Method and plant for chemical looping oxidation-reduction combustion of a gaseous hydrocarbon feedstock with in-situ catalytic reforming of the feed
In a method and a plant for chemical looping oxidation-reduction combustion (CLC) of a gaseous hydrocarbon feed, for example natural gas essentially containing methane, catalytic reforming of the feed is performed within the reduction zone where combustion of the feed is conducted on contact with an oxidation-reduction active mass in form of particles. The reforming catalyst comes in form of untransported fluidized particles within the reduction zone. The catalyst thus confined in the reduction zone does not circulate in the CLC loop.
1. A method for chemical looping oxidation-reduction combustion of a gaseous hydrocarbon feed, comprising:
performing combustion of a gaseous hydrocarbon feed within a fluidized-bed reduction zone through contact with a redox active mass in form of particles,
performing catalytic reforming of said feed within said reduction zone on contact with a reforming catalyst distinct from the redox active mass, said catalyst being in a form of untransported fluidized particles confined within and not transported out of said reduction zone to produce syngas,
performing combustion of the syngas produced by catalytic reforming within said reduction zone through contact with said redox active mass, and
sending to a fluidized-bed oxidation zone the redox active mass particles that have stayed in the reduction zone in order to oxidize said redox active mass particles through contact with an oxidizing gas stream.
2. The method as claimed in claim 1 , wherein the size of said catalyst particles is so selected that said particles have a minimum fluidization velocity Umf lower than a given gas velocity Vsg in the reduction zone and a terminal free fall velocity UT greater than said gas velocity Vsg.
3. The method as claimed in claim 1 , wherein the size of the catalyst particles ranges between 1 mm and 30 mm.
4. The method as claimed in claim 1 , wherein gas velocity Vsg in the reduction zone ranges between 3 m/s and 15 m/s.
5. The method as claimed in claim 1 , wherein the reforming catalyst comprises nickel.
6. The method as claimed in claim 5 , wherein the reforming catalyst comprises between 6 and 25 wt. % nickel.
7. The method as claimed in claim 5 , wherein the nickel initially comes in form of nickel oxide, the mass fraction of nickel oxide of the catalyst in relation to the mass fraction of the redox active mass ranging between 0.1% and 15.
8. The method as claimed in claim 5 , wherein the reforming catalyst comprises between 6 and 25 wt. % nickel on an alumina support.
9. The method as claimed in claim 5 , wherein the nickel initially comes in form of nickel oxide, the mass fraction of nickel oxide of the catalyst in relation to the mass fraction of the redox active mass ranging between 1% and 5%.
10. The method as claimed in claim 1 , wherein the redox active mass consists of metal oxides from ores.
11. The method as claimed in claim 1 , wherein the grain size of the redox active mass particles is such that over 90% of the particles have a size ranging between 50 μm and 500 μm.
12. The method as claimed in claim 1 , wherein the gaseous hydrocarbon feed essentially comprises methane.
13. The method as claimed in claim 12 , wherein the gaseous hydrocarbon feed is natural gas, biogas or refinery gas.
14. A plant for combustion of a gaseous hydrocarbon feed as claimed in claim 1 , comprising:
a reduction zone including:
means of injecting said gaseous hydrocarbon feed,
an inlet for a stream of a redox active mass in form of particles,
an outlet for a mixture comprising a gas stream and the active mass particles,
a reforming catalyst in form of untransported fluidized particles confined within and not transported out of said reduction zone, and
an oxidation zone provided with a feed point for redox active mass particles that have stayed in the reduction zone, means of injecting an oxidizing fluidization gas, and an outlet for an oxygen-depleted oxidizing gas and oxidized redox active mass particles.
15. The plant as claimed in claim 14 , wherein the reduction zone is a reactor comprising:
a basal part for catalyst particles re-acceleration, in form of an inverted truncated cone,
a substantially cylindrical intermediate part topping said basal part,
a cylindroconical top part for disengagement of the catalyst particles, topping said intermediate part.
16. The method as claimed in claim 1 , wherein the size of the catalyst particles ranges between 1.5 mm and 5 mm.
17. The method as claimed in claim 1 , wherein gas velocity Vsg in the reduction zone ranges between 5 m/s and 10 m/s.
18. The method as claimed in claim 1 , wherein the grain size of the redox active mass particles is such that over 90% of the particles have a size ranging between 100 μm and 300 μm.