Cleaning up ethanol plants

As the ethanol industry continues to boom, so does it’s search for new and better ways of increasing profitability. One of the best ways to reduce operating costs is to identify process improvements. As a manufacturing business partner for industrial liquid filtration, Eaton has teamed up with ethanol producers in helping them retain the potency levels of their caustic chemicals – which is essential in keeping bacteria out of the fermentation process.

“By visiting ethanol plants and learning as much as we can about the challenges of the process, we’ve been able to offer filtration solutions with real return-on-investment payoffs,” said Bruce Law, Marketing Development Manager for Eaton. “Recently, we worked with a large ethanol plant in the U.S. that was losing profitability due to the rising cost of caustic fluid. By developing a clean-in-place (CIP) loop off the caustic tank using a single mechanically cleaned DCF 1600 filter, we were able to help them overcome their caustic challenges. An added benefit of the process was that it also helped keep their spray balls from getting clogged.”

In ethanol production, caustic chemicals are used to kill harmful bacteria that destroy the yeast needed to complete the fermentation process. Plants use a series of tanks filled with corn mash, enzymes and water. This mixture is heated and allowed to ferment – with each tank being in a different stage of fermentation. When the process is complete, the tanks are emptied and the contents sent to distillation.

To keep production levels high, the emptied tanks must be readied for the next batch as soon as possible. Naturally, the longer the tank is empty for cleaning or maintenance, the less revenue is generated.

After rinsing the tanks with water, the final step is to spray the insides with a caustic rinse containing sodium hydroxide. This phase of the process is absolutely critical to fermentation. If the caustic doesn’t effectively clean the tank, it can easily become a breeding ground for bacteria. Bacteria growth means costly downtime and a lengthy, expensive cleaning before the tank can be used again.

One of the challenges of the CIP process is that the caustic must be kept at a certain potency level in order to be effective. Any bio-solids left in the tanks after the rinse cycle may absorb the caustic and decrease its ability to decontaminate the tanks.

“It takes constant vigilance to maintain these chemicals at the right levels. When caustic is absorbed by debris, you have to add fresh chemicals to the tank and that costs money,” said Law. “Plus, the longer the debris is in contact with the chemicals, the more caustic it can absorb.”

As ethanol plants look to expand their operations to meet the growing needs of consumers, they quickly realize that the additional volume also requires the need for more frequent – and more efficient – CIP cleanings. To address this operational challenge, Eaton began CIP testing with its DCF 1600 in early 2005. The test results exceeded expectations, with ROI gained in just over 5 months.

“This is based on the savings they (customers) would realize by continuously removing the debris and circulating the liquid through the filter – considerably extending caustic life,” said Law. “Because each plant is set up differently, there are really several places a customer can decide to place a filter for optimum results. For example, they can install the filters in the CIP loop and filter the entire flow, or they could install the filter as a side stream off the CIP mix tank.”

The CIP loop is active about every 2 hours based on the size of the tanks and the length of fermentation. The loop off the CIP mix tank could be run on a continuous basis with product making multiple passes through the filter. In this location the flow rates could be reduced to filter a side stream that would turn over tank capacity approximately every 10 – 15 minutes.

In the second half of 2005, the large U.S. ethanol plant was hit with two price increases from the caustic supplier. The increased cost of the caustic and the more frequent CIP cleanings made installing the filters a priority. Based on the research and test units, the plant installed the recommended filters in the CIP loop off the CIP mix tank– which helped deflect these rising costs and maintain profitability.