On June 2, 2014, the Environmental Protection Agency (EPA) issued its Clean Power Proposal for reducing CO2 emissions from existing plants in accordance with Section 111(d) of the Clean Air Act. The agencys goal is to reduce CO2 emissions from existing power plants by 30% from 2005 CO2 emissions levels by 2030. The proposed regulations provide the states with unprecedented flexibility to achieve compliance through the use of four building blocks:
- Unit-specific efficiency improvements;
- Re-dispatch from coal-based to natural gas-based units;
- Expanded use of low- and zero-carbon generating capacity; and
- Expanded use of demand-side energy efficiency.
The EPA has initiated a one-year comment period for the proposed regulations ending in June 2015. States would prepare implementation plans by 2016, with EPA acceptance of the state plans scheduled for 2017. Compliance would be phased in over the period 2020 through 2030. Unit-specific efficiency improvements and demand side management represents significant compliance opportunities for owners of coal-fired power plants. Moreover, in addition to the four building blocks proposed by the EPA, we believe that CO2 emissions can be reduced further through the use of cap-and-trade programs and improved transmission system efficiency.
Unit-Specific Efficiency Improvements
Coal is responsible for producing 40% of the worlds electricity, as well as 39% of its CO2 emissions.1 As illustrated in the table below, there are several different variations of coal, all of which produce more CO2 emissions than natural gas.
CO2 Emission Factors
Type of Fuel
CO2 Emission Factor3
Coal-fired power plants (CFPPs) use steam turbine technology, which is significantly less efficient than modern combined-cycle gas turbine technology. Coal/steam technology efficiency has improved from nominal levels of 11,000 BTU/KWh, but it is still not as efficient as combined-cycle gas turbine technology efficiency, which is less than 7,000 BTU/KWh.
Over the past several years, environmental regulations have dominated discussion about CFPPs. Energy efficiency has received less attention. In 2009, the National Energy Technology Laboratory sponsored a workshop titled Opportunities to Improve the Energy Efficiency of Coal Fired Power Plants.4 Workshop participants included representatives from owners and operators of CFPPs, equipment manufacturers and engineering firms. The workshop group found that energy efficiency varied significantly among CFPPs and that efficiency could be improved by as much as 10%.
Some owners of CFPPs have focused on energy efficiency improvements and implemented best management practices. Others may have focused attention on regulatory impacts and deferred energy efficiency improvements. We encourage owners and operators of CFPPs to audit energy efficiency at each of the units that are scheduled to remain in service, and implement changes that are technically and economically feasible.
The EPA expects unit-specific energy improvements in the range of 4% to 6%, which would help achieve the goal of reducing CO2 emissions by 30%. However, adding pollution control technology to existing coal plants generally decreases energy efficiency. Among the pollution control technologies currently receiving the greatest attention is carbon capture and sequestration (CCS). Existing CCS technologies are very energy intensive and would consume as much as 30% of the energy produced by a coal fired power plant. Although the EPA has not proposed CCS as a building block for CO2 reduction at this time, research into the technology continues both in the U.S. and internationally.
In order for a supercritical pulverized coal plant to comply with the EPAs proposed new standards, its CO2 emissions would need to decrease by 40%. There currently is no way to accomplish this without using CCS. With CCS, the waste CO2 is removed from the coal plants emission stream and then stored at a sequestration site. One key problem with the use of CCS is that the process would use a large percentage of a plants energy output, and would be a cost burden to both producers and consumers.
Currently, the energy required to remove CO2 from a sources emission stream is about 30%5, but it is not yet possible to capture and store CO2 on the scale of a large coal plant. If CCS technology were perfected to allow for its use at large coal plants, electricity costs would increase significantly, despite the fact that nearly 95% of them are located within 50 miles of a CO2 sequestration site.
Four different types of carbon capture methods are being researched and tested, including post-combustion capture from coal plants using amines; pre-combustion capture from integrated gasification combined cycles (IGCC); oxy-combustion capture from pulverized coal; and post-combustion from natural gas combined cycles.6
One of the first large-scale experiments with CCS in the U.S. began in 2009 when American Electric Powers Mountaineer Plant in West Virginia attached a chemical plant to its power plant in order to capture and store CO2. During a two-year span, more than 37,000 metric tons of CO2 were captured, compressed and stored underground. In 2011, climate change legislation that would have required this CCS approach failed in the U.S. Senate, thus ending the project. In North Dakota, one plant is capturing CO2 and transporting it to Saskatchewan for storage in oil reservoirs. The main concerns with underground storage of CO2 include the possibility of leaks that could harm humans and the environment as well as the chance that earthquakes could be caused by injecting CO2 into areas where rock is brittle and faulted.1
China burns nearly as much coal as the rest of the world combined, and has taken the lead on CCS technology. The state-owned utility, China Huaneng Group, along with many other partners including Missouri-based Peabody Energy, has built the GreenGen facility in Tianjin. Valued at $1 billion, GreenGen was developed to extract CO2 from a CFPP and store it underground. A similar effort launched by Shenhua Group the Wulanmulun project is under way in Mongolia. The Wulanmulun facility converts coal into a liquid form and then stores it in an underground saltwater aquifer.
Despite these advances, no facility in the world currently captures and stores carbon emissions on the scale of a large coal-fired power plant. The CCS process will use a large percentage of a plants energy output, and will lead to significant additional costs for both producers and consumers. However, investments in this technology are necessary if the world is going to continue to burn coal.7
Demand Side Management Programs
The EPAs Clean Power Proposal guidelines include Demand Side Management (DSM) as the second potential compliance path available to states and utilities.. Unlike reducing source emissions or improving transmission systems, DSM focuses on reducing usage on the customer side of the emissions process. Improving energy efficiency or reducing demand at the point of use translates directly to reduced generation at the power plant. The keys to implementing DSM will be verification of the energy savings and the translation of those savings into greenhouse gas (GHG) reductions.
The good news is that the connection between improved DSM and reduced GHG emissions has been recognized, calculated, tracked and reported on for decades. The U.S. Department of Energy has developed internationally recognized protocols that have been used since 1995 on both federal and non-federal projects to measure and verify actual energy savings. The EPA has developed and regularly updates a list of regional factors that translate electric generation into GHG emissions based on the active generating plants specific to each region. In other words, both the ability to verify energy savings and the ability to translate those savings directly into GHG emission reductions are already in place and accepted in federal contracting.
Cap-and-trade programs are another compliance strategy that states can use to comply with the new standards. The Acid Rain Program and Clean Air Interstate Rule (CAIR) are two examples of cap-and-trade programs that have successfully lowered SO2 and NOx emissions. The Acid Rain Program has resulted in a 40% decrease in SO2 emissions since the 1990s and a 65% decrease in acid rain levels since 1976.8 CAIR consists of three separate trading programs: an annual NOx program, an ozone season NOx program, and an annual SO2 program.
In 2011, CAIR was replaced by the Cross-State Air Pollution Rule, which aims to reduce emissions that contribute to ozone and fine particle pollution.9 This type of cap-and-trade approach could be used with coal to reduce CO2 emissions. Each state would have its own emissions cap based on the primary type of fuel used. States with more coal-based electricity would have a higher cap that could be reduced in phases over time. Emission credits could be stored or traded within a states electric system. These programs would shift the burden of electricity generation to lower emitting plants that would run more often, thus decreasing emissions in the state and nationwide.
Transmission System Efficiency Improvements
Emission levels also can be lowered through efficiency improvements in the bulk power delivery process, which involves moving electric energy across the grid over large distances to specific locations. There are three primary causes for inefficiency in this process. First, approximately 6% to 8% of the energy is lost during bulk delivery due to thermal friction depending on voltage and conductor size. While these percentages may seem small, this inefficiency can wind up costing billions of dollars. Another form of inefficiency in power delivery is transmission congestion, which occurs when electricity flow is restricted due to capacity limits or safety constraints within the grid. When this happens, a system operator is forced to find alternative electrical paths, often from a less efficient resource. Finally, a number of U.S. power generation facilities have been labeled as reliability must-run plants, and are required to operate regardless of their efficiency to maintain voltage levels within large urban areas.
Several technologies have been developed to offset energy losses in transmission systems by relieving transmission congestion. High voltage direct current (DC) lines are replacing alternating current (AC) lines due to the fact they have 25% lower line losses, two to five times the capacity, and the ability to control the flow of power more closely. Flexible AC Transmission Systems, or FACTS, stabilize voltage, which allows lines to be loaded more heavily, thus increasing usage by 20% to 40%.
Transmission lines, which operate more efficiently at higher voltages, could be made more efficient simply by knowing more about the current conditions of each individual line at a given time. Energy is often lost during the time between production and delivery due to factors such as wire resistance, weather, and operating electrical load. However, improvements in efficiency can be made by allowing for more grid flexibility and having a better understanding of the exact location and behavior of the lines.
Shifting to a dynamic line rating monitoring system will enable greater utilization of higher voltage lines by increasing the capacity of lower voltage lines. This system allows for better utilization by including computer software that determines the capacity of a transmission line based on real-time monitored clearances and conductor temperature. Using this thermal monitoring, operators would then be able to change the load of certain lines as necessary in order to prevent a short circuit. Through these advances in transmission and delivery efficiency, more energy would reach its intended destination without being lost. In the long run, this would lessen the energy that needs to be produced.
The EPAs new draft greenhouse gas regulations have the potential to result in meaningful CO2 reductions through the use of flexible building blocks. Additional tools for achieving CO2 reduction will be identified during the comment period and developed during the implementation period. Currently, the states are focused on reducing emissions at the combustion source through carbon capture and storage and cap-and-trade programs, as well as through demand side management and efficiency improvements in the transmission system. Advanced technology and creative thinking will make it possible to lower emissions while still providing citizens with stable and reliable energy supply. We encourage the EPA and the states to explore all available options including cap-and-trade programs and improved transmission system efficiency as they develop and implement their compliance strategies.
1Nijhuis, Michelle. "Can Coal Ever Be Clean?" National Geographic (n.d.): n. pag. Web.
2Coal. Rep. N.p.: Center for Climate and Energy Solutions, n.d. Web.
3United States of America. U.S. Energy Information Administration. FAQ: How Much Carbon Dioxide Is Produced When Different Fuels Are Burned? N.p.: n.p., n.d. Web.
4Eisenhauer, Jack & Scheer, Richard. National Energy Technology Laboratory. Opportunities to Improve the Efficiency of Existing Coal‐fired Power Plants
5United States of America. Congressional Research Service. EPA Standards for Greenhouse Gas Emissions from Power Plants: Many Questions, Some Answers. By James E. McCarthy. N.p.: n.p., 2013. Web.
6International Energy Agency. Cost and Performance of Carbon Dioxide from Power Generation. By Matthias Finkenrath. N.p.: n.p., 2011. Web.
7Mann, Charles C. "Renewables Aren't Enough, Clean Coal Is the Future." Wired n.d.: n. pag. Web.]
8"Acid Rain Program." Wikipedia. N.p., n.d. Web.
9United States of America. Environmental Protection Agency. NOx Budget Trading Program- Basic Information. N.p.: n.p., n.d. Web.