The World’s Most Efficient Coal-Fired Power Plants

Coal-fired plants in the U.S. have a fleetwide average thermal efficiency that hovers around 32.5% high heating value (HHV), according to the U.S. Energy Information Administration. That figure has undetermined uncertainty because of disparate data sources, but the figure is nonetheless useful for discussion purposes. The World Coal Institute estimates that the average global efficiency of coal-fired plants is 28%. State-of-the-art ultrasupercritical (USC) plants continue to push beyond the 40% thermal efficiency barrier. Yet even with the most efficient technology, fuel supply quality, the availability (or unavailability) of high-temperature boiler materials, and cooling water source often limit the actual operating efficiency of new plants. Short of correcting the performance of all plants to a universal standard, such as the ASME Power Test Codes, direct comparisons between efficiency claims are impractical.

No Common Performance Standards

No single source identifies the world’s most efficient coal-fired power plant. It’s almost impossible to vet reported plant ratings because few plants do performance tests using internationally accepted test codes; instead, they report original design goals without all the caveats. The need for emission control devices and other large power-consuming equipment varies widely around the globe, which also complicates a direct comparison of plant net efficiency claims. Others merely talk about their gross power rating and ignore auxiliary power usage altogether.

Most still report thermal efficiency based on the lower heating value (LHV) of coal instead of the HHV approach because the resulting calculated thermal efficiency is higher. Using LHV rather than HHV can push up the reported plant efficiency by as much as 10%, depending on the water content of the coal.

Finally, seawater or ocean water – cooled plants have an efficiency advantage over plants that use cooling towers, perhaps as much as 1.5 percentage points. Attempting to make all these corrections to some common standard is impossible, so we’ll go with the numbers reported by owners and you can do the mental arithmetic.

There Are Many Highly Efficient Plants Around the Word

In addition to the unquestioned high efficiency of Vattenfall’s Nordjylland Power Station Unit 3, Denmark also is home to another very efficient coal-fired power plant. The two-unit Avedøre Power Station, owned and operated by DONG Energy, is configured to supply thermal energy to Copenhagen’s district heating system and 30% of the electricity needs of eastern Denmark. Unit 1 fires only coal, while Unit 2 can "use a wide variety of fuels: natural gas, oil, straw and wood pellets," according to DONG Energy’s web site, giving credence to the utility’s claims that Unit 2 is the "largest biomass-fueled plant in the world." Also, according to DONG, "Avedøre Power Station’s Unit 2 utilises as much as 94% of the energy in the fuels and has an electrical efficiency of 49% [elsewhere the efficiency is reported as 49.7%]. An achievement that makes the unit one of the most efficient in the world." Unit 2, installed in 2001, uses USC technology. The combined rating of both units is 810 MW, and the plant can supply 900 MW (thermal equivalent) to the district heating system. Steam conditions are 300 bar (4,350 psi), 580C/600C (1,076F/1,112F).

Journeying south, Niederaussem K, owned and operated by RWE Power, is a 1,000-MW USC lignite-fired power plant located near Cologne, Germany. Niederaussem K entered commercial service in 2002. RWE Power reports the plant’s net thermal efficiency as 43.2% LHV (37% HHV), staking claim to the title of "most efficient lignite-fired plant in the world." The operating steam pressure is 260 bar with 580C/600C main and reheat steam temperatures. The Rheinisch brown coal consumed by the plant has a heat content of 3,392 to 4,508 Btu/lb with 51% to 58% moisture content.

In Japan, New Unit 1 and New Unit 2 (commercial operation July 2009) of the Isogo Thermal Power Station, located in Yokohama City, are seawater-cooled, 600-MW USC plants owned by the Electric Power Development Co., Ltd. (J-POWER). In celebrating the start-up of Unit 2, J-POWER noted that this plant "achieves the world’s highest standard both in terms of decreasing the environmental burden and increasing energy efficiency." The plant burns bituminous coals sourced from Japan and other international coal markets. The reported steam pressure is 25 MPa (3,625 psi) with 600C/610C steam temperatures producing an "over 42%" plant thermal efficiency. However, LHV was used in that calculation, so 40.6% (HHV) is comparable.

Korean South-East Power Co. (KOSEP) completed the last unit at its Younghung Thermal Power Plant (a 2005 POWER Top Plant) in 2004. The last two units operate at supercritical steam conditions of 24.7 MPa and 566C/566C. Both of these 800-MW units are seawater-cooled and burn conventional bituminous coals. KOSEP reports each of the units, with 11 stages of feedwater heating, has a net thermal efficiency of 43.8% (LHV) or about 42.5% (HHV) burning bituminous coals.

Genesee 3, jointly developed by EPCOR and TransAlta Energy Corp. (also a 2005 POWER Top Plant), belongs on our short list of high-efficiency coal-fired plants. The plant, located outside of Edmonton, Alberta, Canada, burns subbituminous coals producing steam at a supercritical 25 MPa steam pressure with 570/568C steam temperatures. The plant reports a 41% thermal efficiency (LHV), or about 40% HHV.

In the U.S., AEP began construction of the nation’s first USC power plant in November 2008. The 600-MW John W. Turk Jr. plant expects a 39% net thermal efficiency (HHV). The plant, designed to operate at 3,625 psia with steam conditions of 1,115F/1,130F at the boiler outlet, is scheduled to begin commercial service in 2012.

Our apologies in advance to the owners of the many very efficient power plants that we have unintentionally overlooked. Send us your numbers, and we’ll be sure to include your stats in the next issue of POWER.