Conversion of hydrocarbons to carbon dioxide and electrical power
A process for the conversion of a hydrocarbon to CO 2 and electrical power is described which includes subjecting a gas mixture of a hydrocarbon feed stream and steam to an integrated reforming process including stages of steam reforming in a gas-heated reformer and secondary reforming to generate a reformed gas mixture, increasing the hydrogen content of the reformed gas mixture by subjecting it to one or more water-gas-shift stages, cooling the resulting hydrogen-enriched reformed gas and separating condensed water therefrom, passing the resulting de-watered hydrogen-enriched reformed gas to one or more stages of carbon dioxide separation to recover carbon dioxide, combusting the remaining hydrogen-containing fuel stream with an oxygen containing gas in a gas turbine to generate electrical power and passing the exhaust gas mixture from the gas turbine to a heat recovery steam generation system that feeds one or more steam turbines to generate additional electrical power.
1. A process for the conversion of a hydrocarbon to CO 2 and electrical power comprising the steps of:
(i) subjecting a gas mixture comprising a hydrocarbon feed stream and steam to steam reforming by passing the mixture over a catalyst disposed in externally-heated tubes in a gas-heated reformer to form a primary reformed gas,
(ii) partially combusting the primary reformed gas with a first oxygen-containing gas, and bringing the resultant partially combusted gas towards equilibrium over a secondary reforming catalyst in an autothermal reformer to form a secondary reformed gas mixture comprising hydrogen, steam and carbon oxides,
(iii) passing the secondary reformed gas mixture without intermediate cooling to the gas-heated reformer to heat the tubes therein and form a partially cooled reformed gas mixture,
(iv) increasing the hydrogen content of the partially cooled reformed gas mixture by subjecting it to one or more water-gas-shift stages thereby producing a hydrogen enriched reformed gas,
(v) cooling the hydrogen-enriched reformed gas to below a dew point of the steam therein to condense water and separating condensed water to give a de-watered hydrogen-enriched reformed gas,
(vi) passing the de-watered hydrogen-enriched reformed gas to one or more stages of carbon dioxide separation to generate a carbon dioxide stream and a hydrogen-containing fuel stream, and
(vii) combusting the hydrogen-containing fuel stream with a second oxygen-containing gas in a gas turbine to generate electrical power and an exhaust gas mixture and passing the exhaust gas mixture to a heat recovery steam generation system to provide steam for one or more steam turbines and generate additional electrical power.
2. A process according to claim 1 wherein the hydrocarbon feed comprises >85% by volume methane.
3. A process according to claim 1 wherein a portion of the hydrogen-containing fuel stream is mixed with the hydrocarbon feed stream prior to mixing with steam.
4. A process according to claim 1 wherein the hydrocarbon feed stream is heated prior to primary reforming by heat exchange with the hydrogen-enriched reformed gas.
5. A process according to claim 1 wherein the hydrocarbon and steam mixture is heated prior to steam reforming by heat exchange with the partially cooled reformed gas mixture.
6. A process according claim 1 wherein the oxygen containing gas fed to the autothermal reformer is air.
7. A process according to claim 1 wherein the partially cooled reformed gas is subjected to two or more water gas shift stages selected from the group consisting of a high temperature shift stage, a medium temperature shift stage, a low temperature shift stage, and combinations thereof.
8. A process according to claim 1 wherein the condensed water is fed to a steam generator to provide at least a portion of the steam required for steam reforming.
9. A process according to claim 1 wherein the carbon dioxide separation stage is performed using an amine- or physical wash- solvent system.
10. A process according to claim 1 wherein the carbon dioxide separation stage is performed using a membrane system.
11. A process according to claim 1 wherein the oxygen-containing gas fed to the gas turbine is air.
12. A process according to claim 1 wherein a portion of the hydrocarbon feed stream is fed to the gas turbine.
13. A process according to claim 12 wherein the portion of hydrocarbon fed to the gas turbine is ≦50% volume of the hydrocarbon feed stream.
14. A process according to claim 1 wherein the heat recovery steam generation system generates high-pressure, intermediate-pressure and low-pressure steam fed to high-pressure, intermediate-pressure and low-pressure steam turbines.
15. A process according to claim 1 wherein the recovered carbon dioxide is compressed and used for the manufacture of chemicals, or sent to storage or used in enhanced oil recovery processes.
16. A process according to claim 12 wherein the portion of hydrocarbon fed to the gas turbine is ≦25% volume of the hydrocarbon feed stream.
17. A process according to claim 12 wherein the portion of hydrocarbon fed to the gas turbine is ≦10% volume of the hydrocarbon feed stream.