furnace

Abstract

The present invention relates to an electrically heated furnace, particularly a furnace for chemical reactions, and more particularly, in one embodiment, provides an electrically heated furnace comprising: a. a furnace chamber including: 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; iii. one or more gas inlets; and iv. one or more gas outlets; the electrically heated furnace further comprising: b. an external recirculation loop connecting the one or more gas outlets of the furnace chamber to one or more gas inlets of the furnace chamber such that gas exiting the one or more gas outlets of the furnace chamber flows to the one or more gas inlets and is recirculated back to the furnace chamber; and c. at least one gas analyzer or detector and / or at least one pressure monitor for pressure measurement provided on the external recirculation loop.

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] Conventional furnaces typically have one or more radiator sections in the lower part where burners transfer heat to the process tubes, and a convection section where heat from the hot combustion gases is transferred to the process or utility tubes before being released to the atmosphere. Electrical heating has also been proposed to provide heat for the cracking, for example, by using heating elements located in the furnace walls or heating coils located on the reactor tubes. Direct electrical heating of the reactor tubes has also been proposed.

[0004] Although the optimum design for an electrically heated cracking furnace differs from the optimum design for a conventional burner-heated cracking furnace, in some circumstances it may still be advantageous to retrofit an existing burner-fired furnace to use electric heating rather than building a new furnace from scratch. Specifically, this allows the majority of the existing system to be used with little or no modification, including the process feed system, the furnace physical structure, the process piping, and the downstream quench system.

[0005] Applicant has now discovered an improved design for an electrically heated furnace, particularly one that is applicable to "new build" applications and is also suitable for retrofitting existing cracking furnaces. Summary of the Invention [Means for solving the problem]

[0006] Accordingly, in a first aspect, the present invention provides an 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; iii. one or more gas inlets; iv. one or more gas outlets; a furnace chamber including: Electric heating furnaces are b. an external recirculation loop connecting one or more gas outlets of the furnace chamber to one or more gas inlets of the furnace chamber; c. at least one gas analyzer or detector and / or at least one pressure monitor for measuring pressure on the outer recirculation loop; Further provided are:

[0007] Furthermore, in a second 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; iii. one or more gas inlets; iv. one or more gas outlets; a furnace chamber including: Electric heating furnaces are b. an external recirculation loop connecting one or more gas outlets of the furnace chamber to one or more gas inlets of the furnace chamber; c. one or more heaters for heating the gas in the external recirculation loop; Further provided are:

[0008] The present invention provides an electrically heated furnace in both a first and second aspect.

[0009] An electrically heated 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, thereby heating the reactants passing through the process tube(s) and causing the reaction to occur.

[0010] 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.

[0011] 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.

[0012] As mentioned above, 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 powered heating 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 powered heating means can be, specifically, multiple electrically powered heating elements located on the walls of the furnace chamber. In another embodiment, the multiple electrically powered heating 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 powered heating 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.

[0013] Furnaces may generally include a power supply located outside the furnace chamber that supplies electricity to the electrically powered heating means. The problem with electrically heated furnaces is that they require the supply of electrical energy to a furnace that is not only hot, but also has a hazardous "ATEX" zone, where the environment outside the furnace is an "ATEX" zone. "ATEX" generally refers to zones where flammable gases are present or present that could create an explosion hazard. An example of a suitable system can be found in WO 2021 / 214256, which provides a movable current supply element. More preferably, the electrical supply utilizes one or more enclosures (also sometimes referred to as "ATEX boxes" as used herein) that are externally connected to the furnace chamber. Electrical connections to the heating means may be provided by one or more electrical connecting rods or other connections that penetrate the enclosure walls and the furnace wall.

[0014] Furnace chambers of the present invention also include one or more gas inlets and one or more gas outlets. Generally, there can be multiple inlets and / or multiple outlets.

[0015] The one or more gas inlets and the one or more gas outlets each allow for the removal of gas from the furnace chamber, particularly from the furnace chamber volume outside the one or more process tubes.

[0016] The one or more gas inlets and one or more gas outlets are preferably located on opposite sides of the furnace chamber. (As used herein, "side" also includes the top and bottom.) This allows gas to flow throughout the entire furnace chamber as it transitions from the one or more inlets to the one or more outlets. Multiple inlets and / or outlets can be used, for example, to distribute the gas flow throughout the volume of the furnace chamber. However, alternatively or additionally, baffles can be used to optimize gas flow through the furnace chamber.

[0017] In a highly preferred embodiment, one or more gas inlets are located at the base of the furnace chamber and one or more gas outlets are located at or near the top of the furnace chamber, such that gas travels generally vertically upward through the furnace chamber from the one or more gas inlets to the one or more gas outlets.

[0018] It should be noted that, particularly in preferred embodiments where the furnace is a modified burner-based furnace, the furnace chamber may include a vent. As used herein, a vent is an outlet through which gases from the furnace chamber are exhausted to the atmosphere or at least to the exterior of the furnace. In a conventional furnace, this may be, for example, a chimney. In contrast, the one or more gas outlets of the present invention are outlets connected to an external recirculation loop. (One or more gas outlets may be considered recirculated gas outlets. Similarly, one or more gas inlets may be considered recirculated gas inlets.)

[0019] Also, in embodiments where a chimney or other vent is present, the gas outlet(s) are preferably provided on the furnace chamber body and are separate from any vent(s). However, while the gas outlet(s) are provided in addition to the vent(s), it is within the scope of the invention that the gas outlet(s) can be taken from the base of a vent / chimney rather than directly from the furnace chamber, or that the vent / chimney can be on a recirculation loop.

[0020] An important feature of the present invention is the provision of an external recirculation loop connecting one or more of the furnace chamber's gas outlets to one or more of the furnace chamber's gas inlets. Specifically, the external recirculation loop provides a connection such that gas exiting one or more of the furnace chamber's gas outlets flows to one or more of the furnace chamber's gas inlets. The gas is thereby recirculated to the furnace chamber. More generally, in the furnaces of the present invention, gas flows through the furnace chamber, exits the furnace chamber through one or more gas outlets, and then returns to one or more gas inlets through the external recirculation loop and thus to the furnace chamber. The recirculated gas may be referred to herein as "recycled gas" and should be distinguished from the reactant and product gases (which may be referred to as "process gas") in one or more process tubes.

[0021] In a first aspect of the present invention, at least one gas analyzer or detector and / or at least one pressure monitor for pressure measurement is provided on the external recirculation loop. Thus, during use, gas is drawn from the furnace chamber through one or more gas outlets and enters the recirculation loop. Analysis and / or pressure measurements of the gas in the recirculation loop can be made as the gas circulates back into the furnace chamber through one or more gas inlets. It should be noted that these measurements are made on the gas in the recirculation loop, which is the gas from the furnace chamber. This is independent of any analysis on the reactants fed to one or more process tubes or the products removed from one or more process tubes.

[0022] In preferred embodiments, at least one gas analyzer or detector is provided on the outer recirculation loop. Optionally, at least one pressure monitor may be provided in addition to the at least one gas analyzer or detector in such embodiments.

[0023] In a second aspect of the invention, one or more heaters are provided in the external recirculation loop to heat gas therein. Thus, in use, gas is drawn from the furnace chamber through one or more gas outlets and enters the recirculation loop. The gas is heated in the recirculation loop and then returns to the furnace chamber through one or more gas inlets.

[0024] In a preferred embodiment, at least one gas analyzer or detector and / or at least one pressure monitor for measuring pressure may be provided on the outer recirculation loop, and one or more heating devices may be provided on the outer recirculation loop for heating the gas in the outer recirculation loop. Most preferably, at least one gas analyzer or detector is provided on the outer recirculation loop, and one or more heating devices are provided in the outer recirculation loop for heating the gas in the outer recirculation loop.

[0025] In some embodiments, there may be two or more recirculation loops. For example, there may be a first recirculation loop connecting one or more gas outlets to one or more gas inlets, and a second recirculation loop connecting one or more different gas outlets to one or more gas inlets. In such embodiments, at least one gas analyzer or detector and / or at least one pressure monitor for pressure measurement may be provided on one or both recirculation loops, and / or one or more heaters may be present on one or both recirculation loops. Preferably, one or more heaters are present on both recirculation loops. However, more preferably, there is a single recirculation loop in which all gas outlets are combined to form a single conduit that then supplies gas to one or more gas inlets of the furnace chamber.

[0026] Many advantages result from the construction of the present invention.

[0027] For example, the use of external heating allows for additional heat input to the gas, and therefore to the furnace chamber and process tubes. This can result in improved control of the energy input to the process. It also means that because the gas entering the furnace chamber is hotter (than without external heating), the process tubes at or near one or more gas inlets, for example at the base of the furnace chamber, receive more heat than they would otherwise. This can allow for more uniform heating across the furnace tubes and improved yield.

[0028] Furthermore, in the case of retrofitting an existing burner-fired furnace, it may not be possible to supply the required heat load of the furnace simply by installing new electric heating means in the existing furnace chamber. In such cases, providing additional heating in the external recirculation loop allows part of the heat load to be transferred to the external recirculation loop.

[0029] This is also advantageous with respect to providing an external recirculation loop with gas analysis / detection and / or pressure monitoring. In particular, gas analysis is more easily performed on the recirculation loop than attempting to analyze the gas inside the furnace chamber. Also, gas analysis on the recirculation loop can more quickly identify any changes or problems with the gas medium inside the furnace chamber. In particular, a relatively large recirculation loop flow rate (relative to the furnace chamber volume) can be used to ensure that the furnace chamber atmosphere is effectively sampled. For example, the volumetric flow rate (recirculation rate) of the recirculation loop can be from 2% to 100% of the furnace chamber volume (per minute) (i.e., volume X m 3 In this case, the flow rate is Xm 3 0.02 times / min and Xm 3 / min). This means that the gas in the furnace chamber has an average residence time of 1 to 50 minutes. If one or more heaters for heating the gas are provided in the external recirculation loop, the optimum recirculation flow rate will generally be selected based on the desired temperature of the recirculated gas after heating. Additionally or alternatively, multiple gas outlets can be used so that the recirculated gas represents the atmospheric pressure in multiple parts (if not all) of the furnace chamber. In contrast, if the analyzer is provided within the furnace chamber itself, multiple analyzers may be required for effective coverage of the furnace volume. (A typical furnace chamber volume for a conventional furnace for decomposition of 1,2-dichloroethane is, for example, 200 m 3 500m from 3 (Steam cracking furnaces for ethane cracking can be similarly sized or even larger. Effectively sampling the entire area of ​​such a furnace requires multiple analyzers.)

[0030] In an embodiment, the gas in the furnace chamber may circulate within the furnace chamber itself (as well as within an external recirculation loop). This also means that individual gas outlets can sample gas circulating from other parts of the furnace chamber, rather than from a single, static location, which is advantageous because it can be achieved without a relatively large volume flow rate within the external recirculation loop. This therefore allows for faster identification of any changes or problems with the gas medium throughout the furnace chamber. (In such embodiments, the volumetric flow rate (recirculation rate) in the recirculation loop can be in the ranges described above, but in such cases is preferably at the lower end of the ranges described above, such as 2% to 25% of the furnace chamber volume per minute. However, the volumetric flow rate (recirculation rate) of the recirculation loop can be lower than 2% of the furnace chamber volume per minute, especially if efficient circulation is obtained within the furnace itself. Thus, in embodiments in which the gas within the furnace chamber circulates within the furnace chamber itself, the volumetric flow rate (recirculation rate) in the recirculation loop can be in the range of 0.5% to 25%, such as 0.5% to 5%, of the furnace chamber volume per minute.) Circulation within the furnace chamber in such embodiments can be achieved by any suitable means, including one or more fans within the furnace chamber, one or more baffles within the furnace chamber, and / or by the placement and positioning of multiple gas inlets for recirculated gases entering the furnace chamber from an external recirculation loop, for example, to supply airflow into the furnace chamber. In the most preferred embodiment, circulation within the furnace chamber is achieved at least in part by convection within the furnace chamber. For example, heating may occur on the walls of the furnace chamber, causing gases to rise at the walls of the furnace chamber as they heat up, and then cool and descend in the center of the furnace chamber, where they warm upon contact with the process tubes, causing circulation by convection.

[0031] More specifically, in conventional cracking furnaces, process tubes are known to rupture, potentially causing hydrocarbons or other reactants and products to enter the furnace chamber. In conventional furnaces, these are mixed with the hot burner combustion product stream, which typically contains CO and O (because excess O is added to ensure complete combustion), and then exhausted. In the present invention, gas is recirculated, and the concentration of leaking components can rise rapidly. Therefore, analysis of the recirculated gas in the recirculation loop can quickly identify even small leaks of hydrocarbons or other reactants / products into the furnace chamber. The most appropriate analyzer or detector will depend on the process. This can be, for example, an analyzer or detector for detecting hydrocarbons, ammonia, hydrogen, or hydrogen chloride. Preferably, in an ethylene dichloride (EDC) production process, an EDC or HCl analyzer or detector is provided. (As used herein, an analyzer will provide a concentration, while a detector will provide an alarm if a component is detected.)

[0032] Typically, the recirculation gas can be an inert gas (such as N2, CO2, or argon) or can contain oxygen, such as a gas mixture of air or an inert gas with 1% to 21% oxygen. A small amount of oxygen in the furnace, such as 1% to 10 vol% oxygen, may be desirable, for example, for optimal operation of the electric heating means. Therefore, in preferred embodiments, an O2 analyzer or detector is also provided. The presence of O2 (e.g., when using an inert gas) or a deviation from the expected oxygen content (e.g., when using a gas containing oxygen) can indicate an external air leak into the system. This could be, for example, a leak into the furnace chamber or a leak into the recirculation loop.

[0033] In some embodiments, a pressure monitor can be provided on the external recirculation loop. Typically, the reactants in the process tube are at a much higher pressure than the gases in the furnace chamber. Therefore, pressure fluctuations (particularly pressure increases) on the external recirculation loop can also be used as an indication of a leak from the process tube. If the furnace chamber itself is at a pressure higher than atmospheric pressure, which is preferred in some embodiments, a decrease in pressure can indicate a leak from the furnace chamber to the external environment.

[0034] The recycle gas may include steam.

[0035] Analysis / detection / monitoring therefore provides a significant safety advantage by quickly detecting potentially dangerous situations. For example, measurements indicating deviations from expected values ​​for hydrocarbons, HCl, or oxygen will then trigger a safety response. This response will be selected by one skilled in the art and will generally depend on the particular gas detected and its magnitude. For example, a small increase in oxygen may need to be monitored, but operation can potentially continue. In contrast, a reactant or product leak, such as a hydrocarbon leak, an HCl leak, or an ammonia leak (depending on the process), will result in the process being shut down. In this scenario, various measures can be taken, including purging the furnace chamber and / or flushing the process tubes, as will be understood by one skilled in the art.

[0036] Generally (i.e., in the first or second embodiment), the furnace may be equipped with a suitable fan or blower in the recirculation loop, or a gas ejector, to enable the necessary recirculation. Fresh gas for the furnace chamber / recirculation loop may be introduced either in the furnace chamber (by one or more separate fresh gas inlets) or in the recirculation loop. If an ejector is used, the fresh gas is suitably introduced into the ejector as a drive gas.

[0037] In a second aspect of the present invention, one or more heaters are provided to heat the gas in the external recirculation loop. In the first aspect, one or more heaters are also preferably provided to heat the gas in the external recirculation loop. Therefore, the following description applies to the second aspect and also to embodiments of the first aspect in which one or more heaters are provided to heat the gas in the external recirculation loop.

[0038] The heater(s) heating the gas in the external recirculation loop may be any suitable heater. However, the invention is also particularly advantageous when the external heating is provided by one or more electric heating means. As with the heating within the furnace chamber, any suitable electric heating means may be provided.

[0039] Typically, during use, the majority (i.e., greater than 50%) of the total heat that needs to be supplied comes from the electric heating elements within the furnace chamber. Therefore, the installed heating capacity of the electric heating elements within the furnace chamber ("internal" heating or heating capacity) is usually greater than the installed heating capacity of the heater that heats the gases in the external recirculation loop ("external" heating or heating capacity). (As used herein, "installed heating capacity" means the amount of heating power available, regardless of whether all of this capacity is used for heating during use.)

[0040] Typically, in a modified furnace, the size of the furnace chamber may limit the number of heating elements that can be provided within the furnace chamber, and therefore the installed heating capacity. In such an embodiment, the installed heating capacity within the furnace chamber is maximized (given its size constraints), and sufficient external heating is provided to provide the desired total heating capacity of the furnace.

[0041] In a typical embodiment, the installed heating capacity within the furnace chamber is 50% to 95% of the total installed heating capacity (i.e., the total heat capacity of the electrically powered heating means located within the furnace chamber and one or more heaters that heat the gas in the external recirculation loop), for example 60% to 90% of the total installed heating capacity.

[0042] In absolute terms, the total effective installed thermal capacity can be selected as needed based at least on the material to be heated and its throughput, i.e., the scale of the process. The total effective installed thermal capacity can be, for example, 5 MW to 200 MW, such as 5 MW to 100 MW. The installed thermal capacity of the electrically powered heating means located in the furnace chamber can be 4 MW to 175 MW, with a typical installed thermal capacity of one or more heaters heating the gas in the external recirculation loop being 1 MW to 100 MW.

[0043] In one embodiment, the total available installed thermal capacity may be between 5 MW and 60 MW, the electrically powered heating means located in the furnace chamber having an installed thermal capacity between 4 MW and 50 MW, and the one or more heaters heating the gas in the external recirculation loop having an installed thermal capacity between 1 MW and 30 MW. In a most preferred embodiment, the total available installed thermal capacity may be between 5 MW and 30 MW, the electrically powered heating means located in the furnace chamber having an installed thermal capacity between 4 MW and 25 MW, and the one or more heaters heating the gas in the external recirculation loop having an installed thermal capacity between 1 MW and 15 MW.

[0044] However, notwithstanding the above typical ranges, there is no fundamental reason why the installed heat capacity of any external heater cannot be greater than the installed heat capacity within the furnace chamber, and / or why all of the heat added during use cannot be obtained from the external heater.

[0045] More generally, during use, the ratio of heat transferred from the external heater in the external circulation loop to the total heat transferred from the furnace (internal heating + external heating) can be between 5 and 100%, however, a preferred ratio is between 5 and 50%, i.e. preferably, the majority of the total heat is transferred by the electric heating elements in the furnace chamber and not by the external heater.

[0046] In general, the present invention provides the ability to adjust this ratio as needed: the total heat applied, and the relative heat applied in the furnace chamber and recirculation loop, can be adjusted based on, for example, the feedstock being cracked.

[0047] In one embodiment, the recirculation loop includes a box, conduit, or multiple conduits that carry the recirculated gas and house electrically powered heating elements or coils located on the interior walls or dispersed within the gas stream. The heating elements or coils may be equipped with fins to improve heat transfer.

[0048] In another embodiment, the recirculation loop is made up of a single conduit or multiple conduits connected in parallel, which is heated externally in a box containing electrically powered heating elements. This outer box can be of much simpler design than the furnace chamber, since there are no reactants or products.

[0049] In another embodiment, the recirculation loop is made up of one conduit or multiple conduits connected in parallel, which are directly electrically heated. [Brief explanation of the drawings]

[0050] [Figure 1] 1 shows a schematic representation of an electrically heated furnace comprising a furnace chamber (1) with a serpentine process tube (2) and a heating element (13). [Figure 2] Schematically shows a furnace formed by attaching an electric heating element and a recirculation loop (5) to a conventional combustion furnace chamber. DETAILED DESCRIPTION OF THE INVENTION

[0051] FIG. 1 shows one embodiment of a particularly preferred configuration. In particular, FIG. 1 shows a schematic representation of an electrically heated furnace comprising a furnace chamber (1) with a serpentine process tube (2) and a heating element (13). The furnace chamber has a gas inlet (3) and a gas outlet (4), four of each shown, although there may be more or fewer. Gas removed from one or more gas outlets is passed through a recirculation loop (5) using a circulation fan (6). The gas is heated in an external heating box (7), which is also electrically heated. Fresh gas is introduced through line 8, which is equipped with an analyzer (9) for analyzing, for example, HCl and O2. The furnace further comprises a chimney (10), from which reaction gases are introduced into the process tube (2) through an inlet (11) and products are removed through an outlet (12).

[0052] FIG. 2 shows another embodiment of a particularly preferred configuration. Specifically, FIG. 2 shows a schematic of a furnace formed by attaching an electric heating element and recirculation loop (5) to a conventional furnace chamber. This type of configuration can be used for retrofitting / conversion of existing gas-fired furnaces, allowing for the utilization of existing furnace chamber and process piping, as well as feed control and product inspection (work-up). As shown, the furnace chamber comprises a conventional gas-fired furnace chamber having a radiant section (1a) and a convection section (1b). The gas-fired heater (burner) in the radiant section has been replaced with an electric heating element (13a). The process piping routes reactant gases through the convection section (1b) and then the radiant section (1a), similar to conventional / existing furnace configurations. The furnace chamber has a gas inlet (3) and a gas outlet (4). Gas removed from the gas outlet (4) is passed through the recirculation loop (5) using a circulation fan (6). The gas is recirculated into the furnace chamber through the inlet (3) after being heated in an external heating box (7) for heating the gas in the recirculation loop. Heating can be achieved, inter alia, by using an additional electric heating element (13b) in the external heating box (7). An analyzer (9), e.g., for analyzing HCl and O2, is also provided on the recirculation loop (5), along with a pressure monitor (14). Although not shown, an inlet for the introduction of fresh inert gas or air can be provided on the recirculation loop.

[0053] Although both Figures 1 and 2 show a furnace including both an analyzer and external heating in the external recirculation loop, it should be understood that the external recirculation loop may include only one or more analyzers or only a heater for heating gases within the external recirculation loop and still be in accordance with the first and second aspects of the present invention, respectively.

[0054] The furnace of the first or second aspect of the invention may be used in any process that is typically operated in a furnace where reactants or process fluids pass through heated process tubes, including any process that has traditionally or historically operated in a fired furnace (burner-based).

[0055] Thus, in a third aspect, the present invention provides a process for carrying out a chemical reaction, the process comprising: a. providing a furnace according to the first and / or second aspect of the present invention; b. passing one or more reactants through one or more process tubes; c. circulating the gas through one or more gas outlets, a recirculation loop, one or more gas inlets, and the furnace chamber; d. heating the reactants in one or more process tubes to effect reaction of the reactants in the process tubes; Includes.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] Typically and preferably, the process tube (or each, if there are two or more) of such a furnace is in the form of a serpentine tube located in or near the vertical plane in the center of the furnace chamber, so that heat can be applied from heating elements on both sides of the furnace chamber.

[0061] 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 decomposition in conventional (hydrocarbon burner) systems.

[0062] 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, e.g., in the range of 350°C to 550°C, where decomposition occurs in a later section. In other embodiments, the EDC-containing stream introduced at the inlet may be heated ("preheated") outside the furnace, e.g., to a temperature sufficient to vaporize any liquid-phase EDC. In such cases, the EDC-containing stream is in the vapor phase at the inlet of the process tube.

[0063] 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.

[0064] The furnace may include one or more heaters that heat the gas in the external recirculation loop. As mentioned above, the ratio of the heat transferred by any external heaters in the external circulation loop to the total heat transferred from the furnace (internal + external) may be between 5% and 100%. However, a preferred ratio is between 5% and 50%, i.e., preferably, the majority of the total heat is transferred by electric heating elements within the furnace chamber rather than by external heating elements.

[0065] Also, as mentioned above, the present invention provides the ability to adjust this ratio as needed. The total amount of heat applied, and the relative heat applied in the furnace chamber and recycle loop, can be adjusted based on, for example, the feed being cracked. (This may be based on different hydrocarbon feeds, e.g., ethane vs. naphtha cracking may have different requirements, or may vary depending on the "state" of the feed as it enters the process, e.g., whether the EDC is liquid or gaseous as it enters the furnace.)

[0066] As mentioned above, the (recycle) gas can be an inert gas or a gas containing oxygen. Generally, an inert atmosphere is preferred, but when using certain types of electric heating elements, small amounts of oxygen (e.g., a gas mixture containing an inert gas and less than 10 vol% oxygen) may be desirable.

[0067] The furnace chamber can be operated above atmospheric pressure, which is advantageous in terms of potential external contamination by air, as it ensures that gases within the furnace chamber "leak out" rather than air "leak in."

[0068] (Example) The present invention can be illustrated by the following example, which illustrates the retrofitting of a conventional (burner-based) EDC (ethylene dichloride) cracking furnace. The retrofitted furnace is as shown in FIG.

[0069] The EDC cracking furnace produces 160 kt of VCM (vinyl chloride monomer) per year. The EDC feed rate is 53 t / h, which is fed to the convection section of the cracking furnace and then sent to the radiant section.

[0070] The decomposition rate is approximately 60%.

[0071] Before the conversion, the pyrolysis furnace was heated by natural gas burners arranged in rows on the sidewalls of the radiant section of the furnace. Flat-flame burners heated the process tubes in the radiant section. The flue gas then passed through the convection section of the furnace. At the top of the furnace, the flue gas was rejected through a chimney and sent to the atmosphere or to a separate heat recovery step.

[0072] The required heat load of the burner is 17.9 MW, most of which is discharged as flue gas from the cracking furnace.

[0073] The electrolysis furnace is shown in Figure 2 and is equipped with an external recirculation loop. This loop recirculates gas from the top of the furnace (top of the convection section) through the external electrically heated section and back to the radiant section. Analyzers are installed on the recirculation loop for analysis of HCl and O2. These constantly analyze the recirculated gas stream. Specifically, the presence of HCl or a change in O2 concentration will quickly identify the presence of a leak from the process tube.

[0074] In this example, nickel-chromium-aluminum heating elements are used as the electrical heating means in both the radiant and externally heated sections of the cracking furnace. To crack 53 t / h of EDC, 9.8 MW of heat is provided by the electrical heating elements in the radiant section of the cracking furnace and 4.1 MW of heat is provided by the externally heated section. The recycle gas leaves the convection section at 450°C (which is the same as the effluent flue gas of a "conventional" furnace) and is heated to 800°C in the externally heated section before being reintroduced into the radiant section. The recycle gas flow rate is approximately 30,000 Nm 3 / h(500Nm 3 / min).

[0075] Compared to burner-based operation, the total heat input of the electrolysis furnace configuration (4.1 + 9.8 MW) is significantly reduced due to the elimination of high flow rates of hot flue gases exiting the process (specifically, the process according to the invention only loses about 0.5 MW of energy due to heat losses). [Explanation of symbols]

[0076] 1 Furnace room 2 Process pipe 3 Gas inlet 4 Gas outlet 5 Recirculation Loop 6 Circulation Fan 7 External heating box 8 lines 9 Analyzer 10 Chimney 11 Entrance 12 Exit 13 Heating element

Claims

1. An electrically heated furnace, 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; iii. one or more gas inlets; iv. one or more gas outlets; The furnace chamber includes: The electric heating furnace is b. an external recirculation loop connecting the one or more gas outlets of the furnace chamber to the one or more gas inlets of the furnace chamber such that gas exiting the one or more gas outlets of the furnace chamber flows to the one or more gas inlets and is recirculated to the furnace chamber; c. at least one gas analyzer or detector and / or at least one pressure monitor for measuring pressure on the outer recirculation loop; The electric heating furnace further comprises:

2. 10. The electrically heated furnace of claim 1, further comprising one or more heaters for heating gas in the external recirculation loop.

3. An electrically heated furnace, 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; iii. one or more gas inlets; iv. one or more gas outlets; The furnace chamber includes: The electric heating furnace is b. an external recirculation loop connecting the one or more gas outlets of the furnace chamber to the one or more gas inlets of the furnace chamber such that gas exiting the one or more gas outlets of the furnace chamber flows to the one or more gas inlets and is recirculated to the furnace chamber; c. one or more heaters for heating gas in the external recirculation loop; The electric heating furnace further comprises:

4. 4. An electrically heated furnace according to claim 2 or 3, wherein the one or more heaters for heating the gas in the outer recirculation loop are one or more further electric heating means.

5. 5. The electrically heated furnace according to claim 1, wherein the plurality of electrically operated heating means arranged within the furnace chamber include a plurality of electrically operated heating elements arranged on a wall surface within the furnace chamber.

6. 5. The electrically heated furnace according to claim 1, wherein the plurality of electrically operated heating means arranged in the furnace chamber are means for directly electrically heating the process tube(s).

7. 7. The electrically heated furnace according to claim 1, wherein the furnace chamber has a plurality of gas inlets and / or a plurality of gas outlets.

8. 8. The electrically heated furnace of claim 1, wherein the one or more gas inlets are located at a base of the furnace chamber and the one or more gas outlets are located at or near a top of the furnace chamber.

9. 9. The electrically heated furnace of claim 1, wherein the furnace chamber may include, in addition to the one or more gas outlets, a vent through which gas from the furnace chamber is vented to the atmosphere or to the outside of the electrically heated furnace.

10. 10. The electrically heated furnace of claim 1, wherein at least one gas analyzer or detector for detecting one of hydrocarbons, ammonia, hydrogen, oxygen, or hydrogen chloride is provided on the outer recirculation loop.

11. 11. The electrically heated furnace of claim 10, wherein an analyzer or detector for hydrogen chloride detection or ethylene dichloride (EDC) detection is provided on the external recirculation loop.

12. 12. The electrically heated furnace according to claim 10 or 11, wherein two or more analyzers or detectors are provided on the outer recirculation loop, at least one of which is an analyzer or detector for detecting oxygen.

13. 13. The process of any of claims 1 to 12, wherein the volumetric flow rate of the outer recirculation loop is from 2% to 100% of the volume of the electrically heated furnace per minute.

14. 14. The process of claim 1, wherein the gas within the furnace chamber is circulated within the furnace chamber itself, the circulation being caused by one or more of the following: one or more fans within the furnace chamber; one or more baffles within the furnace chamber; the installation and positioning of multiple gas inlets for recirculated gas entering the furnace chamber from the external recirculation loop to supply airflow into the furnace chamber; and / or by convection within the furnace chamber.

15. 15. The process of claim 14, wherein the volumetric flow rate of the outer recirculation loop is between 0.5% and 25% of the volume of the electrically heated furnace per minute.

16. A process for conducting a chemical reaction, comprising: a. Providing an electrically heated furnace according to any one of claims 1 to 15; b. passing one or more reactants through said one or more process tubes; c. circulating gas through the gas outlet, the external recirculation loop, the gas inlet, and the furnace chamber; d. heating the reactants in the one or more process tubes to effect reaction of the reactants in the process tubes; The process includes:

17. 17. The process of claim 16, wherein the electrically heated furnace operates at a temperature in the process tube ranging from 300°C to 1200°C.

18. 18. The process according to claim 16 or 17, 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.

19. 19. The process of any of claims 16 to 18, wherein an inert gas or a mixture of inert gas and less than 10 vol% oxygen is circulated within the furnace chamber and the recirculation loop.

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