FIELD OF THE INVENTION

[0001] This invention relates to plasma torch assemblies, and more particularly, to such assemblies having retractable plasma torches that can be used with gasification reactors.

BACKGROUND

[0002] Plasma gasification reactors (sometimes referred to as PGRs) are a type of pyrolytic reactor known and used for treatment of any of a wide range of materials including, for example, scrap metal, hazardous waste, other municipal or industrial waste and landfill material, and vegetative waste or biomass to derive useful material, e.g., metals, or a synthesis gas (syngas), or to vitrify undesirable waste for easier disposition.

[0003] PGRs and their various uses are described in, for example, U.S. Patent No. 7,632,394 by Dighe et al., issued Dec. 15, 2009, titled "System and Process for Upgrading Heavy Hydrocarbons"; U.S. Patent Application Publication No. 2009/0307974 by Dighe et al., titled "System and Process for Reduction of Greenhouse Gas and Conversion of Biomass"; U.S. Patent Application Publication No. 2010/0199557 by Dighe et al., titled "Plasma Gasification Reactor"; and U.S. Patent Application Publication US2012/0199795 by Gorodetsky et al., titled "Enhanced Plasma Gasifiers for Producing Syngas", all of which are incorporated by reference herein for their descriptions of PGRs and methods practiced with them.

[0004] One manner of operating such a PGR is for gasifying material to produce a syngas from a feed material. The feed material may include, as examples, one or more of materials such as biomass, municipal solid waste (MSW), coal, industrial waste, medical waste, hazardous waste, tires, and incinerator ash. In some installations, the PGR can produce syngas that contains useful amounts of hydrogen and carbon monoxide for subsequent use as a fuel.

[0005] Heat from an electric arc can be fed into a cupola, furnace, or other reactor vessel to enhance the operation thereof by providing a very hot gas stream which may be either oxidizing or reducing and can also be mixed with particulate material. The electric arc can be produced in a plasma torch in which the electric arc ionizes the gas which is blown out of the end of the torch, producing a hot gas stream which generally operates in the range of, for example, 10,000° F (5,538° C).

[0006] In various operating scenarios, it would be desirable to remove the torch from the reactor vessel or to vary the position of the torch to change the location of the hot gas stream within the reactor vessel.

SUMMARY

[0007] In one embodiment an apparatus includes a gasifier vessel; an orifice in a wall of the gasifier vessel; a plasma torch; a torch support structure connected to the wall of the gasifier vessel and having an opening configured to receive the plasma torch, the torch support structure including a shroud gas spool configured to inject shroud gas into the opening and around the torch and an isolation valve configured to prevent gas flow between an internal environment of the gasifier and an external environment outside of the torch support structure when the plasma torch is retracted; and an actuator configured to extend the plasma torch into the gasifier vessel through the orifice and to retract the plasma torch from the gasifier vessel.

[0008] In another embodiment, an apparatus includes: a gasifier vessel; an orifice in a wall of the gasifier vessel; a plasma torch; a torch support structure connected to the wall of the gasifier vessel and having an opening configured to receive the plasma torch, the torch support structure including an isolation valve configured to prevent gas flow between the internal environment of the gasifier and the external environment outside of the torch support structure when the plasma torch is retracted, and a purge spool having first and second annular seals with openings for receiving the plasma torch, with a plenum between the first and second annular seals to prevent gas flow between an internal environment of the gasifier and an external environment outside of the torch support structure when the plasma torch is retracted but the isolation valve is not yet fully closed; and an actuator configured to extend the plasma torch into the gasifier vessel through the orifice and to retract the plasma torch from the gasifier vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is cross-sectional view of a retractable plasma torch assembly.

[0010] FIG. 2 is another cross-sectional view of the retractable plasma torch assembly of FIG. 1.

[0011] FIG. 3 is another cross-sectional view of the retractable plasma torch assembly of FIG. 1.

[0012] FIG. 4 is a cross-sectional view of another retractable plasma torch assembly.

DETAILED DESCRIPTION

[0013] In one aspect, the present invention relates to plasma torch assemblies that can be used in combination with a reactor vessel, such as a gasification or vitrification reactor.

[0014] FIG. 1 is cross-sectional view of a retractable plasma torch assembly 10 including a purged removal port apparatus 12 for a retractable plasma torch 14. Components illustrated in FIG. 1 include a retractable plasma torch 14 and a torch support structure 16. The torch support structure 16 includes a shroud air spool 18, an isolation valve 20, and a purge gas spool 22. The assembly is shown in combination with a gasifier vessel 24 including a gasifier shell 26, a layer of refractory material 28, a taphole 30, and a plasma torch nozzle 32 (also called a tuyere). In this simplified diagram, a number of components are omitted or simplified in order to clearly highlight the functioning of the purged removal port apparatus 12.

[0015] With continued reference to FIG. 1, the plasma torch 14 is shown in the installed position, in which it can be operated as required (e.g. for taphole heating) within the internal environment 34 of the gasifier vessel 24. The plasma torch 14 can be a water-cooled torch, and is shown to include a cylindrical portion that can be positioned along an axis 36 of a generally cylindrical opening 38 in the torch support structure 16 and the nozzle 32, using equipment such as an actuator 40. The actuator 40 can be a linear actuator mechanism, for example, a piston, screw, or rack and pinion. In FIG. 1, the distal end 42 of the plasma torch 14 is shown to be embedded in a bed of process material 44. However, in other embodiments, the distal end 42 of the plasma torch 14 need not be embedded in a bed of process material 44.

[0016] The torch support structure 16 is connected to the gasifier vessel 24. As shown in FIG. 1, the shroud air spool 18 is fixed to the plasma torch nozzle 32 and comprises a port 46 through which shroud air 48 (or alternatively, steam or oxygen-enriched air) can be supplied to protect certain components of the plasma torch 14 and to focus a hot gas flow 50 produced by the plasma torch 14. Under normal operation, shroud air 48 is supplied at a pressure greater than the pressure within the internal environment 34, thereby preventing egress of syngas from the internal environment 34 through the plasma torch nozzle 32. A shroud air isolation valve 66 is fitted on the port 46 and is in the open position to enable the supply of the shroud air 48 through the port 46. The shroud air isolation valve 66 shown FIG. 1 is depicted as a slide gate type, but could be any type of valve capable of achieving a gas-tight seal between the port 46 and an external environment 52.

[0017] Isolation valve 20, which could be any full port valve such as a slide gate or ball valve, is fixed between the shroud air spool 18 and the purge gas spool 22. Isolation valve 20 may be closed to produce a gas-tight seal between the internal environment 34 and the external environment 52 in instances where the plasma torch 14 is removed for maintenance purposes. However, FIG. 1 depicts the plasma torch 14 in the installed position, so isolation valve 20 is in the open position.

[0018] Purge gas spool 22 includes a port 70 and annular sealing members 56, 58 which are located annularly intermediate the plasma torch 14 and an interior surface of the purge gas spool 22. The sealing members 56, 58 may have a relatively snug fit between the plasma torch 14 and the purge gas spool 22 such that they cause a significant resistance to gas flow through the annular plenum between the plasma torch 14 and the purge gas spool 22. Between the sealing members 56, 58 is a purge gas plenum 60. The purge gas spool 22 is employed to prevent egress of syngas from the interior environment 34 when the plasma torch 14 is removed for maintenance.

[0019] With continued reference to FIG. 1, it should be noted that the flange 62 on the plasma torch 14 serves as a physical stop to prevent further penetration of plasma torch 14 into the gasifier vessel 24. In other applications involving a fixed plasma torch, such a flange may be employed for sealing purposes. However, in this embodiment, the plasma torch 14 may be variably positioned during normal operation, so a seal between the internal environment 34 and the external environment 52 must be achieved by other means (i.e. through the shroud air sealing mechanism described above, and/or the purge gas sealing mechanism described below), without the use of the flange 62.

[0020] FIG. 2 is another cross-sectional view of the retractable plasma torch assembly 10 of FIG. 1. In FIG. 2, plasma torch 14 is in the process of being removed for maintenance and is offline. Shroud air flow through the shroud air spool 18 is turned off and isolation valve 20 is in the process of being closed, but is still at least partially open. In this configuration, it is possible that syngas 64 from the interior environment 34 could flow through the plasma torch nozzle 32 and past the open isolation valve 20. The shroud air isolation valve 66, now shown in the fully closed position, is employed to prevent egress of syngas through the port 46 on the shroud air spool 18.

[0021] In the situation presented in FIG. 2, a flow of purge gas 68 (e.g. nitrogen) is supplied through port 70 and into the purge gas plenum 60. Due to the sealing action of the sealing members 56, 58, the flow of purge gas 68 will pressurize the purge gas plenum 60. If the pressure within the purge gas plenum 60 is maintained above the pressure of the internal environment 34, any leakage across the sealing members 56, 58 will only involve outflow of purge gas from the purge gas plenum 60 into the internal environment 34 and the external environment 52. Leakage of syngas 64 across the sealing members 56, 58 and into the external environment 52 would not be possible.

[0022] FIG. 3 is another cross-sectional view of the retractable plasma torch assembly 10 of FIG. 1 with the plasma torch 14 fully removed. Isolation valve 20 is fully closed and achieves a gas-tight seal between the internal environment 34 and the external environment 52, thereby preventing egress of any syngas 64.

[0023] It can be appreciated that the apparatus described above can also be employed in a similar fashion to allow for re-insertion of the plasma torch 14 into the plasma torch nozzle 32. It can also be understood that this apparatus does not require shutdown of the gasifier vessel 24, and thus enables "online" removal and re-insertion of the plasma torch 14. It should also be noted that variations on the above-described apparatus are possible, particularly those utilizing only one of either the purge gas spool 22 or the shroud air spool 18 for sealing under all conditions. For example, in an embodiment utilizing only the shroud air spool 18 (without the purge gas spool 22), the shroud air 48 (shown in FIG. 1) may be supplied at a sufficiently high pressure (i.e. a pressure higher than the internal environment 34 and the external environment 52), such that egress of any syngas 64 from the internal environment 34 and ingress of any air from the external environment 52 is prevented, even in situations where the plasma torch 14 is fully removed and the isolation valve 20 is fully open. It can be understood that such an arrangement, while functional in terms of sealing, may require a significantly greater supply of shroud air 48 compared to the embodiment depicted in FIGs 1-3, and may not be a preferred embodiment.

[0024] The embodiment of FIGs. 1-3 includes a water-cooled, retractable plasma torch assembly 10 that includes an optional purged removal port (either the shroud air spool 18 or the purge gas spool 22, as only one of these components would be required to ensure sealing under all conditions). A linear actuator 40 (which could be hydraulic, pneumatic, electric, or other type) can be installed outside of the gasifier vessel 24 and serves to extend and retract the plasma torch 14.

[0025] A nozzle 32 serves as an orifice through which to extend/retract the plasma torch 14 within the gasifier vessel 24. The nozzle 32 can include refractory lining where required for thermal protection. For example, the refractory lining 28 of the gasifier can extend into the nozzle as shown in FIGs. 1-3.

[0026] A build-up removal mechanism 72 can be included to remove any solidified slag build-up which may accumulate on the water-cooled surface of the plasma torch 14. In the embodiment of FIGs 1-3, a mechanical rapping device is employed as the build-up removal mechanism 72. Alternative mechanisms, such as vibratory device or scraper, and mounted either within or external to the gasifier vessel, are also possible but not depicted in FIGs 1-3.

[0027] FIG. 4 is another cross-sectional view of a retractable plasma torch assembly 10 that includes many of the elements of FIGs. 1-3, and further includes a scraper 74 mounted adjacent to the nozzle opening. In other embodiment, multiple build-up removal mechanisms can be used, such as for example both the mechanical rapping device72 (shown in FIGs. 1 and 2) and the scraper 74.

[0028] In various embodiments a plasma torch, configured to deliver a jet or plume of hot gas flow (also referred to as superheated gas flow) to a chamber, is used in combination with a structure (i.e., the shroud inlet assembly) that delivers a relatively cool gas (i.e. a shroud gas) around the superheated gas stream. The shroud inlet assembly can deliver two or more combinations of cold gas flow that surround the superheated gas flow. The shroud inlet assembly can be connected to a tubular or conical chamber of a tuyere, with openings at either end, which transmits all gas flows to the process of the gasifier or furnace. The chamber can be lined with a refractory material, and can be cooled by a fluid, potentially with a water jacket or a tubular cooling coil which can be embedded within the refractory material. The gas flow within the tuyere chamber can be directed in a way such that the superheated gas remains centered and flowing along a central axis, with the shroud gases flowing between the superheated gas and the chamber wall.

[0029] Depending on the process design, internal pressure within the reactor vessel may be below atmospheric pressure (negative gauge pressure), above atmospheric pressure (positive gauge pressure), or approximately equal to atmospheric pressure (neutral pressure). Additionally, reactor vessels that normally operate at negative or neutral pressures may be designed to handle positive pressure excursions resulting from anomalous operating conditions (e.g. introduction of water in the feed of a MSW gasifier). In the case of MSW gasifiers (which generate a gas mixture termed "syngas", comprising primarily H ₂ and CO gas), a pressure seal is important for several reasons, including: prevention of air infiltration into the gasifier vessel, which could result in unwanted conversion of carbon or CO gas into C0 ₂ (by the introduction of oxygen from the ambient air), as well as dilution of the syngas product (by the introduction of nitrogen from the ambient air); and prevention of syngas egress into the external plant environment, which could pose a safety hazard to plant personnel.

[0030] In reactor vessels such as municipal solid waste (MSW) gasifiers and electric arc furnaces (EAFs), molten fluid (e.g. slag, metal) is removed through an opening in the vessel wall termed a "taphole". Molten fluid exiting the taphole flows in a conduit (referred to as a "launder") to a collection point for cooling, disposal, and/or further processing into a saleable product. This process is referred to as "tapping" and may be performed on a continuous or batch basis.

[0031] In tapping processes, the taphole may be plugged, thereby preventing outflow of molten fluid from the vessel. Taphole plugging may be intentional (e.g. injecting a clay into the taphole for batch tapping operations) or may be unintentional (e.g. molten fluid from the vessel gradually solidifies within the taphole, causing a blockage). In either case, the taphole must eventually be unplugged to allow for further tapping. Unplugging can be achieved by various means. One approach utilizes a plasma torch to melt through the plugged taphole from the exterior of the vessel. Generally, this approach to unplugging is known as "lancing". However, in some cases, external access to the taphole for the purposes of plugging/unplugging may be considerably restricted by obstacles such as launders and slag granulation equipment. Additionally, some tapping operations may require manual operators in close proximity to the molten fluid, which presents a potential safety hazard. The retractable torch assembly described herein can be used to enable unplugging of a taphole without external access to the taphole and without requiring manual operation in the vicinity of the taphole.

[0032] While particular aspects of the invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.