Plate exchangers of heavy-duty design and used in demanding environments such as boilers firing oil, coal, wood or solid waste fuels, metallurgical furnaces, etc. are units specially designed to alleviate following deficiencies of tubular exchangers:

1. direct impact of dust particles on heat transfer surface
2. flow separation at the rear of the tube
3. stress of tube to tube-sheet connection

Deficiency 1 can result in premature erosion and corrosion of the heat transfer surface.

Figure 1

Figure 2

Figure 1 shows the erosion strength of a particle function of the angle of impact on the surface. The highest erosion strength occurs at 30° and remains high between 20° and 90°. In figure 2 we can see that a tube is exposed to these angles of attack for most of the front area of the tube. This fact is limiting considerably the maximum gas velocity for the design of the tubular exchangers. In certain cases the direct impact of the dust particles on the tubes can also accelerate the corrosion (scaling) rate of the tube.

Deficiency 2 can equally result in accelerated erosion and corrosion at the rear side of the tube.

Figure 3

Figure 3 shows the separation zone for the gas flow around the tube. The vortices behind the tube create a fluctuating flow condition. These frequent fluctuations of gas velocity on the heat transfer surface and the direct impact of the dust particles entrained in the vortex create favourably conditions for high rates of erosion and corrosion. This aspect has been proven by numerous researchers based on both laboratory tests and field data. Deficiency 3 is inherent to tubular designs. Indeed, the tube to tube-sheet connection is characterized by severe stress concentrations. Due to the rigidity of the tube-sheet these concentrations of stress cannot be relaxed (e.g. by plastic deformation) and will eventually result in fatigue cracking after a relative short number of operating cycles, particularly at high temperatures.

CORPEX™ plate-type exchangers alleviate these deficiencies as explained below.

A. NO IMPACT OF DUST PARTICLES ON HEAT TRANSFER SURFACE

Figure 4. CORPEX™ flow channel

In the design of CORPEX™ exchangers we have totally eliminated any direct impact of dust particles on heat transfer surface. Figure 4 demonstrates this concept. The heat transfer core is provided with replaceable caps at both inlet and outlet of the channel. Only these caps are exposed to angles of impact larger than 0°. All heat transfer surface is exposed to 0° angle of impact of dust particles. This is a major improvement, which allows designing for gas velocities larger than in the case of tubular designs.

The direct results of this lack of impact are: