There is a new kid on the block when it comes to biomass energy: torrefaction—the process of making biocoal out of biomass. Working to discover all of its advantages is Douglas G. Tiffany of the University of Minnesota and a team of partners. Currently, torrefied biomass boasts a reduction in greenhouse gasses by 85% per unit of energy substituted for coal. There is a lot to be excited about and a lot to learn. CERTs’ Co-Director, Joel Haskard, was able to interview Tiffany and get the inside scoop. Read on to see how torrefaction could be changing biomass efficiency forever!
Joel Haskard: Tell me about your recent project on torrefaction.
Douglas G. Tiffany: Over a year ago, I sought and received a grant from the Initiative for Renewable Energy and the Environment (IREE) to investigate the economics of torrefaction, a process of making biocoal out of biomass. Collaborating with me on this project were Dr. Vance Morey and Dr. Nalladurai Kaliyan of Bioproducts and Biosystems Engineering and Won Fy Lee, a graduate student in Applied Economics. Vance and Nalladurai focused on life cycle analysis and engineering issues, while Won and I modeled the profits of the businesses that would produce and use the biocoal or steam generated from the torrefaction process. My design for this project was to determine if the torrefaction plant and the users of its products could all find economic advantage from this technology. In my economic analyses, I want to learn the conditions for profitable, sustainable activities.
Haskard: What is torrefaction?
Tiffany: Torrefaction is a process of roasting biomass at 250-300 degrees C. in the absence of oxygen to produce biocoal. The source of the energy to drive the reaction comes from the biomass. Significant off-gasses are produced by the process and can be combusted to dry raw biomass or be used for other processes. Coffee beans are typically roasted by torrefaction. By excluding oxygen from the heated biomass, the biomass is transformed, but not combusted.
Haskard: It sounds like the torrefied biomass or “biocoal” loses a lot of its weight but keeps much of its energy content, is that correct?
Tiffany: Yes, the biomass loses about 30% of its dry matter and 10% of its energy. This has the effect of increasing the energy density of biomass by about 30% and making it dry, brittle, and easy to grind to the particle sizes of coal with which it may be mixed before combustion at a coal-fired power plant.
Haskard: Does this help with transportation? It seems transportation of heavy, diffuse biomass resources has often been a major impediment to project implementation.
Tiffany: Yes, torrefied biomass is a more efficient form for transportation because the moisture and some of the mass has been removed. The torrefied biomass, or biocoal, is hydrophobic, meaning that it sheds water. This property is useful so that biomass does not take up moisture when stored in outdoor yards or in open railcars.
Haskard: What were some of your findings in regards to greenhouse gases?
Tiffany: Because biocoal arises from biomass and uses process energy from itself, the Greenhouse Gasses released by its production and ultimate combustion are minimal and primarily represent the activities of harvesting the biomass and transporting the biocoal. When the energy of biocoal is substituted for some of the energy of fossil coal, a substantial reduction of 90% occurs. Biocoal blends as high as 30% by mass have been tested in pulverized coal power plants and would result in GHG reductions of 25.6%.
Haskard: How do the economics of biocoal stack up against coal, the big (cheaper) kid on the block?
Tiffany: Here’s where things get difficult. Biocoal will cost more than fossil coal for two main reasons. 1) Biocoal requires biomass that will probably cost $70 or more delivered to the torrefaction plant in the case of corn stover and it takes 1.7 tons of corn stover at 17% moisture to produce 1.0 ton of biocoal at zero moisture. 2) Fossil coal is very cheap in the U.S. For example Powder River Basin low sulfur coal is delivered to Minnesota power plants for less than $40 per ton, while more energy dense bituminous coal is delivered in eastern states for $69 on average. Costs to process a ton of biocoal are typically $42 per ton on top of the cost of the raw biomass. Biocoal has other advantages besides lower GHG emissions, and it is lower in SOx emissions, NOx emissions and can comply with state renewable energy standards.
Haskard: It seems like there is a real bang for the buck when you can utilize the steam from the torrefaction process by co-locating it with some place that could use the steam for power, like an ethanol plant. Can you speak further on that?
Tiffany: In our study, we found that there was typically an advantage of $25 per ton of biocoal produced for torrefaction plants that were co-located next to a business that could use steam produced by the off-gasses. This turns into a big financial advantage over an independent torrefaction plant, a “lonely plant.” Because ethanol plants are judged to a certain extent on the amount of GHGs associated with each gallon of ethanol produced and used, we modeled the situation of a torrefaction plant that was co-located next to an ethanol plant. We also modeled the potential impacts of currently absent carbon taxes.
Haskard: What sorts of impacts would carbon taxes have on the economics of ethanol plants using renewable steam extracted from a torrefaction plant?
Tiffany: Ethanol plants would be rewarded for using steam produced from renewable off-gasses from biomass from a torrefaction plant instead of using natural gas, which is the typical practice. This would occur even if the U.S. should eventually apply carbon taxes at low rates to most energy sources, whether petroleum, natural gas, coal, etc. Current law doesn’t offer this sort of incentive; but if applied, consumers would be rewarded for the GHG emissions displaced by using ethanol blends in their gasoline and biocoal blends at the power plants that supply their electricity.
Haskard: Are there any specific torrefaction projects here in Minnesota moving forward?
Tiffany: There have been some significant research activities at academic and commercial entities in Minnesota. Bepex International conducted quite a bit of research on torrefaction of corn stover, a very abundant and typically dry biomass source. Bepex, through their Torrsys subsidiary designed and operated some pilot equipment to produce biocoal that could be tested in test burns at several power plants. The Natural Resources Research Institute (NRRI), associated with the UMD, has conducted research on the fine points of torrefaction methods of various types of wood and wood wastes. Power utilities like Xcel and others have participated in test-burns of torrefied biomass or biocoal.
Haskard: Where can I see torrefaction plants that are commercial and operating today?
Tiffany: In Mississippi, Georgia, Maine, and British Columbia you can see commercial torrefaction facilities in operation. Most of the production of biocoal at these facilities is destined for export out of North America to Germany, the Netherlands, and Great Britain. The European countries have targets to meet with respect to GHG reductions and already face prices of imported coal above $100 per ton. Biocoal at $140 per ton plus transportation is a competitive choice for electricity producers in those countries that are engaged in reducing GHG emissions.
