(714d) Feedstock Preprocessing, Fractionation, and Blending to Improve Overall Cost, Supply, and Quality Considerations for Catalyzed and Uncatalyzed Fast Pyrolysis

Authors: 
Aston, J. E., Idaho National Laboratory
Thompson, V. S., Idaho National Laboratory
Lacey, J. A., Idaho National Laboratory
Thompson, D. N., Idaho National Laboratory
The success of lignocellulosic biofuels and biochemical industries depends on an economical and reliable supply of high-quality biomass. As such, biomass cost, supply, and quality are critical parameters to consider when choosing feedstocks and locations for biorefineries. Biomass cost is dependent upon feedstock type, location, availability, transportation costs, and the quality specifications required by the conversion technology. Biomass quality depends on inherent feedstock properties, field and storage conditions, and any preprocessing methods used to improve quality. Biomass quantity depends on location, field conditions, annual weather, and collection and storage conditions. Because of these variables, it is necessary to develop strategies that enable supply chain improvements in biomass quality and consistency to improve lower overall conversion costs and improve yields, while also securing a less risky feedstock supply.

The presented work examines the interdependencies of these variables and how they affect the biomass blends required by biomass depots and/or biorefineries to achieve the lowest cost feedstock with sufficient quality at the quantities needed for biorefinery operation. Four biomass depots were proposed in South Carolina to each produce 200,000 tons of feedstock per year. These depots supply a centrally located 800,000 ton biorefinery that converts the feedstocks to bio-oil using either catalyzed or uncatalyzed fast pyrolysis. The four depots utilize biomass based upon availability, but the feedstock or feedstock blend still met the minimum quality requirements for the biorefinery. Costs were minimized by using waste biomass resources such as construction and demolition waste, logging residues, and forest residuals. Preprocessing methods such as air classification and water washing or acid leaching were used to upgrade biomass quality. Air classification was found to be an effective method for separating low- and high-ash fractions of woody residues. For example, a high-ash fraction of logging residues was generated that contained approximately 50 wt% of the total original ash content, but less than 8 wt% of the original organic content. Dilute-acid leaching was then effectively used to remove between 85% (25°C, 0.5 wt% acid) and 98% (90°C, 1.0 wt% acid) of the alkali and alkaline earth metals from the high-ash fraction, making it suitable for recombination with the low-ash fraction. Various combinations of such preprocessing methods were tested to produce an array of blends that were available for recombination to produce least-cost blendstocks that met various conversion specifications. For both uncatalyzed and catalyzed fast pyrolysis, all four depots produced blends that met quality and quantity specifications at a cost lower than using a single feedstock.