Spiral wound wrapping

Spiral Wound. A spiral-wound cartridge has two flat membrane sheets (skin side out) separated by a flexible, porous permeate drainage material. The membrane sandwich is adhesively sealed on three sides. The fourth side of one or more sandwiches is separately sealed to a porous or perforated permeate withdrawal tube. An open-mesh spacer is placed on top of the membrane, and both the mesh and the membrane are wrapped spirally around the tube (Fig. 16). 

At the same time internal and external reinforcing wraps may be spirally wound into or on to the hot enamel. 

Small laboratory spiral-wound modules consist of a single membrane envelope wrapped around the collection tube, as shown in Figure 3.42. The membrane area of these modules is typically 0.2 to 1.0 m2. Industrial-scale modules contain several membrane envelopes, each with an area of 1-2 m2, wrapped around the central collection pipe. The multi-envelope design developed at Gulf General Atomic by Bray [113] and others is illustrated in Figure 3.43. Multi-envelope... 

Figure 4.15 shows the cross section of the spiral wound module.24 The spiral construction starts with two sheets of membrane placed back to back with a nylon tricot mesh spacer material in between. This tricot spacer provides the permeate channel for the membranes. These sheets of membrane and spacer are glued on 3 sides so that the permeate can only exit the spacer on one side. This set of membranes and spacer is called a "leaf." Leaves are then placed together with a low density polypropelene mesh spacer to provide the feed/reject channel for the membranes. The thickness of the mesh feed spacer can be adjusted from 28 mils to 34 mils to accommodate higher solids influent water (thicker feed spacers are more forgiving with respect to fouling with suspended solids than thinner spacers—see Chapter 4.4.2.3). The entire collection of leaves and mesh feed spacers are then wrapped around a perforated permeate collection tube so that the open side of the leaf is toward the perforated permeate tube (see Figure 4.16). Note that an 8-inch diameter membrane module has about 16 leaves, and each leaf is about 50 inches in length.

The typical spiral-wound membrane, as shown in Figure 4.20, consists of four layers wrapped around a central collection pipe membrane, spacer (providing a permeate channel), membrane, and a new spacer (providing a feed channel). The feed-side spacer acts as a turbulence promotor, whereas on the permeate side the flow is directed toward the central pipe. The spiral-wound membrane will typically be a polymeric composite material, and is much used also for liquid separation. The packing density of this type of module will depend on the channel height, but is usually within the range of 300-1000 m /m [1]. Several modules may be assembled in one pressure vessel. 

The spiral-wound module is in fact a plate-and-frame system wrapped around a central collection pipe, similar to a sandwich roll. The basic structure of this module is illustrated in Fig. 10. Membrane and permeate-side spacer material are then glued along three edges to build a membrane envelope. The feed-side spacer separating the top layer of the two flat membranes also acts as a turbulence promoter. The feed flows axial through the cylindrical module parallel along the central pipe and the permeate flows radially toward the central pipe. In order to make the membrane length shorter, several membrane envelopes are wound simultaneously. The spiral-wound module is featured by... 

The spiral-wound membrane is essentiaUy a flat membrane wrapped around a perforated tube, through which the effluent streams out of the membrane. As can be seen (Fig. 3.13C) that sandwich is actuaUy four layers a membrane, a feed channel, another membrane, and a permeate channel, which forces aU the separated material toward that perforated tube in the center. This type of membrane is an intermediate step between the flat, laboratory membrane and the hoUow-fiber membrane, at least in terms ot surface area per unit volume and stability. 

Membrane separation devices are assembled in a number of forms. In a flat sheet form the membrane is laid over a flat porous support. A unit would include a large number of the flat sheets separated by spacers and stacked together. In another configuration the fiat sheet may be spiral-wound with spacers around a perforated tube. Other arrangements involve tubular membranes or hollow fiber membranes assembled in bundles. In the tubular module the membrane is wrapped around a tubular... 

In the spiral-wound mounting, a porous hollow tube is spirally wrapped with a porous sheet for the feed flow, and a membrane sheet and a porous sheet for the product flow to give a spiral sandwich-type wrapping. The spiral module is encased in a pressure vessel, and the feed flow through the porous sheet is in an axial direction to the porous tube. As the feed flow passes through the porous sheet, a portion of the flow passes through the membrane into the porous sheet for the product. From there, the product flows spirally to the porous center tube. The retentate stream is discharged from the downstream end of the porous sheet for the feed flow. 

The typical spiral-wound manbrane, as shown in Figure 7.21, consists of four layers wrapped around a central collection pipe membrane, spacer (providing a permeate channel), membrane, and a new spacer (providing feed channel). The feed-side spacer acts as a turbulence promoter, whereas on the permeate... 

Spiral-wound loose wrap or full-fit modules (FFM) are used in many pharmaceutical systems because there are no brine seals to prevent the by-pass of feed water. When a brine seal is utilised, a large pocket of water remains stagnant around the RO membrane. Since the water is not chlorinated in the case of PA membrane elements, stagnant water is... 

In the spiral-wound type, a planar membrane is used and a flat, porous support material is sandwiched between the membranes. Then the membranes, support, and a mesh feed-side spacer are wrapped in a spiral around a tube. In the hollow-fiber type, fibers of 100 to 200 iJ,m diameter with walls about 25 /rm thick are arranged in a bundle similar to a heat exchanger (LI, Rl). 

Spiral wound membrane modules are well-known in water desalination and are better than plate frame and tubular modules due to their high water flux, lower salt permeability and lower operational cost. Several membrane elements are connected with each other in a spiral mode and wrapped around a centrally installed permeate tube (Fig. 4.5). The whole setup is placed inside a pressurized tubular vessel where the feed water passes through the membranes axially down the module. 

Many factors affect the performance of spiral-wound gaskets such as tightness of wraps, material of filler and strips, height of strips, diameter of opening, and surface finish. The gasket seating surface finish is about 125 rms. 

In the spiral-wound configuration an envelope is formed with two membrane sheets separated by a porous support material. Typically the module consists of several such envelopes. The material between the membranes (permeate channel spacer) supports them against the operating pressure and defines the permeate flow channel. The envelope is sealed on three sides. The fourth side is sealed to a perforated permeate collection tube, and the envelope is wrapped around the collection tube with a net-like spacer sheet that has two functions ... 

Applying UTDR to a spiral-wound module is complicated by multiple reflections that occur from each of the interfaces associated with the wrapping material and concentric membrane, membrane support, and channel-spacer layers as shown in the schematic cross section in Figure 33.2. Two methods that have been developed to address this... 

Figure 33.2 Cross section of a spiral-wound membrane module having 12 membrane layers and an outer wrapping that is encased in a housing onto which a UTDR transducer is attached schematic shows reflections fi om the outer wrapping and second and third membrane layers.

Chai et al. (2001) used UTDR to smdy calcium-sulfate fouling from aqueous solutions in a 2521 Koch spiral-wound reverse osmosis (RO) membrane module. Only the reflections from the outer wrapping and the second and third membrane layers denoted by a, (3, and 7 in Figure 33.2 were smdied. The UTDR system consisted of a 3.5-MHz transducer having a focal length of 7 cm (Research Institute of Acoustics, Chinese Academy of Science), pulsar receiver (Panametrics 5052 PRX), and digital oscilloscope (Nicolet Pro 50). 

Commercial membrane systems are arranged in different module types (Table 20.2). Hollow fiber modules are very compact and find application in gas separation. Silicone membranes for vapor-gas separations are typically produced as spiral-wound modules, which contain wrapped flat sheet composite membranes glued along three sides and attached to the permeate chcumel. 

Composite membranes of 12 in x 9 ft were submitted to Osmonics, MN, for fabrication into spiral wound modules of approximately 14 in width and a diameter of 2 in. The membrane with polyester backing was wrapped around the PVC center tube and sealed with epoxy around the edges. Polypropylene turbulence promoters acted as spacers between two membranes. Two types of tubular modules, one with 20 tubes and the other with 14 tubes, were constructed. The length of the tube was 14 in. 

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