Iron fuel combustion arrangement

Abstract

The present invention related to an iron fuel combustion arrangement comprising an iron fuel burner arrangement, and a suspension generation arrangement for providing a suspension comprising iron fuel, wherein said suspension generation arrangement is positioned upstream of said burner arrangement, wherein said suspension generation arrangement comprises a housing with a substantially vertical central axis for transporting a stream of iron fuel towards said burner arrangement, wherein said suspension generation arrangement further comprises an injection element extending at least partly in said housing, for injecting compressed gas into said stream of iron fuel, wherein said suspension generation arrangement further comprises a mixing portion connected to said housing downstream of said injection element wherein in use said stream of iron fuel and said injected gas are mixed to provide said suspension comprising iron fuel.

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 CC>2-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 CC>2-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.

[0009] In recent years, a lot of research has therefore been carried out into a feasible alternative that is fully CC>2-emission-free. Iron fuel has the potential to meet that need and to become the candidate of choice. 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 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. One of the challenges lies in the stability of the combustion of iron fuel. A stable combustion of iron fuel allows for a reliable energy source, and increases efficacy of the combustion arrangement. On top of that, a stable combustion ensures a predictable output of the combustion process, both in terms of heat generated and properties of the remaining iron oxide. The former is important to make the combustion arrangement commercially viable, the latter is important to improve the circularity of the overall iron fuel technology.

[0012] Therefore, there is a need for an iron fuel combustion arrangement that provides an improved combustion stability.

[0013] SUMMARY

[0014] It is an object of the present invention to provide an improved iron fuel combustion arrangement.

[0015] It is a further object of the present invention to provide an iron fuel combustion arrangement with an improved combustion stability.

[0016] The present invention therefore relates, in a first aspect, to an iron fuel combustion arrangement comprising an iron fuel burner arrangement, and a suspension generation arrangement for providing a suspension comprising iron fuel, wherein said suspension generation arrangement is positioned upstream of said burner arrangement, wherein said suspension generation arrangement comprises a housing with a substantially vertically oriented central axis for transporting a stream of iron fuel towards said burner arrangement, wherein said suspension generation arrangement further comprises an injection element extending at least partly in said housing, for injecting compressed gas into said stream of iron fuel, wherein said suspension generation arrangement further comprises a mixing portion connected to said housing at a position downstream of said injection element wherein in use said stream of iron fuel and said injected gas are mixed to provide said suspension comprising iron fuel.

[0017] In a second aspect, the present invention further relates to a process for introducing a suspension comprising iron fuel into an iron fuel burner arrangement of an iron fuel combustion arrangement according to any of the preceding claims, comprising: - providing a stream of iron fuel into a housing with a substantially vertically oriented central axis, - transporting said stream of iron fuel in a substantially vertical direction towards said burner arrangement, - injecting, during transport of said stream of iron fuel, compressed gas into said stream with an injection element extending at least partly in said housing, - mixing said stream of iron fuel and said injected gas in a mixing portion downstream of said injection element to provide said suspension comprising iron fuel, and - introducing said suspension comprising iron fuel into said burner arrangement.

[0018] The inventors have found that the known arrangements for combustion processes, which are suitable for example for combustion of coal, coallike material, waste and biomass are not suitable or less suitable for the combustion of iron fuel. For combusting iron fuel, specific design requirements are applicable which are different from these known arrangements.

[0019] Combustion of iron fuel namely has different chemical and physical properties when compared to other fuels or bulk solids. A further, highly important difference is that iron fuel is intended to be used as a burnable clean energy medium in which the iron powder can be used in a circular manner, meaning that the waste product of the iron fuel after burning, i.e. the rust or iron oxide powder, is to be collected and should be suitable to be converted back into iron powder. In more traditional combustion processes, the combustibles are treated as waste after having been combusted. As mentioned, the properties of iron fuel are very different from other fuel types like diesel, coal or coal-like materials. As such, the parameters for traditional combustion processes do not suffice and are not able to meet the requirements for such a combustion process in terms of i) fuel supply, ii) stable, continuous combustion, iii) completion of the combustion, iv) general performance of iron fuel combustion arrangements, v) for the purpose of reusing residual iron oxide powder and vi) heat exchanging performance.

[0020] Particular challenges exist in burning the iron fuel consistently. The inventors have surprisingly found that an iron fuel combustion arrangement comprising a suspension generation arrangement for providing a suspension comprising iron fuel according to the present invention allows for the desired homogeneity in the spread of iron fuel particles over the diameter of the mixing portion for transporting a stream of iron fuel towards said burner arrangement. In addition, the particle size distribution of iron particles over the diameter of the mixing portion has the required homogeneity for a more stable combustion of the iron fuel. Moreover, the arrangement according to the present invention allows for a stable supply of iron fuel over time so that pulsating of the supply is reduced or avoided. This improves the stability of the iron fuel combustion arrangement.

[0021] The above-mentioned benefits are achieved by the present invention even for high suspension density of e.g. 1-5 kg / m3and / or fuels having a high bulk density of e.g. 2 - 5 tons / m3 as could be normal operating conditions for an iron fuel combustion arrangement. These conditions may apply irrespective of the total mass flow of the fuel.

[0022] EXAMPLES

[0023] Iron fuel combustion arrangement

[0024] As stated above, the present invention relates in a first aspect to an iron fuel combustion arrangement comprising an iron fuel burner arrangement, and a suspension generation arrangement for providing a suspension comprising iron fuel, wherein said suspension generation arrangement is positioned upstream of said burner arrangement, wherein said suspension generation arrangement comprises a housing with a substantially vertical central axis for transporting a stream of iron fuel towards said burner arrangement, wherein said suspension generation arrangement further comprises an injection element extending at least partly in said housing, for injecting compressed gas into said stream of iron fuel, wherein said suspension generation arrangement further comprises a mixing portion connected to said housing at a position downstream of said injection element wherein in use said stream of iron fuel and said injected gas are mixed to provide said suspension comprising iron fuel.

[0025] Said injection member can be envisioned as a needle or tube through which a compressed gas can be supplied. In particular, the compressed gas may be compressed air. The air may be fresh air, introduced in the iron fuel combustion arrangement for the first time, or the air may be recycled or spent air, having already been combusted. In particular, by using a mixture of spent air and fresh air, the amount of oxygen in the air be selected. In an example, the injection element has the same diameter throughout and is straight. In an alternative example, said injection member comprises a venturi. In yet another example, the injection element may be fed with compressed gas from the side of the housing and inject the compressed gas in the middle of the housing.

[0026] The compressed gas may for instance have an overpressure relative to the environment of at least 0,5 bar, such as at least 1 bar, in particular at least 2 or 3 bar. It is beneficial when the pressure ratio between the compressed gas and the stream into which the compressed gas is released is higher than the critical pressure ratio, so that sonic flow conditions for the compressed gas can be obtained. At the same time, to obtain compressed gas a gas compressor must typically be operated. To reduce operating costs, the overpressure of the gas is therefore preferably minimized. Looking at operating costs, the compressed gas may have a pressure of at most 4 barg, preferably at most 2 barg, such as about 1 ,2 barg, about 1 ,5 barg or about 1 ,7 barg.

[0027] The provided suspension comprising iron fuel may e.g. be a suspension of iron fuel suspended in air, iron fuel suspended in a recirculated flue gas, iron fuel suspended in a gaseous fuel, and / or iron fuel suspended in a gas that is a combination of the above-mentioned gasses. For example, the suspension may be a combustible suspension. It is also possible for the suspension to become combustible only at a later stage, for instance when it has entered the burner arrangement.

[0028] The housing may e.g. receive both the iron fuel and the compressed gas. In embodiments, the housing may have a circular diameter. However, also rectangular diameters may be possible for the housing. As will be described in the below in more detail, the housing may have a non-constant diameter, in particular the housing may have a tapering portion at which tapering portion the injection element may mouth.

[0029] The required minimal length of the mixing portion depends on the desired characteristics (e.g. degree of homogeneity, speed), of the suspension upon exit of the mixing portion. Further, there might be dimensional restrictions in view of the height restrictions for the entire combustion arrangement due to limited available space. The suspension density is unaffected by the length of the mixing portion.

[0030] In an example, the housing for transporting a stream of iron fuel towards the burner arrangement comprises a frustoconical portion and optionally a tube-shaped portion connected to said frustoconical portion at the wide end of said frustoconical portion.

[0031] In an example, the sides of said frustoconical portion have an angle of between 10 and 45 degrees with respect to the central axis of said housing. An advantage of such an angle is that no iron fuel powder will rest on the structural wall of the housing but, rather, all iron fuel powder in the housing will fall down.

[0032] In an example the mixing portion is defined by a tube which is connected to said frustoconical portion of said housing, at the narrow end thereof (i.e. downstream).

[0033] The skilled person will appreciate that the cross-section of the frustoconical portion and / or the tube-shape portion of the housing does not have to be circular, but may have other shapes, for example a hexagonal shape.

[0034] In an example, said injection element has an outlet in streamwise direction. There is a balance to the diameter of the injection element, the positioning of the outlet thereof inside the housing and the diameter of the housing. When the difference in diameter between the injection element and the housing is relatively small, the flow of particles around the injection element (i.e. inside the housing) is expected to be low. This effect may be more pronounced when the housing comprises a frustoconical portion that introduces a narrowing of the housing. When positioning the outlet of the injection element higher, i.e. where the diameter of the frustoconical portion is relatively large, this may lead to an improved flow, but also to a reduced mixing of the compressed gas with the stream of iron fuel. Another way to achieve improved flow of the iron stream would be to increase the diameter of the (narrow portion of the) housing compared to the diameter of the injection element. Thus, it is beneficial to ensure sufficient flow through the housing while still ensuring a good mixing effect between the compressed gas and the stream of iron fuel.

[0035] In preliminary tests, an optimum has been found where the injection element mouths above the inlet of the mixing portion at a height of about 3,5 times the diameter of the mixing portion. These preliminary tests were carried out for a housing that has a tapering frustoconical shape towards the mixing portion, the tapering angle being around 10 degrees and the ratio between the (outer) diameter of the injection element and the (inner) diameter of the housing at the point of injection being around 0.35. It is expected that for other tapering angles and / or ratio’s and / or absolute dimensions this injection height may be at a different position. It is expected that the optimal ratio between a height from the outlet of the injection element to the inlet of the mixing portion and a diameter of the mixing portion is in between 2 and 6, preferably 3 and 4.

[0036] In an example, the said suspension generation arrangement further comprises a centering element arranged for securing said injection member centrally with respect to said housing. This ensures correct positioning of the injection member such that the outlet is in the streamwise direction and, preferably, centered with respect to the housing. It has been found by the inventors that precise positioning of the injection member compared to the design specifications may be critical in obtaining the desired suspension. Likely due to the compressed gas being used, a misalignment of even a few millimeters in positional orientation or a few degrees in angular orientation may lead to highly undesirable suspensions. In preferred examples the injection member may be aligned with the central axis of the housing.

[0037] In an example, said suspension generation arrangement further comprises a fuel inlet associated with said housing, for introducing said stream of iron fuel into said housing. When the housing comprises a tube-shaped portion upstream of a frustoconical portion, it is preferred that the inlet is located in the tube-shaped portion upstream of a frustoconical portion.

[0038] In an example, said fuel inlet is arranged at an angle with respect to the central axis of said housing, the angle being at most 45 degrees. In a specific example, said inlet has an angle with respect to the central axis of said housing of at most 40 degrees, preferably at most 30 degrees. The steeper the angle, the less iron fuel remains behind in said inlet.

[0039] In an alternative example, the fuel inlet is arranged coaxially with respect to the central axis of the housing. For example, the fuel may be introduced in the housing near the top of the housing.

[0040] In an example, the iron fuel combustion arrangement further comprises a fuel outlet associated with said housing for bringing said stream of iron fuel in contact with said compressed gas, the fuel outlet being arranged at an angle with respect to the central axis of said housing, the angle being at most 45 degrees. The fuel outlet is not to be mistaken for the suspension outlet. Through the suspension outlet, a suspension, i.e. a mixture of iron fuel and gas, exits. Through the fuel outlet, iron fuel exits - although gas will typically be present here at the iron fuel outlet there has been no mixture between the iron fuel and the compressed gas introduced through the injection element.

[0041] In an example, a cross-section of the mixing portion is constant, preferably in both shape and size. This design will allow the turbulent air injected into the iron fuel to optimally mix and suspense both media.

[0042] In the following examples, the provision of additional gas, from a source differing from the injection element, is discussed. In exemplary embodiments, this additional gas is air.

[0043] In an example, said mixing portion is a first mixing portion, which extends into a second mixing portion having a larger cross-sectional area than said first mixing portion, and wherein, in use, in said second mixing portion additional gas is added to said suspension comprising iron fuel. The additional gas may have a substantially atmospheric pressure and may, thus, be cheaper to obtain than the compressed gas used in the first mixing portion. The separate tunability of the required gas for the generation of the suspension and the required gas for the desired suspension density provides the benefit of minimalization of the required amount of compressed gas by the use of gas that is more available and less costly.

[0044] The required minimal length of the second mixing portion depends on the desired characteristics (e.g. degree of homogeneity, speed), of the suspension upon exit of the second mixing portion. Further, there might be dimensional restrictions in view of the height restrictions for the entire combustion arrangement due to limited available space. The suspension density is unaffected by the length of the second mixing portion.

[0045] In an example, said additional gas is added as a circumferential gasstream, preferably parallel to the stream of the suspension comprising iron fuel. This allows to gradually mix the additional gas to the suspension exiting the first mixing portion.

[0046] In an example, said first mixing portion is tube-shaped with a constant cross-sectional shape and size. In a specific example, said second mixing portion is also tube-shaped with a constant cross-sectional shape and size.

[0047] In an example, said iron fuel combustion arrangement further comprises an additional tube-shaped portion radially outside of said mixing portion and extending into said second mixing portion, wherein said additional tube-shaped portion defines a passage that is an inner annular space defined between the first mixing portion and said additional tube-shaped portion, and wherein, in use, said inner annular space provides an said additional gas inlet to said suspension comprising iron fuel.

[0048] In an example, the iron fuel combustion arrangement further comprises a passive iron fuel spreader, arranged upstream of the housing, for spreading the stream of iron fuel over a surface area. Preferably the iron fuel spreader is passive in the sense that it is stationary and does not comprise moving parts, while still achieving the effect of spreading the stream of iron fuel over a surface area.

[0049] Process for introducing a suspension comprising iron fuel into an iron fuel burner

[0050] As stated above, the invention relates in a second aspect to a process for introducing a suspension comprising iron fuel into an iron fuel burner arrangement of an iron fuel combustion arrangement according to any of the preceding claims, comprising: providing a stream of iron fuel into a housing with a substantially vertically oriented central axis, transporting said stream of iron fuel in a substantially vertical direction towards said burner arrangement, injecting, during transport of said stream of iron fuel, compressed gas into said stream with an injection element extending at least partly in said housing, mixing said stream of iron fuel and said injected gas in a mixing portion downstream of said injection element to provide said suspension comprising iron fuel, and introducing said suspension comprising iron fuel into said burner arrangement.

[0051] In an example, said process further comprises, prior to introduction of said suspension comprising iron fuel into said burner arrangement: adding additional gas to said suspension comprising iron fuel, preferably wherein said additional gas is added as an circumferential gasstream parallel to said suspension comprising iron fuel.

[0052] 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.

[0053] 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.

[0054] BRIEF DISCRIPTION OF THE DRAWINGS

[0055] The present invention is described hereinafter with reference to the accompanying drawings in which embodiments of the present invention are shown and in which like reference numbers indicate same or similar elements. The invention is in no manner whatsoever limited to the embodiments disclosed therein.

[0056] Fig. 1 provides a schematic overview of a first exemplary embodiment of the iron fuel combustion arrangement according to the present invention.

[0057] Fig. 2 is a close-up of the suspension generation arrangement from Fig. 1.

[0058] Fig. 3 shows the suspension generation arrangement 200 from Fig. 2, including an CFD rendering of an exemplary flow case and the associated distribution of iron fuel particles throughout the suspension generation arrangement 200 when in use.

[0059] Fig. 4 shows the particle distribution of the iron fuel particles in gas near the outlet of the suspension generation arrangement 200 of Fig. 3.

[0060] Fig. 5 shows a close-up of a second exemplary suspension generation arrangement in a cross-sectional view.

[0061] Fig. 6 shows a different cross-sectional view of the suspension generation arrangement of Fig. 5.

[0062] Fig. 7 shows an exemplary embodiment of an iron fuel divider which may be arranged above a suspension generation arrangement.

[0063] DETAILED DESCRIPTION

[0064] The present invention is elucidated below with a detailed description.

[0065] Fig. 1 shows an iron fuel combustion arrangement 1 comprising an iron fuel burner arrangement 300, and a suspension generation arrangement 200 for providing a suspension comprising iron fuel. The suspension generation arrangement 200 is positioned upstream of the burner arrangement 300.

[0066] Fig. 2 shows the suspension generation arrangement 200 from Fig 1 in more detail. The suspension generation arrangement 200 comprises a housing 210 with a substantially vertically oriented central axis A (represented in Fig. 2 by a dashed line) for transporting a stream of iron fuel towards the burner arrangement. The suspension generation arrangement 200 further comprises an injection element 220 extending at least partly in the housing 210, for injecting compressed gas, e.g. compressed air, into the stream of iron fuel. The suspension generation arrangement 200 further comprises a mixing portion 230 downstream of the injection element 220 wherein - in use - the stream of iron fuel and the injected gas are mixed to provide the suspension comprising iron fuel.

[0067] The housing 210 comprises a frustoconical portion 211 and a tubeshaped portion 212 connected to said frustoconical portion 211 at the narrow end of said frustoconical portion 211. The narrow tube-shaped portion 212 defines the mixing portion 230. The sides of said frustoconical portion 211 may for instance have an angle of between 10 and 45 degrees with respect to the central axis A of the tube 210.

[0068] The injection element 220 has an outlet in streamwise direction and is arranged centrally, along the central axis A of the housing 210. The injection element 220 ends in the frustoconical portion 211 , at some height above an inlet of the mixing portion 230. The suspension generation arrangement 200 may further comprises a centering element 270 that secures the injection member 220 with respect to the housing 210.

[0069] The suspension generation arrangement 200 further comprises a fuel inlet 240 associated with the housing 210, for introducing said stream of iron fuel into the housing 210. The fuel inlet 240 may for instance have an angle with respect to the central axis A of said housing 210 of at most 45 degrees. This may in particular be advantageous when the inlet is passive, i.e. does not comprise an active drive element I makes use of the force of gravity to introduce the stream of iron fuel into the housing. In alternative, non-shown, embodiments where an active drive element is used to introduce the stream of iron fuel into the housing, the angle of the fuel inlet with respect to the central axis of the housing may be substantially zero.

[0070] The mixing portion 230 is a first mixing portion, which extends into a second mixing portion 250 having a larger cross-sectional area than the first mixing portion 230. In use, in the second mixing portion 250 additional gas, e.g. additional air, is added to the suspension comprising iron fuel.

[0071] The additional gas is added as a circumferential gas stream, parallel to the stream of the suspension comprising iron fuel.

[0072] The first mixing portion 230 may be tube-shaped. The second mixing portion 250 may also tube-shaped. With “tube-shaped” is meant in the context of the present invention that the interior is open and the element has some length. The crosssection may be circular, but this is not required.

[0073] The iron fuel combustion arrangement 1 further comprises an additional tube-shaped portion 260 radially outside of the first mixing portion 230 and extending into the second mixing portion 250. The diameter reduction between additional tube-shaped portion 260 and second mixing portion 250 is here abrupt. Of course, this reduction may be implemented more gradually, e.g. by using a conical tube portion that bridges the space between the additional tube-shaped portion 260 and the second mixing portion 250. The additional tube-shaped portion 260 defines a passage that is an inner annular space defined between the first mixing portion 230 and the additional tube-shaped portion 260. In use, the inner annular space provides additional gas to the suspension comprising iron fuel. Gas inlets 265 provide gas to the additional tube-shaped portion 260. The additional tube-shaped portion 260 also functions as a chamber wherein the additional gas from several inlets 265 is assembled before it is dispersed into the second mixing portion 250 downstream. The additional gas is added as a circumferential gasstream, parallel to the stream of the suspension comprising iron fuel.

[0074] The gas from inlets 265 can ‘rest’ in the additional tube-shaped portion 260 such that the additional gas has a less turbulent flow upon entering the second mixing portion 250, such that disturbance of the flow of the suspension comprising iron fuel is minimized.

[0075] Gas inlets 265 into the additional mixing portion 260 may be concentric around the first mixing portion 230. There may be for instance 2-6 gas inlets 265.

[0076] Fig. 3 shows the suspension generation arrangement 200 from Fig. 2, including a CFD computation of one exemplary flow case and the distribution of iron fuel particles throughout the suspension generation arrangement 200 when in use. In particular, it may be observed that upstream, in the housing, the iron fuel particles are initially packed very tightly onto each other. Downstream of the injection element 220 outlet, all iron fuel particles are first blown to the side of the mixing portion 230 due to the overpressure of the gas exiting the injection element 220. However, moving towards the end of the mixing portion 230 the gas and the iron fuel particles start to mix, where some space is created in between the iron fuel particles and a suspension of iron particles in gas is created. Moving further downstream, in particular to the exit of the mixing portion 230 where additional gas is added to the iron fuel particles through gas inlets 265 and via additional tube-shaped portion 260, it can again be observed that the iron-fuel-gas mixture gradually expands in width as the mixture flows in the downstream direction, filling the entire width of the mixing chamber and more and more gas being present between the iron fuel particles to form the desired suspension.

[0077] From Figure 4, which shows a cross sectional view of the suspension at the end of the second mixing portion as indicated in Fig 3, but on a different scale, , it may especially be noted that the distribution of the particles, in a comparison of the top half to the bottom half as well as in a comparison of the left-hand half to the righthand half, is deemed well-distributed. Darker spots here represent smaller particles; so that it may especially be noted that distribution over the cross-sectional area is not significantly different for smaller or larger particles, which is deemed advantageous. In radial direction the distribution is not perfect as more particles are relatively contained near the centre of the tube than near the outer ends of the tube, however the result obtained herewith is deemed workable although it may be up for further improvement.

[0078] In Figures 5 and 6 an alternative embodiment of a suspension generation arrangement is shown. When comparing the suspension generation arrangement of Figures 5 and 6 to the one shown in Figures 1 and 2, it may be observed that in the design of Figures 5 and 6 the fuel inlet 240 is arranged near the top of the housing 210, whereas the inlet to the injection element 220 is arranged at the side of the housing 210. The injection element 220 is centralized in the housing 210, taking in compressed gas from the side and injecting it in the mixing chamber 230. The iron fuel, after introduced in the housing 210 through the inlet 240, flows around the injection element 220 and is introduced in the mixing chamber 230 and brought into contact with the compressed gas at the fuel outlet 245. While the outlet of the injection element 220 remains aligned with the central axis A through the housing, the fuel outlet 245 is arranged at an angle to said central axis A.

[0079] A further difference between the embodiment of the suspension generation arrangement shown in Figures 5 and 6 and the one shown in Figures 1 and 2 is that in the former the total length of the injection element 220 relative to the housing 210 is shortened. This leads to a relatively stiffer design, so that a centralized position of the injection element 220 outlet in the mixing portion 230 can be obtained with greater precision. Compared to the embodiment shown in Figures 1 and 2, an better mixed suspension may be obtained with the embodiment shown in Figures 5 and 6 while less compressed gas is needed.

[0080] Shown in Figure 7 is an iron fuel spreader 100 which may be positioned upstream of the housing and which may already spread the iron fuel over the surface. In particular, when the iron fuel falls down under the influence of gravity, as it hits the bars 101 it is spread out over the circumference of the tube surrounding the iron fuel spreader 100. By arranging the bars 101 in different layers and at various angles with respect to each other, the best spreading is obtained without any moving parts or other energy source being used.

[0081] A suspension with well-distributed iron fuel particles can be burned more efficiently in the burner, so that e.g. the height of the burner may be reduced, the ratio of burned particles vs unburned particles is improved and / or a higher temperature may be reached. This is all deemed favourable.

[0082] Modifications and additions to the method and arrangement disclosed above are obvious to those skilled in the art and covered by the scope of the appended claims.

Claims

CLAIMS1. Iron fuel combustion arrangement comprising an iron fuel burner arrangement, and a suspension generation arrangement for providing a suspension comprising iron fuel, wherein said suspension generation arrangement is positioned upstream of said burner arrangement, wherein said suspension generation arrangement comprises a housing with a substantially vertically oriented central axis for transporting a stream of iron fuel towards said burner arrangement, wherein said suspension generation arrangement further comprises an injection element extending at least partly in said housing, for injecting a compressed gas into said stream of iron fuel, wherein said suspension generation arrangement further comprises a mixing portion connected to said housing at a position downstream of said injection element wherein in use said stream of iron fuel and said injected gas are mixed to provide said suspension comprising iron fuel.

2. Iron fuel combustion arrangement according to claim 1 , wherein said housing comprises a frustoconical portion and optionally a tube-shaped portion connected to said frustoconical portion at the wide end of said frustoconical portion, preferably wherein the sides of said frustoconical portion have an angle of between 10 and 45 degrees with respect to the central axis of said housing.

3. Iron fuel combustion arrangement according to any of the preceding claims, wherein said injection element has an outlet in streamwise direction.

4. Iron fuel combustion arrangement according to claim 3, wherein said suspension generation arrangement further comprises a centering element arranged for securing said injection member centrally with respect to said housing.

5. Iron fuel combustion arrangement according to any of the preceding claims, wherein said suspension generation arrangement further comprising a fuel inlet associated with said housing, for introducing said stream of iron fuel into said housing.

6. Iron fuel combustion arrangement according to claim 5, wherein said fuel inlet is arranged coaxially with respect to the central axis of said housing.

7. Iron fuel combustion arrangement according to claim 5 or 6, further comprising a fuel outlet associated with said housing for bringing said stream of iron fuel in contact with said compressed gas, the fuel outlet being arranged at an angle with respect to the central axis of said housing, the angle being at most 45 degrees.

8. Iron fuel combustion arrangement according to any of the preceding claims, wherein a cross-section of said mixing portion is constant, preferably in both shape and size.

9. Iron fuel combustion arrangement according to any one of the preceding claims, further comprising a passive iron fuel spreader, arranged upstream of the housing, for spreading the stream of iron fuel over a surface area.

10. Iron fuel combustion arrangement according to any of the preceding claims, wherein a ratio between a height between the outlet of the injection element and the inlet of the mixing portion and a diameter of the mixing portion is in between 2 and 6, preferably 3 and 4, more preferably about 3,5.

11. Iron fuel combustion arrangement according to any of the preceding claims, wherein the compressed gas has a pressure of at least 1 barg, and preferably at most 4 barg, more preferably at most 2 barg, such as about 1 ,2 barg, about 1 ,5 barg or about 1 ,7 barg.

12. Process for introducing a suspension comprising iron fuel into an iron fuel burner arrangement of an iron fuel combustion arrangement according to any of the preceding claims, comprising: providing a stream of iron fuel into a housing with a substantially vertically oriented central axis, transporting said stream of iron fuel in a substantially vertical direction towards said burner arrangement, injecting, during transport of said stream of iron fuel, compressed gas into said stream with an injection element extending at least partly in said housing, - mixing said stream of iron fuel and said injected gas in a mixing portion downstream of said injection element to provide said suspension comprising iron fuel, and introducing said suspension comprising iron fuel into said burner arrangement.

Images