Dryer Innovations

Dryer manufacturers serving U.S. ethanol producers talk to EPM about changes in their technologies over the years and advances yet to come.
By Ron Kotrba | June 05, 2007
Rather than viewing dryer systems simply as large machines to dry residual distillers grains, people should think of them as "little plants manufacturing a product that people want to sell," says Jeff Noland, executive vice president of Ronning Engineering Co. Inc. "We want to look at this as an ingredient production system, not as a dryer. I think it would be extremely important for people to look at it this way." This is because the feed industry—a customer of the ethanol business—is demanding consistent product within agreed upon specifications. Noland says the drying temperature of the grains even affect how animals digest distillers dried grains with solubles (DDGS), particularly swine. Low-temperature drying, like what Ronning's systems offer, helps ensure product digestibility for swine and keeps the pig producers happy.

Ronning has been manufacturing distillers grains dryers for 11 years, but a company with one more year's experience controls a dominant share of the U.S. dry-mill dryer market. ICM Inc. owns approximately 80 percent of the U.S. ethanol industry dryer market share, according John Caffrey, director of ICM's energy team, who says it took the company 8½ years to install its 50th dryer system. Only 2½ years later that milestone was doubled. Today the company is installing nearly one full dry drum per business day of the year, Caffrey says.

Improving an already robust design whose original engineering has yet to exhaust half its expected lifespan is an interesting concept. "We don't really even know the life span of our dryers," he says. "We've only had dryers in operation for about 12 years—the first one we ever did is still running. We've made significant improvements though. We're guessing [a dryer's life span is] about 30 years, at least." The direct-fired natural gas rotary dryer system makes up for 90 percent of ICM's business, Caffrey says. With 80 percent market saturation, this is by far the most common system used today for drying distillers grains.

Changing With the Times
ICM has made significant design improvements in the past 12 or more years, which is mostly in response to customer feedback, Caffrey says. "We take customer feedback very seriously because they've literally helped us design a better product for the entire industry," he says. The biggest changes in ICM's gas-fired dryer design are automation, safety and reliability. Improved access to key areas for easier maintenance and additional safety guarding are just a few examples of how ICM's gas-fired dryers have been upgraded over the years. "We've also added water deluge and fire systems in all of our dryers, basically to not only improve on maintenance recommendations but also to make sure that they are clean," Caffrey says. Additional steam suppression in the ducting, cyclones in the back of the drop box, and stiffened front-end controls all have been part of the ICM dryer evolution. With the added safety and controls features in ICM systems, there are far fewer instances where a dryer system overheats to the extent that the distillers grains product is burned.

With the high cost of stainless steel, companies are focusing research on developing new alloys with the same performance characteristics as stainless steel at a lower price. ICM is no different, and it's centering upcoming research and development efforts on developing materials to remain profitable despite exorbitant steel prices. "We need to find an alloy that gives us the same corrosion resistance and is acceptable for our operations, but at a lower cost," Caffrey tells EPM.

Even though ICM's presence dominates the marketplace, there are other companies whose innovations have not gone unnoticed; and as the industry grows, competition is expected to increase. To stay ahead of the expected competition Noland tells EPM about advances in Ronning's dryer system technology over the past 11 years. "It's pretty clear when you start comparing our product to our competitors that, what we can do with a dryer of a certain size, it takes them a substantially larger dryer to do," he says. Ronning dryers can dry between 25 percent and 50 percent more grains than a comparably sized model built by its competitors. That allows some companies to purchase only one dryer instead of two. One of Ronning's biggest "advanced three-stage" dryers can satisfy the drying needs of a 75 MMgy plant.

Ronning builds a single-pass dryer, which means the material goes in one end and out the other without changing directions. As the dryer rotates, material is falling through a traveling column of air. The three stages cause the material to fall and combine and, essentially, buffer itself at different rates and quantities, Noland says. The front is the curing step. The wet grains enter where temperatures are at their highest in the process but material spends less time in contact with the metal surfaces, and more time falling through the air column. "That's 15 percent of the length of the dryer," he says. Most of the dryer consists of "phase two," or the second staging of the grains, called the open-flighting section, where a combination of radial fins and related technologies do a primary amount of the heat transfer. "Then, in the back end, we accumulate product in the cool end of the system to bring the temperature down," he says. "It's three completely different material retention strategies all built into the same dryer."

In response to the industry and its customers, Ronning like other dryer manufacturers, has implemented some changes to its dryer systems. "Number one—no surprise—they're bigger," he says. "We have basically doubled capacity in the past two years, which is really just a lengthening and the addition of more heat transfer surface in the second section of the dryer. It's not like we're making radical changes. The big change has been in the area of the firing method—customers are moving toward an indirect-fired approach more often than not."

Direct-fired dryers blow air directly from the furnace, which is blended with ambient air for slight cooling, and is blown right through the product. With the indirect-fired dryer systems, also called closed-loop, steam generated from evaporating the moisture out of the product is pulled back in by fan, and is reheated and reused. "The cool thing about it is that you're able to put the off-gas from that dryer into a thermal oxidizer that's integrated with the furnace, so you don't have a separate regenerative thermal oxidizer," Noland says, which saves on space and operating costs. "The capital costs [for indirect-fired dryer] are a little higher, which isn't popular, but basically you save yourself another burner because you don't have to have another incinerator," he tells EPM. Seventy-five percent of the dryer requests Ronning receives now are for indirect-fired dryer systems, which cost between $6.5 million and $6.8 million, Noland says. A direct-fired system of the same capacity costs about $1.5 million less.

"What we're working on more than anything right now is improving upon evaporative efficiency," Noland says. "We have a patent in process right now for pre-drying products that we believe will make a huge difference." Ultimately, Noland says Ronning's dryer systems have an edge over the competition thanks to innovations the company has imbued in its products over the years, leading to what he says is lower energy requirements and operating costs. "Lower [British thermal unit] requirements per pound of water evaporated—that's our major focus," he says. "And lower electrical requirements."

Rotary dryers are popular, but significant advances have been made in steam-tube dryer technology, which, while not nearly as pervasive in the ethanol industry yet, could represent one of the largest opportunities in market growth.

Steam-Tube Dryer
Although 90 percent of ICM's dryer business is based on gas-fired systems, the demand for its steam-tube dryer systems is picking up, Caffrey says. "They are growing in demand as far as sales and applications," he says. ICM already has a couple of its steam-tube dryer systems installed, and one project underway that requires six units. "If we get three or four plant projects like that, it puts a lot of steam-tube dryers out there relatively quickly," he says. Another company serving the ethanol industry, Davenport Dryer LLC, has been in existence for three years, says Bob Bateman, vice president of engineering with Davenport Dryer. "All of the employees are ex-employees of Davenport Machine and Foundry (DMF)," he says, adding that he has 28 years of experience with the former company. Davenport Dryer was started by the four key managers of the former DMF.

"The most prevalent dryers in dry-mill ethanol plants are the rotary drum dryer and the ring dryer, but what we specialize in is the rotary steam-tube dryer," Bateman says. The steam can come from a variety of sources, like a natural gas or solid fuel fired boiler in the plant, excess steam from a power plant, or steam coming off an electricity-generating turbine. In its young existence as Davenport Dryer, the company has built and shipped 16 dryers in the past two years. Nevertheless, improvements have been incorporated since its first few models. "Primarily we have improved our reliability through better design for the mechanical structure and mechanical components," he says. The design of the shell itself, the riding rings or tires as some call them, the trunnion roll bases and the gear-drive assemblies are all areas Davenport Dryer has improved upon from its original design. "The basic mechanical design is not new," Bateman says. "It's been evolving over the years in different industries … it's really a matter of taking proven technology from other industries and applying it to the ethanol industry."

One advantage of Davenport's steam-tube dryer design is low-temperature drying. "Gas-fired dryer people talk about low-temperature drying, but they're still talking about inlet temperatures up around 600 to 700 degrees Fahrenheit," Bateman says. "Our steam-tube dryers can operate at a range from 250 to 350 degrees Fahrenheit—that's the hottest point inside the dryer." Also, his company's dryers are easier to operate because there are no flames to control, or air flow balancing challenges, he says. Like ICM, Davenport Dryer has incorporated lower-cost materials to save on production costs while retaining reliability. The dryers built by Davenport are custom-sized so applications as small as 5 feet in diameter by 15 feet long are possible, up to a large-sized dryer with dimensions of 13 feet in diameter by 100 feet long.

Perhaps the biggest innovation in dryer technologies is automation. ICM has developed its own automated process controls (APC), linking dryer functions to the plant's distributed control system (DCS). "One of the biggest improvements in automation was a moisture analyzer that feeds back to the DCS with real-time information on how dry the material is," Caffrey says. "It gives an alarm to the operator through the system sooner, if something happens where the feed is getting too dry."

ICM's APC was developed in-house, but another company, Pavilion Technologies Inc., offers its own APC system for all ethanol industry dryer systems. "We build a model of a production process and use it to control and optimize the process based on business objectives, such as increasing yield, throughput, reducing raw material and energy use, and improving quality," says Matt Tormollen, vice president and chief marketing officer for Pavilion. The conventional DDGS-producing ethanol plant with limited wet-grain production consumes 35 percent to 40 percent of its natural gas in the dryer systems, he says.

What Pavilion created is a model of future performance, based on real-time information feed. "Based on those future predictions, we then optimize the actual process … What we're really trying to do is reduce the variability of the drying process yet maximize the amount of moisture in the final product but still within the customer specs." When the variability is reduced, this decreases the amount of energy per pound of drying, in addition to increasing the capacity of the dryer system to allow for more product throughput.

Essentially, Pavilion's APC leverages the computational strength of the model to manage the interrelationship between tens and hundreds of variables—something quite impossible for a human to optimize. Pavilion recently patented a batch application for model predictive control, which incorporates fermentation into dryer optimization techniques. "Applying model predictive control to batch is a novel concept that's not been done before," Tormollen says. "We call it hybrid modeling." Controlling and optimizing the amount of water in the fermentation process is important because it reduces unneeded moisture in the grains at the back end of the plant. Tormollen says the Pavilion solution requires an investment commensurate with the expected return. "One customer recently realized $2.5 million in annual revenue, just based on dryer controls," he says.

Mike Tay, technical account manager with Pavilion, says some producers look to continue enhancing DDGS quality by improved lab measurement and tracking, while others are interested in flash dryers to reduce drying temperatures. "However, we believe the application of model predictive control to DDGS drying has been the most recent, key innovation that has delivered significant, demonstratable customer value," he says.

Ron Kotrba is an Ethanol Producer Magazine staff writer. Reach him at rkotrba@bbibiofuels.com or (701) 746-8385.