Cellulosic feedstocks of the future

Source: By Holly Jessen, Ethanol Producer Magazine • Posted: Friday, September 18, 2015

Focusing solely on the big three cellulosic ethanol producers, corn is still king, even in second-generation advanced biofuels.  Corn stover is the feedstock of choice of Abengoa Bioenergy, DuPont Advanced Biofuels and Poet-DSM, at least in the near-term.

There are, however, a handful of other feedstocks that are gaining traction as potential feedstocks of the future, says Kelly Tiller, president and CEO of Genera Energy Inc. Specifically, switchgrass, miscanthus, biomass sorghum, sweet sorghum and energy cane are all currently being grown at commercial-scale production levels. Although there are other crops of interest, of course, Tiller zeros in on those six, counting corn stover, because they’ve been shown to work on the large-scale and are economically feasible, she tells Ethanol Producer Magazine.

Genera Energy provides biomass supply solutions to a variety of industries, including advanced biofuels. The company works with farmers and landowners, in some cases handling everything from land management, planting, harvest, transportation and storage. Although the company isn’t able to go into specifics, due to confidentially agreements with clients, Tiller said Genera is actively working in 10 states.

Corn Stover
Poet LLC, Abengoa and DuPont provided EPM with statements about the feedstock of today as well as what might come down the line. “We are certainly looking into additional feedstocks for the future, but our efforts today are primarily focused on corn crop residue in our joint venture with DSM,” says Matt Merritt, director of public relations for Poet. “Corn crop residue offers many benefits, not the least of which is feedstock logistics and the opportunities for colocation with grain ethanol plants.”

Abengoa is currently most interested in corn stover and wheat straw at its Kansas biorefinery, says Chris Standlee, executive vice president of global affairs for Abengoa Bioenergy, because of the large amount of those crops available locally. “In short, we are still ramping up production capacities at Hugoton, and at this point the only feedstock we have used there is corn stover,” he says. “We will use wheat straw as we increase production rates closer to capacity, but even at full capacity we will probably only use 10 percent to 20 percent wheat straw and almost all the rest will be corn stover.”

Energy sorghum, which Standlee says looks promising as a feedstock, is grown locally in one of several test plots, managed by an Abengoa subsidiary that is dedicated to developing new feedstocks for the production of cellulosic sugars. The company also has a small 30-acre plot of switchgrass planted on the land where the ethanol plant is built. Finally, the facility could also convert other grasses harvested locally, depending on factors such as price, availability and accessibility. “Other feedstocks will be used when it makes economic sense for us to do so, or when we want to run a test for a particular feedstock for possible use at other facilities,” he says.

DuPont, Nevada, Iowa, facility will focus on maximizing production and productivity using corn stover says Jan Koninckx, global business lead for advanced biofuels. However, the company, which will celebrate its cellulosic ethanol plant grand opening on Oct. 30, is investigating the potential of other feedstocks, including sugarcane bagasse, switchgrass, biomass sorghum and empty fruit bunch, a residue of palm oil production, all of which can be processed using DuPont’s design. “We are using our pilot plant in Tennessee to validate other feedstocks,” he says.

Sam Jackson, vice president of business development for Genera Energy, describes corn stover as an opportunistic feedstock. It’s secondary to corn-grain production and, in some cases, can actually help solve problems when some is removed from the field. “But the same circumstances that offer economic advantages for collecting stover biomass also introduce some disadvantages in material handling and processing,” he says. “Dirt and other materials picked up off the ground when harvesting stover can cause significant problems in downstream processing and stover moisture content can be highly variable, which can introduce costs and processing challenges.”

Perennial Grasses 
With corn stover taking up a lot of attention, there hasn’t recently been as much buzz about purpose-grown energy crops such as switchgrass and miscanthus. But planting and harvesting of these crops is actually happening at fairly large scale, Tiller says. Today, the crops are more commercially viable because the time needed to establish plantings has been reduced. It is possible, Tiller says, to harvest switchgrass and miscanthus in the first year, but full productivity is now possible by about the second year.

Native grasses also offer the second benefit of conservation value. The crop provides wildlife habitat, soil stabilization and even the ability to improve degraded soils over time. Harvest of perennial grasses can also be spread out over three or four months, or perhaps longer, in some cases, Tiller adds.

Crops like switchgrass and miscanthus, which are harvested dry, produce feedstocks that are consistent, clean and have low variability, Jackson says. On the flip side, the grasses also have low bulk densities, which results in challenges and additional costs in storage and transport.

Sorghum Varieties 
There’s also commercial activity happening with the annual energy crops biomass sorghum and sweet sorghum, Tiller says. One big advantage of sorghum is that is requires less water than other row crops, so it’s particularly attractive in areas under drought stress or more mindful of water conservation. The crop also has some value as a silage or forage crop.  “So that gives you a lot of flexibility in terms of being able to diversify those market outlets,” she says.

In addition, since sorghum is an annual crop that is already produced and harvested in a similar manner to other row crops, it can be harvested with existing equipment and knowledge. In other words, there’s less of a learning curve.

Biomass sorghum is a crop that provides high yield and flexibility in land use from year to year, Jackson says. On the other hand, it’s typically harvested at about 50 percent or higher moisture levels. “High moisture may limit the ability to cost-effectively mill a feedstock to fine particle sizes, store it for long periods of time, or use in some combustion processes,” he says.

Energy Cane
This crop can be grown in a limited geographic area, such as in the Gulf Coast or Southern California, Tiller says. Energy cane requires tropical conditions. Still, it’s a crop worth mentioning due to its tremendous yield potential, she says.

Feedstock Value
One exciting advancement in recent years, as more of these crops are planted and harvested on commercial scale, is yield information. “It’s one thing to have yields that are coming out of a laboratory or a designed experiment, but what we are seeing is very good documentation of very good, real world data on large scale,” she says. “And, they are quite good. I think, again, it’s validation for the true yield potential and information that some of the assumptions are valid and achievable in real world situations.”

Still, Tiller and Jackson agree, all tons are not created equal. While it’s true that tons are an easy way to compare feedstocks, such as comparing the number of tons harvested per acre or the cost per ton of delivered material, there’s more to consider. “While these are useful data points, they only tell part of the story,” Jackson adds.

For example, in a comparison of a crop that yields 7 tons per acre, with a delivered price of $75-per ton and a crop yielding 12 tons per acre with a delivered price of $60 per ton, high yield and lower cost might not necessarily make the $60 crop the most attractive feedstock, he points out. If the $75 a ton crop is of a consistent and high quality with good storability, low handling costs and good conversion rates, it may actually be the better deal in the end.

“The true cost associated with any biomass feedstock is the accumulation of cost from preparing the land for planting, crop production and management, harvesting, aggregation, logistics, storage, material handling, preprocessing and conveyance into the conversion facility’s process,” he says. “To truly compare each feedstock, that total cost should be calculated as the starting point for comparing the cost of feedstock A vs. B. But to truly understand the relative value of a given feedstock, a more appropriate metric is the total cost of that feedstock represented in one or more marketable products derived from the biomass.”

In the end, there isn’t one single best feedstock. “All feedstocks have comparative advantages and disadvantages,” Jackson says, “and any feedstock’s value in a finished product depends on the region and the specific downstream material handling, pre-processing and conversion process, in addition to all of the characteristics and costs that are feedstock-specific.”