Patent Description:
The present subject-matter relates to a plasma torch using steam as the main plasma forming gas.

Plasma torches working with steam as the main plasma forming gas have many applications. Plasma torches which use steam as the main plasma forming gas produce a plasma plume with a high concentration of H+ and OH- ions. The steam plasma plume rich in these chemically very reactive species can be used in a wide range of applications starting from coal gasification to hazardous waste treatment [see references <NUM> to <NUM> detailed hereinbelow]. Steam plasma torches have been very successful in achieving difficult chemical conversion particularly for the destruction of chlorinated and/or fluorinated hydrocarbons [see references <NUM> to <NUM> detailed hereinbelow].

Steam plasma plume rich in H+ and OH- ions can only be achieved by internal injection of the steam in the plasma torch assembly, i.e. the injected steam should dissociate into H+ and OH- ions in the plasma plume becoming the main plasma forming gas If steam is injected at the tip of the plasma torch, then the injected steam will undergo limited or zero dissociation, thereby producing a non-reactive plasma plume, which is evident by the poor destruction efficiency of such systems [see reference <NUM> detailed hereinbelow].

The existing plasma torches which use steam as the plasma forming gas have limitations, such as external steam injection, low gross power, higher electrode erosion and complex design with moving parts inside the plasma torch assembly [see references <NUM> to <NUM> detailed hereinbelow]. In most plasma torches, where steam is used as one of the plasma forming gases, steam is injected externally towards the exit of the plasma torches.

External steam injection results in a nonreactive steam plasma plume and/or a plasma plume which has very low concentration of H+ and OH- ions [see reference <NUM>]. When steam is injected externally, the interaction of this externally injected steam with the main plasma plume will be limited and hence the injected steam will not reach higher temperatures necessary for the formation of reactive H+ and OH- ions [see reference <NUM>]. This results in a plasma plume with low or zero concentration of H+ and OH-ions. Steam plasma with low concentration of reactive ions results in the loss of its ability to drive chemical reactions.

High power steam plasma torches are also unavailable for industrial applications. Currently available steam plasma torches are limited to lab-scale with a torch gross power of < <NUM> kW [see references <NUM> and <NUM> detailed hereinbelow]. The medium power plasma torch systems, which are available, suffer from problems such as high electrode erosion; reported electrode lives are in the order of <NUM> hrs or lower [see reference <NUM> detailed hereinbelow]. Also, the medium power plasma torch systems have complex designs requiring moving components inside the plasma torch assembly, making them practically unsuitable for long term industrial applications [see reference <NUM>]. <CIT> disclose a prior art DC steam plasma torch. The torch includes a first and second electrode and a first and second swirl generator. The first swirl generator receives primary working gas and generating a swirl in the same. The second swirl generator receives auxiliary working gas and generating a swirl in the same. The article "<NPL>, describes use of a plasma torch in a steam plasma arc refrigerant cracking system (SPARC). <CIT> discloses another prior art DC steam plasma torch comprising a swirl generator.

Therefore, there is a need for a high power steam plasma torch systems with higher electrode life times while running on steam as the main plasma forming gas.

It would thus be highly desirable to be provided with a novel steam plasma torch system.

Therefore, the embodiments described herein provide in one aspect a high power DC non transferred plasma torch system, comprising a plasma torch assembly housed for instance in a stainless steel housing, a cooling skid, a steam skid, a DC plasma power supply, a gas flow control cabinet, an ignition control cabinet, a control cabinet along with a programmable logic controller for the system, a torch ignition sequence, a torch control sequence and a human machine interface.

The embodiments described herein provide in another aspect a plasma torch system, comprising a plasma torch assembly, a cooling system for the plasma torch assembly, a steam system for the plasma torch assembly, a plasma power supply, a gas flow control system, and an ignition control system, and a controller for the plasma torch system.

The embodiments described herein provide in a further aspect a plasma torch assembly, comprising an electrode assembly for igniting the plasma torch assembly, a gas delivery system, a cooling system, and a steam delivery system adapted for injecting steam directly into the plasma plume.

For a better understanding of the embodiments described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, which show at least one exemplary embodiment, and in which:.

A vortex stabilized DC steam plasma torch system is herein described, which alleviates the shortcomings of other systems, such as:.

- injecting steam directly in the plasma arc to have highly ionized gas rich in reactive H+ and OH- ions in the plasma plume (for effective reactions);.

- use of button type cathode designs which do not require any moving parts and/or external high frequency energy sources for torch ignition, thereby resulting in a simpler design; and.

- use of a button type cathode, tubular ignition electrode and tubular anode with steam injected in between the tubular ignition electrode and the tubular anode, which results in a feature that prevents bridging of the electrode.

The present steam plasma torch system provides:.

The present system is a high power DC plasma torch system which uses internally injected steam as the main plasma forming gas, thereby resulting in a very reactive steam plasma plume. In the present system, superheated steam is injected directly into the plasma plume using a water cooled vortex versus the current state of the art wherein steam is injected at the tip of the plasma torch. Also, in the present system, there are no moving components inside the plasma torch assembly such as those found in the state of the art technology which uses an electrode motion system to short the electrodes and separate the electrodes apart to ignite an electric arc.

As shown in <FIG>, a plasma torch system S includes a plasma torch assembly <NUM>, a cooling skid <NUM> which provides the necessary cooling to the plasma torch assembly <NUM>, a steam skid <NUM> which supplies and controls the flow of superheated steam to the plasma torch assembly <NUM>, an ignition and power integration control cabinet <NUM> which houses the torch ignition contactor and water-power manifolds, a DC plasma power supply <NUM> which provides DC power to the ignition and power integration control cabinet <NUM> through a positive cable 48x and negative cable 48y, a gas flow control cabinet <NUM> which controls the flow of ignition and shroud gases, a control cabinet <NUM> housing a programmable logic controller for the entire system, and a human machine interface <NUM>, which provides an interface for the operator to communicate and control the entire system parameters, such as gas flow, steam flow, and torch power.

As shown in <FIG>, the plasma torch assembly <NUM> includes:.

The plasma torch housing <NUM> is for instance a single unit fabricated out of stainless steel and is equipped with a standard front mounting flange <NUM> to facilitate easy mounting of the torch assembly onto reactors/vessels equipped with standard flanged connecting ports.

The three torch electrodes <NUM>, <NUM>, <NUM> are co-axially mounted into the plasma torch housing <NUM> with a fixed gap between each electrode such that when assembled, the gap between the cathode <NUM> and the ignition electrode <NUM> is just sufficient to create a self-sustaining plasma forming condition during the ignition step of the ignition sequence. Similarly, the gap between the ignition electrode <NUM> and the anode <NUM> is just sufficient to transfer the arc from the ignition electrode <NUM> and the anode <NUM>, without losing the plasma forming condition, during the transfer step of the torch ignition sequence.

The vortex generators <NUM>, <NUM>, <NUM> are fabricated and mounted co-axially to match their center lines with that of the electrodes, to create a tangential gas flow pattern for minimizing electrode erosion. The cooling channels <NUM>, <NUM>, <NUM> and <NUM>, which are for example carved out either in a high temperature plastic housing or as an annulus between the electrode and the stainless steel housing, are fabricated to create a high velocity cooling flow circuit along the length of each electrode thereby avoiding or impeding film boiling conditions.

A cathode base <NUM> machined out for instance of a nonconducting high temperature polymer is mounted, e.g. with bolts, to the torch housing <NUM>. A cathode holder <NUM> fabricated from a copper rod, is for instance thread-mounted into the cathode base <NUM>. The conical cathode <NUM> is for example threaded into the cathode holder <NUM>. The cathode holder <NUM> serves as a fluid conduit for the torch cooling water and also conducts DC power <NUM> to the plasma torch assembly <NUM>.

A cathode manifold <NUM>, fabricated for example out of a nonconducting high temperature polymer, is for instance threadably mounted around the cathode <NUM>, and connects the cathode cooling channels <NUM> to the ignition electrode cooling channels <NUM>.

Cooling water <NUM> supplied from the cooling skid <NUM>, passes through a power manifold housed inside the ignition and power integration control cabinet <NUM>. The DC cables 48x and 48y coming from the power supply <NUM> are also connected to the power manifolds. The power manifold mixes both the electric power and the cooling water and conveys both power and the cooling water to the plasma torch assembly <NUM> through power hoses <NUM> and <NUM>. The power hoses <NUM> and <NUM> are made of flexible rubber with a copper wire as a central core. DC power flows through the central copper wire whereas the cooling water flows in the annular space of the power hoses <NUM> and <NUM>.

The cooling water enters the plasma torch assembly <NUM> through the cathode holder <NUM>, travels up to the back of the cathode <NUM>, thereby providing the necessary cooling for the cathode <NUM>, and flows out through the radial apertures of the cathode holder <NUM> via the cathode manifold <NUM> towards the ignition electrode <NUM>.

Also, the cathode manifold <NUM> provides shroud/ignition gas flow channels <NUM> and conveys the shroud/ignition gas <NUM>/<NUM> to the vortex generator <NUM> that is for instance threaded around the cathode <NUM>.

An ignition tube <NUM> fabricated out of any conductive metal, such as brass or copper, surrounds the cathode manifold <NUM> and connects an ignition plug <NUM> to the ignition electrode <NUM>. An ignition cable <NUM> connects the ignition contactor housed in the control cabinet <NUM> and the ignition plug <NUM>. The ignition electrode <NUM> is for instance threaded to front end of the ignition tube <NUM> and the ignition plug <NUM> is for instance threaded to the rear end of the ignition tube <NUM>. The cooling water coming out of the cathode <NUM> travels along the length of the ignition tube <NUM> to reach the ignition electrode <NUM>.

A shroud tube <NUM> fabricated out of high temperature polymer secures the ignition tube <NUM> in its place and a series of channels bored in the tube act as a fluid conduit for an auxiliary gas <NUM>, such as argon, air, nitrogen, oxygen or similar. The auxiliary gas <NUM> injected through auxiliary gas ports <NUM> travels in the aperture of the shroud tube <NUM> to reach the auxiliary gas vortex generator <NUM>.

The auxiliary gas vortex generator <NUM>, which is for example fabricated out of stainless steel with tangential drilled holes to create a gas swirl to stabilize the arc column, is for instance threadably mounted onto the ignition electrode <NUM>. The auxiliary gas <NUM> is injected during the torch ignition sequence. The auxiliary gas <NUM> provides the necessary driving force to transfer the arc from the ignition electrode <NUM> to the anode <NUM> during the ignition sequence.

The steam vortex generator assembly <NUM> comprises the stainless steel steam vortex generator <NUM> and a ceramic insulated steam feed tube <NUM>, fabricated out of brass tube. The steam vortex generator <NUM> and the steam feed tube <NUM> are assembled into a water cooled body, fabricated out for instance of stainless steel, and is sandwiched between the auxiliary gas vortex <NUM> and the anode assembly <NUM>. An insulating high temperature ceramic ring, such as a high alumina ceramic ring <NUM>, placed between the auxiliary gas vortex <NUM> and the steam vortex generator assembly <NUM> provides electrical isolation between the ignition electrode <NUM> and the anode <NUM>.

The cooling water leaving the ignition electrode <NUM> travels through the cooling channels <NUM> of the steam vortex generator assembly <NUM> for providing just sufficient cooling for the steam vortex generator assembly <NUM>. The steam feed tube <NUM> is for example threadably mounted to the steam vortex generator <NUM> and a two-step design ensures that the steam feed tube <NUM> remains locked when assembled. Inlet superheated steam <NUM> flows through the ceramic insulated steam feed tube <NUM> to reach the steam vortex generator <NUM>. The steam vortex generator assembly <NUM> is designed to minimize contact surfaces between the superheated steam <NUM> and the water cooled steam vortex generator assembly <NUM> in order to prevent steam condensation along its path before reaching the steam vortex generator <NUM>.

The anode assembly <NUM> comprising the tubular anode <NUM>, fabricated out of copper, and water cooling channels <NUM> around the anode <NUM>, fabricated out of stainless steel, is for example bolted onto the torch housing <NUM>. Silicon based O-rings are used to seal the water cooling channels <NUM> from leaks. The cooling water coming from the steam vortex generator assembly <NUM> flows through the cooling channels <NUM> of the anode <NUM> and provides the necessary cooling before exiting through a cooling water outlet port <NUM>. The cooling water outlet port <NUM>, which is fabricated out of electrically conducting material such as stainless steel, serves as a conduit to connect the cooling water return hose <NUM> and also conducts DC power to the anode <NUM>.

The torch ignition and control program, which is installed in a programmable logic controller (PLC) housed inside the control cabinet <NUM>, is used to ignite and control the plasma torch assembly <NUM> according to an operator input power set point. The human machine interface <NUM> communicates the operator input power set point to the PLC. The entire system is linked to the Human machine interface (HMI) <NUM> and to the PLC via a communication network cable <NUM>.

Claim 1:
A high power DC non transferred plasma torch system (S), comprising a plasma torch assembly (<NUM>), a cooling skid (<NUM>) for cooling the plasma torch assembly (<NUM>), a steam skid (<NUM>) for supplying and controlling a flow of superheated steam to the plasma torch assembly (<NUM>), an ignition control cabinet (<NUM>) housing the torch ignition contactor, a DC plasma power supply (<NUM>) for providing DC power to the ignition control cabinet (<NUM>), a gas flow control cabinet (<NUM>) for controlling a flow of ignition and shroud gases, a control cabinet (<NUM>) housing a programmable logic controller for the system having installed a torch ignition sequence, a torch control sequence and a human machine interface (<NUM>) thereon; wherein the plasma torch assembly (<NUM>) comprises a shroud/ignition gas vortex generator (<NUM>) mounted between a conical cathode (<NUM>) and a tubular ignition electrode (<NUM>), and an auxiliary gas vortex generator (<NUM>), mounted in front of the ignition electrode (<NUM>);
and
a water-cooled vortex generator assembly (<NUM>) with insulated superheated steam injections tubes (<NUM>) are connected to a steam vortex generator (<NUM>) mounted in the back of a tubular anode (<NUM>) for injecting the superheated steam to a plasma plume.