The high water content in turbine oil will accelerate the deterioration of the oil, produce sedimentation, sludge, etc., leading to oil film damage and metal component corrosion, thereby increasing the friction between various friction pairs, causing bearing overheating, causing failure of the speed control system or equipment failure. The demulsification performance index is mainly used to evaluate the water separation performance of turbine oil. The shorter the demulsification time of turbine oil, the faster the separation of oil and water in the oil tank after water enters the lubricating oil system; On the contrary, it indicates that the oil and water cannot be effectively separated in the fuel tank. When steam accidentally enters the lubricating oil system, turbine oil with good demulsification performance can separate most of the water from the oil during the static process of the oil tank, reducing the burden on the filtration and water removal device, and restoring the water content in the turbine oil to normal in a short period of time.
At present, domestic power plants implement GB/T 7596-2008 and GB/T 14541-2005 standards for quality monitoring of turbine oil during operation, requiring that the demulsification time of turbine oil should not exceed 30 minutes. However, due to the fact that the residence time of turbine oil in the oil tank generally does not exceed 9 minutes, even if the demulsification time of the oil is not more than 30 minutes, it is still not possible to effectively ensure that the water content in the turbine oil meets the standard under the condition of steam leakage in the unit. For newly put into use or overhauled units, the demulsification time of turbine oil is also more likely to exceed the standard due to impurities introduced into the lubricating oil system during equipment manufacturing or incomplete cleaning of cleaning agents used during major repairs.
Does exceeding the demulsification time of turbine oil mean that the oil quality has deteriorated and needs to be replaced or other remedial measures need to be taken? Based on an example of monitoring the quality of turbine oil during operation in a certain power plant, this article analyzes:
A power plant in Jiangsu has two 600MW units, which were put into operation at the end of 2005 and the beginning of 2006. The steam pressure and temperature parameters of the units are 24.2 MPa/566 ℃. Since its commissioning, the Great Wall L-TSA32 turbine oil that meets the superior grade specifications of GB 11120-1989 L-TSA turbine oil standard has been used and has never been completely replaced. As the operating time of the unit increases, the demulsification time of the turbine oil gradually increases. The demulsification time of steam turbine oil that has been in operation for six months to one year has approached or exceeded 30 minutes, but at this time, the micro water content of steam turbine oil is less than 50mg/kg, which still has a significant margin compared to the limit value required by GB/T 7596-2008 standard (≤ 100mg/L).
After operating these two units for one year, the demulsification time of the turbine oil during operation reached about 50 minutes. At this time, by partially replacing with new oil or adding demulsifier, the demulsification time of the turbine oil can be significantly shortened, and the demulsification time of the turbine oil can be maintained within 60 minutes for a long time, resulting in stable operation of the unit.
Therefore, even if the demulsification time of the turbine oil during operation has exceeded 30 minutes, as long as the water content in the turbine oil is low, the oil will not emulsify. If the other performance indicators of the turbine oil are within the normal range at this time, it indicates that the turbine oil has not deteriorated. The anti emulsification performance of the turbine oil can be improved and its service life can be extended by adding demulsifiers or adding new oil.
For the above working conditions, it is recommended to use a Meifel centrifugal oil filter in combination to timely remove moisture and impurities in the turbine oil, solve the problem of oil emulsification from the source, significantly extend the service life of the turbine oil (2-3 times), reduce equipment failure rate, reduce unit shutdown time, and thus increase overall economic benefits.
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