If coal is to be a viable long-term fuel for a significant percentage of electricity generation, research and development is needed to increase thermal efficiency, demonstrate cost-effective and secure carbon dioxide capture and storage, further improve emission controls, and reduce water demands.
Coal-fired power plants currently supply nearly half of the electricity consumed worldwide. Globally, coal continues to be the primary fuel for affordable and reliable electric power production due to its low cost and because many countries have indigenous coal resources, which provide a level of energy independence.
However, if coal-fired generation is to remain a major source of electricity, it faces significant economic and environmental challenges. Although solutions to these challenges are possible, much is unknown or untested. Meeting the challenges of coal will require research to improve existing technologies and to develop new breakthrough technologies. It will also require a commitment to an aggressive schedule of technology development, demonstration, and scale-up in a broad array of design processes.
The Electric Power Research Institute (EPRI) has proposed a strategy to meet future global rising electricity demand by deploying a “full portfolio” of clean energy technologies (assuming a carbon-constrained future) that simultaneously reduces pollutant emissions and water use. This full portfolio includes not only renewable energy resources, end-use energy efficiency, advanced light water reactor nuclear plants, and electric transportation, but also advanced coal generation with carbon capture and storage (CCS).
To capitalize on coal’s advantages and help mitigate its weaknesses, research and development (R&D) needs to achieve the following five key goals:
- Improved plant efficiency, via high-temperature materials and higher turbine inlet temperatures.
- Cost-effective, scalable CO2 capture, in new or retrofit applications.
- Environmentally safe and permanent storage of CO2.
- Improved emission control systems, producing near-zero emissions (NZE) of all pollutants.
- Advanced cooling and water management methods to reduce water demand and pollutant discharges.
Improving Efficiency
R&D to improve the thermodynamic efficiency of coal power plants is a key part of any strategy to make coal generation more viable in the future. Increased efficiency, produced by operating at higher steam temperatures, reduces fuel costs and the amount of CO2 generated per unit of plant output; a 9 percentage point efficiency gain results in a 20% reduction in CO2 emissions, as Figure 1 shows. Higher-efficiency plants can also have better part-load operation and operating flexibility, making lower emissions of other pollutants possible and cutting balance-of-plant costs, due to reduced size, water consumption, and waste generation and consumables.
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| 1. Highs lead to lows. High-efficiency advanced pulverized coal power plants substantially reduce fuel costs as well as CO2 and other emissions. (Efficiencies are based on higher heating value.) Source: EPRI |
Currently, the majority of pulverized coal (PC) plants in the U.S. are subcritical, with an average efficiency of about 33% (based on higher heating value [HHV]). Supercritical plants, which typically operate at 3,600 psi and temperatures up to 1,050F, provide significant efficiency improvements over subcritical units, achieving efficiencies of 38% (HHV). Ultrasupercritical (USC) plants, which have been in operation for years in Europe and Japan, and more recently China, have main steam conditions of 4,200 psi and 1,100F and generating efficiencies of up to 42% (HHV). In the U.S., the first new USC PC plant, American Electric Power’s (AEP’s) John W. Turk, Jr. Power Plant, is expected to be commissioned in late 2012.
The primary technology advance needed to enable construction of coal-fired boilers and turbines with even higher efficiencies is the development of metal alloys that retain their strength at very high temperatures and resist corrosion, creep, and other aging mechanisms. These materials also must be cost-effective to manufacture and fabricate into boiler and turbine components.
Aggressive R&D programs for alloy development and evaluation in Europe, Japan, and the U.S. have identified ferritic steels capable of meeting the duty requirements of USC plants up to approximately 1,150F. Several European projects have researched achieving steam conditions of about 1,290F and 5,500 psi with the help of nickel-based alloys.
In the U.S., the Advanced USC (A-USC) Project is under way to build on these capabilities. The project aims to identify, evaluate, and qualify high-temperature materials technology for construction of coal-fired boilers and turbines. The U.S Department of Energy (DOE), through the National Energy Technology Laboratory (NETL), is the majority funder; significant co-funding comes from the Ohio Coal Development Office. Energy Industries of Ohio is managing the program, and EPRI is providing overall technical direction and coordination. The U.S. project seeks to achieve steam temperatures up to 1,400F for an A-USC plant.
As part of this project, two research teams (one for boilers and one for turbines) have been working to identify, fabricate, and test advanced materials and coatings with mechanical properties, steamside oxidation resistance, and fireside corrosion resistance suitable for higher temperatures. These A-USC plants are anticipated to become commercially available after 2020, following successful operation of a demonstration plant.
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