Haze pollution has been a serious atmospheric environmental problem as a function of the massive emission of fine particles (PM2.5). Due to the high specific surface area, a large amount of toxic heavy metals and other elements can be adsorbed on the surface of PM2.5, and the fine particles cannot be separated by conventional dust collecting equipment. Improving the control of PM2.5 emissions is one of the main targets with respect to reducing environmental pollution of coal-fired power stations. The utilization of flue gas conditioning, chemical agglomeration technology coupled existing pollution control facilities are most likely to achieve engineering application of PM2.5 disposal, which can realize collaborative removal of various pollutants.
The effect of humidifying flue gas conditioning on dust characteristics and fine particle removed by electrostatic precipitator (ESP) were investigated. In addition, the synergistic removal of various pollutants induced by low low temperature electrostatic precipitator (LLESP), as well as the coupled humidifying flue gas conditioning for facilitating the reduction of pollutants, were analyzed. Experimental results showed that humidifying flue gas conditioning was beneficial for the removing of PM2.5, and higher concentration of PM2.5 resulted in more significant promoting effect. The humidification conditioning effect increased with the increasing of atomized water under the same flue gas temperature. Agglomeration characteristic of PM2.5 tended to increase as a function of sulfuric acid condensed by SO3 deposited on fly ash. Humidification conditioning cooperated with LLESP spurred the removal of SO3 and PM2.5.
Based on the coal-fired thermal system, physical properties of PM2.5 with and without the addition of chemical agglomerant was exhibited, and the promoting effect of ESP by the presence of agglomerant was illustrated in typical operating condition. Besides, various experimental parameters like different agglomerants were tested. The experimental results performed that the peak particle size of number concentration increased from 0.15μm to 0.4μm with the addition of agglomerant, and the peak particle size keeps growing in the presence of wetting agent. Simultaneously, chemical agglomeration improved the removal efficiency of PM2.5 by 40% under the typical operating condition. The organic agglomerants present more significant effect than inorganic agglomerants due to the long molecular chain and plentiful effective groups. Chemical agglomeration effect could be enhanced by a series of methods, such as combining various agglomerants, adding wetting agent and lowering the resistance agent. The effect of chemical agglomeration increases with the concentration of agglomeration concentration. The pH value affected the formation of effective groups in the polymer chain, which led to the change of the chemical agglomeration effect. The moderate temperate of flue gas lay in the range of 140 ~ 160℃ as excessive temperature suppressed agglomeration performance, while the droplets evaporation was limited in low temperature. With the increasing of electrostatic precipitator voltage, the promotion effect was improved.
In order to further synergistically facilitate the removal of PM2.5, experiments on preparing agglomeration solution using desulfurization wastewater were carried out, and the zero discharge of desulfurization wastewater was also studied. The physical properties of PM2.5 after the evaporation treatment of desulfurization wastewater were explored. The promoting effect of ESP by desulfurization wastewater evaporation was investigated in typical operating condition. Furthermore, the effect of chemical agglomeration combined with desulfurization wastewater evaporation on enhanced removal of PM2.5 was revealed. The result exhibited that atomized wastewater droplets could adhere to fine particles, and accelerated the growth of PM2.5. Moreover, desulfurization wastewater evaporation promoted the removing of PM2.5 by 10 ~ 25%. The promotive effect was inclined to decrease as the solid content in desulfurization wastewater was above 5%. The agglomeration performance of atomized droplets was dramatically improved when agglomerant added into desulfurization wastewater. The fine particles decreased by 20 ~ 40% at the outlet of ESP. The high salinity content in desulfurization wastewater was responsible for the adverse agglomeration performance.
Based on the fine particles generated characteristics in the wet desulfurization process, chemical agglomeration inhibited fine particles generated in the process of desulfurization, and the influencing factors were studied in Simulated and Thermal state experiment platform. Results showed that fine particles in the outlet and fine particles content in the desulfurization slurry were positively correlated, after adding chemical agent, particle size distribution of peak increased, fine particles content in the desulfurization slurry reduced, fine particles emission concentration decreased at the outlet of desulfurization tower. Chemical agent type and concentration have important influence on fine particles emission, salt resistant agent effect is good, with the improving of agglomeration concentration, fine particle emissions reduced. Desulfurization slurry temperature, concentration, pH value and the impurity ions content also played a vital role in the agglomeration properties. On the one hand, these factors affected desulfurization gypsum crystals particle size distribution in the slurry, on the other hand impact on the performance of agglomerants, working condition of operating parameters. Using coal-fired thermal experiment platform, chemical agglomeration agent can reduce export fine particles emissions under the typical working conditions, due to the desulfurization serous contains more impurities such as coal fly ash, reunion effect is reduced.