Heat exchangers are used throughout the petrochemical industry. Selecting the right type — and understanding why it suits the duty — prevents premature failure, improves energy efficiency and avoids unplanned shutdowns and product loss.

1. Heat pipe exchangers

Heat pipe exchangers are widely used for waste heat recovery under harsh conditions, including high-sulphur fuel production. High-temperature heating and cracking units are critical to the process: the flue gas of a naphtha cracker for light olefins, for example, leaves at 200–400 °C. An air preheater of the heat pipe type uses the residual heat of that exhaust gas to preheat combustion air, which both saves energy and reduces emissions. Combined arrangements of several tubular exchanger types are now common practice and deliver good energy-saving results.

2. Spiral baffle exchangers

The spiral baffle exchanger is a modern, high-efficiency unit used worldwide. China's petrochemical industry began adopting it in the 1950s and by the mid-1960s was producing it in volume. Compared with conventional exchangers it offers a high heat transfer coefficient and a self-scouring effect that resists fouling deposition. It handles heating and cooling of alcohols, resins, urea, light olefin monomers, gasoline and diesel, ammonia water, chlorine water, brine, strong acids and alkalis, and nitrogen-hydrogen-ammonia gas mixtures.

3. Thin-film evaporators

Thin-film evaporators are used for caustic soda concentration, sodium sulphide evaporation and the drying of resins and rubbers. Compared with conventional cast-iron vessels they offer:

1) a small footprint, mechanised evaporation and simple, efficient operation;

2) strong heat transfer driven by the rotor scraper, with a short surface residence time, so scaling and coking are largely avoided and deposits are easy to remove;

3) a heat transfer oil furnace that consumes far less coal and saves energy;

4) easier scale-up, replacing batch vessels and reducing error during industrialisation.

There are limits. The groove scraper is normally PTFE, which resists corrosion but not high temperature — graphite or similar materials should be used instead. The process line is seamless tube and traditionally had to be replaced monthly; stainless steel or corrosion-resistant lined pipe, such as a fluoroplastic-lined exchanger, avoids this.

4. High-efficiency plate exchangers

Petrochemical duties demand high pressure and high temperature. Welded plate exchangers are compact, light, easy to install, low in cost and excellent in heat transfer, which makes them popular offshore — cooling lubricating oil and fresh water, cooling intermediate products at the well site and heating crude oil. The limitation is that the process is hard to model precisely; a poorly designed flow path can cause significant loss. Resistance analysis of the cooling plate exchanger, assuming a linear liquid distribution along the channel, allows the relationships between channel length, actual mass vapour fraction and volumetric vapour fraction to be simulated against real data. Because partial condensation forms a liquid film on the surface, a compact type such as the plate-fin unit should be considered, and the geometry — not only surface area and margin — must be matched to the duty.