Minna S. Tiainen

Slagging tendency of peat ash

The combustion of peat in power plant boilers has increased in recent years in Finland. Whereas the operation of such power plants is generally smooth, the slagging of peat ash can, in some cases, lead to a plant shutdown, thus causing significant economic losses to the entire energy-production chain. It is therefore important to predict the slagging tendency of ash in a given peat type prior to combustion. In this work we discuss the factors involved in the slag formation of peat samples. The work centers both on standard peat ash and on the samples collected from an actual power-plant boiler. The formation and properties of ash particles have been studied with scanning electron microscopy combined with automatic image analysis. X-ray powder diffraction data complement the microscopic studies.

Coatings on Bed Particles From FB-Combustion of Different Biomasses

The FB-combustion of several biomass fuels (bark, wood in different forms, biosludge, chicken litter, REF and forest residue) with different bed materials (quartz, natural sand, and recently introduced GR Granule) has been studied in this work. The bed samples have been collected during the laboratory, pilot, and full scale tests. The chemical composition of the coating layers and agglomerates were characterized by SEM-EDX. Line scans, point analyses, and X-ray maps were used to characterize the coating layers further. It was observed that the chemical composition of the coating of the bed particles depends both on the fuel type and on the bed material. The thickness of coating layers was also dependent on fuel and combustion history. The coatings were often seen to contain several superimposed layers. The innermost layer mainly contained alkali silicates, whereas the outermost layer was calcium-rich or magnesium-rich. In some cases the coating layers seem to protect the bed particles from agglomeration.Copyright

Chemical Characterization of Bed Material Coatingsby LA-ICP-MS and SEM-EDS

Bed material coatings and the consequent agglomeration of bed material are main ash-related problems in FB-boilers. The bed agglomeration is a particular problem when combusting biofuels and waste materials. Whereas SEM-EDS together with automated image processing has proven to be a convenient method to study compositional distribution in coating layers and agglomerates, it is a relatively expensive technique and is not necessarily widely available. In this contribution, we explore the suitability of LA-ICP-MS to provide analogous information of the bed.

The Suitability of the Fuel Mixture of Horse Manure and Bedding Materials for Combustion

The mixture of horse manure and bedding materials (peat and sawdust) appear to be a potential biofuel. The chemical compositions of horse manure, bedding materials, and the mixture of these have been characterized by SEM-EDS and ICP-OES. In addition, the compositional distribution of ash of these materials has been determined and this facilitates the estimation of their propensity for ash-related problems in boilers. NOx and SOx emissions from the co-combustion are also discussed on the basis of the chemical composition of fuel mixtures. It seems that co-combustion of horse manure and bedding materials in FB boilers is suitable for small-scale energy production.

Determination of Amorphous Material in Peat Ash by X-ray Diffraction

The combustion of peat in power plant boilers has increased in recent years in Finland. While boilers involving pulverized fuel are still common, the utilization of fluidized bed boilers is rapidly increasing. FCB boilers are best suited for fuel with a low energy value because the increased efficiency is beneficial for the community heat distribution. Peat has a low energy value and high water content and therefore resembles low rank lignitic coal [Moilanen et al., 1993]. The sulfur content of Finnish peat, however, is very low. The inorganic material inherent in peat is typical to that of the plants in the bog [Spedding, 1988] and therefore the slagging tendency of peat ash can be expected to be dependent on the bog from which the peat is originating. Generally the operation of power plants utilising peat is unproblematic, but in some cases severe slagging may occur leading to a plant shutdown thus causing significant economical losses to the entire chain of energy production. Therefore the slagging tendency of peat ash needs to be predicted from the peat fuel prior to its combustion. The slagging of peat ash is connected with the high iron content leading to the formation of low melting point iron aluminosilicates [Heikkinen et al., 1997]. The partial melting of ash particles might lead to agglomerate formation in the fluidized bed. While SEM-EDS connected with an automated image analysis provides a convenient method to investigate the formation of the coating on the bed particle as well as the nature of the adhesive material binding the bed particles [Virtanen et al., 1997], The ease of agglomerate formation and slagging can also be tested by inspecting the compression strength of ash that can be considered as a measure for the degree of sintering of the ash particles [Hupa et al., 1989]. Since the melting and sintering—and ultimately slagging—all involve the formation of amorphous material in ash, it is important to devise an independent method to determine its content. The X-ray powder diffraction (XRD) technique is commonly used to identify the crystalline phases in solid samples. However, it also offers the option to determine the