In the U.S. ethanol industry, the process of dewatering either whole or thin stillage for the production of distillers grains typically happens via centrifugation. In its most up-to-date DDGS Handbook published in 2020, the U.S. Grains Council says the whole or thin stillage mixture used to create distillers grains “is centrifuged to separate coarse solids from liquid.” There is no mention of alternative processes.As Greg Benz, an engineer with more than 40 years of experience in the design of agitation, fermentation and bioreactor systems knows, the use of centrifuge decanters for the production of distillers grains is, in fact, the go-to option for corn dry mill ethanol plants. But he believes there may be room for improvement. Benz is collaborating with Ling Du, president of Terrace International, who holds a Ph.D. in agricultural engineering from the University of Illinois at Urbana-Champaign and also has experience in corn wet milling and grain processing. The two are promoting an alternative to the centrifugal process: the diaphragm filter press.Understanding the Diaphragm Filter Press&nbsp; The physics of a filter press are quite different from a centrifuge, which uses the power of gravity to separate solids from liquids through the act of spinning. Some versions spin around a horizontal axis, while others utilize a vertical axis. A diaphragm filter press works on size differences provided through filter media, according to Benz. Using differently sized filter cloths, the press is able to perform the separation process by pumping a semi-solid mix through variable media. The systems are quite large and include rows of plates that hold the cloth filters. “Two big differences between the processes,” Benz says, “are how much power the equipment packages use and how wet the final products are.”The diaphragm filter press Benz advocates for is built and supplied by Terrace International, a Shanghai-based company. The system is essentially a plate-and-frame filter press with added steps and automation, he says. In a standard plate-and-frame system, pumps are used to push material into a filter chamber. From there, he explains, the pressure created by the pump drives the solids through the filter cloth. The resulting separation is only as good as the amount of pressure the pumps can create.The Terrace version adds another step. Once the standard plate-and-frame system pump reaches capacity, a diaphragm plate system goes into action. Engineered with inflatable diaphragm plates set on every other plate in the filtration system, more solids and liquids are squeezed out of the filter cake as the diaphragm plates are filled with air. As the plates expand, they provide additional pressure on the cake mix, a step that helps press out more water from the mix. Think of it as squeezing juice from an orange, Benz says.The Intricacies of the Diaphragm Press&nbsp; Benz believes the main reason an ethanol plant might consider moving to a diaphragm press for distillers grains production is reducing the amount of energy the facility uses in the drying process. “They end up having a more economical plant operation because they are drastically reducing the amount of water that has to be dried,” he says.By Benz’s calculations, typical cake moisture post diaphragm filter press is roughly 40 to 50 percent versus 60 to 70 percent using a decanter (horizontal axis centrifuge). Again, these numbers come from Benz; decanter manufacturers may have different figures. Moisture levels don’t represent the only difference between the two, Benz believes.With a diaphragm filter press process, there are no visible solids in the filtrate after processing through the press, while there are some visible in the decanter, Benz claims. Looking at the effect of inlet feed solids concentrations on outlet cake moisture, there are none in the diaphragm filter press. But, according to Benz, the outlet cake moisture in a decanter fluctuates as inlet feed solids rise and fall.On the maintenance side, diaphragm presses can’t fail catastrophically, so they don’t have to be checked or maintained very often. For normal operations of the units, filter plates need to be replaced after three to five years. The filter clothes, made of polypropylene, can last six months or more. Decanters, on the other hand, can fail catastrophically and do require frequent inspection, Benz says. The skill level required to operate a filter press is low, while for a decanter it can be high, he adds.Terrace International’s presses are fully automated and can be controlled with a programmable system. The charge pump is driven by an electric motor. The action of opening and closing the plates is done by a combination of hydraulics and an electric motor. The pressurization of the diaphragm plates can be performed by plant-provided pneumatic pressure or another electric pump. A conveyor for the dried mix isn’t always included in the scope of the systems, but it can be, Benz says. And overall, there really isn’t any operating labor.A diaphragm press also differs in operational time from a decanter. According to Benz, the filter press time, including pressing, squeezing and drying, is about four to six hours, and it happens through a batch process. The respective spatial footprints of the systems are also of note. Although they require less energy than a centrifuge setup, they do require more space.“The setups come in different sizes,” Benz says. A large installation could end up requiring a significant amount of plant space. For a recent customer, the estimate for an entire setup of the 13 filter presses needed to meet the demands of the plant, each unit would span a space of six feet wide by 30 feet long.There are other differences between a press and a centrifuge. According to Benz, due to rotary friction, decanters require much more energy per unit of production than filter presses, and the wear rate of the decanter components results in more expensive upkeep, Benz claims.“The main drawbacks of the diaphragm filter press are its spatial footprint and its batch operation,” he says.Even with the differences in processing time and floor space required, Benz says “the total energy consumption is still much less in the end.”Diaphragm Filter Presses In the U.S.&nbsp;&nbsp; In the U.S., filter press technology has not taken off within the ethanol industry, Benz says. They are, however, being used in the mining sector, he explains, noting that the technology has roots in that industry. Generally, filter press use is more common in China.Benz has been connected to China for many years. Prior to forming his own consulting business, he worked for an agitation equipment firm that serviced clients around the world, including those in Shanghai. After working for years and forming relationships with clients there, Benz formed a business partnership with Ling to sell and promote Terrace International systems, including the diaphragm filter press, across several industries. To this day, Benz is still a member of the American Chamber of Commerce in Shanghai.His time in the country has shown him just how popular the diaphragm filter press is. He says there are more than 50 companies in China using it for DDG production and more than 400 presses in service at those production facilities. For the most part, he adds, producers there don’t use decanter technology as much, instead favoring the filter press method.Benz is now working to spread the word on this alternative option for DDG production in the U.S. that doesn’t involve the established decanter method. The closest thing he has to field trial data for interested parties in the U.S. is from the technology’s use in China. And while he knows potential American customers still view the technology as new or different, he says the broad use of diaphragm filter presses in China lends credibility to the effectiveness of the equipment. Author: Luke Geiver &nbsp;&nbsp; Contact: writer@bbiinternational.com&nbsp;

2024-03-28 - A Proposal To Press (Ethanol Producer Magazine)

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Is the diaphragm filter press a viable alternative to the centrifuge decanters used in dry mill DDGS production? A pair of engineers from the U.S. and China think so.  

A Proposal To Press

A Proposal To Press

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