Unit 2 adopts D300P model of Dongfang Steam Turbine Company, which was designed and developed in the late 1990s. Although the advanced technology at that time was applied, it was affected by factors such as manufacturing and processing capacity, with low efficiency and high heat consumption. In addition, with the operation of the unit, some defects of the original design are gradually exposed, which further affects the efficiency, and there are many problems in economy, safety and reliability.
2. 1. Turbine side
Economically, the heat consumption rate of steam turbine of Unit 2 is high. On July 20 13, Anyang Power Plant entrusted Henan Electric Power Research Institute to conduct performance test on No.2 steam turbine. The results show that the corrected heat consumption rate is 8 14 1.39kJ/kWh under the condition of 300MW, which is 249.89kJ/kWh higher than the design value of 7892kJ/kWh, which affects the coal consumption of power supply by 9.76g/kWh. At the same time, there are problems such as poor drainage of No.7 low-pressure heater.
In terms of safety and reliability, the steam turbine of Unit 2 has the problems of large vibration of 1 tile at startup and high temperature of 1 tile and No.2 tile at operation.
2.2 boiler side
There is air leakage in the secondary seal in the top ladle, and there is more dust accumulation; The amount of superheated desuperheating water is large. Under the load of 300MW, the superheated desuperheating water quantity is 42t/h, and the reheated desuperheating water quantity is19t/h. ..
Third, the feasibility of transformation.
The purpose of energy-saving transformation is to further save energy and reduce consumption. In addition to reforming the traditional steam turbine flow passage, the initial steam parameters are improved, that is, the boiler heating surface needs to be reformed to increase the heating area, and the heating surface material needs to be upgraded to improve the main reheat parameters. The transformation of steam turbine flow passage has been carried out in China for many years, and the main domestic steam turbine manufacturers have made at least dozens or even hundreds of achievements, and the technology is very mature, so the determination of the transformation scheme is mainly concentrated on the heating surface of the boiler.
Because the parameter upgrade has not been implemented in China before, the risk of upgrading is great. For this reason, before the renovation of Unit 2, Datang Group organized many manufacturers and industry experts to fully demonstrate the way and range of heating and boosting of the project, and made a lot of calculations and in-depth analysis and research. On this basis, three schemes are put forward: one is to raise the main steam temperature to 545℃; The second is to increase the main steam temperature to 570℃; Thirdly, increase the main steam temperature and reheat steam temperature to 550℃/570℃ and the pressure to 18.2MPa, as follows:
According to the hoisting parameter requirements of the scheme and the heat balance diagram of the steam turbine, the boiler manufacturers have calculated the boiler heat of three reconstruction schemes respectively, and the calculation results are as follows:
Thermal calculation result of boiler after parameter upgrading (design coal type)
Judging from the calculation results:
In the first scheme, the boiler does not need to be reconstructed with large heating surface, which can meet the requirements of the reconstruction scheme.
In the second scheme, the main steam temperature on the boiler side is only 566℃, which can not meet the requirements of transformation, and the corresponding heating surface must be transformed. The preliminary accounting is to lengthen the length of high-tube coil, with an area increase of about 15%, the length of large-screen superheater increased by 500mm, with an area increase of about 5%, and at the same time, a tube coil was added at the low-tube coil, with an area increase of 20%. Considering that the reheat steam temperature margin of the original boiler is too small, the reheater system can reduce the longitudinal pitch of high reheat, increase the number of tubes and increase the area by necessary modification of the heating surfaces of high reheat, low reheat and medium reheat.
Due to the limitation of the height and width of the boiler, there is no heating surface in the boiler. After calculation, the main steam temperature of scheme 3 can only reach 553℃, and the reheat steam temperature is 568℃, which can not meet the requirements of reconstruction, and the heating surface needs to be reconstructed. Specifically, the superheater and reheater systems are carried out in the way of Scheme 2.
From the perspective of project investment:
Compared with the first scheme, the boiler side investment is less, and only the medium temperature reheater needs to be reformed. The reconstruction cost is about 3.5 million yuan, but the corresponding steam turbine heat consumption is 7875kJ/kWh, which is lower than other schemes and will not be considered.
The transformation scope of Scheme II is mainly high-temperature superheater, low-temperature superheater and high-temperature reheater (after contacting the boiler room to collect data and calculate, Scheme II thinks that the inlet temperature of reheater will be reduced by about 10℃ after the through-flow transformation, so the transformation scope will be expanded, and the areas of low-temperature reheater and large-screen superheater need to be increased). Although the transformation scope of the scheme is large, the corresponding design heat consumption is 790 kJ/kWh. The benefits are also obvious.
In the third scheme, in addition to the transformation scope mentioned in the second scheme, due to the increase of steam pressure, it involves replacing multiple headers and supporting valves (safety valve, PVE valve, etc.). ) should also be replaced, and the corresponding design heat consumption is 7755kJ/kWh. Compared with the second scheme, the investment income is lower, and it is no longer possible to add more heating surfaces due to the limitation of boiler height and width. Therefore, the third scheme cannot be implemented in the actual transformation.
Through the comprehensive comparison of the feasibility, investment and benefits of the above schemes, it is determined to carry out the transformation according to the second scheme, and adopt the scheme of increasing the main reheat temperature and reheat temperature to 570/570℃ respectively and keeping the pressure unchanged, so as to achieve the purpose of increasing the main reheat steam temperature of the boiler. Without changing the external structure of the boiler body, the working capacity of the steam turbine is improved and the heat consumption of the steam turbine is reduced by necessary transformation of the heating surfaces such as high reheat, high reheat and low superheat.