Improved apparatus and method for the production of molten iron

Abstract

The invention relates to an improvement of an apparatus to produce molten iron by direct reduction of iron ore. The apparatus comprises a smelting and reduction vessel and a cyclone part provided on top of the smelting and reduction vessel, the cyclone part being in open connection with the smelt reduction vessel and to an improved method to produce molten iron.

Description

[0001] IMPROVED APPARATUS AND METHOD FOR THE PRODUCTION OF MOLTEN IRON

[0002] Field of the invention

[0003] The invention relates to an improvement of an apparatus to produce molten iron by direct reduction of iron ore. The apparatus comprises a smelting and reduction vessel and a cyclone part provided on top of the smelting and reduction vessel, the cyclone part being in open connection with the smelt reduction vessel and to an improved method to produce molten iron.

[0004] Background of the invention

[0005] In steel manufacturing melting cyclones can be used in the pre-reduction and melting of iron ore. In this context iron ore is defined as metalliferous material containing iron oxides. Such a melting cyclone is provided with means to inject iron ore and means to inject oxygen from a number of locations around the circumference of the melting cyclone. The iron ore and oxygen are injected in an about tangential direction therewith generating a vortex or whirling flow inside the melting cyclone. At the same time, a reducing off-gas is introduced into the cyclone which in combination with the injected oxygen is partly combusted resulting in sufficiently high temperatures to melt the iron oxides. The vortex or whirling flow in the cyclone promotes mixing of the injected oxygen and the reducing off-gas and also heat exchange with the iron oxides. As a result of the swirl motion, solid iron ore particles and molten iron ore are separated from the gas and collect on the wall of the cyclone wall from where they flow downward under the influence of gravity to accumulate in a vessel where final reduction takes place. Such melting cyclones are known for instance from EP0726326 and EP0735146.

[0006] The process for producing molten iron as described in EP0726326 involves a direct reduction of iron ore in a pre-reduction stage followed by a final reduction stage, comprising the steps of

[0007] (a) in the pre-reduction stage conveying iron ore into a melting cyclone and prereducing it there by means of a reducing off-gas originating from the final reduction stage,

[0008] (b) effecting a post-combustion in the reducing off-gas in the melting cyclone by supplying oxygen thereto so that said iron ore in the melting cyclone is at least partly melted,

[0009] (c) permitting the pre-reduced and at least partly melted iron ore to pass downwardly from the melting cyclone into a metallurgical vessel situated beneath it in which the final reduction takes place,

[0010] (d) effecting the final reduction in the smelting reduction vessel in a molten slag layer therein by supplying coal and oxygen to the smelting reduction vessel and thereby forming a reducing off-gas, and effecting a partial post-combustion in the reducing off-gas in the smelting reduction vessel by means of the oxygen supplied thereto, the coal being supplied directly into the molten slag layer,

[0011] (e) wherein the post-combustion ratio (PCR) defined as in which CO2, CO, H2O and H2 are the concentrations in percent by volume of these gases on exiting the smelting reduction vessel, is not more than 0.55, and

[0012] (f) wherein the partial post-combustion in the smelting reduction vessel at least partly occurs in the molten slag layer.

[0013] The process is a smelting reduction process with two directly coupled process stages in which the production of liquid pig iron takes place.

[0014] It is a combination of a melting cyclone which is placed above a smelting reduction vessel forming a continuous, once through process. The plant is shaped like a wine bottle: a "bottle" at the bottom and a thin "neck" at the top. The geometry and gas flows of this furnace causes a cyclone to form in the melting cyclone when the iron ore is injected into this cyclone together with oxygen. The high temperature in the cyclone causes the iron ore to melt and partly pre-reduce.

[0015] These molten and pre-reduced iron ore droplets then drip down the furnace wall to the place where the "neck" widens into the "bottle". Here the droplets fall from the wall into the molten slag in the smelting reduction vessel. The slag sits on top of the liquid iron bath in the bottom of the furnace and is very turbulent. Between the cyclone and the slag layer, oxygen is injected through water cooled lances to generate heat by partly combusting the gases (mainly CO) being released from the final reduction reaction step that takes place in the slag. Powder coal is injected into the slag layer, again through water cooled lances. The reduction reaction now continues "as normal" in the bottom of the furnace, with the partially reduced iron ore further reducing to regular pig iron and the whole separating into two molten layers (a top layer of slag and a bottom layer of molten pig iron). Both layers can be tapped individually and the pig iron can be used immediately in the remainder of the basic oxygen steelmaking process. The partially combusted process gasses released from the slag move upwardly to the cyclone and are combusted further at the top of the smelting reduction vessel due to the introduction of oxygen and the heated gases ensure that the ore injected into the cyclone is partly reduced and melted. The combustion before the cyclone is also a partial combustion, but the PCR is obviously higher than that of the gases leaving the slag layer. Any remaining combustible gases move further upwards away from the cyclone. So the combustible gases that were formed because of the injection of carbonaceous material into the slag layer which leave the slag layer with a certain postcombustion ratio (PCR) get combusted just before the entry of the cyclone to heat the cyclone and melt and pre-reduce the injected iron ore in the cyclone.

[0016] In the context of this invention, the gas leaving the cyclone upwardly is referred to as the off-gas.

[0017] In this known process, on leaving the melting cyclone, the off-gas contains considerable amounts of sensible heat and, depending on the PCR, still considerable amounts of chemical energy. The sensible heat in the off-gas may be used in different ways. The sensible heat in the off-gas of typically about 5 GJ per ton of crude iron can be converted in a boiler into steam and then into electricity.

[0018] In the known process the off-gas leaves the melting cyclone at a temperature of about 1500°C and is dedusted after the heat exchanger or boiler. The known process is also disclosed in US2021040572-A1 and incorporated herein by reference.

[0019] The high temperature of the off-gas causes several problems that need to be solved. Salts, FeO, Zinc and Sulphur compounds tend to become stickier and form accretions on the ducts and need to be removed mechanically. And in case the accretions do not stick they may come loose, drop down and damage the apparatus or disturb the process. Not only the ducts suffer from these accretions, but also the heat exchanger or boiler suffer from caking of these compounds.

[0020] Objectives of the invention

[0021] It is the object of the invention to provide an apparatus that prevents the formation of accretions in the downstream sections of the off-gas system.

[0022] It is also an object of the invention to reduce or prevent the formation of NOx.

[0023] It is also an object of the invention to improve the energy efficiency of the method of producing molten iron.

[0024] It is also an object of the invention to improve the recyclability of the various byproducts of the method of producing molten iron.

[0025] It is also an object of the invention to reduce the environmental impact the production of molten iron.

[0026] Description of the invention

[0027] One or more of the objects is reached with an apparatus comprising a metallurgical vessel (1) for producing molten iron (8) by direct reduction of iron ore, comprising i) a smelting reduction vessel (3), in which in operation of the apparatus the iron ore undergoes a final reduction with production of a off-gas and said off-gas undergoes a partial post-combustion, means for supplying carbonaceous material (6), e.g. coal or biochar, to said metallurgical vessel, means for supplying oxygen, and ii) a melting cyclone (2) on top of the smelting reduction vessel (3) in which in operation of the apparatus said iron ore undergoes a prereduction and is melted, said melting cyclone (2) being on top of and in direct and open communication with said smelting reduction vessel (3) for transfer of the pre-reduced iron ore thereto and for flow of the post-combusted off-gas from the metallurgical vessel (1), wherein said smelting reduction vessel (3) comprises iii) a top part, in which said partial post-combustion of said off-gas takes place and a bottom part for accommodating an iron bath (8) having a molten slag layer (7) in which said final reduction of said iron ore takes place, the apparatus further comprising an off-gas duct (14) mounted on top of the melting cyclone (2) for leading away the off-gas, and one or more of:

[0028] A. an inlet for oxygen containing gas (27) at or near the entry of the off-gas duct to enable increasing the temperature of the off-gas by combusting offgas, and

[0029] B. a gas quench (16) further downstream (i.e. in the direction of the off-gas stream) to enable reducing the temperature of the off-gas before leading the off-gas to one or more high temperature dust filters (18b) for dedusting the off-gas prior to leading the off-gas to a high temperature heat exchanger (19a).

[0030] It should be noted that when the off-gas enters the off-gas duct that the stream direction of the off-gas is away from the metallurgical vessel in the direction of the high temperature heat exchanger. This streaming direction is referred to as downstream in the context of this description and the claims.

[0031] The advantage of the apparatus according to the invention compared to the prior art as described in EP0726326 and EP0735146 is that the dedusting of the off-gas that is being led away from the cyclone through the off-gas duct is dedusted at a higher temperature than in the prior art. The technical consequence is that the gas stream is dedusted and clean when it enters the high temperature heat exchanger. This prevents the high temperature heat exchanger from being polluted with dust and it prevents the coagulation of the dust particles by sulphur compounds that tend to form at low temperatures. These coagulations form scales on the high temperature heat exchanger and impede the exchange of heat. As the gas stream according to the invention is cleaned at high temperatures these sulphur compounds do not form, and therefore the high temperature heat exchanger stays clean. The high temperature heat exchanger may be a boiler for generating steam.

[0032] Another advantage is that in the prior art process any CO that is present in the off-gas needs to be burned before the dedusting in the baghouse in the prior art process, because after the dedusting the gas is too cold for efficient burning. However, the burning of the CO before the dedusting means that the heat is released when the temperature of the off-gas is already high. This is potentially damaging for the baghouse filter. Also, the burning of the CO when the off-gas is still at a high temperature increases the risk of NOx formation.

[0033] On the other hand, if the CO is too cold it does not burn properly anymore. In the prior art apparatus the exit temperature of the gas after the dedusting is between 135 and 260 °C because that is the temperature range wherein baghouse filters are designed to operate continuously. This is also too cold for an efficient catalytic de-NOx- treatment of the gas stream. Consequently, the gas stream exiting the baghouse needs to be reheated for the de-NOx-treatment which is inefficient from an energy and cost perspective.

[0034] In the method according to the invention the CO which is still present in the offgas exiting the cyclone is available to be burned at the entry of the off-gas duct. An oxygen inlet is provided at the beginning of the off-gas duct and CO can be burned to maintain a desired high temperature in the off-gas duct. Any excess CO that is not needed to maintain this high temperature stays in the off-gas. In the process and apparatus according to the invention the gas stream is dedusted at a high temperature in a high temperature dust filter at a temperature which is considerably higher than the maximum operating temperature of a baghouse filter. The cleaned gas stream enters the high temperature heat exchanger at a temperature where the sulphur compounds do not yet form, so no hard scale is formed onto the high temperature heat exchanger interior. The burning of the excess CO present in the cleaned off-gas can now take place just before the inlet of the high temperature heat exchanger. This causes no extreme temperatures in the high temperature heat exchanger which extends the life span of the high temperature heat exchanger compared to the prior art process. The resulting superheated steam emerging from the high temperature heat exchanger can be used, e.g. for the generation of electricity. An additional advantage is that the gas stream exiting the high temperature heat exchanger does not need to be reheated for the de-NOx-treatment of the gas stream after the gas stream exits the high temperature heat exchanger because the temperature is still high enough for an efficient de-NOx process.

[0035] In an embodiment the off-gas duct has an inclined section, a riser section, and a downward section, wherein the inlet for oxygen containing gas is provided at or near the entry of the off-gas duct to enable controlling the temperature of the off gas in the initial part of the duct above the melting point of iron oxide. Under these conditions part of the carried over iron oxide can run back into the process as liquid. The gas quench further downstream of the oxygen inlet allows reducing the temperature of the off-gas. The advantage of this configuration is that the iron oxides are solidified and are no longer sticky. Consequently, there are no accretions in this region of the gas duct.

[0036] In an embodiment the off-gas duct is provided with internal water-cooling channels and a duct for leading the steam generated in the cooling channels to the high temperature heat exchanger. This steam can be added to the high temperature heat exchanger and thereby effectively use the heat present in the off-gas duct.

[0037] In an embodiment a water / mist injection system is provided in the downward section to control the temperature of the off-gas prior to entering the high temperature dust filter. This ensures that the temperature of the off-gas is controlled to a temperature suitable for the subsequent high temperature dust filter system. A control loop may be used based on a measured temperature difference between the gas temperature before entering the water / mist injection system and the temperature of the gas prior to entering the high temperature dust filter system. More water or mist may be used if the temperature of the off-gas is too high for the filter system. The control loop may also include the input of a temperature gauge after the gas quench.

[0038] Preferably the high temperature dust filter has an operational temperature of at least 300°C and at most 900°C. Preferably the high temperature dust filter has an operational temperature of at least 500°C and up to 750°C. More preferably the operational temperature is between 550 and 650°C. This range allows to run the offgas dedusting and further treatment smoothly and efficiently because the subsequent heat-exchanger, de-NOx and de-SOX processes can all be run at their optimal operating temperatures and intermediate low temperature heat exchangers allow efficient use of excess heat e.g. for raw material drying. There is no inefficiency in the process caused by the need to cool the off-gas and reheat it later in the process like in the prior art apparatus and process.

[0039] In an embodiment the high temperature dust filter comprises a ceramic filter, such as a candle filter, or a stainless-steel wire mesh filter. The high temperature dust filter may be preceded by one or more cyclone dust filters. This allows the removal of different coarser fractions first before entering the gas stream into the more delicate high temperature dust filter, which may comprise ceramic or stainless-steel mesh filters which may be damaged or clogged-up when confronted with the coarse fractions.

[0040] In an embodiment the high temperature heat exchanger is preceded with an incinerator to burn-off any remaining combustible material in the off-gas after leaving the high temperature dust filter. This enables making optimal use of any remaining combustible material in the off-gas stream.

[0041] Preferably the apparatus is provided with de-SOx means, which are optionally preceded by de-NOx means. Depending on the amount of nitrogen present in the upstream process (e.g. when using air or enriched air instead of high purity oxygen) the amount of NOx also varies. If no nitrogen is present in the upstream process, or if the process conditions are such that no NOx is produced, then the de-NOx-ing is not needed.

[0042] De-NOx may be performed by Selective Catalytic Reduction (SCR), by Selective Non-Catalytic Reduction (SNCR), by absorption wherein a scrubber is used to remove the NOx from the off-gas, by adsorption which involves passing the off-gas through a bed of solid adsorbent material, such as activated carbon or zeolite, which then captures the NOx or by Plasma Treatment in which the off-gas is passed through a high-energy plasma field, which breaks down the NOx into nitrogen and oxygen.

[0043] For the method and apparatus according to the invention the SCR-method is deemed well suited. Particularly efficient catalysts for the selective catalytic reduction of NOx are metal oxide catalysts including titanium dioxide, vanadium pentoxide and tungsten trioxide and I or molybdenum trioxide as disclosed in (US3279884). By bringing NH3 in contact with the off-gas including the NOx the catalytic reaction results in the formation of N2 and H2O. The de-NOx is preferably executed at a temperature above the boiling point of water and therefore the water and nitrogen may be transported with other components in the off-gas through one or more low temperature heat exchangers to effectively use the sensible heat in the gas stream. The off-gas is cooled down to a suitable operating for the de-SOx-step.

[0044] The de-SOx may be performed in a wet flue gas cleaning apparatus in which limestone is used as the absorption agent and which produces gypsum as a useable end-product. During the de-SOx the off-gas is scrubbed of SOx and cools down. The cool off-gas, consisting mainly of CO2, that leaves the de-SOx-means can now either be recycled as cold recycle off-gas towards the gas quench in the riser section of the off-gas duct, or any excess cold off-gas can be led towards a carbon-bed reactor where harmful substances such as mercury, cyanide and arsenic are washed out to be safely processed before the off-gas is discarded or processed in CCU or CCS.

[0045] According to a second aspect the invention is also embodied in a method for producing iron by direct reduction of iron ore using the apparatus according to the invention comprising the comprising the steps of:

[0046] (a) in a pre-reduction stage conveying iron ore into a melting cyclone (2) and pre-reducing it there by means of a reducing off-gas originating from a final reduction stage, (b) effecting a post-combustion in the reducing off-gas in the melting cyclone (2) by supplying oxygen thereto so that said iron ore in the melting cyclone (2) is at least partly melted,

[0047] (c) permitting the pre-reduced and at least partly melted iron ore to pass downwardly from the melting cyclone into a smelting reduction vessel (3) situated beneath the melting cyclone (2) in which the final reduction stage takes place,

[0048] (d) effecting the final reduction in the final reduction stage in the smelting reduction vessel in a molten slag layer (7) therein by supplying carbonaceous material, e.g. coal or biochar, and oxygen to the metallurgical vessel and thereby forming a reducing off-gas, and effecting a partial postcombustion in the reducing off-gas in the metallurgical vessel by means of the oxygen supplied thereto, the carbonaceous material being supplied directly into the molten slag layer (7),

[0049] (e) wherein the post-combustion ratio (PCR) is defined as: in which CO2, CO, H2O and H2 are the concentrations in percent by volume of these gases on exiting the smelting reduction vessel (3), is not more than 0.55, and wherein the partial post-combustion in the smelting reduction vessel (3) at least partly occurs in the molten slag layer;

[0050] (f) leading the off-gas upwardly away from the melting cyclone (2) through the off-gas duct for removing the dust from the off-gas in one or more high temperature dust filters (18a, 18b),;

[0051] (g) utilizing the sensible heat in the off-gas in a high temperature heat exchanger (19a);

[0052] (h) removing sulphur compounds from the off-gas in de-SOx means (21b) and optionally removing de-NOx in de-NOx means (21a);

[0053] (i) thereby producing a cold recycle off-gas (23);

[0054] (j) optionally returning the cold recycle gas (23) back to the gas quench in the riser part of the off-gas duct;

[0055] (k) tapping the molten slag (7) and the molten iron (8).

[0056] In an embodiment the nitrogen oxides are removed from the off-gas in de-NOx means between the heat exchanging step and the removal of the sulphur compounds

[0057] In an embodiment the chemical energy in the off-gas is at least partly and preferably fully preserved in the off-gas until incineration immediately preceding the high temperature heat exchanger. This is done by limiting the amount of oxygen added to the off-gas immediately above the cyclone. The temperature control of the off-gas is important, but it should not be hotter than needed. By controlling the temperature of the off-gas and tailoring the amount of oxygen added at that position in the installation, the excess combustion of CO may be prevented, thereby saving the chemical energy for a later stage, e.g. just before the high temperature heat exchanger to produce superheated steam. The chemical energy of the off-gas can be exploited more economically, and the amount of NOx formed just above the cyclone can be reduced if the temperature at that location is not higher than necessary.

[0058] In an embodiment the sensible heat in the off-gas after de-NOx and before de- SOx is used to preheat the iron ore or carbon prior to introduction in the smelting reduction vessel or melting cyclone. The temperature of the off-gas after de-NOx may be between 260 and 300°C, e.g. about 280°C.

[0059] In an embodiment the de-SOx is performed in a wet flue gas cleaning apparatus in which limestone is used as the absorption agent and which produces gypsum as a useable end-product. During the de-SOx the off-gas is scrubbed of SOx and cools down. The cool off-gas, consisting mainly of CO2, that leaves the de-SOx-means can now either be recycled as cold recycle off-gas towards the gas quench in the riser section of the off-gas duct, or any excess cold off-gas can be led towards a carbon-bed reactor where substances such as mercury, cyanide and arsenic are washed out to be safely processed before the off-gas is discarded or processed in CCU or CCS.

[0060] In an embodiment the off-gas duct (14) has an inclined section (15a), a riser section (15b) and a downward section (15c).

[0061] In an embodiment a temperature control loop is provided by measuring the temperature T1 of the off-gas exiting the riser part (15b) of the off-gas duct and controlling said temperature by actuating the gas quench (16) in the riser part (15b) of the off-gas duct and / or by controlling the amount of oxygen entering the inclined section (15a) of the off-gas duct so as to control the amount of post-combustion of the off-gas exiting the cyclone (2), preferably wherein T1 is controlled between 900 and 1100°C, preferably between 950 and 1050 °C.

[0062] In an embodiment a temperature control loop is provided by measuring the temperature T2 of the off-gas exiting the last of the one or more coarse dust filters (18a) and controlling said temperature by actuating the water / mist injection in the downward section (17) of the off-gas duct so as to control the temperature of the offgas entering the high temperature dust filter, preferably wherein T2 is controlled between 500 and 750°C, preferably between 550 and 650 °C. Figures

[0063] The invention is further explained by means of the following, non-limitative figures.

[0064] Figure 1 shows a melting cyclone A to which iron ore concentrate is supplied with a carrier gas through a supply system B. At the same time substantially pure oxygen is supplied to the melting cyclone A via a supply system C. Directly beneath the melting cyclone and in open connection with it is a metallurgical vessel D. The iron ore is prereduced in the melting cyclone A and melted by a reducing off-gas originating from the metallurgical vessel D. In this off-gas a post-combustion is maintained with the oxygen in the melting cyclone A. The 15 to 30% pre-reduced and molten iron ore trickles at a temperature of preferably 1400-1600°C down the wall E of the melting cyclone A directly into the metallurgical vessel D. The off-gas leaves the melting cyclone A at a temperature of 1200-1800°C. This sensible heat is converted in a boiler H into steam, from which electricity may be generated. After boiler H the off-gas still contains chemical energy by which electricity may also be generated.

[0065] In the metallurgical vessel D there is during operation a melt F of pig iron with a molten slag layer G on top of it. Typically, this molten slag layer G is 2m thick. Substantially pure oxygen is supplied to a lance I in the metallurgical vessel. In the off-gas duct a boiler H is provided to convert sensible heat into steam, from which electricity may be generated.

[0066] In figure 2 a smelting apparatus 1 is shown which has a smelt cyclone 2 and below the smelt cyclone a smelting reduction vessel 3 according to the prior art. 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 a 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. The smelting vessel 3 may be provided with oxygen lances as well (not shown) to inject oxygen above the slag level when the smelting apparatus is in operation to adjust heating and reduction requirements of the process.

[0067] The smelting reduction vessel 3 is provided with oxygen lances 12 in shell or roof portion 11 of the smelting reduction 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.

[0068] Further lances 6 are provided to inject coal and / or additives in the molten slag layer 7. For the injection of iron ore through injection lances 4 and the injection of coal and additives through lances 6 recycled off-gas is used which contains 80-89% CO2. 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 reduction vessel 3 by sequential tapping through a slag tap hole 10.

[0069] The off-gas is guided through an inclined off-gas duct part 15a downstream of the smelting reduction 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 reduction vessel. In this manner most of the iron droplets present in the off-gas can be recovered. Instead of the inclined off-gas duct part other forms are possible as well such as a twisted duct part, a spiralled 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 and be allowed to flow back and end up in the smelting reduction vessel. The temperature in the inclined off-gas duct part 15a is in a range of 1600-1900° C.

[0070] The inclined off-gas duct part 15a 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 over 80%.

[0071] In this example the off-gas is further cooled by means of heat exchanger 17 with a steam driven electric generator device in the downward section 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 the off-gas goes through a cold cyclone dust separator 18 wherein the off-gas is at least partially cleaned. After passing through the cold dust cyclone and steam driven electric generator the off-gas goes through the bag filter 19 wherein most if not almost all dust is removed from the off-gas. 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 24 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 the off-gas duct 14 is needed. In the given example an overpressure in the order of 10 to 500 kPa is enough to get enough cooling gas in off-gas duct 14 to cool the off-gas. 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 molten 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%. By using oxygen with a higher purity the CO2 content can be further increased.

[0072] 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 molten slag layer 7 can be taken from the CO2 processing unit as described further below.

[0073] 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 reduction vessel 3 is operated at sufficient pressure.

[0074] The volume of the off-gas that is used for CCS or CCU is taken from the main duct and fed through duct 25 to a CO2 processing unit (not drawn) wherein the off-gas is further purified, dried, cooled and compressed for CCS.

[0075] The part of the off-gas that is not used for either CCS or CCU is discharged through stack 22. The NOx component in the off-gas is preferably removed as far as possible.

[0076] Figure 3 shows the same apparatus as the prior art apparatus of figure 2, but with the set-up according to the invention. The high temperature dust filter 18b is located immediately after the one or more coarse material filters 18a and before the high temperature heat exchanger 19a where superheated steam is produced. After the high temperature heat exchanger 19a and the optional fan 20 the gas stream is de- NOx-ed and subsequently de-SOx-ed in facility 21a and 21b.

[0077] Figure 4 shows an embodiment of the apparatus according to the invention in more detail. Starting with the metallurgical vessel 1 on the bottom left corner molten iron and molten slag are tapped and coal, oxygen, iron ore and additives are added as shown in figure 3. The off-gas is led upwardly to the top of the cyclone 2 and at the beginning of the off-gas duct oxygen may be added (27) to allow an increase of the temperature by post combustion of part of the off-gas. The temperature of the off-gas in the off-gas duct 14 is preferably controlled to about 1500° C. The temperature of the off-gas is lowered by the gas quench 16 and at the top of the off-gas duct the temperature has decreased to about 1000°C. The gas quench is fed with the cold recycle gas 23. Steam at a temperature of more than 200°C can be obtained at the top of the off-gas duct and this steam can be fed into the high temperature heat exchanger 19a. In the downward section of the off-gas duct 15c water / mist is introduced 29 and the gas-stream is dedusted in the one or more coarse dust filters 18a, preferably cyclone filters, and thereafter in the high temperature dust filter 18b. Preferably the temperature of the gas is then between 550 and 650°C and typically about 600 °C. The resulting clean gas stream is then fed into the high temperature heat exchanger 19a and the excess CO in the gas stream is burnt to increase the temperature of the off-gas to produce superheated steam in the high temperature heat exchanger which can then me used to drive a turbine to generate electricity (not shown). After the high temperature heat exchanger the temperature of the off-gas has reduced to about 280°C and led into the de-NOx unit 21a. Ammonia is added to allow de-NOx-ing in the de-NOx-vessel. The gas is then further cooled in one or more low temperature heat exchangers and led to the de-SOx-vessel 21b. In this case the system is a wet system where gypsum (CaSO4) is produced using limestone and water. A carbon bed unit 26 may remove undesired elements or compounds such as Hg, HCN and As from the off-gas. The FeO fraction in the dust recuperated from the filters 18a can be fed back into the process. The finer dust may comprise ZnO in case zinc containing materials are injected into the smelt cyclone or the smelting reducing vessel and into a part comprising e.g. certain salts and heavy metals which need to be disposed of with care. The ZnO-dust from the dust collected by the high temperature dust filter may be separated out and utilised to produce new zinc metal.

[0078] In Figure 5a the part in the dashed box in figure 4 is enlarged to further illustrate the structure of the apparatus according to the invention.

[0079] Any reference numbers in the claims should not be construed as limiting the scope of the appended claims.

[0080] List of reference numbers

Claims

CLAIMS1. An apparatus comprising a metallurgical vessel (1) for producing molten iron (8) by direct reduction of iron ore, comprising i) a smelting reduction vessel (3), in which in operation of the apparatus the iron ore undergoes a final reduction with production of a off-gas and said off-gas undergoes a partial post-combustion, means for supplying carbonaceous material (6), e.g. coal, to said metallurgical vessel, means for supplying oxygen, and ii) a melting cyclone (2) on top of the smelting reduction vessel (3) in which in operation of the apparatus said iron ore undergoes a prereduction and is melted, said melting cyclone (2) being positioned on top and in direct and open communication with said smelting reduction vessel (3) for transfer of the pre-reduced iron ore thereto and for flow of the post-combusted off-gas from the metallurgical vessel (1), wherein said smelting reduction vessel (3) comprises iii) a top part, in which said partial post-combustion of said off-gas takes place and a bottom part for accommodating an iron bath (8) having a molten slag layer (7) in which said final reduction of said iron ore takes place, the apparatus further comprising an off-gas duct (14) mounted on top of the melting cyclone (2) for leading away the off-gas, and one or more of:A. an inlet for oxygen containing gas (27) at or near the entry of the offgas duct to enable increasing the temperature of the off-gas by combusting off-gas, andB. a gas quench (16) further downstream (i.e. in the direction of the offgas stream) to enable reducing the temperature of the off-gas before leading the off-gas to one or more high temperature dust filters (18b) for dedusting the off-gas prior to leading the off-gas to a high temperature heat exchanger (19a).

2. Apparatus according to claim 1 wherein the off-gas duct (14) has an inclined section (15a), a riser section (15b) and a downward section (15c).

3. Apparatus according to claim 1 or 2 wherein the off-gas duct (14) is provided with internal water cooling channels and a duct for leading steam generated in the cooling channels to the high temperature heat exchanger (19a).

4. Apparatus according to any one of claim 1 to 3 wherein a water / mist injection system (29) is provided in the off-gas duct, preferably in the downward section (15c), to control the temperature of the off-gas prior to entering the high temperature dust filter (18b).

5. Apparatus according to any one of claim 1 to 4 wherein the high temperature dust filter (18b) comprises a ceramic filter or a stainless steel wire mesh filter wherein the high temperature dust filter (18b) has an operational temperature between 300°C and 900°C.

6. Apparatus according to any one of claim 1 to 5 wherein the high temperature dust filter (18b) is preceded by one or more cyclone dust filters (18a).

7. Apparatus according to any one of claim 1 to 6 wherein the high temperature heat exchanger (19a) is preceded with an incinerator (28) to burn-off any remaining combustible material in the off-gas after leaving the high temperature dust filter.

8. Apparatus according to any one of claim 1 to 7 wherein downstream of the heat exchanger (19a) de-SOx means (21b) are provided, and wherein optionally de- NOx means (21a) between the heat exchanger (19a) and the de-SOx means (21b) are provided.

9. Method for producing molten iron by direct reduction of iron ore using the apparatus according to any one of claims 1 to 8 comprising the steps of(a) in a pre-reduction stage conveying iron ore into a melting cyclone (2) and pre-reducing it there by means of a reducing off-gas originating from a final reduction stage,(b) effecting a post-combustion in the reducing off-gas in the melting cyclone (2) by supplying oxygen thereto so that said iron ore in the melting cyclone is at least partly melted,(c) permitting the pre-reduced and at least partly melted iron ore to pass downwardly from the melting cyclone into a smelting reduction vessel (3) situated beneath the melting cyclone (2) in which the final reduction stage takes place,(d) effecting the final reduction in the final reduction stage in the smelting reduction vessel (3) in a molten slag layer (7) therein by supplying carbonaceous material, e.g. coal or biochar, and oxygen to the metallurgical vessel and thereby forming a reducing off-gas, and effecting a partial postcombustion in the reducing off-gas in the metallurgical vessel by means of the oxygen supplied thereto, the carbonaceous material being supplied directly into the molten slag layer (7),(e) wherein a post-combustion ratio (PCR) is defined as:in which CO2, CO, H2O and H2 are the concentrations in percent by volume of these gases on exiting the smelting reduction vessel (3), and is not more than 0.55, and wherein the partial post-combustion in the smelting reduction vessel (3) at least partly occurs in the molten slag layer (7);(f) leading the off-gas upwardly away from the melting cyclone (2) through the off-gas duct for removing the dust from the off-gas in one or more high temperature dust filters (18a, 18b),;(g) utilizing the sensible heat in the off-gas in a high temperature heat exchanger (19a),(h) removing sulphur compounds from the off-gas in de-SOx means (21b) and optionally removing de-NOx in de-NOx means (21a)(i) thereby producing a cold recycle off-gas (23);(j) optionally returning the cold recycle gas (23) back to the gas quench in the riser part of the off-gas duct;(k) tapping the molten slag (7) and the molten iron (8).

10. Method according to claim 9 wherein the off-gas duct (14) has an inclined section (15a), a riser section (15b) and a downward section (15c);11. Method according to claim 9 or 10 wherein NOx is removed from the off-gas in de-NOx means (21a) between the step of utilizing the sensible heat in the offgas in the high temperature heat exchanger (19a) and the step of removing sulphur compounds from the off-gas in de-SOx means (21b).

12. Method according to any one of claims 9 to 11 wherein the chemical energy in the off-gas exiting the melting cyclone (2) is at least partly and preferably fully preserved in the off-gas until its incineration in the incinerator (28) immediatelypreceding the high temperature heat exchanger (19a) to heat the off-gas before entering the high temperature heat exchanger (19a).

13. Method according to any one of claims 9 to 12 wherein the sensible heat in the off-gas after the optional de-NOx and before de-SOx is used to preheat the iron ore prior to introduction into the melting cyclone (2) or to preheat the carbonaceous material, e.g. coal or biochar, prior to introduction in the smelting reduction vessel (3) or wherein the sensible heat in the off-gas after the optional de-NOx and before de-SOx is used to preheat the iron ore prior to introduction into the melting cyclone (2) and to preheat the carbonaceous material prior to introduction in the smelting reduction vessel (3)14. Method according to any one of claims 9 to 13 wherein a carbon based adsorbent, such as activated carbon, is used (26) is used for processing the optionally de- NOx-ed, the de-SOx-ed and cold off-gas to remove undesired elements or compounds such as Hg, HCN and As from the cold off-gas before returning the cold off-gas to the gas quench in the off-gas duct as cold recycle gas (23) or before the cold off-gas is discarded or processed in Carbon Capture and Utilisation or (CCU) or Carbon Capture and Storage (CCS).

15. Method according to any one of claim 9 to 14 wherein the PCR of the reducing off-gas after the combustion in step b is higher than the PCR of the reducing offgas after step d.

16. Method according to any one of claim 15 wherein a temperature control loop is provided by measuring the temperature T1 of the off-gas exiting the riser part (15b) of the off-gas duct and controlling said temperature by actuating the gas quench (16) in the riser part (15b) of the off-gas duct and / or by controlling the amount of oxygen entering the inclined section (15a) of the off-gas duct so as to control the amount of post-combustion of the off-gas exiting the cyclone (2), preferably wherein T1 is controlled between 900 and 1100°C, preferably between 950 and 1050 °C.

17. Method according to any one of claim 9 to 16 wherein a temperature control loop is provided by measuring the temperature T2 of the off-gas exiting the last of the one or more coarse dust filters (18a) and controlling said temperature by actuating the water / mist injection (29) in the downward section (15c) of the offgas duct so as to control the temperature of the off-gas entering the high temperature dust filter, preferably wherein T2 is controlled between 500 and 750°C, preferably between 550 and 650 °C.

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