A two-level degassing unit is the basic element of systems designed for vacuum filtration of oils. In fact, this is a sealed metal container divided into two parts (levels). Special nozzles are arranged inside of the container and serve to provide a surface extention for the vacuum filtration of oil. This function can be performed by cylindrical Raschig rings. The main benefit of a Raschig rig is large surface ratio to the volume of flow and low oil flow resistance.
An oil pump feeds the oil that is being processed into the vacuum filtration system through a special mesh filter (coarse mesh filter). After this, oil is heated to between 50-60ºC. Then the oil is fed to the first level of the degassing sytem where it undergoes diffusion. The oil flows down the surface of the Raschig rings in a thin layer under the influence of its own weight. At the same time the space above oil in the first level is subjected to vacuum with a special vacuum pump. Vapours of moisture and gases released during the procedure are pumped out through the zeolite tube and air filter.
The zeolite tube helps to absorb water vapor out of a steam-gas mixture. Once the necessary volume of transformer oil is treated by this device, it is necessary to let the zeolite in the tube dry. The air filter is required to protect the vacuum pump from zeolite dust which can become airborne during the process of drying the zeolite.
A large amount of water vapor and gases are vented in the first level of degassing system. The oil then flows by gravity to the second level. It undergoes the final drying and degassing process at the second level. The desired level of degassing is achieved in the second reservoir due to a second vacuum pump which is joined in series with the main vacuum pump.
An electric pump supplies the dried and degassed oil from the second level of the vacuum filtration degassing system to a container for pure oil or back to the transformer after passing it through a fine mesh filter.
In most cases vacuum filtration systems designed for transformer oil treatment are called high vacuum degassing systems. We recommend you to find out more about Globecore’s high vacuum degassing at Oil.GlobeCore.com.