Iron fuel combustion arrangement

Abstract

An iron fuel combustion arrangement, comprising: - a combustion unit arranged for combusting iron fuel thereby generating an iron oxide containing medium; - a separation unit having a height direction and arranged downstream of said combustion unit, said separation unit comprising a separation chamber arranged for separating said iron oxide containing medium into iron oxide particles and a gas stream, wherein said separation chamber has a separation chamber cross-sectional area at a top side of said separation chamber; wherein said separation unit comprises: - an inlet, positioned at said top side of said separation chamber and having an inlet cross-sectional area having an inlet cross-sectional width, said inlet is arranged for introducing said iron oxide containing medium in said separation unit in a downward direction; - a particle outlet, positioned at a bottom side of said separation chamber and having a particle outlet cross-sectional area having a particle outlet cross-sectional width, said particle outlet is arranged for discharging said iron oxide particles from said separation unit; - a gas outlet, positioned at said top side of said separation chamber or at a sidewards side of said separation chamber and having a gas outlet cross-sectional area, said gas outlet is arranged for discharging said gas stream from said separation unit, wherein said gas outlet is oriented in an upward direction away from said particle outlet at an inclination angle up to 50 degrees relative to said height direction of said separation unit.

Description

[0001] TITLE Iron fuel combustion arrangement

[0002] TECHNICAL FIELD

[0003] The present invention relates to an iron fuel combustion arrangement.

[0004] BACKGROUND

[0005] Energy is indispensable. The amount of energy consumed worldwide has increased enormously over the last decades. Although the amount of energy originating from renewable energy sources such as wind and solar has increased over the last decades and especially over the last years, a large part of the energy still originates from fossil fuels.

[0006] With the use of fossil fuels also comes the highly undesirable carbon dioxide, CO2, emission. And in order to achieve climate objectives, the total CO2 emission should be reduced significantly. To this end, carbon-neutral fuel, and even more carbon-free fuel, is a preferable source of energy and promising resource to fulfil worldwide energy requirements but still meet the climate objectives. Carbon-neutral fuel is considered fuel that does not release more carbon into the atmosphere than it removes, whereas carbon-free fuel produces no net-greenhouse gas emissions or carbon footprint at all. Typically, with carbon-neutral fuel, CO2 or other greenhouse gasses are used as feedstock.

[0007] Heat intensive industries are responsible for a large part of the total CO2 emissions. But for many industries there are currently few or no fossil fuel alternatives available that on the one hand are scalable, and on the other hand able to provide sufficient energy with a high degree of certainty and consistency yet are completely CO2- emission-free.

[0008] Solar energy and wind energy can partly meet this need. However, due to the fact that they are intermittent, they are often not, or insufficiently suitable to replace fossil fuels and to meet the demand for energy from these industries at all times. In recent years, a lot of research has therefore been carried out into a feasible alternative that is nearly CC>2-emission-free. Iron fuel has the potential to meet that need and to become the candidate of choice.

[0009] Iron fuel is a very promising fuel in which energy is stored in the iron powder when and where needed. In the right conditions, iron powder is flammable and has the property that when the iron powder is burned, a lot of energy is released in the form of heat. This heat can then be used to generate hot air, hot water, steam, or electricity for use in any kind of application or industry. Another important property of iron powder is that only rust remains during combustion, while the amount of CO2 which is released during the combustion of the iron powder is significantly reduced. The rust, as a product, can be easily collected and converted back into the iron powder in a sustainable manner, which makes it a close to circular process.

[0010] The fact that the iron fuel is circular and easy and safe to transport makes it an ideal clean and sustainable alternative for fossil fuels to meet the demand for energy in various industries but also in all kinds of other applications.

[0011] Although the use of iron fuel may already be a proven clean and sustainable alternative to fossil fuels, there are also several challenges. As said, during said combustion of the iron fuel, rust (iron oxide) is formed as product. Even though the iron oxide can be collected in an easy manner from the gas stream that contains said iron oxide, a substantial amount of iron oxide dust, i.e., very small iron oxide particles, is also formed in the process of iron fuel combustion. It is highly preferable that these dust particles are also separated and collected from said gas stream containing iron oxide particles.

[0012] Known technologies for collecting the dust from gas streams include dust filters and cyclones. Dust filters excel at low particle concentrations and small particle diameters. Cyclones can separate a broad range of particle diameters and can handle large particle concentrations. However, both mentioned technologies have their limitations for the current user case. In the process of iron fuel combustion, a continuous separation process is required. A dust filter required frequent operational maintenance as the particle concentration in the gas stream is relatively high, e.g., 100 to 200 g / m3, and is therefore not suited. A cyclone would be able to separate the particles, but must operate with a certain rotational speed as the cyclone is centrifugally driven. This results in a high pressure loss that must be compensated to arrange sufficient flow through the system. The most optimal way to do this is to have an arrangement having a horizontal inlet, sufficient height, and an (approximately) 90 degree-curved section. However, a lot of iron oxide particles can accumulate in said curved section, which may result in various issues, such as blockages in the iron fuel combustion arrangement. Thus, the use of a cyclone directly after the combustion unit requires a 90 degree turn in the iron fuel combustion arrangement, which is not preferred. Furthermore, the mixture of the iron oxide particles and the gas entering the cyclone has a high temperature (up to 700 °C), which would make the use of a cyclone extremely costly.

[0013] The above-mentioned problems were solved by implementing a separator that uses the downward momentum and inertia of the iron oxide particles as a method of separation. However, such separators are found to have limited effectiveness and do not reach today’s standards.

[0014] There is therefore a need for a more common or applicable design to improve the separation of the iron oxide from the gas stream wherein the above-mentioned problems are solved.

[0015] SUMMARY

[0016] It is an object of the present invention to provide an improved iron fuel combustion arrangement.

[0017] The foregoing object is achieved according to a first aspect of the present invention that relates to an iron fuel combustion arrangement, comprising: a combustion unit (3) arranged for combusting iron fuel thereby generating an iron oxide containing medium; a separation unit (5) having a height direction (H1) and arranged downstream of said combustion unit, said separation unit comprising a separation chamber (7) arranged for separating said iron oxide containing medium into iron oxide particles and a gas stream, wherein said separation chamber has a separation chamber cross- sectional area (A1) at a top side (9) of said separation chamber; wherein said separation unit comprises: an inlet (11), positioned at said top side of said separation chamber and having an inlet cross-sectional area (A2) having an inlet cross-sectional width (W1), said inlet is arranged for introducing said iron oxide containing medium in said separation unit in a downward direction; a particle outlet (13), positioned at a bottom side (15) of said separation chamber and having a particle outlet cross-sectional area (A3) having a particle outlet cross-sectional width (W2), said particle outlet is arranged for discharging said iron oxide particles from said separation unit; a gas outlet (17), positioned at said top side of said separation chamber or at a sidewards side (19) of said separation chamber and having a gas outlet cross- sectional area (A4), said gas outlet is arranged for discharging said gas stream from said separation unit, wherein said gas outlet is oriented in an upward direction (Z) away from said particle outlet at an inclination angle (a) up to 50 degrees relative to said height direction of said separation unit.

[0018] The iron fuel combustion arrangement according to the first aspect has the advantage that, compared to known separation units, more iron oxide particles are collected and thus, less iron oxide particles flow along the gas stream out of the separation unit through the gas outlet. More iron oxide particles can slide back into the separation chamber of the separation unit and to the particle outlet. Thus, having a gas outlet in such a position improves the separation. Known separation units can collect up to 88 wt.% of the iron oxide particles, whereas the separation unit according to the invention can collect up to 97 wt.% of the iron oxide particles. The weight percentages are based on the total weight of the iron oxide that is formed in the iron fuel combustion process. Additionally, the iron fuel combustion arrangement according to the present invention can easily be scaled up or down or turned down while retaining the technical effects and advantages of the present iron fuel combustion arrangement.

[0019] Furthermore, the separation of the iron oxide particles from the gas stream which is achieved with the iron fuel combustion arrangement according to the present invention requires no moving parts and involves no high-velocity sharp impact angles of the iron oxide particles with solid walls, thereby minimizing erosion propensity. This is beneficial because the frequency of required maintenance work on the equipment is greatly reduced. Thus, the iron fuel combustion arrangement according to the present invention requires less downtime which saves costs and allows a continuous separation process.

[0020] In the iron fuel combustion arrangement, the height direction corresponds to the central vertical axis of the arrangement.

[0021] In a second aspect, the present invention relates to an iron fuel combustion arrangement, comprising: a combustion unit arranged for combusting iron fuel thereby generating an iron oxide containing medium; a separation unit having a height direction and arranged downstream of said combustion unit, said separation unit comprising a separation chamber arranged for separating said iron oxide containing medium into iron oxide particles and a gas stream, wherein said separation chamber has a separation chamber cross-sectional area at a top side of said separation chamber; wherein said separation unit comprises: an inlet, positioned at said top side of said separation chamber and having an inlet cross-sectional area having an inlet cross-sectional width, said inlet is arranged for introducing said iron oxide containing medium in said separation unit in a downward direction; a particle outlet, positioned at a bottom side of said separation chamber and having a particle outlet cross-sectional area having a particle outlet cross- sectional width, said particle outlet is arranged for discharging said iron oxide particles from said separation unit; a gas outlet, positioned at said top side of said separation chamber or at a sidewards side of said separation chamber and having a gas outlet cross-sectional area, said gas outlet is arranged for discharging said gas stream from said separation unit, wherein said iron fuel combustion arrangement further comprises a vibration unit for generating vibrations and wherein said gas outlet is oriented in an upward direction away from said particle outlet at an inclination angle up to 80 degrees relative to said height direction of said separation unit.

[0022] In the arrangement according to the second aspect, the vibration unit, such as a sonic vibrator or vibrating hammer or beater, generates vibrations. These vibrations result in the gas outlet to vibrate, which further improves the removal of iron oxide particles lying on a bottom side of the gas outlet. This results in more iron oxide to be collected by the separation unit and thus, improves the separation.

[0023] Other effects and advantages of the first aspect are also applicable to the second aspect of the present invention. Corresponding embodiments disclosed below for the first aspect are also applicable for the second aspect according to the present invention, unless stated otherwise.

[0024] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present iron fuel combustion arrangement is elucidated below with a detailed description.

[0026] In an embodiment, said inclination angle is from 10 to 40 degrees, preferably between 15 and 30 degrees, more preferably between 20 and 25 degrees, relative to said height direction of said separation unit. Such a small - or sharp - angle makes it more difficult for iron oxide particles to follow gas streamlines through the gas outlet and results in more particles to slide back downwards into the separation chamber to the particle outlet. Thus, it improves the separation of the iron oxide particles from the gas stream. In an embodiment, said separation chamber cross-sectional area at said top side where said inlet mouths into said separation chamber is at least 2 times as large, for example 2 to 10 times as large, such as 3 times as large, 6 times as large, or 8 times as large, as said inlet cross-sectional area. Hence, the inlet may be connected to or extend into said separation chamber. This has the effect that the gas, when the iron oxide containing medium enters the separation unit, significantly expands which results in a “dead zone” in the separation chamber of the separation unit. The gas is pulled through the gas outlet because the pressure in the gas outlet, and further downstream of said gas outlet, is lower compared to the pressure in the separation chamber of the separation unit. In this “dead zone”, the drag force created by the gas streamlines is not sufficiently strong to overcome the downward momentum which is supported by the gravitational pull, such that the particles continue their path downwards towards the particle outlet instead of following the gas streamlines towards the gas outlet. This improves separation of the particles from the gas stream.

[0027] In an embodiment, said inlet cross-sectional area is from 50 to 200% of said gas outlet cross-sectional area, preferably 65 to 170%, more preferably 80 to 140%, even more preferably 90 to 110%, most preferably said inlet cross-sectional area is equal to said gas outlet cross-sectional area. This is advantageous because the velocity magnitudes of the iron oxide containing medium entering the separation unit and the gas stream exiting the separation unit do not differ much I are about equal, e.g., 5 m / s for a separation unit having an inlet having a cross-sectional width of 600 mm, and this improves separation of iron oxide particles and gas.

[0028] For example, the inlet cross-sectional area may have a cross-sectional width of between 200 and 1000 mm, such as between 400 and 800 mm or between 500 and 700 mm.

[0029] In an embodiment, said inlet further comprises an inlet end that extends into said separation chamber, said inlet end having an inlet end length that is from 10 to 50% of said inlet cross-sectional width, preferably 13 to 35%, more preferably 15 to 20%. This has the effect that the gas flow recirculates in the separation unit domain (separation chamber) and streams along the top side of separation chamber. By continuing the inlet end in the domain, the downward flow of the iron oxide containing medium is not affected by the recirculation current of the gas stream. This improves the separation performance.

[0030] In an embodiment, said inlet further comprises a conical inlet end that extends into said separation chamber, or in case the inlet comprises the inlet end, said conical inlet end is positioned at a lower edge of said inlet end and extends into said separation chamber, wherein said conical inlet end widens at a conical angle of from 0 to 15 degrees, preferably 5 to 15 degrees, more preferably 6 to 12 degrees. This further induces separation of the iron oxide particles from the gas stream.

[0031] The conical inlet end may have a conical inlet length that is from 10 to 50% of said inlet cross-sectional width, preferably 13 to 35%, more preferably 15 to 20%. This has the effect that the gas flow recirculates in the separation unit domain (separation chamber) and streams along the top side of separation chamber. By continuing the inlet end in the domain, the downward flow of the iron oxide containing medium is not affected by the recirculation current of the gas stream. This improves the separation performance.

[0032] In an embodiment, said gas outlet cross-sectional area has a rectangular shape. Such a shape is beneficial for the separation of the particles from the gas stream. Preferably, said gas outlet cross-sectional area has a rectangular shape and has a width to height ratio of 1 :1 or larger, such as 2: 1 , 4:1 , 6:1 , or 10:1. The gas has a lower flow rate nearby a boundary layer of the wall / side of the gas outlet. Hence, a rectangular shape results in a relatively large boundary layer at the bottom side of the gas outlet such that the gas flow rate is reduced nearby said boundary layer allowing iron oxide particles to slide back into the separation chamber and to the particle outlet, which improves the separation of the particles from the gas.

[0033] Said rectangular shape of said gas outlet may have a width of from 700 to 1500 mm, such as 1000 to 1300 mm and / or a height of from 200 to 400 mm, such as 250 to 300 mm. A gas outlet having a cross-sectional area with smaller dimensions than disclosed above results in an increase of the velocity of the gas exiting the separation unit through the gas outlet. This makes iron oxide particles more inclined to follow the gas streamlines, which reduces the separation efficiency. By having a gas outlet with larger dimensions than disclosed above, the gas velocity is reduced and particle separation from the gas stream is improved.

[0034] In an embodiment, said arrangement further comprises a blower unit arranged upstream of said gas outlet or a suction unit arranged downstream of said gas outlet for creating an under pressure inside said gas outlet such that said gas stream is respectively blown or sucked through said gas outlet. Due to the difference in pressure in the separation chamber and the gas outlet and further downstream of said gas outlet, the gas is forced to stream towards the parts where the pressure is lower, thereby creating gas streamlines from the separation chamber through the gas outlet. Due to the “dead zone” in the separation chamber, the effect of the suction unit has no substantial effect on changing the path of the particles and thus, the particles continue their path downwards towards the particle outlet instead of following the gas streamlines towards the gas outlet. This improves separation of the particles from the gas stream.

[0035] The cross-sectional area of the particle outlet may have a rectangular shape or a circular shape. The preferred shape depends on how the particle outlet can best be connected to the next component of the arrangement, e.g., an iron oxide collector unit.

[0036] As an example, the particle outlet cross-sectional area may have a length of from 100 to 200 mm, such as 125 to 175 mm and / or a width of from 100 to 200 mm, such as 125 to 175 mm. Said length and said width may also be of the same size.

[0037] In an embodiment, said separation unit comprises a protrusion positioned inside said separation chamber and above said particle outlet, optionally said protrusion being an extension of a bottom side of said gas outlet. The protrusion limits the amount of iron oxide particles that are initially separated but move back upwards due to strong gas streamlines before the particles are collected at the bottom. The protrusion may have a protrusion length that is from of from 30 to 80% of said particle outlet cross-sectional width, preferably 45 to 75%, more preferably 60 to 70%. Such a length provides an optimal balance between preventing particles moving back of upwards and allowing particles to move downwards to the particle outlet of the separation unit.

[0038] In an embodiment, said separation chamber has a funnel-like shape, such as a frustopyramidal shape, or a frustoconical shape. The funnel-like shape has the benefit that it allows compact discharge of the iron oxide particles. With “frustopyramidal”, or truncated pyramid, is meant that the separation chamber is shaped like a pyramidal frustum, thus a frustum made by chopping off the top of a pyramid. With “frustoconical”, or truncated cone, is meant that the separation chamber is shaped like a conical frustum, thus a frustum made by chopping off the top of a cone.

[0039] Said funnel-like shape comprises one or more walls, each wall of said one or more walls positioned at a wall angle up to 50 degrees relative to said height direction of said separation unit, preferably said wall angle is equal to said inclination angle of said gas outlet. The effect of the angle of the one or more walls of the separation chamber is that the iron oxide particles will slide down to particle outlet and it thus prevents particle build up at the wall(s) inside the separation unit. This also prevents iron oxide particles to be picked up by the gas streamlines and exiting the separation unit through the gas outlet along the gas stream. Hence, particle separation is improved.

[0040] In an embodiment, the funnel-like shape is a frustoconical shape. This is advantages as it increases the structural integrity and durability of the separation unit, at the expense of manufacturability.

[0041] In a preferred embodiment of the iron fuel combustion arrangement, said inclination angle of said gas outlet is 10 to 40 degrees relative to said height direction of said separation unit, wherein said separation chamber cross-sectional area at said top side where said inlet mouths in said separation chamber is at least 2 times as large as said inlet cross-sectional area, and wherein said gas outlet cross-sectional area of said gas outlet has a rectangular shape. In an embodiment, the separation unit is cooled by a medium, e.g. water, that is flowing around the separation unit. In such an embodiment, the separation unit is also operating as a heat exchanger, heating the medium that flows around the separation unit. As the iron fuel is combusted to generate heat, operating the separation unit as a heat exchanger may use the generated heat in a more efficient way, leading to a higher conversion rate between the theoretical amount of energy stored in the iron fuel and the amount of energy delivered after combusting it.

[0042] The iron fuel combustion arrangement comprising the separation unit as described in one of the embodiments above is suitable for use in a system designed for driving high-energy-density-requiring processes having a size of from 0.01 MW to 2000 MW, preferably 0.1 MW to 1000 MW, more preferably 1 MW to 500 MW, most preferably between 5 MW and 100 MW. With such a design, the system is applicable to many sizes of industrial and non-industrial processes.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention is described hereinafter with reference to the accompanying drawings in which embodiments are shown and in which like reference numbers indicate the same or similar elements. The invention is in no manner whatsoever limited to the embodiments disclosed therein.

[0045] Fig. 1 shows, in a schematic and illustrative manner, a cross-sectional side view of part of an example of the iron fuel combustion arrangement;

[0046] Fig. 2 shows, in a schematic and illustrative manner, a cross-sectional side view of an example of the separation unit;

[0047] Fig. 3 shows, in a schematic and illustrative manner, an isometric view of an example of the separation unit;

[0048] Fig. 4 shows, in a schematic and illustrative manner, a cross-sectional side view of an example of the separation unit.

[0049] DETAILED DESCRIPTION OF THE DRAWINGS

[0050] Fig. 1 shows a cross-sectional view from a side of part of the iron fuel combustion arrangement 1. The iron fuel combustion arrangement 1 comprises a combustion unit 3 arranged for combusting ion fuel thereby forming an iron oxide containing medium comprising iron oxide. The arrangement 1 further comprises a separation unit 5 having a height direction H1. The separation unit 5 is arranged downstream of the combustion unit 3 and comprises a separation chamber 7 arranged for separating the iron oxide containing medium into iron oxide particles and a gas stream, wherein said separation chamber 7 has a separation chamber cross-sectional area A1 at a top side 9 of the separation chamber 7.

[0051] The separation unit 5 comprises an inlet 11 , positioned at the top side 9 of the separation chamber 7, a particle outlet 13, positioned at a bottom side 15 of the separation chamber 7, and a gas outlet 17, positioned at a sidewards side 19 of the separation chamber 7. The inlet 11 is arranged for introducing the iron oxide containing medium in the separation chamber 7 in a downward direction. The particle outlet 13 is arranged for discharging the iron oxide particles from the separation unit 5. The gas outlet 17 is arranged for discharging the gas stream from the separation unit 5.

[0052] A more detailed cross-sectional side view of the separation unit 5 is shown in Fig. 2. The inlet 11 comprises an inlet end 21 and a conical inlet end 23, that extends into the separation chamber 7. The conical inlet end 23 is positioned at a lower edge 25 of the inlet end 21 and widens at a conical angle p. The inlet end 21 has a length L1 and the conical inlet end 23 has a length L2.

[0053] The separation unit 5 further comprises a protrusion 27 positioned inside the separation chamber 7 and above the particle outlet 13. The protrusion 27, having a length L3, is an extension of a bottom side 29B of the gas outlet 17.

[0054] In Fig. 2 it is further shown that the gas outlet 17 is oriented in an upward direction Z away from the particle outlet 13 at an inclination angle a relative to the height direction H1 of the separation unit 5.

[0055] The separation unit 5 has a funnel-like shape and comprises walls, wherein the walls are positioned at a wall angle y relative to the height direction H1 of the separation unit 5. In the example of the separation unit 5 shown in Fig. 2, the wall angle y equals the inclination angle a. Fig. 3 shows an isometric view of the separation unit 5. The funnel-like shape of the separation unit 5 is a frustopyramidal shape, also known as a pyramidal frustrum. The separation chamber 7 has a separation chamber cross-sectional area A1 at the top side 9. The inlet 11 opens in the separation chamber 7 at the top side 9 and has a cylindrical shape having a cross-sectional area A2 and a cross-sectional width W1.

[0056] The separation unit 5 is provided with a beam-shaped particle outlet 13 at the bottom side 15 positioned in the upward direction Z. The particle outlet 13 has a cross- sectional area A3 that is rectangular shaped having a cross-sectional width W2.

[0057] At the sidewards side 19 of the separation chamber 7, a rectangular shaped gas outlet 17 is provided. The gas outlet 17 has a cross-sectional area A4 and has a width W3 and a height H2.

[0058] Another cross-sectional side view of the separation unit 5 is shown in Fig. 4. In Fig. 4, the behaviour of the iron oxide particles and gas stream inside the separation unit 5 is illustrated. The particles, shown as black dots, enter the separation chamber 7 via the inlet 11 from above in the downward direction Z. The bulk of the particles continue their path downwards (shown as thick, grey solid arrows) towards to particle outlet 13 to be collected below the separation unit 5 in, for example, an iron oxide particle collector (not shown). A portion of the iron oxide particles, especially the smallest particles, tend to follow the gas streamlines (shown as black dashed arrows) into the gas outlet 13. Even though this portion of particles initially follows the path of the gas to the gas outlet 13, these particles slide back via the bottom side 29B of the gas outlet 17 into the separation chamber 7 to the particle outlet 13 (shown as the thin, grey solid arrows) to be collected below the separation unit 5.

[0059] To help even more of the particles which initially follow the path of the gas to the gas outlet 17 slide back into the separation chamber 7 to the particle outlet 13, the bottom side 29A, 29B of the gas outlet 17 may be made of a double-walled structure. The bottommost wall 29B should then of course be of a solid and uninterrupted material, while the upper wall 29A of the double-walled structure may be perforated. This particular structure may ensure that relatively “dead”, i.e. non-moving, air is trapped inside the double walls. This dead air does not carry particles upstream against the force of gravity as it is not moving. At the same time, relatively large particles which were carried into the gas outlet 17 but which fall down along the trajectory of the gas outlet 17 are trapped inside the double wall structure 29A, 29B and fall back towards the particle outlet 13.

[0060] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

[0061] The scope of the present invention is defined by the appended claims. One or more of the objects of the invention are achieved by the appended claims.

Claims

1. An iron fuel combustion arrangement (1), comprising:- a combustion unit (3) arranged for combusting iron fuel thereby generating an iron oxide containing medium;- a separation unit (5) having a height direction (H1) and arranged downstream of said combustion unit (3), said separation unit (5) comprising a separation chamber (7) arranged for separating said iron oxide containing medium into iron oxide particles and a gas stream, wherein said separation chamber (7) has a separation chamber cross-sectional area (A1) at a top side (9) of said separation chamber (7);wherein said separation unit (5) comprises:- an inlet (11), positioned at said top side (9) of said separation chamber (7) and having an inlet cross-sectional area (A2) having an inlet cross-sectional width (W1), said inlet (11) is arranged for introducing said iron oxide containing medium in said separation unit (5) in a downward direction;- a particle outlet (13), positioned at a bottom side (15) of said separation chamber (7) and having a particle outlet cross-sectional area (A3) having a particle outlet cross-sectional width (W2), said particle outlet (13) is arranged for discharging said iron oxide particles from said separation unit (5);- a gas outlet (17), positioned at said top side (9) of said separation chamber (7) or at a sidewards side (19) of said separation chamber (7) and having a gas outlet cross-sectional area (A4), said gas outlet (17) is arranged for discharging said gas stream from said separation unit (5), characterized in that said gas outlet (17) is oriented in an upward direction (Z) away from said particle outlet (13) at an inclination angle (a) up to 50 degrees relative to said height direction (H1) of said separation unit (5).

2. Iron fuel combustion arrangement (1) according to claim 1, wherein said inclination angle (a) is from 10 to 40 degrees, preferably between 15 and 30 degrees, more preferably between 20 and 25 degrees, relative to said height direction (H1) of said separation unit (5).

3. Iron fuel combustion arrangement (1) according to claim 1 or 2, wherein said separation chamber cross-sectional area (A1) at said top side (9) where said inlet (11)16mouths into said separation chamber (7) is at least 2 times as large, such as 3 times as large, as said inlet cross-sectional area (A2).

4. Iron fuel combustion arrangement (1) according to any of the preceding claims, wherein said inlet cross-sectional area (A2) is from 50 to 200% of said gas outlet crosssectional area (A4), preferably 65 to 170%, more preferably 80 to 140%, even more preferably 90 to 110%, most preferably said inlet cross-sectional area (A2) is equal to or smaller than said gas outlet cross-sectional area (A4).

5. Iron fuel combustion arrangement (1) according to any of the preceding claims, wherein said inlet (11) further comprises an inlet end (21) that extends into said separation chamber (7), said inlet end (21) having an inlet end length (L1) that is from 10 to 50% of said inlet cross-sectional width (W1), preferably 13 to 35%, more preferably 15 to 20%.

6. Iron fuel combustion arrangement (1) according to any of the preceding claims, wherein said inlet (11) further comprises a conical inlet end (23) that extends into said separation chamber (7), or, when dependent to claim 5, said conical inlet end (23) is positioned at a lower edge (25) of said inlet end (21) and extends into said separation chamber (7), wherein said conical inlet end (23) widens at a conical angle (P) of from 0 to 15 degrees, preferably 5 to 15 degrees, more preferably 6 to 12 degrees.

7. Iron fuel combustion arrangement (1) according to claim 6, wherein said conical inlet end (23) has a conical inlet length (L2) that is from 10 to 50% of said inlet crosssectional width (W1), preferably 13 to 35%, more preferably 15 to 20%.

8. Iron fuel combustion arrangement (1) according to any of the preceding claims, wherein said gas outlet cross-sectional area (A4) has a rectangular shape, preferably said gas outlet cross-sectional area (A4) has a rectangular shape and has a width to height (W3:H2) ratio of 1:1 or larger.

9. Iron fuel combustion arrangement (1) according to any of the preceding claims, wherein said arrangement (1) further comprises a blower unit arranged upstream of17said gas outlet (17) or a suction unit arranged downstream of said gas outlet (17) for creating an under pressure inside said gas outlet (17) such that said gas stream is respectively blown or sucked through said gas outlet (17).

10. Iron fuel combustion arrangement (1) according to any of the preceding claims, wherein said separation unit (5) comprises a protrusion (27) positioned inside said separation chamber (7) and above said particle outlet (13), optionally said protrusion (27) being an extension of a bottom side (29A, 29B) of said gas outlet (17).

11. Iron fuel combustion arrangement (1) according to claim 10, wherein said protrusion (27) has a protrusion length (L3) that is from of from 30 to 80% of said particle outlet cross-sectional width (W2), preferably 45 to 75%, more preferably 60 to 70%.

12. Iron fuel combustion arrangement (1) according to any of the preceding claims, wherein said separation chamber (7) has a funnel-like shape, such as a frustopyramidal shape, or a frustoconical shape.

13. Iron fuel combustion arrangement (1) according to claim 12, wherein said funnel-like shape comprises one or more walls, each wall of said one or more walls positioned at a wall angle (y) up to 50 degrees relative to said height direction (H1) of said separation unit (5), preferably said wall angle (y) is equal to said inclination angle (a) of said gas outlet (17).

14. Iron fuel combustion arrangement (1) according to claim 12 or 13, wherein said funnel-like shape is a frustoconical shape.

15. Iron fuel combustion arrangement (1) according to any of the preceding claims, wherein said inclination angle (a) of said gas outlet is 10 to 40 degrees relative to said height direction (H1) of said separation unit (5), wherein said separation chamber cross-sectional area (A1) at said top side (9) where said inlet (11) mouths in said separation chamber (7) is at least 2 times as large as said inlet cross-sectional18area (A2), and wherein said gas outlet cross-sectional area (A4) of said gas outlet (17) has a rectangular shape.5

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