Membrane cleaning tubular

UF membranes are mnde commercially in sheet, capillary, and tubular forms, Sheet membrane is used in plate-and-fiame devices, slack devices, and spiral elements. Capillary membranes are generally 0.4-1 mm diameter, are self-supporting, and are pressurized from inside. Usually, they are mnde with a skin on both inside and outside surfaces so that they can be pressure reversed for cleaning. Tubular devices are cast on supports and are generally in the 10-25 mm diameter moge. 

The major advantages of the tubular reverse osmosis configuration are the ability to tolerate high suspended solids concentrations in the feed and the possibility of mechanical membrane cleaning. The disadvantages are the excessive number of tube end fittings in proportion to the active membrane area in each pressure vessel, the bulkiness of the reverse osmosis plant and the high cost. 

Spiral-wound modules consist of several flat membranes separated by turbulence-promoting mesh separators and formed into a Swiss roll (Figure 16.18). The edges of the membranes are sealed to each other and to a central perforated tube. This produces a cylindrical module which can be installed within a pressure tube. The process feed enters at one end of the pressure tube and encounters a number of narrow, parallel feed channels formed between adjacent sheets of membrane. Permeate spirals roward the perforated central tube for collection. A standard size spiral-wound module has a diameter of about 0.1m, a length of about 0.9 m and contains about 5 m2 of membrane area. Up to six such modules may be installed in series in a single pressure tube. These modules make better use of space than tubular or flat sheet types, but they are rather prone to fouling and difficult to clean. 

Parkin, M.F. and Marshall, K.R., "The Cleaning of Tubular Cellulose Acetate Ultrafiltration Membranes", N.Z. Journ. 

Tubular 20-30 Very high Easily mechanically cleaned Tolerates high solids High capital and membrane replacement cost... 

These modules are easy to clean. Typically, a sponge ball is shot down through the feed channel or tube to physically remove debris from the surface of the membrane. In most tubular applications, the membranes need to be cleaned on a daily basis. This is because the nature of the solution being treated by the membranes generally contains high concentrations of suspended solids and organics, which collect on the membrane. 

Membranes are typically made of cellulose acetate or aromatic polyamides because of their high permeability to water and low permeability to salts. They are normally produced in tubular or spiral-wound modules, which are then packed inside a reaction vessel. Their fouling can be minimized by either pretreating the influent streams or diluting them with the clean water produced. 

The term membrane element refers to the basic form in which a membrane is prepared. There are three types of membrane elements flat sheets, hollow hbers, and tubular membranes. The device within which the membrane element is housed is referred to as the membrane module. The design of the membrane module largely depends on the type of membrane element, as well as on additional requirements such as the need for cleaning and disassembling, the required transmembrane pressure (TMP), and the required hydrodynamic conditions. Some of the different modules types are (see Figures 18.3 through 18.7) ... 

The lifetime of the tubular membranes in the Borregaard industries plant (1120 m, PCI) has been about 1 year, when cleaning is made daily with an alkahne detergent. The tubular membranes need only a minimum of pretreatment and can even handle fibers. The 20 kg/mol cutoff polysulfone membrane has mostly been used at high temperature operation (70°C). In addition, a spiral wound RO (polyamide membrane from Osmonics) is used to concentrate the UF permeate from 7% of total solids to 14% before evaporation [47,67]. 

Serviceability and maintenance. Being on the outer surface of tubular elements, the membranes are readily accessible to Inspection and cleaning. Assembly and disassembly of modules can be accomplished easily and quickly in the fluid. Good mechanical reliability of the system. The membrane elements are subjected to compressive stresses only, therefore, non-corrosive materials of lower tensile strength may be used. 

The membrane separation plant is tubular ultraflltration (UF) and the pilot-plant operation was on a batch basis with a volume reduction factor approaching 40. The UF membrane had a maximum permeate flux of around 300 L/m hr at maximum 6 kg/cm inlet pressure and 3.8 m/s fluid velocity with a clean membrane. The flux typically dropped and approached 80 L/m hr at the end of a day s operation. The retentate from UF separation was returned to the feed tank whereas the permeate was routed to the sewer. Design of a full-scale plant was performed using a flux value of 40 L/m hr and volume reduction of 20x. 

A folly automated, tubular RO plant for removing 200 kL/day of water from a food stream costs about 400.000. excluding buildings, prei rest men 1 utilities, and installation, which were included in the Soo-Hoo sredy. Energy requirements are about 3 W- h/L. and membrane replacement costs are 180,000/year. Cleaning frequency dictates annual membrane replacement in this process application. 

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