Jinpei Yan

Separation of PM2.5 from combustion based on vapor condensation and scrubbing

Abstract Vapor heterogeneous condensation on the surfaces of PM 2.5 was used to increase the removal efficiency of PM 2.5 from combustion. An experimental device was set up to investigate the influence of particle initial size distribution, the amount of vapor addition, and the ratio of liquid to gas on removal efficiency. The particle size distribution and concentration at the outlet of scrubber were measured by Electrical Low Pressure Impactor (ELPI). The microstructure and major element compositions of fine particles were explored by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that the physico-chemical properties of fine particles from coal and oil are very different. And it has considerable influence on heterogeneous nucleation behavior. The removal efficiency of PM 2.5 of coal combustion is higher than that of oil. Both number and mass removal efficiencies increase with the increase in particle size and additional amount of vapor. The removal efficiency of 81% and 72% can be achieved for coal and oil combustion of fine particles with particle diameters of 0.4 μm at 0.08 kg/m 3 gas, respectively. Moreover, the collection efficiency can be improved with an appropriate ratio of liquid to gas.

Experimental Investigation on Improving the Removal Effect of WFGD System on Fine Particles by Heterogeneous Condensation

Heterogeneous condensation of water vapor as a preconditioning technique for the removal of fine particles from flue gas was investigated experimentally in a wet flue gas desulfurization (WFGD) system. A supersaturated vapor phase, necessary for condensational growth of fine particles, was achieved in the SO2 absorption zone and at the top of the wet FGD scrubber by adding steam in the gas inlet and above the scrubbing liquid inlet of the scrubber, respectively. The condensational grown droplets were then removed by the scrubbing liquid and a high-efficiency demister. The results show that the effectiveness of the WFGD system for removal of fine particles is related to the SO2 absorbent and the types of scrubber employed. Despite a little better effectiveness for the removal of fine particles in the rotating-stream-tray scrubber at the same liquid-to-gas ratio, The similar trends are obtained between the spray scrubber and rotating-stream-tray scrubber. Due to the formation of aerosol particles in the limestone and ammonia-based FGD processes, the fine particle removal efficiencies are lower than those for Na2CO3 and water. The performance of the WFGD system for removal of fine particles can be significantly improved for both steam addition cases, for which the removal efficiency increases with increasing amount of added steam. A high liquid to gas ratio is beneficial for efficient removal of fine particles by heterogeneous condensation of water vapor.