The essence of contact treatment consists in – mixing oil with bleaching earth (clay). The resulting substance is heated to complete adsorption processes. Then it is filtered to separate oil from clay.
The composition of bleaching clay often includes aluminum hydrated silicate. Though absorbing properties of earths are determined not only by their chemical composition but also by their particles structure and size, pore diameter and humidity.
Clay with moisture content of 10-15% is most active. Since the rate of diffusion of the adsorbed substance into internal pores depends on the degree of grinding, the finer the grinding, the more active is clay. But excessive grinding is undesirable – making it difficult to filter the earth. It is recommended to use clay with grinding degree of 200 mesh (since at least 90% of bleaching agent must pass through a sieve consisting of 200 holes per inch).
Oil contact treatment process is needed for the final “polishing”: removing polar impurities – resins, soaps, low molecular acids, etc. The result of this treatment is improvement of oil color and increasing of its dielectric properties (reduction of the dielectric loss tangent).
Adsorption treatment in a moving bed of adsorbent is used in the industry for transformer oil.
In general, the scheme of treatment of transformer oil can be described as follows: hydrogenation of distillate – distillation of hydrogenation product – dewaxing – contact or percolation treatment with an adsorbent, or hydrotreatment (if necessary)
Hydrotreating and hydrocracking remove chemical compounds of hydrocarbons and sulfur that are part of transformer distillate. It produces low-boiling oil-products. This is both a fundamental difference and an advantage of this method.
Good transformer oil can be obtained by post-treatment and dewaxing.
GlobeCore is one of the leading manufacturers of transformer oil treatment and regeneration equipment. CMM-R plants use a unique technology of adsorption treatment. Its distinguishing feature is – reactivation of sorbent (Fuller’s earth) directly in the plant. The sorbent can be used multiple times as a bleaching agent with no need to recycle. Transformer oil after being processed by СММ-R plants fully comply with norms, allowing its re-use. This ensures financial savings and reliability of transformer equipment.