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Dense and Sock Catalyst Loading Compared
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Dense and sock catalyst loading compared compared
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John T. Wooten Catalyst Handling Service Wilmington, Del.
Dense loading is preferable to sock loading in several instances. The advantages of dense loading include increa capacity, run length, reactor integrity, and product qualit y.
Sock loading, as a result of its tendency to create void spaces, may not maximize a reactor's capacity. Sock loadi
hand, because it is more tolerant to particulate matter in the feed and distributes catalyst in a less dense state, m
to dense loading in some situations. Sock loading often comes at a lower cost. For those refiners who do not requ handle the increased capacities that dense l oading allows, it is a viable option.
Maximum performance for catalytic processes will require that those involved with the catalyst handling are well tr
aware of the desired results expected by the catalyst manufacturer and the refiner. It is most important that discus
conducted with the facility operations, engineering, and maintenance d epartments, and with a representative of th manufacturer.
Sock-loading method Prior to the 1970s, the standard method for loading catalyst in a fixed bed reactor was sock loading.
In sock loading, a canvas tube conveys the catalyst from the reactor inlet manway to the bottom of the reactor ca sock is attached to a loading hopper or funnel at the reactor inlet, which discharges the catalyst through the sock surface in a manner which prevents the individual cylinders from finding a stable, horizontal rest position. The various horizontal and vertical positions.
The positioning of catalyst cylinders in random orientations encourages bridging of cylinders and void spaces bet
During reactor operations, these bridges and void spaces tend to collapse. Bed density then increases as the bed
Dense-loading methods
Since 1970, refiners, catalyst manufacturers, and catalyst-loading contractors have developed dense-loading dev dramatically reduce void spaces and bridging. Dense loading can increase catalyst bed densities by as much as
Moreover, unlike sock loading, dense loading does not require personnel inside the reactor to distribute the cataly
the sock. Workers inside the reactor require breathing air and weight distribution shoes Sign up to vote to onprevent this titlecrushing of the underneath their weight.
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Dense loading is accomplished by introducing the catalyst cylinders into the reactor in a manner that allows each
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The difference between air-propelled and a kinetic-propulsion systems is the manner in which the catalyst is distr
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catalyst bed. Fig. 1 [113,980 bytes] shows an example of each method.
With kinetic energy, the catalyst is distributed by an air motor that rotates a particle distributor. Kinetic systems us
rotating blades, or a series of rubber strips to distribute catalyst from the loader to the outer walls of the reactor. T and the horizontal distance of travel for the catalyst are controlled, in part, by rpm settings on the air motor.
In an air-propelled system, air is introduced i nto a sparger situated in the center of the loader pipe, above the defl
of air emerge from horizontal radial holes i n the sparger, directed outward through the annular gap. The air pressu in a standard apparatus.
The RSI (Reactor Services International) Super COP is a modified version of the Atlantic Richfield Co. (ARCO) C Packing (COP) method for dense loading. Both methods use air to distribute the catalyst.
The Super COP uses two deflector plates, and the ARCO COP uses one. In the Super COP, the lower deflector p catalyst to the center of the reactor, while the upper plate feeds catalyst to the outer walls of the reactor.
Operation and troubleshooting During dense loading, it is important to minimize sudden surges of catalyst to the loading distributor. The loading therefore, must regulate the catalyst feed rate with the supply of catalyst.
To accomplish this, the catalyst feed hopper or funnel must be sized for the delivery speed and container size of t general, the delivery container and catalyst feed hopper should hold at least 28 cu ft of catalyst.
Foreign particulate, tape, tie straps, or plastic liners from drums or super sacks should be prevented from entering
loader. Foreign matter will block the catalyst distributor or redirect the catalyst unevenly, which causes a maldistri
to the reactor bed. A 0.75 in. x 1.5 in. screen inserted into the catalyst feed hopper will prevent foreign particles fr loader. Regardless of the dense-loading method selected, the catalyst feed pipe and distributor should be perpendicular times. An uneven distributor will produce a sloped bed. Even though the density calculation will be unchanged,
with liquid-phase processes, feed rates follow the slope of the catalyst bed causing preferential or uneven conver temperatures.
Improper settings of the catalyst feed rates, distributor air pressures, and distributor rpm settings will produce une
distribution (Fig. (Fig. 2 [134,889 bytes]). bytes]). Uneven distribution usually manifests itself in a bed surface which has a cent
"doughnut" configuration. Higher air pressures, as with COP methods, will displace this mound but if the Sign up to vote on this outward, title increased too much, the bed level will be higher at the reactor wall.
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After 10-25% of the catalyst has been loaded, the loading personnel should inspect the bed to determine if it is fir
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Catalyst manufacturers have arranged to have their catalyst tested for adequate strength. The primary test, called
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test, tests the ability of the catalyst to withstand striking the catalyst-bed surface at vertical terminal velocity. This greater than that striking the reactor wall.
Catalysts strong enough to withstand the abrasion of falling between particles in an elongated sock have generall satisfactory for COP loading.
Capacity limitations for dense loading The achievement of maximum performance when the reactor is operating at maximum feed rate requires careful the reactor pressure drop.
Pressure drop problems can be avoided by selecting a catalyst with a shape that allows more free space in the be
sock loading. With sock loading, ho wever, the weight of catalyst charged to the reactor is limited. This limitation re
performance that is substantially less than can be achieved with dense loading of small diameter catalyst, which i amount of catalyst contacted by the feed to the reactor, and thus improves the overall effectiveness.
Initial pressure drop after start-up, with a new charge of catalyst, is a function of the size and shape of catalyst, th
procedure, the feed rate, and the percent vaporization. Refiners using dense-loading techniques realize that initia
will be significantly greater than that experienced with sock loading. Pressure drops with dense loading can initiall a factor of 1.5 to 2.5 than those with sock loading.
Because of more-uniform catalyst distribution and improved flow distribution, reactor-pressure drop is often lower loaded catalyst later in the run.
To accommodate dense loading of the reactor catalyst, the capacities of the feed pump and recycle-gas compres
sufficient to overcome the increased pressure drop i n the reactor. Some feeds may contain fouling substances su
or polymers, which if not removed by filtering, may contribute to a higher pressure drop and a shortened run time.
pump and recycle gas capacities are not sufficient or if the feed contains fouling substances which cannot be filte loading may not be an appropriate alternative for catalyst loading.
It should be noted, that even with sock-loaded beds, shrinkage in the bed depth during onstream operation may c
significant increase in pressure drop and lead to damage of the internals in a fixed bed reactor. Shrinkage may als feed to bypass the catalyst in a radial flow reactor.
Advantages of dense loading In existing vapor-only reactors or two-phase units at low conversions, dense-loading may: Sign up to vote on this title
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Increase capacity or run length, with no additional capital investment for reactors
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The function of a redistributor is to redirect the flow of the feed gas to compensate for uneven loading. Redistribut
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baskets and mechanical pieces welded to the reactor.
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