Natural gas can't be easily used in an existing coal-fired
plant, so just switching to gas is not an answer in itself, even if you
assumed that enough gas was available to fire coal-fired units -- a bad
assumption, in the US, at least.
Just a comment for interested
Listers:
Natural gas can in fact
be fired quite easy in an utility style coal plant, provided of course
that gas burners have been installed.
The funny thing
is that it is easier to fire full power on gas, than to cofire gas
with coal on a -say- 50/50 basis.
The reason being that
the water vapor in the flue gas from natl gas and the fly ash in
the flue gas from coal don't like each other very
well......
After a while it gets
quite messy in the ESP (electrostatic fly ash filters) from condensation mixed
into the fly ash. And the fly ash transportation systems may not handle the
resulting drab.
So, full power on gas in
a coal boiler with gas burners...runs like a champ.
A smaller percentage of
gas cofired, say up to 20%........no sweat, the coal flue gas keeps the
temperatures high enough to avoid much condensation.
A large percentage of
gas cofired, say above 40%.......requires careful special
design.
In reality, gas
firing, even in a modern coal boiler at 40-44% efficiency, is unattractive
since a Gas turbine plant delivers 55-60% efficiency (which is about half
as much again over that coal plant).
We have used natl gas
for years as a 100% back-up fuel in case coal circuit
disruptions or FGD (desulphurization) plant
downtime.
Andries
