Oil pump selection
Determination of the type of oil pump: Commonly used oil pumps can be divided into gear pump, vane pump and plunger pump according to the structure. The gear pump is used in the low pressure system and is not sensitive to oil pollution; the vane pump has uniform output flow, small pulsation and low noise, but the oil absorption characteristics are not so good and sensitive to oil pollution; the plunger pump is easy to get high precision cooperation and leakage. Small, high volumetric efficiency, together with vane pumps are often used in high pressure systems and are also sensitive to oil contamination. Therefore, the vacuum oil purifier uses a gear pump as the inlet and outlet pumps.
Determination of oil pump parameters
Determination of working pressure of oil pump: In order to improve the reliability of the system and prolong the service life of the pump, the normal working pressure of the oil pump in the vacuum cleaner is 70~80% of the rated pressure of the pump. Since the system operates under negative pressure conditions and there are no actuators such as hydraulic cylinders and hydraulic motors, the working pressure of the oil pump should not exceed 0.5 MPa.
The working flow of the oil pump is determined: the flow rate of the oil pump must be greater than the maximum flow rate when the system is working.
Determination of the power of the pump motor: Generally, the operating parameters of the pump should be in the high-efficiency area of ​​the pump's efficiency curve, often in accordance with 0.8. Considering that the motor generally allows a short time overload of 25% and then other conditions, the motor power can be determined.
Heater selection
The oil temperature for normal operation is below 80 °C. Combined with the relationship between saturated vapor pressure and temperature, the vacuum is determined to be 0.06 MPa. At this time, the evaporation temperature of water is 70 ° C, and the oil can maintain its performance. Therefore, the oil needs to be heated to 60~70 °C. For high altitude, it is necessary to increase the heating temperature due to the lower vacuum.
The heating power determines the rate of oil purification and regeneration. If the power is too small, the heating time will increase, which will reduce the purification efficiency. If the power is too large, the cost will increase and the installation will be difficult. Since the oil is a poor conductor of heat, the power capacity of a single heater should not be too large to avoid excessive deterioration of the oil around it, so it is important to select a heater of appropriate power.
Vacuum equipment design and calibration
The design of the vacuum tank: the water evaporated in the vacuum tank exists in the form of tiny bubbles. When the temperature and vacuum conditions are satisfied, the evaporation process is carried out on the surface and inside of the liquid at the same time, because the oil in the tank is in motion, The gas that has escaped from the liquid surface is carried away by the vacuum pump, and the air bubbles that are not escaping are caught in the oil and brought back to the tank by the oil discharge pump. At normal pressure, part of the water vapor is recondensed into water and mixed into the oil system. Therefore, the nominal flow rate of the oil purifier is the main parameter of the whole design. The structure can be either vertical or horizontal. It is proved that the volume of the vacuum tank should be 3-5 times of the nominal flow of the oil purifier.
The strength calculation of the vacuum tank includes the calculation of the plate pressure of the cylinder, the wall thickness of the cylinder and the head, and the check.
Selection of vacuum pump: The choice of vacuum pump is mainly based on the total amount of gas that the pump needs to pump. Because the pumping rate of the vacuum pump determines the vacuum degree of the vacuum tank, the pumping rate should be considered to be greater than or equal to the displacement of the drain pump. 1-2 times; and can ensure that the gas pressure of the tank and the pipe is drawn to 0.06 MPa or lower within 1-2 min.
Selection of condenser: After the condenser is installed in the vacuum tank, the common structure is air-cooled, the structure is simple and the price is low, but the cooling effect is worse than the water-cooled type. The condenser is to ensure that the water vapor and light oil pumped out by the vacuum pump can be condensed into a liquid. The main parameter for selecting the condenser is the heat dissipation area.
Filter selection
Filter classification: The filtration accuracy of the filter is expressed by the particle size of the impurities. Generally, it can be divided into four types: coarse filter, ordinary filter, fine filter and ultra-precision filter, respectively: coarse filter larger than 100μm. 10 to 100 μm is a common filter, 5 to 10 μm is a fine filter, and 1 to 5 μm is an ultra-fine filter. The choice of filtration accuracy of oil filter is mainly affected by two factors.
1. The need for oil. For example, insulating oils must pass high-precision filtration to achieve high insulation values, while large-modulus gears require much more impurities.
2. The viscosity of the oil. High viscosity oils cannot pass through the fine mesh and require reduced precision.
When selecting a filter, the greater the oil-passing capacity, the better. The main considerations are as follows:
Has sufficient oil-passing capacity and low pressure loss;
The filtration accuracy meets the requirements;
The filter element has sufficient strength;
The filter element has good corrosion resistance and can work for a long time under the specified temperature;
Filter replacement, easy to clean and maintain.
If a one-sided emphasis on the cleanliness of the oil and the use of a precision filter, it will increase the operating cost of the oil filter. because:
(1) The filter element is often clogged, requiring frequent cleaning or even replacement of the filter element.
(2) Increase the axial pressure so that the oil can pass through the filter faster, but it will often crush the filter.
(3) Add a preheating tank to increase the temperature and reduce the viscosity.
In general, the filtration accuracy of the fine filter stage is selected as:
(1) Insulating oil, 1 to 5 μm is selected.
(2) Below 46# lubricating oil and turbine oil, choose 10~20μm.
(3) The internal combustion engine oil and gear oil are selected from 20 to 50 μm.
Reasonable process
The general control requirements for turbine oil are particle size and water content, while anti-fuel requires an additional acid value indicator. The influencing factors are:
The most efficient way to deal with solid particle impurities is the suitable filter element. The ability of the filter element to intercept dirt and dirt is critical, which directly affects the performance of the filter material and the design and production level of the filter element. The particle size of common oil purifiers is controlled at NAS8-9, and the filter can be considered 5-10μm. The two-stage oil purifier can be upgraded to the NAS6 level, and the filter element is considered to be 1-3μm.
The key to moisture treatment is the rate of dewatering through the purification unit each time. Generally, the oil with a water content of <50ppm to be purified is circulated through a single-stage oil purifier for more than three times. The water content of the performance index is ≤7ppm, and the water content of the two-stage oil purifier is ≤3ppm.
The oil purifier system used for the treatment of insulating oil requires no more than 50 ppm of water content, otherwise the treatment effect is not good.
When there is an abnormality in the operation of the system, if the water content of the oil system is too high or there are too many impurities, the auxiliary equipment such as the plate and frame pressure type oil filter should be used for pretreatment, otherwise the treatment effect is not good.
Reasonable combination of functions
Conventional oil purifiers mainly use strong magnetic separation (removing metal particles in oil), vacuum flash separation (demulsification, dehydration and de-light hydrocarbons), pressure filtration separation (removal of mechanical impurities in oil) In addition, according to the separation engineering, a coalescing separation method, an adsorption separation method, or the like can be added.
For the oil purification device with breakdown voltage or acid value, the polymer adsorption regeneration device can be added to remove the acidic substance after the vacuum system, and the breakdown voltage can reach 75kv after treatment, and the oil acid value is ≤0.03mgKOH/g.
For the cleanliness and cleanliness requirements of NAS16381, the treatment of solid impurities is not a high-precision filter element, but a filter with different precision filters should be used for step-by-step filtration.
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