Resistivity

Resistivity, which is a characteristic of particles in an electric field, is a measure of a particle's
resistance to transferring charge (both accepting and giving up charges). Resistivity is
a function of a particle's chemical composition as well as flue gas operating conditions
such as temperature and moisture. Particles can have high, moderate (normal), or low
resistivity.
In an ESP, where particle charging and discharging are key functions, resistivity is an
important factor that significantly affects collection efficiency. While resistivity is an
important phenomenon in the inter-electrode region where most particle charging takes
place, it has a particularly important effect on the dust layer at the collection electrode
where discharging occurs. Particles that exhibit high resistivity are difficult to charge. But
once charged, they do not readily give up their acquired charge on arrival at the collection
electrode. On the other hand, particles with low resistivity easily become charged and
readily release their charge to the grounded collection plate. Both extremes in resistivity
impede the efficient functioning of ESPs. ESPs work best under normal resistivity conditions.
Resistivity is the electrical resistance of a dust sample 1.0 cm2 in cross-sectional area, 1.0
cm thick, and is recorded in units of ohm-cm. A method for measuring resistivity will be
described later in this lesson. Table

 gives value ranges for low, normal, and high resistivity.