Production of hydrocarbons by steam reforming and Fischer-Tropsch reaction

1. A process for the production of hydrocarbons comprising;

a) subjecting a mixture of a hydrocarbon feedstock and steam to catalytic steam reforming to form a partially reformed gas,

b) subjecting the partially reformed gas to partial combustion with an oxygen-containing gas and bringing the resultant partially combusted gas towards equilibrium over a steam reforming catalyst to form a reformed gas mixture,

c) cooling the reformed gas mixture to below the dew point of the steam therein to condense water and separating the condensed water to give a de-watered synthesis gas,

d) synthesising hydrocarbons from said de-watered synthesis gas by the Fischer-Tropsch reaction and

e) separating the hydrocarbons from co-produced water,

wherein >50% by weight of the co-produced water from the Fischer-Tropsch reaction is fed to a saturator wherein the co-produced water is contacted with the hydrocarbon feedstock to provide at least part of the mixture of hydrocarbon feedstock and steam subjected to steam reforming.

2. A process according to claim 1 wherein the reformed gas mixture is generated by;

a) subjecting a mixture of the hydrocarbon feedstock and steam to steam reforming by passing the mixture over a catalyst disposed in externally-heated tubes in a heat exchange reformer to form a primary reformed gas,

b) subjecting the primary reformed gas to secondary reforming by partially combusting the primary reformed gas with an oxygen-containing gas and bringing the resultant partially combusted gas towards equilibrium over a secondary reforming catalyst to form the reformed gas mixture.

3. A process according to claim 2 wherein the reformed gas mixture is used to heat the tubes of the heat exchange reformer, thereby producing a partially cooled reformed gas mixture.

4. A process according to claim 1 wherein the reformed gas mixture is generated by

a) subjecting a hydrocarbon feedstock/steam mixture to at least one stage of adiabatic steam reforming to provide a pre-formed gas, and

b) passing the pre-reformed gas to an autothermal reformer where it is partially combusted with an oxygen-containing gas and the partially combusted gas is passed through a bed of steam reforming catalyst to form the reformed gas mixture.

5. A process according to claim 2 wherein the hydrocarbon feedstock is divided into two streams: a first stream is mixed with steam and a second stream is combined with the partially reformed gas wherein the second hydrocarbon stream comprises between 5 and 50% by volume of the hydrocarbon feedstock.

6. A process according to claim 1 wherein carbon dioxide is separated from the de-watered synthesis gas prior to synthesis of the hydrocarbons and is added to the partially reformed gas before the partial combustion thereof.

7. A process according to claim 1 wherein a tail gas from the synthesis of hydrocarbons is added to the partially reformed gas before partial combustion thereof.

8. A process according to claim 1 wherein the de-watered synthesis gas is subjected to a step of hydrogen separation before it is passed to the Fischer-Tropsch hydrocarbon synthesis stage.

9. A process according to claim 1 wherein the process is operated at an overall steam ratio below 1.5.

10. A process according to claim 1 wherein >75% by weight of the co-produced water from the Fischer-Tropsch reaction is fed to the saturator.