Experimental Investigation Of Desulfurization Slurry Droplets Measurement By Digital Holographic Microscopy

Popularization of wet desulfurization unit reduces the thermal power plant emissions of SO2effectively, but produces the potential problems of slurry droplets emission carried by flue gas after demister and gypsum rain. At present, the measurement of slurry droplets is still dominated by sampling methods because of the lack of effective online measurement technology. The development of in situ, real-time and on-line measurement technology is not only the requirements of engineering application, but also the demands of energy-saving and emission reduction. The research of slurry droplet measurement using digital holographic coaxial microscopy was carried out. In order to simulate characteristics of droplets in flue gas and simplify the measurement environment, experimental investigations were carried out in this paper. Combining ultrasonic atomization technology with Digital Holographic Microscopy and Phase Doppler Anemometry, a set of optical system for the measurement of atomized droplet size distribution and concentration was designed. The main contents are as follows:1Research on principle of Digital Holographic Microscopy and its accuracyAfter the introduction to the theory of Digital Holographic Microscopy, the relationship between visibility, particle size error, z axis positioning error of particle Fraunhofer number was studied for the accuracy of slurry droplet measurement simulation. Results are shown as follows:the visibility of particle decreases with the distance between the particle and CCD image plane increasing. The fluctuation of visibility is obvious when the particle is close to the CCD image plane, and relatively better with a large distance. Size error decreases first with the increase of distance and then increases exponentially. Z axis positioning error basically remains the same, substantially less than10%. Based on the two criterions (Fraunhofer number less than0.25, visibility greater than0.1), the optimal particle measurement range of z direction can be determined.2Experimental study on the measurement of ultrasonic atomized dropletsUltrasonic atomized slurry samples were measured by Digital Holographic Microscopy and Phase Doppler Anemometry simultaneously. Droplet size distribution and concentration were obtained under different atomization amount. Particle size distribution measured by Digital Holographic Microscopy was unimodal with obvious peak, mainly between0.59-5μm. The particle size distribution obtained by Phase Doppler Anemometry was relatively flat within the scope of0-5μm, with average diameter2μm, and the results were similar to Digital Holographic Microscopy. Particle number concentration measured by Digital Holographic Microscopy was large than Phase Doppler Anemometry. This was because the Phase Doppler Anemometry will remove the signal of particles which pass the measuring area at the same time, resulting in the smaller particle number concentration. Droplet mass concentration was log normal distribution after batch processing with Digital Holographic Microscopy. When the average concentration was greater than8418.9mg/m3, the hologram visibility was poor, and the measurement error increased. The concentration range for slurry droplet measurement was0.82-8418.9mg/m3with Digital Holographic Microscopy in this set of experimental device.3Slurry droplet online measurement prototype designBased on experimental investigations assisted by ultrasonic atomization technology, a prototype suitable for real slurry droplet measurement was designed, and the composition of the various parts was introduced. The structure of measuring probe was introduced specifically. For the complex environments in flue, protective gas system and pressure balance system were considered, and a special sample cell was designed. The prototype structure is applying for a patent. The future will have the very good application prospect.