Attention to Detail

BIOFerm’s long-term AD operations and maintenance (O&M) strategy leads to efficient outages and little down time.
By Anna Simet | December 23, 2015

When Rosendale Dairy in Pickett, Wisconsin, undergoes an outage, the operations team on site has undergone extensive training in preparation for the task at hand. This training ensures staff can recognize anomalies and take corrective actions in advance.

Completed in 2013, the $7 million project is located at the largest dairy in Wisconsin, and is the third digester in collaboration between the University of Wisconsin-Oshkosh and BIOFerm Energy Systems. The wet fermentation digester utilizes manure from the farm’s 8,500 cows, and is designed to process approximately 350 tons of manure per day.

Consisting of a 2G Cenergy-supplied, combined-heat-and-power module utilizing a Jenbacher 420 engine and complete gas treatment system, the system possesses 1.4 MW electric capacity, power that is purchased by utility Alliant Energy, and 1.5 MW thermal capacity, heat that is used to maintain consistent temperatures inside of the biodigesters—an essential piece to the AD puzzle where winters are very cold.

The anaerobic digester was designed and constructed by BIOFerm, a subsidiary of AD veteran The Viessmann Group of Germany. BIOFerm is also charged with maintaining and operating the plant, and keeping tabs on individual plant components is a key part of BIOFerm’s O&M strategy. “Preventative maintenance software is deployed at our facilities from start-up, aiding the operations staff in tracking inventory, wear and tear, scheduling of tasks, and critical component performance information.” says Whitney Beadle of BIOFerm. “Trend data on performance is integral to controlling costs at our facilities and impacting future plant design by choosing components with desired characteristics.” Areas of typical preventative maintenance include the separators, screens, pumps and engine. “Our operations staff also conducts  numerous visual inspections of the entire facility and key process areas, including client and customer interface,” she explains. Though it varies by system, at the Rosendale Dairy Digester, BIOFerm typically has at least two employees at the site during a partial outage, and four operators on-site during a complete outage.

Vast experience operating plants—it is BIOFerm’s fourth completed digester project in the U.S., and Viessmann has built over 400, mainly in Europe—has enabled the company to really dial in to each piece of equipment’s maintenance needs. “If, for example, we know a piece of equipment typically needs replaced or repaired at around 3,000 hours, we start watching it closely at around 2,500 hours,” Beadle says. “This way, if we start seeing any changes in performance, we go ahead and schedule maintenance early to avoid trickier complications.”

As is the case with any electricity-generating plant, unforeseen events occur, even despite thorough maintenance strategies. “Our [BIOFerm’s] maintenance team is trained to handle the unexpected outages from unpreventable circumstances, and errors can be detected via cell phone alert and viewed with smart phones, tablets, etc.,” Beadle says. Some instances of unexpected downtime at Rosendale have occurred to repair pumps, sand separating equipment—Rosendale is equipped with McLanahan sand separation technology that filters out and recycles animal bedding cleaning pits or sand from manure. “These [unplanned] outages typically last two to three hours,” Beadle says, adding that another reason for an unforeseen outage may be because of issues experienced by the electrical company. In that case, the digester may have to undergo an unplanned outage for safety purposes.  This is done to avoid producing excess [methane] gas that wouldn’t be converted to electricity and flared instead.

Rosendale’s two 30-foot tall, 80-foot diameter COCCUS digester tanks each possess a capacity of 1 million gallons.  BIOFerm’s trademarked COCCUS design is complete-mix with a mesophilic temperature operating range, designed for input materials with low solids content (between 8 and 12 percent). Tanks are reinforced with concrete and contain two or three REMEX paddle mixers, which are designed to achieve optimum fermentation via deep, slow and continuous agitation.

The digesters can normally last about 1.5 to 2 days of downtime without experiencing a huge temperature change, depending on the time of year, Beadle says. “During this time, the mixers are able to continue stirring,” she says. “Although every plant is different, we typically don’t like to drop below 100 degrees Fahrenheit at the Rosendale digester, which ideally runs at around 108 to 109 degrees Fahrenheit.”

For longer outages, BIOFerm typically brings in boilers to keep temperatures at the appropriate levels, Beadle adds. “If the temperatures aren’t maintained, the system will experience an upset, and the microorganisms don’t grow, causing reduced feeding into the system and an upset in biogas production.”

Authors: Anna Simet
Managing Editor, Biomass Magazine