module16_transcript.pdf

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Welcome back. Module 16 covers bioenergy. This is the sixth module on renewable energy. We're

going to look at the different forms and uses of bioenergy. So let's get started.

The final module on renewable energy is bioenergy. This is one of the most important forms of

renewable energy that we use and have used for thousands of years. There are several forms.

There's biomass, which is solid and typically used for heat and power. And this is things like wood and

straw and cow dung and waste. It's a lower energy density than coal. So coal has an energy density of

about 20 million BTU per ton. And biomass typically has an energy density of about 10 million BTU per

ton.

There's also biogas, which is similar to methane or natural gas. It's mostly methane, with 60% to 70%

methane with a balance of CO2. And that's made from the decomposition of organic waste. Things like

the land fall gas are a form of biogas.

There's also biofuels, which are liquid fuels like ethanol and biodiesel and biobutanol, which are a liquid

fuel we can use for transportation, though they have a lower energy density than gasoline or diesel.

There's several pathways for bioenergy, but they all start with the biomass. They all start with taking

sunshine and converting to into bio materials through photosynthesis. And the biomass could be used

in direct combustion for heating and cooking and power generation. You can use it in wood stoves and

wood boilers and pellet stoves and homes, waste to energy power plants-- that kind of thing.

We can take the bioenergy and burn it to make heat and to make electricity directly. We can take that

biomass and convert it to biogas and then combust that biogas for heating and cooking and power

generation. Things like landfill gas capture systems or anaerobic digesters do that. They take the

organic materials, the bio materials, the biomass, convert it into gas, and then we could use that biogas

like we'd use natural gas.

And then there's biomass to liquid fuels. We start with a solid bioenergy form. And they convert that

through a biorefinery or some other method to make alcohols we can use in combustion engines.

Bioenergy resources are abundant nationwide. We've got a map here showing different productivity in

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thousands of tons per year for different counties-- a lot of grasses and woods in the upper Great Plains,

in the southeast, in the West coast, for example. So there's a lot of bio materials that we could harvest

each year in a renewable way for energy.

We talked earlier about is how there's not much wind in the southeast, but there is a lot of bioenergy in

Southeast. There's not a lot of bioenergy in West Texas, where there is a lot of wind and sunshine. So

the renewable energy resources are available everywhere. But it's not the same form available

everywhere. Each region has a different form available for its use.

Bioenergy is attractive for several reasons. CO2 is actually consumed during the growth of the biomass

because of photosynthesis. So it takes CO2 out of the atmosphere, which is good. The CO2 that's

admitted during combustion would have been released from decomposition anyway. So if you have

some wood out on a forest floor, as it decomposes, it releases CO2. So that wood is going to releaseCO2 anyway naturally, so if you release that CO2 while you're burning it, it kind of doesn't count against

you because you're getting some useful energy out of it in the process.

It's also renewable. It grows back. It's domestic. And it feels natural. So people like the way it feels to

use bioenergy. There are several drawbacks to bio energy. Just like all the forms of energy, there are

some drawbacks. It's very land intensive. It's very water intensities, because you use water for the

growth and photosynthesis.

There are concerns about indirect land use changes, such as deforestation in other parts of world. As

we ramp up our use of biofuels like ethanol in the United States, that affects jungles in Brazil, for

example. So there's deforestation, indirect land use, that occurs elsewhere.

There's also this invitation for a moral dilemma between food and fuel, especially if we're using corn or

soy for biofuels. And it's also an inefficient use of photons. When we have photons coming to the land,

we have choices for how we use those photons. And using it to grow crops is actually a less efficient

way to go than, for example, using solar panels.

Let's talk about biomass. Let's start there. There was a famous study done in 2005, called the Billion

Ton Study, produced by the US Department of Agriculture and the Department of Energy, that looked to

see if there was potentially a billion tons of biomass available in a renewable, sustainable way each

year. And they concluded it's actually 1.3 billion tons of biomass available each year.

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And this is looking at wood waste and logging residues, manure, crop waste, tree trimmings, yard

clippings. So there's a lot of tonnage out there. And if we look at about 10 million BTU per ton average

energy density for biomass, it works out that our biomass in the United States could provide about 13

quads each year as an upper limit nationally.

Now, that's good news. 13 quads of our energy can come from bio resources. The bad news is that's

less than a sixth of our total annual consumption. So it's going to be hard to grow the biomass we need

to solve all our energy consumption needs if things don't change dramatically.

Other forms of biomass include municipal solid waste. Americans generate about 250 million tons of

MSW or municipal solid waste each year. To put it in context, we produce and mine about a billion tons

of coal each year. So this is a quarter billion tons of municipal solid waste that's also generated.

The generation has peaked a years ago and been dropping recently as we've gone to less packaging

and more efficient uses of our materials. And the per capita generation has leveled off at about 4.4

pounds of trash per person per day, which is the rate of generation of waste in the United States. We

generate more waste than just about every other country on a per capita basis.

Much of the municipal solid waste treatment is actually very energy dense. It has many fibers and

plastics that could be used as a fuel source. There are things like paper and paper board that have a lot

of tonnage and a lot of energy. Glass and metals are not as useful from my energy perspective, but the

plastics are very energy dense.

In fact, the energy density of plastics is often higher than coal or other fuels. And then there's rubber

and leather, textiles, wood, et cetera. So there's a lot of things in the municipal solid waste stream,

several of which are very useful as fuels if we could take them out of the landfill stream and instead use

them and harvest them as a fuel for energy.

About half of municipal solid waste today is landfill in the United States. The rest is recycled,

composted, or incinerated. Walking through this chart, of the 250 million tons per year generated in the

United States, about 30 tons is separated for energy recovery and waste to energy. About 20 million

tons per year is composted. About 140 million metric tons per year is sent to landfill.

And about 26% is pulled off for recycling, of which 90% is actually recycled-- about 60 million tons. And

the rest goes back to the landfill. But we could use that 10% stream as a SRF-- what we call solid

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recovered fuel. So these are plastics and papers that we try to recycle but can't, but we can instead use

and make as fuel pellets to displace coal.

The way this breaks down per person is that each of us generates 4.4 pounds of municipal solid waste

per day on average. 1.5 pounds of that is composted or recycled. 0.5 pounds is incinerated for energy

recovery. And 2.4 pounds is landfill. That trash is a useful fuel source if we harvest it the right way.

Waste incinerators are one way to get direct generation of electricity from municipal solid waste.

They're also known as waste to energy or W2E or energy recovery. This is generally unpopular in the

United States because of concerns about emissions. And as of 2010, the US only had about 86 waste

to energy plants nationwide, with a total capacity of just a few gigawatts.

By contrast, waste energy is very popular in Europe. Europe has land constraints. They don't have

places for landfills that are affordable. So they tend to burn the trash and get energy out of it. So we

have a different view about it in the United States compared to Europe.

The total energy generation takes us 29 million tons per year of energy recovery stream and uses it at

10 million BTU per ton, and generated about 300 trillion BTU per year of useful energy, which is a small

part of our overall energy mix as a nation.

If we could find a way to get more of that waste stream turned into useful fuel, we could solve some of

our energy problem. Here's one example of how you might do it. These are unrecyclable plastics. They

were sent to the recycling facility, but they were contaminated with organic matter-- things like baby

diapers that have organic matter in them but are very energy dense. You can push them through a

machine to make fuel pellets out of it. You can burn those pellets in places like cement kilns.

This is a picture of some research my group did looking at using those pellets to displace fossil fuels.

And it works just fine. So we can use the biomass from our waste streams as an alternative fuel.

Organic waste can also be turned into biogas through anaerobic decomposition. Coming back to how

organic waste decomposes, they can decompose in two general ways. If the organic waste

decomposes aerobically, it generates CO2. Like if you have wood out on a forest floor decomposing, it

generates CO2.

But if you have it decomposed anaerobically, which means not in the presence of oxygen, it actually

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forms methane, CH4. There's no oxygen to oxidize it, so it forms methane. Biogas, or renewable

natural gas-- some people call it RNG-- could be used just like natural gas. So if you use anaerobic

decomposition of these organic wastes, you generate CH4 or RNG or biogas, and then you use it just

like natural gas for cooking and heating and power generation.

There are several organic waste streams that are relevant. Landfill gas is a very famous one, where we

actually mine for biogas at landfills by punching holes in landfill to capture the biogas that comes out

from the anaerobic digestion of municipal solid waste. The landfill prevents oxygen from getting down to

the decomposition. So it's like a huge anaerobic digester. Collect that gas, and then use it to make

electricity. Austin uses landfill gas to make electricity.

You can also burn the waste directly to get electricity. The landfill gas is basically just an indirect method

of that. You're using the waste to the landfill, turning it into gas, and then burning it 40 years later. So

we can burn the waste today for energy or put in a landfill, collect the gas decades later, and then burn

it.

We also have municipal wastewater, which is a stream of organic-rich water that we can decompose

anaerobically. We can decompose the sludge anaerobically to get biogas out of it. We do that in Austin,

Texas, and other cities are looking at it as well. And also, you can do this at agricultural operations,

where you do anaerobic digestion of manure. In the United States, we generate a lot of manure, and

that can create this biogas that then is useful as a power source.

Here's one illustration of our research. It's called cow power. It's one possible solution. You convert

agricultural manure to biogas through anaerobic digestion. In the United States, we generate about 100

million tons of manure a year, which is enough, if it were converted to biogas, to generate about 2% of

our electricity needs. And it also would create a second revenue stream for farmers. So the economics

might workout advantageously for the farmers.

And in terms of environmental liability, manure into a valuable commodity, fuel-- so you might solve

several problems at once. What do you do with the manure? What do you do with your fuel? All these

things-- so it's an opportunity to take environmental problems and solve multiple environmental

problems in a way that's economically profitable.

Let's talk about liquid fuels, biofuels, which is the final form of bioenergy. Recent policies in the United

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States have prioritized biofuels, especially corn ethanol, to displace petroleum. It has several policy

supports. One is mandates to purchase biofuels. So we are required by law to purchase biofuels up to a

certain fraction.

There are agricultural subsidies to help produce the biofuels and make them cost less to the consumer.

There are tax credits to make it cheaper for us to purchase biofuels. Those tax credits were $0.51 per

gallon, though they expire in 2012 after 10's of billions of dollars of subsidies. And there for a while were

tariffs on imported ethanol to make other ethanol-- for example, from sugar cane from Brazil-- more

expensive. That also expired. So for decades, there's been a lot of policy support for biofuels in the

United States, in particular for corn ethanol.

The Energy Independence and Security Act of 2007-- some people call it EISA 2007-- called for

aggressive penetration of renewable fuels. This is the schedule that was called out for-- and billions ofgallons per year of renewable fuel that we are expected to consume starting from 2006 all the way to

2022 on a schedule increasing up to 36 billion gallons in the year 2022.

So it is a volumetric mandate that we, as a nation, must consume 36 billions gallons in 2022. That

works out to be about 20% of our total volumetric consumption of light duty transportation fuels.

Today's consumptions about 140 billion gallons a year of gasoline. It's about 40 billion gallons a year of

diesel. The Energy Independence and Security Act of 2007 capped corn ethanol at 15 billion gallonsper year. The rest should come from cellulosic sources. And that 15 billion gallons a year is roughly

10% of our annual consumption, or at least what it's expected to be in 2022.

So we are already filling up our cars with E10, which is 10% ethanol and the balance of petroleum,

whether we need to or not. So this is the biofuel's push. We already have about 15 gallons a year that

we're consuming.

If we go back over this chart again, the rest of the biofuels are supposed to be made up of somethingother than corn ethanol. So of the 36 billions gallons expected in 2022, up to 15 billion gallons is from

corn. The other 21 billion gallons a year must come from something other than corn.

Just to update you on the biofuels terminology-- the first letter indicates the fuel. B is four biodiesel,

regardless of the source. And then the number tells you the fraction. E is for ethanol, regardless of the

source. It's not clear how we'll label biobutanol-- whether that would also use a B or BB.

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The second number indicates the percentage. So here's some standard blends. B5 is diesel blended

with 5% biodiesel. So that's 5% biodiesel and 95% petroleum-based diesel. B20 is 20% biodiesel and

80% petroleum-based diesel. E10 is very common in the United State today. That's 10% ethanol and

90% gasoline from petroleum sources. E85 is gasoline from petroleum blended with 85% ethanol.

E85 is about the upper limit for most combustion engines that run on gasoline. Diesel engines can

actually take B100. You can do a 100% replacement of biodiesel for diesel.

Alcohols, like ethanol, are just a hydrocarbon with an OH attached. Ethanol is just ethane plus OH. And

ethane is C2H6. So ethanol is just C2H5OH. So there's an OH put on at the end. Methanol is just

methane plus OH. Propanol is just propane plus OH and so forth. So it's just a hydrocarbon, but the OH

is added. And that makes the chemistry a little bit different and the performance just a little different.

There are several different sources of alcohol. Starches like corn are what we use in the United States.

This gives you the least amount of energy return per unit mass. It also requires several steps. You take

the starch, which you process into sugars. And once you have sugars, you can ferment them into

alcohol.

You can also start with sugars, which is what Brazil uses with sugar cane, where you actually get more

energy output per unit mass and per land. So that tends to be a pretty energy productive way to go.

And there, because you're not starting with starches, you can go straight from the sugar to the alcohol

with a fermentation step.

And then you have cellulosic materials, like corn stover or wood chips or switchgrass. This is a much

more difficult. You start with the cellulosic materials and then get to as starch, then go to a sugar, then

go to the alcohol. So there are more steps involved. And the idea is that cellulosic materials might be

able to grow without the irrigation, without the tillage, without the topsoil erosion. So it should be easier

on the land and more sustainably produced, but is more difficult to break down. It requires enzymes to

break down the lignin in the cellulosic materials to get them to the starch. And enzymes are really a

code word for money, so it costs money to break down the cellulosic materials.

Ethanol has some benefits. Wheel to well, it should reduce your CO2 reductions if you're not talking

about indirect land use changes, at least. And the changes depend on how you do it. If you make corn

ethanol today the normal way, you might get a 19% reduction in CO2 emissions If you use natural gas

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for your fermentation, then you might get a 20(% reduction in CO2 emissions. And if you use biomass

for your heat for fermentation, you get 52% % reduction.

So this is one of the dirty secrets of ethanol-- that we tend to use fossil fuels to generate the heat for

fermentation. And today, we use a lot of coal, which is one reason why we don't save as much carbon

as we might anticipate. But as we go from coal to natural gas and then to biomass, you might reduce

your carbon emissions overall, well to wheel. And then the idea is that as you go to cellulosic materials,

the carbon reductions would be even better because you would grow those cellulosic materials without

the fertilizers and without the other energy inputs.

Once you have the alcohol, you get a performance benefit in the car. It's an oxygenate for CO, which

means you can take the carbon monoxide and actually oxidize it to CO2. Now, that's bad from a

greenhouse gas project perspective, but it's good from an air emissions perspective, because CO is a

pollutant. And that alcohol gives you higher octane, which house higher compression ratios and higher

performance in the car. So ethanol has some benefits.

Alcohol fuels in general, though, have drawbacks, too. The ethanol has a lower energy content than

gasoline by about 30%. So you'll get worse fuel economy, and you won't go as far in your car, because

there's less energy in the fuel.

Today, there's a sparse refueling and distribution infrastructure for the alcohols, although that's getting

better every year. And ethanol can corrode conventional pipelines, which means you need to build

dedicated pipelines to move the ethanol around, or do what we do today, which is transport the fuels by

truck or rail using diesel. So we use diesel to move our biofuels around. So we're using petroleum to

move the fuels around that will displace the petroleum. So those are some of the drawbacks of alcohol

fuels in general.

And corn-based ethanol, in particular, has its own set of drawbacks. One is that it takes about as much

energy to make the corn ethanol as that corn ethanol has in it as a fuel. So it's not very definitively

energy positive. Generally, you want a lot more energy to fuel than it took to make it. But we're near

even for corn-based ethanol.

It also consumes vast amounts of fossil fuels at the farm. We use natural gas-based fertilizers,

petroleum-based herbicides and pesticides. We use heat for fermentation from natural gas or coal and

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diesel-powered trucks and farm equipment. So it's not as much a displacement from fossil fuels as you

might expect.

And there is limited land capacity. We need land to grow corn, and a lot of land. So we're using half our

corn crop nationally to meet our corn fuel mandates. And we're starting to run out of agricultural lands

we can use that are suitable for it.

Another problem is once you have the corn, it cannot be piped, so you have to truck it around using

diesel again. And the whole process uses a lot of water. You use a lot of water to grow the corn and

then to refine it at the biorefinery. At the same time, there's expedited topsoil erosion, which negatively

impacts the nitrogen cycle. So we have fertilizer to put on the soil. That soil runs off into the streams

with the nitrogen. That creates a dead zone in the Gulf of Mexico that's quite large. So there are a lot of

problems with corn-based ethanol that we have to keep track of.

Once we have the corn, it goes to a biorefinery. Those biorefineries are smaller than petroleum

refineries. Today, we have 209 biorefineries with a capacity of about 15 billion gallons per year. And

compare that with 149 petroleum refineries with a capacity of 140 billion gallons per year. So we have

25% fewer refineries for petroleum that have 10 times higher overall output. So this is one of the

differences between the bio world and the petroleum world.

With petroleum, you have larger centralized facilities that can process more. And they're piped aroundand connected by a pipeline infrastructure. With bio materials, each biorefinery serves an area of about

100 miles or so. So you have to have many more of them that are smaller, because you're moving the

materials by truck instead of pipe. So the whole structure of the industry is different for biorefineries

than it is for petroleum refineries.

Brazil also makes ethanol, but does so in a different way. It has a whole different approach. First of all,

they started in the 1970s, earlier than we did. We've really been at it seriously since the '90s or the

2000s. They started their Pro-Alcohol program in the '70s just to solve some energy independence

issues around petroleum.

They also have different air quality laws in Brazil. It's easier to use higher blends of ethanol in the

engines without violating the air quality laws in Brazil. Their cars are all flex fuel with onboard computers

to adjust between fuel mixes. So it's very easy for you, as a consumer, to switch between E85 or

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ethanol and petroleum-based gasoline, because your car will adjust on the fly. All the cars have that

option.

Also, the market system allows for easy price comparison. When you pull up, you can just choose one

or the other based on whatever's cheapest that week. It's a very well-penetrated set of fuels into the

system, so there's many options and a lot of cars to go with it. And it's easy for the consumer to make

different choices.

And the biggest difference is that Brazil uses sugar, not corn. Sugar gives you higher energy content

per unit mass. It does not require irrigation. It does not require the fertilizers or the herbicides or the

pesticides. It has been grown for 500 years in the same spot without topsoil erosion. It was brought to

Brazil in 1532, and they've grown it in this location, so they know that it's sustainable or compatible with

long term use on the land.

Also, sugar is a semi-perennial, not an annual. They get three crops per year and they only to replant

every five years, which is different than corn. So they get a lot more productivity using sugar instead of

corn. And that's one of the big differences between Brazil's success with alcohol-based based fuels and

what the US is trying with corn today.

Biodiesel also looks appealing. You could use waste in many nonfood crops. So that helps you avoid

some of the food versus fuel dilemmas. And also, if you use things like restaurant grease, as peopledrive by, your tailpipes will smell like tortilla chips, which is one of the benefits of using restaurant

grease as a form of biodiesel.

It has similar energy content as petroleum-based diesel fuel. So it's a one for one substitution in your

diesel engine. Rudolf Diesel demonstrated his new diesel engine at the Paris World Fair in 1901 using

peanut oil, a form of biodiesel, essentially. So we know it works. It's got pretty good energy

performance. It's another option.

You can make biodiesel from a variety of feed stocks. You can use soybean oil, which is the most

common source in the United States. You can use canola or rapeseed oil, which is the most common

source in the EU. You can also use palm oil, which is the leading source of biodiesel in the world. This

mostly comes from the Far East and places like Malaysia and Indonesia.

You can also use coconut oil, which has high concentration of saturated fatty acids, or beef lard and

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waste grease-- that kind of thing. You could also use algae, which has high potential productivity, but is

still in experimental stages today. So there's a variety of feed stocks. The world leader so far is palm oil.

Unfortunately, palm oil plantations are a leading cause of deforestation in places like Malaysia. So as

we tear down the jungles to build these palm oil plantations, the question becomes are we releasing

more CO2 from the deforestation than the CO2 benefits we're getting from using a biofuel? So this is

one of those trade offs that gets pretty tricky and difficult to quantify about biofuel use. In summary, it's

going to be hard to grow our way out of this energy problem.

Make sure you come back for the next lecture. But in the meantime, go online, do the exercises, and

they'll reinforce all the concepts and the things we talked about this time on this topic.

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