Cooling Considerations

FROM THE APRIL ISSUE: Experts discuss different approaches to optimize cooling towers and limit summer production slowdowns.
By Matt Thompson | March 26, 2020

For many plants, summer production slowdowns are a necessary part of doing business. Warm, humid weather means cooling towers can’t maintain a low enough temperature in fermenters, causing production to slow. But, experts say, those slowdowns don’t necessarily need to happen every summer.
Jeff Prochaska, industry technical consultant for grains, oilseeds and biofuels at Nalco Water, says optimizing a cooling system requires a mechanical and engineering methodology. “In the last few years, the cooling tower systems have become bottlenecks in the summer months and so the plants have been asking themselves, ‘What do I do now? Do I add another pump to my cooling tower? Do I add another chiller? Should I add another cell to my cooling tower? Should I add another cooling tower, and if so, do I just make a bigger one or do I get a new cooling tower?’ So, we saw a need for helping people make decisions.”

Prochaska says taking a mechanical and engineering approach to cooling systems involves giving plant managers and owners detailed data about their systems and how they’re performing and evaluating the options for upgrading and optimizing the systems. “It’s not just chemistry, it’s an engineering evaluation where we look at how the cooling towers are performing, how the pumps are performing, how the heat exchangers are performing and how the fans on the cooling tower are performing.”

He says the reasons a cooling system may not be operating as efficiently as it could be are varied. One issue is airflow. “They’re not getting enough airflow, because the fill is partially plugged or partially fouled, or deteriorating,” Prochaska says. “If you don’t have air flow, you’re not going to get cooling.” Water flow is another issue, he adds. “Those are two trends that we see that people should look into—how much water are they actually pumping, and how much air is actually being pulled through the tower,” he says.

The way heat exchange valves and pumps work together affects cooling tower water flow. “There are a lot of heat exchangers and not all of the heat exchangers are being operated at the same time,” Prochaska says. “So, there are valves that are not always open, and when valves are closed, they put back pressure on the pumps and then the pumps can’t produce the flow they’re designed to because they’re pumping against too much pressure.” Determining why a system may not be using as much water as it’s designed to is part of the mechanical and engineering approach Prochaska advocates.
Pipe corrosion may be another reason water flow is restricted. They get clogged with rust and tubercles, causing major friction loss, Prochaska says.

Andrew Ledlie, global director of digitization strategies for industrial water technologies at Solenis, agrees. He says Solenis often sees “piping that’s failing in 10 years with pinhole leaks due to pitting, and a lot of times it’s microbiologically related.” When a system is designed to last 25 or 30 years, “replacing 10-year-old equipment is not factored into the financial model and investment returns of the business,” Ledlie says.

Biofilm Battles
Ledlie says the industry’s age plays a role in how cooling systems are viewed. “This industry is still very young and so all of the efforts have been toward the process side, not on what we call utilities, which is water and steam and energy that’s required to drive the operation,” Ledlie says. “So as a very young industry, it doesn’t have a long history of operations optimization behind it.”

Don Holt, applications team manager for Solenis, notes that the ethanol industry offers unique challenges to fighting biofilm. He says cooling towers “[suck] in a ton of air against a fine spray of water, and [they] scrub out a lot of dirt and organics, maybe more so than in other industries where the cooling towers are not surrounded by corn fields.” He adds the source of the water used can also impact bacterial growth.

Getting a handle on these factors to control biofilm and bacterial growth can help plants maximize their cooling capacity in warm weather, Ledlie says. He points to one of his ethanol plant customers as an example of a successful biofilm control program. “[Biofilm] had been a problem previously until they put these new tools in place when they replaced the cooling tower,” Ledlie says. Those tools led to a dramatic reduction in the amount of time the chillers needed to run, he adds.

And that isn’t necessarily a common view within the ethanol industry, Ledlie says. When he talks with companies that perform maintenance on cooling towers, Ledlie says he asks them how often they see clean towers that aren’t coated with biofilm. “They say only the new ones,” Ledlie says. “It’s a pervasive problem.”

Paradigm Shift
Whether cooling tower operation is affected by a system that needs to be upgraded, or by biofilm buildup, Ledlie and Prochaska agree that the difficulties experienced by cooling systems in warm, humid weather is a source of lost revenue for many plants. “If the fermenters start to get warm, or even hot, they get stressed; they don’t produce as much alcohol, so cooling is very important in the summer months to maximize production in many plants,” Prochaska says. He adds most U.S. corn ethanol plants experience production losses during summer months, and for some plants this could mean a loss of $500,000 to $1 million. “If a plant could optimize their cooling system, they could reduce production losses,” he says.

Ledlie agrees. He says many plants view a summer slowdown as part of normal operations and haven’t explored ways to maintain production levels in warm weather. “I think that’s your paradigm, so you kind of have a hard time thinking, ‘Maybe we could do something to prevent that,’ because it’s not perceived as a solvable problem.”

Cooling systems aren’t seen as revenue generators, but as costs to the plant. “It’s not a heavy focus because it’s not part of the revenue, it’s part of the cost side,” Holt says. All industries could benefit from changing that viewpoint. “I think it is definitely at an overall paradigm shift globally that you need to take a look at some of your costs actually as revenue generators.”

Prochaska says he’s seen more interest in working with cooling systems to limit production cuts. “I’m seeing more people trying to figure that out,” he says. “Some people are trying to do it on their own, and we get contacted to come into plants and do these studies for them. Every plant has found it extremely useful.”

Establishing a Baseline
While they advocate for different approaches to maintaining and optimizing cooling systems, both Ledlie and Prochaska say measuring current cooling system performance is an important first step in determining how to best manage a system.

“Find out how much air is going through, find out how much water you’re pumping and find out what the efficiency of your cooling tower is,” Prochaska says. “That way, if there is something you need to do, you can do it before it gets hot and humid.”

“It’s really important to get baseline data because you can’t improve what you’re not measuring,” Ledlie says. That measurement can be relatively inexpensive. “It’s not a huge capital investment for some instrumentation,” Ledlie adds.

He also advises finding personnel who are interested in learning new skills and will take the time to understand the intricacies of the cooling systems, and how to control biofilm in them. “Find some of those curious people in the plant who have enough training that they can at least hit the ground running, and encourage them to spend some time looking at the utility operations,” Ledlie says.


Author: Matt Thompson
Associate Editor, Ethanol Producer Magazine
701.738.4922
mthompson@bbiinternational.com