Clean slate? Clean plates!
How to know when it’s time to replace your heat exchanger plates
Author: Jamie Zachary
It’s a time of renewed optimism and fresh beginnings. Perhaps a few resolutions, too?
The new year represents a clean slate for your plant’s equipment, including your moving bed heat exchanger (MBHE).
In cases that involve vertical plate technology, that includes the plates themselves, which likely saw plenty of front-line action over the past 12 months and might be showing early signs of aging.
How do you know it’s time to replace your plates?
Although it is the least likely scenario, the most obvious sign that a plate needs to be replaced is if it’s leaking.
Yet a visual inspection can also indicate that a plate may need to be replaced. In addition to dents or gouges caused by foreign objects (e.g. from broken pieces from upstream equipment, cleaning tools, etc.) areas of a plate that looked “over polished” or have localized striations are indications of accelerated wear.
“Two things I look at are the smoothness of the plate dimple circular welds and the condition of the protective plate caps, if applicable. If either are worn smooth, that’s an early indicator that the plates need to be more thoroughly inspected and, potentially, replaced,” says Peter Menchenton, Vice President, Operations at Solex. (It is recommended to contact Solex prior to replacing a plate as, in many cases, worn or damaged plates can be repaired and put back into service.)
How does wear occur?
Menchenton notes that plates can be prone to accelerated wear over time if the heat exchanger is not operating properly.
“One of the root causes of accelerated wear is product blockages. Our moving bed heat exchangers are designed to operate most effectively when the product is moving uniformly through the unit,” he says.
“Obstructions within the plate bank of a heat exchanger reduce the cross-sectional area in these sections. If the feed rate remains constant, product velocity increases and ramps up the wear rate exponentially.”
Menchenton adds increased product velocity not only increases plate wear, but can cause temperature variations at the outlet, potentially resulting in product that doesn’t meet optimum downstream process or storage requirements
Jason Gass, Technical Design & Project Specialist at Solex, notes accelerated plate wear also occurs if the product level in the heat exchanger is too low and the top of the plates are exposed to a falling product stream
“The impact velocity can be five to 10 times greater on the edges of those plates versus if the plates were fully submerged, and this can dramatically increase the wear rate,” he says, recommending regular inspections of the level probe throughout the year.
Additional causes of plate wear
The abrasiveness of different materials can also impact plate wear. Oilseeds such as rapeseed or canola, for example, are extremely hard and durable, and can therefore be abrasive on plates when moving outside of recommended velocities. This is compounded when these materials come into the units with foreign material such as chaff, which can also cause blockages.
Lastly, heat exchanger plates are subject to wear on the inside, as well. To recap . . . MBHEs that use a vertical plate design cool different materials by conduction. Free-flowing particles enter the exchanger and slowly pass between a parallel series of plates that contain a counter-current flow of water or other heat transfer fluids. Heat transfers from the material to the heat transfer fluid via the steel plate wall.
When the heat transfer fluid is compromised – for example, it contains higher-than-desired concentrations of chlorides or compounds that corrode stainless steel – then the plates can be slowly eaten from the inside. This typically occurs in situations involving open-loop systems: for example, water from cooling towers.
“In short, plates can either be eaten from the inside or worn down on the outside,” says Menchenton. “Routine inspection and monitoring are relatively inexpensive but effective methods of reducing failure risk.”
The benefits of regular maintenance
Gass recommends the key to getting the most out of heat exchanger plates is making sure the unit is regularly maintained.
Also, make sure the upstream cleaning systems upstream of the heat exchanger are working properly.
“And finally, it’s important the unit operates as it was designed – that means avoiding drastic increases to the velocity of material going through it,” says Gass.
“If the material is coming in at the rate and quality that the unit was designed for, and the quality of the heat transfer fluid is maintained, plates can easily last upward of 15 to 20 years or longer.”
Do you have additional questions about how to service your heat exchanger? Or do you need to order spare/replacement parts? The Solex Technical Services department is here to help maximize operational availability and reduce your operating and maintenance costs.
Contact a member of our team today!
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This entry was last updated on 2022-1-12
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