Study On Desulfurization Performance And Mechanism Of Semi-dry Hydrated Ash

At present,the emission of SO₂ from flue gas of coal-fired boilers is one of the main pollution sources.The most widely used desulfurization technology of power plant boilers is limestone-gypsum method of wet desulfurization,which has been relatively mature.Semi-dry desulfurization has good adaptability to small and medium-sized boilers.No Gap Desulfurization technology developed by China Coal Research Institute utilizes hydrated ash which prepared by mixing fly ash and hydrated lime for cyclic desulfurization.The desulfurization performance of hydrated ash is the key factor determining the desulfurization efficiency of this technology.However,the traditional preparation process of hydrated ash is cumbersome and not economical.In order to combine the preparation of hydrated lime with desulfurization process,the original fly ash or circulating fly ash were mixed with lime to prepare hydrated lime at low temperature and low water content,and the hydrated lime with different water content and mixing ratio was prepared in a hydration reactor.Then the hydrated ash was placed in a fixed-bed reactor and the desulfurization performance was tested with simulated flue gas.Finally,an engineering test was carried out in an airflow bed to study the influence of process conditions on the desulfurization performance of hydrated ash.The main research contents and conclusions are as follows:?1?According to the difference between the desulfurization reaction rate and the diffusion rate of desulfurization curve on the fixed bed,the desulfurization process is divided into two reaction stages:the power section and the transition section.According to the change of desulfurization reaction rate in the desulfurization process of the flow bed,the desulfurization reaction is divided into three regions:the normal reaction zone,the deceleration reaction zone and the pseudo equilibrium zone.The first two regions are the critical stage of the desulfurization reaction,and the removal amount of SO₂ accounts for 89%of the total amount of the inlet SO₂.?2?According to the pore structure of hydrated ash after hydration reaction under different water content and mixing ratio,it is concluded that when the water content is 10%and the mixture ratio is 0:1,the specific surface area of hydration ash is the largest,which is more conducive to the desulfurization reaction.The desulfurization performance of hydrated ash is related to the content of effective material and its pore structure.According to pore structure change of hydrated ash before and after reaction and the desulfurization result on the fixed bed.It is concluded that the change of specific surface area can reflect the degree of desulfurization reaction.?3?By analyzing the desulfurization results on the fixed bed,it can be concluded that when raw fly ash or recycled fly ash is mixed with lime to prepare hydrated ash,the optimum mixture ratio is 3:1 and 1:3,respectively.And as the moisture content increases,the effective desulfurization time increases,and the maximum desulfurization efficiency decreases.In desulfurization test of the flow bed,the higher the water content,the higher the proportion of lime in the ash,and the lower the initial concentration of SO₂,the desulfurization efficiency was higher.?4?According to the results of fixed bed desulfurization,when the water content is 15%and the hydration time is 3h,for hydrated lime prepared by mixing raw fly ash with lime,the optimum desulfurization process conditions are as follows:the desulfurization temperature is 80°C,the initial concentration is 200?L/L,and at this time the effective desulfurization time is 53.13 min,the maximum desulfurization efficiency is 100%.For hydrated lime prepared by mixing circulating fly ash with lime,the optimum desulfurization process conditions are:the desulfurization temperature is 70°C,the initial concentration 200?L/L,and the effective desulfurization time is 93.95 min,the maximum desulfurization efficiency is99.12%.?5?In the desulfurization experiment of flow bed,when the boiler loads are different,the desulfurization reaction time,the reaction temperature,and the initial concentration are different.Therefore,the humidifying water which make the highest utilization rate of the effective material in the hydrated ash are related to the mixture ratio and the boiler load.The higher the ratio of lime,the lower boiler load,the optimum humidification water was smaller.When the boiler load is 76.7%and the humidifying water volume is 0.27 t/h,the mixture ratio of the hydrated ash is3:1-2:1,the utilizationof effective material in the hydrated ash was highest.When the boiler load is 36.7%-100.0%,the corresponding initial concentration of SO₂ is350?L/L-700?L/L.When the humidification water is 0.27t/h and the mixture ratio is1:0,when the initial concentration of SO₂ is 350?L/L-550?L/L,the utilization of effective material in the hydrated ash was highest.