WO2008122527A2

WO2008122527A2 - Method and device for preparing a reducing agent for use in a metal making process, metal making process and metal making apparatus using said device

Info

Publication number: WO2008122527A2
Application number: PCT/EP2008/053733
Authority: WO
Inventors: Mark Bernard Denys; Jan Zuidema; Jeroen Martijn Link; Hendrikus Koenraad Albertus Meijer
Original assignee: Corus Technology Bv
Priority date: 2007-04-04
Filing date: 2008-03-28
Publication date: 2008-10-16
Also published as: CN101688258A; RU2009140757A; AU2008235542A1; CN101688258B; AU2008235542B2; RU2477755C2; BRPI0810043A2; ZA200906882B; BRPI0810043B1; WO2008122527A3; BRPI0810043A8

Abstract

The invention relates to a method of preparing a reducing agent having an elevated temperature for use in an metal making process, comprising a) a pyrolysing step of heating a carbonaceous starting material using a heat source wherein the starting material is pyrolysed to a degree of pyrolysis of at most 80% into a partially charred carbonaceous product having an elevated temperature and producing a pyrolysis off-gas comprising volatile substances from the carbonaceous starting material, b) a combustion step of combusting the pyrolysis off-gas, thereby producing a combusted off-gas, wherein the thermal energy of the combusted off-gas is used as the heat source in step a) by bringing the combusted off-gas into direct contact with the carbonaceous starting material and/or wherein the thermal energy of the combusted off-gas is used as the heat source in step a) by heating the carbonaceous starting material without directly contacting the carbonaceous starting material. The invention also relates to a preferred device for performing the method according to the invention, a metal making process, such as an iron making process, making use of the reducing agent preparation process and apparatus for carrying out this process.

Description

METHOD AND DEVICE FOR PREPARING A REDUCING AGENT FOR USE IN A METAL MAKING PROCESS, METAL MAKING PROCESS AND METAL MAKING APPARATUS USING SAID DEVICE

The present invention relates to a method and device for preparing a reducing agent having an elevated temperature for use in a metal making process, and a metal making process and apparatus using said device.

Metal making processes using reducing agents are well known in the art. EP 0 936 272 discloses a method and device for smelting metal ore, i.e. iron ore, wherein iron oxide and hot char as reducing agent are fed into a primary reactor to reduce the iron oxide and thereby form a molten pool of elemental iron producing an iron oxide containing slag layer.

The hot char is prepared in a secondary reactor from carbon containing substance comprising fixed carbon and a hydrocarbon containing volatile matter by partially oxidizing the volatiles. A fuel gas comprising hydrocarbons, CO, CO₂, steam and H₂ having a CO:CO₂ ratio of more than 0.25 is simultaneously produced in the secondary reactor. This fuel gas is combusted such that a projected flame is produced, which flame is directed into the iron oxide consisting slag layer.

The primary reactor may comprise a converter and a melting cyclone on top of it, also known as Cyclone Converter Furnace (CCF). Iron ore fines are introduced in the melting cyclone. Oxygen and fuel in the form of a gas stream from the converter are also introduced in the melting cyclone. As a result the iron ore is pre-reduced and melted. Due to the cyclonic action the liquid metal stream is separated from the gas stream.

The liquid pre-reduced iron ore flows downwardly along the inner wall of the melting cyclone into the converter, where a further or final reduction takes place. The reducing agent required in the converter is introduced as hot char from the secondary reactor, coal or a combination thereof. Oxygen is introduced in the converter using one or more lances. In the secondary reactor coal may be partially oxidized using an oxidizing agent, such as (oxygen enriched) air or oxygen. Examples of the secondary reactor comprise a fluidized bed for granular coal feeds with a narrow particle size distribution, a spouted bed reactor for granular coal feeds with a broader particle size distribution and an entrained flow reactor with pulverized coal feeds.

EP 0 726 326 discloses a process and an apparatus for producing molten metal, i.e. pig iron, by direct reduction of iron ore in a pre-reduction stage in a melting cyclone followed by a final reduction stage in a converter as a metallurgical vessel. This known process comprises the steps of conveying iron ore into the melting cyclone in the pre-reduction stage and pre- reducing it there by means of a reducing process gas originating from the final reduction stage in the metallurgical vessel.

Also post-combustion of the reducing process gas in the melting cyclone is carried out by supplying oxygen so that the iron ore in the melting cyclone is at least partly melted. The pre- reduced and at least partly melted iron ore passes downwardly from the melting cyclone into the metallurgical vessel situated beneath. The final reduction in the metallurgical vessel is effected in the slag layer by supplying coal in a solid particulate form directly into the slag layer and oxygen to the metallurgical vessel thereby forming the reducing process gas. This reducing process gas is partially post-combusted by supplying oxygen. The partial post-combustion is at least partly effected in the slag layer, such that the post-combustion ratio is not more than 0.55. The remaining reducing process gas is consumed in the melting cyclone. It is said that notwithstanding the low post-combustion degree in the metallurgical vessel, a low coal consumption results. This known process produces more export gas with a greater chemical energy content, the lower the post-combustion ratio is set. This process also allows the use of less costly high volatile coal.

WO 2004/031324 discloses a method and apparatus for the treatment of a material under pyrolitical conditions. This known apparatus comprises a housing, in which an extrusion screw is provided. An example of a starting material to be treated comprises coal resulting in char or coke. The screw arrangement reduces the problems related to the plastic phase during reaction, such as stickiness, poor mixing properties affecting heat transfer and processability. It is also said that this known apparatus itself can be used to reduce iron ore to steel using a reducing agent.

While the prior art discussed above illustrate various attempts to improve the ironmaking process, there is still a need to further optimize these processes, particularly in view of coal consumption, energy consumption and emission of environmentally harmful by-products such as carbon dioxide.

A first object of the invention is to prepare a reducing agent such as partially charred coal in a energy efficient manner.

An object of the invention is to reduce the coal consumption in metalmaking. A further object is to reduce CO₂ emissions in metalmaking.

Yet another object is to allow for the (partial) replacement of coal by one or more alternative energy sources, thereby allowing for a further reduction of CO₂ emission.

Still another object is to provide off-gases produced have a high CO₂ content, which can be reused or stored without the need for costly CO₂ capture measures. According to a first aspect of the invention a method of preparing a reducing agent having an elevated temperature for use in an metal making process is provided, comprising a) a pyrolysing step of heating a carbonaceous starting material using a heat source wherein the starting material is pyrolysed to a degree of at most 80% into a partially charred carbonaceous product having an elevated temperature and producing a pyrolysis off-gas comprising volatile substances from the carbonaceous starting material, b) a combustion step of combusting the pyrolysis off-gas, thereby producing a combusted off-gas, wherein the thermal energy of the combusted off-gas is used as the heat source in step a) by bringing the combusted off-gas into direct contact with the carbonaceous starting material and/or wherein the thermal energy of the flow combusted off-gas is used as the heat source in step a) by heating the carbonaceous starting material without directly contacting the carbonaceous starting material. The carbonaceous starting material is partially charred by partial pyrolysis to form the reducing agent. The partially charred carbonaceous product is the reducing agent.

In the method according to the first aspect of the invention a carbonaceous starting material is only partially pyrolysed by heating in step a). The off-gas of this partial pyrolysis step comprises volatile components such as hydrocarbons. This pyrolysis off-gas is combusted in step b). This combustion step b) produces a combusted off-gas. This combusted off-gas is used to heat carbonaceous starting material freshly fed and the already partially charred carbonaceous starting material in step a) in order to supply the heat required for partial pyrolysis. Heating may be effected directly, i.e. by direct contact of the combusted off-gas with the material to be heated, or indirectly, i.e. not by direct contact of the combusted off-gas with the material to be heated, or directly and indirectly. In this way a reducing agent for use in an ironmaking process is prepared in a highly energy sufficient manner, which allows for an improved efficiency in a ironmaking process. The method of the invention can be regarded as a pre-treating process of the carbonaceous starting material into a reducing agent having an elevated temperature to be directly used in the ironmaking process, enabling a higher carbon and energy efficiency and an off-gas having a high PCR, for instance at the cyclone exit, when using a CCF apparatus for metal making, particularly for iron making. The inventors have found that the optimisation of the pyrolysis in combination with metal making generates a potential energy efficiency improvement of over 25% per tonne of produced metal. This potential is achieved by the replacement of cold coal by hot char, and by the inherent increase of efficiency because the lower consumption of coal means that less gas is produced which needs to be heated resulting in less heat losses per tone of hot metal. The cold coal would otherwise be heated in a process that only partially uses the coal being fed (post-combustion ratio of about 45%) and looses its off-gas at a high temperature of about 1700⁰C. Both factors mean that the bath smelter chemically and thermally is not an efficient reactor for heating cold materials. Simultaneous direct and indirect heating of the carbonaceous starting material may be achieved by splitting the flow of combusted off-gas in at least a first and a second flow of combusted off-gas, and wherein the thermal energy of the first flow of combusted off-gas is used as the heat source in step a) by bringing the flow into direct contact with the carbonaceous starting material and wherein the second flow of combusted off-gas is used as the heat source in step a) by heating the carbonaceous starting material without directly contacting the carbonaceous starting material.

The maximum amount of pyrolysis of the coal is governed by the desire to create sufficient amounts of gas for it to be used as pyrolysis off-gas to be used to heat the carbonaceous starting material. The inventors found that a suitable degree of pyrolysis is at most 50%. Preferably the degree of pyrolysis is between 5 and 50%, and more preferably between 10 to 40%. Depending on the coal type and the moisture level, a preferable degree of pyrolysis is between 15 and 25% and a temperature of between 400 and 900⁰C. An preferable temperature range was found to be between 600 and 800⁰C.

It is noted that in the context of this invention the expression "pyrolysed" means that the carbonaceous starting material is heated to a predefined temperature essentially in the absence of any substantial amounts of oxygen (oxygen free atmosphere or low partial pressure of oxygen). As a result of this heating a broad variety of reactions take place thereby forming a plurality of products. The solid products are indicated by the term "char", while the fluid products in particular the gaseous components are the so-called "volatiles". Preferably, step a) and b) are performed in distinct zones separated from one another in order to minimize the risk of oxygen or other oxidant being present in the step a) zone at an unacceptable level. Partial pyrolisation means that the resulting partially charred carbonaceous product still contains significant amounts of volatiles which are subsequently available during later use of the partially charred carbonaceous product. It is preferable that just enough volatiles are stripped from the carbonaceous starting material to sustain the pyrolisation process and to allow the char to attain the desired elevated temperature. Preferably at most 50% of the total amount of volatiles have been released from the carbonaceous starting material.

Treatment of coal under pyrolytical conditions is a known process per se for preparing char or coke. See e.g. WO-A-2004/031324. Generally such a process comprises three stages. First the coal is heated, after which the coal becomes at least partially plastic and loses volatiles (while it is still heated). After a certain period of time the plastic coal has lost a certain amount of volatiles. Thus the chemical composition of the coal changes over time. As a result the coal becomes brittle and turns into char or coke, while still losing volatiles.

Examples of suitable carbonaceous starting material comprise all kind of coal. The method according to the invention allows for the use of normal and high volatile coal as starting material, which are less costly than low volatile coal. The invention can also process alternative carbonaceous sources such as biomass, thereby allowing for partial substitution of coal as carbonaceous starting material. During start-up of the pyrolisation process a significant amount, up to 100% of externally supplied combustible gas, such as CO or natural gas, may be required to initiate the partial pyrolisation of the carbonaceous starting material and the resulting generation of volatiles. Once pyrolisation has started, the amount of externally supplied combustible gas may be reduced, preferably to a level where no external sources are needed, and the process becomes self-sustaining in this respect. The amount of external sources also depends from the type of carbonaceous starting material that is used. In the invention the volatiles, mostly hydrocarbons, are vaporized from the carbonaceous starting material during heating and partial charring of the starting material in step a). The volatiles are used as fuel in the subsequent combusting step b). The heat generated by combusting is contained in the hot combusted off-gas, and subsequently transferred to fresh carbonaceous starting material and the already partially charred product. As a result the temperature of this product is raised further, while the combusted off-gas cools. In a preferred embodiment the step a) zone comprises a once-through reactor, more preferably an extruder type reactor, in particular one having a intermeshing double extrusion screw. The intermeshing double extrusion screw may be of the counter rotating type. Such a reactor is beneficial for this kind of materials, because the unfavourable sticking properties of the resulting char product are mechanically counteracted. Such a preferred reactor is known per se from WO 2004/031324, the disclosure of which is incorporated in its entirety by reference.

Preferably the oxygen containing gas used in the method according to the invention for combusting the pyrolysis off-gas is preheated, thereby raising the combustion efficiency. Preferably the temperature of the oxygen containing gas after preheating is between 400 and 700⁰C.

In order to increase the heat transfer efficiency the hot combusted off-gas and the carbonaceous starting material that is being partially charred are fed in counter flow. E.g. the hot combusted off-gas from step b) is cooled to about 500⁰C, while the product finally resulting from step a) has a temperature of about 700⁰C.

In a further preferred embodiment step a) is carried out in such a manner that the resulting pyrolysis off-gas comprises an amount of volatiles that is sufficient for providing the required heat for heating and partially pyrolysing of the carbonaceous starting material after combustion of the pyrolysis off-gas, while the partially charred carbonaceous product comprises the remaining volatiles. In fact, this mode of operation is self-sustaining: the heat generated by combustion of the pyrolysis off-gas and transferred to "fresh" starting material is just sufficient to allow a suitable amount of pyrolysis off-gas to be produced by heating this

"fresh" material. Only during start-up of the process externally supplied combustible gas, such as natural gas or CO, may be needed. For this purpose, means for supplying such externally supplied combustible gas may be provided.

According to a second aspect of the invention a method for producing molten metal by direct reduction of metal ore in a pre-reduction stage followed by a final reduction stage is provided, comprising the steps of

(a) in said pre-reduction stage feeding metal ore into a pre-reduction zone and pre- reducing it there by means of a reducing process gas originating from a final reduction zone,

(b) effecting a post-combustion in said reducing process gas in said pre-reduction zone by supplying oxygen thereto so that said metal ore in said pre-reduction zone is at least partly melted, (c) permitting the pre-reduced and at least partly melted metal ore to pass from said pre-reduction zone into the final reduction zone situated downstream as seen in the direction of flow of the iron ore in which said final reduction takes place, and

(d) effecting said final reduction in said final reduction zone in a slag layer by supplying a reducing agent and an oxygen containing gas to said final reduction zone thereby forming said reducing process gas, and (e) effecting a partial post-combustion of said reducing process gas in said final reduction zone by means of said oxygen containing gas supplied thereto, wherein a reducing agent is fed into the final reduction zone, said reducing agent having been prepared according to the method of the invention. In this process according to the invention metal ore, such as iron ore, is fed into the prereduction zone, where a pre-reduction is performed using a reducing process gas derived from a final reduction zone. Advantageously, the pre-reduction zone is a melting cyclone. Metal ore, such as iron ore, is fed into the top of the pre-reduction zone. In case the pre-reduction zone is a melting cyclone, the ore is fed tangentially into the cyclone. The reducing process gas is introduced at the lower end of the pre-reduction zone, i.e. the open lower end in case the prereduction zone is a melting cyclone. The reducing process gas is combusted with oxygen containing gas that is separately injected into the pre-reduction zone . In a melting cyclone, this initiates a cyclonic movement. In the context of this invention, oxygen containing gas comprises at least 30% of oxygen, and preferably at least 90% or even 95%. It is also possible to use industrially pure oxygen gas or even more pure oxygen gas. The iron ore is molten in-flight by the heat generated in the pre-reduction zone and the liquid ore is collected at the periphery walls. As the reducing process gas comprises CO and H₂, the liquid ore is partially reduced during its travel down due to gravity along the cyclone inner walls. A final reduction is carried out in the final reduction zone using the reducing agent prepared according to the invention, thereby producing a pool of liquid iron and a reducing process gas comprising CO and H₂. The endothermic reduction reaction predominantly takes place in a liquid slag layer floating on top of the pool of molten iron. The heat required is supplied by partial combusting the reducing gases with oxygen by injecting oxygen containing gas, such as industrially pure oxygen, through lances onto the slag layer. In a preferred embodiment the final reduction zone is a converter.

Although the process as described can be used to reduce any metal ore that can be reduced using a carbonaceous material as a starting material, such as nickel ore, copper ore, cobalt ore, zinc-ore, the device is particularly applicable to the production of iron from iron ore. In addition to the benefits and advantages described above the use of a partially pyrolysed carbonaceous material having an elevated temperature in this type of metal making process, such as an iron making process, allows for a staged but at the end essentially complete oxidation of the carbonaceous material as mined into a fully combusted process off- gas, e.g. having a CO₂ content of up to 96%. Simultaneously the present process allows for a lower coal consumption (about 550 kg per tonne iron produced or less) and in a decrease in emission of process off-gas (in the order of 20-30%). Advantageously, the stages of partial coal charring, pre-reduction and final reduction are all hot coupled, thereby avoiding temporary storage and reducing heat losses.

In a preferred embodiment of this process according to the invention the process off-gas exiting the pre-reduction zone has a post-combustion ratio defined as CO '_n2 + H_nO

PCR =

CO₂ + CO + H₂O + H₂

in which CO₂, CO, H₂O and H₂ are the concentrations in percent by volume of these gases on exiting the pre-reduction zone such as a melting cyclone, wherein the PCR is more than 0.60, preferably more than 0.75, more preferably at least 0.90, and even more preferably at least 0.95.

In a further preferred embodiment oxygen containing gas is supplied to the final reduction zone such as a metallurgical vessel by means of a multiple lance arrangement in order to increase heat transfer, reduce heat losses and suppress dust losses. Preferably the lances are arranged with respect to the final reduction zone in such a way that the hot combusted gases flow towards the central axis of the final reduction zone, so as to direct the hot gasses away from the walls of the final reduction zone. This way the hot gases do not come into contact with the walls of the final reduction zone such as a metallurgical vessel which prolongues the lifetime of the walls and provides good mixing. Moreover, the gases flowing towards the central axis are pushed upwardly, i.e. upstream as seen in the direction of flow of the iron ore, thereby achieving efficient use of thermal energy in the process, the inventors found that in case of using a substantially rotation-symmetrical final reduction zone, the use of at least 3 substantially equi-angularly distributed lances along the circumference of the final reduction zone is preferable. The use of 3 lances provides a good and stable flow within the metallurgical vessel. More lances provide an even more stable flow, and provides process redundancy.

Although the method as described can be used to reduce any metal ore that can be reduced using a carbonaceous material as a starting material, such as nickel ore, copper ore, cobalt ore, zinc-ore, the device is particularly suitable for the production of iron from iron ore.

The invention also provides preferred embodiments of a device and an apparatus for performing the reducing agent preparation method and metalmaking process discussed above.

According to a third aspect the invention relates to a device for preparing a reducing agent having an elevated temperature for use in a metal making process, comprising at least one heating chamber having an inlet for feeding a carbonaceous starting material and an outlet for discharging a partially charred starting material having an elevated temperature and also having an outlet for discharging a pyrolysis off-gas comprising volatile substances originating from the carbonaceous starting material, conveyor means arranged in said heating chamber for conveying the carbonaceous starting material from the inlet to the outlet , a combustion chamber for combusting the pyrolysis off-gas, the chamber having an inlet for the pyrolysis off-gas connected to the outlet for discharging a pyrolysis off-gas from the heating chamber, and having an outlet for combusted off-gas, means for transferring the heat contained in the combusted off-gas to the carbonaceous starting material in the heating chamber by direct and/or indirect contact of the combusted off-gas with the carbonaceous starting material. During operation of this device according to the invention, carbonaceous starting material loaded at the inlet is heated in the heating chamber to a temperature sufficient for partially pyrolysing thereof, while being conveyed to the outlet of the heating chamber. The pyrolysis off- gas is collected and subsequently burned in the combustion chamber, which is preferably separated from the heating chamber. The combusted off-gas produced is used in the heating chamber. The advantages discussed above with respect to the method according to the invention are equally applicable to this device according to the invention. In particular the device according to the invention allows for an efficient use to be made of the heat that is present in the combustion off-gas, as explained hereinabove.

Preferably the device according to this aspect of the invention is a once-through reactor, more preferably an extruder type reactor. The conveyor means of the extruder type reactor according to the invention preferably comprises a intermeshing double extrusion screw, which may be a counter rotating intermeshing double extrusion screw. According to a fourth aspect the invention relates to an apparatus for the production of molten iron by direct reduction of metal ore such as iron ore, comprising

(a) a device according to the invention for preparing a reducing agent having an elevated temperature;

(b) a metallurgical vessel for performing a final reduction of the iron ore; (c) supply means for supplying partially charred carbonaceous starting material derived from said device, into a slag layer formed, in operation of the apparatus, above a molten bath of metal originating from the reduced metal ore in the metallurgical vessel; (d) supply means for supplying oxygen to said metallurgical vessel; (e) discharge means for discharging molten metal and slag from said metallurgical vessel;

(f) a melting cyclone located above and in open connection with said metallurgical vessel so as to form a single reactor therewith, process gas passing in operation from said metallurgical vessel directly into said melting cyclone and at least partially melted pre-reduced metal ore passing from said melting cyclone directly into said metallurgical vessel;

(g) supply means for supplying metal ore into said melting cyclone; (h) supply means for supplying oxygen into said melting cyclone;

(i) discharge means for discharging process gas in a flow stream from said melting cyclone.

Although the device as described can be used to reduce any metal ore that can be reduced using a carbonaceous material as a starting material, such as nickel ore, copper ore, cobalt ore, zinc-ore, the device is particularly suitable for the production of iron from iron ore. The invention is further illustrated by means of the attached drawings, wherein: Figure 1 schematically shows a preferred embodiment of an extrusion type reactor for performing a preparation method of a reducing agent having an elevated temperature for use in an ironmaking process according to the invention. Figure 2 schematically shows an embodiment of an apparatus for the production of molten iron by direct reduction of iron ore according to the invention.

A preferred embodiment of an device for preparing a reducing agent having an elevated temperature is shown in Figure 1. The extrusion type device is indicated in its entirety by reference numeral 10. The device 10 comprises a double-walled housing 12. Two extrusions screws 14 are arranged parallel to each other in the interior of the housing 12. In the view of figure 1 only one extrusion screw is visible. The interior of the housing 12 defines a heating chamber 16. The housing 12 is provided with an inlet 18 for carbonaceous starting material to be charred near a first end 20 of the housing 12, which is in fluid communication with the heating chamber 16. A product outlet 22 for discharging partially pyrolysed starting material is positioned at the opposite second end 24 of the housing 12. The top wall 26 of the housing 12 is also provided with one or more pyrolysis off-gas outlets 28 being also in fluid communication with the heating chamber 16, for discharging the gaseous products of the partial pyrolysis occurring in the heating chamber 16 and other volatiles. The outlets 28 are connected via suitable collecting piping 30 to a burner device - generally indicated by 32 - for combusting the pyrolysis off-gas. In the burner device 32 the collected pyrolysis off-gas comprising hydrocarbons and other volatiles is combusted at least partially with oxygen containing gas, such as air (not shown), preferably preheated air, and a hot combusted off-gas is obtained. This combusted off-gas is returned to the device 10. In the embodiment shown the combustion off-gas is divided in two separate flows. A first flow of combusted off-gas passes at the second end 24 of the housing 12 into the hollow axes 34 of the screws 14 and exits at the first end 20. A second flow of combusted off-gas is introduced at the second end 24 via inlet 36 into an annular space 38 between the inner and outer wall of the double-walled housing 12. At the first housing end 20 this second flow is discharged through outlet 40. Thus both flows of combusted off-gas are in counterflow to the flow of carbonaceous starting material in the heating chamber 16. Thereby heat is transferred from both flows to the carbonaceous starting material. The combusted gas cools to approximately 500⁰C or less, while the partially pyrolysed product leaves the outlet 22 having a temperature of about 700⁰C. The residence time in the extruder type reactor 10 may vary, typically about 5-10 minutes will be sufficient to obtain a self- sustaining reaction. The two screws 14 each have a hollow axis 34, which is provided with a spirally configured blade 42. These blades 42 may be hollow as well for circulating a heating fluid such as the combusted off-gas. The blades 42 of the two screws 14 are intermeshed with little mechanical clearance. During start-up of the pyrolysis process externally supplied combustible gas, such as natural gas or CO, may be needed. For this purpose, means for supplying such externally supplied combustible gas (not shown) to the device 10 may be provided. If the caloric value of the pyrolysis off-gas is higher than required for sustaining the partial charring process, the excess caloric value may be used for other purposes. For this purpose, an additional outlet (not shown) for leading away part of the pyrolysis off-gas may be provided to device 10.

In an experiment involving an extruder type reactor comprising a single extrusion screw the method according to the invention was tested experimentally and it was found that at a temperature of 700 ⁰C an amount of volatiles was released from the coal before the hot partially charred coal was released at the end of the reactor which is sufficient to sustain the process in terms of heat needed. From heat and mass balance work it was concluded that the amount of volatiles released, even for low volatile coal, is able to drive the process in terms of heat needed. This surprising result enables to avoid using external fuels to supply the necessary heat to the process.

Figure 2 diagrammatically shows an embodiment of a metal making apparatus, such as an iron making apparatus, 100 of the CCF type according to the invention. The apparatus comprises one or more reducing agent preparation devices 10 as shown schematically in figure 1 and detailed above. Furthermore the iron making apparatus 100 comprises melting cyclone 102 as a pre-reduction zone for pre-reducing and melting fine iron ores that are fed tangentially at 104. Beneath the melting cyclone 102 a converter vessel 106 as a final reduction zone is arranged, of which the open top 108 of vessel 106 is connected to the open bottom 112 of the melting cyclone 102 for allowing reducing process gas to pass from the vessel 106 to the melting cyclone and allowing partially reduced and molten iron ore to flow downwardly into vessel 106. A pool 114 of liquid metal is present at the bottom of the vessel 106 having a slag layer 116 floating on top. Oxygen is fed to both the cyclone 102 and converter 106, e.g. by suitable supply lines 122 to the cyclone 102. Usually oxygen will be injected onto the slag layer 116 in the converter vessel 106 by means of a multiple lance assembly of which only two lances 118 are shown in Figure 2. Hot partially charred coal having an elevated temperature derived from the reducing agent preparation devices 10 is also delivered to the converter through inlet 124 for reducing the partly reduced and molten iron ore derived from the cyclone 102 according to Fe_xO_y + C (char) -> Fe + CO. A gas, such as nitrogen, may be bubbled through the molten pool 114 from bottom nozzles (not shown) for agitation of the lower area of slag layer 116. The reducing process gas comprising CO and evolving from the slag layer 116 is partly combusted with the oxygen supplied. A PCR of about 45% in the reducing process gas upon exiting the converter 106 is advantageous. The reducing process gas is further combusted in the cyclone 102 by the oxygen supplied, as well as for pre-reducing the in-flight melting iron ore to Fe_xO_y. The molten iron ore flowing down the walls may be further reduced to FeO. At the top 110 the exiting flue gases have a PCR of 100% at a temperature of about 1800⁰C. The fully combusted flue gases can, after dedusting, drying and compression, be directly used for CO₂ storage. The hot metal and slag can be tapped using conventional tapping holes 120.

Claims

1. Method of preparing a reducing agent having an elevated temperature for use in an metal making process, comprising a) a pyrolysing step of heating a carbonaceous starting material using a heat source wherein the starting material is pyrolysed to a degree of pyrolysis of at most 80% into a partially charred carbonaceous product having an elevated temperature and producing a pyrolysis off-gas comprising volatile substances from the carbonaceous starting material, b) a combustion step of combusting the pyrolysis off-gas, thereby producing a combusted off-gas, wherein the thermal energy of the combusted off-gas is used as the heat source in step a) by bringing the combusted off-gas into direct contact with the carbonaceous starting material and/or wherein the thermal energy of the combusted off-gas is used as the heat source in step a) by heating the carbonaceous starting material without directly contacting the carbonaceous starting material.

2. Method according to claim 1 , wherein step a) is carried out in a once-through reactor (10), preferably an extruder type reactor, more preferably an extruder type reactor comprising an intermeshing double extrusion screw (14).

3. Method according to one of the preceding claims, wherein step b) is carried out with a preheated oxygen containing gas, preferably having a temperature of between 400 and 700⁰C.

4. Method according to one of the preceding claims, wherein in step a) the combusted off- gas is fed in counter flow to the carbonaceous starting material.

5. Method according to one of the preceding claims, wherein step a) is carried out in such a manner that the resulting pyrolysis off-gas comprises an amount of volatiles that is sufficient for providing the required heat for heating and partially pyrolising the carbonaceous starting material after combustion of the pyrolysis off-gas, while the partially charred carbonaceous product comprises the remaining volatiles.

6. Method according to one of the preceding claims, wherein the carbonaceous starting material comprises coal.

7. Process for producing molten metal by direct reduction of metal ore in a pre-reduction stage followed by a final reduction stage, comprising the steps of (a) in said pre-reduction stage feeding metal ore into a pre-reduction zone and pre- reducing it there by means of a reducing process gas originating from a final reduction zone,

(b) effecting a post-combustion of said reducing process gas in said pre-reduction zone by supplying an oxygen contaning gas thereto so that said metal ore in said pre-reduction zone is at least partly melted,

(c) permitting the pre-reduced and at least partly melted iron ore to pass from said prereduction zone into the final reduction zone situated downstream as seen in the direction of flow of the iron ore in which said final reduction takes place, and (d) effecting said final reduction in said final reduction zone in a slag layer (116) by supplying a reducing agent and an oxygen containing gas to said final reduction zone thereby forming said reducing process gas, and (e) effecting a partial post-combustion of said reducing process gas in said final reduction zone by means of said oxygen containing gas supplied thereto, wherein a reducing agent is fed into the final reduction zone, said reducing agent having been prepared according to the method of one of the preceding claims.

8. Process according to claim 7, wherein the off-gas exiting the pre-reduction zone has a post-combustion ratio defined as CO_n + H_nO

PCR = '2

CO₂ + CO + H₂O + H₂ in which CO₂, CO, H₂O and H₂ are the concentrations in percent by volume of these gases on exiting said pre-reduction zone, which is more than 0.60.

9. Process according to one of the preceding claims 7 or 8, wherein the oxygen containing gas is supplied to the final reduction zone by means of a multiple lance arrangement, arranged in such a way that the hot combusted gases flow towards the central axis of the final reduction zone, so as to direct the hot gasses away from the walls of the final reduction zone.

10. Device for preparing a reducing agent having an elevated temperature for use in an metal making process, such as an iron making process, comprising at least one heating chamber (16) having an inlet (18) for feeding a carbonaceous starting material and an outlet (22) for discharging a partially charred starting material having an elevated temperature and also having an outlet (28) for discharging a pyrolysis off-gas comprising volatile substances originating from the carbonaceous starting material; conveyor means (14) arranged in said heating chamber (16) for conveying the carbonaceous starting material from the inlet (18) to the outlet (22) ; a combustion chamber (32) for combusting said pyrolysis off-gas having an inlet for said pyrolysis off-gas in fluid communication with the outlet (28) for discharging a pyrolysis off-gas into said heating chamber and having an outlet for combusted off- gas, - means (34, 38, 42) for transferring the heat contained in the combusted off-gas to the carbonaceous starting material.

11. Device according to claim 10, wherein said conveyor means comprises a intermeshing double extrusion screw (14).

12. Apparatus (100) for the production of molten iron by direct reduction of iron ore, comprising

(a) at least one device (10) according to claim 10 or 11 ;

(b) a metallurgical vessel (106) for performing a final reduction of the iron ore; (c) supply means (124) for supplying partially charred carbonaceous starting material derived from the device (10), into a slag layer (116) formed, in operation of the apparatus, above a molten bath (114) of iron in the metallurgical vessel (106); (d) supply means (118) for supplying oxygen containing gas to said metallurgical vessel (106), (e) discharge means (120) for discharging molten iron and slag from said metallurgical vessel (106);

(f) a melting cyclone (102) located above and in open connection with said metallurgical vessel (106) so as to form a single reactor therewith, process gas passing in operation from said metallurgical vessel (106) directly into said melting cyclone (102) and at least partially melted pre-reduced iron ore passing from said melting cyclone (102) directly into said metallurgical vessel (106),

(g) supply means (104) for supplying iron ore into said melting cyclone, (h) supply means (122) for supplying oxygen into said melting cyclone

(i) discharge means (110) for discharging process gas in a flow stream from said melting cyclone (102).