Patent Description:
The Technology and Economic Assessment Panel (TEAP) of the United Nations Environmental Program (UNEP) has reviewed and approved a total of twelve technologies for the destruction of ozone depleting substances (ODS) [<NUM>], For descriptive purposes, these approved technologies can be broadly classified as incineration technologies, plasma technologies including arc and radio frequency plasma, and other non-incineration technologies [<NUM>], The most widely used current practice, both by ODS processing rate and by the number of processing units, for destruction of ODS is either by incineration or by argon plasma technology [<NUM>-<NUM>], Both technologies use thermal oxidation as the main mechanism of destruction. ODS are fed into refractory lined reactors, which areoperating at diminished oxygen levels lead to formation of soot, which is hard to remove. Argon plasma technology requires high flow rates of high purity argon, which makes it expensive to use.

As ODS are inherently fire inhibitors, extreme process conditions are needed for their destruction. Incinerators require large quantities of fossil fuels to achieve the high temperature necessary for ODS destruction. Ozone depleting substances are fed into the high temperature zone of the incinerators in relatively small quantities along with air or oxygen [<NUM>-<NUM>], Often these incinerators do not have secondary combustion chambers and the off gases generated are simply diluted, before emitting to the atmosphere. Consequently, these incinerators require large quantities of fossil fuels to destroy small quantities of ODS, generate large quantities of flue gases containing significant amount of Ch, F2, NOx, SOx. VOC, which are hard to remove from the flue gases [<NUM>-<NUM>], Also, incineration processes pose a very high potential of emitting toxic products of incomplete combustion, such as dioxins and furans [<NUM>].

<CIT> is related to a method and an apparatus for treating hazardous organic waste in which fluid waste is sprayed into a plasma torch in a high temperature zone. Within this high temperature zone, it is heated and then oxidized in a second zone. A combustion gas is created, which is then lead into a cooling zone, where it is rapidly cooled by water spraying.

Plasma destruction technologies use argon, nitrogen or CO2 as the plasma forming medium to transfer energy from an electric arc into high destruction temperatures [<NUM>, <NUM>-<NUM>]. These technologies still use thermal oxidation as their main destruction method. Direct current plasma torches are used to heat the refractory lined reactors to high destruction temperatures. ODS, air and steam are introduced into the destruction zone and the ODS are combusted. The primary destruction mechanism in these systems is still thermal oxidation and hence has similar problems such as production of CI2, F2 and CF4, which are hard to remove from the flue gas. In these processes, the presence of excess oxygen and air in the high temperature zone still poses the potential formation of NOX, whereas operating at diminished oxygen levels lead to formation of soot, which is hard to remove. Argon plasma technology requires high flow rates of high purity argon, which makes it expensive to use.

Therefore, there is a need in the art for an improved technology for the destruction of ozone depleting substances.

It is therefore an aim of the present invention to provide a novel system for destroying ozone depleting substances.

Therefore, in accordance with the present invention, there is provided a two step process for the destruction of a precursor material using steam plasma in a reactor, wherein the precursor material is hydrolyzed as a first step in a high temperature zone of the reactor, followed by a second step of medium temperature oxidation of the reactant stream in a combustion zone of the reactor where combustion oxygen or air is injected and immediate quenching of the resulting gas stream to avoid the formation of unwanted by-products.

Also in accordance with the present invention, there is provided an apparatus for carrying out the above process, including a non transferred direct current steam plasma torch, an externally cooled three zone steam plasma reactor including a corrosive resistant refractory lining, means for attaching the plasma torch to the reactor, means for introducing the precursor material in the form of gas vortex or fine liquid spray or solid particles into the plasma plume of the plasma torch, means for introducing the combustion air or oxygen into the combustion zone of the reactor, means for exiting the reactant mixture from the reactor and means for quenching the reactant mixture located at the exit end of the reactor.

Further in accordance with the present invention, there is provided an apparatus for the destruction of a precursor material, comprising a reactor including a high temperature zone and a combustion zone, the high temperature zone being adapted for hydrolyzing the precursor material, the combustion zone being adapted to effect medium temperature oxidation of the reactant stream where combustion oxygen or air is injected, and a quenching means is provided at an exit end of the reactor for quenching of the resulting gas stream to avoid the formation of unwanted by-products.

Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of embodiments thereof, given by way of example only with reference to the accompanying drawings.

Reference will now be made to the accompanying drawings, showing by way of illustration an illustrative embodiment of the present invention, and in which:.

Figure Ia is a schematic representation of a complete system for destroying ozone depleting substances in accordance with one embodiment of the present invention;.

The present invention uses a steam plasma hydrolysis system S for the destruction of ODS. The main mechanism of destruction in this invention is the plasma steam hydrolysis. In this system, a custom designed steam plasma torch is used as the sole source of energy to heat the refractory lined primary reaction chamber to temperatures close to <NUM>. Superheated steam formed from regular water is used as the main plasma forming gas, along with a small quantity of inert gas. Highly reactive steam plasma, i.e. hydrogen and hydroxyl ions present in the steam plasma, are used to convert the ODS into CO, HCl and HF, in an oxygen starved environment. The produced CO is combusted downstream in the process followed by an instantaneous water quench. Oxygen starved environment eliminates the formation of toxic substances such as Cl<NUM>, F<NUM> and CF<NUM> and a rapid quench eliminates the formation of dioxins and furans. The acid gases formed in the process can either (i) be neutralized with an alkali or (ii) first scrubbed with water to recover a weak acid mixture and then neutralized for the unrecoverable portion of the acid gases. In both cases, a cleaned effluent gas stream comprising mainly CO<NUM> is emitted to the atmosphere.

Now turning to the figures of the appended drawings, the present steam plasma hydrolysis system S will be described in more details.

A precursor material <NUM> is injected, either in the form of a gas vortex or a fine spray of liquid or a stream of solids, into the system S as shown in <FIG>. The precursor material <NUM>, to be destroyed, is fed adjacent to a plasma torch <NUM> via a specially designed flange <NUM>. This flange <NUM> is water cooled, made of acid resisting material and is specially designed to facilitate intimate mixing of the fed precursor material <NUM> with the high temperature viscous steam plasma plume.

An outside heating source, typically a steam plasma torch <NUM>, is used as the source for heating the refractory lined reactor to a temperature of <NUM>. The plasma torch <NUM> is designed and built with features, to avoid condensation of the superheated steam inside the torch before reaching the plasma arc. These features of the plasma torch include, (I) direct injection <NUM> of the main plasma forming gas, superheated steam, to the torch vortex so that it does not condense on its way to the arc plume and minimizing superheated steam passage inside the torch body; (ii) cooling of the plasma torch body with a hot fluid (propylene glycol-water mixture), circulating in a high pressure closed loop, to avoid superheated steam condensation; and (iii) use of high temperature resistant polymers such as Vespel™ or PEEK for torch internal components.

The steam plasma torch <NUM> includes a metallic cathode <NUM>, a metallic ignition anode <NUM> and a metallic working anode <NUM>, which are arranged as shown in <FIG>. A plasma arc is initiated with helium or another monoatomic gas between the cathode <NUM> and the ignition anode <NUM>. Once the arc is stabilized <NUM>,<NUM> a plasma forming steam is injected at <NUM> and the arc is transferred from the ignition anode <NUM> to the working anode <NUM>. Nitrogen, helium, argon or mixture thereof is used as a shroud gas <NUM>. The shroud gas <NUM> protects the metallic cathode <NUM> from premature oxidation and hence increases the working life of the cathode <NUM>. Superheated steam is used as the main plasma forming gas <NUM>.

The steam plasma torch <NUM>, in-addition to acting as a heat source, provides reactive oxygen, hydroxyl and hydrogen ions necessary for the destruction of the precursor material <NUM> and prevents the formation of undesired side products, such as Cl<NUM>, F<NUM>, CFX. The overall reaction can be summarized as :.

CHxClyFz + aH<NUM>O -> zHF +yHCl+ aCO + öH<NUM> + cH<NUM>O.

A refractory lined reactor <NUM> is used to destroy the precursor material <NUM>. A corrosion resistant high durable refractory lining <NUM> is used as the working refractory in the reactor <NUM>. For example, a high alumina refractory (> <NUM>% alumina content), such as Kricon <NUM>™ or similar which is known to resist to corrosive HF and HCl gases, is used as the working refractory.

The internal walls of the reactor <NUM> are coated with acid resistanthigh temperature metallic coating such as hastealloy™ or similar. The external walls of the reactor <NUM> are cooled externally, either by air or by water, for safety reasons and to limit heating of the furnace room.

The refractory lined reactor <NUM> comprises of three zones, asshown in <FIG>. These three zones are:.

Combustion air or oxygen <NUM> is added to the reactor <NUM>, as also shown in <FIG>. The combustion air or oxygen <NUM> is metered to the reactor <NUM> to control the temperature in the low temperature zone of the reactor <NUM> while achieving complete combustion and eliminating the formation of undesirable byproducts such as CI2.

A water quench unit <NUM> is attached right at the outlet of the combustion zone <NUM> of the reactor <NUM>, as seen in <FIG>. A set of spray nozzles <NUM> create a fine spray of water <NUM> in the quench unit <NUM>, which spray of water <NUM> instantaneously cools the gases. This instantaneous quenching of the gases will prevent the reformation of dioxins and furans. The quench unit <NUM> is built as a double-walled water-cooled pipe section with acid resisting material.

A scrubber tank <NUM> is attached at the bottom of the quench unit <NUM>, as best shown in <FIG>. The scrubber tank <NUM> uses acid resistant plastic sealing material on all sealing surfaces. The internal walls of the scrubber tank <NUM> are lined with an acid resistant Teflon™-based coating such as Halar® CCTFE, or similar, The scrubber tank <NUM> acts as a reservoir for collecting the quench water <NUM> and provides the necessary water head for a scrubber water recirculation pump <NUM> (see <FIG>).

A standard flue gas cleaning technology, i.e. either a wet off-gas cleaning technology using an acid gas neutralizing scrubber <NUM> (as shown in <FIG>) or a dry gas cleaning technology, is used to remove acid gases from the flue gas.

An induced draft fan <NUM> draws the off gases through the system S and creates a slightly negative pressure in the system S, as shown in <FIG>. The entire system S is maintained under a slight negative pressure (couple of inches of H2O column) to prevent any escape of acid gases from the system S. At the outlet of the ID fan, the off-gases are exhausted to a stack <NUM>.

In operation, the steam plasma torch <NUM> heats the reactor <NUM> to the desired operating conditions and the precursor material <NUM> is injected into the plasma plume. The highly reactive hydrogen and hydroxyl ions present in the steam plasma hydrolyze the precursor material <NUM> in the high temperature hydrolysis zone <NUM>. Additional steam <NUM> is added to the hydrolysis zone <NUM>. The reacted stream flows through the narrow tubular zone <NUM>, which provides the necessary turbulence and residence time for reaction to reach the combustion zone <NUM> of the reactor <NUM>. The combustion air or oxygen <NUM> is added to the reactor <NUM> and the off gases exiting the reactor <NUM> enter the water quench <NUM> located at the exit of the combustion zone <NUM>. The off gases are rapidly quenched by the fine10 spray of water <NUM> created by the spray nozzles <NUM>. The liquid stream settles in the scrubber tank <NUM>, whereas the off gases exit the scrubber tank <NUM> and pass through a standard off gas cleaning technology. Either wet scrubbing technology or dry scrubbing technology is used to clean the off gases from acid gases such as HF and HCl and to convert them to innocuous salts. The induced draft fan <NUM> is used to drive the off gases through the system S and create a slightly negative pressure in the system S.

Caustic soda or another alkali from a tank or drum <NUM> is fed to the scrubber water recirculation line <NUM> by a dosing pump <NUM> to continually adjust the pH of the scrubber solution, neutralizing any acid components (HCl, HF) from the off gases. Neutralized water <NUM> is removed from the scrubber tank by a blow down line <NUM>.

Now turning to <FIG>, a variant steam plasma hydrolysis system S' is described and which includes a gas cleaning option (ii) whereby a weak acid is produced followed by neutralization of the acid gases.

The gases leaving the quench unit <NUM> are sent to an acid recovery tank 22b, wherein diluted acid is used to scrub the acid gases leaving the quench unit <NUM>. The acid recovery tank 22b is attached directly at the bottom of the quench unit <NUM>, as best shown in <FIG>. The acid recovery tank 22b uses acid resistant plastic sealing material on all sealing surfaces. The acid recovery tank 22b acts as a reservoir for collecting the quench water <NUM> and provides the necessary liquid head for a recirculation pump <NUM> (<FIG>). Fresh water <NUM> is added either continuously or in an on/off mode to the acid recovery tank 22b in order to control the acid concentration.

The gases travel counter current to the flow of scrubbing liquid in a packed acid scrubber unit <NUM>. The acid gases get scrubbed as they travel through the acid scrubbing unit <NUM>. Weak acid mixture, stream <NUM>, which gets collected at the bottom of the acid recovery tank 22b is removed periodically from the acid scrubbing tank unit <NUM>.

The scrubbed gas stream, stream <NUM>, leaving the acid scrubbing unit <NUM> enters a gas cleaning scrubber unit <NUM>. A scrubber tank unit <NUM> is attached at the bottom of the gas cleaning scrubber unit <NUM>. The scrubber tank unit <NUM> uses acid resistant plastic sealing material on all sealing surfaces. The scrubber tank unit <NUM> acts as a reservoir for collecting the scrubbing water and provides the necessary water head for a scrubber water recirculation pump <NUM>.

Caustic soda or another alkali from a tank or drum <NUM> is fed to a scrubber water recirculation line <NUM> by a dosing pump <NUM> to continually adjust the pH of the scrubber solution, neutralizing any acid components (HCl, HF) from the off gases. Neutralized water <NUM> is removed from the gas cleaning scrubber tank by a blow down line <NUM>.

A standard flue gas cleaning technology, i.e. either a wet off-gas cleaning technology using the neutralizing scrubber <NUM> (as shown in <FIG>) or a dry gas cleaning technology, is used to clean the flue gas.

Claim 1:
A two step process for the destruction of a precursor material using steam plasma in a reactor, wherein the precursor material is hydrolyzed as a first step in a high temperature zone of the reactor, followed by a second step of medium temperature oxidation of the reactant stream in a combustion zone of the reactor where combustion oxygen or air is injected and immediate quenching of the resulting gas stream to avoid the formation of unwanted by products, wherein the steam plasma is created by a non transferred direct current steam plasma torch, whereby an electric arc created between metallic electrodes and superheated steam forms a high temperature plasma plume at an exit end of the plasma torch, which is rich in reactive hydrogen and hydroxyl ions, and wherein the plasma torch preferably uses a small amount of an inert gas such as nitrogen, argon or helium or a mixture thereof as the shroud gas to protect the back electrode from excessive oxidation.