Researchers Estimate “Sun-to-Fuel” Fuel Yields from Different Biomass-based Processes, Propose New Process to Deliver Higher Yield
14 June 2010
|Estimated values of the overall annual biofuel yield from 1 m2 of land area with annual solar incident energy of 6307 MJ/ m2·y. Credit: ACS, Singh et al. Click to enlarge.|
A team from Purdue University has estimated the “sun-to-fuel” (S2F) yield for liquid hydrocarbon fuel via different biomass pathways and found that the S2F yield for self-contained processes that mainly rely on the biomass to supply all the energy need is “quite low”. Even at a high biomass collection rate of 6.25 kg/m2·y, only ~1.16% of the solar energy is estimated to be recovered as liquid fuel.
The researchers also found that the S2F yield can potentially be increased by a factor of 1.5-3 when all the available land area is not used to grow dedicated fuel crop but the solar energy falling on a portion of the land area is harnessed as hydrogen which is then used in novel augmented biomass conversion processes to increase biomass carbon yield as liquid fuel.
In a paper on their work published 7 June in the ACS journal Environmental Science & Technology, they propose a novel standalone H2Bioil-B process, in which a portion of the biomass is gasified to provide H2 for the fast-hydropyrolysis/hydrodeoxygenation of the remaining biomass, as a means to increase the yield.
Due to the relatively low efficiencies for growing dedicated biomass for transportation fuel and the limited availability of SAW [sustainably available waste] biomass, there is a need to critically examine the amount of liquid fuel that can be produced from a given quantity of biomass. First, we need to understand the potential of self-contained process where biomass is the main source of energy and liquid fuel production is maximized. Second, we need to develop augmented processes that will synergistically use supplemental energy available at much higher efficiencies to increase liquid fuel production. This will provide us the potential to efficiently increase liquid fuel production from a given quantity of biomass and thereby an assessment of the degree to which biomass can play a role in a transportation fuel infrastructure.
—Singh et al.
Two main contributing factors to the low S2F yield for self-contained process are:
- The relatively low recovery of solar energy as biomass energy; and
- The fact that less than 50% of the biomass carbon recovery in the liquid fuel is from self-contained processes.
Augmented processes are estimated to have higher S2F yield because hydrogen is harvested from solar energy with a much higher efficiency than biomass.
The energy content on a per carbon basis for biomass sources such as Switchgrass, Poplar, and sugars is only two thirds of the energy content of the molecules composing gasoline. This means that when biomass carbon molecules are upgraded to a high energy density liquid fuel such as gasoline, even for a 100% energy efficient conversion process, about one-third of the biomass carbon atoms will be rejected as low energy molecules such as CO2.
With reasonably optimistic process conversion efficiencies, we find...that roughly only half of the biomass carbon is recovered as high energy density liquid fuel. Most likely, the lost carbon will be in its low-energy state as CO2. Considering the fact that solar energy to biomass carbon is a low-efficiency process, it is attractive to find processes that will economically either reduce or eliminate the loss of condensed biomass carbon as CO2 during the biomass to liquid fuel conversion process.
It is possible to envision thermochemical as well as biochemical conversion processes using supplementary sources of energy such as heat, H2, or electricity to increase production of high energy density liquid fuel per ton of biomass. We have focused here on thermochemical routes. It is worth noting that for self-contained biomass conversion processes both biochemical as well as gasification/FTD processes were found to provide similar yields. Therefore, we expect that the yields calculated from thermochemical processes using supplemental energy should provide good target estimates for the corresponding non-thermochemical processes as well.
—Singh et al.
|H2Bioil-B process where a portion of the feed biomass (32-42%) is fed to the gasification zone to provide H2 for fast-hydropyrolysis and HDO of the remaining biomass fed to the hydropyrolysis zone. Credit: ACS, Singh et al. Click to enlarge.|
In the proposed H2Bioil-B process, depending on the efficiency of gasification section, 32-42% of the total biomass is gasified to produce a syngas which is sufficient to hydropyrolyze and hydrodeoxygenate the remaining fraction of the biomass that is directly fed to the hydropyrolysis zone.
The hot gas from the gasifier is directly injected in the pyrolyzer zone. If needed, the temperature of the exhaust gas prior to its injection in the pyrolyzer zone may be adjusted. Also, if required, a hot or a cold recycle stream may be injected between the gasifier and the pyrolyzer zone to provide better temperature control in the pyrolyzer section of the reactor.
The researchers found that while a process such as H2CAR [hybrid hydrogen-carbon process], based on gasification/FT chemistry, can recover nearly 100% biomass carbon, it would also need approximately 0.33 kg H2/L oil produced. On the other hand, fast hydropyrolysis/ HDO-based H2Bioil has a potential to recover ~70% biomass carbon with 0.11 kg H2/L oil.
They estimated the H2Bio-B process is estimated to be able to produce 125-146 ethanol gallon equivalents (ege)/ton of biomass of high energy density oil. The augmented version of fast-hydropyrolysis/hydrodeoxygenation, where H2 is generated from a nonbiomass energy source, is estimated to provide liquid fuel yields as high as 215 ege/ton of biomass.
This H2Bioil-B process, after successful experimental demonstration, could result in a high energy density liquid fuel yield that is greater than other known self-contained processes.
—Singh et al.
Navneet R. Singh, W. Nicholas Delgass, Fabio H. Ribeiro and Rakesh Agrawal (2010) Estimation of Liquid Fuel Yields from Biomass. Environ. Sci. Technol., Article ASAP doi: 10.1021/es100316z
This is what I figured, if you add some H2 you can use more CO and get more fuel. You could gas shift and get more H2 but end up with more CO2, this seems like a better method.
Posted by: SJC | 14 June 2010 at 06:42 AM
These are all pants - you HAVE to use anaerobic digestion to get the most distance from sunlight falling on an acre of land. Making biogas, cleaning it and upgrading it to biomethane, then running trucks on dual fuel diesel-compressed biomethane will give DOUBLE the distance.
If its cars you are after, the Passat Ecofuel on compressed biomethane is by far the best.
There are so many reports that show this - cant understand why the authors did not pick these up.
Posted by: baldwincng | 14 June 2010 at 07:00 AM
Currently 1.5 acres of good farm land are required to make enough agro-fuel for one average gas guzzler and 0.5 acres (min) are required to feed one human. (NB: large beef eaters require much more because beef (like plants) are very poor energy converters, less than 9% efficient, i.e. require 11+ units to produce one unit.
Recent solar cells, with up to 30% efficiency, could do a much better job and could be installed in desert land, unused roofs etc and not use any farm land. Wind energy is another good source that would not compete with food production.
Posted by: HarveyD | 14 June 2010 at 07:42 AM
PV it is then.
Posted by: clett | 14 June 2010 at 08:40 AM
clett: The only problem with PV is the high cost energy storage required for low or no sunlight hours. The same applies, to a lesser degree, for Wind turbines. Short of affordable e-energy storage, those two clean energy sources need complementary replacement energy. Hydro is ideal because it can be turned on and off at will and the huge water reservoirs are excellent low cost storage units. NG power plants can also be used to supplement Sun and Wind variable power sources. Managing the power mic may be a challenge. Eventually, PHEVs and BEVs could help to supply some of the needed energy.
Posted by: HarveyD | 14 June 2010 at 09:50 AM
I'm with Clett. PV to a battery is probably even more efficient. I would like to see the same analysis for fueling a Nissan Leaf using PV. How many MJ/m2-yr do we get for a BEV?
Posted by: HealthyBreeze | 14 June 2010 at 09:50 AM
PV to EV payback starts to look good when you compare it to fuel costs. Sure you put the power on the grid during the day and charge at night, but is a good deal if you can get an affordable system in the future.
Posted by: SJC | 14 June 2010 at 10:59 AM
Answering my own question, a square meter of PV (10% efficient, 40 degrees north latitude, ~300 clear days per year) produces about 450 Mj/m2-yr. If you have a BEV with 50 Kilowatt hours of storage, that square meter will recharge your batteries about 2.5x per year.
If a 1500 square foot house has about half its roof sloped towards the south, it can have about 60 square meters of PV, which would supply about 150 full battery recharges per year. Since most people would only need to recharge 60-75 times per year, the system could be 30 square meters, or the rest could be for powering the house itself. Of course, once the juice is in the batteries, those Mj can be converted into travel 2-4x more efficiently than any combustion process.
Conversely, using biomass would require several hectares per vehicle owner to grow, harvest, transport, refine, transport, and distribute, with profit and energy costs built in for each farmer, refinery worker, trucker, and gas station attendant.
Sure PV is still expensive, and lithium batteries are still expensive, but the land use is at least 50-100x more efficient than the best biofuels.
Posted by: HealthyBreeze | 14 June 2010 at 11:10 AM
The answer isn't PV there is insuficient doping material available to supply all the silicon arrays world wide.
The solution is low tech Solar Thermal with fused salt storage. Hundreds of megawatt plants of this sort are already in operation in Calif. A new very large one is planned in Algeria to be built by Siemens. This will export electricity to Europe using DC transmission lines.
Posted by: Mannstein | 14 June 2010 at 12:22 PM
Maybe an easier way to do the math on PV is in Kwhr instead of megajoules. If a driver needs 50 Kwhr per week for their BEV, then they need a PV system that produces ~7 Kwhr/day, or a 1 to 1.5 Kwhr peak system time 5-8 hours per day. Such a system would cost, what $12K to $20K minus your local incentives? Your Nissan Leaf costs $20K-$25K depending on your local incentives? The PV system also increases the value of your home equity. So, $30K to $40K for a vehicle with a lifetime supply of fuel, and a more valuable home.
Posted by: HealthyBreeze | 14 June 2010 at 02:08 PM
Lets not forget the price of good farm land ($10,000 to $20,000) an acre or about $15K to $30K per average gas/ethanol guzzler. That alone would buy a large long life storage battery, The other associated agro-fuel cost would buy most of the PVs required. In other words, PVs + storage batteries may be cheaper than farm land + all other ethanol production and delivery cost.
Grain ethanol is certainly not the answer.
Posted by: HarveyD | 14 June 2010 at 02:15 PM
"Phosphorus atoms, which have five valence electrons, are used in doping n-type silicon..."
I do not see any shortage of phosphorus for doping silicon.
Posted by: SJC | 14 June 2010 at 02:19 PM
The most efficient route of renewable energy utilization is still solar and wind to electricity. The surplus of this electricity can be stored locally in the form of H2 for direct use as vehicle fuel, home heating, CHP, or backup electrical generation.
The future consumers will be presented with choices of whether to use higher-cost, less-efficient and more polluting carbon-based fuel, or lower-cost, more efficient, and non-polluting H2.
Posted by: Roger Pham | 14 June 2010 at 06:15 PM
....and also biofuels form multiple sources and hydrocabons converted from CO2. It needs to be a mix of all - better than putting all eggs in one basket.
Personally, I'm not keen on EVs until they can offer the performance and range of an efficient ICE, because I have a car for long distance road trips, not clogging up city streets. I couldn't afford to change anyway - i'm a bangernomics man.
Posted by: Scott | 15 June 2010 at 01:26 AM
Most families in USA and Canada have 2 or 3 vehicles. One EV per family (by 2020?) could be a goal to achieve on the way to total electrification by 2030. The family member who does more in city travel should use the EV. Polluting ICE vehicles could be progressively banned (or have to pay a special fee) for city center areas.
Posted by: HarveyD | 15 June 2010 at 06:19 AM
@ Roger Pham,
No. I do not think local H2 storage is desirable. It leaks, explodes, and wastes half the energy produced by your local PV or windpower converting to H2 and back to electricity (or worse, combustion). Nickel-Iron batteries lack the portability of lithium, but make up for it with extreme durability. Supposedly some of the Edison nickel-iron batteries made more than a century ago still work fine. With smart charging regimes Nickel-Iron batteries should be far more efficient than H2 for storing renewable energy.
Posted by: HealthyBreeze | 15 June 2010 at 08:46 AM
Hydrogen is a big industry even right now, and H2 is stored under pressures right now. There are thousands of industrial applications for stored H2. With increasing advancement in H2 adsorptive materials, we will be able to store more and more H2 with less and pressures.
Leakage and explosion are engineering issues for any kind of fuels, for which there are ways to prevent. Petroleum and Natural Gas do leak and explode as well, but we have learned to deal with those risks. Even lithium battery have risk of fire, and lead-acid battery have risk of explosion.
How come Nickel-Iron battery is not in popular use, if it is so good?
Posted by: Roger Pham | 15 June 2010 at 11:28 AM
HB: Any idea if those extremely long lasting battaeries are still available and how much they cost per Kwh?
Posted by: HarveyD | 15 June 2010 at 11:30 AM
http://www.beutilityfree.com/pdf_files/NiFeFlyer.pdf shows a price list and specs on on page 2. They are quoted in Ah, not Kwhr, with a 1220 Ah cell going for $1008.
@ Roger Pham,
NiFe batteries are more expensive than lead-acid batteries, and in vehicles their decades-long life was not needed, so they never really took off. Also, they don't do well below freezing temperatures. Their characteristics are better suited for stationary, getting-off-the-grid, indoor applications which may improve their economies of scale.
Posted by: HealthyBreeze | 15 June 2010 at 02:42 PM
"I do not see any shortage of phosphorus for doping silicon."
Not true if one proposes to use PV to supply the bulk of electricity used on the planet. This finding according to a recent IEEE Transactions paper.
Posted by: Mannstein | 15 June 2010 at 02:47 PM
@ Roger Pham
"How come Nickel-Iron battery is not in popular use, if it is so good?"
These batteries have poor self-discharge characteristcs and high internal resistnce. Their main advantage is extremely long life and rugged construction.
For advanced Nickel Iron batteries the energy density is projected as 55 Wh/kg and 110 Wh/L. Expected production cost is 250 $/kWh.
These are hardly stellar characteristics for traction applications.
Posted by: Mannstein | 15 June 2010 at 03:05 PM
Who is proposing PV as the "bulk electricity on the planet"? We were just talking about home roof top systems supplying the house and EV in an on grid system.
Posted by: SJC | 15 June 2010 at 04:29 PM
The diagram looks odd to me. The bottom orange block, H2, appears directly from the sun.
But H2 doesn't come directly from the sun. I have to assume they omitted two boxes like those shown for Electrolytic H2 into the H2Bioil Process.
The diagram may have been made that way to avoid clutter???
Mannstein reminds us solar thermal concentration with salt/storage is alive and running. That strikes me as the best approach for utilities.
The world has a lot of empty desert, and in North Africa, at least, the NIMBY voters won't stop it.
Posted by: Ken | 15 June 2010 at 09:12 PM
It realy depends on where the field is. In alot of places the best thing to do is convert biomass into gas for shipment via pipeline simply because the biomass and the consumer are far apart AND operate at different scheduals.
Posted by: wintermane2000 | 15 June 2010 at 11:21 PM
Biological organisms are energy harvesting and utilizing entities. We, ourselves, use plants as the basis for providing energy for our body systems, and plants are poor harvesters of solar energy. Photosynthesis is only about 4% efficient.
But the advantage of plants is that they do the hard job of concentrating nutrients for us and are comparatively easy to manage and at low cost. Harvesting solar energy directly at higher efficiency and using that energy to synthesize carbohydrates and amino acids for biological use would be much more costly.
There is a lesson here for biofuel production. Absolute efficiency is not an end all or be all. Cost, established infrastructure, an entrenched knowledge base, and the quality of energy form are factors that have greater importance than efficiency.
Posted by: fred schumacher | 16 June 2010 at 06:54 AM