May 10 Demand for liquefied natural gas (LNG)
and coal is soaring to meet the energy needs of booming
economies in Asia, particularly China and India. And with that
demand comes growing greenhouse gas emissions.
The LNG sector is set to grow dramatically over the next two
decades, with about A$200 billion in investments planned for
LNG is cleaner than coal in terms of carbon emissions and
toxic pollutants but extraction, processing and shipping the gas
in liquid form is an emissions-intensive exercise.
Following are details comparing the two fuels.
HOW CLEAN IS LNG?
Burning LNG in power plants produces roughly 40 percent
fewer greenhouse gas emissions compared with black coal. This is
based on a series of studies that compared the total lifecycle
emissions of both fuels based on extraction, production,
shipping and burning in power plants overseas.
LNG also has a higher energy value, meaning it generates
more electricity per tonne than black coal.
Studies have compared Australian LNG and black coal exported
and burned in Chinese power plants to test LNG's advantage in
emissions, particularly when displacing coal.
The results vary but for LNG produced in Australia, a higher
portion of the emissions are from the LNG production process
than digging up and shipping black coal.
For example, Australia produces about 20 million tonnes of
LNG a year and 500 million tonnes of black coal and a smaller
portion of brown coal. Total emissions from the nation's LNG
production total about 8 million tonnes versus about 27 million
tonnes for the entire coal mining industry.
A 2008 report by consultancy WorleyParsons for Woodside
Petroleum found that LNG generated 7.1 megawatts/hour
per tonne versus 3 MW/hr for black coal when both fuels were
burned in high-efficiency power plants.
Overall, the emissions intensity for LNG burned in a
combined-cycle gas turbine plant was 0.44 tonnes and 0.72 for
black coal burned in a power plant with an ultra-super critical
boiler, rising to 1.02 tonnes for a sub-critical plant.
Still, LNG's overall advantage is heavily dependent on the
CO2 content of the gas field and the efficiency of the
coal-fired power plant it is being compared with. The advantage
is greatest if the CO2 gas field content is low, say two
percent, and if the power plant uses sub-critical boiler design.
In China, where much of Australia's gas will be burnt, the
government is pressing for new power plants to be much more
Many new LNG fields, particularly in Australia, have much
higher CO2 contents or have to pipe from extensive coal-seam
networks. For a related factbox, see: [ID:L3E7FS0HJ]
The planned 8.4 mtpa Ichthys project in the Northern
Territory, a venture between Inpex and Total , will
extract raw gas from two fields, with average CO2 content of 8
and 17 percent respectively, compared to 2 percent for
Woodside's Pluto LNG project due to start production this year.
Inpex says the project will produce 7 million tonnes of
greenhouse gases a year and just over a third will come from the
CO2 stripped from the raw gas.
WHAT ARE THE DIFFERENCES DURING PRODUCTION?
Coal mines can produce large amounts of greenhouses gases,
CO2 and methane, which is a much more powerful greenhouse gas
than CO2. But the amounts vary greatly and can be hard to
measure. Other sources of emissions are from earth-moving
equipment and electricity generation.
Overall, though, Australia's large coal mining industry has
a lower emissions profile during production than LNG.
For example, for the year ending June 2010, Rio Tinto Coal
Australia reported total emissions of 3.44 million tonnes based
on coal production of 47.5 million tonnes.
By comparison, Inpex and Total's Ichthys
project will produce its 7 million tonnes of emissions from an
8.4 million tonne per year LNG project.
LNG PRODUCTION: MAIN SOURCES OF EMISSIONS?
For LNG to be liquefied, the CO2 has to be stripped out and
is usually vented into the atmosphere. The higher the CO2
content, the greater the energy needed to remove the CO2 and the
greater the carbon footprint of the project.
Generally, for low-CO2 content gas fields, the vast majority
of emissions are from pumping the natural gas to the processing
plant and then chilling it to minus 161 degrees Celsius.
But for fields with a high CO2 content, the equation changes
ARE COAL-SEAM GAS PROJECTS CLEANER?
No. While coal-seam gas has a low CO2 content, usually about
2 percent, these projects have much larger fuel combustion
emissions from running compressors that extract and pipe the gas
to the LNG plant. These projects usually involve thousands of
wells and many hundreds of kilometres of piping.
The emissions intensity of these investments tend to be near
the top end for LNG projects.
WHAT CAN BE DONE TO REDUCE LNG EMISSIONS?
Carbon capture and storage, long-term tree plantations or
buying carbon credits from clean-energy projects elsewhere can
offset some or all of the emissions. Higher carbon pricing in
Australia could encourage investments in these schemes to offset
Chevron's A$37 billion Gorgon project in Western Australia
is planning to inject 3.3 million tonnes, or 40 percent of its
CO2 emissions, into deep rock formations and is the only
Australian project currently to do this. It will cost the
company A$2 billion.
LNG projects are also turning to more efficient gas turbines
to run compressors and to generate power as well as capturing
more of the waste heat from the production process, and more of
the LNG that evaporates.
(Reporting by David Fogarty; Editing by Simon Webb)