Single and two-stage electrostatic demisters for biomass pyrolysis application

Single-stage and two-stage tubular electrostatic precipitators were designed. A nitrogen stream containing very fine droplets of fogging oil was forced through the electrostatic precipitator chamber. It was found that 98.6 wt% of the oil droplets present in the turbulent jet were mechanically collected on the inner walls of the test chamber. When the electrode was energized at 13 kV, 92.37 wt% of the droplets that had not been mechanically separated were collected in single-stage mode. The collection efficiency was increased to 93.18 wt%, when the electrostatic precipitator was operated in two-stage mode. Voltage-current (V-I) characteristics of the single-stage and two-stage electrostatic precipitators were studied in detail for different test conditions. Nitrogen impurities played a major role in determining the V-I characteristics. They became less relevant with the introduction of mist in the nitrogen stream, presumably due to the presence of water vapor in the gas. The two-stage tubular electrostatic precipitator was scaled up and tested on a fluidized bed pilot plant used for the pyrolysis of biomass. A droplet collection efficiency of 95 wt% was observed. Such demisters will extend, to the product recovery train, the process intensification gains of short residence time processes such as fast pyrolysis. (C) 2009 Elsevier B.V. All rights reserved.