WO2014071464A1

WO2014071464A1 - A two-stage smelting process and apparatus

Info

Publication number: WO2014071464A1
Application number: PCT/AU2013/001301
Authority: WO
Inventors: Rodney James Dry; Jacques Pilote
Original assignee: Technological Resources Pty. Limited
Priority date: 2012-11-12
Filing date: 2013-11-12
Publication date: 2014-05-15
Also published as: CN104870656A; JP2016502598A; CN104870656B; CA2890267A1; EA030240B1; EA201590779A1; KR20150082345A

Abstract

A two-stage molten bath-based smelting process for producing molten metal from a metalliferous feed material includes (a) preheating metalliferous feed material in a preheater and (b) injecting preheated metalliferous feed material and a solid carbonaceous material into a molten bath of a smelting vessel and smelting metalliferous feed material in the molten bath and forming molten metal and an offgas. The process includes cooling and cleaning the offgas from the smelting vessel and producing a fuel gas. The preheating stage (a) includes preheating the metalliferous feed material by generating heat by combusting at least a part for the fuel gas that is supplied to the preheating stage at a temperature of less than 300º C.

Description

A TWO-STAGE SMELTING PROCESS AND APPARATUS TECHNICAL FIELD The present invention relates to a two-stage process and apparatus for smelting a metalliferous material.

The term "metalliferous material" is understood herein to include solid feed material and also includes within its scope partially reduced metalliferous material.

The present invention relates more particularly, although by no means exclusively, to a two-stage molten bath-based smelting process and apparatus for producing molten metal from a metalliferous feed material which is initially preheated and then injected into a smelting vessel that has a strong bath/slag fountain generated by gas evolution in the molten bath, with the gas evolution being at least partly the result of carbonaceous material injected into the molten bath.

In particular, although by no means exclusively, the present invention relates to a process and apparatus for smelting an iron-containing material, such as an iron ore, and producing molten iron.

The present invention relates particularly, although by no means exclusively, to a smelting process in a smelting vessel that includes a main chamber for smelting metalliferous material.

BACKGROUND ART

A known molten bath-based smelting process is generally referred to as the Hlsmelt process and is described in a considerable number of patents and patent applications in the name of the applicant.

The Hlsmelt process is associated particularly with producing molten iron from iron ore or another iron-containing material.

In the context of producing molten iron, the Hlsmelt process includes the steps of:

(a) forming a bath of molten iron and slag in a main chamber of a smelting vessel;

(b) injecting into the bath: (i) iron ore, typically in the form of fines; and (ii) a solid carbonaceous material, typically coal, which acts as a reductant of the iron ore feed material and a source of energy; and (c) smelting iron ore to iron in the bath.

The term "smelting" is herein understood to mean thermal processing wherein chemical reactions that reduce metal oxides take place to produce molten metal.

In the Hlsmelt process solid feed materials in the form of metalliferous material and solid carbonaceous material are injected with a carrier gas into the molten bath through a number of lances which are inclined to the vertical so as to extend downwardly and inwardly through the side wall of the main chamber of the smelting vessel and into a lower region of the vessel so as to deliver at least part of the solid feed materials into the metal layer in the bottom of the main chamber. The solid feed materials and the carrier gas penetrate the molten bath and cause molten metal and/or slag to be projected into a space above the surface of the bath and form a transition zone. A blast of oxygen-containing gas, typically oxygen-enriched air or pure oxygen, is injected into an upper region of the main chamber of the vessel through a downwardly extending lance to cause post-combustion of reaction gases released from the molten bath in the upper region of the vessel. In the transition zone there is a favourable mass of ascending and thereafter descending droplets or splashes or streams of molten metal and/or slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.

Typically, in the case of producing molten iron, when oxygen-enriched air is used, the oxygen-enriched air is generated in hot blast stoves and fed at a temperature of the order of 1200°C into the upper region of the main chamber of the vessel. If technical-grade cold oxygen is used, the technical-grade cold oxygen is typically fed into the upper region of the main chamber at or close to ambient temperature.

Off-gases resulting from the post-combustion of reaction gases in the smelting vessel are taken away from the upper region of the smelting vessel through an off-gas duct.

The smelting vessel includes refractory-lined sections in the lower hearth and water cooled panels in the side walls and the roof of the main chamber of the vessel, and water is circulated continuously through the panels in a continuous circuit.

The Hlsmelt process enables large quantities of molten iron, typically at least 0.5 Mt/a, to be produced by smelting in a single compact vessel.

The Hlsmelt process includes solids injection into a molten bath in a smelting vessel via water-cooled solids injection lances. In addition, a key feature of this process is that it operates in smelting vessels that include a main chamber for smelting metalliferous material and a forehearth connected to the main chamber via a forehearth connection that allows continuous metal product outflow from the vessels. A forehearth operates as a molten metal-filled siphon seal, naturally "spilling" excess molten metal from the smelting vessel as it is produced. This allows the molten metal level in the main chamber of the smelting vessel to be known and controlled to within a small tolerance - this is essential for plant safety. Molten metal level must (at all times) be kept at a safe distance below water-cooled elements such as solids injection lances extending into the main chamber, otherwise steam explosions become possible. It is for this reason that the forehearth is considered an inherent part of a smelting vessel for the Hlsmelt process.

The term "forehearth" is understood herein to mean a chamber of a smelting vessel that is open to the atmosphere and is connected to a main smelting chamber of the smelting vessel via a passageway (referred to herein as a "forehearth connection") and, under standard operating conditions, contains molten metal in the chamber, with the forehearth connection being completely filled with molten metal.

The present invention is partly the result of experience gained on a

demonstration plant that operated the Hlsmelt process. This plant was constructed in Perth, Western Australia in 2002-2003 when natural gas prices were below $A3/GJ. By the time this first-of-a-kind plant was fully operational some years later, natural gas had risen above $A8/GJ. As a consequence, the "as built" configuration (which was designed for high natural gas consumption due to the original low cost) came under severe economic pressure.

Fluidized bed preheating of iron ore (prior to injection into the smelting vessel) using a circulating fluidized bed in the plant comprised one of the more significant natural gas users on the plant.

The fluidized bed preheater was operated with natural gas and air combustion in direct contact with iron ore to generate the heat required to preheat iron ore. This form of the Hlsmelt process is described hereinafter as the "decoupled" mode of operation because the preheater did not take advantage of available energy from the smelting vessel to preheat iron ore.

The plant was designed to use hot smelter offgas (nominally 1000°C) as fuel gas in the ore preheater. This form of the Hlsmelt process is described herein as the "hot-coupled" mode of operation. Although considerable experience was gained with the decoupled mode in the plant, the hot-coupled mode was never implemented due to concerns, primarily safety concerns related to leakage of carbon monoxide-containing gas from the unit.

The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere.

SUMMARY OF THE DISCLOSURE

The process and apparatus of the present invention (i) avoids the risks and safety concerns associated with carbon monoxide leakage in the hot-coupled mode, (ii) utilises confidential (to the applicant) operational experience gained using the decoupled mode and (iii) avoids the use of natural gas (or other imported fuel gas).

Unlike prior art in the area in the name of the applicant (e.g.

PCT/AU2005/000284, PCT/AU2007/000542 and PCT/AU2007/000534), the process and apparatus of the present invention cools smelter offgas to a considerably lower temperature, typically to below about 300°C (and typically above 200°C). In the process and apparatus of the present invention, typically all the smelter offgas is collected, cooled to the considerably lower temperature and de-dusted (e.g. in a wet scrubber). Once cooled and cleaned, at least a portion of this gas is then split off for use as fuel gas in a fluidized bed iron ore preheating unit. The process of the present invention is described herein as a "cold coupling" mode of operation.

In general terms, the present invention provides a two-stage molten bath-based smelting process for producing molten metal from a metalliferous feed material includes (a) preheating metalliferous feed material in a preheater and (b) injecting preheated metalliferous feed material and a solid carbonaceous material into a molten bath of a smelting vessel and smelting metalliferous feed material in the molten bath and forming molten metal and an offgas. The process includes cooling and cleaning the offgas from the smelting vessel and producing a fuel gas. The preheating stage (a) includes preheating the metalliferous feed material by generating heat by combusting at least a part for the fuel gas that is supplied to the preheating stage at a temperature of less than 300°C.

The present invention provides a two-stage molten bath-based smelting process for producing molten metal from a metalliferous feed material which includes (a) preheating metalliferous feed material in a preheater and (b) injecting preheated metalliferous feed material and a solid carbonaceous material into a smelting vessel containing a bath of molten material in the form of molten metal and molten slag and generating a bath/slag fountain via gas evolution in the molten bath and generating an offgas and smelting metalliferous feed material in the molten bath and forming molten metal, with the preheating stage including preheating the metalliferous feed material by combusting a fuel gas that is supplied to preheating stage (a) at a temperature of less than 300°C, with the fuel gas being produced from offgas discharged from the smelting vessel.

The fuel gas that is supplied to preheating stage (a) may be at a temperature of at least 200°C.

Offgas discharged from the smelting vessel is typically available at a pressure in the range 0.5-1.0 bar gauge.

Typically, offgas discharged from the smelting vessel is at considerably higher temperatures than the target maximum temperature of 300°C for preheating stage (a). The process may include cooling offgas discharged from the smelting vessel to the temperature of less than 300°C.

The process may include cleaning offgas before preheating stage (a).

One option for cooling and cleaning the offgas is a wet scrubber.

Another offgas cooling and cleaning option is a gas cooler followed by a dry baghouse or electrostatic precipitator (ESP).

Any other suitable cooling and cleaning option may be used.

If a wet scrubber is used, it will generally include a pressure-control valve (which is used to control pressure in the smelter). This valve, which forms part of the scrubbing process, requires a pressure drop of (at least) about 0.4 bar to achieve the required gas cleanliness. The resulting cool, cleaned gas is therefore available in the pressure range about 0.1-0.6 bar g. Downstream equipment such as hot blast stoves and waste heat boilers can operate satisfactorily with fuel gas at the lower end of this pressure range. However, a fluidized bed ore preheater will generally require somewhat higher pressure in the fuel gas (toward the upper end of the range) in order to function correctly. In cases where it is not possible to maintain a sufficiently high pressure in the gas mains, a blower or compressor can be used to boost pressure in the iron ore preheater portion of the gas (although this is a more costly option which is generally not preferred).

If a gas cooler followed by a dry baghouse (or ESP) is used instead of a wet scrubber, then it will generally have a pressure-control valve (equivalent to that in a wet scrubber) immediately downstream of the filtration elements. Pressure drop across the filtration elements will typically be less than about 0.1 bar. With this type of gas cleaning system it is possible to split the gas after the filtration elements and before the main pressure control valve, thus making gas available for the iron ore preheater at a pressure only about 0.1 bar g (or less) below that of the smelter top space. In such cases it is somewhat less likely that a gas blower or compressor will be needed, and it is more probable that the system can function with a direct connection between the gas cleaner and the iron ore preheater. However, in cases where a high pressure drop (for gas mixing and distribution) is needed in the ore preheater, a gas blower or

compressor may still be required.

This "cold coupling" mode of operation essentially meets the three

requirements described above and offers a practical alternative to the conventional Hlsmelt plant gas flow configuration. These requirements are (i) avoiding the risks and safety concerns associated with carbon monoxide leakage in the hot-coupled mode, (ii) utilising confidential (to the applicant) operational experience gained using the decoupled mode and (iii) avoiding the use of natural gas (or other imported fuel gas) The process may include adjusting the pressure of offgas as required for the preheating stage.

In the context of a metalliferous feed material in the form of iron ore, the present invention provides a method of operating a two-stage smelting process utilising a smelting vessel and an iron ore preheating unit. The smelting vessel may include a refractory-lined main chamber and a refractory- lined forehearth connected to the main smelting chamber via a forehearth connection. The process may include the following steps:

(i) injecting granular coal, flux, and preheated iron ore, typically in the form of fines of less than 6 mm in a major dimension, into the molten bath via injection lances, with the preheated iron ore typically being at 300°C or hotter at a feed point into the injection lances;

(ii) injecting an oxygen-containing gas (typically hot oxygen-enriched air or cold technical-grade oxygen) into a gas top space above the molten bath in the smelting vessel to generate heat by way of combustion of combustible gases in the top space in order to sustain smelting reactions in the bath;

(iii) generating the bath/slag fountain via ascending and thereafter descending droplets and splashes from the molten bath such that heat is transferred from the top space to the bath in order to sustain the smelting reactions; (iv) removing molten iron semi-continuously or continuously via the forehearth and removing slag periodically via a water-cooled slag tapping device mounted in a side-wall of the vessel;

(v) cooling smelter offgas discharged from the smelting vessel to below about 300°C, and typically above 200°C, and removing dust particles and generating a cool, clean fuel gas with a heating value in a range 2-4 MJ/Nm³ (LHV basis);

(vi) feeding at least a portion, typically between 15% and 35%, of the fuel gas to the ore preheater at a temperature below about 300°C either directly (if pressure is sufficient for operation of the preheater) or via a pressure-boosting blower or compressor (if the gas pressure is not sufficient);

(vii) combusting this fuel gas with air or oxygen enriched air in direct contact with iron ore feed material, typically granular iron ore, such as iron ore fines, and heating the iron ore feed material to a temperature in a range 600 to 1000°C; and

(viii) feeding the resulting hot metalliferous material (typically via a hot lock hopper system) into the smelting vessel as described in step (i).

The present invention also provides an apparatus for a two-stage molten bath- based smelting process for producing molten metal from a metalliferous feed material which includes (a) a preheater for preheating metalliferous feed material and (b) a smelting vessel containing a bath of molten material in the form of molten metal and molten slag and generating a bath/slag fountain via gas evolution in the molten bath and generating an offgas and smelting preheated metalliferous feed material from the preheater in the molten bath and forming molten metal, and (c) an offgas treatment system for cooling offgas discharged from the smelting vessel and supplying the cooled offgas at a temperature of less than 300°C, and typically above 200°C, to the preheater for use as a fuel gas for preheating metalliferous feed material in the preheater.

The offgas treatment system may include a wet scrubber.

The offgas treatment system may include a gas cooler followed by a dry baghouse or electrostatic precipitator.

The offgas treatment system may be any other suitable system. BRIEF DESCRIPTION OF THE DRAWINGS

The two-stage direct smelting process and apparatus in accordance with the present invention is described further by way of example only with reference to the accompanying drawings, of which:

Figure 1 is a diagram that shows one embodiment of a Hlsmelt direct smelting flowsheet configured to operate in the "cold coupling" mode in accordance with the present invention; and

Figure 2 is a diagram that shows another although not the only other embodiment of a Hlsmelt direct smelting flowsheet configured to operate in the "cold coupling" mode in accordance with the present invention.

DESCRIPTION OF EMBODIMENTS Figure 1 shows a Hlsmelt direct smelting process flowsheet configured to operate in the "cold coupling" mode.

A metalliferous feed material in the form of iron ore 1 (optionally blended with some flux material) is fed into ore preheater 2 which, in this example, is a circulating fluidized bed, but may be any other suitable pre-heater. Hot iron ore at about 850°C is removed from the bottom of the fluidized bed and fed, together with small proportion of dust from a multiclone separator 24, into hot lock hopper system 3. Hot ore is then fed from the lock hopper system 3 to injection lances 6 in smelting vessel 7. The top space pressure in smelting vessel 7 is maintained at around 0.8-1.0 bar g. Hot ore arrives at the feed point into lances 6 (before being mixed with coal/flux) at about 400-700°C.

Coal 4 and flux 5 are also fed into injection lances 6, the coal having first been dried and ground in a coal mill.

Solids injection lances 6 inject all the solids into the bath and smelting occurs according to the normal Hlsmelt process as described earlier.

Molten metal 8 is discharged via a forehearth and slag 9 is discharged via a water-cooled slag notch.

Technical-grade oxygen from oxygen plant 10 and air 11 , after compression, are mixed and heated in hot blast stoves 12 to (typically) 1200°C and 35-40% oxygen by volume. This hot blast stream 13 enters the top space of smelting vessel 7 via a top lance 22 that extends vertically into the smelting vessel 7 and combusts process gas generated in the smelting vessel 7 in order to generate heat for the smelting process. A stream of offgas indicated by the arrow 14 that is discharged at high temperatures (typically well above 1000°C) and high flow rates from smelting vessel 7 is treated directly in an offgas treatment system that cools and cleans the offgas for use as a fuel gas.

More specifically, the hot offgas is cooled in hood 15 and is thereafter scrubbed in wet scrubber 16. Clean gas 17 at a temperature in a range of 150-300°C , typically at a temperature of about 250°C and a heating value typically in a range 2-4 MJ/Nm³ (LHV basis) is controlled to a pressure of nominally 0.4-0.5 bar g and is then split into the following three portions:

(i) Fuel gas 18 which is ducted directly (if pressure is sufficient) or indirectly via a blower or compressor (if pressure is too low) to ore preheater 2. Fuel gas 18 comprises 10-40%, typically 10-30%, more typically 20%, of the flow from smelting vessel 7 and is combusted with air 19 (in the ore preheater 2) to generate heat for preheating incoming iron ore to ore preheater 2.

(ii) Fuel gas 20 which is used to fire the hot blast stoves 12.

(iii) Fuel gas 21 which is burned in a waste heat boiler 23 for steam and power generation.

Figure 2 shows a Hlsmelt direct smelting flowsheet configured in a second, although not the only other possible, version of "cold coupling" mode.

Iron ore 201 (optionally blended with some flux material) is fed into ore preheater 202 which, in this example, is a circulating fluidized bed. Hot iron ore at about 850°C is removed from the bottom of the fluidized bed and fed, together with small proportion of dust from a multiclone separator 226, into hot lock hopper system 203. Hot ore is then fed from the lock hopper system to injection lances 206 in smelting vessel 207. The top space pressure in smelting vessel 207 is maintained at around

0.8-1.0 bar g. Hot ore arrives at the feed point into lances 206 (before being mixed with coal/flux) at about 400-700°C.

Coal 204 and flux 205 are also fed into injection lances 206, the coal having first been dried and ground in a coal mill.

Solids injection lances 206 inject all the solids into the bath and smelting occurs according to the normal Hlsmelt process as described earlier.

Molten metal 208 is discharged via a forehearth and slag 209 is discharged via a water-cooled slag notch.

Technical-grade oxygen from oxygen plant 210 and air 211 , after compression, are mixed and heated in hot blast stoves 212 to (typically) 1200°C and 35-40% oxygen by volume. This hot blast stream 213 enters the top space of smelting vessel 207 via a top lance 228 that extends vertically into the smelting vessel 207 and combusts process gas in the smelting vessel 207 in order to generate heat for the smelting process.

A stream of offgas indicated by the arrow 214 that is discharged at high temperatures and high flow rate from smelting vessel 207 is treated directly in an offgas treatment system that cools and cleans the offgas for use as a fuel gas.

More specifically, the hot offgas is cooled in hood 215 to about 800-1000°C and thereafter is split into (a) one portion 216 comprising about 10-40%, typically 10-30%, more typically 20%, of the flow from smelting vessel 207 and (b) a second portion 221 comprising the balance.

Gas stream 216 is then cooled to a range of 150-300°C , typically to a temperature of about 250°C in gas cooler 217, and thereafter dust is removed in baghouse 218. Cool, clean gas 219 at a pressure about 0.1 bar g below that of the smelter top space and a heating value typically in a range 2-4 MJ/Nm³ (LHV basis) is then fed directly to the ore preheater 202 where it is combusted with air 220.

Gas stream 221 is cooled and scrubbed in wet scrubber 222 to produce clean fuel gas stream 223 at a temperature of about 250°C and a heating value typically in a range 2-4 MJ/Nm³ (LHV basis). This gas is then split into:

(i) Fuel gas 224 which is used to fire the hot blast stoves 212.

(ii) Fuel gas 225 which is burned in a waste heat boiler 230 for steam and power generation.

The above-described embodiments of a Hlsmelt direct smelting process configured to operate in the "cold coupling" mode in accordance with the present invention are effective alternatives to current operating modes for the Hlsmelt process.

Many modifications may be made to the embodiments of the process of the present invention described in relation to the Figures without departing from the spirit and scope of the invention.

By way of example, whilst the embodiments are described in the context of the Hlsmelt direct smelting process, it can readily be appreciated that the present invention is not so limited and extends to any two-stage molten bath-based smelting process that includes a metalliferous feed material preheating stage and a smelting stage.

By way of example, whilst the embodiments are described in the context of smelting iron ore, it can readily be appreciated that the present invention is not limited to this material and extends to any suitable metalliferous material.

Claims

CLAIMS:

1. A two-stage molten bath-based smelting process for producing molten metal from a metalliferous feed material which includes (a) preheating metalliferous feed material in a preheater and (b) injecting preheated metalliferous feed material and a solid carbonaceous material into a smelting vessel containing a bath of molten material in the form of molten metal and molten slag and generating a bath/slag fountain via gas evolution in the molten bath and generating an offgas and smelting metalliferous feed material in the molten bath and forming molten metal, with the preheating stage including preheating the metalliferous feed material by combusting a fuel gas that is supplied to preheating stage (a) at a temperature of less than 300°C, with the fuel gas being produced from offgas discharged from the smelting vessel.

2. The process defined in claim 1 includes cooling offgas discharged from the smelting vessel to the temperature of less than 300°C.

3. The process defined in claim 2 includes cleaning offgas before preheating stage (a).

4. The process defined in claim 3 includes cooling and cleaning offgas in a wet scrubber.

5. The process defined in claim 3 includes cooling offgas in a gas cooler and cleaning offgas in a dry baghouse or electrostatic precipitator.

6. The process defined in any one of the preceding claims includes adjusting the pressure of offgas as required for the preheating stage.

7. The process defined in any one of the preceding claims includes the following steps in a situation where the metalliferous feed material is iron ore:

(i) injecting granular coal, flux, and preheated iron ore into the molten bath via injection lances;

(ii) injecting an oxygen-containing gas into a gas top space above the molten bath in the smelting vessel and generating heat by way of combustion of combustible gases in the top space in order to sustain smelting reactions in the bath;

(iii) generating the bath/slag fountain via ascending and thereafter descending droplets and splashes from the molten bath such that heat is transferred from the top space to the bath in order to sustain the smelting reactions;

(iv) removing molten iron semi-continuously or continuously via the forehearth and removing slag periodically via a water-cooled slag tapping device mounted in a side-wall of the vessel; (v) cooling smelter offgas discharged from the smelting vessel to below 300°C and removing dust particles and generating a cool, clean fuel gas with a heating value in a range 2-4 MJ/Nm³ (LHV basis);

(vi) feeding at least a portion of the fuel gas to the ore preheater either directly or via a pressure-boosting blower or compressor;

(vii) combusting the fuel gas with air or oxygen enriched air in direct contact with iron ore feed material and heating the iron ore feed material to a temperature in a range 600 to 1000°C; and

(viii) feeding the resulting hot metalliferous material into the smelting vessel in step (i).

8. The process defined in claim 7 wherein step (vi) includes feeding between 15% and 35% of the fuel gas to the ore preheater.

9. An apparatus for a two-stage molten bath-based smelting process for producing molten metal from a metalliferous feed material which includes (a) a preheater for preheating metalliferous feed material and (b) a smelting vessel containing a bath of molten material in the form of molten metal and molten slag and generating a bath/slag fountain via gas evolution in the molten bath and generating an offgas and smelting preheated metalliferous feed material from the preheater in the molten bath and forming molten metal, and (c) an offgas treatment system for cooling offgas discharged from the smelting vessel and supplying the cooled offgas at a temperature of less than 300°C to the preheater for use as a fuel gas for preheating metalliferous feed material in the preheater.