Alternative fuels for cement manufacturing: Quick and flexible semi-quantitative analysis with Omnian

Introduction

To reduce energy costs, CO₂ emissions, and dependence on fossil fuels, cement companies are increasingly using alternative fuels. These types of fuels originate from different sources, such as household and industrial waste (e.g., plastics), used tires, biomass, waste oils, sewage sludge, and even animal remains.

Prior to combustion, the elemental composition of the fuel has to be screened. This will ensure that the concentrations of the various elements (such as sulfur, chlorine, and heavy metals) are below the safety thresholds.

X-ray fluorescence (XRF) is a proven analytical technique that has been successfully used on a wide range of samples. The European norm EN 15309:2007 provides guidelines for the analysis of homogeneous waste and soil-like materials using XRF. 

Figure 1. Examples of alternative fuel samples: (1) industrial plastic waste, (2) sewage sludge, (3) household waste, (4) wood chips, (5) rubber granules, (6) textiles from tires.

Omnian is Malvern Panalytical’s semi-quantitative analysis solution, designed specifically for qualitative screening and concentrations evaluation without a dedicated calibration.

Omnian has been successfully used on high-end WDXRF spectrometers. It is also available for the Epsilon 4 EDXRF benchtop systems. This powerful combination brings together the strengths of Omnian with the ease of use of Epsilon 4.

The Omnian analysis program performs an automatic qualitative analysis, followed by a standardless determination of the composition using an algorithm with fundamental parameters calculations. Omnian is designed to provide fast, reliable quantification in the default ‘black box’ mode. However, the data collected is comprehensive and can be reviewed in more detail if required. 

This application note shows the performance of Omnian on Epsilon 4 for the analysis of various reference materials, chosen for their representational value of real alternative fuels. All samples were measured using the default Omnian calibration and settings.

The samples are measured as loose powders, which are placed directly into a sample cup with a polymer bottom foil. Similar sample cups are used for liquids. The user only needs to check the amount of sample and place the cup inside the instrument.

Biomass

The standard NCS DC73349, which is a mixture of bush branches and leaves, was selected as a typical biomass sample. Cellulose (C₆H₁₀O₅) was chosen as the balance compound. Table 1 compares the measured concentrations with the certified values, demonstrating a good correlation between the two. Even for light elements in such challenging materials, this standardless analysis provides a good indication of the concentration ranges.

Animal remains

As an example of animal remains, a bovine liver standard reference material (NIST NBS 1577a) was selected (see data in Table 2). As balance, we chose to use C₁₈H₃₆O­₂N₂. The loose powder analysis in the fourth column already gives a good indication of the elemental concentrations of the sample and is already in agreement with the certificate.

To demonstrate the flexibility of Omnian and the influence of sample preparation, the fifth column shows the results when the same standard is prepared as a pressed pellet. The data show that choosing pressed pellets will improve accuracy, particularly for low Z elements, such as Na, Mg and P. 

Table 2. Omnian results compared to certified concentrations for bovine liver standard.

Fuels, oils, and petrochemicals

A lubricating oil standard (Lube Oil 16) manufactured by VHG Labs Inc. (LGC Standards, USA) was measured as an example of Omnian’s performance when testing fuel, oil, or liquid petrochemicals. For the analysis, five milliliters were poured into a liquid cup. CH₂ was automatically calculated as a balance compound by the Omnian software.

Table 3. Comparison between Omnian results and the certified concentrations for an oil standard from VHG Labs Inc., USA.

Results in Table 3 demonstrate good agreement between certified and measured values for minor to trace concentrations in a liquid sample.

Sewage sludge

As an example of sewage sludge, Slovak reference material 188-WT-H sewage sludge from municipal water treatment was analyzed. The loose powder results (Table 4) give a good indication of the concentration of the elements in the sample. CO₂ was taken as the balance compound.

Table 4. Certified values (right column) compared with the Omnian results measured on municipal treatment of sewage sludge: 188-WT-H.

Conclusion

This application note demonstrates the ability and flexibility of Omnian, in combination with an Epsilon 4 EDXRF spectrometer, to analyze different types of alternative fuels with a single method.

This study demonstrates Omnian’s capability on the Epsilon 4 to measure samples as loose powders. The data obtained show good agreement with expected concentrations. The analysis error is less than expected from sampling heterogeneous alternative fuels.

Omnian provides the necessary insight to use the alternative fuels safely and ensure they will not affect the process (quality and safety) or the environment. The user can further improve accuracy, especially for lighter elements, by presenting samples as denser pressed pellets.