Spring and summer months mean rising ambient temperatures and humidity levels, which have a negative impact on the efficiency of cooling towers and ethanol plants in general. To operate smoothly in higher temperatures, proper planning and process adjustments are necessary.

To help you better prepare your plant, here are seven best practices for making best use of your cooling water resources and controlling fermentation temperatures:

Have your chiller inspected in advance.

In most regions of the United States, for example, cooling towers alone don’t provide sufficient cooling resources to run fermentation and downstream processes at the same capacity as during cooler months. To supplement this lack of resources, many plants have chillers—refrigeration systems that focus cooling within the process. Admittedly, these chillers require a large amount of electricity to start and run, which introduces additional operating costs. However, the cost of operating a chiller is minimal when compared to lost production caused by fermenting at too high a temperature.

Avoid unforeseen start-up issues and delayed availability by making sure your chiller is inspected and readied for use well ahead of hot weather.

Consider increased copper content.

Another thing to do before the summer is to revisit your copper permits. Chillers can increase the copper content of cooling water blow-down (the water drained from cooling towers to remove mineral build-up). Discuss your permitted copper levels with your water treatment vendors to avoid potential mishaps.

Develop a strategy for allocating chilled water resources.

Confirm that your plant is effectively balancing cooling water between fermentation and downstream processes. Fermentation will demand much of your available chilled water, but some may need to be routed to selected distillation exchangers, for example.

It’s wise to map out cooling tower control valves and open percentages to develop a heat exchange strategy based on your plant design. When in doubt, prioritize resources to fermentations during the highest metabolic state. Yeast generates the most heat while growing, which typically occurs 12-24 hours into fermentation (assuming 50+ hour fermentation times).

Standardize your chilled water allocation procedure across all operating shifts.

It’s important to develop a standard procedure for all of your plant’s operating teams to follow. Reducing process variability will minimize the chance of incidental hot fermenters, or fermenters that achieve a temperature of 96°F (35.5°C) or greater for a sustained period of time. Hot fermenters can harm yeast, stunt growth, and cause conditions that are favorable to bacterial infection. These issues can lead to lower alcohol fermentation, increased organic acid concentrations, and higher sugar concentrations after fermentation is complete (i.e. ferm drop).

Avoid repeatedly turning your chiller on and off.

Once the chiller is turned on, minimize the number of times you turn the chiller off again. The largest cost associated with running a chiller is the high peak electrical demand needed to turn the machine on. Once it is on, it is best to leave it that way.

Decrease corn solids loading into the fermenter

Reducing the amount of fermentable material will help control yeast metabolism and temperatures. Check your temperature forecast every 24 hours and plan solids loading accordingly to avoid yeast stresses. The higher the temperature, the lower your solids loading should be.

In addition, cool mash going into the fermenter to as close to 88°F (31°C) as possible. Starting the process out at a cooler-than-usual ambient temperature will help ensure your yeast doesn’t heat past the upper limit of 96°F (35.5°C).

Start monitoring supplemental nitrogen more regularly.

Your mindset should be to give yeast what they need when they need it. Whether your plant’s nitrogen source is ammonia or urea, warmer months demand that plants pay closer attention to how nitrogen is being dosed. Nitrogen accelerates yeast metabolism and is needed to mitigate yeast stresses—heat, for example. However, if you dose too much nitrogen too fast, you could end up generating more heat. It’s a delicate balance that regular monitoring and adaptation can help you find.

Furthermore, if you’re not already using a protease consider adding one to your process during the summer months. Proteases supply amino nitrogen that helps yeast combat heat stress and can reduce the need for supplemental nitrogen.

What about your plant?

What does your plant do to help address and prevent issues caused by rising temperatures? Has your plant had success employing any of the strategies listed above? Use the comment box below to ask questions or share your experience.

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Jonathan Dancy

I’m a Biofuels Technical Service Scientist for Novozymes and my goal is to deliver scientific solutions to customers based on their production goals. I enjoy fishing, riding motorcycles, snow skiing and kayaking the New River in the mountains of NC.

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