Separation spiral-wound membrane element

Spacers A mesh-like material used in flat-sheet modules (e.g. plate, spirals, pleated sheet) to separate successive layers of membranes. Spacers control the feed channel dimensions in these modules. Serve as turbulence promoters in spiral-wound membrane elements. 

The spiral wound membrane packaging configuration is shown in Figure 4.8. Basically, the spiral wound element consists of two sheets of membrane separated by a grooved, polymer reinforced fabric material. This fabric both supports the membrane against the operating pressure and provides a flow path... 

A very rapid development has taken place in the use of membranes for gas separation. Reviews are given in [664-666]. The most popular process for purge gas recovery using membranes is based on the use of hollow fibres, although other types such as spiral wound membranes and stacks of flat elements have also been used. 

In order for membranes to be used in a commercial separation system they must be packaged in a manner that supports the membrane and facilitates handling of the two product gas streams. These packages are generally referred to as elements or bundles. The most common types of membrane elements in use today include the spiral-wound, hollow fiber, tubular, and plate and frame configurations. The systems currently being marketed for gas separation are of the spiral-wound type, such as the SEPAREX and Delsep processes, and the hollow-fiber type such as the Prism separator and the Cynara Company process. 

Spiral-wound elements, as shown in Figure 2, consist primarily of one or more membrane "leaves, each leaf containing two membrane layers separated by a rigid, porous, fluid-conductive material known as the "permeate channel spacer." The permeate channel spacer facilitates the flow of the "permeate", an end product of the separation. Another channel spacer known as the "high pressure channel spacer" separates one membrane leaf from another and facilitates the flow of the high pressure stream through the element. The membrane leaves are wound around a perforated hollow tube, known as the "permeate tube", through which the permeate is removed. The membrane leaves are sealed with an adhesive on three sides to separate the feed gas from the permeate gas, while the fourth side is open to the permeate tube. 

The SEPAREX system will recover over 90% of the hydrogen at a purity of 96+% for recycle, while increasing the heating value of the fuel gas from -550 BTU/SCF to -950 BTU/SCF. The projected flow rates and gas purities for the membrane separation are shown in Table II. Under the bone-dry feed conditions the cellulose acetate membrane is not affected by HCl. Special materials of construction and adhesives have been used in the fabrication of the spiral-wound elements to ensure their resistance to HCl in the gas streams. 

Seperation Unit. The elements of a separation process. Separation units of a separation process could be, for example, a gas centrifuge, a membrane module, a tray of distillation column or the evaporator of a multiple effect plant. It should be kept in mind, however, that in plate-and-frame modules as well as in modules of the spiral-wound-type usually every block or pressure-vessel contains more than one separation unit ... 

Membrane contactors provide a novel approach to the solution of many such problems (especially of the second and third kind) of contacting two different phases, one of which must be a fluid. Essentially, a porous membrane, most often in hollow-fiber form, is the basic element in such a device. Any membrane in flat or spiral-wound or hollow-fiber or any other form has two interfaces since it has two sides. However, conventional separation processes involve usually one interface in a two-phase system, for example, gas-liquid, vapor-liquid, liquid-liquid, hquid-supercritical fluid, gas-solid, liquid-solid, and the like. Membrane contactors allow the creation of one immobilized phase interface between two phases participating in separation via the porous membrane. Three types of immobilized phase interfaces in two-phase configurations are relevant ... 

In this section, we want to describe the fundamentals of diffusion across membranes and the actual physical construction of the membrane. We will extend these basic ideas to specific types of separations in latter sections. The fundamentals of diffusion across membranes include the effects of partition coefficients, concentration units, and resistances in series. The physical construction of membranes includes both the membranes themselves and the modules in which the membranes are used. The membranes themselves may be symmetric or asymmetric the modules include hollow fibers, spiral-wound elements, and plate-and-frame assemblies. 

In this section, we apply the general ideas of diffusion presented in the previous section to the separation of gaseous mixtures. In principle, these separations are straightforward one simply pumps a high-pressure mixture down one side of a membrane. The membrane is commonly a hollow fiber, though it can equally be a spiral-wound element or plate-and-frame array. Some components in the gas mixture dissolve in the membrane and diffuse across it faster than other components. The more permeable species can be collected in the permeate the less permeable species are concentrated in the retentate. 

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