We hear a lot about dry natural gas used to fuel electric generators. But we hear less about wet natural gas, or so-called natural gas liquids that are the underpinnings of everyday consumer...
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.
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.