Energy from Coal
Coal is odd stuff. It varies so much that sometimes you're not sure that
it actually IS coal.
In parts of Yorkshire you can find lumps of sea coal on the beach
. At Lyme Regis, where it's in compressed layers, you often find lumps of
it washed up by the sea or coming out of the cliffs, uusually described
by boffins as "shale". Brown coal from Germany is almost like peat,
but it creates a
stink when you burn it - it's full of sulphur and other nasties. Anthracite
is shiny and black and almost clean when you touch it. And ordinary coal
varies a lot- sometimes it even contains fossils. This isn't surprising
considering that coal is the crushed remains of prehistoric forests.
I found a fossil leaf once on a bit of coal, and there are lots of examples
in museums.
Coke is different; it's coal with the dirtier bits removed,
made by heating coal in a furnace without letting it burn. This is how
they make "smokeless" fuel.
Coal is mainly CARBON. Pencil leads are made of the same stuff, and
you probably know that it's called graphite.
It burns incredibly cleanly. I knew a guy years ago who had to machine
pieces of graphite
-he used to take waste lumps home to burn on his fire. It contains an
amazing amount of energy and sits there in the grate burning with NO
smoke at all, glowing almost white-hot, with a pale blue flame ... in many ways
an ideal fuel, unless you have to pay for it.
He said the only fuel to compare with it was old shoes, which
surprised me.
Now ... carbon looks like this: the black dots are carbon
atoms:
Coal is similar to this - here's a picture I found many years
ago:
and here's a close-up of part of it:
You can see this coal contains not only carbon but O and N
(oxygen & nitrogen). You often get sulphur, too. This is bad news, because
if you burn the coal, the smoke is acidic - and this means ACID RAIN.
Ordinary coal often contains about 2% sulphur by weight.
So if you burn 100 tons of coal, you're burning 2 tons of sulphur. Here's what
happens:
Sulphur + oxygen -----> sulphur dioxide
2 tons .........2 tons ...........4 tons
Add water to the sulphur dioxide, and you've got a little over 6 tons of
sulphuric acid going up the smoke stack.
You can stop the acid going up the chimney by absorbing it and
then chucking away (or using, if you can find a use for it) the spent
absorber. Unfortunately the best absorbers
are made from limestone, which means more quarries - big ones.
Every 4 tons of sulphur dioxide needs 6 tons of limestone.
In the process you make about 6 tons of Plaster of Paris for every 100
tons of coal. You can
fix a few thousand broken legs, and make a lot of plasterboard, but
what can you do with the rest?
Landfill?
If so, what about local streams and ponds? Will they get
polluted?
So far we've only looked at acid rain, but there's another
problem - the "greenhouse" effect.
When you burn 100 tons of coal you form about 360 tons of carbon
dioxide, all of which goes up the chimney.
When it reaches the upper atmosphere it starts to act rather like the
glass in a greenhouse. The sun's rays hit the ground and the air warms up.
The heat is trapped by the carbon dioxide, which is the "glass"
and our planet gets a lot hotter
than it should. At least, that's what the environmentalists say, and there
seems to be increasing evidence that they're right.....it's unproveable,
of course, which is why there's so much argument about it.
Many countries
have flatly refused
to limit their carbon dioxide emissions, including the U.S.A.....
How much coal is burned in UK power stations?
According to government statistics, about 50 million metric tons
a year.
That's 50,000,000 tonnes, or about a million tons a week.
You can work out the sulphur dioxide, sulphuric acid and carbon dioxide
for yourself.
Humans breathe out carbon dioxide, too .... we could even do some sums
to see if we give out more than the power stations -
but that'll have to be done on another page.....
Nigel Deacon / Habitat 21
