Start-up heater for ammonia reactors

1. An internal start-up heater for an ammonia reactor, said heater comprising:

a plurality of elongated electric heating members extended in a longitudinal axis of said heater; and

a plurality of supporting plates for said heating members, each supporting plate comprising an outer frame and supporting beams in a parallel arrangement, with opposite ends fixed to the outer frame, the supporting beams being disposed in a plane perpendicular to said longitudinal axis and in lanes between the heating members, being in contact with said heating members,

wherein said supporting plates are arranged in at least one set having at least a first and a second plate, the first plate having said supporting beams disposed in a different arrangement compared to supporting beams of the second plate.

2. The heater according to claim 1 , wherein said at least one set comprises at least a first plate with parallel supporting beams disposed in a first direction in said plane perpendicular to the longitudinal axis of the heater, and at least another plate with parallel supporting beams disposed in a second direction in said plane and perpendicular to said first direction.

3. The heater according to claim 1 , wherein said at least one set comprises at least a first plate with supporting beams according to a first direction in said plane perpendicular to the longitudinal axis of the heater, and at least another plate with supporting beams parallel and staggered with respect to beams of said first plate.

4. The heater according to claim 1 , wherein the parallel supporting beams of said plates are equally spaced.

5. The heater according to claim 1 , wherein at least some of the plate sets comprise plates with supporting beams extending in alternate lanes between rows and/or columns formed by said elongate heating members, so that each plate set has at least one supporting beam in each of said lanes.

6. The heater according to claim 5 , wherein the heater comprises at least one set of four plates, comprising in sequence:

a first plate with parallel and equally-spaced supporting beams extended in alternate lanes between the heating members;

a second plate with supporting beams extended in alternate lanes between the heating members, the supporting beams of the second plate being perpendicular to the beams of said first plate;

a third plate with supporting beams parallel and staggered with respect to the first plate, so that beams of said third plate (MG) extend in parallel and alternate lanes with respect to beams of the first plate;

a fourth plate with supporting beams parallel and staggered with respect to the second plate, so that beams of said fourth plate extend in parallel and alternate lanes with respect to beams of the second plate.

7. The heater according to claim 6 , wherein said heating members are arranged in a square pitch.

8. The heater according to claim 5 , wherein said beams of the plates are extended in diagonal lanes between the heating members.

9. The heater according to claim 5 , wherein said beams of the plates are extended in orthogonal lanes between the heating members.

10. The heater comprising a plurality of consecutive four-plate sets in accordance claim 6 .

11. The heater according to claim 1 , wherein each of said heating members is an electrical armored resistance comprising an external shell and an electric heating element inside said shell, said heating element being electrically insulated from said shell.

12. An ammonia converter adapted to react hydrogen and nitrogen for the production of ammonia, said converter comprising a vessel and an internal start-up heater according to claim 1 .

13. A method for revamping an ammonia converter comprising a vessel and a start-up heater inside said vessel, the method comprising the steps of:

extracting the existing start-up heater from said vessel, and

fitting into said vessel a start-up heater in accordance with claim 1 .