It is foreseeable that recovery boiler particulate emission limits in the United States and Canada will continue to get more stringent with time. Because of this, continued improvement of emission control equipment, as well as a better understanding of how operating parameters affect performance, are necessary. Although electrostatic precipitators (ESPs) are often viewed as a mature technology, many improvements in ESP technology continue to be developed. In recent years, academic efforts have improved the understanding of recovery boiler operating conditions on ESP performance. Additionally, advancements in materials, power supplies, and design continue to improve the efficiency and reliability of ESPs. This paper discusses how recovery boiler and electrostatic precipitator (ESP) operating factors affect ESP performance based on process simulations and practical experience, and how these learnings can be implemented to improve future operation of existing ESPs.

The electrical resistivity of ash particles is an important parameter that determines the efficiency of electrostatic precipitators. This systematic study examines the resistivity of recovery boiler precipitator ash as a function of electrical field strength, time of exposure, particle composition, and gas composition and temperature. Synthetic ash and actual ash samples from several pulp mills are used. The results show that most ash samples tested had a resistivity between 109 and 1010 Ω·cm, but one of the samples had an unusually high resistivity, 1012 Ω·cm. The resistivity increases with temperature up to about 140°C, then decreases. At a given temperature, the resistivity decreases with increasing moisture and sulfur dioxide concentration in the gas. Resistivity also increases with an increase in chloride content in the ash, but is not affected by the carbonate, sulfate, and potassium contents. The results imply that recovery boilers burning liquors with high solids and high chloride contents produce ash with higher resistivity, making it more difficult for electrostatic precipitators to capture.