There are different types and brands of heat exchangers, so how do you pick a model for your petrochemical plant?
The Basics: Introduction to Heat Exchangers
According to Hydrocarbon Processing, of all the process operations in a refinery or petrochemical plant, heating and cooling streams are perhaps the most pervasive. “A typical refinery has anywhere from 200 exchangers, on the low end, to almost 350 for a large, complex refinery,” the publication states.
A heat exchanger, also called a sample cooler, is used to cool process stream samples. Each heat exchanger is a uniquely designed small tube within a shell. The fluid that must be cooled flows through the tube side, and the cooling fluid – usually water – flows through the shell side. A grab sample then can be taken of the cooled fluid, and/or it can be analyzed or piped to in-line process instrumentation for continuous monitoring of chemical properties.
As their name implies, heat exchangers can both cool and heat water, steam, gases and hydrocarbons within a petrochemical plant. For example, petrochemical plants often produce volatile hydrocarbon samples exceeding temperatures of 500°F (260°C) that need cooling, while other fuels, such as diesel, may need to be heated before being sent to a diesel generator.
Within a petrochemical plant, liquids generally do not need to be heated, and heating may change the physical properties of a liquid so it would no longer serve as a representative sample. However, many liquids and gases/vapors within a petrochemical plant – including various glycols, olefins such as ethylene, propylene or butadiene, isomers such as benzene, toluene or xylene, and natural gas liquids (NGLs) such as ethane, propane and butane – need to be cooled. Fortunately, the right heat exchanger can cool any liquid or vapor.
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Choosing the right heat exchanger
Heat exchangers generally feature one to five square feet of heat transfer surface, but spiral heat exchangers can be designed for more heat transfer surface if required. For safety and plant efficiency, it’s critical to choose the right heat exchanger for the right application. Things to consider:
- the specific type and viscosity of fluid to be cooled or heated
- the process fluid or gas temperature
- flow rate
- liquid or gas phases
Different sample cooler designs offer different tube and shell diameters and materials, wall thicknesses or lengths, and designed to meet varying requirements such as a Canadian Registration Number (CRN), Pressure Equipment Directive (PED), TÜV, ASME Section VIII, and Material Test Reports (MTRs). Types of heat exchangers include:
Single Helical Tube
A compact heat exchanger with high efficiency for cooling high temperature and/or high pressure liquid or gas samples, this is the highest efficiency heat exchanger commercially available. It can handle temperatures to 1100°F at 5000 psig (593°C at 345 bar) and can be made to specification in a wide range of materials and configurations to meet EPRI/ASTM/ASME guidelines, with many models available with the ASME section VIII code stamp, CE or CRN registrations.
With high efficiency in a small footprint for high pressure applications, this type of heat exchanger consists of a multi-tube spiral assembly inserted into a shell, where two paths are created for full counterflow heat transfer that is more efficient than a typical shell and tube heat exchanger. Its spring-like design means it can handle pressure ratings up to 10,000 psi (689 bar), and temperature ratings up to 1000°F (540°C). It is compact and lightweight, and highly resistant to thermal and pressure shock.
Dual Tube Coil (DTC)
A helically wound tube-in-tube full counterflow design for a variety of lower flow applications, this heat exchanger has a fully drainable inner and outer coil with no dead spots or crevices. It is available in a wide variety of materials.
Learn more about heat exchangers for petrochemical plants.