### Re: How many btu are there in a dollar bill? (Or a piece of paper?)

Date: Thu Nov 3 10:51:28 2005
Posted By: Todd Whitcombe, Associate Professor, Chemistry
Area of science: Physics
ID: 1127719494.Ph
Message:
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Interesting question. And actually, much more difficult than it would
first appear!

I would like to point out, initially, that I am from Canada and our
dollar bill is now a coin. Hence, I couldn't simply go to the lab and
check this one out! (Nor was I willing to burn up a five dollar bill for
the sake of science.)

So, what is the heat content of a dollar bill? At first blush, one might
think to simply look up the heat of combustion for paper (13.21 kJ/g -
give or take - or 12.44 Btu/gram) and then look up the mass of a dollar
bill (3.46 ounces per 100 or 1 gram per bill). Using these two numbers,
the answer would then be 12.44 Btu per dollar bill.

Except that dollar bills aren't made from paper. Paper money is actually
made from "linen" and the rag content of the money is supposed to be a
secret to protect the money supply from counterfeiters. That said, it
would appear that the paper money is typically about 25% cloth - and
since linen is a cellulosic material, it should have pretty close to the
same heat of combustion. However, its burning characteristics are
significantly different from paper.

Also, paper money is printed with inks and such. They will reduce the
heat content available from a dollar bill as the inks tend to be
inorganic and not particularly combustible. Some of the heat content
available from burning the cellulose would need to go into volatilizing
the ink. Hence, it would be slightly less than 12.44 BTU per bill. But
probably not a lot.

To further complicate things, though, if you were to actually burn money
to generate electricity, you would have to deal with the issue of
combustion of the dollar bills. They don't burn very well when piled
together. There is no way for oxygen to get to the core of the stack and
hence, they tend to burn on the surface. Try burning a telephone book to
see this effect.

Consequently, if you truly want to compare the burning of money with say
a fuel like methane (natural gas), you need to account for the efficiency
of the combustion process. Natural gas burners operate at virtually 100%
combustion as it is easy to mix oxygen and gas. Burning money is going to
be significantly less efficient - probably closer to 30% - unless the
money is either introduced one bill at a time or burnt in an incinerator
where there is some other source of fuel for the flame (i.e. natural gas).

The "straight up" recoverable energy is probably closer to 4 BTU per
bill. And then there are the inefficiencies associated with converting
heat to steam and using the steam to drive the turbines and the turbines
to driven the generators that produce the electricity. I have seen this
number quoted as 23% but I suspect that is a little low. One the other
hand, it is not even close to 100%.

So, is burning "money" energy efficient? Probably not. At 13,210 joules
per gram and with one watt being one joule per second, a paper bill could
run (at 100% energy conversion) a 1500 Watt hair dryer for about 9
seconds. Not enough time to really dry your hair. And realistically, if
you take all of the inefficiencies and losses due to conversion into
account, that time is probably closer to 1 second.

On the other hand, with soaring fuel prices, sometimes it does feel like
we are burning money!

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