Iron fuel combustion arrangement

Abstract

The present invention therefore relates to an iron fuel combustion arrangement comprising a combustion chamber for combusting a combustible medium comprising iron fuel to provide a combusted medium comprising iron oxide and a separation unit downstream of said combustion chamber for filtering iron oxide from said combusted medium. Said combustion chamber includes radiative and / or convective heat exchange. Said iron fuel combustion arrangement further comprises a cooling section located downstream of said combustion chamber and upstream of said separation unit. Said cooling section comprises first air inlet means providing air having a temperature below the temperature of said combusted medium comprising iron oxide for cooling said combusted medium comprising iron oxide. Said cooling section comprises a converging portion arranged to increase the speed of said combusted medium comprising iron oxide passing from said combustion chamber to said separation unit to increase homogeneity of said combusted medium comprising said air provided by said first air inlet means.

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 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 integrating an iron fuel combustion arrangement in existing buildings where the space for a combustion arrangement may be limited, or on location where the height of the total installation is limited for example due to local regulations. The known iron fuel combustion arrangements can be quite large due to the required length of the combustion chamber to maximize heat exchange.

[0012] Therefore, there is a need for an iron fuel combustion arrangement that provides an improved balance between dimensions of the combustion arrangement and efficiency of the arrangement.

[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 balance between dimensions of the combustion arrangement and efficacy of the arrangement.

[0016] The present invention therefore relates to an iron fuel combustion arrangement comprising a combustion chamber for combusting a combustible medium comprising iron fuel to provide a combusted medium comprising iron oxide and a separation unit downstream of said combustion chamber for filtering iron oxide from said combusted medium. Said combustion chamber includes radiative and / or convective heat exchange. Said iron fuel combustion arrangement further comprises a cooling section located downstream of said combustion chamber and upstream of said separation unit. Said cooling section comprises first air inlet means providing air having a temperature below the temperature of said combusted medium comprising iron oxide for cooling said combusted medium comprising iron oxide. Said cooling section comprises a converging portion arranged to increase the speed of said combusted medium comprising iron oxide passing from said combustion chamber to said separation unit to increase homogeneity of said combusted medium comprising said air provided by said first air inlet means.

[0017] The present disclosure relates to an arrangement for a combustion process for iron fuel combustion. The inventors have found that the known arrangement for combustion processes which are suitable for example for combustion of coal, coal-like material, waste and biomass are not suitable or less suitable for the combustion of iron fuel. For combustion iron fuel, specific design requirements are applicable which are different from these known arrangements.

[0018] Combustion of iron fuel has different chemical and physical properties when compared to conventional fuels. Another 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. 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.

[0019] The inventors have found that the addition of air having a temperature below the temperature of the combusted medium comprising iron oxide allows for faster cooling of said combusted medium comprising iron oxide.

[0020] When relatively cool air is added to the combustion chamber during combustion, it is necessary that this cooler air mixes with the hotter combusted medium. The inventors have found that the presence of a converging portion downstream of the first air inlet means causes an increase in the speed of the combusted medium. This increase in speed enhances the mixing of the added air with the already present combusted medium. Thus, it increases the homogeneity of the combusted medium comprising the air provided by the first air inlet means.

[0021] The presence of the converging portion to increase the homogeneity greatly reduces the residence time of the combusted medium that is required for sufficient cooling of the combusted medium. In particular, it is desirable that the iron oxide particles comprised in the combusted medium reach a temperature that is below their sintering temperature at the separation unit. This also means that the mixing length can be shortened, leading to a more compact (less tall in the case of a vertical arrangement) combustion chamber.

[0022] By the addition of relatively cool air compared to the combusted medium, part of the heat of the iron oxide containing medium may be unutilized in the heat-exchange (i.e. the heat-exchange in the combustion chamber may be suboptimal). However, the additional cooling allows for achieving a temperature range of the iron oxide containing medium at the separation unit that allows for recovery of the iron oxide in higher quantity and / or higher quality (e.g. particle size distribution) than when the temperature of the iron oxide at the separation unit would be outside of this range. This contributes to an overall optimization of the iron fuel process, since the iron oxide can be reduced into iron fuel and be combusted again.

[0023] The inventors have surprisingly found that the combination of air inlet means to provide relatively cool air and a converging portion to enhance the mixing of this cool air with the combusted medium comprising iron oxide (and the variations possible with e.g. the amount and temperature of the air and the angle and length of the converging portion) provide a system that can be used to balance the efficacy of the combustion arrangement with the available or desired dimensions of the arrangement.

[0024] Thus, in the boiler process realised with the iron fuel combustion arrangement according to the present invention both heat-exchange and cooling take place. After combustion of the iron fuel, an iron oxide containing medium is transferred through the combustion chamber towards a separation unit disposed downstream of the combustion chamber. During the transfer of the iron oxide containing medium, heat-exchange takes place with a heat-exchange medium. In addition, the iron oxide containing medium is cooled with a cooling medium in the cooling section, during the transfer towards to the separation unit. This, desirably, results in a temperature of the iron oxide of below the sintering temperature of the particles at said separation unit. This temperature allows separation of the iron oxide from the gas flow and thus collecting obtained iron oxide in high quantity and quality.

[0025] It was further found that by the addition of additional air to the combusted medium, the particle density is decreased. This leads to a reduced load in the downstream components of the combustion arrangement, leading to less wear on components and thus extended life span of the arrangement.

[0026] EXAMPLES

[0027] Within the combustion chamber, there may be a first section for combustion of the iron fuel, and a second section wherein the iron fuel combustion is completed, and wherein there are stable conditions for heat exchange. Heat exchange may take place in at least a part of the first and / or second section. Generally, it is preferred that heat exchange takes with a heat exchange medium takes place in at least a part of the second section.

[0028] In an example, said air provided by said first air inlet means has a temperature below the sintering temperature of iron oxide particles

[0029] In a further example, said air provided by said first air inlet means has a temperature below 800 °C, preferably below 500 °C, more preferably below 200 °C The temperature may also be below 50°C or below 30°C.

[0030] Iron oxide particles that come into contact with a wall surface may stick to the wall surface (slagging), specifically when the temperature of the iron oxide is above the sintering temperature of the particles. The sintering temperature is defined as the initial temperature where particles start to sinter to each other. The definition of this temperature is stated by ISO 3252:1999. Tests for determining this temperature for iron fuel are known as dilatometry, and are performed by the following standards: DIN51045 I ASTM E831 (2019) and ASTM E228 (2017), the name for the tests is dilatometry. This temperature may be 700°C, but it may also be higher, such as 800°C. This leads to contamination of the combustion arrangement, as well as loss of iron oxide. It should be understood that it is possible that not all iron fuel particles are fully converted into iron oxide particles during combustion. The term “iron oxide particles” is to be understood in the context of the present description to mean that the vast majority of the particles are iron oxide particles, but some non-oxidized or partly oxidized particles may be present.

[0031] In a further example, said converging portion forms an inclination angle a in respect of the longitudinal axis x of the iron fuel combustion arrangement. In a specific example, said inclination angle a is between 45 and 60 degrees.

[0032] This angle is selected such that recirculation of currents is minimized. The optimum angle may depend on the angle of the air inlets in the forward direction. The greater the angle a, the higher the increase in speed of the combusted medium. A greater speed leads to better homogenization of the combusted medium comprising the air provided by the first air inlet means. However, a greater angle a may lead to more deposition of particles on the walls of the converging portion.

[0033] In a further example, the smallest diameter of the cooling section is 25-99% of the largest diameter of the combustion chamber. The smallest diameter of the cooling section may for instance be 25-60%, or 30-40% of the largest diameter of the combustion chamber. When the smallest diameter is small compared to the diameter of combustion chamber, it may lead to higher speeds. This may need to be avoided, such that sufficient residence time and proper mixing can be achieved, as well as deposition of particles on the walls of the converging portion may be minimized. It may also lead to a too high density of the iron oxide mixtures that may result in agglomeration, slagging and fouling issues downstream of the combustion equipment. On the other hand, when the difference between the diameters is small, a smaller the increase in speed of the combusted medium due to the converging portion will occur.

[0034] In a further example, said cooling section comprises a throat portion positioned downstream of said converging portion.

[0035] In a further example, said cooling section further comprises second air inlet means downstream of said first air inlet means, arranged to provide a boundary layer between said combusted medium comprising iron oxide and walls of said converging portion for preventing iron oxide deposition at said walls. What is meant with boundary layer in the present disclosure, is that said combusted medium comprising iron oxide is guided towards the separation unit in such a way that no or at least less iron oxide deposition takes place at these walls of the converging portion. It may also lead to less deposition of iron oxide to the walls of the throat portion. In addition, the boundary layer may prevent or reduce degradation of iron oxide particles.

[0036] In a further example, said second air inlet means are further arranged for cooling said combusted medium. This means that they are arranged for providing air having a temperature below the temperature of said combusted medium comprising iron oxide. At least some of the air provided in the boundary layer will interact or mix with the combusted medium, and a lower temperature of this air may thus contribute to further cooling of the combusted medium.

[0037] In a further example, said first and / or second air inlet means comprise at least two air inlets disposed tangentially or radially in the circumference wall. The first and / or second air inlet means may comprise for example 2-100 air inlets, for instance at least four or at least six inlets. These inlets may be evenly distributed across the circumference of the cooling section.

[0038] In a further example, said first and / or second air inlet means comprise at least two air inlets angled in a forward direction. When the air inlets are angled in a forward direction, i.e. in a downstream direction, the air will stay closer to the wall of the converging portion and optional throat portion and less mixing will take place with the combusted medium. This is particularly preferred for the air inlets of the second air inlet means for the formation of a boundary layer.

[0039] In a further example, said first and / or second air inlet means are for providing environmental air. The environmental air may be conditioned e.g. to reduce moisture content.

[0040] In a further example, any one or more of said first and / or second air inlet means is connected to an output of said combustion arrangement for recirculation of flue gas into said cooling section. This recirculated flue gas may have a higher temperature than environmental air, for example the temperature may be around 200°C. The recirculated flue gas may be filtered prior to entry into the combustion chamber.

[0041] In a further example, said first and / or second air inlet means comprise one or more air inlets and one or more control valves for control of the supply of air of a respective air inlet of said air inlets.

[0042] In a further example, said combustion chamber and / or said cooling section has a circular or polygon shaped cross-section, or a cross-section which consists of a transition from a circular to a polygon or vice versa.

[0043] In a further example, any one or more of said first and / or second air inlet means are comprised in an airbox housing. This airbox housing is a housing arranged to distribute the air to be provided between the individual air inlets.

[0044] 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.

[0045] 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.

[0046] BRIEF DISCRIPTION OF THE DRAWINGS

[0047] 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 the same or similar elements. The invention is in no manner whatsoever limited to the embodiments disclosed therein.

[0048] Fig. 1 shows a schematic example of the iron fuel combustion arrangement according to the present invention.

[0049] Fig. 2 shows another schematic example of the iron fuel combustion arrangement according to the present invention.

[0050] DETAILED DESCRIPTION

[0051] The present invention is elucidated below with a detailed description. In Fig. 1 , a schematic overview of the iron fuel combustion arrangement 100 according to the present invention is shown. The iron fuel combustion arrangement 100 comprises a burner arrangement 110, a combustion chamber 120 for combusting a combustible medium comprising iron fuel, and a separation unit 130 downstream of said combustion chamber for filtering iron oxide from said combusted medium.

[0052] The combustion chamber 120 is positioned downstream of the burner arrangement 110.

[0053] The iron fuel combustion arrangement 100 further comprises a cooling section 130 located downstream of the combustion chamber and upstream of the separation unit.

[0054] The cooling section 140 comprises first air inlet means 150 providing air having a temperature below the temperature of the combusted medium comprising iron oxide for cooling the combusted medium comprising iron oxide. For example, the air provided by the first air inlet means 150 has a temperature below the sintering temperature of iron oxide particles. The air provided by said first air inlet means 150 may for instance have a temperature below 800 °C, below 500 °C, below 200 °C, below 50°C, or even below 30°C.

[0055] The cooling section 140 further comprises a converging portion 160 arranged to increase the speed of the combusted medium comprising iron oxide passing from the combustion chamber 120 to the separation unit 130 to increase homogeneity of the combusted medium comprising the air provided by the first air inlet means 150.

[0056] In Fig. 1 , the first air inlet means 150 are positioned in the circumference wall of the cooling section 140, positioned upstream of the converging portion 160. The skilled reader will appreciate that the first air inlet means 150 can also be positioned in the circumference wall of the converging portion.

[0057] The cooling section 140 further comprises second air inlet means 155 downstream of the first air inlet means 150. In Fig. 1 , the second air inlet means 155 are positioned in the circumference wall of the cooling section 140, positioned upstream of the converging portion 160. The skilled reader will appreciate that the second air inlet means 155 can also be positioned in the circumference wall of the converging portion. The second air inlet means 155 are arranged to provide a boundary layer between the combusted medium comprising iron oxide and walls of the converging portion 160 for preventing iron oxide deposition at the walls. The second air inlet means 155 are further arranged for cooling the combusted medium comprising iron oxide.

[0058] The first air inlet means 150 and / or second air inlet means 155 may be configured for providing environmental air.

[0059] The first air inlet means 150 and / or the second air inlet means 155 comprise at least two air inlets disposed tangentially or radially in the circumference wall of the cooling section 140.

[0060] In the iron fuel combustion arrangement 100 shown in Fig. 1 , the second air inlet means 155 of the cooling section 140 comprise at least two air inlets angled in a forward direction. The forward-angled at least two air inlets may protrude into the cooling section 140, which leads to improved prevention of iron oxide deposition at the walls, improved cooling of the combusted medium comprising iron oxide, and / or improved gas flow in general. The first and / or second air inlet means 150, 155 may be for providing environmental air. One of said second air inlet means 155 is connected to an output 180 of said combustion chamber for recirculation of flue gas into said cooling section.

[0061] The cooling section 140 further comprises a throat portion 165 positioned downstream of the converging portion 160.

[0062] The cooling section 140 has a smallest diameter in the converging portion 160 and / or the throat portion 165. The smallest diameter is 25-99% of the largest diameter of the combustion chamber 120.

[0063] The converging portion 160 forms an inclination angle a in respect of the longitudinal axis x of the iron fuel combustion arrangement. The angle a is between 45 and 60 degrees.

[0064] The combustion chamber 120 as shown in Fig. 1 has a shape that is straight, thus has a cylindrical (or prism) shape. However, the shape combustion chamber 120 may also widen in the upstream or downstream direction, thus may have a conical (or frustrum) shape.

[0065] Fig. 2 shows another schematic example of the iron fuel combustion arrangement according to the present invention. Fig. 2 is identical to Fig. 1 except that there are no first and second air inlet means 150 and 155 in the cooling section 140. In the example of Fig. 2, the cooling section 140 comprises air inlet means 255. In Fig. 2, the air inlet means 255 are positioned in the circumference wall of the cooling section 140, positioned upstream of the converging portion 160. The skilled reader will appreciate that the air inlet means 255 can also be positioned in the circumference wall of the converging portion.

[0066] The air inlet means 255 are arranged to provide a boundary layer between the combusted medium comprising iron oxide and walls of the converging portion 160 for preventing iron oxide deposition at the walls. The air inlet means 255 are further arranged for cooling the combusted medium comprising iron oxide.

[0067] The air inlet means 255 may be configured for providing environmental air.

[0068] The air inlet means 255 comprise at least two air inlets disposed tangentially or radially in the circumference wall of the cooling section 140.

[0069] In the iron fuel combustion arrangement 100 shown in Fig. 1 , the air inlet means 255 of the cooling section 140 comprise at least two air inlets angled in a forward direction. The forward-angled at least two air inlets protrude into the cooling section 140, which leads to improved prevention of iron oxide deposition at the walls, improved cooling of the combusted medium comprising iron oxide, and / or improved gas flow in general. The air inlet means 255 may be for providing environmental air. One of said air inlet means 255 is connected to an output 180 of said combustion chamber for recirculation of flue gas into said cooling section.

[0070] 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 (100) comprising a combustion chamber (120) for combusting a combustible medium comprising iron fuel to provide a combusted medium comprising iron oxide and a separation unit (130) downstream of said combustion chamber for filtering iron oxide from said combusted medium, wherein said combustion chamber includes radiative and / or convective heat exchange wherein said iron fuel combustion arrangement further comprises a cooling section (140) located downstream of said combustion chamber and upstream of said separation unit, wherein said cooling section comprises first air inlet means (150) providing air having a temperature below the temperature of said combusted medium comprising iron oxide for cooling said combusted medium comprising iron oxide; wherein said cooling section comprises a converging portion (160) arranged to increase the speed of said combusted medium comprising iron oxide passing from said combustion chamber to said separation unit to increase homogeneity of said combusted medium comprising said air provided by said first air inlet means.

2. Iron fuel combustion arrangement according to claim 1 , wherein said air provided by said first air inlet means has a temperature below the sintering temperature of iron oxide particles.

3. Iron fuel combustion arrangement according to claim 1 or 2, wherein said air provided by said first air inlet means has a temperature below 800 °C, preferably below 500 °C, more preferably below 200 °C, even more preferably below 50°C, most preferably below 30°C.

4. Iron fuel combustion arrangement according to any of the preceding claims, wherein said converging portion forms an inclination angle a in respect of thelongitudinal axis x of the iron fuel combustion arrangement, preferably wherein said inclination angle a is between 45 and 60 degrees.

5. Iron fuel combustion arrangement according to any of the preceding claims, wherein the smallest diameter of said cooling section is 25-99% of the largest diameter of said combustion chamber.

6. Iron fuel combustion arrangement according to any of the preceding claims, wherein said cooling section comprises a throat portion (165) positioned downstream of said converging portion.

7. Iron fuel combustion arrangement according to any of the preceding claims, wherein said cooling section further comprises second air inlet means (155) downstream of said first air inlet means, arranged to provide a boundary layer between said combusted medium comprising iron oxide and walls of said converging portion for preventing iron oxide deposition at said walls.

8. Iron fuel combustion arrangement according to claim 7, wherein said second air inlet means are further arranged for cooling said combusted medium.

9. Iron fuel combustion arrangement according to any of the preceding claims, wherein said first and / or said second air inlet means comprise at least two air inlets disposed tangentially or radially in the circumference wall of said cooling section.

10. Iron fuel combustion arrangement according to any of the preceding claims, wherein said first and / or said second air inlet means comprise at least two air inlets angled in a forward direction.

11. Iron fuel combustion arrangement according to any of the preceding claims, wherein said first and / or said second air inlet means are for providing environmental air.

12. Iron fuel combustion arrangement according to any of the preceding claims, wherein any one or more of said first and / or said second air inlet means are connected to an output (180) of said combustion arrangement for recirculation of flue gas into said cooling section.

13. Iron fuel combustion arrangement according to any of the preceding claims, wherein said first and / or said second air inlet means comprise one or more control valves for control of the supply of air of said respective inlet.

14. Iron fuel combustion arrangement according to any of the previous claims, wherein any one or more of said first and / or said second air inlet means is comprised in an airbox housing.

15. Iron fuel combustion arrangement according to any of the preceding claims, wherein said combustion chamber and / or said cooling section has a circular or polygon shaped cross-section, or a cross-section which consists of a transition from a circular to a polygon shaped or vice versa.

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