The function of a heat exchanger in the processing environment is pretty straightforward. Typically it involves cooling one location by moving the heat being generated to another location that needs an increase in temperature. Where things get a bit more complicated is that these devices are needed in applications that can be as simple as an automotive radiator to those as complex as an anaerobic digester used in the creation of biofuels.
Just like all processing equipment, the demands for improved energy efficiency standards and enhanced performance requirements from products with a smaller footprint have been key heat exchanger developments. And one of the most popular ways to realize these gains has been through the implementation of new and improved materials used in heat exchanger design and production.
Although improving overall operational efficiency continues to be a driving force, additional factors, such as pressure tolerances, temperature range, the ability to handle a varying degree of media, flow capacity and cleanability, are also key ingredients impacting the composition mix of new heat exchanger technology. By delivering in all these areas, facilities not only benefit from improved performance in managing and delivering heat, but also in reducing production downtime, and exposure to product or system failure.
Polymer Power
Due to the harsh nature of many chemicals, shell and tube-type heat exchangers used in such processes are usually composed of fluoropolymers. Fluoropolymers offer greater versatility and corrosion resistance in handling exposure to more aggressive substances, which are typically in fluid form. Examples of such polymers include PTFE, PFA, FEP and PVDF.
While the use of such materials is far from revolutionary, the manner in which these materials are being used has helped in improving efficiency, cutting costs and decreasing the equipment’s overall size. This is important to remember as elements like heat exchanger tube diameter, thickness, corrugation and length all play a role in specifying the right exchanger for a given application.
The wider-spread use of these polymers, as either a liner or in a more expanded role, and their improved performance, have helped decrease maintenance concerns, extend heat exchanger product life, and allow these units to operate in more demanding temperature- and pressure-based applications.
Heavy Metal
The technology behind printed circuit heat exchangers and the diffusion-bonded nature of their composition has been around for more than 20 years. However, the wider-spread use of these plate-type heat exchangers has also been key in helping many facilities realize significant benefits as they consume less space, accommodate greater heat and pressure tolerances, and can handle a wider variance of media, regardless of their caustic nature.
The more rugged nature of these exchangers stems, in part, from their composition. Diffusion-bonded heat exchangers are constructed from flat metal plates, with fluid flow channels either chemically etched or pressed into place. The exact configuration of these channels depends upon temperature and pressure-drop constraints.
The plates are then stacked and pressed together at a temperature just beneath the melting point to form a stronger, more compact core. These stacks of plates are converted into solid blocks that contain the flow passages. The blocks are then welded together to form the complete heat exchanger core.
The metal used for these heat exchangers has expanded in recent years to include a wider variety of options that can reflect preferences based on application and, of course, cost:
- Carbon steels. The main benefits here are a lower cost and very good thermal conductivity.
- Chromium-molybdenum steels. They have better oxidation-resistant qualities, but their thermal conductivity is lower, and they are more expensive than carbon steels.
- Ferritic stainless steels. They offer higher thermal conductivity and a lower thermal expansion coefficient, and are less expensive than other materials for the same service. These steels do well in resisting oxidation, as well as sulfur and carbon-containing flue gases. The one drawback is that they lose strength after lengthy exposure to high temperatures.
- Austenitic stainless steels. They’re considered the strongest among steels for use at high temperatures and do not lose strength after very long usage at high temperatures. They also resist oxidation at high temperatures, but are more expensive.
The takeaway in examining these heat exchanger composition trends is to reinforce the importance of fully understanding your application, and how these new and enhanced material options can positively impact your facility’s outcomes. By knowing more about what’s inside these heat exchangers, plant personnel can better understand how such products can aid in improving energy usage, while consuming less physical space and reducing maintenance intervals — all of which are obvious key factors influencing output.
