon monoxide content of at least 80%,
the molten metal bath consisting essentially of frorn
one to 5 percent carbon, minor amounts of sulfur,
phosphorus, and silicon, the balance substantially iron,
the molten metal bath having a slag layer thereon,
the improvement comprising: a) injecting a coolant
into the molten metal bath beneath the surface of the
bath, the coolant being a fuel-rich gas selected from
the group consisting of hydrogen, carbon monoxide,
methane, and any mixture thereof; and b) maintaining
the temperature of the mo].ten metal bath between 1350C
and 1600C by monitoring the molten metal bath tempera-
ture and increasing or decreasing the çoolant flow rate
to lower or raise the bath temperature respectively as
required.
According to an apparatus aspect of the
invention there is provided an apparatus for generating
a reducing gas and reducing iron oxide, the apparatus
comprising: a) a molten bath gasifier for producing
a gasifier gas; b) a generally vertical shaft furnace
for the direct reduction of iron, the furnace having
particle introducing means at the top thereof, particle
removal means at the bottom thereof for establishing
a descending burden therein, reducing gas introduction
means between the particle introducing means and the
particle removal means and a spent top gas outlet for
removing spent top gas from the upper portion of the
furnace; c) a first conduit communicating with the
gasifier and the reducing gas introduction means for
removing reducing gas from the gasifier and introducing
2 -
mab/~l
~2~)~Z~7
reducing aas to the shaEt furnace; d) mean~ for cooling
and cleaning the spent gas removed from the upper
portion of the shaf-t furnace; e) a second conduit com-
municating with the spen~ top gas outlet and the cooling
and cleaning means; f) acid gas re~oval means for
removing CO2 from the cleaned, cooled spen~ top gas;
g) a third conduit communicating with the top gas
cooling and cleaning means and the acid gas removal
system; h) a fourth conduit communicating between the
acid gas removal system and the bo~tom of the gasifier;
i) a fifth conduit communicating between the acid gas
removal system and the first conduit; j) a sixth
conduit communicating between the acid gas removal
system and the first conduit and having heating means
therein; k) means for injecting solid fossil fuel into
the bottom of the gasifier beneath the bath line; and .
1) means for injecting oxygen into the gasifier beneath
the bath line.
This invention is better understood by
referring to the following detailed description and
the appended drawings in which:
Figure 1 is a schematic diagram of a pre-
ferred embodiment of the invention showing a molten
bath gasifier for supplying reducing gas to a shaft
furnace and the necessary auxiliarv equipment.
mab/ `
"
12()4Z~7
}igure ~ is a schcn~ltic di~gr;lm simil;lr to Fi~lI`C 1 showillg ~n altcrnative
flow shcet.
Figure 3 is yet another alternative flow sheet for achieving thc objects
of the present invention.
Referring nol~ to ~igure l, a moltcn bath gasifier 10 contains a molten
iron bath 12 and a fluid slag 14. Cooling coils 16 surround the gasifier; fuel
such as coal from source 20 is injected into the bath through the bottom of the
gasifier. A flu.~ such as lime from source 2~ is injected into the bath as
needed to adjust the fluidity of the slag and to assist in sulfur removal.
lQ Oxygen from source 24 is also injected into the bath through the bottom of the
gasifier to oxidize and gasify the fuel to carbon monoxide.
Suitable fuels are coal, a hydrocarbon, charcoal, coke oven gas, or any
mixture thereof. The preferred fuel is powdered coal.
External cooling of the gasifier is provided by coils 16. I~ater from
source 28 passes through the coils and emerges as steam from line 30. It is
desired to maintain the operating temperature of the gasifier at about 1500~ C.
Steam ~rom source 32 or carbon dioxide-lean top gas from line 34 or a
combination controlled by valve 36 are injected into the molten bath through
line 38. The temperature of the bath is monitored by a device (not shown)
which controls the operation of valve 36 and thus the injection of steam and/or
cleaned top gas.
Mblten slag 14 is re ved from the gasifier at outlet 40 as required. Hot
partial oxidation gas (reducing gas) is removed from gasifier 10 through line 42after which it is tempered or quenched to a temperature below slag fusion
temperature by carbon dioxide-lean top gas from line 44 in quencher 46. Heated
carbon dioxide-lean top gas from line 48 is added to the quenched reducing gas
and the resulting mixture is intorduced to direct reduction furnace 50 through
line 52. Iron oxide from bin 54 is fed into furnace 50 ~hrough line 56 to
form a packed bed burden therein. The downwardly moving iron oxide burden is
B
12~ 7
Teduced to mc~alli~ed iron by co~lterc-lrlellt flow of the reducing gas.
~talli~ed iron i~ rell~ved at outlct 58 from the furnace and spent top gas is
remo~ed from the furnace via line 60. If desircd, lime or limestone nuy be
fed to the furnace through line 56 to form a part of the descending burden.
The heat in the spent top g~s will calcine the lime. If there is any appreciable
sulfur in the reducing gas, it will combine with the calcium as calcium sulfide
.lhich is rel~oved ~ith the m~tallized iron along with any unreacted calcium oxide
through discharge pipe 58. ~is will prevent contamination of the direct
reduced iron with sulfide as well as preventing contamination of the spcnt
top gas.
Because of ~lermodynan~c restrictions, not all of the hydrogen and carbon
noxide in the reducing gas will react with the iron oxide, thus the spent
top gas removed through line 60 contains valuable hydrogen and carbon monoxide.
The spent top gas is passed through cooler 62 and scrubber 64 to reduce the gas
temperature and remove water and dust from the gas. A portion of the cleaned,
cooled top gas passes through lines 66 and 68 to be used as fuel for burner 70.
Combustion air is provided from source 72 and additional fuel may be injected
from source 74 if necessary for proper operation of burner 70. If it is
desired to produce export fuel for other processes, such export fuel may be
withdrawn Erom line ~6 through line 76 and stored in tank 78.
The major portion of the spent top gas from line 66 is compressed in
compressor 80, then cleaned of carbon dioxide in an acid gas removal system 82.
Ihe resulting C02-lean top gas is used in three ways, first to cool the molten
metal bath through lines 34 and 38; second, to temper the gasified reducing gas
~hrough line 44; and third, to be introduced to heater 84 through line 86 to be
re-heated for controlling the temperature of the reducing gas in line 52.
In operation, the temperature of the mDlten metal bath is maintained at a
desired operating temperature of between 1350 and 1600 C, preferably about
1500 C. The temperature of the reducing gas in line 52 is maintained between
, ,,, .~ ..
~, ~
12~42~37
S00 and 900 C, and prefer~bly at a ten~elature of about 850 C to pro~ide a
reducinx ~as ~hich will react with the iron oxide burdcn, but will not n~et
e metallized iron product.
An alternative embodiment shown in Figure 2 includes a sulfur ren~al
system 90 into which calcium oxide is fed througll line 92 and thc reaction
product~ calcium sulfide is removed through line 94. ~luS a substantially
sulfur-free reducing gas is introduced to furnace 50 through line 52.
In an alternative embodiment shown in Figure 3, the coolant injected intogasifier 10 through line 38 is cleaned, cooled, spent top gas having the same
composition as in line 66. ~le carbon dioxide removal system 82 provides fuel
- rich gas for line 44, a portion of which is injected into gasifier 10 above
the molten metal bath through line 98. This provides a somewhat cooler reducing
gas in line 42, being on the order of about 1500~ C. This reducing gas.is then
reduced to a temperature of about 850 C in quencher 46 prior to its injection
into the direct reduction furnace 50.
From the foregoing, it is readily apparent that we have developed a
. method and apparatus for generating a reducing gas in a molten metal bath,
in cooperation with a shaft furnace for the direct reduction of iron oxide to
metallized iron. The process is highly efficient and results in a substantially
sulfur-frèe ~etallized iron as well as a substantially sulfur-free spent top
gas.
