Abstract. In thermochemical utilization of biomass, ash produced during the process is a major problem that can result in decreased performance and increased in difficulty during operation. Preliminary assessment of potential ash related troubles prior to the use of a specific biomass is valuable, even if it is only a general guideline. In this work, tendency of ash slagging, fouling and agglomeration in thermal processing of biomass was evaluated. Reference peered reviewed data including mineral content and fusion temperature of selected biomass ash were used to calculate multiple indicators (base to acid ratio, slagging index, fouling index, agglomeration index, slag viscosity index, and ternary diagram of main biomass ash composition) adopted from coal research. Major ash forming elements (Fe, Ca, Mg, K, Na, Al, Si) were found to be of relevance to ash melting and deposit behavior. For conventional biomass available locally, woody biomass (wood and wood sawdust) may be combusted without slagging or fouling problem, while non-woody biomasses (bark, husk, straw) are highly probable to experience some of these problems. The ash fusibility predictive models for woody and non-woody biomass were found to be effective. Mitigation can then be designed possibly via fuel blending to avoid or minimize the impact of biomass ash related trouble.

The Mae Moh mine in northern Thailand, with its abundant lignite, is the primary energy source for the Mae Moh power plant, which uses pulverized coal combustion in superheated boilers to generate electricity for domestic consumption. The lignite reserves remaining in the mine may contain up to 40% CaO. Given this high calcium content, more frequent and severe slagging problems are likely to occur. To better understand the potential slag problem, this research investigates the characteristics and properties of the slag by collecting and analyzing different samples of boiler slag from the Mae Moh power plant. Employing scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray fluorescence, and X-ray diffraction, the surface morphologies of the different slag samples were found to be similar. The majority of the crystal surfaces were agglomerates of particle-like clay and irregular granules stacked together. The most abundant elements in the slag were oxygen, aluminum, silica and calcium. The major chemical components included CaO, SiO 2 , Al 2 O 3 , Fe 2 O 3 , and MgO. The minerals found in the slag were anorthite, gehlenite, akermanite, diopside, and esseneite. An increasing base-to-acid ratio reduced ash flow temperature. The Mae Moh lignite showed a medium to high slagging tendency. Increasing the slagging index led to a decrease in the ash fusibility temperature, due mainly to increasing amounts of Fe 2 O 3 and CaO. From this study, the high CaO and Fe 2 O 3 in the Mae Moh lignite clearly resulted in increased intensity of slag.

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Thermal behaviors and combustion kinetics of Thai lignite with different SO3-free CaO contents were investigated. Nonisothermal thermogravimetric method was carried out under oxygen environment at heating rates of 10, 30, and 50°C min−1 from ambient up to 1300°C. Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods were adopted to estimate the apparent activation energy (E) for the thermal decomposition of these coals. Different thermal degradation behaviors were observed in lignites with low (14%) and high (42%) CaO content. Activation energy of the lignite combustion was found to vary with the conversion fraction. In comparison with the KAS method, higher E values were obtained by the FWO method for all conversions considered. High CaO lignite was observed to have higher activation energy than the low CaO coal.