Apparatus for steam plasma arc hydrolysis of ozone depleting substances

Abstract

An apparatus for the destruction of a precursor material includes a steam plasma reactor having a high temperature zone and a combustion zone. The high temperature zone is adapted for hydrolyzing the precursor material, whereas the combustion zone is adapted to effect medium temperature oxidation of the reactant stream where combustion oxygen or air is injected. A quenching unit is provided at an exit end of the reactor for quenching a resulting gas stream to avoid the formation of unwanted by-products.

Claims

1. 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 a resulting gas stream to avoid the formation of unwanted by-products.

2. The apparatus according to claim 1, wherein the high temperature zone of the reactor includes a conical converging, high temperature, steam hydrolysis zone which provides a necessary residence time for complete hydrolysis of the precursor material, wherein a narrow tubular zone is provided between the high temperature zone and combustion zones for providing a necessary turbulence and additional residence time for the reactions, and wherein the combustion zone of the reactor includes a conical diverging, medium temperature, combustion zone which provides a residence time for complete combustion of the process stream.

3. The apparatus according to claim 1, wherein there are provided a non transferred direct current steam plasma torch, 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.

4. The apparatus according to claim 3, wherein the three zone steam plasma reactor is externally cooled and includes a corrosive resistant refractory lining.

5. The apparatus according to claim 1, wherein the plasma torch includes a setup of metallic electrodes namely cathode, ignition anode and working anode arranged in a spaced relationship such that a direct current electric arc exists between the cathode and the working anode and uses an inert gas, such as helium, nitrogen, argon or a mixture thereof, as the shroud gas and uses steam as the main plasma forming gas and has a plasma plume exiting at the anode end.

6. The apparatus according to claim 1, wherein the quenching means produces a spray of cold water through which the process stream exiting the reactor passes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1a is a schematic representation of a complete system for destroying ozone depleting substances in accordance with one embodiment of the present invention;

(3) FIG. 1b is a schematic representation of a complete system for destroying ozone depleting substances in accordance with another embodiment of the present invention; and

(4) FIG. 2 is a vertical cross-sectional view of a destruction section of the present system for destroying ozone depleting substances.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

(5) 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 1500 C. 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.sub.2, F.sub.2 and CF.sub.4 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.sub.2 is emitted to the atmosphere.

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

(7) A precursor material 1 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. 2. The precursor material 1, to be destroyed, is fed adjacent to a plasma torch 4 via a specially designed flange 12. This flange 12 is water cooled, made of acid resisting material and is specially designed to facilitate intimate mixing of the fed precursor material 1 with the high temperature viscous steam plasma plume.

(8) An outside heating source, typically a steam plasma torch 4, is used as the source for heating the refractory lined reactor to a temperature of 1500 C. The plasma torch 4 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 3 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.

(9) The steam plasma torch 4 includes a metallic cathode 2, a metallic ignition anode 6 and a metallic working anode 8, which are arranged as shown in FIG. 2. A plasma arc is initiated with helium or another monoatomic gas between the cathode 2 and the ignition anode 6. Once the arc is stabilized 10, a plasma forming steam is injected at 3 and the arc is transferred from the ignition anode 6 to the working anode 8. Nitrogen, helium, argon or mixture thereof is used as a shroud gas 5. The shroud gas 5 protects the metallic cathode 2 from premature oxidation and hence increases the working life of the cathode 2. Superheated steam is used as the main plasma forming gas 3.

(10) The steam plasma torch 4, in-addition to acting as a heat source, provides reactive oxygen, hydroxyl and hydrogen ions necessary for the destruction of the precursor material 1 and prevents the formation of undesired side products, such as Cl.sub.2, F.sub.2, CF.sub.x. The overall reaction can be summarized as:
CH.sub.xCl.sub.yF.sub.z+aH.sub.2O.fwdarw.zHF+yHCl+aCO+bH.sub.2+cH.sub.2O

(11) A refractory lined reactor 14 is used to destroy the precursor material 1. A corrosion resistant high durable refractory lining 16 is used as the working refractory in the reactor 14. For example, a high alumina refractory (>98% alumina content), such as Kricon 34 or similar which is known to resist to corrosive HF and HCl gases, is used as the working refractory.

(12) The internal walls of the reactor 14 are coated with acid resistant high temperature metallic coating such as Hastealloy or similar. The external walls of the reactor 14 are cooled externally, either by air or by water, for safety reasons and to limit heating of the furnace room.

(13) The refractory lined reactor 14 comprises of three zones, as shown in FIG. 2. These three zones are:

(14) 1) a conical converging, high temperature, steam hydrolysis zone 11, wherein the fed precursor material 1 undergoes steam hydrolysis;

(15) 2) a narrow tubular zone 13, which creates high temperature turbulent mixing of the gases and facilitates completion of the hydrolysis reaction; and

(16) 3) a conical diverging, medium temperature, combustion zone 15, wherein the gases are combusted with the combustion air or oxygen.

(17) Combustion air or oxygen 9 is added to the reactor 14, as also shown in FIG. 2. The combustion air or oxygen 9 is metered to the reactor 14 to control the temperature in the low temperature zone of the reactor 14 while achieving complete combustion and eliminating the formation of undesirable by-products such as Cl.sub.2.

(18) A water quench unit 20 is attached right at the outlet of the combustion zone 15 of the reactor 14, as seen in FIG. 2. A set of spray nozzles 18 create a fine spray of water 17 in the quench unit 20, which spray of water 17 instantaneously cools the gases. This instantaneous quenching of the gases will prevent the reformation of dioxins and furans. The quench unit 20 is built as a double-walled water-cooled pipe section with acid resisting material.

(19) A scrubber tank 22 is attached at the bottom of the quench unit 20, as best shown in FIG. 2. The scrubber tank 22 uses acid resistant plastic sealing material on all sealing surfaces. The internal walls of the scrubber tank 22 are lined with an acid resistant Teflon-based coating such as Halar CCTFE, or similar. The scrubber tank 22 acts as a reservoir for collecting the quench water 19 and provides the necessary water head for a scrubber water recirculation pump 28 (see FIG. 1a).

(20) A standard flue gas cleaning technology, i.e. either a wet off-gas cleaning technology using an acid gas neutralizing scrubber 24 (as shown in FIG. 1a) or a dry gas cleaning technology, is used to remove acid gases from the flue gas.

(21) An induced draft fan 26 draws the off gases through the system S and creates a slightly negative pressure in the system S, as shown in FIG. 1. The entire system S is maintained under a slight negative pressure (couple of inches of H.sub.2O 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 23.

(22) In operation, the steam plasma torch 4 heats the reactor 14 to the desired operating conditions and the precursor material 1 is injected into the plasma plume. The highly reactive hydrogen and hydroxyl ions present in the steam plasma hydrolyze the precursor material 1 in the high temperature hydrolysis zone 11. Additional steam 7 is added to the hydrolysis zone 11. The reacted stream flows through the narrow tubular zone 13, which provides the necessary turbulence and residence time for reaction to reach the combustion zone 15 of the reactor 14. The combustion air or oxygen 9 is added to the reactor 14 and the off gases exiting the reactor 14 enter the water quench 20 located at the exit of the combustion zone 15. The off gases are rapidly quenched by the fine spray of water 17 created by the spray nozzles 18. The liquid stream settles in the scrubber tank 22, whereas the off gases exit the scrubber tank 22 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 26 is used to drive the off gases through the system S and create a slightly negative pressure in the system S.

(23) Caustic soda or another alkali from a tank or drum 25 is fed to the scrubber water recirculation line 31 by a dosing pump 30 to continually adjust the pH of the scrubber solution, neutralizing any acid components (HCl, HF) from the off gases. Neutralized water 21 is removed from the scrubber tank by a blow down line 32.

(24) Now turning to FIG. 1b, 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

(25) The gases leaving the quench unit 20 are sent to an acid recovery tank 22b, wherein diluted acid is used to scrub the acid gases leaving the quench unit 20. The acid recovery tank 22b is attached directly at the bottom of the quench unit 20, as best shown in FIG. 2. 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 19 and provides the necessary liquid head for a recirculation pump 41 (FIG. 1b). Fresh water 42 is added either continuously or in an on/off mode to the acid recovery tank 22b in order to control the acid concentration.

(26) The gases travel counter current to the flow of scrubbing liquid in a packed acid scrubber unit 43. The acid gases get scrubbed as they travel through the acid scrubbing unit 43. Weak acid mixture, stream 44, which gets collected at the bottom of the acid recovery tank 22b is removed periodically from the acid scrubbing tank unit 22.

(27) The scrubbed gas stream, stream 45, leaving the acid scrubbing unit 43 enters a gas cleaning scrubber unit 46. A scrubber tank unit 47 is attached at the bottom of the gas cleaning scrubber unit 46. The scrubber tank unit 47 uses acid resistant plastic sealing material on all sealing surfaces. The scrubber tank unit 47 acts as a reservoir for collecting the scrubbing water and provides the necessary water head for a scrubber water recirculation pump 48.

(28) Caustic soda or another alkali from a tank or drum 52 is fed to a scrubber water recirculation line 54 by a dosing pump 51 to continually adjust the pH of the scrubber solution, neutralizing any acid components (HCl, HF) from the off gases. Neutralized water 49 is removed from the gas cleaning scrubber tank by a blow down line 53.

(29) A standard flue gas cleaning technology, i.e. either a wet off-gas cleaning technology using the neutralizing scrubber 46 (as shown in FIG. 1b) or a dry gas cleaning technology, is used to clean the flue gas.

(30) Although the present invention has been described hereinabove by way of embodiments thereof, it may be modified, without departing from the nature and teachings of the subject invention as described herein.

REFERENCES

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