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7 Sep, 2009 02:11 pm
On the other hand, there are some renewable fuel options that have either proven themselves as solid contenders, or have not yet demonstrated fatal flaws that would disqualify them at this point. In this essay I will cover some of those. First, I will cover a pair of first generation biofuels that have proven that they can compete with oil on a cost basis, and then a pair of next generation biofuels that I believe will be competitive.
The First Generation Contenders
Sugarcane ethanol, especially from tropical regions like Brazil, has some unique attributes that have enabled it to compete on a head to head basis with gasoline pricing. Specifically, during the production of sugar, the bagasse (sugarcane residue) is pulverized and washed many times. Many soluble inorganic constituents that may normally pose an ash problem for a boiler are washed out in the process. What remains after processing is a pretty clean biomass feed for the boilers. The normally vexing logistical issues aren't there because the biomass is already at the plant as a result of the sugarcane processing. So they essentially have free boiler fuel, which minimizes the fossil fuel inputs into the process. That enables ethanol production that is relatively cheap, and that is largely decoupled from the impact of volatile fossil fuel prices.
There are several reasons we don't do sugarcane ethanol in the United States. Last year I made a visit to the largest sugar producer in Louisiana, and they explained to me that the economics of their by-product molasses generally favor putting it into animal feed. If they had a year-round growing season as they do in the tropics, it is more likely that the animal feed market would start to become saturated, and conversion into ethanol might be more attractive. Further, a bagasse boiler is a major capital expense, so there needs to be a high level of confidence that in the future ethanol will be a more economical outlet than animal feed. For Brazil, this is certainly the case.
The ultimate downside of sugarcane ethanol will come about if the U.S. and Europe begin to rely heavily on tropical countries for their fuel needs - thus encouraging a massive scale-up. First, ethanol imports don't do much for domestic energy security. More importantly, it may encourage irresponsible usage of the land in an effort to feed our insatiable appetite for fuel. I think the ideal situation is to produce the sugarcane ethanol and use it locally, rather than try to scale it up and supply the world. In this way, sugarcane ethanol could be a long-term contender for providing fuel for the tropics, but not a long-term contender for major fossil fuel displacement outside of the tropics.
The other major first generation contender is palm oil - which also comes with a lot of environmental risk. Palm oil is derived from the African Oil Palm. The oil palm is a prolific producer of oil, which can be used as fuel (and food). This is also a plant that thrives in the tropics, and is capable of annually producing upwards of 500 gallons of oil per acre. To my knowledge there is no other oil crop that consistently demonstrates these sorts of yields (acknowledging that algae could theoretically produce more).
The price of palm oil over the past 5 years or so has traded in a range comparable to that of crude oil; $50-$75 a barrel for the most part (although like petroleum, prices shot up to around $150/bbl in mid-2008). Palm oil can be used unmodified in a diesel engine, although some precautions are in order (and I don't recommend it). It can also be processed to biodiesel, or hydrocracked to green diesel. The extra processing will generally make the final product somewhat more expensive than petroleum, but demand has still been strong due to biofuel mandates.
The risks with palm oil are significant, though. Palm oil presents an excellent case illustrating both the promise and the peril of biofuels. Driven by demand from the U.S. and the European Union (EU) due to mandated biofuel requirements, palm oil has provided a valuable cash crop for farmers in tropical regions like Malaysia, Indonesia, and Thailand. The high productivity of palm oil has led to a dramatic expansion in most tropical countries around the equator. This has the potential for alleviating poverty in these regions.
But in certain locations, expansion of palm oil cultivation has resulted in serious environmental damage as rain forest has been cleared and peat bogs drained to make room for new palm oil plantations. Deforestation in some countries has been severe, which negatively impacts sustainability criteria, because these tropical forests absorb carbon dioxide and help mitigate greenhouse gas emissions. Destruction of peat land in Indonesia for palm oil plantations has reportedly caused the country to become the world’s third highest emitter of greenhouse gases.
Because palm oil is capable of competing on price, it was originally viewed as a very attractive source of biofuels. In recent years, countries have begun to rethink their policies as the environmental implications of scaling up palm oil production began to unfold. As is so often the case, the seemingly good idea of biofuel mandates has had some pretty serious unintended consequences.
Next Generation Biofuel Contenders
Here is how I would define a next generation Biofuel Contender: A technology that is capable of supplying 20% of our present liquid fossil fuel consumption on a net energy basis.
Yes, 20% is rather arbitrary, but it weeds out a lot arguments over many potential small contributors. I will focus in this essay on the United States, because I am most familiar with our energy usage and biomass availability, but these arguments should be applicable in many places around the world.
Consider for a moment the amount of energy locked up inside the 1.3 billion tons of dry biomass that the Department of Energy suggests can be sustainably produced each year. Woody biomass and crop residues - the kind of biomass covered in the 1.3 billion ton study - contains an energy content of approximately 7,000 BTUs per pound (bone dry basis). The energy content of a barrel of oil is approximately 5.8 million BTUs. Thus the raw energy contained in 1.3 billion tons of dry biomass is equivalent to the energy content of 3.1 billion barrels of oil, which is equal to 42% of the 7.32 billion barrels the United States consumed in 2008.
This calculation tells you a couple of things. First, the 42% represents an upper limit on the amount of oil that could be displaced by 1.3 billion tons of biomass. The true number would be much lower because energy is required to get the biomass to the biorefinery and then to process it. So replacing oil with biomass isn't going to be a trivial task, and a process must be capable of turning a respectable percentage of those biomass BTUs into liquid fuel if it is to be a contender.
Imagine a process that only captures 25% of the starting BTUs as liquid fuel. The liquid fuel production of 1.3 billion tons would then be 10.5% of our oil usage instead of 42% - and that's before we consider the energy requirements from the logistical operations (like getting that wood to the biorefinery). This is the realm of the pretenders; they waste a lot of BTUs during the production of their liquid fuel. What we really need is a process that can capture >50% of the BTUs as liquid fuels. That's what it will take to be a contender, and quite frankly I don't believe cellulosic ethanol has a chance of pulling this off on a large scale.
However, there are at least two technologies that can achieve net liquid fuel yields in excess of 50% of the BTU value of dry biomass. These technologies are flash pyrolysis and gasification. I will talk about each below.
Flash pyrolysis involves rapidly heating up biomass to around 500°C. The reaction takes place in about 2 seconds, and the products are pyrolysis oil (also called bio-oil) and char. The process can handle a wide variety of feedstocks, the oil yield is approximately 70% by weight, and the energy content per pound of oil is similar to the starting material. Thus, approximately 70% of the initial BTUs are captured in the oil before we have to start subtracting out energy inputs.
Char is frequently mentioned as a great soil amendment (as terra preta, for instance), but I don't really know if there is a market for it. As someone recently said to me, it may be like biodiesel and glycerin. In theory there are all kinds of uses for glycerin, but the market was quickly saturated as biodiesel production ramped up. Glycerin suddenly became a disposal problem. Terra preta does in fact appear to be a great soil amendment, but people are going to have to show that they will buy it. It seems to me that the ideal solution would be to use the char to help heat the biomass, unless the ash properties are problematic for the process.
There are definite downsides to flash pyrolysis. Heating up to 500°C will subtract from the net energy production, and while heat integration is possible, it would be more difficult to achieve in a hypothetical mobile unit (which I think could finally provide an outlet for the millions of acres of trees destroyed by the Mountain pine beetle). The properties of the raw oil are such that it isn't suitable for transport fuel as produced. It is not a hydrocarbon and is very acidic. Without upgrading, it can't be blended with conventional diesel. There are various issues around reproducibility and stability, especially if the biomass quality varies. The oil is suitable for power generation or gasification, and can be upgraded to transportation fuel, albeit at greater expense and lower overall energy efficiency.
With those caveats, it is still a contender. It could be knocked out of contention as a viable transportation fuel if the upgrading process is too expensive or energy intensive, but at present no fatal flaw has emerged. There are a number of companies involved in pyrolysis research. Dynamotive Energy Systems has been working on this for a while (I first wrote about them in 2007). UOP - a company that specializes in product upgrading for refineries - has teamed with Ensyn to form a joint venture called Envergent Technologies. The company intends to make pyrolysis oils from biomass for power generation, heat, and transport fuel (this is where UOP's skills will come into play).
Gasification: Biomass to Liquids
The following example is just one reason I think gasification is going to play a big part in our future. During World War II, the Germans were cut off from liquid fuel supplies. In order to keep the war machine running, they turned to coal to liquids, or CTL (coal gasification followed by Fischer-Tropsch to liquids) for their liquid fuel needs. At peak production, the Germans were producing over five million gallons of synthetic fuel a day. To put matters into perspective, five million gallons probably exceeds the historical sum of all the cellulosic ethanol or synthetic algal biofuel ever produced. Without a doubt, one week's production from Germany's WWII CTL plants dwarfs the combined historical output of two technologies upon which the U.S. government and many venture capitalists are placing very large bets.
South Africa during Apartheid had a similar experience. With sanctions restricting their petroleum supplies, they turned to their large coal reserves and once again used CTL. Sasol (South African Coal, Oil and Gas Corporation) - out of necessity - has been a pioneer in gasification technology. Today, they have a number of gasification facilities, including the 160,000 bbl/day Secunda CTL facility, which has been highly profitable for the company (but very expensive relative to oil prices when constructed). In total, Sasol today synthetically produces about 40% of South Africa's liquid fuel.
While we can speculate on the source of future fuel supplies in a petroleum constrained world, we do know that two countries that already found themselves in that position turned to gasification as a solution. The technology has a track record and is scalable. The same can't be said for many of the technologies upon which we are pinning our hopes (and taxpayer dollars). We hope these other technologies scale and that technical breakthroughs allow them to compete. But gasification has already proven itself as a viable go-to option. There are presently a number of operating CTL and GTL plants around the world. Shell has been running their Bintulu GTL plant for 15 years, and is currently building the world's largest GTL plant with a capacity of 140,000 barrels/day.
The biomass to liquid fuel efficiency for gasification is around 70% (See Section 1.2.2: Second-Generation Biofuels), a number cellulosic ethanol will never approach. In short, no other technology to my knowledge can convert a higher percentage of the embedded energy in biomass into liquid fuels.
Of course there's always a catch. Despite large reserves of coal, the United States has not turned to gasification as a solution. Why? High capital costs. At the end of the day the desire to keep fuel prices low consistently overrides our desire for energy security. (There is also environmental pressure over using coal gasification which should not be an issue for waste biomass gasification).
But biomass is more difficult to handle, so there are added costs above those of coal gasification. So you are talking about a process that is more capital intensive than a conventional oil refinery, or even a cellulosic ethanol plant. But what you save on the cellulosic ethanol plant ultimately costs a lot in overall energy efficiency. Until someone actually scales up and runs a cellulosic ethanol plant, we can only speculate as to whether the process is truly a net energy producer at scale.
Interestingly, one of the "cellulosic ethanol" hopefuls that we often hear so much about - Range Fuels - is actually a gasification plant. (Ditto Coskata). The front end of their process is intended to produce syngas in a process very similar to that of World War II Germany. For their back end they intend to produce ethanol, which in my opinion is an odd choice that was driven purely by ethanol subsidies. But this is definitely not the optimal end product of a gasification process. They are going to lose a lot of efficiency to byproducts like methanol (which is actually a good end product for a gasification plant) - and that's assuming they get their gasification process right. They are then going to expend some of their net energy trying to purify the ethanol from the mixed alcohols their process will produce.
The question for me is not whether BTL can displace 20% of our petroleum usage. It absolutely can. The question is whether we are prepared to accept domestic fuel that will cost more to produce. In the long run - if oil prices continue to rise - then BTL plants that are built today will become profitable. The risk is that a sustained period of oil prices in the $50-$70 range will retard BTL development. But I don't expect that to happen.
In my opinion, the question of which next generation biofuels can compete comes down to fossil fuel prices. If oil prices are at $50 for the next 10 years, it will be difficult for renewable fuels to compete. Despite the many promises of technologies that will deliver fuel for $1 a gallon, I think that target is likely to be reached only on paper. My view on which technologies will be competitive is based on 1). An expectation of an average oil price over the next 10 years that exceeds $100/bbl; 2). An expectation that we will need to efficiently convert the available biomass. I expect biomass prices to rise as well, and inefficient technologies that may be competitive if the biomass is free and fossil fuel inputs like natural gas are low-priced will not survive as the prices of both rise.
Originally published on R-Squared Energy Blog
Robert Rapier's career has been devoted to energy issues. He has worked on cellulosic ethanol, butanol production, oil refining, natural gas production, and gas-to-liquids (GTL). His previous job was as the Engineering Director for Accsys Technologies, but he is presently in Hawaii helping to build a bioenergy company.