Experimental Research On Crystallization Of Ammonium Sulfate By Flue Gas Direct Heating

Typical technology and equipment of ammonium sulfate crystallization in Ammonia desulfurization process are analyzed and a new type of gas-liquid direct heat crystallization system has been designed by improvement and innovation on the traditional ammonia flue gas desulfurization technology. The system provides the advantages of energy-saving, environmental protection, high heat transfer efficiency and easy scaling because Steam Heating system has been abolished by gas-liquid direct heat evaporating to crystallize ammonium sulfate using of flue gas thermal energy.The mathematical analysis of crystallization and gas-liquid direct heat evaporation process is conducted. The relevant formulas of crystallization kinetics and heat and mass transfer of gas-liquid heat evaporation are derived. The experimental setup and measurement methods of key parameters are designed by analyzing of Influencing factors of crystallization and heat transfer process.The experimental study on flow characteristics of heating evaporation process of crystallizer were carried out and the effect of flue gas flow, gas distributor type, crystallizer flow patterns and solution viscosity on bubble size and distribution and on the bed void fraction were analyzed. The main results are described as follows. Solution viscosity has a decisive impact on bubble size and distribution. In air-ammonium sulfate system, the average diameter of the bubble is only about 0.5 mm and particle size distribution is even. The effect of solution viscosity on bed gas holdup is associated with crystallizer flow patterns. Increase of the viscosity in straight bubble column can enhance the bed gas holdup, but the effect of viscosity on the bed gas holdup can be neglected in circulating bubble column. Under the experimental conditions, the range of average gas holdup in crystallizer using single jet gas distributor is from 0.12 to 0.17 and the average gas holdup in the main bed is from 0.40 to 0.70.The experimental study on crystallization characteristics of crystallizer were carried out and the effect of flue gas flow, gas distributor type, crystallizer flow patterns and the initial temperature of hot-air on the ammonium sulfate crystal size distribution and yield were analyzed. The main results are described as follows. Hot air flow is a key means to control ammonium sulfate crystal yield and the initial temperature of hot air is important parameter to control ammonium sulfate crystal size and yield. The size and yield can improve by using circulating bubble column. Under the experimental conditions, there are larger size, more even distribution and higher yield of ammonium sulfate crystal in circulating bubble column crystallizer using single jet gas distributor, in which the range of ammonium sulfate crystals main particle size is from 180μm to 420μm. By adjusting the initial temperature of hot air, the range of ammonium sulfate crystals main particle size can be increased from 200μm to 2000μm in circulating bubble column crystallizer using single jet gas distributor. The circulating bubble column crystallizer using single jet gas distributor is an ideal efficient energy-saving crystallization system because its heat exchanger efficiency is 88.6% by calculating experimental date.