Plate exchangers

Fouhng factors are typically Mo of TEMA values or a percent oversurfacing of 10-20 percent is used. ( Sizing Plate Exchangers Jeff Kernel, Chemical Engineering, November 1993). 

A spiral-plate exchanger is fabricated from two relatively long strips of plate, which are spaced apart and wound around an open, split center to form a pair of concentric spiral passages. Spacing is maintained uniformly along the length of the spiral by spacer studs welded to the plate. 

Spiral-plate exchangers are fabricated from any material that can be cold worked and welded. Materials commonly used include carbo steel, stainless steel, nickel and nickel alloys, titanium, Hastelloys, and copper alloys. Baked phenolic-resin coatings are sometimes applied. Electrodes can also be wound into the assembly to anodically protect surfaces against corrosion. 

The spiral-plate exchanger usually should not be used when a hard deposit forms during operation, because the spacer studs prevent such deposits from being easily removed by mechanical cleaning. When, as for some pressures, spacer studs can be omitted, this limitation is not present. 

Other types of plate-and-frame heat exchangers are double-wall-plate exchangers, welded-plate exchangers, wide-gap-plate exchangers, and brazed-plate exchangers. Each type is briefly described below. 

At a 12.5 psi pressure drop in water to water applications, the surtoce heat transfer rote achieved in a Graham plate exchanger exceeds that of a shell and tube unit by a factor of 3.4. Similar or higher improvement toctors are obtained with other fluids. 

A spiral plate exchanger is illustrated in Figure 9.90 in which two fluids flow through the channels formed between the spiral plates. With this form of construction the velocity may be as high as 2.1 m/s and overall transfer coefficients of 2.8 kW/m2 K are frequently obtained. The size can therefore be kept relatively small and the cost becomes comparable or even less than that of shell and tube units, particularly when they are fabricated from alloy steels. 

Figure 9.90. Spiral plate exchanger (b) with cover removed...

It is possible to calculate U through Eq. (12.3), the global heat-exchange co-eflicient. Table 12.7 presents the experimental results. U varies from 3900 to 5000 W m and has a mean value of 4500 W m These values are in the same order of magnitude of the coeffleients obtained in plate exchangers and are higher than the ones obtained in tubular reactors, and far away from values measured in batch reactors. 

Alloying with palladium (0.15 per cent) significantly improves the corrosion resistance, particularly to HC1. Titanium is being increasingly used for heat exchangers, for both shell and tube, and plate exchangers replacing cupro-nickel for use with sea water. 

FIGURE 6.3 /iPLC system with automatic plate exchanging mechanism. 

Use of plate exchangers to exchange process heat with cooling water circuit. 

Figure 8.8. Plate and spiral compact exchangers, (a) Plate heat exchanger with corrugated plates, gaskets, frame, and corner portals to control flow paths, (b) Flow patterns in plate exchangers, (i) parallel-counter flows (ii) countercurrent flows (iii) parallel flows throughout, (c) Spiral exchanger, vertical, and horizontal cross sections.

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