U.S. DEPARTMENT OF ENERGY PROPOSES TECHNOLOGY OPTIONS TO REDUCE CO2

In 1995 human activities in the United States resulted in CO2 emissions totaling about 1,440 million metric tons of carbon (MtC). Human activity-related (anthropogenic) emissions of other greenhouse gases (GHG), such as methane and nitrous oxide, represented the equivalent of another 220 MtC. Nearly all of the anthropogenic GHG emissions, about 1,500 MtC, resulted from energy production and use, primarily the combustion of fossil fuels. The energy sector represents about 90 percent of US GHG emissions. These data make it clear that significant reductions in GHG emissions can be accomplished only through changes in energy economy, i.e. more effective production, distribution and use of energy.

A new US Department of Energy (DOE) study, titled "Technology Options to Reduce Greenhouse Gas Emissions," outlines 50 technology pathways that could reduce greenhouse gas emissions. These technology pathways address three areas: energy efficiency, clean energy, and carbon sequestration (see Table 1).

Table1Table 1

Energy Efficiency

Improving the efficiency of energy use in the US by developing advanced technologies can offer immediate and significant carbon reductions. Incremental and breakthrough technologies hold the promise of buildings that consume half the energy of current new construction, industries (such as forest products) that can meet all of their energy needs internally, cars that offer three times the fuel economy of current vehicles, and farms that are more productive and enable greater carbon fixation while using less energy. Many technological opportunities exist for improving the efficiency of the U.S. economy.

Clean Energy

The development and use of advanced energy production technologies has a large potential for reducing GHG emissions without increasing energy costs. Technological approaches include using fuels with lower or zero carbon content; increasing the useful energy output per unit of carbon emitted; and capturing carbon emissions to prevent their entry into the atmosphere. With successful development, these advanced technologies generally have the potential to reduce carbon emissions by 25 to 50 percent or more in the time-frame beyond 2020. Their potential for carbon emission reductions by 2010 is considerably more limited because of stock turnover rates in energy production.

Fossil resource development and fossil power generation technologies are described in further detail below.

Fossil Resource Development

Because of the desire to reduce CO2 emissions per unit of energy expended, fossil fuels containing a lower carbon/hydrogen ratio need to be developed. Therefore, any major clean fossil-fuel-based alternative energy plan must center on enhanced production of natural gas, the efficient conversion of abundant fossil feedstocks into electricity, clean transportation fuels and chemical feedstocks whose impact would be to reduce net CO2 emissions compared to current sources for these commodities.

For example, the cost-effective conversion of natural gas to clean transportation fuels and commodity chemicals offers a significant potential for GHG emissions reduction while allowing greater use of domestic natural gas supplies. Breakthrough technologies under development include deriving diesel fuel from natural gas which far exceeds conventional diesel fuels in emission reductions, converting natural gas or synthesis gas to methanol or gasoline, and liquefying natural gas in remote areas.

To make full use of abundant supplies of low-cost solid fuels, such as coal, petroleum coke, biomass and municipal wastes, the integrated gasification combined cycle (IGCC) process represents a unique combination of technologies that offers industry low-cost, highly efficient options for meeting a variety of market requirements. In combination with synthesis gas conversion technologies, it is the only advanced power generation technology that is capable of coproducing a wide variety of commodity and premium products in addition to power to meet future market requirements.

While natural gas is expected to capture an increasing share of the new market for fossil fuels during the next decade, the 2010 to 2020 time-frame should usher in a significantly larger potential for natural gas and for more highly efficient coal-based IGCC technologies. If research efforts were well funded and successful, breakthrough developments in catalysts, simulations, membrane separations, and overall gas-to-liquids conversion (including IGCC-based) technology would be pilot-scale tested by 2010. Allowing for further improvements and scale-up to commercial size plants, a major impact could be expected by 2020.

The US Energy Information Administration predicts that, barring significant technology developments or policy changes, carbon emissions from coal will rise from 460 to 550 MtC between 1995 and 2015, while carbon emissions from natural gas for power generation will rise from 50 to 125 MtC during that period. To reduce this projected increase in carbon emissions, several approaches are being studied.

By 2020, introduction of high-efficiency coal-based technologies could significantly reduce carbon emissions. By 2050, total carbon emissions could be below those produced from the electricity sector in 1990 (a reduction of about 210 MtC per year).

The high-efficiency coal-based pathway increases power generation cycle efficiency by combining two or more advanced energy conversion cycles. Ideas being developed include low-emission boiler systems, pressurized fluidized bed combustion, IGCC, and high-efficiency power systems.

Low- or no-carbon fuels-such as natural gas, synthesis gas or hydrogen-used in the technologies being proposed for accelerated development in this initiative could lead to a significant reduction of carbon emissions after 2020. Fuel cells and gas turbines are currently in use, taking advantage of plentiful supplies of natural gas.

These two pathways, high-efficiency coal and low-carbon fuels, converge in a third group of technologies that integrates production of power, fuels, and/or chemicals, maximizing use of available energy. Unlike the first 2 pathways, which focus on electricity generation, this pathway strives to optimize the entire cycle of carbon utilization by incorporating coprocessing concepts and the tenets of industrial ecology. Such processes would have essentially zero carbon emissions and could result in 100 percent reduction of carbon after 2030.

For the high-efficiency coal-based pathway, about $70 million per year is currently being spent on DOE programs. For the low-carbon fuel pathway (fuel cells and advanced turbines), about $90 million per year is currently being spent.

Carbon Sequestration and Management

Carbon sequestration involves the reduction of net carbon emissions by capturing and sequestering CO2 after combustion, decarbonizing fuel before combustion, or increasing the absorption of CO2 from the atmosphere. These approaches are required for the continued use of fossil fuels as energy sources with reduced impacts on concentrations of atmospheric CO2. For both approaches, there are a number of technological options, ranging from storage of CO2 in the ocean or in geologic formations to chemical or biological stimulation of the absorption of CO2 from the atmosphere. The developmental status of the carbon sequestration technologies varies widely. For example, the injection of CO2 into oil wells or coal seams to enhance oil or methane production is a commercial practice today, whereas the soil biochemistry is not yet adequate to identify the most promising means for increasing soil uptake of atmospheric CO2. It is generally believed that net carbon emission reductions from carbon sequestration could be very high in the time-frame of the late 2030s and beyond.

Conclusions

According to DOE, by 2030 a vigorous research, development and demonstration (RD&D) program could deliver a wide array of cost-effective technologies that together could reduce the nation's carbon emissions by 400 to 800 MtC per year. To make effective progress against realistic goals and expectations, an outlay of approximately $1 billion per year above what is presently dedicated to these efforts would be a prudent investment of resources. DOE believes that many technological opportunities exist that could significantly contribute to this goal without harming the nation's economy. A strategic plan that includes deployment policies to complement technology RD&D will be necessary for success. Plans will need to be formulated that reflect both the economic and technological implications of deploying these technologies. Hence, development of a climate change technology strategy is the recommended next step. The development process should include review of technology policy options to complement technology development options, and a detailed plan for supporting implementation which addresses technology goals. RD&D program plans, policies that support deployment, and fiscal resources. According to DOE, the implementation of a technology strategy to reduce greenhouse gas emissions will serve as an investment insurance policy. It should reduce the threat of climate change from fossil fuel use and provide acceptable technologies that produce savings and revenues that would far exceed the cost of an accelerated research program.


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