Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Evaluation of pulverised coal/secondary fuel particle sizing methods

Part A presents the evaluation of the sizing systems for different coal / secondary fuel mixes.

The applicability of different particle size distribution systems and methods was tested for several secondary fuels and their mixtures with primary fuels. The investigated systems were different sieve methods, laser diffraction, optical microscopy and SEM.

The screen sizing systems (shaker and air-jet) are equally applicable for non-fibrous materials. For strongly fibrous materials the air-jet screener should be used.

The laser-optical methods used showed good results when particle size distribution was within the measuring range of the analyser.

Optical methods like optical microscopy and scanning electron microscopy in combination with particle detection software was not successful. Reasons are the segregation of the particle and fuel components during sample preparation due to the size and density differences and the inaccurate detection and isolation of single particles in a mixed fuel with the software available.

The particle size investigations of the grinding products show that all supplemental fuels shift the overall particle size distribution of the fuel mix towards larger particle sizes.

Qualitative evaluation concerning the impact of co-grinding is possible with the tools applied. For a quantitative determination of the impact of co-grinding more detailed information about composition of the fuel and sieve fractions is necessary.

Part B provides detailed information on the fuel composition and the distribution of the inorganic matter in the size fractions in form of a substantial database.

Four coal / secondary fuel systems were investigated in terms of element distribution in pure materials and in fuel mixtures. Two coal / secondary fuel systems were investigated in terms of the element distribution in the sieve fractions.

In order to determine the composition of the fuel and the inorganic matter in the fuel, a comprehensive database of the components in the sieve fractions had to be set up. This included Thermo Gravimetric and Proximate Analysis as well as Ultimate and XRF-Analysis of all fuels and sieve fractions produced, see also Part A. Proximate, ultimate, heating value and chlorine analysis were done on the fuels and selected sieve fractions. Ultimate and XRF analysis were performed on lab ashes of all fuels and selected sieve fractions. The ashes were produced in a lab oven at 550°C and 815°C.

The bio-waste fuels show the typical characteristic in the proximate and elemental analysis with high volatile, lower fix-C and lower carbon content. There is almost no chlorine and little to no sulphur in the bio-waste. Nitrogen is not present in paper sludge, ranges in the same level as coal for wood pellets and is clearly increased for cacao-shells with a four times higher value compared to coal based on the energy input.

Characteristic properties of the single fuels could be found, which indicate that a determination of the presence of one or the other fuel in a certain size fraction might be possible. However, the selective and inhomogeneous behaviour of some properties, for example the ash content, in the different size fractions has to be considered.

TGA-characteristics provide information in how much the fuels behave homogeneously and therefore give helpful information on which assumptions are justifiable when carrying out the determination of the composition of the sieve fraction and on the evaluation of the results obtained.

To compare the results of XRF – Analysis, especially for 550°C lab ash samples of biomass, the data has to be normalised. This was done by a special approach in order to determine the loss of sample weight due to the release of CO2 from CaCO3.

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Universität Stuttgart
Pfaffenwaldring 23
70569 Stuttgart
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