Transformer Oil Purification Methods
Each of the transformer oil purification methods has its advantages and disadvantages. Best results are achieved when using the combination of classic and innovative GlobeCore approaches.
All transformer oil purification methods can be divided into chemical, physical and physicochemical.
Chemical purification methods include acid and alkaline purification, restoring of oil with metal hydroxides. They remove asphaltenic compounds, resins, acid, compounds, some heteroorganic compounds and water from oil.
Acid purification processes oil with concentrated sulfuric acid. This method is based on different interactions of sulfuric acid with hydrocarbons and impurities. Normal temperature does not give a reaction. When the temperature is increased, there is only a partial dissolution. Therefore, during the purification, the oil products must be heated to 40-50 °C. It decreases oil viscosity and improves its mixing with sulfuric acid, which reacts with unsaturated hydrocarbons most intensively
The effectiveness of such treatment depends on the amount and concentration of acid, the time of its contact with oil and the temperature and the process.
In practice, 96% of sulfuric acid is used. Its expenditure is on average 3-5% of the oil mass, and the time of mixing is 25-30 minutes.
During alkaline purification oil is treated with sodium hydroxide, sodium carbonate and trisodium phosphate. Alkali can affect organic, naphthenic and carboxylic acids. As a result of this reaction water-soluble sodium salts (soaps) are formed. They are removed along with the water alkali solution after sedimentation.
Metal hydride regeneration involves oil treatment of oil with calcium, lithium and aluminum compounds. It removes not only water, but also carboxylic acids. The disadvantage of this method is a high cost of reagents, and necessity to clean the oil from solids and neutralizing gaseous substances that escape during the reaction.
Physico-chemical method is based on the use of special substances – coagulants, ion-exchange resins or adsorbents.
Coagulation is coarsening and precipitation of asphalt-resinous substances that are contained in oil in fine particles. Organic and inorganic electrolytes, surfactants, non-electrolytes, colloidal structures in surfactant solutions and hydrophilic macromolecule compounds may act as coagulants.
Adsorption – is another method of oil purification, based on the properties of certain substances (adsorbents) to retain contaminants on the outer surface of the granules and the inner surface of the capillaries. Both natural (bleaching clay) and synthetic (silica gel, alumina, zeolites) substances may perform the function of adsorbents.
The ion exchange purification precipitates into sediment acids, metal salts of calcium, aluminium and magnesium but retains additives.
The main distinguishing feature of physical methods is removing mechanical impurities, fuel, water, tarry asphalt-like and coke-like substances.
Most commonly used in practice is filtration and use of force fields.
Gravitational cleaning is considered the simplest approach, where suspended solid contaminants and water microdroplets are precipitated by gravity. The deposition rate of the particles depends on the height of the oil column, the size of the impurities as well as on the density and viscosity ratio of the deposited substances and the oil. To increase deposition rate – the oil temperature is increased. The highest temperature is 90 °C. If oil temperature goes above this mark, oil begins to boil, which is unacceptable.
Centrifugal force field is used to increase the efficiency of oil purification from mechanical particles. But only if density of particles exceeds the density of oil.
Magnetic field is used to remove solid ferromagnetic particles from transformer oil. It is created by means of either permanent electric current or electromagnets. Apart from particles with magnetic properties the magnets can also draw some other contaminants. This effect is achieved by electrification of non-magnetic bodies.
Vibration cleaning removes solids, with the amplitude of vibration causing coagulation. Electrostatic cleaning can also be applied as one of purification methods for transformer oil. In this conditions – contaminants, moving together with liquid, rub against surroundings under the influence of friction forces and receive a charge of a certain sign. In the electric field the contaminants that received a charge are drawn to the oppositely charged electrodes.
Filtration is separation of suspended solids from oil by means of porous filter material. This method is quite common due to the relative technical simplicity and reliability.
Integration of different methods is necessary in order to restore properties (for oil purification) of transformer oil. The accuracy of its combination determines the final result.
GlobeCore offers versatile oil purification equipment. The operation is based on both classical and innovative purification methods. GlobeCore uses authentic oil purification technologies making their plants most effective. GlobeCore technology is three in one: environmentally friendly, profitable and saves fuel and energy resources!