Liquid purification or separation – With repair or assembling means
Reexamination Certificate
1999-05-05
2001-05-01
Savage, Matthew O. (Department: 1723)
Liquid purification or separation
With repair or assembling means
C210S321800, C210S321890, C210S451000, C210S455000
Reexamination Certificate
active
06224763
ABSTRACT:
FIELD OF INVENTION
This invention relates to hollow fiber membrane devices for fluid processing. More particularly, it relates to double open ended hollow fiber bundle device and methods of assembling such devices.
BACKGROUND OF THE INVENTION
Hollow fiber membrane devices for fluids processing are generally assembled in a fashion resembling a shell-and-tube heat exchanger. A plurality of hollow fibers are arranged in an elongated bundle and encased in a shell containment housing. The hollow fibers are embedded in a tube sheet at both ends, which tube sheet is normally fabricated from a resin material. The fluid processing devices using hollow fiber membranes may be configured either as a shell side feed device or a bore side feed device.
In the shell side feed configuration, the fluid to be treated is introduced to the outside of the hollow fibers, and a portion of the fluid permeates through the fiber wall into the lumens of the hollow fibers. The permeate fluid is removed from one or both ends of the fiber lumens. The non-permeate fluid is discharged from a region on the shell side that is often longitudinally distant from the fluid inlet to achieve a desired co-current or countercurrent flow configuration. Clearly, in the shell side feed configuration, at least one tube sheet should be made in such a fashion that the bores of the hollow fibers communicate through the tube sheet and are open to the exterior face of the tube sheet that is opposite the fiber bundle. Such a tubesheet is referred to as an active tube sheet, which allows for introduction of a fluid to or removal from the fiber lumens. Depending on whether one or both tube sheets are active, the fiber bundle is considered to be single open-ended or double open-ended. Most commercial hollow fiber membrane devices for fluid separation adapt the shell side feed configuration.
Alternatively, in a bore side feed separator, the fluid to be treated can be admitted to the fiber lumens at one end of the hollow fiber device, and a non-permeate fluid exits from the fiber bores at the other end of the device. This requires two active tube sheets, one at each end of the fiber bundle. This latter configuration has been used for certain applications such as nitrogen production from air.
In fluid processing by membranes, a significant pressure differential across the membrane is often required to provide the driving force for mass transfer from one side of the membrane to the other side of the membrane. Compared to shell side feed, a more even flow distribution of feed on membrane surface is achieved in the bore side feed hollow fiber devices, which is beneficial to an efficient operation. Further, in the bore side feed configuration, only the fiber wall and the end caps are pressurized, and the pressure at the shell side of the membrane device is substantially low, which reduces the mechanical strength requirement of the casing shell of the device. However, when a pressurized fluid moves to or from the fiber bores, significant pressure is exerted on the tube sheets. Because there are no balancing forces on the inner surface of the tube sheets, the pressure causes the fiber bundle to collapse between the tube sheets.
Various prior art devices have support means for the fiber bundle and the tube sheets. U.S. Pat. No. 4,961,760 issued to Caskey et al. teaches a boreside feed hollow fiber membrane fluid separation device which has a cylindrical tube sheet support means which encases the hollow fiber bundle and embeds in the tube sheets at either end of the bundle. The tube sheet support means must be integrated into the hollow fiber bundle at the time of manufacture, adding to the expense and complexity of the hollow fiber bundles.
Alternatively, there are devices in which the casing itself acts as the tubesheet support means by having a cross-sectional diameter less than the diameter of the tubesheet. However, in these devices, at least one tube sheet must be formed in place after the hollow fibre bundle has been inserted into the casing which is a cumbersome procedure. In U.S. Pat. No. 4,929,259, a device is disclosed which requires formation of resin plugs to augment the tube sheets after they have been assembled with the casing shell.
SUMMARY OF INVENTION
This invention relates to fluid processing devices containing a double open-ended hollow fiber bundle for bore-side feed fluid processing.
The present invention provides a design of hollow fiber membrane devices suitable for bore side feed and yet allows for slip-in installation of a pre-formed fiber bundle with two tube sheets. At least one tube sheet is supported by a split disk to balance the force resulting from the pressure difference exerted longitudinally cross the tube sheet. Advantageously, the fiber bundle with both tube sheets can be formed prior to insertion into a casing shell or housing. The present invention requires no subsequent processing on the tube sheets after they are inserted into the housing. Moreover, the hollow fiber membrane device of this invention is easy to disassemble. The replacement of hollow fiber membrane bundle in the membrane device is straightforward, and the membrane containment vessel is reusable without needing any machining work. These features are especially desired for on-site service of membrane devices.
Basic components of the device of this invention include a plurality of hollow fiber membranes arranged in an elongated bundle encased in a fluid impermeable shell housing. At each end of the fiber bundle, the fibers are embedded in a tube sheet fabricated of an epoxy or other resin material. The fiber bundle is arranged such that the hollow fibers communicate through the tube sheet with the fiber bores being open on the exterior surface of the tube sheets that are opposite of the fiber bundle. At least one tube sheet is supported by a support means comprised of a split disk placed against the tube sheet in the region adjacent to an annular area on the interior surface of the tube sheet that is facing the fiber bundle. First and second end caps are arranged and adapted for sealing the shell casing at the first and the second ends of the housing near the first and the second tube sheets, respectively. At least one end cap is adapted to receive a tube sheet. This device can have a number of ports for fluid introduction and discharge, depending on specific applications, as discussed below. At least one fluid entrance port is used to direct a fluid into the bores of the hollow fiber membranes at one end of the fiber bundle, and at least one fluid exit port is located at the other end of the fiber bundle to discharge a fluid from the bores of the hollow fibers. A space is defined between the external surface of the hollow fibers and the housing. In a four-port device, a fluid inlet and a fluid outlet in the housing located near the two ends of the fiber bundle communicate with this space. If there is a fluid outlet and no fluid inlet in the housing, the device becomes a three fluid-port device. If both fluid inlet and outlet in the housing are absent or plugged, the device becomes a two-port device. Other multi-port configurations are, of course, possible.
The hollow fibers in the devices can be any hollow fiber membranes, porous or non-porous, polymeric or non-polymeric, depending on specific applications. In a preferred embodiment, the hollow fibers are arranged around a center core in a cylindrical shape. The center core may be a tube or a rod, fabricated of plastic or metal materials, which extends to both tube sheets of the fiber bundle.
Thus, in one aspect of the invention, the invention comprises a bore side feed hollow fiber membrane fluid separation device comprising:
(a) a cylindrical housing having an internal diameter and first and second ends wherein said first end includes a support flange;
(b) a plurality of hollow fiber membranes arranged in a longitudinal bundle, said bundle having first and second ends and an external diameter;
(c) a first tube sheet having an external face and an internal face and having a diameter les
Feng Xianshe
Ivory John
Bennett Jones LLP
Savage Matthew O.
LandOfFree
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