关键词: 液柱交叉流, 柴油机尾气, PM_2.5分离, 热泳, 传质强化

Abstract: Based on the mechanism and mathematic model for PM_2.5 particle motion to and absorption by a falling liquid cylinder (FLC)proposed in paper（Ⅰ）, a pilot experiment rig was designed for PM_2.5 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 PM_2.5 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 (d_c=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%—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.

Key words:  , flow crossing falling liquid cylinder；diesel exhausts；PM_2.5 removal；thermophoresis；mass transfer enhancement