The development of clean coal combustion technology is widely carried out in the world today, pursuing high efficiency and low emission of coal-fired units. New thermal power generation technologies such as supercritical and ultra-supercritical units, large-scale CFB (Circulating Fluidized Bed Boiler), PFBC (Pressurized Fluidized Bed Gas-Steam Combined Cycle), IGCC (Integral Gasification Gas-Steam Combined Cycle), and GTCC (Gas-Steam Combined Cycle) are widely used in the developed countries of the world for their high efficiency and superior environmental performance. high efficiency and superior environmental performance, have been widely used in developed countries around the world. China has also carried out a lot of work on the research, development and application of clean coal combustion technology, which has become a popular technology for thermal power generation units in China. The application of all these new technologies requires high-temperature alloys with excellent performance to provide assurance.
Supercritical and ultra-supercritical power station boilers with high-temperature alloys
China is the world’s largest coal-burning country, however, the current thermal power unit average stand-alone capacity of less than 100MW, a considerable portion of ultra-high-pressure, high-pressure steam parameters of the unit, the sub-critical 300MW units accounted for less than 50% of the total installed capacity of thermal power. The average coal consumption of power supply reaches 399g/(kW-h), which is 70~80g/(kW-h) or more than 25% higher than the advanced level in foreign countries, with too much wastage of resources and serious emission of exhaust gas. The development of supercritical and ultra-supercritical units is one of the effective and economic ways to improve coal utilization and reduce environmental pollution. With the continuous increase of steam temperature, the efficiency of the unit is increasing, and the coal consumption of power supply is decreasing. 2005, the parameters of foreign ultra-supercritical units have reached 33.5MPa,610℃/630℃/630℃. It is expected that by 2015 the parameters will reach 40MPa,700℃/720℃/720℃. With the further increase of steam parameters, the requirements for high-temperature materials are getting higher and higher. Superheater and reheater is the most severe working environment in the boiler components, bear the greatest pressure, the highest temperature, therefore, the material is required to have good creep resistance, but also to meet the tube to the steam side of the oxidation resistance and the flue gas side of the corrosion resistance requirements.
Sub-critical, supercritical and ultra-supercritical units of the net efficiency and power supply coal consumption steam parameters unit net efficiency / % power supply coal consumption / g (kw-h) 117MPa.538/538 ℃ 37 ~ 38330 ~ 34024MPa,538/538 ℃ 40 ~ 41310 ~ 32030MPa.566/566/566 ℃ 44-45290 ~ 300 At present, the key high-temperature alloy materials required for supercritical and ultra-supercritical power station boilers in China mainly rely on imports. The developed GH2984 alloy can be recommended for superheater and reheater tube alloy in ultra-supercritical unit boilers. Domestic and foreign high-parameter ultra-supercritical superheater tubing with high-temperature alloy chemical composition is shown in Table 73-18. These alloys have good creep properties and oxidation corrosion resistance, suitable for the manufacture of superheater and reheater tubing.
At the end of the 1960s, the Institute of Metals of the Chinese Academy of Sciences began to develop a suitable for our country’s high-parameter ship main boiler superheater tube for long-term use of the new iron-based high-temperature alloy GH2984. To the 1970s developed and produced for the new main boiler superheater tubes, loaded with the ship and by the ten years of actual use of the sea assessment. Comprehensive inspection shows that the GH2984 tube intact, can continue to use. GH2984 alloy is the main superheater tube material, its main properties and the United States Special Metals Corporation in 2003 officially announced the nickel-based alloy Inconel 740 alloy at the same level, while the price is much cheaper, which for our country’s ultra-supercritical unit has long been made a good superheater and reheater material technology reserves. GH2984 alloy’s main features are as follows: (1) high Fe, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature, high temperature.
(1) high Fe no Co chemical composition. Compared with similar alloys, GH2984 alloy does not contain cobalt, Inconel 740, Inconel 617 and Nimonic 263 and other alloys contain 12% ~ 21% Co. And GH2984 alloy Fe up to 32% ~ 34%, the corresponding nickel content is reduced, the other alloys Fe are impurity elements, see Table 73-18. Considerable economic benefits.
(2) excellent mechanical properties of strength. Alloy room temperature to high temperature tensile strength and 650 ~ 750 ℃ lasting strength is very good. Room temperature and 700 ℃ tensile strength is significantly higher than the commonly used high-performance pipe alloys Inconel 625 and Nimonic 263. enduring strength is higher than Nimonic 263, similar to Inconel 625. At 700 ℃, 30 000h and 100000h lasting strength, and Inconel 740 alloy at the same level, while 650 ℃ and 750 ℃ lasting strength is basically the same.
(3) good chemical properties of corrosion resistance. Due to the alloy’s Cr content of 18% ~ 20%, can form a dense and solid Cr2O3-based oxide film, so good oxidation resistance and thermal corrosion resistance. In addition, the alloy has excellent resistance to intergranular corrosion, in a variety of different heat treatment states or welding do not occur after grain boundary corrosion.
(4) more stable microstructure. Alloy by 700 ℃ x (1000 ~ 18000) h after long-term aging of the organization and mechanical properties of the research results show that the alloy organization and properties are more stable to meet the needs of large ships and ultra-supercritical power plant boilers for long-term use.
(5) easy to form process performance. The alloy has good cold and hot pressure processing performance, especially excellent pipe forming performance.
High Temperature Alloys for Coal Gasification and Liquefaction
Integral Gasification Gas-Steam Combined Cycle (IGCC) technology, is currently one of the world’s most advanced and efficient coal-fired power generation methods, and is recognized as an advanced technology for clean coal combustion. Nine IGCC units have been put into operation in the world since the first IGCC power plant was put into operation in 1972. The main advantages of the integrated gasification combined cycle are: 1.
1. Wide adaptability of fuel can utilize low-grade coal with high sulfur content, high ash content and low calorific value. The adaptability of fuel mainly depends on the form of gasifier used and the way of feeding. For the dry powder charging system, it can be suitable for all kinds of coal from anthracite to lignite; for the wet charging gasification process, it is suitable for the coal with lower ash and inherent moisture; for the coal with high ash melting point, co-solvents (e.g. limestone) should be added;
2. high thermal efficiency if at the same time using high-temperature purification technology (heat loss reduction), the thermal efficiency of IGCC can be expected to reach 52%; 3. excellent environmental performance compared with the same capacity of the coal-fired power plant, SO2 emissions reduced by more than 90%, CO2 emissions are also reduced accordingly, basically no emission of dust; 4. saving water resources water consumption is only about half of the conventional thermal power plants. American Metal Performance Society (AMPS), Technology Research Institute (TRI) and other units of many iron, nickel, cobalt-based high-temperature alloys in the gasification atmosphere for the evaluation of corrosion resistance. The test atmosphere was 24% H2, 18% CO, 12% CO2, 39% H2O, 5% CH4, 0.5-1% H2S, gas pressure 68 atm, temperature 900-982°C, and a maximum time of 700 to 10,000 h. The results showed that almost all alloys started with the formation of a protective oxide film on the surface, and continued the test with the destruction of the oxide film and formation of on the surface and the inner surface of the Sulfides. The total metal corrosion consists of two parts of data, i.e., the sum of the thickness of the oxide layer and the depth of sulfide penetration. Based on extrapolated data from 10,000h measured and long time tests, many alloys have a total corrosion depth after 10,000h of less than 5.08×10 m. Long term operation in gas at 982°C,0.5% H2S or 900°C,1% H2S or similar conditions is promising. Considering the above corrosion rate (<500μm/a), high temperature alloys used in coal gasification or similar atmospheres are: cobalt-based alloys: Haynes 188, Stellite 6B, X-40, Co-Cr-W-1 nickel-based alloys: INCONLE 617, INCONLE 657, INCONLE 738, INCONLE 739, Nimonic 80A Iron-based alloys: NIMONIC 155,RA330,RA333,INCOLOY 800,T63WC,310 Stainless steel, Fe-18Cr-SAI-Mo-Hf,Fe-18Cr-5Al-Y,MA956E (Fe-19Cr-5A1-0.45Y2O3) The results of the U.S. long-time test concluded that: Nickel-based, cobalt-based alloys show better corrosion resistance when exposed for a long time. In high temperature 982 ℃, high sulfur 1% H2S gas, high chromium and iron free nickel, cobalt based alloys are better than alloys with high iron content.Dapkunas et al. believe that, 870 ~ 982 ℃ gasification environment, the alloys have to have a better corrosion resistance, the chromium content of at least 20%, long time use is preferred to 25%.310 stainless steel and Ni-30Cr alloys with titanium, aluminum, molybdenum, manganese, silicon, etc., and the results indicate that: add titanium, aluminum, molybdenum, manganese 310 stainless steel and Ni-30Cr alloy with titanium, aluminum, molybdenum, manganese, silicon and so on, the results pointed out that: add 2% ~ 3% Ti alloy to improve the film adhesion. Add the appropriate amount of aluminum has a similar effect, but the oxide film is easy to peel off in the cooling process; manganese is harmful, manganese is easy to penetrate the chromium oxide film quickly diffuse to the metal surface to form MnS layer, thus accelerating corrosion.
Post time: Aug-05-2023
