Method for treating desulfurization slag

Abstract

A method for treating desulfurization slag involves conveying desulfurization slag from pig iron desulfurization to a unit where the desulfurization slag is melted at a temperature of at least 1,400 C. In the unit, a thorough mixing is achieved. The treatment takes place in the unit under oxidizing conditions. Sulfur dioxide is generated and collected from the roasting gas and supplied for further utilization.

Claims

1. A method for treating desulfurization slag, comprising: (a) providing desulfurization slag comprising sulfur, from pig iron desulfurization, (b) conveying said desulfurization slag to a unit including a burner, said unit assuring a thorough mixing, (c) melting the desulfurization slag at a temperature of at least 1,400 C., wherein a value of the burner is set to 1.3-1.6 during said melting, (d) setting the burner to a value greater than 2.0 to generate a roasting gas including SO.sub.2, (e) collecting the generated SO.sub.2, and (f) supplying said generated SO.sub.2 for further utilization.

2. The method of claim 1, further comprising adding quicklime to the desulfurization slag in the unit.

3. The method of claim 1, further comprising tapping of a treated desulfurization slag and feeding the treated desulfurization slag into pig iron production.

4. The method of claim 3, wherein the treated desulfurization slag has a sulfur content of less than 0.1% by mass.

5. The method of claim 3, wherein the treated desulfurization slag has a sulfur content of less than 0.01% by mass.

6. The method of claim 1, wherein the unit is a top blown rotary converter.

7. The method of claim 1, wherein the value of the burner during melting is set to 1.4-1.5.

8. The method of claim 7, further comprising adding quicklime to the desulfurization slag in the unit.

9. The method of claim 7, further comprising tapping of a treated desulfurization slag and feeding the treated desulfurization slag into pig iron production.

10. The method of claim 7, wherein a treated desulfurization slag has a sulfur content of less than 0.1% by mass.

11. The method of claim 7, wherein a treated desulfurization slag has a sulfur content of less than 0.01% by mass.

12. The method according to claim 1, wherein the unit is a top blown rotary converter.

13. A method for treating desulfurization slag, comprising: (a) providing desulfurization slag comprising sulfur, from pig iron desulfurization, (b) conveying said desulfurization slag to a unit including a burner, said unit assuring a thorough mixing, (c) melting the desulfurization slag at a temperature of at least 1,400 C., wherein a value of the burner is set to 1.3-1.6 during said melting, (d) setting the burner to a value greater than 2.0 to generate a roasting gas including SO.sub.2, CO and dust, (e) afterburning at a temperature of at least 800 C., (f) cooling the roasting gas, (g) collecting the generated SO.sub.2, (h) removing the dust, and (i) supplying said generated SO.sub.2 for further utilization.

14. The method of claim 13, further comprising adding quicklime to the desulfurization slag in the unit.

15. The method of claim 13, further comprising tapping of a treated desulfurization slag and feeding the treated desulfurization slag into pig iron production.

16. The method of claim 13, wherein a treated desulfurization slag has a sulfur content of less than 0.1% by mass.

17. The method of claim 13, wherein a treated desulfurization slag has a sulfur content of less than 0.01% by mass.

18. The method according to claim 13, wherein the unit is a top blown rotary converter.

19. The method according to claim 13, further comprising: (a) determining a volume percent of exhaust gas components CO and SO.sub.2 in an exhaust gas during the melting of the slag and during generating the roasting gas, (b) when the volume ratio of SO.sub.2 to CO exceeds unity, setting the burner value to greater than 2.

20. The method of claim 19, further comprising adding quicklime to the desulfurization slag in the unit.

Description

(1) The invention will be explained by way of example in conjunction with the drawings. In the drawings:

(2) FIG. 1: shows the process sequence;

(3) FIG. 2: shows the relationship between the release of CO and SO.sub.2;

(4) FIG. 3: shows the effect of admixing quicklime on the melting point of the slag.

(5) According to the invention, the desulfurization slag is heated to temperatures greater than 1,400 C. At lower desulfurization temperatures, the material handling is made significantly more difficult due to agglomeration. According to the invention, the process is carried out in a unit that permits a sufficient turbulence and thus thorough mixing, particularly in a so-called rotary converter (TBRC top blown rotary converter) or a short rotary furnace. In this case, a slightly oxidizing atmosphere is used and the sulfur is released in the form of SO.sub.2 roasting gas. In order to be able to operate the burner of the rotary converter independent of the oxygen demand of the roasting process, the reaction oxygen can be supplied by means of a separate lance.

(6) The slag is processed until no more SO.sub.2 roasting gas is released; the rotary converter ensuring a good homogenization. The value of the burner during the melting of the slag is set to 1.3-1.6, preferably 1.4-1.5. The excess oxygen is necessary in order to quickly convert the carbon contained in the pig iron fraction of the slag to CO and CO.sub.2. Otherwise, the pig iron, which is low-melting due to the presence of the carbon (melting point of approx. 1,200 C. according to the iron/carbon diagram), rapidly precipitates out as regulus of iron and constitutes a separate phase. For the actual roasting (sulfur bonded into the slag released as SO.sub.2), the value of the burner is preferably set to >2.0 in order to ensure a sufficient quantity of excess oxygen.

(7) The optimum value of the process can be set based on the exhaust gas components CO and SO.sub.2 and the percentages of them in the exhaust gas. In addition, the change-over point can be determined by the decrease of the CO concentration and the increase in the SO.sub.2 concentration and correspondingly, the value can also be changed over.

(8) A standard exhaust gas measurement can advantageously be used for regulating the process and exhaust gas analysis can be used to optimize the regulation.

(9) In this connection, the unit used according to the invention permits an optimum, simple charging in which, when necessary, the thorough mixing of the molten slag can be improved in that the turbulence is increased through more powerful rotary motion.

(10) In a preferred embodiment, the slag is supplied to the unit not in the cold state, but with the highest possible residual heat in order to accelerate the release of the gases.

(11) It is also possible, particularly when using a TBRC, to process relatively small charges; both the excess air and the supply of heat can be optimally adjusted by means of the oxygen/natural gas burner.

(12) In order to keep the slag molten and to ensure a molten tapping, up to 20% quicklime can be added to the unit or more precisely stated, to the slag in the unit. The admixture required can be taken from FIG. 3; this depends on the composition of the slag. The CO-containing exhaust gas undergoes afterburning; then the exhaust gas, which contains a high level of SO.sub.2, is conveyed in a known way to sulfuric acid production.

(13) In an exemplary embodiment according to the invention, desulfurization slag travels via corresponding transport devices 1 into a slag pit 2 in which the desulfurization slag is stored in a hot state. By means of a corresponding crane system (not shown), the slag is also always presorted by means of an apron conveyor 3 via a hot grating. From the hot grating 4, the slag travels into a weighing hopper 5 and from the weighing hopper 5, travels into the rotary converter 6. By means of another weighing hopper 7, which contains quicklime, the rotary converter can be correspondingly charged with quicklime. In the rotary converter, the slag is treated with the quicklime at more than 1,400 C., in particular 1,450 C., for 0.5 to 2 hours, depending on the time at which the release of SO.sub.2 roasting gas is complete. The value of the burner in the melting of the slag is preferably set to 1.4-1.5. The excess oxygen is necessary in order to quickly convert the carbon contained in the pig iron fraction of the slag to CO and CO.sub.2. Otherwise, the pig iron, which is low-melting due to the presence of the carbon, (melting point of approx. 1,200 C. according to the iron/carbon diagram), rapidly precipitates out as regulus of iron and constitutes a separate phase. For the actual roasting (sulfur bonded into the slag released as SO.sub.2), the value of the burner is preferably set to >2.0 in order to ensure a sufficient quantity of excess oxygen. Then the tapping takes place in which the tapped slag is conveyed by means of a slag pot 8 to another slag pit 9, and from the slag pit 9, travels into a slag preparation area 10 in which the slag is divided into the fraction >10 mm in size (brittle iron) and a fraction <10 mm in size (fine iron). In this case, the brittle iron is used for further processing in the blast furnace, while the fine iron is conveyed to the sintering plant.

(14) The roasting gas is conveyed from the rotary converter into an afterburning unit 11, undergoes afterburning in this afterburning unit, then is preferably cooled to approximately 400 C. to 500 C., undergoes dust removal, and is then conveyed to the sulfuric acid plant 12.

(15) In the method according to the invention, it is advantageous that the desulfurization slag is desulfurized and this sulfur is conveyed to a utilization where it is used in the form of sulfuric acid. It is thus possible to remove sulfur from pig iron production.

(16) A slag treated according to the invention has an assured sulfur content of less than 0.1% by mass, most often even of 0.01% by mass, relative to the weight of the slag and therefore when conveyed back into pig iron production, supplies a sulfur load that is negligible.

(17) In addition, this method is primarily advantageous for an integrated ironworks, since in addition to the desulfurization, the iron is fully utilized internally and can be supplied directly to the pig iron production.

(18) In addition, it is possible to avoid dumping and interim storage, which are very costly, one aspect of which is a significant reduction of the sulfur input into the pig iron production. A sulfur sink in the internal circulation is achieved through the production of sulfuric acid. The sulfuric acid produced in this case is a valuable byproduct.