DE2543425A1 - Low moisture lime flux for steel obtained by calcining limestone or dolomite - Google Patents

Abstract

A moisture proof flux, for use in producing steels with reduced H2 content is made be calcining limestone or dolomite to produce calcium oxide and immediately reacting the calcium oxide particle surfaces with CO2-containing gas to convert 2-30 wt.% of the calcium oxide to a calcium carbonate film. Preferably the calcined material is contacted with gas containing >=20% CO2 at 300-750[deg]C the reaction preferably being completed by slow cooling from 400[deg]C to 300[deg]C over >=20 minutes.

Description

Method of making steel using

A Carbon Dioxide Treated Flux The invention relates to a method of making steel in which the hydrogen content in the molten Steel by using a flux that has increased moisture resistance has, can be reduced.

The invention also relates to a flux and a method its manufacture.

In general, it is influenced by the water content of the positive agent used the hydrogen content in a steel is essential. Especially the one for refining Quick lime, which is indispensable of steel, or the OaO, which is usually in large quantities is highly hygroscopic, as it is an essential substance for manufacture of steel, especially with low hydrogen content, is an essential one The problem with steel production is therefore the water content of the used To keep quick lime as low as possible. The quick lime can by thermal decomposition of limestone in a calciner or an oalcining oven, e.g. a rotary kiln0 After calcining, the hard lime reacts with the water vapor of the air and the amount of water absorbed increases rapidly in a practically linear fashion. Hence the adverse effect of the water content to exclude in the quick lime, one must expediently this immediately after after calcining in a furnace for steel production. This can be however, it is often difficult to carry out from the plant and out of this The quick lime was often used in an electric furnace or the like before use. dried in a special drying oven to the amount of moisture absorbed to be kept as low as possible before use.

Nevertheless there were still difficulties with hydrogen uptake, caused by the remaining water in the flux.

On the other hand, attempts have already been made in the production of Steel in electric ovens instead of the highly hygroscopic one used so far To use Atzkalks limestone, which has practically no hygroscopic properties to reduce the hydrogen content in the steel. A big problem however, the use of limestone in an electric furnace poses the major one Decomposition heat represents an increased consumption of electrical energy than also an inevitable delay in steel production due to the delayed Flowability has the consequence. It also had to be taken into account that in the case of a converter, in which the heat supply must be restricted, the too the amount of limestone used must be severely limited and the stability of the refining process when using limestone due to insufficient flowability or the increased converter ejection compared to the usual refining processes Use of quick lime is decreasing.

After calcining, the quick lime reacts with water vapor when it cools or carbon dioxide from the air and converts into Ca (OH) 2 and CaC03. The water vapor normally present in the atmosphere is several times that ten times, or in summer even more than a hundred times the amount of carbon dioxide in the air, so that the reaction with water vapor takes place preferentially.

In the context of the invention it has now been found that the response ability Quick lime with steam can be greatly reduced if you use the fresh Quick lime immediately after calcining in contact with a carbon dioxide atmosphere with a low water content and brings the surface of the quick lime particles in CaCO3 transferred, which has practically no hygroscopic properties. Under the "surface" of the caustic lime is not only the outermost surface of the particles, but also the inner surface of imperfections or pores within the particles to understand.

The object of the invention is therefore the previous disadvantages in the Avoid using quick lime for steel refining.

The invention therefore provides a method (1) for producing steel, which uses a flux obtained by contacting calcined and decomposed limestone and / or dolomite with a C02-containing gas and converting from 2 to 30th; of the calcined and decomposed material in CaCO 3 and Z or MgOO 3 was obtained.

The invention also provides a method (2) according to method (1), used in a reducing refining process.

The invention also provides a method (3) according to method (1), used in an oxidizing refining process.

The invention also provides a flux for use in Steel making by bringing the calcined into contact and decomposed limestone and / or dolomite with a gas containing CO2 and converting it from 2 to 30% of the calcined and decomposed material in CaCO3 and / or MgCO3 was produced.

The invention also provides a method (4) for producing the flux described above, in which a calcined and decomposed limestone and / or dolomite with a C02-hal term gas at temperatures between ambient temperature and the calcination and decomposition temperature of the limestone and / or dolomite brought into contact with 2 to 307o 'of the calcined and decomposed material converted into CaCO3 and / or MgCO3.

The invention also provides a method (5) according to method (4), in which a C02-containing gas is used which contains at least 20% CO2.

The invention also provides a method (6) according to method (4), in which the reaction is carried out at temperatures between 300 and 7500C.

The invention also provides a method (7) according to method (4), in which each particle of the calcined and decomposed material is mutually exclusive is moved so that the particles and the 002-containing gas are evenly with one another can react.

The invention also provides a method (8) according to method (4), at which the reaction ends at a final temperature of 350 ° O or below to be led.

The invention also provides a method (9) according to method (5), which is heated to 300 to 4000C for at least 20 minutes.

The invention also provides a method (10) according to method (4), in which a gas is used in the reaction, that is not more as 1% H20 and obtained by drying a C02-containing gas that was produced by decomposing the raw material.

In the context of the invention, quick lime can be used, the one Has a content of about 80 to 100% CaCO 3; one material is suitable as dolomite with a content of about 53 to 66 OaCO3 and about 34 to 47% MgCO3. The invention can be used with dolomite as well as quick lime.

The invention will now be illustrated by the following examples in which Limestone was used, and the drawings are further explained.

In the drawings: FIG. 1 is a graphical representation of FIG Dependence of the conversion into CaO03 on the time at different temperatures; Fig. 2 is a graph showing the relationship between the amount of moisture absorbed on time at different temperatures; 3 is a graphical representation the dependence of the amount of moisture absorbed by the quicklime on the CaC03 conversion and the reaction conditions; Fig. 4 shows the change in reaction temperature between CaO and C02 depending on the reaction time.

In Fig. 1, the reaction between quick lime and carbon dioxide or C02 shown in a device with constant temperature. According to Fig. 1, the reaction between CaO and C02 proceeds very quickly at higher temperatures. At 60,000, the quick lime or CaO converts to in the course of about 10 minutes about 30 wt.% in CaO03 um, while at 200 to 300 ° C only a conversion of about 1% takes place.

The conversion decreases at ambient temperature. In Fig. 2 is the moisture absorption of conventional quick lime and quick lime according to the invention graphically compared, with the quicklime at the specified temperature with the carbon dioxide reacted and then left to stand in air of 75% humidity at 200G became. From this it follows that the moisture absorption of with Arohlendioxid (A) treated quick lime only about 1/10 or less than untreated quick lime (b) and the absolute value of the implementation increases with time.

Regarding the influence of the treatment temperatures, it was wound that a treatment at higher temperatures and higher conversion dragging speed in CaC03 results in less moisture absorption, but even quicklime, that at lower temperatures with a lower rate of conversion into CaC03 has also been treated with sufficient resistance to moisture absorption on. For this reason, temperatures can vary between ambient and the The decomposition temperature of the caustic lime.

The conversion between CaO and C02 can be both with ordinary Execute pressure or under pressure. However, the execution under normal pressure is to be preferred as there is no device for increasing or decreasing pressure is required.

The above conversion is an exothermic reaction, the higher Temperature advances more rapidly than when the temperature is low. From the economic From a standpoint, it is most convenient to make the 0a0 at a higher temperature and to use the heat still present after calcining. Same effect Obviously one obtains if one repeats 0a0 from ordinary temperature heated.

Commercially available pure C02 gas or exhaust gas can be used as CO2 gas use the calciner that has been dried to the point that it is no longer contains than 1% H20. If it contains more water, the formation of Ca (OH) 2 is favored, which is not wanted.

In Fig. 3 is the relationship between the conversion to CaCO3 and the Resistance to moisture absorption for the conversion between CaO and CO2 at various temperatures (ordinary temperature up to 750 ° C) and various Duration (10 minutes to 360 minutes) shown. As the conversion to CaCO3 increases the resistance to moisture absorption. If you have quicklime is used, which has been converted to 2 to 30%, the following result is obtained: The surface of all the walls of the particles, including the pores of the quicklime, is covered with a film of non-hydrated 0a0O3, which makes the hygroscopic Properties of the particles are reduced.

If such quick lime is added to molten steel, it forms CO2 gas, which is the water vapor formed from quicklime or other additives diluted, thereby preventing the diffusion of hydrogen into the molten steel will.

In this way it is possible to measure the hydrogen content of molten Decrease steel.

Furthermore, the melt flow of quick lime is accelerated because it is effective Bath movement at the interface between the molten slag and the still non-molten quicklime takes place. In addition, the so treated Quick lime hardly pulverized by impact or abrasion, as it is covered by a film of CaCO3 surrounded0 If the conversion to CaCO3 is less than 2%, the influence takes place to the reduction of the hygroscopic properties of the quick lime or the prevention the diffusion of hydrogen into the molten steel; on the other hand is the If the conversion is more than 30%, there are disadvantages similar to those when using Limestone instead of quicklime.

Example 1 Limestone was placed in a rotary kiln using Heavy oil calcined as fuel. The quicklime obtained in this way or the 0a0 existed from a mixture of lumps, particles and powder and the temperature used was more than 9000C. This was followed by using a vibrating sieve sifted and thus a clay lime with a controlled particle size of 10 to 30 mm obtain. The lumps and powder were discarded. This is to achieve that the particles obtained in this way are passed through the C02 gas in the next stage of the process can be converted almost uniformly into CaCO3 in a simple manner and thereby the Reactivity and the processing conditions in the steelmaking furnace be made uniform.

For this purpose, the regulated size CaO particles were rotated in one rotation offset rotary kiln introduced and at the same time N2 gas or tuft with low moisture content, so that the CaO particles on a have been cooled down at a certain temperature. This was done for the following purpose: The OaO particles react with gaseous CO2, the more violently the higher the temperature. By the heat of reaction that is formed increases the temperature of the CaO particles so that the implementation is accelerated more and more. The strength of the on the surface of the CaO 3 bilms formed from CaO particles do not have to be large, as long as the strength is practical is uniform. If the film is strong, the amount of limestone will be high, what has the aforementioned disadvantages with undesirable results.

In the following Table I are the results of Experiment No. 1 - 4 reproduced, in which the amount of treated CaO-droplets applied Temperature, the amount of C02 introduced, the amount of CaC03 converted and the amount of moisture absorbed are compiled. For comparison purposes is Table 1 also shows the absorbed moisture of CaO particles at high temperature were dried (experiment no. 5), as well as normal CaO particles (experiment no. 6) listed.

Table I Conditions for treatment with CO2 and results Conditions of treatment with CO2 test results Type of used- Treated temperature bypass- Linger- Conversion- Absorb- Attempted quick lime amount, kg / the main CO2 time in lung in te humid No. Charge reaction amount, the main CaCO3 * activity zone, ° C m³ / h reaction% amount,% zone, min. at isothermal Implementation with 1 71 515 to 525 8.5 to 9.5 22 6.8 0.04 to 0.08 CO2 treated Quicklime 2 "73 530 to 545 10.0 to 10.7 38 8.1 0.02 to 0.07 3 "70 600 to 610 12.1 to 13.0 58 14.2 0.02 to 0.04 in the case of cooling tion with CO2 4 70 600 to 300 7.2 - 8.5 0.07 to 0.11 treated Quicklime at high tem- temperature 5 - - - - - 0.05 to 0.10 drier Quicklime not behane 6 delter - - - - - 2.1 to 2.7 Quicklime In Table I, the amount of moisture absorbed (%) was calculated after the quick lime was left to stand for 16 hours in an atmosphere having a water vapor pressure of 15 to 20 mm. In the WrO 5 experiment, the quick lime was heated again to 9000 ° C. for 360 minutes and the water content was analyzed immediately afterwards.

The change in the temperature of the 0a0 in this example in the Above mentioned experimental rotary kiln is shown in Fig. 4, in which the isothermal Reaction zone as the main reaction zone and the subsequent sensing zone as an additional one Reaction zone is designated.

The initial temperature (A) of the CaO particles introduced into the rotary kiln was about 900 ° C. During the rotation of the furnace and cooling in the open air the initial temperature (ß) for the reaction with the 1O2 gas for the isothermal reaction 515-52500, 530-545 ° C and 600-610 ° C, respectively, as listed in Table I. These temperatures were practically constant until the end point (a) was reached The supply of CO 2 gas was maintained and then was in the following additional reaction zone cooled to ambient temperature with further supply of CO2 gas.

In these isothermal reaction experiments it was found that the Reaction temperature of the main reaction zone preferably between 300 and 750 ° C and in particular should be between 400 and 650 ° C.

The amount of CO2 to be introduced to maintain the temperature can be set in essentially from the amount of heat discharged from the furnace, the amount of CaO treated, the particle size of the treated CaO and the like.

The amount of CO2 gas to be added can, however, be determined regulate more precisely by an electrical thermocouple that at a certain point is introduced inside the CaO particle layer and electrically with a valve for the gas supply is connected, In the cooling reaction, in which the amount of supplied amount of 002 gas lower than the isothermal reaction type is, the temperature gradually decreases as shown in Fig. 4 because the amount of heat generated is not as great as the amount of heat discharged. In In this case, the temperature of the CaO particles decreases locally and rapidly, so that a reaction film with sufficient properties cannot be obtained.

Because of this, the amount of moisture absorbed in this one Case slightly larger than in the isothermal course of the reaction, If on the other hand there is an excess is applied to CO2 gas, the amount of heat generated is greater than that which is discharged Amount of heat, which increases the temperature of the CaO particles and increases the thickness of the film becomes too big. This is the reason why the implementation with C02 gas at almost the same Temperature should be executed.

As can be seen from Table I, the amount of moisture absorbed is in the isothermal reaction in experiment 1 0.04 to 0.08% by weight, in experiment 2 0.02 up to 0.07% by weight and in experiment 3 0.02 to 0.04% by weight, determined after 16 hours Standing in an atmosphere with a water vapor pressure of 15 to 20 mm Hgo when attempting 4 is the absorbed value determined for the cooling reaction under the same conditions Moisture amount 0.07 to 0.11% by weight. These values are all very small and amount to only several tenths of the value of 2.1 determined for untreated quick lime up to 2.7% by weight and thus have excellent moisture resistance, which is no worse than the one in attempt. 5 found moisture content of 0.05 to 0.10 wt, -f at a Ca0, the longer time immediately before use was dried at high temperature.

Example 2 The influence of the end point of the treatment temperature was with regard to the treatment conditions used in Example 1 examined. As can be seen from Fig. 3, the end point of the treatment temperature exerts a strong one Influence on the moisture resistance of the treated material. A comparison the endpoints with the same content of OaX03 formed shows that the absorbed Amount of moisture at an end point of 400 ° C several times greater than at an end point of 3000C. The difference becomes smaller when the endpoint is 35,000 or below If the treatment temperature end point is 30000 or less, exercise the end point does not have any significant influence from 0 This means that the end point should preferably be 35,000 or less.

An investigation into the influence of cooling speed in the vicinity the end point of the treatment temperature showed that it was to achieve a satisfactory Moisture resistance is necessary, gradual cooling between 400 and 3000C for at least 20 minutes. The extent of the cooling depends also on the heat discharged from the furnace, the amount of quicklime used and the Concentration of the applied C02 gas. Balls the concentration of C02 20% or less, sufficient cooling cannot always be passed achieve the heat of reaction alone, but if an adiabatic device for Preventing heat from being discharged from the furnace or using an additional heating device are used from the outside, a lower concentration of the reaction gas can be achieved apply, Example 3 When refining in an ID tonverter, an according to the invention was used Quick lime treated with C02 gas with a content of 5.2 to 5.8 OaC03 as CaO starting material used and too Ordinary quick lime was used for comparison purposes.

The amount of quicklime used was about 35 kg / to steel, calculated as CaO. The results are summarized in the following Table II: Table II Type of water content avg. avg. avg. use heat in quicklime un- content P content H content deten number indirectly before (%) after (%) after (parts pr Quick lime of the use of the Ver million) blow blow after Fade away with 0.2 to 0.4% 0.08 0.012 0.9 CO2 gas 3 (average treated delter Ät zk; alk usual- 3.5 to 5.4% licher 5 (average 0.08 0.014 1.5 Caustic lime 4.8%) Example 4 In the reduction phase of refining in an electric furnace, quicklime treated according to the invention with CO2 gas and having a CaCO3 content of 6.3 to 6.6% was used as CaO. The results obtained here were compared with the results obtained when using ordinary quick lime0 The amount of quick lime used was about 20 kg / to steel, calculated as CaO. The results are summarized in the following Table III: Table III Type of water content avg. avg. avg. use- heat- in quicklime un- H-content H-content S-content, deten number indirectly before (parts per (parts per%, after Quick lime | | of use | Million) | Million) terminate after termination of end of the end of the reduction Oxidation | reduction period period period with C02 gas 3 Q, 1 to 0.3% 1.3 2.0 0.003 treated (average Quicklime dried 4 1.1 to 2.0% 1.3 3.8 0.004 (Average Quicklime Example 5 A steel that had been decarbonized and dephosphorized in a converter was transferred to a pouring ladle, into which quicklime, fluorspar and alumina were added, and then slag was refined by arc heating. A quick lime treated according to the invention with CO 2 gas with a CaCO 3 content of 6.5 to 6.9% was used as CaO, and for comparison purposes, ordinary dried quick lime was used. The amount of quick lime used was about 45 kg / to steel, calculated as CaO.

The results are summarized in the following Table IV: Table IV Type of water content avg. avg. #H use heat coefficient directly H-content H-content (parts deten before the (parts per (parts per per Quick lime use million) million) million) after finished after finished completion of completion of Converter casting pan Fading kidney with CO2 gas 5 0.1 to 0.3% 1.3 2.1 0.8 treated (Average Quicklime dried neter 4 1.1 to 2.0% 1.4 4.5 3.1 (Average 1.5%) Note: zH = hydrogen uptake during refining in a ladle. Example 6 In this example, a graphite electrode provided with a central hole was used0 Argon was introduced through this central hole0 The diameter of the electrode was 350 mmo The diameter of the central hole was 21 liters. The amount of argon introduced through the central hole was 100 l / minO per electrode. Under these conditions the same quick lime treated with CO 2 as in Example 3 was used. The average hydrogen content in the converter after the end of the blowing was 1.5 parts per million; after completion of the ladle refining, the average hydrogen content was 1.9 parts per million and the value of hH was 0.4 parts per million.

Example 7 A tapping of molten steel from a 60 ton converter as well as a mixture of quick lime, fluorspar and iron oxide were placed in a pouring pan transferred0 The tapping time was 4 to 5 minutes. A quick lime was used according to the invention Quick lime treated with CO2 gas with a CaCO3 content of 6.4 to 6.6% is used and ordinary quick lime was used as a comparative substance. The quick lime was in an amount of 5.0 kg / to steel, calculated as CaO, the iron oxide in an amount of 2.3 kg / to of steel, the fluorspar in an amount of 1.8 kg / to of steel and the alumina added in an amount of 0.9 kg / to steel.

The results are shown in Table V below. Table V C,% P,% Parts per million After the Fading in 0.08 0.018 1.2 converter use of treated with CO2 0.07 0.009 1.3 deltem quicklime to the Racking use of 0.07 0.012 1.9 Quicklime As can be seen from the preceding examples, according to the invention, quick lime can be produced at low cost which has extremely low hygroscopic properties. Therefore, if this quicklime is used in a converter, an electric furnace, a ladle, an electric slag furnace and the like, the hydrogen content of the steel can be reduced considerably compared to the known method, so that a vacuum degassing of the molten steel or a heat treatment for the purpose Dehydration is superfluous and the same effect is achieved as when using ordinary CaO, which has been dried for a long time in a special device with considerable fuel consumption shortly before use. The invention thus creates an advanced process in which both fuel is saved and the process steps are simplified.

Claims (1)

P a t e n t a n s p r ü c h e 1. Process for the production of steel, characterized in that a flux is used that is in contact with bring calcined and decomposed limestone and / or dolomite with a CO2-containing Gas and converting from 2 to 30% of the calcined and decomposed material to Ca003 and / or MgCO3 was produced. 2. The method according to claim 1, characterized in that the Flux used in a reducing refining process4 3rd process according to claim 1, characterized in that the bleaching agent in an oxidizing Refining process used. 4. Flux for use in the manufacture of steel, manufactured by mixing calcined and decomposed limestone and / or dolomite with a C02-containing Bringing gas in contact and 2 to 30% of the calcined decomposed material in CaCO3 andX or MgCO3 converts 50. A method of making a flux according to claim 4, characterized in that calcined and decomposed limestone andtor Dolomite with a gas containing CO2 at a temperature between ordinary temperature and the calcination and decomposition temperature of the limestone and / or dolomite brings in contact up to 2 to 30% of the calcined and decomposed material in OaCO3 and / or MgCO3 are transferred. 6o method according to claim 5, characterized in that the C02-containing Gas contains at least 20% aO2. 70 The method according to claim 5, characterized in that the Implementation at temperatures between 300 and 750 ° C executes. 8. The method according to claim 5, characterized in that each Particles of the calcined and decomposed material in mutual motion is subjected so that the particles and the C02-containing gas are uniform with each other react. 9. The method according to claim 5, characterized in that the Reaction carries out at a final temperature of 350 ° C or less. 10. The method according to claim 6, characterized in that temperatures between 300 and 4000C for at least 20 minutes. 11. The method according to claim 5, characterized in that one Gas with a content of not more than 1% H20 is used, obtained by drying a C02-containing gas was obtained, which when decomposed in the implementation used starting material was formed.