Method for off-gas composition control in a metal smelting apparatus

Abstract

A method for off-gas composition control, wherein the off-gas results from a smelting apparatus for smelting a metalliferous feed material, wherein the smelting apparatus includes a smelting vessel, a smelt cyclone mounted on the smelting vessel and in connection with the inside of the smelting vessel and an off-gas duct connected to the smelt cyclone, wherein the method provides that an oxygen containing gas containing 95% oxygen or more is injected into the smelt cyclone and that the feed material is injected into the smelt cyclone with a carrier gas other than nitrogen gas.

Claims

1. A method for off-gas composition control, wherein the off-gas results from a smelting apparatus for smelting a metalliferous feed material, wherein the smelting apparatus comprises a smelting vessel, a smelt cyclone mounted on the smelting vessel and in connection with the inside of the smelting vessel and an off-gas duct connected to the smelt cyclone, and wherein the method comprises the steps of: injecting the metalliferous feed material with a first carrier gas into the smelt cyclone, wherein the first carrier gas comprises at least one hydrocarbon gas selected from methane, ethane and propane, or comprises at least 70 volume % carbon dioxide, injecting an oxygen containing gas into the smelt cyclone, injecting coal with a second carrier gas into the smelting vessel, wherein the second carrier gas comprises at least one hydrocarbon gas selected from methane, ethane and propane, or comprises at least 70 volume % carbon dioxide, injecting an oxygen containing gas into the smelting vessel, optionally injecting fluxes with a third carrier gas into the smelting vessel, wherein the third carrier gas comprises at least one hydrocarbon gas selected from methane, ethane and propane, or comprises at least 70 volume % carbon dioxide, wherein the oxygen containing gas contains 95 volume % oxygen or more and wherein the first carrier gas, the second carrier gas, and the third carrier gas are not a nitrogen gas, discharging the off gas from the smelting apparatus, wherein the off gas has a CO2 content of 80-89 volume %.

2. The method according to claim 1, wherein the oxygen containing gas contains at least 95 volume % oxygen.

3. The method according to claim 2, wherein the metalliferous feed material is injected into the smelt cyclone with a hydrocarbon gas as the first carrier gas.

4. The method according to claim 1, wherein the metalliferous feed material is injected into the smelt cyclone with a hydrocarbon gas as the first carrier gas.

5. The method according to claim 4, wherein methane, ethane or propane is used as the second carrier gas.

6. The method according to claim 1, wherein the coal is injected into the smelting vessel with a hydrocarbon gas as the second carrier gas.

7. The method according to claim 6, wherein methane, ethane or propane is used as the second carrier gas.

8. The method according to claim 1, wherein the metalliferous feed material is injected into the smelt cyclone with a carbon dioxide containing gas as the first carrier gas.

9. The method according to claim 8, wherein the carbon dioxide containing gas for use as the first carrier gas is the off-gas resulting from smelting of the metalliferous feed material after cleaning and cooling of the off-gas.

10. The method according to claim 9, wherein the cooling of the off-gas resulting from the smelting of the metalliferous feed material includes the quenching of the off-gas by means of a quenching medium.

11. The method according to claim 10, wherein the quenching medium is a carbon dioxide containing gas.

12. The method according to claim 11, wherein the quenching medium is the off-gas resulting from smelting of the metalliferous feed material after cleaning and cooling of the off-gas, wherein the carbon dioxide containing gas is cooled to a temperature in a range of 20-200° C.

13. The method according to claim 11, wherein the quenching medium is the off-gas resulting from smelting of the metalliferous feed material after cleaning and cooling of the off-gas, wherein the carbon dioxide containing gas is cooled to a temperature in a range of 20-100° C.

14. The method according to claim 10, wherein the quenching medium is the off-gas resulting from smelting of the metalliferous feed material after cleaning and cooling of the off-gas.

15. The method according to claim 10, wherein the carbon dioxide containing gas is cooled to a temperature in a range of 20-200° C.

16. The method according to claim 10, wherein the carbon dioxide containing gas is cooled to a temperature in a range of 20-100° C.

17. The method according to claim 1, wherein the coal is injected into the smelting vessel with a carbon dioxide containing gas as the second carrier gas.

18. The method according to claim 1, wherein water vapour present in the off-gas resulting from smelting the metalliferous feed material is removed from the off-gas by means of condensation.

19. The method according to claim 1, wherein the off-gas resulting from smelting the metalliferous feed material is passed through a SOx scrubber to remove sulphur compounds.

20. The method according to claim 1, wherein the off-gas resulting from smelting the metalliferous feed material is passed through a dust cyclone to remove dust present in the off-gas.

21. The method according to claim 1, wherein the off-gas resulting from smelting the metalliferous feed material is passed through a gas scrubber to remove NOx components present in the off-gas.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be further explained on hand of the example shown in the drawing, in which schematically a smelting vessel, smelt cyclone and off-gas duct with cleaning and cooling devices is shown.

DETAILED DESCRIPTION OF THE DRAWING

(2) In the drawing a smelting apparatus 1 is shown which has a smelt cyclone 2 and below the smelt cyclone a smelting vessel 3. The smelt cyclone 2 is provided with injections lances 4 to feed a metalliferous feed material such as iron ore into the smelt cyclone together with flux as far as necessary by means of an conveying gas. For the heating and partial melting of the injected iron ore oxygen is injected into the smelt cyclone 2 by means of a set of oxygen lances 5. The oxygen injected is typically oxygen gas purified for industrial purposes with a purity of about 95% O2.

(3) The smelting vessel 3 is provided with oxygen lances 12 in shell or roof portion 11 of the smelting vessel 3 to inject oxygen above the slag level when the smelting apparatus is in operation to adjust heating and reduction requirements of the process. The same purified oxygen gas is used as above described.

(4) Further lances 6 are provided to inject coal and/or additives in the slag layer 7. For the injection iron ore through injection lances 4 and the injection of coal and additives through lances 6 recycled off-gas is used containing 80-89% CO2.

(5) The molten iron 8 produced in the smelting reduction process is continuously discharged from the vessel 3 through a forehearth 9. The slag 7 resulting from the process is discharged from smelting vessel 3 by sequential tapping through a slag tap hole 10.

(6) The off-gas is guided through an inclined off-gas duct part 15 downstream of the smelting vessel and the smelt cyclone. The inclined off-gas duct part has an inclination in the range of 50-90°, typically 60-70° to the vertical which provides that any liquid iron that is entrained in droplets by the off-gas will end up against the wall of the inclined duct part and will flow back and end up in the smelting vessel. In this manner most of the iron droplets present in the off-gas can be recovered resulting in that more than 90% of the iron present in the off-gas can be recovered. In recent trials the results were even better and it was determined that even 99% of the iron present in the off-gas was recovered. Instead of the inclined off-gas duct part other forms are possible as well such as a twisted duct part, a spiraled duct part, an undulating duct part and the like as long as the shape is such that the entrained iron droplets will end up against the wall of such duct part. The temperature in the inclined off-gas duct part 15 is in a range of 1600-1900° C.

(7) The inclined off-gas duct part 15 is followed by a cooling/quenching device 16 in the off-gas duct 14 with which the temperature of the off-gas is lowered to a temperature of 1200° C. or lower. The quenching medium is recycled off-gas with a CO2 content in a range of 80-89%. The CO2 content in the recycled off-gas could even be higher if oxygen gas with a purity of 99% or even 99.5% is used in the process.

(8) In this example the off-gas is further cooled by means of heat exchange with a steam driven electric generator device 17 further downstream of the cooling/quenching device 16. Cooling with other means is also possible with for instance ventilator cooling, but cooling wherein at least part of the heat energy is recovered is preferred. After passing the steam driven electric generator 17 the off-gas goes through a cold cyclone dust separator 18 wherein the off-gas is at least partially cleaned. Instead of a cold dust cyclone 18 also a high temperature dust cyclone could be used which should be positioned upstream of steam driven electric generator 17 and downstream of the cooling/quenching device 16, for instance at the horizontal duct portion at the top of duct 14.

(9) After passing through hot or cold dust cyclone and steam driven electric generator 17 the off-gas goes through the bag filter 19 wherein most if not almost all dust is removed from the off-gas.

(10) Downstream of the bag filter or bag house 19 a desulphurisation unit 21 is provided for the removal of SOx compounds. Part of the cleaned off-gas after the desulphurisation unit 21 is used as cooling gas for the cooling/quenching device 16 for which a return duct 23 with compressor 26 is provided. By compressing the off-gas at least part of the water vapour in the off-gas will condense and the condensed water is subsequently removed from the return duct 23. For the use of the cooling gas in the cooling/quenching device an overpressure with respect to the pressure in duct 14 is needed. In the given example an overpressure in the order of 10 to 500 kPa is enough to get a sufficient amount of cooling gas in duct 14 to cool the off-gas.

(11) For the carrier gas for injecting iron ore through lances 4 into cyclone 2 and/or injecting coal and/or additives through lances 6 into the slag layer 7, the cleaned off-gas after the desulphurisation unit 21 can be used. To this end a return duct with compressor connected to the main duct after the desulphurisation unit 21 should be provided. The cleaned and cooled off-gas at this point has a CO2 content in the range of 80-89%. In one of the trials an off-gas was obtained with 88.8% CO2, 2.4% O2, 4.6% N2 and 4.0% H2O.

(12) Alternatively the carrier gas for injecting iron ore through lances 4 into cyclone 2 and/or injecting coal and/or additives through lances 6 into the slag layer 7 can be taken from the CO2 processing unit 27 as described further below.

(13) In order to pass the off-gas through the off-gas duct 14, cooling/quenching device 16, steam driven electric generator 17, cold dust cyclone 18, and bag filter 19 a fan 20 is provided in the off-gas duct 14 downstream of the bag filter 20. The fan 20 is not necessary if the smelting vessel 3 is operated at sufficient pressure.

(14) The volume of the off-gas that is used for CCS is taken from the main duct and fed through duct 25 to a CO2 processing unit 27 wherein the off-gas is further purified, dried, cooled and compressed. In duct 25 the off-gas is passed through a gas scrubber (not shown) to remove any NOx components that might still be present in the off-gas. For CCS purposes it is necessary to compress the off-gas for which the processing unit 27 is provided with compressors 28,29,30. The off-gas is compressed in successive stages to a final overpressure in the order of 8-15 MPa or any other overpressure as might be required by the specifications of the installation used for the purpose. After processing unit 27 the compressed gas is further transported through duct 31. After this stage most if not all of the impurities are removed that could affect storage of the CO2 gas a purity of 99% CO2 can be realised.

(15) In the example given in the drawing the carrier gas for injecting iron ore through lances 4 into cyclone 2 and/or injecting coal and/or additives through lances 6 into the slag layer 7 is taken from the CO2 processing unit 27. A return duct 24 is provided after the first compressor 28 of the CO2 processing unit 27 is provided. After the first compressor 28 the carrier gas used for injection has an overpressure which is suitable for the purpose. With the installation shown in the drawing this is in the order of 1-3 MPa.

(16) The part of the off-gas that is not used for either CCS and CCU is discharged through stack 22 but not before the NOx component in the off-gas is removed as far as possible.