EP0397134B1 - Shaft furnace for melting of iron - Google Patents

Description

The invention relates to a shaft furnace in which metallic insert is melted with the addition of slag-forming additives and coke, wind being blown in in several areas lying one above the other and in the lower area a wind quantity leading to substoichiometric combustion of coke is blown in and in the upper area one for complete Combustion of the gases present is sufficient amount of wind is added, the middle area is in the melting zone and the upper area is provided for preheating the batch.

Such cupola furnaces are known from German patent 540017.

Cupola furnaces usually stand on a base plate. The furnace jacket is made of sheet steel and is fireproof or lined without a lining. The furnace jacket forms the furnace shaft. The furnace is classified from a top stage. The bottom of the furnace is formed by the sole inclined towards the tapping gutter. Above the sole is the so-called stove, which is filled with filling coke. The liquid iron that is melted in the melting zone collects in the hearth. The wind provided passes through wind pipes into an annular wind box surrounding the furnace or into a ring pipe built into the wind box and from there to the wind nozzles, also called blow molds or wind molds. The hot furnace gases (top gas) are drawn up through the furnace shaft into the chimney or into a cleaning system.

The melting process is as follows:

The batches thrown in through the inspection opening fill the furnace shaft up to the level of the gout platform. The rising hot furnace gases heat the iron charge, which gradually slides into the furnace shaft due to the continuous melting. After reaching the The iron becomes liquid in the melting zone and drips through the coke bed. The coke bed is formed by the filling coke column from the sole to the melting zone. The melting zone is above the wind nozzles through which the wind is blown. In hot wind operation, highly heated combustion air is fed to the wind vents. The wind temperature is usually 400 - 600 ° C. In order to make this wind heating economical, various methods have been developed, e.g. B. the top gas waste heat recovery with top gas combustion or external heating.

The hot-wind cupola ovens have been designed in a wide variety of variations. Among others Cupola furnaces with wind blowing at different levels were already known at the beginning of this century.

All cupola furnaces have the problem of thermal efficiency, which has been worked on from the start. In cold wind cupola furnaces and many hot wind cupola furnaces, the thermal efficiency is often below 50%, e.g. B. 40%. The thermal efficiency can be improved with a hot wind by partially recovering the heat from the blast furnace gas. However, the efficiency itself remains poor.

The invention has set itself the task of creating a new shaft furnace with a better thermal efficiency. The invention is based on the consideration that the temperature in the furnace is at a considerable distance from the temperature which corresponds to the thermal requirements.

In this objective, the invention differs from the above-mentioned German patent.

The main reason for the poor thermal efficiency of known shaft furnaces is a significant energy loss from the endothermic reduction of CO₂, which is caused by the combustion of carbon by wind added in the furnace. This CO₂ is reduced to CO by the carbon coke inside the furnace. This consumes energy in an area where it would be better used to melt and overheat the iron.

According to the invention, a significant improvement in the thermal efficiency is achieved by the requirements of the claim. Using the known wind supply in different levels, a wind quantity leading to substoichiometric combustion of the coke is blown in in the lower region, while a somewhat smaller wind quantity is added in the middle region and a wind quantity sufficient for the combustion of still existing CO is added.

The shaft furnace according to the invention thus looks similar to a conventional cupola furnace, but it differs fundamentally from it. The wind is fed so that the endothermic reduction of CO₂ to CO cannot take place because only a minimum of CO₂ is generated in the lower furnace area.

The central area of the nozzles is 300 to 700 mm from the lower area, the upper area from the central area 500 to 2500 mm.

The blow molds or wind molds of the upper area extend spirally over a shaft height of 1,500 to 2,500 mm. The number of nozzles there is preferably 6 to 20.

40 to 60% of the total air volume is added in the lower area, 20 to 50% of the total air volume in the middle area and 20 to 35% of the total air volume in the upper area.

The wind temperature in the lower range is 700 to 1 200 ° C, z. B. 900 ° C. This wind temperature arises from appropriate heating of the hot wind, preferably using a recuperator. As already explained above, the heat contained in the blast furnace gas is largely recovered in the recuperator. The amount of heat still missing to achieve the desired temperature is supplied by external heating. The heating is preferably carried out with the aid of a gas burner and / or oil burner, the combustion gases giving off their heat to the hot wind via a heat exchanger or overheating to the desired temperature taking place in the heat exchanger.

The heating of the wind to higher temperatures is also a fundamental problem that is solved by the invention.

The modern cupola furnaces are fed with hot air generated in a gas / air heater / exchanger by recovering all or part of the energy contained in the gases escaping from the cupola furnace.

These gases are contaminated with dusts. The dusts soften at a relatively low temperature. Once softened, they stick to the pipe wall and block the air heater. It is therefore necessary to limit the air temperature to approx. 750 ° C.

The problems of constipation are eliminated by the air superheating according to the invention. The overheating starts from the usual heated wind.

According to an older proposal, wind overheating per se is already provided, but with the help of a plasma burner. The plasma torch contains an economically extremely complex solution.

According to the invention, less expensive devices such as air superheaters which operate on the basis of electrical resistors are used for the wind superheaters. Optionally, air / gas heat exchangers can also be used which are operated with a suitable fuel, in particular natural gas or heating oil.

In the middle area, cold wind or hot wind with normal temperature, max. fed at a temperature up to 600 ° C.

A cold wind supply is sufficient in the upper area.

While the lower amount of air in the lower area combined with the high wind temperature means that an atmosphere is created which is rich in CO (only as little as necessary is oxidized in it, where mainly liquefied metal has to be overheated) , the supplied amount of wind in the second wind form area generates a sufficient amount of energy for melting by burning coke and a certain amount of CO, which was generated shortly before in the area of the lower wind forms.

The wind quantity provided in the upper area is used to burn CO, which has arisen in the area of the lower wind form. The energy generated by this combustion is used to preheat the metallic batch to a temperature close to the melting point.

It is known to add the wind to cupola furnaces via spirally arranged wind forms (DE-PS 423400). It is the solution known as the Poumay oven.

There was no way in the Poumay oven to measure and control the wind distribution between the lower wind forms and the upper spirally arranged wind forms. As a result, the total amount of wind was added through a single wind ring.

In contrast, in the shaft furnace according to the invention, the wind quantity for three areas (zones) is provided with a quantity control. In addition, temperature control of the wind is preferably provided for the lower and middle area (zone).

The Poumay furnace was used in many European foundries, but no longer from 1925, since there was no control of the air supply and the cupola furnace did not work reliably without constant intensive monitoring. The air for the spirally arranged wind nozzles was taken from the wind box that feeds the main nozzles.

Excessive wind blowing creates a higher temperature in the Poumay ovens, creating a new melting zone that interferes with the function of the cupola. The Poumay ovens have therefore proven unsuitable in practice.

The alternative to the Poumay ovens were ovens with several rows of wind nozzles arranged in a uniform manner. If part of the CO is burned at the level of the bottom row, the wind blown into the top row only hits CO₂ (and nitrogen) that is generated in the bottom row. He no longer encounters CO. For this reason, no further combustion takes place.

In the shaft furnace according to the invention with the spiral arrangement of the wind nozzles according to the invention in the upper region and the wind feed according to the invention, the expansion of the gas resulting from the combustion pushes the unburned gas back from the opposite side, where it is burned by one of the upper nozzles, etc. .

• die mit schlechtem Wirkungsgrad behaftete Überhitzung des Eisens durch Überhitzung des Windes verbessert wird,
• es möglich ist, im Bereich des Koksbettes und kurz darüber stark reduzierend zu fahren und damit alle mit der Oxydation von Eisen verbundene Nachteile zu vermeiden,
• weil die in Spiralen angeordnete Nachverbrennung in der Vorwärmungszone das Auftreten von hohen Temperaturen vermeidet, die eine Rückreaktion nach Boudouart zur Folge hätte.

In summary, the significant improvement in efficiency of the new shaft furnace occurs because

• the poor efficiency of overheating of the iron is improved by overheating the wind,
• it is possible to drive in the area of the coke bed and just above it in a strongly reducing manner and thus to avoid all the disadvantages associated with the oxidation of iron,
• because the afterburning arranged in spirals in the preheating zone avoids the occurrence of high temperatures, which would result in a back reaction according to Boudouart.

Various exemplary embodiments of the invention are shown in the drawing.

Figure 1 shows a schematic representation of the shaft column with wind form areas A (superheater), B (melting area) and C (preheating). While the wind forms in areas A and B each lie in one plane, the 6 to 20 wind forms provided in area C are distributed spirally over a shaft column height of 1.5 to 2.5 m.

Figure 2a shows a schematic representation of the wind supply for a conventional hot wind cupola furnace with two rows of nozzles. The blower 1 presses the recirculated air into a recuperator 3. The recuperator outlet is regulated at 4 and 5 with flaps.

Figure 2 b shows a schematic representation of the wind supply for a shaft furnace according to the invention (capacity 15 t / h with 40% steel and 60% circulation and cast break). In the exemplary embodiment, a hot wind amount of 2,500 m 3 at a temperature of 500 ° C. is fed to the central region B. In the lower area A, 4,000 m³ of wind are fed. The 4,000 m³ come from the recuperator 3 with a temperature of 500 ° C like the 2 500 m³ provided for the area B. However, the 4,000 m³ wind provided for the area A in a heat exchanger 6 to 800 ° C or a higher temperature overheated. The heat exchanger 6 is operated with external energy (for example, electrically or with gas).

A bypass 7, which is provided with a flap control 9, is optionally also provided for the recuperator 3. Part or all of the air quantity supplied by the blower 1 can be pushed past the recuperator 3 into the line leading to the wind form region B via the bypass 7.

In the exemplary embodiment, the blower 2 feeds 2,000 m³ of cold air into the area C with the wind molds 11. The wind supply is regulated with a flap 10.

The other figures show different application examples of the invention.

Figures 3, 3 a, 4 and 4 a refer to 1 ton of iron.

Figure 3 shows the temperature and the energy profile in the shaft furnace;

The gas temperature curve is designated 20. Curve 21 corresponds to the iron temperature. The curve 22 corresponds to the accumulated, minimally required amount of energy from the furnace sole to the gout. It can be seen that curve 21 is at some distance from curve 20.

Figure 4 shows the temperature and energy profile in different zones of a conventional hot-wind cupola.

The curve 27 corresponds to the minimally required energy accumulated from the furnace sole to the gout. Curve 27 corresponds to curve 22 in FIG. 3 in the area of the preheating. In the lower area of the cupola furnace, 90 thermies (1 thermie = 4.20 megajoules) are required to reduce CO₂ to CO. The gas temperature curve is designated 25, the iron temperature 26.

• Im Bereich der Zone A wird das Flüssigeisen überhitzt. Der Energiebedarf beträgt im Ausführungsbeispiel 80 Thermien.
• In der Zone B liegt der Schmelzbereich und der Beginn der Überhitzung. Der Energiebedarf für den neuen Schachtofen beträgt im Ausführungsbeispiel 120 Thermien. Für herkömmliche Kupolöfen müssen dagegen zusätzlich beim gewählten Beispiel 90 Thermien für die endotherme Reaktion des CO₂ zu CO aufgewandt werden. Das bedeutet eine gesamte Energiemenge von 210 Thermien in herkömmlichen Öfen.
• In der Zone C findet das Vorwärmen der Charge statt. Dort ist der Energiebedarf 280 Thermien sowohl bei einem herkömmlichen Ofen als auch bei dem erfindungsgemäßen Schachtofen.

3 and 4 are zones A and B and C from FIG. 1:

• In zone A, the molten iron is overheated. The energy requirement in the exemplary embodiment is 80 thermals.
• Zone B is the melting range and the beginning of overheating. In the exemplary embodiment, the energy requirement for the new shaft furnace is 120 thermals. For conventional cupola furnaces, on the other hand, in the example chosen, 90 thermals must be used for the endothermic reaction of CO₂ to CO. That means a total of 210 thermal energy sources in conventional ovens.
• In zone C, the batch is preheated. There, the energy requirement is 280 thermals both in a conventional furnace and in the shaft furnace according to the invention.

Figure 5 shows another representation of the temperature profile and energy profile for both furnaces.

The triangles M, N, O, P for the shaft furnace according to the invention and M, N, O1, P1 for the conventional cupola furnace symbolize the total energy requirement per ton of liquid iron in each zone of the two furnaces. This also includes the wall losses.

The result is that the energy requirement of the conventional cupola furnace is higher (600 thermies versus 510 thermies, i.e. 15%) than in a shaft furnace according to the invention. The shaft furnace according to the invention has a correspondingly better efficiency.

In the above calculation, the 90 thermies that were used to reduce CO₂ are as follows:

Of 100 kg of carbon, which are fed to the cupola furnace, about 70 kg are burned in the lower region to produce a gas of about 17% CO₂. This CO₂ is reduced in zone B and converts to a gas with approximately 12% CO₂. However, the reduction consumes about 30 kg of carbon and about 90 thermal thermal energy.

This loss occurs to a greater or lesser extent in each cupola furnace.

• In einer ersten Zone der Windform A wird ein Teil des Kokses verbrannt unter Zugabe einer geringen Windmenge bei hoher Temperatur. Auf diesem Wege wird genügend Energie frei, um das bereits verflüssigte Metall zu überhitzen. Es entsteht eine sehr CO-reiche Athmosphäre mit wenig Neigung zur Oxydation.
• In einer zweiten Zone der Windform B wird eine ergänzende Windmenge zugeführt. Der Wind ist nicht oder nur gering erwärmt. Auf diese Weise wird genügend Schmelzenergie durch Verbrennung eines Teils des Kokses sowie einer Teilmenge des CO frei, welches in der unteren Zone A gebildet wurde.
• Schließlich wird Wind in einer dritten separaten Zone zugegeben. Dies geschieht über eine ausreichende Anzahl von Windformen, die spiralförmig im oberen Schachtbereich des Ofens angeordnet sind. Diese Luft ist erforderlich, um das in den unteren Schichten gebildete CO zu verbrennen. Die durch diese Verbrennung frei gewordene Energie ermöglicht das Aufheizen der metallischen Charge bis an Temperaturen im Bereich des Schmelzpunktes.

The illustration according to FIG. 6 highlights another very important advantage of the new furnace. While in the conventional cupola furnace the liquefied metal drops pass through a CO₂-rich, ie oxidizing zone in the lower furnace area, the corresponding zone in the new furnace is particularly rich in CO in this hottest area:

• In a first zone of wind form A, part of the coke is burned with the addition of a small amount of wind at high temperature. In this way enough energy is released to overheat the already liquefied metal. The result is a very CO-rich atmosphere with little tendency to oxidize.
• A supplementary amount of wind is supplied in a second zone of wind form B. The wind is not or only slightly warmed. In this way, enough melting energy is released by burning part of the coke and part of the CO that was formed in the lower zone A.
• Finally wind is added in a third separate zone. This is done via a sufficient number of wind forms, which are arranged in a spiral in the upper shaft area of the furnace. This air is required to burn the CO formed in the lower layers. The energy released by this combustion enables the metallic batch to be heated up to temperatures in the region of the melting point.

Claims (1)

1. Shaft furnace, in which a metallic charge is melted with addition of slag-forming admixtures and coke, wherein wind is blown in in a plurality of zones lying one above another and, in the lower zone (A), a wind quantity leading to a sub-stoichiometric combustion of coke is blown in and in the upper zone (C) a sufficient quantity of wind is added for the complete combustion of the gases present, wherein the middle zone lies in the smelting zone and the upper zone is provided for preheating the charge, characterized in that the middle zone (B) is at a distance of 300 to 700 mm from the lower zone (A), the upper zone (C) is at a distance of 500 to 2,500 mm from the middle zone (B) and the upper zone (C) extends through a shaft height of 1,500 to 2,500 mm with a spiral arrangement of tuyères, the quantity of wind added in the zone (A) amounting to 40-60% of the total wind quantity, the quantity of wind added in the middle zone (B) amounting to 20-50% of the total wind quantity, and the quantity of wind added in the upper zone (C) amounting to 20-35% of the total quantity of wind.

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