Abstract

Limestone-gypsum wet flue gas desulfurization (WFGD) often produces a certain amount of wastewater with complex water quality and heavy metal pollution which should be treated properly before release. Spaying the desulfurization wastewater into flue duct and using exhausted flue gas heat for evaporation is a promising and economical technology for achieving zero wastewater discharge in thermal power plant. To enable a more in-depth understanding on evaporation of FGD wastewater spray, a visual wind tunnel test rig based on the atomized droplet laser measuring system was built to reveal the impact factors on droplet thermal-fluid behavior. The dominant impact factors such as compressed air pressure and flow rate in air-blast spray nozzle, hot air temperature and velocity in the evaporation tunnel were analyzed to discuss the droplet size distribution and evaporation performance through alternating operate condition. A discrete mathematical model that combines both Eulerian and Lagrangian framework was established to validate the experiment result. It is concluded that introducing high pressure compressed air into the nozzle can contribute to the dispersion of droplets and enhance the evaporation rate. Proper flow rate in spray nozzle is required to avoid incomplete droplets evaporation. Air temperature and velocity in the evaporation tunnel apply positive impact on droplet size distribution and evaporation performance. Numerical simulation results of both dominant factors impact on evaporation behavior and total evaporation rate showed consistency with the experimental outcome.

Highlights

  • Coal-fired power plants are facing the most stringent pollution discharge policy nowadays [1,2]

  • Due to the confinement and inconvenience of observing and measuring the actual droplet evaporation process in the spray of flue gas desulfurization (FGD) wastewater to the flue duct, previous studies mostly focused on the numerical simulation aspects and experimental investigations are seldomly found

  • It is concluded that the air-blast spray nozzle parameters, including the compressed air pressure in nozzle cavity and spray nozzle flow rate, have a significant impact on the droplet evaporation performance

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Summary

Introduction

Coal-fired power plants are facing the most stringent pollution discharge policy nowadays [1,2]. Concentration and clarification, spraying desulfurization wastewater into the flue duct and using exhaust flue gas heat for evaporation is an effective and economical technology [8,13,14]. Several numerical studies have been carried out on FDG wastewater droplet evaporation to evaluate the thermal performance, and investigate the effect of design and operating parameters A combined Eulerian-Lagrangian discrete mathematical model was established to validate the experiment result Results from both experimental and numerical analyses will be useful to better demonstrate FGD wastewater spray evaporation treatment technology

Experimental Section
Boundary Conditions and Numerical Approach
Experimental Results
Effect of Flow Rate from Spray Nozzle
Effect of Air Velocity
Numerical Results of the Evaporation Rate
Concluding Remarks
Full Text
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