FUEL CRACKING IN A FLUIDIZED BED SYSTEM

Abstract

A process for thermally cracking a fuel, said process comprising the steps ofon a solid carrier in a first reaction cracking fuel thereby producing Hydrogen and Carbon speciesin a second reaction combusting said Carbon on the solid carrier wherein the first and second reaction is carried out in at least one fluidized bed.

Claims

1. A process for thermally cracking a fuel, said process comprising the steps of on a solid carrier in a first reaction cracking fuel thereby producing Hydrogen and Carbon species in a second reaction combusting said Carbon on the solid carrier wherein the first and second reaction is carried out in at least one fluidized bed.

2. A process according to claim 1 wherein the first and second reaction is carried out in a first and second fluidized bed.

3. A process according to claim 1, wherein the fuel is C.sub.xH.sub.yO.sub.z such as methane.

4. A process according to claim 1, wherein the carbon species comprises free carbon, graphite, amorphous carbon, nanotubes and/or coke.

5. A process according to claim 1, wherein the first and second fluidized bed are worked sequentially.

6. A process according to claim 1, wherein the solid carrier is cycled between the first and second fluidized bed, preferably the first reaction is carried out in the first fluidized bed and the second reaction is carried out in the second fluidized bed.

7. A process according to claim 1, wherein the solid carrier is a heat carrier and/or a nucleation precursor.

8. A process according to claim 1, wherein the solid carrier comprises sand, natural ore, MAl.sub.2O.sub.3, MSiO.sub.2, dolomite, CaO, Coal and/or Carbon particles.

9. A process according to claim 1, wherein cooled solid carrier is transferred from the first fluidized bed to the second fluidized bed and/or where hot solid carrier is transferred from the second fluidized bed to the first fluidized bed.

10. A process according to claim 1, wherein a fuel is provided to the first reaction, a product stream comprising H.sub.2 is withdrawn from the first reaction, a regeneration gas is provided to the second reaction and/or a flue gas is withdrawn from the second reaction.

11. A process according to claim 1, wherein a fuel is provided to the first reaction in the first fluidized bed, a product stream comprising H.sub.2 is withdrawn from the first reaction in the first fluidized bed, a regeneration gas is provided to the second reaction in the second fluidized bed and/or a flue gas is withdrawn from the second reaction in the second fluidized bed.

12. A process according to claim 1, wherein heat from the second reaction is transferred through a barrier separating the first and second fluidized bed.

13. A fluidized bed system comprising a first fluidized bed containing at least a solid carrier and a second fluidized bed containing at least a solid carrier, wherein the system is arranged to be operated in a manner where the solid carrier in the first and/or second fluidized bed alternatingly is used to crack a fuel and is regenerated in a combustion process.

14. A fluidized bed system according to claim 13 comprising a first vessel containing at least the first fluidized bed and a second vessel containing at least the second fluidized bed.

15. A fluidized bed system according to claim 13 comprising means for providing and/or regulating a gas flow comprising a fuel and or/a gas flow comprising a regeneration gas.

16. A fluidized bed system according to claim 13 comprising means for withdrawing and/or regulating a flue gas and/or a product stream comprising H.sub.2.

17. A fluidized bed system according to claim 13 wherein the second vessel and first vessel shares at least one wall.

18. A fluidized bed system according to claim 13 wherein the second vessel at least partly encloses the first vessel.

19. A fluidized bed system according to claim 13 comprising means for circulating the solid carrier between the first and second vessel and/or vice versa.

20. A fluidized bed system according to claim 13 comprising means for retrieving solid carrier from a product and/or flue gas stream.

21. A fluidised bed system according to claim 13 arranged to carry out a process comprising the steps of: on a solid carrier in a first reaction, cracking fuel thereby producing Hydrogen and Carbon species in a second reaction, combusting said Carbon on the solid carrier wherein the first and second reaction is carried out in at least one fluidized bed.

22. A H.sub.2 product provided by the process according to claim 1.

Description

FIGURES

[0087] Details of the process and system are further described below with reference to the accompanying drawings. The figures are exemplary and are not to be construed as limiting to the invention.

[0088] FIG. 1 shows a system 1 having two fluidized beds i.e. a first bed 2 and second bed 3 arranged to be worked sequentially. The first and second bed is arranged in a first and second vessel respectively.

[0089] A fuel supply 6 is arranged to supply fuel to the first and second fluidized bed. The fuel supply is regulated by valves 7 whereby fuel can be administered and regulated to the first and/or the second bed. A regeneration gas supply 8 is arranged to supply regeneration gas to the first and second fluidized bed. The regeneration gas supply is regulated by valves 9 whereby regeneration gas can be administered to the first and/or the second bed. From each fluidized bed a product line 10 leads reaction products away from the bed/vessel.

[0090] The present sequential system can be operated by regulating the valves to allow fuel such as CH.sub.4 to one bed, e.g. the first while allowing regeneration gas to the other bed (e.g. second bed). This way fuel will be cracked in the first bed while solid carrier is regenerated in the second bed. When the solid carrier in the first bed is spent and/or the solid carrier in the second bed is regenerated the system can be switched so that fuel will be cracked in the second bed while solid carrier is regenerated in the first bed.

[0091] By using two or more beds in this sequential manner it is possible to have a continuous or at least substantially continuous flow of H.sub.2 from the system. If needed, the first and/or second bed can be flushed by an inert in between the step of cracking and regeneration in the beds.

[0092] FIG. 2 Shows a system wherein two fluidized beds are arranged to share a wall thereby allowing heat to transfer from the regeneration bed to the reaction bed through the shared wall.

[0093] More precisely the first fluidized bed 12 wherein the cracking process is carried out is arranged in a first tubular vessel 13. Around the first vessel is arranged a second vessel 14 containing the second fluidized bed 15 wherein the regeneration takes place. The first and second vessel shares a wall 16. I.e. the system is based on an inner tubular vessel 13 and an outer concentric vessel 14 arranged so that the heat from the regeneration process is transferred optimally to the cracking process.

[0094] The system further comprises means in form of pipes 17 for leading product from the cracking reaction in the first vessel 13 as well as means in form of pipes 18 leading flue gas from the regeneration reaction in the second vessel 14. In connection with the means for removing product gas and flue gas are means for retrieving solid carrier from a product and/or flue gas stream here in form of cyclones 19. From the cyclones the retrieved solid carrier is returned to at least one of the fluidized beds such as to the second vessel i.e. for regeneration.

[0095] The solid carrier is cycled from the second vessel to the first vessel through means for circulating the solid carrier between the first and second vessel here in form of openings 20. The flow from the second to the first vessel can e.g. be driven by the pressure difference in the two vessels. In the present setup the speed of gas flow in the first vessel may be larger than in the second vessel depending on the specific diameters etc.

[0096] FIG. 3 shows an alternative embodiment of a system with two connected vessels, a first 13 and a second vessel 14, the vessels containing a first fluidized bed 12 and a second fluidized bed 15 respectively. In the present embodiment the first 13 and second vessel 14 are arranged as separate vessels connected by means 20 for circulating the solid carrier between the first and second vessel. The means for circulating the solid carrier between the first and second vessel 20 allows spent solid carrier to migrate from the top of the first fluidized bed 12 to the lower part of the second fluidized bed 15. Similarly the means for circulating the solid carrier between the first and second vessel 20 allows regenerated solid carrier to migrate from the top of the second fluidized bed 15 to the lower part of the first fluidized bed 12.

[0097] As for the two previous examples the embodiment in FIG. 3 also comprises means for supplying fuel 6 and means for supplying regeneration gas 8. The systems also comprises means for removing product gas 17 and flue gas 18 from the fluidized beds as well as cyclones 19 arranged to retrieve solid carrier from the gas stream exiting the fluidized beds/vessel and allowing the retrieved solid carrier to be returned to the first and/or second fluidized bed.

[0098] FIG. 4 shows a schematic representation of the present process and system.

[0099] The flow shows how cooled solid is transferred from the first fluidized bed 12 to the second fluidized 15 via means 20. In the first fluidized bed fuel is processed in a cracking reaction and the product consisting of or comprising H.sub.2 is taken out via means 17. Fuel is provided to the first fluidized bed via fuel supply means 6. In the second fluidized bed 15 the solid is regenerated and at the same time heated. From the second fluidized bed the heated solid is transferred to the first fluidized bed via means 20. Regeneration gas is added via means 8 and flue gas is let away via an outlet 18.

[0100] Fresh solid may be added to the system e.g. via a feed 21 to the second fluidized bed as well as it is possible to remove spent carrier via a solid discharge 22.

EXAMPLE: HEAT AND MASS BALANCE

[0101] A general H&M balance has been carried out in Excel using the HSC Chemistry Add-on.

[0102] Assumptions [0103] 5000 Nm3/h of methane are being cracked [0104] Pressure is set as atmospheric [0105] Methane is also used when extra heat is needed (through combustion)

[0106] Air/methane ratio=1.2 [0107] Solid is fed to the re-heater at 1000 C. and leaves the reactor at 1200 C. [0108] The heat carrier is supposed to be alumina (Cp=1.268 kJ/kg at 1000 C.) [0109] Carbon is supposed amorphous (Cp=1.93 kJ/kg at 1000 C.) [0110] Reverse shift is not considered as methane cracking is believed to be more critical

[0111] Results are summarized in FIG. 5.