DE2748232A1 - Desulphurisation of molten iron and steel or stack gases - using rare earth oxide under deoxidising conditions - Google Patents

Abstract

Molten iron and steel or stack gases are desulphurised using a rare earth oxide in the presence of a separate deoxidising agent or atmos., the oxide reacting with sulphur to product rare earth sulphides and/or oxysulphides. The method is esp. useful in the treatment of hot metal, in a ladle or transfer car by simple addition of the rare earth oxide, by injecting the oxide in a carrier gas such as Ar or N2, or by the use of an active lining. The method can also be used in steel making where vacuum desulphurisation is carried out by an active lining in the ASEA-SKF process and circulation vacuum degassing processes.

Description

Process for the desulfurization of iron and steel and

Gases, such as exhaust gases The invention relates to a method for desulphurisation of iron, steel, exhaust gases and the like, with the rare oxides Grounding in the presence of an agent such as carbon, reducing gases if necessary in a vacuum for reducing the oxygen content with the sulfur to be removed with the formation of sulfides of the rare earth metals, oxysulfides of the rare earth metals or their mixtures are implemented.

The invention relates to a method for desulfurizing iron and steel and similar materials. It relates in particular to a method for external desulfurization of iron and steel, exhaust gases, coal gases and the like under Use of the rare earth metal oxides.

The external desulfurization of molten iron and steel is done done for some time. With the bulk of the iron produced today and Stahls this is a recognized and even necessary procedure. With the currently methods used for desulphurization are generally magnesium metal, Magnetic cokeJ calcium oxide, calcium carbide or mixtures of calcium oxide and calcium carbide used. When using all of these materials for desulfurization occur Not only does it pose great difficulties, but the cost is also considerable. As well as CaO and CaC2 must of course be stored under dry conditions as CaO hydrates and CaC2 releases acetylene on contact with moisture. Magnesium is of course highly flammable and must be stored and stored very carefully be handled. Furthermore, when disposing of the used desulphurisation slag, which contain unreacted CaC2, difficulties.

It has now been found that these storage, material handling and disposal difficulties can be reduced significantly by using rare earth oxides used in a bath of molten iron or steel with low oxygen content. The process can be used in the desulphurisation of pig iron or steel, where carbon monoxide is released by the reaction when coal is used as a deoxidizer is used, is diluted with an inert gas such as nitrogen, or in vacuum degassing of the melt to increase the effectiveness of the reduction by reducing the likelihood of that oxysulfides are formed. The principle can also be used to desulfurize Exhaust gases from boilers, etc. can be used.

According to the invention a method for the desulfurization of molten Iron and steel as well as from exhaust gases and the like made available, in which the rare earth oxides or rare earth metal oxides in the presence of a deoxidizer with the sulfur to be removed with the formation of rare earth sulfides and / or rare earth oxysulfides and / or their mixtures are implemented.

The hot metal is preferably in a pan or a truck with the rare earth oxides by simply adding and mixing the rare earth oxides or by injection process, in which the rare earth oxides in the molten bath in or using a carrier gas such as argon or nitrogen an active lining or an active coating ", i.e. a rare earth oxide coating, carried out in the container. In any case, the chemical reactions that occur are: 2CeO2 (s) + [C] = Ce2O3 (s) + CO (g) ................. (1) RE2O3 (s) + [C] | [S] lw / o = RE2O2S (s) + CO (g) ...... (2) and RE2025 (s) + 2 [C] + 2 / S 71w / o = RE253 (s) + 2CO (g) ... ( 3) That Sulphide or oxysulphide product is either attached to the "active" liner or it is removed by flotation and in the slag lining and the vessel lining are absorbed, depending on the method used for the supply of the rare earth oxides.

The desulphurisation products of iron saturated with carbon with rare earth oxides depends on the partial pressure of the CO, pCO and the Henrian sulfur activity in metal, hs, ab.

Using cerium as an example for the rare earth metal, one can calculate the following standard free energy changes of the equilibrium constants at 15000C for different desulfurization reactions from the thermodynamic values in the literature. Response # G ° Cal. K1773 2CeO2 (s) + [C] = Ce2O3 (s) + CO (g) 66000-53.16T pCO = 3041 Ce2O3 (s) + [C] + [S] lw / o = 18220-26.43T pCO / hs = 3395 Ce2O2S (s) + CO (g) Ce2O2S (s) +2 [C] +2 [S] lw / o = 66180-39.86T p²CO / hS² = 3.6 Ce2S3 (s) + 2CO (g) 3/2 Ce2O2S (s) +3 [C] +5/2 127050-72.1T p3CO / hS5 / 2 = [S] lw / o = Ce3S4 (s) + 3CO (g) 1.25 Ce2O2S (s) +2 [C] + [S] lw / o = 120860-61, OT p2Co / h5 = 0.027 2CeS (s) + 2CO (g) C (s) +1/2 O2 (g) = CO (g) -28200-20.16T pCO / p1 / 2 = 7.6 x 10-7 1/2 S2 (g) = [S] lw / o -31520 + 5.27T hS / p1 / 2S2 = 5.4 x 10² The thermodynamic values of desulfurization with lanthanum oxide La203 are similar, although in this case LaO2 is unstable and no conversion accordingly takes place.

In the foregoing general description of the invention, explains the specific objectives, purposes and benefits.

Other objects, purposes and advantages of the invention are apparent from the following Description and the accompanying drawings.

Fig. 1 is a stability diagram showing the wt% sulfur as Partial pressure of CO.

2a and 2b show Ce2S3 and Ce2025 layers on a CeO2 pellet.

Figure 3 is a graph of what is theoretically required CeO2 for the removal of 0.01 wt.% 5 / 907.2 kg of hot metal.

Fig. 4 is a graph showing the volume of nitrogen is shown, which is required to achieve a given partial pressure of CO produce.

Fig. 5 is a graph showing the CeO2 requirements as a function of the partial pressure of CO, and Fig. 6 is a stability diagram of the exhaust systems that are treated according to the method according to the invention.

From the above explanations for the free energy it can be seen that these free energy changes are used to determine the stability fields of Ce203, Ce202S, Ce2S3, Ce3S4 and CeS, expressed as the partial pressure of CO, and the Henrian sulfur activity in the melt at 1500 ° C can. The resulting stability diagram is shown in FIG. 1. The boundary lines between the phase fields result from the following relationships: Limit equation Ce203 - Ce2O2S log pCO = log hs + 3.53 Ce2O2S - Ce2S3 log pCO = log hS + 0.28 Ce2O2S - Ce3S4 log pCO = 0.83 log hS + 0.03 Ce2O2S - CeS log pCO = 0.5 log h8 - 0.79 Ce2S3 - Ce3S4 log h5 = -1.47 Ce3S4 - CeS log h, = -2.45 The phase fields of FIG. 1 are also given as Henrian activity of oxygen, hO. Furthermore, the approximate value [wt.% S] in the molten iron is given using an activity coefficient fS # 5.5 for saturated graphite conditions.

The coordinates of these points B, C, D and E on the diagram are given below: Coordinates BCDE pCO atm. 9.8x10-3 6.5x10-2 1.0 1.0 hS 3.5x10-3 3.4x10-2 5.3x10-1 2.9x10-4 Approximate 6.4x10-4 6.2x10-3 9.6x10-2 5.3x10-5 value [wt.% S] Points B and C represent simultaneous equilibria between the oxysulfides and the two sulfides at 15000C.

These univariate points are only a function of temperature. the Points E and D are the minimum sulfur levels or activities at which oxysulfides and Ce2S3 at pCO = 1 atm. is formed. The hot -4 saturated with carbon Metal can be caused by oxysulphide formation below h5 - 2.9x10 (/ wt% s7 - 5.3x10 5) pCO = 1 atm. not be desulfurized.

However, low sulfur levels can be obtained using the Partial pressure of CO decreased.

The conversion of is illustrated in Figures 2a and 2b. These show Ce2S3 and Ce202S layers on a pellet of CeO2 (which is first rearranged in Ce203) when immersed in graphite-saturated iron at ~ 16000C, which initially contains 0.10% by weight S, for 10 hours. The final sulfur content is ~ 0.03% by weight and the test is carried out under argon, where pCO «1 atm.

The conversion of the oxide to the oxysulfide and sulfide is a controlled one Mass transfer and, as with the known external desulfurization with CaC2, is vigorous stirring or vigorous agitation in the simple addition process necessary. In the "active lining" process, circulation of the hot metal may be required.

From Fig. 1 it is evident that the external desulfurization of graphite-saturated iron is thermodynamically possible using rare earth oxides. For example, it follows from the diagram that sulfur contents in the hot metal of -0.5 ppm (point E) by cerium oxide addition itself pCO = 1 atm. can be obtained. The desulfurization in this case is carried out by the conversion sequence take place, for which 2 moles of CeO2 are required to remove 1 gAtom of sulfur.

The effectiveness of sulfur removal per kg or added lb of CeO2 can, however, be significantly increased by the formation of sulfides. 1 mole of CeO2 per gatom of sulfur is required for CeS formation and 2/3 mole of CeO2 for Ce253 formation. Theoretical CeO2 requirements for the removal of 0.01 wt.% S / 907.2 kg hot metal for the various desulfurization products are listed below and are shown graphically in FIG. Product kg CeO / 0.01 m3CO / 0.54 kg m Co / 0.01 wt% S. Wt.% Ss 907.2 CeO2 (ft CO / 907.2 kg hot kg of hot Ne- 1b CeO2 metal (ft3 CO / tall (1b CeO2 / @ 0.01 w / o S.THM) 0.01 w / o SX Ce2O2S 0.975 (2.15) 0.0595 (2.1) 4.5 CeS 0.499 (1.1) 0.119 (4.2) 4.5 Ce3S4 0.363 (0.8) 0.119 (4.2) 3.4 Ce2S3 0.318 (0.7) 0.119 (4.2) 3.0 THM = US tonne of hot metal The volume of carbon monoxide formed in m3 CO / 0.454 kg CeO (ft3 CO / lb) and m3 CO / 0.01 wt.% S / 907.2 kg hot metal (ft3 CO / 0, 01 w / o S.THM) are also listed in the table above for the desulphurisation product. For effective desulfurization, the partial pressure of the carbon monoxide should be sufficiently low so that oxysulfide formation is avoided. For example, it follows from FIG. 1 that oxysulfide does not form in the melt saturated with graphite until [% by weight 52 <0.01, when pCO # 0.1 atm. amounts to. However, it will form when [wt% S] - 0.10 at pCO = 1 atm. is. If the pCO is reduced to 0.1 atm. In the desulfurization process, the hot metal can be reduced to 0.01 wt.% S with a CeO2 addition of 0.33 kg / 0.01 wt.% Sulfur (0.72 lb. / 0.01 wt.% S), which is removed per 907.2 kg (1 US ton) of hot metal, can be desulfurized.

The choice of the method of reducing the partial pressure of carbon monoxide depends on economic and technical considerations. In an injection process however, calculations can be made for the volume of injection gas such as nitrogen required to produce a given pCO. Thus: VN2 = VCO (1-pCO) / pCO where 3 VCO is the m (ssf) of CO formed / 0.454 kg (lb) added CeO2 means, VN the m3 (scf) of the required N2 / 0.454 kg (lb) added CeO2 means, and pCO is the desired partial pressure of CO in atm. means.

The results of these calculations of Ce2S3 formation are shown in Fig. 4, where the /Gew.% SZ in equilibrium with Ce2S3 (s) as a function is represented by pCO.

From this figure it is evident that the volume of N2 / 0.454 kg (lb) CeO2 required for the formation of Ce2S3 is excessive and that, if an injection process is used, the balance between the sulfide and the Oxysulfide formation would be needed. For example, if hot metal from 0.05 to 0.01 wt% S at pCO = 0.2 atm. should be desulphurized, ~ 16 m2 (scf) N2 / 0.454 kg CeO2 is required for Ce2S3 formation and the sulfur content would be fall to 0.02 wt%. The remaining 0.01 wt% S would be used for oxysulfide formation removed.

From Figure 3 it can be seen that 0.907 kg (lb) CeO2 / 907 kg hot metal (U.S. ton of hot metal) Ce2S3 formation and 0.907 kg (2 lbs) are required for Ce2O2S formation, resulting in a total requirement of 1.81 kg (4 lbs) CeO2 / 907.2kg hot metal results.

Similar calculations were made as those above for the establishment of Fig. 5, where the CeO2 requirements in kg / 907.2 kg (abs) hot metal as Function of pCO.

Are large volumes of nitrogen in an injection process is used, the heat carried away by the nitrogen as perceptible heat becomes, not great. But the increased losses from radiation can be large. Injection rates with CaC2, for example, are on the order of 28.3 dm (0.1 scf) N2 / 0.454 kg CaC2.

Vacuum treatment is another method for reduction the partial pressure of carbon monoxide. This is with the external desulfurization of impractical with hot metal, but not in steel making (see the following Versions).

Still another method for external desulfurization using One of the rare earth oxides is the use of active linings on which the carts for the hot metal by cannon spraying or flame spraying with rare earth oxides be lined. This is where the oxides turn into oxysulfides during transport of the hot metal is transferred from the blast furnace to the steelmaking plant and the Oxides are regenerated through atmospheric oxidation when the car is emptied will. It is assumed that the conversion of a 2 mm (0.080 ") layer of oxide to oxysulfide to reduce the sulfur content of the hot metal decreased by ~ 0.02 wt .-% sulfur. This method has the following advantages: 1. A continuous regeneration of the rare earth oxides through atmospheric oxidation, when the car is emptied.

2. The reaction times are on the order of hours.

3. The absence of sulfur-rich desulfurization slag.

4. The absence of suspended sulfides in the hot metal.

The mechanical integrity and service life of an "active" Lining is of course critical and can cause some air pollution problems be associated with oxide regeneration through atmospheric oxidation.

For steelmaking applications, vacuum desulfurization can be performed with a active lining or an "active" surface in the ASEA-SKF process and in the vacuum degassing circulation method.

The following gas composition is used for desulfurization 1000 ° C on: Composition% by volume CO, 16 CO 40 H2 40 N2 4 3 3 H2S 0.3 (0.832 m3, 200 grains / 100 ft This equilibrium gas composition is represented by point A shown in the diagram explained in Fig. 6, where CO / CO2 = 2.5 and H2 / H2S are. This point lies within the Ce202S phase field and at a constant CO / CO2 desulphurization with Ce203 he will accept the position up to point B. At the Point B will be H2 / H2S ~ 104 and the concentration of H2S will 0.004 vol.% (3 3 grains / 2.83 m3 = ~ 3 grains / 100 ft3). Behind this point desulfurization is no longer possible.

In the above description, certain preferred embodiments have been made explained. However, the present invention is also intended to include such embodiments are included that have not been explicitly explained.

Claims (10)

Claims 1. A method for desulfurization of molten material Iron, steel, exhaust fumes and similar materials that contain sulfur as an impurity contain, characterized in that the following steps are carried out: (a) Rare earth oxides in the presence of one, namely a separate deoxidizer, or a deoxidizing atmosphere with the sulfur to be removed to form of rare earth sulphides, rare earth oxysulphides or mixtures of these compounds converts, and (b) removes the oxysulfides and sulfides. 2. Process for the desulfurization of molten iron, steel, exhaust gases and like materials containing sulfur as an impurity according to claim 1, characterized in that the oxygen potential is low at Reduction of the partial pressure of CO is maintained. 3. The method according to claim 2, characterized in that the partial pressure of CO below about 0.1 atm. is held. 4. Process for the desulfurization of molten iron and steel according to claim 1, characterized in that the rare earth oxide to the molten metal bath by injecting the rare earth oxide under the Surface of the molten metal bath is added in a stream of inert gas, which is sufficient to lower the carbon monoxide formed during the reaction to a value below about 0.1 atm. to dilute. 5. Process for the desulfurization of molten iron and steel according to claim 4, characterized in that nitrogen is used as the inert gas. 6. Process for the desulfurization of molten iron and steel according to claim 1, characterized in that the rare earth oxide to the molten Metal bath is given, which is subjected to a vacuum that is sufficient, the partial pressure of carbon monoxide below about 0.1 atm. to keep. 7. Process for the desulfurization of molten iron and steel according to claim 1, characterized in that the molten metal is in a container is poured, which has a surface covering or a surface lining made of rare Contains earth oxides. 8. Process for the desulfurization of molten iron and steel according to claim 7, characterized in that the lining or the covering consists of rare earth oxide is at least 2 mm thick. 9. Process for the desulfurization of molten iron and steel according to claim 7, characterized in that the lining or the covering of the The rare earth container is regenerated with oxygen after the desulfurized Molten metal was removed and before another bath of molten Metal is poured into the container. 10. Process for the desulfurization of molten iron and steel according to claim 7, characterized in that the container is exposed to a vacuum is sufficient to have a partial pressure of carbon monoxide below 0.1 atm. to surrender.