Cement manufacturing is an energy-intensive process. High fuel costs are a primary issue, and alternative fuels have emerged as a potential solution. The cement industry is now burning a variety of alternative fuels or waste products in its kilns.
The chemical composition of alternative fuels determines their performance as well as their pollution potential. Elements such as chromium (Cr), cobalt (Co), nickel (Ni), vanadium (V), zinc (Zn), tin (Sn) and antimony (Sb) contribute to fuel efficiency by providing transfer mechanisms into the clinker and surroundings.
However, alternative fuels can also contain toxic elements such as lead (Pb), cadmium (Cd), mercury (Hg) and thallium (TI) that could affect kiln performance or pollute the environment. Thus knowing the exact chemical composition of alternative fuels is a critical but extremely challenging part of the cement production process.
Let’s talk about some of the reasons why this mineral analysis can be difficult: Alternative fuels can be organic or inorganic components in solid, liquid or high-viscosity forms. A wide variety of materials are used for alternative fuels, including tyres, wood, plastics, animal waste and other organic wastes, resulting in a range of matrices and concentrations in samples of “unknown” nature. Often they can be heterogeneous solids, pastes or liquids with an admixture of water and organic solvent.
Since the nature of matrix, elements and their concentration range can vary significantly from sample to sample, it becomes a complicated and expensive task to set up specific calibration programs to analyze alternative fuel samples. Typical materials handled in the production of cement, such as limestone, clay, bauxite, iron ore, slag, gypsum, fly ash, clinker, cement and additives, can be analyzed using well-established standards and matrix-specific programs. However, matching standards or well-characterized type standards are not always available for alternative fuels. X-ray fluorescence (XRF) is one of the best techniques for handling this application and mining applications.
XRF can handle difficult and dirty samples of unknown origin, often with very little sample preparation, and quantify the elements present within the limits of sensitivity and standard errors. Standard-less XRF analysis techniques provide quantitative data when reference material can’t be procured, for example, waste processing, or unstable materials. The strength of standard-less analysis is that it can directly and quickly analyze all elements in any type of sample with fairly accurate results, down to ppm levels. Whereas true calibration programs offer greater accuracy, standard-less XRF analysis programs eliminate the need for matrix-specific calibrations by using well-prepared samples.
The two primary types of XRF systems are energy-dispersive XRF (EDXRF) and wavelength-dispersive XRF (WDXRF). WDXRF technology is well established for high sensitivity down to low atomic number elements, high repeatability and element selectivity in order to achieve the performance needed for routine industrial applications. WDXRF is also exploited for its wide dynamic range and extremely good reliability for laboratory applications. EDXRF is a convenient technology to screen all kinds of materials for quick identification and quantification of elements with no or little sample preparation.