Cement, Energy and Environment

Kishore Rathore L. Rajasekar Sanjeev Srivastava Ultratech Cement Ltd, Technology & Research Cell Mumbai, India Abstract Electrostatic precipitators (ESP's) are commonly used for collection of particles in industrial applications. There are many ESP's around the world not meeting today's requirements due to aging, process changes and more stringent regulations for emission limits. Before ESP performance improvements can be considered, measures must be taken to ensure that the equipment is mechanically sound. Once this is accomplished there are various upgrade technologies available to improve the ESP performance. In order to choose the most appropriate upgrading technology it is necessary to have a good knowledge about the site-specific conditions. Measures can be taken to: • • • • Avoid or reduce the effect of high resistivity dust Reduce re-entrainment of dust caused by rapping or high gas velocity Change the mechanical ESP design by replacing internals and/ or rapping system Upgrade the ESP energy supply and control systems • Optimize gas distribution and reduce sneakage • Increase the ESP size • Change the particle size distribution with agglomeration technologies This paper demonstrates one such approach. however, the necessary steps are identified and can be re-sequenced as needed to match the logistics of a particular situation Introduction Electrostatic precipitators (ESP's) have been used for a long period of time to control particle emissions. Many ESP's around the world have been in operation for several decades. More stringent em1ss1on requirements and more challenging conditions due to fuel switching and other process changes result in a need for improved collection efficiency and ESP upgrade. On many occasion it is possible that the measured collection efficiency is suboptimal. In that case, if restoring ESP performance to its "best" performance would meet your emission goals, then it makes sense to proceed through the full optimization study, which includes on-line diagnostics, off-line diagnostics, and repair. However, if the "best" performance the unit could hope to attain would still fall short of performance goals-for example, if expectation is to have more restrictive emissions limits or plan to burn lower-sulfur coal, which produces higher– resistivity fly ash- it will be necessary to conduct a major overhaul or implement new control measures. If ESP's current collection efficiency matches or exceeds its "best" performance, the optimization steps are unlikely to make any appreciable improvement. A significant performance boost then would requ ire the technologies or asset up-gradation. The applicabi li ty and the possibil ities with different retrofit technologies can be investigated, once the ESP is restored to its original condition. In order to evaluate a precipitator, certain data are required for the analysis. Mandatory inputs include gas temperature and velocity 16 • ( ' "<:/( {