RADIAL OR AXIAL-RADIAL CHEMICAL REACTOR WITH A FINE CATALYST

Abstract

Reactor for catalytic chemical reactions comprising a catalyst bed with an annular-cylindrical form crossed by a radial flow or mixed axial-radial flow, wherein the bed is delimited by cylindrical walls made gas-permeable by means of slits and the catalyst bed is formed by particles of catalyst with a nominal minimum size such that: the ratio between a transverse dimension of the slits and the nominal minimum size of the particles of catalyst is smaller than or equal to 0.6; the catalyst bed contains no more than 3% by weight of particles with an actual size smaller than said nominal size.

Claims

1-11. (canceled)

12. A reactor for catalytic chemical reactions, the reactor comprising: a catalyst bed with an annular-cylindrical form and a radial or mixed axial-radial crossing flow; at least a first cylindrical wall and a second cylindrical wall that delimit the catalyst bed being in direct with the catalyst, the second cylindrical wall being coaxial and internal relative to the first wall; wherein the first wall and the second wall include passages to make the first and second walls gas-permeable; wherein the passages are slits having an elongated form in a longitudinal direction of the slit and a respective transverse dimension in a transverse direction that is perpendicular to the longitudinal direction; wherein the catalyst bed is formed by particles of catalyst that have a nominal minimum size such that: a) a ratio between the transverse dimension of the slits and the nominal minimum size of the particles of catalyst is less than or equal to 0.6; b) the catalyst bed contains no more than 3% by weight of particles with a size smaller than the nominal size, wherein a minimum size of the catalyst is defined as a square root of a maximum square free flow area of a sieve that retains the catalyst, the sieving of the catalyst being performed according to the standard test method of ASTM D4513-11.

13. The reactor according to claim 12, wherein the nominal minimum size of the particles of catalyst is smaller than 1.5 mm.

14. The reactor according to claim 12, wherein the transverse dimension of the slits is smaller than or equal to 1 mm.

15. The reactor according to claim 12, wherein the catalyst contains spherical particles.

16. The reactor according to claim 12, wherein the catalyst contains non-spherical particles.

17. The reactor according to claim 12, wherein the catalyst bed contains no more than 2% by weight of particles with an actual size smaller than the nominal size.

18. The reactor according to claim 12, wherein a quantity of particles with an actual size smaller than the nominal size is determined with a sieve having a square mesh with a side equal to the nominal minimum size.

19. The reactor according to claim 12, wherein the catalyst bed and the cylindrical walls are part of a cartridge which can be extracted from a shell of the reactor.

20. The reactor according to claim 12, for converting a gaseous flow of reagents so as to obtain a gaseous flow of products.

21. The reactor according to claim 12 for performing ammonia synthesis using a make-up gas containing hydrogen and nitrogen.

22. A method for loading catalyst into a reactor for catalytic chemical reactions wherein: the reactor includes at least a first cylindrical wall and a second cylindrical wall that delimit a space able to contain the catalyst, the second wall being coaxial and internal relative to the first wall, so that loading of the catalyst between the two walls forms a cylindrical-annular catalyst bed with a radial or axial-radial crossing flow; the first wall and the second wall comprise passages to make them gas-permeable, one of the walls being adapted to act as a distributor of a gaseous flow containing the reagents and the other wall being adapted to act as a collector of a gaseous flow containing the reaction products; wherein the passages are slits having an elongated form with a respective longitudinal dimension in a longitudinal direction of the slit and a respective transverse dimension in a transverse direction which is perpendicular to the longitudinal direction; wherein the catalyst to be loaded is formed by particles of catalyst which have a nominal minimum size; wherein a ratio between the transverse dimension of the slits and the nominal minimum size of the particles of catalyst is less than or equal to 0.6; wherein a minimum size of the catalyst is defined as a square root of a maximum square free flow area of a sieve which retains the catalyst, the sieving of the catalyst being performed according to the standard test method of ASTM D4513-11, the method comprising: sieving the catalyst before introducing the catalyst into the reactor so that the introduced catalyst contains no more than 3% by weight of particles with a size smaller than the nominal size.

Description

DESCRIPTION OF THE FIGURES

[0034] FIG. 1 shows in schematic form a radial flow reactor.

[0035] FIG. 2 shows a part of a perforated wall of the reactor according to FIG. 1.

[0036] FIG. 3 shows the statistical distribution of the size of granules of a catalyst.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0037] FIG. 1 shows in schematic form a reactor 1 which comprises: a shell 2, a catalyst bed 3, a first perforated cylindrical wall 4, a second perforated cylindrical wall 5, and a central collector 6

[0038] A gaseous flow of reagents entering the inlet 7 crosses the bed radially from the space 8 towards the central collector 6 and, from the latter, reaches the outlet flange 9.

[0039] The flow crossing the catalyst bed may be directed towards the centre (inward flow) as in FIG. 1 or directed towards the outside (outward flow).

[0040] The catalyst bed 3 has a cylindrical annular form with a substantial radial symmetry about an axis X-X.

[0041] In some embodiments the bed 3 and the perforated walls 4, 5 are part of a cartridge removable from the shell 2.

[0042] FIG. 2 shows a detail of the first perforated wall 4 which has slits 10 which make the wall gas-permeable. The perforated wall 5 is realized in a similar manner. The figure shows for easier illustration a section of the cylindrical wall.

[0043] Each of the slits 10 has an elongated shape and extends mainly along a longitudinal axis A-A. In a transverse direction, which is perpendicular to said axis A-A, the slits have a dimension of width s.

[0044] The relationship between said dimension s and the size of the particles of catalyst essentially determines the ability of the slit 10 to retain the same catalyst.

[0045] The perforated walls 4 and 5 have advantageously slits 10 with the same dimension s.

[0046] FIG. 3 shows a typical statistical distribution of the size of particles of a commercial catalyst which has a minimum declared particle size d.sub.1 and maximum declared particle size d.sub.2. For example a catalyst with a commercially declared size of 1-2 mm has d.sub.1=1 mm and d.sub.2=2 mm.

[0047] The ratio between said transverse dimension s of the slits 10 of both the walls 4 and 5 and said nominal minimum size d.sub.1 of the particles of catalyst is less than or equal to 0.6. Moreover the catalyst bed 3 contains no more than 3% by weight of particles with a size smaller than d.sub.1.

[0048] The particles of catalyst with a size smaller than d.sub.1 are indicated by the area 11 in FIG. 3.

[0049] It has been found that a particularly advantageous embodiment is obtained with s=0.6 mm and d.sub.1=1 mm.

EXAMPLE

[0050] Different types of catalyst were tested in order to assess their tendency to obstruct the slits in a permeable wall. A flat sheet-metal wall with slits having an average length of 60 mm and width of 0.6 mm, located at the bottom of a tube, was used.

[0051] The tube was filled with catalyst and then water run through it for a period of 10 hours. At the end of the test the degree of occlusion of the slits due to the particles of catalyst was assessed.

[0052] Using an industrial catalyst with nominal dimensions of 1.5-3 mm a degree of occlusion ranging from 2% to 3% of the total available through-flow area was observed.

[0053] Using an industrial catalyst with nominal dimensions of 1-2 mm containing more than 5% by weight of particles with size smaller than 1 mm a degree of occlusion ranging from 10% to 30% of the total available through-flow area was observed.

[0054] Using a catalyst sieved according to the invention, containing less than 3% by weight of particles with a size smaller than 1 mm, a degree of occlusion of the total available through-flow area ranging from 3% to 5% was observed.