Both open-ended modules

The conventional hollow-flber-type RO element is a single open-ended (SOE) structure, in which the pressure drop of the permeated water in the bore side of the hollow fibers prevents the development of a large-sized (longer) RO element [70]. In this work, a both open-ended (BOE) element was devised to reduce the permeate pressure drop. Medium-sized Toyobo RO module HJ9155 (CTA) was used for the test. It has been confirmed that the permeate flow rate of BOE was greater by about 30% than that of SOE. 

Fujiwara N and Matsuyama H, The analysis and design of a both open ended hollow fiber type RO module. Journal of Applied Polymer Science 2008,110, 2261-2211. 

Toyobo s newest innovative RO module builds on the proven reliability of the HM-type module. The new technology is based on both open-ended (BOE) hollow-fiber membrane stmctures versus single open-ended hoUow-fiber membrane stractures. The... 

Figure 2.20 Both open-ended (BOE) hollow-fiber module.

Hollow fine fiber membranes are extremely fine polymeric tubes 50-200 micrometers in diameter. The selective layer is on the outside surface of the fibers, facing the high-pressure gas. A hollow-fiber membrane module will normally contain tens of thousands of parallel fibers potted at both ends in epoxy tube sheets. Depending on the module design, both tube sheets can be open, or as shown in Figure 8.1, one fiber end can be blocked and one open. The high-pressure feed gas flows past the membrane surface. A portion of the feed gas permeates the membrane and enters the bore of the fiber and is removed from the open end of the tube sheet. Fiber diameters are small because the fibers must support very large pressure differences feed-to-permeate (shell-to-bore). 

The two most common separation modules for the gas and liquid separation processes are the hollow fiber and spiral wound constmaions shown in Figure 7. The hollow fiber module consists of hollow fibers placed in a cylindrical pressure chamber and encapsulated in a thermosetting pol)uner (e.g., epoxy) at both ends. The feed stream is usually on the shell side of the module, and the permeate stream is collected from the open ends of the hollow fibers. Optionally, the feed stream can be delivered to the bore of the hollow fibers with the permeate stream on the shell side. The spiral wound module comprises repeating layers of a spiral wound sheets constmetion which contains alternating layers of the membrane, feed stream spacer, membrane, and permeate stream spacer. Proper sealing of the spiral wound layer construchon allows for separation of the feed stream horn the permeate stream and flow of the permeate stream to the permeate stream outlet. 

The second type of hoUow-fiber module is the bore-side feed type illustrated in Figure 23b. The fibers in this type of unit are open at both ends, and the feed fluid is usually circulated through the bore of the fibers. To minimize pressure drops inside the fibers, the fibers often have larger diameters than the very fine fibers used in the shell-side feed system and are generally made by solution spinning. These so-called capillary fibers are used in ultrafiltration, pervaporation, and in some low to medium pressure gas appHcations. Feed pressures are usually limited to less than 1 MPa (150 psig) in this type of module. 

Ultrafiltration hollow-fiber modules are usually made with a shell and tube configuration. The fibers are potted at both ends of the module with the fiber lumen open for recirculation of the process stream (Figure 21). Naturally, strainers or prefilters must be utilized to eliminate plugging of the fibers. At Nude-pore, it has been shown that larger diameter hollow fibers, 1.5 to 3mm in i.d., are much less prone to fouling. Fortunately, all UF hollow fiber systems can be back-washed and are amenable to a number of cleaning techniques. 

The modules employed in a membrane fractionating column must be different from those used in cascades in hollow fiber modules, for example, the fibers cannot be U-shaped and must be open at both ends. In Reference 5, a module is described based on this principle. 

The tube-and-shell, or tubular, membrane module is easily adapted for use with drawn tubular membranes as well as membranes that are made by depositing a thin permselective metal layer onto a porous tube support. There are three significant variants to this module design. One is based on the membrane tubes fixed to a header at each end of the membrane tube. The second is similar in that both ends of the membrane tubes are fixed to a header, but to the same header. In the second design, the membrane tubes are bent into a U shape, which can be easily done with small diameter metal tubes. The third is based on a single header, to which open sides of closed-one-ended membrane tubes are fixed. The closed-ends of the membrane tubes are suspended freely. This latter design is more common for commercial applications, due to free thermal expansion and greater membrane durability (see above discussion), whereas laboratory test-and-evaluation practices favor the first variant for its ease of assembly. If the membrane is a drawn, thin-walled tube, the membrane tube will usually be brazed to the header. This is more difficult if the membrane tubes are to be fixed at both ends to head-... 

A particularly attractive version of pulsed-flow modulation uses the GC inlet pressure as the preset pressure (45,46). Thus, when the valve is opened, both ends of column Ca are at the same pressure, and carrier-gas flow in Ca stops (stop-flow operation). Stop-flow operation is used to enhance the resolution of a targeted component pair without signiflcantly changing the elution pattern and resolution of other components in the mixture. The concept is illustrated by the band trajectory plots shown in Figure 5.23 for a pair of components labeled 1 and 2 that are completely separated by the first column but coelute from the column ensemble. The solid-line plots are for the case without a stop-flow pulse, and the broken-line plots for the case with a 5-s-wide pulse occurring at the time indicated by the vertical lines. 

In order to evaluate if the fibers in a membrane module are blocked or have any defects Feng and Ivory proposed the following procedure. The shell side of the module should be connected to a pure gas supply at a constant pressure where one end of the lumen side is closed (Figure 5.18). Then permeate flow rate measurements are performed. In the second step the first end is closed and the second end should be opened. If all fibers are unblocked then the module performance should not differ in both cases. The whole procedure should be repeated for various pressures in order to obtain a linear dependence of the flow rate from the pressure which indicates that there is no internal leakage caused by defects in the membrane. 

Larger membrane modules having surface area about 700 - 800 cm were also prepared and tested. These modules were constructed using about 80 -100 PEI hollow fibers of 35 cm length. These fibers were potted at both ends using epoxy resin into 11/4 inches diameter steel tube having an outlet on the side. The module was sealed at both ends by means of steel end caps fitted with 0-rings. Fiber lumens were open at both ends. 

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