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- Niklasson, Fredrik, 1968, et al.
(författare)
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Estimation of the temperature in the bottom region of a fluidized-bed furnace burning biomass
- 2006
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Ingår i: Science in Thermal and Chemical Biomass Conversion. - 1872691978
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Konferensbidrag (refereegranskat)abstract
- The heat and mass balance of the bottom region of a fluidized bed boiler burning biomass is established with the aim of determining the furnace temperature. The influence on the temperature by the flow of solids in the upper part of the bottom region is investigated. Heat and mass balances of gas and fuel were applied over a control volume containing the bottom region, i.e. both the bed and the adjacent splash zone. The mass balance is based on given input flow rates of gas and fuel and concentrations in the gas leaving the control volume. The measured gas concentrations were used to determine the rate of fuel burnout inside the control volume. Pressure drop measurements along the height of the furnace estimate the solids concentration. Experiments were performed in a furnace with a cross-section area of 2.2 m2. The walls of the furnace are refractory lined up to a height of 2 m and, for simplicity, the control volume is chosen from the air distributor up to this height. Two fuel mixtures were used: one biomass and one of biomass and coal. The results show that the gas temperature at the top of the control volume strongly depends on the flow-rate of fine particles present in the fluid, even when the volume fraction of particles is small. The particles carry heat to the freeboard, where they transfer heat to the walls before returning to the bottom region. This process has previously been neglected in models of fluidized-bed combustion under bubbling conditions, overestimating the fluid temperature.
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- Thunman, Henrik, 1970, et al.
(författare)
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Composition of Volatile Gases and Thermochemical Properties of Wood for Modeling of Fixed or Fluidized Beds
- 2001
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 15:6, s. 1488-1497
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Tidskriftsartikel (refereegranskat)abstract
- The modeling of the conversion of solid fuel in combustion or gasification systems needs a description of the composition of the volatile gases that leave a fuel particle of typical size in a fixed or fluidized bed during devolatilization. Much work has been published on release of volatiles, but a general model of the composition of volatile gases and a comprehensive presentation of the related thermochemical properties of the fuel are still missing. Here, a simplified model is presented whose structure is valid for any solid fuel. The model consists of a heat and mass balance complemented by empirical data. The empirical coefficients have to be specified for certain classes of fuel: the fuels treated in this paper are one type of hardwood and one of softwood, having particle sizes in the range used in utility boilers. The species in the volatile gases are represented by the time mean mass fractions of CO2, CO, H2O, H-2, light hydrocarbons, and heavy hydrocarbons. In addition, a comprehensive set of data is presented for such properties of wood that are needed for modeling of conversion in fixed and fluidized beds. The data are taken from the literature and from measurements carried out in the present work.
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