Filtration module

A continuous cross-flow filtration process has been utilized to investigate the effectiveness in the separation of nano sized (3-5 nm) iron-based catalyst particles from simulated Fischer-Tropsch (FT) catalyst/wax slurry in a pilot-scale slurry bubble column reactor (SBCR). A prototype stainless steel cross-flow filtration module (nominal pore opening of 0.1 pm) was used. A series of cross-flow filtration experiments were initiated to study the effect of mono-olefins and aliphatic alcohol on the filtration flux and membrane performance. 1-hexadecene and 1-dodecanol were doped into activated iron catalyst slurry (with Polywax 500 and 655 as simulated FT wax) to evaluate the effect of their presence on filtration performance. The 1-hexadecene concentrations were varied from 5 to 25 wt% and 1-dodecanol concentrations were varied from 6 to 17 wt% to simulate a range of FT reactor slurries reported in literature. The addition of 1-dodecanol was found to decrease the permeation rate, while the addition of 1-hexadecene was found to have an insignificant or no effect on the permeation rate. 

The cross-flow filtration method is applied mainly to hyper- and ultrafiltration as well as to some microfiltration.8 In cross-flow filtration the slurry solution or suspension fed to the filter flows parallel to the filter medium or membrane. The filtration product (permeate or filtrate) leaves the filtration module at right angles to the filter medium (the membrane). The traditional perpendicular flow filtration (where the flow of the suspension is directed at right angles to the filter medium and the permeate leaves the filter medium in the same direction) entails filter cake buildup, whereas cross-flow filtration is intended to prevent such filter... 

The objective of the present study is to develop a cross-flow filtration module operated under low transmembrane pressure drop that can result in high permeate flux, and also to demonstrate the efficient use of such a module to continuously separate wax from ultrafine iron catalyst particles from simulated FTS catalyst/ wax slurry products from an SBCR pilot plant unit. An important goal of this research was to monitor and record cross-flow flux measurements over a longterm time-on-stream (TOS) period (500+ h). Two types (active and passive) of permeate flux maintenance procedures were developed and tested during this study. Depending on the efficiency of different flux maintenance or filter media cleaning procedures employed over the long-term test to stabilize the flux over time, the most efficient procedure can be selected for further development and cost optimization. The effect of mono-olefins and aliphatic alcohols on permeate flux and on the efficiency of the filter membrane for catalyst/wax separation was also studied. 

The prototype shell-and-tube type cross-flow filtration modules (Pall Corp.) used for filtration tests are welded into a stainless steel shell enclosure. The modules have an inlet (filtrate) and outlet (retentate) port (both at tube sides) with Vi-inch tubing ends, and a permeate port, located near the midpoint of the shell side of the unit. The stainless steel filter membranes have a nominal pore size of 0.1 pm. The surface of the filter media is coated with a proprietary submicron layer of zirconia. 

The pilot-scale SBCR unit with cross-flow filtration module is schematically represented in Figure 15.5. The SBCR has a 5.08 cm diameter and 2 m height with an effective reactor volume of 3.7 L. The synthesis gas passes continuously through the reactor and is distributed by a sparger near the bottom of the reactor vessel. The product gas and slurry exit at the top of the reactor and pass through an overhead gas/liquid separator, where the slurry is disengaged from the gas phase. Vapor products and unreacted syngas exit the gas/liquid separator and enter a warm trap (373 K) followed by a cold trap (273 K). A dry flow meter downstream of the cold trap measures the exit gas flow rate. 

FIGURE 15.5 Schematic of the pilot-scale integrated SBCR unit with cross-flow filtration module. 

Laboratory Pilot-Scale Tests in SBCR with Cross-Flow Filtration Module Using FT Catalyst/Wax Slurry... 

In order to develop a continuous flux maintenance procedure, the present study examined the transmembrane flux values from the cross-flow filtration module with a filtration media area of 0.0198 m2 (0.213 ft2), a slurry density of approximately 0.69 g/cm3 at 200°C, 17 kg of simulated FT wax with a catalyst loading of 0.26 wt%, and a TMP between 0.68 and 1.72 bar (10-25 psig). The filtration process was run in a recycle mode, whereas clean permeate was added back to the slurry mixture, thus allowing the catalyst concentration to remain approximately constant over the course of the run (given minor adjustments for about 5 ml permeate and slurry samples collected throughout the test). 

After completion of these tests, if the absolute air filtration modules are operating within accepted limits, repeat steps 1 and 2 with operational personnel present and the fill equipment running. If at any time there is a deviation from accepted parameters, the various components of the systems in operation are reviewed. 

The Water Storage Module stores water for use in the TCC, Reagent Storage and Preparation, Neutralization, Biotreatment, and Effluent Filtration Modules. Process water is received from the plant water supply and is stored in the Process Water Tank. 

The Effluent Filtration Module removes most of the remaining suspended solids from the SBR supernatant in the Continuous Backwash Sand Filter. The filter effluent is stored in the Filtered Effluent Surge Tank for transfer to the Federally Owned Treatment Works. 

It is interesting to note that the problem of operation with large pressure differences between the feed/retentate side and the permeate compartment of membrane filtration modules was identified long ago. The concept of operation under low uniform transmembrane pressure (UTMP) was pioneered and first... 

Dynamic filtration modules present a relative movement between the membrane and the module, or between the membrane and a rotor. Thus, it is possible to adjust the shear stress independently of the feed flow rate and of the transmembrane pressure drop. 

Dynamic filtration modules are basically of two types rotating disc filter (RDF) and vortex flow filter (VFF). In the latter, the filtration module has a cylindrical shape and has a rotating concentric cylindrical mesh in its interior. The rotational movement of the internal cylinder generates a Taylor-Couette flow in the annular gap (Roth et al., 1997), creating Taylor vortices that minimize concentration polarization and mesh fouling. Continuous perfusion processes based on this type of filter and operating continuously for up to 100 days have been reported (Mercille et al., 1994). 

The glucose was determined enzymatically (Yellow Springs Instruments). The response time of the complete analyzer system was ca. 37 min, of which 5 min are due to the transfer distance of 3 m between the reactor, filtration module and analyzer system. The continuous air segmented flow analyzers have the disadvantage that after 3-4 days operation, microorganisms growth was detected in the non aseptic analyzer system. 

Boundary layer formulation. Many membrane processes are operated in cross-flow mode, in which the pressurised process feed is circulated at high velocity parallel to the surface of the membrane, thus limiting the accumulation of solutes (or particles) on the membrane surface to a layer which is thin compared to the height of the filtration module [2]. The decline in permeate flux due to the hydraulic resistance of this concentrated layer can thus be limited. A boundary layer formulation of the convective diffusion equation can give predictions for concentration polarisation in cross-flow filtration and, therefore, predict the flux for different operating conditions. Interparticle force calculations are used in two ways in this approach. Firstly, they allow the direct calculation of the osmotic pressure at the membrane. This removes the need for difficult and extensive experi-... 

Two other filtration modules, which both formed part of automated radioimmunoassay systems, have been developed. - One of these, was based on conventional continuous flow techniques. At the filtration stage, a continuously moving strip of glass fiber filter paper was strengthened and wetted, the reaction mixture was filtered, and the precipitate was washed by two streams of buffer. The strip was dried and overlaid with cellulose adhesive tape before being counted as it passed between two end-window radioactivity detectors and wound onto a take-up spool. In the second system, glass fiber filter disks are mounted at intervals over perforated segments of a flexible plastic carrier tape. The contents of five... 

Hollow fiber MF system consisted of 40 cross-flow filtration modules, 6 cm in diameter, 50 cm long, and 1 m ... 

Fig. 5 (A) The self-contained terminal HEPA filtration module (TFM). (B) Arrangement of TPMs in the T-Bar ceiling in a conventional-flow application. (Courtesy of American Air Filter, Inc., Louisville, Kentucky.)...

Conventional airflow (also known as turbulent, or non-unidirectional airflow) incorporates HEPA filters, located in-duct, or as room terminal filtration modules (TPMs Fig. 5). Often confused with LAP, conventional airflow does not meet that definition because it allows multiple-pass circulating characteristics or a non-parallel airflow direction, or both. This type of airflow is incapable of producing first air, and is normally used as secondary or buffer filtration in treating a processing or compounding space that contains laminar airflow devices (LAFDs) to maintain primary critical work surface conditions, or in treating other... 

The terminal HEPA filtration module (TFM) is a self-contained HEPA filter and plenum unit (Fig. 11), which may be used to provide laminar or conventional airflow to a clean space, or may be dedicated as a LAF workstation.f The TFM is available with a 10 in. (optional 12 inch) collar for connection by a circular supply duct to a central air handling system (Fig. 5A) or as a free-standing, fully powered unit containing a motor and blower. It is normally installed in a... 

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