Laser Measurements of Entrained Particles in Recovery Boilers, 2004 Paper Summit, Spring Technical & International Environmental Conference, (including Papermakers; Process Control, Electrical & Information; Product & Product Quality)

Two different laser diagnostic techniques have been implemented in kraft recovery boilers to provide important information on entrained particles. One technique, based on single-particle scattering of a low-power laser source, measures the velocity, concentration, and size distribution of particles within the flow. For application to recovery boilers, this technique was designed to measure the range of particle sizes known as intermediate size particles (ISPs), roughly from 2–100 µm in diameter. The other diagnostic technique, known as laser-induced breakdown spectroscopy (LIBS), uses a pulsed, high-power laser beam to create a localized plasma spark in the flow, allowing the measurement of the elemental composition of the entrained particles. This technique is most sensitive for particles less than 10 µm in diameter. Implementing these laser diagnostic techniques in recovery boilers proved to be challenging. For the particle scattering measurement, the use of a narrow aperture was found to be effective in minimizing background signals associated with the dense sodium fume. For the LIBS measurement, a new waterjacketed optics probe was designed and implemented. Both diagnostic techniques were employed at two representative recovery boilers in the U.S. The particle scattering diagnostic demonstrated similar trends in mean ISP concentration, ISP size distribution, and temporal variation of ISP concentration at the two boilers. The LIBS measurements showed the presence of a number of major chemical components as well as trace metal elements in the entrained particles.