A Numerical Study On FGD' Characteristic By Spraying The Ash Wastewater From Coal-Fired Boiler

The environment pollution greatly restricts the continue development of national econmy. The SO₂ and the ash wastewater emitted by burning coal is the main pollution resource of air and water. Desulfurization of flue gas by using ash wastewater has some advantages such as using rubbish to harness rubbishm, saving energy, low operation fee.Numerical study on FGD by Spraying the Ash Wastewater in the flue was made in this thesis.We laid a strong emphasis on the heat transfer between SO₂ in the flue gas and spraying droplets in the flue gas channel.1. The two phase flow model of flue gas and droplet was firstly discussed, in which the flow of continuous phase and disperse phase was involved. Finally the standard k-ε model and stochastic trajectory model was adopted to compute the flow of continuous phase and disperse phase.2. The droplets evaporation model and SO₂ absorption model were studied respectively. Fnially the heat and mass transfer equation for computing droplets evaporation and mass transfer rate equation for SO₂ chemic absorption in the alkalescence liquor were present.3 . Using the theory of standard k-s model and stochastic trajectory model to establish numerical model in the spraying reaction segment, and use Fluent to simulate it. Finally, we get the effect of spraying characters (including initial diameter and velocity of spray droplets etc.) and the volume ratio of liquid to gas on the outlet average temperature and velocity, and the droplet phase's motion trace. On thebasis of element analysis, the control equations for the interactive effects between spraying mist and flue gas are established. The change tendency of different parameters of the liquid and gaseous phase along the flue is analyzed by numerical modeling. The desulfurization efficiency is calculated and analyzed as a function of droplet velocity, droplet diameter, gas velocity, gas inlet temperature, SO2 inlet concentration, the volume ratio of liquid to gas, the length of spraying reaction segment, Ca/S, Ca(OH)2 particle diameter. The result shows that droplet diameter, gas velocity, SO2 inlet concentration, the volume ratio of liquid to gas, the length of spraying reaction segment, Ca/S and Ca(OH)2 particle diameter are key parameters that affect desulfurization efficiency most and gaseous diffusion is important to the desulfurization process.4. In the study of experimental and practical applications, we have carried out two experiments and have a technical and economical analysis of the technology for FGD .After a full analysis of the experimental data, the advantages of this new technology are concluded. It's proved that it is economical, effective and particularly suitable for the low-to-medium capacity and reconstruction of boiler's desulfurization system.The study in this thesis offers useful references and guidance for the engineering design and practical operation of the FGD by spraying the ash wastewater in the flue.