EP1997915A1 - Method for controlled coke burning in cupola furnaces - Google Patents

Abstract

A method for operating a fossil fuel fired shaft furnace (1) involves accelerating an oxygen-containing transport medium in a jet nozzle (5) and sucking in an injector blast (6) using the generated reduced pressure. The injector blast and transport medium are combined to give a jet nozzle stream (9), which is supplied to the furnace together with a residual blast (10). An independent claim is included for a corresponding shaft furnace (1), having a jet nozzle (5) on the downstream end of a transport medium supply line (3) and a line (10) for supplying a residual blast into the furnace, the novel feature being that an injector blast line (6) opens into the transport medium supply line or the jet nozzle.

Description

The invention relates to a method for operating a shaft furnace, in particular a cupola, for melting a metal-containing insert, wherein the shaft furnace is heated by combustion of a fossil fuel. Furthermore, the invention relates to a shaft furnace, in particular cupola, for melting a metal-containing insert, with at least one supply line for a pumped medium, at the downstream end of a drive nozzle is connected, and with a residual draft line for supplying a residual wind in the shaft furnace.

In a cupola, a set of iron, which usually consists of pig iron, cast iron, steel scrap and other ferro alloys, is melted. Foundry coke is generally used as the fuel in the cupola furnace, which is burnt by reaction with oxygen, thereby releasing the quantities of energy necessary to melt the iron charge.

Originally, the coke was burned with air as the oxidant. Meanwhile, however, the use of oxygen-enriched air during melting in the cupola furnace to the technical standard. The advantage over the use of air is that higher combustion temperatures can be generated and the melting process is faster.

From the EP 0 762 068 A1 is a method for supplying combustion air into a cupola known, in which an oxygen-containing medium is injected into the cupola and the resulting negative pressure is utilized to suck more combustion air in the cupola.

In practical operation of shaft furnaces, there are currently no reliable decision aids for adjusting the melting process. As a fossil fuel usually foundry coke is used, whose quality is subject to strong fluctuations. In the previously known methods for operating shaft kilns, these fluctuations are hardly taken into account.

Object of the present invention is therefore to show a method for operating a shaft furnace and a corresponding shaft furnace, which allows a better control of the melting process.

The method, this object is achieved by a method of the type mentioned above, wherein an oxygen-containing medium is accelerated in a motive nozzle 'and an injector wind sucked by means of the resulting in the acceleration of the oxygen-containing fluid under pressure and combined with the fluid to a motive nozzle stream, and that Treibdüsenstrom and a residual wind in the shaft furnace are passed.

The shaft furnace according to the invention has at least one supply line for a pumped medium, at the downstream end of a drive nozzle is connected, and a residual draft line for supplying a residual wind in the shaft furnace, wherein the shaft furnace is characterized in that in the feed line for the fluid or in the motive nozzle Injector vent line opens.

The term "shaft furnace" is understood in particular to mean a cupola furnace, in particular for melting gray cast iron and nodular cast iron. But other shaft furnace systems for melting, for example, mineral wool, copper or aluminum can be operated according to the invention.

The term "insert" is intended to include metal-containing charges that are fed to a shaft furnace for melting. As already mentioned, this includes in particular the so-called iron or cold set, consisting of pig iron, cast iron, steel scrap and / or other ferrous additives. Depending on the type of shaft furnace but also copper or aluminum-containing batches are conceivable as an application:

For the purposes of this application, the terms "wind", "residual wind" and "injector wind" are understood to mean the oxygen-containing gas streams supplied to the shaft furnace, in particular air streams supplied under elevated pressure.

According to the invention, a controlled amount of oxygen is fed to the shaft furnace for conversion of the fossil fuel. This is done by having a oxygen-containing conveying medium, that is, an oxygen-containing gas or gas mixture, defined amount and / or defined flow rate is injected into the shaft furnace.

Additional oxygen is supplied to the shaft furnace via the injector wind and the residual wind. The delivery medium flows out of the drive nozzle or nozzles at high speed and generates a negative pressure, which according to the invention is used to suck in the injector wind. The sucked amount of injector depends on the one hand on the amount and flow rate of the fluid from, on the other hand, but can also be regulated separately. The mixture of accelerated fluid and aspirated injector wind forms a motive jet stream that provides oxygen to the combustion process in the shaft furnace. Additional oxygen is supplied to the shaft furnace with the residual wind. As a rule, pressurized air is available as residual wind.

In a preferred embodiment, the injector wind and the residual wind come from the same source. Thus, for example, a wind line or wind device is provided, which carries a certain amount of hot air, that is under elevated pressure, hot air. On this wind line is on the one hand the Injektorwindleitung, on the other hand, the residual wind line connected. The entire available hot blast amount is divided accordingly into a proportion which is sucked in by the Injektorwindleitung of the pumped medium and in a residual residual wind which is fed to the shaft furnace via the residual draft line.

It is also possible to provide a separate supply for the injector wind and the residual wind. For example, the shaft furnace may be provided with a first wind line from which the injector wind is withdrawn and with a second wind line from which the residual wind is taken. Although this design is technically more complex to implement than the above-described embodiment with a common wind line for residual wind and injector wind. On the other hand, however, by separate wind lines or wind devices for injector wind and residual wind their pressure and temperature conditions can be set independently, creating additional degrees of freedom to control the combustion process in the shaft furnace. In addition, can be used as an injector wind directly from the environment sucked air become. It is also possible to suck in with the pumped medium other gases or substances and to supply the combustion in the shaft furnace.

Preferably, the motive jet stream reaches the shaft furnace at a higher kinetic energy than the residual wind. The flow rate of the motive nozzle flow is advantageously between 40 m / s and 250 m / s.

Preferably, coke is used as fossil fuel. The quality of the coke varies in practice very strong, which it is regularly necessary to follow up and adjust the combustion parameters in order to achieve optimum conversion of the coke and thus an optimal melting process. By injecting the motive nozzle stream according to the invention at a high flow rate, the oxygen can be injected far into the interior of the shaft furnace and thus specifically influence the conversion of the coke.

The amount and / or the flow rate of the oxygen-containing delivery medium and / or the injector wind are advantageously controlled as a function of the temperature and / or the CO content of the top gas of the shaft furnace. Different coke qualities and different compositions of the melted feed introduced into the shaft furnace affect the composition of the blast furnace gas, i. the combustion gases. By analyzing the CO content and / or the blast furnace temperature conclusions about the combustion process and the melting process can be drawn.

By varying the flow velocity of the motive nozzle stream, the oxygen content of the motive nozzle stream and / or the amount thereof, the melting process can always be adapted to the desired objective. Other parameters that can be used to control the motive nozzle flow are melt performance, furnace pressure and exhaust gas analysis. In addition, it is advantageous to regulate the amount and / or the flow rate of the oxygen-containing delivery medium and / or the injector wind in dependence on the temperature and / or the pressure of the injector wind.

As the conveying medium is preferably an oxygen-containing gas stream having an oxygen content of more than 90%, preferably more than 95%, particularly preferred more than 99% used. But oxygen-enriched air can be used as a pumped medium.

The oxygen content of the motive jet stream resulting from the combination of the conveying medium and the injector wind is particularly preferably chosen to be between 25% and 65%. About the oxygen content of the motive jet current is another parameter available, via which the combustion of the fossil fuel can be controlled. For example, by increasing the oxygen content, the combustion can be intensified, that is, the temperature of the combustion gases is increased and more fossil fuel is burned per unit time.

The implementation of the fossil fuel in the shaft furnace can be significantly better controlled by the invention defined addition of oxygen by means of the motive jet current than in the previously known methods in which substantially undefined amounts of air are fed to the shaft furnace via wind lines.

In the method according to the EP 0 762 068 A1 Although an oxygen-containing medium is also injected into the shaft furnace and sucked with its help further combustion air. However, the intake of the combustion air is unregulated. The quantity of combustion air introduced into the shaft furnace thus depends on numerous factors which are not under the control of the operating personnel. According to the invention, by contrast, a defined amount of injector wind or generally an oxygen-containing gas mixture is sucked in by means of the delivery medium.

The control of the combustion and the melting process takes place substantially on the amount, speed and composition of the motive jet. It has therefore been found to be advantageous to supply between 30% and 60% of the total oxygen necessary for the conversion of the fuel to the shaft furnace via the motive jet stream.

The flow guidance of the motive nozzle flow is preferably adapted to the dimensioning of the furnace, that is to say in particular to the furnace cross section, the shaft height and the entry height.

The maximum quantity of the injector wind sucked in by the conveying medium depends on the parameters of the conveying medium flow: the stronger the suction effect caused by the conveying medium flow, the more the injector wind can be sucked in and fed to the shaft furnace. However, it has also proved to be advantageous to additionally influence the amount of the sucked injector wind or gas mixture, for example via flaps, valves or throttles, in order to be able to control the fuel conversion in the furnace even better. On the other hand, it is also possible by changing the pressure ratios in the injector vent line, i. the supply line for the injector wind to influence the suction and so to vary the amount of injector wind.

For example, technical oxygen is introduced via Laval nozzles into a special jet nozzle chamber. A pre-designed proportion of the primary wind amount is sucked controlled by the resulting negative pressure as Injektorwindanteil. With the adjustment of the Injektorwindanteiles a control valve, there are different oxygen enrichments, and correspondingly high exit velocities in the melting zone. The remaining residual primary wind passes with significantly less amount and speed in the region of the melting zone.

The control of the shaft furnace is advantageously carried out in response to one or more of the following parameters: temperature, composition or analysis of the gaseous or effluent gas, melt parameters such as melting temperature, furnace specific data, composition or analysis of the slag withdrawn from the shaft furnace. Previously recorded operating data can be used here in order to optimally adjust the oxygen supply to the furnace as a function of the current operating parameters and to achieve a process management which corresponds to the technological requirements.

Performance deviations can be detected and assigned quickly. By depositing the practical melt results, the kiln mode can be adjusted historically in a self-correcting database. Quality influences on, for example, different coke inserts are recognized immediately.

The possibility of reacting flexibly to the melting process is extended.

The oxygen enrichment of the motive jet stream, the rate of entry and the ratio of total oxygen used are important criteria of the process according to the invention. Thus, the oxygen can be used depending on the performance. Changes in coke quality are quickly apparent and can be adjusted.

The shaft furnace according to the invention has at least one supply line for a pumped medium, at the downstream end of which a motive nozzle is connected, and a residual blast line for supplying an oxygen-containing gas mixture into the shaft furnace. According to the invention opens into the supply line for the fluid or in the motive nozzle Injektorwindleitung.

Preferably, the supply line for the pumped medium is connected to a supply device, for example a tank, for technically pure oxygen. The technically pure oxygen can be added via the Injektorwindleitung a defined amount of air so as to adjust the oxygen content in the resulting mixture of oxygen and air. This mixture is accelerated in the motive nozzle, preferably a Laval nozzle, and introduced into the shaft furnace as a motive nozzle stream.

In a preferred embodiment, the line for the motive nozzle stream first opens into the residual draft line, which then leads the residual wind and the motive nozzle stream into the shaft furnace. In the area of the mouth of the motive nozzle in the residual draft line creates a negative pressure, which sucks more air through the residual draft line.

Furthermore, it is favorable to design the supply of the conveying medium, the injector wind and / or the motive nozzle stream in a water-cooled manner in order to adapt or influence the temperature conditions.

The invention has numerous advantages compared to the previously used methods. The combustion of the fossil fuel is significantly improved and it requires less fuel. The emissions or immissions are substantially reduced. Quality variations of the fuel, in particular different coke qualities, can be taken into account. Controlled combustion of the fuel reduces burnout of the refractory material in the furnace. Furthermore, due to the controlled use of oxygen, the silicon and manganese erosion is reduced.

The invention makes it possible to specifically intervene in the melting process of shaft furnaces and cupola systems. The efficiencies and environmental results are significantly improved.

About the adjustment of the amount of injector wind as a function of the amount of supplied as a conveying medium technical oxygen and the distribution of the primary wind in Injektorwindmenge and residual amount of wind enters an oxygen-air mixture in controllable amounts and speeds in the oven.

The additional activation or deactivation of individual motive nozzles, the combustion reaction of the fuel used can be further optimized.

Further, the range of existing equipment can be extended to include additional substances that promote the desired reactions by increasing the temperature (e.g., additional fuel). Or it is possible to enter substances which can be disposed of without damage in the course of the reaction (for example filter dust) or substances which flexibly adapts the analysis (graphite, Si, SiC and inert carriers).

The separation of the primary wind into the residual primary wind and the injector wind and the metrological detection allow the number of control parameters to be expanded, refined and set in greater detail. By a more flexible adaptation to different melt rates, it is thus possible to enable a performance-dependent kiln mode of operation via the coke reaction with oxygen.

In the oxygen input methods known hitherto, the amount of oxygen used is generally adapted to the melting conditions and introduced in concentrated form than 100% of technical oxygen in different manners at high speeds. The necessary kinetic energy is due both to the level of the oxygen supply pressure and to the amount of technical oxygen used. Together with the hot wind, technical oxygen meets the materials used, primarily coke, and essentially loses its energy potential here. The oxygen is thus introduced mainly into the melting zone via the high proportion of energy and the mass of the hot blast. The coke pieces in front of the nozzles already consume some of the oxygen, the remainder reaches the melting zone with little overall enrichment.

With the present invention, the same melting performance is now generated at the same temperature and analysis with less total oxygen input. The invention enables a large performance spectrum with different feed velocities in the motive nozzle with a uniform mixture feed. An oxygen introduction technique is available which realizes the most varied amounts of oxygen at the same concentration and controllable deposition rates. The possibility of reacting flexibly to the melting process is extended. The oxygen enrichment of the propellant nozzle mixture, the rate of entry and the ratio of the total oxygen content used are the most important criteria of a new kiln method.

Figur

schematisch eine erfindungsgemäße Zuführung von Sauerstoff und Luft zu einem Kupolofen.

The invention and further details of the invention are explained in more detail below with reference to the embodiment shown in the drawing. This shows the

figure

schematically an inventive supply of oxygen and air to a cupola.

In the figure, an inventive injection of oxygen or oxygen-enriched hot blast in a cupola 1 is shown. To the cupola 1 extends an annular wind ring 2, which is supplied with hot air at a temperature of, for example, between 200 ° C and 500 ° C.

Furthermore, several, for example eight, devices (lances) for the supply of oxygen are distributed around the circumference of the cupola furnace 1. Technically pure oxygen is fed via an oxygen line 3 with a static pressure of for example 10 to 15 bar a motive nozzle chamber 4. In the motive nozzle chamber 4 is a designed as a Laval nozzle drive nozzle 5, in which the oxygen flow is accelerated. About the resulting negative pressure part of the hot wind located in the wind ring 2 is sucked in via the Injektorwindleitung 6 and merged with the oxygen stream 3 and mixed. The sucked by the Injektorwindleitung 6 hot blast amount can be controlled via a throttle, flap or a suitable valve 7. In this way, a pre-designed proportion of the hot wind flowing in the wind ring line 2 can be sucked in and mixed with the oxygen in an adjustable concentration. The amount of injector wind, that is, the amount of hot wind sucked in by the injector draft line 6, is detected by a suitable meter 8. The resulting motive nozzle stream is then injected into the shaft furnace 1 via a lance 9 at a high flow rate of, for example, more than 240 m / s.

The residual hot wind remaining in the wind ring line 2 also passes into the shaft furnace 1 as a residual wind via the residual draft line 10 at a markedly reduced quantity and speed. The speed of the residual wind is reduced from 20 m / s to 11 m / s, for example compared to a conventional method.

In the illustrated embodiment, the residual wind and the motive jet stream are combined in an exhaust nozzle 11 before being directed into the shaft furnace 1.

Example:

In the wind ring 2 a total Heißweindmenge of 9670 Nm ³ / h is provided. 152 Nm ³ / h of technically pure oxygen at a temperature of 17 ° C are supplied via each of the oxygen feeds 3 and accelerated in the driving nozzle 4. In the process, 2360 Nm ³ / h of the entire hot air are sucked off as injector wind and mixed with the oxygen. It turns in the Lance 9 a mixing temperature of 339 ° C a. The exit velocity of the motive jet is 120 m / s. The remaining in the wind ring 2 hot air is passed as a residual wind over the residual draft line 7 at a speed of 74 m / s in the shaft furnace 1.

Depending on the required process conditions, the oxygen enrichment in the lance 9 can be adjusted between 25% and 100% by the amount of injector wind sucked in. The exit velocity of the motive nozzle stream and thus the radial flow velocity into the shaft furnace 1 can be increased to over 240 m / s.

Claims (11)

Method for operating a shaft furnace (1), in particular a cupola, for melting a metal-containing insert, the shaft furnace (1) being heated by combustion of a fossil fuel, characterized in that an oxygen-containing delivery medium (3) accelerates in a motive nozzle (5) is sucked and an injector wind (6) by means of the resulting in the acceleration of the oxygen-containing medium (3) resulting negative pressure and the conveying medium (3) to a motive nozzle stream (9), and that the motive nozzle stream (9) and a residual wind (10) in the shaft furnace (1) are passed. A method according to claim 1, characterized in that the injector wind (6) and the residual wind (10) are withdrawn from a common wind line (2). Method according to one of claims 1 or 2, characterized in that the combustion of the fossil fuel on the amount and / or flow rate of the oxygen-containing conveying medium (3) and / or the Injektorwindes (6) is controlled. Method according to one of claims 1 to 3, characterized in that coke is used as fossil fuel. Method according to one of claims 1 to 4, characterized in that the amount and / or flow rate of the oxygen-containing conveying medium (4) and / or the Injektorwindes (6) in dependence on the temperature of the injector wind (6) and / or the CO content the top gas of the shaft furnace (1) can be adjusted. Method according to one of claims 1 to 5, characterized in that as the conveying medium (3) oxygen having a purity of more than 90%, preferably more than 95%, more preferably more than 99%, is used. Method according to one of claims 1 to 6, characterized in that the motive nozzle stream (9) has an oxygen content between 25% and 65%. Method according to one of claims 1 to 7, characterized in that the motive nozzle stream (9) between 30% and 60% of the total necessary for the implementation of the fuel oxygen feeds the shaft furnace (1). Method according to one of claims 1 to 8, characterized in that the amount of sucked by the conveying medium (3) injector wind (6) is regulated. Shaft furnace (1), in particular cupola, for melting a metal-containing insert, with at least one supply line (3) for a pumped medium, at the downstream end of a drive nozzle (5) is connected, and with a residual wind line (10) for supplying a residual wind in the Shaft furnace (1), characterized in that in the supply line (3) for the fluid or in the motive nozzle (5) an injector vent line (6) opens. Shaft furnace (1) according to claim 10, characterized in that the residual draft pipe (10) and the Injektorwindleitung (6) open into a common wind line (2).

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