660-MW unit starts at China’s highest-altitude coal plant to help stabilize grid

A 660-megawatt coal-fired unit began commercial operations Thursday in Golmud, in China’s northwestern Qinghai Province, after completing a 168-hour trial run, state broadcaster CCTV News reported. It is the first of two units at China’s highest-altitude ultra-supercritical coal power project, which sits at an average elevation of about 9,350 feet (2,850 meters).

The project is designed to help stabilize Qinghai’s power grid by adjusting its output as renewable generation fluctuates. Bringing the first unit online meant tackling two problems inside the boiler.

Thin air makes it harder to burn coal efficiently, and the fuel’s high alkali content can cause slag and ash to build up.

Burning coal in thin air

Lower atmospheric pressure at the site reduces the amount of oxygen available for combustion. The project uses oxygen-assisted startup to help get the boiler firing and separate combustion controls to keep it running steadily when the unit is operating at very low output.

Engineers also customized the boiler to handle high-alkali coal, which can leave deposits inside the system. Together, the changes allow the unit to burn the fuel while varying its output to match demand on the grid, according to CCTV News.

The unit uses ultra-supercritical technology, which typically operates with steam above 1,076°F (580°C) and at pressures above 24 megapascals.

Those conditions allow a plant to generate more electricity from the same amount of coal. CCTV News reported that the project uses less coal per unit of electricity supplied than China’s national benchmark.

Giving renewables flexible backup

The ability to keep the boiler running at very low output gives the grid more flexibility when renewable generation is strong. The coal unit can cut its output during those periods and increase it when renewable generation falls, or the grid needs more power.

Zhao Falin, the project’s chief manager at Huadian Golmud Co., said the two units are expected to generate 6 billion kilowatt-hours of electricity annually once both are operating. That would be enough to meet the yearly electricity needs of about 6.6 million residents, he said.

Zhao added that the project would improve the stability and reliability of Qinghai’s grid by providing backup capacity as more renewable power comes online.

Recycling water for the second unit

The plant treats and reuses reclaimed municipal wastewater from Golmud. The water circulates through a closed-loop system that, according to the report, allows the plant to operate with zero wastewater discharge. The project also reported that it puts 100 percent of its solid waste to use.

CCTV Newsreported that preparations are underway for the second 660-megawatt unit’s full-system startup. The project aims to have both units in commercial service by the end of the year, bringing its combined generating capacity to 1,320 megawatts.

The second unit will add as much generating capacity as the first. Once both are running, the project will also provide flexible backup as Qinghai brings more renewable generation online.

Source: https://interestingengineering.com/energy/660-mw-coal-plant-unit-enters-service