"Secondary reheat is an effective way to utilize coal cleanly and efficiently," Huang Huanpao, deputy general manager of Beijing Guodian Zhishen Control Technology Co., Ltd., told a reporter from Energy magazine. "Secondary reheat can be traced back to the 1960s abroad. However, the largest installed capacity of a single unit using secondary reheat abroad is only about 700,000 kilowatts. Secondary reheat of a 1,000-kilowatt thermal power unit is a Chinese innovation."
Double reheat technology mainly involves adding a first-stage reheater (boiler) and an ultra-high-pressure cylinder (steam turbine) to a conventional single-stage reheat unit to further improve steam parameters (temperature and pressure). These improved parameters then enhance the unit's coal combustion efficiency, thermal cycle efficiency, and power generation efficiency.
This necessitates the redesign and remanufacturing of the equipment, and the equipment processes are also significantly different from before. It can be said that the 1,000 kW double reheat unit is currently the most structurally complex coal-fired unit in the world.
Such a large-scale and complex system places higher demands on the control system of thermal power plants. "Initially, we had some doubts about having Beijing Guodian Zhishen Control Technology Co., Ltd. develop this system," Zhang Sumin, deputy general manager of Guodian Taizhou Power Generation Co., Ltd., told the reporter from Energy magazine. "We preferred to have a company with experience in double reheat projects abroad do it."
The number of companies developing control systems for thermal power plants is large, leading to fierce competition. Besides foreign companies, a significant number of domestic enterprises are also involved in the competition. In November 2013, Guodian Zhishen signed a DCS and simulation supply service contract with Guodian Taizhou Power Generation Co., Ltd., undertaking the research, development, manufacturing, supply, and engineering application services of the power plant's DCS and simulation system.
The second phase of the Guodian Taizhou Power Plant's 1,000 MW ultra-supercritical unit double reheat project is a demonstration project under the National Science and Technology Support Program project "Research and Engineering Application of Key Technologies for High-Efficiency and Low-Emission 1,000 MW Ultra-Supercritical Units with Temperatures Exceeding 600℃," specifically the sub-project "Engineering Demonstration of Key Technologies for 1000MW Ultra-Supercritical Units with Double Reheat." This is the world's first application of ultra-supercritical double reheat technology in a 1,000 MW unit and is a national demonstration project for energy conservation and emission reduction in coal-fired power generation.
To better overcome technical challenges, Guodian Zhicheng changed its previous DCS engineering work model. From the initial stages of equipment manufacturing and system development, it actively engaged in technical exchanges with power equipment manufacturers, design institutes, and the Taizhou Power Plant, and organized a joint R&D team to participate in the entire system development. "In the traditional approach, we rarely directly interacted with the main equipment manufacturers (boiler manufacturers, turbine manufacturers, etc.)," said Huang Huanpao. "The boiler and turbine are the controlled objects of the DCS. The application of double reheat boilers and turbines in China is a first, and there was no experience to draw upon in operation and control technology. To achieve good control results, it was essential to understand and master the process principles and dynamic and static characteristics of the controlled objects. Our initial contact with the controlled objects greatly helped us design precise control schemes."
From research and development to on-site commissioning, Beijing Guodian Zhishen Control Technology Co., Ltd. organized its most elite team of talents to participate in the research and development of the secondary reheat DCS control system and control technology. This successfully ensured that Unit 3 passed the 168-hour trial operation and was put into operation on September 25, 2015, and Unit 4 passed the 168-hour trial operation and was put into operation on January 13, 2016.
Remarkable results
The application of double reheat technology has had a direct and positive impact on the Guodian Taizhou Power Plant.
The Guodian Taizhou Power Plant, which participated in the construction, is the world's first 1,000-megawatt ultra-supercritical double reheat coal-fired power generating unit. It is a national science and technology support program project and a demonstration project of the National Energy Administration. It has completely independent intellectual property rights and was completed and put into operation in September 2015. It is the world's most efficient thermal power unit in terms of power generation, lowest coal consumption for power supply, and best environmental protection indicators. The unit's power generation efficiency is 47.82%; the coal consumption for power supply is 266.5 grams/kWh, and the coal consumption for power generation is 256.8 grams/kWh, which is 48.5 grams/kWh lower than the domestic average coal consumption for power generation in 2015 (305.3 grams/kWh). For the same amount of power generation, it can save 533,500 tons of standard coal annually, which is equivalent to reducing carbon dioxide emissions by 1,387,100 tons. The SO2 concentration at the desulfurization system outlet is 15 mg/Nm3, far below the national ultra-low emission standard (35 mg/Nm3), and the desulfurization efficiency reaches 99.2%. The NOx concentration at the denitrification system outlet is 31 mg/Nm3, far below the national ultra-low emission standard (50 mg/Nm3), and the particulate matter emission concentration is 2.3 mg/Nm3, far below the national ultra-low emission standard (10 mg/Nm3), meeting and exceeding the emission standards of the gas turbine.
Behind these impressive figures lies the support of the DCS control system developed by Beijing Guodian Zhishen Control Technology Co., Ltd. Zhang Sumin remarked to a reporter from *Energy* magazine, “The high-efficiency operation data achieved by the Guodian Taizhou Power Plant Phase II project can be attributed primarily to the application of double reheat technology. The DCS system developed by Guodian Zhishen has played an indispensable role in this success. They not only developed a targeted DCS control system for the world's first 1,000 MW double reheat ultra-supercritical unit, but also ensured that from its commissioning in September 2015 until now (June 2016), the unit has not experienced a single unplanned outage due to control system malfunctions. This is something I never expected.”
The stable and efficient system benefits from the continuous innovation of Beijing Guodian Zhishen Control Technology Co., Ltd. in the research and development of DCS. Firstly, they developed and successfully applied a high-performance complete set of automated control systems (DCS) for double reheat units with independent intellectual property rights. Secondly, they developed and successfully applied control strategies and technologies for double reheat units, effectively solving the control challenges of double reheat units. Thirdly, they developed and successfully applied unit automatic start-stop control technology (APS), achieving a new breakthrough in the level of unit automation. Fourthly, they developed a simulation model and a high-precision, fully excited simulation system platform for double reheat units, providing effective means for the research, development, simulation testing, and optimization of control strategies, improving the efficiency of on-site commissioning, and shortening the on-site commissioning cycle. Fifthly, they developed and applied a safety operation protection and control scheme suitable for double reheat units.
The advanced and reliable control system and technology provide important support for the safe and efficient operation of the world's most efficient coal-fired power generation unit with the lowest coal consumption and the best overall performance, marking that Guodian Zhicheng Company's DCS technology has reached the international leading level.
It is foreseeable that double reheat technology will be promoted along with the trend of clean coal utilization. Guodian Zhicheng Company, which first developed a domestically produced DCS system for a 1,000 MW ultra-supercritical double reheat unit, has undoubtedly taken a leading position in this field.
However, Guodian Zhicheng has already set its sights on markets beyond thermal power. "Control systems are interconnected in the industrial field. In the future, they can be applied in other fields such as nuclear power, wind power, and chemicals," said a relevant person in charge.
It is understood that Guodian Zhicheng is already attempting to apply double reheat technology to nuclear power units. In addition, Guodian Zhicheng has sufficient experience in applications in industrial sectors such as chemicals. It is believed that with the success of double reheat technology in megawatt-class units, Guodian Zhicheng will achieve even greater success in the field of industrial automation.
