A new-generation power plant that turns coal into a gas before burning it is planned for Tianjin.

By KEITH BRADSHER


TIANJIN, China - China’s frenetic construction of coal-fired power plants has raised worries around the world about the effect on climate change. China now uses more coal than the United States, Europe and Japan combined, making it the world’s largest emitter of gases that are warming the planet.

But largely missing in the handwringing is this: China has emerged in the past two years as the world’s leading builder of more efficient, less polluting coal power plants, mastering the technology and driving down the cost.

While the United States is still debating whether to build a more efficient kind of coal-fired power plant that uses extremely hot steam, China has begun building such plants at a rate of one a month.

Construction has stalled in the United States on a new generation of low-pollution power plants that turn coal into a gas before burning it, although Energy Secretary Steven Chu said on May 7 that the Obama administration might revive one power plant of this type. But China has already approved equipment purchases for just such a power plant, to be assembled soon in a muddy field here in Tianjin.

“The steps they’ve taken are probably as fast and as serious as anywhere in power-generation history,”said Hal Harvey, president of ClimateWorks, a group in San Francisco that helps finance projects to limit global warming.

China has begun requiring power companies to retire an older, more polluting power plant for each new one they build.

Cao Peixi, the president of the China Huaneng Group, the country’s biggest state-owned electric utility and the majority partner in the joint venture building the Tianjin plant, said his company was committed to the project even though it would cost more than conventional plants.

“We shouldn’t look at this project from a purely financial perspective,”he said.“It represents the future.”

Without doubt, China’s coal-fired power sector still has many problems, and global warming gases from the country are expected to continue increasing. Even among China’s newly built plants, not all are modern. Only about 60 percent of the new plants are being built using newer technology that is highly efficient, but more expensive.

With greater efficiency, a power plant burns less coal and emits less carbon dioxide for each unit of electricity it generates. Experts say the least efficient plants in China today convert 27 to 36 percent of the energy in coal into electricity. The most efficient plants achieve an efficiency as high as 44 percent, meaning they can cut global warming emissions by more than a third compared with the weakest plants.

In the United States, the most efficient plants achieve around 40 percent efficiency, because they do not use the highest steam temperatures being adopted in China. The average efficiency of American coal-fired plants is still higher than the average efficiency of Chinese power plants, because China built so many inefficient plants over the past decade. But China is rapidly closing the gap.

After relying until recently on older technology,“China has since become the major world market for advanced coal-fired power plants with high-specification emission control systems,”the International Energy Agency said in a report on April 20.

China’s improvements are starting to have an effect on climate models. In its latest annual report last November, the I.E.A. cut its forecast of the annual increase in Chinese emissions of global warming gases, to 3 percent from 3.2 percent, in response to technological gains, particularly in the coal sector, even as the agency raised slightly its forecast for Chinese economic growth. “It’s definitely changing the baseline, and that’s being taken into account,”said Jonathan Sinton, a China specialist at the energy agency.

But by continuing to rely heavily on coal, which supplies 80 percent of its electricity, China ensures that it will keep emitting a lot of carbon dioxide; even an efficient coal-fired power plant emits twice the carbon dioxide of a natural gas-fired plant.

Perhaps the biggest question now is how much further China can go beyond the recent steps. In particular, how fast will it move toward power plants that capture their emissions and store them underground or under the seafloor?

Coal remains the cheapest energy source in China. China has the world’s third-largest coal reserves, after the United States and Russia.

By adopting“ultra-supercritical”technology, which uses extremely hot steam, and by building many identical power plants at the same time, China has cut costs dramatically through economies of scale. It now can cost a third less to build an ultra-supercritical power plant in China than to build a less efficient coal-fired plant in the United States.