Heat Exchanger – Page 2 – What Is Piping: All about Piping Engineering

What is a Reboiler Reboilers are a typical heat exchanger that produces vapor to drive fractional distillation separation. In classical fractional distillation services, all the vapor to drive the separation comes from the reboiler. (Alternatively, externally generated vapor, feed preheat, or inter-reboiler systems may be used). Proper reboiler operation is vital to effective distillation. The selection of the proper type of reboiler for any specific service is the most difficult job of reboiler design. Reboilers normally are shell-and-tube exchangers that heat up the fractionation column fluid utilizing the heat transfer from steam. Specific services may use other specialized designs including stab-ins, plate-fins, spiral-plate, and others. The purpose here is not to go into the design details of each specific type but rather to examine the selection criteria that favor one configuration over another. Since shell-and-tubes are so common, most of the discussion focuses on them but some factors favoring other designs are covered as well. Factors influencing Reboiler Type Selection Many factors influence reboiler type selection. In the end, all these factors reduce economics. Every plant will weigh the trade-off between these factors differently. No one-size-fits-all selection exists. Major factors include: Plot space availableTotal duty requiredThe fraction of tower liquid traffic vaporizedFouling tendencyTemperature approach availableTemperature approach requiredCorrosion of the fluid.Design temperature and Pressure.Characteristics of the reboiler boiling fluid.Heating medium requirements. Reboiler Configurations All of the above-mentioned factors affect the desired configuration of the Reboiler. The major configuration selections include: Forced reboiler versus natural circulation reboilerTube side versus shell side vaporization inside reboilerOnce-through versus process recirculation reboilerSingle-shell versus multiple-shell systemsVertical versus horizontal reboilerStab-in bundlesOther types Figures 1 to 4 show common types of reboilers. Figure 1 shows two horizontal, shell-side boiling configurations. Figure 1A is a recirculating thermosyphon reboiler. Figure 2A is a once-through thermosyphon reboiler. Figure 2 shows vertical configurations. Figure 2C is a tube-side boiling configuration with the once-through flow and Figure 2D is a shell side boiling recirculating thermosyphon. Figure 3E shows a kettle reboiler and Figure 3F shows a forced-circulation reboiler. Figure 4G illustrates a stab-in bundle and figure 4H shows a forced-circulation, fired heater. Fig.1: Horizontal Shell Side Boiling Reboilers Fig. 2: Vertical Reboilers Fig. 3: Flooded bundle reboilers Fig. 4: Stab-in and fired heater reboilers Reboiler Type Selection Table Table 1 includes the major factors in making a choice for the reboiler type selection. FactorFavored typesDisfavored typesLow bottoms product fraction compared to boil-upRecirculatingKettleOnce-throughHigh bottoms product fraction compared to boil-upOnce-through reboilerRecirculatingLow relative volatility systemsRecirculating High relative volatility systemsOnce-throughRecirculatingLarge exchanger size or high duty requirementsHorizontal reboilerVertical reboilerSmall exchangersVerticalStab-in Leaks hazardous or difficult to deal withStab-in Exotic materialsStab-in Tight temperature approachSpiral-platePlate-finShell-and-tubeSolids presentKettleSpiral-platePlate-finThermally unstable productsRecirculating (no baffle)KettleOnce throughTight plot planVerticalHorizontalAmple plot planHorizontal High temperaturesFired heaters High heat fluxesForced circulationFlooded bundlesNatural circulationTable. 1: Reboiler type selection table Other systems in addition to the ones shown here are also possible. Of course, every reboiler system's final choice will depend upon specific design details involved. Many reboiler systems have specific characteristics that favor designs that might not be immediately apparent. Few more resources for you… Piping Design and Layout Piping Stress Analysis Piping Materials Piping Interface Further Studies https://en.wikipedia.org/wiki/Reboiler https://www.chemicalprocessing.com/articles/2012/select-the-right-reboiler/