Experiment And Numerical Simulation Theory Study On A Novel Type PCF Dedust And Desulphurization Scrubber

As seen from the present status of air pollution in China, particles and SO2, emitted from the coal-fired industrial boilers, are still the main air pollutants influencing the urban air quality. As the requirements for air pollution control are becoming increasingly strict, there is a constant demand for more effective pollution control technologies. And, present work should put emphasis on the research and development of the devices suitable for Chinese situations and possessing own intellectual property rights. In our dissertation, a novel type device-PCF dedust and desulphurization scrubber was developed based on amount of home and abroad literatures. Meanwhile, some related investigations were conducted on the device combining the experiment, numerical theory and CFD simulation. The main work and conclusions are listed as follows:Experimental analysis of PCF scrubber performance. Firstly, we studied the physical-and chemical-properties of the fly-ash and limestone. And consequently, the work is to investigate the device performance including resistance, dust collection, desulphurization and dewatering performance. Some reasonable parameters were obtained according to the experimental results.A dust collection theory model of the PCF scrubber was established on the basis of wetting dust collection mechanisms. Due to the fact that the dominant particle collection mechanisms are different in different zones of the PCF device, the device was divided into different zones and put emphasis on the effects of preliminary treating chamber, self-excitation channel, self-excitation chamber and inner cylinder. Based on the mechanisms, the sub-model for each zone is firstly established. After this, the sub-model synthesizes and evaluates the individual components of a process as a whole. The dedust efficiency at different operating conditions were predicted employing the theory model and compared the predicted data with that of experiment.Based on the two-film theory, a theoretical model of SO2absorption into the droplets of limestone slurry has been developed within the novel wet-type PCF device. This model treated flue gas as the studied object and assumed that the composition of droplets and absorption rate of SO2remain unchanged in a time step size. Chloride ion (Cl-), calcium ion (Ca2+) and eight dissolved species (H+, OH-, SO2(aq), CO2(aq), HSO3-, HCO3-, SO32-and CO32-) were considered to define the liquid phase composition. During the flue gas flow, we considered that the absorption of SO2and desorption of CO2into the gas phase. Meanwhile, the second purification of self-excitation chamber on the SO2was supplemented to improve the model accuracy. Using the established model predicted SO2removal efficiency at different work conditions and some auxiliary experiments were conducted to validate the predicted results. The results show that the SO2absorption rate in spay zone (preliminary treating chamber) is controlled by a combination of gas-and liquid-film diffusions in the range of tested operating conditions.Flow characteristics and performance of the PCF scrubber were simulated using a computational fluid dynamics (CFD) software package (Fluent). In the simulation, structural grid method was used to grid, Reynolds stress model (RSM) was employed to describe the gas phase, discrete phase model (DPM) was used in the droplet trajectory, discrete random walking (DRW) model was used to reflect the influence of turbulence on droplet trajectory, and pressure-velocity couple SIMPLE method was used to resolves the coupled continuity equation and momentum equations.The results show that:①With the gas velocity increasing, pressure drop increases, dedust efficiency and dewatering performance enhance slightly, and desulphurization efficiency decreases.②The liquid-gas ratio (L/G) has great effect on the dedust efficiency and desulphurization efficiency. In a restricted range of liquid-gas ratio, they both increase with the increase of L/G. However, the water content in outlet flue gas is not changed greatly with the L/G change.③Although the introduction of guiding plates increases the pressure drop, the comprehensive performance of the PCF device is improved greatly.④Compared with other scrubbers, the PCF device possesses many virtues such as lower pressure drop, larger flue gas treatment capacity, higher absorption rate, good dewatering performance, and so on.⑤The models of dust collection and desulphurization proposed in present study are effective models to evaluate and predict the dust collection and desulphurization performance of the novel type PCF device. The data of prediction and experiment show good agreement.⑥The CFD method visualizes the flow field such as velocity field, pressure field, concentration field, droplet trajectory, and so on, which can help us observe the phenomena directly, illustrate the flow characteristics in the scrubber and further knowledge the flow field rule. So, this method has powerful engineering application virtues.In the end of this dissertation, we investigated the practical application of the PCF device combining with engineering projects. The results illustrate that the dust and SO2concentrations and Ringelmann number in the flue gas purified by the PCF device are much lower than the national and local standards. Moreover, the PCF wet dedust and desulphurization technology possesses an excellent social benefit, environmental benefit and economic benefit, and thereby leads to a promising future of application.