Combination of structured catalyst elements and pellets
A steam reformer is provided which comprises at least one externally-heated tube. Each tube comprises a first catalyst bed comprising a first catalyst in particulate form and a second catalyst supported on a structure, wherein said first catalyst bed is located between the inlet of the tube and the second catalyst supported on said structure. A process for steam reforming of a feed gas mixture using said steam reformer is also provided.
1 . A steam reformer, said steam reformer comprising at least one externally-heated, vertically-arranged tube, said at least one tube comprising an inlet at an upper end of the tube for a feed gas mixture and an outlet at a lower end of the tube for a reformed gas mixture,
wherein each tube comprises: a first catalyst bed comprising a first steam reforming catalyst in particulate form; and a second steam reforming catalyst supported on a structure, wherein said first catalyst bed is located between said inlet and said second catalyst supported on said structure,
wherein said at least one tube comprises two or more externally-heated tubes, wherein each tube has the same arrangement of first and second catalysts.
2 . The steam reformer according to claim 1 , wherein the first catalyst bed extends between 5-30% of the length of the tube between the inlet and the outlet.
3 . The steam reformer according to claim 1 , wherein at least one of said tubes further comprises a second catalyst bed, said second catalyst bed being located between said inlet and said first catalyst bed.
4 . The steam reformer according to claim 1 , wherein the steam reformer is a fired reformer.
5 . The steam reformer according to claim 1 , wherein the at least one tube is a bayonet tube.
6 . The steam reformer according to claim 1 , wherein the at least one tube is externally heated via heat exchange with a hot gas configured to flow in a volume around said at least one tube.
7 . The steam reformer according to claim 6 , wherein the hot gas is a reformed product gas from one or more other steam reformers, and wherein the steam reformer is configured such that the hot gas is mixed with the reformed gas mixture from the tubes.
8 . The steam reformer according to claim 1 , wherein the first catalyst comprises particulate refractory support material, which has been impregnated with or co-precipitated with a catalytically-active metal.
9 . The steam reformer according to claim 1 , wherein the first catalyst bed comprises first catalyst in the form of cylindrical pellets, said pellets optionally having one or more through-holes.
10 . The steam reformer according to claim 9 , wherein said cylindrical pellets have a length/diameter ratio in the range 0.4-2.2.
11 . The steam reformer according to claim 1 , wherein the second catalyst is coated on said structure.
12 . The steam reformer according to claim 1 , wherein the second catalyst comprises a refractory support material, which has been impregnated with or co-precipitated with a catalytically-active metal.
13 . The steam reformer according to claim 1 , wherein the structure is made of a metal or ceramic material.
14 . The steam reformer according to claim 1 , wherein the structure is in the form of one or more cylindrical units which include perforations and/or tubes and/or vanes and/or fins configured to cause the feed gas to flow both axially and radially as it passes through the units.
15 . The steam reformer according to claim 14 , wherein the cylindrical units are configured to be stackable such that they are self-supported within the at least one tube.
16 . The steam reformer according to claim 1 , wherein the first catalyst comprises the same catalytically-active metal as the second catalyst.
17 . The steam reformer according to claim 1 , further comprising one or more intermediate elements located between said first catalyst bed and said structure.
18 . The steam reformer according to claim 17 , wherein the intermediate element is a third bed of particles.
19 . The steam reformer according to claim 17 , wherein the intermediate element is a support element.
20 . The steam reformer according to claim 1 , wherein said feed gas mixture comprises a hydrocarbon and steam.
21 . The steam reformer according to claim 1 , wherein the first catalyst bed extends substantially from said inlet, or—when present—said second bed, to said structure.
22 . The steam reformer according to claim 1 , wherein the structure extends substantially from said first catalyst bed, or—when present—said intermediate element, to said outlet.
23 . The steam reformer according to claim 1 , wherein the steam reformer is configured to be used without one or more pre-reformers arranged upstream said steam reformer.
24 . A process for steam reforming of a feed gas mixture, said process comprising the steps of:
a. providing a steam reformer according to claim 1 ,
b. passing feed gas mixture through the at least one tube of said steam reformer from said inlet to said outlet, such that the feed gas mixture first contacts the first catalyst bed and then the second catalyst supported on structure.
25 . The process according to claim 24 , wherein said feed gas mixture comprises at least 5 ppb of sulfur.