Vertical heat exchangers

If severe heat-transfer requirements are imposed, heating or cooling zones can be incorporated within or external to the CSTR. For example, impellers or centrally mounted draft tubes circulate Hquid upward, then downward through vertical heat-exchanger tubes. In a similar fashion, reactor contents can be recycled through external heat exchangers. 

Certain corrosive conditions require that special consideration be given to complete drainage when the unit is talcen out of service. Particular consideration is required for the upper surfaces of tube sheets in vertical heat exchangers, for sagging tubes, and for shell-side baffles in horizontal units. 

Figure 9.20 Schematic representation of vertical heat exchanger showing location of cracks in the vapor space.

Falling-film absorbers. These are usually vertical heat exchangers with the cooling medium in the shell and the absorption taking place in the tubes. The solvent flows downward, while the gas may enter either at the bottom (countercurrent flow) or at the top (cocurrent flow). 

The distilled toluene vapours enter water cooler 17, a steel enameled vertical heat exchanger of the vessel in a vessel type with the heat exchange surface of 4 m2. There toluene condenses and is collected in collector 18, from where it self-flows into settling box 19. The settled toluene is sent to regeneration and re-used in manufacture. 

This condition was tested for water in columns with diameters up to 5.5 m and g varying between 0.1 ms-1 and lms 1. Further, is was found to be satisfactory for non-Newtonian slurries containing up to 10wt% of solids. The gas holdup may be affected by internals. For vertical heat exchange tubes present in the columns, Saxena et al. carried out an extensive research programme [39-43], The gas holdup increases if the internals in the column prevent bubble coalescence [43], Saxena et al. correlated their results in a relation based on the so-called drift velocity concept ... 

Vertical heat exchangers assembled on the internal wall of the combustor. 

Due to the liquid circulation caused by the stirrer in the tank, helical coils should only be used with axially operating stirrers (propeller and pitched-blade stirrers), which are, on the other hand, not suitable for gas dispersion. Thus in bioreactors vertical heat exchange tube bundles are preferably used as baffles (see Fig. 1.3c). Occasionally, baffles are executed as hollow bodies, so that they can serve as heat exchangers. 

The quality of cooling water and steam must he considered when selecting materials of construction. The chosen materials may be resistant on the process side, but fail on tbe utility side. For example, 316 stainless steel may be applicable for vertical heat exchanger tubing that handles a weak organic acid on the process side, but it may fail from chloride stress cracking on the waterside. A duplex stainless steel may be a better choice. 

A concrete well is formed in the lower part of each box to install the tank of passive heat removal system (PHRS). The reactor mono-block is installed inside the PHRS tank and is fixed on the support ring of the tank cover. Twelve immersible vertical heat exchangers are also installed in the PHRS tank to transfer heat from the PHRS tank water to the cooling water. 

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