Scientists develop new coating to protect the largest million-kilowatt peak-shaving unit in Northwest China

Deserts, Gobi, Danxia, ​​snow-capped mountains... It is a scenic corridor that integrates many extreme scenery; grottoes, the Great Wall, borders, ancient cities... It is a civilization corridor that integrates many cultural heritages. Today, the Hexi Corridor has boarded the giant wheel of new energy development and has taken the lead in realizing the comprehensive transformation of energy consumption and energy production, becoming an energy corridor that continuously supplies China with powerful "Gansu green electricity".

In recent years, the Gansu Provincial Party Committee and the Provincial Government have attached great importance to energy security and energy base construction, and have built a tens of millions kilowatt wind power base in Jiuquan, four million kilowatt photovoltaic power generation bases in Zhangye, Jinchang, Wuwei and Jiuquan, and a million kilowatt wind power base in Tongwei.

By the end of 2023, Gansu's installed capacity of renewable energy power generation has exceeded 50 million kilowatts, accounting for about 60% of the province's total installed capacity, ranking second in the country. In 2023, the circle of friends of "Gansu Green Power" continued to expand, with 432 million kilowatt-hours of green power sold throughout the year, delivered to 25 provinces across the country, and the scale of renewable energy delivery ranked second in the country. "Green Power" has become Gansu's bright business card.

Wind and solar power abandonment rates are high, thermal power comes to the rescue

Wind and light are climate resources with random and volatile characteristics, and they do not change with the demand of the power grid. Although Gansu Province has developed clean energy rapidly, it faces "difficulties in consumption", "difficulties in external transmission" and "difficulties in peak load regulation". Along the way, "abandonment" has almost covered all the "wind and light" of new energy. In 2015, the wind abandonment rate in the province reached 39%, and the solar abandonment rate reached 31%. The amount of wind and solar abandonment reached 10.8 billion kWh, accounting for 36.97% of the renewable energy power generation capacity.

In order to solve the problem of "abandoning wind and solar power" in the Hexi Corridor, the construction of the 6×1000MW unit of Changle Power Plant, the largest peak-shaving thermal power plant in the northwest region, Gansu Power Investment, started. In 2021, the province's renewable energy power generation reached 44.6 billion kWh, with an utilization rate of 96.83%. Gansu's electricity export reached 51.755 billion kWh, effectively guaranteeing the power demand in Hunan and other central China regions; as the only supporting peak-shaving power source for Qi Shao DC, Changle Power Plant played a "leading" role in the export and consumption of new energy.

How do thermal power units achieve "peak load regulation"? Usually, there are obvious peak and valley periods in electricity demand . For example, during the daytime, Gansu Province's electricity load is at a low point. At this time, wind and solar resources are superimposed, and the output of thermal power needs to be adjusted to the minimum. If the peak load regulation capacity is insufficient, it will cause energy waste; during the peak load period at night, the supply of new energy is insufficient, and thermal power needs to be fully generated. At this time, "peak load regulation" plays an important role. Taking the 1000MW ultra-supercritical unit of Changle Power Plant as an example, during peak electricity consumption, the power of the thermal power unit can be adjusted to 1000MW for full load operation to ensure that the power supply can meet the peak demand; and during the valley period, the unit load is reduced from 1000MW to about 350MW to ensure the output of new energy.

Xinjiang coal encounters "bottleneck"

Nano coatings show their magical powers

In recent years, as my country's coal resource mining has moved westward, Xinjiang coal has become the main type of coal used by thermal power companies in Gansu and other surrounding provinces due to its rich reserves, easy mining, low price, high calorific value and short transportation distance.

However, the types of coal currently mined contain high levels of alkali metals, chlorine or sulfur, which can easily lead to coking of the boiler radiation heating surface, high-temperature corrosion, pipe bursts, high coal consumption and other problems, seriously affecting the safety and economy of power station boilers. With the expansion of the "Xinjiang coal export" market, coking and high-temperature corrosion caused by burning Xinjiang coal have become key technical problems that need to be urgently solved in the national thermal power industry.

Over the years, the main methods used at home and abroad have been to change the boiler structure and add kaolin to reduce the coking and high-temperature corrosion and tube bursting problems on the boiler radiation heating surface as much as possible, or to increase the thickness of the water-cooled wall by surfacing welding or thermal spraying protective coatings to extend the life of the boiler water-cooled wall. However, due to high costs and reduced thermal efficiency, the problem cannot be fundamentally solved.

In recent years, the team led by Gao Xianghu, a researcher in the Low Carbon Energy Materials Group of the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, has focused on the key materials of power stations and the research on key technologies for the protection of radiation heating surfaces and energy saving and efficiency improvement of large power station boilers. Inspired by ceramic glaze, the team independently developed a nano high entropy protection and energy saving and efficiency improvement ceramic coating , which has made breakthroughs in key technologies such as ceramic material anti-coking, high temperature corrosion resistance, infrared efficiency enhancement, high thermal conductivity, and adjustable thermal expansion coefficient , thereby achieving the coupling of protection and energy saving and efficiency improvement, which can meet the use needs of large peak-shaving power stations and other conventional thermal power stations.

Thermal power generation refers to the use of coal combustion to generate heat, and through radiation heat exchange, the water in the water-cooled wall tube is heated into high-temperature, high-pressure steam, thereby driving the turbine to rotate and converting mechanical energy into electrical energy. The nano high-entropy protection and energy-saving efficiency ceramic coating is sprayed on the radiation heating surface (water-cooled wall, superheater), and can rely on the heat when the boiler is started to thermally cure itself to form a dense ceramic layer; and a strong chemical bond can be formed between the coating and the substrate, making it difficult to peel off in the harsh environment of the furnace.

The heated surface of the sprayed protective material is like wearing a "steel armor", blocking the invasion of external corrosive media , reducing the adhesion of molten materials in the high-temperature flue gas of the boiler to the tube wall, and protecting the surface of the water-cooled tube wall from coking and high-temperature corrosion; and the coating and the substrate have matching thermal conductivity and thermal expansion coefficient, which does not affect the heat transfer efficiency and service life of the boiler. At the same time, the protective material also has infrared radiation effect, which can enhance the radiation heat transfer in the furnace and reduce the flue gas temperature at the furnace outlet; enhance combustion, increase the burnout rate of coal powder, reduce coal consumption, and improve the adaptability of coal types.

On the "scenery" track, from a "big province" to a "strong province"

After more than a year of operation, the surface of the water-cooled wall tube in the furnace is smooth and dense, without coking, and the attachments are easy to remove. There are no pits and tube wall thinning and other corrosion conditions, which fully proves the excellent high-temperature corrosion resistance and anti-coking performance of this technology. It is reported that this technology will be demonstrated on a large scale in Gansu ultra-supercritical 1000MW peak-shaving units in 2025.

At present, there are 19 ultra-supercritical 1000MW thermal power peak-shaving units in operation and under construction in Gansu. The nano-high entropy protection and energy-saving and efficiency-enhancing ceramic coating will ensure the safe operation of the coal-fired power peak-shaving units that have been put into operation and are under construction in Gansu Province, and provide technical support for the decision-making and deployment of the Gansu Provincial Party Committee and the Provincial Government to "build a 100 billion-level new energy industrial chain" and the export of Longdian electricity, and help Gansu Province to smoothly transform from a "big wind and solar power province" to a "strong wind and solar power province".

The research results will be promoted to Xinjiang, Qinghai, Inner Mongolia, Guizhou and other provinces to accelerate the transformation of coal-fired power, promote the optimal combination of coal-fired power and new energy, ensure the clean and efficient use of coal, and provide technical support for the transformation of my country's coal-fired power into a basic, supporting and regulatory power source.

References

[1] Ma Jun, Zhang Guoshan, Gao Xianghu, et al. Research on the application of nano high entropy ceramic coating in the anti-coking and corrosion resistance of ultra-supercritical 1 000 MW unit boiler [J/OL]. Thermal Power Generation: 1-10 [2024-05-20]. https://doi.org/10.19666/j.rlfd.202401003.

Planning and production

Produced by Science Popularization China

Author: Gao Xianghu, Liu Baohua (Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences)

Producer丨China Science Expo

Editor: Yinuo

Proofread by Xu Lai and Lin Lin