Where processes use heat, you will normally find heat exchangers. They come in all shapes and sizes, but plants depend on them, and they can cost a lot to operate. Brian Joe is one of the leading promoters of Plantweb Insight within Emerson, and he likes to talk about how adding sensors able to communicate data via WirelessHART to Plantweb Insight analytics platforms can help reduce costs and improve heat exchanger performance.
Last January 2019 he wrote an article for Process Heating magazine (Read the earlier blog post here.) explaining how that approach can be applied to air-cooled heat exchangers. Brian wrote a follow-up article for the March 2019 issue, Improving Heat Exchanger Performance Via Wireless Technology, where he examines how the same technologies can be applied to liquid-to-liquid closed-system heat exchangers.
Two of the most common configurations are shell-and-tube and plate heat exchangers. Shell-and-tube designs send the process fluid (usually a liquid) through a group of parallel tubes that are enclosed by a shell. The transfer fluid flows around inside the shell as directed by baffles, and heat is transferred through the tube walls. Plate heat exchangers use a stack of alternating-shaped plates that seal around the outside edges to form liquid passages. There are additional passages in the corners that allow the process and transfer fluids to flow between alternate plates.
So how can operators improve performance from these installations? Every heat exchanger has its theoretical maximum, but many have much room for improvement.
Monitoring the critical temperature, flow and pressure variables in a heat exchanger with WirelessHART instruments provides the data required for analysis to optimize operation and maintenance. Using preconfigured apps to perform the analysis greatly simplifies this task. When combined, these two technologies substantially simplify the task of improving heat exchanger performance.
The ways these technologies are applied differ somewhat between air-cooled and liquid-cooled heat exchangers, but ultimately, it’s all about promoting the most effective interface between the two sides of the exchanger.
Creating conditions for effective heat transfer with any equipment configuration depends on two things: fully distributed fluid flow and unimpeded heat transfer. Fluid flows must be continuous and spread out over the entire surface area. Movement creates turbulence, avoiding the formation of thermal barriers and boundary layers where much of the liquid is kept away from the actual transfer surface. The heat transfer surface must be free of any deposits that can serve as insulation. Sometimes, these are carried and deposited by the liquids, or they may be the result of corrosion. Any solids on the metal on either side can reduce the heat transfer effectiveness. If the deposits are thick enough, they also can impede flow, compounding the problem.
Instrumentation, when applied effectively, can provide data, which when analyzed using Plantweb Insight can indicate the level of efficiency and where problems may be developing. Both articles provide more detailed suggestions, so give them a read.
You can find more information like this and meet with other people looking at the same kinds of situations in the Emerson Exchange365 community. It’s a place where you can communicate and exchange information with experts and peers in all sorts of industries around the world. Look for the Condition Monitoring and IIoT Groups, and other specialty areas for suggestions and answers.
Posted by Deanna Johnson, Rosemount Measurement & Analytical Global Marcom Manager, Emerson Automation Solutions
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