Japan says it can make coal cleaner. Critics say the plan is “almost impossible.”

The world’s advanced economies have committed to phasing out coal over the next seven years. But not Japan, which is alone in claiming that coal can be less harmful to the planet.

Nowhere is that more evident than in the country’s largest coal-fired power plant in Hekinan, a small city in central Japan where 400,000 tons of jet-black piles are spread over a plot the size of 40 football fields.

Starting next spring, Jera, the company that owns the site, wants to demonstrate that it can mix ammonia – which does not emit carbon dioxide when burned – with coal in its boilers. The use of this new technology is sparking a debate over whether it is better to find cleaner ways to use coal, or to phase it out as soon as possible in favor of renewable energy.

The company says the ammonia method could reduce dangerous emissions in the fight against global warming. In an effort originally conceived — and heavily subsidized — by the Japanese government, it is one of several energy companies planning to use ammonia in a process marketed as “clean coal.”

Ammonia allows the companies to “use the plants we have instead of building new ones from scratch,” said Katsuya Tanigawa, the general manager of Jera’s Hekinan site.

Japan gets nearly a third of its electricity supply from coal, one of the world’s dirtiest energy sources. But critics say using ammonia only increases Japan’s dependence on fossil fuels and potentially increases carbon emissions as the ammonia is produced. Burning ammonia can also produce nitrous oxide, which is toxic to humans and another emission that needs to be managed.

“We need to reduce emissions from coal plants now, not research technology that may or may not be feasible,” said Katrine Petersen, senior policy advisor at E3G, a think tank.

Concerns about energy in Japan have grown exponentially since an earthquake and tsunami in 2011 caused a triple meltdown at the Fukushima Daichi nuclear power plant. Immediately after the disaster, Japan shut down all of its nuclear power plants, causing 30 percent of the country’s electricity supply to fail overnight. To compensate, the country’s energy companies rushed to build new coal plants even as the world moved away from fossil fuels.

Japan’s Prime Minister, Fumio Kishida, recently stepped up efforts to restart the country’s nuclear power grid, but the communities hosting the plants have resisted.

Japan, the world’s third-largest economy, has few of its own natural resources and can produce only 11 percent of its energy needs without fuel imports — one of the lowest self-sufficiency rates of the richest countries in the world.

At a meeting of environment ministers from the Group of 7 Leaders in Sapporo this spring, Japan was the only country to refuse to commit to zero coal use by 2030.

The country’s government and energy industry point to numerous hurdles to the rapid deployment of renewables, including Japan’s geographic isolation, mountainous terrain, deep-sea water and the annual typhoon season.

Along with China, which President Xi Jinping recently said would follow its own “pace and intensity” in cutting carbon emissions, Japanese officials say their country also has its own timetable and methods.

“We want to climb the same mountain to the same peak,” said Atsushi Kodaka, the director of the Commerce Department’s energy strategy office. “But our climbing route doesn’t have to be the same as everyone else’s.”

The energy industry is also reluctant to give up coal because it has spent so much to build new power stations lately. Since 2011, Japanese energy companies have built 40 coal-fired power stations — nearly a quarter of Japan’s total coal-fired network — and a new Jera power station went online last month.

Together with industry, the Japanese government has pledged about 152 trillion yen (about $1.1 trillion) over 10 years to help the country achieve net zero carbon emissions. The Department of Commerce says it will reduce coal-based generation to 19 percent of power supply by 2030, with ammonia technology making up about 1 percent, and that is likely to rise.

Jera knows it needs to convince a potentially skeptical audience of its plans, so it places ads in movie theaters and hands out coupons promoting its efforts to develop “zero-emission thermal power.”

Japan also hopes to eventually export the technology to neighboring countries in Asia, where it has helped build new coal-fired power stations in recent years.

“We are trying to reduce dependence on coal itself in such countries,” said Masashi Watanabe, a natural resources and energy planner at the Ministry of Commerce. “Co-firing ammonia could be a solution.”

In Hekinan, welders recently secured the top of a 700-tonne storage tank at the sprawling Jera factory. Several large orange pipes were scattered on the ground, waiting to be fitted into a pipeline that will carry ammonia to the plant’s boilers.

In a recent test, the company mixed a mixture of 0.02 percent ammonia with fist-sized lumps of coal in a boiler heated to 1,500 degrees Celsius, more than 2,700 degrees Fahrenheit. Getting to the next goal will be more challenging.

In March, the company plans to begin testing mixtures containing as much as 20 percent ammonia, becoming the first in the world to do so.

Even if the technology works, obtaining a steady, affordable and clean supply of ammonia could put a significant strain on the world’s supply of the compound needed to produce fertilizer.

From the government itself Green growth strategy recognizes that if all Japanese coal-fired power plants used 20 percent ammonia, “they would need about 20 million tons of ammonia per year” – equivalent to the total volume of ammonia currently traded on the world market.

Such supply constraints made it “almost impossible” to implement the ammonia plan, said Hajime Takizawa, a climate and energy researcher at the Institute for Global Environmental Strategies, a government-funded independent research group. However, the government says that once the technology is proven to work, suppliers will meet demand.

But the production of ammonia itself requires electricity, which, according to current methods, is usually generated from fossil fuels such as coal or natural gas. In one common process, water is heated to extremely high temperatures — as high as 2,000 degrees Celsius or 3,632 degrees Fahrenheit — so that hydrogen atoms can be split off and combined with nitrogen. (Check your high school science textbooks for the chemical formula of ammonia!)

Heating that water requires a lot of electricity, and the ammonia supplies that will initially go to Japan will probably be made with so-called gray or brown electricity. So while burning ammonia in a power plant in one place reduces carbon emissions, making ammonia in another place can generate more carbon emissions.

As a result, the ammonia method has “very small mitigation potential,” said Masayoshi Iyoda, the leader of the Japanese team for 350.org, a climate activist group.

Suppliers say they will eventually use renewable energy to make ammonia or capture the carbon emitted during the manufacturing process and bury it in the ground. Analysts say that given the cost of such methods, mixing ammonia and coal will be more expensive than simply using renewable energy such as wind power directly.

Ultimately, critics say, Japan is prioritizing ammonia technology to protect entrenched industrial interests from new renewable energy suppliers. “They are fully aware that they are losers in this shift,” said Kimiko Hirata, one of the founders of Climate Integrate, a research and advocacy group. “So they’re very big on protecting the status quo and vested interests for as long as possible.”