What Elements Are Analysed in Fuel?
May 22 2021
Typical crudes are made up of 84.5% carbon, 13% hydrogen and up to 3% sulphur, as well as small percentiles of oxygen, nitrogen, salts and metals. While all fuel types share similar molecular structures, physical properties can vary hugely between grades. Below we spotlight some of the elements analysed during fuel assays, and why they matter.
Sulphur is one of the most important elements analysed in fuel assays, determining everything from price to feedstock suitability. Unless actively removed during the refining process, the naturally occurring component is present in both gasoline and diesel. Sulphur levels determine the quality of crude, with low concentrations classified as “sweet” and high concentrations classified as “sour”. Sweet is generally more desirable as high sulphur levels can compromise emission control systems, increase air pollution and compromise engine performance.
A naturally occurring trace element, nickel can play both a positive and negative role in petroleum refining and fuel suitability. Concentrations can vary drastically, with some samples containing a handful of parts per million (ppm) and others topping 250 ppm. When converting crude oils to auto fuels, high concentrations of nickel can interfere with processes such as fluid catalytic cracking (FCC). This can trigger reactions like carbonisation. In other cases, nickel can be beneficial and help to catalyse upgrading processes such as nitrogen removal and produce petrochemicals.
When combined with sodium and exposed to high temperatures, vanadium can damage marine engines and cause major operational issues. The naturally occurring element is often present in heavy fuel oils and is not only detrimental to engine performance but can also increase emissions and create a significantly larger environmental footprint. For this reason, most marine fuel assays include a detailed analysis of vanadium.
Trace amounts of metals such as iron are often found in fuels and can cause issues like equipment corrosion and catalyst deterioration. Sequential multi-element flame atomic absorption spectrometry is a common method used to determine iron levels in fuel and help refiners optimise feedstock selection.
While not always desirable in conventional fuels, iron has been building a reputation as a green fuel alternative. Cheap and easy to burn at high temperatures, fine-ground iron powder releases energy during the oxidisation process without emitting carbon. The only by-products are rust and iron oxide, making iron powder a surprisingly sustainable alternative. A Bavarian brewery has been spearheading the use of iron powder as an alternative fuel source, with German scientists pledging to convert coal-fired power plants into iron fuel plants by 2030.
Furnace setup can have a big impact on combustion analyser performance. TE Instruments representative Sebastian Sanchez explores the pros and cons of both methods in ‘Total Sulfur and Total Nitrogen analysis – Horizontal versus Vertical furnace arrangement.’
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