BOILER FOR IRON FUEL COMBUSTION ARRANGEMENT

Abstract

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

Claims

1. 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 an 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 iron 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 by mixing the 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 said solid iron oxide particles at said separation unit.

2. The iron fuel boiler process according to claim 1, wherein a temperature of said iron oxide is achieved of below 800 C. at said separation unit.

3. The iron fuel boiler process according to claim 1, wherein said iron fuel boiler arrangement comprises air inlet means arranged for said cooling step.

4. The iron fuel boiler process according to claim 1, wherein said iron fuel boiler arrangement comprises water inlet means arranged for said cooling step.

5. The iron fuel boiler process according to claim 1, wherein said step of cooling is performed during said exchange of heat.

6. The iron fuel boiler process according to claim 5, wherein said step of cooling is performed during part of said exchange of heat.

7. The iron fuel boiler process according to claim 1, further comprising the step of: exchanging heat between said gas flow and said boiler of an iron fuel boiler arrangement, with a heat-exchange medium after said separation of said iron oxide from said oxide containing medium.

8. The iron fuel boiler process according to claim 1, wherein said step of cooling comprises: cooling down said iron oxide containing medium while said oxide containing medium is directed away from a wall surface of said iron fuel boiler arrangement.

9. The iron fuel boiler process according to claim 8, wherein 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.

10. The iron fuel boiler process according to claim 8, wherein 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.

11. The iron fuel boiler process according to claim 1, wherein said transfer of said iron oxide containing medium towards said separation unit takes place in a vertically downwards direction.

12. The iron fuel boiler process according to claim 1, wherein 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 10 m, are separated from said oxide containing medium.

13. The iron fuel boiler process according to claim 1, wherein said separation unit is a gravimetrical-based and/or momentum-based separation and/or centrifugal-based separation.

14. The iron fuel boiler process according to claim 1, further comprising a step of cooling down the separated iron oxide particles to a temperature of below 180 C.

Description

DETAILED DESCRIPTION

[0023] The present invention is elucidated below with a detailed description.

[0024] 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.

[0025] The iron fuel boiler arrangement comprises a boiler with a heat-exchange 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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/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.

[0032] 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.

[0033] 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.

[0034] 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 10 m are separated from said oxide containing medium

[0035] 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 system. This embodiment is particularly relevant for the separation of particles >20 m. 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 m and preferably >5 m. The centrifugal-based system is preferably a cyclone.

[0036] 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.

[0037] 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

[0038] With the boiler process according to the invention, one or more objects of the invention are achieved.

[0039] 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 heat-exchange 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.

[0040] 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.