A new method for quantification of fluidized bed agglomeration tendencies: A sensitivity analysis

A new method for quantification of fluidized bed agglomeration tendencies for different fuels has been developed and evaluated. A bench scale fluidized bed reactor (5 kW), specially designed to obtain a homogeneous isothermal bed temperature, is used. The method is based on controlled increase of the bed temperature by applying external heat to the primary air and to the bed section walls, In addition, temperature homogeneity is secured by switching from normal fuel feeding to a propane precombustor. The initial agglomeration temperature is determined by on- or off-line principal component analysis of the variations in measured bed temperatures (four values) and differential pressures (four). To determine potential effects of all the process related variables, an extensive sensitivity analysis was performed. Experiments were performed according to a statistical experimental design to evaluate the effects of eight different process analytical variables on the determined agglomeration temperature of a biomass fuel. The results showed that for a given fuel, the amount of bed material, heating rate, fluidization velocity, and air to fuel ratio during both "ashing" and heating did not influence the determined agglomeration temperature. Only ash to bed material ratio, the ashing temperature, and the bed material particle size had significant effects on the agglomeration temperature, but still the effects were relatively small. The agglomeration temperature of the fuel could be determined to 899 degrees C (avg) with a reproducibility of +/-5 degrees C (SD). The inaccuracy was determined to be +/-30 degrees C (SD). Based on the results, the method was standardized with respect to ash to bed material ratio, bed material particle size, and ashing temperature. Relative agglomeration temperatures of different fuels, fuel, and additive combinations can thus be determined with a high precision.