Off the rails

The northwest quadrant of Michigan’s Lower Peninsula is one of the more beautiful places one could visit in this country. Just outside of the Manistee National Forest near the city of Cadillac lies the tiny town of McBain. This is the home of Viking Energy, an 18-megawatt (MW) energy plant powered by renewable biomass fuel. While most of the fuel used at the McBain plant comes from forestry byproducts, a meaningful percentage of that fuel is supplemented with used railroad ties that are brought in from around the Midwest.

Energy derived from biomass and other organic waste, and even municipal refuse, continues to grow in importance as a source of reliable power generation. Wind and solar may contribute a higher percentage of power to the grid, but biomass fuels have definitely come into their economic own in the last decade. As a result, more generators are looking to this seemingly never-ending supply as a means to contribute to the nation’s insatiable appetite for energy.

Biomass fuels can be derived from numerous different waste streams, from clean construction wood, to agricultural residue to forestry slash. And in northwest Michigan, timber is big business. Not surprisingly, wood waste from the forestry industry is a very reliable fuel source for Viking Energy. However, it also comes with a big challenge. “If you want to know the heating value [British thermal unit rating] of wood, you have to ask what kind of tree it came from,” explains Plant Manager Tom Vine. “Powering our generators with mixed wood fuel can create peaks and valleys in energy output, which is not a very desirable condition for a power plant.”

A CONSISTENT FEED

Having spent nearly 25 years in nuclear energy generation, refueling was a concern Vine used to have to deal with only every two years or so. But now that he oversees a biomass plant, refueling is something he is concerned with nearly every minute of every day. Power output depends explicitly on the heating value of the wood chips being fed to the boiler, and keeping that mix consistent requires a precise science of blending multiple sources to create an evenly burning fuel. That’s where the railroad ties make such a difference.

“Railroad ties are extremely dry and extremely dense,” Vine continues. “When we blend it with the higher moisture, less dense wood from the timber industry, we are able to generate a wood chip blend that burns with much more predictability. That allows us to regulate our power output and maintain a consistent feed to the grid.”

Not only is Viking Energy exclusively fueled by biomass, the company also is a producer of its own fuel, accepting raw materials from the marketplace and processing them on-site into the 2-inch to 3-inch wood chip specification required for an efficient burn in their boiler. The railroad ties are supplied by a rail maintenance company that performs work on the thousands of miles of track throughout the Midwest.

“The U.S. railroad industry replaces about 21 million ties each year,” says Vine. “So if they weren’t burned for power, they’d end up in the landfill. And that’s a lot of railroad ties.” But with the recent completion of a rail spur leading to their property, Viking Energy is ensured a steady supply of those ties are offloaded directly into their shredders to be converted to fuel.

MAKING A DIFFERENCE

Having access to a nearly unlimited number of reclaimed railroad ties is great. Turning those rail ties into fuel, however, is yet another challenge that falls under Vine’s oversight. That task was previously handled by a high horsepower high-speed grinder, which got the job done but not without numerous issues. The grinder’s tremendous cost related to its high fuel consumption and its lack of durability in tackling the heavily contaminated rail ties were just two problems.

“Our original grinder could produce a decent fuel chip, but it just guzzled fuel,” Vine says. “And if one large rail plate were to get in there, it could easily take us down for half a day and cost upwards of $20,000 in damage. We certainly took care to clean the material prior to feeding, but even if just 1 percent of the contaminants get by us, that can do some significant damage.”

After conducting a lengthy process of due diligence on options for new equipment, Viking Energy finally decided on a Doppstadt DW 3060 slow-speed shredder in spring 2014. About six months later, the company also took delivery of a Doppstadt AK 530 high-speed grinder. The two machines in tandem are able to plow through nearly 250 tons of rail ties per day, with virtually no downtime or failures due to the material being processed. Another benefit of the change is that it has made an enormous difference to the company’s bottom line.

“We are running both of these machines on less fuel than it took to run our previous high-speed grinder alone. The fuel efficiency of the Doppstadts is just tremendous.”

Doppstadt DW series slow-speed shredders deliver low-speed, high-torque reduction through a tooth-and-comb mechanism that is designed to process robust source material. If the shaft encounters too much resistance in the hopper due to the presence of an unshreddable contaminant (such as a steel rail plate) the automatic breakaway system engages, and the material is simply passed out of the shredding chamber. The comb quickly reengages and processing continues uninterrupted.

Because the DW shredders are designed to perform a primary material reduction, the output is typically a rough 12-inch to 18-inch spec, clearly not suitable for boiler fuel. By discharging directly into the hopper of the AK 530 high-speed grinder, Viking Energy is able to produce a consistent, boiler spec fuel in a single pass through the two machines. An overband magnet on the DW discharge conveyor ensures any last metal contaminants are removed before feeding the AK grinder. The solution is an ideal fit for consistent, high-volume production of biomass-derived fuel for energy generation.

ON-SITE ADVANTAGE

Vine turned to Alta Equipment, Wixom, Michigan, to handle the sale and to provide support for the machines. The attention and commitment he has experienced has exceeded expectations. “We do most of our own maintenance, but Alta has been able to step in and help, primarily on the 3060,” he says. “We also appreciate that they have both the 3060 and 530 in their rental fleet. We recently changed out the wear plates on our 530 and were able to secure another machine for a short time so that we didn’t lose those days of productivity.”

When asked what he finds to be the most challenging part of running a biomass power plant, Vine unequivocally points to having a consistent supply of good, quality fuel. He sees Viking’s unique ability to process materials on-site as a real advantage. “You’re forced to have a more local or regional fuel source, so you tend to be more engaged with your material suppliers,” he explains. “That’s where the operation we have with railroad ties is so important. By blending them in, it allows us to maintain a much more consistent stream.” That’s crucial to the stability of the company’s boiler. “Trying to run on forest residue alone creates such yo-yo output from the plant,” Vine says.

The challenges, Vine says, are what he finds most appealing about his position. “With a small plant, the economics are much more challenging than on a larger scale. But being able to work on the efficiency and optimization and working to make our plant run better and more consistently is a challenge I always look forward to.”

The article was submitted by Avon, Ohio-based Ecoverse. More information is available at www.ecoverse.net.