Study explores energy balance of Fischer-Tropsch diesel via autothermal reforming of pyrolysis oil from biomass residue; spreadsheet offered as tool
Researchers from the Stevens Institute of Technology, BASF Catalyst and Golden BioMass Fuels Corporation report on their investigation of an energy balance, in broad outline, for the production of a high-quality synthetic diesel from residual crop biomass via a Fischer-Tropsch route in a paper published in the ACS journal Energy & Fuels.
They incorporated the material and energy balance for the study into an Excel spreadsheet, which they are making available in the hope of providing greater transparency, as well as ease of scenario manipulation than has generally been found in the literature. The particular process explored in the paper consists of:
- harvesting surplus biomass (such as crop residue);
- locally pyrolyzing the biomass into pyrolysis oil (PO), char, and noncondensable gas (NCG);
- transporting the PO to a remote central processing facility;
- converting the PO at this facility by autothermal reforming (ATR) into synthesis gas (CO and H2); and
- Fischer–Tropsch (FT) synthesis of the syngas into diesel fuel.
|Modelled process for the conversion of biomass into liquid transportation fuel. Credit: ACS, Manganaro et al. Click to enlarge.|
In carrying out our calculations, we have made several assumptions about the values of the process parameters. These parameters, of course, can be modified as better input data become available. The material and energy balance has been incorporated into an Excel spreadsheet. The scope and our approach to the energy budget using a widely available spreadsheet hopefully provides greater transparency, as well as ease of scenario manipulation than has generally been found in the literature. The estimated energy efficiencies computed with the spreadsheet are comparable to those obtained with Aspen software.—Manganaro et al.
The team found that the process considered, in which a portion of the char and noncondensable gas are used to supply heat to the drying and pyrolysis steps and under the assumptions made, has an energy efficiency to liquid fuel on the order of 40%—i.e., 40% of the initial energy in the biomass will be found in the final liquid fuel after subtracting out external energy supplied for complete processing, including transportation as well as material losses.
If the energy of the remaining char and NCG is added to that in the product diesel oil, the total recovered energy is estimated to be 50% of the initial energy content of the biomass. If char and NCG are not used as a heat source in the process, the energy efficiency of the produced diesel drops from 40% to 15%.
It must be realized that the distribution of energy content among the fast pyrolysis products PO, char, and NCG is 69%, 27%, and 4%, respectively. Therefore, using char and NCG to provide fuel for the drying and pyrolysis steps is very critical in maintaining high energy efficiency of the product fuel. The weight of diesel fuel produced is estimated to be 13% of the initial weight of biomass, implying that 1 t of biomass (30% moisture) will produce 1.0 barrels of diesel oil. The pyrolysis of biomass to PO, char, and NCG is estimated to have an intrinsic energy efficiency of 90%. For the model considered, trucking biomass to a central facility without first converting it to PO is estimated to reduce energy efficiency by 1%.—Manganaro et al.
Using the process modelled, replacing ~15% of current petroleum consumption in the United States would require the gathering of biomass from a substantial portion of the land area of the major crop-producing states, the team concluded.
Clearly, there are many, many conceptual variations and refinements to be explored, not to mention an experimental terra incognita.—Manganaro et al.
J. Manganaro, B. Chen, J. Adeosun, S. Lakhapatri, D. Favetta, A. Lawal, R. Farrauto, L. Dorazio and D. J. Rosse (2011) Conversion of Residual Biomass into Liquid Transportation Fuel: An Energy Analysis. Energy Fuels, Article ASAP doi: 10.1021/ef200327e