Membrane-replacement

Because of limited commercial experience with anode coatings in membrane cells, commercial lifetimes have yet to be defined. Expected lifetime is 5—8 years. In some cases as of this writing (ca 1995), 10-years performance has already been achieved. Actual lifetime is dictated by the membrane replacement schedule, cell design, the level of oxygen in the chlorine gas, and by the current density at which the anode is operated. 

Membrane-replacement cost (assuming seven-year life)... 

Membrane Characterization The two important characteristics of a UF membrane are its permeability and its retention characteristics. Ultrafiltration membranes contain pores too small to be tested by bubble point. Direc t microscopic observation of the surface is difficult and unreliable. The pores, especially the smaller ones, usually close when samples are dried for the electron microscope. Critical-point drying of a membrane (replacing the water with a flmd which can be removed at its critical point) is utihzed even though this procedure has complications of its own it has been used to produce a Few good pictures. 

Cleaning membranes to restore their efficiency is normal in UF. Food and dairy systems require daily cleaning in any event for hygiene more frequent cleaning is economically intolerable. A few industrial systems operate for six months between cleanings. Cleaning shortens membrane life, and it is often the major determinant of membrane-replacement frequency. 

Disposables For smaller MF applications, short membrane life is a traditional characteristic. In these apphcations, costs are dominated by the disposables, and an important characteristic of equipment design is the ease, economy, and safety of membrane replacement. 

Membrane Replacement Membrane replacement is a significant cost facdor, but membrane hfe and rehability are now reasonable. Membranes are more susceptible to operating upsets than more traditional equipment, but their field-reliability record in properly engineered, properly maintained installations is good to excellent. In N9 separations, membrane hfe is veiy long. 

R/0 unit Reverse Osmosis Unit for water purification in small aquariums and miniature yard-ponds, utilizes a membrane under pressure to filter dissolved solids and pollutants from the water. Two different filter membranes can be used the CTA (cellulose triacetate) membrane is less expensive, but only works with chlorinated water and removes 50-70% of nitrates, and the TFC membrane, which is more expensive, removes 95% of nitrates, but is ruined by chlorine. R/0 wastes water and a system that cleans 100 gallons a day will cost ft-om 400 to 600 with membrane replacement adding to the cost. A unit that handles 140 gallons a day will cost above 700,00. 

Annualized fixed cost of modules including membrane replacement ( /yr)... 

Dead-end filtration through membrane filters is common in some industries where high purity is imperative. When clogged, the membrane has to be replaced. The water is first purified, and the filters serve as a final polisher. They are unsuitable for applications where they have to remove any significant concentration of particulate matter, as the cost of membrane replacement can become very high. 

A good estimate is that each of these areas comprise 25% of the capital cost. Membrane replacement and a pump rebuild may be required after 5 to 6 years, so some provision for these costs should clearly be made because they are not insubstantial. 

Laboratory Microfiltration membranes have countless laboratory uses, such as recovering biomass, measuring particulates in water, clarifying and sterilizing protein solutions, and so on. There are countless examples for both general chemistry and biology, especially for analytical proc ures. Most of these apphcations are run in dead-end flow, with the membrane replacing a more conventional medium such as filter paper. 

In ion-selective FETs (ISFETs), an ion-selective membrane replaces the gate electrode. When an enzyme-loaded gel is combined with the membrane, the device can be used to measure substrates which enzymically generate charged species. 

SPEC was essentially able to market their Zr02-based ultrafiltration membranes to an already existing market in the sense that these membranes replaced polymeric UF membranes in a number of applications. They also developed a certain number of new applications. For Ceraver, the situation was different. When the Membralox membranes were first developed, microfiltration was performed exclusively with dead-end polymeric cartridge filters. In parallel to the development of inorganic MF membranes, Ceraver initiated the development of cross-flow MF with backflushing as a new industrial process. 

Operation Maintenance Cost (Incl.chemicals and membrane replacement), cent.cu. m 10-12 12-18 22-25 4-5 4-5 4-5 22-25 12-18... 

Operation Maintenance Cost (incl.chemicals and membrane replacement), cents/cu. m... 

Plate and frame systems offer a great deal of flexibility in obtaining smaller channel dimensions. Equations 4 and 5 show that the Increased hydrodynamic shear associated with relatively thin channels Improves the mass-transfer coefficient. Membrane replacement costs are low but the labor involved is high. For the most-part, plate and frame systems have been troublesome in high-pressure reverse osmosis applications due to the propensity to leak. The most successful plate and frame unit from a commercial standpoint is that manufactured by The Danish Sugar Corporation Ltd. (DDS) (Figure 15). 

Two of the major operating costs of RO plants are electrical power and membrane replacement. Table 1 summarizes the estimated costs for RO system of various sizes in 1995 dollars (D15442H, p. 20 D16192M, p. 103). 

Shows the same value in Crack in the glass membrane/Replace the electrode. 

Labor and operating costs are low. The system is highly automated allowing for minimal operator intervention. The two major operating costs are power and membrane maintenance. Allied-Signal s commitment and continued research and development of the AQUATECH membranes and stack design ensures longer lifetime on the membrane and even more power efficient units. Membrane replacements are facilitated by cell modules pre-assembled for easy installation. 

Standard cell sizes are up to 30 by 45 in. In an individual stack the compartments are in parallel, but several stacks in series are employed to achieve a high degree of ion exchange. The ion exchange membrane is not depleted and does not need regeneration. The mechanism is that an entering cation under the influence of an emf replaces an H+ ion from the resin and H+ from solution on the opposite face of membrane replaces the migrating cation. 

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