Bed restraint for an adsorber

Details Bed restraint for an adsorber Bed restraint for an adsorber

1999-09-01

2002-01-01

Spitzer, Robert H. (Department: 1724)

Gas separation: apparatus

Solid sorbent apparatus

With means to compress or compact solid sorbent bed

C096S137000, C096S152000

Reexamination Certificate

active

06334889

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to adsorbent beds, and in particular relates to systems for restraining particulates in the adsorbent beds that are subject to the forces of gas or fluid flow. The particulates are restrained against movement resulting, for example, in fluidization of the adsorbent bed. More particularly, in a cylindrical adsorbent bed, a bladder at an end of the adsorbent bed applies pressure to the adsorbent packing of the bed to restrain the packing, i.e. to keep the adsorbent packing from moving and becoming fluidized.
BACKGROUND OF THE INVENTION
In an adsorber apparatus, the flow capacity of adsorbent beds is limited by the flow at which the bed becomes fluidized. When the bed becomes fluidized the adsorbent begins to degrade and channeling causes the efficiency of the adsorption process to drop considerably. When an adsorbent bed is properly restrained fluidization will not occur and the capacity of the adsorption process will thereby not be limited by this point. Restraining the bed therefore will permit a significant increase in flow capacity and thus a corresponding reduction in capital costs.
Improvements in gas separation process performance are currently being realized as a result of enhanced adsorption rate. Furthermore, adsorption rate considerations have resulted in a number of configurations calling for small particles throughout the adsorber as well as layers or mixtures of particles of different average particle size. For example, it is known that using particles having a larger size can reduce fluidization and minimize pressure drop. On the other hand, smaller particles are preferred for overcoming limitations to process performance such as, for example, the adsorption rate. However, fluidization is more likely to occur at decreasing flow velocity as the size of particles is decreased, thereby limiting the particle size for a process conducted at given flow rate, i.e., particles of a particular size establish a fluidization limit, a maximum flow velocity which if exceeded requires either the reduction in flow velocity or the constraint of the particles at one or both ends of the bed. Fluidization can be eliminated or reduced for all particle sizes in axial flow adsorbers if the free adsorbent surface of the bed is constrained. Other reasons for constraining adsorbents in axial flow adsorbers include elimination of scouring of the top of the bed due to high velocity purge or repressurization flows, shop-loading of adsorber vessels and prevention of “bumping” or temporary lifting due to pressure disturbances from valve operations.
Apparatus used for pressure swing adsorption cycles generally employ cylindrical vessels adapted for either a radial flow or an axial flow pattern. Vessels adapted for an axial flow pattern are often preferred due to a simple construction which avoids a number of problems or design complexities inherent with vessels adapted for a radial flow pattern. However, with axial flow the limitation of fluidization of the bed must be addressed.
Adsorbent particles are inherently constrained in most vertically oriented radial flow adsorbers as the flow is lateral to the vertical axis. This makes the gravity vector normal to the flow velocity vector, and allows for relatively easy installation of an adsorbent restraint assembly.
In contrast, axial flow adsorbers have the velocity and gravity vectors aligned, which has historically made the installation of an adsorbent restraint assembly relatively difficult. Therefore for example in upflow axial flow vessels the top surface of the adsorbent bed is typically unobstructed leaving adsorbent particles free to fluidize under sufficient lifting conditions, e.g., a volume or a velocity of fluid sufficient to overcome the force of gravity acting on the particles. Fluidization of this nature is also a concern with downflow axial beds, in which regeneration and desorption flows would subject the particles to possible fluidization.
Faster cycles and smaller bed size are also desirable, particularly in the design of vacuum pressure swing adsorption (VPSA) systems. To achieve this design objective, feed velocities are increased. Present axial bed oxygen VPSA systems operate with an average superficial feed velocity of, for example, 0.15-0.3 m/sec for a bed size of 600-800 pounds of adsorbent per ton per day of oxygen. This feed rate and the corresponding bed design results in operation of the system at near fluidization levels. In fact, overlapping countercurrent equalization flow steps have been incorporated into the process at the beginning of the feed step to help restrain the adsorbent under the high initial feed flow.
As a result of operation at levels close to fluidization, some commercial beds have experienced bed fluidization due to valve failure or poorly chosen cycle tuning parameters. This fluidization disturbs the uniform dense packing of large sections of the adsorber bed, resulting in subsequent gas flow maldistribution and associated poor process performance. Thus, a simple, effective restraint system for the top surface of a particulate adsorbent bed in an adsorber having an axial flow pattern would be desirable to improve adsorption rates.
In addition to particle restraint within an adsorber vessel chamber, it is also desirable to provide for uniform flow through the adsorber bed, to eliminate unnecessary void volume and to provide full access to the interior of the vessel. Uniform flow through the adsorber bed ensures that the gas or liquid material being treated is uniformly exposed to the adsorbent particles. Eliminating unnecessary void volume reduces the loss of processed product or unprocessed feed that is trapped in the apparatus after the adsorption process is complete. Full access to the interior of the vessel permits the apparatus to be maintained, and permits the sieve material to be maintained, loaded or changed.
DESCRIPTION OF THE PRIOR ART
A number of approaches to solve or circumvent the adsorbent bed fluidization problem have been used or proposed. Flow direction, special packings, and restraints of various designs are among the prior art solutions to this problem. Related prior art includes the following patents.
In U.S. Pat. No. 5,492,684, Buchanan et al. describe a method and system for the removal of contaminants such as sulfur oxides from waste gages using a graded-bed system. The graded-bed system uses beds with solid sorbents of two or more particle sizes in separate sections of the bed. In one embodiment the solid sorbents are arranged so the larger sorbent particles are disposed in the entrance region of the graded-bed system. In operation, a waste gas stream is passed over and through the solid sorbents so that contaminants, such as sulfur oxides and/or nitrogen oxides are adsorbed. The sorbent bed is then contacted with a reducing gas to desorb the sulfur oxides. The use of expandable means applied to the bed to insure the stability of the bed is not disclosed.
U.S. Pat. No. 4,337,153 to Prior discloses an improved resin tank for a water softening apparatus including an expandable chamber that enlarges during fluid flow through the tank to displace any free space in the tank, thereby maintaining the compactness of the water softening material. The expandable chamber is formed by an elastomeric sleeve that is secured to and surrounds a portion of a downward extending fluid conduit and overlies at least one aperture formed in the conduit wall through which fluid communication is established. The pressure drop normally occurring during fluid flow through the tank generates a pressure differential on the sleeve wall that causes it to enlarge if there is free space in the tube. In an alternate embodiment, the fluid communication between the conduit and the chamber is provided by a pitot tube that is disposed in the conduit fluid flow path and is operative to communicate the velocity pressure of the fluid flowing down the conduit to the chamber.
A bed of particulate ion-exchange material, in U.S. Pat. No. 4,294,699 by Hermann, is conf

Affiliated with

Also associated with

Rating

Bed restraint for an adsorber does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Bed restraint for an adsorber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bed restraint for an adsorber will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2826530