Can gas turbine combined cycle power generation reduce environmental pollution?

Current situation and demand of 1 gas turbine combined cycle power generation

Since 1980s, with the establishment of the new concept of total energy system of gas turbine and its combined cycle, the progress of material science and manufacturing technology, especially the change of energy structure and the increasingly strict requirements of environmental protection, the status of gas turbine and its combined cycle unit in the world power system has changed significantly. It can be used not only as emergency, standby power supply and peak load, but also as basic load and intermediate load. Since 2 1 century, the world gas turbines have entered a new development period, and the introduction, development and application of gas turbines in China have also entered a new development stage. The technical progress of gas turbine mainly shows in the increase of single unit capacity, the improvement of thermal efficiency and the reduction of pollutant emission. At present, more than 1/3 of the world's annual installed capacity is gas-steam combined cycle units, the United States is close to 1/2, and Japan's thermal power accounts for 43%. According to incomplete statistics, the total capacity of the existing gas-steam combined cycle generator set fueled by oil and natural gas in the world has exceeded 400 GW. At present, the single power of gas turbine has been

When it exceeds 300MW, the thermal efficiency of simple cycle exceeds 39%; The combined cycle power has exceeded 780 MW, and the combined cycle thermal efficiency has exceeded 58. 5%. Dry low NOx combustion technology makes the NOx emission of natural gas and distillate oil lower than 25mg/kg and 42mg/kg respectively, which improves the position and function of gas turbine in energy and electricity.

From the current technical level of thermal power generation in the world, in addition to supercritical power generation technology (USC), circulating fluidized bed (CFB) and pressurized fluidized bed combined cycle (PFBC) with desulfurization and dust removal devices, burning gas-steam combined cycles such as natural gas, fuel oil and coal gasification is an important measure to improve the efficiency of thermal power plants and reduce pollutant emissions. According to relevant research and forecast, the total demand for gas turbines in China will reach about 34 000 MW in the next 10 year. China has begun to use the West-East Gas Pipeline, oil and natural gas from the East China Sea and the South China Sea, import liquefied natural gas (LNG) and develop clean energy such as coal gasification. A batch of 300 MW gas-steam combined cycle power plants have been built or will be built and put into operation soon. It can be said that with the improvement of localization rate and the reduction of construction cost, the large gas-steam combined cycle generator set burning natural gas and coal gas will surely become an important part of China power industry.

2 The concept of total energy system of gas-steam combined cycle

Gas-steam combined cycle is a cycle that combines two independent power cycles with different working fluids through energy exchange, taking into account the advantages of high-temperature heating of gas turbine Brayton cycle and low-temperature heat loss of steam turbine Rankine cycle, forming a brand-new design concept of total energy system, integrating the advantages of advanced technology of gas turbine, waste heat boiler and steam turbine power generation, and improving the efficiency of combined cycle. For example, the subcritical parameters and the power generation efficiency of reheat gas-steam combined cycle of the current three-pressure boiler are all above 60%.

The high-temperature heat source temperature (initial temperature of gas turbine) in the conventional gas-steam combined cycle is as high as11000 ~1300℃, which is much higher than the main steam temperature of 540~566℃ in the general steam cycle, while the low-temperature cold source temperature (condenser temperature) in the gas-steam combined cycle is 29 ~ 300℃. Therefore, the thermal efficiency of combined cycle is much higher than that of any single cycle. In the combined cycle, it is more obvious to improve the efficiency of gas turbine ηgt than to improve the efficiency of waste heat boiler ηHRSG and steam turbine ηSt to the same extent. Therefore, when designing the combined cycle, we should first choose the gas turbine whose power and efficiency can meet the requirements as the design starting point, and then consider whether the configuration of waste heat boiler and steam turbine system and form is reasonable from the perspective of efficiency and investment of the whole combined cycle. The research shows that the maximum efficiency of gas turbine in combined cycle does not mean to obtain the best combined cycle efficiency. When the initial temperature of gas is constant, the high pressure is lower than the exhaust temperature of gas turbine. Although the efficiency of gas turbine itself is higher than that of low pressure ratio gas turbine, the energy utilization rate, steam parameters and steam cycle efficiency of waste heat boiler are low. However, the low pressure is higher than the exhaust temperature of the gas turbine. Although the efficiency of gas turbine itself is lower than that of gas turbine with high pressure ratio, steam cycle can achieve high efficiency by using mature technologies of high temperature, high pressure, subcritical and reheat. When evaluating whether a gas turbine is suitable for a combined cycle, we should not only consider its efficiency, but also consider its efficiency of matching the steam cycle and the efficiency of the overall combined cycle. The simple cycle gas turbine has the best pressure ratio and exhaust temperature at a certain initial temperature. The combined cycle also has an optimal pressure ratio and exhaust temperature, and the efficiency is the highest at a certain initial gas temperature. This optimum pressure ratio is much lower than that of the simple cycle, which is very close to the pressure ratio when the specific work of the simple cycle gas turbine reaches the maximum. This optimal exhaust temperature is better than that of a simple cycle.

The exhaust temperature is much higher. Therefore, in order to obtain the maximum efficiency of the combined cycle, it is necessary to choose not only an efficient gas turbine, but also the highest possible initial gas temperature and the best pressure ratio and exhaust temperature of the combined cycle. That is to say, the maximum efficiency of combined cycle can only be obtained by taking into account the efficiency of gas cycle and steam cycle.

3 Development trend of gas-steam combined cycle

Gas turbine and its combined cycle is a multi-disciplinary and high-density high-tech, and the traditional method to improve performance is continuous improvement.

The initial temperature of the turbine, the compressor pressure ratio is increased accordingly, and the related components are improved. In the early 1950s, the initial temperature (T3) of the steam turbine was only 600℃~700℃, and it increased by about 65438 00℃ on average every year due to the improvement of the performance of heat-resistant materials. After 1960s, with the help of air cooling technology, T3 increased by 20℃ annually on average. Since 1970s, advanced aviation technology and traditional new turbine technology have been fully absorbed, and their performance has been continuously improved along the traditional way. Now a batch of new high turbine initial temperature technical products "F, FA, FB, H" have been developed, which represent the highest level of commercial industrial gas turbines, T3= 1 430℃, which may be the turbine initial temperature limit that traditional cooling technologies and materials can reach. The main feature of the new generation of products being developed is the use of steam cooling technology, and the materials of high-temperature components are still mainly from super alloys. The shell of gas turbine is made of CrMO steel, and the rotor shaft and runner are made of Inconel706, which adopts directional crystallization and single.

Crystal materials, Co-Cr-Al-Y spraying and other advanced technologies, some static parts are made of ceramic materials, and the initial temperature is raised to T3= 1 500℃~ 1 600℃. Adopt intelligent microcomputer control system to pay more attention to environmental protection. The concept of future gas turbine will be based on the latest aerospace technology and new materials. The burner will work at or near the theoretical combustion air volume, and T3 will reach 1 600℃~ 1 800℃. At present, the blade superalloy with melting point of 65438 0200℃ and density of 8 g/cm3 will be eliminated, and the new advanced material should be low density (

4 Performance comparison of two cycles

In the field of thermal power, gas-steam combined cycle generator set has greater comparative advantages than conventional coal-fired turbine generator set.

The power supply efficiency of (1) gas turbine combined cycle is much higher than that of conventional coal-fired steam turbine cycle. The efficiency of the existing combined cycle has exceeded 58~60%. Its high thermal efficiency not only far exceeds the conventional coal-fired steam turbine power plant, but also exceeds the expected value (45. 2% ~47.7%, not deducting desulfurization value) ultra-supercritical parameters of coal-fired steam turbine unit.

(2) The construction cost is lower than that of coal-fired steam turbines and nuclear power units. For a 2 000MW power plant, the unit investment of turbine generator set, gas turbine generator set and gas-steam combined cycle unit is about 6 000, 2 122 and 6 530 yuan /kW respectively.

(3) The factory can be built by stages, and the capital utilization is the most effective. The construction period is short, only 5~ 10 months.

(4) Use less land and water.

(5) The single machine has large capacity, quick start and stop, good operation flexibility and is suitable for two-shift operation. Increasing the proportion of gas turbines in the total installed capacity will improve the operation of the power grid, provide more flexible standby power supply for the power grid and increase the flexibility of peak shaving.

(6) The operation reliability is high, the availability rate is as high as 85% ~95%, and it is easy to "black start" quickly, which is helpful to improve the safety of power grid operation.

(7) When natural gas or liquid fuel is used, general pollutants are rarely discharged. When burning natural gas, it can also greatly reduce carbon dioxide emissions. If the amount of CO2 emitted by fuel is 0, L compared with the unit energy released by fuel combustion, then the CO2 emitted by coal and natural gas combustion is about 1. Twenty-two to zero. 67.

Discussion on development countermeasures of gas-steam combined cycle

Although China's gas turbine power generation began in the late 1950s, its long-term development was slow due to the fuel policy. At present, the design and manufacturing level of gas turbine power generation devices in China is far from the advanced countries in the world, and the installed capacity and operation management level are not commensurate with the development of China's power grid. In order to promote the rapid and healthy development of gas turbine power generation in China, some immature suggestions are put forward here to attract jade.

(1) Scientific orientation, overall planning and perfect policies. In combination with the national 11th Five-Year Development Plan, scientifically position the development of gas turbines and their combined cycle power generation equipment, formulate the medium and long-term strategic development plan and short-term arrangement of China gas turbines and their combined cycle power generation equipment, formulate and improve the gas turbine industry development policy and supporting policies and regulations such as fuel, electric energy and heat energy prices, and increase capital and technical investment. According to the law of market economy, on the basis of introducing a batch of advanced complete sets of 300MW gas-steam combined cycle demonstration projects, taking into account the introduction of large, medium and small advanced practical technologies, the technical level of gas turbines and their combined cycle power generation equipment in China will be rapidly improved through Industry-University-Research combination, digestion and absorption and innovation.

(2) Strictly control the technical quality of imported equipment. We should combine the mechanical and electrical industries, replace the market with technology first, improve the reliability, comprehensive technical and economic performance and optimization level of imported units and power stations, improve the localization rate of spare parts and reduce maintenance costs. Efforts should be made to change the current situation that the domestic electromechanical industry is fragmented, the imported technology is scattered, the introduction is repeated, the matching is poor, and even the equipment and technology with backward performance are introduced.

(3) Improve the national manufacturing technology level. On the basis of existing manufacturing technology, aiming at the most advanced foreign level, we will introduce a number of advanced and applicable models, key design technologies, software, key manufacturing processes, control and protection systems and testing technologies in a planned way. On the basis of digestion and absorption, we will strive to innovate and constantly improve the localization rate, design, manufacturing and supporting capabilities of key components. Develop a complete set of domestic units with reliable operation, high cost performance and independent intellectual property rights as soon as possible. It is suggested that R&D centers and manufacturing bases of gas turbines and their combined cycle units should be established in the central and western regions (such as Chengdu and Wuhan), and the products should be introduced to the domestic and foreign markets as soon as possible. Tmall us wechat reminds: remember to protect yourself when traveling in foggy days.

(4) Strengthen the introduction, production and scientific research of key high-temperature metal materials. At present, the highest initial temperature of gas turbine reaches 1 500℃~ 1 600℃, and the most advanced new materials for aerospace industry are directly adopted abroad. Generally speaking, foreign manufacturers will not transfer the most advanced manufacturing technology. In China, it is necessary to combine military and civilian work with Industry-University-Research to organize joint scientific and technological research, realize the localization of key materials as soon as possible, and reduce costs.

(5) Strengthen the research of rotor structural dynamics and vibration analysis, fault diagnosis and treatment of gas-steam combined cycle units, especially the rapid diagnosis and treatment of compressor surge and bearing vibration of large-scale units with single shaft (that is, compressor+gas turbine+steam turbine+generator connected in series to form a single shaft).

(6) China is rich in coal resources. In order to replace the traditional coal-fired turbine generator set, the technology of coal-fired gas-steam combined cycle has matured. When IGCC combined cycle is composed of 9H gas turbine, the single power can be increased to 550MW, and the power supply efficiency can be increased to 50% ~62%. The country should speed up the process of IGCC integrated gasification gas-steam combined cycle power generation and clean coal-fired generating units to meet the needs of the sustainable development of China power industry.