Environmental Engineering Reference
In-Depth Information
Coal into gas
Coal can also be turned into a gas - above ground in one process and
below in another. The more widely developed above-ground process is
called an Integrated Gasification Combined Cycle unit. This turns coal,
as its name suggests, into a synthetic gas.
This synthetic gas can then be separated into CO
2
for CCS storage or
for industrial use in chemicals and plastics and hydrogen (for use in gas
turbines). That is the “gasification” part of the IGCC process. The “com-
bined cycle” part of it is something that has created a minor revolution in
electricity generation efficiency. This takes the exhaust gas from the gas
turbine (which functions a bit like a jet engine) and passes it through a
heat-recovery steam boiler that drives a second turbine, whose electricity
output is combined with that of the gas turbine. When the original fuel is
gas, not coal, this technology is known as a Combined Cycle Gas Turbine
(CCGT).
The technique for producing synthetic gas or syngas from coal is called
underground coal gasification. The aim here is to burn coal underground,
especially in seams too deep or thin to be easily mineable, to produce syn-
thetic gas, separable into hydrogen for a CCGT and CO
2
for CCS.
Coal into oil
A much older technology, Coal-to-Liquids (CTL), can create synthetic oil
out of solid coal. This was originally exploited by states that had no access
to conventional oil. It was especially useful to Germany after it lost access to
oilfields in the closing years of World War II, and to apartheid South Africa
after the 1950s after it became subject to international trade sanctions.
But it is hard to see how CTL could be adapted to carbon capture and
storage, and even if it could not be, it produces more emissions in the man-
ufacture and use of the synthetic oil than burning the coal in the usual way.
Carbon capture and storage:
wish fulfilment or wishful thinking?
The great advantage of carbon capture and storage (CCS) technologies, if
they work, would be to prolong the fossil-fuel age, with all its convenience.
As the Stern Review noted in 2006, “CCS technologies have the significant
advantage that their large-scale deployment could reconcile the continued
use of fossil fuels over the medium to long term with the need for deep
