Heat exchangers used in gas production facilities are shell-and-tube, double-pipe, plate-and-frame, bath-type, forced-air, or direct-fired. In this chapter we will discuss the basic concepts for sizing and selecting heat exchangers. This is just a brief overview of this complex subject and is meant to provide the reader with a basis upon which to discuss specific sizing and selection details with heat exchange experts in engineering companies and with vendors.
Bath-type heat exchangers can be either direct or indirect. In a direct bath exchanger, the heating medium exchanges heat directly with the fluid to be heated. The heat source for bath heaters can be a coil of a hot heat medium or steam, waste heat exhaust from an engine or turbine, or heat from electric immersion heaters. An example of a bath heater is an emulsion heater-treater of the type discussed in Volume 1. In this case, a fire tube immersed in the oil transfers heat directly to the oil bath. The calculation of heat duties and sizing of fire tubes for this type of heat exchanger can be calculated from Heat Transfer Theory.
In an indirect bath heat exchanger, the heating medium provides heal to an intermediary fluid, which then transfers the heat to the fluid being heated. An example of this is the common line heater used on many gas well streams to keep the temperature above the hydrate formation temperature. A fire tube heats a water bath, which provides heat to the well stream flowing through a coil immersed in the bath.