In the upcoming September 1 edition of the journal Environmental Science and Technology, Paulina Jaramillo, W. Michael Griffin and H. Scott Matthews compared the greenhouse gas as well as SOx, and NOx life-cycle emissions for different fossil fuel combinations used to generate electricity: natural gas, liquefied natural gas (LNG), synthetic natural gas (SNG) via coal gasification-methanation, and coal. The objective of this study was to compare the emissions of NG/LNG/SNG versus coal.
At first instance, their estimates suggest that with the current fleet of power plants, a mix of domestic NG, LNG, and SNG would have lower GHG emissions than coal. But if advanced technologies with carbon capture and sequestration (CCS) are used coal and a mix of domestic NG, LNG, and SNG would have very similar life-cycle GHG emissions. For SOx and NOx they find there are significant emissions in the upstream stages of the NG/LNG life-cycles, which contribute to a larger range in SOx and NOx emissions for NG/LNG than for coal and SNG. Thus, LNG imported from foreign countries and used for electricity generation could have 35 percent higher lifecycle greenhouse gas emissions than coal used in advanced CCS power plants.
Investing in LNG infrastructure today could make sense if it helps moderate natural gas prices and keeps existing natural gas power plants running. But making this investment ultimately locks us into certain technologies that make it harder for us to change paths in an increasingly carbon-constrained world. - H. Scott Matthews, associate professor in Carnegie Mellon's Civil and Environmental Engineering Department.The 1990s saw a surge in construction of natural gas power plants, fueled by cheap natural gas, low investment requirements and the idea that natural gas was less carbon-intensive than coal. Since these plants were constructed, natural gas prices have skyrocketed as the North American natural gas supply has become more limited. These gas plants are now operating at a very low capacity, fueling the energy industry's interest in increasing gas supply by using LNG:
energy :: sustainability :: Bioenergy with Carbon Storage :: biomass :: biogas :: fossil fuels :: coal :: natural gas :: LNG :: carbon capture and storage ::
Those decisions are complicated by the fact that natural gas prices may stay high because of maturing North American gas fields. Natural gas production in North America has been flat or down in each of the past six years, according to the federal government's Energy Information Administration. Increasingly, domestic natural gas will be drawn from nontraditional and more expensive sources that require the development of more complex networks to extract and deliver it to the U.S. market.
However, the increased imports of LNG and all of its indirect impacts could eliminate the environmental benefits of natural gas over coal when future carbon mitigation technologies such as carbon capture and storage (CCS) are adopted.
The researchers point out that LNG has many indirect impacts compared to domestic gas. LNG is extracted in a foreign country, liquefied, put into a tanker to cross oceans, and then regasified and put into pipelines when it reaches the U.S. Each of these steps leads to indirect environmental impacts, such as carbon dioxide emissions from changing from gas to liquid and back. In addition, the facilities and tankers necessary to liquefy, move and regasify the natural gas expected are not plentiful and those in the works will not be up-and-running for several years.
The Carnegie Mellon research team also argues that the U.S. shouldn't rush to invest large amounts in a new infrastructure, such as the LNG infrastructure, without analyzing all the indirect implications of those investments compared to alternative supply options. In addition, utilities and the government should put more effort into conservation and energy efficiency that could help reduce the need for large investments. As the options grow more complicated, the choices become harder and harder.
The Carnegie Mellon suggestions are fundamental, but they do not take into account the emergence of a new energy concept, based on coupling biogas production to LNG export infrastructrues. Biopact is currently conducting a basic lifecycle and economic feasibility assessment of the opportunity to produce biogas close to such existing LNG facilities. The concept consists of capturing and storing carbon dioxide from biogas which results in carbon-negative and ultra-clean biomethane (schematic, click to enlarge). This upgraded bio-based gas is then integrated into the existing LNG upstream.
Given the fact that separating CO2 from biogas before it is combusted is considerably less costly than capturing carbon from fossil fuels, we predict it might become a feasible option to couple biogas with CCS to existing LNG infrastructures. Storage of the carbon dioxide can occur in oil and gas fields to enhance the recovery of these resources, or in (onshore) saline aquifers which hold large potential and are found to be abundant near some of the largest current LNG sites in the Global South (more here: "Deep geological CO2 storage: principles, and prospecting for bioenergy disposal sites", *.pdf).
In December of this year, the United Nations Climate Change Conference will convene in Bali, Indonesia, to prepare the post-Kyoto future. This meeting will be crucial for the future of carbon markets. Some are working towards the adoption of measures that allow bioenergy producers to bank in on carbon-negative biofuels. It is within this context that the commercial feasibility of carbon-negative biogas production coupled to LNG will be determined. If enough voices favor a transition towards a global carbon market, then such projects might become profitable.
Biopact will share preliminary results of its assessment at the upcoming Sparks & Flames energy conference at which the organisation will chair a session on carbon-negative energy, part of the Gas Storage and Trading Summit.
The Carnegie Mellon insights on the GHG emissions of LNG might have to be adapted with these new perspectives in mind, and vice-versa.
On another note, even though co-firing biomass with coal is already practised on a relatively large scale in Europe, the study did not look at the use of biomass in CCS-power plants.
Jaramillo, P.; Griffin, W. M.; Matthews, H. S., "Comparative Life-Cycle Air Emissions of Coal, Domestic Natural Gas, LNG, and SNG for Electricity Generation", Environ. Sci. Technol. 2007; ASAP Article; DOI: 10.1021/es063031o
Haszeldine, R. S.,"Deep geological CO2 storage: principles, and prospecting for bioenergy disposal sites", Draft for Paris IEA meeting - September 24, 2004
Biopact: Pre-combustion CO2 capture from biogas - the way forward? - March 31, 2007.