Cement, Energy and Environment

- THE FUTURE OF ELECTROSTATIC PRECIPITATORS UlfRichtei~ Bob Tylonmd Tcny Fnrmc1~ BHA Group, Inc., US!\, The emission reduction varies from country to country and from industry to indush-y, but is quite drama tic. Especiall y in developed countries, air quality has improved markedly, while industrial output has increased. Typical emissions have draped from approximately 150 mg/Nm~ in 1960, to 10mg/Nm 3 (dry) in 2001. The trend in many countries is to continue this reduction, as technological ad vances make it possible to achieve almost total elimina tion of particula te from industrial gas s treams. Fabric filter dust collectors have come to the fore recently, as new technology filter media make it possible to achieve filtration rates in excess of 99.9%. But what about the tried-and-true ESPs tha t have been the industry s tandby for years? Can th ey meet the cha ll enge of s tringent particulate regula tions? How is it possible to tell which units have potential, and which need to be upgraded? The efficiency of an ESP is very dependent on different operation parameters: • • • • • • • • Moisture content of the gas. Flue gas chemistry. Particle size distribution and chemical composition of the particula te. Particulate electrical resistivity. Gas temperature. Primary combus tion material. Raw material. Secondary combustion ma terial. • • Start and stop operation. Transition phases of different operating condition and different raw ma terials as well as different fuels. What are the technical developments that enable p recipita tors to bl as effective as fabric filters? After all, for the las t 40 yrs, precipita tor design has been essentially unchanged, w ith the exception of plate-to-plate spacing, wh ich has increased from 250 mm to approximately 400 mm. O ther p recipitator technology advances, introduction of the thyristor at the end of the 1970s was a significant development, in the 1990s micropul se transformers and high fr equency transformer s were introduced. Precipitator voltage controls rode the wave of computing, and old analogue controls gave way to computeri sed, digital control systems. These advances provide the company wi th the courage to assert tha t ESPs have a bright future, even where very low particula te emissions are demanded. There are several current developments in information technology and compu.terised con trol that can greatly enhance the performance and reliability of most exis ting precipitators: • • • • • • CO monitoring: Computerised precipitator control: An a utomated start-up and shutdown logic system: Remote diagnostics: External rapping: On going development of high voltage power supplies.