Method of treating unburnt methane by oxidation by plasma
A method of treating a methane residue in a gas mixture at a temperature lying in the range 200° C. to 500° C. and including at least methane at a concentration lying in the range 50 ppm to 2500 ppm and oxygen at a concentration lying in the range 0.5% to 12% by volume. According to the invention, the methane residue is treated by a plasma having energy density lying in the range 15 J/L to 100 J/L generated in a plasma reactor by applying a high voltage electrical signal between an internal electrode and an external electrode of the plasma reactor, the external electrode being cylindrical in shape and surrounding the internal electrode, and at least one of the electrodes being covered in a dielectric material to create a dielectric barrier discharge in the gas mixture and convert part of the methane residue into carbon monoxide.
1 . A method of treating a methane residue in a gas mixture, said method comprising a step of introducing said gas mixture into a plasma reactor and a step of generating a plasma in the plasma reactor, wherein:
the gas mixture introduced into the plasma reactor has a temperature lying in the range 200° C. to 500° C. and includes at least methane at a concentration in the range 50 ppm to 2500 ppm and oxygen at a concentration lying in the range 0.5% to 12% by volume; and
wherein a plasma having energy density lying in the range 15 J/L to 100 J/L is generated during the plasma generation step by applying a high voltage electrical signal between an internal electrode and an external electrode of said plasma reactor, said external electrode being cylindrical in shape and surrounding the internal electrode, and at least one of said electrodes being covered in a dielectric material for creating a dielectric barrier discharge in the gas mixture and converting part of the methane residue into carbon monoxide.
2 . A treatment method according to claim 1 , wherein the plasma has energy density lying in the range 36 J/L to 58 J/L.
3 . A treatment method according to claim 1 , wherein the mixture from the plasma reactor is subsequently introduced into a catalytic device having a catalyst for converting the residual mixture into carbon dioxide.
4 . A treatment method according to claim 1 , wherein the catalyst is deposited in the plasma reactor.
5 . A treatment method according to claim 3 , wherein said catalyst is an oxide of the alumina or silica type, or a mixture of both.
6 . A treatment method according to claim 3 , wherein the catalyst is selected from catalysts based on the following metals: Pt 0.1% to 1 W by weight, Pd 0.1% to 2 W by weight, or a mixture of both.
7 . A treatment method according to claim 3 , wherein the gas mixture further comprises water at a concentration lying in the range 2% to 15% by volume.
8 . The use of the treatment method according to claim 1 , wherein said gas mixture comes from the combustion of natural gas or a liquid fuel or from a stationary or moving combustion source.
9 . A use according to claim 8 , wherein source is an engine.
10 . A use according to claim 8 , wherein source is a boiler.