Abstract:

Aiming at investigation of the agglomeration process and characteristics of fine particles in the flue gas under the effect of an acoustic field, a stochastic model that describes the agglomeration of fine particles in a plane standing wave acoustic field was established using a direct simulation Monte Carlo method. The modelling was based on the dynamical processes, including the particle motion and interaction induced by the acoustic field, the collision between particles, and the consequent agglomeration or rebound upon particle collision. The model comprehensively considers the interaction mechanisms between particles, such as orthokinetic interaction, gravity sedimentation, acoustic wake effect, mutual radiation pressure effect, and Brownian diffusion. The particle collision is regarded as a random event, and the occurrence of collision is judged by a random algorithm. The acoustic agglomeration processes of fine particles in flue gas were numerically simulated using the presented stochastic model. Based on the model validation by comparison with experimental data, the evolution of the particle parameters over time was demonstrated, and the effects of flue gas temperature and pressure on the performance of acoustic agglomeration were discussed. The results indicate that as the acoustic agglomeration progresses, the particle number concentration peak drops, the total particle number concentration reduces, and the computed particles demonstrate a tendency of increasing in size and decreasing in number weight. As the flue gas temperature increases from 315 K to 1015 K, the acoustic agglomeration performance significantly enhances initially, whereas when the flue gas temperature is higher than 415 K, the sensitivity of acoustic agglomeration performance to the temperature weakens. The acoustic agglomeration effect diminishes monotonically as flue gas pressure rises when the acoustic field intensity remains constant. Particularly, when the pressure raises up to 1 MPa, the acoustic agglomeration effect becomes rather weak.

Key words: aerosol, flue gas, Monte Carlo simulation, acoustic agglomeration, fine particles

摘要：

为探究声场作用下烟气中细颗粒的凝并过程和特性，采用直接模拟Monte Carlo方法，从声场引发颗粒运动与相互作用、颗粒间发生碰撞、碰撞颗粒继而发生凝并或反弹的动力学过程出发，建立了描述平面驻波声场中细颗粒凝并的随机模型。模型中综合考虑了同向相互作用、重力沉降、声尾流效应、互辐射压力效应、布朗扩散等颗粒间相互作用机制，将颗粒碰撞视为随机事件，通过随机算法判断碰撞是否发生。基于所建立的随机模型对烟气中细颗粒声凝并过程开展数值模拟，在利用实验数据验证模型的基础上，展示了颗粒参数随时间的演变规律，探讨了烟气温度和压力对声凝并效果的影响。结果表明，声凝并过程中，颗粒数目浓度峰值下降，总数目浓度降低，计算颗粒呈现粒径增大、权重降低的规律；烟气温度由315 K升高到1015 K的过程中，声凝并效果起初显著增强，当烟气温度高于415 K后，声凝并效果对温度的敏感性减弱；在声场强度保持不变时，随着烟气压力的升高，声凝并效果单调下降，特别是当压力升高到1 MPa时，声凝并效果很弱。

关键词: 气溶胶, 烟气, Monte Carlo模拟, 声凝并, 细颗粒