Waste Water Treatment at Electric Power Stations
Removal of petroleum products (boiler oil and other oils) from water at state-managed district electric power stations, heat power stations and nuclear power plants is one of the most complex issues in maintenance of water chemical systems. Petroleum product concentrations in some waste waters can reach 1000 mg/L, while it increases drastically in case of emergencies and unit discharges. High volatility of such substances in the process of vaporization causes pollution of distillate products in which these substances may accumulate in concentrations of up to 10 mg/L.
Furthermore, as a rule, boiler oil and other petroleum products are poorly dissolvable in water and resistant to biochemical oxidation. Such properties increase the risk of pollution of natural waters with such products. Thus, during 2-7 days petroleum product concentrations in water decrease just by 15% at temperatures up to 50°C, and by 40-50 at temperatures up to 200°C.
Hydromechanical systems including grit catchers, oil separators, settling ponds, and filters, are one of the most widely known and used waste water treatment systems.
Such filters are filled with various materials, including activated charcoal. Adsorption capacity of various filtering materials is given below (kg/kg):
Filtering material |
Adsorption capacity (kg/kg) |
BAU activated charcoal |
0.89 |
Expanded-clay aggregate |
0.33 |
Boiler slag |
0.21 |
Burnt rock |
0.26 |
Anthracite |
0.2 |
Sulfonated coal |
0.22 |
Petroleum coke |
0.23 |
Silica sand |
0.11 |
Supply of hot water steam under pressure of 0.03-0.04 MPa through the upper dispenser rather than washing provides the best results for regeneration of sorption filters. Steam heats petroleum products caught by the filter and displaces the products from the filtering layer. At the same time, steam is condensing. Steam flow required for regeneration (on a condensate basis) does not exceed 1-2 volumes of the filtering layer. Duration of the regeneration process depends on petroleum products removed and the degree of pollution of the filter. The process normally takes 2-3 hours. Displacement of petroleum products from the filter is accompanied by increase in concentration of the products in condensate, which is followed by decrease in such concentrations.
Condensate can be discharged through the inlet to oil separator. Such technique prevents increase in water flow through the waste water treatment facilities. Physical and chemical methods (e.g. adsorption) provide for removal of emulsified and suspended particles (of less than 100 μm) and dissolved impurities.