Wringing Out the Last Drop with Increased Plant Efficiency

Producers are always on the lookout for ways to produce more ethanol from the same amount of grain. As the industry grows, more vendors are offering new technologies and experimental procedures that translate into increased gallons and higher plant efficiency—good news for an industry hungry to ramp up production.
By Holly Jessen | August 01, 2006
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It's one thing to produce ethanol. It's another thing—a definitively more worthwhile thing—to produce ethanol as efficiently as possible, with increased throughput and higher yields. Taking it even further, accomplishing that while decreasing plant costs is the ultimate goal of every facility.

Five speakers with precisely that in mind tackled the subject of efficiency in "Maximizing Your Current Operations," a June 21 session at the 2006 FEW. The presentations included those describing modifications to jet cookers and sieve beds, as well as utilizing novel cleaning technology.

Shear Point Cookbook
At Golden Triangle Energy Co-op Inc., a project to automate the shear point of the jet cooker was completed. Sometimes referred to as "P-jet" or a hydroheater, many—but not all—ethanol plants have a jet cooker, said Ron Bennett, maintenance manager at Golden Triangle Energy. By installing HydroThermal Corp.'s patented K-5 Autopilot to control the shear mechanism, steam pressure was controlled at the slurry inlet, resulting in better starch conversion and increased yield.

If the gap between the steam nozzle and the combining tube is too large, there's low shear and low pressure drop with incomplete starch conversion, said Jim Zaiser, vice president of engineering and operations for HydroThermal, which assisted with the Golden Triangle project. "This results … in an incomplete starch conversion, which is a loss of efficiency," he said.

If the gap is too small, there's high shear and excessive pressure drop. That results in excessive wear and increased pumping cost.

Finding the "sweet spot" to provide the correct amount of differential pressure between the slurry tank and discharge from the jet cooker was a process of trial and error. To begin, Golden Triangle Energy started with 30-pounds-per-square-inch (psi) differential pressure, both before and after the jet, Bennett said. A 10-fermentor sampling size was completed over a period of 15 to 20 days before that was increased by increments of five psi for another test.

With each sampling size, the sugar and alcohol concentration was evaluated via the kinetics curve. As more fermentable sugars became available, the enzyme dose was adjusted for the amount of fermentable sugars available. The changes resulted in producing more ethanol while grinding the same amount of corn. At the end of the project, optimizing the shear point resulted in a 1 percent increase in weight per volume of ethanol production, a conservative estimate, Bennett said, adding that pressure optimization would be different at each plant due to a variety of factors.

Another step was to set the autopilot to automatically adjust the pressure slightly on a continuous basis, Bennett said. That keeps the jet cooker from fouling internally and freezing in one spot. If fouling was to occur, the equipment would be damaged by subsequent attempted adjustments. To do this without the autopilot, a worker would have to stand there with a wrench and manually adjust it. "That wouldn't be feasible or sane," Bennett said.

The total cost of the project was about $50,000, including the autopilot, and installation and start-up services, Zaiser said. He estimated that the 1 percent production increase at a 20 MMgy plant would produce about $400,000 worth of ethanol at $2-per-gallon prices. "In less than two or three months, it's paid for," Zaiser said.

Pumping Up the Volume
A project at Glacial Lakes Energy LLC successfully increased ethanol yields with an advanced process control system for the distillation and sieve process. David Culver, director of operations at the Watertown, S.D., plant said the initial motivation behind the project was optimizing the dryer system. The goal was more consistent moisture content in the DDGS, as well as decreased natural gas consumption.

Michael Tay, technical account manager for Pavilion Technologies then suggested a distillation and sieves project as an extension of that, Culver said. At that time, the ethanol plant's sieves were a significant bottleneck for a good part of the year. As a result, the plant couldn't be operated at full speed all the time. "We could run the rest of the plant faster than we could run the sieve," he said, adding that the production process had to be slowed periodically to allow the sieves to catch up.
Glacial Lakes Energy contracted Pavilion to install an advanced process control system. This advanced process system is able to control flow, water and temperature all at the same time, Culver said.

The most significant benefit was that the ethanol plant was producing more gallons of ethanol from the same amount of corn by bumping up the amount of water in the ethanol. Increasing yields is key to plant efficiency, and the most direct way to increase yields is tighter control and increased moisture, Tay said.

Before the system was installed, 200-proof ethanol leaving the plant typically contained 0.2 percent moisture, Culver said. That's well below the highest standard of 0.8 percent allowed in water-content parameters. Increased water content, within the parameters resulted in a 0.145 percent increase in ethanol yield.

Decreased man-hours spent on distillation tweaks also resulted. In the past, adjustments to the system needed to be done manually by an operator.

Sieve/distillation capacity was also increased between 6 percent and 9 percent after the project was completed, Tay said. Installing the advanced process control wasn't the only thing that had a positive impact on capacity, however.

Another adjustment was adding more beads to the sieve beds, Culver explained. Glacial Lakes Energy also increased the size of the sieve bead pump. "It was just some easy and quick changes we could do for increased capacity," he said, adding that the changes gained about one or two gallons versus seven or eight gallons from installing advanced process control.

A decrease in the use of natural gas was also a project goal. By the time the project was completed, that decrease couldn't be shown because changes in plant production threw off the benchmark numbers, Culver said. But that doesn't mean that part of the project was unsuccessful. "Over time, we think we're seeing some of those energy savings," he said.

Cleaning for Efficiency
Clean-in-place (CIP) technology was also presented as something that can improve the efficiency of an ethanol plant. Peter Fernholz, vice president of research and development and global CIP for Ecolab Inc., gave a presentation comparing current CIP practices with an experimental technology Ecolab has developed.

In general terms, the experimental treatment is a per-oxygen penetrant chemistry applied in a pretreatment step, Fernholz said. The pretreatment step helps reduce cleaning time during the alkaline cycle, which activates the chemistry and disrupts the soil. He compared the difference to cleaning an oven with a bucket of water versus using oven cleaner to loosen the soil.

During a six-month study, also conducted at Glacial Lakes Energy, Ecolab cleaned one evaporator each week, Fernholz said. Later, CIP time was reduced 60 percent, down to 3.25 hours from 7.75 hours.

A six-month study of the experimental chemistry at Heartland Corn Products in Winthrop, Minn., also showed positive results. The study concluded that CIP time could be reduced 43 percent, from 9.25 hours to 5.25 hours with better results. "Downtime, in this case, meant dollars in terms of efficiency," Fernholz said.

The most significant conclusion of the studies is that CIP time can be reduced 40 percent to 60 percent, according to Fernholz. Ethanol plants are spending a lot of time on CIP, and there is room to reduce that significantly.

Fernholz recommended that a separate acid CIP system should be considered when designing new plants or retrofitting existing plants. Alkaline is broken down, and quality and performance is compromised, when it is used to clean fermenters as well as evaporators, he said.

Energy savings due to cleaner heat exchanger tubes was not able to be measured. However, plant mangers reported that they felt intuitively that there were energy savings, he said.

Another important issue is animal-feed-friendly chemicals. Anything used during the cleaning will, at the end of the process, transfer to the distillers grains. Fernholz called this a critical issue that, to date, has not been adequately addressed.

Holly Jessen is an Ethanol Producer Magazine staff writer. Reach her at hjessen@bbibiofuels.com or (701) 746-8385.