By Liu Zhijiang
Department of Electric Power Management,
Shenhua Group Co., Ltd.
Primary energy reserves in China are largely based on coal, with small contributions from oil and gas. In fact, coal accounts for over 90% of China’s total fossil energy reserves, meaning that China will continue to rely heavily on coal over the long term. However, China is working to reduce the environmental footprint of coal utilization, including emissions of particulate matter (PM), sulfur dioxide (SO2), nitrogen oxides (NOx), and CO2. Thus, a major focus in the country is to increase the use of high-efficiency, low-emissions (HELE) coal technologies and meet the dual objectives of providing power and realizing environmental and social responsibility.
Shenhua Shenwan Energy Company’s Anqing Power Plant Phase II’s 2×1000-MW expansion project is a prominent example of HELE coal-fired power in China. In this project, Shenwan adopted a series of design innovations to optimize environmental performance based on the specific features of China’s coal-fired power sector as well as Shenhua Group’s development strategy to be a world-class supplier of clean energy. Using the latest technological achievements, Shenwan constructed a high-capacity, efficient, and low-emissions coal-fired power plant, which is currently considered to be the state of the art in China. For example, the plant boasts the highest steam parameters in China (see Table 1), resulting in the efficient utilization of coal with extremely low emissions.
The Anqing Power Plant is located in the middle and lower reaches of the Yangtze River. With recent continuous growth of the regional economy, insufficient power supply has emerged as a bottleneck restricting economic and social development. The construction and commissioning of the Anqing Power Plant’s Phase II 2×1000-MW units have fundamentally alleviated the power shortage in the Anqing region and have increased the stability of the local grid. This has supported increased growth in industrial and agricultural production and an expanding
service sector in the region and the larger province.
The scope of the construction of the Anqing Phase II project included two identical ultra-supercritical coal-fired power units, including limestone-gypsum wet desulfurization (FGD) and selective catalytic reduction (SCR) denitrification facilities that were built simultaneously.
Construction commenced on 1 March 2013, and the two units were commissioned with the compulsory 168 hours of full-load testing on 31 May and 19 June 2015. Thus, the effective construction period was just over 22 months. The project investment was 6.096 billion yuan (US$950 million) or 3048 yuan/kW (US$478/kW).
The main operating indicators as measured during the full-load test prior to commercial operation are as follows: unit #3 consumed 272.5 g/kWh of coal with a parasitic energy consumption rate of 4.01%; unit #4 consumed 273.9 g/kWh of coal with a parasitic energy consumption rate of 4.06%. Thus, both units operated more efficiently than an average 1000-MW unit in China in 2014, which consumed 287.65 g/kWh of coal with an average parasitic energy consumption of 4.08%.1
The emissions were also measured during the full-load test and were lower than the national emission standards for natural gas-fired power plants. Since passing the 168-hour test, the units and their emissions control systems have continued to operate at the same high standards. In addition to low emissions, 100% of the fly ash, slag, and desulfurization by-products are utilized during normal operation and no wastewater is discharged.
Through research and collaboration between engineers, technicians, and design institutes, the optimization of cost and key operating parameters was carried out concurrently. This helped to save more than 40 million yuan (US$6.3 million) in project investment.
By optimizing purchasing, maximizing competitiveness, and lowering the procurement cost, the best possible price performance ratio was obtained. For the desulfurization system’s absorber alone, the cost was reduced by 12 million yuan (US$1.9 million) compared to the original project budget.
Construction Cost Controls
With effective control of construction costs, the project investment of 6.096 billion yuan (US$950 million) was 547 million yuan (US$85.7 million) lower than the approved project budget of 6.643 billion yuan (US$1.04 billion), and the construction costs were reduced by 8.2%. The unit investment of 3048 yuan/kW (US$477.5/kW) was 152 yuan/kW (US$23.8/kW) lower than the budgeted amount. Cost-saving measures meant that the total project investment was less than that for comparable units in China.
Efficiency was maximized at the Anqing Phase II units mainly by increasing the initial steam parameters and adopting new technologies. Eighty-five new technologies were adopted at the plant, raising the power plant efficiency significantly and reducing coal consumption and emissions.
Perhaps the most important factor related to efficiency was the installation of the ultra-supercritical (USC) steam turbines, which decreases the amount of coal needed per unit of power produced compared to plants that operate at supercritical or subcritical steam conditions. The USC Anqing units are able to operate at steam cycle pressure and temperatures of 28 MPa/600˚C/620˚C—the first time such high parameters were used in China on a plant of this size. Currently, the rated pressure upstream of the main valve of the top three 1000-MW ultra-supercritical steam turbine plants is 25 or 26.25 MPa. Among them, the Waigaoqiao No. 3 plant has the highest pressure, 27 MPa, at the main valve, with main steam and reheat steam temperatures of 600˚C (see Figure 1). After considering all technology options, a main steam pressure of 28 MPa and a reheat steam temperature of 620˚C were selected. Compared to the steam parameters used by conventional 1000-MW units, the Anqing steam turbines’ heat consumption is 53 kJ/kWh lower and the standard coal consumption for power generation was reduced by 1.94 g/kWh. The annual savings, based on standard coal costs, are about 19.8 million yuan (US$3.10 million).
Many other technological approaches were also taken to improve the efficiency. For example, grade-9 regenerative extraction (i.e., extracting steam from nine different locations in the turbine to optimize boiler feedwater heating) was adopted. As compared to the typical grade-8 regenerative extraction, heat consumption was reduced by 10 kJ/kWh and standard coal consumption for power generation was reduced by 0.34 g/kWh.
A high-yield water cooling tower designed to save energy compared to a conventional cooling tower (see Figure 2) was used for the first time at a 1000-MW unit in China, reducing the circulating pump lift by 10–11.5 m and reducing noise by 8–10 dB. About 3790 kW/hr of parasitic energy was saved, reducing the plant’s power consumption by 0.38%, and the standard coal consumption for power generation was reduced by about 1 g/kWh.
Another approach to saving energy was capturing the waste heat in the flue gas and using it to preheat the boiler feedwater. Operating at the designed full load, the flue gas heat exchanger recovers 44,000 kW of heat, which reduced heat consumption by 45 kJ/kWh, and reduced the plants’ standard coal consumption by 1.65 g/kWh.
Minimizing the backpressure on the steam turbines is another approach to increasing the efficiency of the power plant. Thus, at the Anqing units the backpressure for the units was optimized to improve overall efficiency, with an operating design value of 4.89 kPa. Based on this rated backpressure, heat consumption was reduced by 30 kJ/kWh and the standard coal consumption for power generation was reduced by about 0.75 g/kW for every 1 kPa of reduction in the turbine backpressure. In comparison to a standard unit backpressure of 5.1 kPa, heat consumption was reduced by 6.3 kJ/kW and the standard coal consumption for power generation is reduced by about 0.21 g/kWh.
Through the 11 energy-saving projects that have been implemented, the total heat consumption reduction was 152.1 kJ/kWh in total, and the standard coal consumption for power generation was reduced by a total of 5.51 g/kWh. Assuming an annual operating time of 5500 h, 30,305 tonnes of standard coal can be saved by each of the Anqing units per year.
Comparing the Anqing units with China’s national average for similarly sized plants, their coal consumption is 15.15 g/kWh lower, saving 83,325 tonnes of standard coal per unit every year—a combined savings of 166,650 tonnes of standard coal each year. This means that CO2 emissions can be reduced by about 416,700 tonnes per year, which is a 5% decrease compared to the average 1000-MW plant in China. Compared to the national average of new coal-fired power plants (i.e., 318 g/kWh in 2014) these two units represent a nearly 15% decrease in CO2 emissions.
ULTRA-LOW EMISSIONS TECHNOLOGIES
The Anqing Phase II project incorporated highly advanced flue gas treatment technologies, based on an ultra-low emission technology roadmap. The roadmap includes an electrostatic precipitator (ESP) with a low-temperature economizer, spin exchange coupling FGD, and a rotary tube bundle PM demister. Several of these flue gas treatment devices offer cobenefits that further reduce net emissions.
There are three separate processes in the power plant that remove PM from the flue gas. The high-frequency ESP with three chambers and five electric fields forms the first segment of particulate emissions control. The removal efficiency of PM in the ESP is up to 99.86–99.9% with a concentration around 25 mg/Nm3. The secondary PM removal segment is the efficient spin exchange coupling FGD that removes 60% of the remaining PM. The third approach to PM removal is the low-temperature economizer + rotary tube bundle PM demister, which has a PM removal efficiency of more than 70%. Compared to other PM capture options, the investment and operating costs for the advanced tube bundle PM removal technology were lower, it takes up less space, and it fits well into the general layout of new construction and retrofit projects. In total, the final target of an outlet concentration of PM less than 3 mg/Nm3 can be achieved—exceeding the requirement for a natural gas power plant in China.
The efficient spin exchange coupling wet FGD removes SO2 with an efficiency of 97.8–99.7% (see Figure 3). In the spin exchange coupling efficient-FGD technology, a device termed a “turbulator” has been added between the entering flue gas and first level of the FGD tower, which changes the flow state of the incoming gas from laminar to turbulent and reduces the gas film resistance, so as to increase the liquid-gas contact area, increase the gas-liquid mass transfer rate, and thus increase FGD and PM removal efficiency. This system also requires less power consumption than other FGD systems. In the compulsory 168-hour unit test run, the FGD efficiency reached 99.7%.
For removing NOx, low-NOx combustion and SCR using urea as a reducing agent results in a minimum denitrification efficiency of 95%.
Together, this low-emissions technology chain drastically reduces emissions of PM, SO2, NOx, heavy metals, etc. Not only are the emissions less than the national standards where the Anqing plant is sited,2 they are also lower than the emission limits for newly built coal-fired power units in the central regions. In addition, the new units at Anqing actually surpass the limits for gas-fired units as prescribed in the “Action Plan for Coal Energy Saving, Emission Reduction, Upgrading and Alteration (2014–2020)” from the National Development and Reform Commission, Ministry of Environmental Protection and National Energy Administration (see Table 2 for emissions results from the 168-hour test run).3
Anqing Phase II’s 2×1000-MW ultra-supercritical expansion project is Shenhua Shenwan Energy Company’s first project to integrate state-of-the-art HELE technologies. The resulting operations have met the expected efficiency and emissions goals. This power plant can serve as a model for China and the international community about what can be achieved regarding construction costs, economic indicators, and emissions reductions when the best HELE technologies are implemented. Through additional optimization of operations, key indicators are expected to further improve. This project is a significant demonstration of the clean and efficient utilization of coal, and the associated reduction in the environmental impact, which is a story worth telling.
- China Electricity Council. (2015). 2014 national coal-fired power 600-MW grade unit energy efficiency benchmarking and competition materials. (In Chinese)
- Administration of Quality Supervision, Inspection and Quarantine of the Ministry of Environmental Protection. (2011, 29 July). GB13223-2011. Emission Standard of Air Pollutants for Coal-fired Power Plants. China Environmental Science Press, 2–3. (In Chinese)
- National Energy Administration, Ministry of Environmental Protection, National Development and Reform Commission. (2015). Action plan for coal energy saving, emission reduction, upgrading and alteration (2014–2020) [EB/OL], news.bjx.com.cn/html/20140922/548573-2.shtml (In Chinese)
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