USDA Researchers Develop Pyrolysis Reactor For Localized Conversion of Biomass to Bio-Oil as an Intermediate Stage in Fuels Processing
06 April 2007
Researchers at the US Department of Agriculture’s Agricultural Research Services (ARS) have built a pilot-scale (2.5 kg of biomass/hour) fluidized-bed fast pyrolysis reactor to convert perennial grasses to bio-oil, and have tested the reactor on switchgrass.
The prototype reactor produces a quantity of bio-oil that is 60% of the weight of the switchgrass fed into the reactor, with energy conversion efficiencies ranging from 52 to 81%. The char produced would provide all the energy required for the endothermic pyrolysis reaction process.
After testing the composition and fuel properties of the produced liquid, the researchers found that the energy content was about the same as the parent switchgrass but the energy density was more than 2.5X greater.
One economic problem for the transport of large quantities of biomass—such as switchgrass—to refineries for further processing is its bulk and light weight. A technical—and economic—problem is breaking down the cellulosic material to release the sugars that can be fermented to produce ethanol.
Both issues potentially could be addressed by the localized conversion of the biomass to bio-oil for subsequent upgrading to fuels and chemicals, according to the researchers.
The study, the results of which will be published in Industrial and Engineering Chemistry Research, can be used to design similar tests for other grasses and for the design and scale-up of reactors for larger operations.
One possible outcome would be the development of small-scale, distributed pyrolysers that could be used by farmers locally to produce the pyrolytic oil. Farmers could then sell the product as a crude product to oil refiners, who in turn, would convert it into transportation or heating fuels.
This could take off if the feedstocks included forestry thinnings, sawdust and municipal plant waste. However the big capital cost would seem to be the central refinery if it used FT technology. Until such a refinery can be demonstrated there is no point in small operators buying pyrolysis units. It somewhat reminds me of the days when small farms left out containers of fresh milk for the dairy manufacturer to pick up.
Posted by: Aussie | 06 April 2007 at 02:28 PM
The article seemed oddly written. At least to me. That doesn't reflect on the process.
It would certainly be good to reduce biomass volume and weight right where it is grown.
I wonder about the emissions from the reactor.
Posted by: K | 06 April 2007 at 02:44 PM
The emissions will suck, but the whole enterprise can still be close to carbon negative if feedstocks have long roots, like switchgrass and poplar.
I think the business case is pretty important. Would farmers prefer to bale their feedstocks like hay, chip their feedstocks like tree trimmers, and send the much compressed feedstocks to a central mill, or just forklift feedstocks into the hopper of a mobil pyrolizer and have oil come out the other end.
Will farmers own, rent or share these pyrolizers? Will it be just two trailers that pull up to your ranch; a pyrolizer and an empty tanker?
Frankly, I think the less capital equipment required of each farmer, the faster this takes off, so I'm guessing the switchgrass gets put through a wood chipper and fills the kind of giant rectangular tubs they put on flat-bed trucks to transport fruit for canning.
I would have liked more details on how close to biodiesel the output is.
Posted by: C Harget | 06 April 2007 at 03:07 PM
Maybe they would pyrolyze the grass and ship the oil for FT processing. It would depend on the cost of one over the other. They have reduced the weight of the grass by making the oil, that saves shipping weight and bulk.
Who knows, with enough farms a pipeline for the oil may be possible. The good thing is that they can use the char to run the process...very good.
Posted by: SJC | 06 April 2007 at 03:22 PM
Actually it would be great if they could use another power source (Maybe nuclear, but likely too large for the application) and use bury the char, making it carbon negative.
Posted by: Mike Z | 06 April 2007 at 03:56 PM
I would have liked more details on how close to biodiesel the output is.
Not related to biodiesel at all. Trust me, biodiesel is going nowhere, fast. You can get an idea of bio-oil properties here.
Somebody call the White House and inform un-Curious George that Cellulosic Ethanol has been canned.
Posted by: Engineer | 06 April 2007 at 03:59 PM
Don't make that call yet. Afterall, cost effective FT is still not a sure-fire thing. I would suggest we work on direct refinning first.
Posted by: Mike Z. | 06 April 2007 at 04:24 PM
Converting solid biomass to liquid biocrude close to where it is harvested makes sense from a logistics point of view. Seems wasteful to let all that heat just go to waste, though. For example, it could be used to dry a secondary wet biomass stream that feeds a separate BTL process.
The optimum of the sum should be greater then the sum of the optima. This matters because satisfying energy demand by capturing solar energy in real time (as it were) is much more difficult than doing so using fossil fuels that had millions of years to accumulate.
Posted by: Rafael Seidl | 07 April 2007 at 03:51 AM
F-T processing is hugely wasteful. There are probably other processes (plain high-pressure thermal conversion) to turn bio-oil into hydrocarbons with much smaller losses.
The bio-oil process only gets about 70% of the feedstock energy into the oil product. Torrefaction achieves about 90%, and can produce a pelletized product which is dense, stable and hydrophobic. The product is also well-suited to use in direct-carbon fuel cells, which bio-oil is not.
Posted by: Engineer-Poet | 07 April 2007 at 04:08 AM
I agree, I don't know how FT got into the discussion. Bio oil can be refined like petro oil as far as I know. There might even be a lot less impurities to deal with. One way or the other, it seems like we can use switchgrass and other biomass for fuel. I have been reading how much VC money is flowing into renewable energy lately. It sounds like some of them believe that it may be possible to make a profit.
Posted by: SJC | 07 April 2007 at 10:27 AM
Seems like this would be useful at the local co-op level. Something that would be put in next the grain elevator. The feedstock would be transported only 5 to 10 miles where an expert could run the conversion to oil.
Posted by: tom deplume | 07 April 2007 at 11:42 AM
Oh yeah, I could see that. Farms could have acres planted in switchgrass to preserve the soil and rotate with food crops. The roots of the grass go very deep and prevent soil erosion. This would be another source of revenue to the farmer and might lighten up on farm subsidies a bit.
Posted by: SJC | 07 April 2007 at 02:25 PM
You can't rotate with switchgrass; it's a perennial which takes several years to come up to full productivity. So's Miscanthus. On the other hand, the current wisdom appears to be that these things require replanting every 10-15 years; you could squeeze in a few years of crops in between, and plow in a bunch of charcoal for good measure.
Posted by: Engineer-Poet | 07 April 2007 at 08:51 PM
Fresh bio-oil can be used directly as a substitute for fuel oil in heating or for firing steam turbines. It can't be kept around very long, however. It's a witches brew of unstable hydrocarbons, which will slowly polymerize to form nasty tars and gums.
There's a decent case for converting bio-oil to synthesis gas for making any of the zillion things that can be made from synthesis gas. FT synthesis to produce diesel fuel is one possibility, but not always the best. Its energy efficiency is about 65%. The waste heat is evolved at temperatures of 250 - 350 C, which is too low for efficient power generation, but good for many other applications.
As long as FT synthesis is matched with one or more other application that can use its waste heat, its relatively low energy efficiency doesn't matter. All of the thermal energy in the feedstock will be used, one way or another, and the linear alkanes that FT synthesis produces make beautiful clean-burning fuels. They can be stored forever without degrading, making them ideal for emergency backup generators.
Posted by: Roger Arnold | 07 April 2007 at 11:40 PM
70% bio-oil efficiency * 75% gasifier efficiency * 65% F-T efficiency = 34% field-to-tank. After 40% efficiency of a diesel engine, field-to-crankshaft falls to 13.6%. The waste heat in the fuel production system would be about 36%, most of it low-grade. We can't run our industry and vehicles that way.
It would make more sense to auto-reform the bio-oil in molten-carbonate or solid-oxide fuel cells (50% efficient or so); after bio-oil's ~70% production efficiency, you'd have throughput of about 35% field-to-terminals, with another 35% as heat. All the waste heat is high-grade (650°C or better), which can run a secondary gas turbine with a tertiary steam-turbine bottoming cycle (or industrial process heat).
We no longer have the luxury of designing around the legacy internal combustion engine. It has to go.
Posted by: Engineer-Poet | 08 April 2007 at 06:16 AM
As for storable fuels, charcoal lasts thousands of years and does not evaporate. Direct-carbon fuel cells are up to 80% efficient, and the charcoal can be produced by slightly different processing of biomass. Torrefaction yields more energy than bio-oil (~90% vs. ~70%) and produces a more stable product too.
Posted by: Engineer-Poet | 08 April 2007 at 06:21 AM
Do you pyrolyze with no oxygen or partial oxidize and gasify? To me, if pyrolyze is 70%
and gasifying is 70%, I can pipe the SNG right to peoples garages and run their cars today. If I pyrolyze I have at least one other step and then I have to deliver it by tanker truck with more accidents and more evaporation and more refineries.
Posted by: SJC | 08 April 2007 at 09:13 AM
The ICE works fine and last a long time. Engineers and policy makers do not have the luxury of designing based on pixie dust. What works trumps efficiency.
Since the US and the EU are rich, we have the luxury of investigating pixie dust as energy source. With computer management systems, it may be much more practical to pre-process biomass at the farm to reduce energy used for transportation of biomass.
Posted by: Kit P. | 08 April 2007 at 11:53 AM
Modern electric motors often run 20 years without service, and they're still quite cheap.You mean, like biomass-to-liquids? <cough>
We have considerably more experience with commercial high-temp fuel cells (molten-carbonate and solid-oxide) than with commercial bio-liquid fuels from cellulose. Direct-carbon fuel cells are essentially MCFC's and they can achieve 80% efficiency (verified in tests). Experience with secondary batteries goes back over a century, and we are making huge advances. "Pixie dust" is a good description of a fuel scheme which we know will be woefully inadequate based on the numbers claimed by its proponents. That's pretty much any scheme which aims to produce bio-fuel for vehicular combustion engines.Fortunately, the most efficient machine is also one of the most reliable: the electric motor.
When energy is at a premium, the processing should be aiming at the greatest end-to-end efficiency. This looks like either carbonization (if biomass can be used immediately) or torrefaction (if it must be preserved for extended storage).
SJC: The bio-oil process is an anaerobic thermal decomposition in a narrow temperature range and in a very short time. See this Bio-oil paper, page 20.It is the most service-intensive part of a modern vehicle and usually has little value once the vehicle is worn out.
Posted by: Engineer-Poet | 08 April 2007 at 08:11 PM
Direct Carbon fuel cells would be great, if we ever get them cheap enough and durable enough (especially considering contamination from almost all fuels). But we’re not near there yet – unless you have insider info. most of us aren’t aware of.
Bio-oil has a lot of fuel potential as it is. It does decompose over a couple of years, but add 10% ethanol and it lasts much longer.
Bio-oil can be used in slow diesels, but not directly in Otto cycle engines (i.e., with spark plugs). But during WW2, European cars without gasoline used portable charcoal gasifiers to generate CO as fuel. Bio-oil could be similarly partially burned into CO but that wouldn’t take advantage of another bio-oil property: High temperatures without extra oxygen quickly decomposes bio-oil into even lighter molecules containing C, H, and some O. So I expect that straightforward bio-oil fuel processing before cylinder injection would allow bio-oil to fuel Otto engines.
And so bio-oil could fuel either diesels or Otto engines of range-extending onboard generators (considering advanced lithium ion batteries could provide short-range energy and high power for acceleration and hill-climbing).
In summary, it’s conceivable that we could replace ALL petroleum-based vehicle fuels by using plug-in series-hybrid electric drives powered by our most advanced lithium-ion batteries along with range-extending gensets fuelled with bio-oil.
And for real 4-wheel-drive simplicity, consider using the range-extending engine to drive only the front wheels, with the battery-powered motor driving the back wheels. By doing so, only the road would be needed to link the engine to the electrical motor at the back (so the engine would not need a separate generator but instead would need a transmission to the front wheels).
Posted by: Jay D | 08 April 2007 at 09:43 PM
Thanks for the article link. It says that you can get bio-oil AND higher energy content gases. This may indeed be something to look into. You could get bio oil and SNG with the same reactor. I just like the delivery system of NG (SNG) and CNG in cars would really clean up the air and take the pressure off supply from refineries.
Posted by: SJC | 09 April 2007 at 11:55 AM
Jay are you suggesting fuel cells are not practical for transportation? You are right and I will add that they are not very practical way to make electricity either. It is really hard to beat a steam turbine for practicality. It takes a large building to hold a 1600 MWe steam turbine generator, it will take a small state to hold the same amount of fuel cells. Or those pesky trad
Let me point out that there are many good ways of doing things. Motors works fine and last a long time. Steam turbines work fine and last a long time. The ICE works fine and last a long time. I can provide a long list of things that have been tried and do not work. Electric motors without electricity.
Okay now, who wants to plug a car into an extension cord and buy expensive dirty batteries to store electricity made from coal. Duh, no one!!! Who want to keep doing things the same way while farmers get rich instead of Arabs?
Does anyone know what you call bio-oil when it skilled on the ground?
Posted by: Kit P. | 09 April 2007 at 02:48 PM
I would assume that you might call it a bio oil spill, but what is your point? There is oil around from oil fields as well. Refineries are not the cleanest places around and this might be more of the same, except CO2 neutral and domestically made. One incremental improvement at a time, if that is what it takes.
Posted by: SJC | 09 April 2007 at 06:10 PM
The claimed scale of a 3 GW DCFC powerplant is the size of a 2-story office building".
Bio-oil consists largely of organic acids, such as acetic acid. You spill it on the ground, and bacteria eat it.
Posted by: Engineer-Poet | 09 April 2007 at 07:04 PM
EP, you are right about bacteria eating it. However, the EPA will call it hazardous waste and swoop in to protect them. It is a real shock that renewable energy gets treated the same way by EPA and OSHA.
It is a real bummer when your favorite plant is better at environment remediation for heavy metals than a renewable energy source.
Posted by: Kit P. | 10 April 2007 at 04:33 PM