furnace

Abstract

The present invention relates to an electrically heated furnace, particularly a furnace for chemical reactions, comprising: a. a furnace chamber including: i. one or more process tubes extending through the furnace chamber; and ii. a plurality of electrically heated heating means disposed inside the furnace chamber for heating the one or more process tubes; and b. an electrical power supply disposed outside the furnace chamber for supplying electrical power to the electrically heated heating means, wherein a. the electrical power supply comprises one or more enclosures connected to but spaced apart from the exterior of the furnace chamber; and b. the electrically heated heating means are connected to an electrical power supply source within the enclosure by one or more electrical connecting rods passing through the wall of the enclosure via one or more hermetic electrical feedthroughs. The present invention also provides a process for conducting chemical reactions in a furnace.

Description

[Technical Field]

[0001] The present invention relates to electrically heated furnaces (sometimes referred to herein as reactors), particularly chemical reactors, such as furnaces for cracking hydrocarbons such as ethane, naphtha, 1,2-dichloroethane, etc. The present invention also relates to electrically heated furnaces used for heating petroleum or chemical products or for gas processing. [Background technology]

[0002] Furnaces for cracking hydrocarbons such as ethane, naphtha, and 1,2-dichloroethane are well known. Historically, the reaction has been carried out by passing the hydrocarbon reactants through externally heated reactor tubes located within the furnace to provide heat for the endothermic cracking reaction. In traditional processes, the required heat has been obtained by burning fuel in burners located within the furnace.

[0003] It has also been proposed to supply heat by electrical heating, for example by using heating elements located in the furnace walls or heating coils located on the reactor tubes, and direct electrical heating of the reactor tubes has also been proposed.

[0004] The problem with electrically heated furnaces is that they require electrical energy to be supplied to the furnace, not only because of the high temperatures, but also because the external environment outside the furnace is a hazardous "ATEX" area. "ATEX" generally refers to areas where there is or is a risk of flammable gases present that could create an explosion hazard. Therefore, any source of ignition must be avoided.

[0005] It is known to provide enclosures for electrical connections in ATEX areas, but special problems arise with electrically heated furnaces due to the very high operating temperatures, the high power inputs, and the need to transmit power through the furnace wall.

[0006] Connecting rods are commonly used to transfer power through the furnace wall. If the furnace is located in an ATEX area, the problem is to find a safe and reliable way to connect the rods to the power supply cable.

[0007] In WO2021214256, the issue of electrical connections to a cracking furnace is addressed by using a purged junction box and gas-permeable connections to the furnace. Specifically, inert gas is supplied to the junction box and then routed to the furnace. The inert gas flow prevents gas from escaping from the furnace. However, in such a system, the furnace is still effectively in an "open connection" with the junction box, which therefore requires significant monitoring. Specifically, during expansion to reactive conditions, it remains difficult to ensure a reasonably good seal and to ensure that flow through all "openings" is prevented, making it necessary to ensure that a significant inert gas flow is maintained. In the event of loss of inert gas flow, contaminated air from outside could enter the junction box, or gases from within the furnace could enter the junction box. Furthermore, loss of inert gas to any box would require a complete shutdown of the furnace.

[0008] Furthermore, WO 2021180864 and US 2023116690 describe reactor vessels suitable for steam cracking that are equipped with a connecting chamber for the electrical connection of heating rods. The connecting chamber, like WO 2021214256, is directly connected to the reactor vessel and is designed to be gas-permeable to the reactor vessel. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2021214256 [Patent Document 2] International Publication No. 2021180864 [Patent Document 3] U.S. Publication No. 2023116690 [Patent Document 4] International Publication No. 2021214256 Summary of the Invention [Means for solving the problem]

[0010] The applicant has developed an improved system in which the power supply connections are completely hermetically isolated from the furnace and from the external environment. In particular, the invention provides an electrical connection arrangement suitable for operation in hazardous flammable areas (ATEX areas).

[0011] Accordingly, in a first aspect, the present invention provides an electrically heated furnace, the electrically heated furnace comprising: a. A furnace chamber, i. one or more process tubes extending through the furnace chamber; ii. a plurality of electrically powered heating means disposed within the furnace chamber for heating one or more process tubes; a furnace chamber comprising: b. power supply means located outside the furnace chamber for supplying electrical power to the electrically powered heating means; Equipped with a. The power supply means is connected to the outside of the furnace chamber but comprises one or more enclosures spaced apart from the furnace chamber; b. The electrically powered heating means is connected to a power supply source within the enclosure by one or more electrical connecting rods passing through the enclosure wall, the electrical connecting rods passing through the enclosure wall via one or more hermetic electrical feedthroughs.

[0012] The present invention provides an electrically heated furnace.

[0013] The furnace comprises a furnace chamber having one or more process tubes extending therethrough. Typically, during use, reactants pass through the interior of the process tubes. The process tube(s) are heated, whereby the reactants or process streams passing through the process tube(s) are heated to cause the reaction to occur.

[0014] Furnaces of this general configuration are known for a variety of different chemical processes, including the heating of petroleum or chemical products and gas processing, although other heating means are used. The process pipe(s) can be, for example, a single straight pipe that each passes through the furnace chamber once. Alternatively, the process pipe(s) can have multiple straight sections connected by elbows or 180° bends within the furnace, for example, to form a serpentine structure.

[0015] Particularly useful furnaces for the process of the present invention are those for cracking hydrocarbons such as ethane, naphtha, 1,2-dichloroethane, and the like.

[0016] Such conventional reactors utilize burners located on the walls of the furnace chamber that combust fuel to generate the heat required to heat the process tube(s). In the present invention, the process tube(s) are electrically heated. Specifically, there are multiple electrically heated means located within the furnace chamber to heat one or more process tubes. Any suitable heating means can be provided. In one embodiment, the multiple electrically heated means can be, specifically, multiple electrically heated heating elements located on the walls of the furnace chamber. In another embodiment, the multiple electrically heated means can be, specifically, multiple heating coils, each located within the furnace chamber adjacent one or more process tubes. In another embodiment, the multiple electrically heated means can be, specifically, means for directly electrically heating the process tube(s). Also, combinations of different heating means can be used, including combinations of the above examples.

[0017] The furnace also comprises power supply means located outside the furnace chamber for supplying electrical power to the electrically powered heating means.

[0018] In particular, the invention provides electrical connections inside one or more enclosures (also referred to herein as "ATEX boxes"), which are connected to the exterior of the furnace chamber but are spaced apart from it. In particular, the connections to the heating means are provided by electrical connection rods passing through the wall of the enclosure, which rods pass through the wall of the enclosure via one or more hermetic feedthroughs.

[0019] The term "sealed" as used herein, as more generally understood by those skilled in the art, means that the enclosure is completely airtight, so that gas cannot escape from or enter the enclosure (once sealed).

[0020] Suitable hermetic electrical feedthroughs are known for use in other fields, such as PAVE Technology, Inc.'s PAVE SEAL (Pressure and Vacuum Electrical Terminal Seal), or BARTEC's Bushing Conductor Studs or DOUGLAS Electrical Components' STUDSEAL HIGH-CURRENT FEEDTHROUGHS. These seals typically use one or more epoxy, ceramic, or glass seals. They can be rated up to 200°C.

[0021] To ensure that such a seal is adequate, the one or more enclosures are spaced apart from the outside of the furnace chamber. For example, the side / wall of the enclosure facing the outer wall of the furnace chamber can be spaced apart from the outer wall by 5 to 70 cm, more preferably 10 to 50 cm. This can be achieved, for example, by using appropriate spacer boxes or brackets, or by using other connecting means that maintain the required distance from the wall of the furnace chamber. The appropriate spacing between the one or more enclosures and the furnace chamber wall can be selected by those skilled in the art, but generally depends on the temperature inside the furnace chamber and the power characteristics (current, voltage) transmitted to the internal electric heating means of the furnace chamber via the connecting rod.

[0022] Inside the furnace chamber, temperatures are very high, typically between 500°C and 1300°C depending on the application. Although an insulating layer is installed on the inner walls of the furnace chamber, heat is still transferred to the furnace chamber walls. Typical furnace chamber wall temperatures are significantly higher than the ambient temperature.

[0023] The heating means and connecting rods inside the furnace are exposed to high temperatures. Heat is transferred by conduction through the connecting rod, but the current generates heat in the connecting rod by the Joule effect. Both cause the temperature of the connecting rod to rise. (Any suitable electrically conductive metal can be used for the connecting rod. However, at least in or near the furnace, the connecting rods are preferably made of a material that can withstand repeated or prolonged high temperatures. Examples include alloys such as nickel-chromium (NiCr), iron-chromium-aluminum (FeCrAl), and molybdenum disilicide (MoSi).)

[0024] By spacing the enclosure away from the furnace chamber wall, the temperature at the tip of the connecting rod is reduced at the enclosure, allowing electrical connection to the electrical supply at a location with a moderate temperature that is acceptable for the cable and enclosure.

[0025] A particular advantage of the present invention is that there is no need to provide cooling means in the enclosure (for the avoidance of doubt, it is possible to provide cooling means in the enclosure; however, this would introduce additional complications where unnecessary; therefore, preferably, cooling means is not provided in the enclosure).

[0026] In the most preferred embodiment of the present invention, one or more enclosures are spaced from the outside of the furnace chamber by the use of suitable spacer box(es). The term "spacer box" as used in this context means that the space between the furnace chamber and the enclosure box itself is enclosed (i.e., "boxed"). In a preferred embodiment, the spacer box(es) is / are airtight to the external environment / atmosphere. However, the spacer box does not need to be airtight to the atmosphere of the furnace chamber. In a preferred embodiment, the atmosphere inside the spacer box during use is the same as the interior of the furnace chamber (outside the process tube). (Generally, a suitable gas atmosphere is provided inside the furnace chamber during use of the furnace. Typically, an inert or mostly inert atmosphere is preferred, although a small amount of oxygen may be desirable for use with certain types of heating elements, as discussed below.) It should be noted that, while cooling means are preferably not provided in the enclosure box, the junction box can be cooled, for example, by providing a cooling panel through which a cooling fluid can flow.

[0027] In one embodiment, the outer wall of the furnace chamber and the side / wall of the enclosure through which the connecting rod passes can be substantially parallel to one another, and therefore the spacing between them is the vertical distance between them. (Typically, both the outer wall of the furnace chamber and the side / wall of the enclosure are essentially vertical, and therefore the distance can be a horizontal distance.) If the planes are not substantially parallel, the spacing should be measured as the vertical distance between the outer wall of the reactor furnace chamber and the location where the connecting rod exits the enclosure.

[0028] An advantage of this embodiment is that a connecting rod can be used where a single rod passes through both the furnace chamber wall and the enclosure wall (and in preferred embodiments with a spacer box, the connecting rod also passes through the spacer box between them). Examples of this are shown in Figures 2 and 4, as described below.

[0029] In another embodiment, the enclosure can be oriented so that the wall of the enclosure through which one or more connecting rods pass (and thus one or more sealed electrical feedthroughs are present) forms a predetermined angle, e.g., 45 to 90 degrees, more preferably 90 degrees, with respect to the wall of the furnace chamber. For example, a first set of one or more connecting rods can be provided that pass through one or more sealed electrical feedthroughs in the enclosure. These connecting rods can then be connected to a second set of one or more connecting rods that pass through the wall of the furnace chamber (and subsequently connected to the heating means). In a particularly preferred embodiment, the connecting rods of the first set are connected to the connecting rods of the second set inside the spacer box. The connecting rods of the first set can be connected to the connecting rods of the second set by flexible connections that allow the two sets of connecting rods to be non-axial. An example of this is shown in FIG. 3 and described below. A particularly advantageous feature of this embodiment is that relatively short connecting rods can be used in either set, particularly the first set. This makes it easier to accommodate the expansion of the connecting rods during heating. (Besides providing a better seal for the first set of connecting rods due to their "smaller" expansion, an advantage of the second set of connecting rods is that they can be fixed in place in the furnace chamber wall and do not need to be movable to accommodate expansion.) In one embodiment, the length of the first set of connecting rods is less than 40 cm, and / or the length of the second set of connecting rods is less than 70 cm. The connecting rods can also be made of different materials. For example, the connecting rods passing through one or more hermetic electrical feedthroughs can be made of a less expensive material such as copper, while the material of the second set can be selected to have a low coefficient of expansion and / or be otherwise preferred for connection to heating elements inside the furnace, such as an iron-chromium-aluminum (FeCrAl) alloy. (For the avoidance of doubt, connecting rods with sections of different materials can also be used in a "straight" configuration, as in FIGS. 2 and 4.)(For example, a cheaper material, such as copper, can be used for one or more sections of the enclosed electrical feedthrough, while another material, such as an FeCrAl alloy, can be used for sections closer to or within the furnace.) A further advantage of the smaller connecting rods and angled orientation is the ease of accessing the space between the enclosure and the furnace, for example, to replace one or more connecting rods or connectors.

[0030] Some examples of particularly preferred configurations are shown in the following figures. [Brief explanation of the drawings]

[0031] [Figure 1] 1 shows a schematic representation of a furnace having a furnace chamber in which a closed box is connected to the outer wall of the furnace chamber via a spacer box. [Figure 2] A detailed view of one of the enclosures connected to the furnace chamber is shown. [Figure 3] 10 shows a detailed view of an alternative arrangement for connecting the enclosure to the furnace chamber. [Figure 4] A further example of the present invention is given below. DETAILED DESCRIPTION OF THE INVENTION

[0032] FIG. 1 shows a schematic diagram of a furnace having a furnace chamber (1) with a sealed box (2) connected to the outer wall of the furnace chamber via a spacer box (3). Within the furnace chamber are a number of heating elements (4) that heat process tubes (5). This drawing is presented for ease of illustration only, and no particular attention should be paid to the relative scale or number of particular features. For example, as shown, there are six sealed boxes and six process tubes, although in practice there may be many more of each, and the box (2) may be very small relative to the furnace chamber (1).

[0033] FIG. 2 shows a detailed view of one of the enclosures connected to the furnace chamber. In FIG. 2, it can be seen that the furnace wall has a layer of insulation (1a) surrounded by an outer wall (1b), and the enclosure has a body (2a) and a sealed lid (2b). As shown in FIG. 2, the enclosure is connected to a spacer box (3) extending from the furnace chamber wall, providing a separation distance "d." (As shown, the enclosure is bolted to the spacer box (3) with bolts and gaskets (not shown) to provide a seal between the interior volume of the spacer box (3) and the outside atmosphere.) Also shown in FIG. 2 are two connecting rods (6) that connect to the heating elements (4), pass through the furnace chamber wall, pass through the enclosure wall via a sealed electrical feedthrough (7), and connect to a power supply cable (8). While this number of rods is shown, it need not be two.

[0034] Due to the distance "d", the temperature of the sealed electrical feedthrough (7) can be maintained significantly below the temperature of the outer walls of the furnace chamber, allowing a reliable airtight seal to be maintained.

[0035] FIG. 3 shows a "detailed view" of an alternative configuration for connecting the enclosure to the furnace chamber. In FIG. 3, it can be seen that the furnace chamber wall again includes a layer of insulation (1a) surrounded by an outer wall (1b). As shown in FIG. 3, the enclosure, having a body (2a) and a lid (2b), is connected to a spacer box (9) extending from the furnace chamber wall, providing a separation distance "d." This spacer box has a sealed lid (9b) that can be opened to allow access. Also shown in FIG. 3 is a first connecting rod (6a) connected to a second connecting rod (6b) via a flexible connection (10) to provide an overall electrical connection between the power supply cable within the enclosure and the electric heating means (4). Note that, again, while this number of first and second sets of rods is shown, it is not necessary to have one in each set as shown. It is also possible, for example, to connect a single first rod to two or more second rods, or to connect multiple first rods to multiple second rods.

[0036] As mentioned above, a particular advantage is that this configuration can provide a spacer box (9) with a hermetic lid (9b) that can be used to easily access the junction box and hermetic feedthroughs.

[0037] Figure 4 shows a further embodiment of the invention. In this case, the furnace chamber (1), enclosure (2) and other components are substantially similar to those of Figure 2, except that the heating element (4) is not present on the furnace chamber interior wall. Instead, the process pipe (5), shown schematically in Figure 3, is heated directly, and the connecting rod is connected directly to the process pipe (5) by a flexible connector (11).

[0038] The furnace of the present invention can be used in any process that is typically operated in a furnace where reactants or process fluids are passed through heated process tubes, including any process that has traditionally or historically been operated in a fired furnace (burner-based).

[0039] Thus, in a second aspect, the present invention provides a process for carrying out a chemical reaction, the process comprising: a. providing a furnace according to a first aspect of the present invention; b. passing one or more reactants through one or more process tubes; c. heating the reactants using electrically powered heating means to effect reaction of the reactants within the process tube; Includes.

[0040] The reaction temperature will depend on the particular process and is not particularly limited, but in preferred processes the furnace typically operates at process tube temperatures ranging from 300°C to 1200°C.

[0041] The process can be catalytic or non-catalytic. In the former case, the catalyst can be provided within the process tube as a catalyst bed or as a coating on the inside of the process tube.

[0042] Examples of suitable processes include steam and other cracking processes, various reforming processes such as steam reforming and dry reforming, alkane dehydrogenation processes, and the like.

[0043] In a particularly preferred embodiment, the process is a decomposition process, specifically a process for decomposing 1,2-dichloroethane (EDC) to produce vinyl chloride monomer (VCM). The decomposition of EDC to produce VCM is well known in the art. The present invention operates in a furnace, similar to the operation of conventional processes, by passing a stream containing EDC through process tubes within a furnace chamber and heating the tubes to heat and decompose the EDC therein.

[0044] Typically, and preferably, the process tube (or each, if more than one) of such a furnace is in the form of a serpentine tube located at or near the vertical plane in the center of the furnace chamber. Heat can then be applied from heating elements on either side of the furnace chamber. This is shown conceptually, for example, in Figure 1, where the process tube can be thought of as representing a horizontal section of the serpentine tube.

[0045] The EDC-containing stream is heated to a temperature sufficient to cause decomposition of the EDC. Typically, this temperature is at least 350°C, and preferably in the range of 350°C to 550°C. Temperatures, residence times, etc. can be selected by one skilled in the art to obtain the required degree or rate of decomposition. In particular, these can be similar to those of conventional (hydrocarbon burner) systems.

[0046] The EDC-containing stream can be introduced in a form in which the EDC is in the liquid phase. In this case, the EDC is vaporized in an earlier section of the process tube(s) and then further heated to a temperature in the range of 350°C to 550°C, at which point the decomposition reaction occurs in a later section. In other embodiments, the EDC-containing stream introduced at the inlet may be heated ("preheated") outside the furnace, for example, to a temperature sufficient to vaporize any liquid EDC. In such cases, the EDC-containing stream is in the vapor phase at the inlet of the process tube.

[0047] However, the furnace can also be designed and used for other processes such as steam cracking, etc. The furnace can also be designed to heat petroleum or chemical products.

[0048] As mentioned above, a suitable gas atmosphere can be provided within the furnace during the process. Generally, an inert or mostly inert atmosphere is preferred, although a small amount of oxygen may be desirable for use with certain types of heating elements. The furnace chamber can be a closed system, meaning that no significant amount of gas enters or leaves the chamber during normal operation, or it can be equipped with means for allowing a steady flow of gas, such as an inert gas or a gas mixture containing an inert gas, into and out of the furnace chamber. The advantage of this latter system is that the effluent gas can be analyzed to check for any contaminants, which may indicate, for example, a leak of reactants from the process tube or an air leak from outside the furnace.

[0049] The furnace chamber may be, or alternatively may be, kept pressurized, which is advantageous against possible leaks from the outside, as it ensures that gases within the furnace chamber "leak out" rather than air "leak in."

[0050] In the most preferred embodiment of this second aspect, the one or more enclosure boxes are spaced from the outside of the furnace chamber by the use of suitable spacer box(es), as described with respect to the first aspect. In a preferred embodiment, the spacer boxes are airtight to the external environment / atmosphere, but not to the furnace atmosphere. Thus, during the process of the second aspect of the invention, the atmosphere within the spacer boxes is the same as the atmosphere within the furnace chamber (outside the process tube).

[0051] In a particularly advantageous embodiment, the atmosphere in the spacer box is not only the same as the atmosphere in the furnace chamber, but also the same pressure, both the spacer box and the furnace chamber being at high pressure. This ensures that gas in the spacer box "leaks out" rather than air "leaks in."

[0052] The present invention has the advantage of minimizing the amount of inert gas required for the electrical connection system, which in turn minimizes gas flow and associated heat losses from the furnace chamber.

[0053] (Example) The electric heater / enclosure system was modeled using computational fluid dynamics (CFD). The system is identical to Figure 2, except that the connecting rod (6) transitions from the enclosure (2) to a single heating element (4) within the furnace chamber (1). The distance d is 500 mm. The walls within the furnace chamber have 300 mm of insulation (1a). The connecting rod is 20 mm in diameter along its length; the first 400 mm of the connecting rod (where it passes through the furnace wall at the end) is FeCrAl alloy, and the remainder is copper.

[0054] A current of 262.5 A is applied from a power supply inside the enclosure to the heating element through the connecting rod. The temperature inside the furnace chamber is 816°C. The connecting rod at the junction of the FeCrAl section and the copper section (outside the furnace chamber but close to the furnace wall) is approximately 135°C. At the wall of the spacer box, i.e., 50 cm from the outside of the furnace chamber, the temperature of the connecting rod is approximately 60°C. This temperature is suitable for the use of PAVE Technology's PAVE seal to pass the connecting rod through the enclosure wall. [Explanation of symbols]

[0055] 1 Furnace room 1a Insulation layer 1b Exterior wall 2 Closed box 2a Main unit 2b Sealing lid 3 Spacer Box 4 heating elements 5 Process Pipe 6 connecting rod 7. Sealed Electrical Feedthrough

Claims

1. a. A furnace chamber comprising: i. one or more process tubes extending through the furnace chamber; ii. a plurality of electrically powered heating means disposed within the furnace chamber for heating the one or more process tubes; the furnace chamber, b. power supply means located outside the furnace chamber for supplying electrical power to the electrically powered heating means; Equipped with a. the power supply means includes one or more enclosures connected to the exterior of the furnace chamber but spaced apart from the furnace chamber; b) an electrically heated furnace, wherein the electrically powered heating means is connected to an electrical power supply within the enclosure by one or more electrical connecting rods passing through the wall of the enclosure, the electrical connecting rods passing through the wall of the enclosure via one or more hermetic electrical feedthroughs.

2. 2. The electrically heated furnace of claim 1, wherein the plurality of electrically heated means can be a plurality of electric heating elements, a plurality of electric heating coils, or a plurality of means for direct electric heating of the process tube(s), or a combination thereof.

3. 3. The electrically heated furnace of claim 1 or 2, wherein the one or more enclosure boxes are spaced from the exterior of the furnace chamber by the use of one or more spacer boxes.

4. 4. The electrically heated furnace of claim 3, wherein the spacer box(es) are airtight to the external environment / atmosphere.

5. 5. An electrically heated furnace according to claim 3 or 4, wherein the spacer box(es) are not airtight with respect to the furnace chamber, and in use the atmosphere inside the spacer box(es) is the same as the atmosphere in the furnace chamber.

6. 6. The electrically heated furnace according to claim 1, wherein the wall of the enclosed box through which the one or more connecting rods pass (and thus the one or more sealed electrical feedthroughs are present) is positioned at an angle, such as 90 degrees, to the wall of the furnace chamber.

7. 7. The electrically heated furnace of claim 6, wherein a first set of one or more connecting rods is provided that passes through the one or more hermetic electrical feedthroughs of the enclosure, and the first set of one or more connecting rods is then connected to a second set of one or more connecting rods that passes through the wall of the furnace chamber.

8. 8. The electrically heated furnace of claim 7, wherein the first set of connecting rods are connected to the second set of connecting rods inside a spacer box.

9. 9. An electrically heated furnace according to claim 7 or 8, wherein the length of the first set of connecting rods is less than 40 cm and / or the length of the second set of connecting rods is less than 70 cm in length.

10. 10. An electrically heated furnace according to any one of claims 7 to 9, wherein the first set of connecting rods and the second set of connecting rods are made of different materials.

11. A process for conducting a chemical reaction, comprising: a. Providing an electrically heated furnace according to any one of claims 1 to 10; b. passing one or more reactants through said one or more process tubes; c) heating the reactants using the electrically heated means to effect reaction of the reactants within the process tube; The process includes:

12. 12. The process of claim 11, wherein the electrically heated furnace operates at a temperature in the process tube ranging from 300°C to 1200°C.

13. 13. The process according to claim 11 or 12, wherein the process is for the decomposition of 1,2-dichloroethane (EDC) to produce vinyl chloride monomer (VCM), and preferably the EDC-containing stream is heated in the process tube to a temperature in the range of 350°C to 550°C.

14. 14. The process according to any one of claims 11 to 13, wherein an inert or mostly inert gas atmosphere is provided in the furnace chamber.

15. 15. The process of claim 14, wherein the furnace chamber is maintained above atmospheric pressure.

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