June 15, 2007

Climate change concerns drive projects to curb CO2

Bill Ellison, PE

In a carbon-constrained world, CO₂ capture and storage (CCS), although considered the most radical of the carbon abatement technologies (CATs), seems to be favored over combustion and steam cycle improvements alone. However, CCS is the least commercially developed of the CAT options; at present, there are only field prototypes for its various forms.

 

Nonetheless, most of the means needed to implement CCS are currently available, and recent developments suggest the processes may eventually be feasible, even as a retrofit to existing plants burning pulverized coal (PC).

For any of the CCS designs, the goal will be to optimize the power generation process for CO₂ capture. In the U.S., that effort is now a work in progress. Separating CO₂ from the high-flow and high-volume flue gases with the low CO₂ concentrations that PC-fired plants produce will be especially challenging. Accordingly, a key interim step (in advance of designing a CCS system) will be finding ways to make the flue gas treatment systems at old and new PC plants "CO₂-capture-ready."

An analysis by the International Energy Agency (IEA) suggests that CCS alone, in one form or another, promises the greatest overall reduction in CO₂ by year 2030: up to 8 metric gigatons per year, or almost 30% of projected energy-related emissions of the greenhouse gas (GHG) by that date. CCS could even provide as much as 55% of the CO₂ decrease that Europe says it will need to achieve by 2100. The prospects for doing so are even brighter if CO₂ market "prices" rise as high as $25 to $30/metric ton.

Peering into the future

In one of the sessions of ELECTRIC POWER 2007's two "Environmental Regulatory Issues, Strategies, and Technologies" tracks, Grant Grothen, PE—GHG programs director for Burns & McDonnell's energy division—presented a tutorial on the various remedial opportunities. He began by reminding the audience of an inconvenient truth: Combustion of 1 ton of PRB coal produces 1.8 tons of CO₂.

As a result, if and when massive amounts of CO₂ begin to be captured from PC, fluidized-bed, or integrated gasification combined-cycle (IGCC) plants, the industry will have no choice but to use both underground reservoirs and the oceans' depths to sequester it. Grothen also emphasized that although emissions of other gases such as methane and hydrochlorofluorocarbons produce, on a per-ton basis, a far more powerful greenhouse effect than those of CO₂, carbon dioxide represents 84% of the problem.

The scale of the problem is daunting. America's CO₂ emissions are more than twice those of Europe and constitute 25% of the world's CO₂ emissions from the burning of fossil fuels as a whole (Figure 1). China is creeping up and may surpass the U.S. as early as next year. U.S. power plants produce about 2.4 billion tons of the heat-trapping gas annually; the transportation sector is close behind at just under 2 billion tons; industry contributes 1 billion tons. A forest covering four million acres (larger than the state of Connecticut) would be required to sequester just the CO2 produced by a 750-MW supercritical coal-fired plant. Yet Grothen said he expects the generation industry to be dominated by coal plants equipped with CCS technologies, and by the next generation of nuclear plants, by 2040.

 

 

In another session, Joe Bugica of EPRI reviewed the diverse approaches that will have to be applied to power generation in a carbon-constrained world. He cited the need for specific technology advancements capable of significantly reducing CO₂ emissions over the coming decades. Among them are:

• Smart grids (see article, p. 68) and communications infrastructures, which will enable end-use efficiency gains, demand response, distributed generation, and the leveraging of the energy storage capacity of plug-in hybrid vehicles.
• New grid infrastructures able to deliver reliable electricity service from supplies composed of as much as 20% to 30% renewable capacity in certain regions.
• Significant expansion of nuclear power, the continued safe and economic operation of the existing reactor fleet, and a viable strategy for managing spent fuel.
• Commercial-scale IGCC plants that capture 90+% of the CO₂ they produce.

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