Heat exchangers regenerator

The use of copper and copper alloys should be avoided. The corrosiveness of a rich amine solution is the highest in the case of hydrogen units and town gas units, where only COj is handled, and moderate in the case of FCC units where COj + HjS (H2S/(C02 + HjS) = 0.01) is handled, and lowest in the case of hydrodesulfuiization, where only HjS is handled. Equipment that undergoes maximum corrosion are lean/iich heat exchangers, regenerators, reboUers, reclaimers, and overhead condensers. 

Regenerative heat exchangers of both the fixed-bed and moving-bed types (67) have been considered for MHD use. The more recent efforts have focused on the fixed-bed type (68), which operates intermittently through recycling. A complete preheater subsystem for a plant requites several regenerators with switch-over valves to deflver a continuous supply of preheated air. The outlet temperature of the air then varies between a maximum and a minimum value during the preheat cycle. 

Phtnalic anhydride is made by oxidation of naphthalene at temperatures of 340 to 380°C (644 to 716°F) controlled by heat exchangers immersed in the bed. At these temperatures the catalyst is stable and need not be regenerated. The excellence of temperature control was a major fac tor for the adoption of this process, but it was obsolesced by 1972. 

In a recuperative heat exchanger, each element of heat-transferring surface has a constant temperature and, by arranging the gas paths in contra-flow, the temperature distribution in the matrix in the direction of flow is that giving optimum performance for the given heat-transfer conditions. This optimum temperature distribution can be achieved ideally in a con-tra-flow regenerator and approached very closely in a cross-flow regenerator. 

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