JPS589939A - Method and plant for baking green pellet of metal ore - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for processing ore. In particular, the present invention relates to a method of calcining pellets of ores, such as iron ore, to solidify the pellets.

Iron ore pellets are widely used as a charge in blast furnaces and direct reduction plants to make iron and steel.

The seven advantages of using iron ore pellets in iron and steel manufacturing processes are that they upgrade otherwise unusable low-grade iron ore to a high grade, making it acceptable as a charge material, and that it It is possible to use minute particles of iron ore, which cannot be directly charged, as a raw material for making green pellets.

That's true.

Typically, green iron ore pellets contain both magnetite and hematite. Typically, the initial stage of the pelletizing process is to form spheres of iron ore with a diameter of 1 to 6 cm. Because iron ore is typically moist, a binder such as bentonite is typically used to impart strength to the green pellets before being calcined.

Other additives that may be included within the pellets are solid fuels such as coke, coal, or charcoal, which act as a heat source during pellet firing. The pellets are then preheated, calcined in an atmosphere containing excess oxygen, and cooled. During preheating and calcination, at least some of the magnetite and other low oxide irons are oxidized to hematite. This reaction, as well as the accompanying heat release, recrystallizes the hematite and causes grain growth. The result is strong, hard iron oxide pellets that are resistant to crushing during hendling prior to use in iron or steel manufacturing processes. There are many known methods for preheating, calcining, and cooling iron ore pellets. One of the well-known methods is the grate kiln method.

In this method, the green pellets are fed onto a moving chain rack, where they are first dried at about 3QO°C, and then heated to about 1000°C in a preheating device using hot exhaust gas from the kiln or pellet cooler. The preheated pellets are then sent to a kiln where they are calcined to about 1340°C and discharged to an air inlet cooler.

The cooler is typically one-stage or two-stage. The air used to cool the pellets is used as a secondary air source to the burners used to fire the pellets in the kiln. (Typically, the kiln is a rotary kiln.) The burner may be fueled with oil or gas, or a mixture of both. Alternatively, finely divided solid fuels (such as pulverized coal) may be used as fuel.

The pellets are then sent to a cooler, typically of the rotary type. The cooler may be of the one-stage or two-stage type as described above.

Preheating is necessary to give the pellets sufficient strength to transport them to the kiln. Typically, a relatively shallow layer of green pellets is used on the moving grate. For example, the layer ranges in depth from 150 to 200 mm. Utilizing such a layer, drying can generally be carried out by downward blowing and cycling. However, upward blow drying, which is particularly sensitive to heat, may be used in addition.

The gas flow through the three elements (kinetic grate, rotary kiln, and rotary cooler) in a grate-type kiln plant is unified. Typically, cold air is supplied to the cooler, where a portion of it is heated to between 1000 and 11
heated to 00°C. Also, fuel and primary air are supplied to the burner to obtain the temperatures of 1250 to 1650° C. required for firing the pellets. Gas is 90
It leaves the kiln at 0 to 1100°C and is sent directly to the preheating section of the plant. Typically, the gas is forced through the pellet bed by a fan and then sent to a dust collector. Typically, the cleaned gas is sent to a drying section, optionally cooled, and finally exhausted to the atmosphere. Various types of gas treatment equipment can be employed. For example, in a dry area,
Gas can be recovered from the cooler for reuse.

In order to completely oxidize the magnetite, excess air is fed to the kiln along with secondary air so that the excess oxygen content is 20% of the process gas content. Thus, despite using hot gas from the kiln to preheat and dry the green pellets, a large amount of heat is lost. It has previously been believed that a relatively large amount of excess air needs to be supplied to facilitate the oxidation of magnetite to hematite. If the pellets contain a significant proportion of unoxidized magnetite, they are relatively difficult to reduce in a blast furnace or in a direct reduction process. However, under normal operations, up to 40% of the magnetite may remain unoxidized upon exiting the kiln. therefore,
The oxidation continues in the cooler and some of the released heat is given to the secondary air Kjl, but most of the energy gained by oxidizing the magnetite is lost. Since the oxidation of magnetite stops at about 800° C., the oxidation of magnetite tends to be incomplete. Additionally, any oxidation in the cooler absorbs oxygen from the secondary air, which enters the kiln relatively nitrogen-rich. This urine kill reduces the excess oxygen, so additional air must be supplied to maintain the required excess oxygen level. This results in higher fuel consumption without increasing production.

In order to eliminate oxidation of the pellets in the cooler, British Patent Publication No. 1,527.070 discloses that during drying and preheating the pellets are oxidized by directing at least one downward flow of oxygen to the pellets on the grate. He proposes a method that completely oxidizes the fuel before it enters the cooler. However, the inventor has disclosed that the British patent publication no.
, No. 070 may cause excessive grain growth within the pellet. If the magnetite oxidizes too quickly, and if the oxidation continues rapidly, the heat from the oxidation will heat the pellets before they enter the kiln, and the pellets will not be maintained at this high temperature during firing in the kiln. Otherwise, the temperature will increase further and the excessive grain growth described above will occur.

The fewer grains and the greater the hematite grain growth, the greater the strength of the pellet.

However, if the pellets are too strong, they will not be crushed at the required points in the blast furnace or direct reduction plant, slowing down the reduction rate in the blast furnace or direct reduction plant, and reducing the efficiency of the blast furnace or direct reduction plant. Put it away.

British Patent Publication No. 1.52' Otsu 070 briefly discusses the possibility of enriching the combustion gas and air with oxygen in grate kiln furnaces. This method is not recommended in British Patent Publication No. 1,527,070. Conversely, the amount of gas circulating in a pelletizing plant is so large that increasing the oxygen concentration significantly would require an uneconomical amount of oxygen, and a large portion of the additional oxygen would be wasted. It is being

The grate kiln method is just one known method for pelletizing iron ore. Other known methods include straight grate methods, circular grate methods, and circular kiln methods. What all those methods have in common is that they involve drying, preheating, calcining and cooling the pellets.

The purpose of the present invention is to improve the efficiency of pellets by utilizing the fuel used to create the calcination temperature.
Typically, a method is provided for sintering iron ore pellets.

According to the invention, the pellets are sequentially dried and preheated;
passing the green pellets at a selected rate through a calcined and (turf) cooled plant, preheating the pellets in an oxygen-containing atmosphere to a temperature at which oxidation of the less oxidized metal portions begins; The pellets are fired in an oxygen-containing atmosphere and the pellets exit the turf by at least one fuel burner supplied with air to support combustion of the fuel and provide oxygen in the firing atmosphere. The burner and atmosphere are supplied with air at an insufficient flow rate to sufficiently oxidize the less oxidized portions, and the additional oxygen required to achieve sufficient oxidation is commercially pure oxygen, or a method for firing green pellets of iron ore containing low oxidation metals oxidizable up to high oxidation of the metal, characterized in that the fuel burner, or one or more fuel burners, is fed from a source of oxygen-enriched air. provided.

The method according to the invention is particularly suitable for the calcination of green pellets consisting of a mixture of hematite and magnetite.

Typically, green pellets contain up to 40% magnetite by weight, with most of the remainder being hematite, moisture, and
It is a caking agent. Preferably, the pellets contain from 30% to 40% magnetite by weight.

Generally, even if a small amount of residual magnetite in hematite is tolerated, oxidation is insufficient unless substantially all of the magnetite is converted to hematite.

The process according to the invention is particularly suitable to be carried out in plants with conventional grate kilns. However, it may also be implemented in other types of plants for pelletizing iron ore.

The above-mentioned or other plants for burning green pellets can be easily adapted to carry out the method according to the invention. Typically, such plants can be operated with a 20% excess oxygen supply to the firing atmosphere. The source of oxygen is normally air. Commercial oxygen or oxygen-rich Oxygen may be enriched with oxidized air. Air contains about 20% oxygen by volume, so
The amount of commercially pure oxygen required to replenish the firing atmosphere is on the order of one fifth of the reduction in the amount of air fed to the combustion atmosphere and/or burner. Therefore, the amount of gas flowing through the kiln in a grate kiln plant can be significantly reduced, thereby making it possible to reduce the flow rate of combustion fuel without loss of kiln temperature. Additionally, the oxygen-enriched air, or commercially available additional flow rate of oxygen, may be selected to ensure that substantially complete oxidation of magnetite to hematite occurs in the kiln. This can be achieved without the need to enrich the preheated atmosphere with oxygen, as described in British Patent Publication No. 1.
527.070 eliminates the problem of premature oxidation of magnetite that may occur.

One advantage of maximizing the amount of oxidation of low oxidants occurring in the kiln or firing section is that the amount of oxidation in the turf is reduced. Since oxidation is an exothermic reaction, fuel requirements in the kiln or firing section are concomitantly reduced.

In addition to or in lieu of the savings in fuel, the method according to the invention, when applied to an existing conventional grate kiln plant, can increase the rate of transport of pellets through the plant. For example, the amount of air supplied to the burner and/or kiln atmosphere can be reduced by a selected amount, and this reduction (with respect to the rate of supply of molecular oxygen) increases the rate of supply of molecular oxygen to the firing atmosphere. The reduction in oxygen is compensated for by supplying commercially available pure oxygen or oxygen-enriched air to the firing atmosphere. This increase can be used to oxidize more magnetite to hematite. Therefore, the velocity of pellets passing through the plant can be increased without any significant increase in fuel consumption.

There are many locations where commercially pure oxygen or oxygen-enriched air can be introduced into the plant. In grate kiln plants, commercially pure oxygen or oxygen-enriched air is preferably added to the cooler atmosphere, which is then passed through the kiln. If the cooler is two stage, commercially pure oxygen or oxygen enriched air is added to the first stage of the cooler. If the pellets contain some unoxidized magnetite as they enter the cooler, the amount of oxygen supplied to the cooler can be selected to complete the acidification of the magnetite and hematite. For example, in a rectangular configuration using straight or circular grates, oxygen-enriched air, or commercially pure oxygen, may be placed in the cooler itself or in the immediate vicinity of the cooler and firing section. It can be added to the air supplied upstream of the cooler.

In a grate kiln plant, commercially pure oxygen or oxygen-enriched air may alternatively or additionally be supplied to the air passing from the cooler to the firing section in close proximity to the cooler and the firing section. may be added to
Another additional or alternative location for adding commercially pure oxygen or oxygen-enriched air is in the piping supplying the primary air to the kill/burner. Additionally, another alternative or additional location for adding oxygen is to the burner flame in firing section IIIK, where commercially pure oxygen or oxygen-enriched air is supplied from a lance below the flame. Passed directly into the flames.

It is generally preferred to use commercially pure oxygen rather than oxygen-enriched air in the process according to the invention. The reason for this is that the oxygen-enriched air contains nitrogen which merely increases the amount of gas in the plant to be heated without obtaining any useful oxidizing effect. however,
In some cases, particularly inexpensive sources of oxygen-enriched air are available, and the cost may outweigh this nitrogen-containing disadvantage compared to commercially pure oxygen.

The invention also includes within its scope pellets calcined by the method according to the invention.

The invention will now be described by way of example with reference to the accompanying drawing, which schematically shows a grate kiln type plant for calcining green pellets of iron ore.

It will be appreciated that other than the piping that adds commercially pure oxygen to the first stage of the cooler, the plant shown in the figure is quite conventional.

The plant shown in FIG. 1 includes a first stage dryer Wt4, a second stage dryer 6 and a kinetic grate 2 operable to send green pellets through a preheater 8, a dryer 4,6, and a preheater 8. are arranged in series with respect to each other and have a common device for supplying high temperature gas to them. The hot gas exchanges heat with the pellets, drying and preheating them.

The grate 2 is typically sufficient to support the pellets, but may take the form of a kinematic chain that allows hot air to pass through the grate. Preheating device 8
A shoe) 10 is attached to the outlet end of the tube. At the bottom of the chute there is a burner 14 that burns coaxially to the lower end of the kiln.
There is an upper inlet end of the kiln 12 with a. The burner 14 is supplied with primary air via a pipe 16 and with gaseous or liquid fuel via a pipe 18. Below the outlet end of the rotary kiln 12 are a first stage 22 and a second stage 2.
An annular rotary cooler having 4 is provided.

One or more fans 26 supply ambient temperature air to the cooler through the cooler floor. The first stage 22 of the cooler 20 communicates with the outlet end of the rotary kiln 22, thereby
Secondary air for combustion of fuel supplied to the burner 14 is supplied.

The first stage 22 of the cooler 20 has piping for supplying air thereto, and the second stage 24 has piping 2 for supplying air thereto.
It has 8. Commercial source of pure oxygen (not shown)
A pipe 32 connected to the fan 26 terminates in a pipe 30 downstream of the fan 26 .

This source may be a cryogenic plant for separating air. Such plants are well known.

Oxygen sent to the first cooling stage 22 of the cooler 20 contacts the pellets being cooled in the cooler 20 and passes through the first stage cooler 2 while directing air to the kill/12 via piping 26.
Leave 2. Hot combustion gases from kiln 12 are routed to fan 3 via piping 38 terminating at the top of preheater 80.
It is attracted by 6. In this way, the combustion gases flow downwardly through the pellets on the moving grate of the preheater 8. In this way, high-temperature gas
- Perform preheating by feeding the pellets.

The hot gas then exits the preheating device 8 via pipe 40 and is drawn into the top of the second stage drying device 6. The gas is directed downwardly through the dryer 6 and imparts heat to the pellets passing through the dryer. The resulting waste gas exits the bottom of the drying device 6 and is led to a chimney (not shown).

Heating in the first stage dryer 4Vc is provided by taking air exiting the second stage 24t of the cooler 2°, heating the air in a heating device 46, and directing the heated air through the bottom of the dryer 4. Ru. The hot air flows upwardly over the moving pellets through the dryer 4 and into the pipe 48.
The air is discharged from the top of the drying device 4 to a chimney (not shown) through a pipe.

It is recognized that there are many other alternative arrangements for drying and preheating the pellets.

In typical normal operation of the illustrated plant, without adding any commercially pure oxygen to the first stage 22 of the cooler 2o via the inlet 30, the superposition ratio is typically 60 to 4.
0% magnetite and 0.7% be/tonite by weight,
It contains 8.0% water by weight, the remainder being hematite, and is typically 12.7 mm (0.5 inch) to 25 mm in diameter.
．． A 4mm (1 innote) grease pellet is fed onto the moving gray plate, with a depth of 150 to 200 mm.
Provides a layer of MiJ. The pellets are dried in the first stage drying device 4.
It is heated to about 600° C. when leaving the second stage drying device, to about 700° C. when leaving the second stage drying device, and to 1000° C. when leaving the preheating device. The atmosphere leaving the kiln and entering the preheater contains oxygen. The reaction between magnetite and oxygen is approximately 800
℃, some grain growth occurs in the preheating device 8, but this is due to the fact that the pellets are transferred from the grate to the chute 1.
This is sufficient to provide the pellets with sufficient mechanical strength to withstand any impact that occurs during transport to the rotary kiln 12.

The amount of air supplied to the burner 14 via the first stage 22 of the cooler 20 and the line 16 is selected to provide 20% more molecular oxygen than is required for complete stoichiometric combustion of the fuel. Ru. Typically, the pellet is 1340°
It exits the rotary kill 712 at C (or other temperature range from 1250 to 1650 C) and falls into a rotary cooler where a 500 to 700 mm hot layer is maintained.

At least a portion of the amount of unoxidized magnetite ore entering the first stage 22 of the cooler 20 is oxidized by the cooling air supplied to said first stage. Air exiting the first stage 22 of the cooler 20 is routed to the rotary kill/kill to provide secondary air for the burner 14 as previously described. Air exiting the second stage cooler is supplied to the first stage dryer 4 as described above.

Typically, the pellets are cooled to a temperature in the range of 200 to 300°C and then transferred from the second stage of cooler 20 to the blast furnace.
Or sent directly to a reduction plant.

A typical example of operation of the method according to the invention in the aforementioned plant saves fuel and kills/12
Burner 14 in order to completely oxidize the magnetite within itself.
The flow rate at which air is sent through the piping 16 to the fan 26
The combined flow rate with which air is delivered to the first stage 22 of the recooler 20 is reduced by, for example, 15%, while commercially pure oxygen is pumped through the inlet 30 into the combined flow rate before said reduction takes place. It is added at a flow rate of 6 to 4% of the flow rate.

Therefore, the gas flowing out from the kiln 12 to the preheating device 8 is reduced by about 10%. In this way, rotary kiln,
There is less heating gas at the kiln, and the fuel supply flow rate to the kiln can be reduced.

The fuel supplied to the burner 14 may be liquid or gaseous. If gaseous fuel is supplied, it typically provides a long, "slow" flame, in which case the pellets must achieve the desired temperature of approximately 1640°C unless the fuel is supplied at a relatively high flow rate. I tend not to. First stage 22 of cooler 20
By adding oxygen to the secondary air passing from the kiln 12 to the kiln 12, the flame length can be shortened to achieve the desired pellet temperature without the use of extra fuel. In other words, adding commercially pure oxygen or oxygen-enriched air to the secondary air can shorten the flame length, resulting in greater fuel savings when relatively long flames are used in rotary kilns. There is huge potential.

[Brief explanation of the drawing]

The figure is a schematic diagram of a great kiln type plant that burns green iron ore pellets. In the figure, 2...Grate, 4...First stage drying device, 6...
Second stage drying device, 8... Preheating device, °12... Kiln, 14... Burner, 16.18... Piping, 20.
...Cooler, 22...First stage cooler, 24...First stage cooler, 2 too...Fan, 28,30.32...
Piping, 36... Fan, 38.40... Piping, 46
...Representative for heating device: 4 persons, Akira Asamura, procedural amendment (method), Showa tag, June 19, 2016, Mr. Commissioner of the Japan Patent Office, 1, case indication, Showa S year patent application No. b, a'ybh-No. 3. , Relationship with the case of the person making the amendment Patent applicant 4, Agent 5, Date of amendment order July 2q, 1985 6, Number of inventions increased by amendment 7, Subject of amendment

Claims (1)

Claims: 1) oxidizable to a high degree of oxidation, comprising passing the green pellets at a selected rate through a plant where the pellets are sequentially dried, preheated, calcined, and cooled (in a cooler); A method for firing green pellets of metals containing low oxidation metals, in which the pellets are preheated in an oxygen-containing atmosphere to a temperature at which oxidation of the low oxidation portions begins, supporting combustion of the fuel and providing oxygen to the firing atmosphere. The pellets are fired in an oxygen-containing atmosphere by at least one burner supplied with air to oxidize the pellets, each at a flow rate insufficient to fully oxidize the low oxidation fraction until the pellets leave the cooler. Air is supplied to the burner and atmosphere, and the additional oxygen required to provide sufficient oxidation is supplied to the fuel burner from a commercial pure oxygen or oxygen-enriched air source.
Alternatively, a method for calcination of green pellets of metal ore, characterized in that green pellets of metal ore are fed to one or more fuel burners or to a calcination atmosphere. 2. Scope of Claims A method for firing green metal ore, characterized in that the green pellets contain a mixture of magnetite and hematite. 6) Scope of Claims A method according to claim 2, characterized in that the pellets contain 60 to 40% by weight of magnetite. 4) A method for firing green pellets of metal ore, characterized in that all magnetite is converted to hematite in the method according to claim 2 or 6. 5) A method for firing green pellets of metal ore, characterized in that the method according to any one of claims 1 to 4□ is carried out in a great kiln type plant. 6) A method according to claim 5, characterized in that commercially pure oxygen or oxygen-enriched air is added to the atmosphere in the cooler, which atmosphere then passes through the kiln. How to fire IJ+v+n pellets. 7) In the method according to claim 6,
A method for firing green pellets of metal ore, characterized in that the rinsing is in two stages, and commercially pure oxygen or oxygen-enriched air is added to the first stage of the cooler. 8) Any one of claims 1 to 4
When carried out in a plant using straight or circular grates, commercially pure oxygen or oxygen-enriched air is supplied to the silica. Features of green pellets of metal ore) 1- Method of firing. 9) A method of firing green pellets of metal ore as generally described with reference to the accompanying drawings. 10) Green pellets 6 of metal ore calcined by the method set forth in any one of claims 1 to 9. 11) Green pellets 6 of metal ore calcined by the method set forth in any one of claims 1 to 9. A plant for burning green pellets of metal ores, characterized in that it has equipment for supplying commercially pure oxygen, or oxygen-enriched air, in order to be able to carry out the described method.