TECHNICAL FIELD
[0001] This invention relates to an oxygen-gaseous fuel supply apparatus in a downdraft
type Dwight-Lloyd sintering machine which produces high-quality sintered ore as a
raw material for a blast furnace by enriching oxygen and supplying gaseous fuel.
RELATED ART
[0002] In general, a sintered ore as a main raw material for a blast furnace iron-making
method is produced through a process flow as shown in FIG. 1. The raw material for
the sintered ore includes fine iron ore, undersize granules of the sintered ore, recovery
powder produced in an ironworks, a CaO-containing auxiliary material such as limestone,
dolomite or the like, a granulation auxiliary agent such as quicklime or the like,
coke breeze, anthracite and so on, which are cut out from respective hoppers 1 onto
a conveyer at a predetermined ratio. The cut-out raw materials are added with a proper
amount of water, and mixed and granulated in drum mixers 2 and 3 to form quasi-particles
having a mean particle size of 3∼6 mm as a sintering raw material. Then, the sintering
raw material is charged onto an continuous type sintering machine pallet 8 at a thickness
of 400∼800 mm from surge hoppers 4 and 5 disposed above the sintering machine through
a drum feeder 6 and a cutout chute 7 to form a bed 9 also called as a sintering bed.
Thereafter, carbonaceous material in a surface part of the bed is ignited by an ignition
furnace 10 disposed above the bed 9, while air above the bed is sucked downward through
wind boxes 11 located just beneath the pallet 8 to thereby combust the carbonaceous
material in the bed sequentially, and the sintering raw material is melted by combustion
heat generated at this time to obtain a sintered cake. The thus obtained sintered
cake is then crushed and granulated, and agglomerates of about not less than about
5 mm in size are collected as a product sintered ore and supplied into the blast furnace.
[0003] In the above production process, the carbonaceous material in the bed ignited by
the ignition furnace 10 is continuously combusted by air sucked from top down through
the bed to form a combustion melting zone having a certain width in a thickness direction
(hereinafter referred to as "combustion zone" simply). The molten portion of the combustion
zone obstructs the flow of the sucked air, which is a factor of causing an extension
of the sintering time to deteriorate the productivity. Also, the combustion zone is
gradually moved from the upper part to the lower part of the bed as the pallet 8 moves
downstream, and a sintered cake layer finishing the sintering reaction (hereinafter
referred to as "sintered layer" simply) is formed in a portion after the passing of
the combustion zone. Further, as the combustion zone is transferred from the upper
part to the lower part, moisture included in the sintering raw material is vaporized
by combustion heat of the carbonaceous material and condensed into the sintering raw
material in the lower part not yet raising the temperature to form a wet zone. When
the water concentration exceeds a certain degree, voids among the particles of the
sintering raw material as a path of the gas sucked are filled with water, which is
a factor of increasing airflow resistance like the melting zone.
[0004] FIG. 2 shows distributions of pressure drop and temperature in the bed when a combustion
zone moving in the bed of 600 mm in thickness is located at a position of about 400
mm above the pallet in the bed (200 mm below the surface of the bed). The pressure
drop distribution shows 60% in the wet zone and 40% in the combustion zone.
[0005] The production volume by the sintering machine (t/hr) is generally determined by
productivity (t/hr • m
2) × area of the sintering machine (m
2). That is, the production volume by the sintering machine is varied depending on
width and length of the sintering machine, thickness of a bed of the raw material,
bulk density of the sintering raw material, sintering (combustion) time, yield and
the like. In order to increase the production volume of the sintered ore, therefore,
it is considered that it is effective to shorten the sintering time by improving air
permeability of the bed (pressure drop) or to increase the yield by increasing the
cold strength of the sintered cake before crushing.
[0006] FIG. 3 shows a transition of temperature and time at a certain point in the bed at
high productivity and low productivity of the sintered ore, or at fast moving speed
and slow moving speed of the sintering machine pallet, respectively. The time kept
at a temperature of not lower than 1200°C starting the melting of sintering raw material
particles is represented by T
1 in case of the low productivity and T
2 in case of the high productivity, respectively. In case of the high productivity,
the moving speed of the pallet is fast, so that the high-temperature zone retention
time T
2 becomes short as compared with T
1 in case of the low productivity. However, as the time kept at a high temperature
of not lower than 1200°C is shortened, the sintering becomes insufficient, and hence
the cold strength of the sintered ore is decreased to lower the yield. Consequently,
in order to produce the high-strength sintered ore in a short time with a high yield
and a good productivity, it is required to take some measures for prolonging the time
kept at a high temperature of not lower than 1200°C to increase the cold strength
of the sintered ore.
[0007] FIG. 4 is a schematic view illustrating a process wherein the carbonaceous material
in the surface part of the bed ignited by the ignition furnace is continuously combusted
by the sucked air to form the combustion zone, which is moved from the upper part
to the lower part of the bed sequentially to form the sintered cake. Also, FIG. 5(a)
is a schematic view illustrating a temperature distribution when the combustion zone
is existent in each of an upper part, a middle part and a lower part of the bed within
a thick frame shown in FIG. 4. The strength of the sintered ore is affected by the
product of the temperature of not lower than 1200°C and the time kept at this temperature,
and as the value becomes larger, the strength of the sintered ore becomes higher.
Accordingly, the middle part and the lower part in the bed are pre-heated by combustion
heat of the carbonaceous material in the upper part of the bed carried with the sucked
air and thus kept at a high temperature for a long time, whereas the upper part of
the bed is lacking in the combustion heat due to no preheating and hence combustion
melting reaction required for sintering (sintering reaction) is liable to be insufficient.
As a result, the yield of the sintered ore in the widthwise section of the bed becomes
smaller at the upper part of the bed as shown in FIG. 5(b). Moreover, both widthwise
end portions of the pallet are supercooled due to heat dissipation from the side walls
of the pallet or a large amount of air passed, so that the high-temperature zone retention
time required for sintering cannot be secured sufficiently and the yield is also lowered.
[0008] As to these problems, it has hitherto been performed to increase the amount of the
carbonaceous material (coke breeze) added in the sintering raw material. However,
it is possible to raise the temperature in the sintered layer and prolong the time
kept at not lower than 1200°C by increasing the addition amount of coke as shown in
FIG. 6, while at the same time, the highest achieving temperature in the sintering
exceeds 1400°C and the decrease of the reducibility and cold strength of the sintered
ore is caused by the reason as described below.
[0009] In Table 1 of Non-patent Document 1 are shown tensile strength (cold strength) and
reducibility of various minerals generated in the sintered ore during the sintering.
In the sintering process, a melt starts to be generated at 1200°C to produce calcium
ferrite having the highest strength and a relatively high reducibility among constitutional
minerals of the sintered ore as shown in FIG. 7. This is the reason why the sintering
temperature is required to be not lower than 1200°C. However, when the temperature
is further raised and exceeds 1400°C, precisely 1380°C, calcium ferrite starts to
be decomposed into an amorphous silicate (calcium silicate) having the lowest cold
strength and reducibility and a secondary hematite of a skeleton-crystal form easily
causing reduction degradation. Also, the secondary hematite constituting a start point
of the reduction degradation of the sintered ore raises the temperature up to a zone
of Mag. ss + Liq. and is precipitated in the cooling as shown in a phase diagram of
FIG. 8 from the results of the mineral synthesis test, so that the production of the
sintered ore through a path (2) instead of a path (1) shown in the phase diagram is
considered to be important for suppressing the reduction degradation.
Table 1
Type of mineral |
Tensile strength (MPa) |
Reducibility (%) |
Hematite |
49 |
50 |
Magnetite |
58 |
22 |
Calcium ferrite |
102 |
35 |
Calcium silicate |
19 |
3 |
[0010] That is, Non-patent Document 1 discloses that the control of the highest achieving
temperature, the high-temperature zone retention time and the like during combustion
is a very important control item for ensuring a quality of the sintered ore and the
quality of the sintered ore is substantially determined depending on these controls.
Therefore, in order to obtain a sintered ore having a high strength and excellent
reduction degradation index (RDI) and reducibility, it is important that calcium ferrite
produced at a temperature of not lower than 1200°C is not decomposed into calcium
silicate and secondary hematite. To this end, it is necessary that the highest achieving
temperature in the bed during sintering does not exceed 1400°C, preferably 1380°C,
while the temperature in the bed is kept at not lower than 1200°C (solidus temperature
of calcium ferrite) for a long time. In the invention, the time kept in the temperature
range of not lower than 1200°C but not higher than 1400°C is hereinafter called as
"high-temperature zone retention time".
[0011] Moreover, there are proposed some techniques for improving the aforementioned deterioration
of the yield in the upper part of the bed to increase productivity. For example, Patent
Document 1 proposes a technique for improving the strength, productivity and yield
as a product of the sintered ore by adding pyro genie gas to air sucked into the sintering
raw material in addition to coke added in the sintering raw material and combusting
them at the sintering zone in the production of the sintered ore. In the technique
of Patent Document 1, however, there is a problem causing deterioration of reducibility
(RI) of a product sintered ore because it is attempted to improve the strength, productivity
and yield of the sintered ore by combusting coke and gaseous fuel to raise the highest
achieving temperature in the sintering.
[0012] Patent Document 2 proposes a technique wherein a mass flow rate of an oxygen-containing
gas supplied into the bed is set to 1.01∼2.6 times of a mass flow rate of an oxygen-containing
gas supplied in an area calcining the upper part of the bed at the time of sufficiently
calcining the upper part of the bed to thereby increase differential pressure in the
bed and violently accelerate the moving speed of the combustion melting zone, whereby
the productivity is increased and a product with a high yield and excellent quality
is obtained. In the technique of Patent Document 2, however, the thickness of the
bed and the moving speed of the pallet can be increased to improve the productivity
of the sintering machine, while the moving speed of the combustion melting zone and
the highest achieving temperature are also increased, so that there is a problem causing
the deterioration of the reducibility of the product sintered ore.
[0013] Patent Document 3 proposes an oxygen-enriching operation method wherein an oxygen
concentration in air sucked into the bed for combustion is enriched to not less than
35% during the sintering of the upper part of the bed on the pallet to increase the
productivity and the product yield. In the technique of Patent Document 3, however,
combustibility of coke is improved and the highest achieving temperature is increased
by enriching the oxygen concentration in combustion air to not less than 35%, while
there is a problem that the high-temperature zone retention time of not lower than
1200°C required for sintering is short by the improvement of the combustibility.
[0014] As a technique for solving the above problems, the inventors have proposed techniques
in Patent Documents 4∼6 and so on, wherein the amount of the carbonaceous material
added into the sintering raw material is decreased and various gaseous fuels diluted
to not more than the lower flammable limit are introduced into the bed from above
the pallet to combust the gaseous fuels in the bed at downstream side of the ignition
furnace of the sintering machine to thereby control both of the highest achieving
temperature and the high-temperature zone retention time in the bed to adequate ranges.
[0015] When the techniques of Patent Documents 4~6 are applied to decrease the amount of
the carbonaceous material added into the sintering raw material and introduce the
gaseous fuels diluted to not more than the lower flammable limit to combust the gaseous
fuels in the bed, the gaseous fuels are combusted in the bed (in the sintered layer)
after the combustion of the carbonaceous material as shown in FIG. 9, so that the
width of the combustion melting zone can be enlarged in the thickness direction without
exceeding the highest achieving temperature over 1400°C, and hence the high-temperature
zone retention time can be effectively extended.
PRIOR ART DOCUMENTS
PATENT DOCUMENTS
NON-PATENT DOCUMENT
SUMMARY OF THE INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0018] In the conventional techniques of Patent Document 4-6, however, it is not sufficiently
disclosed how long to keep the high-temperature zone of not lower than 1200°C but
not higher than 1400°C and which region to supply the diluted gaseous fuel in order
to produce the high-quality sintered ore having a high strength and an excellent reducibility.
[0019] Further, it should be noted in the techniques of Patent Documents 4-6 that air containing
21 vol% of oxygen as a combustible gas combusting the carbonaceous material or gaseous
fuel is used as it is in the determination of ranges of the highest achieving temperature
and the high-temperature zone retention time suitable for the sintering. Because,
the atmosphere in the bed during the actual sintering is supposed to be different
from atmospheric air due to the combustion reaction of the carbonaceous material or
gaseous fuel, and gaseous atmosphere in the bed is varied depending on the change
in the ingredient or composition of the combustible gas, and hence the highest achieving
temperature and the high-temperature retention time during the sintering are naturally
varied. Accordingly, it is necessary to change the operating conditions of the sintering
machine depending on the characteristics of the combustible gas. In the conventional
techniques, however, influences of the characteristics of the combustible gas, especially
the oxygen amount included in air upon the sinterability and the quality of the sintered
ore are not hardly studied.
[0020] Therefore, the inventors have revealed the high-temperature zone retention time required
for the sintering and determined an adequate region to be supplied with the gaseous
fuel and also studied the influence of the combustible gas upon the highest achieving
temperature and high-temperature zone retention time in the sintering, and consequently
developed a method for producing a sintered ore with a high strength and an excellent
reducibility by supplying the gaseous fuel to a region where the high-temperature
retention time in the sintering by combustion heat of the carbonaceous material is
less than 150 seconds to prolong the high-temperature zone retention time and enriching
the oxygen concentration in air to more than 21 vol% but less than 35 vol% in the
region supplied with the gaseous fuel, which is filed as Japanese patent application
No.
2011-058651.
[0021] In the technique proposed in Japanese patent application No.
2011-058651, oxygen is enriched by arranging an oxygen supplying pipe in a hood disposed above
the bed in the region supplied with the gaseous fuel and blowing oxygen into air.
However, it is not sufficiently disclosed how to supply oxygen in the hood in order
to prevent leakage to the outside and enrich oxygen efficiently and safely.
[0022] Also, since the oxygen supplying pipe is not especially limited, when a pipe made
of a rolled steel material for general structure (SS steel), for example, used as
general city gas piping is used as the oxygen supplying pipe, if an oxygen blowing
port (nozzle or opening port) of the oxygen supply pipe is ignited for some reason,
there is a fear that the pipe is burned out instantly by a high-purity oxygen flowing
in the pipe to cause serious operation troubles.
[0023] Patent Document 7 discloses an oxygen-gaseous fuel supply apparatus for a sintering
machine in accordance with the preamble of claim 1.
[0024] It is, therefore, an object of the invention to provide an oxygen-gaseous fuel supply
apparatus suitable for use in a sintering machine supplying a gaseous fuel and simultaneously
conducting a sintering operation for enriching oxygen and without a fear of burning
out by oxygen.
MEANS FOR SOLVING PEOBLEM
[0025] The inventors have made various studies for solving the above problems. As a result,
it has been found out that it is most preferable to arrange a plurality of baffle
plates in plural rows in the horizontal direction and in plural steps in the vertical
direction at intervals in a vertical mid position of the hood disposed in the apparatus
supplying the gaseous fuel and to arrange gaseous fuel supply pipes below the baffle
plates so as to supply the gaseous fuel, and also to arrange oxygen supply pipes above
the baffle plates to blow oxygen into air downwardly from the horizontal line, and
also that a portion with the risk of burnout is constituted with a pipe made of copper
alloy and/or Ni alloy in order to prevent the burnout of the oxygen supply pipe for
supplying oxygen to the sintering machine due to oxygen, and hence the invention has
been accomplished.
[0026] That is, the invention is an oxygen-gaseous fuel supply apparatus for a sintering
machine by blowing oxygen into air inside a hood disposed above a raw material bed
at a downstream side of an ignition furnace to enrich oxygen, and further sucking
air supplied with a gaseous fuel diluted to not more than a lower flammable limit
by wind boxes arranged below a pallet and introducing into the bed, and combusting
the gaseous fuel and carbonaceous material in the bed to produce a sintered ore, wherein
baffle plates each made of a chevron plate material are arranged in plural rows at
intervals in the horizontal direction and in plural steps in the vertical direction
so as to arrange the intervals in a zigzag form in a vertical mid position of the
hood, and gaseous fuel supply pipes for supplying the gaseous fuel into air are arranged
below the baffle plates, and oxygen supply pipes for supplying oxygen to blowing ports
for blowing oxygen into air are arranged above the baffle plates; characterised in
that the oxygen supply pipes and blowing ports are configured to blow oxygen of high
concentration of not less than the oxygen concentration in air from the blowing ports
at a high speed of not less than 10m/s and at least a portion of the oxygen supply
pipes are piping disposed in the hood and made of copper alloy and/or Ni alloy for
preventing burnout when oxygen is blown; wherein an oxygen supply main pipe is provided
with a flashback arrester disposed outside of the hood and in the vicinity of the
hood.
[0027] The oxygen-gaseous supply apparatus according to the invention is characterized in
that the oxygen supply pipes are arranged so as to set the blowing direction of oxygen
downwardly from the horizontal line.
[0028] Also, the oxygen-gaseous supply apparatus according to the invention is characterized
in that each of the oxygen supply pipe is arranged above an interval between the baffle
plates so as to direct the blowing direction of oxygen toward the interval between
the baffle plates.
[0029] Further, the oxygen-gaseous supply apparatus according to the invention is characterized
in that each of the oxygen supply pipe is arranged above a top of the baffle plate
so as to direct the blowing direction toward the interval between the baffle plates.
[0030] In addition, the oxygen-gaseous supply apparatus according to the invention is characterized
in that at least a portion of the oxygen supply pipes disposed in the hood is made
of a copper alloy containing not less than 60 mass% of copper and/or Ni alloy containing
not less than 60 mass% of Ni.
EFFECT OF THE INVENTION
[0031] According to the invention, it is possible to prevent burnout of the oxygen supply
pipe by oxygen and to enrich oxygen by supplying oxygen into air in the hood of the
gaseous fuel supply apparatus without leaking oxygen to the outside in the production
of the sintered ore by supplying the gaseous fuel with a downdraft type Dwight-Lloyd
sintering machine, so that a high-quality sintered ore as a raw material for a blast
furnace having a high strength and an excellent reducibility can be produced safely
and stably.
BRIEF DESCRIPTION OF DRAWINGS
[0032]
FIG. 1 is a schematic view illustrating a sintering process.
FIG. 2 is a graph showing a temperature distribution and a pressure drop distribution
in a sintered layer.
FIG. 3 is a view showing a temperature distribution in a bed at a high productivity
and a low productivity, respectively.
FIG. 4 is a schematic view illustrating a change inside a bed with the advance of
the sintering progress.
FIG. 5 is a view illustrating a temperature distribution when a combustion zone is
existent in each position of an upper part, a middle part and a lower part of a bed
and a yield distribution of a sintered ore in a widthwise section of the bed.
FIG. 6 is a view illustrating a temperature change in a bed in accordance with a change
(increase) in an amount of a carbonaceous material.
FIG. 7 is a view illustrating a sintering reaction.
FIG. 8 is a phase diagram illustrating a process of producing a secondary hematite
of a skeleton-crystal form.
FIG. 9 is a view illustrating a change of a temperature distribution in a sintered
layer by supplying a gaseous fuel.
FIG. 10 is a schematic view illustrating an example of the oxygen-gaseous fuel supply
apparatus for supplying gaseous fuel and oxygen.
FIG. 11 is a schematic view analyzing an influence of a blowing direction of oxygen
upon leakage of oxygen.
FIG. 12 is a view illustrating an embodiment of a method for supplying oxygen.
FIG. 13 is a view illustrating another embodiment of a method for supplying oxygen.
FIG. 14 is a view qualitatively showing an influence of a concentration and a flow
rate of oxygen upon burnout of an oxygen supply pipe.
FIG. 15 is a schematic view illustrating a piping system of an oxygen-gaseous fuel
supply apparatus for supplying gaseous fuel and oxygen.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
[0033] The method for producing a sintered ore by applying the technique of the invention
is the same as the techniques disclosed in Patent Documents 4~6 in a point that sintered
ore is produced by charging a sintering raw material containing fine iron ore and
carbonaceous material on a circularly-moving pallet with a downdraft type sintering
machine to form a bed, igniting the carbonaceous material on the surface of the bed
in an ignition furnace, sucking air containing gaseous fuel diluted to not more than
a lower flammable limit in a hood arranged above the bed in the downstream of the
ignition furnace with wind boxes arranged below the pallet to introduce in the bed,
and combusting the gaseous fuel and the carbonaceous material in the bed.
[0034] Accordingly, it is preferable that the gaseous fuel is supplied in a region that
the high-temperature zone retention time kept at not lower than 1200°C is insufficient
when sintering is conducted by combustion heat of the carbonaceous material and the
amount of carbonaceous material added in the sintering raw material is reduced depending
on the amount of the gaseous fuel supplied so as to prevent the highest achieving
temperature from exceeding 1400 °C.
[0035] As the gaseous fuel supplied in the bed can be preferably used, for example, a by-product
gas of an ironworks such as blast furnace gas (B gas), coke oven gas (C gas), a mixed
gas of blast furnace gas and coke oven gas (M gas) or the like, a flammable gas such
as LNG (natural gas), city gas, methane gas, ethane gas, propane gas or the like and
a mixture gas thereof. Moreover, unconventional natural gas (shale gas) collected
from a shale layer and different from the conventional natural gas can be used like
LNG.
[0036] The gaseous fuel supplied in the bed is preferable to be diluted to not more than
the lower flammable limit thereof. When the concentration of the diluted gaseous fuel
is higher than the lower flammable limit, it is combusted above the bed, so that there
is a fear of losing the supplying effect of the gaseous fuel or causing explosion.
On the other hand, when the concentration of the diluted gaseous fuel is high, it
is combusted in a low-temperature zone and hence there is a fear that the gaseous
fuel may not contribute to the extension of the high-temperature retention time effectively.
Therefore, the concentration of the diluted gaseous fuel is preferably not more than
3/4 of the lower flammable limit at room temperature in air, more preferably not more
than 1/5 of the lower flammable limit, further preferably not more than 1/10 of the
lower flammable limit. However, when the concentration of the diluted gaseous fuel
is less than 1/100 of the lower flammable limit, the heat generation amount by the
combustion is short and the effects of increasing the strength of sintered ore and
improving the yield cannot be obtained, so that the lower limit is set to be 1% of
the lower flammable limit. With regard to the natural gas (LNG), since the lower flammable
limit of LNG at room temperature is 4.8 vol%, the concentration of the diluted gaseous
fuel is preferably in a range of 0.05∼3.6 vol%, more preferably in a range of 0.05∼1.0
vol%, further preferably in a range of 0.05∼0.5 vol%.
[0037] The method for producing sintered ore by applying the technique of the invention
is characterized by supplying the gaseous fuel and enriching oxygen like that of Japanese
Patent Application No.
2011-058651. Because, a gaseous atmosphere in the sintering is shifted to an oxidation direction
by enriching oxygen to increase a ratio of calcium ferrite produced in the sintered
ore through sintering and decrease a ratio of calcium silicate formed, whereby a sintered
ore with a high strength and an excellent reducibility can be obtained, while not
only the sintering reaction can be increased to shorten the sintering time but also
the combustion position of the carbonaceous material in the gaseous fuel and the sintering
raw material can be moved to a lower temperature side to expand a base of temperature
distribution curve in the bed by simultaneously conducting the supply of the gaseous
fuel and the enrichment of oxygen, whereby the high-temperature zone retention time
can be extended, and hence the quality of the sintered ore can be improved while increasing
the productivity.
[0038] The effect by the enrichment of oxygen can be obtained even in small amounts when
the oxygen concentration included in air to be sucked in the bed is more than the
oxygen concentration in air (21 vol %), but oxygen is preferably enriched to not less
than 24.5 vol%. While, when the oxygen concentration in air is not less than 35 vol%,
the cost required for the oxygen enrichment exceeds the benefit obtained. Therefore,
it is preferable to add oxygen to be enriched so that the oxygen concentration in
air is set to a range of more than 21 vol% but less than 35 vol%. It is more preferably
a range of 24.5∼30 vol%, further preferably a range of 24.5∼28 vol%.
[0039] As a method (apparatus) for enriching oxygen as mentioned above, it is necessary
as shown in FIG. 10 that baffle plates are disposed in plural rows at intervals in
the horizontal direction and in plural steps in the vertical direction so as to arrange
the intervals in a zigzag form in the vertical mid portion of the hood arranged above
a raw material bed supplying a gaseous fuel, and gaseous fuel supply pipes for supplying
the gaseous fuel into air are disposed below the baffle plates, whereby raw gaseous
fuel is blown into air at a high speed causing a blow-out phenomenon to instantly
form a diluted gaseous fuel of not more than the lower flammable limit, or a gaseous
fuel diluted to not more than the lower flammable limit is blown into air to supply
the gaseous fuel into air, while oxygen supply pipes are disposed above the baffle
plates to blow oxygen into air for enrichment.
[0040] The reason why the gaseous fuel is supplied to the lower portions of the baffle plates
as described above is that since the gaseous fuel such as LNG or the like is generally
lighter than air, the leakage of the gaseous fuel from above the hood is prevented
by disposing the baffle plates or by throttling air blown downward between the intervals
of the baffle plates to increase the flow rate.
[0041] Also, the baffle plate is not especially limited as long as the gaseous fuel supplied
in the lower portion thereof is prevented from being leaked upward and air containing
oxygen enriched above can be smoothly flown downward. However, it is desirable that
plate materials formed into a chevron shape (mountain-like shape) are arranged in
plural rows at intervals in the horizontal direction and in plural steps so as to
render the intervals into a zigzag form (in a tournament form) or a labyrinth form
in the vertical direction as shown in FIG. 10. As to the specification of the baffle
plate, for example, when a sintering machine has a machine width of 6 m, it is desirable
that the width of the baffle plate is approximately 200∼500 mm, and the interval between
the baffle plates is approximately 50∼200 mm in the horizontal direction and approximately
50∼200 mm in the vertical direction, and the number of steps is approximately 2~5.
Moreover, it is preferable to arrange the baffle plates so as to render pressure drop
in the opening port into approximately not more than 10 mmAq from a viewpoint of preventing
the leakage of the gaseous fuel above the hood.
[0042] In FIG. 10 is illustrated an example of blowing the gaseous fuel from the gaseous
fuel supply pipes in the horizontal direction. However, the blowing direction is not
particularly limited and may be horizontal or downward as long as the gaseous fuel
is uniformly mixed with air and diluted to not more than the lower flammable limit
before introduction into the bed.
[0043] The reason why oxygen is blown above the baffle plates is that since a specific gravity
of oxygen is higher than that of air, a ratio of leaking outside of the hood is low,
or if leakage is caused, oxygen has no danger like the gaseous fuel, and since oxygen
blown from the supply pipes is uniformly diluted to a target concentration while passing
through the interval between the baffle plates and then mixed with the gaseous fuel,
direct contact between oxygen of high concentration and the gaseous fuel can be prevented.
[0044] Moreover, oxygen supplied from the supply pipes is not necessarily pure oxygen. However,
the amount of oxygen supplied is extraordinarily large as compared to the gaseous
fuel, so that it is not preferable that the oxygen concentration is decreased since
the amount of oxygen blown from the pipes is increased.
[0045] As the direction of blowing oxygen from the oxygen supply pipes, however, the downward
direction is preferable as compared to the horizontal line from a viewpoint of preventing
the leakage of oxygen outside of the hood. In FIG. 11 are shown simulation results
of an amount of oxygen leaked outside of the hood through a cross wind of 10 m/s between
the horizontal direction and the downward direction of blowing oxygen when oxygen
is blown from the oxygen supply pipes into air above the baffle plates in the hood
to concentrate the oxygen concentration from 21 vol% to 27 vol%. As seen from this
figure, when oxygen is blown in the horizontal direction, there is a tendency of easily
causing leakage of oxygen.
[0046] When the direction of blowing oxygen from the oxygen supply pipes is downward, the
oxygen supply pipes may be arranged above the interval between the baffle plates to
blow oxygen toward the interval between the baffle plates as shown in FIG. 12. In
this oxygen blowing method, since oxygen jet is directly blown between the baffle
plates, there is a merit that oxygen can be sucked smoothly to suppress the leakage
upward.
[0047] Alternatively, the oxygen supply pipes may be arranged above the tops of the baffle
plates to blow oxygen toward the interval (spacing part) between the baffle plates
as shown in FIG. 1 3. In this oxygen blowing method, since oxygen can be supplied
from one oxygen supply pipe toward two intervals, there is a merit of decreasing the
number of the oxygen supply pipes depending on conditions.
[0048] Next, there will be explained prevention from burnout of the oxygen supply pipe in
the gaseous fuel supply apparatus through oxygen.
[0049] As mentioned above, in the oxygen-gaseous fuel supply apparatus shown in FIG. 10,
one or more rows of baffle plates are arranged at intervals in a vertical mid portion
of the hood arranged above the bed in the region supplied with the gaseous fuel, and
the gaseous fuel supply pipes are arranged below the baffle plates to blow raw gaseous
fuel at a high speed causing a blow-out phenomenon to thereby instantly dilute the
gaseous fuel to not more than the lower flammable limit, while oxygen supply pipes
are arranged above the baffle plates to supply oxygen toward the baffle plates. This
apparatus is designed so that the direct contact between oxygen of high concentration
and the gaseous fuel can be prevented since oxygen supplied from the oxygen supply
pipes is uniformly diluted to a target concentration to be enriched while passing
through the intervals between the baffle plates and joined with the gaseous fuel.
Moreover, oxygen supplied from the pipes may not be pure oxygen.
[0050] Since gaseous fuel such as LNG or the like is lighter than air, the baffle plates
arranged above the gaseous fuel supply pipes prevent the gaseous fuel from being leaked
and lost above the hood. Moreover, oxygen is higher in the specific gravity as compared
to the gaseous fuel, so that a fear of diffusing oxygen out of the hood is slight
unless a strong wind blows.
[0051] In a worrying point of the oxygen enriching apparatus, however, a fire source is
always existent because the sintering raw material is sintered by combustion heat
generated in combustion of coke and gaseous fuel in the sintering machine. Therefore,
when the oxygen supply pipe is made of, for example, a rolled steel material for general
structure (SS steel) or the like usually used as city gas piping, even if non-oil
treatment is applied, there is a fear that if an oxygen blowing port of the oxygen
supplying pipe (nozzle or opening port) is ignited for some reason, the oxygen supply
pipe is burnt out instantly up to a valve stand by reaction heat of iron and oxygen.
[0052] Since the gaseous fuel supplied from the gaseous fuel supply pipes is blown at a
high speed causing a blow-out phenomenon, ignition can be prevented. Even if ignited,
combustion is caused only at the ignited portion and hence the pipes themselves are
never burnt out. Also, the amount of oxygen supplied is large as compared with the
gaseous fuel, so that oxygen of high concentration is blown from a large blowing port
at a high speed of not less than 10 m/s. However, as the oxygen concentration becomes
higher and the flow rate becomes faster, the burnout through oxygen is easily caused
as shown in FIG. 14, so that it is important to take measures for the burnout of the
pipes.
[0053] In the invention, therefore, in order to prevent the burnout of the oxygen supply
pipes as described above, at least a fire-source existing portion of the oxygen supply
pipe arranged in the hood (header, branch pipe, nozzle or the like) is a piping made
of copper alloy and/or Ni alloy. Since the copper alloy or Ni alloy is small in the
ionization tendency as compared with iron, rust as an ignition source is hardly formed
in the pipe, while these alloys form a dense oxide film hardly passing oxygen on their
surfaces and hence further oxidation is suppressed and the burnout is hardly caused.
[0054] From the above viewpoints, the copper alloy is preferable to contain not less than
60 mass% of Cu and includes, for example, Cu-Zn alloy (brass) containing 60∼70% of
Cu, Cu-Ni alloy (white copper, cupronickel) containing 70∼90% of Cu, Cu-Sn alloy (bronze)
containing 65∼98% of Cu, Cunife of Cu: 60 mass%-Ni: 20 mass%-Fe: 20 mass%, Be copper
containing approximately 2 mass% of Be and so on. Also, the Ni alloy is preferable
to contain not less than 60 mass% of Ni, and includes, for example, Inconel, Monel,
nichrome and so on. Among them, copper and pure Ni are more preferable because they
are excellent in the oxidation resistance. In Table 2 are shown oxidation resistances
of various alloys in a high-temperature oxidizing atmosphere of not lower than 500°C
for reference.
Table 2
Alloy |
Chemical composition (mass %) |
Evaluation of oxidation resistance* |
Cu |
Ni |
Fe |
Others |
Pure Ni |
- |
100 |
- |
- |
⊚ |
Pure Cu |
100 |
- |
- |
- |
⊚ |
Monel |
34 |
63 |
- |
Fe, Mn and the like: 3 |
⊚ |
Be copper |
98 |
- |
- |
Be: 2 |
|
Cupronickel (white copper) |
70-90 |
10-30 |
- |
- |
⊚ |
Cunife |
60 |
20 |
20 |
- |
○ |
Brass |
60-70 |
- |
- |
Zn: 30-40 |
○ |
Inconel |
- |
72 |
13 |
Cr: 15 |
○ |
Nichrome |
|
80 |
- |
Cr: 20 |
○ |
Hastelloy B-2 |
- |
69 |
1 |
Mo and the like: 30 |
○ |
Hastelloy C22 |
- |
56 |
3 |
Cr, Mo and the like: 41 |
Δ |
Bronze |
65-98 |
- |
- |
Sn: 2-35 |
Δ |
SUS304 |
- |
8 |
74 |
Cr: 18 |
Δ |
Carbon steel |
- |
- |
99 |
Mn and the like: 1 |
× |
Al alloy |
- |
- |
- |
Al and the like: 100 |
× |
Mg alloy |
- |
- |
- |
Mg and the like: 100 |
× |
* Evaluation of oxidation resistance; ⊚ : Very stable
○: Stable (Usable)
Δ: Oxidation depending on condition
×: Ignition possible |
[0055] FIG. 15 is a schematic view illustrating the supply piping system of the gaseous
fuel and oxygen in the gaseous fuel supply apparatus of FIG. 10. For example, when
oxygen is referred, it is shown that oxygen is supplied to a header through an oxygen
supply main pipe and further supplied to a plurality of branch pipes attached to the
header and blown from plural nozzles attached to the branch pipe or plural opening
ports arranged therein. In the invention, all the oxygen supply pipes are not necessarily
made of copper alloy or Ni alloy, whereas it is necessary that at least a part of
the pipe close to the fire source in the hood (branch pipe, nozzle or the like) is
made of copper alloy or Ni alloy. In order to more enhance the safety, both the header
and the oxygen supply main pipes are preferable to be made of copper alloy or Ni alloy.
[0056] Further, it is preferable that a flashback arrester (flame arrester) is arranged
on the oxygen supply main pipe at a position outside of the hood but in the vicinity
of the hood. It is thereby possible to further enhance the safety. The flashback arrester
is not particularly limited, but a backfire valve, a dry type safety device or the
like can be preferably used. In this case, it is preferable that the portion from
the flashback arrester to the header is made of copper alloy or Ni alloy.
[0057] As the oxygen supply pipe located in the upstream side from the flashback arrester
can be used an usual steel pipe, but it is preferable to use one made of SUS and subjected
to the non-oil treatment
INDUSTRIAL APPLICABILITY
[0058] The technique of the invention is usable not only for steel-making, particularly
a method of producing sintered ore used as a raw material for blast furnace, but also
can be used as an agglomeration method of other ores.
DESCRIPTION OF REFERENCE SYMBOLS
[0059]
- 1 :
- hopper for raw material
- 2:
- drum mixer
- 3:
- rotary kiln
- 4,5:
- surge hopper
- 6:
- drum feeder
- 7:
- cutout chute
- 8:
- pallet
- 9:
- bed
- 10:
- ignition furnace
- 11:
- wind box
- 12:
- cut-off plate