EP0596095B1 - Process and device for heating and melting lumps of sponge iron - Google Patents

Abstract

In order to heat sponge iron up to temperatures of about 850 °C without substantial oxidation losses, the sponge iron is successively supplied to at least two separate pre-heating stages with different temperatures and in which the temperature and the gaseous atmosphere are individually controlled so that in the first pre-heating stage having the lowest temperature a chemically neutral gaseous atmosphere is set and in the last pre-heating stage having the highest temperature a reducing gaseous atmosphere is set. The hot gas for the pre-heater is taken at least partially from the waste gas of the melting furnace to which the pre-heated sponge iron is supplied.

Description

The invention relates to a method according to the preamble of claim 1. Furthermore, it relates to a device according to the preamble of claim 10.

In a known method of the type mentioned, metallic iron carriers are heated in a batch preheater arranged above a melting furnace and then fed to the melting furnace. An economical mode of operation is only possible in this case if materials are used as the iron carrier which do not have too great a reactivity to oxygen, because only then can the energy content of these exhaust gases be economically used for preheating by post-combustion of the exhaust gases from the melting furnace. If direct, reduced material, i.e. lumpy iron sponge, preheated, then its high reactivity, especially at temperatures above 500 ° C, requires a reducing atmosphere to prevent greater oxidation losses when the iron sponge is heated. For this purpose, the sponge iron mixed with coke was heated in a preheater. However, such a process requires a considerable excess of high-energy exhaust gases and requires gas consumers in the vicinity of the plant.

The invention has for its object to enable a preheating of the highly reactive sponge iron to temperatures of about 850 ° C without substantial oxidation losses and at the same time to avoid an excess of high-energy exhaust gases in a method of the type mentioned in the preamble of claim 1. Furthermore, a facility for carrying out this method is to be specified.

The method according to the invention is characterized by the features of claim 1. Advantageous embodiments of the method can be found in claims 2 to 9. The device according to the invention is characterized by the features of claim 10. Advantageous embodiments of this device are described in the remaining claims.

In the method according to the invention, the different reactivity of the sponge iron at different high temperatures is made usable by preheating the sponge iron in several stages and assigning a certain temperature and a certain gas atmosphere to each of the preheating stages. While at high temperatures of 800 to 900 ° C the sponge iron can only be heated with reducing gases, it is possible to preheat the lower temperature, such as 250 or 500 ° C, to heat the sponge iron in a neutral atmosphere. By means of suitable individual control of temperature and gas atmosphere in the individual preheating stages, a significant increase in economy can be achieved. With the device according to the invention, the subdivision into different preheating stages and the control of temperature and gas atmosphere in these preheating stages can be implemented in a structurally particularly simple manner.

The invention is explained in more detail with reference to a figure which shows a schematic representation of the individual method steps of an embodiment of the invention.

The figure schematically shows a process for melting sponge iron 10 with four preheating chambers 11 to 14 arranged one above the other, which are lined with refractory material, a cupola furnace 15 which is transportable and is arranged under the fourth preheating chamber 14, a coke oven 16 with a feed line 17 to the cupola furnace 15, a recuperator 18, a gas cleaning system 19 and a coal store 20.

The first preheating chamber 11 is rectangular and has a gas outlet 21, which is connected via a line 22 to the gas cleaning system 19, and a charging opening 23, through which sponge iron 10 and limestone 24 can be introduced into the first preheating chamber 11. The bottom of the first preheating chamber 11 is slidably mounted and designed to open and close the preheating chamber 11 as a slide 25 in order to bring predetermined amounts of sponge iron 10 and limestone 24 directly into the preheating chamber 12 below.

Furthermore, the preheating chamber 12 is stepped in the upper area and is also rectangular.

Due to the graded design, a gas space 26, i.e. a solid-free area is formed in the preheating chamber 12.

The third and fourth preheating chambers 13, 14 are designed corresponding to the second preheating chamber 12, namely also stepped and with a slide 28 and 29 as an intermediate floor between the chambers 12/13 and 13/14. The slider 25, 28 and 29 are maximally displaceable across the width of the respective stage below, so that the opening of the iron sponge 10 and the limestone 24 resulting from the movement of the slider 25, 28 or 29 into the preheating chamber located below it 12, 13 and 14 fall or can be carried out. The material flow from the first into the fourth preheating chamber 11, 14 can thus be controlled via the slides 25, 28 and 29.

The fourth preheating chamber 14 has no slide. Rather, it tapers in the lower region and is connected to the cupola furnace 15 via a metering flap 33. The preheating chamber 12, 13 and 14 is provided with a burner 30, 31 and 32, respectively, which opens into the associated gas space 26, 27 and 50 of the relevant preheating chamber. In addition, the fourth preheating chamber 14 in the lower half on another burner 34.

The preheating chambers 11 to 14 are arranged directly one above the other and offset. The third preheating chamber 13 is arranged on the lower stage of the fourth preheating chamber 14, the second preheating chamber 12 on the lower stage of the third preheating chamber 13 and the first preheating chamber 11 on the lower stage of the second preheating chamber 12. The preheating chambers 11 to 13 have gas inlets 35, 36 and 37, which are each arranged directly above the relevant slide 25, 28 and 29 in the adjacent side wall of the adjacent, stepped preheating chamber 12, 13 and 14, respectively.

The cupola furnace 15 is of a known type with a coke bed 48 which can be supplemented with coke 38 from the coke store 16 via the feed line 17.

Furthermore, the cupola 15 has a tap opening 39, burner 40 and an exhaust gas opening 41. This is connected via a line 42 to the recuperator 18 and to the burners 30 to 32 and 34 in such a way that the exhaust gas from the cupola 15 is passed in a controllable ratio, partly to the recuperator 18 and partly to the burners 30 to 32, 34 can. About 40 to 80% of the exhaust gas is fed into the recuperator 18 to heat the combustion air to about 815 ° C. and the rest to the burners.

Furthermore, the coal store 20 and an oxygen source 43 are each connected to the burners 30 to 32, 34, 40 via lines 44. Air 45 can be fed to the burners 30 to 32, 34 via a line 46.

The air preheated in the recuperator 18 is fed to the burner 40 via a line 47 and can be blown into the cupola furnace together with coal from the coal store 20 in order to reduce coke consumption.

Lime and / or preheated air or coal can be introduced in the required amount via the burners 30 to 32, 34, 40. Instead of or in addition to coal, other fossil fuels such as natural gas, oil or synthetic fuels can also be introduced into the preheating chambers 12 to 14 or the cupola furnace 15.

In addition, the exhaust gas from the cupola 15 can be supplied to the preheating chambers 12 to 14 by means of the burners 30 to 32, 34 and the line 42.

The illustrated and explained device is intended for heating and melting sponge iron 10, which is very reactive with oxygen, by means of fossil fuels in order to obtain liquid iron with a carbon content of over 3% and a temperature over 1400 ° C.

For example, 1075 kg of sponge iron 10 is required per 1000 kg of iron obtained. The sponge iron 10 has a typical composition of 85 to 90% metallic iron, 0.5% carbon and 10% iron oxide. The sponge iron 10, together with limestone 24, is introduced into the first preheating chamber 11 via the charging opening 23. Here, 115 kg limestone is preferably added per ton of iron produced.

Due to the arrangement of the cupola 15 and the preheating chambers 11 to 14 one above the other, the mixture of sponge iron 10 and limestone 24 can fall into the preheating chamber 12, 13, 14 below when the respective slides 25, 28 and 29 are opened. The amount to be dispensed into the next preheating chamber 12, 13, 14 is determined by the displacement of the slide 25, 28 or 29 and the duration in which the slide 25, 28 or 29 remains in the open position, controlled.

By opening the metering flap 33, the preheated iron sponge 10 and the lime in a predetermined, weighed amount then pass from the fourth preheating chamber 14 into the cupola furnace 15.

Neutral conditions prevail in the first preheating chamber 11, i.e. neither oxidizing nor reducing conditions. The sponge iron 10 and the limestone 24 are heated here to 250 ° C. by the hot gases flowing out of the preheating chamber 12 and flowing in through the gas inlet 35. The gas flows through the bed of lumpy iron sponge 10 and lumpy limestone 24 introduced into the first preheating chamber 11 and gives off heat to sponge iron 10 and limestone 24. Via the gas outlet 21 and the line 22, the gas is passed to the gas cleaning system, where it is cleaned.

The temperature and the atmosphere, that is to say the gas composition in the individual preheating chambers 11 to 14, are determined by temperature measuring and gas analysis devices (not shown here). The neutral / reducing conditions in the individual preheating chambers 11 to 12 can then be set and maintained or changed by means of the burners 30 to 32, 34. This control is computer-based in a known manner.

The burners 30 to 32, 34, in accordance with the requirements in the individual preheating chambers 11 to 14, blow exhaust gas from the cupola furnace 15 into the preheating chamber 12, 13 or 14, either cooled or via the recuperator. In addition, the burners 30 to 32, 34 can burn coal with air 45 and / or oxygen in order to additionally heat the preheating chamber 12, 13, 14.

The sponge iron 10 and the limestone 24 become about 250 ° C. in the first preheating chamber 11, about 500 ° C. in the second preheating chamber 12, and about in the third preheating chamber 13 800 ° C and heated to about 850 ° C in the fourth preheating chamber 14.

In the third and fourth preheating chambers 13 and 14, the heating takes place under reducing conditions, in that exhaust gas from the cupola furnace 15 is passed into the preheating chambers 12 and 13 accordingly. The carbon monoxide content in the gas mixture CO ₂ + CO should be over 25%.

Up to the fourth preheating furnace 14, the limestone 24 is converted into lime and then serves in the cupola furnace 15 as a flux for the molten sponge iron 10.

The heated sponge iron 10 and the lime are then introduced into the cupola furnace 15 by means of the metering flap 33. The cupola 15 is provided with the coke bed 48, the coke 38 having a size of up to about 20 cm.

In the cupola furnace 15, hot air preheated to 850 ° C. is blown into the coke bed 48 via the burner 40 by the recuperator. Because of the energy released in this way, sponge iron and lime melt and flow together through the coke bed 48. As the melt passes down through the coke bed 48, the temperature of the melt rises further and carbon dissolves in the iron. The melt, which has a composition of over 3% carbon and over 95% pure iron, then collects at the foot of the cupola furnace 15. The melt can then be brought out of the cupola furnace 15 for further processing via the tap hole 39.

The amount of coke required for the process is about 175 kg per ton of iron recovered. The amount of coke 38 required for the process can be reduced if additional coal is used for heating either in the cupola furnace 15 or in the preheating chambers 12 to 14.

The amount of coke can be further reduced to 80 to 100 kg per ton by supporting the combustion processes with oxygen and additional fuels such as coal, natural gas, oil or synthetic fuels.

Claims (15)

1. A process for heating and melting sponge iron in lump form,

   in which the sponge iron is charged into a preheater,

   heated therein by passing hot gases through the fill in heat exchange relationship,

   then passed from the preheater on to a coke bed heated by means of oxygen or hot air in a melting furnace and there melted, and

   the molten material after passing through the coke bed is collected in the lower part of the melting furnace, wherein

   the hot gas for the preheater is at least partially obtained from the waste gas of the melting furnace,

      characterised in that
      the operation of heating the sponge iron in the preheater is effected in at least two separate preheating stages at different temperatures, to which the sponge iron is successively fed, and in which the temperature and the gas atmosphere are respectively individually controlled in such a way that, by virtue of the temperature and the composition of the hot gases which are introduced into the preheating stages, a chemically neutral gas atmosphere is set in the first preheating stage at the lowest temperature and a reducing gas atmosphere is set in the last preheating stage at the highest temperature.
2. A process according to claim 1 characterised in that the reducing gas atmosphere has the ratio: $$\frac{\text{CO}}{{\text{CO}}_{\text{2}}\text{+CO.}}\text{> 25\%}$$

   
3. A process according to claim 1 or claim 2 characterised in that, when there are more than two preheating stages with different stepped temperature values, the ratio $$\frac{\text{CO}}{{\text{CO}}_{\text{2}}\text{+CO}}$$

   

   is set to a value which rises with the temperature value.
4. A process according to one of claims 1 to 3 characterised in that there are provided four preheating stages in which approximately the following temperatures are set:

   Stage 1: 250°C

   Stage 2: 500°C

   Stage 3: 800°C

   Stage 4: 850°C.
5. A process according to one of claims 1 to 4 characterised in that the hot gases of a preheating stage at higher temperature are at least partially introduced into a preheating stage at lower temperature.
6. A process according to claim 5 characterised in that the hot gases are mixed with additional gases before being introduced into the preheating stage at lower temperature, to control the temperature and the gas atmosphere of said preheating stage.
7. A process according to one of claims 1 to 6 characterised in that waste gas from the melting vessel is introduced into the individual preheating stages and control in respect of temperature and gas atmosphere in the individual preheating stages is effected by adding waste gas from the melting vessel, which gas has been cooled in a recuperator, and partial combustion of said waste gas or an additional fuel with an oxygen-bearing gas, in particular air.
8. A process according to one of claims 1 to 7 characterised in that air is preheated in the recuperator, the air being fed to the combustion zone of the coke bed of the melting furnace as hot air.
9. A process according to one of claims 1 to 8 characterised in that sponge iron in lump form is heated jointly with limestone in the preheater and then fed to the melting furnace.
10. Apparatus for heating and melting sponge iron in lump form, comprising a preheater which is arranged above a melting furnace (15) and which at the top has a charging means (23) for the sponge iron (10) and a gas outlet (21), and at the bottom a discharge means (33) for the discharge of the heated sponge iron from the preheater into the melting furnace (15), and also in at least one of the side walls nozzles and/or burners (30, 31, 32, 34) for the introduction of hot gases into the preheater, characterised in that the preheater includes at least two preheating chambers (11, 12, 13, 14) which are respectively arranged one above the other, wherein the uppermost chamber (11) in the upper region includes the gas outlet (21) and the charging means (23) for the sponge iron (10) and the lowermost chamber (14) contains the discharge means (33) in the bottom region, and also provided in the region of the intermediate bottom member between two adjacent chambers is a discharge means (25, 28, 29) for the discharge of sponge iron from the respective upper chamber into the respective lower chamber and a gas inlet (35, 36, 37) for the introduction of gas into the respective upper chamber, wherein the gas inlet (35, 36, 37) is communicated with the respective lower chamber (12, 13, 14) and with a respective gas space (26, 27, 50) into which at least one nozzle and/or burner (30, 31, 32) open.
11. Apparatus according to claim 10 characterised in that the preheating chambers (11, 12, 13, 14) of the preheater are of rectangular cross-section and are arranged in mutually laterally offset relationship, forming a respective gas space (26, 27, 50).
12. Apparatus according to claim 10 or claim 11 characterised in that the intermediate bottom members are in the form of sliders (25, 28, 29).
13. Apparatus according to one of claims 10 to 12 characterised in that the gas inlets (35, 36, 37) are formed in the region of the intermediate bottom members (25, 28, 29) by a respective gap between the respective intermediate bottom member and an upwardly adjoining chamber wall.
14. Apparatus according to one of claims 10 to 13 characterised in that the discharge means of the lowermost chamber (14) is in the form of a metering flap (33).
15. Apparatus according to one of claims 10 to 14 characterised in that associated with each preheating chamber (11, 12, 13, 14) are at least one temperature sensor and at least one gas sensor for individual control of the temperature and gas atmosphere in the respective preheating chamber.

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