Cellulosic Feedstocks of the Future

by Holly Jessen (Ethanol Producer Magazine) Commercial-scale production and harvest of several annual and perennial biomass feedstocks is under way, paving the way for biofuels, biopower and biobased products. -- ... 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.

“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 ( Chris Standlee, executive vice president of global affairs for Abengoa Bioenergy) 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.

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.

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 (Sam Jackson, vice president of business development for Genera Energy) 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.

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.” READ MORE / MORE