A team from Pacific Northwest National Laboratory (PNNL) and Idaho National Laboratory has evaluated the process economics and greenhouse gas (GHG) emissions for the conversion of 11 biomass feedstocks to produce transportation fuels via fast pyrolysis and then pyrolysis oil upgrading via hydrodeoxygenation. An open-access paper on their work appears in the journal Fuel.

Simplified block flow diagram for fast pyrolysis and upgrading to produce hydrocarbon fuel blendstocks from biomass. Meyer et al.

The team used 6 pure feeds (pine, tulip poplar, hybrid poplar, switchgrass, corn stover, oriented strand board) and five blends. Feedstock blends combined pine, tulip poplar, hybrid poplar, switchgrass, and oriented strand board in various ratios.

The assumptions in the analysis are based on “field to wheel” data generated from a multistep experiment that started from biomass preparation and was followed by biomass feedstock conversion to pyrolysis oil, and then finished by pyrolysis oil upgrading to produce hydrocarbon liquid fuel.

They found that for all eleven feedstocks, the largest cost contribution to MFSP is capital-related costs, which is approximately 30%–40% of the minimum fuel selling price (MFSP) and includes capital depreciation, income tax, and return on investment.

Feedstock cost (approximately 30% of MFSP), hydrotreating catalyst cost (13%–18% of MFSP) and labor cost (12%–15% of MFSP) also contribute significant cost to MFSP.

Fuel life cycle GHGs for gasoline fuel blendstock from pyrolysis and upgrading. GHG reduction from the 2005 petroleum gasoline baseline of 93.08 g CO₂-e/MJ. Meyer et al.

The final fuel product yield is one of the most significant parameters affecting the process economics.

They found that the highest product yield is from pine feedstock, while switchgrass feedstock gives the lowest yield. Using blends (woody mixed with herbaceous), with which the product yield is still reasonable, may further improve process economics compared to pure feedstocks because of the lower feedstock price for blends.

Blend feedstocks cost less than pure feedstock because of greater diversity in feedstock choices, lower risk, and lower transportation costs.

However, they observed that GHG reduction does not necessarily align with favorable economics.

Process parameters that most significantly affect the life cycle GHG emissions (from feedstock production to vehicle operation) are:

1. natural gas used for hydrogen production and electricity usage in fast pyrolysis and pyrolysis oil upgrading;

2. energy usage in the feedstock harvesting, transport, and preprocessing operations; and

3. nitrogen fertilizer usage for growing biomass.

Resources

• Pimphan A. Meyer, Lesley J. Snowden-Swan, Susanne B. Jones, Kenneth G. Rappé, Damon S. Hartley (2020) “The effect of feedstock composition on fast pyrolysis and upgrading to transportation fuels: Techno-economic analysis and greenhouse gas life cycle analysis,” Fuel, Volume 259 doi: 10.1016/j.fuel.2019.116218.