Design of Shell and Tube Heat Exchanger with Super Heated Steam

Depending on the orientation of the exchanger and amount of superheat, you may not need excess margin. In a plant I am most familiar with, many distillation reboilers were vertical-tube, thermosyphon with steam on the shell side. The steam was supplied by turbine exhaust and from let-down stations and often had 50 degF or more superheat. Several times, concerns of fouling due to excess temperature in the superheat zone as well as excess area requirements were raised; however, none of them I recall were valid. The reasoning usually followed this logic: The steam inlet is some distance down from the top tubesheet, due to mechanical construction constraints. There is steam in this zone which has given up some of its heat, and is therefore saturated or even wet. The incoming steam moving up to fill this zone mixes with the wet steam and condensate draining down, effectively desuperheating the steam before it reaches a substantial area of the tubes. If you have access to Kern's Process Heat Transfer, on page 282 there is some discussion around this point.

Obviously, your situation may be different. Particularly, if the superheat represents a high % of the total enthalpy, I think.

Type of Heat from super-heated steam to saturated steam is sensible heat whereas from saturated steam to condensation it is latent heat. In some applications like refrigeration air cooled condensers sub cooling increases the refrigeration effect.

what do you expect of your exhaust "steam" be? still superheat?saturated? or sub-cooled?

first, it would be helpful to plot your process in the T-L (temperature vs length of heat exchanger) diagram indicating the inlet and outlet conditions (or in each state point i.e., superheat, saturated and sub-cooled) of your working fluids (both steam and the heated fluid) for easy appreciation and calculation. determine the log mean temp diffrence and the rest of the parameters for the design.

good luck!