EP1739194A1 - Method of supersonic injection of an oxidationagent in a melting furnace - Google Patents

Abstract

Operating a melting furnace by supplying charge material, fuel and an oxidizing agent to a melting zone comprises injecting the oxidizing agent through peripheral ultrasonic injectors in supersonic pulses and adjusting the on/off ratio of the injectors and the number of injectors in use as a function of a predetermined or continuously determined oxidizing agent supply so that the supply is continuously maintained and a flow pattern that uniformly covers the melting zone is produced.

Description

The invention relates to a method for operating a melting furnace, wherein the feedstock, fuel, and at least one oxidizing agent are fed to a molten zone, wherein the oxidizing agent is injected by means of several, arranged around the circumference of the furnace at preferably equal angular intervals injectors at supersonic velocity in the molten zone, and the injection takes place at least in one process section by a chronological sequence of flow and rest phases (pulses) of the individual injectors.

A known method for ultrasonic injection of an oxidizing agent into a cupola furnace is described in US Pat EP 0 946 848 B1 described. In this process, the metallic starting materials to be melted and coke are supplied as energy carriers in the upper part of the furnace shaft. In the lower part of the furnace shaft, air and additionally oxygen are injected to burn the energy carrier and to produce a hot melting zone. The supply of oxygen raises the temperature in the melting zone and increases the melting performance of the cupola. In order to increase the penetration depth of the oxygen stream, this is injected together with a fuel gas by means of so-called oxygen injection lances at supersonic velocity in the molten zone. For this purpose, Laval nozzles are inserted into the oxygen injection lances.

However, controlling the amount of oxygen introduced into the molten zone via a Laval nozzle is problematic. For physical reasons, it is not possible to control the amount of oxygen without throttling the flow velocity to or below the speed of sound. As a result, in the case of a predetermined configuration of oxygen injection lances designed for an operating state of the melting furnace, the oxygen input into the melting furnace can not be reduced without canceling the supersonic velocity and thus its effect with regard to the penetration depth of the oxygen flow.

In the EP 1 242 781 B1 An improved method for operating a melting furnace is described in which the injection of oxygen in the form of pulses, d, h. by a time sequence of flow phases during which oxygen is injected, and rest periods during which no oxygen is supplied with ultrasound, takes place. If a plurality of oxygen injection lances arranged symmetrically around the circumference of the melting furnace are used, the oxygen lances can be operated synchronously, ie simultaneously pulsating, or asynchronously, ie offset in time from one another; However, the pulse durations of all injectors are always the same to allow a uniform supply of oxygen. In order to regulate the total amount of oxygen supplied, the total duration of the flow phases is varied by changing the ratio of the periods from flow phase to resting phase as well as the pulse frequency; Preferably, the duration of the flow phases is between 50% and 99% of the duration of the entire process section.

The method has proven itself well in practice. When used in terms of their oxygen input capacity oversized ovens but sometimes rest periods are required, the total duration of 50% of the duration of each process section significantly exceeds. This leads to an unfavorable influence on the melting result.

The invention is therefore based on the object of specifying a method by means of which the melting operation in a melting furnace, in particular in a shaft furnace, which is equipped with several injectors for injecting an oxidant at supersonic speed, well dosed and uniform.

This object is achieved on the basis of the method described above according to the invention in that the ratio of the flow and resting phase of the injectors and the number of injectors injecting with ultrasound is varied in such a way depending on a predetermined or continuously determined quantity of oxidizing agent to be supplied according to a predetermined program a steady course of the quantity of oxidizing agent supplied with ultrasound and a flow pattern substantially uniformly covering the melting zone are achieved.

According to the invention, therefore, the supply of the oxidizing agent, which is introduced with ultrasound into the molten zone, is controlled according to a program. If the amount of the total amount of oxidant to be supplied with ultrasound falls below a value set by the program, one or more injectors will be switched off, with a "disconnected" injector, as understood here, not supplying the smelting furnace with any oxidizing agent or oxidizing agent at subsonic speed. The same applies to the case in which the value of the total amount of oxidizing agent to be supplied by ultrasound exceeds a certain value predetermined by the program: one or more injectors are then "switched on", ie they now supply oxidizing agents with ultrasound. In the operation of the melting furnace, two conditions must always be met: Firstly, the course of the amount of oxidant supplied with ultrasound should be continuous, ie. simultaneously with the change in the number of ultrasonically injecting injectors, the oxidant supply should be adjusted via the injectors injecting thereafter with ultrasound via a corresponding change in the ratio of flow and quiescent phase such that the total quantity of oxidant supplied with ultrasound corresponds to that required for this time. On the other hand, a uniform flow pattern covering the melting zone is to be achieved, i. the ultrasonically injecting injectors are each arranged on the furnace so that a uniform loading of the molten zone is ensured with oxidizing agent.

mit $$T=T_{i\mathit{eff}}+T_{c\mathit{eff}}$$

The amount of oxidizing agent which is ultrasonically supplied to the furnace per unit time can be described by the following formula: $$\left(1\right)D=\frac{\left(N-N_c\right)\cdot Q\cdot \left(T-T_{c\mathit{eff}}\right)}{T}$$

With $$T=T_{i\mathit{eff}}+T_{c\mathit{eff}}$$

D :

Menge des in die Schmelzzone mit Ultraschall eingeleiteten Oxidationsmittels pro Zeiteinheit

T_ieff:

Effektive Dauer der Fließphasen der Injektoren

T_ceff :

Effektive Dauer der Ruhephasen der Injektoren

N:

Gesamtzahl an Injektoren

N_c :

Zahl der nicht zugeschalteten Injektoren

Q:

maximaler Fluss durch einen Injektor pro Zeiteinheit

It is

D :

Amount of oxidant introduced into the molten zone per unit time

T _heff :

Effective duration of the flow phases of the injectors

T _ceff :

Effective duration of resting phases of the injectors

N:

Total number of injectors

N _c :

Number of unconnected injectors

Q :

maximum flow through one injector per unit time

The term "effective duration of the flow phases" or "effective duration of the rest phases" should be understood to mean the total duration possibly distributed over one or more pulses during which the injector is open, ie in flow phase, or closed, ie in rest phase. During a flow phase, the oxidant is injected at supersonic velocity into the melt zone, and during a quiescent phase, injection is throttled to a velocity below supersonic velocity or shut off altogether. The range of adjustment of the amount of oxidant injected into the molten zone is between zero (at zero flow duration) and the maximum amount of exhaust of all injectors used (full load operation of all injectors and zero duration of the dwell phase). Thus, the amount of oxidant injected into the molten zone with ultrasound varies widely. Depending on the required total amount of oxidizing agent to be supplied with ultrasound per unit time, the number of connected injectors and the respective effective opening duration according to the above formula (1) can be easily calculated. Formula (1) therefore provides a good basis for automated control of the injectors. By specifying the per unit of time to be supplied with ultrasound amount of oxidant can be determined by means of a computer program, the number of connected injectors and the effective duration of the flow and rest phases. In such a computer program also empirically recorded values can be included on the optimal for the respective setting pulse rate and possibly an optimized sequence of different pulses and on and the optimal working range of the injectors used.

By the interplay of change in the ratio of flow and quiescent phase on the one hand and change in the number of ultrasonically injecting injectors on the other hand, the influx of oxidant into the melting zone both in time as well as spatially optimized. The oxidant flow is influenced very accurately, without affecting the ultrasound injection. Too long periods of rest, during which no oxidizing agent is injected with ultrasound, are avoided as well as a non-uniform application of the melting zone. The emission of pollutants such as NO _x and CO is significantly reduced. Likewise, the consumption of materials in the furnace, as well as the consumption of fuels, coke and electrical energy can be reduced. The method according to the invention is particularly suitable for melting processes in which a melting zone is produced by burning a fuel with an oxidizing agent in a melting furnace in which a feedstock is melted. For this purpose, the shaft furnaces come into question, especially cupolas, such as hot blast. Warm wind, cold wind, secondary wind, long-term, or rotary kilns. The feed is added to the furnace, for example, in the form of steel scrap, cast broke, pig iron or chips. It also uses non-metallic aggregates such as coke, silicon carbide, ferrosilicon, ferromanganese, lime and gravel. The oxidizing agent is preferably oxygen. In addition, a further oxidizing agent, for example air, can be introduced into the melting zone in a time-constant or likewise pulsating manner.

Advantageously, the supply of oxidant is controlled such that when the difference between the maximum possible power of all ultrasonically injecting injectors and the amount of oxidant to be supplied to ultrasound corresponds to the maximum power of a single injector, the number of ultrasonically injecting injectors decreases by one and then, when the amount of oxidant to be supplied with ultrasound exceeds the maximum possible power of all injectors injecting ultrasound, the number of injectors injecting ultrasound is increased by one, with the amount of oxidant to be supplied by ultrasound injection then being uniformly distributed to the ultrasonically injecting injectors. At full load, all injectors of the melting furnace work in continuous operation. When it is necessary to reduce the supply of ultrasonically oxidized oxidant, all the injectors initially go into pulsed operation, ie, all the injectors will operate in a flow-phase and quiescent-sequence sequence, as in FIG EP 1 242 781 B1 described method, wherein the total supplied with ultrasound amount of oxidizing agent is adjusted by changing the ratio of flow and rest phase. The lower the need for oxidizing agent, the longer the duration of the rest periods of the injectors. If the demand drops such that the sum of the rest phases of all injectors overall corresponds to the maximum output of a single injector, one of the injectors is switched off. The total flow of the ultrasonically injected oxidant is distributed evenly to the connected injectors, ie the remaining connected injectors operate initially at full load, and go into the pulse-wise operation, as soon as the demand is further reduced. The same applies to an increase in demand.

Preferably, the shutdown is such that the remaining connected injectors are evenly distributed around the circumference of the furnace. However, it is also possible that the injectors are operated asymmetrically on the furnace and after a not too long time a change of the connected injectors takes place. The goal is in any case to apply the molten zone of the furnace as evenly as possible with oxygen.

Work the connected injectors in pulsed mode, provides a yet again advantageous embodiment of the invention provides that the flow and rest phases of the switched injectors are coordinated so that the switched injectors are driven alternately to each other. Thus, a very uniform exposure of the molten zone is achieved with oxidizing agent in terms of time.

The invention will be explained in more detail below with reference to an exemplary embodiment:

Steel scrap, shavings, pig iron, recycled material and non-metallic aggregates such as coke and lime are continuously added to the upper part of the shaft of a cupola furnace. In the lower part of the shaft, air - the so-called furnace wind - is introduced via a wind ring and from there into the melting zone. The supply rate of air is constantly 10 000 m ³ / h. In the lower part of the furnace shaft are around the melting zone around six identical with each other oxygen injection lances arranged at equal angular intervals. By means of the oxygen injection lances, technical oxygen is injected at supersonic velocity into the molten zone. By this injection results in a large penetration depth of the oxygen stream, so that the temperature increases in the melting zone and the melting performance of the cupola is increased. In the oxygen injection lances each Laval nozzles are used.

The regulation of the oxygen supply is carried out as follows: In the Voillastbetrieb the supply takes place via all injectors. With a reduction in oxygen demand, the injectors go into pulse-wise operation, i. the supply of oxygen takes place in these lances at discrete time intervals in the form of a sequence of flow phase and resting phase, the duration of which results from the respective oxygen requirement. The lower the oxygen requirement, the longer the duration of the rest periods of the injectors. In order to make the oxygen supply as uniform as possible, the injectors are driven alternately in pulses of different lengths, but care is taken that the injection always takes place substantially symmetrically to the central axis of the furnace. If the oxygen demand is reduced by a value corresponding to the performance of an injector - or an integer multiple thereof - one or more injectors are switched off, the shutdown taking place in such a way that the still connected injectors act as uniformly as possible on the melting zone of the shaft furnace , At the same time shorten with shutdown of the injector or the injectors, the resting phases of the connected injectors accordingly to make sure a steady transition of Oxidationsmittelmengenzufuhr. The connected injectors are operated in the same way as described above. In this operating state, it is expedient to control the connected injectors alternately. In order to ensure a uniform use of the injectors, the injectors switched off during the described method step are preferably switched on in subsequent method steps or during the melting of a subsequent batch, so that in each case a change of zuzuschaltenden injectors takes place.

Claims (4)

A method for operating a melting furnace, wherein the feedstock, fuel, and at least one oxidizing agent are fed to a molten zone, wherein the oxidant is injected into the molten zone by means of a plurality of injectors arranged at preferably equal angular intervals around the circumference of the furnace at preferably equal angular intervals, and injecting at least in a process section takes place by a temporal succession of flow and rest phases (pulses) of the individual injectors,
characterized,
in that , depending on a predetermined or continuously determined quantity of oxidizing agent to be supplied according to a predetermined program, the ratio of flow and resting phases of the injectors and the number of injectors injecting ultrasound are varied such that a steady course of the amount of oxidizing agent supplied with ultrasound and a melting zone in the essentially uniformly covering flow pattern is achieved. A method according to claim 1, characterized in that in each case when the difference between the maximum power of all injecting ultrasound injectors and the total supplied with Ultraschallalleüsung oxidant amount of the maximum power of a single injector, the number of ultrasonic injectors injectors is reduced by one and then, if the amount of oxidant to be supplied with ultrasonic injection exceeds the maximum power of all the injectors injecting ultrasound, then the number of injectors injecting ultrasound is increased by one, each of which subsequently distributes the amount of oxidant to be supplied with ultrasonic injection evenly to the injectors injecting ultrasound. A method according to claim 1 or 2, characterized in that each injecting with ultrasound injectors are arranged uniformly around the circumference of the furnace. Method according to one of the preceding claims, characterized in that the flow and resting phases of operating in the pulse mode with ultrasonic injectors injectors are coordinated such that the injecting with ultrasound injectors are driven alternately.