Reactor having bellows expansion unit between catalyst addition/withdrawal conduit and grid plate

A pressurized vertically-oriented catalytic reactor vessel has a fluid flow distribution grid plate fixedly mounted transversely in the reactor lower portion for supporting a bed of particulate catalyst above the grid plate, and has at least one elongated conduit for catalyst addition/withdrawal extending upwardly through the reactor lower head and the grid plate. The catalyst addition/withdrawal conduit has a concentric bellows type expansion unit sealably attached at its lower end to the upper side of the grid plate, the bellows unit being sealably attached at its upper end to the catalyst conduit, so that the conduit can thermally expand vertically, and gas leakage cannot occur around the conduit and the grid plate into the catalyst bed.

BACKGROUND OF INVENTION
 This invention pertains to fluidized bed type catalytic reactors. It
 pertains particularly to such reactors having an addition/withdrawal
 conduit for particulate catalyst extending through a flow distribution
 grid plate located in the reactor lower portion, with the conduit being
 sealably attached to the grid plate by a bellows type expansion unit.
 A known pressurizable ebullated bed catalytic reactor adapted for operation
 at elevated temperature and pressure conditions and having a lower grid
 plate for supporting a bed of particulate catalyst, with the grid plate
 containing multiple riser tubes each covered by a bubble cap for upward
 fluid flow is generally disclosed by U.S. Pat. No. 3,475,134 to Weber et
 al. Particulate catalyst is periodically added to and withdrawn from the
 reactor ebullated bed through an elongated conduit extending upwardly
 through the reactor lower head and through the grid plate. From past
 operating experience, such conduits have been a problem because they
 sometimes fail prematurely near the grid plate due to severe erosion by
 the randomly moving catalyst particles in the ebullated bed. Such erosion
 by the catalyst particles is apparently caused by hydrogen gas passing at
 high velocity through gaps which sometimes occur in a split flange type
 seal which is usually used around the conduit above the grid plate, for
 permitting necessary vertical thermal expansion movement of the conduit
 relative to the grid plate. Because of these undesired erosion problems in
 such reactors, an improved configuration for sealably attaching the
 catalyst addition/withdrawal conduit to the reactor grid plate is needed.
 SUMMARY OF INVENTION
 This invention provides a pressurizable fluidized bed catalytic reactor
 having an innovative construction for sealably attaching an elongated
 catalyst addition/withdrawal conduit to a flow distribution grid plate in
 the reactor lower portion, by providing a concentric bellows type
 expansion unit located adjacent to the outside surface of the conduit
 portion which protrudes through the grid plate and into the reactor
 catalyst bed. The invention includes the pressurizable reactor vessel
 having the grid plate fixedly mounted transversely in the reactor lower
 portion for supporting a bed of particulate catalyst, and arranged for
 upward fluid flow distribution therethrough. The reactor has the elongated
 catalyst addition/withdrawal conduit extending through the reactor lower
 head and upwardly through the grid plate into the catalyst bed, and a
 concentric bellows unit is sealably attached at its lower end to the grid
 plate and is sealably attached at the bellows unit upper end to the
 conduit. The reactor is adapted for sustained operation at elevated
 temperature of 600-900.degree. F. and pressure of 500-3000 psig. The
 bellows unit of this invention is suitable to accommodate both radial and
 vertical thermal expansion of the elongated conduit relative to the grid
 plate.
 The bellows type expansion unit configuration of this invention
 advantageously provides a flexible and reliable sealing means around the
 catalyst addition/withdrawal conduit portion extending above the grid
 plate. The bellows unit cost can be traded off against the cost of a
 previously used split flange joint sealing arrangement for which undesired
 erosion problems have been experienced.

DESCRIPTION OF INVENTION
 As shown by FIGS. 1 and 2, a vertically-oriented pressurizable ebullated
 bed type catalytic reactor vessel 10 includes a cylindrical-shaped wall
 11, a lower hemispherical head 11a welded pressure-tightly onto the wall
 and a reactor support skirt 11b. The reactor 10 may have an inner thermal
 insulation layer 11c provided against the cylindrical wall 11 and head
 11a. The reactor has a grid plate 12 fixedly mounted transversely in the
 reactor lower portion for upward fluid flow distribution into a catalyst
 bed 13. The grid plate 12 is sealably attached to the reactor bottom head
 11a by a cylindrical shaped support skirt ring 14 and a circumferential
 bolted joint 15, and supports the particulate catalyst bed 13 located
 above the grid plate 12. Multiple riser tubes 16 are provided extending
 vertically through the grid plate 12 for upward uniform flow of gas and
 liquid, each tube having its lower end slotted at 17 and its upper end
 portion covered by a bubble cap 18, fixedly attached to the tube 16 by a
 bolt and nut at 19.
 An elongated conduit 20 for catalyst addition/withdrawal from catalyst bed
 13 extends from outside the reactor 10 through opening 11d in the support
 skirt 11b, and is attached pressure-tightly at 20a to an elongated sleeve
 11e which is attached pressure tightly at its upper end to the reactor
 lower head 11a. The conduit 20 extends upwardly through a plenum space 21
 which is lined by a metal casing 21a and through the grid plate 12. The
 conduit 20 may include at least one coupling joint 20b, and may have an
 upper return bend 20c shaped for substantially excluding catalyst
 particles in the bed 13 from entering the conduit, except during any
 particulate catalyst withdrawal operations from the bed.
 The catalyst addition/withdrawal conduit 20 which enters the reactor 10
 through the lower head 11a will become elongated towards the center of the
 reactor and upwards towards the top of the reactor as the reactor reaches
 its normal high temperature operation conditions. Because there is usually
 inadequate space for providing an expansion loop in the conduit 20 within
 the plenum space 21 below the grid plate 12, this arrangement requires
 that the conduit 20 be able to slide vertically relative to the grid plate
 12. An expansion bellows unit 22 which is provided sealably attached to
 the conduit 20 will not only seal off any possible gas or catalyst leakage
 through the grid plate 12 and around the conduit 20, but it will also
 provide for thermal expansion of the catalyst addition/withdrawal conduit
 20 relative to the reactor wall 11 and head 11a and the grid plate 12.
 Such thermal expansion occurs during reactor startup operations while the
 reactor reaches its usual operating condition of 600-900.degree. F.
 temperature and 500-3000 psig pressure.
 As best shown by FIG. 2, the concentric bellows unit 22 includes an
 elongated outer sleeve element 23 sealably attached to a bellows element
 24 and surrounds that portion of the conduit 20 located immediately above
 the grid plate 12. The lower end of the bellows element 24 should be
 located above the bubble caps 18 by a distance "A" of at least 3 inches,
 and need not exceed about 6 inches. The elongated outer sleeve 23 and the
 bellows element 24 of the bellows unit 22 of this invention each have an
 inner diameter slightly larger than the outer diameter of the protruding
 conduit 20, so as to provide an annular clearance space 25 between the
 conduit 20 and sleeve 23 to permit necessary axial movement of the conduit
 20 relative to the grid plate 12. The clearance space 25 should have a
 radial clearance of at least about 0.12 inch to accommodate radial thermal
 expansions, and the radial clearance need not exceed about 0.30 inch. The
 outer sleeve 23 is attached pressure-tightly at its lower end to the upper
 surface of the reactor grid plate 12 by means of a bolted flange 26 and
 stud bolts and nuts 26a. The bellows element 24 is attached
 pressure-tightly at its upper end to the outside diameter of the conduit
 20 by a seal weld 27. Alternatively if desired, the bellows 24 may be seal
 welded at 27 to a reinforcing collar ring 30, with the collar being seal
 welded at 29 to the conduit 20. Also, a lower annular clearance space 31
 is provided between the grid plate 12 and the conduit 20 similar to the
 upper clearance space 25.
 During operations of the catalytic reactor 10, the bellows expansion unit
 22 will be loaded in tension and will not encounter any problems from
 catalyst accumulation from bed 13 at the outside of the bellows element
 24. During such reactor operations, the lower annular space 31 provided
 between the grid plate 12 and the annular space 25 inside the bellows unit
 22 and the outside surface of the conduit 20 will be filled with hydrogen
 gas from a gas buffer zone 32 provided below the grid plate 12 and above
 the riser tube gas entry slots 17, so that there will be no undesired coke
 formation in these annular spaces during reactor extended operations.
 During such operations, the pressure within annular space 25 will exceed
 the pressure in ebullated bed 13 by a differential pressure of 10-40 psi,
 and preferably by 15-30 psi differential pressure. The bellows element 24
 is suitable for accommodating the differential pressure, and also provides
 a vertical movement for the conduit 20 relative to the grid plate 12 of
 1-3 inches.
 With this reactor design improvement for the addition/withdrawal conduit
 20, the multiple riser tubes 16 and attached bubble caps 18 located above
 the grid plate 12 will provide better liquid and vapor flow distribution
 from the plenum space 21 upwardly into the catalyst bed 13, and there will
 be less potential for coking in the catalyst bed due to any undesired
 short circuit of hydrogen gas passage through the split-flange type seal
 which was previously used around the conduit 20.
 If desired, the reactor 10 may have two separate catalyst
 addition/withdrawal conduits extending upwardly through the grid plate 12,
 the first conduit 20 being for catalyst addition upwardly into the
 fluidized bed 13, and a second conduit (not pictured) provided for
 catalyst withdrawal downwardly from the fluidized bed 13. Each separate
 conduit 20 the other not pictured extending through the grid plate 12 is
 provided with a bellows unit 22 attached pressure-tightly at its lower end
 to the grid plate 12, and attached at its upper end pressure-tightly to
 each conduit similarly as described above. Also, the catalyst addition
 conduit 20 has its upper end terminated at a level above the upper end of
 catalyst withdrawal conduit (not pictured).
 This invention will be further described by a typical construction example,
 which should not be construed as limiting in its scope.
 EXAMPLE
 A vertically-oriented catalytic reactor is provided having a bed of
 particulate catalyst supported above a flow distribution grid plate
 located in the reactor lower portion. An elongated conduit for catalyst
 addition/withdrawal extends upwardly through the reactor lower head and
 the grid plate, and is sealably attached to the grid plate upper side by a
 bellows unit. Important dimensions and relationships for the reactor and
 the bellows unit are as follows:

Reactor outside diameter, ft. 15
 Reactor wall thickness, in. 8
 Reactor operating temperature, .degree. F. 700-800
 Reactor operating pressure, psig 2000
 Grid plate thickness, in. 12
 Conduit outside diameter, in. 3
 Bellows and sleeve inside diameter, in. 3.5
 Radial clearance between conduit and bellows, in. 0.25
 Vertical movement of conduit relative to grid plate, in. 2
 Vertical distance (A) between bubble caps and bellows, in. 6
 Catalyst particle size, in. 0.030-0.060
 Because the bellows unit is sealably attached at its lower end to the grid
 plate and is sealably attached at its upper end to the catalyst
 addition/withdrawal conduit, the conduit has adequate horizontal and
 vertical movement relative to the grid plate, and hydrogen gas leakage
 from below the grid plate around the conduit is prevented.
 Although this invention has been described broadly and also includes a
 preferred embodiment, it will be understood that modifications and
 variations can be made within the scope of the invention which is defined
 by the following claims.