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Coal No More: What If?

An analysis of what risks would have to be taken to significantly reduce carbon emissions by using natural gas in the short run.

Fortnightly Magazine - September 2006

In 2004, 52 percent of U.S. power supply was generated by about 310 GW of relatively inefficient coal-fired steam-electric capacity, which emitted 32 percent of U.S. anthropogenic carbon dioxide (CO 2), or 517 million metric tons (mmt) of carbon. Clearly, a key objective in the relatively near term ( i.e., by 2025-2030) should be to reduce this large source of anthropogenic carbon emissions in the form of CO 2. The preferred option has been natural-gas-fired combined-cycle systems, which emit only about one-third as much carbon and have an investment cost of only about $500/kW. The systems also have a lower heating-value efficiency of 60 percent, which is equivalent to a heat rate of 6,300 Btu/kWh (higher heating value basis).

Ideally, a sound objective would be to replace the existing 311-GW coal-fired steam-electric capacity with natural-gas-fired combined-cycle units, but at an average operating factor of 70 percent, this alone would require 11.7 trillion cubic feet of gas (Tcf)/year. Then there is the projected growth in total electric power industry capacity of about 922 GW in 2003 to about 1,186 GW in 2030. This should be met with natural-gas-fired combined-cycle units until a revival of nuclear power and the commercialization of the modified Integrated Coal Gasification Combined-Cycle (IGCC) process. IGCC involves a catalytic water gas shift step that converts the entire output into hydrogen and carbon dioxide (CO 2) and the CO 2 is removed and sequestered in suitable underground formations or in the deep ocean. Although IGCC technology has been developed and demonstrated, investment costs (excluding the cost of CO 2 sequestration) are still in the $2,000/kW range.

Eventually, of course, the objective is to convert the electric system to use inexhaustible, emission-free sources of power and, over the longer range, photovoltaic, and solar-thermal power.

U.S. natural gas for combined-cycle power generation falls far short of the goals listed above. Construction of the roughly 4 billion cf/d capacity Alaska pipeline would help, as would a sharp increase in liquefied natural gas (LNG) imports, but the prospects for Alaskan natural gas for the lower-48 states still are uncertain and the projections for increasing U.S. LNG imports are not very reassuring. To resolve these problems, an all-out effort is required to commercialize the modified IGCC process with CO 2 sequestration.

Replacing Existing Coal Capacity

In terms of gas-supply availability, what is the feasibility of replacing the existing 311 GW of U.S. coal-fired-steam-electric capacity operating at 70 percent load factor and replacing it with natural-gas-fired combined-cycle capacity operating at a 60 percent lower heating value efficiency corresponding to a higher heating value of 6,300 Btu/kWh with an investment cost of only $500/kW? This would essentially eliminate conventional pollutant emissions and reduce CO 2 emissions by two-thirds in an effort to control

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