Pyrolysis of forest residues: an approach to techno-economics for bio-fuel production

Authors: CARRASCO, JOSE - University Of Maine; GUNUKULA, SAMPATH - University Of Maine; Boateng, Akwasi; Mullen, Charles; DESISTO, WILLIAM - University Of Maine; WHEELER, CLAYTON - University Of Maine

Submitted to: Fuel
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2016
Publication Date: 1/5/2017
Publication URL: https://handle.nal.usda.gov/10113/5695407
Citation: Carrasco, J.L., Gunukula, S., Boateng, A.A., Mullen, C.A., Desisto, W.J., Wheeler, C.M. 2017. Pyrolysis of forest residues: an approach to techno-economics for bio-fuel production. Fuel. 193:477-484.

Interpretive Summary: Utilization of bio-renewable resources as replacement for fossil fuels can decrease the net release of greenhouse gases and thereby mitigate climate change. One technological platform being studied for conversion of biomass to biofuels is pyrolysis, the heating of a material in the absence of oxygen. When applied to biomass, pyrolysis produces a liquid called “bio-oil” that can be refined via hydrotreatment to “green” gasoline, jet or diesel fuels that are identical to those produced from petroleum. Although this process is clearly attractive from an environmental standpoint, for the technology to be adopted commercially, it must produce products cost-competitively to petroleum refining. Biomass resources vary in price and availability on a regional basis. “Hog fuel” which is a secondary woody residue produced from mill byproducts such as sawdust, bark and shavings is a relatively inexpensive biomass resource widely available in Maine. Therefore, software called Aspen Plus® was used to develop a model of a plant that would convert 2000 metric tons per day of “hog fuel” to gasoline and diesel fuel. This model was used to perform a techoeconomic analysis (TEA) which allows one to size equipment and estimate both capital and operational costs associated with a project. In this simulation the hydrogen required refining of the bio-oil was derived from solid (bio-char) and gaseous (syn-gas) co-products of the pyrolysis process, eliminating the need for production of hydrogen from fossil fuel sources (e.g. natural gas). The total capital investment for a grass-roots plant was estimated to be US$266 million with an annual operational cost of US$130 million. With a 30 year project life, a minimum fuel selling price was determined to be US$4.86 per gallon. The economic concerns are related to low pyrolysis yields and short hydrotreating catalyst lifetimes. This information will be useful for anyone considering development of a biomass pyrolysis based biorefinery.

Technical Abstract: The techno-economics for producing liquid fuels from Maine forest residues were determined from a combination of: (1) laboratory experiments at USDA-ARS’s Eastern Regional Research Center using hog fuel (a secondary woody residue produced from mill byproducts such as sawdust, bark and shavings) as a feedstock for pyrolysis to establish product yields and composition, and (2) Aspen Plus® process simulation for a feed rate of 2000 dry metric tons per day to estimate energy requirements and equipment sizes. The simulated plant includes feedstock sizing and drying, pyrolysis, hydrogen production and hydrotreatment of pyrolysis oils. The biomass is converted into bio-oil (61% yield), char (24%) and gases (15%) in the pyrolysis reactor, with an energy demand of 17%. The bio-oil is then hydrotreated to remove oxygen, thereby producing hydrocarbon fuels. The final mass yield of gasoline/diesel hydrocarbons is 16% by mass with a 40% energy yield based on the dry biomass fed, and this yield represents a fuel production of 51.9 gallons per dry metric ton of feedstock. A unique aspect of the process simulated herein is that pyrolysis char and gases are used as sources for both thermal energy and hydrogen, greatly decreasing the need to input fossil energy. The total capital investment for a grass-roots plant was estimated to be US$266 million with an annual operational cost of US$130 million. With a 30 year project life, a minimum fuel selling price was determined to be US$4.86 per gallon. The economic concerns are related to low pyrolysis yields and short hydrotreating catalyst lifetimes.