| The traditional chemical processing methods such as neutralization, precipitation, flocculation and enrichment are hard to remove chlorine ion in the steam power plant waste water of the FGD. The treated waste water can not be reused in the system for the high concentration of chlorine ion may cause corrosion. If waste heat of boiler gas can be used to treat the FGD waste water by spray evaporation processing, the microns solid particles in waste water and dust suspended in flue will be caught when they entering electrical precipitator and discharged with the ash. The treatment method can not only attain the environmental protection requirement by realizing zero discharging desulfuration, but also make practical value by saving operation costs of units.Meanwhile, it needs as soon as possible to fully evaporate the FGD waste water with spray evaporation processing. If the tiny sprayed droplets of the waste water into the flue gas can not be fully evaporated in a short time, the incomplete evaporated droplets will corrode the gas tunnel and the electrical precipitator. The characteristics of the gas and dust may change in a certain level when the spray evaporation technology is applied. The dust removal efficiency is very sensitive to the properties of the flue gas and dust. Evaporation quality of droplet group, pneumatic crushing characteristics of restricting the droplet evaporation time, droplet evaporation characteristics and the affect on the flue gas in the spray evaporation processing technology are the key study problems. At present, spray evaporation technology has been applied in many fields all the world, such as cooling on power of exhaust system, spray cooling on laser surgery, spraying process. However, the systematic researches on the above key problems of spray evaporation technology are few. Therefore the research on evaporation quality of droplet group, pneumatic crushing characteristics of droplet and the evaporation characteristics will enrich and promote the academic researches of pray evaporation technology. It can also promote the innovation and application of spray evaporation processing technology on FGD waste water.Based on analyzing the capacity of the boiler and the FGD waste water, and the characteristic size of the flue gas, the evaporation treatment system and method on FGD waste water in themal power plant is proposed in the paper. At the same time, the principle of the evaporation treatment and its mechanism are analyzed. Furthermore, the four key problems are studied particularly, including the mass evaporated of the droplet groups and the key factors that influence the mass evaporated, the characteristics of droplets breakup and evaporation, and the effects of evaporation treatment on the dust cleaning of the gas flow. Finally, the concrete scheme of the FGD waste water with evaporation treatment is made, and on the basis of the results of the key problems, the concrete parameters of the evaporation treatment method about the FGD waste water in the 300WM boiler is presented.?The principle of the method of the FGD waste water with evaporation treatment and its research models are gotten. It is found that the effect of the distortion of the droplet on the evaporation rate of the droplet must be considered in numerical study of the FGD waste water with evaporation treatment. The TAB model can also factually reflect the distortion and breakup process of the droplet when the gas flow acts to the droplet after analyzing the principle and the mechanism of the key problems about the FGD waste water with evaporation treatment, such as the mechanisms of the breakup and evaporation of the droplet. Besides, there's no need to consider the effect of the flow circulation inside droplet on the evaporation rate while numerical studying is applied.?The mass evaporated of the droplet group in each unit time is the biggest when the temperature of the flue gas is 453K and the mean diameter of the droplet group is 50?m after analyzing the efficiency of the boiler and the mass evaporated of the droplet group. Regarding to the mass evaporated of the droplet group in the FGD waste water with evaporation treatment, the Eulerian-Lagrangian discrete drop phase model was applied in the numerical study about the effects of the arrangement mode and spraying direction of the nozzles, the temperature and the velocity of the flue gas, and the ratio of the liquid and the gas on the mass evaporated of the droplet group. Little effect on the mass evaporated was found of the arrangement mode and spraying direction of the nozzles, and the velocity of the flue. In contrast, the higher temperature of the flue gas and the bigger mean diameter of the droplet group, the easier the FGD waste water with evaporation treatment can be carried out.?The breakup of the droplet with diameter 0.3mm?0.4mm contributes to cutting the life time of the droplet. With regarding to the characteristic of the droplet breakup in the FGD waste water with evaporation treatment, the Eulerian- Eulerian Volume of Fluid model was applied in the numerical study to investigate its effects on the characteristic of the droplet breakup, such as the velocity and the density of the flue, and the diameter and initial velocity of the droplet, as well as the effect of the mul-droplet colliding on the life time of the droplet. It was found that the breakup of the droplet with diameter 0.3mm?0.4mm contributed to cutting the life time of the droplet as to the circumstance of the flue gas and the droplet considered in the paper. Besides, the function of colliding between the droplets has some benefits.?The life time of the droplet is within 1s when the Ph of the droplet is seven and the diameter of the droplet is not bigger than 50?m. With regard ingto the characteristic of the droplet evaporation in the FGD waste water with evaporation treatment, the mathematic models of the movement and evaporation of the droplet were established after the substance of the droplet considered. The effects of the following factors on the characteristic of the droplet evaporation were studied, such as the substance, diameter and the initial velocity of the droplet, and the temperature and the velocity of the flue gas. It was found that the life time of the droplet was shorter when the Ph value of the droplet was not bigger than seven. The effect of the flue temperature on the characteristic of the droplet evaporation is stronger. The higher flue gas temperature is more beneficial to the FGD waste water with evaporation treatment. The effects of the flue velocity and the initial velocity of the droplet on the waste water with evaporation treatment are very little.?The FGD waste water with evaporation treatment improves the precipitation efficiency. After the application of evaporation treatment, the dust specific resistance is reduced due to the enhancement of the flue humidity and the lowering of the flue temperature, as a result, it's enhancing the precipitation efficiency. Besides, the diameter of the dust become bigger, therefore the precipitation efficiency is more enhanced under taking no account of the second flying upwards of the dust. So, the FGD waste water with evaporation treatment improves the precipitation efficiency to some certain extents.?The concrete scheme and the example of the FGD waste water with evaporation treatmentOn the basis of the research results of the key problems pre-mentioned, the concrete arrangement mode and the number of the nozzles were determined by calculating the volume of the boiler and the waste water, and the characteristic size of the flue gas considered roundly. For the scheme of the FGD waste water with evaporation treatment in 300WM boiler, two rows nozzles, totally 168, were arranged, and the vertical and horizontal distance between the nozzles was 0.3 m and 5 m respectively. This paper expounds the FGD waste water evaporation treatment technology and scheme of the thermal power plant, especially for the characteristic of the mass evaporated of the droplet group, and that of the droplet breakup and the droplet evaporation. It is useful for the deeper investigation of the FGD waste water with wvaporation treatment. The results not only enrich the researches on the desulfuration waste water with evaporation treatment, but also provide theoretical fundament for the relative technology, such as engine exhausting, and the laser surgery, and sprinkling technics. |
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