EP4731797A1

EP4731797A1 - Plant for the production of briquettes of direct reduced iron and process thereof

Info

Publication number: EP4731797A1
Application number: EP24740047.6A
Authority: EP
Inventors: Andrea Tavano; Luca TOMMASI; Stefano MAGGIOLINO; Jorge Eugenio MARTINEZ MIRAMONTES
Original assignee: Danieli and C Officine Meccaniche SpA; HYL Technologies de SA de CV
Current assignee: Danieli and C Officine Meccaniche SpA; HYL Technologies de SA de CV
Priority date: 2023-06-21
Filing date: 2024-06-20
Publication date: 2026-04-29
Also published as: IT202300012828A1; CN121666457A; WO2024261130A1

Abstract

A plant for the production of briquettes of direct reduced iron (DRI) comprising: - a feeding line of direct reduced iron (DRI); - at least one briquetting machine (4, 4') for compacting the direct reduced iron (DRI) into briquettes, arranged downstream of said feeding line (1); wherein a carbon dosing device (5, 13), upstream of said at least one briquetting machine (4, 4'), is provided to add carbon into the direct reduced iron (DRI), whereby the carbon is compacted together with the direct reduced iron (DRI) in said at least one briquetting machine (4, 4'); wherein at least one heating device is provided, arranged upstream of said at least one briquetting machine (4, 4'), to heat the carbon; and wherein at least one recovery system (19) is provided, arranged upstream of said at least one briquetting machine (4, 4') to recover volatile substances which may be released from the carbon during heating by means of said at least one heating device.

Description

PLANT FOR THE PRODUCTION OF BRIQUETTES OF DIRECT REDUCED IRON AND PROCESS THEREOF * * * * *

Field of the invention

The present invention relates to a plant for the production of briquettes of direct reduced iron (DRI) and the process thereof, said briquettes being adapted to be melted in an electric steelwork furnace.

Background art

The steel sector as a whole is responsible for the emission of about 7% of global carbon dioxide production into the atmosphere. This contribution is due, in particular, to full-cycle steel production, i.e., to the processing of iron ore in blast furnaces to produce pig iron (carbon content greater than 2.06%) and then in converters (BOFs), which use oxygen to oxidize the carbon in excess and take the percentage thereof to the appropriate level (not higher than 2.06%) for steel alloys. With the full cycle, the carbon dioxide production per ton of tapped steel can reach 1800-1900 kg.

To reduce these emissions, the use of electric melting furnaces is becoming more and more established in place of the full cycle; said electric melting furnaces using recycled steel scrap as feedstock and resulting in lower carbon dioxide emissions because the steel base is already prepared and only steel grade melting and adjustment operations are required.

However, competition for supplies of steel scrap for use in electric furnaces is increasing, so other supply sources, possibly also starting from iron ore itself, are being appropriately investigated.

In this regard, direct reduced iron production technology has been developed using an appropriate reactor, which reduces the iron ore to make it suitable for use in a melting furnace.

This technology, named direct reduction, uses natural gas, which is split into its hydrogen component and its carbonaceous component, to appropriately reduce iron oxide according to the following known reactions: Fe2Os + 3H2 -> 2Fe + 3H2O (endothermic) Fe2Os + 3CO -> 2Fe + 3CO2 (exothermic). Hydrogen and carbon monoxide react with oxygen from iron oxide and are transformed into water and carbon dioxide according to the aforesaid reactions. The ore treatment process by means of direct reduction technology produces a direct reduced iron pellet (DRI) suitable for use in the melting process, with a suitable carbon content.

Furthermore, this technology is much less impactful than the full cycle, as DRI production, with melting by means of the electric furnace, emits less than half as much carbon dioxide, amounting to about 600-1000 kg/ton of tapped steel.

However, the use of a make-up gas, which is fed into the reduction circuit, containing a significant amount of carbon (a gaseous hydrocarbon-containing gas, such as natural gas, coke oven gas, Corex Gas, syngas, and so on) has mainly two disadvantages:

- the emission, anyway, of considerable amounts of greenhouse gases (CO2);

- a relatively high content of carbon monoxide (CO) in the reducing gas flow which enters into the reactor, which can determine a relatively high production of particulate matter during the reduction reaction and, because of the temperature increase due to reduction with carbon monoxide, which is exothermic, can increase the risk of generating agglomerates, hindering the movement of the solid mass.

A successive development to further reduce carbon dioxide emissions from steel melting is to use hydrogen instead of natural gas as process gas in a direct reduction. In this case, the steelmaking process by means of direct reduction and melting in an electric furnace produces about 112-220 kg of carbon dioxide per ton of tapped steel.

The chemical reaction which occurs if pure hydrogen is used as the process gas is:

Fe2Os + 3H2 -> 2Fe + 3H2O (endothermic).

Clearly, if the hydrogen share were still partially diluted with hydrocarbons, the reactions would still be the same as above.

Steel is a ferrous alloy composed mainly of iron and carbon, the latter in a percentage not exceeding 2.06%. Disadvantageously, by eliminating or reducing the amount of carbon in favor of a process gas comprising mostly hydrogen, the DRI resulting from the reduction of iron ore would lack the required percentage of carbon, which must thus be supplemented in the melting furnace.

The problem with this integration lies in the inefficiency of carbon addition in the melting process; indeed, the carbon is insufflated into the bath by means of special lances, and, to reach the bath properly, it must cross the slag layer and resist the suction of the flue gas system which draws in process flue gas during melting. Statistically, about 25-30% of the injected carbon does not enter the bath and is trapped in the slag or carried away along with the flue gas. Furthermore, there is no assurance that the carbon reaching the bath will mix evenly in the bath.

Therefore, the need is felt to make an innovative plant and process thereof to produce a material suitable for melting in an electric furnace for steel production, overcoming the aforesaid drawbacks.

Summary of the invention

It is an object of the present invention to make a plant for the production of briquettes of direct reduced iron (DRI) which makes it possible to prevent any volatile carbon matter, which is potentially combustible and explosive, from making the hot agglomeration process of direct reduced iron (DRI) and carbon dangerous, and to prevent the cracking of the briquette and a decrease in its density with the risk of crumbling of the briquette itself.

It is another object of the present invention to make a plant for the production of briquettes of direct reduced iron (DRI) which makes it possible to obtain hot briquettes already having the necessary and sufficient composition features, in terms of carbon, to become steel after melting in an electric furnace.

It is a further purpose of the present invention to make a related process for the production of briquettes of direct reduced iron (DRI) which produces the aforesaid briquettes without the need to inject large amounts of natural gas upstream into the direct reduction process and without the need to subsequently insufflate carbon into the melting bath inside the electric furnace to ensure steel production. The present invention achieves these and other purposes, which will be apparent in light of the present description, by means of a plant for the production of briquettes of direct reduced iron (DRI) which comprises

- a feeding line for feeding direct reduced iron (DRI);

- at least one briquetting machine to compact the direct reduced iron (DRI) into briquettes, arranged downstream of said feeding line; wherein a carbon dosing device, arranged upstream of said at least one briquetting machine, is provided to add carbon into the direct reduced iron (DRI), whereby the carbon is compacted together with the direct reduced iron (DRI) in said at least one briquetting machine; wherein at least one heating device is provided, arranged upstream of said at least one briquetting machine, to heat the carbon; and wherein at least one recovery system is provided, arranged upstream of said at least one briquetting machine, to recover the volatile substances which can be released from the carbon during heating thereof by means of said at least one heating device.

According to a further aspect of the invention, a process for the production of briquettes of direct reduced iron is provided, which can be carried out by means of the aforesaid plant, comprising the following steps: a) feeding direct reduced iron (DRI) by means of a feeding line to at least one briquetting machine; b) compacting the direct reduced iron (DRI) into briquettes by means of said at least one briquetting machine; wherein an addition of carbon into the direct reduced iron (DRI), by means of the carbon dosing device, is provided between step a) and step b) whereby said carbon is compacted into briquettes together with the direct reduced iron (DRI) in said at least one briquetting machine; wherein carbon heating is provided upstream of said at least one briquetting machine, by means of the at least one heating device; and wherein a recovery of the volatile substances which can be released from the carbon during said heating is provided, by means of the at least one recovery system, before the carbon reaches said at least one briquetting machine. Advantageously, the solution of the invention allows obtaining a material suitable to be melted in an electric steelwork furnace, said material also deriving from a production with low emissions of carbon dioxide into the atmosphere, and said material being appropriately treated and prepared before being loaded into the melting furnace to have the characteristics suitable to be melted for steel production, eliminating the need to insufflate carbon into the melting bath and related problems.

In particular, the solution of the invention allows obtaining briquettes containing a sufficient amount of carbon to impart the carbon percentage corresponding to the desired steel grade, and possibly an additional amount which makes it possible to aid melting and slag creation.

The production process provides the agglomeration of DRI pellet, preferably hot, into briquettes by means of presses commonly applied in this type of industry.

A particularity of the process according to the invention is that an amount of carbon is added to the DRI pellet and appropriately pressed together with said pellet to form the briquette.

Briquetting is an operation performed hot, so that the temperature of the DRI itself, possibly directly exiting a direct reduction reactor, is used to deform it, defining the shape of the briquettes and giving a minimum density of 5 kg/dm³ to the agglomerate.

However, when carbon is heated to at least 900°C, preferably in a range of 940- 960°C, for example to about 950°C, in the absence of air, volatile components of carbon can be released along with residual moisture, producing a mixture of CO and short- and long-chain polycyclic aromatic aliphatic hydrocarbons. These volatile components, which are potentially combustible and explosive, would make the hot agglomeration process between DRI and carbon dangerous, and also, through their formation, there could be cracking of the forming briquette and a decrease in density with the risk of crumbling of the briquette itself. Advantageously, the solution of the invention avoids these drawbacks.

A possible variant of the invention provides that the carbon added to the direct reduced iron for briquette formation is contained inside the briquettes and not on the surface. This variant allows to avoid that, later on in the melting furnace, the carbon added to the direct reduced iron may react too soon due to the temperature of the melting furnace environment and the slag, not entering the metal bath properly and, therefore, impairing the delivery of carbon to the metal bath itself.

Further features and advantages of the invention will be more apparent in light of the detailed description of the preferred, but not exclusive embodiments.

The dependent claims describe particular embodiments of the invention.

Brief description of the drawings

The description of the invention refers to the accompanying drawings, which show non-limiting examples, in which:

Figure 1 is a diagram of a first embodiment of a plant according to the invention;

Figure 2 is a diagram of a second embodiment of a plant according to the invention;

Figure 3 is a diagram of a third embodiment of a plant according to the invention;

Figure 4 shows a diagram of a fourth embodiment of a plant according of the invention;

Figure 5 shows a diagram of a fifth embodiment of a plant according to the invention.

Description of illustrative embodiments of the invention

Some examples of a plant for the production of briquettes of direct reduced iron, which is the object of the present invention, are illustrated by referring to Figures 1-5.

In all embodiments of the invention, the plant for the production of briquettes of direct reduced iron (DRI) comprises:

- a feeding line of direct reduced iron (DRI);

- at least a briquetting machine 4, 4’ to compact the direct reduced iron (DRI) into briquettes, arranged downstream of the feeding line;

- a carbon dosing device 5, 13, arranged upstream of the at least one briquetting machine 4, 4’, to add carbon into the direct reduced iron (DRI), whereby the carbon is compacted together with the direct reduced iron (DRI) in said at least one briquetting machine 4, 4’; - at least one heating device, arranged upstream of said at least one briquetting machine 4, 4’, to heat the carbon;

- at least one recovery system 19, arranged upstream of said at least one briquetting machine 4, 4’ to recover volatile substances which may be released from the carbon during the heating by means of said at least one heating device.

In all embodiments of the invention, the recovery system 19 can comprise, for example, at least one duct 25 for extracting the volatile substances from the environment in which the carbon is heated and conveying them to a recovery chamber 26, to which the duct 25 is connected.

In a first variant of the plant of the invention, the direct reduced iron (DRI) feeding line comprises:

- a direct reduction reactor 1 for reducing iron oxides loaded from the top of said reactor and producing hot direct reduced iron (HDRI);

- at least one inlet duct 2 of a process gas containing gaseous hydrogen, preferably with a gaseous hydrogen content of at least 30% by volume, for introducing the process gas into a reduction area 3 of the direct reduction reactor 1.

Generally, the systems for the production of direct reduced iron (DRI) ore comprise the direct reduction reactor 1 , into which iron oxide, in the form of pellets and/or lumps, is loaded, and the process gas inlet duct 2, which belongs to a line for treating and supplying reducing gas, comprising hydrogen and carbon monoxide and adapted to reduce said iron oxide in the reactor.

The reducing gas is injected into reduction area 3 of the reactor at a high temperature. The iron oxide material is supplied from the top into the reduction area 3 of the reactor 1 , and reacts with the hot reducing gas, made to go up in counter-flow through the iron oxide, and is finally unloaded as hot DRI. Optionally, the iron oxide material has a grain size of about 2.5-19 mm; preferably about 5-15 mm.

The reactor 1 can be of the static-bed type, or of the moving-bed type, or of the fluidized-bed type, or of the rotary or kiln type. In a moving-bed reactor, the process gas is typically introduced into the central part of the reactor, made to rise in counter-flow through the iron oxide, and then extracted, reprocessed, and recycled in a reduction circuit. The flue gas which exits the reactor is dedusted, deprived of reaction products (H2O and CO2), and compressed; it is then mixed with a make-up gas. The flow of gas, defined by the mixture of the new make-up gas and the recycled flue gas after appropriate treatment, is sent to a heating unit, which takes it to the temperature required by the reduction process, normally higher than 850 °C.

The heated flow of gas, into which oxygen can be injected to increase the temperature thereof even further, is sent to the reactor, into which the iron oxides to be reduced are introduced from the top and flow downward there-through, while the DRI (reduction product) is extracted at the opposite end of said reactor.

In this description, the term "process gas" indicates commercially pure gaseous hydrogen or a gas mixture obtained by mixing a make-up gas containing gaseous hydrogen, and possibly a make-up gas containing gaseous hydrocarbons, with the flue gas or exhaust gas of the reactor treated in a recovery and treatment line.

In a second variant of the plant of the invention, the direct reduced iron (DRI) feeding line is a feeding line of cold direct reduced iron (CDRI), coming from a storage system. In this case, any heating device is provided to heat the direct reduced iron upstream of the briquetting machine.

The at least one briquetting machine 4, 4’ comprises, for example, one or more presses for agglomerating pellets of direct reduced iron (DRI) into briquettes, e.g., in the form of one or more pairs of counter-rotating drums 20, 20’ (Figures 4 and 5) provided with mutually mirrored or specular perimetral concavities 21 , 2T and adapted to form, during rotation thereof, a respective briquette for each pair of mutually facing perimetral concavities.

The briquettes are then fed into an electric steelwork furnace.

In some embodiments (Figures 1 and 2), the plant of the invention is provided with a carbon dosing device 5, arranged between the direct reduction reactor 1 and the at least one briquetting machine 4, to add a predetermined amount of carbon into the direct reduced iron, whereby the carbon is compacted together with the direct reduced iron in said briquetting machine 4.

In a variant of the invention, the carbon dosing device 5 is a worm screw dosing device which allows precise dosing of carbon. Other possible examples of dosing devices comprise:

- a loading system, which adds carbon by advancing said carbon by means of a vibrating table inside a tunnel; or

- a rotary valve; or

- an auger.

The movement of the worm screw, or of the vibrating table or of the rotary valve, is appropriately controlled to adjust the addition of carbon into the direct reduced iron.

Preferably, as shown for example in Figure 1 , a carbon tank 6, arranged upstream of dosing device 5, is provided to feed said dosing device 5.

The following can be further provided, as shown in the example in Figure 2,

- a binding additive tank 7, arranged upstream of the dosing device 5, and

- a mixing device 8, arranged downstream of the carbon tank 6 and the binding additive tank 7 and upstream of the dosing device 5, to produce a mixture of predetermined amounts of carbon and binding additive and feed the dosing device 5 with said mixture.

By way of example, the binding additive can be of the inorganic type, e.g., cement or bentonites or sodium silicates, or of the organic type, e.g., starch, or consisting of a mixture thereof. Binding additives are useful to impart mechanical properties and surface hardness to briquettes, which bring benefits, for example, in subsequent transport steps.

Advantageously, the carbon heating device is arranged upstream of the at least one briquetting machine 4.

In a first preferred variant of the plant of the invention, diagrammatically shown in Figure 3, the heating device comprises a flue gas recovery duct 10, which recovers at least partially the flue gas or exhaust gas exiting the direct reduction reactor 1 , and a heat exchanger 9 to heat the carbon by means of said flue gas. In this variant, the recovery system 19 cooperates with said heat exchanger 9.

As an example, the flue gas exiting the direct reduction reactor 1 can at least partially be sent directly inside the worm screw dosing device, or inside the tunnel of the vibrating table dosing device, to heat, by advancing in counter-flow, the carbon which is conveyed towards the addition zone for the addition into the direct reduced iron. In this variant, the recovery system 19 cooperates directly with the worm screw dosing device 5 or with the tunnel of the vibrating table dosing device. In a second preferred variant of the plant of the invention, shown in Figure 1 , the heating device comprises heating elements 11 arranged on the carbon tank 6 and/or on the carbon dosing device 5. In this variant, the recovery system 19 cooperates with the carbon tank 6 and/or with the carbon dosing device 5.

In a third preferred variant of the plant of the invention, shown in Figure 2, the heating device comprises heating elements 11 arranged on the mixing device 8 and/or on the carbon tank 6 and/or on the carbon dosing device 5. In this variant, the recovery system 19 cooperates with the mixing device 8 and/or the carbon tank 6 and/or the carbon dosing device 5.

For example, the heating elements 11 can be in the form of tubular resistors, possibly coiled around the device or tank to be heated, or film resistors applied to the outer surface of said device or tank.

In a further variant of the plant of the invention, the carbon heating device comprises a sealed heating chamber provided with at least one dosing element, defining the carbon dosing device, to feed the briquetting machine 4. This dosing element can preferably be a rotary valve. In this further variant, the recovery system 19 cooperates with said sealed heating chamber.

In all variants, the carbon, even during its heating, can be inerted with inert gases, e.g., nitrogen.

In other preferred embodiments of the plant of the invention, shown in Figures 4 and 5, the at least one briquetting machine 4, 4’ comprises:

- a first briquetting machine 4 adapted to produce first briquettes 23 comprising carbon and direct reduced iron (DRI);

- and a second briquetting machine 4’, preferably having larger dimensions than the first briquetting machine 4, arranged below said first briquetting machine 4 and adapted to produce second briquettes 24 of direct reduced iron (DRI) which include a respective first briquette 23 therein.

Both the first briquetting machine 4 and the second briquetting machine 4’ comprise a respective pair of counter-rotating drums 20, 20’. In each pair of counter-rotating drums, said counter-rotating drums 20, 20’ are provided with respective perimetral concavities 21 , 21 ’ mutually specular relative to a vertical plane, and are adapted to form, during rotation thereof, a respective briquette for each pair of mutually facing perimetral concavities. In particular, when two perimetral concavities are mutually facing, they are pressed against each other to compress the material by deforming the latter and defining the briquette. Only one set of perimetral concavities per drum is visible in Figures 4 and 5. However, multiple sets of perimetral concavities, or rather circumferential concavities, can be provided along the longitudinal extension of the drum to increase the productivity of the briquetting machine.

Advantageously, synchronization means 22 are provided to synchronize the first briquetting machine 4 and the second briquetting machine 4’ so that a first briquette 23 formed by a pair of perimetral concavities 21 of the first briquetting machine 4 forms the core of a second briquette 24 formed by a pair of perimetral concavities 2T of the second briquetting machine 4’.

In the embodiment of Figure 4, both the first briquetting machine 4 and the second briquetting machine 4’ are arranged symmetrically relative to a common vertical plane, and the synchronization means 22 are configured to synchronize the first briquetting machine 4 and the second briquetting machine 4’ so that the first briquette 23 falls between two perimetral concavities 21 ’ of the counter-rotating drums 20’ of the second briquetting machine 4’, previously filled with direct reduced iron (DRI), before said two perimetral concavities 21 ’ are fully facing each other.

Instead, in the embodiment of Figure 5, the first briquetting machine 4 is arranged above a first drum of the counter-rotating drum pair 20’ of the second briquetting machine 4’, and the synchronization means 22 are configured to synchronize the first briquetting machine 4 and the second briquetting machine 4’ so that the first briquette 23 falls into a perimetral concavity 21 ’ of said first drum, previously filled with direct reduced iron (DRI), before said perimetral concavity completely faces a respective perimetral concavity 21 ’, previously filled with direct reduced iron (DRI), of a second drum of said pair of counter-rotating drums 20’. In both embodiments in Figures 4 and 5, the carbon heating device comprises a first sealed heating chamber 12 provided with at least one respective dosing element 13, defining the carbon dosing device, for feeding the first briquetting machine 4. In this case, the recovery system 19 cooperates with said sealed heating chamber 12.

In the embodiment of Figure 4, the feeding line of direct reduced iron (DRI) comprises a second sealed heating chamber 14 provided with at least one respective dosing element 15 for dosing a first predetermined amount of direct reduced iron (DRI) for the first briquetting machine 4.

Preferably, mixing means 18 arranged upstream of said first briquetting machine 4 are provided for mixing a predetermined amount of carbon, fed by means of the dosing element 13, with said first predetermined amount of direct reduced iron (DRI) fed by means of the dosing element 15.

Additional dosing elements (not shown) can be provided at the inlet of the first sealed heating chamber 12 and the second sealed heating chamber 14, respectively.

Instead, in the embodiment in Figure 5, the direct reduced iron (DRI) feeding line is adapted to feed direct reduced iron (DRI) into the same sealed heating chamber 12 for heating the carbon. In this case, a carbon dosing element 13 is provided at the inlet of sealed chamber 12, and a further dosing element 13’ is provided at the outlet of said sealed chamber 12 to dose carbon and direct reduced iron to be fed to the first briquetting machine 4. Preferably, in this case, mixing means 18, arranged within said first sealed heating chamber 12, are provided for mixing carbon with direct reduced iron (DRI).

In both embodiments of Figures 4 and 5, the feeding line of direct reduced iron (DRI) comprises at least one further sealed heating chamber 16, e.g., two sealed heating chambers 16, provided with at least one respective dosing element 17 to dose a second predetermined amount of direct reduced iron (DRI) for the second briquetting machine 4’, in particular to dose the amount of direct reduced iron to be poured into the respective perimetral concavities 21 ’ of the drums 20’.

The mixing means 18 can comprises, for example, augers, paddles or other suitable means, preferably motorized. Preferably, both the first briquetting machine 4 and the second briquetting machine 4’ are arranged within an inert environment maintained by gas injections, such as nitrogen and/or argon.

The internal environment of the sealed heating chambers 12, 14, 16 is also preferably an inert environment, maintained by gas injections, such as nitrogen and/or argon.

The dosing elements 13, 13’, 15, 17 can consist of either a rotary valve or an auger or worm screw device.

The use of rotary valves, also known as rotocells or star valves, can be particularly advantageous. These rotary valves provide a rotating star-shaped body inside a casing, such as a cast iron casing made by casting, and are actuated by a gearmotor unit which can be controlled by means of an inverter. By virtue of the inverter, that is an electronic apparatus capable of varying the voltage and frequency of the output alternating current relative to the input alternating current, it is possible to change the rotation speed of the valve as desired. In this manner, the amount of material which is fed downstream can be precisely controlled.

Also in the embodiments of Figures 4 and 5, preferably, the carbon tank 6 and possibly also the binding additive tank 7 and the mixing device 8 are provided, arranged upstream of the sealed heating chamber 12.

A process for the production of briquettes of direct reduced iron (DRI) by means of a plant according to the present invention is described below.

In all its embodiments, the process of the invention comprises the following steps: a) feeding direct reduced iron (DRI) by means of the feeding line to at least one briquetting machine 4, 4’; b) compacting the hot direct reduced iron into briquettes by means of the at least one briquetting machine 4, 4’; wherein the addition of carbon into the hot direct reduced iron, by means of the carbon dosing device 5, 13, is provided between step a) and step b) whereby the carbon is compacted into briquettes together with the direct reduced iron in said at least one briquetting machine 4, 4’; wherein a carbon heating is provided, by means of the at least one heating device, upstream of said at least one briquetting machine 4, 4’ to facilitate the briquette formation operations; and wherein a recovery of the volatile substances which may be released from the carbon during said heating is provided, by means of the at least one recovery system 19, before the carbon reaches said at least one briquetting machine 4, 4’.

These volatile substances are extracted by means of at least one duct 25 from the environment in which the carbon is heated and conveyed to a recovery chamber 26 to which the duct 25 is connected.

Downstream of said recovery chamber 26, said volatile substances can be, for example, sent:

- to a condensation chamber, in which the volatile CO component, that can be used as a combustible gas, and a bituminous mass, that can also be used as a fuel, are separated by means of injections of water and/or steam;

- to the sealed heating chamber(s) or any tank or device in which the heating of carbon and/or DRI takes place to contribute to the heating itself, by conduction with the walls, which in turn heat the material contained in said chamber or in the internal volume of the tank or device;

- to other utilities which require heat, such as the process gas heater which heats the process gas in the direct reduction reactor feeding line.

Preferably, the carbon to be added is heated in an inert atmosphere by means of the at least one heating device to a temperature of at least 900°C, preferably in a range of 940-960°C; while the direct reduced iron (DRI) is fed to the at least one briquetting machine 4, 4’ at a temperature of at least 650°C, preferably in a range of 660-700°C.

It is advisable that the heating of carbon takes place not only in an inert atmosphere but also under controlled pressure, such as under slight vacuum for the suction of any volatile substances.

In a variant of the process, the hot direct reduced iron at a temperature of at least 650°C comes directly from a direct reduction reactor 1 , in turn fed from above with iron oxides and fed at a reduction area 3 with a process gas, comprising a gaseous hydrogen content equal to at least 30%, preferably from 60 to 100%, by volume.

The direct reduction reactor 1 is either prevalently or totally fed with hydrogen as process gas so that the reduction operation of the iron oxide of the loaded material is not excessively relevant in terms of carbon dioxide production.

The expression “prevalently fed with hydrogen” indicates the supply of a process gas consisting of at least 30% hydrogen by volume, preferably at least 60% hydrogen by volume. However, in a preferred embodiment, the process gas flow fed to the reactor is 100% gaseous hydrogen, whereby direct emissions of carbon dioxide from the reduction process are canceled.

These percentages refer to the energy introduced into the direct reduction plant, compared to alternative sources; therefore, they must not be understood as representing the volume of introduced gas.

In the case of a process gas containing gaseous hydrogen with a content of gaseous hydrogen equal to at least 30% by volume, the rest of the composition can comprise carbon monoxide, water, carbon dioxide, methane, and nitrogen.

The gas containing gaseous hydrogen can come from any external source which uses, e.g., partial combustion or reforming of natural gas, electrolysis, or any other process capable of generating such a gas.

In an alternative variant of the process, cold direct reduced iron comes from a storage system and is heated to a temperature of at least 650°C before being fed to at least one briquetting machine 4, 4’.

Preferably, the amount of carbon to be added is comprised in the range of 0.1 % to 5.0% of the mass of direct reduced iron to be compacted.

Preferably, the predetermined amount of carbon to be added is suitable to obtain briquettes having a carbon percentage higher than at least 1 % of the percentage required for the production of a predetermined steel grade in a melting furnace. The percentage of carbon which is required to be imparted to the briquettes will vary as a function of the percentage of hydrogen in the process gas.

In particular, obtaining briquettes with a carbon percentage greater than 2-5% of the percentage needed to produce the predetermined steel grade can be useful for forming slag in the electric furnace and compensating for any excesses in oxygen adduction in the decarburization stages of the bath, or for supplying additional carbon to the scrap recycling processes.

Optionally, the carbon can be either powder, preferably with a size smaller than 2 mm³, or granular, preferably with a size larger than 0.5 cm³.

In a first preferred variant, the carbon is heated using heat from flue gas or exhaust gas exiting the direct reduction reactor 1 by means of the flue gas recovery duct 10 which crosses the heat exchanger 9, which in turn is passed through by the carbon (Figure 3).

In particular, the heat exchanger can consist of the dosing device 5 itself, in which the flue gas exiting the direct reduction reactor 1 is at least partially conveyed to heat, advancing in counter-flow, the carbon which is transported to the addition zone for the addition into the direct reduced iron.

In this case, the recovery of any volatile substances of the carbon occurs by means of the recovery system 19 cooperating with said heat exchanger.

In a second preferred variant, the carbon is heated using heating elements 11 arranged on the carbon dosing device 5 and/or on the carbon tank 6 arranged upstream of the dosing device 5 (Figure 1 ). In this case, the recovery of any volatile substances of the carbon occurs by means of the recovery system 19 cooperating with the carbon dosing device 5 and/or the carbon tank 6.

In a third preferred variant, the carbon is heated using heating elements 11 arranged on the carbon dosing device 5 and/or on the carbon tank 6 and/or on the mixing device 8 (Figure 2). In this case, the process comprises the production of a mixture of predetermined amounts of carbon and binding additive, supplied from the respective tank 7, by means of the aforementioned mixing device 8, and the feeding of the dosing device 5 with said mixture. In this case, the recovery of any volatile substances of the carbon occurs by means of the recovery system 19 cooperating with the carbon dosing device 5 and/or the carbon tank 6 and/or the mixing device 8.

In a fourth preferred variant, the carbon heating is performed in a sealed heating chamber 12 (Figures 4 and 5) provided with at least one respective dosing element 13, defining the carbon dosing device. In this case, the recovery of any volatile substances from the carbon occurs by means of the recovery system 19 cooperating with said sealed heating chamber 12.

However, the heating of the carbon upstream of the at least one briquetting machine 4, 4’ can be made by any known system, such as burners or use of steam.

In all variants, the volatile substances which could be released from the carbon during its heating are recovered by means of the at least one recovery system 19, which cooperates with the environment in which the carbon is heated, before the carbon reaches the briquetting machine 4, 4’.

Preferably, step b) of briquette production comprises, preferably in an inert environment, the production of first briquettes 23, comprising carbon and direct reduced iron (DRI), by means of a first briquetting machine 4, and then the production of second briquettes 24 of direct reduced iron (DRI) which include therein a respective first briquette 23, by means of a second briquetting machine 4’. Advantageously, in this first process variant, there is provided a synchronization of the first briquetting machine 4 and the second briquetting machine 4’ so that a first briquette 23, formed by a pair of perimetral concavities 21 of the two counterrotating drums 20 of the first briquetting machine 4, forms the core of a second briquette 24 formed by a pair of perimetral concavities 21 ’ of the two counterrotating drums 20’ of the second briquetting machine 4’.

With reference to the embodiment in Figure 4, the synchronization of the first briquetting machine 4 and the second briquetting machine 4’ is such that a first briquette 23 falls between two perimetral concavities 21 ’ of the counter-rotating drums 20’ of the second briquetting machine 4’, previously filled with direct reduced iron (DRI), before said two perimetral concavities 21 ’ are completely facing each other. Preferably, the direct reduced iron, optionally ground, is fed to a second sealed heating chamber 14, separate from the first sealed heating chamber 12 and provided with at least one respective dosing element 15 which doses a first predetermined amount of direct reduced iron (DRI) for the first briquetting machine 4. In this case, preferably there is provided a mixing, by means of the mixing means 18, of a predetermined amount of carbon, fed by means of the dosing element 13, with the first predetermined amount of direct reduced iron (DRI) fed by means of the dosing element 15.

Instead, with reference to the embodiment in Figure 5, the synchronization of the first briquetting machine 4 and the second briquetting machine 4’ is such that the first briquette 23 falls into a perimetral concavity 21 ’, previously filled with direct reduced iron (DRI), of a first drum 20’ of the second briquetting machine 4’, before said perimetral concavity completely faces a respective perimetral concavity 2T, previously filled with direct reduced iron (DRI), of a second drum of said pair of counter-rotating drums 20’. Preferably, in this variant, the direct reduced iron (DRI), optionally ground, is fed into the same sealed heating chamber 12 as the carbon. The dosing element 13 (Figure 5) doses the amount of carbon entering the sealed chamber 12, while the further dosing element 13’ doses carbon and direct reduced iron to be fed to the first briquetting machine 4. Preferably, a mixing of carbon and direct reduced iron is provided by means of the mixing means 18 inside the sealed heating chamber 12.

In a preferred variant, the carbon is inserted into the sealed heating chamber 12, e.g., by means of at least one rotary valve 13, or volumetric rotary valve, adapted to transfer a predefined volume of solid carbon from the external environment, preferably at room temperature, to that of the heating chamber, which is at a higher temperature, e.g., about 900°C.

The carbon can be evacuated from the sealed heating chamber 12 by means of a further rotary valve 13’ to preserve temperature and pressure inside the chamber, for later sending the heated carbon to the briquetting machines.

With reference to both embodiments in Figures 4 and 5, a further amount of direct reduced iron (DRI), optionally ground, is fed into a further sealed heating chamber 16, e.g., two sealed heating chambers 16, provided with at least one respective dosing element 17. The dosing elements 17 dose a second predetermined amount of direct reduced iron (DRI) for the second briquetting machine 4’, in particular they dose the amount of direct reduced iron to be poured into the respective perimetral concavities 2T of the drums 20’. In all embodiments of the process of the invention, the briquetting preferably takes place in an inert environment, which is kept inert by means of injections of gases such as nitrogen and/or argon.

Preferably, the agglomerate of carbon and direct reduced iron can have a concentration by weight of 15% carbon, which is then diluted between 1 and 4% in the final briquette.

The internal environment of heating chambers 12, 14, 16, or any tank or device in which heating of carbon and/or direct reduced iron takes place, is also preferably an inert environment, maintained by means of injections of gases, such as nitrogen and/or argon.

Claims

1 . A plant for the production of briquettes of direct reduced iron (DRI) comprising:

- a feeding line of direct reduced iron (DRI);

- at least one briquetting machine (4, 4’) for compacting the direct reduced iron (DRI) into briquettes, arranged downstream of said feeding line (1); wherein a carbon dosing device (5, 13), upstream of said at least one briquetting machine (4, 4’), is provided to add carbon into the direct reduced iron (DRI), whereby the carbon is compacted together with the direct reduced iron (DRI) in said at least one briquetting machine (4, 4’); wherein at least one heating device is provided, arranged upstream of said at least one briquetting machine (4, 4’), to heat the carbon; and wherein at least one recovery system (19) is provided, arranged upstream of said at least one briquetting machine (4, 4’) to recover volatile substances which may be released from the carbon during heating by means of said at least one heating device.

2. A plant according to claim 1 , wherein said at least one briquetting machine (4, 4’) comprises:

- a first briquetting machine (4) adapted to produce first briquettes (23) comprising carbon and direct reduced iron (DRI);

- and a second briquetting machine (4’), arranged below said first briquetting machine (4) and adapted to produce second briquettes (24) of direct reduced iron (DRI) which include a respective first briquette therein.

3. A plant according to claim 2, wherein both the first briquetting machine (4) and the second briquetting machine (4’) comprise a pair of counter-rotating drums (20, 20’) provided with perimetral concavities (21 , 21 ’), that are mutually mirrored, and adapted to form, while rotating, a respective briquette for each pair of mutually facing perimetral concavities; and wherein synchronization means (22) are provided to synchronize the first briquetting machine (4) and the second briquetting machine (4’) so that a first briquette (23) formed by a pair of perimetral concavities (21) of said first briquetting machine (4) forms a core of a second briquette (24) formed by a pair of perimetral concavities (21’) of the second briquetting machine (4’).

4. A plant according to claim 3, wherein both the first briquetting machine (4) and the second briquetting machine (4’) are arranged symmetrically relative to a common vertical plane; and wherein said synchronization means (22) are configured to synchronize the first briquetting machine (4) and the second briquetting machine (4’) so that the first briquette (23) falls between two perimetral concavities (21’) of the counter-rotating drums (20’) of the second briquetting machine (4’), previously filled with direct reduced iron (DRI), before said two perimetral concavities (21’) are fully facing each other; or wherein the first briquetting machine (4) is arranged above a first drum of the pair of counter-rotating drums (20’) of the second briquetting machine (4’); and wherein said synchronization means (22) are configured to synchronize the first briquetting machine (4) and the second briquetting machine (4’) so that the first briquette (23) falls into a perimetral concavity (21 ’) of said first drum, previously filled with direct reduced iron (DRI), before said perimetral concavity (21’) completely faces a respective perimetral concavity (21 ’), previously filled with direct reduced iron (DRI), of a second drum of said pair of counter-rotating drums (20’).

5. A plant according to any one of the claims from 2 to 4, wherein the heating device comprises a first sealed heating chamber (12) provided with at least one respective dosing element (13), defining the carbon dosing device, for feeding the first briquetting machine (4).

6. A plant according to claim 5, wherein said feeding line of direct reduced iron (DRI) comprises a second sealed heating chamber (14) provided with at least one respective dosing element (15) for dosing a first predetermined amount of direct reduced iron (DRI) for the first briquetting machine (4); preferably wherein mixing means (18), arranged upstream of said first briquetting machine (4), are provided for mixing a predetermined amount of carbon with said first predetermined amount of direct reduced iron (DRI); or wherein said feeding line of direct reduced iron (DRI) is adapted to feed direct reduced iron (DRI) into said first sealed heating chamber (12); preferably wherein mixing means (18), arranged within said first sealed heating chamber (12), are provided for mixing carbon with direct reduced iron (DRI).

7. A plant according to claim 6, wherein said feeding line of direct reduced iron (DRI) comprises at least one further sealed heating chamber (16) provided with at least one respective dosing element (17) for dosing a second predetermined amount of direct reduced iron (DRI) for the second briquetting machine (4’).

8. A plant according to claim 5 or 6 or 7, wherein said at least one respective dosing element (13, 15, 17) is at least one rotary valve or auger or worm screw device.

9. A plant according to any one of the claims from 1 or 4, wherein a carbon tank (6), arranged upstream of the dosing device (5), is provided to feed said dosing device (5); preferably wherein said heating device comprises heating elements (11 ) arranged on the carbon tank (6) and/or the carbon dosing device (5), and wherein said recovery system (19) cooperates with said carbon tank (6) and/or said carbon dosing device (5).

10. A plant according to claim 9, wherein the following are further provided

- a binding additive tank (7), arranged upstream of the dosing device (5), and

- a mixing device (8), arranged downstream of the carbon tank (6) and binding additive tank (7) and upstream of the dosing device (5), to produce a mixture of predetermined amounts of carbon and binding additive and feed said mixture to the dosing device (5); preferably wherein said heating device comprises heating elements (11) arranged on the mixing device (8) and/or carbon tank (6) and/or carbon dosing device (5), and wherein said recovery system (19) cooperates with said mixing device (8) and/or said carbon tank (6) and/or said carbon dosing device (5).

11 . A plant according to any one of the preceding claims, wherein said feeding line of direct reduced iron (DRI) comprises

- a direct reduction reactor (1) for reducing iron oxides loaded from the top of said reactor and produce hot direct reduced iron (HDRI);

- and at least one process gas inlet duct (2) to introduce process gas, containing gaseous hydrogen, preferably with a gaseous hydrogen content of at least 30% by volume, into a reduction area (3) of the direct reduction reactor (1 ); preferably wherein said heating device comprises a recovery duct (10) of flue gas exiting said direct reduction reactor (1 ) and a heat exchanger (9) for heating the carbon by means of said flue gas; and wherein said recovery system (19) cooperates with said heat exchanger (9).

12. A process for the production of briquettes of direct reduced iron (DRI), by means of a plant according to any one of the preceding claims, comprising the following steps: a) feeding direct reduced iron (DRI) by means of a feeding line towards the at least one briquetting machine (4, 4’); b) compacting the direct reduced iron (DRI) into briquettes by means of said at least one briquetting machine (4, 4); wherein an addition of carbon into the direct reduced iron (DRI), by means of the carbon dosing device (5, 13), is provided between step a) and step b), whereby said carbon is compacted into briquettes together with the direct reduced iron (DRI) in said at least one briquetting machine (4, 4’); wherein a heating of the carbon is provided upstream of said at least one briquetting machine (4, 4’), by means of the at least one heating device; and wherein a recovery of the volatile substances which may be released from the carbon during said heating is provided, by means of the at least one recovery system (19), before the carbon reaches said at least one briquetting machine (4, 4’).

13. A process according to claim 12, wherein the carbon is heated in an inert atmosphere by means of the at least one heating device to a temperature of at least 900°C, preferably in a range of 940-960°C; and wherein the direct reduced iron (DRI) is fed to the at least one briquetting machine (4, 4’) at a temperature of at least 650°C, preferably in a range of 660-700°C; preferably wherein the direct reduced iron (DRI) at a temperature of at least 650°C comes from a direct reduction reactor (1 ), fed from the top with iron oxides, and fed at a reduction area (3) with a process gas, comprising a gaseous hydrogen content equal to at least 30%, preferably from 60 to 100%, by volume; or wherein cold direct reduced iron (DRI) comes from a storage system and is heated to a temperature of at least 650°C before being fed to the at least one briquetting machine (4, 4’).

14. A process according to claim 12 or 13, wherein step b) comprises, preferably in an inert environment, the production of first briquettes (23), comprising carbon and direct reduced iron (DRI), by means of a first briquetting machine (4), and subsequently the production of second briquettes (24) of direct reduced iron (DRI) which include therein a respective first briquette (23), by means of a second briquetting machine (4’).