Chemical-looping combustion method with ashes and fines removal in the reduction zone and plant using same

1. A method for chemical-looping combustion of a hydrocarbon-containing feed of solid particles in which an oxygen-carrying material in form of particles circulates, said method comprising at least:

contacting of the hydrocarbon-containing solid feed particles with the oxygen-carrying material particles in a first reaction zone R 1 operating under dense fluidized bed conditions to produce gaseous effluents carrying the oxygen-carrying material particles,

combustion of the gaseous effluents from the first reaction zone R 1 in the presence of the oxygen-carrying material particles in a second reaction zone R 2 ,

separation of unburnt solid feed particles, of fly ashes and of the oxygen-carrying material particles within a mixture coming from the second zone R 2 in a fast separation zone S 3 yielding a first stream comprising combustion fumes that contain a major part of the unburnt solid feed particles and the fly ashes, and a second stream comprising a major part of the oxygen-carrying material particles, the second stream being sent to an oxidation zone R 0 ,

dedusting of the combustion fumes from the fast separation zone S 3 in a fumes dedusting zone S 4 so as to discharge a dedusted gas stream and a stream of particles containing fly ashes and dense particles predominantly comprising oxygen-carrying material particles and unburnt solid feed particles,

division of the stream of particles separated in dedusting stage S 4 into two streams in a stream division zone D 7 , one stream being recycled to first reaction zone R 1 operating under dense fluidized bed conditions, the other stream being sent to an elutriation separation zone S 5 ,

elutriation separation of the fly ashes from the dense particles in said elutriation separation zone S 5 so as to recover the fly ashes and to recycle the dense particles to the first reaction zone R 1 .

2. A method as claimed in claim 1 , comprising:

sedimentation of furnace ashes agglomerated in the bottom of first reaction zone R 1 in a fluidization zone S 6 located beneath first reaction zone R 1 ,

extraction of a particle stream comprising at least 10 mass % of agglomerated furnace ashes.

3. A method as claimed in claim 2 , wherein zone S 6 is fluidized by a gas with a fluidization gas rate in the largest cross-section of flow of the zone S 6 that does not exceed 3 times the minimum rate of fluidization of the oxygen-carrying material.

4. A method as claimed in claim 3 , wherein extraction of the agglomerated ashes in fluidization zone S 6 is performed using a cooled screw.

5. A method as claimed in claim 1 , wherein the solid feed is selected from among coal, coke, pet coke, biomass, bituminous sands and domestic waste.

6. A method as claimed in claim 1 , wherein the oxygen-carrying material is a pulverulent solid whose particle size is such that 90% of the grain size distribution ranges between 150 and 300 microns.

7. A method as claimed in claim 1 , wherein said one stream recycled to the first dense fluidized-bed reaction zone R 1 represents at least 50% of the stream of particles separated in the dedusting zone S 4 flowing into the stream division zone D 7 .

8. A method as claimed in claim 7 , wherein said one stream recycled to first dense fluidized-bed reaction zone R 1 represents at least 80% of the stream division zone D 7 .

9. A method as claimed in claim 1 , wherein the fly ash concentration in the mixture circulating in the combustion zone of the second reaction zone R 2 is below 5 wt. %.

10. A method as claimed in claim 9 , wherein the fly ash concentration in the mixture circulating in the combustion zone of the second reaction zone R 2 is below 1 wt. %.

11. A plant for carrying out chemical-looping redox combustion of a solid hydrocarbon feed according to the method as claimed in claim 1 , said plant comprising at least:

a first reaction zone R 1 comprising a solid feed supply line, a fluidization gas supply line and a supply line for the oxygen-carrying particles from oxidation zone R 0 ,

a second reaction zone R 2 receiving a gaseous effluent containing particles from the first reaction zone R 1 ,

a fast solid particle separation zone S 3 receiving combustion fumes from the second reaction zone R 2 containing fly ashes, oxygen-carrying material particles and unburnt solid feed particles, and comprising a discharge line for discharging a major part of the oxygen-carrying material particles to the oxidation zone R 0 ,

a fumes dedusting zone S 4 receiving through an inlet lighter particles entrained by the combustion fumes from the fast separation zone S 3 ,

a stream division zone D 7 receiving through an inlet a stream of particles separated from the fumes the fumes dedusting zone S 4 , said stream of particles separated from the fumes dedusting zone S 4 comprising fly ashes and dense particles predominantly made up of oxygen-carrying material particles and unburnt solid feed particles,

an elutriation separation zone S 5 receiving through an inlet a minor part of the particle stream divided in stream division zone D 7 , comprising a supply line allowing a supply of a fluidization gas and a discharge line allowing discharge of lighter particles comprising fly ashes and oxygen-carrying material fines,

a line coming from the stream division zone D 7 for recycling directly a major part of the particle stream divided in the stream division zone D 7 to the first reaction zone R 1 ,

a line coming from the elutriation separation zone S 5 for recycling dense particles separated by the elutriation separation zone S 5 to the first reaction zone R 1 .

12. A plant as claimed in claim 11 , wherein the cross-section of flow of second reaction zone R 2 is smaller than the cross-section of flow of the first reaction zone R 1 .

13. A plant as claimed in claim 11 , comprising a sedimentation zone for the agglomerated furnace ashes arranged beneath first reaction zone R 1 and comprising:

an agglomerated ashes supply line,

a fluidization zone S 6 ,

one or more lines allowing a fluidization gas to be fed,

a discharge line for recycling the oxygen-carrying material particles to the first reaction zone R 1 ,

a line for extraction of a particle stream containing at least 10 mass % of agglomerated furnace ashes.

14. A plant as claimed in claim 13 , wherein fluidization zone S 6 is a truncated zone with a half angle with respect to the vertical less than or equal to 15°.