Este curso destina-se a introduzir os alunos para as questões de energia no século 21 - incluindo alimentos e combustíveis - que estão inseparavelmente ligados - e vai discutir a produção e utilização de energia a partir de perspectivas da biologia, engenharia, economia, ciência climática e das ciências sociais. Este curso irá cobrir a atual produção e utilização de energia, bem como as consequências dessa utilização, examinando as reservas de energia fóssil finita, como alimentos e energia estão ligados, os impactos sobre o ambiente e o clima e os impactos sociais e econômicos da nossa atual produção e uso da energia e dos alimentos. Após as palestras introdutórias, vamos examinar as áreas emergentes da energia sustentável, produção de combustível e alimentos, enfatizando a importância do desenvolvimento de métodos de produção energeticamente eficientes e sustentáveis, e como estas novas tecnologias podem contribuir para substituir os suprimentos decrescentes de combustíveis fósseis e reduzir as consequências da emissão de dióxido de carbono para o ambiente. Este curso também irá abranger a importância de criar um futuro energético sustentável para todas as sociedades, incluindo as do mundo em desenvolvimento. As palestras serão preparados e entregues pelos principais professores da UC San Diego e Scripps Institution of Oceanography e profissionais da indústria em todas estas áreas de especialização.
Lifecycle Assessment of Fossil and Renewable Fuels Part 1
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Do curso por University of California San Diego
O futuro da energia
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Social Issues, Economics, and Politics
Examines how energy production and use affects the economy, our wellbeing, and our heath. It will also look at how energy impacts the poorest communities, the external costs of traditional energy, and how we can regulate energy and incentivize renewable energy. Additionally, this section identifies what a Life Cyle Assessment is and how it is used with renewable and non-renewable fuels. Lastly, it looks at the United States’ past and present energy policies, and the current state of international policy on climate change.
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Dr. Stephen MayfieldProfessor of Molecular Biology
University of California San Diego
[MUSIC]
Hi, my name's Alissa Kendall.
I'm an Associate Professor at the Department
of Civil and Environmental Engineering at UC Davis.
And today I'm going to talk about
Lifecycle Assessment of Fossil and Renewable Fuels.
So the first question is why do we actually
need to use life cycle assessment to examine fuels?
If we think about conventional gasoline that comes from
crude oil the life cycle is dominated by combustion,
meaning most of the energy used, and emissions that
come from the fuel happen when you burn it.
And the part that it takes to make the fuel and deliver
it to you, the pre-combustion, doesn't have a very large role to play.
But if we look into the future and we
examine unconventional oil recent, resources for fuels, such as
oil shale the pre-combustion can be as much as
about 45% of the life cycle energy and emissions.
And if we look at renewable fuels like bio-fuels,
the pre-combustion becomes the dominant source of energy in emissions.
and, and in this case, you can see it's really important that we examine their
environmental performance using a life cycle perspective where
we account for the pre-combustion and combustion processes.
So the reason that we, we think bio-fuels are a good idea as a renewable
fuel is that, in theory, they takes Co2 out of the atmosphere as plants grow.
So, so whatever biomass we're using requires some kind of
plant matter to grow and then when we convert it to
a liquid fuel and combust it, we send that Co2 back
up to the atmosphere, leading to no net change in Co2.
Unfortunately, there's a lot going on in between those two
steps that can lead to greenhouse gas emissions and energy use.
So first we have to grow a feed stock.
Most of the time, this requires something like a farming process or
another production system, which requires nitrogen
fertilizer, some kind of equipment use.
And will have other sources of greenhouse gas emissions that
are, that are less directly related to the actual process.
Then we have to convert the plant matter into liquid fuels.
So plants don't necessarily want to be a liquid fuel.
And so this can take quite a bit of energy, and cause emissions, as well.
And then, finally, we get to that last combustion step,
where we send that Co2 back up to the atmosphere.
Certain processes are actually much harder for us to model.
So, for example, we often generate co-products.
These are products that we produce alongside
the bio-fuel in, in a conversion facility.
And we have to figure out how we're going to assign
some of the environmental burdens to that product versus the bio-fuel.
Likewise, we have bio-geochemical emissions that happen when
we grow plants usually or in a field.
And those include nitrous oxide emissions which
happen when we put nitrogen fertilizer on soils.
And soil carbon changes as well as indirect effects such as land use change.
These indirect effects are caused because we divert land or crops into bio-fuels,
and thus spur farmers somewhere around the world to, to make up the difference.
We send market signals that say we need some more crops to be planted.
The petroleum fuel life cycle looks quite different.
Of course, we're going to acquire fossil oil from the ground or,
and then we're going to send fossil Co2 up into the atmosphere.
So this shows us why we're definitely leading to
a net increase in Co2 when we burn fossil fuels.
We also have to do some other things in between, just like a bio-fuel.
So we have to acquire the crude oil we have to convert the crude oil into the,
the fuels that we use through a refining process, and then we combust those fuels.
As with the bio-fuel life cycle, there are certain
processes which are a little harder for us to model.
So, refineries produce a whole suite of products, and we
have to figure out how to assign burdens among those.
And you can have things like fugitive emissions, which occur during the oil
well development and, and extraction, which can
be pretty hard to characterize as well.
So, those are the life cycles of, of fossil and renewable fuels.
Lifecycle Assessment is a way to actually, to, to model all of
those environmental flows that are going in and out of those production processes.
And the idea here is that you track material and
energy resources into the life cycle, and waste and pollution out.
And you always look all the way up the supply
chain to try to get the entire cradle to grave impacts.
But you also look up the supply chain
for every input that you're putting into the system.
So you can think of this as looking up the
supply chain and out, in order to try to capture
all of the energy used and emissions and other kinds
of environmental impacts that are caused when we produce fuel.
So most Lifecycle Assessment methods break up the, the actual study into three steps.
The first is the goal, definition, and scope.
The most important I, one of the many important items,
but probably the most important for fuels is system boundary definition.
This basically says what processes do we have to include, what can we leave out?
Because you can imagine that the analysis can be sort
of infinitely large unless we, we bound the analysis somewhere.
During the life cycle inventory stage, we actually do the accounting process
where we'll be tracking all the inputs to a system and outputs.
And then at the impact assessment stage,
we have to translate this big spreadsheet of
environmental flows which don't really make sense to
a lot of us, into something that's meaningful.
Usually in metrics that, that tell us something
about environmental impacts or impacts on human health.
So we're going to look at one of the
important steps there in the goal, definition and scope.
So this is about system boundary decisions.
So, I'm going to give some historical context.
If you look at early Lifecycle Assessments, or LCAs of, say,
corn ethanol many of them ignored bio-geochemical emissions from the field.
Both because of a lack of knowledge, but
also because green house gasses weren't the biggest concern.
and, and these are very important for green house
gasses but not for a lot of other environmental impacts.
You'll often see people leave out things like plant construction as well.
However, as time goes on, we tend to expand this modeling system boundaries.
So, every study now you'll see will include
these bio-geochemical emissions especially the nitrous oxide emissions.
And even more recently studies have really
had to include indirect land use change effects.
In the late 2000s we found that we, we found out,
essentially, that, that making bio-fuels can cause a whole lot of
indirect effects leading to greenhouse gas emissions that are larger than
the emissions within the direct supply chain or production system here.
In the second step of Lifecycle Assessment, the inventory stage,
we track all of the inputs, so we look at things
like primary materials, secondary materials, energy and then all the
outputs, so air pollutants, water
effluent, solid waste, and also co-products.
What you'll notice in fuel LCAs, is they tend
to limit themselves to just energy and greenhouse gas emissions.
So this is a narrow version of Lifecycle Assessment.
For co-products you'll see that it requires some additional
methodological decisions that we're actually going to look at next.
So the way that we can deal with co-products are
that we can allocate burdens based on some kind of value.
So, the economic value, for example, of multiple products
coming out of a system, or some physical characteristic.
So in a refinery, maybe you would allocate burdens based on the energy
content of different products coming out
since it's largely an energy production system.
The other approach is quite different.
So this is the value-based allocation.
And this is typical of what you do for petroleum fuels out of a refinery.
The section approach system expansion or displacement
is a, is a bit more complicated.
Here, you model the whole system.
And what you end up doing is essentially subtracting the, the burdens of
production for these other co-products so you're
just left with a primary pro, product.
So that doesn't make a lot of sense, and
it never does until we look at an example, okay?
So this is typical of bio-fuels.
So we're going to look at a bio-fuels example.
So this is a modern corn ethanol facility what we call a dry mill.
And the primary products are ethanol, and
dried distillers grains and solubles, or DDGS.
The primary use of this co-product is cattle feed.
So if we think about how, how the
cattle feed market works business as usual then we
can figure out what credit we might assign
to this product coming out of the ethanol plant.
So, business as usual in the Midwest where we, where we
have corn ethanol plants are to feed cows corn and soybean meal.
And in theory when we introduce this product into the market, this DGDS
we displace all of the soybean meal and quite a bit of the corn.
So we would credit the corn ethanol facility with avoiding
the production of soybean meal and some of the corn.
And that's how we, that's how we get a greenhouse
gas intensity factor or energy intensity factor just for the ethanol.
So this is actually some, some values in the California's Low Carbon Fuel Standard.
The Low Carbon Fuel Standard in California requires
that we evaluate fuels from a life cycle perspective.
espe, well the carbon intensity of fuels from a life cycle perspective.
So what I'm showing you here is the carbon intensity of gasoline, okay?
So, the X axis here is grams of Co2 equivalent per mega joule, and
these are different fuels that have already
been approved in the Low Carbon Fuel Standard.
So, what you'll note is that some of the fuels are worse than gasoline.
But what you'll also note is that the indirect effects, so land
use change effects actually dominate the life cycle of sugar cane ethanol here.
And are extremely important in the corn ethanol life cycle as well, and are
is basically the driver for why these
fuels don't do that much better than gasoline.
So value is including these indirect effects
in your system boundaries is really, really important.
All right.
So the summary of, of, of Lifecycle Assessment for bio-fuels is
that it's really important for us to examine these fuels from
a life cycle perspective if we're really going to be able to
compare fossil and renewable fuels, on a, on a fair basis.
Also one important factor in LCA is that it's really a quantitative method
for calculating environmental impacts from a system
wide perspective, rather than a qualitative approach.
And life cycle modeling decisions can really
have an enormous impact on how fuels perform.
And we saw this in the Low Carbon
Fuel Standard results where indirect effects dominate the life
cycle of, of Brazilian sugar cane ethanol and
are very important in the corn ethanol life cycle.
But also in the system boundary decisions
and co-product allocation methods that we use.
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