Solid fuels biomass combustion

Except for submerged combustion processes that are used for treatment of aqueous dissolved and suspended biosolids and a few other special combustion processes, the combustion of virgin and waste biomass involves solid fuels. Stoichiometric combustion data for four types of biomass, two coals, and one... 

Keywords Packed-bed combustion, thermochemical conversion of biomass, solid-fuel combustion, fuel-bed combustion, grate combustion, biomass combustion, gasification, pyrolysis, drying. 

Complex pyrolysis chemistry takes place in the conversion system of any conventional solid-fuel combustion system. The pyrolytic properties of biomass are controlled by the chemical composition of its major components, namely cellulose, hemicellulose, and lignin. Pyrolysis of these biopolymers proceeds through a series of complex, concurrent and consecutive reactions and provides a variety of products which can be divided into char, volatile (non-condensible) organic compounds (VOC), condensible organic compounds (tar), and permanent gases (water vapour, nitrogen oxides, carbon dioxide). The pyrolysis products should finally be completely oxidised in the combustion system (Figure 14). Emission problems arise as a consequence of bad control over the combustion system. 

Fabrication. Processes for fabricating solid fuel pellets from a variety of feedstocks, particulady RDF, wood, and wood and agricultural residues, have been developed. The pellets are manufactured by extrusion and other techniques and, in some cases, a binding agent such as a thermoplastic resin is incorporated during fabrication. The fabricated products are reported to be more uniform in combustion characteristics than the raw biomass. Depending on the composition of the additives in the pelletized fuel, the heat of combustion can be higher or lower than that of the unpelletized material. 

Conceptually speaking, the technology for combustors is similar to that used for coal combustion (see Chapter 9) if solid biomass fuels are used. Typically used configurations for biomass combustion include [41] (1) pile-burned, (2) stoker-fired, (3) suspension-fired, and (4) fluidized-bed combustors. 

Moilanen, A., Kurkela, E., Laatikainen-Luntama, J. (1999). Ash behaviour in biomass fluidised-bed gasification. In Gupta et al. (eds.). Impact of mineral impurities in solid fuel combustion. New York Kluwer Academic / Plenum Publishers. Pp. 555 - 567. 

Biomass combustion is a complicated process involving drying of solid fuel, pyrolysis and oxidation of pyrolysis gases and carbon. Many modelling studies to describe combustion performance have been based on these three stages (4, 5, 14, IS). In order to further investigate the effects of biomass characteristics on the observed combustion performance, a simple stoichiometric model for wet biomass combustion was employed to describe the overall reaction process (Eqn. 3) 15). An empirical mole of biomass is arbitrarily normalised to one atom of carbon by the formula C H Oj. 

For fuels with a high content of volatile matter, the gas combustion downstream of the bed is crucial for emission control. The fuel bed is the Drst stage in the combustion process and generates the conditions for the latter part. A review of available literature on the experimental simulation of solid fuels confirms that the knowledge of coal combustion is more detailed than that of biomass and municipal solid waste. The knowledge of biomass gasification devices today is extensive however, sec for example La... 

Biomass pyrolysis though is one of the fint process man developed, is being studied extensively since the last two decades to obtain liquid, gaseous and solid fuels and chemicals. It is well recognised that pyrolysis plays a key role in any of the thermochemical conversion process be it combustion, gasification, liquefaction, production of char or active carbon. In this context, selection of feedstock and optimal utilisation of the products can play a vital role [1], This paper suggests a criteria to select an appropriate biomass or find its relative suitability to the conversion processes. 

Ideally, fuel sources for cooking and distilling fuel alcohol would come from solid fuels, such as coal, wood and crop residues. Such practice would minimize the amount of high-quality liquid and gaseous fuels consumed for heating and increase the total quantity of liquid fuels available. Alternative fuels include natural and LP gas and fuel oil alcohol product mined solid fuels (coal, peat, anthracite) crop and forest residues, farm and forest fuel crops and combustible wastes methane gas produced from animal wastes and biomass and solar radiation. 

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