Persistent Organic Pollutants (POP)
The combustion of coal can theoretically cause the generation of persistent organic pollutants – POP, such as dioxins, furans and polycyclic aromatic hydrocarbons – PAH. Nevertheless, the technology used in modern coal-fired power plants, including grinding the coal into very fine particles, a short residence time of the particles in the boiler and optimum fuel to air ratio, ensures nearly complete combustion while preventing the creation of such pollutants and their accumulation in the ash at hazardous concentrations. Indeed, the findings of tests that were performed on various ashes in Europe confirm this assessment.
The Coal Ash Administration committed itself, at the request of the Ministry of the Environment, to study this phenomenon in Israeli coal ash.
Individual coal ash samples were tested in the power stations in accordance with the program prepared by the profession-scientific (pollutants) team of the Coal Ash Board, in consultation with the chief scientist of the Ministry of the Environment and sent for testing in the TAUW laboratories in Holland:
These are the principal findings of the tests1 :
- The general measurable level of the dioxins and furans in Israeli coal is very low and is found in the 0 – 0.78 ng I-TEQ/kg range. The upper limit, on the assumption that the concentrations that cannot be measured are on the threshold detection level of the instruments, is in the <0.42 – <1.11 ng I-TEQ/kg2 range.
- The measurable concentrations of PAH in Israeli coal ash are lower and found in the 1 – 0.02mg/kg range. Carcinogenic PAH was found in only 4 out of 8 samples of ash with an overall concentration of <0.28mg/kg. The concentration of PAH in bottom ash is higher than that in fly ash.
- These findings are similar to the finding obtained for the Dutch ash. In Holland, since fly and bottom ash are used as construction materials, they must meet the demands of the standard determined for these materials: a PAH concentration lower than 50mg/kg3.
- The low level of dioxins in the coal ash is due to the complete and rapid combustion in the boilers in the modern coal-driven power stations, which prevent the creation of soot (which according to its carbon structure is most suitable for the creation of dioxins) and the presence of SO3 (which is obtained from SO2), which hinders the generation of dioxins even at lower temperatures in the gas-cooling areas at the exit from boiler.
- The combustion conditions in the coal-driven power stations (high temperature, short stay in boilers, fuel/air ration) causes the conversion of almost all the carbon to carbon dioxide, thereby preventing the generation of significant concentrations of PAH compounds.
3The Israeli standard determines a maximum value of PAH 40 mg/kg in agricultural land.