JPS6050737B2 - Methods and equipment for increasing the value of metallurgical slag - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for increasing the value of metallurgical slag, in particular basic slag from the production of steel wires, as well as equipment for carrying out this method.

Metallurgical slags produced from the smelting of non-phosphorous cast iron by blowing industrially pure oxygen into the converter currently find only limited use.

These uses are primarily agricultural, where they are used in small quantities for land improvement due to their high CaO content, or in blast furnace charges as fluxes and carriers for iron. However, it is only used in small quantities due to the presence of impurities (phosphorus, alkali) that are very harmful to the slag.

These slags are also used in road construction, but problems occur when the lime content of these slags is very high (swelling). Large surpluses of unused slag are generally dumped into pota heaps. This is a particularly inconvenient solution, as this material is considered unrecoverable and the slag surplus requires a total loss of expenditure. In order to increase the value of these slags, the inventor added to the liquid slag an alumina carrier and a silica carrier (fly ash from thermal power plants, in some cases blast furnace slag (preferably in liquid form)). We have already recommended that you do so.

This addition has the effect of converting the liquid slag into a metallurgical binder. Furthermore, in order to reduce most of FeO and most of MnO, there is a method in which a sufficiently active reducing agent is added and oxygen is blown into the gas atmosphere generated from the slag during the reduction process. Although the results obtained in this way have proved satisfactory, certain disturbances sometimes occur in the reaction between the slag and the added components.

The present invention aims at a method by which this disadvantage can be avoided.

During the course of this research, the inventor confirmed that the best results could be obtained by operating in the following manner: (1
) First add an alumina carrier and a silica carrier.

Alumina serves to control the chemical composition of the slag. (2) Add a reducing agent such as carbon.

Since the liquid mixture has a low melting point, it presents the most suitable conditions for reducing iron and decanting the reduced metal. (3) Next, lime is added to obtain the basicity of Bortland cement.

(4) Operate at a temperature high enough to allow active reaction of the added components.

Therefore, liquid slag has an alumina carrier, a silica carrier,
The process, object of the present invention, for converting the basic slag resulting from the oxygen smelting of hematite cast iron into Bortland cement by adding a reducing agent and a reducing agent is essentially characterized in that: To react with the metal oxide (FeO(5Mn0)) contained in the slag, maintain a highly reducing atmosphere (free of H2O and as little as possible of CO2) during at least a short part of the operation. , after reducing the monometal oxide,
Adding lime to the slag to obtain the composition of Bortland cement, during the majority of the process, a bath of the slag is used to support the reaction of the components added to this slag (alumina, silica, reducing agent, lime). To heat.

Experiments have shown that in order to easily remove the reduced product of FeO(5Mn0) it is better to increase the fluidity of the slag by feeding alumina and/or silica.

Such a supply also has the effect of bringing the alumina content of the slag closer to the desired value. The addition of these substances is important because magnesia (M) is often present in excess in slag.
It also has the effect of diluting or neutralizing some amount of gO). Once these metal components (Fe, Mn) have been removed, it is only necessary to introduce enough lime into the slag so that the final lime content is comparable to that common in Boltland cement. Bye. The above materials (alumina carrier, silica carrier, reducing agent, lime) are preferably in the form of natural or ground fine powders.

In this powdered state they are introduced into a bath of slag (preferably after being suspended in a gas). According to an advantageous embodiment of the invention, the introduction of materials such as alumina carrier, silica carrier and lime in powder form and suspended in a gas into the slag bath and the heating are carried out on the one hand. This is carried out in a burner which is supplied with a combustion auxiliary gas consisting of an oxygen-rich gas, optionally pure oxygen, on the one hand, and a combustible gas, such as natural gas, on the other hand. Generally, the combustion auxiliary gas is supplied to the burner in its central part, and the combustible gas is supplied peripherally around the combustion auxiliary gas.
Mixing of the two gases takes place easily in the burner upstream of the outlet hole. Advantageously, the powder material is injected into the slag, preferably suspended in the combustible gas fed to the burner. If the combustion auxiliary gas is air, the air is advantageously preheated. Obviously, the purpose of the burner is to preheat the powder material to be injected into the slag and to keep the slag in a fluid state sufficient to initiate the reaction and allow it to proceed as quickly as possible. This is particularly important in the case of lime. The reducing agent added is likewise in powder form and preferably suspended in the gas.

In this state, it can be injected into the slag with a coaxial two-feed burner as well. However, it is possible to replace the combustion auxiliary gas, and even the combustible gas, with a neutral or inert (possibly preheated) gas. According to the invention, heating is carried out electrically during this stage of operation in highly reducing catalysts.

For example, this is carried out by immersing the electrodes of an electric furnace in the slag. Even if the reducing agent is not injected into the slag in a coaxial dual-feed burner, such burners can be used if the combustion auxiliary gas is replaced by a neutral or inert gas (possibly heated). can be used during this stage of the reaction as a means of stirring the bath.

Likewise, according to the invention, the injection of the powder material into the slag, when it is carried out in a burner, is advantageously carried out by dipping the tip of the burner into the bath of the slag.

The rate of formation of the desired product can be increased and a better homogeneity of the components added to the slag can be obtained by carrying out as follows: carrier component of alumina, silica The carrier component and the reducing agent are introduced into the slag simultaneously.

In this case, heating of the slag and components is preferably carried out in a preferably coaxial dual-feed burner, as already mentioned above. Heating is then continued until the alumina component and silica component are melted, after which the heating method is preferably electrical. For example, an electric furnace is used. According to one advantageous mode of operation, the three components introduced into the slag:
That is, alumina, silica, and reducing agent are incorporated using a single material that contains them all.

For example, such materials are inferior coal, slag waste, fly ash rich in uncombustibles, ie recovered materials with low intrinsic value.

It is of course possible to make slight modifications to the above additions depending on the composition or changes in composition of the starting materials.

The invention also encompasses various variations of carrying out the above method.

According to the first of these variants, alumina, silica and reducing agent are added simultaneously or separately;
Iron-containing powder (brown dust), recovered powder from blast furnaces, recovered powder from hot blast furnaces, etc. are added. This variant makes it possible to advantageously recover the iron contained in the powder which would otherwise be lost during the classical steelmaking process. In fact, these iron-containing powders contain harmful elements such as alkali, sulfur, phosphorus, lead, and zinc that can only accumulate in metallic iron. According to the second of these variants, a lime-containing component is suitably introduced, for example a desulfurization slag resulting from a lime desulfurization operation or a Cac2 desulfurization operation.

One advantage of this second variant is the recovery of the metallic iron contained in the pre-desulfurization slag.

This operation consists of grinding the components of the slag and magnetically separating them. In addition to the recovery of iron, this variant has the advantage of making it possible to utilize a particularly cheap source of lime. The reduction of the metal oxides is carried out until the final product contains an amount of iron oxide corresponding to an iron content of 2% to 5%.

However, since this final content cannot always be achieved reliably by reduction, it may be adjusted by adding iron-containing powder (brown dust) simultaneously with the lime after the reduction step.

The following table compares the chemical composition of LD slag (i.e., slag resulting from oxygen smelting of red iron cast iron) and Boltland cement.

The invention likewise aims at an installation with which such a method can be carried out easily.

One installation suitable for the invention consists essentially of: (a) at least one furnace having a vertical axis;
Its height is preferably approximately equal to its diameter and its internal volume is large enough to avoid any flooding during the slag transformation reaction process in said furnace, said furnace comprising: for example at least At least one slag heating mechanism, the end of which is composed of a burner for heating the slag, preferably located below the level of the bath, one tapping cylinder and one tilting mechanism for discharging from the furnace, preferably with a regular discharge rate. one device for adding lime to the slag; at least one device for adding a reducing agent for the solid constituents (alumina, silica, oxides (e.g. iron and manganese) present in the slag, for the action of said reducing agent); one tap for discharging the metal thus obtained (iron or manganese-containing cast iron); (b) below the tap of the furnace located at the furnace power shell discharge position as described in paragraph (a); The rotary furnace to be arranged, with an inlet hole and an outlet hole, has its axis of rotation approximately horizontal and slightly inclined towards its outlet hole; The interior of the furnace contains means for maintaining a temperature which causes the reaction of the lime and the reduced slag to form Bortland cement clinker.

According to a first aspect of the invention, the burner constituting the slag heating mechanism also constitutes a device for adding solid components such as an alumina carrier, a silica carrier, a reducing agent and lime. . According to a second aspect of the invention, the burner contains two coaxial tubes, the inner tube serving for the passage of combustion auxiliary gases and the space contained between the inner and outer tubes being combustible. The arrangement of these two tubes is such that mixing of the two gases takes place inside the burner, slightly upstream of the outlet hole.

The inner wall of the outer tube constituting the burner is 20 mm from its outlet end.
Refractories that are electrically melted over a length of T1rm or less (in this case, those made of CaO are preferable)
Advantageously, it is already protected against wear by being coated or constructed with.

This protection is particularly important when the solid material to be injected into the slug is suspended in flammable gases passing through the burner in the space contained between the inner and outer tubes. According to another aspect of the invention, the inner tube constituting the burner terminates near the outlet slightly more recessed than the outer tube.

This recess has a length of less than 87 m, so as to create at its end a small chamber suitable for the complete completion of the calcination reaction. According to yet another aspect of the invention, the inner tube of the burner and its feed mechanism are advantageously constructed of a refractory material, such as sintered alumina. This aspect is extremely important if the gas passing through the inner tube is preheated (hot air or hot neutral or inert gas).
According to the invention, a burner with two coaxial tubes is housed in the side wall of the furnace so that its outlet end is immersed in a bath of slag.

In this case, it is advantageous that the average level at which the burner is accommodated in the side wall of the furnace is such that when tilting the furnace for discharge, the outlet end of the burner protrudes over the surface of the burner during the lifting process. be. Also according to the invention, a burner with two coaxial tubes for adding lime can be installed in a furnace filled with slag, or in a discharge stack through which the slag flows, or in a jet of slag leaving the furnace. It is located near the slag discharge pipe.

Furthermore, according to the invention, it is advantageous for the burner with two coaxial tubes to be equipped with a cooling circuit (preferably by water circulation).

According to one variant of the invention, a burner with two coaxial tubes is mounted at the end of one of the pipes leading into the furnace so as to immerse the outlet hole of the burner in the slag bath.

And the mouthpiece is also equipped with a cooling circuit (preferably by water circulation). Similarly, furnaces with vertical shafts are conveniently coated with refractories of good quality and good conductors of heat (e.g. MgOl, magnesia-chromium, monocarbonate), and the cooling of their walls is controlled by the treated slag. A portion is allowed to solidify onto the wall, thus forming an auxiliary protective layer for the wall.

A particularly important aspect of this equipment is that it includes an electrical device (e.g. induction circuit, arc electrode, containing a plasma medium) that facilitates the reduction process of iron oxides, manganese oxides. There are things that can be combined.

According to the invention, it is advantageous for the installation to contain two furnaces with vertical axes as opposed to a single approximately horizontal rotary furnace.

Such an installation has the advantage that in practice the rotary furnace can be fed continuously. The two furnaces with vertical axes operate alternately and in synchrony with a steelmaking converter. According to one variant of the invention, a furnace with a vertical axis and a substantially horizontal rotary furnace are combined into one furnace that can be rotated about a vertical axis.

The furnace includes a pivot axis lying in fixed bearings, the common axis of rotation of the fixed bearings being arranged perpendicular to the longitudinal axis of the furnace. These pivots then allow the furnace to be tilted to bring it into a vertical or lying position. The attached FIG. 1, given by way of non-limiting example, shows the equipment used to enhance the value of so-called LD slag as follows and under the following conditions.

Furnace 1 with vertical axis height 3.60n1, diameter 5.10
This is an rT1 electric furnace. The furnace is fitted with a removable lid 2 and current is introduced through three removable electrodes 3 across the lid. After removing the lid 2, 35 tons of liquid LD slag is put into the furnace 1.

This LD slag has the following composition: Ca=48%, SlO2=
13%, MgO=5%, MnO=4%, Fe oxide=22
%, and a process is added to it to transform it into Boltland cement. The following composition: SlO
2=60%, Al. 4.45 tons of dry fly ash with O3=30% and CaO=10% are charged.

This charging is performed by a burner 4 located on the side wall of the furnace 1. That is, when the axis of the furnace 1 is vertical, the end of the burner 4 is immersed in a bath of slag 5. This burner is used during this stage and is also used to heat the slag 5. The burner 4 essentially contains two coaxial tubes, the inner tube serves for the passage of combustion auxiliary gas, which is air preheated to 950°C, and the space contained between the outer and inner tubes is natural. Helps in the passage of combustible gases.

The inner tube is constructed of sintered alumina and is provided with a helix for effective mixing of the auxiliary combustion gas and the combustible gas at the outlet of the burner. The fly ash in fine powder form is suspended in a combustible gas which serves to introduce it into the slag. This burner 4 is additionally equipped with a stabilization mechanism for the neutral or inert gases that are of interest during the next steps of the process. Furnace 1 is made of magnesia bricks.
cm thick by direct bonding, and appropriate cooling of the wall of the furnace 1 solidifies a portion of the slag 5 thereon, thus forming an auxiliary protective layer of this wall.

Burner 4 is equipped with a water cooling circuit which connects the end of the burner to furnace 1 beyond this auxiliary protective layer.
It allows for intrusion into the inside of. This first stage lasts approximately 1 hour, during which the slag bath is heated to 1550'C.
is maintained.

Thereafter, the electrode 3 is immersed in the slag, and 2.5 tons of powdered coal (reducing agent) is poured into the slag.

Electrical energy is used during this second stage, since a highly reducing medium must be maintained in order to allow the ongoing reaction (i.e. the reduction of the iron oxides and manganese oxides contained in the slag) to proceed favorably. Ru. Of course, in the process of this second stage, the burner 4 will be stopped as a supply device for combustion auxiliary gas, but at that time it will be used as a stirring means for the bath, and its neutral or inert gas stabilization mechanism will be used. is forced to undergo oxygen substitution. The pulverized coal is suspended in combustible gas passing through the space contained between the outer and inner tubes of this burner 4. This gas then serves to introduce pulverized coal into the bath of slag 5. During this second stage, the slag stagnation boils under the action of generating reducing gas (CO).

After a reduction period of about 1 millimeter, the bath becomes quiet and the decanted metals (iron and manganese) are extracted from the furnace through the tap 6. The amount of electricity used during the second stage here is 3700k
Reach Wh. At the same time as the decanted metal is extracted from the tap 6, the furnace 1 is discharged in combination with the injection of lime into the slag. This constitutes the third stage of the process. The lime is introduced at the level of the discharge tube 7 using a submerged burner 8.

This burner likewise essentially contains two coaxial tubes, the inner tube being supplied with hot air and the space between the inner and outer tubes being supplied with natural gas. Lime with a particle size of less than 200 micrometers is suspended in the natural gas.

The inner tube is constructed of sintered alumina and equipped with a spiral for effective mixing of hot air and natural gas at the burner outlet. Near the burner outlet, the end of the inner tube is slightly more recessed than the outer tube. This recess is approximately 4 wt long and forms at its end a small combustion chamber convenient for complete reaction. Within this combustion chamber, the inner wall of the outer tube has a C
Protected against undesired wear by a coating made of electrofused refractory made of aO, i.e. CaO! has been done. The lime charging operation lasts for half an hour, and the amount of lime charged reaches 8.75 tons. Furnace 1
The discharge is carried out by tilting the furnace so that the slag flows along the discharge pipe 7 and reaches the rotary furnace 9. The length of rotary furnace 9 is 1
5m and its diameter is 4m and 3. The furnace 9 has a rotation axis that is approximately horizontal and slightly inclined towards its outlet hole 10. This furnace 9 is likewise equipped with burners 11 in order to maintain the temperature at a level that ensures that the reaction of lime and slag takes place with the formation of clinker 12 of the Bortland cement.
Contains. At the outlet of the furnace 9, the clinker is processed in the cooling and grinding equipment of the classical cement industry. The hot air of the burner is produced in a heat recovery facility which operates on the one hand with dust from cement production and on the other hand with cooled gas from the converter.

The amount of cement made by adding 25 tons of LD slag reaches 36 tons.

In addition, 5 tons of liquid metal (iron contained in slag and cast iron containing manganese) is recovered which can be recycled into the steel manufacturing process. The amount of thermal energy used is 9.87 Gcal, i.e. kg of clinker. This amount of energy is 3-4 times less than that consumed during the normal production of cement.Another test was carried out under similar conditions using liquid blast furnace slag instead of fly ash. However, the energy consumption was further reduced by 38%.In order to continuously feed the rotary furnace 9, the equipment used contained two furnaces 1 with vertical axes to a single furnace 9. do.

The furnace 1 operates alternately and in synchronization with the converter of the LD steelmaking. The accompanying FIG. 2 shows, as a non-limiting example, a coaxial two-tube burner.

The outer tube 13 of the burner contains a cooling circuit 14 by means of water circulation.

The inner wall of the outer tube 13 is protected against wear over a length of 15 mm from its outlet end 15 by a coating of an electrofused refractory 16 of CaO. The inner tube 17 is slightly retracted from the outer tube 13 and terminates near the outlet.

This recess is 57,070 mm long and forms a small combustion chamber convenient for complete combustion reaction. The inner tube 17 and its supply mechanism (not shown) are constructed of sintered alumina to allow passage of preheated gas.

[Brief explanation of the drawing]

FIG. 1 shows one piece of equipment used in the present invention.

Claims (1)

[Claims] 1. A method for converting basic slag produced by oxygen refining of hematite cast iron into Portland cement by adding an alumina carrier, a silica carrier, and a reducing agent, comprising: (1) reduction. In order to react the agent with the metal oxides (FeO and MnO) contained in the slag, a highly reducing atmosphere (
(2) after reducing the metal oxides, maintaining on the molten slag the slag with at least one electric arc during the short period of time; (2) after reducing the metal oxides; Adding lime to slag to obtain the composition of Portland cement, (
3) heating the slag bath during most of the process to support the reaction activity of the components added to the slag (alumina, silica, reducing agent, lime); Method for converting into portland cement. 2. Equipment for carrying out the method according to claim 1, characterized in that it consists of: (a) at least one furnace with a vertical axis;
Its height is approximately equal to its diameter and its internal volume is large enough to avoid any flooding, and the furnace includes: (1) at least one furnace for heating the slag during the reduction process; an electric arc electrode and at least one burner for heating the slag, the terminal end of the electrode and burner being a slag heating mechanism located below the surface of the slag bath; (2) a discharge tube and a slag heating mechanism for discharging from the furnace; (3) one device for adding lime to the slag; (4) at least one device for adding solid components (alumina, silica and reducing agents for iron oxides, manganese oxides present in the slag); , (5) one outlet for discharging the metal obtained by the above reduction, (b) (a
A rotary furnace to be located below the discharge tube when the furnace according to paragraph 2 is in the discharge position; the rotary furnace with an inlet hole and an outlet hole is substantially horizontal and rotates slightly inclined towards the outlet. It has a shaft and the furnace also contains means for maintaining a temperature within the furnace which causes the reaction of the lime and the reduced slag to form a Portland cement clinker.