Plate-and-frame exchangers are an arrangement of gasketed, pressed metal plates aligned on carrying bars and secured between two covers by compression bolts. The pressed metal plates are corrugated in patterns to provide increased surface area, to direct the flow in specific directions, and to promote turbulence. The plates are gasketed such that each of the two fluid streams flow in parallel between alternate pairs of plates. In addition to directing the flow patterns, the plate gasket keeps the fluids retained within the plate pack. Figure 3-13 shows a plate-and-frame exchanger.
Major advantages of plate-and-frame exchangers include the following: They have a low cost (especially for corrosive service), they are lighter and smaller than comparable shell-and-tube heat exchangers, full counter current flow and an LMTD correction factor are not required, and a close temperature approach is possible. Standard components allow simple stocking of spare parts, low maintenance, easy accessibility, and easy expansion by adding more plates. Metal plate-and-frame exchangers are particularly attractive for seawater and brackish water services. However, because of the design of plate-and-frame exchangers, wherein fluids are separated and retained across gasketed surfaces, they are limited to moderate temperature and pressure applications. In addition, some operators do not allow the use of plate-and-frame exchangers in hydrocarbon service or limit their use to pressures below 150 psig to 300 psig and temperatures less than 300°F. Plate-and-frame exchangers cannot be used for high viscosity liquids and slurry/suspended solids.
Because the plates are made of thin pressed metal, materials resistant to corrosive attack can be easily selected. Plates are standard and mass-produced. Specific applications are dealt with by changing plate arrangements. Stainless steels, monel, titanium, aluminum bronze, and other exotic metals may be used if desired. It is important to select the gasket materials to be compatible with the fluids and temperatures being handled.
