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Thermochemical Processing: Converting Biomass into Fuels and Chemicals

By: Robert C. Brown, Director, and Robert Mills, Communications Specialist, Bioeconomy Institute, Iowa State University

The use of fermentation to produce ethanol from corn and other biomass is well known in the agricultural world. There are, however, other technologies that can convert biomass into fuels and chemicals. Foremost among these are thermochemical processes, which use heat and catalysis to break down biomass to intermediates that can be upgraded to transportation fuels.

Thermochemical processing uses heat and pressure to convert various types of feedstocks into fuels and chemicals.

Thermochemical processing uses heat and pressure to convert various types of feedstocks into fuels and chemicals.

One advantage of thermochemical processing is that the end result can be “drop-in fuels,” those that are fully compatible with the existing fuel infrastructure. While not perfect, these drop-in fuels are good enough to run in today’s engines without modification.

Another advantage to thermochemical processing is that most systems can work with a variety of biomass feedstocks. Often the feedstock is lignocellulosic biomass, such as corn stover, switchgrass, miscanthus, wood, etc. But thermochemical processing can also use lipid-rich biomass such as distillers dried grains and algae as well as mixed wastes from commercial and municipal sources.

There are two basic types of thermochemical processing, indirect and direct liquefaction. Indirect liquefaction includes gasification, where the solid biomass is heated to create synthesis gas, or syngas, that is subsequently upgraded to liquid fuels. Various catalysts are then used to convert the gas into alcohols or hydrocarbons. The advantages of gasification is that the process produces a uniform product and it is commercially proven. Gasification, however, requires technologies to clean the gases, which are still under development, and the capital costs can be high.

Direct liquefaction uses heat and pressure to convert the biomass into liquids which can then be further upgraded into finished products. Direct liquefaction includes pyrolysis and solvent liquefaction. In the case of pyrolysis, biomass is heated in the absence of oxygen. The process yields bio-oil, syngas, and a solid product known as biochar. The bio-oil can be upgraded to drop-in fuels. Pyrolysis can be performed at relatively small scales, allowing it to take place close to the source of biomass rather than moving biomass to one large, centralized processing facility. One of the major problems with pyrolysis is that the bio-oil is unstable, complicating its conversion into fuels.

Iowa State University researchers discuss a new pyrolysis pilot plant during its construction. The plant is now up and running and is used to research the multi-stage fractionation of bio-oil, a process that promises a way to economically convert biomass into many value-added products.

Iowa State University researchers discuss a new pyrolysis pilot plant during its construction. The plant is now up and running and is used to research the multi-stage fractionation of bio-oil, a process that promises a way to economically convert biomass into many value-added products.

At Iowa State University, we have invented a process to condense the pyrolysis gases in fractions, resulting in better, more stable products. The economics of fast pyrolysis are promising. In addition to producing fuels and chemicals from the bio-oil, the biochar may also have economic value. Consisting mostly of carbon, biochar can be used a soil amendment, helping retain moisture and nutrients. There is also research underway to use biochar as a filter medium for purifying water.

Solvent liquefaction, or solvolysis, is similar to pyrolysis except that it is performed in a solvent at elevated pressure. Though the fundamental chemistry of solvolysis is not well understood, the technology has promising economics. The process can upgrade bio-oil in a way similar to oil refining, and it can create sugars which can be further upgraded without expensive enzymes.

In addition to extensive research into thermochemical technologies, there are also many efforts underway to commercialize these technologies. Like all start-ups, these efforts have met with various degrees of success. There are, however, several pilot-scale systems being tested and commercial plants being built.

Bioenergy is a complex topic. There are many pathways from raw material to finished product. What’s more, bioenergy technology must be viewed in context of larger energy issues and policies. You can learn more in a book written for the general public, “Why are We Producing Biofuels,” by Robert C. Brown and Tristan R. Brown. The book is available on Amazon. You can read the first chapter for free online at: http://www.brownia.com/content/whyareweproducingbiofuels_excerpt.pdf.

Fuel In The Field

If not in its infancy, biomass farming is perhaps still toddling along. Yet, most indicators point to a significant increase in production and an additional source of revenue for farmers, as well as a variety of other benefits, depending on the crop being grown.

Signs point to a number of infrastructure, process and equipment enhancements that will make the harvesting, transportation and storage of biomass much more efficient in the next few years, if not sooner.

Many areas in the Corn Belt actually produce higher yields if a portion of the stover is removed.

Many areas in the Corn Belt actually produce higher yields if a portion of the stover is removed.

For starters, consider the harvesting of corn stover, which in many areas of the country can increase corn yields for the following year. Also, perennial grasses such as miscanthus and switchgrass can be grown on marginal land, require little in the way of inputs, and offer a number of environmental benefits, such as helping to filter runoff and prevent erosion.

Among such biomass-producing crops, stover already has a foothold. It’s readily available in many parts of the Corn Belt, where a partial harvest does help yields.

Now farmers and the biofuels industry are looking ahead at increased production of all things biomass, including the crops mentioned above, as well as energy sorghum, woody biomass and more. The U.S Department of Energy predicts total crop- and pastureland planted in bioenergy crops will increase from less than 10 million acres today to between 60 and 80 million acres over the next 15 years.

As a result of this increased demand, new processes and technologies are in development to help make the gathering and transport of biomass, particularly stover, more efficient and profitable for the farmer. Especially promising is single-pass harvesting, which promises the operator considerable time and fuel savings over other methods currently in use.

“AGCO has a unique solution for single-pass harvesting equipment with their new series of combines that are single-pass compatible,” says Dr. Matt Darr, assistant professor of Agricultural & Biosystems Engineering at Iowa State University. “AGCO is also a leader in the industry with single-pass baling products to provide producers and large energy companies the opportunity to make single-pass harvesting a reality within a supply chain.”

The technology in Hesston® by Massey Ferguson balers is ready-made to handle stover, as well as other biomass crops. Already, the Hesston 2170XD large square baler has earned its stripes for how densely it can pack the bulky crops, says David Ibbetson, a Kansas-based custom baler who uses two 2170XD balers to bundle some 15,000 bales each year in Iowa. He also uses Hesston round balers to bundle another 1,500-plus bales closer to his home in Yates Center.

Several other pieces of equipment that will aid in the harvesting of residue are now in the pipeline at AGCO. One such tool is a corn header that can harvest upwards of 150% higher volumes of corn and MOG. Another is a receiver chute that’s attached to the front of the baler and allows it to take in MOG without it being deposited on the ground before baling. “By having the baler accept the residue directly,” explains Maynard Herron, AGCO’s engineering manager at its Hesston, Kan., plant, “you cut in half the amount of ash in the bale. Those cleaner bales, of course, are more valuable and make this approach to stover more profitable to the farmer.”

playstoverWatch a video of Iowa State’s Dr. Matt Darr explaining when harvesting corn stover can increase yields, save money and time, and generate revenue at http://www.myfarmlife.com/crops/the-case-for-stover/.

Continue the conversation: Do you harvest stover? If so, have you seen a benefit on your farm?

If you would like to learn more about AGCO’s Biomass Solutions, please visit: www.bit.ly/AGCOBiomass.