Posted on May 11th, 2008 No comments
There’s probably no topic more important to those of us who fly General Aviation aircraft than the continued availability of aviation fuel. For those of you who may not be familiar with aviation, the fuel used in aircraft is made the old fashioned way because it uses tetraethyl lead to increase the octane rating. High octane fuel is necessary because about 30% of the aviation fleet use high compression engines, and those aircraft use 70% of the aviation fuel. The engine I’ll be putting in my Cozy MKIV will require this fuel. Leaded fuel has been outlawed by the EPA for all other uses, but aviation fuel got an exemption for a period of 30 years. That period ends in 2010, which is coming up soon.
I agonized over the decision over whether to use a high or low compression engine in the Cozy but I figured that with all the aircraft fleet that need 100LL, there would be some fuel developed that would come to the rescue, possibly an ethanol based biofuel. Of course, with an experimental aircraft, I could always put lower compression pistons in the engine and use autogas, if I had to, but that’s not ideal. So I was very excited to hear about this new fuel that is being developed that has so many advantages that it’s hard to believe it’s true.
I emailed the owner of the company and he responded. That’s always a good sign. Not only that, he graciously referred me to his associates on the project if I had any more questions about it. I’m really hoping that these guys are successful. Here’s the report I got from Avweb:
“Not only can our fuel seamlessly replace the aviation industry’s standard petroleum fuel [100LL], it can outperform it,” says John Rusek, a professor at Purdue University and co-founder of Swift Enterprises. The company recently unveiled a new general aviation fuel that it says will be less expensive, more fuel-efficient and environmentally friendlier than any on the market. Unlike other alternative fuels, Rusek said, SwiftFuel is made of synthetic hydrocarbons that are derived from biomass, and it can provide an effective range greater than 100LL, while costing about half as much to produce. “Our fuel should not be confused with first-generation biofuels like E-85 [85 percent ethanol], which don’t compete well right now with petroleum,” Rusek said. Patented technology can produce the 1.8 million gallons per day of fuel used by GA in the U.S. by using just 5 percent of the existing biofuel plant infrastructure, the company said.
The synthetic fuel is 15 to 20 percent more fuel-efficient, has no sulfur emissions, requires no stabilizers, has a 30-degree lower freezing point than 100LL, introduces no new carbon emissions, and is lead-free, Rusek said. In addition, he said, the components of the fuel can be formulated into a replacement for jet/turbine fuels. The company now is working with the FAA to evaluate the fuel.
Posted on April 6th, 2008 2 comments
My friend Peter asked if I would write about the amount of water it takes to produce a gallon of ethanol. I have often heard this figure to be quoted at 1000 gallons of water per gallon of ethanol. I wasn’t sure how accurate this was, so I started doing some investigation. I found that I live in a county in Colorado that has the most irrigated acres of any of Colorado’s 63 counties, accounting for 11% of the state’s total. I found that corn requires a moderate amount of irrigation as far as crops go, about 16.5 inches per year in my county. Alfalfa has the highest watering requirements or about 23 inches and melons only require about 8 inches annually. When you compare irrigation requirements with Colorado’s average rainfall of 15.5 inches per year, it is obvious that more than half of the corn’s water requirements must come from irrigation and this is even more apparent when you consider that corn only grows for 3 months out of the year and during those months, the rainfall total is only about 5 or 6 inches.
Some of the irrigation is provided through surface canals fed by mountain runoff and some is from center pivot irrigation which brings water up from deep wells. I will calculate the energy cost per acre of using a center pivot irrigator assuming a 200-foot deep well and a 50 psi pressure at the pivot’s center.
Since an acre is 43,560 sq ft. and we need to apply 16.5″ of water to it during the corn growing season, this comes out to 59,895 cu. ft. or 497,128 gallons of water per acre. Last year’s average Colorado irrigated corn yield was 189 bushels/acre and the average conversion rate is 2.7 gallons of ethanol per bushel of corn. So the ethanol yield per acre is 456 gallons. Dividing that into 497,128 shows that the number of gallons of water to produce a gallon of ethanol in Colorado is around 1100. This seems quite substantial. Colorado has a very dry climate where virtually no crops can grow without irrigation. In most of the corn belt states like Iowa and Illinois, the average rainfall is closer to 40 inches per year, and so irrigation shouldn’t be necessary and thus even though it may take just as much water to grow corn as it would in Colorado, the rain will fall whether you’re growing grass, or forest, or corn, so I don’t think that the amount of water consumption is as much of a concern as it is in states like Colorado where water is considered a scarce resource.
I mentioned I’d also do the energy calculation for lifting the water from a 200 foot well. 497,128 gallons of water weigh about 4.1 million lbs. and lifting that much water 200 feet and maintaining 50 psi at the center pivot would require 1300 M ft-lbs of energy. This is equivalent to 490 kWh. Derating for a pumping efficiency of 65% we can estimate it would require about 760 kWh in electricity consumption per acre at a cost of $76/acre using $.10/kWh for the electricity rate. With corn selling for around $4.60/bushel, this accounts for about 9% of the value of the corn. So spending $76/acre seems like a reasonable trade-off considering that without irrigation, the corn yield in Colorado would be close to nothing.
Water is the most renewable of all natural resources but sometimes it’s treated like it’s a scarce or even endangered resource. The stuff does literally fall from the sky. So I guess it all depends on one’s situation as to whether water is scarce or plentiful. If you are in the middle of a flood, water is anything but scarce, yet if you’re dying of thirst, it can be more precious than gold.
Is it worth 1000 gallons of water to produce 1 gallon of ethanol? Again it depends on one’s perspective. If you need to drive a car for 20 miles, 1000 gallons of water will be of no help, but a gallon of ethanol certainly would be. And in the majority of corn-growing states, not planting corn on the land will not prevent rain from falling on it so there’d be no real water savings.
Posted on February 14th, 2008 2 comments
I recently received a pointer to this blog article which references a NY Times piece about articles in Science that state that biofuels actually increase global warming by pulling land into the agricultural pool that was previously a carbon sink. The first of these Science papers is focused on the ethanol industry in the U.S.
During the past 14 years, 15 separate studies have shown that ethanol has a net positive energy balance. Only one study has contradicted it, but the researchers of that study (Pimental and Patzek) wrote the same paper 4 times so you may hear that the ratio is 15:4. It’s the one that always gets quoted (usually unknowingly) when someone tells you it takes more energy to produce a gallon of ethanol than you can get out of it. Now it appears ethanol opponents will have another study to quote, this time about biofuels creating additional greenhouse gases.
In looking in the supporting materials in Science Express, I found this curious assertion:
If corn-based ethanol could not receive a credit for removing carbon from the atmosphere – deleting the feedstock uptake credit from the GREET model– it would increase greenhouse gas emissions by 48%. It follows that if the use of land to grow corn for ethanol has the net effect of reducing land-based carbon sequestration, the overall effect will be a bigger release of greenhouse gasses.
In other words, they are stating that when comparing greenhouse gases from corn to gasoline, corn should not get a credit for having removed carbon from the atmosphere. Instead they think it should be compared to growing a forest or prairie in the place of farmland which would allow the carbon to be sequestered year after year. Forests and prairies give back carbon to the atmosphere every year when their leaves and grasses die. In the case of forests, every few decades the trees die, or burn, or are used for some other purpose and thus also give back their carbon in a brief instant of geological time. Unless you’re burying the carbon deep under the earth’s surface or oceans, any carbon taken in by plants is given off in a few months or decades. Soils also have a limited capacity to hold carbon and eventually reach a homeostasis after only a few decades. So I consider the logic used in this study to be flawed.
But I will expect that every biofuel opponent will quote it with abandon, never realizing that the authors of the paper are not comparing biofuels with fossil fuels, but rather biofuels with some imaginary state of affairs where forests that capture but do not release carbon to the atmosphere have been replaced by farmland.
All land capable of sustaining plants, whether it be used for farming, prairie, or forest eventually reaches a homeostasis when it comes to CO2 sequestration. Farming allows us to take advantage of the CO2 to carbohydrate conversion that occurs on land whereas prairies and rainforest that go unharvested do not. But in the end, they all return CO2 back to the atmosphere in a relatively short span of geological time. The only counter-examples are swamps that can, over the course of millions of years, turn vegetation into coal by trapping a tiny percentage of carbon each year.
Posted on January 27th, 2008 4 comments
Last week I toured the Front Range Energy ethanol plant in Windsor along with 9 other members of the Northern Colorado Clean Energy Network many of whom are also members of the Northern Colorado Renewable Energy Society. I had requested the tour because I had a desire to see this facility up close to find out what is involved in an operation capable of producing 40 million gallons of ethanol per year. The company manager, Dan R. Sanders, and FRE employees very graciously set up a tour for our group and explained the details of ethanol production at the facility.
Ethanol has been an additive in auto fuels in the U.S. for many years. In addition to making the gasoline burn cleaner, ethanol increases the fuel’s octane rating and helps reduce our dependence on imported gasoline by more than 5 billion gallons per year. While this is still a small percentage of the U.S. consumption rate of 140 billion gallons of gasoline each year, its recent growth rate is impressive as is the rate of ethanol plant expansion and construction. I’ve written about E85 ethanol previously, including using it in vehicles that were not designed for it as well as in aircraft.
I am aware that ethanol is still controversial in some circles primarily due to some persistent myths such as it taking more energy to produce a gallon of ethanol than it returns, which is not true. Ethanol production in this country provides 40% more energy than it requires to produce it and that number continues to improve, but more importantly, ethanol’s energy has 3 times the value to consumers than the type of energy it uses, which is usually natural gas. When it comes to energy, some types of energy are worth much more than others because of convenience or compatibility with existing infrastructure. It’s the reason you probably don’t heat your house with coal, even though it’s the cheapest fuel per BTU by a significant margin.
The Front Range Energy plant was built in 2005 and began producing ethanol in 2006. Our tour included a 35 minute presentation to describe the operation in detail by Amanda Huber, the process manager, who walked us through each step in the highly automated process of converting corn into ethanol. She also answered many questions from our members. We were then taken through the facility by the company manager to see and hear all the equipment up close. The words that come to mind to describe the plant’s equipment are large, loud, and highly automated. There are many large cylindrical tanks connected with numerous pipes and pumps. The smell of the plant reminded me of the smell of our kitchen when we make pizza dough.
The corn arrives to the plant by both truck and rail and is stored in two impressively large 500,000 bushel storage silos. The corn from local growers arrives by truck and the corn from outside the region, primarily Nebraska, arrives by train. From the storage silos, the corn moves by conveyor to the hammer mills where flailing hammers pound the dried kernels through screens containing holes that will only allow particles smaller than about 1/10 of an inch to pass. This helps to expose the starch inside the kernel, which accounts for about 65% of the corn by weight. From the hammer mills, the corn passes to the slurry blender which mixes it with water and enzymes and cooks for several hours. It is inside this slurry cooker that enzymes begin to break the corn starches down into fermentable sugars.
From the slurry cooker, the mixture passes through some liquefaction stages and then on to one of four 535,000-gallon fermentation tanks. Additional enzymes and yeast are added to the mash, as it’s called at this stage, and it is allowed to ferment for about 50 hours. This stage is critical to monitor because it’s where the sugars are converted to alcohol and if this process is not properly controlled, it could ruin the entire batch. They use a combination of analytical instrumentation to monitor the health of the yeast as well as the concentrations of sugar, alcohol, and acids in this tank. After the fermentation step is complete, the mixture will contain somewhere between 15-18% alcohol. Another output of the fermenters is carbon dioxide which could be vented to the atmosphere, but in this plant it is fed directly to another plant that condenses it and provides it to bottling plants for carbonating drinks and for making other CO2 products such as dry ice.
The mix is moved from the fermenters to a 735,000 gallon beer well which feeds the distillers. Using a combination of heat and vacuum, the alcohol is separated from the rest of the mix using a beer column to produce alcohol in a 70% concentration and then it is transferred to a rectifier column to get the concentration to 95%. Alcohol and water form an azeotrope at this concentration, meaning that distillation can no longer further separate the water and alcohol. So the next stage is to run the mixture through a molecular sieve to remove the remaining water and produce anhydrous ethanol. The ethanol is then denatured to make it unfit for human consumption by mixing it with about 5% gasoline. It is then pumped into one of two 500,000 gallon tanks where it awaits transportation by truck or rail car to its destination.
From the bottoms of the distillation towers, the solids and water are pumped to a centrifuge which separates the water from the solids. The solids then become wet distiller’s grain which is used as an animal feed. In some plants, this grain needs to be dried so that it will not spoil during transportation and storage, but in northern Colorado, because of its proximity to numerous cattle feedlots and dairies, it can be shipped in its moist state directly to the dairies and feedlots. Trucks remove approximately 1100 tons of this material a day from the plant. If the distiller’s grain had to be dried, it would more than double the amount of natural gas consumed by the plant, so there is definitely a benefit to having large meat packing and dairy industries nearby.
I have simplified my description of this process considerably. There are many auxiliary steps to achieve a high level of efficiency for the plant. For example, there are steps for adding nitrogen to the fermenters, recycling the water, regenerating the molecular sieve, extracting and remixing syrup with the grain, and recovering alcohol which I did not mention. This plant has a lot of very sophisticated and finely-controlled processes. If you’d like to see a little more detail, there is an explanation complete with a diagram at the ICM website, the company that designed and built the FRE plant.
As an engineer, one area I found particularly fascinating was the control room which had a series of computer screens that showed a pictorial view of the real-time status of every level, temperature, flow, and pressure of the entire process from beginning to end, all being monitored by one person. The plant is so automated that it can be run by as few as 3 people. The plant only requires 32 full time employees to run a 24-hour a day, 365-day per year schedule. The plant is able to process 55,000 bushels of corn into 145,000 gallons of ethanol every day of the week and have minimal plant downtime, typically less than 7 days over the course of a year. The plant achieves a yield of 2.7 gallons of ethanol per bushel of corn.
I was curious to know how close to the nameplate value this plant was producing. I had interpreted the nameplate value to be the maximum output if everything ran perfectly every hour of the year. I was very impressed that the plant regularly exceeds the 40M gallon per year nameplate value by more than 20%. So, unlike power generating plants, an ethanol plant has a conservative nameplate value to take into consideration issues that may cause periodic downtime.
Another thing that impressed me was how aware the company manager was of power consumption in the plant. At this plant, a gallon of ethanol requires 15,000 BTU in natural gas and .5 kWh of electric energy. Since ethanol contains 76,300 BTU per gallon of thermal energy, and .5kWh is equal about 1600 BTUs, the excess energy is about 60,000 BTU per gallon.
There is a controversial study by Pimentel and Patzek that is referenced frequently by skeptics about how ethanol has a negative energy balance of 20% meaning that it takes 20% more energy to produce ethanol that it delivers as fuel. However, two separate USDA studies contradict that study, the most recent one showing a 40% net positive energy balance. Yet the numbers the USDA uses, often called ‘optimistic’ by critics, are not as high as the actual numbers from this operating plant. For example, the USDA cites portion of energy attributed to the ethanol plant as 49,700 BTU/gallon. Yet here is an actual plant using only 16,600 BTU in combined natural gas and electricity per gallon. Even if they had to dry the distiller’s grain, they’d still be under 34,000 BTU/gallon. So I don’t think that the USDA study is overly optimistic. It seems to me to be very conservative.
And, like I mentioned before, energy balance is only part of the equation. The cost per BTU of various forms of energy vary significantly so if you take one type of energy that is worth $7/MBTU, such as natural gas, and covert it into energy that is worth $23/MBTU, such as automotive fuel, then energy balance is overshadowed by the net increase in economic value of the energy.
I got a lot of positive feedback from the rest of the members about the plant tour. It was a great to have a chance to see firsthand how ethanol is made. We really appreciated the professionalism and hospitality shown to us by the knowledgeable staff at the Front Range Energy plant.