EP0110806A1 - Regulating system for delivering solid materials to a blowing lance - Google Patents

Abstract

An insufflation lance (1 mounted on a quick fixing system (2) which is connected to a set (5) of rigid tubes (3) and joints (4) can be connected at will to a circuit (8) purge gas supplier or a circuit (7) supplier of carbonaceous material. The circuit (8) sends a determined flow of argon from one source (30) or nitrogen from another source (31 ) by adequately controlling a flow regulator (11). The carbonaceous material supply circuit (7) is connected to the nitrogen source (31) and essentially comprises a flow regulator (11a) as well as an airlock blowing with a cellular metering device (40). When the conduits show a slight blockage during the recarburization phase, the pressure detected by a sensor (50) increases and a computer (14b) controls a reduction in the speed of rotation of the metering wheel (48) When successive reductions in the metering speed do not result in unclogging conduits, the computer (14b) starts the shutdown of the recarburization circuit (7) and the sending of nitrogen or argon under high pressure (sweep circuit 8) on the conduits so as to cause the desired poaching and then restart the recarburization operation.

Description

The present invention relates to a system for adjusting the supply of solids to a lance used to supply a metal bath, in particular a cast iron bath in the process of refining. The invention describes in particular a system, suitable for the introduction of granulated combustible material using neutral carrier gases into the metal being refined in the context of the LD, LD-AC or LBE processes.

Processes are known which plan to recarburize metal baths by adding carbon from above. Thus, patent application FR 2 459 835 provides for blowing calcium carbide on the surface of the bath, and this by using refining oxygen as the vehicle for the carbide. It turns out that the carbide carried by the oxygen does not oxidize in the jet, which may a priori surprise. On the other hand, carbides are compounds that are obtained by reactions consuming large amounts of energy which should exclude such a process at a time when energy is expensive.

It would therefore be logical to provide for the use of carbon in the form of anthracite, coke dust or other suitable carbonaceous material. In this case, it is unlikely that insufflation can be carried out in the manner described in patent application FR 2 459 835 without premature oxidation, possibly in the form of vehement combustion, destructive of equipment. It is therefore necessary to inject the carbonaceous material using of a non-oxidizing gas and possibly provide a gaseous protective screen between the flow of carbonaceous material and the neighboring jets of refining oxygen.

The experiments of the depositors have shown that in order to have a good absorption of the carbonaceous material by the bath, it is necessary that the latter not only present well-defined oxygen and carbon concentrations, but that in addition the material carbonaceous has sufficient kinetic energy at the outlet of the lance to enter the bath. This high kinetic energy, which is also required to avoid premature combustion of the carbonaceous material above the bath, is obtained using a powerful flow of gas. Since this neutral gas jet exerts a cooling effect, it is essential to introduce the required quantity of carbonaceous material into the bath in as short a blowing time as possible. However, a gas jet having a high solids concentration creates problems of clogging of the supply conduits and of the nozzle of the lance.

The constraint of recarburizing the bath in reduced time is also reinforced if nitrogen is chosen as the carrier gas for reasons of cost price. The nitrogen jet strikes the surface of the metal bath in the immediate vicinity of the refining oxygen. However, it is well known that the degree of dissolution of nitrogen in liquid steel increases with temperature.

The object of the invention is to propose a system capable of rapidly injecting a high quantity of granulated combustible material into a metal bath from above.

This object is achieved thanks to the adjustment system according to the invention which comprises at least one source of compressed gas, a circuit supplying carbonaceous material suspended in a gas, at least one circuit supplying sweeping gas, means for metering the different gas and carbonaceous material flow rates and means for separately or jointly connecting said circuits to a conduit leading to the lance. Preferred embodiments of the invention are described in the subclaims.

Other characteristics and advantages will emerge from the description of the schematic diagram shown in FIG. 1 which shows a possible embodiment of the system for adjusting the supply of the lance.

We distinguish the insufflation lance 1 which can be a multiflux lance used to supply the bath jointly with oxygen and granulated material, as described for example in patent application LU 84.176, or else a monoflux lance used to inject only granulated material in the bath. In the latter case, the refining oxygen and possibly the post-combustion oxygen is supplied by a separate lance. The lance 1 is mounted on a quick fixing system 2, integral with a carriage or any other mobile system, not shown, used to approach the lance at the desired distance from the surface of the bath. The fastening system is connected to a set 5 of rigid tubes 3 and articulations 4, known as shears as well as to a safety device 6 which detects possible leaks in the body of the lance 1. The leak detection is particularly important in multiflow lances which jointly supply the fuel which is normally abrasive and the oxidizer and can for example be carried out using a sheath filled with a fluid, which surrounds the duct of carbonaceous material the lance and a pressure sensor which monitors the fluid pressure. In case of breaking the sensor records a Variati _- one pressure it transmits to the safety device 6 which stops the blowing operation. One can also design a cooling circuit so as to achieve at the same time a separation between the fuel and oxidizer conduits, as described in patent application LU (A 733). In this case, monitoring of the cooling circuit pressure also allows leak detection.

The shears 5 can be connected at will to the circuit 7 supplying carbonaceous material or to the circuit 8 supplying sweep gas by acting on the respective electromagnetic valves 9 ment 10.

The circuit-8 is used to send a determined flow of argon from the source 30 or nitrogen from the source 31 to the lance 1 by opening / closing the valves 21 resp. 22 and by adequately controlling the flow regulator 11. The regulator 11 essentially consists of a pressure sensor 19, a pressure variation sensor 18 and a temperature sensor 20 connected respectively to converters 17 , 16 and 15 which transform the signals picked up into electrical signals that can be processed by the computer 14. The latter determines, depending on the operating mode of the crucible or the state of blockage of the conduits, the required flow rate which it transmits to the regulating valve 12 by means of the amplifier 13. Note that for reasons of clarity, the calculator figure has been drawn in several different places (provided with the references 14a and 14b). Between the valve 22 and the nitrogen source 31 are located the valves 24 and 26 as well as a pressure regulator 25 which prevents the source 31 from applying pressures. excessive to the purge gas supply circuit 8. A one-way valve 53 prevents any feedback from the carbon material supply circuit 7 to the purge gas supply circuit 8.

The circuit 7 supplying carbonaceous material is only connected to the nitrogen source 31 and essentially comprises a flow regulator 11a as well as a blast airlock with a cellular metering device 40. The airlock allows the flow rate of the mixture to be continuously varied. introduce and this by simply acting on the speed of rotation of the wheel of the cellular metering device 48. The flow rate of carrier gas passing through the blowing lance can thus be modified independently of the quantity of solid matter. The airlock includes a conduit 41 leading to the pressurization system of the carbonaceous material reservoir 47, as well as conduits 42 to 46 connected to the fluidization system of the carbonaceous material. A sensor 50 monitors the pressure in the conduits downstream of the airlock 40 and acts via the converter 49 and the computer 14b on the speed of rotation of the cellular metering device 48. The flow regulator lIa of the circuit supplying carbonaceous material 7 is of a conception close to that of the regula 11 controlling the flow of sweeping gas and the elements performing equivalent functions are identified by the same numbers increased by the letter a. Note that the pressure prevailing in the duct is identified using the sensor 19a upstream of the pressure regulator 25a and the valves 24a and 26a and practically indicates the pressure of the nitrogen source 31.

It is obvious that instead of a single computer, individual computers, in this case preferably analog, can also be used for regulating the flow rate of carbonaceous matter and sweeping gas and for regulating the metering device. alveolar. In this case the amplifiers 13 and 13a are replaced by amplifier-regulators which receive their instruction from the computer 14b which then controls the concentration of solid matter in the gas by acting on the amplifier-regulator 13a and on the speed of rotation of the metering wheel. The computer 14b is then also connected to the amplifier-regulator 13 to measure the flow of sweeping gas. An additional coordination between the different elements of the installation can be ensured by an operator.

The installation also includes several manometers 51 as well as electromagnetic valves 52.

• Lors de la phase de recarburation la vanne 9 est ouverte tandis que la vanne 10 est fermée. Le débit de gaz porteur ainsi que celui de matière carbonée sont réglés aux valeurs maximales compatibles avec les capacités de l'installation (source, conduites, sas etc.) et les exigences métallurgiques (capacité d'absorption du carbone par le bain etc.). Dès que les conduites accusent un début de bouchage, qui peut nattre dans les conduits situés en aval du sas de soufflage à doseur alvéolaire, la pression répérée par le capteur 50 augmente et le calculateur 14 commande une réduction de la vitesse de rotation de la roue du doseur 48 de sorte à diminuer la charge en matière solide dans le flux gazeux. Si ensuite la pression chute, la vitesse de rotation de la roue 48 est de nouveau augmentée. Dans le cas contraire une réduction supplémentaire de la vitesse de rotation est commandée. Lorsque des opérations successives de réduction de la vitesse de rotation de la roue 48 n'aboutissent pas au débouchage des conduits, le calculateur 14 commande l'arrêt du circuit 7, la fermeture de la vanne 9 et l'ouverture de la vanne 10. Ensuite la vanne régulatrice 12 est ouverte au maximum de sorte à envoyer selon l'ouverture ou la fermeture des vannes 21 et 22, de l'azote ou de l'argon sous pression élevée sur la cisaille 5 et la lance 1. Si le débouchage désiré s'opère, la pression mesurée par le capteur 50 chute et la recarburation peut reprendre.

The system works as follows:

• During the recarburization phase, the valve 9 is open while the valve 10 is closed. The carrier gas flow rate as well as that of carbonaceous material are adjusted to the maximum values compatible with the capacities of the installation (source, conduits, airlock, etc.) and metallurgical requirements (capacity for absorbing carbon by the bath, etc.). . As soon as the pipes show a start of blockage, which can occur in the pipes located downstream of the blast airlock with a honeycomb metering device, the pressure detected by the sensor 50 increases and the computer 14 commands a reduction in the speed of rotation of the wheel. of the metering device 48 so as to reduce the load of solid material in the gas flow. If the pressure then drops, the speed of rotation of the wheel 48 is again increased. Otherwise, an additional reduction in rotation speed is ordered. When successive operations to reduce the speed of rotation of the wheel 48 do not result in the unblocking of the conduits, the computer 14 controls the stopping of the circuit 7, the closing of the valve 9 and the opening of the valve 10. Then the regulating valve 12 is opened to the maximum so as to send, depending on the opening or closing of the valves 21 and 22, nitrogen or argon under high pressure on the shears 5 and the lance 1. If the unblocking desired operation takes place, the pressure measured by the sensor 50 drops and recarburation can resume.

Between two recarburization operations the valve 9 is closed and the valve 10 open and allows a small flow of gas (nitrogen, preferably argon) to flow through the shears 5 and the lance 1 so as to prevent clogging of the conduits due to an agglomeration of carbonaceous material deposited in the tubes or blockage of the lance head caused by projections.

The operation of the system has been explained using sources of argon or nitrogen. It is quite obvious that one can envisage the use of any gas compatible with the constraints of a chemical order ie. any non-oxidizing gas, which does not exclude the use of recycling gas. Similarly, the operations of unclogging the conduits have been described by opening respectively closing the electromagnetic valves 9 and 10. It is also possible to jointly open the valves 9 and 10 and adjust the different flow rates of gaseous and solid material so as to result in the desired unclogging . Without departing from the scope of the invention, it is also possible to envisage controlling the electromagnetic valve 10 by pulses. In the latter case, it is necessary to choose the frequency as well as the rise times of the signals controlling the opening / closing of the valve 10 so as to avoid the creation of vibrations in the conduits or the appearance of excessive pressures, destructive of the material.

Claims (8)

1. System for adjusting the supply of solids to a blowing lance used to supply a metal bath, in particular a cast iron bath in the process of refining, characterized in that it comprises at least one source of compressed gas , a circuit for supplying carbonaceous material suspended in a gas, at least one circuit for supplying sweeping gas, means for metering the different flow rates of gas and carbonaceous material and means for connecting said circuits separately or jointly on a conduit leading to the spear. 2. System according to claim 1, characterized in that the circuit supplying carbonaceous material suspended in a gas is connected to one of said gas sources and comprises a system for metering the gas flow followed by a blast airlock alveolar. 3. System according to claim 2, characterized in that the speed of rotation of the cell wheel of the cellular metering device is a function of the pressure prevailing in the duct located downstream of the blowing airlock with cellular metering device. 4. System according to claim 1, characterized in that the / the purging gas supplier circuits are connected to one / sources of gas under pressure and comprise a gas flow metering system constituted by a flow regulating valve, sensors to measure temperature, pressure and variation of gas pressure. 5. System according to claim 4, characterized in that a computer controls the degree of opening of the regulating valve as a function of the temperature, of the pressure and of the variation of the pressure of the gas as well as of the operating regime of the installation. 6. System according to claim l, characterized in that the means for separately or jointly connecting the gas and carbonaceous matter supply circuits suspended in a gas on the conduit leading to the lance are constituted by electromagnetic valves, preferably controlled by computer. 7. System according to claim 1, characterized in that the conduit leading to the lance is constituted by a system of rigid tubes and articulations. 8. System according to claim 1, characterized in that it comprises means for detecting leaks in the body of the lance or in the lance head and means for stopping the blowing operation in the event of a leak.

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