Treatment and Regeneration of PCBs in Transformer Oil by a Chemical Process (Case Study: Tehran Besat Power Plant)

Document Type : Research Paper


1 MSc Graduated, Soil & Water Pollution Supervisor, Tehran Province DOE

2 Associate Professor, Graduate Faculty of Environment, University of Tehran.

3 Chemistry Engineer, Pardis Kish Company Manager


PCBs belong to a broad family of man-made organic chemicals known as chlorinated hydrocarbons. They have a range of toxicity and vary in consistency from thin, light-colored liquids to yellow or black waxy solids. Due to their non-flammability, chemical stability, high boiling point, and electrical insulating properties, PCBs were used in hundreds of industrial and commercial applications including electrical, heat transfer, and hydraulic equipment; as plasticizers in paints, plastics, and rubber products; in pigments, dyes, and carbonless copy paper; and many other industrial applications.PCB (or PCBs) is a category, or family, of chemical compounds formed by the addition of Chlorine (Cl2) to Biphenyl (C12H10), which is a dual-ring structure comprising two 6-carbon Benzene rings linked by a single carbon-carbon bond.
Polychlorinated biphenyl, commonly referred to as PCB, was in widespread use as a dielectric fluid due to its special physical and chemical properties. Since then, PCBs have developed a notorious reputation due to their potential for environmental contamination and for their potential to react to form other, highly toxic substances. Under incomplete combustion, PCBs can form products such as furans and dioxins. Due also to the stability of PCB and its potential for environmental accumulation and harm. Many different process can and have been used to destroy PCBs, but each has its limitations and potential risks. High temperature incineration has been widely used, but has the inherent risk that if inadequate temperatures are attained at the point of destruction of the PCB, dioxins and furans can be formed.
Another dechlorination process is the gas-phase reduction, in which the main difference is the chemical used as reducing reagents. The molten salt process has been used on a small scale since 1950 [9]. In the process, a bed of alkaline molten salt, usually sodium carbonate oxidizes organic materials. Any chlorine, sulfur, phosphorous, or ash products in the feed are converted to inorganic salts and retained in the salt bed. This process cannot treat soils and other materials with a high content of inert material. With bench and pilot scale systems, PCBs was destroyed in molten sodium carbonate/sodium chloride with efficiencies of 99.99 Percent. Destruction efficiency with chlordane was apparently not determined. Indeed, the use of performance measures, "destruction efficiency" and DRE, in describing the performance of this technology suggests that one may have been used inaccurately. i.e., destruction efficiency can be determined only if all process residues are analyzed for the presence of undestroyed chemicals of concern.
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  Materials & Methods:
Chemical dehalogenation (or dechlorination) is a chemical process used to remove halogens (usually chlorine) from a chemical contaminant by hydrogen or a reducing radical containing hydrogen donor.
In the case of based catalyzed dechlorination, the process key is the hydrogen donor with an oxidation potential low enough to produce nucleophilic hydrogen in the presence of base Na+. On the other hand, for the Eco-Logic process gaseous hydrogen at high temperature is the reducing reagent to destroy chlorinated organic compounds.
Chemical dehalogenation technologies are applicable to halogenated aromatic compounds, including PCBs, PCDDs, PCDFs, ….
Treated transformer oil was segregated from the contents (Fig.1.).
Figure 1- PCB Destruction Flow Chart
Results and Discussion:
In this study a practical and efficient disposal dechlorination process has been reported for Tehran Besat Power Plant PCBs less than 10000 ppm. The transformer oil containing commercial PCB mixtures (Aroclor 1242, 1254 and 1260) was treated by chemical process. 74000 lit (666000Kg) of PCBs oil (less than 7000 ppm) from Tehran Besat power plant sent to site plan. Content of 4 transformer oil samples is reported in Fig.2.
Results of PCB content of transformer oil sample. The diluted is cleaned with solvent  and then analyzed by a capillary Gas Chromatograph with an electron capture detector for the detection of PCBs. Results are reported as mg of PCB per liter of oil (ppm). Samples containing less than 2 mg/l PCB will be reported as  
Figure.2- Tehran Besat Power Plant PCBs waste less than 7000 ppm
The destruction and   removal efficiency of PCBs was 99.99% and/ or less than 2 ppm. After destruction, the reactor content was drained. The treated transformer oil was segregated from the contents by filtering, washing, dehydrating under vacuum. Such segregation steps described standard treatment of treated transformer oil before reuse. Treated transformer oil passed IEC60296 (oil quality standard). We have developed a safe, inexpensive and efficient chemical dechlorinating process for the disposal of Besat Plant PCBs directly in transformer oil. Disposal/decontamination of slightly PCB contaminated transformer oils could be established in Iran quite rapidly if decisions and resources can be secured. A destruction and removal of PCBs in Transformer Oil by a Chemical Process is one of the commercial technologies. Considerable PCB issue in Iran and firm steps needs to be taken in order to avoid releases in the environment from inappropriate waste management or spillage.


Main Subjects

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