横掠液柱流的微粒运动机理及PM2.5捕获(Ⅱ)重型柴油机尾气PM2.5捕获效率

摘要

根据(Ⅰ)报提出的液柱交叉流PM2.5颗粒附面运动与吸收机理及模型计算方法,设计了以钻井废水吸收钻井柴油机尾气PM2.5的液柱交叉流吸收现场试验装置.吸收器具有高温绝热蒸发与低温绝热冷凝两个操作空间,柴油机尾气通过绝热蒸发空间降温增湿,携带水蒸气到绝热冷凝空间通过扩散在液柱表面冷凝,形成热泳和扩散双重强化PM2.5吸收分离机制.模型计算显示该机制下0.01～1.0μm范围内颗粒粒径与分离效率关系不显著,设计工况下单液柱分离效率1.17％～1.36％.由200排三角形布置的液柱构成的吸收器总体分离效率90％～93％.该过程可同时蒸发废水461.2 kg· h-1.但颗粒分离效率随蒸发负荷及液柱温度的上升而降低,温升10℃、单液柱分离效率降低60％.现场模型试验装置监测数据与本文模型计算总分离效率基本接近.%Based on the mechanism and mathematic model for PM2.5 particle motion to and absorption by a falling liquid cylinder (FLC) proposed in paper ( I ). a pilot experiment rig was designed for PM2.5 separation from heavy-duty diesel exhaust with a falling liquid cylinder absorber (FLCCA). It was built to match an 810 kW diesel engine on a drilling field, with drilling wastewater as the liquid medium circulated in FLCCA. The separation space of FLCCA is divided into two parts according to the function of humidifying or dehumidifying, through which an inner circulation of water vapor is generated to enhance PM2.5 deposition by the effects of diffusion and condensation. It is shown from the calculation that the separation efficiency for particles of different sizes, within 0. 01-1. 0 μm, is only slightly changed owing to the combined enhancement effects of the normal component of the superficial gas velocity, the thermophoretic velocity and the water vapor diffusion velocity, all of which are towards the surface of the cylinder. The calculated separation efficiency of a single liquid cylinder (dc = 4 mm) reaches 1. 17%-1. 36% under the designed operation condition. The total separation efficiency of the FLCCA equipment consisting of 200 rows of staggered arranged FLC is calculated between 90 H-93%. An evaporation rate of 461. 2 kg · h-1 wastewater can be obtained in the separation process combined with heat and mass transfer. The particle separation efficiency will decrease with the increase of evaporation rate and liquid cylinder temperature. The separation efficiency will decrease 60% corresponding to a 10℃ increase in the liquid cylinder temperature. The calculation results are satisfactory, verified by the onsite measurement for the efficiency of particle removal from the drilling diesel engine exhausts. 5%-10% of negative deviation to the calculated separation efficiency is regularly observed during a half year onsite inspection. It is consistent to the prediction due to the frequent appearance of a positive deviation to the designed liquid cylinder temperature.