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ABSTRACT
In China, cost of energy supplied to rural areas or remote region is significantly high due to large transmission and distribution losses. These problems may be solved by introducing new energy systems such as bio-energy utilization. In this work, a mathematical model of biomass combustion in a circulating fluidized bed was developed. The model was an unsteady state and 1D kinetic model which enables to predict the gas composition and reaction temperature. Effects of some important operating conditions (oxygen ratio, system pressure, and water content) and hydrodynamic parameters (distance from the distributor, and particle size) on NO emission were studied. Results showed that for higher ER (the ratio of the amount of air to stoichiometric air), more NO emission occurs because higher ER leads to higher combustion temperature and a significant improvement in the endothermic gas–gas and solid–gas reactions. It was also found that the operating pressure does not have a significant influence in the flue gas composition; however, it can improve the economic aspects of the process.
Nomenclature
| a | = | decay constant (dimensionless) |
| Ar | = | Archimedes number (dimensionless) |
| B | = | volume fraction occupied by bubbles |
| dp | = | particle diameter (mm) |
| g | = | acceleration due to gravity (m/s2) |
| ∆P | = | pressure changes (atm) |
| U | = | superficial gas velocity (m/s) |
| Umf | = | minimum fluidization velocity (m/s) |
| z | = | axial distance from the distributor (m) |
| zd | = | height of the dense bed in the riser (m) |
Greek symbols
| = | volume fraction of bed occupied by bubble | |
| = | average voidage of bed | |
| = | cross-sectional average solids holdup | |
| = | cross-sectional average solids holdup at dense region | |
| = | cross-sectional average solids holdup at dilute region | |
| = | gas viscosity (Pa s) | |
| = | gas density (kg/m3) | |
| = | particle density (kg/m3) |