EP1154825A1

EP1154825A1 - Method for optimising the operation of a tank furnace

Info

Publication number: EP1154825A1
Application number: EP99964668A
Authority: EP
Inventors: Jean-Luc Roth; Marc Solvi
Original assignee: Paul Wurth SA
Current assignee: Paul Wurth SA
Priority date: 1998-12-23
Filing date: 1999-12-23
Publication date: 2001-11-21
Anticipated expiration: 2019-12-23
Also published as: DE69912003D1; LU90333B1; DE69912003T2; TW473546B; AU3043200A; WO2000038496A2; WO2000038496A3; ATE251487T1; EP1154825B1

Abstract

The invention concerns a method for optimising the operation of a tank furnace comprising nozzles which consists in making fine particles of prereduced ore. The fine particles of prereduced ore are mixed with a solid carbon reducing agent, the fine prereduced ore particles having a size distribution less than 2 mm and the solid carbon reducing agent having a size distribution less than 200 mu m. The mixture is injected hot through the nozzles into the tank furnace, wherein the fusion of the prereduced ore particles takes place.

Description

Method for optimizing the operation of a shaft furnace

The invention relates to a method for optimizing the operation of a shaft furnace.

Bowls have long been used for the production of pig iron and over the years have been modified and improved to increase their productivity. As a result, a certain number of factories are at the limit of the production capacity of their shaft furnaces, in particular because the limit of the load of the wind blowers is reached.

One way to increase productivity in spite of this is to place part of the iron ore in the form of pre-reduced iron (DRI) at the level of the jaw. The disadvantages of this solution are a high processing cost, and the obligation to put the DRI in the form of balls or briquettes.

Another solution is to use the crucible from the shaft furnace as a “smelter”, by injecting DRI fines into the nozzles. However, it is necessary to take into account the additional thermal requirement generated by this injection, and take care not to block the nozzle cavity. It is thus possible to increase the production of cast iron from the shaft furnace, however the parameters of the shaft furnace must be modified appreciably.

The document DE 312 935 C describes the introduction of pre-reduced iron ore finely divided, by the nozzles into the crucible of the blast furnace. In order to separate the gangue, lime is either mixed in advance with the prereduced, or added to the nozzles. Finally, finely ground carbon can be added to the hot wind in the nozzles. The injection of pre-reduced iron ore by the nozzles with coal seems advantageous to provide part of the heat necessary for the fusion of the pre-reduced. However, the application of the measures described in document DE 312 935 C results in blockage of the nozzle cavities, and a lowering of the temperature of the molten metal in the crucible of the blast furnace.

It would be advantageous to have a method for increasing the production of pig iron in a shaft furnace. The object of the present invention is to provide a method for optimizing the operation of a shaft furnace.

According to the invention, this objective is achieved by a process for optimizing the operation of a shaft furnace comprising nozzles comprising the following steps: a) manufacture of fine particles of pre-reduced iron; b) mixing the fine particles of pre-reduced iron with a solid carbonaceous reducing agent, the fine particles of pre-reduced iron preferably having a particle size less than 2 mm and the solid carbonaceous reducing agent preferably having a particle size less than 200 μm; c) injection of the mixture into the shaft furnace through the nozzles; d) fusion of the pre-reduced iron particles.

One of the advantages of this process consists in the fact that the operating principle of the shaft furnace is not disturbed. In addition, the production of pig iron is rapidly increased, thanks to the nature of the mixture proposed by the present process. In fact, a mixture of pre-reduced iron particles and carbon reducer is injected into the shaft furnace where these particles are reduced and melted and the carbon reducer is consumed. The particle sizes chosen for the carbon reducer and the fine particles of pre-reduced iron allow the injection of a mixture which is well assimilated by the blast furnace. It is therefore essential not only to make a mixture of the prereduced and the carbonaceous reducer, but also to choose the particle sizes of the components of the mixture. The injection of such a mixture ensures stable operation of the nozzles and coke cavities opposite the nozzles. As the mixture contains a carbon reducer, the additional thermal requirements associated with the injection can be covered by the energy released during the oxidation of the carbon reducer.

Advantageously, an intimate mixture of fine particles of pre-reduced iron and of solid carbonaceous reducing agent is injected. This can be obtained by providing a transport distance of the mixture before its injection into the shaft furnace through the nozzles equal to at least 25 times, preferably 50 times, the diameter of the orifice ejection of the mixture at the nose of the nozzle. An intimate mixture facilitates the melting of the mixture in the crucible of the blast furnace.

Once the injection speed has stabilized, the placing of coke in the charge of the shaft furnace can be adapted. This is another aspect of the optimization of the shaft furnace since it can save the coke introduced by the mouth.

The solid carbon reducer that is used is normally carbon.

According to a first embodiment, a mixture is produced comprising 300 to 600 kg of carbon per tonne of fine particles of pre-reduced iron. Up to 6% additional pig iron obtained by melting the pre-reduced iron, it is not necessary to change the operating parameters of the blast furnace. Preferably, between 6% and 20% additional pig iron, about 100 m ³ additional pure oxygen is introduced into the shaft furnace per tonne of pre-reduced iron particles. Thus the proposed mixture makes it possible to significantly increase the quantity of cast iron produced in the shaft furnace by limiting the modification of operating parameters. It will be noted that the present process can be implemented on any production site with a shaft furnace such as a blast furnace. It is not necessary that the production site has a pre-reduction furnace, it is simply necessary to carry out the mixing before the introduction into the hot wind of the nozzles.

According to a second embodiment, the mixing and injection of the fine particles of pre-reduced iron and of the solid carbonaceous reducing agent are carried out hot. As the injected mixture is hot, the additional thermal requirements associated with the injection are low and can be easily covered by the energy released during the oxidation of the carbonaceous reducing agent. Mixing and hot injection can advantageously be carried out when a pre-reduction oven, e.g. a multi-stage oven is located near the blast furnace.

Preferably, the quantity of oxygen introduced into the shaft furnace is adjusted. That is to say that the quantity of oxygen introduced into the furnace is adapted so as to have sufficient oxygen for the traditional operation of the blast furnace and the oxidation of the carbonaceous reducing agent added to the iron ore. pre-reduced. This adaptation, which generally consists in increasing the quantity of oxygen introduced into the blast furnace, is a function of the quantity of carbonaceous reducing agent injected but also of its quality. This additional supply of oxygen is achievable, either by increasing the oxygen concentration of the hot wind, or by increasing the flow of hot wind, or even by injecting pure oxygen directly into the nozzles, hot or cold.

The solid carbon reducer that is used is normally carbon. By mixing with the hot pre-reduced iron particles, the coal is advantageously brought to a temperature at which it is released from its volatile fraction.

During this mixing, it may be useful to inject an oxygen-containing gas in order to burn the volatile matter contained in the coal. The heat released during the combustion of the volatile materials of the coal can be used in step a) for the manufacture of fine particles of pre-reduced iron or else to heat the mixture of particles of pre-reduced iron and of coal.

By injecting a hot mixture, it is also possible to modify the parameters of the shaft furnace in order to further increase its productivity:

- all of the oxidant, oxygen, is brought in for the combustion of the carbonaceous reducing agent necessary for the fusion of the pre-reduced iron particles;

- the temperature of the hot wind is lowered so as to keep the flame temperature constant;

The wind / oxygen control leads to a reduction in coke consumption for “through” cast iron, a reduction in the wind flow rate, and a CO enrichment of the gas from the shaft furnace.

It will be noted that the lowering of the wind temperature and the simultaneous increase in the calorific value of the top gas make it possible to make a substantial saving on the cost of heating the wind, and on the maintenance of the cowpers, saving which comes add to that made on coke. In addition, the reduction in wind flow gives a potential for increased productivity compared to the blower limit.

According to another preferred embodiment, slag-forming agents are also added during step a) or step b). These slag-forming agents are chosen, preferably from the group consisting of lime, limestone and magnesia as well as their mixtures.

Advantageously, a sufficient quantity of carbon will be used during step b) to completely reduce and melt the pre-reduced iron particles in the shaft furnace.

According to a preferred embodiment, an excess of coal is used during step b) which is sufficient to cover the coal requirements of the shaft furnace. This avoids having to inject carbon separately through the nozzles.

Other features and characteristics of the invention will emerge from the detailed description of two advantageous embodiments presented below, by way of illustration, with reference to the attached drawing. This shows:

Fig. 1: Schematic diagram of the coupling of a pre-reduction oven and a shaft oven. In its conventional operation, a shaft furnace such as a blast furnace is supplied from the top, the top, with agglomerated ore and coke. Hot air, and in some cases coal, is blown into the bottom of the blast furnace. The blown air burns part of the carbonaceous fuel to generate the heat necessary for the chemical reactions and for the fusion of iron in the bottom of the blast furnace, while the rest of the carbonaceous fuel as well as part of the gases reduce the iron oxides. . In the lower part of the blast furnace, the crucible, are the molten iron and the slag.

Air is blown into the blast furnace via nozzles located just above the crucible. This air was previously heated in "cowpers", which deliver what is called the "hot wind". Cowpers are refractory brick regenerators placed in a circular metal enclosure covered with a dome. Before introducing air into the cowpers, the refractories are brought to temperature by burning blast furnace gases and a rich gas (natural gas for example).

The well-operated blast furnace operates at the limits of its productivity. It uses the maximum hot wind flow for its blowers, and, to minimize coke consumption, this wind is heated to the maximum temperature achievable in cowpers: between 1200 and 1300 ° C. This has in return an expensive maintenance of the cowpers, whose refractories and the metal carcass are at the limits of the stresses authorized by the state of the art. In the long term, refractories are destroyed by high temperature thermal cycles and the metal carcass is attacked by cracking corrosion. Finally, a rich gas must be used in addition to blast furnace gas to reach the necessary flame temperature.

In the present case, to optimize the operation of the blast furnace, and to increase its productivity, a mixture of fine particles of pre-reduced iron and coal is injected through the nozzles. The fine particles of pre-reduced iron have a particle size of less than 2 mm, preferably less than 1 mm if it is desired to inject large quantities. The solid carbonaceous reducing agent, carbon, is preferably so-called “pulverized” carbon with a particle size less than 200 μm and a median diameter less than 100 μm. The mixture is therefore advantageously prepared upstream of the nozzle and brought by a pipe into the nose of the nozzle, where it is introduced into the hot wind through an injection orifice.

Care will also be taken to inject an intimate mixture of the pre-reduced iron particles with the coal, which allows stable operation of the nozzles and coke cavities opposite the nozzles. This is ensured by mixing upstream of the injection tube and by respecting a distance of transport of the mixture representing at least 25 times (preferably 50 times) the diameter of the orifice for ejecting the mixture in the hot wind at nozzle nose.

Uncontrolled injection of prereduct and carbon could clog the nozzles and / or significantly decrease the temperature of the liquid metal bath in the crucible of the blast furnace. The recommended injection conditions in the context of the present will therefore be advantageously observed for the various embodiments presented below, namely the injection of the cold and hot mixture.

1. Injection of the cold mixture

A first embodiment of the present method proposes the mixing and the injection of the cold mixture. That is to say, the blast furnace is not coupled with a pre-reduction reactor.

As part of the injection of the cold mixture, a blast furnace is used by way of example, the operating characteristics of which are as follows:

- coke setting 270 kg / tfonte

- injection into fatty coal nozzles 200 kg / t _f0nt e

- wind at 1200 ° C, oxygenated to 25.6% O ₂ which corresponds for 850 m ³ wind / tf ₀ nte to a consumption of pure oxygen of 54 m ³ O ₂ / tf _θn te.

The pre-reduced iron ore injected has the characteristics of a commercial-grade pre-reduced iron ore, that is to say 5 to 8% gangue, metallization from 90 to 95%, and 0 to 2% carbon.

Under these conditions, 1 tonne of pre-reduced iron ore gives 0.9 to 0.95 tonne of iron.

A range of injection of a pre-reduced iron ore / coal mixture allowing the blast furnace to absorb this injection with a minimum of modification of the basic parameters is as follows:

Combine with each tonne of pre-reduced iron ore injected 300 kg of coal (or even up to 600 kg depending on the quality of the pre-reduced iron and the quality of coal used) while substantially maintaining the flow and temperature of the hot wind. After starting the injection, adjust the coke setting by subtracting approximately 60% of the quantity of coal associated with the injection of DRI (Example: if one injects a quantity of pre-reduced iron ore giving 10% of additional cast iron, the coke setting with the through charge may be reduced by (300 X 10 X 0.60) / 100 = 18 kg COke / through cast iron) - From 6% additional pig iron, and up to 20% additional pig iron produced from pre-reduced iron ore, around 100 m ³ of pure oxygen per tonne of pre-reduced will be added to maintain the flame temperature at the nozzles, beyond the quantity giving 6% additional melt. Which leads to enriching the hot wind:

- for 6% additional pig iron, no O _{2 is added} , ie a concentration of 25.6% O ₂ ;

- for 12% additional pig iron, 12 m ³ pure O ₂ / t through- _{bottom is added} , ie a concentration of 26.6% O ₂ ; - for 18% additional pig iron, 25 m ³ pure O ₂ / tf _0n through you are added, _i.e. 27.6% O ₂ .

2. Hot injection of the mixture

In the second embodiment, a mixture of hot pre-reduced iron ore and coal is injected into the crucible of the blast furnace, as soon as it leaves the pre-reduction furnace, through the nozzles of the blast furnace. The coupling of a blast furnace and a pre-reduction reactor, such as a stage oven, is particularly advantageous because it improves the operation of the two reactors. We use here a conventional deck oven, such as that described in the patent

US-2, 089,782, in which the iron ore is prereduced by a solid carbonaceous reducer. It is a multiple hearth oven, the hearths being annular and spaced vertically. Loading and unloading decks are arranged alternately. The former have an open central circular part; the seconds have a series of orifices spaced along the periphery of the sole. The oven is also provided, in its central part, with a vertical rotation shaft to which are attached rakes extending over the entire radius of the hearths. The iron ore is introduced through the upper part of the furnace and falls on the first loading floor. Rakes, driven by the rotation shaft vertical, spread the iron ore and bring it back to the central opening through which it falls on the lower unloading floor. The rakes then direct the iron ore to the peripheral orifices, through which it falls on the bottom loading floor. These steps are repeated until the iron ore reaches the lowest stage. The iron ore is then removed and we speak of pre-reduced iron ore. The reducing material, carbon, can be introduced at the level of the first loading floor, but also at a lower level. As the iron ore descends into the furnace, the gases produced by the reductions rise: it is a counter-current reactor. The reduction gases are burned in the upper part of the oven by injecting air or oxygen. The high temperatures prevailing inside the oven are reached with additional energy such as natural gas. The rakes, by their permanent brewing, allow an intimate mixture of iron ore and coal. The angles and the speed of the rakes are calculated to avoid crushing and agglomeration of the ore.

Of course, any reactor capable of producing pre-reduced iron from iron ore can be used within the scope of the present.

In Figure 1, the operation of the method according to the present invention is presented using a block diagram. At the top of a tiered furnace 10 iron ore is introduced in the form of fines. The arrow 12 illustrates the gradual reduction of the iron ore which descends the stages of the stage furnace 10. The arrow 13 symbolizes the ascending reduction gases. Fine particle sizes of iron ore and coal allow good heat exchange and promote chemical reactions. It will be noted that the reduction carbon can be inserted on the upper hearth, or in a lower part of the tiered oven 10. Preferably, bonding agents and slag forming agents chosen from the group are also injected into the tiered oven. lime, limestone and magnesia as well as their mixture. These agents are introduced at the same time as the iron ore or on lower soils in suitable proportions to give the slag of basicity aimed at the blast furnace. At the end of the pre-reduction, the iron ore is at a temperature of around 1000 ° C. We then add a quantity of coal necessary for its fusion in the blast furnace. The mixture of smelting coal and pre-reduced iron ore can be done either in the last zone of the stage furnace 10, or in a separate enclosure. In both cases, the mixture causes a rise in temperature of the coal, the volatile materials of which pass into the gas phase; the temperature of the mixture is approximately 500 ° C. The addition of air or oxygen makes it possible to burn a fraction of these volatile materials, thereby raising the temperature of the mixture to 600 ° C., and completing the devolatilization of the coal. The rest of the volatile gases are directed to the stage oven 10 in which it is burned, achieving a partial saving of the auxiliary energy. In addition, it will be noted that the fact of mixing the iron ore and its smelting coal in the last zone of the stage furnace 10 or in a separate enclosure makes it possible to take advantage of the volatile materials of the coal in the pre-reduction reactor, then that we don't know how to exploit them in the blast furnace.

The next step is to transfer the degassed mixture to a blast furnace 14, which can be done pneumatically. Then, the mixture is injected through the nozzles into the crucible of the blast furnace 14. The latter is in turn supplied in the traditional manner with agglomerated ore and coke. The path of the agglomerated ore through the blast furnace is represented by the arrow 16, the arrow 18 symbolizes the path of the blast furnace gases which escape through the blast pipe. Cowpers, generators of hot wind, are designated by the reference 20.

Ultimately, during the casting of the shaft furnace, iron will be recovered from the melting of the agglomerated ore as well as from the iron from the melting of fines.

In order to take advantage of the injection of the mixture to improve the operation and efficiency of the blast furnace, it is necessary to make some adjustments. The following table presents the variations of the operating parameters of the blast furnace with an optimized injection of pre-reduced fines (85% metallization) giving 10% additional melt. depending on the level of coal injection (100 to 200 kg / 1 cast iron)

For 250 t / h of pig iron, the desired production surplus is 25 t / h, for a total production of 275 t / h of pig iron. To do this, 29 t / h of DRI fines mixed with 12 t / h of lean smelting coal are injected through the nozzles. The temperature of the mixture deposited in the nozzles is between

400 and 600 ° C. The parameters of the shaft furnace have been modified:

- all of the oxidant, oxygen, is brought in for the combustion of DRI fines;

The quantity of oxygen introduced into the furnace is therefore adapted so as to have sufficient oxygen for the traditional operation of the blast furnace and the oxidation of the carbon reducer added to the pre-reduced iron ore. In this example, the adaptation of the quantity of oxygen consists of a 2.7% increase in the oxygen concentration of the hot wind. Another alternative would be to increase the flow of hot wind, or to inject oxygen, hot or cold, directly through the nozzles. A rate of 2.7% additional oxygen corresponds to the injection of 12 t / h of lean coal. This rate obviously varies according to the quantity and the quality of this carbonaceous reducer.

The wind / oxygen control leads to a reduction in the consumption of coke for "through" cast iron, a reduction in the wind flow rate, and a CO enrichment of the gas from the oven to the shaft. It will be noted that the lowering of the wind temperature and the simultaneous increase in the calorific value of the furnace gas make it possible to achieve a substantial savings on the cost of heating the wind, and on the maintenance of cowpers, an economy which is added to that made on coke. In addition, the reduction in wind flow gives a potential for increased productivity compared to the blower limit.

The present process therefore makes it possible to increase the overall production of the blast furnace. The deck oven is particularly advantageous in this process, because of its counter-current operation, because it allows better energy exploitation of volatile materials from coal.

3. Notes:

As indicated above, in the traditional use of the blast furnace, a certain additional quantity of coal is injected by the nozzles. This additional coal can be injected independently, but can also be mixed at the same time as the smelting coal with pre-reduced iron ore. In addition, part of the fusion carbon and / or the additional carbon can be injected at the same time as the reduction carbon in the stage oven, which does not in any way harm the reduction reactions.

It will be noted that the mixture which is injected here (pre-reduced iron ore, smelting coal, bonding agents) has a very interesting health characteristic: it is “self-deepening. In fact, it contains the reducing agent, the fuel and the "flux" necessary for its fusion in the crucible of the blast furnace.

Finally, it will be noted that if there is no longer any pre-reduced iron ore to be injected, for example following a breakdown of the pre-reduction oven, the blast furnace can be quickly restored to its traditional operating mode.

Claims

claims

1. Method for optimizing the operation of a shaft furnace comprising nozzles comprising the following steps: a) manufacture of fine particles of pre-reduced iron; b) mixing the fine particles of pre-reduced iron with a solid carbon reducer, the fine particles of pre-reduced iron having a particle size less than 2 mm and the solid carbonaceous reducing agent having a particle size less than 200 μm; c) injection of the mixture into the shaft furnace through the nozzles; d) fusion of fine particles of pre-reduced iron.

2. Method according to claim 1, characterized in that an intimate mixture of fine particles of pre-reduced iron and solid carbon reducer is injected.

3. Method according to claim 2, characterized in that the distance of transport of the mixture before its injection into the shaft furnace by the nozzles is equal to at least 25 times, preferably 50 times, the diameter of the orifice ejection of the mixture at the nose of the nozzle.

4. Method according to any one of the preceding claims, characterized in that the coke setting of the charge of the shaft furnace is adjusted, once the injection regime has been established.

5. Method according to any one of the preceding claims, characterized in that the solid carbonaceous reducer is carbon.

6. Method according to claim 5, characterized in that a mixture is produced comprising 300 to 600 kg of coal per ton of fine particles of pre-reduced iron.

7. Method according to claim 6, characterized in that between 6% and 20% of additional pig iron obtained by the fusion of the pre-iron particles- duit about 100 m ³ additional pure oxygen is introduced into the shaft furnace per tonne of pre-reduced iron particles.

8. Method according to any one of claims 1 to 5, characterized in that the mixing and the injection of the fine particles of pre-reduced iron and of the solid carbonaceous reducing agent are carried out hot.

9. Method according to claim 8, characterized in that one adapts the amount of oxygen introduced into the shaft furnace.

10. Method according to any one of claims 8 or 9, characterized in that the mixture of step b) is brought to a temperature at which the solid carbonaceous reducing agent is released from its volatile fraction.

11. Method according to any one of claims 8 to 10, characterized in that an oxygen-containing gas is injected during the mixing of the solid carbonaceous reducer and hot pre-reduced iron in order to burn the volatile materials contained in the solid carbon reducer.

12. The method of claim 11, characterized in that the heat released during the combustion of volatile matter from the solid carbonaceous reducer is used in step a) for the manufacture of fine particles of pre-reduced iron.

13. Method according to claim any one of the preceding claims, characterized in that addition of slag forming agents during step a) or step b).

14. The method of claim 13, characterized in that the slag forming agents are chosen from the group consisting of lime, limestone and magnesia as well as their mixtures.

15. Method according to any one of the preceding claims, characterized in that a quantity of solid carbonaceous reducing agent is used during step b) sufficient to completely reduce and melt the pre-reduced iron particles.

16. Method according to any one of claims 1 to 8, characterized in that an excess of solid carbonaceous reducing agent is used during step b).

17. The method of claim 10, characterized in that the excess of solid carbonaceous reducer is sufficient to cover the needs for solid carbonaceous reducer of the shaft furnace.