Coal gasification as a transition plan to build lead time to develop sustainable, climate-friendly energy technologies.
Editor's Note Several of the sources for this article and accompanying sidebars are referenced numerous times. While the note numbers are roughly sequential, they may occasionally appear out of order because an earlier source is again referred to-with its original number.
In past writings I have questioned the overly alarmist projections of some experts concerning the impact on global climate resulting from the emission of so-called "greenhouse gases" due to human activities. Such greenhouse gases include carbon dioxide, methane, nitric oxide, and halogenated carbon compounds, but for our purposes CO2 remains the key concern.1, 2, 3, 4
I still challenge those dubious projections. Yet I also believe it would be prudent to limit emissions of greenhouse gases from human activities-that is, to limit emissions to levels that the more objective climatologists consider as acceptable. Such levels are higher, perhaps, than some would favor. However, I contend that this "middle way" would restrain global warming to manageable levels, improving on "business-as-usual," and thus allow for the necessary lead time to bridge the "Carbon Gap"-the century-long transition to commercially sustainable and climate-friendly energy technologies, by year 2100.
At the very least, there is danger in maintaining the status quo for carbon emissions. Over the past several hundred years, anthropogenic CO2 emissions have increased from pre-industrial times, when atmospheric CO2 concentrations were about 280 parts per million by volume (ppmv). The level reached 367 ppmv in 2000. And such concentrations conceivably could rise as high as 900 ppmv by 2100, under some highly unlikely business-as-usual scenarios. 5 This path would imply cumulative anthropogenic carbon emissions of roughly 2,200 billion metric tons (gigatonnes) between 1991 and 2100.6, 7
Even the most confirmed contrarians of theories of human-induced climate change would agree that this scenario would be too risky.8
Of course, the plan I propose to moderate carbon emissions still would entail a continued, transitional reliance on fossil fuels. It would produce a significant further increase in atmospheric concentrations of CO2 over the next century-to about 550 ppmv by 2100. It would imply cumulative anthropogenic emissions of about 1,000 gigatonnes of carbon (GtC) over the period from 1991-2100, and lead to a doubling of the pre-industrial level of atmospheric CO2. A substantial number of climatologists now believe that this doubling would be acceptable, however, though it would carry certain implications for global climate.
Others, such as Dr. Robert H. Williams, at Princeton Environmental Institute, would prefer a more stringent ceiling of 450 ppmv for atmospheric concentrations of CO2. This tighter limit would imply anthropogenic carbon emissions of 650 gigatonnes on a cumulative basis during the period from 1991 to 2100, when it would be expected that new energy technologies would take over.
This strict limit favored by Williams and others would likely result in further increases of no more than 2° C (3.6° F) in average global surface temperature.
Yet I tend to side with the climatologists that support the more forgiving limit-of between 650 and 1,000 gigatonnes in carbon emissions through the end of the 21st century. Those experts are willing to accept these higher, but manageable, levels of anthropogenic carbon emissions, as they would lead to further increases in average global surface temperatures of no more than about 2° to 2.5° C (3.6° to 4.5° F).2, 6, 7
Of course, these predicted changes in temperature reflect median-level assumptions for various factors that can affect weather and climate. These factors include feedback effects that are due primarily to changes of water vapor concentrations in the troposphere and stratosphere, and of cloud height and reflectivity resulting from the additional warming.
Yet this measured approach appears prudent. The predicted increase in average global surface temperature over the next 100 years still would fall within the range of natural temperature fluctuations that have occurred during the current 10,000-year-old interglacial period, known as the Holocene Age.9
Nevertheless, by 2100 we would need a truly sustainable and essentially carbon-emission-free global energy system. And that need will force private industry and government policymakers to address two basic questions:
- Bridge Technologies. First, what fuels, options, or strategies are available, and which offer the greatest opportunity for success, to sustain the level of human economic and social progress made possible today by fossil fuels,10 yet also manage carbon emissions and global warming during the century-long transition to more sustainable energy technologies?
- Sustainable Technologies. Second, which fuels, resources, or processes will offer the best hope for developing commercially sustainable energy technologies that can achieve the desired equilibrium by year 2100?
From the data presented in the Second and Third Scientific Assessment Reports (SAR and TAR) issued by the Intergovernmental Panel on Climate Change (IGCC),6, 7 it appears that it should certainly be possible to stay within the 1,000 gigatonnes constraint while pursuing an orderly transition to a sustainable energy system. That conclusion assumes that anthropogenic carbon emissions fall sharply to a level that is sequestered naturally by the global ecosystem, after peaking at about 12 gigatonnes annually between 2030 and 2040.
This level of natural sequestration is currently about four gigatonnes annually, of which two gigatonnes of carbon are sequestered by the oceans and 2 gigatonnes by increases in biomass, primarily through afforestation in the Northern Hemisphere.
By contrast, the more stringent constraint of 650 gigatonnes would permit a peak in annual emissions of only 10 gigatonnes, around 2025, followed by a sharp decline.
In a broader sense, however, the question turns into a choice of sustainable energy sources that will have the lowest cost impact after they have been fully developed and commercialized.
For instance, we might choose to bridge this century-long Carbon Gap and to rely for the task on "high-tech" but inherently intermittent renewable sources of energy, such as wind, solar thermal, and photovoltaic power.
Or we might fall back on traditional fossil fuels-augmented by new technologies that minimize carbon emissions.
The potential use of nuclear breeder reactors will also be examined. Yet the outlook seems poor for using biomass or "energy crops" (such as corn ethanol) to bridge the gap, due to the problems of excessive land requirements, high labor intensity, and potentially harmful environmental impacts.2
Several other strategies should also be considered for extending the lead time for achieving true sustainability. Such strategies include using natural gas to displace coal as the currently dominant fuel for power generation, as well as an interim source of hydrogen for highly efficient, electromotive surface transport and distributed generation. They might also include improved efficiency of the use of petroleum liquids as a transportation fuel. A revival of nuclear fission reactor power might also assist in bridging the gap.
However, the longest extension in lead time for achieving sustainability could be gained by continued reliance on coal for power generation, but augmented by adopting a modification of the Integrated Coal Gasification-Combined Cycle (IGCC) process.
Under the modified IGCC process, coal is first gasified under pressure with steam and oxygen to hydrogen, carbon monoxide and CO2. These gasification products are then catalytically processed with additional steam to essentially all hydrogen and CO2. The CO2 is then removed and sequestered in suitable geological formations or the deep ocean, before the hydrogen is used for power generation or as a transportation fuel.13, 14, 15 This option would provide a long-term source of carbon-emission-free hydrogen.
Unfortunately, the IGCC process fails to meet the criteria of long-run sustainability. Even coal is exhaustible. Also, we do not know the total capacity for CO2 sequestration, nor understand all its possible environmental impacts.
Nevertheless, though it is not yet economically competitive, the technology of coal gasification and conversion of coal-derived syngas to hydrogen and CO2 with subsequent CO2 removal is commercially available today. Of course, further development is required on the problem of how to sequester CO2, such as in deep saline acquifers, along with a demonstration on an industrial scale.
Long-Run Sustainability with High-Tech Renewables
The problem with the high-tech renewable power options is that they are inherently intermittent and difficult to integrate with the electric power grid.
Hydrogen is a potential energy storage medium, especially so for direct current (DC) photovoltaic power. That is because excess generation during periods of high insolation could be used for water electrolysis, the high-purity hydrogen stored, and then reconverted to electricity in fuel cells-preferably low-temperature Proton Exchange Membrane (PEM) units-during periods of low or no insolation. However, this is a relatively low-efficiency option, given the combined energy losses of electrolysis and fuel cell power generation. And a key problem is the additional parasitic power requirement for hydrogen compression-from the current PEM electrolyzer levels of 100 to 150 pounds per square inch (psi) to the minimum 3,000 psi required for efficient storage. Also, the investment costs of such electrolytic hydrogen energy storage systems are still quite high. However, Proton Energy Systems, Inc. in Wallingford, Conn. recently has developed systems capable of operating at 2,000 psi and expects to soon reach the 3,000 psi level.16
Wind Power. Wind turbines are the most technically advanced and most widely used high-tech renewable power source both in the United States and abroad. But wind energy carries with it the problems of intermittency and grid management, due to large variations in output. It is possible, however, to store wind power economically by compressing air into underground reservoirs, such as mined caverns, and then recovering it with expansion turbines driven by this compressed air, after heating it with some fuel during periods of low wind velocity.17 Yet there does remain the question of what the source of this fuel would be in a fully sustainable and carbon emission-free system. It may have to be hydrogen produced with some of the wind power in high-pressure electrolyzers.16
Also, wind power unfortunately faces strong opposition to the "environmental pollution" caused by wind turbines systems as high as 370 feet, especially in the offshore installations widely used in northern Europe.
In the United States and Europe, wind power is now nominally competitive with other power sources, in part as a result of government subsidies. In the United States, wind power has enjoyed a 1. 7 cent/kWh tax credit, and there are additional state subsidies. It is now a multibillion dollar per year global industry, with about 17,000 megawatts of global capacity as of year-end 2000, using turbines with outputs as high as two MW.17 The cost of wind power in areas of high average wind velocity has dropped below four cents/kWh, and an eventual level of 3.5 cents/kWh is expected.
One of Europe's largest users of wind power-Denmark-is considering a phase-out of its various subsidies. That stems not only from dispatchability problems, but also because a study has shown that environmental benefits of using wind turbines instead of gas for power generation are far less than the subsidies to wind turbines.18 Moreover, in high population density areas such as western Europe, where wind turbine farms generally can be located only offshore, the available wind power capacity falls short of total power needs.
In the United States, by contrast, some 95 percent of exploitable wind resources of moderate or better quality are located in the sparsely populated 12 states of the Great Plains, with a generation potential of three times current U.S. capacity. The problem, then, is how to turn this intermittent power source into "baseload" electricity that would justify the construction of costly high-voltage transmission lines to the load centers.17 The least-cost solution appears to be the compressed air energy storage (CAES) technique noted above. For small, decentralized installations, the new high-pressure electrolytic hydrogen storage technology eventually may also become economically feasible.16 Of interest is that China has huge, high-quality wind resources in Inner Mongolia, which represent a large fraction of the world's practically exploitable resources (about three times present global generation), but again remote from the major markets.17
Solar Photovoltaics. One area of high-tech renewable power source development and commercialization in which the United States has taken the lead is photovoltaics. An early, cost-effective application of photovoltaic power would be in areas with moderate to high levels of annual insolation to electric-grid-connected buildings, or installations with relatively large roof areas compared to the volume of occupied space. They could use photovoltaic "solar roofs" to generate electricity to offset the purchase of grid power by using the net metering concept. This option involves increases in use of grid power during periods of relatively low or zero insolation, plus a buy-back by the local utility of any excess power generated during periods of high insolation, all at the prevailing rates. That poses a rather complex technological challenge, since the relatively low-voltage DC power generated by photovoltaic modules composed of amorphous thin-film, single crystalline, and polycrystalline silicon must be converted efficiently to 120 volt, 60-cycle alternating current. Also, the conventional electric meter must be replaced by an installation that meters both purchased and self-generated power. Nevertheless, the Clinton administration launched a one million "Solar Roofs" demonstration project in the United States that utilizes the net metering technology of the cooperating utilities. It has shown promising results.
In a moderate climate zone with an average annual insolation of about 1,500 kWh/square meter, a 200 m2 roof installation on a single-family residence operating at 10 percent system efficiency could generate 30,000 kWh/year, but with wide fluctuations of daily and seasonal output. This total is probably in excess of typical annual residential power requirements, except when electric air-conditioning is used. Fortunately, peak air-conditioning requirements coincide with peak periods of insolation. The use of photovoltaic power for electric heating, even with efficient heat pumps, is more problematical, because peak heating requirements coincide with the lowest levels of insolation.
British Petroleum, which has acquired a large photovoltaic equipment manufacturer (BP Solar, formerly Solarex), is also installing "solar roofs" in 200 gasoline service stations in the United States to demonstrate the feasibility of industrial PV applications. The installed cost of amorphous thin-film silicon arrays for solar roofs in new residential housing is expected to fall to $2.70 to $3.00/peak watt by the mid-2000s. That would bring the levelized cost of electricity down to nine to 10 cents/kWh in southern California and 12 to 13 cents/kWh in southern New York-both competitive with retail electricity prices. 17 This assumes net metering, home mortgage financing, and credit for income tax deductions of home mortgage interest.
The Intermittency Problem. The basic problem of making distributed or centralized photovoltaic systems cost-competitive, however, is how to deal with the large daily and seasonal variations in output.
Of course, it would require an area of only about 150 x 150 km of photovoltaic arrays-about the size of New Hampshire-to replace all 3.5 billion kWh of U.S. power consumption in 2000.2 That assumes PV arrays operating at 10 percent efficiency and at a Middle Atlantic insolation rate of 1550 kWh/m2/year. However, it seems impractical to construct large central installations to feed power to the existing grid and provide for energy storage of sufficient capacity to offset the large seasonal variations.
Electrolytic hydrogen is a promising photovoltaic energy storage medium, but only for decentralized systems, in spite of the combined efficiency losses of water electrolysis and hydrogen reconversion to electricity in fuel cells. As noted before, new technology has sharply reduced the parasitic power requirements of hydrogen compression.16 Nevertheless, hydrogen from other sources, such as coal gasification, could conceivably become a fungible energy commodity similar to natural gas. The economic and operational feasibility of creating such a transmission, distribution, and storage system for hydrogen needs to be addressed, because of the obvious advantages of hydrogen as an energy carrier in tandem with electricity as a mainstay of a sustainable energy system.
Similar considerations apply to wind and solar-thermal power, so that the entire vision of using high-tech renewable energy sources as the replacement for fungible fossil fuels-oil, gas, and coal-depends on a solution to the intermittency and wide output swings problems. It also seems unlikely that it will be practical to rely on distributed photovoltaic systems to solve this problem, because of the large variations of solar insolation with latitude.
Small distributed systems with outputs as low as 0.5-1.0 peak kW may be practical with battery storage in much of the developing world, generally located in high insolation areas. Such small on-site sources of power could meet the most essential requirements of the more than two billion people still without electric service. Yet even if the installed cost of photovoltaic arrays is eventually reduced to $3/peak watt,17 with the added cost of batteries and power conditioning equipment, such small systems still may be out of reach of most of the people in the developing world.
The key challenge we face today is to evaluate the most promising technologies to bridge the Carbon Gap. That means achieving the most rapid and cost-effective transition from today's predominant dependence on fossil fuels and combustion processes for providing useful energy services (heating, cooling, lighting, refrigeration, shaft horsepower, passenger-miles, ton-miles, etc.) to high-tech renewable or essentially inexhaustible energy sources.
Nuclear breeder reactors would offer an ideal, emission-free, and essentially inexhaustible source of baseload power if generated in such inherently safe and proliferation-proof designs as the Integral Fast Reactor.19 However, this would require enormous additional investments in research, development, and demonstration and faces much public opposition. And the economics of this power supply option are also highly uncertain.
Thus, the lead time for meeting most stationary energy requirements with renewable or essentially inexhaustible sources of power, and most transportation fuel needs with electrolytic hydrogen, at acceptable costs, may therefore substantially exceed the allowable time when anthropogenic carbon emissions must be sharply curtailed.
The simplest and most cost-effective approach to gain lead time for achieving sustainability of the United States and global energy systems would be to optimize the use of conventional hydrocarbon fuels by more aggressive development of their existing resource base, and further increases in their utilization efficiency. One key question is how natural gas can serve in this role.
Natural gas enjoys the virtue of a low carbon intensity. In terms of fuels, wood carries the highest ratio of atomic carbon to hydrogen, at 10:1. Coal offers a lower ratio of only 2:1, while oil carries a ratio of only 1:2, and natural gas only 1:4.20, 21
Natural gas is the ideal transition fuel for power and hydrogen generation and other energy needs.22, 23, 24 Many new, more efficient technologies are being developed and commercialized for using liquid petroleum fuels in surface and air transport. Fortunately, the carbon content of the 20,000 trillion cubic feet (Tcf) of technically recoverable and currently commercial resources of natural gas (about four times the proved reserves) is only 290 gigatonnes. The 3,000 billion barrels of technically recoverable crude oil and natural gas liquids (about three times the proved reserves) carry a carbon content of only 340 gigatonnes (see Tables 1 and 2).25, 26, 27 Thus, the upper limit of carbon emissions of these hydrocarbon fuels is only 630 gigatonnes-well below the 1,000 GtC cumulative 1991 to 2100 anthropogenic carbon emission constraint assumed in my recommended plan to stabilize atmospheric CO2 concentrations at 550 parts ppmv. In fact, a 630-gigatonne emission level would fall below even the more strict limit of 650 GtC required for a stabilization level of 450 ppmv.
Nevertheless, a reliance on natural gas, oil, and natural gas liquids implies a phasing out of the use of the most abundant but most problematic fossil fuels-coal and lignite. And it is doubtful that relying primarily on these less-abundant hydrocarbon fuels will provide a sufficient lead time to develop and deploy a carbon-emission-free and sustainable global energy system.
Instead, we must also find cost-effective, carbon-emission-free technologies to utilize the 1.1 to 1.8 trillion short tons of proved reserves of coal and lignite, and about seven trillion short tons of technically recoverable resources, which contain 700 to 1,100 and 4,500 gigatonnes of carbon, respectively (see Tables 1 and 2).
But with these uncertainties in the required lead time to bridge the Carbon Gap, a peak in emissions of about 12 GtC/year, between 2030 and 2040, seems to be unavoidable under the moderate goal of 1,000 GtC cumulative emissions and 550 ppmv CO2 concentration by 2100.6 (The more stringent case of 650 gigatonnes of carbon emissions and a 450 ppmv CO2 concentration would imply a peak rate of 10 GtC/year carbon emissions in about 2025.)
These prospects make it imperative to arrive at an early confirmation of the economic and technical feasibility of the coal-fired power generation coupled with CO2 separation and sequestration. A second point to confirm is an updated assessment of the economically recoverable North American and global natural gas resources to determine how much lead time they could provide in conjunction with more efficient use of economically recoverable liquid petroleum resources. And third, in parallel, it seems prudent for the United States and other industrial countries to resume and/or accelerate nuclear breeder reactor development as a baseload power back-up for the most promising renewable power technologies.
Coal Gasification To Gain Lead Time
A promising alternative would be to gasify coal and lignite to hydrogen, and use this hydrogen as the transition fuel for central and distributed power generation, and surface and air transport. The CO2 produced in this option would be separated and then sequestered in suitable geologic formations or the deep ocean.13, 14, 28
Because of the global abundance of coal and lignite, the coal gasification and CO2 sequestration option could provide as much as a century of lead time for development and commercialization of sustainable and carbon-emission-free energy technologies. However, this option also carries with it many unresolved questions.28
For example, should the coal gasification facilities be centralized, with development of a costly transmission, distribution, and storage grid for hydrogen, similar to the existing pipeline grid for natural gas? Or should one rely on dispersed sources of power generation, such as the modified IGCC Process?
The IGCC Process.
As noted before, the first step under the modified IGCC Process is pressure gasification of coal in an entrained flow process with oxygen and steam to carbon monoxide, hydrogen, and CO2. That is followed by catalytic water gas shift of the carbon monoxide with additional steam to hydrogen and CO2, removal of sulfur compounds (either before or after water gas shift depending on the sulfur resistance of the shift catalyst) and, finally, CO2 removal and sequestration.15
There is little doubt that the modified IGCC option is more cost-effective and practical since the construction of a hydrogen grid would be prohibitively capital-intensive, because it has been shown that the conversion of the existing natural gas grid to hydrogen is not feasible.29, 30 Table 3 summarizes the promising projected economics of the modified IGCC option, which provides for 90 percent CO2 removal, and compares them with natural gas-fired combined-cycle power generation and supercritical and ultra-supercritical pulverized coal combustion, both with and without 90 percent CO2 removal.15
Although individual processing steps for such modified IGCC plants have been practiced commercially, they have not been fully integrated to optimize efficiency and minimize investment cost. The Electric Power Research Institute (EPRI) has estimated that it may take as long as 25 years to fully develop, demonstrate, and commercially deploy the economically optimal configuration of the IGCC process and require the expenditure of several billion dollars for research and development.31
Carbon Sequestration. Nevertheless, there are many physical, chemical and environmental problems with CO2 sequestration.2 In addition, there is the substantial cost of CO2 transport and disposal.
The issue of the adequacy of the available CO2 storage capacity is of special importance. For example, the roughly 1,000 gigatonnes of carbon (GtC) contained in the proved global reserves of coal (Table 2) would generate about 70,000 Tcf of CO2. The ultimate global resource base of natural gas is at most 20,000 Tcf, so that depleted gas reservoirs could not accommodate this amount of CO2. The storage potential of depleted oil reservoirs and the quantities of CO2 that can be used for enhanced recovery of petroleum liquids and natural gas are also quite limited.
The ocean, with an inventory of 38,000 to 40,000 GtC (in the form of CO2), would seem to be the ideal sink for disposing of at most 5,000 GtC of fossil fuel carbon, but this option also faces the greatest uncertainties.2 Deep aquifers are a promising on-shore option that has been used for natural gas storage, but the potential capacity, security of storage, and environmental impacts for CO2 storage have not been assessed. The International Energy Agency (IEA) estimated the global storage potential in the ocean by dissolution, dispersion (towed pipe or dry ice) or isolation (CO2 lake at ocean bottom) to be as high as 27,000 GtC, and in deep aquifers as high as 2,700 GtC.2
Fortunately, we probably have 20 years of lead time before we must resolve these questions, if we optimize the recovery and utilization of global hydrocarbon resources. But the use of the IGCC/carbon sequestration option for central power generation could become the key element in extending the lead time for total phase-out of fossil fuels, especially if the investment cost and efficiency of IGCC plants could be further improved.
Why Not Biomass?
Biomass, or energy crops in general, cannot meet global energy needs because of prohibitive land and large parasitic energy requirements, high labor intensity, and unacceptable environmental impacts.2
First, reliance on biomass to replace a significant portion of fossil fuel use would disturb the land carbon cycle. Second, reliance on a fuel such as corn ethanol would force the world to give over huge areas of land to energy crops.
Disrupting the Carbon Cycle. If a substantial portion of mature forest lands were converted to fast-growing energy crops, it would reduce the total inventory of biomass active in the 11-year land carbon cycle of revegetation, and would disrupt the cycle. At present the Earth has an inventory of about 550 gigatonnes of carbon (GtC) in the terrestrial biota. Some 50 GtC of this total is lost each year to soil and detritus, but is replaced by 50 GtC of net photosynthesis (100 GtC of photosynthesis less 50 GtC of plant respiration annually).6 (The annual loss of about 2 GtC to deforestation mostly in the tropics is offset by a roughly equal amount of afforestation, mostly in the Northern Hemisphere.)
Acres of Corn. In 1997, the Illinois Institute of Technology Energy + Power Center evaluated this option both in terms of feasibility of replacing U.S. gasoline or total U.S. petroleum liquids consumption with corn ethanol, and the economics of this option.11 It was found that just to replace 1996 U.S. gasoline consumption would have required more than all available cropland. To replace total 1996 U.S. petroleum consumption would have required 60 percent of the entire U.S. land area (if this were feasible) and substantially more than the combined area of U.S. cropland, pastures, and meadows.
Vehicle of Consensus
Nearly all major manufacturers of automobiles, trucks, and buses are near commercialization of PEM fuel cell vehicles using hydrogen to provide very efficient electromotive propulsion.
Of course, there is still an ongoing debate over how this hydrogen would be delivered-by on-board pressurized or liquefied storage or on-board reforming of petroleum fuels or methanol-but the consensus is rapidly shifting to on-board storage.12
Yet as to the source of this hydrogen for surface transport over the foreseeable future, the consensus appears that packaged natural gas steam reformers would be least costly. They also would offer the lowest "well-to-wheels" CO2 emissions of any current option, such as water electrolysis with grid power, of which more than half is still generated from coal in the United States.
- Henry R. Linden, "CO2 Does Not Pollute: But Kyoto's Demise Won't End Debate,", May 15, 2001, pp. 22-28.
- Henry R. Linden, "Let's Focus on Sustainability, Not Kyoto," , March 1999, pp. 56-67.
- Henry R. Linden, "The Bush Plan and Beyond: Toward a More Rational U.S. Energy Policy," , July 1, 2001, pp. 34-41.
- Henry R. Linden, "The United States Can No Longer Stay on the Sidelines in Formulating a Rational Global Climate Change Policy," (Guest Editorial) , , Oct. 2001, pp. 80-84.
- Jesse H. Ausubel, "Does Energy Policy Matter?" , July 20002, pp. 2-6.
- J.T. Houghton, et al, eds., "Climate Change 1995, The Science of Climate Change," Contribution of Working Group I to the Second Assessment Report of the Intergovernmental Panel on Climate Change (IGPCC), 1996, Cambridge Univ. Press.
- J.T. Houghton, et al, eds., "Climate Change 2001: The Scientific Basis," Contribution of Working Group I to the Third Assess. Report of IGPCC (2001), Cambridge Univ. Press, Cambridge, U.K. and New York.
- "Earth Track," , The Heartland Institute, Chicago, IL, Sept. 2002, pp. 2, 4.
- Bette Hileman, "Web of Interactions Makes It Difficult to Untangle Global Warming Data," , April 27, 1992, pp. 7-14, 16, 18-19.
- Henry R. Linden, "A Comparison of the Performance of Industrial and Developing Countries in Creating Social and Economic Well-Being Through the Prudent Use of Energy Commodities," , Jan./Feb. 2002, pp. 74-83.
- Henry R. Linden, "Pathways to a Sustainable Global Energy System." Presented at the Goddard Engineering Colloquium, Goddard Space Flight Center, Greenbelt, Md, October 6, 1997.
- Henry R. Linden, "Let's Be Rational About Hydrogen as a Vehicular Fuel," , March 15, 2002, pp. 8-9.
- Williams, R.H., Private communication. "Affordable Electricity from Fossil Fuels for Stationary and Mobile Applications, with Near-Zero Pollutant and CO2 Emissions." Review draft of Princeton University Center for Environmental Studies report dated Jan. 2, 1999.
- Williams, R.H., 1996,"Fuel Cell Decarbonization and Fuel Cell Applications and Sequestration of the Separated CO2," PU/CEES Report No. 295, Princeton, NJ: Princeton Univ. Center for Energy and Environment Studies.
- "Evaluation of Innovative Fossil Fuel Power Plants with CO2 Removal," Electric Power Research Institute, Palo Alto, Calif., and U.S. Department of Energy, Office of Fossil Energy, Germantown, Md. and NETL, Pittsburgh, Pa., Interim Report, Document No. 1000316, Dec. 2000.
- "Proton Energy Systems Opens New Connecticut Facility, is Poised for Growth," , Aug. 2002, pp. 4-6.
- Robert H. Williams, "Facilitating Widespread Deployment of Wind and Photovoltaic Technologies," , Spring 2002.
- "Denmark Backing off Wind Power Support," , April 2002. pp. 5-6.
- Yoon I. Chang, "Status of Progress in IFR Development," Paper No. 94-JPG-NE-14, presented at the American Society of Mechanical Engineers Joint International Power Generation Conference, Phoenix, Ariz., Oct. 2-6, 1994.
- Jesse H. Ausubel, "Mitigation and Adaptation for Climate Change," , Fall 1993, pp. 15-30.
- Robert A. Hefner III, "Energy and the U.S. Marketplace-Toward Environmentally Sustainable Economic Growth," The GHK Company, Oklahoma City, Okla. E-mail: email@example.com.
- Henry R. Linden, "Fuel for Thought: Some Questions on the Future of Gas-Fired Generation," , Dec. 1999, pp. 26-35.
- Henry R. Linden, "Fossil Fuels and Energy Policy: Understanding the New Natural Gas Economy," , Nov. 15, 2000, pp. 56-63.
- Henry R. Linden, "Let's Be More Positive About Natural Gas!," , June 15, 2002, pp. 28-32.
- Energy Information Admin., "International Energy Outlook 2002," March 2002, Document No. DOE/EIA 0484 (2002).
- "Worldwide Look at Reserves and Production," , Dec. 24, 2002, pp. 126-127.
- Energy Information Admin., "U.S. Crude Oil, Natural Gas, and Natural Gas Liquids Reserves, Annual Report 2000," Dec. 2001, Document No. DOE/EIA-0216(2000).
- Henry R. Linden, "Alternative Pathways to a Carbon-Emission-Free Energy System," , Fall 1999, pp. 17-24.
- D.P. Gregory, D.Y.C. Ng, and G.M. Long, "The Hydrogen Economy," pp. 226-80 in , J. O'M. Bockris, ed. (1972), Plenum Publishing, New York.
- R.B. Rosenberg and D.P. Gregory, "Hydrogen, an Energy System Concept." Paper SPE 4108, presented at the 47th annual Fall Meeting of the Society of Petroleum Engineers of AIME, San Antonio, Tex., Oct 8-11, 1972.
- "EPRI Sees Benefits to Coal R&D," Sept. 2, 2002, p. 12.
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