Spiral-plate evaporators

The spiral assembly can be fitted with covers to provide three flow patterns  

Axial flow units perform well as natural circulation calandrias. Spiral-plate units are also effective for condensers and for heat recovery applications. 

---

Plate evaporators may be constructed of flat plates or corrugated plates, the latter providing an extended heat transfer surface and improved structural rigidity. Two basic types of heat exchangers are used for evaporation systems plate-and-frame and spiral-plate evaporators. Plate units are sometimes used because of the theory that scale will flake off such surfaces, which can flex more readily than curved tubular surfaces. In some plate evaporators, flat surfaces are used, each side of which can serve alternately as the liquor side and the steam side. Scale deposited while in contact with the liquor can then be dissolved while in contact with the steam condensate. There are still potential scaling problems, however. Scale may form in the valves needed for cycling the fluids and the steam condensate simply does not easily dissolve the seale produced. 

Spiral-plate evaporators may be used instead of tubular evaporators, and offer a number of advantages over conventional shell-and-tube units centrifugal forces improve heat transfer the compact configuration results in a shorter liquid pathway they are relatively easily cleaned and resistant to... 

Modules Eveiy module design used in other membrane operations has been tried in peivaporation. One unique requirement is for low hydraulic resistance on the permeate side, since permeate pressure is veiy low (O.I-I Pa). The rule for near-vacuum operation is the bigger the channel, the better the transport. Another unique need is for neat input. The heat of evaporation comes from the liquid, and intermediate heating is usually necessary. Of course economy is always a factor. Plate-and-frame construc tion was the first to be used in large installations, and it continues to be quite important. Some smaller plants use spiral-wound modules, and some membranes can be made as capiUaiy bundles. The capillaiy device with the feed on... 

Like evaporators, RO works on most plating baths and rinse tanks. Most RO systems consist of a housing that contains a membrane and feed pump. There are four basic membrane designs plate-and-frame, spiral-wound, tubular, and hollow-fiber. The most common types of membrane materials are cellulose acetate, polyether/amide, and polysulfones.29... 

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 ... 

The use of evaporation to increase the driving force allows one to use a highly selective membrane and still retain a reasonable flux. However, evaporation complicates both the equipment and the analysis. Typical permeate pressures are quite low (0.1-100 Pa) tLeeper. 1992T Because of this low pressure, permeate needs a large cross-sectional area for flow or the pressure drop caused by the flow of the permeate vapor will be large. Thus, plate-and-frame, spiral-wound, and hollow fibers with feed inside the fibers are used commercially. Figure 17-13 shows that a vacuum pump and a condenser are required... 

Should high temperature be necessary for pyrolysis or to accelerate a reaction, the TLC plate is laid on an aluminium plate, itself lying on an asbestos mat. The layer is then heated with an infra red heater at a distance of 10—20 cm. The so-called quartz surface evaporator (30 cm diameter) has proved most useful in our work (Firm 70). The heating spirals reach temperatures up to 800° C and, like the quartz reflector, are not attacked by the usual acid vapours. Heidbbink [284] has recommended in connection with pyrolysis of the substances, that the chromatograms should be previously placed in a atmosphere of gas, e. g., CI2, Brg NOg. 

---