NL2036153B1 - Burner and combustion method - Google Patents

Abstract

TITLE BURNER AND COMBUSTION METHOD The present disclosure relates to a burner and a method to combust a powder material from a group at least comprising metal and/or metalloid and/or alloy powders and iron powder. The burner comprises a chamber defining a space to accommodate a combustion flame and a powder material inlet, debouching at a base of the combustion flame in the space. Further the burner comprises at least one 10 air inlet into the combustion chamber, configured to generate a swirling inner airflow enveloping the combustion flame; and an outer airflow between the swirling inner airflow and an inside wall of the chamber. FIGURE SELECTED FOR FRONT PAGE PUBLICATION 15 FIGURE 1.

Description

BURNER AND COMBUSTION METHOD

FIELD

The present disclosure relates to the field of burners and methods to combust a powder material from a group at least comprising metal and/or metalloid and/or alloy powder and iron powder.

Practical implementations may comprise use in the energy sector, propulsion and power, industrial burners, boilers, water and waste treatments systems, the food industry, the mining industry, the chemical industry, and more.

BACKGROUND

Burners and methods in general are known, in particular for combusting metal powders and more in particular for combusting iron particles.

Fossil fuels are known to be unsustainable and damaging to the environment. Sustainable energy carriers, for example, hydrogen and ammonia, might provide a suitable alternative to fossil fuels. Some of the benefits of a combustion of hydrogen include that it does not produce carbon dioxide and that it is a sustainable carrier of energy. especially when produced with renewable energy.

Using hydrogen can therefore reduce carbon dioxide emissions. Hydrogen is also a clean carrier of energy with reduced adverse side-effects to the environment since the production of hydrogen only requires water and electricity.

In the further development of hydrogen as an energy carrier, production, storage and use of hydrogen will play an important role. Currently, hydrogen is being delivered to sites with pipelines, as liquid hydrogen or as highly compressed gas. Transporting hydrogen as a cryogenic liquid or as compressed gas are capital and energy-intensive processes which result in an increase in the cost of hydrogen. Consequently, a need developed for a storage system that can store energy and which allows for ease of transportation thereof. Research has been done towards different ways of storing energy, including the use of reversible chemical reactions and absorption of hydrogen by various metals and metal alloys to form metal hydrides or ammonia.

In this case the focus is on the use of metal as an energy carrier in the quest to resolving the above-mentioned important missing elements in the energy transition to long-term and large-scale storage of sustainable energy without emission of carbon oxide or Re. In order to gain energy from metal as an energy carrier, the metal is being combusted to form metal oxide or dioxide. The delivered metal oxide may subsequently be reduced to the starting metal again in an energy consuming process that stores said energy. To ensure the sustainability of the process, the process needs to be a cyclic conversion process in which both combustion and reduction are repeatable, stable, and clean.

There remains a need for an oxidation/combustion process that is well controllable and stable, including controlled ignition of the metal. No process currently available allows for fast and highly efficient conversion of metal particles to easy-to-capture metal oxide particles with a minimal amount of fouling and with minimal loss of material. The available processes also do not provide for minimal unwanted emissions of pollutant gases, including carbon oxide dioxide, nitrogen oxide, or nanoparticles.

Particularly, using normal air at lean conditions, the combustion of metal powders results in ignited iron particles that burn extremely fast. As a consequence, particle temperatures may overshoot gas mixture temperatures to values that lead to excessive evaporation of the metal and metal oxide and, therefore, may lead to loss of mass of the individual metal particles. The evaporated metal or metal oxide mass finally ends up in smoke and nano-particle matter. This matter can be captured, for example, with absolute filters, to avoid smoke emissions but it might still lead to fast filter contamination and blockage. A portion of nanoparticles would be sedimented or deposited on an inside the burner and affect its performance. This mass cannot easily be used in subsequent steps of a reduction-combustion cycle. Excessive evaporation is therefore detrimental to this cycle in the recycling of metal powder.

SUMMARY

The system according to the present disclosure provides improvements over the prior art. In order to achieve this goal, a burner according to the present disclosure to combust a powder material from a group at least comprising metal and/or metalloid and/or alloy powder and iron powder comprises: - a chamber defining a space to accommodate a combustion flame; - a powder material inlet, debouching at a base of the combustion flame in the space; - at least one air inlet into the combustion chamber, configured to generate: * a swirling inner airflow enveloping the combustion flame; and * an outer airflow between the swirling inner airflow and an inside wall of the chamber.

In one embodiment the burner, further comprises a burnt powder discharge from the chamber.

Then, the burnt powder discharge may be arranged in the chamber opposite the powder material inlet, relative to the combustion flame.

In an additional or alternative embodiment, the bummer may further comprise an exhaust gas discharge. Then, the exhaust gas discharge may be arranged at the powder material inlet.

In an embodiment having the burnt powder discharge and the exhaust gas discharge, the burnt powder discharge and the exhaust gas discharge may be combined into a singular discharge.

In an additional or alternative embodiment, the combustion flame in the combustion chamber maybe is oriented downward from an upper end of the combustion chamber, wherein the powder material inlet may lead downward into the combustion chamber to the base of the combustion flame.

In an additional or alternative embodiment, the swirling inner airflow may flow in a direction extending from the powder material inlet along the combustion flame.

In an additional or alternative embodiment, the outer airflow may flow in a direction different from and preferably opposite to a flow direction of the swirling inner airflow.

In an additional or alternative embodiment, the outer airflow may swirl around the inner airflow between the swirling inner airflow and the inside wall of the chamber.

In an additional or alternative embodiment, the air inlet may be arranged opposite the powder material inlet relative to the combustion flame.

In an embodiment having the swirling outer airflow and the air inlet opposite the powder material inlet, the air inlet may be configured to generate the swirling outer airflow by at least tangential introduction into the chamber near the inside wall thereof. Alternatively, the air inlet may be arranged at the powder material inlet to generate the swirling inner airflow by at least approximate tangential introduction into the chamber.

In an additional or alternative embodiment, the air inlet may comprises an exhaust gas feedback to mix exhaust gas into at least one of the inner swirling airflow and the outer airflow, to reduce an oxygen concentration therein. Then, the air inlet may be controllable to set the oxygen concentration to a predetermined value. Preferably, the controlled oxygen concentration from the air inlet is as low as 5%, preferably 8%, but usually 5 to 15% oxygen concentration

In an additional or alternative embodiment, the burner may further comprise an inverter configured to invert the swirling inner airflow and convert the inverted inner airflow into the outer airflow.

In an additional or alternative embodiment, the burner may further comprise a guide configured to invert the outer airflow and convert the inverted outer into the swirling inner airflow.

In an additional or alternative embodiment, the burner may further comprise a separator between the swirling inner airflow and the outer airflow. Then, the separator may comprises an oxygen mixture supply assembly. and the oxvgen mixture supply assembly may comprise jets on at least one of the inside and the outside of the separator. Then, at least some of the jets may be connected to the air inlet. However, alternatively the oxygen mixture supply assembly may comprises an exhaust gas feedback, to which the jets are connected to mix exhaust gas into a further airflow from the jets, to set an oxygen concentration therein. Then, the air inlet is controllable to set the oxygen concentration to a predetermined value, and preferably, the controlled oxygen concentration from the air inlet is at least 12%, and preferably at least 15% oxygen concentration.

In embodiments with a separator, it may be generally cylindrical and connected to a likewise generally cylindrical injection port shield surrounding the powder material inlet and the air inlet. Then, the separator may have a diameter which is at least approximately 1,5 times larger than a diameter of the shield.

Further, the present disclosure relates to a method of combusting a powder material from a group at least comprising metal powder and iron powder, wherein the method comprises: - generating a combustion flame in a chamber;

- supplying a powder material at a base of the combustion flame; - generating a swirling inner airflow enveloping the combustion flame; and - generating an outer airflow between the swirling inner airflow and an inside wall of the chamber.

Thus, the above described burner may embody the method and provide a potential physical implementation thereof.

BRIEF DESCRIPTION OF THE DRAWING

In the appended drawing, embodiments of fluid heating systems and components thereof are shown in non-limiting embodiments, wherein the same or similar elements, components and functional aspects may be designated throughout the drawing with the same or similar reference signs and wherein:

FIG. 1 exhibits a schematic representation of a burner in a first embodiment of the present disclosure;

FIG’s. 2 and 3 exhibit perspective views of a detail of the embodiment in FIG. 1:

FIG. 4 exhibits a top view of the detail of the embodiment in FIG’s. 2 and 3; and

FIG. 5 exhibits a schematic representation of a bumer in a second embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Metal fuels, in particular though not exclusively iron powder, may well be a key solution for the large-scale and long-term storage and import of sustainable energy for industry and society in the near future, to prevent or reduce CO; emissions , and/or other types of greenhouse gasses. Hydrogen, ammonia, e-fuels, and high temperature salts are other candidates with important disadvantages, which disadvantages do not occur when using metal fuels, and iron powder in particular. In this regard, a novel and inventive approach to a self-sustainable metal combustion burner is presented in this disclosure.

Results of confidential testing show that a self-sustained iron flame can be established inside the bummer according to the present disclosure under low oxygen concentrations (~ 10% Oa) and for low overall equivalence ratios (~ 0.2), without any assisting extra heat sources. This finding 1s significant in mitigating the partial evaporation of metal particles and circumventing nano-particle formation and related mass losses. Moreover, the burner is based on a novel concept for the next generation of the metal firing burners with hardly any or preferably no CO; and very low or even no

NO, emissions. Moreover, implementing the concept in a laboratory setup showed satisfying results to significantly improve two major issues in the iron powder bumers. These issues are iron powder flame (self-)stabilization and uninterrupted operation of the burner by preventing the iron oxide sedimentation on an inner wall of the burner.

Prior art burner designs for combustion of fossil fuels (e.g. coal powder) were initially used to burn metal powder. However, these prior art burners exhibited poor flame stabilisation and deposition of iron oxide on an inner wall of the burner. Flame stabilization during plain iron powder combustion is, however, achievable with assistance, such as by a pilot burner, and iron oxide splashing and 5 subsequent sedimentation on the burner’s inner wall can be prevented through provision of only slightly more complex airflows, relative to the prior art.

In the present disclosure, a new concept is revealed for a metal combustion-based burner that can produce high thermal energy with no or hardly any carbon mono/dioxides and very low or no nitric oxides footprints. The proposed concept could improve the iron flame stabilization and prevent or at least reduce the iron oxide sedimentation on the inner surface of the bumer by establishing multiple flame regions and high velocity secondary air jets or airflows inside the combustion chamber of the burner and also rearranging the combustion air flow pattern inside the burner, so that flame stability and operability of the burner can be realized for a longer periods of time, which is required for practical applications. To this end, for all embodiments disclosed herein, an air jet or airflow explicitly means a flow of gas, containing sufficient oxygen for the metal or iron powder to combust or be oxidized.

FIG’s. 1 — 4 show a burner 15 in a first embodiment according to the present disclosure. A second embodiment of a bumer 30 according to the present disclosure is shown in FIG. 5.

In FIG’s. 1 — 4, burner 15 is configured to combust a powder material, and in particular, though not exclusively iron powder. To this end, burner 15 comprises a chamber 17 defining a space 16 to accommodate a combustion flame 4. In this embodiment, chamber 17 is a mainly cylindrical and upright vessel or tank. Therein, space 16 is positioned inside an also mainly cylindrical and upright separator 18. It is noted here that separator 18 is optional. Further, burner 15 has a powder material inlet 1, debouching at a base of combustion flame 4 in space 16 inside separator 18 for iron powder to impinge against counter flow impingement 14, which can be defined alternatively as a ‘redirecting element’ or ‘flow deflector’ and is arranged at or near the end of powder material inlet tube 1, to scatter the iron powder particles. The counter flow impingement 14 can be embodied as a cone (as shown), a partial sphere, or any other suitable iron powder scattering or dispersing shape. The term “counter flow impingement” shall encompass redirecting elements for redirecting the particle flow in various suitable directions, including perpendicular or in a positive and negative angles compared with the flow 2. Powder material inlet 1 is oriented downward and combustion flame 4 extends downward from inlet 1, underneath counter flow impingement 14. Above a downward oriented open end of inlet 1, a pilot burner 2 is formed to contribute to flame stabilization and more in particular initial heating of the burner 15 and the inbound flow from powder material inlet 1.

At least one air inlet is provided to supply driver gas 11, for example outside air or any other suitable oxygen-containing gas mixture, into combustion chamber 16, and more in detail into pilot burner 2. In the shown embodiment, in particular in FIG’s. 2 — 4, the air inlet comprises four ejectors

10 that tangentially inject sucked-in outside air or another source of driver gas 11 (and optionally a portion 8 of exhaust gasses) into a mixing chamber confining pilot burner 2 via tangentially angled nozzles 12, to generate a swirling inner airflow 3 from inside the mixing chamber confining pilot burner 2, to swirl downward to envelop combustion flame 4 in swirling airflow 3 for stabilisation of flame 4 and to prevent deposition of iron oxide particles on interior surfaces of separator 18 (if present) and/or inner surface of chamber 17. Any number of ejectors 10 and nozzles 12 may be employed or other means of generating swirling inner airflow 3 can be deployed, where flame 4 is stabilized thereby. For example straight jets of air may be generated and transformed into swirling flow 3 using vanes or blades.

Iron powder particles are picked up by swirling airflow 3, after having been scattered by counter flow impingement 14 to slow down the iron powder particles (and prevent that these move too fast through flame 4 to be combusted therein), and are swirled into flame 4 on the interior of swirling airflow 3 to be burnt or oxidized. From flame 4, particles of iron oxide are released and captured in the interior of swirling airflow 3 to be transported towards an open and downward oriented end of separator 18. To use a metaphor, the iron oxide particles fall through the eye of a storm formed by swirling flow 3.

An open end of central powder injection port 1 is surrounded by a generally cylindrical injection port shield 22 having a diameter, which is connected to separator 18, which is also generally cylindrical and shields combustion space 16 that surrounds combustion flame 4. Separator 18 has a larger diameter than shield 22. Preferably, the diameter of separator 18 is at least 1.5 times the diameter of shield 22. This difference is required to create vortices which leads to flame stabilization.

At the open downward oriented end of separator 18, a flow 6 exits separator 18 with said flow 6 comprising exhaust gas of flame 4 with flving iron oxide particles therein and swirling airflow 3.

Below the open and downward oriented end of separator 18, flow 6 is inverted in direction and turns upward to move up on the outside of separator 18 and inside inner wall of chamber 17. Through such inversion of the flow 6, possibly induced using suction from above or closure of a burnt powder discharge port 7 or any other suitable means (wherein the discharge port 7 or any alternative means for inverting flow 6 may define an inverter configured to invert the swirling inner airflow and convert the inverted inner airflow into the outer airflow), sufficiently heavy iron oxide particles in flow 6 have an impulse to keep moving towards bumt powder discharge port 7 and iron oxide particles are separated from inverting flow 6. Thus, deposition of particles on inner wall of chamber 17 is prevented.

Flow 6 is inverted by the above mentioned inverter at or formed by burnt powder discharge port 7, and particles are removed from flow 6 in the inversion trajectory, whereby a remaining mixture of exhaust gas from flame 4 and swirling airflow 3 moves up in the direction of arrow 19 between outside of separator 18 and inside of chamber 17. At this time, upward inverted flow 6 may or may not swirl around separator 18. Separator 18 thus optionally separates the downward swirling airflow 3 and upward inverted flow 6, but may be omitted to allow that the outer upward inverted flow along arrow

19 of remaining mixture of exhaust gas from flame 4 and swirling airflow 3 (without as much as possible of the particles) moves upward along arow 19 between the swirling inner airflow and an inside wall of the chamber. This separation of particles from flow 6 in the inversion trajectory further prevents particle deposition on an inner wall of chamber 17, since particles remain at burnt powder discharge port 7 and are not carried upward along arrow 19. Further, an optional heat exchanger 13 is arranged between an outside of separator 18 and an inside of chamber 17. to control a temperature of recirculated exhaust gas 8 and/or discharged exhaust gas out of exhaust gas discharge 9, using air flow rates blowing through the heat exchanger 13. Outer flow of remaining mixture of exhaust gas from flame 4 and swirling airflow 3 without particles flows upward to exhaust gas discharge 9, which is therefore at the same end of cylindrical chamber 17 as powder material inlet 1 and ejectors 10. A portion 8 of the upward inverted flow 6 is not outputted through exhaust gas discharge 9, but fed back into ejectors 10 through perforations therein to be recirculated, providing a heavily diluted mixture with the supply of fresh air 11 to nozzles 12 for forming swirling airflow 3. The mix of portion 8 of the exhaust gas and fresh air 11 significantly drops the oxygen concentration at nozzle 12, where by such depletion in oxvgen concentration can contribute to better control of the first stage of the combustion process in flame 4. In an embodiment, the ejectors 10 may be actively controllable (for instance by controlling a size of the above mentioned perforations) to set or adjust the amount of exhaust gas 8 to be taken in by ejectors 10 to form a mixture with driver gas 11, e.g. outside air, and thereby determine an oxygen concentration present in swirling airflow 3. Ejectors 10 may thus mix driver gas 11, e.g. fresh air, with exhaust gas 8, which is admitted into the ejectors 10 as a controllable portion of the exhaust gas flow to exhaust gas discharge 9. Indeed, mixing exhaust gas 8 and fresh air 11 significantly drops the oxygen concentration of airflow 3 from nozzles 12, for example, resulting in as little as 5%, preferably 8%, usually 5 to 15% oxygen concentration.

In the interior of separator 18 an optional secondary oxygen mixture supply assembly is provided that in the illustrated embodiment includes fresh air jets 5 with conduits 21, or another embodiment of jets for injecting another oxygen-containing gas mixture, which are form in or with the separator 18.

To promote or at least maintain round going motion of swirling airflow 3, jets 5 may exhibit a tangentially oriented outflow in a same direction as that of swirling flow 3. Likewise, jets 5 may be arranged on the outside of separator 18, to promote — if desired - the upward swirl of upward inverted flow 6. If it 1s desired that outer upward inverted flow 6 along arrow 19 is swirling, like inner downward swirling airflow 3, jets 5 on the outside of separator 18 (not shown) may exhibit a tangential outflow orientation. Jets 5 may be embodied as rings 20 of outflow openings or jets 5 in the interior or on the outside of separator 18. Fresh air may be provided to jets 5 via conduits 21, extending in or along separator 18, from the same end of chamber 17 as where the powder material inlet 1 and sjectors 10 are provided. Alternatively, jets 5 may be supplied with the same mixture of outside (fresh) air and exhaust gas as nozzles 12, and may be supplied from ¢jectors 10. However, in the shown embodiment, do not need to generate a swirling flow.

Jets 5 are arranged in the shown embodiment at a height or distance from central powder injection port 1. A this height iron powder is partially burnt. This distance below central powder injection port 1 may preferably be 1.5 to 2 times a diameter of separator 18. After establishing the initial powder-rich flame 4, jets 5 on the interior of separator 18 provide a secondary airflow in additional to the swirling inner airflow 3, as part of the oxygen mixture supply assembly. Here, jets 5 are directed centrally inward from the periphery of space 16 to insert fresh air (possibly with exhaust gas mixed in like described above for nozzles 12). Jets 5 cause no swirling in this embodiment (swirl number SN is 0), but may contribute to tightness of the swirling inner airflow 3 around flame 4.

In one embodiment, secondary oxygen mixture supply assembly includes a plurality or rings of jets 5, such as four ring of jets. In the embodiment of FIG. 2, three rings 20 are shown. In an embodiment individual jets or group or rings 20 of jets 5 may be controlled, operated or deployed independently. The concentration of oxygen injected by jets 5 may be the same as that created for nozzles 12 (see above) and then jets 5 may be connected to ejectors 10, like nozzles 12. However, the required oxygen concentration from jets 5 may differ from an oxygen concentration for nozzle 12. In more detail, a desired oxygen concentration for jets 5 may be 12% or higher and preferably 15% or higher. In general, the oxygen concentration from jets 5 may be required to be higher than the oxygen concentration in the swirling inner airflow 3. In this way, the established fluid dynamics pattem inside the bumer/combustor can improve iron dust/powder flame stability in the combustor/burner.

Therefore, in this embodiment of the present disclosure, it is possible to simultaneously improve flame stabilization and also prevent the iron oxide sedimentation on the inner surface of the chamber 17 and the optional separator 18 by rearranging the combustion air flow pattern inside the burner/combustor and providing a swirling inner airflow 3 and an outer airflow 19, which may or may not be made to swirl and is in this embodiment flowing in an opposite direction relative to the swirling inner airflow. A burner built according to this concept can generate a combustion zone with high energy release density with no or hardly any CO, and very low or no NO, footprints. To the best knowledge of the creators of the present disclosure, using this kind of fluid dynamics arrangements in a metal burning combustors/bumers to promote the self-sustainable iron flame stability and preventing thickening of the iron oxide sediments on the inner wall of the bumer chamber 17 or — if provided — separator 18 is novel.

In relation to the embodiment in FIG. 5, the following is noted.

Metal energy carriers, in particular though not exclusively iron powder, may well be a key solution for the large-scale and long-term storage and import of sustainable energy for industry and society in the near future, to prevent or reduce CO: emissions. Hydrogen and ammonia are other candidates with important disadvantages. which disadvantages do not occur when using metal energy carriers, and iron powder in particular. In this regard, a novel and inventive approach to a self- sustainable metal combustion burner is presented in this disclosure.

Results of testing show that a self-sustained tornado form of iron flame can be established inside the burner even under normal ambient air conditions (21% O-), but also at very low oxygen concentrations (~ 10% Oz) and for low overall equivalence ratios (~ 0.2), without any assisting extra heat sources. This finding is significant in mitigating the partial evaporation of metal particles and circumventing nano-particle formation and related mass losses. Moreover, the bumer in the embodiment of FIG. 5 exhibits also a configuration with two airflows which may have opposite (inverted) directions of motion, and in the below embodiment an inner swirling flow for flame stabilization is generated from an outer flow (that may or may not also swirl) to prevent iron oxide deposition. More in particular, this embodiment has an outer swirling flow that is inverted to generate inner swirling airflow. The airflows in reverse or opposite directions constitute an innovative concept proposed by the applicants for the next generation of the metal fuel burners with hardly any or preferably no CO, and very low or even no NO, emissions. Moreover, using the preferably reversed or at least opposing swirling flows showed satisfying results to significantly improve two major following issues in the iron powder burners. These issues are iron powder flame (self-)stabilization and uninterrupted operation of the burner by preventing the iron oxide sedimentation on an inner wall of the burner.

The same as with the above embodiment of FIG’s. 1 — 4, flame stabilization during plain iron powder combustion is achievable with assistance, such as by a pilot burner, and iron oxide splashing and subsequently sedimentation on the bumer’s inner wall can be prevented through provision of only slightly more complex airflows, relative to the prior art.

The below embodiment of FIG. 5 according to the present disclosure is distinguished from prior art configurations in that the configuration of the present invention prevents vortex breakdown, thus enabling more efficient heat transfer and better flame stabilization, by using at least two airflows, of which the inner airflow swirls around the flame for stabilisation of flame 4 and outer airflow along arrow 19 may swirl and may progress in an opposite direction (or may be straight and / or may move in the same direction). to support the inner swirling airflow to prevent breakdown of the swirl or vortex of the inner swirling airflow, and at the same time prevent iron oxide deposition on the inner wall of the chamber. It is preferred to have the outer airflow along arrow 19 swirl like swirling inner airflow 3 to strengthen the outer flow using centrifugal force, whereby a swirling outer airflow reaches a longer distance in the direction of arrow 19.

In this embodiment of the present disclosure in FIG. 5, a new concept for a metal combustion- based burner is disclosed, that can produce high thermal energy with hardly any or preferably even no carbon mono/dioxide and very low or possibly even no nitric oxides and nano-particulate matters footprints. The herein proposed concept could improve the iron flame stabilization and prevent or at least reduce the iron oxide sedimentation on the inner surface of the chamber of the burner by establishing a tornado shaped flame inside the combustion chamber of the burner and also rearranging the combustion air flow patterns inside the chamber of the burner, with two or more airflows, of which the inner airflow swirls to form a vortex, just like in the embodiment of FIGs. 1 — 4, and an outer airflow to support the swirling inner flow for stabilisation of flame enveloped by the inner swirling airflow, so that both improved flame stability and operability of the burner for longer periods of time can be realized. which is required for practical applications. To this end, for all embodiments disclosed herein, an air jet or airflow explicitly means a flow of gas, containing sufficient oxygen for the metal or iron powder to combust or be oxidized.

In fact, the peripheral or outer airflow (that may or may not swirl) may be introduced from an end of the chamber in the burner opposite the introduction of iron powder and move towards the end where the iron powder is introduced. The outer airflow may then be inverted or reversed so that outer airflow is transformed into swirling inner airflow whereby the inner swirling airflow results in at least one of the following or other beneficial effects:

I - cool the burner’s or the chambers inner wall due to the outer possibly swirling flow, that may be diluted with injected cold air in the outer airflow along the inner wall; 2 - prevent fouling on the inner surface of the chamber of the bumer on an inside wall due to its flow razor effect which stems from its strong shear flow along the inner surface of the chamber; 3 — stabilize the flame at the centre of the burner where the metal powder is injected due to its secondary or outer possibly swirling flow, potentially at very high swirl number (SN of 10 or more, or even 25 or more) which surrounds the flame and falling metal powder.

In FIG. 5, burner 30 is configured to combust a powder material, and in particular, though not exclusively iron powder. To this end, burner 30 comprises a chamber 31 defining a space 16 to accommodate a combustion flame 4. In this embodiment, chamber 31 is a mainly cylindrical and upright vessel or tank having an M-shaped dome 32 at a top end and a cone shaped end 34 at a bottom end. Further, burner 30 has a powder material inlet 1, debouching at a base of combustion flame 4 in space 16 for iron powder to impinge against counter flow impingement 14, which is arranged at or near the end of powder material inlet tube 1, to scatter the iron powder particles. The counter flow impingement 14 can be embodied as a cone (as shown), a partial sphere, or any other suitable iron powder scattering or dispersing shape. The term “counter flow impingement” shall encompass redirecting elements for redirecting the particle flow in various suitable directions, including perpendicular or in a positive and negative angles compared with the flow 2. Powder material inlet 1 is oriented downward and combustion flame 4 extends downward from inlet 1, underneath counter flow impingement 14.

Above a downward oriented open end of inlet 1, an in cross section M-shaped dome 32 is formed. to contribute to flame stabilization and more in particular initial heating of the burner 15 and the inbound flow from powder material inlet 1.

At least one air inlet is provided to supply fresh air 11, or another oxygen-containing gas mixture, into combustion chamber 16. In the embodiment of FIG. 3, the air inlet 1s formed in an oxygen mixture supply assembly that in the illustrated embodiment comprises two nozzles 12 at an end opposite M-shaped dome 32, where inlet 1 enters the chamber 31. Nozzles 12 tangentially inject sucked-in outside air 11, to generate a swirling outer airflow along arrow 19. At the dome 32, the direction of the outer airflow along arrow 19 is reversed or inverted and inner swirling airflow starts to extend downward, enveloping flame 4. Consequently, dome 32 forms a guide configured to invert the outer airflow and convert the inverted outer into the swirling inner airflow. It is noted that because the outer airflow along arrows 19 is made to swirl by the tangentially oriented nozzles 12, and because ofthe M-shape of the dome, the inner airflow 3 swirls. In principle, in an alternative embodiment that is not shown, nozzles 12 may be directed upward to generate a straight (non-swirling) airflow along arrow 19, where vanes or blades inside dome 32 may be used to impart a swirling movement on the inverting airflow to generate the swirling inner airflow 3.

Swirling inner airflow 3 envelops combustion flame 4 for stabilisation of flame 4 to prevent deposition of iron oxide particles on interior surfaces of separator 18, shown in FIG. 1, and/or inner surface of chamber 17, while upward outer airflow along arrow 19 serves to strengthen or at least maintain the swirling inner airflow 3 over a height of the chamber 31, and sheer motion of the outer airflow along arrow 19 along an inner surface of chamber 31 furthermore serves to prevent iron oxide deposition.

Any number of nozzles 12 may be emploved or other means for generating outer airflow along arrow 19 and / or swirling airflow 3 can be deployed, where flame 4 is stabilized thereby. For example straight jets of air may be generated and transformed into swirling flow 3 using vanes or blades.

Iron powder particles are swooped away in swirling inner airflow 3 from counter flow impingement 14, after having been scattered by counter flow impingement 14 to slow down the iron powder particles (and prevent that these move too fast through flame 4 for combustion thereof). and are swirled into flame 4 on the interior of swirling airflow 3 to be burnt or oxidized. From flame 4, particles of iron oxide are released and captured in the interior of swirling airflow 3 to be transported towards an open and downward oriented end of chamber 31. To use a metaphor, the iron oxide particles fall through the eye of a storm formed by swirling flow 3.

At the open downward oriented open end 33 of chamber 31, iron oxide particles are discharged from chamber 31 in what remains of swirling inner airflow 3. Yet, a cone shaped bottom portion 34 of chamber 31 containing end 33 is protected from iron oxide deposition by the swirl of what remains of swirling inner airflow 3.

Likewise, upward airflow along arrow 19, which may or may not swirl around swirling inner airflow 3 to enhance or at least maintain swirling inner airflow 3, moves upward along arow 19 between the swirling inner airflow 3 and an inside wall of the chamber 32 to prevent particle deposition on inner wall of chamber 32.

Swirling inner airflow 3 moves downward to open end 33 forming an exhaust gas discharge, where also iron oxide particles are discharged. Open end 33 is therefore at the opposite end of cylindrical chamber 31 relative to powder material inlet 1, but at the same end as nozzles 12.

A portion of the upward airflow along arrow 19 doesn’t reach the dome 32, but is inverted on the way upward to dome 32 to join swirling inner airflow 3. Along the path corresponding with arrow 19, outer airflow is preheated. Portions of the outer airflow along arrow 19 that reach dome 32 and are there inverted contribute to fuelling flame 4.

As shown in FIG. 5, iron powder is centrally and downwardly injected into the burner 30 and surrounded by intensive swirling inner airflow 3 (having a swirl number of more than 2, and more typically 10 or more) induced by two nozzles 12, that may be embodied as elbow pipes, and injecting inner airflow to swirl by tangential injection. Nozzles 12 are arranged at some distance from the central axis along which powder material inlet 1 extends to realise tangential injection and generate swirling inner airflow 3 to induce flame 4 to resemble a whirlwind or tornado. The formation of a whirlwind or tornado flame causes expansion of the hot gases (almost nitrogen) around the burner's centerline due to combustion, which in tum leads to a low density and a kind of central tornado flame because of the difference in density between the heavier colder gases near the burner's walls and the hot gases staying close to the centerline. The whirlwind or tornado flame further causes a recirculation flow of (still hot but partly cooled) exhaust gases back from the position of nozzles 12 upward in the outer airflow along arrow 19, which outer airflow along arrow 19 mixes with the hot gases near nozzles 12. This creates an inward flow around whirlwind or tornado shapes flame 4. This recirculation stabilizes the whirlwind or tornado shape of flame 4. Notwithstanding, due to the outer airflow along arrow 19, the design is capable of preventing for the most part splashing iron oxide and sedimentation thereof on the inner wall of the chamber 31.

Therefore, also in this embodiment, iron flame stabilization can be considerably improved, and also iron oxide sedimentation on the inner surface of the chamber 31 may be reduced by rearranging the combustion air flow pattern inside the chamber 31 to include the outer flow along arrow 19 on an outside of swirling inner airflow 3.

Nozzles 12 are arranged near the bottom of the chamber 31. In the shown embodiment of FG. 5, nozzles 12 are at a distance from powder material inlet 1, that is at least two times the inner diameter of the burner (ID), which is considered to assist embedding the centrally stabilized swirling iron powder flame 4 and simultaneously create a fluid flow blanket along arrow 19 that keeps the inner wall of chamber 31 cool and prevent iron oxide sedimentation thereon.

A burner 30 configured according to the present disclosure generates a combustion zone 16 with a high energy release density with hardly or no CO, and very low or no NO, and nano-particles footprints. In the configuration of FIG. 5, a required amount of the combustion air, exhaust gases (EG), or both is or are injected with at least 10% oxygen content and more. Outer high velocity swirling airflows moving upward along arrow 19 are injected by nozzles 12 from the bottom of the chamber 31, to be inverted and form swirling inner airflows 3 to envelop flame 4 and iron powder injection inlet 1. This substantiates that the swirling jets can have any suitable configuration respect to the iron powder’s injection port. This can be such as elbow pipes with a swirling surface perpendicular to the powder injection inlet 1, and the direction of the air exiting the jets can be generally perpendicular to or along walls of the chamber 31 or in an upward direction respect to the downward direction of the powder injection inlet 1. This arrangement causes a counter-current upward swirling flow inside chamber 31 in FIG. 5, relative to the swirling inner flow 3. This flow pattern significantly prevents sedimentation of iron oxides particles that would otherwise be driven or drawn to the wall of the chamber 31 by centrifugal forces, due to the presence of swirling shear flow along arrow 19 and along surface of the inner wall of chamber 31, which works as a flow razor. Moreover, this upward swirling pattem along arrow 9 and the inner wall of chamber 31 is inverted and turned into downward central swirling inner airflow 3. when once it reaches the M-shaped dome 32 of the chamber 31.

Therefore, the downward iron powder stream injected at the centre and top of chamber 31 envelops flame 4 and powder inlet 1.

It is further noted here that the reverse swirling flow has also function of recuperating energy extracted from the burnt particles which cross the swirl flow at the bottom (close to injection of cold air) to the central core flow where ignition and combustion of iron particles happens, which functions as an internal energy recirculation mechanism and may provide super-adiabatic conditions for the combustion zone.

The tangentially located swirling nozzles 12 on the wall of chamber 31 could be evenly distributed peripherally at the injection section in another number than two, or for instance with even or odd numbers of the jets. Based on FIG. 5, the EGR process could be established either as an internal recirculation of the post-combustion gases or as an external exhaust gas recirculation in which the incoming combustion air could be diluted using post-combustion exhaust cooled down gases for the sake of depletion of the oxygen concentration in the combustion air. Moreover, swirling nozzles 12 could be distributed in several locations on the burner wall downstream of the iron powder injection inlet 1 (relative to the downward swirling airflow 3). The nozzles may be oriented downward, upward, or perpendicular relative to the axial direction of iron powder flame 4 inside the chamber 31.

The burner 30 of the present invention has a chamber 31 with a generally cylindrical body and an outlet cone 34 or funnel having a generally conical shape. However, the M-shaped dome 32 at a top section of chamber 31 could be either flat or doughnut shaped, but is preferably shaped to induce the desired reversal of outer airflow along arrow 19 into swirling inner airflow 3. Dimensions of the swirl nozzles 12 and the bumer ID were selected based on creating high momentum shear flow on the inner wall of the burner and establishing high swirl number flow at the central zone of the burner, where the primary iron powder flame 4 is to be formed and stabilized.

In this embodiment of FIG. 5, heat exchanger 13 and separator 18 of the embodiment of

FIG’s. 1 — 4 are omitted. An M-shaped dome like the one at the top of chamber 31 in FIG. 5 may be provided at the bottom of chamber 17 in the embodiment of FIG’s. | — 4 to enhance reversal of the airflows. Instead of opposing airflows, the airflows could move be in the same direction. Instead of a reversal of one airflow into the other, two distinct flows may be employed (which would exhibit cross over from one flow into the other). Consequently, the skilled person confronted with these alternatives for specific aspects of the two embodiments disclosed herein above and shown in the appended drawing, would immediately and unambiguously realize that the scope of protection according to appended claims should not be unduly limited to aspects of the specifically disclosed embodiments.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps. operations, elements. components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of embodiments of the present invention has been presented for purposes of illustration, but is not intended to be exhaustive or limited to the implementations in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the present invention. The embodiments were chosen and described in order to best explain the principles and some practical applications of the present invention, and to enable others of ordinary skill in the art to understand the present invention for various embodiments with various modifications as are suited to the particular use contemplated.

Claims (25)

CONCLUSIONS 1. A burner for burning a powder material from a group comprising at least: metal and/or metalloid and/or alloy powder and iron powder, the burner comprising: - a chamber defining a space for a combustion flame; - an inlet of powder material, opening at the base of the combustion flame into the space; - at least one air inlet into the combustion chamber, configured to generate: * a swirling inner air stream enveloping the combustion flame, and * an outer air stream between the swirling inner air stream and an inner wall of the chamber. 2. The burner of claim 1, further comprising a discharge of burned powder from the chamber. 3. The burner according to any of the preceding claims, further comprising an exhaust gas outlet. 4. The burner of any preceding claim, wherein the combustion flame in the combustion chamber is directed downwardly from an upper end of the combustion chamber, the inlet of powder material leading downwardly into the combustion chamber to the base of the combustion flame. 5. The burner according to any one of the preceding claims, wherein the swirling inner air stream flows in a direction extending from the inlet of powder material along the combustion flame. 6. The burner according to any of the preceding claims, wherein the outer air stream flows in a direction different from, preferably opposite to, a flow direction of the swirling inner air stream. 7. The burner of any one of the preceding claims, wherein the outer air stream swirls around the inner air stream between the swirling inner air stream and the inner wall of the chamber. 8. The burner according to any of the preceding claims, wherein the air inlet is arranged opposite the powder material inlet with respect to the combustion flame. 9. The burner of claims 7 and 8, wherein the air inlet is configured to generate the swirling outer air stream by at least tangential introduction into the chamber near the inner wall thereof. 10. The burner according to any of claims 1 to 7, wherein the air inlet is arranged at the inlet of powder material to generate the swirling inner air stream by at least approximately tangential introduction into the chamber. 11. The burner of any preceding claim, wherein the air inlet includes an exhaust gas feedback to mix exhaust gas in at least one of the inner swirling air stream and the outer air stream to reduce the oxygen concentration therein. 12. The burner of claim 11, wherein the air inlet is adjustable to set the oxygen concentration to a predetermined value 1n. 13. The burner of claim 12, wherein the controlled oxygen concentration from the air inlet is as low as 5%, preferably 8%, but usually 5 to 15% oxygen concentration. 14. The burner according to any of the preceding claims, further comprising an inverter configured to reverse the swirling inner airflow, thereby converting the swirling inner airflow into the outer airflow. 15. The burner of any one of the preceding claims, further comprising a guide configured to reverse the outer airflow and convert the reversed outer airflow into the swirling inner airflow. 16. The burner according to any of the preceding claims, further comprising a separator between the swirling inner air stream and the outer air stream. 17. The burner of claim 16, wherein the separator comprises an oxygen mixture supply assembly. 18. The burner of claim 17, wherein the oxygen mixture supply assembly comprises radiators on at least one of the interior and exterior of the separator. 19. Burner according to claim 18, wherein at least some of the emitters are connected to the air inlet. 20. The burner of claim 18, wherein the oxygen mixture supply assembly includes an exhaust gas feedback to which the emitters are connected for mixing exhaust gas into a further air stream from the emitters to establish an oxygen concentration therein. 21. The burner of claim 20, wherein the air inlet is adjustable to set the oxygen concentration to a predetermined value. 22. The burner of claim 21, wherein the controlled oxygen concentration from the air inlet is at least 12%, and preferably at least 15% oxygen concentration. 23. The burner according to any of claims 16 to 22, wherein the separator is generally cylindrical and is connected to a substantially cylindrical injection port shield surrounding the powder material inlet and the air inlet. 24. The burner of claim 23, wherein the separator has a diameter at least about 1.5 times larger than a diameter of the shield. 25. A method for burning a powder material from a group comprising at least metal and/or metalloid and/or alloy powder and iron powder, the method comprising: - generating a combustion flame in a chamber; - feeding a powder material to the base of the combustion flame; - generating a swirling inner air stream enveloping the combustion flame; and - generating an outer air stream between the swirling inner air stream and an inner wall of the chamber.