TECHNICAL FIELD

The present disclosure relates in general to a furnace configured for treatment of particulate matter in a controlled gaseous environment. The present disclosure further relates to the use of such a furnace for thermal treatment of particulate matter. The present disclosure further relates in general to a method for thermal treatment of particulate matter.

BACKGROUND

There is a variety of processes wherein a carbonaceous particulate matter may need to be subjected to thermal processing at a high temperature and in a controlled gaseous environment. Such processes cannot be performed in any type of furnace and it is therefore important to have a proper furnace configuration for the intended use.

In addition to being able to be used at desired temperatures, the furnace should for example also be able to withstand abrasion caused by particulate matter treated in the furnace coming into contract with the walls of the furnace. Furthermore, contamination of the carbonaceous particulate matter needs to be avoided since it may deteriorate the desired characteristics of the carbonaceous particulate matter. Contamination of the carbonaceous particulate matter may for example occur if hetero elements or impurities are released from the furnace walls, for example due to the interaction between furnace wall and the particulate matter. Ceramic materials commonly used in high temperature furnaces may typically cause such contamination and should therefore be avoided.

Furthermore, in some processes for treating carbonaceous particulate matter, there may be a desire to be able to perform the thermal treatment in an atmosphere comprising one or more halogens. Certain halogens may risk causing corrosion, at least at high temperatures, to parts of the furnace. Such corrosion may shorten the service life of the furnace and/or cause considerable downtime for replacement of corroded parts of the furnace. SUMMARY

The object of the present invention is to provide a furnace suitable for high temperature treatment of particulate matter, in particular carbonaceous particulate matter, in a controlled gaseous environment, even if the gaseous environment comprises one or more halogens.

The object is achieved by the subject-matter of the appended independent claim(s).

The present disclosure provides a furnace configured for treatment of particulate matter in a controlled gaseous environment. The furnace comprises a processing chamber and a furnace wall extending in a longitudinal direction of the furnace, said furnace wall comprising an interior surface facing the processing chamber. The furnace wall comprises a first rigid graphite layer, optionally lined with a flexible graphite sheet on an inside surface thereof, forming the interior surface of the furnace wall. Said first rigid graphite layer is configured to provide structural integrity to the furnace wall. The furnace wall further comprises a first thermal insulation layer arranged outside of the first rigid graphite layer, the first thermal insulation layer comprising refractory felt. The furnace wall may optionally further comprise a second thermal insulation layer arranged outside of the first thermal insulation layer. The furnace wall further comprises a gas-proof layer arranged between the first rigid graphite layer and the first thermal insulation layer, or between the first thermal insulation layer and the optional second thermal insulation layer. Moreover, the furnace wall comprises a metal casing layer forming an exterior of the furnace.

Due to the configuration of the furnace wall, the present furnace is particularly suitable for high temperature treatment of carbonaceous particulate matter, in a controlled gaseous environment comprises one or more halogens. More specifically, the first rigid graphite layer, in addition to providing structural integrity to the furnace wall, ensures that the furnace wall is able to resist the abrasion caused by particulate matter treated in the furnace and that the furnace may be operated at high temperatures, such as 900 °C to at least 1500 °C. Moreover, since the interior surface of the furnace wall is formed of graphite, the risk for contamination of particulate matter to be treated inside the furnace is minimized. Furthermore, the gas-proof layer ensures that gaseous species from the interior of the furnace is not able to reach the metal casing layer. This is particularly advantageous when the controlled gaseous environment in the furnace comprises halogens, which may otherwise cause corrosion to the metal casing layer and thereby reducing the lifetime of the furnace considerably. Moreover, the first thermal insulation layer and the optional thermal insulation layer ensures that the metal casing layer is sufficiently thermally protected. The fact that the first thermal insulation layer comprises refractory felt ensures that the furnace may be operated at high temperatures and may also reduce the risk for stresses caused by difference in thermal expansion of the different layers inside the furnace wall, which may otherwise risk damaging the furnace wall and thereby reduce the lifetime of the furnace.

The gas-proof layer may suitably be formed of graphite foil, or of a chemical vapor deposition (CVD) coating of graphite. Preferably, the gas-proof layer is formed of a flexible graphite foil. A graphite foil or a CVD coating inter alia has better sealing properties and better strength than for example a carbon foil not comprising graphite.

The refractory felt may be selected from the group consisting of carbon felt, graphite felt and zirconia felt. These are all suitable options due to their thermal insulation properties as well as being resistant to halogens.

The first graphite layer may be directly bonded to the first thermal insulation layer or the gas-proof layer.

The furnace wall may further comprise an induction coil. Thereby, an induction furnace is achieved. The induction coil may suitably be arranged outside of the first thermal insulation layer.

The induction coil may be encapsulated by an electrical insulation material, preferably encapsulated in refractory concrete. If so, the refractory concrete may also contribute to the structural integrity of the furnace wall.

When the furnace wall comprises an induction coil, the furnace wall may further comprise a susceptor layer arranged outside of the first rigid graphite layer. If so, the gas-proof layer may be arranged between the first rigid graphite layer and the susceptor layer. Thereby, the gas-proof layer may be protected against thermal shock as may occur if the gas-proof layer is arranged such that it will function as a (primary) susceptor.

The susceptor layer may suitably be in the form of a second rigid graphite layer. A rigid graphite layer is corrosion resistant and may be used at high temperature and is therefore suitable for use as a susceptor in the present furnace. Furthermore, a second rigid graphite layer also contributes to the structural integrity of the furnace wall and therefore enables a thinner first rigid graphite layer, if desired. Furthermore, in case the furnace wall comprises an induction coil, the furnace wall may further comprise a magnetic yoke arranged outside of the induction coil. Thereby, the magnetic field generated inside the furnace wall may be guided.

The furnace wall may further comprise cooling means to facilitate cooling of the processing chamber. Any suitable cooling means may be used, for example a water-based cooling system. The cooling means may suitably be arranged outside of the gas-proof layer. The cooling means may for example be arranged between the gas-proof layer and the first thermal insulation layer. When the furnace wall comprises an induction coil, the cooling means may be arranged to cool the induction coil in addition to cooling of the processing chamber, and may be arranged adjacent to the induction coil.

The first rigid graphite layer may suitably have a thickness, as seen in a direction perpendicular to the longitudinal direction of the furnace, of at least 1 cm, preferably at least 1.5 cm. Thereby, it is ensured that the furnace wall has a desired structural integrity even at high temperatures.

The first thermal insulation layer and/or the optional second thermal insulation layer may be configured to contain pressurized gas. Thereby, the risk of diffusion of gaseous species from the interior of the furnace through the gas-proof layer may be avoided even if the gas-proof layer would be damaged.

The optional second thermal insulation layer may comprise ceramic or carbon (including graphite fibers) fibers.

The first rigid graphite layer may be formed of a cylindrical tube. Thereby, the number of joints in the interior surface of the furnace wall is reduced, which reduces the risk for leakage of gaseous species through the furnace wall extending in the longitudinal direction of the furnace.

The furnace according to the present disclosure may be a fluidized bed reactor. A fluidized bed reactor is a type of furnace that is well suited for high temperature treatment of particulate matter in a controlled gaseous environment.

The fluidized bed reactor may suitably comprise a distributor through which the fluidizing gas passes into the processing chamber, said distributor being formed of porous rigid graphite. Thereby, the risk of contaminating the carbonaceous particulate matter is minimized while still achieving a desired flow of fluidizing gas without having to form distinct through-openings therefore in the distributor.

Alternatively, the furnace according to the present disclosure may be a rotary kiln. A rotary kiln is particularly advantageous for example when desiring to treat a large amount of particulate matter in a continuous manner.

The furnace according to the present disclosure may also be another type of furnace, for example a batch furnace or a tunnel furnace, such as a pusher furnace.

The present disclosure further provides a method for thermal treatment of particulate matter. The method comprises subjecting the particulate matter to an atmosphere comprising one or more halogens at a temperature of at least 800 °C, preferably at least 900 °C or at least 1000 °C, in the furnace as described above.

The particulate matter may for example be selected from the group consisting of hard carbon powder, hard carbon granules, carbon nanotubes, charcoal granules and charcoal powder.

The present disclosure also relates to the use of the above-described furnace for thermal treatment of particulate matter, such as carbonaceous particulate matter, in a gaseous environment comprising one or more halogens at a temperature of at least 800 °C, preferably at least 900 °C or at least 1000 °C.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 schematically illustrates a cross sectional view of an example of a fluidized bed reactor,

Fig. 2 schematically illustrates a cross sectional view of an example of a rotary kiln,

Fig. 3 schematically illustrates a cross sectional view of a first exemplifying embodiment of the furnace wall of the furnace according to the present disclosure, Fig. 4 schematically illustrates a cross-sectional view of a second exemplifying embodiment of the furnace wall of the furnace according to the present disclosure,

Fig. 5 schematically illustrates a cross-sectional view of a third exemplifying embodiment of the furnace wall of the furnace according to the present disclosure.

Fig. 6 schematically illustrates a cross-sectional view of a fourth exemplifying embodiment of the furnace wall of the furnace according to the present disclosure,

Fig. 7 schematically illustrates a cross-sectional view of a fifth exemplifying embodiment of the furnace wall of the furnace according to the present disclosure, and

Fig. 8 schematically illustrates a cross-sectional view of a sixth exemplifying embodiment of the furnace wall of the furnace according to the present disclosure.

DETAILED DESCRIPTION

The invention will be described in more detail below with reference to exemplifying embodiments and the accompanying drawings. The invention is however not limited to the exemplifying embodiments discussed and/or shown in the drawings, but may be varied within the scope of the appended claims. Furthermore, the drawings shall not be considered drawn to scale as some features may be exaggerated in order to more clearly illustrate the invention or features thereof.

In the present disclosure, the term "layer" is used to describe a constituent component of a furnace wall that may be distinctively identified from adjacent constituent components. A layer may be in the form of a rigid or flexible component or a coating, but is not intended to describe any means for bonding (such as an adhesive) or attaching adjacent constituent components to each other. A layer may be composed of a single layer or comprise a plurality of sublayers without departing from the term "layer" as long as the plurality of sublayers have the same configuration. For example, a plurality of thermally insulation layers comprising the same type of fibers and arranged immediately adjacent to each other are herein intended to jointly form a layer.

In accordance with the present disclosure, a furnace configured for treatment of particulate matter in a controlled gaseous environment is provided. The furnace according to the present disclosure is particularly suitable for high temperature processing, such as at a temperature of about 800 - 1500 °C, of particulate matter in a controlled gaseous environment, in particular a gaseous environment comprising one or more halogens. The particulate matter may be carbonaceous particulate matter. More specifically, the particulate matter may be selected from the group consisting of hard carbon powder, hard carbon granules, carbon nanotubes, charcoal granules and charcoal powder.

The furnace according to the present disclosure comprises a processing chamber configured to contain the particulate matter and a furnace wall extending in a longitudinal direction of the furnace. In addition to the longitudinally extending furnace wall, the furnace naturally also comprises end walls arranged at the longitudinally opposing ends of the furnace. These end walls may have the same configuration, in terms of constituent materials and layers, as the longitudinally extending furnace wall. Alternatively, these end wall may have a different configuration than the longitudinally extending furnace wall. Unless explicitly disclosed otherwise, the term "furnace wall" will in the following be used to describe the wall of the furnace which is extending in the longitudinal direction of the furnace.

The furnace wall may be arranged to circumscribe the processing chamber. According to one alternative, the furnace wall may be rotational symmetrical around a longitudinal axis of the furnace. In other words, the furnace wall may have a cylindrical shape. Alternatively, the furnace wall may be circumscribing the processing chamber while having a (hollow) rectangular cross section. A rectangular cross section may however in some cases be less preferred as it may increase the risk for stagnation zones depending on desired flow of process gas through the processing chamber. The furnace wall may have the same cross-sectional shape and size along the entire longitudinal extension thereof. Alternatively, the furnace wall may be tapering from one longitudinal end towards the opposing longitudinal end of the longitudinally extending furnace wall, such that the cross- sectional size decreases along the longitudinal extension of the furnace.

The furnace wall comprises an interior surface facing the processing chamber of the furnace and an exterior surface facing towards the surroundings of the furnace. In the following, when directions like "inside of" or "outside of" are given, these shall be interpreted as referring to the corresponding directions of the furnace. Thus, when a first layer is described to be arranged outside of a second layer, such a first layer shall be considered to be arranged further from the interior (i.e. the processing chamber) of the furnace than said second layer. As mentioned above, the furnace according to the present disclosure comprises a furnace wall extending in a longitudinal direction of the furnace. Said furnace wall comprises a first rigid graphite layer forming the interior surface of the furnace wall. The first rigid graphite layer is configured to provide structural integrity to the furnace wall, either independently or together with one or more additional layers of the furnace wall. The first rigid graphite layer further provides a resistance to abrasion caused by particulate matter treated in the furnace for example impinging the interior surface of the furnace wall.

A rigid graphite layer may be produced from graphite powder (and optionally a binder) by extrusion, compression molding or hot-isostatic pressing. The result is a rigid body, such as a rigid sheet, tube or the like, which possesses structural integrity. A rigid graphite layer is also thermally conductive.

The first rigid graphite layer may optionally be lined with a flexible graphite sheet on an inside (interior) surface thereof, in which case said flexible graphite sheet forms the interior surface of the furnace wall. The flexible graphite sheet lined on the inside surface of the first rigid graphite layer may be a lining which is accepted to be worn down over time by the abrasion caused by the particulate matter treated inside the furnace.

The first rigid graphite layer may suitably have a thickness, as seen in a direction perpendicular to the longitudinal direction of the furnace, of at least 1 cm, preferably at least 1.5 cm, in order to provide sufficient structural integrity to the furnace wall. The first rigid graphite layer may preferably have a thickness of at least 2 cm, at least 3 cm, or at least 5 cm. The first rigid graphite layer suitably has a thickness of at most 15 cm or at most 12 cm, but the present disclosure is not limited thereto.

The furnace wall further comprises a first thermal insulation layer arranged outside of the first rigid graphite layer. The first thermal insulation layer comprises or consists of refractory felt. The first thermal insulation layer is primarily intended to thermally protect other parts of the furnace wall, in particular the exterior surface of the furnace wall, against the high temperature inside the furnace. The fact that the first thermal insulation layer comprises or consist of refractory felt ensures that said layer is both thermally resistant as well as corrosion resistant to gaseous species, such as one or more halogens, that may be diffusing into the furnace wall from the interior of the furnace.

The first thermal insulation layer may suitably have a thickness of at least 0.3 cm, at least 0.5 cm or at least 0.8 cm, as seen perpendicular to the longitudinal extension of the furnace. The thickness of the first thermal insulation layer may be up to 20 cm or up to 10 cm, but is not limited thereto. The furnace wall may optionally further comprise a second thermal insulation layer arranged outside of the first thermal insulation layer. The second thermal insulation layer may be made of the same material as the first thermal insulation layer, or of a different material. However, the second thermal insulation layer suitably comprises ceramic or carbon fibers, for example in the form of a refractory felt.

The furnace wall further comprises a gas-proof layer. The gas-proof layer is a layer configured to prevent diffusion of gaseous species, such as halogens, therethrough. The gas-proof layer is arranged between the first rigid graphite layer and the thermal insulation layer, or between the first thermal insulation layer and the optional second thermal insulation layer. In case the second thermal insulation layer is present, the gas-proof layer may, if desired, be arranged so as to encapsulate the first thermal insulation layer. In such a case, the gas-proof layer may be described to be present both inwardly of and outwardly of the first thermal insulation layer. In case the furnace wall does not comprise the second thermal insulation layer, the gas-proof layer should however preferably not be arranged so as to encapsulate the first thermal insulation layer as this may increase the risk for formation of a heat bridge through the gas-proof layer to the exterior of the furnace, although the risk therefore may be relatively low.

The gas-proof layer may for example have a thickness of from 0.1 mm to 20 mm, suitably from 0.2 mm to 5 mm, but is not limited thereto.

The furnace wall further comprises a metal casing layer forming an exterior of the furnace. The metal casing may for example be formed of steel. The metal casing layer may serve the purpose of providing protection to the furnace wall against external influences on the furnace and/or facilitating mounting the furnace to a surface on which the furnace should rest.

The gas-proof layer may suitably be formed of graphite foil or a coating of graphite deposited by chemical vapor deposition (CVD). Preferably, the gas-proof layer is formed of flexible graphite foil. However, in some cases, a stiffened graphite foil may alternatively be used as gas-proof layer.

Graphite foils are as such previously known. A flexible graphite foil may for example be produced by compressing or otherwise compacting expanded graphite particles. One example of a method for producing a flexible graphite foil is described in US 3,404,061. Flexible graphite foils generally have a high thermal conductivity. Furthermore, forming a coating of graphite by means of CVD on various types of substrates is also previously known and will therefore not be described in more detail herein.

The refractory felt of the first thermal insulation layer may be selected from the group consisting of carbon felt, graphite felt and zirconia felt. Such refractory felts are both thermally insulating and have excellent corrosion resistance to gaseous species such as halogens.

A carbon felt or graphite felt may be produced by carbonizing/graphitizing a needled, non-woven blanket of carbon precursor fibers. Such a felt is flexible and thus does not provide any structural integrity to the furnace wall. However, it is also possible to use a rigid carbon or graphite felt, if desired, for the purpose of providing some structural integrity. This may be achieved by adding a graphite based resin to the carbon felt or the graphite felt and allowing said graphite based resin allowed to solidity in the felt. Both a carbon felt and a graphite felt may either be PAN-based or Rayon-based.

Other refractory felts, such as zirconia felt, may for example be produced by forming a slurry comprising refractory fibers, vacuum-molding the slurry to obtain a dried felt, and thereafter sintering the dried felt.

According to some embodiments, the gas-proof layer is arranged immediately adjacent the first rigid graphite layer. According to other embodiments, the first thermal insulation layer is arranged immediately adjacent the first rigid graphite layer. "Immediately adjacent" is here intended to mean that there is no other layer or structural component arranged between two layers described to be immediately adjacent to each other, other than possibly means used for attaching or bonding the layers to each other (such as an adhesive). In other words, the first rigid graphite layer may be directly bonded to the first thermal insulation layer or to the gas-proof layer, depending on the respective embodiments.

The furnace wall may further comprise cooling means. Any suitable cooling means may be used, for example a water-based cooling system. In a water-based cooling system, cooling water, preferably deionized water, is transported in tubes or pipes. By providing cooling means, cooling of the processing chamber is facilitated. In embodiments where the furnace wall comprises cooling means, the cooling means are preferably arranged outside of the gas-proof layer, such as between the gasproof layer and the first thermal insulation layer. The furnace may be an induction furnace, in which case the furnace wall further comprises an induction coil. The induction coil may suitably be arranged outside of the first thermal insulation layer. The induction coil may be encapsulated in an electrically insulating material, such as refractory concrete. This may for example be achieved by casting refractory concrete around the induction coil.

When the furnace comprises an induction coil, the first rigid graphite layer may also function as susceptor. Alternatively, the furnace wall further comprises a susceptor layer arranged outside of the first rigid graphite layer but inside of the induction coil. If so, the gas-proof layer is suitably arranged between the first rigid graphite layer and the susceptor layer. The susceptor layer may suitably be in the form of a second rigid graphite layer.

Moreover, when the furnace wall comprises an induction coil, the furnace wall may optionally further comprise a magnetic yoke arranged outside of the induction coil. The purpose of such a magnetic yoke is to guide the magnetic field generated by the induction coil.

When the furnace wall comprises an induction coil, the cooling means may be arranged to cool the induction coil in addition to cooling of the processing chamber. In such embodiments, the cooling means may be arranged adjacent to the induction coil. For example, a water-based cooling system may be encapsulated along with the induction coil in an electrically insulating material, such as refractory concrete.

If desired, the first thermal insulation layer and/or the second thermal insulation layer may, if arranged outside of the gas-proof layer, be configured to contain pressurized gas. This has the advantage of avoiding risk of diffusion of gaseous species from the interior of the furnace through the gas-proof layer in case the gas-proof layer would be damaged for some reason. In such a case, the pressurized gas would instead be diffused in the opposite direction through the gas-proof layer thereby efficiently preventing the gaseous species from the interior of the furnace reaching parts of the furnace which may be susceptible to corrosion if exposed to such gaseous species. The same advantageous effect may alternatively be achieved in case of the furnace wall comprising a cavity arranged immediately outside of the gas-proof layer, said cavity being configured to contain pressurized gas or being configured to allow a continuous flow of gas therethrough. Thus, according to one embodiment, the furnace wall further comprises a longitudinally extending cavity arranged outside of the gas-proof layer, said cavity being configured to contain pressurized gas or being adapted for a continuous flow of gas through the cavity. The gas contained in the first or second thermal insulating layer, contained in the cavity, or flowing through the cavity may suitably be an inert gas, such as argon or nitrogen.

The furnace according to the present disclosure may be configured to be heated by means of electrical resistance heating elements arranged inside the furnace, suitably graphite resistance heating elements. Alternatively, the furnace may be an induction furnace, i.e. a furnace configured to be heated by means of induction. According to a third alternative, the furnace may be configured to be heated by using a part of the furnace wall as a resistance heating element. More specifically, the first rigid graphite layer may be configured to act as a resistance heating element. In such a case, the first rigid graphite layer is electrically connected to a power source of the furnace.

The furnace according to the present disclosure may suitably be a fluidized bed reactor or a rotary kiln. Alternatively, the furnace according to the present disclosure may be another type of furnace, for example a batch furnace or a tunnel furnace, such as a pusher furnace.

Moreover, the furnace according to the present disclosure may be a continuous furnace, which means that it is configured for continuous processing of particulate matter. Alternatively, the furnace according to the present disclosure may be configured for batch treatment of particulate matter.

Figure 1 schematically illustrates a cross sectional view of an example of a fluidized bed reactor 1 (hereinafter abbreviated FBR) configured for treatment of particulate matter in a controlled gaseous environment. The FBR 1 is a vertically arranged furnace and thus has a longitudinal axis A which is perpendicular to the ground on which the FBR 1 is arranged. The FBR 1 comprises a processing chamber 3 and a furnace wall 4 extending in the longitudinal direction of the FBR 1. The furnace wall 4 surrounds the processing chamber and may typically have a cylindrical configuration, although the present disclosure is not limited thereto. In other words, the furnace wall 4 may be rotational symmetrical around the longitudinal axis A. Furthermore, the longitudinally extending furnace wall 4 is at its opposing longitudinal ends connected to furnace end walls 5. The furnace end walls 5 may for example have the shape of a truncated cone as shown in the figure, or be dome-shaped. It is naturally also possible that one of the furnace end walls 5 has the shape of a truncated cone whereas the opposing furnace end wall 5 is dome-shaped.

The FBR 1 further comprises an inlet 6 configured for introducing particulate matter to be processed in the processing chamber and an outlet 7 through which treated particulate matter may be removed from the processing chamber 3. Although the outlet 7 is here shown to be arranged at the top of the FBR, the outlet 7 may be arranged at other positions of the FBR. Process gas may be removed from the processing chamber 3 via the same outlet 7 as the particulate matter or from another outlet (not shown). The FBR 1 further comprises an inlet 8 for introducing fluidizing gas, via a distributor 9, into the processing chamber 3. Although not shown in the figure, the FBR 1 may comprise one or more additional inlets and/or outlets for introducing or evacuating for example process gas.

When a FBR, like the one shown in Figure 1, is used for thermal treatment of carbonaceous particulate matter, the distributor 9 may suitably be made of porous rigid graphite. This reduces the risk of unintentional contamination of the carbonaceous particulate matter otherwise resulting from release of impurities from the material of the distributor. Furthermore, using porous rigid graphite in the distributor avoids the need of machining through-openings in the distributor for allowing the fluidizing gas to pass therethrough. In fact, porous rigid graphite achieves in itself a good distribution of the fluidizing gas into the processing chamber without causing a substantial pressure drop.

Figure 2 schematically illustrates a cross sectional view of an example of a rotary kiln 2 configured for treatment of particulate matter in controlled gaseous environment. The rotary kiln 2 may be horizontally arranged or inclined in relation to a horizontal plane, the horizontal plane corresponding to the ground on which the rotary kiln 2 is arranged. In other words, the longitudinal axis A of the rotary kiln A may be parallel to said horizontal plane or inclined relative to said horizontal plane. The rotary kiln 2 comprises a processing chamber 3 and a furnace wall 4 extending in the longitudinal direction of the rotary kiln 2. The furnace wall 4 surrounds the processing chamber and may typically have a cylindrical configuration. In other words, the furnace wall 4 may be rotational symmetrical around the longitudinal axis A. Furthermore, the longitudinally extending furnace wall 4 is at its opposing longitudinal ends connected to furnace end walls 5. The furnace end walls 5 may for example have the shape of a truncated cone as shown in the figure or be dome-shaped, although other shapes are also possible. It is naturally also possible that one of the furnace end walls 5 has the shape of a truncated cone whereas the opposing furnace end wall 5 is dome-shaped. The rotary kiln 2 further comprises one or more devices 10 configured to rotate the rotary kiln 2 around the longitudinal axis A.

The rotary kiln 2 further comprises an inlet 6 configured for introducing particulate matter to be processed in the processing chamber 3, and an outlet 7 through which treated particulate matter may be removed from the processing chamber 3. Process gas may be introduced via inlet 6 and evacuated through outlet 7, or vice versa in case of counter-current flow of process gas in relation to the movement of particulate matter through the rotary kiln as seen in the longitudinal direction thereof. Alternatively, or additionally, process gas may be introduced/evacuated through one or more additional inlets and/or outlets (not shown). The processing chamber 3 may, if desired, comprise a feeding mechanism (such as a feed screw) configured to assist the movement of the particulate matter from the inlet to the outlet of the rotary kiln 2.

Figure 3 schematically illustrates a cross sectional view a first exemplifying embodiment of the furnace wall 4 of the furnace according to the present disclosure, such as a fluidized bed reactor 1 as shown in Figure 1 or a rotary kiln as shown in Figure 2. The furnace wall 4 has an interior surface 12 facing the processing chamber of the furnace, and an exterior surface 14 facing the surroundings of the furnace.

The furnace wall 4 comprises a (first) rigid graphite layer 20 configured to provide structural integrity to the furnace wall. Said rigid graphite layer 20 forms the interior surface 12 of the furnace wall 4. The furnace wall further comprises a gas-proof layer 22 arranged outside of the rigid graphite layer 20. The gas-proof layer 22 may be a flexible graphite foil, which may for example be bonded to the rigid graphite layer 20 by means of a suitable adhesive therefore. Such adhesives are known in the art and will therefore not be described in more detail herein. Alternatively, the gas-proof layer 22 may be a graphite coating deposited by means of CVD on the rigid graphite layer 20. The furnace wall 4 further comprises a (first) thermal insulation layer 24 arranged outside of the gas-proof layer 22. The thermal insulation layer 24 comprises or consists of refractory felt. The thermal insulation layer 24 may be bonded to the gas-proof layer 22 by means of an adhesive, or (albeit less preferred) mechanically mounted thereto. Furthermore, the furnace wall 4 comprises a metal casing layer 26 arranged outside of the thermal insulation layer 24. The metal casing layer 26 forms the exterior surface 14 of the furnace wall 4. The thermal insulation layer 24 may be mechanically mounted to the metal casing layer 26 or adhered thereto by means of an adhesive.

In addition to providing structural integrity to the furnace wall 4, the rigid graphite layer 20 serves as an abrasion resistant layer of the furnace wall 4. In other words, the rigid graphite layer 20 protects the furnace wall 4 from abrasion caused by the particulate matter treated in the furnace. However, a rigid graphite layer may often be quite porous, and gaseous species from the interior of the furnace may diffuse through the rigid graphite layer 20. This could potentially, depending on the gaseous species, cause corrosion to the metal casing layer 26. In order to avoid this, the furnace wall comprises the gas-proof layer 22 which serves the purpose of preventing transport of gaseous species from the interior of the furnace to the outer metal casing layer 26. The thermal insulation layer 24 serves the purpose of thermally protecting the metal casing layer 26 from the high temperature inside the furnace.

The thermal insulation layer 24 may, if desired, be configured to contain pressurized gas, such as pressurized nitrogen. This has the advantage of avoiding gaseous species from the interior of the furnace reaching the metal casing layer 26 even if the gas-proof layer 22 would be damaged. Instead of allowing gaseous species passing through the damaged gas-proof layer in the direction towards the exterior of the furnace, pressurized gas supplied to the thermal insulation layer 24 would pass through the furnace wall 4 towards the interior of the furnace.

According to one alternative, the rigid graphite layer 20 may be used as a resistance heating element, if desired. This may for example be a case where it may be difficult to arrange resistance heating elements inside the furnace, i.e. inside of the furnace wall 4. Using the rigid graphite layer as a resistance heating element may be achieved by electrically connecting the rigid graphite layer to a power source.

Figure 4 schematically illustrates a cross-sectional view of a second exemplifying embodiment of the furnace wall 4 of the furnace according to the present disclosure. The second exemplifying embodiment corresponds to the first exemplifying embodiment shown in Figure 3 except that the rigid graphite layer 20 is lined with a flexible graphite sheet 18 on the interior surface of the rigid graphite layer 20. The flexible graphite sheet 18 thus forms the interior surface 12 of the furnace wall 4 according to the second exemplifying embodiment. The purpose of the flexible graphite sheet 18 may be to provide a (temporary) interior gas-proof layer of the furnace wall when the furnace is first taken in use, or a refurbishing of the furnace wall 4 after the furnace has been used for a period of time. However, since the interior surface 12 of the furnace wall may be exposed to abrasion, the flexible graphite sheet 18 will likely be worn down after a certain period of time. When present, the flexible graphite sheet 18 may also have the advantage of a more homogenous thermal distribution along the furnace wall.

Figure 5 schematically illustrates a cross-sectional view of a third exemplifying embodiment of the furnace wall 4 of the furnace according to the present disclosure, such as a fluidized bed reactor 1 as shown in Figure 1 or a rotary kiln as shown in Figure 2. The furnace wall 4 has an interior surface 12 facing the processing chamber of the furnace, and an exterior surface 14 facing the surroundings of the furnace. Like in the first exemplifying embodiment shown in Figure 3, the furnace wall 4 according to the third exemplifying embodiment comprises a (first) rigid graphite layer 20 configured to provide structural integrity to the furnace wall. Said rigid graphite layer 20 forms the interior surface 12 of the furnace wall 4. The furnace wall 4 further comprises a first thermal insulation layer 24 arranged outside of rigid graphite layer 20. The thermal insulation layer 24 comprises or consists of refractory felt. The first thermal insulation layer 24 may be bonded to the rigid graphite layer 20 by means of a suitable adhesive therefore.

Unlike the first exemplifying embodiment shown in Figure 3, the furnace wall 4 according to the third exemplifying embodiment further comprises a second thermal insulation layer 25. The second thermal insulation layer 25 is arranged outside of the first thermal insulation layer 24. The second thermal insulation layer 25 may comprise or consist of refractory felt or comprise other refractory material. If comprising or consisting of refractory felt, the second thermal insulation layer 25 may be made of the same material as the first thermal insulation layer 24 or comprising a different refractory felt material. The furnace wall 4 further comprises a gas-proof layer 22 arranged between the first thermal insulation layer 24 and the second thermal insulation layer 25. The gas-proof layer 22 may be a flexible graphite foil, which may for example be bonded to one or both of the thermal insulation layers 24, 25 by means of a suitable adhesive therefore. Alternatively, the gas-proof layer 22 may be a graphite coating deposited by means of CVD on any one of the thermal insulation layers 24, 25.

Furthermore, the furnace wall 4 comprises a metal casing layer 26 arranged outside of the second thermal insulation layer 25. The metal casing layer 26 forms the exterior surface 14 of the furnace wall 4. The second thermal insulation layer 25 may be mechanically mounted to the metal casing layer 26 or adhered thereto by means of an adhesive.

The different layers of the furnace wall according to the third exemplifying embodiment serves the same purpose as described above with regard to the first exemplifying embodiment described with reference to Figure 3. Just like the first thermal insulation layer 24, the second thermal insulation layer 25 serves the purpose of thermally protecting the metal casing layer 26 from the high temperature inside the furnace.

Furthermore, the second thermal insulation layer 25 may, if desired, be configured to contain pressurized gas, such as pressurized nitrogen. This has the advantage of avoiding gaseous species from the interior of the furnace reaching the metal casing layer 26 even if the gas-proof layer 22 would be damaged. It should here be noted that there is no purpose of supplying pressurized gas to the first thermal insulation layer 24 according to the third exemplifying embodiment as such gas would be lost to the interior of the furnace due to the porosity of the rigid graphite layer 20.

According to an alternative to the exemplifying embodiment illustrated in Figure 5, the second thermal insulation layer 25 shown in Figure 5 may be substituted with a longitudinally extending cavity through which there is a continuous flow of gas (preferably flow of inert gas) or a longitudinally extending cavity configured to contain a pressurized gas (preferably an inert gas), if desired.

Furthermore, it should here be noted that the furnace wall 4 shown in Figure 5 may also comprise the flexible graphite sheet 18 shown in Figure 4, if desired. Such a flexible graphite sheet 18 would in such a case be arranged so as to form the interior surface 12 of the furnace wall 4.

Moreover, although not shown in the Figure 5, the furnace wall 4 according to the third exemplifying embodiment may optionally comprise an additional (second) gas-proof layer arranged between the rigid graphite layer 20 and the first thermal insulation layer 24, if desired. Such an additional gasproof layer may have the same configuration as the gas-proof layer 22 described above.

The furnace wall 4 according to the first, second or third exemplifying embodiment may optionally comprise cooling means arranged to cool the processing chamber. Although not shown in the figures, the cooling means may be arranged outside of the gas-proof layer 22, such as between the gas-proof layer 22 and the first thermal insulation layer 24.

The above described first to third exemplifying embodiments each relate to a furnace which is heated by one or more electrical resistance heating elements, such one or more electrical heating elements either introduced into the furnace or formed by using the rigid graphite layer 20 as a resistance heating element. The furnace may however alternatively be an induction furnace, in which case an induction coil is incorporated in the longitudinally extending furnace wall. Exemplifying embodiments of a furnace wall in case the furnace is an induction furnace is described in the following with reference to Figures 6 to 8.

Figure 6 schematically illustrates a cross-sectional view of a fourth exemplifying embodiment of the furnace wall 4 of the furnace according to the present disclosure, such as a fluidized bed reactor 1 as shown in Figure 1 or a rotary kiln as shown in Figure 2. The furnace wall 4 has an interior surface 12 facing the processing chamber of the furnace, and an exterior surface 14 facing the surroundings of the furnace.

The furnace wall 4 according to the fourth exemplifying embodiment comprises a (first) rigid graphite layer 20 configured to provide structural integrity to the furnace wall. Said rigid graphite layer 20 forms the interior surface 12 of the furnace wall 4. In addition to providing structural integrity to the furnace wall 4, the rigid graphite layer 20 serves as an abrasion resistant layer of the furnace wall 4. In other words, the rigid graphite layer 20 protects the furnace wall 4 from abrasion caused by the particulate matter treated in the furnace. However, a rigid graphite layer may often be quite porous, and gaseous species from the interior of the furnace may diffuse through the rigid graphite layer 20. This could potentially, depending on the gaseous species, cause corrosion other parts of the furnace wall (in particular parts comprising metal) arranged outside of the rigid graphite layer 20. Therefore, the furnace wall 4 comprises a gas-proof layer 22 arranged outside of the rigid graphite layer 20. The gas-proof layer 22 serves the purpose of preventing transport of gaseous species from the interior of the furnace further into the furnace wall 4. The gas-proof layer 22 may be a flexible graphite foil, which may for example be bonded to the rigid graphite layer 20 by means of a suitable adhesive therefore. Alternatively, the gas-proof layer 22 may be a graphite coating deposited by means of CVD on the rigid graphite layer 20.

The furnace wall 4 further comprises a susceptor layer 21 arranged outside of the gas-proof layer 22. The susceptor layer 21 may be bonded to the gas-proof layer 22 by means of a suitable adhesive therefore. The susceptor layer 21 may suitably be formed of a rigid graphite layer. Forming the susceptor layer 21 of graphite has the advantage of being resistant to possible corrosive species entering the furnace wall from the interior of the furnace. Furthermore, forming the susceptor layer of rigid graphite also ensures that adjacent layers within the furnace wall has a similar thermal expansion, thereby reducing the risk for internal stresses within the furnace wall that may risk damaging the furnace wall. Moreover, forming the susceptor layer 21 of graphite has the advantage of the susceptor layer 21, in addition to the rigid graphite layer 20 forming the interior surface 12 of the furnace wall, contributing to the structural integrity of the furnace wall. Thereby, the rigid graphite layer 20 forming the interior surface 12 of the furnace wall 4 can also be allowed to have a reduced thickness.

The furnace wall 4 according to the fourth exemplifying embodiment further comprises a first thermal insulation layer 24 arranged outside of susceptor layer 21. The first thermal insulation layer 24 comprises or consists of refractory felt. The thermal insulation layer 24 may be bonded to the susceptor layer 21 by means of a suitable adhesive therefore. The furnace wall 4 further comprises an induction coil 28 arranged outside of the first thermal insulation layer 24. The induction coil 28 may optionally be cast into an electrically insulating material 27, preferably refractory concrete. If so, the electrically insulating material 1 may, depending on the material selected, also contribute to the structural integrity of the furnace wall 4. The induction coil 28 is configured to heat the susceptor layer 21 through induction heating. This in turn results in the susceptor layer 21 obtaining a high temperature, which is transferred through the thermally conductive gas-proof layer 22 and the first rigid graphite layer 20. The interior of the furnace is thereby heated primarily through radiation from the furnace wall 4.

The furnace wall 4 further comprises a second thermally insulation layer 25 arranged outside of the induction coil 28, and a metal casing layer 26 arranged outside of the second thermally insulation layer 25. The second thermal insulation layer 25 may comprise or consist of refractory felt or be formed of other refractory material. If comprising or consisting of refractory felt, the second thermal insulation layer 25 may be made of the same material as the first thermal insulation layer 24 or comprising a different refractory felt material.

The first thermal insulation layer 24 may, if desired, be configured to contain pressurized gas, such as pressurized nitrogen. This has the advantage of avoiding gaseous species from the interior of the furnace reaching the induction coil 28 and/or the metal casing layer 26 even if the gas-proof layer 22 would be damaged. Instead of allowing gaseous species passing through the damaged gas-proof layer 22 in the direction towards the exterior of the furnace, pressurized gas supplied to the first thermal insulation layer 24 would pass through the furnace wall 4 towards the interior of the furnace. Additionally, or alternatively, the second thermal insulation layer 25 may, if desired, be configured to contain pressurized gas, such as pressurized nitrogen. This has the advantage of avoiding gaseous species from the interior of the furnace reaching the metal casing layer 26.

Although not illustrated in the figure, the furnace wall 4 according to the fourth exemplifying embodiment may, if desired, further comprise an electrical insulation layer arranged between first thermal insulation layer 24 and the induction coil 28 and/or an electrical insulation layer arranged between the induction coil 28 and the second thermal insulation layer 25. Such electrical insulation layer(s) may suitably be formed of mica foil.

Furthermore, the furnace wall 4 illustrated in figure 6 may further comprise a longitudinally extending cavity (not shown) arranged between the gas proof layer 22 and the susceptor layer 21, between the susceptor layer 21 and the first thermal insulation layer 24, or between the first thermal insulation layer 24 and the induction coil 28. Such a cavity may be configured to contain pressurized gas or to allow a continuous flow of gas therethrough.

It should here be noted that the furnace wall 4 may also comprise the flexible graphite sheet 18 shown in Figure 4, if desired. Such a flexible graphite sheet 18 would in such a case be arranged so as to form the interior surface 12 of the furnace wall 4.

Figure 7 schematically illustrates a cross-sectional view of a fifth exemplifying embodiment of the furnace wall 4 of the furnace according to the present disclosure. The fifth exemplifying embodiment corresponds to the fourth exemplifying embodiment described above and shown in Figure 6, except that it further comprises a magnetic yoke 29 arranged outside of the induction coil 28. The magnetic yoke 29 may be arranged between the second thermal insulation layer 25 and the metal casing layer 26, as shown in the figure. If desired, a third thermally insulation layer may be arranged between the magnetic yoke 29 and the metal casing layer 26.

Figure 8 schematically illustrates a cross-sectional view of a sixth exemplifying embodiment of the furnace wall 4 of the furnace according to the present disclosure. Like the fourth exemplifying embodiment, the furnace wall 4 according to the sixth exemplifying embodiment comprises a rigid graphite layer 20 forming the interior surface 12 of the furnace wall 4, a first thermal insulation layer 24 arranged outside of the rigid graphite layer 21, an induction coil 28 arranged outside of the first thermal insulation layer 24 (said induction coil optionally cast into an electrically insulating material 27), a second thermal insulation layer 25 arranged outside of the induction coil 28 and a metal casing layer 26 arranged outside of the second thermal insulation layer 25. However, in contrast to the fourth exemplifying embodiment, the gas-proof layer 22 is arranged outside of the induction coil 28. This is a possible configuration in case the induction coil is formed of a material which is corrosion resistant to gaseous species from the interior of the furnace that may migrate through the furnace wall 4. Furthermore, in such a case, the rigid graphite layer 20 forming the interior surface 12 of the furnace wall 4 may be utilized as susceptor and thereby be induction heated. Thus, there is no need for the susceptor layer 21 present in the furnace wall according to the fourth exemplifying embodiment.

The furnace wall 4 according to the sixth exemplifying embodiment further comprises a third thermal insulation layer 30 arranged between the induction coil and the gas-proof layer 22. The purpose of such a third thermal insulation layer 30 is to reduce the risk of overheating the gas-proof layer 22 due to acting as a (second) susceptor for the induction coil 28. Furthermore, the second thermal insulation layer 25 is arranged outside of the gas-proof layer 22 in order to avoid heat transfer from the gas-proof layer 22 to the metal casing layer 26.

If desired, the second thermal insulation layer 25 may be substituted with a longitudinally extending cavity (not shown), or such a cavity lay be arranged between the gas-proof layer 22 and the second thermal insulation layer 25. Said cavity may be configured to contain pressurized gas, of there may be a continuous flow of gas therethrough.

Although not illustrated in Figure 8, the furnace wall 4 according to the sixth exemplifying embodiment may further comprise a magnetic yoke such as described with reference the fifth exemplifying embodiment (see Figure 7).

Moreover, the furnace wall 4 according to the sixth exemplifying embodiment may, if desired, further comprise an electrical insulation layer arranged between first thermal insulation layer 24 and the induction coil 28 and/or an electrical insulation layer arranged between the induction coil 28 and the third thermal insulation layer 30. Such electrical insulation layer(s) may suitably be formed of mica foil.

Also, furnace wall 4 according to the sixth exemplifying embodiment may comprise the flexible graphite sheet 18 shown in Figure 4, if desired. Such a flexible graphite sheet 18 would in such a case be arranged so as to form the interior surface 12 of the furnace wall 4.

The furnace wall 4 according to the fourth, fifth or sixth exemplifying embodiment may further comprise cooling means arranged to cool the induction coil 28 during operation. Such cooling means may be arranged adjacent to the induction coil 28.

The herein described furnace may for example be used for thermal treatment of particulate matter, such as carbonaceous particulate matter, in a gaseous environment comprising one or more halogens and at a temperature of at least 800 °C. Thermal treatment should herein be interpreted broadly as any type of treatment process performed at an elevated temperature. Examples of carbonaceous particulate matter that may be thermally treated in the furnace include hard carbon powder, hard carbon granules, carbon nanotubes, charcoal granules and charcoal powder. The present disclosure further provides a method for thermal treatment of particulate matter. The method comprises subjecting the particulate matter to an atmosphere comprising one or more halogens at a temperature of at least 800 °C, preferably at least 900 °C or more preferably at least 1000 °C, in the furnace as described herein. The particulate matter may be a carbonaceous particulate matter. More specifically, the particulate matter may be selected from the group consisting of hard carbon powder, hard carbon granules, carbon nanotubes, charcoal granules and charcoal powder.