Development of a total Ash Quality Index and an Ash Quality Label: Comparative analysis of slagging/fouling potential of solid biofuels.

Biomass combustion generates considerable amounts of ash that are related to slagging/fouling problems in combustors. Numerous indices have been proposed in the literature for the evaluation of slagging/fouling tendencies. This paper is focused on the characterization of various biomass ashes in terms of their slagging/fouling tendency. For this purpose, the chemical composition of ash samples from fourteen solid biofuels (and a lignite sample as a reference) was analyzed by scanning electron microscope, energy-dispersive spectroscopy, ion chromatography and elemental analysis. Modification/normalization of the available ash indices was performed by taking into account not only the chemical composition of the ash but also the Gross Calorific Value of the fuels and the amount of the produced ash. Two versatile tools were developed, a total Ash Quality Index (tAQI) and an Ash Quality Label (AQL), in order to express the information derived from various indices with a single number or letter. The modified indices result in different characterization from the unmodified ones and lead to a more objective/fair evaluation of the slagging/fouling tendency. The comparison of large number of indices of large number of samples is enabled via the tAQI and the AQL. Samples with a tAQL ≤ 1 belong to class 'A' (low slagging/fouling problems) while samples with a tAQL > 6 belong to class 'G' (extremely high tendency to slagging/fouling problems). The tAQI and AQL are a novel concept for the categorization and labeling of solid biofuels regarding their slagging/fouling tendency and could contribute to the waste/biomass residue market for energy proposes.

Byzantine wall paintings from Kastoria, northern Greece: spectroscopic study of pigments and efflorescing salts.

This study concerns the investigation of pigments and efflorescence phenomena on the wall paintings of Kastoria, a rural, non-metropolitan Byzantine town. A large number of representative samples were collected from the murals of three churches, dated to post-Byzantine era (14th-17th c. AD). The identified pigments for the red colour were hematite (Fe2O3), cinnabar (HgS) and minium (Pb3O4), while brown and yellow colours were attributed to mixtures of ochres (Fe-oxides and hydroxides) and lime. The utilization of admixtures of iron, lead and mercury compounds was also attested in order to render specific tones on the painted surfaces. Black and dark blue hues were prepared using black carbon and Mn in some cases. Grey colours were assigned to a mixture of black carbon and lime. Green colour is rather attributed to admixtures of Fe-rich minerals and lime and not to the commonly used green earths. Baryte (BaSO4) was also evidenced as a filler or extender. Phosphorous was detected and connected to proteinaceous material and Mo and Sb were traced which are probably affiliated to Fe-oxides. Regarding efflorescing salts, the determined compounds are: calcite, dolomite, gypsum, halite, nitratine, natron and mirabilite, all of which are related to temperature and humidity changes and moisture fluctuations inside the wall paintings.

ESEM-EDX characterisation of airborne particles from an industrialised area of northern Greece.

The aim of this study was to characterise individual airborne particles collected from the Ptolemais-Kozani region (Western Macedonia), northern Greece. Throughout a 1-year period (March 2003 to February 2004), we collected several filters that captured airborne particles at seven sampling sites distributed throughout the area. The airborne particles captured on the filters were then characterised by environmental scanning electron microscopy (ESEM) coupled with energy-dispersive X-ray analysis (EDX). The particles were categorised as geogenic, biogenic and anthropogenic. The main anthropogenic airborne particles were fly ash (released from lignite-fired power plants) and carbonaceous (soot and char) and metalliferous (mainly iron- and copper-enriched) particulates. We present here characteristic ESEM and EDX spectra for the airborne particles and underline the presence of characteristic primary and secondary sulphates.