Occurrence and sources of zinc in fuels

Several studies have shown that the presence of high amts. of Zn, in addn. to other elements, in fuels can be a cause of operational difficulties during combustion due to corrosion and slagging and can also cause environmental and health problems due to emissions.  In nature, Zn is an essential micronutrient for humans, animals and plants, but in excessive amts. it becomes toxic.  This paper presents a review on the content of Zn in different fuels used in energy conversion systems.  Altogether, over 20 different fuels divided among waste, biomass and fossil fuels were studied.  The highest amts. of Zn are present in waste-​derived fuels, particularly in Tire-​Derived Fuel (TDF)​.  In tires, Zn is used as a vulcanizing agent and can reach concn. values of 9600-​16,​800 mg kg^-​1_DS.  Waste Elec. and Electronic Equipment (WEEE) is the second Zn-​richest fuel; while on av. Zn content is around 4000 mg kg^-​1_DS., values of over 19,​000 mg kg^-​1_DS. were also reported.  High amts. of Zn, 3000-​4000 mg kg^-​1_DS., are also found in municipal solid waste (MSW)​, sludge with over 2000 mg kg^-​1_DS. on av. (some exceptions up to 49,​000 mg kg^-​1_DS.)​, and other waste-​derived fuels (over 1000 mg kg^-​1_DS.)​.  Zn can also be found in fossil fuels.  In coal, the level of Zn is quite low, on av. 100 mg kg^-​1_DS., while higher amts. of Zn were reported for oil shale, with values between 20 and 2680 mg kg^-​1_DS.  The content of Zn in biomass is basically detd. by its natural occurrence, typically 10-​100 mg kg^-​1_DS.