An investigation of transport processes involved in flue gas desulfurization.

摘要

Complicated multiphase flows are common in many flue gas desulfurization (FGD) processes. Sorbent particles (lime) are injected into the flue gas in dry FGD processes. The sorbents react with sulfur dioxide in the flue gas to form calcium sulfite and sulfate. A prerequisite for fast reaction and high utilization of the sorbent is rapid and thorough mixing of the sorbent particles with the flue gas stream. Mixing is determined by the flow patterns and by turbulent flow processes which are in turn influenced by the characteristics of the injection jet and interactions with the surrounding stream. To improve the understanding of such flows, the interaction of particle laden jet with concurrent flow was studied experimentally in the particle laden jet injection test facility.; The shearing flow generated by the interaction of particle laden jet and concurrent flow and its effect on mixing, including the structure of the particle laden jet (particle velocity, size and concentration) and local and overall mixing was studied. This study seeks to provide new information concerning interaction of concurrent flow with particle laden jets especially at lower duct to jet velocity ratios, and the onset of flow recirculation in the duct. Non-intrusive optical techniques Laser Doppler velocitmetry (LDV) and phase Doppler anemometry (PDA) were used obtaining particle velocity and size. However, PDA can provide the size for spherical particles only. Many multiphase flows encountered in real life contain irregular shaped particles, a technique which utilizes the particle transit time in the LDV measurement volume and the velocity measured by the LDV to obtain particle size and velocity is developed. This technique is termed as TTLDV. The measurement volume size, the number of fringes and spacing between the fringes, LDV photomultiplier tube (PMT) voltage and gain, laser power are the important parameters which effect the TTLDV performance.; Correlations for predicting the particle velocity profile inside the jet envelope and the potential core length as a function of particle mass loading are developed. The jet spread angle reduces with an increase in mass loading. The jet spreads wider with a decrease in concurrent flow velocity. The jet spread cone angle is found to be around 16 degrees. The presence of particles leads to a reduction in axial and radial turbulence intensities, as well as Reynolds shear stress levels as compared to single phase flows. However, the reduction in the concurrent flow velocity for a given particle laden jet mass loading results in an increase in the turbulence intensity levels. The radial velocity reduces as one moves downstream of the nozzle. However, at a given axial location, as one moves away from the center along the radial direction, the magnitude of the radial velocity component increases. The recirculation of the particle laden jet is observed only for low concurrent flow velocities. The jet spread, turbulence intensities were found to be larger as compared with higher concurrent flow velocities. The recirculation occur downstream of the axial location where all concurrent flow is entrained in to the diverging jet before. A criterion is presented to predict the onset of flow recirculation.