Evaluation of slagging and fouling tendency during biomass co-firing with coal in a fluidized bed

Abstract

Slagging FoulingCo-firing Biomass Fluidized bed a b s t r a c tOver the last decades, several indices based on ash chemistry and ash fusibility have been used to predict the ash behaviour during coal combustion, namely, its tendency for slagging and fouling. However, due to the physicalechemical differences between coals and biomass, in this work only the applicability of an ash fusibility index (AFI) to the combustion and co-combustion of three types of biomass (straw pellets, olive cake and wood pellets) with coals was evaluated. The AFI values were compared with the behaviour of ash during combustion in a pilot fluidized bed and a close agreement was observed between them. For a better understanding of the mechanisms associated with bed ash sintering, they were evaluated by SEM/EDS and the elements present on the melted ash were identified. Evidences of different sintering mechanisms were found out for the fruit biomass and herbaceous biomass tested, depending on the relative proportions of problematic elements. The particles deposited on a fouling probe inserted in the FBC were analyzed by XRD and the differences between the compounds identified allowed concluding that the studied biomasses present different tendencies for fouling. Identification of KCl and K 2 SO 4 in the deposits confirmed the higher tendency for fouling of fruit biomass tested rather than wood pellets. ª

The Influence of Ashing Temperature on Ash Fouling and Slagging Characteristics during Combustion of Biomass Fuels

“…So far, the researchers have put forward several slagging and fouling indices to predict the ash behavior during coal combustion process, but previous studies (Pronobis 2005;Teixeira et al 2012) reported that there is a lack of specific indices for evaluation of slagging and fouling tendency during biomass combustion process. Hence, in this study, the slagging and fouling tendency of biomass ash was evaluated according to the empirical indices for predicting the coal ash behavior during coal combustion.…”

“…The index Rb/a is defined as the base (Fe2O3, CaO, MgO, K2O, Na2O) to acid (SiO2, TiO2, Al2O3) ratio shown in Eq. 4 (Teixeira et al 2012), and this ratio is a mass ratio. Besides, the formulas of these indices that indicate the ash slagging and fouling tendency were also presented in the following Eqs.…”

“…Even for the same kind of biomass fuels, the carbon content of their relevant ashes formed under different ashing temperatures also present substantial differences. Within the various studies of biomass ashes, only a few have focused on the agglomeration characteristics during the thermochemical conversion process of biomass fuels (Scala and Chirone 2008;Niu et al 2010b;Teixeira et al 2012), and the influences of ashing temperature on the properties of different biomass ashes are still incompletely understood or uncertain in many details, so further investigations are required. Considering the biomass availability, area-specific agriculture residues, and related transportation costs, it is important to explore various local biomasses for their suitability as fuels.…”

A Comparative Study of Fouling and Bottom Ash from Woody Biomass Combustion in a Fixed-Bed Small-Scale Boiler and Evaluation of the Analytical Techniques Used

“…As a result of these problems, there is a loss of efficiency due to the reduction of the heat exchange, which results in an increase in the operational and maintenance costs. Therefore, fouling, slagging and corrosion are the main challenges faced by biomass combustion boilers, which are a subject of study for many researchers [4][5][6][8][9][10][11][12][13][14]. The main cause of the formation of these deposits resides in the chemical composition of the biomass used in the combustion.…”

“…The presence of high amounts of alkali metals such as K and Na, and large quantities of Cl, S and Si are primarily responsible for these problems. [6,7,9,12,[14][15][16][17][18]. Many researches have focused on minimizing or removing these problems using methods such as co-firing with other types of fuel, such as different coals [9][10][11]13,[19][20][21] or blends of various biomass species [14,22], and the use of additives such as phosphoric acid [3], ammonium sulfate [19], kaolin [14], halloysite [23], titanium oxide [24], Ca-based additives [25] and others [26][27][28].…”