FIELD
The present invention relates to a direct reduced iron
manufacturing system.
5 BACKGROUND
Iron ore such as fine ore and lump ore is reduced in
solid phase at, for example, approximately 1000°C by modified
natural gas to obtain direct reduced iron (DRI: Direct
Reduced Iron). The direct reduction iron making method is
10 low in usage rate of a reducing gas in a reduction furnace.
Therefore, reduction furnace flue gas is returned to the
reducing gas flow to be reused. Accordingly, efficiency is
increased.
Water (H20) and carbon dioxide (CO2) that are produced
15 in the reduction furnace are inert in the reduction furnace.
Therefore, it is necessary to remove them for reuse. The
water is removed in a cooler or scrubber, and the carbon
dioxide in, for example, a removal unit with an amine-based
solvent or the like (Patent Literature 1).
20
CITATION LIST
P a t e n t L i t e r a t u r e
Patent Literature 1: Japanese Patent Application
National Publication (Laid-Open) No. 2001-520310
SUMMARY
T e c h n i c a l Problem
However, a recovery gas mainly including C02 and H2S,
which has released an acid gas in a regenerator of an acid
30 gas removal unit, cannot be discharged as it is out of the
system. Accordingly, a catalyzer being H2S removal means for
removing H2S is conventionally required. However, if H2S is
treated, for example, with a catalyst and the like, the
catalyst is degraded due to the long-term effects of H2S
removal. Accordingly, it is necessary to replace the
catalyst as occasion demands, which invites an increase in
the cost of the catalyst.
5 Hence, a measure that enables the removal of the
harmful H2S in the recovery gas in a simple method without
installing a catalyzer separately is being desired to appear.
Considering the above problem, the present invention
tackles a problem providing a direct reduced iron
10 manufacturing system that can remove the harmful H2S in the
recovery gas in a system that reduces iron ore directly.
Solution to Problem
According to a first aspect of the present invention in
order to solve the above-problems, there is provided a
15 direct reduced iron manufacturing system including: a gas
reformer for reforming natural gas; a heating unit for
heating a reformed gas reformed by the gas reformer to a
predetermined temperature at which the reformed gas is
supplied to a reduction furnace to form a reducing gas; a
20 direct reduction furnace for reducing iron ore directly into
reduced iron using a high-temperature reducing gas
comprising hydrogen and carbon monoxide; an acid gas removal
unit including an acid gas component absorber for removing,
with an acid gas absorbent, an acid gas component in a
25 reduction furnace flue gas discharged from the direct
reduction furnace, and a regenerator for releasing the acid
gas; and a recovery gas introduction line for supplying a
recovery gas released from the regenerator, the recovery gas
comprising carbon dioxide and hydrogen sulfide, to a
30 reforming furnace of the gas reformer and a furnace of the
heating unit, or only the reforming furnace.
According to a second aspect of the present invention,
there is provided a direct reduced iron manufacturing system
including: a heating unit for heating coal gasification gas
or coke oven gas to a predetermined temperature at which the
coal gasification gas or the coke oven gas is supplied to a
reduction furnace to form a reducing gas; a direct reduction
5 furnace for reducing iron ore directly into reduced iron
using a high-temperature reducing gas comprising hydrogen
and carbon monoxide; an acid gas removal unit including an
acid gas component absorber for removing, with an acid gas
absorbent, an acid gas component in a reduction furnace flue
10 gas discharged from the direct reduction furnace, and a
regenerator for releasing the acid gas; and a recovery gas
introduction line for supplying a recovery gas released from
the regenerator, the recovery gas comprising carbon dioxide
and hydrogen sulfide, respectively to the furnace of the
heating unit.
According to a third aspect of the present invention,
there is provided the direct reduced iron manufacturing
system according to the first or second aspect, further
including a degradation product removal unit for separating
and removirfg a degradation product in the acid gas absorbent.
According to a fourth aspect of the present invention,
there is provided the direct reduced iron manufacturing
system according to the first or second aspect, further
including: a bypass circuit for bypassing a part of a lean
25 solvent to be returned from the regenerator to the absorber;
and a filter interposed in the bypass circuit.
According to a fifth aspect of the present invention,
there is provided the direct reduced iron manufacturing
system according to the first or second aspects, further
30 including: an introduction line for introducing the
reduction furnace flue gas into the acid gas removal unit; a
heat exchanger, interposed on the introduction line, for
heat exchanging the reduction furnace flue gas; a bag filter
provided upstream of the heat exchanger; and a scrubber
provided downstream of the heat exchanger.
Advantageous Effects of Invention
According to the present invention, hydrogen sulfide
5 (H2S) in a recovery gas to be released from a regenerator is
prevented from being discharged directly out of the system.
Brief Description of Drawings
FIG. 1 is a schematic diagram of a direct reduced iron
manufacturing system according to a first embodiment.
10 FIG. 2 is a schematic diagram of another direct reduced
iron manufacturing system according to the first embodiment.
FIG. 3 is a schematic diagram of a direct reduced iron
manufacturing system according to a second embodiment.
FIG. 4 is a schematic diagram of a direct reduced iron
15 manufacturing system according to a third embodiment.
DESCRIPTION OF EMBODIMENTS
Hereinafter, the present invention will be described in
detail with reference to the drawings. The present
20 invention is not limited by the embodiment(s). Moreover, if
there is a plurality of embodiments, the present invention
includes their combination. Moreover, the components in the
embodiments include components that can easily be assumed by
those skilled in the art or substantially the same
25 components.
First Embodiment
A direct reduced iron manufacturing system according to
an embodiment by the present invention will be described
30 with reference to the drawings. FIG. 1 is a schematic
diagram of the direct reduced iron manufacturing system
according to a first embodiment. FIG. 2 is a schematic
diagram of another direct reduced iron manufacturing system
according to the first embodiment. As illustrated in FIG. 1,
a direct reduced iron manufacturing system 10A includes a
gas reformer (hereinafter referred to as the "reformer") 51
for reforming natural gas, a gas heater 56 being a heating
5 unit for heating a reformed gas 52 reformed in the reformer
51 to a predetermined temperature at which the reformed gas
52 is supplied to a reduction furnace to form a reducing gas,
a direct reduction furnace (hereinafter referred to as the
"reduction furnace") 13 for reducing iron ore 12a directly
10 into reduced iron 12b using a high-temperature reducing gas
11 including hydrogen (H2) and carbon monoxide (CO), an acid
gas removal unit 16 having an acid gas component absorber
16a for removing acid gas components in a reduction furnace
flue gas 14 discharged from the reduction furnace 13 with an
15 acid gas absorbent (hereinafter referred to as the
"absorbent") 15, and a regenerator 16b for releasing the
acid gas, and a recovery gas introduction line L8 for
supplying a recovery gas 14B released from the regenerator
16b, the recovery gas 14B including carbon dioxide (C02) and
20 hydrogen sulfide (H2S), to each of a reforming furnace of the
reformer 51 and a furnace of the gas heater 56.
In FIG. 1, a reference numeral 15a denotes a rich
solvent, 15b a lean solvent, 20 a scrubber, 21 a compressor,
22 a cooling scrubber, 23 a reboiler, 24 steam, 25 a cooler,
25 26 a gas-liquid separator, 27 condensed water, L1 a gas
supply line for introducing the reduction furnace flue gas
14 into the acid gas removal unit 16, L2 a rich solvent line,
L3 a lean solvent line, L5 a reboiler line, L6 a gas release
line, L7 a condensed water line, L9 a purified gas discharge
30 line, and Llo a reduction furnace flue gas supply line.
The reducing gas 11 is heated up to a predetermined
high temperature (for example, 900 to 1,050°C) by the gas
heater 56 when being introduced into the reduction furnace
Moreover, it may be configured on an upstream side of
the reduction furnace 13 such that the amount of the
reducing gas 11 is increased by a partial oxidation reaction
5 caused by the introduction of a fuel 70 such as oxygen and
natural gas.
The iron ore 12a is supplied from a top of the
reduction furnace 13 where the reducing gas 11 is introduced,
and the supplied iron ore 12a moves toward the furnace's
10 bottom side. At this point in time, the iron ore (iron
oxide) 12a is reduced into the reduced iron 12b by hydrogen
(H2) and carbon monoxide (CO), which are main components of
the reducing gas 11, in countercurrent contact with the
high-temperature reducing gas 11 simultaneously supplied
15 from a side of the reduction furnace 13 as well as the
hydrogen (H2) and carbon monoxide (CO) are respectively
inverted into water (H20) and carbon dioxide (C02).
The reduced iron ore is taken out as the reduced iron
12b from a lower side of the reduction furnace 13.
20 Moreover, the hydrogen (H2) and carbon monoxide (CO) in
the reducing gas 11 are not used up in the reduction furnace
13, and the majority of the hydrogen (H2) and carbon monoxide
(CO) stays unused and discharged as the reduction furnace
flue gas 14 into the gas supply line L1.
25 The reduction furnace flue gas 14 from the reduction
furnace 13 contains dust generated from the reduction
furnace 13, such as iron powder, which has an adverse effect
on the operation of the acid gas removal unit 16 connected
on the downstream side. Therefore, the scrubber 20 removes
30 the dust as well as the water (H20) produced in the reduction
furnace 13.
In the embodiment, a bag filter 31 and a heat exchanger
32 are installed on the gas supply line L1 for supplying the
reduction furnace flue gas 14.
The installation of the bag filter 31 promotes the
efficiency of removing the dust in the reduction furnace
flue gas 14 prior to the process in the scrubber 20.
5 Moreover, the dust in the reduction furnace flue gas 14
supplied to the heat exchanger 32 is removed to promote the
maintenance of the heat exchange efficiency of the heat
exchanger 32. The bag filter 31 and the heat exchanger 32
are installed when necessary in the direct reduced iron
10 manufacturing system.
The reboiler 23 needs a heat source. However, in the
embodiment, it makes it possible to generate the steam 24 by
the heat exchanger 32 installed as the heat source on the
gas supply line Ll using the heat (gas temperature:
15 approximately 300°C) of the reduction furnace flue gas 14 and
use the generated steam 24.
The reduction furnace flue gas 14 is pressurized by the
compressor 21 interposed on the gas supply line L1 and then
introduced into the cooling scrubber 22. In the cooling
20 scrubber 22, the gas is decreased in temperature by cooling
water, and then introduced into the absorber 16a of the acid
gas. removal unit 16.
In the absorber 16a, the acid gas of carbon dioxide
(C02) and hydrogen sulfide (H2S) is removed from the
25 reduction furnace flue gas 14 by a chemical absorption
reaction of the absorbent 15 to form a purified gas 14A from
which the acid gas has been removed, and the purified gas
14A is discharged into the purified gas discharge line L9
from a top side.
30 The purified gas 14A contains the unused H2 and CO and
accordingly if the purified gas 14A, which has been purified
in the absorber 16a, joins a natural gas 50 side, the
purified gas 14A is supplied through the purified gas
discharge line L9 so as to join the reformed gas 52 after the
separation of condensed water 55 in a gas-liquid separator
54.
In the absorber 16a of the acid gas removal unit 16,
5 the absorbent 15 absorbs and removes the acid gas components
of C02 and H2S from among CO, H2, C02, and H2S contained in
the reduction furnace flue gas 14.
The absorbent 15 that has absorbed C02 and H2S in the
absorber 16a is referred to as the rich solvent 15a. The
10 rich solvent 15a is supplied to the regenerator 16b side
through the rich solvent line L2. The rich solvent 15a
introduced into the regenerator 16b releases the absorbed C02
and H2S in the regenerator by the heat of the steam
superheated in the reboiler 23 to form the lean solvent 15b.
15 The lean solvent 15b is returned again to the absorber 16a
through the lean solvent line L3 to be circulated and reused.
A cooling part (not illustrated) for removing the
entrained absorbent in the purified gas 14A is provided on
an upper side of the absorber 16a.
20 Moreover, in the regenerator 16b, the recovery gas 14B
mainly including the C02 and H2S that have been released from
the rich solvent 15a is discharged out of the system from
its top through the gas release line L6.
The recovery gas 14B is cooled in the cooler 25
25 interposed on the gas release line L6. The condensed water
27 is then separated from the recovery gas 14B in the gasliquid
separator 26. The separated condensed water 27 is
returned into the regenerator 16b through the condensed
water line L7.
30 It is preferred that an amine-based solvent be used as
the absorbent that absorbs the acid gas components (C02, H2S).
A known amine-based solvent with, for example,
monoethanolamine (MEA), diethanolamine (DEA), or Nmethyldiethanolamine
(MDEA) as a main agent can be used as
the amine-based solvent.
The direct reduced iron manufacturing system 10A of the
embodiment illustrates a case of using natural gas as the
5 reducing gas 11.
It is configured such that if gas from the natural gas
50 is reformed to supply the reducing gas 11, the gas
reformer 51 for reforming the natural gas 50 is provided,
and the steam 24 is supplied to cause a steam reforming
10 reaction, a carbon dioxide reforming reaction, or a reaction
of their combination, which leads to the inversion of the
natural gas 50 into hydrogen (H2) and carbon monoxide (CO),
and the reformed gas 52 mainly including hydrogen (H2) and
carbon monoxide (CO) is obtained.
15 The reformed gas 52, which has been reformed in the
reformer 51, is gas-cooled in a gas cooler 53. Afterward,
the condensed water 55 is separated from the reformed gas 52
in the gas-liquid separator 54.
The reformed gas 52 from which the water has been
20 separated is introduced into the gas heater 56, heated to a
predetermined high temperature (for example, 900 to 1,050°C),
and supplied as the reducing gas 11 into the reduction
furnace 13.
Moreover, the recovery gas 14B released from the
25 regenerator 16b mainly includes C02 and H2S, and is
introduced into the reforming furnace of the gas reformer 51
or the furnace of the gas heater 56 by providing the
recovery gas introduction line L8.
H2S is then burned in the furnaces to form sulfur
30 dioxide (SOz), which is diluted by a large amount of
combustion gas discharged from the furnaces, and then an
appropriate process (for example, a desulfurization process)
is performed thereon as flue gasses from the furnaces to be
released into the atmosphere.
Consequently, H2S in the recovery gas 14B to be released
from the regenerator 16b is prevented from being discharged
directly out of the system. Moreover, if H2S is treated, for
5 example, with a catalyst and the like, the catalyst used is
degraded. Accordingly, it is necessary to replace the
catalyst as occasion demands. However, if a combustion
process is performed as in the embodiment, the replacement
becomes unnecessary, which is economic.
10 The steam 24 generated by waste heat of the reforming
furnace, and the steam 24 generated by heat recovered in the
cooler 53 for removing water in the reformed gas 52 emitted
from the gas reformer 51 can be used as the steam 24 of the
reboiler 23 described above.
15 Moreover, in order to avoid the accumulation of CH4 and
N2 being system inert components in the system, a part 14a of
the reduction furnace flue gas emitted from the scrubber 20
is introduced into the reforming furnace of the gas reformer
51 or the furnace of the gas heater 56 through the reduction
20 furnace flue gas supply line Llo, and the combustion process
is performed here on the part 14a.
Moreover, waste heat of the flue gas of the gas
reformer 51 or the furnace of the gas heater 56 is fully
recovered by heat recovery means such as a heat exchanger,
25 and the flue gas is then discharged. For example, steam is
manufactured by the heat recovery means, and can be used in
the reboiler 23 and a heat requiring unit in the system,
used as the power of the compressor 21 by driving a steam
turbine, or used as electric power by generating electric
30 power.
Moreover, it is configured such that if the purified
gas 14A, which has been purified in the absorber 16a, joins
the natural gas 50 to be reused, the purified gas 14A joins
the reformed gas 52 through the purified gas discharge line
L9 on an upstream side of the gas heater 56.
Moreover, the gas heater 56 is omitted in a direct
reduced iron manufacturing system 10B illustrated in FIG. 2.
5 In this case, it may be configured such that the recovery
gas 14B is supplied only to the gas reformer 51 side and the
combustion process is performed only by the reforming
furnace of the gas reformer 51.
If the gas heater 56 is omitted, it is configured on an
10 upstream side of the reduction furnace 13 such that a
partial oxidation reaction is caused on the reformed gas 52
by the introduction of the fuel 70 such as oxygen and
natural gas to increase the amount of the reducing gas 11 as
well as to internally heat the reducing gas 11 up to the
15 necessary temperature (900 to 1050°C), and then introduced
into the reduction furnace 13.
As described above, the recovery gas 14B released from
the regenerator 16b is introduced through the recovery gas
introduction line L8 into the reforming furnace of the gas
20 reformer 51 and the furnace of the gas heater 56, or only
the reforming furnace and accordingly the combustion process
is performed thereon. Thus, the harmful H2S is prevented
from being discharged directly out of the system.
25 Second Embodiment
A direct reduced iron manufacturing system according to
an embodiment by the present invention will be described
with reference to the drawing. FIG. 3 is a schematic diagram
of a direct reduced iron manufacturing system according to a
30 second embodiment. The same reference numerals are assigned
to the same configurations as the direct reduced iron
manufacturing system 10A according to the first embodiment
illustrated in FIG. 1, and their overlapping descriptions
will be omitted.
As illustrated in FIG. 3, a direct reduced iron
manufacturing system 10C of the embodiment illustrates a
case of using coal gasification gas 60 other than natural
5 gas as the reducing gas 11.
In the embodiment, coal is gasified in a gasifier (not
illustrated), and purified to obtain the coal gasification
gas 60, which is heated by the gas heater 56 to be used as
the reducing gas 11.
10 Moreover, in terms of a gas other than the coal
gasification gas 60, it is also possible to use purified
coke oven gas as the reducing gas.
If the purified gas 14A joins the coal gasification gas
60 in the direct reduced iron manufacturing system 10C of
15 the second embodiment, the purified gas discharge line L9 can
be connected to the gas supply line when necessary.
Consequently, the purified gas 14A is caused to join the
coal gasification gas 60, is then heated up to a
predetermined temperature by the gas heater 56 to form the
20 reducing gas 11, and introduced into the reformer 51.
Moreover, the recovery gas introduction line L8 is
provided to introduce the recovery gas 14B released from the
regenerator 16b into the furnace of the gas heater 56.
H2S is then burned in the furnace to form sulfur dioxide
25 (S02), which is diluted by a large amount of combustion gas
discharged from the furnace, and then an appropriate process
(for example, a desulfurization process) is performed
thereon as flue gasses from the furnaces to be released into
the atmosphere.
30
Third Embodiment
A direct reduced iron manufacturing system according to
an embodiment by the present invention will be described
with reference to the drawing. FIG. 4 is a schematic diagram
of a direct reduced iron manufacturing system according to a
third embodiment. The same reference numerals are assigned
to the same configurations as the direct reduced iron
5 manufacturing system 10A according to the first embodiment
illustrated in FIG. 1, and their overlapping descriptions
will be omitted.
As illustrated in FIG. 4, a direct reduced iron
manufacturing system 10D of the embodiment is configured to
10 include, in the direct reduced iron manufacturing system 10A
illustrated in FIG. 1, a degradation product removal unit 17
being degradation product removal means for removing a
degradation product in the acid gas absorbent 15 reused by
circulating through the acid gas removal unit 16, and a
15 filter 41.
The reduction furnace flue gas 14 from the reduction
furnace 13 contains a lot of CO and iron components, and
those that cannot be removed in the scrubber 20 interposed
on the gas supply line LI may mix in the acid gas removal
20 unit 16.
Moreover, a part of the absorbent 15 causes a chemical
reaction with such CO and iron components over long-time
operation and accordingly degradation products are produced
and processing capacity is reduced.
25 The degradation product from CO produces formic acid by
dissolving CO in the reduction furnace flue gas 14 in the
absorbent 15, and the formic acid reacts with the absorbent
such as an amine-based solvent to form salts, which are heat
stable salts and are accumulated in the absorbent 15.
30 The heat stable salts are accumulated in the absorbent
system to cause, for example, an increase in the boiling
point of the absorbent.
If the boiling point is increased, an increase in
temperature in the reboiler 23 of the regenerator 16b
promotes the thermal degradation of the solvent and reduces
the thermal efficiency of the reboiler, which are not
preferable.
5 Moreover, if viscosity is increased, a pressure loss is
increased and foaming occurs, which are not preferable.
Moreover, the degradation product from iron is produced
by the degradation of the absorbent. For example, if an
amine-based solvent is used as the absorbent, its
10 degradation leads to the production of glycines such as
bicine (N,N-Bis(2-hydroxyethy1)glycine). Such glycines form
iron and a chelate complex to prevent film formation on an
iron surface while involving a trivelent iron complex in a
reduction-oxidation reaction to encourage the dissolution of
15 iron and promote corrosion in an accelerative manner, which
are not preferable.
Especially, dust from the iron ore, which flows from
the reduction furnace 13, has a large specific surface area.
Accordingly, a sudden formation of an iron complex is
20 expected.
Moreover, the absorbent 15 itself is also decomposed by
being heated in the reboiler to produce degradation
components. Accordingly, the absorption capacity of the
acid gas is reduced.
25 The absorbent 15 is circulated/reused as the rich
solvent 15a and the lean solvent 15b. Accordingly, the above
degradation products are accumulated in the absorbent 15,
which causes a reduction in processing capacity and
corrosion of equipment.
30 Hence, the present invention is configured so as to
provide a lean solvent branch line L4 that branches from the
lean solvent line L3 for returning the absorbent from the
regenerator 16b to the absorber 16a, provide the degradation
product removal unit 17 to the lean solvent branch line L4,
separate/remove the degradation products, and regenerate the
absorbent. The lean solvent 15b to be supplied to the lean
solvent branch line L;I is controlled as necessary by
5 opening/closing a valve V interposed on the lean solvent
branch line Lq.
The degradation product removal unit 17 is provided to
reduce the concentration of the degradation products
accumulated in the absorbent 15, recover or maintain the
10 performance of the absorbent 15, and maintain and control
the performance of the absorbent 15 over a long period of
time.
For the degradation product removal unit 17, there are
an absorbent regeneration method by distillation using a
15 difference in boiling point between the absorbent 15 used
and the degradation products, a method for concentrating and
separating the degradation products by electrodialysis, a
method for separating the degradation products by ion
exchange, and their combination.
20 A reclaimer of the absorbent regeneration method
includes, for example, a heat exchanger reclaimer.
If the degradation products are to be removed, when one
or both of the degradation products from CO and the
degradation products from Fe exceed their reference values,
25 the valve V is opened to supply a part of the lean solvent
15b to the degradation product removal unit 17, and start
the operation of removing the degradation products.
When the concentration of the degradation products in
the lean solvent 15b is reduced below a predetermined value,
30 the operation of removing the degradation products is
stopped.
It may be configured such that the operation can be
performed when the degradation products from CO (the
concentration of the heat stable salt) exceed a degradation
product removal start reference value, for example, two wt%.
Moreover, it can be configured such that the operation
can be performed when the degradation products from Fe (for
5 example, glycines such as bicine) exceed a degradation
product removal start reference value, for example, five ppm.
It can be configured to start the degradation product
removal operation when either of the degradation products
from CO (the concentration of the heat stable salt) and the
10 degradation products from Fe (glycines such as bicine)
reaches its reference value if both of the values of the
degradation products are measured.
The concentrations of the degradation products are
examples, and are changed as appropriate according to the
15 kind of the absorbent such as an amine-based solvent, and
conditions in the acid gas removal unit.
A sudden increase in iron concentration is expected.
Accordingly, it is necessary to perform concentration
monitoring separately and frequently.
20 The degradation products may be monitored by an
automatic or manual analysis operation and determined by
unillustrated determination means.
Solvents based on amines with low boiling points such
as 1DMA2P (1-dimethylamino-2-propanol: boiling point 124OC),
25 DMAE (N,N-dimethylaminoethanol; boiling point 134OC), MPZ (1-
methylpiperazine: boiling point 138OC), PZ (piperazine:
boiling point 146OC), 2MPZ (2-methylpiperazine: boiling point
15S°C), DEAE (N,N-diethyl-2-aminoethanol: boiling point
161°C), AMP (2-amino-2-methyl-1-propanol: boiling point
30 166OC), EAE (2-ethylaminoethanol: boiling point 170°C),
methylethylamine (MEA: boiling point 170°C), nBAE (2-
butylaminoethanol : boiling point 200°C) , and 4AMPR (4-
piperidinemethaneamine: boiling point 200°C) are used as the
absorbent that absorbs the acid gas components (C02, H2S) to
facilitate, for example, the evaporation and separation of
the degradation products.
5 This is because even if it is an amine-based solvent,
if a solvent based on an amine with a high boiling point
(247OC) such as MDEA (N-methyldiethanolamine) is used, the
degradation products cannot be evaporated and separated by
evaporation using steam and recycling is not efficient.
10 A degraded concentrate 29 concentrated in the
degradation product removal unit 17 is discharged out of the
system.
A stripped gas 30 of the absorbent is returned to a
lower side of the regenerator 16b.
15 As described above, according to the embodiment, the
degradation product removal unit 17 can separate the
degradation products in the absorbent 15 that circulates
through the absorber 16a and the regenerator 16b and
accordingly the need of frequent replacement of the
20 absorbent 15 is eliminated, which enables the promotion of a
dramatic reduction in the amount of use of the solvent
compared with before.
Moreover, the concentration of the solvent degradation
products is continuously controlled. Accordingly, it is
25 possible to suppress the occurrence of foaming, achieve
stable operation, and also suppress corrosion of equipment.
The stabilization of the operation makes it possible to
achieve the safe operation of the entire direct reduced iron
process, and a reduction in cost by a reduction in the
30 consumption amount of the solvent.
The degradation product removal unit 17 needs a heat
source. However, in the embodiment, it makes it possible to
generate the steam 24 by the heat exchanger 32 installed as
the heat source on the gas supply line L1 using the heat (gas
temperature: approximately 300°C) of the reduction furnace
flue gas 14 and use the generated steam 24.
Moreover, the direct reduced iron manufacturing system
5 10D of the embodiment includes a lean solvent bypass line L11
that bypasses a part of the lean solvent 15b to be
introduced into the absorber 16a from the regenerator 16b,
and the filter 41 interposed on the lean solvent bypass line
L11,
10 The filter 41 is installed in the system to further
remove degradation products, impurities, and the like that
cannot be removed in the degradation product removal unit 17,
which enables long-term maintenance of the performance of
the absorbent 15 such as an amine-based solvent.
15 The components that cannot be removed in the
degradation product removal unit 17 include a volatile
degradation factor substance with a boiling point lower than
the absorbent such as an amine-based solvent.
In the embodiment, an activated carbon filter is used
20 as the filter 41. However, as long as the filter can remove
impurities, the filter is not limited to the activated
carbon filter.
The amount of the lean solvent 15b to be bypassed to
the lean solvent bypass line L11 is set to approximately one-
25 tenth of the total amount. However, it may be adjusted as
appropriate depending on the concentration of impurities.

WE CLAIM:
A direct reduced iron manufacturing system comprising:
a gas reformer for reforming natural gas;
a heating unit for heating a reformed gas reformed
by the gas reformer to a predetermined temperature at
which the reformed gas is supplied to a reduction
furnace to form a reducing gas;
a direct reduction furnace for reducing iron ore
directly into reduced iron using a high-temperature
reducing gas comprising hydrogen and carbon monoxide;
an acid gas removal unit including
an acid gas component absorber for removing,
with an acid gas absorbent, an acid gas component
in a reduction furnace flue gas discharged from
the direct reduction furnace, and
a regenerator for releasing the acid gas; and
a recovery gas introduction line for supplying a
recovery gas released from the regenerator, the
recovery gas comprising carbon dioxide and hydrogen
sulfide, to a reforming furnace of the gas reformer and
a furnace of the heating unit, or only the reforming
furnace.
25 2. A direct reduced iron manufacturing system comprising:
a heating unit for heating coal gasification gas
or coke oven gas to a predetermined temperature at
which the coal gasification gas or the coke oven gas is
supplied to a reduction furnace to form a reducing gas;
a direct reduction furnace for reducing iron ore
directly into reduced iron using a high-temperature
reducing gas comprising hydrogen and carbon monoxide;
an acid gas removal unit including
an acid gas component absorber for removing,
with an acid gas absorbent, an acid gas component
in a reduction furnace flue gas discharged from
the direct reduction furnace, and
a regenerator for releasing the acid gas; and
a recovery gas introduction line for supplying a
recovery gas released from the regenerator, the
recovery gas comprising carbon dioxide and hydrogen
sulfide, respectively to the furnace of the heating
unit.
3. The direct reduced iron manufacturing system according
to claim 1 or 2, further comprising a degradation
product removal unit for separating and removing a
degradation product in the acid gas absorbent.
4. The direct reduced iron manufacturing system according
to claim 1 or 2, further comprising:
a bypass circuit for bypassing a part of a lean
solvent to be returned from the regenerator to the
absorber; and
a filter interposed in the bypass circuit.
5. The direct reduced iron manufacturing system according
25 to claim 1 or 2, further comprising:
an introduction line for introducing the reduction
furnace flue gas into the acid gas removal unit;
a heat exchanger, interposed on the introduction
line, for heat exchanging the reduction furnace flue
gas;
a bag filter provided upstream of the heat
exchanger; and
a scrubber provided downstream of the heat