Mechanisms and mitigation of agglomeration during fluidized bed combustion of biomass: A review

Abstract

11A key issue associated with Fluidized Bed Combustion of biomass is agglomeration. The presence of 12 high quantities of alkali species in biomass ash leads to the formation of sticky alkali-silicate liquid 13 phases during combustion, and consequently the adhesion and agglomeration of bed material. This 14 review principally examines probable mechanisms of agglomeration and the effects of operational 15 variables in reducing its severity. Additionally, an overview of monitoring and prediction of 16 agglomerate formation is given. Two key mechanisms of agglomeration are apparent in literature, 17 and both may occur concurrently dependent on fuel composition. Coating-induced agglomeration is 18 defined by the interaction of alkali metals in fuel ash with the bed material, commonly silica sand, to 19 form an alkali-silicate melt. Melt-induced agglomeration is defined by the presence of sufficient 20 amounts of both alkali compounds and silica liquid phases sourced from the fuel ash to form a 21 eutectic mixture. Physical mechanisms, such as tumble agglomeration and sintering, may further 22 enhance either of the coating-induced or melt-induced mechanisms. Of the operational variables volumes of non-combustible contaminants, high moisture contents and, in most applications, 63 requires a large amounts of pre-processing/pre-treatment with specialised transportation. Due to 64 these challenges, technologies such as fluidized bed combustion (FBC) boilers have been employed. 65 FBC offers a number of advantages, such as combustion of different fuel types, blends, and ranges of 66 qualities, features commonly referred to under the umbrella term of [5]. Hundreds 67 Page 4 of 75 of full-scale bubbling fluidized bed (BFB) [6, p. 7] and circulating fluidized bed (CFB) [6, p. 8] boilers 68have been deployed around the world [7, 8] for power generation and/or steam sales to industrial or 69 chemical plant sites. However, each FBC plant development has to overcome slagging, fouling, 70 corrosion and, most significantly, agglomeration issues resulting from the composition and 71 behaviour of the biomass fuel stock [9]. 72

Experimental Studies on Combustion Characteristics of Oil-Palm Biomass in Fluidized-Bed: A Heat Energy Alternative

“…In addition, NO emissions are more dominant in the presence of sources of reactants than volatile-N and char-N. The performance and emissions from combustion with biomass are quite good as the results of research conducted by [34][35][36]. This combustion is achieved when the palm kernel shell is burned using a particle size of 5 mm by giving air around 40-50%.…”

Biomass conversion into valuable products within the integrated management of bio-resources

“…The main technological challenges of the biomass combustion are: presence of non-combustible contaminants, moisture content (if the long term storage isn't appropriate made), pre-treatment and preprocessing stages, adequate transport and rich content of mineral matter and alkaline earth metals (e.g. potassium and calcium) that during the combustion process might lead to the slagging, fouling, agglomeration and corrosion of the reactor [31].…”

“…According to the data provided by accreditate monitors such Eurostat and Worlbioenergy presented in Fig. 1., the foresty residues represent the most predominant biomass resource worlwide, while the forestry and crops residues seems to be the primary biomass sources in the European region, followed by agricultural waste in both cases [3,4] A considerable amount of studies have been published on woody, non-woody and agricultural waste conversion treatments that included: pyrolysis [5], gasification [6], combustion/co-combustion [7,8], bio-oil upgrade [9], transesterification [10], biological treatment [11]. Others concentrated on the biomass logistics and/or supply chain optimization [12].…”

Waste Fuel Combustion: Dynamic Modeling and Control

“…The content of Alkali and alkali earth metals in the fuel, such as K, Na, Ca, Mg can increase agglomeration potential significantly, and if Cl is present this can facilitate the progression even further. Furthermore, modes for agglomeration prediction have been presented by Gatterning [47], agglomeration detection methods have been presented by Bartels et al [48,49], and the mitigation of agglomeration have been presented by Morris et al [50]. Proven methods for predicting agglomeration, controlled agglomeration test as well as fuel and ash analysis, work only for fuels that are relatively homogeneous.…”