Hydroprocessing Associates – Hydropac Catalyst Dense Loading System
The main advantages of dense loading are: •
•
tighter and more uniform catalyst packing, resulting in better reactant flow distribution in the trickle flow regime as is used in hydroprocessing;
catalyst beds do not sag/change flow patterns during the course of a run; and
• more catalyst is loaded into each bed because of the higher loading density, resulting in longer runs.
Hydropac Loader
HPA is using a dense loading method that is referred to as Hydropac loading. The loader receives catalyst into its internal feed bin by sock from a hopper external to the reactor. The loader channels catalyst to the attached distributor disk, which distributes catalyst evenly across the reactor. Disk speed determines the radial velocity of the particles, while gravity determines the axial velocity. As the bed fills with catalyst, the distance between the distributor and the top of the catalyst bed decreases. The distributor’s rotational speed must then be increased to maintain even catalyst distribution across the reactor.
The Hydropac Loader sits on top of the support screen just above the bed being filled with catalyst. An air motor rotates the distributor. An integral tachometer that has a continuous ½ inch LED display ensures that close speed monitoring can be easily achieved. An integral bubble level has been mounted to the top of the Hydropac Loader catalyst
HPA is using a dense loading method that is referred to as Hydropac loading. The loader receives catalyst into its internal feed bin by sock from a hopper external to the reactor.
drum, to provide a means to set and ensure that the drive shaft is plumb. The collar can be moved up or down and sets a primary catalyst flow gap. The adjustment position is on a set of stepped adjustment slots and is secured with the hand knob. The drive shaft is encased in a delrin sleeve where catalyst contacts the shaft, to prevent catalyst grinding and attrition by the rotating shaft. A bearing within a bronze bushing has been used on all of the shaft support spiders. This ensures a smoothly turning shaft in a possible dusty environment. The disk speed can be easily adjusted while the air motor operates at high speed, where it generates its greatest torque. It has a second asymmetric disk below the primary asymmetric disk to improve the uniformity of catalyst distribution. A pair of adjustable slots at the bottom of the compound disk allows continuous adjustment of the centreline catalyst flow. Knurled knobs are provided to permit hand tightening and to avoid the need for tools.
Catalyst Flow Through the Distributor
Catalyst is delivered to the Hydropac Loader by sock. An integral drum retains a feed supply of catalyst to the disk. Catalyst falls through the annular slot formed by the adjustable sleeve and the primary cone of
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the disk. Vertical fins on the primary disk throw catalyst outward to the wall and fills an annular region adjacent to the wall. The centre of the cone is hollow and some catalyst falls through the support spider to a second smaller disk below the first. Again, a set of fins is used to throw catalyst to an annular region adjacent to the area covered by the primary disk. The vertical gap between the two asymmetric disks is adjusted to control catalyst flow to the second annular region. The centreline of the Hydropac Loader is fitted with a pair of sliding gates that allow catalyst to fill the centreline of the reactor. The gaps are adjusted to maintain a flat and level catalyst bed throughout the loading process. The clearance between the bottom tube of the Hydropac Loader and the surface of the disk is used for primary flow adjustment.
Loading Program Calculations
HPA uses a Hydropac Loader program for the PC to aid loading personnel in establishing a loading schedule (rpm versus bed outage). Inputs to the Hydropac Loader program are:
• reactor geometry; •
catalyst types, sizes and quantities to be loaded; and • distributor to be used.
The Hydropac Loader program is based on simple physics and a few empirical correlations. As the bed fills and makes the vertical distance shorter, the rotational speed will have to increase to throw the particles to the wall in less time. This then sets the rotational speed of the distributor. The compound disk has three annular zones of catalyst flow. The relative openings of the slots for each zone determine the loading rate in each zone. Each zone is adjusted to give as flat a catalyst bed as possible and to prevent catalyst from forming a mound and then avalanching into an adjacent hole. Avalanched catalyst will not have the dense orientation of non-avalanched catalyst.
Homogeneous Horizontal Bed Profile
The catalyst is distributed evenly over the cross-sectional area. There will be no repose angle and consequently no rolling of the catalyst, it is therefore homogeneous. The catalytic bed is made up of horizontally even layers of catalyst. This promotes linear reactive flow without channelling.
Non-attrition
Due to the free-fall of the catalyst individually downward, there will be minimal contact between the catalysts. This prevents breakage and attrition from occurring. Since the mass of the individual catalyst is so small, the free-fall speed is never great enough to damage that particular piece of catalyst.
The Hydropac sits just below the trays (6”), enabling the bed to be loaded to its maximum potential height. A droplight can be lowered past it when working to view the bed profile, which is very important when monitoring that the catalyst bed is homogeneous. There is no centre shaft obstructing the catalyst flow to the centre of the bed, which can cause a dip in the bed profile, which will cause the catalyst in the centre to be angled continuously throughout the loading, resulting in the product taking the easiest route through the centre. The Hydropac also has a reversible rotation, critical for loading around transfer tubes and thermocouples. n
HYDROCARBON WORLD – VOLUME 6 ISSUE 1
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