Membrane housing

UF and MF use energy to depolarize membranes so as to increase flux. As is shown in Fig. 22-55, membranes and mechanical equipment are traded off to achieve an overall economic minimum. Three things can drive a design toward the use of more membranes and less mechanical equipment cheaper membranes, veiy high flux, and veiy low flux. The availability of lower-cost membranes is easiest to understand. In the five years ending in 1995, the cost of both membrane area and membrane housings was driven down by competition. 

Muller, E. and Baurmeister, U., Preparation of and optimal membrane housings for hollow fiber membrane ion exchangers, J. Mol. Recognition, 11, 273, 1998. 

The hollow-fiber systems for gas separation or the tubular microfiltration systems have to be pyrolyzed before mounting in the membrane housing, because of the large shrinkage during pyrolysis. That is the most critical step in the fabrication of a separation system. 

Figure 10.4 presents an estimated cost breakdown of desalinated water produced in a typical plant. The main component is, of course, the capital and financial cost, comprised of the cost of the main equipment items feed tanks, pretreatment filtration units, pumps, pressure exchangers and piping, controls, membranes and membranes housing, post-treatment and product tanks. 

Another point concerns the membrane housing. Sealing between a ceramic membrane and a metallic tube can be a problem when high temperatures are used, due to the difference in thermal expansion between the two materials. Specific carbon seals can be used with classical fittings, but a much better system using a sequence of materials with progressive change in properties has been recently developed [83]. 

The inner membrane houses the electron transport chain and ATP synthesis. The inner membrane has numerous folds called cristae, which have a folded structure that greatly increases the surface area where ATP synthesis occurs (Figure 11.1b). 

Ceramic membranes are cast within feed channels, contained in support structures that are then inserted in housings. To reduce energy/flow requirements, up to two to four membrane housings can be connected in series. 

The development of an effective cleaning process has to take into account the nature of the foulants, the thermal and chemical resistance of the membrane material, membrane housing and seals. Typically, membrane manufacturers make specific recommendations regarding the cleaning agents and cleaning procedures that need to be used for different membranes and applications. 

NaSCN solution being highly corrosive, the material for tanks and membrane housings was FRP, while piping and other contacting parts were made from stainless steel 316 L. The FRP feed tank (1 no.), permeate tanks (2 nos), and reject tank (1 no.) of 15 m, 25 m, and 15 m, 5 m capacities respectively, were purchased at the rate of 216 per cubicmeter. The total capital investment for the NF system came to 38,000 excluding expenditure for site preparation. The space required for installation of the NF system was 10 x 8 m. 

Several filter geometries are available for sterile filtration. They consist of flat membranes in a stainless steel press (<293 mm), pleated membranes housed in stainless steel cartridges, and stacked plates in the form of flat segments of membrane filters. 

One recent application in lEC consists of solid phase extraction disks which are used to eliminate matrix interference prior to analysis. The disk contains a membrane composed of resin beads enmeshed in a PTFE membrane, housed in a polypropylene housing. The resin is treated to remove specific ions such as H+ to remove hydroxide, Ag+ for excess halides and Ba to remove sulphate. Other disks such as hydroxide for acid removal and neutral styrene-divinylbenzene to eliminate hydrophobic components which can damage resin based IC columns are being developed [23]. 

In plate and frame systems (see Figure 2.36), the filtrate itself is often used as the backwash fluid. Sometimes, larger membrane housings are used to serve as an accumulation reservoir for the filtrate. A backwash fluid outlet is provided up-stream of the membrane to purge "backwash debris" from the system. Of course, the membrane must be supported on both sides. 

Figure 3.9 Membrane housing (a), catalyst distribution (b) and membrane connectors (c) for a multi-tube membrane reactor [24]...

As the most relevant aspect. Table 6.2 resumes the efforts in the last decade for developing both Pd-based MRs (from dense to composite membranes housing) and non-Pd MRs. 

The air pressure is maintained for a period of time (2-10 min) to observe the rate of decay. A small decrease of 0.1 -0.2 psi/min is considered acceptable and is due to diffusion of the air across the microporous membrane structure (DWI, 2001). A faster decrease in pressure indicates a faulty membrane. As the membrane system is open to atmospheric pressure on the filtrate side, the airflow can be observed to confirm the location of any breach (defects, holes, or tears in the membrane). The system can be automated, but faults will only be detected in a membrane unit. If the unit is comprised of several membrane housings (larger systems may contain in excess of 100 membrane modules), additional diagnoses will be necessary to identify the failed membrane fibers. 

---