Iron fuel combustion arrangement

Technical Field

The present disclosure relates generally to iron fuel burner technology. More specifically, relates the present disclosure to iron fuel combustion arrangements which comprises a combustion chamber and a burner arrangement.

Background of the Invention

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.

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 fulfill worldwide energy requirements but still meet the climate objectives. Carbon- neutral fuel is considered fuel 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.

Heat intensive industries are responsible for a large part of the total CC 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.

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 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 highly 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 converted into 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 no CO2 is released during the combustion of the iron powder. The rust, as waste product, can be easily collected and converted back into the iron powder in a sustainable manner, which makes it a fully circular process.

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.

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 most important challenges is the fact that the iron fuel, when combusted, has the tendency to contamination in the burner or the combustion arrangement. Therefore, the uptime of the combustion is limited, as parts of the combustion arrangement needs cleaning from time to time. This does not aid the potential as an alternative to fossil fuel combustion. There is therefore a need to reduce the effect of combustion. Summary

It is an object of the present disclosure to provide an improved iron fuel combustion arrangement. More particular, it an object to provide for an improved iron fuel combustion arrangement which has a higher uptime, and which is less prone to contamination.

In a first aspect, there is provided, an iron fuel combustion arrangement, comprising a combustion chamber and a burner arrangement, said combustion chamber being arranged for combustion of an iron fuel suspension medium comprising iron fuel and oxygen at a combustible condition, said burner arrangement having a shape that widens towards said combustion chamber, and wherein said burner arrangement comprises: a fuel feeder, arranged for supply of iron fuel in said combustion chamber, wherein said iron fuel is provided in a transport medium. air inlet means, arranged for supply of air comprising said oxygen to said iron fuel, said air inlet means comprising a first and a second inlet stage, said first inlet stage being arranged for said iron fuel suspension medium to swirl towards said combustion chamber, and said second inlet stage being arranged to provide a boundary layer between said iron fuel suspension medium and walls of said burner arrangement and said combustion chamber for preventing iron fuel deposition at said walls, and characterized in that said second inlet stage is further arranged for said iron fuel suspension medium to be brought into a combustible condition beyond a combustion interface in said combustion chamber.

Iron fuel has the potential to solve some of the major drawbacks of more typical renewable energy sources such as wind energy and solar energy due to the ability to store energy. Hence, energy obtained from renewable energy sources such as wind energy and solar energy can be stored in the iron fuel by which the intermittent character of these renewable energy sources is resolved by the iron fuel. The combustion of iron fuel has the potential to meet the current demand of energy.

The combustion of iron fuel results in rust, or at least mostly in rust, and not in CO2. Iron fuel, comprising iron powder, can store energy and be used as a sustainable energy resource. With the iron fuel combustion arrangement according the present disclosure the iron powder can be combusted such that the energy stored in the powder is released. To this end the combustion arrangement may comprise several components or further arrangements, amongst which at least a combustion chamber and a burner arrangement.

The combustion chamber is arranged for combustion of the iron powder at combustible conditions. To this end, the iron powder is mixed with air, meaning at least comprising a certain amount of oxygen.

The burner arrangement has a shape that widens towards the combustion chamber and comprises several parts, amongst which at least a fuel feeder and air inlet means. The fuel feeder provides the iron powder. The iron powder is provided in a medium, gas or air which acts as a carrier and has thus for its main purpose to suspense the iron powder in an air or air like medium. Preferably, the medium also contains additional components such as oxygen and more preferably also nitrogen and/or other substances or compounds.

The air inlet means are arranged to supply the air into the arrangement. The air contains oxygen and has the purpose of mixing with the iron powder to create a medium or mixture of iron powder and oxygen in desired ratio and under desired conditions in which the iron fuel can combust and more precisely combust under defined conditions.

The mixture of iron powder and oxygen, as defined in the present disclosure, is considered a medium which comprises iron powder and oxygen, meaning that it also may contain other substances, compounds or mixtures, amongst which nitrogen, minerals, organic compounds or contaminations, although the main components will be considered the iron powder and oxygen.

An important condition for the combustion of the medium of iron powder and oxygen is the temperature, as it was an insight of the inventors that the temperature must be kept below a sintering temperature, i.e. in accordance with the definition of sintering temperature as defined by ASTM E228 - 17.

When iron powder reaches the sintering temperature, it becomes in a sintering condition which could result in clogging of the arrangement and a loss of iron powder, which should be prevented.

It was a further insight of the inventors that, in order to bring the medium to an optimal condition for combustion under desired process conditions in which sintering conditions prevented such that clogging or other contamination is prevented, the air inlet means should have at least two stages, of which the first stage being arranged or configured to create the medium and thus to provide oxygen for the desired mixture of iron powder and oxygen, whereas the second stage has for its main purpose to provide a boundary layer between the medium and the walls of the arrangement to prevent iron fuel deposition at the walls of the arrangement, i.e. at the walls of either the burner arrangement, the combustion chamber but preferably both.

The inventors found out that the iron fuel deposition on the walls has an effect on the durability and robustness of the arrangement and the quality and stability of the combustion process and thus decreases the uptime because the arrangement has to be cleaned from this deposit from time to time. The deposition may even be that heavy that the burner or even other components of the arrangement cannot be cleaned anymore and should be replaced instead.

By adding an extra air inlet stage, which air inlet stage is configured such that it provides provide a boundary layer between the medium and walls of the burner arrangement and the combustion chamber, the iron fuel deposition at those walls is prevented. As such, not only is it prevented that the iron powder deposits at the walls, the second air inlet stage also prevents sintering of the iron powder upstream of the combustion chamber, and thus in the burner arrangement.

The inventors also found out that conventional, known combustion arrangements typically rely on pre-mixing and nozzles to provide the combustible medium, or in other words, to bring the suspension medium into such a condition in which it can be ignited. Although the pre-mixing may be configured to a certain desired combustible properties with respect one or more of density or fuel I oxygen ratio, pressure, velocity, etc., these properties are influenced significantly and to a certain degree uncontrollably, by the nozzle. The design of the arrangement according to the present disclosure differs from such typical designs in the absence of a nozzle. Contrary to such known designs, with the arrangement according to the present disclosure, the medium is brought into a combustible condition within the combustion chamber, and not at the start of the chamber. Conventional designs typically have ignition means near the nozzle to ignite the medium, which results in a non-optimal condition for combustion and undesired and less controlled process conditions, which increases sintering conditions that may lead to clogging and/or wear of components. The arrangement according to the present disclosure has a first air inlet stage which is arranged for said iron fuel suspension medium to swirl towards said combustion chamber, but also a second inlet stage, which provided both the boundary layer between the medium and walls but is further characterized in that it also brings the medium from a non-combustible condition or at least from a undesired and non- optimal condition for combustion, into a combustible condition. The combustible condition is obtained at and beyond what is referred to as the combustion interface. Hence, by virtue of the configuration of the second air inlet, the position of the combustion interface can be controlled, which position is beyond the start of a first air inlet port of the second inlet stage.

In an example, said second inlet stage is further arranged for said iron fuel suspension medium to be brought into a combustible condition beyond said combustion interface, and wherein said second inlet stage comprises at least two air inlets disposed in the circumference wall of said burner arrangement, and said combustion interface to be configured to be disposed beyond at least one of said two air inlets of said second inlet stage.

The combustion interface may in an example have a hyperbolic, parabolic shape or cross-section or a cone shaped three-dimensional shape. Preferably, the interface concentrates towards the fuel feeder or upstream. Accordingly, the medium may be brought into a combustible condition beyond such shape of interface, such that at least at a or more preferably, some, and even more preferably, all positions of the interface lie beyond at least an air inlet of the second inlet stage.

In an example, said iron fuel combustion arrangement is configured for self-ignition of said iron fuel suspension medium at or beyond said combustion interface, during an operational phase of said iron fuel combustion arrangement.

In an example, said iron fuel combustion arrangement comprises an open connection between said fuel feeder and said combustion chamber.

Conventional combustion arrangements rely on a nozzle which is configured to bring a combustion medium into a combustible condition. Hence, in accordance with the present disclosure, the iron fuel combustion arrangement could be provided with a nozzle between the fuel feeder and the combustion chamber or in other words, at the start or upstream of the combustion chamber. However, in an example, the iron fuel combustion arrangement according to the present disclosure is provided without a nozzle and thus configured to comprise an open connection or open pass way or channel between the fuel feeder and combustion chamber. As such, any swirl of the suspension medium is not cancelled out or influenced by the nozzle, as in known combustion arrangements. Accordingly, the second inlet stage can be arranged for the iron fuel suspension medium to be brought into a combustible condition not at the beginning (upstream) of the combustion chamber, but at a certain position in the combustion chamber, what is defined as combustion interface. Hence, the medium is only then combustible at or beyond this interface. Additionally, the second inlet stage is arranged to provide the boundary layer between the iron fuel suspension medium and walls of the burner arrangement and the combustion chamber for preventing iron fuel deposition at one or more of these walls.

In an example, said fuel feeder is arranged for axial supply of iron fuel in said combustion chamber, wherein said iron fuel is provided in a transport medium. Also, preferably, the first and/or second inlet stage may be configured for tangential and/or axial inlet of air. More preferably, the first inlet stage may be configured for tangential air inlet.

In an example, one or more of said first and second inlet stage comprise at least two air inlets disposed tangentially in the circumference wall of said burner arrangement.

In an example, one or more of said first and second inlet stage comprise at least one air inlet disposed coaxially in the circumference wall of said burner arrangement.

In an example, one or more of said first and second inlet stage comprise at least two air inlets disposed at an angle with said wall of said burner arrangement.

In an example, one or more of said first and second inlet stage comprises a plurality of guide vanes disposed on said burner arrangement wall for providing said boundary layer.

In an example, said plurality of guide vanes are adjustable.

In an example, one or more of said first and second inlet stage comprise multiple groups of air inlets distributed along a longitudinal axis of said burner arrangement.

In an example, a wall of one or more of said first and second inlet stage or a section of a wall between air inlets of one or more of said first and second inlet stage along a longitudinal axis is diverging, converging or parallel.

In an example, one or more of said air inlets of one or more of said first and second inlet stage are comprised in an airbox housing.

In an example, one or more air inlet ports of said air inlets of one or more of said first and second inlet stage are connected to an air duct. In an example, said first inlet stage has an at least approximately cylindrical cross-section.

In an example, said second inlet stage has a circular or polygon shaped cross-section.

In an example, said combustion chamber has a cylinder or polygon three-dimensional shape, or a three-dimensional shape defining a transition across a longitudinal direction from a circular shape to a polygon or more preferably rectangular shape, or vice versa.

In an example, said second inlet stage comprises a baffle plate for central recirculation of in said arrangement, and for improving the flow direction to prevent iron fuel deposition at said walls.

In an example, said combustion chamber comprises in a first section of said combustion chamber: an igniter for igniting said iron fuel suspension medium at said combustible condition in said combustion chamber, and wherein said igniter is preferably an electrical igniter or a chemical igniter.

In an example, said ignitor extends up to said combustion interface.

In an example, said ignitor extends up to said combustion interface, and wherein said second inlet stage comprises at least two air inlets disposed in the circumference wall of said burner arrangement, and said ignitor is disposed beyond at least one of said two air inlets of said second inlet stage.

In an example, said ignitor is configured to ignite said combustible medium at or beyond said combustion interface in a startup phase, and wherein said iron fuel combustion arrangement is arranged for self-ignition during an operational phase. In an example, said second inlet stage comprises: a pre-heating element for pre-heating said iron fuel suspension medium to create said iron fuel suspension medium to be brought to said combustible condition, and wherein said pre-heating element is preferably an electrical heating element or a chemical heating element.

In an example, said combustion chamber comprises a first and a second section, wherein said second section is disposed downstream of said first section, and wherein one or more of said first and second section comprise film air inlet means, wherein said film air inlet means being disposed in a wall of said combustion chamber and arranged to provide a boundary layer between said iron fuel suspension medium and walls of said combustion chamber for preventing iron fuel deposition at said walls of said combustion chamber.

In an example, any one or more of the air inlets and fuel feeder is connected to an output of said combustion chamber for recirculation of flue gas into said combustion chamber, and wherein said iron fuel combustion arrangement further preferably comprises a filter downstream of said combustion chamber for filtering combusted medium from said iron fuel suspension medium.

In an example, the iron fuel combustion arrangement further comprises: an iron fuel tank, connected with said fuel feeder for storage of said iron fuel. an iron fuel feeding system, connected with said iron fuel tank and said fuel feeder for mixing said iron fuel with said transport medium.

In an example, any one or more of the fuel feeder and the one or more air inlets comprise a control valve for control of the supply of air of said respective inlet.

In an example, any one or more of the fuel feeder and the one or more air inlets are arranged for supply of air of said respective inlet at a raised temperature, which raised temperature is preferably below a sintering temperature of said iron fuel suspension medium.

The invention will now be described in more detail by means of specific embodiments, with reference to the enclosed drawings, wherein equal or like parts and/or components are designated by the same reference numerals. The invention is in no manner whatsoever limited to the embodiments disclosed herein.

Brief description of the Drawings

Fig. 1 shows a schematic overview of an iron fuel combustion arrangement;

Fig. 2 shows a cross-sectional view of an iron fuel combustion arrangement according to an aspect of the present disclosure;

Fig. 3-5 show cross-sectional views of air inlets according to an aspect of the present disclosure;

Fig. 6 shows a cross-sectional view of an example of an iron fuel combustion arrangement according to an aspect of the present disclosure;

Fig. 7 shows a cross-sectional view of another example of an iron fuel combustion arrangement according to an aspect of the present disclosure.

Detailed Description

Fig. 1 shows a schematic overview of an iron fuel combustion arrangement 10 according to the present disclosure. The combustion arrangement 10 comprises several components which are divided over several sections of the arrangement.

The iron fuel combustion arrangement comprises a burner arrangement 12, 13 and a combustion chamber 14 and is thus typically divided into section A and section B, representing the burner arrangement and combustion chamber. Upstream 11 of said burner arrangement 12, 13 there can be further components such as a feeder mixing arrangement which mixes the iron powder and a transport medium, which components are not shown in the figures. Also, downstream 15 of the combustion chamber 14 there can be further components such as a product area or after chamber, or a separation unit, which components are also not shown in the figures. These product area and separation unit are arranged to discharge the rust from the chamber and/or to separate the flue gases from the chamber.

The burner arrangement 12, 13 has several segments and comprises at least one segment 12, 13 in which the shape widens towards said combustion chamber. The widening of the burner can be achieved in several manners. The housing of the burner arrangement 13, near the combustion chamber 14, may be cone shaped, but other shapes may also apply. In particular the fuel feeder, 12 in the first segment of the burner arrangement may preferably be cylinder shaped, and the combustion chamber 14 is preferably cylindrical, cube shaped, or cuboid shaped. A segment of the burner arrangement 13 may be shaped such that a transition is provided from the shape of the fuel feeder 12, e.g. cylinder shaped, towards the shape of the combustion chamber 14, e.g. cube or cuboid shaped. As such, the segment of the burner arrangement 13 may be defined as a circle to square transition box.

The burner arrangement 12, 13 and the air inlet means are configured such that the iron powder can be combusted in the combustion chamber 14, beyond a combustion interface 16, which is in Fig. 1 shown as a circular segment but which in a three-dimensional geometry preferably is a circular section, depending on the shape of the burner arrangement and/or the combustion chamber.

In Fig. 2 a first example is shown of a cross-section of an iron fuel combustion arrangement according to the present disclosure. The combustion arrangement comprises a combustion chamber and a burner arrangement as shown in Fig. 1 and defined by A and B, respectively. The combustion chamber is arranged for combustion of iron fuel which is fed from a fuel feeder 21. The iron powder in the fuel feeder mixes with air from air inlets 22, 22a, 22b, 22c, 22d to create what is defined as an iron fuel suspension medium which comprises at least the iron fuel in the form of the iron powder, and oxygen, both in such a mixture and under such conditions that, eventually in the combustion chamber, beyond the combustion interface 16, the medium can be combusted. To this end, the composition of the medium, the temperature, velocity and preferably also pressure define when, where and if the combustion conditions are reached. T o this end, the amount of iron powder, the speed, pressure and temperature of the iron fuel from the fuel feeder 21 as well as the amount of oxygen in the air, and the temperature, pressure and velocity of the air provided by the air inlet means 22, are controlled such the combustion conditions are reached in the combustion chamber, at or beyond the combustion interface 16.

The iron powder is supplied trough a fuel feeder 21 , in which the iron fuel is supplied in the form of a suspension medium in which the iron powder is mixed with a transport medium such as air or gaseous medium comprising one or more of oxygen, nitrogen or other components.

Once the iron powder exits the feeder, it is directed towards the combustion chamber with a certain speed. The iron powder, when mixed with air from the air inlet means 22, is defined as an iron fuel suspension medium. The iron fuel suspension medium may be supplied in the burner arrangement such that the medium achieves a certain swirl pattern which according to the present disclosure comprises a rotational component to the medium flow. The swirl may be achieved by the shape of the fuel feeder, or by additional means added to the fuel feeder, the supply upstream of the feeder or by means added at or near the output of the fuel feeder, e.g. achieved by a baffle plate. The baffle plate or baffle for short, may provide or add to the direction of the air flow and/or the combustible medium.

With the swirl pattern, turbulence is added to the iron fuel suspension medium which improves the mixing of the iron powder and the oxygen in the air. The swirl may also increase the flow rate of the medium.

The swirl pattern of the iron fuel suspension medium is at least mostly provided by the air inlet means 22. When the fuel feeder 21 is arranged to provide the swirl pattern, the air inlet means 22 will further enhance the swirl, but in case the fuel feeder 21 supplies the iron fuel suspension medium in a more conventional manner, the air inlet means 22 will provide the swirl effect.

The air inlet means 22 cover all air inlet ports 22a, 22b, 22c, 22d as shown and located in the burner arrangement A, 12, 13 as shown in Fig. 1 .

The air inlet means are arranged for supply of air comprising the oxygen and the means 22 comprise a first and a second inlet stage. The first inlet stage is arranged for the iron fuel suspension medium from said fuel feeder 21 to swirl towards the combustion chamber as shown in Fig. 2. The second inlet stage is arranged for the iron fuel suspension medium to be brought into a combustible condition beyond the combustion interface 16 as shown in Fig. 2.

The second inlet stage is also arranged to provide a boundary layer between the iron fuel suspension medium and walls of the burner arrangement and the combustion chamber. What is meant with boundary layer in the present disclosure, is that the iron fuel suspension medium is guided towards the combustion chamber in such a way that no or at least less iron fuel deposition takes place at these walls of the burner arrangement, A, and/or the walls of the combustion chamber, B.

According to the present disclosure, the first inlet stage may comprise the first air input ports 22a, 22b which are located closest to the fuel feeder. In such an embodiment, the air inlet ports 22a, 22b of the first inlet stage provide for the same medium characteristics such as temperature, oxygen content, velocity and pressure.

The first inlet stage is arranged to provide the swirl pattern, which is achieved by the configuration of the inlet stage or more particularly the air inlet ports 22a, 22b thereof. These inlet ports are positioned tangentially in the circumference wall of the burner arrangement. The first inlet stage to this end may have a tangential configuration of 2, 3, 4, 5 or more air inlet ports. Although not preferred, one or more of these inlet ports may also have an off-set towards the middle. In a transverse direction of the burner arrangement these air inlet ports may be positioned perpendicular or mostly perpendicular to the longitudinal direction of the burner arrangement, but alternatively, these may also be arranged at an angle such that the air injected into the burner arrangement is supplied in a direction with a forward component. The angle may be provided in longitudinal direction of the burner arrangement but also in the transverse direction thereof, or even in a combination of both.

The swirl pattern may however also be achieved by a different configuration of the first inlet stage, in which the air inlet is disposed coaxially in the circumference wall of the burner arrangement. In such a configuration the air inlet may be provided as a single, ring-shaped coaxial air inlet, but also as a plurality of air inlets disposed and distributed coaxially along the circumference wall of the burner arrangement.

Figures 3, 4 and 5 show different examples of air inlet means, e.g. the air inlet means of the first inlet stage. In Fig. 3 a tangential configuration is shown having two inlet ports 22a, 22b, whereas in Fig. 4 a similar configuration is shown but with three inlet ports, 22a, 22b, 22c. The configuration in Fig. 5 shows the coaxial placed inlet stage in which the iron fuel suspension medium is brought into a swirl pattern swirling from the fuel feeder 21 towards the combustion chamber.

The second inlet stage, as shown in figure 2 with reference 22c, 22d, is arranged for the iron fuel suspension medium to be brought into a combustible condition. What that means is that the oxygen and iron powder is mixed at a desired ratio and in which preferably also certain desired velocity, pressure and temperature of the medium is reached. The air inlet velocity is preferably in the range between 10 and 100meter per second [m/s], more preferably between 20 and 60 m/s. The temperature is preferably in the range between 25 (ambient) and 300 degrees Celsius [°C], more preferably between 60 and 200 degrees Celsius [°C]. The second inlet stage 22c, 22d, is arranged such that the medium can reach a combustible condition not at the first inlet stage 12, not at the second inlet stage 13, both shown in figure 1 , but in the combustion chamber B, 14 downstream of the combustion interface 16.

The second inlet stage 22c, 22d, not only brings the iron fuel suspension medium into a combustible condition beyond a combustion interface 16 in the combustion chamber 14, but also provides a boundary layer between the iron fuel suspension medium and walls of the burner arrangement A, 12, 13, and the combustion chamber B, 14, 15 for preventing iron fuel deposition at any one or more of these walls.

The second inlet stage is in figure 2 shown and embodied as a second pair, 22c, 22d of inlet ports which are disposed tangentially in the circumference wall of the burner arrangement A. It is however emphasized that this is merely an example, as these may also be embodied differently, for example in the form of a coaxially disposed inlet which is arranged in the circumference e of the wall of the burner arrangement. Also, a variant may be embodied in which the second inlet stage is configured by inlet ports disposed at an angle with the wall of the burner arrangement. Moreover, these embodiments may also be combined into a combination of inlet ports having different configurations and/or in which the second inlet stage comprises for example two groups of inlet ports as shown in figures 6 and 7. A groups of air inlet ports can be defined as those inlet ports providing the same characteristics into the combustion chamber or the burner arrangement, e.g. in which inlet ports provide air at any one or more of the same angle into the chamber, the same velocity, pressure and temperature.

The air inlet ports of the first and/or of the second inlet stage may not only have different configurations in terms of positioning at or near the wall of the burner arrangement, but may also have different shapes and can for example be configured as a pipe, a hole in the wall or comprise guide vanes to force the air into a desired direction. Also the shape or geometry of the inlet ports may be constant in longitudinal direction, or may be diverging or converging, and may also be configured to achieve a venturi-effect in which the velocity of the air is increased due to the a decrease in cross-sectional area or diameter of the inlet. The guide vanes may be configured to direct the air stream into a desired direction and has the advantage that the desired direction of air flow can be configured in an efficient and relative simple manner. By selection of material, shape, location and amount, a highly configurable air flow can be achieved. The guide vanes may not only be configured to direct the air into a certain desirable direction, but also to add rotation to the air stream, e.g. to provide or add to the swirl of the air stream.

The wall of the burner arrangement may also have different longitudinal shapes. In particular the wall sections of the first and/or the second stage in between the inlet ports may be consistent in longitudinal direction or may be diverging or converging towards the combustion chamber, alternatively, these may also be stepped or staged. Various examples are for shown in the figures 6 and 7, in which the wall sections are staged or stepped by discrete steps in increasing diameter towards the combustion chamber, as shown in figure 6, and an example in which the wall sections have a diverging geometry.

The longitudinal distance between the inlet ports may be constant but may also differ per group or even per port.

The burner arrangement 12, 13 and in particular the shape thereof configured to have a cross-section as a cylinder, or a polygon. The combustion chamber 14 may also have a cylindrical or polygon shaped cross-section, or a crosssection which consists of a transition from a cylinder to a polygon or vice versa, e.g. to provide a transition between the shape of the burner arrangement and the combustion chamber. The burner arrangement itself may also have a cross-section which consists of a transition from a cylinder-shaped part of the feeder 12 to a polygon shaped cross-section of the first/second stage.

Figure 6 and figure 7 show alternative embodiments with several differences in the features of the iron fuel combustion arrangement according to the present disclosure. Especially the air inlet means, and the shape of the wall sections differ between the two examples. For example, in figure 6 the air inlet means comprise six main air inlet ports 22a, 22b, 22c, 22d, 22e, 22f, belonging to the first and second stage of the burner arrangement. The first inlet stage comprises two inlet ports 22a, 22b, which provide the swirl to the iron fuel suspension medium, and the second inlet stage comprises two groups 22c, 22d and 22e, 22f of inlet ports which provide the boundary layer between the iron fuel suspension medium and walls of the burner arrangement and the combustion chamber to prevent iron fuel deposition at the walls. In the example shown in figure 6, each of the inlet ports are disposed tangentially to provide for a swirl, wherein the first ports 22a, 22b, create the swirl form the cylindrically shaped feeder 21 , whereas the other ports 22c, 22d, 22e, 22f, of the second inlet stage provide a further swirl effect to such a degree that the iron fuel suspension medium to is directed towards the combustion chamber in such a way that the medium still diverges but to a less degree than the diverging longitudinal cross-sectional shape of the walls of the burner arrangement such that the iron fuel suspension medium to is deflected from the wall of the burner arrangement but also from the walls of the combustion chamber.

In figure 6 the combustion chamber also shows additional air inlet ports 24a, 24b which provide a further input of air into the combustion chamber and to provide for a boundary layer between the iron fuel suspension medium and walls of the combustion chamber, also to prevent iron fuel deposition at the walls of the combustion chamber.

In figure 7 the inlet ports are configured differently than those in figure 6. In figure 7 the first inlet stage is defined by the ports disposed tangentially, 22a, 22b, 22c, 22d, 22e, 22f. The second inlet stage is defined by the inlet port 22g, which is configured as a single coaxial inlet.

Further the wall of the second stage of the air inlet means is also different as compared to figure 6, as these show a more gradient transition in increase of diameter of the second stage, whereas the example shown in figure 6 shows a stepped increase in diameter.

The additional air inlet means 24a, 24b may also comprise more inlet ports than those shown in the examples of figures 6 and 7 as these may also be disposed and distributed along a longitudinal direction over the wall of the combustion chamber. Moreover, these may also have different shapes and configurations in accordance with the examples described in relation to inlet ports of the first and/or second stage. Based on the above description, a skilled person can provide modifications and additions to the method and arrangement disclosed, which modifications and additions are all comprised by the scope of the appended claims.