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　　1. Possible harm of water content in turbine oil of power plant

　　There are two possible forms of water in turbine oil: dissolved water and free water. The dissolved water is the water evenly distributed in the oil. Under the operating conditions of the power plant, the large concentration of water dissolved in the oil is about 150mg / L (the specific value is related to the oil composition, temperature, additives, etc.). Free water is the water in oil in the form of small water droplets. These small water droplets have small particle size due to impurities, and sometimes it is difficult to separate them from oil. The appearance of lubricating oil containing free water is turbid, while that only containing dissolved water is transparent. Because of the strong mixing of the turbine oil tank system in the power plant, only the water in excess of the solubility will exist in the form of free water. In other words, if the oil contains free water, the appearance is turbid, and the water content is above 150mg / L. The harm of water content in turbine oil mainly lies in the following aspects:

　　(1) Oil emulsification may occur, resulting in poor adhesion of the lubricating oil, insufficient adhesion of the oil to the friction surface, damage of the oil film, dry friction between the rotor journal and the bearing pad of the bearing, burning of the bearing pad, strong vibration of the unit, and even damage of the machine.

　　(2) The water content of turbine oil will accelerate the oxidation of turbine oil, increase the acid value and produce more oxidation precipitates, thus prolonging the anti emulsification time of turbine oil and deteriorating the anti emulsification performance of oil.

　　(3) The water content of turbine oil will rust the carbon steel pipes and components in the oil system, cause jamming and reduce the sensitivity of action. In serious cases, it will also cause the regulation and security devices to refuse to operate, which will lead to the occurrence of overspeed accident of the unit.

　　(4) The corrosion product produced by water in turbine oil is an important source of particles in the oil. The water content of turbine oil will make the particle size of oil easy to exceed the standard, the filter element of oil filter will be changed frequently, and the workload of operation and maintenance will be heavy. In order to reduce the harm of water content in turbine oil, the water content in lubricating oil is less than 100mg / L according to the quality standard of turbine oil in power plant operation issued by China.

　　2. To analyze the water content of turbine oil, first of all, efforts should be made from the source of water leakage, try to find out the water leakage point, analyze the causes, reduce and eliminate the water leakage. However, the water leakage of many units is a long-term reality, especially some old units, which is difficult to solve due to the limitations of many conditions. Under the condition that the water leakage is difficult to change, it is an effective way to use proper dehydration equipment to remove the water leaked into the turbine oil system. At present, there are three kinds of technologies suitable for dehydration of turbine oil system: coalescence separation, centrifugal separation and vacuum dehydration. The dewatering principle of coalescence and separation in coalescence and separation type oil filter is to use the difference of surface tension between oil and water to gather small water beads into large water beads and separate them. Since the concentration of water that can be dissolved in lubricating oil is about 150mg / L (the specific value is related to the oil composition, temperature, additives, etc.), the coalescence separation oil filter can only treat the water to about 180mg / L, which can not be reduced to below the national standard value of 100mg / L. The advantages of coalescing and separating oil filter are simple structure, no need of heating during dehydration, high free water content, fast dehydration speed, convenient operation and high reliability, so it is more widely used in the power industry than other oil filters.

　　The base oil of compressor oil can be divided into two kinds, one is mineral oil and the other is synthetic oil. The oil prepared by mineral oil has outstanding lubricity. It can form a thick oil film on the parts, which has strong stability. It can ensure that the oil film will not be damaged under high temperature and high speed, and avoid direct friction between parts. The compressor oil made of synthetic oil has low pour point and volatility. Although its cost is slightly higher than that of mineral oil, it has good economic benefit and little environmental pollution.

　　The oil first flows from the inside to the outside and passes through the coalescing filter element. The coalescing filter element is made of special glass fiber and other synthetic materials, which is specially prepared for turbine oil (turbine oil), with good hydrophilicity. Coalescing filter element has dual functions of filtering particle pollutants and coalescing water. The high-precision filter material in the inner layer first filters the particle pollutants of the oil filter in the oil; the demulsification coalescence layer outside gathers the tiny water drops in the oil to form water drops. The larger water droplets will settle to the water collecting tank by their own gravity, and the smaller water droplets will be carried by the oil to the separation filter element before settling. The separation filter element is made of specially treated stainless steel mesh, which has good hydrophobicity. When the oil flows through the separation filter element from the outside to the inside, small water drops are effectively intercepted outside the filter element, only allowing the oil to pass through, not allowing the water to pass through, so as to further separate the water. The oil first enters the coalescer separator after the particles in the oil are removed from the primary oil filter. In coalescing separator, the oil can be removed from water through four processes of filtration, coalescence, sedimentation and separation, and then purified oil can be output. The water settled in the sump is discharged through the drain valve on the sump. At the same time, according to the oil quality, the oil can be directly filtered through the filter to remove the particulate pollutants in the oil, and then the purified oil can be output.