Reboiler types forced-circulation

Advantages and disadvantages will in general correspond to the type of reboiler to which forced circulation is applied. The advantages and disadvantages shown are in addition. 

Reboilers are heat exchangers that are used primarily to provide boilup for distillation and similar towers. All types perform partial vaporization of a stream flowing under natural or forced circulation... 

Forced circulation reboilers may be either horizontal or vertical. Since the feed liquid is at its bubblepoint, adequate NPSH must be assured for the pump if it is a centrifugal type. Linear velocities in the tubes of 15-20 ft/sec usually are adequate. The main disadvantages are the costs of pump and power, and possibly severe maintenance. This mode of operation is a last resort with viscous or fouling materials, or when the fraction vaporized must be kept low. 

Forced-circulation reboilers are especially suitable for handling viscous and heavily fouling process fluids see Chantry and Church (1958). The circulation rate is predictable, and high velocities can be used. They are also suitable for low vacuum operations and for low rates of vaporization. The major disadvantage of this type is... 

The common types of reboilers (Fig. 15.1) are vertical thermosiphon, horizontal thermosiphon, forced-circulation, kettle, and internal. The advantages and disadvantages of each type are compared in Table... 

Kettle-type reboilers are sometimes used with vacuum columns. They eiiminace the need for the circulating pump required with a forced-circulation reboiler, and avoid the temperature elevation cncoimtered in the lower end of a thermosyphon reboiler. The usual arrangement is that of the flooded-bundle type... 

Evaporators employ heat to concentrate solutions or to recover dissolved solids by precipitating them from saturated solutions. They are reboilers with special provisions for separating liquid and vapor phases and for removal of solids when they are precipitated or crystallized out. Simple kettle-type reboilers [Fig. 8.4(d)] may be adequate in some applications, especially if enough freeboard is provided. Some of the many specialized types of evaporators that are in use are represented on Figure 8.16. The tubes may be horizontal or vertical, long or short the liquid may be outside or inside the tubes, circulation may be natural or forced with pumps or propellers. 

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