20、 Obama
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動画の字幕をクリックしてすぐ単語の意味を調べられます！
単語帳読み込み中…
字幕の修正報告
What lights up the screen that you're looking at right now?
Trace back the battery chargers and power cords
and you'll end up at an electrical outlet,
providing easy, safe access to reliable electricity.
But beyond that outlet, the picture gets messier.
It takes a lot of fuel to heat our homes,
preserve our food,
and our power our gadgets around the clock.
And for 40% of the world, that fuel is cheap, plentiful,
and it's called coal.
But coal also releases pollutants into the air,
like sulfur dioxide,
nitrogen oxides,
soot,
and toxic metals, like mercury.
These cause environmental damage, like acid rain,
and serious health problems.
In fact, in 1952, coal burning caused such heavy smog in London
that pedestrians couldn't even see their feet,
and thousands of people died from ill health.
Since then, many countries have deployed technology
to remove most of these pollutants before they reach the air.
But now we have a new air pollution problem on our hands,
one that doesn't show up in a cloud of dark smog,
but in rising seas,
floods,
and heat waves.
It's global climate change,
and again, the main culprit is coal.
It's responsible for 44% of global carbon dioxide emissions,
which trap the sun's heat in the Earth's atmosphere,
instead of letting it escape.
So now the question is how do we remove that bad stuff as well?
That's the idea behind cleaner coal.
Creating cleaner coal is really about trying to contain its ill effects
with the help of special technologies that make the end product more acceptable.
Just like the most intriguing superheroes
often have their own dark powers to overcome,
so we can try and keep coal's negative forces in check.
But why don't we just exterminate coal
if it takes that much effort to clean it up?
Simply, coal is extremely valuable to us, and it's easy to come by.
Compressed underground for ages,
coal holds chemical energy from plants
that were fed from by the sun hundreds of millions of years ago,
long before humans evolved.
That makes coal energy dense, meaning it can be burned 'round the clock.
It's also cheap, if you ignore the pollution costs,
and should last us through the end of the 21st century.
We've already got all the infrastructure in place for harnessing its power,
and globally,
although countries are making a move
towards energy from cleaner and more renewable sources,
there's no sign yet that coal use is slowing down.
In fact, as of 2012,
over 1000 new coal plants have been proposed,
mostly in China and India.
Since for the time being coal is here to stay,
experts say that if we want to reduce its emissions' impact on the atmosphere,
and slow down climate change,
we'll have to think of creative ways of reducing coal's destructive power.
To do that, we need to strip it of its foul forces,
all that toxic carbon dioxide that causes havoc in the atmosphere.
Then, we need to store the CO2 somewhere else.
This mission is called carbon capture and sequestration,
or CCS.
And as if carbon dioxide were some evil genie we didn't want to escape,
once it has been separated from coal,
we've devised ways to banish it underground.
We can do this by injecting it deep into the Earth,
or by placing it deep under the ocean's surface.
Stripping away coal's negative elements can happen in three ways.
First, and most commonly,
as coal burns,
the exhaust gas can be mixed with a compound called monoethanolamine.
Like a forceful power-stripping magnet, this compound bonds to the CO2,
yanking it out of the gas stream
so it can be stored separately underground.
Another method is to relieve coal of its CO2
before it even has a chance to be released as exhaust.
In this process, steam and oxygen swoop in to the rescue
to convert coal into a special product called syngas,
made up of carbon monoxide and hydrogen and some CO2.
Zap that with some water vapor,
and the carbon monoxide gets converted into carbon dioxide,
which can be isolated.
The leftover hydrogen gas is then used as energy to generate electricity,
so there's an added bonus.
A third technique exposes coal to pure oxygen,
instead of burning it in air.
This creates exhaust gas with higher concentrations of carbon dioxide,
which makes it easy to isolate and to banish to the chasms below.
All this can reduce emissions at a power plant by up to 90%,
but as with any superhero struggling with their destructive powers,
it takes a lot of effort to switch over from the dark side.
So these positive pollution-busting forces,
although they're available,
have barely been used in commercial power plants
because they cost a lot.
But ultimately, the bigger problem is that in most parts of the world,
it's still too easy and much cheaper to keep emitting carbon dioxide,
and that makes it tempting to completely ignore coal's dark side.
In this case, the most powerful force for good is regulation,
the rules that can restrict the amount of carbon dioxide
emitted from power plants,
and make energy companies around the world
wary of what they put into the air.
Until then,
every time you turn on a screen or flick a light switch,
coal is lurking in the background,
carrying its dark powers with it wherever it goes.
コツ：単語をクリックしてすぐ意味を調べられます！

読み込み中…

中級

【TED-Ed】How to create cleaner coal - Emma Bryce

1913 タグ追加 保存
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稲葉白兎 2014 年 12 月 26 日 に公開

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