Steam reforming
A process is described for steam reforming a hydrocarbon feedstock containing one or more nitrogen compounds, comprising passing a mixture of the hydrocarbon feedstock and steam through a catalyst bed consisting of one nickel steam reforming catalysts disposed within a plurality of externally heated tubes in a tubular steam reformer, wherein each tube has an inlet to which the mixture of hydrocarbon and steam is fed, an outlet from which a reformed gas containing hydrogen, carbon monoxide, carbon dioxide, steam, ammonia and methane is recovered, and the steam reforming catalyst at least at the outlet of the tubes is a particulate eggshell steam reforming catalyst comprising 2.5 to 9.5% by weight nickel, expressed as NiO, wherein the nickel is provided in a layer at the surface of the catalyst and the thickness of layer is in the range of 100 to 1000 μm.
1 . A process for steam reforming a hydrocarbon feedstock containing 0.1 to 25% by volume of nitrogen gas (N 2 ), comprising passing a mixture of the hydrocarbon feedstock and steam through a catalyst bed consisting of two, three, or more layers of nickel steam reforming catalysts disposed within a plurality of externally heated tubes in a tubular steam reformer, wherein each tube has an inlet to which the mixture of hydrocarbon and steam is fed, an outlet from which a reformed gas containing hydrogen, carbon monoxide, carbon dioxide, steam, ammonia and methane is recovered, the layer of nickel steam reforming catalyst adjacent the inlet of the tubes is a particulate non-eggshell nickel steam reforming catalyst comprising 10-30% nickel, expressed as NiO, and the nickel steam reforming catalyst at the outlet of the tubes is a particulate eggshell steam reforming catalyst comprising 2.5 to 9.5% by weight nickel, expressed as NiO, wherein the particulate eggshell steam reforming catalyst comprises 5-95% of the volume of the catalyst bed, wherein the nickel is provided at the surface of the particulate eggshell steam reforming catalyst in a layer having a thickness of 100 to 1000 μm, and wherein the methane content of the reformed gas is less than 15% by volume on a dry gas basis and the ammonia content of the reformed gas is below 200 ppmv on a dry gas basis.
2 . The process according to claim 1 , wherein the nickel is provided in a layer at the surface of the particulate eggshell steam reforming catalyst and the thickness of layer is in the range of 100 to 800 μm.
3 . The process according to claim 1 , wherein the nickel is supported on a shaped particulate catalyst support comprising alumina, titania, zirconia, or an alkaline earth metal aluminate.
4 . The process according to claim 1 , wherein the hydrocarbon feedstock comprises methane, a pre-reformed gas, an associated gas or natural gas.
5 . The process according to claim 1 , wherein the hydrocarbon feedstock is compressed to a pressure in the range 10 to 100 bar abs.
6 . The process according to claim 1 , wherein the mixture of hydrocarbon feedstock and steam has a steam to carbon ratio in the range 1.8:1 to 5:1.
7 . The process according to claim 1 , wherein the mixture of hydrocarbon feedstock and steam is fed to the inlets of the tubes at an inlet temperature in the range 300 to 650° C.
8 . The process according to claim 1 , wherein the tubular steam reformer contains a plurality of tubes through which the mixture of the hydrocarbon feedstock and steam is passed, and to which heat is transferred by means of a hot gas comprising a combustion gas or a synthesis gas, flowing around the tubes.
9 . The process according to claim 1 , wherein the catalyst bed consists of three or more layers of the nickel steam reforming catalyst wherein in each case the layer of the nickel steam reforming catalyst adjacent the outlets of the tubes is the particulate eggshell steam reforming catalyst.
10 . The process according to claim 9 , wherein there are two or more layers of the nickel steam reforming catalyst within the tubes and the particulate eggshell steam reforming catalyst layer comprises 80% to 20% of the volume of the bed.
11 . The process according to claim 10 , wherein there are two or more layers of the nickel steam reforming catalyst within the tubes and the particulate eggshell steam reforming catalyst layer comprises 75% to 25% of the volume of the bed.
12 . The process according to claim 1 , wherein the process further comprises cooling the reformed gas to below the dew point to condense steam and separating a liquid condensate to form a synthesis gas from the reformed gas.
13 . The process according to claim 12 , wherein the ammonia content of the liquid condensate is below 400 mg/Litre.
14 . The process according to claim 12 , wherein at least a portion of the condensate is recycled and used to generate steam used in the steam reforming process.
15 . The process according to claim 12 , wherein the ammonia content of the liquid condensate is below 200 mg/Litre.
16 . The process according to claim 12 , wherein the ammonia content of the liquid condensate is below 100 mg/Litre.
17 . The process according to claim 12 , wherein the ammonia content of the liquid condensate is below 20 mg/Litre.
18 . The process according to claim 1 , wherein the nitrogen gas content of the hydrocarbon feedstock is in the range of 0.5 to 25% by volume.
19 . The process according to claim 1 , wherein the nitrogen gas content of the hydrocarbon feedstock is in the range of 1 to 10% by volume.
20 . The process according to claim 1 , wherein the methane content of the reformed gas is less than 10% by volume on a dry gas basis.
21 . The process according to claim 1 , wherein the methane content of the reformed gas is less than 5% by volume on a dry gas basis.
22 . The process according to claim 1 , wherein the ammonia content of the reformed gas is below 100 ppmv on a dry gas basis.
23 . The process according to claim 1 , wherein the ammonia content of the reformed gas is below 50 ppmv on a dry gas basis.
24 . The process according to claim 1 , wherein the ammonia content of the reformed gas is below 10 ppmv on a dry gas basis.