DE102005031019A1 - Method for ultrasonic injection of an oxidizing agent into 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, in the starting materials, fuel, and at least one oxidizing agent fed to a melting zone be, wherein the oxidizing agent by means of several, around the circumference the melting furnace at preferably equiangularly arranged injectors at supersonic speed injected into the molten zone will and injecting at least in a process section by a time sequence from flow and resting phases (pulses) of the individual injectors takes place.

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.

The Regulation of over a Laval nozzle However, introduced into the molten zone amount of oxygen is problematic. For physical reasons it is impossible, to reduce the amount of oxygen without the flow velocity to throttle to sound velocity or below. This leads to, that at one for an operating condition of the furnace designed predetermined assembly with oxygen injection lances the oxygen input into the furnace can not be reduced without the supersonic speed and thus their effect on the penetration depth of the oxygen stream repealed.

In the EP 1 242 781 B1 An improved method for operating a melting furnace is described, in which the injection of the oxygen in the form of pulses, ie by a temporal 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 well in practice. When used in terms of their oxygen input capacity oversized ovens are Sometimes, however, periods of rest required, the total duration of 50% of Duration of the respective process section significantly exceeds. this leads to to an unfavorable Influencing the melt result.

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

These Task is based on the method described above according to the invention thereby solved, that in dependence from a predetermined or continuously determined to be supplied Oxidant quantity according to a given program the ratio of flow and resting phase of the injectors as well as the number of ultrasound eindüsenden Injectors is varied so that a steady course of with Ultrasound supplied Oxidant as well as the melting zone substantially evenly covering flow pattern is reached.

According to the invention, therefore, the supply of the oxidizing agent, which with ultrasound in the melting zone is introduced, controlled by a program. If the total amount of oxidizing agent to be supplied with ultrasound falls below one of the values specified by the program, one or more injectors will be switched off, with the "shut off" injector not providing the oxidizing agent or only oxidizing agent with subsonic speed to the smelting furnace in the sense understood here in that the value of the total oxidizing agent to be supplied by ultrasound exceeds a certain value specified by the program: (Then one or more injectors are "switched on", ie now they supply oxidizing agents with ultrasound.) Two conditions always have to be fulfilled during operation of the melting furnace: one is the course of the ultrasound-supplied amount of oxidant to be steady, ie, simultaneously with the change in the number of injecting with ultrasound injectors, the oxidant supply via the hereafter injecting with ultrasound injectors via egg ne corresponding change in the ratio of flow and rest phase can be adjusted so that the total supplied with ultrasound oxidant amount of that required for this time. On the other hand, a uniform flow pattern covering the melting zone is to be achieved, ie the injectors injecting ultrasound are in each case arranged on the melting furnace in such a way that uniform contact with the melting zone with oxidizing agent is ensured.

mit T = Tieff + Tceff The amount of oxidizing agent which is ultrasonically supplied to the furnace per unit time can be described by the following formula:

With T = T ieff + T c rms

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

As "effective Duration of the flow phases "or" effective Duration of rest periods "should while optionally distributed to one or more pulses Total duration to be understood while the injector opens, so in flow phase, or closed, that is in the resting phase. During a flow phase is the oxidant at supersonic speed injected into the molten zone and while a rest phase is the injection throttled to a speed below supersonic speed or completely switched off. The adjustment range for the amount of in the melting zone injected with ultrasound Oxidant moves between zero (one to zero continuous duration of the flow phase) and the maximum design quantity of all injectors used (at Full load operation of all injectors and a zero duration the resting phase). Thus lets The amount of oxidized into the molten zone with ultrasound oxidant vary widely. Depending on the required Total amount of oxidant to be supplied by ultrasound per Time unit, the number of connected injectors and the respective effective opening time be easily calculated according to the above formula (1). The formula (1) offers therefore a good basis for an automated control of the injectors. By specifying the pro Time unit with amount of oxidizing agent to be supplied with ultrasound can by means of a computer program the number of switched Injectors and the effective duration of the flow and rest phases determined become. In such a computer program can also empirically recorded Values over the for the respective setting optimal pulse rate and possibly an optimized Sequence of different pulses and over and the optimal working range the injectors used are included.

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 flow of oxidant is optimized in the melting zone both temporally and spatially. 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 material wear on the furnace, as well as the consumption of fuels, coke and elec energy can be lowered. 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 switched Injectors evenly around the Scope of the furnace are distributed. However, it is also possible that the injectors are operated asymmetrically at the melting furnace and after a not too long time a change of switched on Injectors takes place. In any case, the target is the melting zone of the melting furnace as evenly as possible To apply oxygen.

Work the connected injectors in pulsed mode, sees one again advantageous embodiment of the invention provides that the flow and rest phases the connected injectors are coordinated with each other, that the connected injectors are driven alternately to each other become. This is also in terms of time a very uniform admission achieved the melting zone with oxidizing agent.

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 around the melting zone around six, with each other identical oxygen injection lances are 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 takes place as follows: In full load operation, the supply takes place via all injectors. With a reduction of the oxygen requirement, the injectors go into a pulse-wise operation, ie the supply of oxygen takes place at 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. To the To make oxygen delivery 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.

Becomes the oxygen requirement is reduced by a value of the power an injector - or an integer multiple of it - corresponds, so become one or several injectors shut off, the shutdown in the This is done so that the still switched injectors the melting zone the shaft furnace if possible apply uniformly. Simultaneously shorten with shutdown of the injector or injectors, the resting phases the switched injectors accordingly, to a steady transition to ensure the supply of oxidant. The switched on Injectors are operated in the same way as described above. In this operating state, it is expedient, the connected injectors to drive alternately. To ensure even use of the injectors be ensured in subsequent steps or during the melting of a subsequent batch, those during the described method step switched off injectors, 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 by a temporal succession of flow and rest phases (pulses) of the individual injectors, characterized in that depending on a predetermined or continuously determined supplied oxidizing agent according to a predetermined program, the ratio of flow and rest phase of the injectors and the number of With injectors injecting ultrasound is varied such that a steady course of the amount of oxidant supplied with ultrasound and a flow pattern substantially uniformly covering the melting zone ht is. Method according to claim 1, characterized in that that each case when the difference between the maximum power all ultrasonically injecting Injectors and the total amount of oxidant to be supplied with ultrasonic injection the maximum power of a single injector equals the number the ultrasonically injecting Injectors is reduced by one and then, if the supplied with Ultraschallalleüsung amount of oxidant exceeds the maximum power of all injectors with ultrasound injections, the number of ultrasound injectors is increased by one in each case subsequently those with ultrasonic injection supplied Oxidizer amount evenly the ultrasonic injecting Injectors is distributed. Method according to claim 1 or 2, characterized that each injecting with ultrasound injectors evenly around the Scope of the furnace are arranged. Method according to one of the preceding claims, characterized characterized in that the flow and resting phases of pulsating ultrasonic injectors be coordinated with each other so that the injecting with ultrasound injectors be driven alternately.