Description:

FIELD OF THE INVENTION

The present invention relates to an iron fuel boiler process for iron fuel combustion.

Energy is indispensable. The amount of energy consumed worldwide has increased enormously over the last decades. Although the amount of energy originating from renewable energy sources such as wind and solar has increased over the last decades and especially over the last years, a large part of the energy still originates from fossil fuels.

With the use of fossil fuels also comes the highly undesirable carbon dioxide, CO2, emission. And in order to achieve climate objectives, the total CO2 emission should be reduced significantly. To this end, carbon-neutral fuel, and even more carbon-free fuel, is a preferable source of energy and promising resource to fulfill worldwide energy requirements but still meet the climate objectives. Carbon- neutral fuel is considered fuel does not release more carbon into the atmosphere than it removes, whereas carbon-free fuel produces no net-greenhouse gas emissions or carbon footprint at all. Typically, with carbon-neutral fuel, CO2 or other greenhouse gasses are used as feedstock.

Heat intensive industries are responsible for a large part of the total CC>2-emissions. But for many industries there are currently few or no fossil fuel alternatives available that on the one hand are scalable, and on the other hand able to provide sufficient energy with a high degree of certainty and consistency, yet are completely CC>2-emission-free.

Solar energy and wind energy can partly meet this need. However, due to the fact that they are intermittent, they are often not, or insufficiently suitable to replace fossil fuels and to meet the demand for energy from these industries at all times. In recent years, a lot of research has therefore been carried out into a feasible alternative that is fully CC>2-emission-free. Iron fuel has the potential to meet that need and to become the candidate of choice.

Iron fuel is a very promising fuel in which energy is stored in the iron powder when and where needed. In the right conditions, iron powder is flammable and has the property that when the iron powder is burned, a lot of energy is released in the form of heat. This heat can then be converted into hot water, steam or electricity for use in any kind of application or industry. Another important property of iron powder is that only rust remains during combustion, while no CO2 is released during the combustion of the iron powder. The rust, as a product, can be easily collected and converted back into the iron powder in a sustainable manner, which makes it a fully circular process.

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

Although the use of iron fuel may already be a proven clean and sustainable alternative to fossil fuels, there are also several challenges. Important challenges are to collect as much of the rust that remains after combustion as possible and to ensure that this rust has the right material properties to be converted back into high quality iron powder. Another challenges is how to optimize the heat release in the boiler process. There is therefore a need to improve the boiler process to optimize heat release and/or the collection of rust.

It is an object of the present invention to provide an improved boiler process for iron fuel combustion.

It is a further object of the present invention to provide a boiler process with improved reusability of the iron oxide (rust).

It is a further object of the present invention to provide a boiler process with improved heat release. It is a further object of the present invention to provide a boiler process with improved efficiency.

STATEMENT OF THE INVENTION

The invention relates to an iron fuel boiler process for iron fuel combustion, comprising the steps of: combusting an iron fuel suspension medium comprising iron fuel and oxygen in an iron fuel burner arrangement to obtain an iron oxide containing medium; receiving said iron oxide containing medium into an iron fuel boiler arrangement for transferring said iron oxide containing medium towards a separation unit disposed at the end of said iron fuel boiler arrangement; exchanging heat between said iron oxide containing medium and a boiler of said iron fuel boiler arrangement with a heat-exchange medium during said transfer of said iron oxide containing medium through said iron fuel boiler arrangement; separating iron oxide from said oxide containing medium to obtain solid iron oxide particles and a gas flow; said process further comprising the step of: cooling said iron oxide containing medium with a cooling medium during said transfer of said iron oxide containing medium through said iron fuel boiler arrangement such that a temperature of said iron oxide is achieved of below the sintering temperature of the particles at said separation unit.

The present disclosure relates to a boiler process for iron fuel combustion. The inventors have found that the known boiler processes which are suitable for example for a process of burning coal, coal-like material, biomass, oilbased material and gas are not suitable or less suitable for a process of burning iron fuels. For an iron fuel specific boiler process design requirements are applicable which are different from these known boiler processes. One of the most important differences is that iron fuel is intended to be used as a burnable clean energy medium in which the iron powder can be used in a circular manner, meaning that the by-product of the iron fuel after burning, i.e. the rust, is to be collected and should be suitable to be converted back into iron powder.

Iron powder has many advantages as it is cheap, abundant, easy to transport and has a high energy density. Moreover, the storage and transport have little requirements, whereas other high energy density fuels such as hydrogen for example require extreme cooling for efficient transport and storage. Iron fuel also has zero to less tendency to lose any energy during long periods of storage.

One of the challenges of using iron powder as a sustainable and circular energy medium lies within the boiler process as known boiler processes are simply not suitable for iron fuel application and/or are far from efficient. They may also require excessive maintenance requirements.

What the inventors found was that these requirements could be met with a boiler process where both heat-exchange and cooling take place. An iron oxide containing medium is received into an iron fuel boiler arrangement, and transferred through the boiler arrangement towards a separation unit disposed at the end of said iron fuel boiler arrangement. During the transfer of the iron oxide containing medium, heat-exchange takes place with a heat-exchange medium in a boiler of the boiler arrangement. In addition, the iron oxide containing medium is cooled with a cooling medium during the transfer towards to the separation unit. This results in a temperature of the iron oxide of below the sintering temperature of the particles at said separation unit. This temperature allows separation of the iron oxide from the gas flow and thus collecting obtained iron oxide in high quantity and quality. This temperature is lower than in conventional boiler systems, since such a low temperature would lead to a suboptimal use of radiation heat.

DETAILED DESCRIPTION

The present invention is elucidated below with a detailed description.

As stated above, the invention relates to with a boiler process where both heat-exchange and cooling take place. With heat-exchange in this context is meant direct heat-exchange to another medium, such as water or air. Cooling of the iron oxide medium may take place by mixing with another medium, such as water or air.

The iron fuel boiler arrangement comprises a boiler with a heatexchange medium. This heat exchange medium could be the walls of the boiler, a liquid or gas inside the boiler, or a heat exchange medium that transfers the heat to a downstream (or upstream) process. Examples of a suitable liquid inside the boiler are water and oil. When the heat-exchange medium is water, it may be heated to a temperature of between 80 and 640°C. The limit of 640°C is determined by material limits in industry. The water may have a pressure of above 22, 1 MPa for a supercritical boiler, and below 22,1 MPa, such as 60-6400 kPa, for a subcritical boiler.

In an embodiment of the iron fuel boiler process according to the invention, said iron fuel boiler arrangement comprises water inlet means arranged for said cooling step. Using water as a cooling medium has the advantage that water can retain more heat than air, such that smaller volumes of water are required to accomplish the same cool down.

In an embodiment of the iron fuel boiler process according to the invention, said iron fuel boiler arrangement comprises air inlet means arranged for said cooling step. Air can be added to the boiler arrangement via said air inlet means to cool the iron oxide in said iron oxide containing medium. This air may be environmental air, optionally conditioned e.g. to reduce moisture content. This air may also be cooled, recirculated flue gas. The air may mix with the iron oxide containing medium. Using air as a cooling medium has the advantage that the air may mix with the iron oxide containing medium and does not have to be removed separately from the boiler arrangement.

In an embodiment of the iron fuel boiler process according to the invention, said step of cooling is performed during said exchange of heat. It can be envisioned that heat-exchange and cooling may take place simultaneously during the transfer of the iron oxide containing medium towards the separation unit. This may be for instance for the full duration or substantially the full duration of said transfer of said iron oxide containing medium through said iron fuel boiler arrangement.

In an embodiment of the iron fuel boiler process according to the invention, said step of cooling is performed during part of said exchange of heat. It can be envisioned that for instance heat-exchange may take place during the full duration or substantially the full duration of the transfer of the iron oxide containing medium towards the separation unit, where cooling takes place only during a part of the duration of the transfer. This part may be at the beginning of the transfer, or at the end of the transfer (close to the separation unit), or it may be in the middle of the transfer. Preferably, this part is at the beginning of the transfer.

In an embodiment of the iron fuel boiler process according to the invention, the process further comprises the step of exchanging heat between said gas flow and said boiler of a iron fuel boiler arrangement, and preferably iron fuel boiler arrangement of said iron fuel boiler process, with a heat-exchange medium after said separation of said iron oxide from said oxide containing medium. Thus, the gas flow obtained at the separation unit may subjected to heat-exchange downstream of the separation unit.

In an embodiment of the iron fuel boiler process according to the invention, said step of cooling comprises: cooling down said oxide containing medium while said oxide containing medium is directed away from a wall surface of said iron fuel boiler arrangement. With the term “directed away from the wall surface” in the present description is meant that the amount of particles (e.g. iron oxide particles) that will come in contact with the wall surface of the boiler arrangement is minimized. Iron oxide particles that come into contact with a wall surface may stick to the wall surface (slagging), specifically when the temperature of the iron oxide is above the sintering temperature of the particles. The sintering temperature is defined as the initial temperature where particles start to sinter to each other. The definition of this temperature is stated by ISO 3252:1999. Tests for determining this temperature for iron fuel are known as dilatometry, and are performed by the following standards: DIN51045 I ASTM E831 (2019) and ASTM E228 (2017), the name for the tests is dilatometry. This temperature may be 700°C, but it may also be higher, such as 800°C. This leads to contamination of the burner and boiler arrangement, as well as loss of iron oxide. In a specific embodiment, said iron fuel boiler arrangement comprises a boiler housing geometry arranged for said cooling to direct said oxide containing medium away from said wall surface by said geometry. In a specific embodiment, said iron fuel boiler arrangement comprises air inlet means arranged for said cooling step to direct said oxide containing medium away from said wall surface. In this embodiment, at least part of the air inlets arranged for said cooling step, but not necessarily all, are to direct said oxide containing medium away from said wall surface. In an embodiment, said iron fuel boiler arrangement comprises both a housing geometry arranged and air inlet means arranged for said cooling step to direct said oxide containing medium away from said wall surface.

It should be understood that it is possible that not all iron fuel particles are fully converted into iron oxide particles in the burner process. The term “iron oxide particles” is to be understood in the context of the present description to mean that the vast majority of the particles are iron oxide particles, but some non-oxidized particles may be present.

In an embodiment of the iron fuel boiler process according to the invention, said transfer of said iron oxide containing medium towards said separation unit takes place in a vertically downwards direction. It is to be understood that a vertically downwards direction includes also diagonally downwards directions.

In an embodiment of the iron fuel boiler process according to the invention, separating iron oxide from said oxide containing medium is performed to such a degree that at least 95 wt.% iron oxide particles with a size of at least 10pm are separated from said oxide containing medium

In an embodiment of the iron fuel boiler process according to the invention, said separation unit is a gravimetrical-based separation and/or momentumbased separation system. This embodiment is particularly relevant for the separation of particles >20 pm. In an embodiment of the iron fuel boiler process according to the invention, said separation unit is a gravimetrical-based separation and/or momentum- based separation and/or centrifugal-based separation system. This embodiment is particularly relevant for the separation of particles >10 pm and preferably >5 pm. The centrifugal-based system is preferably a cyclone.

In an embodiment of the iron fuel boiler process according to the invention, the process further comprises a step after said step of separation, of a secondary separation such that a total separation of at least 99 wt.%, preferably at least 99.9 wt.% iron oxide particles from the gas flow is achieved.

In an embodiment of the iron fuel boiler process according to the invention, the process further comprises a step of cooling down the separated iron oxide particles to a temperature of below 180 °C, preferably using a heating transfer medium. In a specific embodiment of this, the separated iron oxide particles are cooled down to a temperature of below 100 °C.

Effects of the invention

With the boiler process according to the invention, one or more objects of the invention are achieved.

The boiler process according to the invention allows for heat exchange during the transfer of the iron oxide containing medium towards the separation unit. The additional cooling ensures that the iron oxide in the iron oxide containing medium cools to such a temperature range that the iron oxide particles can be separated from the gas flow with high efficiency (yield) and that the particles are of good quality to be reduced to iron fuel. By having a cooling step, part of the heat of the iron oxide containing medium may be unutilized in the heat-exchange (i.e. the heatexchange in the boiler arrangement may be suboptimal). However, the additional cooling allows for achieving a temperature range of the iron oxide containing medium at the separation unit that allows for recovery of the iron oxide in higher quantity and/or higher quality (e.g. particle size distribution) than when the temperature of the iron oxide at the separation unit would be outside of this range. This contributes to an overall optimization of the iron fuel process, since the iron oxide can be reduced into iron fuel and be combusted again. 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. 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.