| High hardness water widely exists in people's daily life and industrial production,and the combined water quality pollution of coexistence of hardness and iron and manganese is also increasing,which seriously threatens water supply safety and industrial production.It is imminent to research and develop a technology and equipment that can efficiently remove hardness in water while simultaneously removing iron and manganese in water.Overview of the research progress at home and abroad,chemical crystallization pellet fluidized bed(PFB)technology is a low energy consumption,high-efficiency water softening technology without secondary pollution,but the equipment structure and performance of chemical crystallization PFB need to be further improved,and the application scope has yet to be further expanded.Based on chemical crystallization PFB,a new type of chemical crystallization circulating pellet fluidized bed("circulated pellet fluidized bed")system is studied and developed.This process system can remove hardness and iron and manganese simultaneously.The paper focuses on:(1)induced crystallization kinetics of calcium carbonate and kinetics and modeling of calcium carbonate crystal growth at the bottom of a fluidized bed in chemical crystallization pellet under pilot conditions;(2)simultaneous removal efficiency and mechanism of induced crystallization iron and manganese and the influence mechanism of dynamics for calcium carbonate crystallization;(3)performance study of circulating pellet fluidized bed and optimization of simultaneous removal of hardness and iron and manganese in water;(4)engineering case of chemical crystallization circulating pellet fluidized bed system for simultaneous removal of hardness and iron and manganese in water and analysis of its application.The main conclusions and results are as follows:(1)The factors affecting the dynamics of calcium carbonate induced crystallization and fluidized crystallization were studied,and a model of calcium carbonate crystallization kinetics and a model of the static bed height increasing were established.The experiments show that the growth rate of calcium carbonate-induced crystals is positively correlated with the ratio of p H,supersaturation,and activity of calcium and magnesium ions.The growth rate of calcium carbonate crystals is generally in the order of 10-10m/s.Pilot tests have shown that the growth kinetics of calcium carbonate crystals is positively correlated with rising velocity(Vw)and supersaturation(?),and negatively correlated with seed particle size(dp).When Vw is between 50 and 70 m/h,?is between84.4 and 125.5,and dp is between 0.1 and 0.4 mm,the particle size growth rate model at the bottom of the pellet fluidized bed reactor is G=3.90×10-9Vw1.93dp-1.56?2.13,the model of increasing rate of static bed height is Rh=5.19×10-8Vw1.65dp-0.93?2.58.(2)The effect and mechanism of iron and manganese removal under different conditions were investigated,the influence mechanism of the simultaneous removal of iron and manganese on the kinetics of calcium carbonate crystallization was analyzed,and a circulating pellet fluidized bed tandem process was proposed for the simultaneous and efficient removal of hardness and iron and manganese in water.Experiments show that the removal of iron and manganese is affected by p H,DO and so on,and the effect of p H is stronger than DO.When the concentration of iron and manganese is within4.0mg/L,the p H required for iron removal is higher than 8.5,the manganese requirement is above 10,and the DO requirement for iron removal is lower than manganese.By XPS analysis,iron produced crystalline oxides such as Fe3O4 and Fe OOH during the induced crystallization removal of DO at 5mg/L;manganese produced crystalline oxides of manganese such as Mn(OH)O,Mn2O3,and Mn O2 during the induced crystalline removal process.These crystalline oxides promote heterogeneous nucleation of calcium carbonate and accelerate the growth rate of calcium carbonate crystals.In the pilot test,the concentration of iron and manganese in the water was 1.5mg/L and the flow rate was 60m/h to 100m/h,when Ca(OH)2 was added,the circulating pellet fluidized bed could stably remove iron and manganese,the surface morphology of calcium carbonate particles is loose,and the surface is mainly composed of Fe2O3,Fe OOH,Mn(OH)O,Mn2O3 and Ca CO3.(3)A new type of chemical crystallization circulating pellet fluidized bed reactor has been developed,and its performance characteristics and application advantages have been mastered through pilot and engineering applications.The chemical crystallization circulating pellet fluidized bed reactor has higher crystallization efficiency than the traditional fluidized bed reactor.The particle size of the discharged particles is 2mm-3mm.The particle discharge cycle is more than doubled and it has stronger impact resistance and stability than traditional fluidized bed reactor.(4)A new process of CO2 utilization in circulating pellet fluidized bed of coal-fired power plant based on the concept of circular economy and carbon dioxide emission reduction is proposed.The pilot test showed that the new technology of circulating pellet fluidized bed process system using CO2 to remove high permanent hardness in water and adjust the p H of effluent has the advantages of low cost,good effect,high operation safety and stable performance.CO2 utilizes a new process to effectively use the CO2 waste gas generated by coal-fired power plants.The entire system has no waste water or waste.It realizes the circulation of carbon elements in the system and continuously converts carbon elements from gaseous(CO2)to stable solid(gypsum)output.The system effectively reduced carbon emissions and improved the level of circular economy development of coal-fired power plants.(5)Based on the study and development of the chemical crystallization circulating pellet fluidized bed technology and the optimization of the system process,the system is applied to the engineering practice of simultaneous removal of hardenss and iron and manganese in Dingzhou Power Plant and Jingye Power Plant and all indicators meet the design requirements.The engineering case shows that all the indexs in the Jingye Power Plant project designed a 200m3/h circulating water softening and simultaneous removal of iron and manganese project meet the design and produciton requirements.Dingzhou Power Plant water quality softening project capacity reaches 1200 m3/h-1500 m3/h,hardness removal rate can reach 40%-50%,maximum removal rate of calcium ions can reach 90%,softened effluent water quality is stable;Ca CO3 content in discharged particles is higher 90%,Ca O content is higher than 50%.It is directly used in the desulfurization system of Dingzhou Power Plant,and no waste water is generated in the entire system.Due to the implementation of this system,the circulating water concentration ratio of Dingzhou Power Plant can be increased from 4.5 to 9 times,and the amount of supplementary water and sewage can be reduced by 150 m3/h.The project can save 1.5 million yuan every year and energy saving and emission reduction effect is significant,which has greate environmental,economic and social benefits.Through the engineering application,the developed technology is truly applied to the actual situation,and the existing practical problems of the enterprise are solved. |
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