November 2002
PF 02-05
Profiles
Non-CO2 greenhouse gases –
emissions and control from coal
‘Policies aimed at CH4
and N2O reduction
could be far more
effective than CO2-based
strategies’
‘Total greenhouse gas
abatement costs
(including CH4 and N2O)
will always be less than,
or equal to, the
abatement costs of CO2
alone’
‘Coal mine CH4 projects
may become one of the
most financially sound
methods of greenhouse
gas reduction for many
countries’
The two non-CO2 greenhouse gases
of concern with respect to coal are CH4
and N2O. They have global warming
potentials much greater than that of
CO2 - 23 times for CH4 and 296 times
for N2O, over a 100 year time horizon.
Therefore, although coal’s contribution
to global emissions of these gases may
be less than its contribution to the CO2
budget, much could be achieved by
controlling them. In fact, policies aimed
at CH4 and N2O reduction could be far
more effective than CO2-based
strategies. Because of its short
atmospheric lifetime, any reduction in
CH4 emissions would have a relatively
rapid impact on the greenhouse effect.
This contrasts with the essential but
longer-term problem of reducing CO2
emissions. Similarly, because of its
substantially higher global warming
potential, reductions in N2O emissions
could be a significant contribution to
total reductions in greenhouse gas
emissions.
The estimation of global budgets of
CH4 and N2O is hindered by the lack of
accurate emission factors. However, it
is evident that natural sources dominate
both global and national inventories for
CH4 and N2O. Coal mining is the major
source of CH4 from human activities,
contributing around 12% of global
emissions. Coal mining is also a
significant source of CH4 emissions in
many countries, especially those which
are heavily dependent on coal and are
likely to remain so in the foreseeable
future. Countries which have reduced
coal mining activities in the last decade,
such as Austria, Germany, Italy, Russia,
Spain and the UK, have seen a resulting
decrease in CH4 emissions from this
sector.
In the past, CH4 emissions from coal
mines were viewed simply as a safety
hazard. More recently it has been
shown that the energy from this wasted
fuel may be harnessed in an economic
and, in some cases, profitable manner.
The use of coal mine methane may be a
more cost-effective way of reducing net
CO2-equivalent (CO2-e) emissions in
many coal producing countries than
efficiency improvements or capture
strategies for CO2 emissions reduction.
Methane is already captured from coal
mines in many countries, but only a
small proportion of the total methane is
actually utilised (see the table).
Potential uses for methane from coal
mining activities include:
● sale to natural gas companies;
● generation of electricity;
● on-site use as fuel for drying coal;
● sale to industrial or commercial
facilities nearby; and
● oxidation to produce heat or
electricity.
This report reviews the prospects for
emerging technologies to reduce CH4
emissions from coal mining. Examples
are included of demonstration and
commercial scale projects in countries
such as Australia, Poland and the USA.
The potential for the development of
similar systems in other countries is
also addressed. The greatest amount of
CH4 is released at the beginning of
mining operations and the opening of
new coal seams, when the gas is under
greatest pressure and at the highest
concentration. However, even dilute
CH4 in ventilation air can be combusted
to produce energy in commercially
available oxidation technologies such as
the MEGTEC. Although simple flaring
cannot be considered a use of coal mine
CH4 it would be supported by emission
credits and could represent a net zero
cost environmental solution. CH4 would
be converted to CO2 which has a
significantly lower global warming
potential. Further, the energy from the
combustion flare could be used to
generate electricity.
The formation and release of CH4
and N2O in coal combustion systems
are dependent on combustion
conditions. In general, higher
temperatures lead to higher combustion
efficiencies and lower CH4 and N2O
emissions. Large scale pulverised coalfired systems are insignificant sources
of CH4 and N2O. Fluidised bed
combustion, FBC, systems may not
emit significant quantities of CH4 but
can emit relatively high concentrations
of N2O. This is due largely to the lower
combustion temperature in these
systems (under 850°C) which is not
high enough to destroy all the N2O
formed in the combustion zone. There
are three potential methods for
controlling N2O emissions from FBC
systems, although these are not
regarded as being at the commercial
stage yet:
● combustion modifications,
specifically for FBC systems, such
Capture and utilisation of methane from coal mining
Country
Methane captured (% of
total emitted)
Proportion utilised (% of
total emitted)
China
9
5
Former USSR
28
4
USA
30
19
Germany
63
25
Poland
49
14
UK
18
20
Others
30
14
World average
25
9.7
as raised bed temperatures as well as
technology replacement;
● gas phase destruction using a gas
afterburner to destroy N2O; and
● catalytic controls using transition
and alkaline earth metals to reduce
N2O to N2.
Since fuels such as biomass, which
contain less fuel nitrogen, give rise to
lower emissions of N2O, fuel
switching and blending could be a
simple option for N2O control from
FBC systems. However, since FBC is
not a major source of N2O emissions
even on a regional basis, more
concentrated sources such as the adipic
acid industry are likely to be targeted
for control first. This means that, with
respect to emissions of all non-CO2
greenhouse gases from coal use, CH4
will be the major target for potential
reduction.
The high capital costs of control
equipment, their early developmental
status and the low cost of natural gas in
many countries means that coal mine
CH4 usage is not financially attractive
in many locations. However, when
converted to CO2-e and taking the
predicted CO2-e abatement costs into
account, these projects become more
tempting. In fact, it has been calculated
that total greenhouse gas abatement
costs (including CH4 and N2O) will
always be less than, or equal to, the
abatement costs of CO2 alone. Coal
mine CH4 projects may become one of
the most financially sound methods of
greenhouse gas reduction for many
countries.
The Kyoto Protocol is the main
driving force behind the control of
greenhouse gas emissions. Government
programmes have been set up in
countries such as Australia, Germany,
Russia, and the USA to provide support
and funding for reductions in CH4
emissions from coal mining activities.
The major coal producing countries,
such as China, Russia and countries in
Eastern Europe, would be ideal targets
for mine CH4 capture and use.
However, technological and
institutional barriers will have to be
overcome before such projects become
economically viable. Foreign
investments and possible technology
transfer under commitments such as the
Kyoto Protocol may allow mine CH4
projects to be established in developing
countries.
Each issue of Profiles is based on a
detailed study undertaken by IEA
Coal Research, the full report of
which is available separately. This
particular issue of Profiles is based on
the report:
Non-CO2 greenhouse gases –
emissions and control from coal
Lesley Sloss
CCC/62, ISBN 92-9029-375-6, 51 pp,
September 2002, £255*/£85†/£42.50‡
*
†
‡
non-member countries
member countries
educational establishments within member
countries
IEA Clean Coal Centre is a
collaborative project of member
countries of the International
Energy Agency (IEA) to provide
information about and analysis of
coal technology, supply and use.
The service is governed by
representatives of ten countries
(Austria, Canada, Denmark, Italy,
Japan, the Netherlands, Poland,
Sweden, the United Kingdom and
the USA) and the European
Commission.
Gemini House
10-18 Putney Hill
London SW15 6AA
United Kingdom
Tel: +44 (0)20 8780 2111
Fax: +44 (0)20 8780 1746
e-mail: [email protected]
> Internet: www.iea-coal.org.uk