Study explores energy balance of Fischer-Tropsch diesel via autothermal reforming of pyrolysis oil from biomass residue; spreadsheet offered as tool
16 May 2011
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.
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| 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.
Resources
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
They did a whole lot of work on that spreadsheet. It allows "what if" scenarios for a sort of manual simulation. Good job.
Posted by: SJC | 16 May 2011 at 02:11 PM
50% of the initial energy content of the biomass.
That is an excellent yield. Whether wheat straw, corn stalks or natural gas, there are more ways to power vehicles than depending on OPEC and imported oil.
Posted by: SJC | 17 May 2011 at 08:38 AM
The same question remains. How many countries can produce enough biomass to replace a major portion of the Oil they currently use without reducing essential food and animal feed production? In many countries the answer is very little.
Switching from beef to chicken meat could liberate land to increase biomass for more fuel production. Doing without large pets may be another way. Cutting down on meal size (from 4000 to less than 2000 cal.) could have a double benefit for many and liberate more land mass for biofuel production. My 350 lbs neighbor does not agree.
Posted by: HarveyD | 17 May 2011 at 10:51 AM
I don't know about many countries, I am concerned about the U.S., let the other countries be concerned about their situation. There is no synergy there to make this a U.N. issue.
30% of our petroleum refined gasoline can be replaced by synthetic fuels just gasifying 1 billion tons of biomass each year in the U.S. That is not even including fuel crops that could be grown on marginal land nor coal and natural gas.
I have mentioned all this before and there is ample proof for all of this, but people on here keep talking about a food/fuel dilemma when there is none.
Posted by: SJC | 17 May 2011 at 10:58 AM
The non-condensible gas product isn't storable, but the char certainly is. The NCG might be suitable as a feedstock for other products.
This suggests that the 31% energy used for drying and pyrolysis could be supplied by something else, such as concentrating solar or transient surpluses of wind power. At 17.4 GJ/t and 10 t/ha, surplus biomass like cornstalks would yield about 54 GJ/ha of char+NCG. This is a bit over 16 megawatt-hours of electricity or the sunlight hitting that hectare at 700 W/m^2 for a bit over 2 hours.
If only the char was salvaged, it would equal about 67% of the energy of the diesel product (assuming 40% field-to-product). It would have a myriad of uses, from making gas-turbine fuel in gasogenes to being plowed back into the soil as terra preta. Certainly worth investigating.
Posted by: Engineer-Poet | 20 May 2011 at 10:18 PM