Keeping your shell and tube heat exchanger contaminant-free is critical to creating a high-quality final product. However, every company must face a hard (and sometimes calcified) reality: Fouling happens. When it does, the built-up matter needs to be removed, and the equipment sanitized.
Of course, there are some downsides to cleaning your shell and tube heat exchanger. The process usually needs to be done offline, thus eliminating some production time. Reducing the number of hours your equipment is productive will have an impact on your company's bottom line. Then again, so will fouled material if allowed to continue to build up in your equipment. Further, excessive buildup will reduce heat transfer efficiency, causing processes to increase in price and length of time.
Thus, equipment operators must strike a balance between regular cleaning times and fouling accumulation. To make sure your shut-down day has as low an impact on your business as possible, take these factors into consideration when planning your cleaning schedule:
The Tubular Exchanger Manufacturers Association recommends that companies determine well in advance what they would consider an allowable amount of fouling and take these into consideration when calculating heat transfer resistance, as well as determining a cleaning schedule, according to Conoco Consulting Corp. When your level of fouling nears this level, you'll know it's time to plan your next shut-down day, though you'll usually define a loose maintenance schedule when calculating your fouling allowance.
Engineers typically determine the allowable amount of fouling during the design stage, according to InTechOpen, an open access science, medical and technology book publisher. This is an important factor to take into consideration when calculating the heat transfer coefficient. A higher fouling allowance will result in a lower coefficient, but may also result in fewer necessary cleaning days.
Fouling allowance can be thought of in several different ways, including a percentage of fouled matter as compared to the overall surface area, how clean the equipment is or what the maximum fouling resistance should be.
Cost of operation
Keeping a close eye on the cost of your operations is a good indicator of efficiency and productiveness. As fouling builds up, so too will your cost of operations per hour. The increase in cost is due to greater energy needed to achieve the same heat transfer rate, a lower rate of production, or a combination of the two.
Referencing a 1981 report, "Optimum Cycles for Falling Rate Processes," published in The Canadian Journal of Chemical Engineering, Conoco Systems suggested determining when your process will reach its minimum value to the company. When calculating this, you'll need to take several factors into consideration, including the cost of cleaning, the cost of the lost production time and any interest accumulated due to borrowed funds, if applicable. Compare all this to the cost of reduced efficiency of the heat exchanger.
Your production cycle
No one knows your production cycle better than you and the people at your company. You know when your busy seasons are and when business slows down, as well as when you'll have three-day weekends. Use this knowledge when planning out your cleaning schedule.
With this information, you'll be able to choose a day or several days to shut down your plant for much-needed cleaning without taking away from a busy or usually productive day. Additionally, you know your staff won't feel pressured to make up for lost production time when everything is shiny and new once more. If it makes sense to schedule cleaning over a three-day weekend, take advantage of the day off and turn it into a day offline.
Every operation is different and will require different intervals between cleaning. Some plants may require multiple shut-down days each year; others might be able to hold off for a decade using effective fouling mitigation tactics and discretionary maintenance tasks. It's important to decide what's right for your company so you can ensure consistent quality at as low a cost of production as possible and with minimal disruption to normal business operations.
If you're in the market for a new shell and tube heat exchanger, reach out to the helpful engineers at Enerquip. When you explain your operation and needs, they'll be able to work with you to design and fabricate a custom shell and tube solution that works.