Linjun Yang

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.

Removal characteristics of sulfuric acid aerosols from coal-fired power plants.

ABSTRACT With increasing attention on sulfuric acid emission, investigations on the removal characteristics of sulfuric acid aerosols by the limestone gypsum wet flue gas desulfurization (WFGD) system and the wet electrostatic precipitator (WESP) were carried out in two coal-fired power plants, and the effects of the WFGD scrubber type and the flue gas characteristics were discussed. The results showed that it was necessary to install the WESP device after desulfurization, as the WFGD system was inefficient to remove sulfuric acid aerosols from the flue gas. The removal efficiency of sulfuric acid aerosols in the WFGD system with double scrubbers ranged from 50% to 65%, which was higher than that with a single scrubber, ranging from 30% to 40%. Furthermore, the removal efficiency of WESP on the sulfuric acid aerosols was from 47.9% to 52.4%. With increased concentrations of SO3 and particles in the flue gas, the removal efficiencies of the WFGD and the WESP on the sulfuric acid aerosols were increased. Implications: Investigations on removal of sulfuric acid aerosols by the WFGD and the WESP in the power plants were aimed at the control of sulfuric acid emission. The results showed that the improvement of the WFGD system was beneficial for the reduction of sulfuric acid emission, while the WESP system was essential to control the final sulfuric acid aerosol concentration.

Investigation on the relationship between the fine particle emission and crystallization characteristics of gypsum during wet flue gas desulfurization process

The relationship between the fine particles emitted after desulfurization and gypsum crystals in the desulfurization slurry was investigated, and the crystallization characteristics varying with the operation parameters and compositions of the desulfurization slurry were discussed. The results showed that the fine particles generated during the desulfurization process were closely related to the crystal characteristics in the desulfurization slurry by comparison of their morphology and elements. With the higher proportion of fine crystals in the desulfurization slurry, the number concentration of fine particles after desulfurization was increased and their particle sizes were smaller, indicating that the optimization of gypsum crystallization was beneficial for the reduction of the fine particle emission. The lower pH value and an optimal temperature of the desulfurization slurry were beneficial to restrain the generation of fine crystals in the desulfurization slurry. In addition, the higher concentrations of the Fe3+ ions and the F- ions in the desulfurization slurry both promoted the generation of fine crystals with corresponding change of the morphology and the effect of the Fe3+ ions was more obvious. With the application of the desulfurization synergist additive, it was beneficial for the inhibition of fine crystals while the thinner crystals were generated.

FT-IR study of the SO2 oxidation behavior in the selective catalytic reduction of NO with NH3 over commercial catalysts

Abstract The catalytic oxidation process of SO 2 and the effects of NH 3 , NO and O 2 on its oxidation behavior was investigated with FT-IR spectroscopy. It was found that the SO 2 oxidation occurred via the following steps. SO 2 first absorbed on V 2 O 5 and occupied at O position to form SO 3 2− . Then, it reacted with V 5+ -OH to generate VOSO 4 -like intermediate species, which was promoted to transform into SO 3 and V 2 O 5 by re-oxidizing V 4+ to V 5+ by O 2 . The oxidation of SO 2 was suppressed in the presence of NH 3 and NO due to their competitive absorption on the V 2 O 5 . This indicates that removal of NO x and oxidation of SO 2 are contradictory.

Experimental investigation on the improving removal of fine particles in LIFAC flue gas desulfurization by heterogeneous condensation

Abstract Based on the enlargement of fine particles by heterogeneous condensation, removal of particles from LIFAC (Limestone Injection into the Furnace and Activation of Calcium) desulfurization system was investigated experimentally. Supersaturation required for fine particles growth was achieved by adding adequate steam to the wet flue gas at the inlet of condensation chamber. The enlarged dusty droplets were removed by a high efficiency demister. The particle number concentration, size distribution, temperature and humidity were measured in real time by ELPI (Electrical Low Pressure Impactor) and Vaisala humidity transmitter, respectively. The influences of activation water addition amount, steam addition amount, particle number concentration and demister on the removal of fine particles were investigated. The results indicate that supersaturation improve at first and then drop with the increase of steam addition amount. The removal efficiency of fine particles can be effectively improved by heterogeneous condensation. The removal efficiency rises with the increase of supersaturation, decrease of particle number concentration and the enhancement of performance of the demister.

Improving the removal of fine particles by chemical agglomeration during the limestone-gypsum wet flue gas desulfurization process

Coal-fired power plants are considered a major source of fine particle emissions in China. Aimed to improve the removal efficiency of fine particles during the limestone-gypsum wet flue gas desulfurization (WFGD) process, a novel technology using chemical agglomeration to abate the emission of fine particles is presented herein. The relationship between fine particle emission and the proportion of fine particles in the desulfurization slurry was studied. Additionally, the influence of chemical agglomeration on fine particle size distribution, both in the flue gas and slurry was experimentally investigated. When chemical agglomeration agents were added to the desulfurization slurry, the fine particle removal performance as well as the effects of the operation parameters was also explored via the simulated experimental facility. The results revealed that the fine particles in both the desulfurization slurry and flue gas were significantly enlarged after the addition of the agglomeration agents. This was more marked in the submicron particles. Thus, the proportion of fine particles (< 10 μm) in the slurry decreased from 31.1% to 22.6%. An increase in the desulfurization slurry temperature and liquid-to-gas ratio aided the reduction in fine particle emission. Moreover, the addition of an agglomeration agent in the slurry did not affect the desulfurization efficiency of the desulfurization tower and even promoted the WFGD process. Thus, the proposed chemical agglomeration technique reduced the fine particle emission of the WFGD system by ~30%, while a desulfurization efficiency >90% was maintained.

CO 2 Capture Using Hollow Fiber Membrane Under Wet Ammonia-Based Desulfurization Flue Gas Conditions

The fine particulates and coexistent gaseous components, i.e., SO2 and water vapor in desulfurized flue gas, may severely impact the performance of membrane gas absorption in the long term. In order to gain a better understanding on the effects of the impurities on the membrane performance, the process of membrane absorption for CO2 capture under wet ammonia-based desulfurization flue gas conditions was investigated. Using monoethanolamine (MEA) aqueous solution as absorbent, the operating conditions of polypropylene (PP) hollow fiber membrane for CO2 absorption were optimized firstly, and the best ones were 0.5 mol/L as the concentration of MEA, 1 m3/h as the feed gas flow rate, and 24 L/h as the absorbent flow rate. Then, the PP hollow fiber membrane performance on CO2 capture from desulfurized flue gas was studied. The results revealed that the residual SO2 and water vapor slightly influence the CO2 absorption performance. However, the aerosol particulates formed during desulfurization process deteriorated the absorption properties of microporous membrane leading to the decrease of the CO2 removal efficiency.

Numerical research on the filter performance of PM2.5 on the micro-scale of fibrous assembly

Numerical simulation of the PM2.5 filter phenomenon in the internal microstructures of fibrous assembly was carried out three dimensionally by discrete element method (DEM). Eulerian method and Lagrangian method were employed to deal with the gas phase and solid phase respectively. By the direct tracking of each of the aerosol particles, the collection efficiencies of PM2.5 were calculated under different conditions. The simulation results show that the collection efficiency of PM2.5 decreases with the increase of porosity (e) and linear density (ρ), while is found no variation with the change of particle concentration and flue gas velocity.

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.