Conserving Cooling Power

Neglecting cooling tower maintenance can curtail production, especially in the hot summer months.
By Holly Jessen | June 13, 2016

When it comes to optimization projects, an ethanol plant’s cooling tower typically doesn’t even make the list. In fact, many facilities don’t perform regular cooling tower inspections, says Frank Foster, vice president of Tower Performance Inc.

“Run to failure is kind of what happens,” he says, adding that cooling towers simply aren’t considered a priority piece of equipment. “If people hear the fan turning, motor running and water falling, they assume everything is OK,” he says. “It just doesn’t get the attention that some of the other equipment gets.” TPI, which is headquartered in New Jersey, provides repairs and upgrades to cooling towers and new cooling tower installations.

As chairman of the membership committee of Cooling Technology Institute, a not-for-profit technical organization for owners and operators, suppliers and vendors of cooling towers, Foster knows it’s an issue that isn’t limited to the ethanol industry. It’s the same in the other industries that utilize cooling towers. “They don’t really notice it until it’s really catastrophic or it’s really limiting production,” he says.

Rick Hollendieck, owner of Sys-Kool LLC, a cooling tower company headquartered in Omaha, Nebraska, characterizes the attitude as, no news is good news. “They are a neglected piece of equipment because they aren’t inside the plant, they’re outside the plant out by themselves, and probably aren’t running at prime capacity,” he says. Sys-Kool specializes in analyzing cooling tower operations and then servicing, upgrading or modifying the equipment.

Neal Jakel concurs, saying many don’t understand the basic principles of cooling tower operations. Before managing an Illinois ethanol plant, he spent 15 years building, designing and engineering corn wet mill plants for Cargill Inc., including modifying cooling towers. He now is vice president of strategy and technology for Fluid Quip Process Technologies, which, among other things, does cooling tower optimization projects at ethanol plants.

Understanding how cooling towers work, how they are integrated into the plant’s whole cooling system and how to optimize those systems are learning opportunities for the ethanol industry, Jakel says. He also believes it’s critical that the details of tower design are understood before operational changes are made.

Foster also believes there is a general lack of understanding of cooling tower principles. “I’ve found that they really don’t understand what the cooling tower’s purpose is other than getting cold water,” he says. One thing companies can do is to invite an expert to the plant to talk about cooling tower basics, he suggests.

To learn more about cooling tower operation, Foster recommends companies join CTI, which was established in 1950 to set standards, guidelines and best practices for cooling towers. At the website, members and nonmembers alike can access technical papers, some free and some for a fee, or use the “ask the expert” feature to get help for a specific problem. CTI also can make recommendations on good service and equipment companies, helping companies avoid those that may not have their best interests in mind. “It’s just one stop to find out anything you want to know about cooling towers,” he says.

For Foster, one of the key benefits of becoming a member of CTI is networking with other owner operators. It offers companies the opportunity to speak to other members, some of whom may have already solved an issue they need help with, which can help save a lot of money. 

Keys to Better Operation
Keeping the fill material, sometimes also known as packing, inside a cooling tower clean is important for efficient operation, Hollendieck says. The first step in chemical treatment is to discourage growth of things like algae and bacteria. It’s also important to deal with fouling from dirt and other particles that end up in the cooling tower. “Cooling towers are what I call great air scrubbers,” he says. “Anything that is flying in the air gets sucked into the cooling tower.” 

When fill material is fouled with dirt and calcium, it can be as heavy as 80 or 100 pounds. In comparison, a new 2-foot-by-2-foot-by-6-foot pack of fill weighs only about 20 pounds. Removing and replacing fouled fill improves performance. “They might be running at 70 or 80 percent efficiency because it’s all fouled, and then when we get done, we put it back to 100 percent” Hollendieck says.

Water and air distribution is another area that is vital to cooling tower performance. Hollendieck sometimes sees cooling towers with too much water pumped through them, or overpumping, because operators think the more water flow, the better. On the other hand, some operators under pump. In both cases, air contact with water is reduced, which lowers heat transfer efficiency.

Another misunderstanding about cooling tower operations is that the colder the water is, the better, Jakel says. The reality is that Midwest cooling towers should typically operate at about the same temperature in the summer and the winter. If a cooling tower freezes up, it can cause dangerous ice buildup on the structure and more. “Ideally, during winter operations the water should not be below 60 degrees Fahrenheit in the tower basin,” he says. “If the water gets too cold, then the amount of water needed through the entire plant is reduced, causing a cascade of issues.” A couple of examples are damage to cooling tower packing and fouling and mineral buildup on heat exchangers.

In the summer, to keep water evaporating at a high rate, and therefore providing maximum cooling, it’s important to make sure the cooling tower is performing at maximum design air flow. To measure this, operators should look at the horsepower or amp draw on fan motors, Jakel says. If fans or blades are rated for higher cubic feet per minute of air flow than what they are drawing, this can be adjusted by changing the pitch of the blades for increased air flow. However, operators should keep in mind that air flow can be set too high, sometimes causing packing to lift up, Jakel cautions. “Understanding the details of the tower design is critical before making any fan blade adjustments.” 

Cooling tower or full cooling system optimization projects offer ethanol producers many opportunities for overall operational efficiency. In fact, Jakel believes cooling tower inefficiency is curtailing production at many ethanol plants. “A lot of plants still struggle in the summertime with effectively cooling the fermenters, which dramatically impacts not only rates, but yield and throughput,” he says.

Foster concurs. “It’s a gradual thing,” he tells EPM. “They learn to compensate for lack of performance from the tower. They really don’t go and see if the tower is the culprit for a lack of production.”
Often, when he asks people about their cooling towers they say it’s working fine. Then he asks about what happens in the summer and they reply, “Oh, no. It’s awful in the summertime.”

The summer season, from June to September, is when cooling towers are pushed to provide maximum cooling. “This is one of the reasons why it goes out of sight out of mind,” Foster says. “After they get past the summer season, you can’t tell if the cooling tower is efficient, because it’s so cold, you don’t need it.”

Thermal performance tests, or testing water temperature, is an excellent way for producers to identify cooling tower problems, Foster says. It’s like going to the doctor for a regular checkup. A thermal performance test can set a baseline for how a cooling tower is operating and help determine if it is meeting its original thermal design parameters.

In Sight, In Mind
Hollendieck, Jakel and Foster all stress the importance of regular cooling tower inspections. Different types of inspections should be performed yearly, monthly and sometimes even weekly. Unfortunately, the reality is that many cooling tower operators simply aren’t doing this. Foster estimated it was as high as 80 or 90 percent. “People just don’t put that cooling tower on a priority list,” he says. “Until it breaks and then they will do anything to get it up and running.”

In some ways, Foster understands why cooling tower inspections have fallen through the cracks. He points to the many cutbacks across all types of industries. “Years ago, plants used to have a guy that was in charge of the tower, that’s all he did,” he says. “Now, that person has 16 other roles.”

Still, Foster urged cooling tower operators to put a preventative maintenance program in place. At least once a year, the structure, including mechanical equipment and internals, should be thoroughly inspected. “You’ve got to get inside, because you really can’t tell what’s going on when it’s operating,” he says.  

He also recommends monthly walk-around inspections to look, listen and feel for problems. One thing operators should watch for is unequal water flow in the air inlets, which can signal an internal problem. Hearing abnormal noises or feeling excessive vibration can point to a pending mechanical failure. “Like with your car when you hear it clank and clunk, it’s not supposed to do that,” Foster says. “Same thing with a cooling tower.”

Jakel also talked about the importance of inspecting water flow and distribution, including periodic visual checks and more extensive checks during maintenance shut downs. He noted that setting water diffusers too fine also can cause issues. “This will be evident by excessive misting of water out the top of the tower,” he says. “Some or very little misting is common, but not rain.”

Inlet screens, which prevent debris from entering pumps, should be inspected and cleaned weekly, Jakel adds. If debris enters the water system it can cause multiple problems, including plugging and lowered efficiency. “If the screens get plugged up the water will back up in the tower basin and can overflow,” he says. “A high basin water level is usually an indication that the screens need to be pulled and cleaned.”

Author: Holly Jessen
Freelance Writer