Bottom Tube Sheet Fouling and Cleaning for Falling Film Evaporators
- Posted on 27th May 2025
- in Articles, Falling Film Evaporators, Other
- by John Real
Fouling and build-up within falling film evaporators can exacerbate demands on cleaning-in-place (CIP) operations, including chemical and water usage, as well as valuable production time. On systems that experience particularly bad build-up and fouling, this can also require manual removal of the product residues, further increasing cleaning times and exposing operators and employees to potentially dangerous situations. These residues will cause bacteriological growth issues and, as a result, product quality issues. We have seen cases where the long-lasting fouling in the same spot over time collecting chemicals, which leads to pitting and corrosion of the stainless-steel materials.
Often, the attempted solutions involve more or stronger chemicals, longer cleaning times, or improving spray distributions of the cleaning chemicals, all of which can increase the operational costs to the system. The keys to resolving these issues can sometimes be outside the direct interface between the cleaning operations and the product residue itself, but in addressing other parts of the system design.
GLM Hydro recently assisted one of our dairy clients in the Rocky Mountain region with just such an issue. This client had struggled for a long time with significant fouling on the bottom tube sheet of the falling film evaporators. During the design of the evaporators, a section of the tube sheets had been left open to avoid erosion of the product tubes from the vapors used to evaporate water from the product. These areas became notorious for a build-up of carryover product that would harden onto the surface of the tube sheet, becoming a thick scale of “burn on” product and becoming very difficult to clean. This burn-on would remain long after the cleaning operations on the evaporator would be completed.
Modifications to the CIP had been made in the past, but this seemed to be an intractable problem for our client. GLM took a different approach to this issue – we could not prevent the carryover from coming into contact with this tube sheet area. However, we could help prevent the burn-on of the product. To understand our approach, some background on the mechanics of the evaporation process in falling film evaporators is needed.
To evaporate water from the product in falling film evaporators, live steam or water vapor from the evaporated product is introduced into the shell side of the heat exchanger. The product moving inside the falling film tubes cools the tubes, and the steam or vapors condense on the outside of the tubes, turning from vapor into liquid and transferring the heat from the vapor to the product to evaporate the product inside the tubes. As the vapors condense, they fall down the exterior surface of the tubes to the shell side of the tube sheet.
Typically, the goal is to remove the condensed vapors or condensate (also known as cow water in the dairy industry) as quickly as possible. Significant build-up of condensate on the shell side can decrease the surface area available for the vapors to condense on, reducing the capacity of the evaporator as it prevents the vapors from coming into contact with the tube walls and transferring their heat.
This dairy evaporator had been carefully designed to ensure that absolutely no condensate level could build up on the bottom tube sheet. The condensate outlet was installed in such a way that it was exactly the same level as the bottom tube sheet, so any condensate would immediately drain out of the shell.
However, in the case of this evaporator, this is precisely what we wanted to encourage. By modifying the outlet to encourage a level of condensate to remain in the bottom of the tube sheet, we were able to insulate the tube sheet from the vapors and prevent the evaporation of product that impacted the tube sheet during production, significantly reducing the product side of the bottom tube sheet and reduce the fouling from occurring on the bottom tube sheet to begin with.
Coupling this change with some automation changes around the spray patterns in the bottoms of the evaporator, we were able to eliminate the fouling from all three effects of this evaporator.
GLM was able to consistently provide proper and complete cleaning of the bottom tube sheets during every cleaning operation of this evaporator, thereby eliminating a long-standing issue for our client.
Contact us for more information when your installation has these or any other kind of issues.
John is a Process Industry Expert in Spray Drying and Evaporation, responsible for sales and business development for custom process solutions in the sanitary food, beverage, and dairy industries. John has a wide range of project execution-related experience, including, but not limited to, process engineering, system installation and commissioning support, documentation control, purchasing, and equipment quality control. His hands-on experience ensures that he seeks the best solution for our clients.
In addition, John leads a small team of engineers and designers to ensure the efficient and timely delivery of process engineering, equipment, system changes, and optimization efforts, helping our customers maximize the return on their capital investments.
- Bottom Tube Sheet Fouling and Cleaning for Falling Film Evaporators - May 27, 2025
- Evaporator Woes – Vacuum Control, Velocity, and Carryover - September 25, 2020
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Tags: Bacterial Growth, CIP, Cleaning in Place, Dairy, distribution pan, evaporator, Falling Film Evaporator, fouling, GLM Hydro, Increase production, Tips