Iron fuel system for iron fuel combustion

Abstract

An iron fuel system for iron fuel combustion, configured to generate heat, said system comprising: - a combustion unit arranged for combusting said iron fuel thereby generating an iron oxide containing medium, wherein said combusting releases heat; - a first heat exchanger, configured as an iron fuel boiler arrangement, comprising a heat-exchanging fluid in thermal communication with said iron oxide containing medium for heating said heat-exchanging fluid; - a first-stage separation unit arranged downstream of said first heat exchanger, for separating said iron oxide containing medium into iron oxide and a gas flow, the first-stage separation unit being a momentum-based separation unit; - a second heat exchanger comprising a heat-exchanging fluid in thermal communication with said gas flow for heating said heat-exchanging fluid, wherein said second heat exchanger is arranged downstream of said first-stage separation unit, and - a second-stage separation unit arranged downstream of said second heat exchanger, for further separating said hot gas into iron oxide and a gas flow, the second-stage separation unit being a cyclone-type separation unit.

Description

[0001] TITLE Iron fuel system for iron fuel combustion

[0002] TECHNICAL FIELD

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

[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 CO2 emissions. But for many industries there are currently few or no fossil fuel alternatives available that on the one hand are scalable, and on the other hand able to provide sufficient energy with a high degree of certainty and consistency, yet are completely 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 nearly 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 close to circular process.

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

[0011] Although the use of iron fuel may already be a proven clean and sustainable alternative to fossil fuels, there are also several challenges. As said, during the combustion of the iron fuel, a lot of energy in the form of heat is released that is used to generate hot air, hot water, steam, or electricity.

[0012] One of the challenges lies in making the heat also suitable for use in processes that require energy sources with a high energy density, so called “high- energy-density-requiring processes”. The energy density of heated gases or saturated gases may not be sufficient for such high-energy-density-requiring processes or the processes require higher maintenance, e.g., due to corrosion issues caused by the use of steam (steam contains water droplets).

[0013] The energy density of the saturated gas can be increased by converting the saturated gas into superheated gas. Superheated gas is gas at a temperature higher than its vaporization point at the absolute pressure to which it is compressed. A great value of superheated gas is that it has very high internal energy (much higher energy density than saturated gas) that can be converted into work by expansion, which for example can be used for kinetic reactions through mechanical expansion against turbine blades and reciprocating pistons.

[0014] Unfortunately, in a conventional system the gas must be heated multiple times to be able to exchange enough heat energy from the combustion of iron fuel in the boiler to the heat-exchanging fluid, e.g., water in the case where superheated steam is generated, or it requires a too large (high) combustion unit or multiple heat-exchange units in combination with a combustion unit to be able to exchange enough heat to obtain the superheated steam. And even if such a system would be used, the system would require too much maintenance work because the heat-exchangers placed inside or closely to the combustion chamber would be contaminated in such a way that it negatively affects the operability and efficiency of the heat exchange. This makes it only from an economic point of view already highly unfeasible.

[0015] Furthermore, the resulting iron oxide that is obtained in the combustion of iron fuel may be of such a poor quality, e.g., too fine iron oxide particles, that the iron fuel cannot be recovered well enough in the regeneration process of iron oxide and / or a too large part of the resulting iron oxide may be lost during the combustion process of the iron fuel, e.g., due to attrition or fouling issues. These issues negatively affect the circularity of the process of iron fuel combustion, which is highly undesirable. So conventional iron fuel systems are unsuitable for the production of superheated gas. There is therefore a need for a more common or applicable design to improve heat extraction from iron fuel combustion systems wherein the above- mentioned problems are solved.

[0016] A further problem associated with iron fuel combustion systems is that, although no CO2 is produced for the purpose of generating heat, microparticles may nonetheless escape from the system. This is undesirable. To reduce the volume I amount of microparticles that is exhausted from the system, a filter may usually be arranged before the exhaust. Said filter traps any microparticles still present in the outlet gas at that stage of the system. However, when large volumes of iron fuel are burned in an industrial process, filters may become full rapidly, leading to high maintenance and operation costs I long down-times for the system. This has a negative effect on the price of the produced product (heat I steam I superheated steam) and is deemed undesirable.

[0017] SUMMARY

[0018] It is an object of the present invention to provide an improved iron fuel system for iron fuel combustion.

[0019] The foregoing object is achieved according to a first aspect of the present invention that relates to an iron fuel system for iron fuel combustion, generating superheated gas for driving a high-energy-density-requiring process, said system comprising: a combustion unit arranged for combusting said iron fuel thereby generating an iron oxide containing medium, wherein said combusting releases heat; a first-stage heat exchanger, configured as an iron fuel boiler arrangement, comprising a heat-exchanging fluid in thermal communication with said iron oxide containing medium for heating at a first stage said heat-exchanging fluid to undergo a phase change of said heat-exchanging fluid into a saturated gas; a separation unit arranged downstream of said first-stage heat exchanger for separating said iron oxide containing medium into iron oxide and a gas flow; a second-stage heat exchanger comprising said saturated gas in thermal communication with said gas flow for heating at a second stage said saturated gas to obtain said superheated gas for driving said high-energy-density-requiring process, wherein said second-stage heat exchanger is arranged downstream of said separation unit. Said second-stage heat exchanger is thus not in thermal communication with said iron oxide containing medium.

[0020] Heating of the heat-exchanging fluid such that it undergoes a phase change from fluid to saturated gas does not per se mean that the heat-exchanging fluid is heated just enough to reach that point of phase change to the saturated gas. The saturated gas is a stage that may comprise multiple substages and the heatexchanging fluid can be heated well above the point where the phase change from fluid to saturated gas occurs as long as it remains in the stage of saturated gas and is thus not further heated to the stage of a superheated gas. The superheated gas is considered a separate stage, which may also comprise multiple substages.

[0021] The system according to the invention is equipped with a two-stage heat exchanger such that more high-grade heat can be extracted from the process of iron fuel combustion compared to a system comprising a single-stage heat exchanger. Splitting the heat exchanger in two stages enables positioning the second heat exchanger downstream of the separation unit, which separates the particles from the gas resulting in a “purified” hot gas stream. The high-efficiency extraction of such a two-stage heat exchanger can even be maintained over time while high-maintenance requirements to the second-stage heat exchanger, when positioned upstream of the separation unit as in conventional systems, are significantly reduced or even become obsolete when the second-stage heat exchanger is positioned, in accordance of the present invention, downstream of the separation unit in the purified hot gas stream.

[0022] With “high-grade heat” is meant that the heat extracted from the process of iron fuel combustion, has a higher energy density such that it is of a higher grade or quality. Thus, the heat obtained from the combustion process according to the invention has a higher energy density compared to conventional combustion processes.

[0023] With a “purified” hot gas stream is meant that the gas stream comprises at most 10 wt.% dust, based on the total amount of iron oxide formed during combustion.

[0024] Another advantage is that the iron fuel system according to the present invention allows the generation of superheated gas that can be used in all kinds processes and applications, such as the cracking of organic molecules, where it is important that no liquid, such as water droplets, is formed as this could damage the equipment due to the formation of rust. The presence of water droplets may also result in the imploding of said water droplets in the system / turbine, which may cause cavitation and / or corrosion issues. The cavitation may deform components of the system that has a negative impact on the efficiency of the system and / or, as is also the case for corrosion of the equipment, may even lead to severe damage of the equipment. This results in downtime because maintenance of the equipment is necessary.

[0025] Furthermore, great advantages of an invention often have the consequence of introducing one or more (small) disadvantages, e.g., poor regeneration of iron oxide. Fortunately, the system according to the present invention does not introduce such disadvantages and / or requires concessions on the iron fuel combustion process. Said system does not compromise the efficiency of the regenerating process of iron oxide formed in the combustion process of the iron fuel and thus, the circularity of the process of iron fuel combustion is maintained.

[0026] Examples of other such process or application that use superheated steam are power generation processes, paper production, chemical processes, drying processes, steam turbines for driving machinery, and cleaning and sterilisation processes. EXAMPLES

[0027] In an example, said system further comprises a drum comprising said heat-exchanging fluid that is connected to said first heat exchanger and said second heat exchanger. Said drum may act as a buffer for said heat-exchanging fluid.

[0028] This allows the use of a single system for the heat-exchanging fluid and reuse of the spent heat-exchanging fluid. Furthermore, having the drum to function as a buffer for the heat-exchanging fluid reduces the risk of interruptions of the supply of the heat-exchanging fluid to the heat-exchange stage.

[0029] In yet another example, said heat-exchanging fluid exits said drum via an outlet positioned at or nearby the bottom side of said drum and / or wherein said saturated gas enters said drum via an inlet positioned at or nearby the top side of said drum.

[0030] The saturated gas is used in the second-stage heat exchanger and should remain saturated to convert it into superheated steam. Entering of the saturated gas at or nearby the top side of the drum and exiting of the heat-exchanging fluid at or nearby the bottom side of the drum allows some heat exchange from the saturated gas to the heat-exchanging fluid in the drum but it keeps the gas in its saturated state.

[0031] In another example, said heat-exchanging fluid enters said first heat exchanger via an inlet positioned at or nearby the bottom side of said combustion unit and exits said first heat exchanger via an outlet positioned at or nearby the top side of said combustion unit.

[0032] Such a design allows improved heat exchange between the iron oxide containing medium and the heat-exchanging fluid.

[0033] In yet another example, said system further comprises an air inlet means arranged for supply of air comprising oxygen to said iron fuel. The system may further comprise a fuel feeder arranged for supply of said iron fuel.

[0034] This allows to control the composition of the mixture of gas and iron fuel in the iron fuel combustion process and thus, to control the amount of heat released in said process.

[0035] In yet another example, said system further comprises a pump and / or compressor arranged for transporting said heat-exchanging fluid to said first heat exchanger. Said pump and / or compressor may also be used to increase the pressure of the fluid, for example in case a Rankine fluid is used as heat-exchanging fluid. This reduces the risk of interruptions of the supply of the heatexchanging fluid to the first heat-exchange stage.

[0036] The second-stage separation unit may comprise two cyclone-type separation units. This allows that when the iron fuel combustion unit is operated at half its normal capacity, so that only half of the iron oxide containing medium is present inside the system compared to normal operating conditions, one of the cyclone-type separation units may be inoperative so that the one that is operative is operating at its most efficient operation.

[0037] The iron fuel system may further comprise a bypass arranged downstream of the first-stage separation unit, preferably downstream of the second- stage separation unit, for feeding gas flow substantially cleaned of iron oxide particles and at least partially deprived of oxygen to a burner arrangement. Reusing (part of) the gas reduces gas consumption by the iron fuel system and thus, reduces operating costs.

[0038] In yet another example, said system further comprises a third-stage heat exchanger configured to reheat spent superheated gas from a first part of said high-energy-density-requiring process into reheated gas for driving said high-energy- density-requiring process. The third-stage heat exchanger may extract even more heat from the gas flow exiting the second-stage heat exchanger before it is released into the atmosphere. The gas flow exiting the second-stage heat exchanger may still contain a sufficient amount of heat that can be used to reheat the spent superheated gas in the third-stage heat exchanger. Said system may be arranged for directing said reheated gas to a second part of said high-energy-density-requiring process.

[0039] The spent superheated gas exiting the high-energy-density-requiring process, or other high-energy-density-requiring process, has lost part of its internal energy. The spent superheated gas can be reheated to reheated gas, such that the reheated gas is brought to conditions approaching those of the superheated gas. The reheating improves the efficiency of the system because the exergy is increased in the configuration. Exergy is the maximum amount of work that can be extracted from a medium when brought into equilibrium with the environment. In this case, the potential of the liquid to convert the heat into rotational energy.

[0040] In yet another example, said system further comprises a condenser arranged for cooling spent superheated gas or spent reheated gas. In yet another example, said heat-exchanging fluid has a temperature in the range of from 100 °C to 800 °C, preferably 200 °C to 650 °C, more preferably 350 °C to 550 °C.

[0041] In yet another example, said heat-exchanging fluid has a pressure in the range of from 0.1 MPa to 50 MPa, preferably 1 MPa to 30 MPa, more preferably 2 MPa to 10 MPa.

[0042] Having a heat-exchanging fluid with a temperature and / or a pressure in the ranges given above allows its use in several types of high-energy-density- requiring processes:

[0043] Low-pressure: In low-pressure high-energy-density-requiring process, which are often used for condensing applications;

[0044] Intermediate-pressure: Intermediate-pressure high-energy- density-requiring process are commonly used in power generation applications;

[0045] High-pressure: High-pressure high-energy-density-requiring process are employed in power plants and industrial processes where higher temperatures and pressures are required for efficiency increase and decrease of operational expenses (OP EX).

[0046] In yet another example, said heat-exchanging fluid has a boiling point at or below the boiling point of water, such as water, carbon dioxide, isobutane, isopentane, and propane.

[0047] Organic fluids with boiling points equal to or lower than water can be used as the working fluid. These fluids, known as organic Rankine fluids, can include hydrocarbons such as isobutane, isopentane, and propane, as well as fluorocarbons like R245fa and R134a. Organic Rankine Cycles are often used in applications where lower temperature heat sources, such as waste heat from industrial processes or geothermal energy, are available.

[0048] Supercritical carbon dioxide (SCO2) is another fluid that can be used in the Rankine cycle. At high pressures and temperatures, carbon dioxide can exist in a supercritical state where it exhibits properties of both a gas and a liquid. SCO2 offers advantages such as higher thermal efficiency and lower environmental impact. It is being explored as a potential working fluid in advanced power generation systems. In yet another example, said system comprises a further separation unit arranged downstream of said second-stage heat exchanger.

[0049] The further separation unit enables further reducing the content of iron oxide dust particles in the gas flow and thus results in a more purified gas flow such that the system complies with local emissions standards. Preferably, a total separation of at least 99 wt.%, more preferably at least 99.9 wt.% of the particles from the gas flow is achieved, based on the total amount of iron oxide formed during combustion.

[0050] In yet another example, said separation unit and / or said further separation unit is a gravimetrical-based and / or momentum-based separation and / or centrifugal-based separation system, wherein said centrifugal-based separation system is preferably a cyclone.

[0051] This is particularly relevant for the separation of particles >20 pm, preferably for the separation of particles >10 pm and more preferably >5 pm.

[0052] In yet another example, said system further comprises a further air inlet means arranged for supply of air to said gas flow, and wherein said further air inlet means is arranged downstream of said combustion unit and upstream of said second heat exchanger.

[0053] Introducing air to the gas flow dilutes said gas flow, which reduces the dust load on the second heat exchanger and the risk of clogging of the second- stage heat exchanger.

[0054] In yet another example, said system is designed for driving high- energy-density-requiring processes having a size of from 0.1 MW to 2000 MW, preferably 1 MW to 1000 MW, more preferably 5 MW to 500 MW.

[0055] With such a design, the system is applicable to many sizes of industrial and non-industrial processes.

[0056] In a particularly advantageous set-up, the first separation unit, the separation unit that is arranged downstream of the first-stage heat exchanger, is a momentum-based separation unit where, in particular, the larger diameter mass fraction of the iron oxide particles, e.g. containing the particles larger than e.g. >10 pm, are separated from the gas flow. This first separation unit may then be followed, in the flow direction, by a second-stage heat exchanger where a further exchange of heat between the hot gas flow and a heat exchanging medium is effected. Still considering the streamwise direction, this second-stage heat exchanger may then be followed by a second separation unit, that in particular may be of the cyclone type. Advantageously, only at this point in the gas path, i.e. after substantially all heat has been extracted from the gas flow using the second heat exchanger, (cold or heated) air may be allowed to mix with the (hot) gas flow to operate the cyclone and to further separate the remaining iron oxide particles from the gas flow. Advantageously, the cyclone may be efficiently operated independent of the load condition of the boiler, by taking in more or less air in the cyclone. The combination of a momentum-based separation unit after the first heat exchanger and a cyclone type separation unit after the second heat exchanger and before the exhaust advantageously leads to the best result in terms of a) heat extracted from the iron oxide containing medium after having burned the iron fuel b) maintaining microparticle exhaust within acceptably low limits and c) having acceptably low operating and maintenance costs. On top of that, both separation units can be made from readily available materials, so that production is simplified and costs are reduced. Further advantageously, total system costs may be minimized when relatively standard components are used for the first-stage heat exchanger, the second-stage heat exchanger and the second separation unit.

[0057] A further advantage of having a momentum-based separation unit as the first separation unit is that it may not be required to add any (cold or heated) air to the iron oxide containing medium, in this stage before all heat is extracted from it. Once heat exchange with the second heat exchanger has taken place, at a point in het system where all heat has been extracted from the flue gas, the negative effect of adding (fresh) air to the iron oxide containing medium is negligible from a heat extraction point of viewd and the primary objective at this stage is to remove all iron oxide particles for recycling purposes and to minimise microparticle exhaust. Advantageously, by using a cyclone for this second separation step, any (physical) filter that is positioned in between the second separation unit and the exhaust may be smaller and / or need less maintenance, reducing the system cost.

[0058] A cyclone functions best when a certain volume of air is taken in by the cyclone. Optionally, the cyclone comprising an air inlet, through which a variable volume of air may flow in operation, so that depending on the load with which the iron fuel burner is operated and thus the amount of flow that enters the cyclone, more of less air may be added to the iron oxide containing medium through the inlets when said iron oxide containing medium enters the cyclone, preferably keeping the total volume of gas entering the cyclone constant. The amount of air that is added to the iron oxide containing medium may further depend on the temperature of the medium at this stage, as a hotter medium will have a larger volume than a colder medium. This allows to run the cyclone at the optimal efficiency point, also when less product (heat, steam, superheated steam) is needed and less iron fuel enters the system.

[0059] A similar effect may be achieved by providing more than one cyclone after the second heat exchanger, e.g. in series or in parallel, wherein one or more of the cyclones may be shut off and / or bypassed depending on the operation point of the combustion unit I the amount of iron oxide containing medium flowing through the system, so that the cyclones that are operated are operating at a point near their most efficient operating point.

[0060] Optionally, not all gas exiting the (last) cyclone may flow through the exhaust. Some of the gas may be reintroduced into the combustion unit. This gas may be bypassed either before it has passed through the (last) cyclone, before it has entered the (first) cyclone, or at a stage in between the first and the last cyclone. It may be preferred when said gas is bypassed after having passed through the (last) cyclone, so that as much iron oxide particles as possible are separated from said gas flow.

[0061] It should be understood that the use of a first separation unit which is a momentum-based separation unit in combination with the use of a second separation unit which is a cyclone-type separation unit, and the above-described advantages that are obtained therewith, may be achieved irrespective of the product that is made with the system. That is to say, also when no superheated gas is made, but e.g. hot water, or more regular heated gas such as saturated steam or dry air, the set-up of a combustion unit for combusting iron fuel, followed in streamwise direction by a first- stage heat exchanger, followed in streamwise direction by a first separation unit being a momentum-based separation unit, followed in streamwise direction by a second- stage heat exchanger, followed in streamwise direction by a second separation unit being a cyclone-type separation unit has advantageous effects where it concerns maximal extraction of heat, minimal exhaust of microparticles and minimal maintenance / operational costs. As such, a second aspect of the present disclosure relates to an iron fuel system for iron fuel combustion, configured to generate heat, said system comprising: a combustion unit arranged for combusting said iron fuel thereby generating an iron oxide containing medium, wherein said combusting releases heat; a first heat exchanger, configured as an iron fuel boiler arrangement, comprising a heat-exchanging fluid in thermal communication with said iron oxide containing medium for heating said heat-exchanging fluid; a first-stage separation unit arranged downstream of said first heat exchanger, for separating said iron oxide containing medium into iron oxide and a gas flow, the first-stage separation unit being a momentum-based separation unit; a second heat exchanger comprising a heat-exchanging fluid in thermal communication with said gas flow for heating said heat-exchanging fluid, wherein said second heat exchanger is arranged downstream of said first-stage separation unit, and a second-stage separation unit arranged downstream of said second heat exchanger, for further separating said hot gas flow into iron oxide and a gas flow, the second-stage separation unit being a cyclone-type separation unit.

[0062] With respect to the second aspect of the present disclosure in particular, it should be noted that the heat exchanging medium in the first heat exchanger and the heat exchanging medium in the second heat exchanger may be in fluid communication with each other, but that this is not required and that they may be two isolated heat exchange media

[0063] With respect to the second aspect of the present disclosure in particular, it should be noted that the hot “gas flow” exiting the first-stage separation unit may still contain a (significant) iron oxide portion. In a typical example, the first- stage separation unit may separate about 95 - 98% of the mass fraction of the iron oxide from the iron oxide containing medium, so that the dust load on the second heat exchanger is still rather significant, and that the “gas flow” is still, essentially, an iron oxide containing medium although the concentration of iron oxide is much lower after the first-stage separation unit than after the combustion unit. With respect to the second aspect of the present disclosure in particular, it should be noted that the gas flow exiting the second-stage separation unit may also be referred to as an extra purified gas flow, because said gas flow may still contain a very small portion of iron oxide, said portion of iron oxide being significantly lower than the iron oxide portion that may be present in the hot gas flow exiting the first-stage separation unit.

[0064] With respect to the second aspect of the present disclosure in particular, it is noted that the heat generated in the combustion unit and present in the iron oxide containing medium may e.g. be exchanged with the media in the first and second heat exchangers, e.g. to generate hot water or another hot liquid, to generate steam or another hot gas, or to generate superheated steam.

[0065] With respect to the second aspect of the present disclosure in particular, it is noted that a “momentum-based” separation unit is understood to be a separation unit where a momentum, in particular, a direction of the medium flowing through it is changed thereby separating solid particles from gaseous particles. In particular the direction of the medium may be changed by less than 360 degrees, in contrast to e.g. a cyclone where the medium is understood to be rotated about an axis at least several times.

[0066] It should go without saying that examples and features where were described as being advantageous for the invention defined in the first aspect of the present disclosure, may equally be advantageous for the invention defines in the second aspect of the present disclosure.

[0067] 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.

[0068] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] 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.

[0070] Fig. 1 shows a schematic representation of an example the iron fuel combustion system according to the disclosure.

[0071] Fig. 2 shows a schematic representation of another example the iron fuel combustion system according to the disclosure.

[0072] Fig. 3 shows a schematic representation of another example of the iron fuel combustion system according to the disclosure.

[0073] DETAILED DESCRIPTION

[0074] The present invention is elucidated below with a detailed description.

[0075] An iron fuel system 1 for iron fuel combustion according to the present invention is shown in Fig. 1. In said system 1 is superheated gas generated that is for driving a high-energy-density-requiring process 3.

[0076] The system 1 comprises a combustion unit 7 that is arranged for combusting the iron fuel. In said combustion, an iron oxide containing medium is generated and said combustion releases heat.

[0077] The system 1 further comprises a first-stage heat exchanger 9 which is configured as an iron fuel boiler arrangement and comprises a heat-exchanging fluid 11. The heat exchanging fluid 11 is in thermal communication with the iron oxide containing medium for heating at a first stage the heat-exchanging fluid 11 to optionally undergo a phase change of the heat-exchanging fluid 11 into a saturated gas 13.

[0078] Furthermore, the system 1 comprises a separation unit 15 that is arranged downstream of the first-stage heat exchanger 9 for separating the iron oxide containing medium into iron oxide and a gas flow. In particular, this separation unit 15 may be a momentum-based separation unit.

[0079] The separated iron oxide is collected in an iron oxide collector unit 45. Typically, around 95 - 98 per cent of the mass fraction of the iron oxide particles may be separated from the iron oxide containing medium in the first-stage separation unit 15, in particular the larger and heavier particle fraction. The system 1 further comprises a second-stage heat exchanger 17 e.g. comprising the saturated gas 13 in thermal communication with the gas flow for heating at a second stage the saturated gas 13 to obtain the superheated gas. The superheated gas is for driving the high-energy-density-requiring process 3. The second-stage heat exchanger 17 is arranged downstream of the separation unit 15. Said second-stage heat exchanger 17 is thus not in thermal communication with said iron oxide separated from the iron oxide containing medium in the first separation unit 15. The heat exchanging medium present in the second-stage heat exchanger 17 may, as will be described in the below, be in fluid communication with the heat exchanging medium present in the first-stage heat exchanger 9, although this is not required in all embodiments of the disclosure.

[0080] The system 1 is further provided with a further air inlet means 48 arranged for supply of air to said gas flow. Said further air inlet means 48 is arranged downstream of said combustion unit 7 and upstream of said second-stage heat exchanger 17.

[0081] The gas flow is directed to a further separation unit 46 to separate the finest fraction of dust from the gas flow. In particular, this separation unit 46 may be of the cyclone type. The extra purified gas flow is then directed to a gas outlet 47 to release the gas into the atmosphere or to transport the gas flow to other heat recovery purposes, such as an economizer, air heat exchanger, or other heat recovery heat exchanger. Optionally, a filter is placed in between the cyclone and the exhaust.

[0082] The system 1 also comprises a burner arrangement 43 that is positioned upstream of the combustion unit 7.

[0083] Additionally, the system 1 comprises a drum 19 comprising the heatexchanging fluid 11 and the saturated gas 13. The drum 19 is connected to the first- stage heat exchanger 9 and the second-stage heat exchanger 17 and acts as a buffer for the heat-exchanging fluid 11. The heat-exchanging fluid 11 exits the drum 19 via an outlet 21 positioned at the bottom side of the drum 19 and the saturated gas 13 enters the drum 19 via an inlet 23 positioned nearby the top side of the drum 19.

[0084] The heat-exchanging fluid 11 enters the first-stage heat exchanger 9 via an inlet 25 positioned nearby the bottom side of the combustion unit 7 and exits the first-stage heat exchanger 9 via an outlet 27 positioned nearby the top side of the combustion unit 7. The saturated gas 13 exits the drum 19 at the top side of the drum 19 and the saturated gas 13 enters the second-stage heat exchanger 17 nearby the bottom side of the second-stage heat exchanger 17.

[0085] The system 1 further comprises a fuel feeder 29 arranged for supply of iron fuel and an air inlet means 31 arranged for supply of air comprising oxygen to the iron fuel. The fuel feeder 29 and the air inlet means 31 are arranged upstream of the burner arrangement 43.

[0086] Also, the system 1 comprises a pump 33 arranged for transporting the heat-exchanging fluid 11 to the first-stage heat exchanger 9.

[0087] The system 1 further comprises a condenser 41 arranged for cooling the spent superheated gas before it is transferred back into the drum 19 as the heatexchanging fluid 11.

[0088] The system 101 according to the present disclosure is shown in Fig.

[0089] 2. It comprises the same components as the system 1 shown in Fig. 1 and in addition, the system 101 comprises a third-stage heat exchanger 35 that is configured to reheat spent superheated gas from a first part 37 of the high-energy-density-requiring process 3 into reheated gas for driving the high-energy-density-requiring process 3. The reheated gas is directed to a second part 39 of the high-energy-density-requiring process 3.

[0090] The system 201 according to the present disclosure is shown in Fig.

[0091] 3. It comprises the same components as the system 1 shown in Fig. 1 and in addition, the system 201 comprises two cyclone-type separation units 46a, 46b downstream of the second heat exchanger 17. For example, when the iron fuel combustion unit 7 is operated at half its normal capacity, so that only half of the iron oxide containing medium is present inside the system compared to normal operating conditions, one of the cyclones 46a, 46b may be inoperative so that the one that is operative is operating at its most efficient operation. Further visible is a bypass after the second cyclone 46b, feeding gas flow substantially cleaned of iron oxide particles and (partially) deprived of oxygen to burner arrangement 43. The bypass may however also be positioned anywhere else in the flow path, preferably after the first separation unit 15.

[0092] 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. Embodiments and examples of the first aspect of the present invention are also applicable to the second or further aspects of the present invention.

[0093] CLAUSES

[0094] 1. An iron fuel system for iron fuel combustion, generating superheated gas for driving a high-energy-density-requiring process, such as a steam turbine, said system comprising: a combustion unit arranged for combusting said iron fuel thereby generating an iron oxide containing medium, wherein said combusting releases heat; a first-stage heat exchanger, configured as an iron fuel boiler arrangement, comprising a heat-exchanging fluid in thermal communication with said iron oxide containing medium for heating at a first stage said heat-exchanging fluid to undergo a phase change of said heat-exchanging fluid into a saturated gas; a separation unit arranged downstream of said first-stage heat exchanger for separating said iron oxide containing medium into iron oxide and a gas flow; a second-stage heat exchanger comprising said saturated gas in thermal communication with said gas flow for heating at a second stage said saturated gas to obtain said superheated gas for driving said high-energy-density-requiring process, wherein said second-stage heat exchanger is arranged downstream of said separation unit.

[0095] 2. The iron fuel system according to clause 1 , wherein said system further comprises a drum comprising said heat-exchanging fluid that is connected to said first-stage heat exchanger and said second-stage heat exchanger.

[0096] 3. The iron fuel system according to clause 2, wherein said drum acts as a buffer for said heat-exchanging fluid.

[0097] 4. The iron fuel system according to clause 2 or 3, wherein said heatexchanging fluid exits said drum via an outlet positioned at or nearby the bottom side of said drum and / or wherein said saturated gas enters said drum via an inlet positioned at or nearby the top side of said drum.

[0098] 5. The iron fuel system according to any of the preceding clauses, wherein said heat-exchanging fluid enters said first-stage heat exchanger via an inlet positioned at or nearby the bottom side of said combustion unit and exits said first- stage heat exchanger via an outlet positioned at or nearby the top side of said combustion unit.

[0099] 6. The iron fuel system according to any of the preceding clauses, wherein said system further comprises an air inlet means arranged for supply of air comprising oxygen to said iron fuel.

[0100] 7. The iron fuel system according to any of the preceding clauses, wherein said system further comprises a pump and / or compressor arranged for transporting said heat-exchanging fluid to said first-stage heat exchanger.

[0101] 8. The iron fuel system according to any of the preceding clauses, wherein said system further comprises a third-stage heat exchanger configured to reheat spent superheated gas from a first part of said high-energy-density-requiring process into reheated gas for driving said high-energy-density-requiring process.

[0102] 9. The iron fuel system according to clause 8, wherein said system is arranged for directing said reheated gas to a second part of said high-energy-density- requiring process.

[0103] 10. The iron fuel system according to any of the preceding clauses, wherein said system further comprises a condenser arranged for cooling spent superheated gas, or when dependent on clause 14, for cooling spent reheated gas.

[0104] 11. The iron fuel system according to any of the preceding clauses, wherein said superheated gas and / or, when dependent to clause 8 and / or 9, said reheated gas, has a temperature in the range of from 100 °C to 800 °C, preferably 200 °C to 650 °C, more preferably 350 °C to 550 °C.

[0105] 12. The iron fuel system according to any of the preceding clauses, wherein said superheated gas and / or, when dependent to clause 8 and / or 9, said reheated gas, has a pressure in the range of from 0.1 MPa to 50 MPa, preferably 1 MPa to 30 MPa, more preferably 2 MPa to 10 MPa.

[0106] 13. The iron fuel system according to any of the preceding clauses, wherein said heat-exchanging fluid has a boiling point at or below the boiling point of water at atmospheric pressure, such as water, carbon dioxide, isobutane, isopentane, and propane.

[0107] 14. The iron fuel system according to any of the preceding clauses, wherein said system further comprises a further separation unit arranged downstream of said second-stage heat exchanger.

[0108] 15. The iron fuel system according to any of the preceding clauses, wherein said separation unit and / or said further separation unit is a gravimetricalbased and / or momentum-based separation and / or centrifugal-based separation system, wherein said centrifugal-based separation system is preferably a cyclone.

[0109] 16. The iron fuel system according to any of the preceding clauses, wherein said system further comprises a further air inlet means arranged for supply of air to said gas flow, and wherein said further air inlet means is arranged downstream of said combustion unit and upstream of said second-stage heat exchanger.

[0110] 17. The iron fuel system according to any of the preceding clauses, said system is designed for driving high-energy-density-requiring processes having a size of from 0.1 MW to 2000 MW, preferably 1 MW to 1000 MW, more preferably 5 MW to 500 MW.

Claims

CLAIMS1. An iron fuel system (201) for iron fuel combustion, configured to generate heat, said system comprising: a combustion unit (7) arranged for combusting said iron fuel thereby generating an iron oxide containing medium, wherein said combusting releases heat; a first heat exchanger (9), configured as an iron fuel boiler arrangement, comprising a heat-exchanging fluid (11) in thermal communication with said iron oxide containing medium for heating said heat-exchanging fluid; a first-stage separation unit (15) arranged downstream of said first heat exchanger, for separating said iron oxide containing medium into iron oxide and a hot gas flow, the first-stage separation unit being a momentum-based separation unit; a second heat exchanger (17) comprising a heat-exchanging fluid in thermal communication with said hot gas flow for heating said heat-exchanging fluid, wherein said second heat exchanger is arranged downstream of said first-stage separation unit, and a second-stage separation unit (46a) arranged downstream of said second heat exchanger, for further separating said hot gas flow into iron oxide and a gas flow, the second-stage separation unit being a cyclone-type separation unit.

2. The iron fuel system according to claim 1 , wherein said system further comprises a drum (19) comprising said heat-exchanging fluid that is connected to said first heat exchanger and said second heat exchanger.

3. The iron fuel system according to claim 2, wherein said drum acts as a buffer for said heat-exchanging fluid.

4. The iron fuel system according to claim 2 or 3, wherein said heatexchanging fluid exits said drum via an outlet (21) positioned at or nearby the bottom side of said drum and / or wherein said saturated gas enters said drum via an inlet (23) positioned at or nearby the top side of said drum.

5. The iron fuel system according to any of the preceding claims, wherein said heat-exchanging fluid enters said first heat exchanger via an inlet (25) positioned at or nearby the bottom side of said combustion unit and exits said first heat exchanger via an outlet (27) positioned at or nearby the top side of said combustion unit.

6. The iron fuel system according to any of the preceding claims, wherein said system further comprises an air inlet means (31) arranged for supply of air comprising oxygen to said iron fuel.

7. The iron fuel system according to any of the preceding claims, wherein said system further comprises a pump and / or compressor (33) arranged for transporting said heat-exchanging fluid to said first heat exchanger.

8. The iron fuel system according to any of the preceding claims, wherein said second-stage separation unit comprises two cyclone-type separation units (46a, 46b).

9. The iron fuel system according to any of the preceding claims, wherein said system further comprises a bypass arranged downstream of the first- stage separation unit, preferably downstream of the second-stage separation unit, for feeding gas flow substantially cleaned of iron oxide particles and at least partially deprived of oxygen to a burner arrangement (43).

10. The iron fuel system according to any of the preceding claims, wherein said system further comprises a condenser (41) arranged for cooling spent superheated gas.

11. The iron fuel system according to any of the preceding claims, wherein said heat-exchanging fluid has a temperature in the range of from 100 °C to 800 °C, preferably 200 °C to 650 °C, more preferably 350 °C to 550 °C.

12. The iron fuel system according to any of the preceding claims, wherein said heat-exchanging fluid has a pressure in the range of from 0.1 MPa to 50 MPa, preferably 1 MPa to 30 MPa, more preferably 2 MPa to 10 MPa.

13. The iron fuel system according to any of the preceding claims, wherein said heat-exchanging fluid has a boiling point at or below the boiling point of water at atmospheric pressure, such as water, carbon dioxide, isobutane, isopentane, and propane.

14. The iron fuel system according to any of the preceding claims, wherein said separation unit and / or said further separation unit is a gravimetricalbased and / or momentum-based separation and / or centrifugal-based separation system, wherein said centrifugal-based separation system is preferably a cyclone.

15. The iron fuel system according to any of the preceding claims, wherein said system further comprises a further air inlet means (48) arranged for supply of air to said gas flow, and wherein said further air inlet means is arranged downstream of said combustion unit and upstream of said second heat exchanger.

16. The iron fuel system according to any of the preceding claims, said system is designed for driving high-energy-density-requiring processes having a size of from 0.1 MW to 2000 MW, preferably 1 MW to 1000 MW, more preferably 5 MW to 500 MW.

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