1 on specific dust resistivity D. Pieloth, M. Majid, H. Wiggers, P. Walzel Chair of Mechanical Process Engineering, TU Dortmund, Dortmund/Germany
2 Outline 2 Motivation Measurement of specific dust resistivity Conductivity models a) Dust layer thickness and specific dust resistivity Summary and outlook Test materials used: a) fly ash b) spherical glass dust b)
3 Motivation 3 Steel-Converter HKM/Duisburg Source: Hüttenwerke Krupp Mannesmann / Heinz Kottysch Pit formation by back corona Electrostatic precipitator (ESP) Aim: Better understanding of physical processes within the precipitated dust layer to avoid back corona. Influence of current density, dust properties, gas conditions on back corona. Dust depositions on collection electrodes of a laboratory scale electrostatic precipitator specific dust resistivity
4 Measurement of specific dust resistivity 4 Definition and measurement principle of specific dust resistivity ρ: porosity, morphology, moisture,.. electrodes R = resistance (Ohm s law: U = RI) s = layer thickness A = area of collecting electrode ρ = specific dust resistivity I = strength of current ρ= f ( T, ϕ, x d, ε, U,..) Descending Ascending T d = 55 C 1st PiKo funding period: Detection of particle morphology effects on resistivity ρ and back corona under defined air conditions (with glass particles and fly-ash). Adhesion of dust particles on top layer of dust, detection of release of those particles into gas stream (started laser beam experiments). spherical glas, dt/dt = 3 C/min, j = 0,5 ma/m 2
5 Measurement of specific dust resistivity 5 BTW.. Water vapor adsorption and desorption into dust layers. Moisture Content (g of Water/g of Sample) Desorption Sorption Isotherm Measurements: at other Groups Prof. Tomas, Prof. Tsotsas Magdeburg Fine glass particles: Adsorption supplied by Group of Prof. Tomas, Relative Humidity % Z. Kutelova Water vapor adsorption in spherical glass particles (d 50,3 = 10,7 µm) at standard temperature and pressure conditions, apparatus: Sorptionsanalysator Q5000 SA
6 Measurement of specific dust resistivity 6 Measurement chamber Air outlet HV Supply Enclosure Air conditioning Max. Air Temperatur > 350 C Conditioned air Panic switch Air preheater Adhesion of dust particles on top layer of dust, detection of release of those particles into gas Experimental setup (1st PiKo funding period) 6
7 Conductivity models 7 Surface conductivity Volume conductivity Resistivity of spherical glass particles as a function of air dew point and temperature, method: plate-plate, j = 0.5 ma/m², dust layer thickness = 3 mm
8 Conductivity models 8 Ohm s law does not hold! Source: Riebel et al.: Zum elektrischen Verhalten von Hochohmigen Stäuben, in Press Resistivity of Al 2 O 3 as a function of layer thickness, with negative corona, relative air humidity 4%,T = 20 C
9 Dust layer thickness and specific dust resistivity 9 Ohm s law holds Resistivity of fly ash sample as a function of dust layer thickness and temperature, method: plate-plate, j = 0.5 ma/m², T d = 25 C.
10 Dust layer thickness and specific dust resistivity 10 Typical conditions for electrostatic precipitators at power plants Ohm s law holds Resistivity of fly ash sample as a function of dust layer thickness and temperature, method: plate-plate, j = 0.5 ma/m², T d = 25 C.
11 Dust layer thickness and specific dust resistivity 11 Ohm s law questioned! Ohm s law holds spherical glass dust, d p,50 = 110 µm Resistivity of spherical glass particles as a function of dust layer thickness and temperature, method: plate-plate, j = 0.5 ma/m², T d = 25 C
12 Summary and outlook Measurement of specific dust resistivity as a function of dust layer thickness First results show non-ohmic properties for glass dust Ohm s law holds for fly ash Measurements will continue (Cooperation with Group Prof. Riebel, BTU Cottbus, Diploma - Thesis Y. Lu, TU Dortmund) Adhesion of dust particles on top layer of dust (With E Field) Grateful to DFG for the financial support and to Y. Lu and J. Wesholowski for data acquisition Thank you for your attention! 12
13 Backup 13 Experimental setup
14 Backup 14 Electrode arrangement