Calcination of phosphate in impinging streams. Part I. development,theory and modeling

An impinging-stream reactor, developed and tested for calcination of phosphate with low organic matter content, has proven to be an efficient device for conducting this process. Modeling of the calcination process has been done along two lines. Considering a single particle and assuming that calcination rate is controlled by the heat transfer in the particle, resulted in a criterion for testing the effect of temperature on the enrichment of P205 and other phenomena. Performing a heat balance on the reactor and on the particle, and incorporating physical concepts, led to correlations with only one adjustable parameter for the conversion of carbonates as a function of the operating parameters. The major conclusion drawn from implementation of the model was that phosphate calcination is governed by the internal resistance of the particle to the heat transfer. The calcination efficiency results, as well as the practical experience gained in this study, indicated that the impinging-stream calciner may provide a promising tool for phosphate enrichment, and more generally, for processes involving gas-solid contact at high temperatures.     

轻烧氧化镁气流床煅烧炉热工过程及煅烧风量研究

轻烧氧化镁气流床煅烧炉热工行为研究是其热工参数优化、实现节能降耗的必需的基础性工作之一。基于Euler-Lagrange理论建立了某企业轻烧氧化镁气流床煅烧炉数值计算模型,籍此研究了炉内气固流动、传热及分解过程基本规律,并确定了现有产量下的适宜煅烧风量。结果表明：主炉内煅烧烟气旋流上升,温度中心高、壁面低;副炉内旋流效应骤减,温度趋于均匀;距离烟气入口4~18 m行程范围内,气固换热剧烈,物料快速分解,分解率达96%,而后于24 m处分解完全。将煅烧风量降至原有风量的91.22%、气料体积质量比降至1.46 Nm³/kg,不但提高了炉窑空间利用率,同时吨产品燃耗降低了8.78%。     

Mathematical modeling of an in-line low-NOx calciner

The reduction of the NO_x content in in-line-calciner-type kiln systems can be made by optimization of the primary firing in the rotary kiln and of the secondary firing in the calciner. Because the optimization of calciner offers greater opportunities the mathematical modeling of this reactor is very important. A heterogeneous, dynamic mathematical model for an in-line low-NO_x calciner based on non-isothermal diffusion-reaction models for char combustion and limestone calcination has been developed. The importance of the rate at which preheated combustion air was mixed into the main flow was particularly studied. The results of the simulations indicate that the external heat and mass transfer to the char particles is not limiting. Internal diffusion of O₂, CO, NO and CO₂ is important especially in the reducing zone and the first part of the oxidizing zone of the calciner and the internal heat transport limitation is significant for the endothermic limestone calcination. The rate at which preheated combustion air is mixed into the main flow directly influences the coal combustion rate, and thereby through the rate of heat release from combustion, it also influences the calcination rate and the temperature profile. The mixing rate has some influence on the CO concentration profile and an important influence on the overall degree of fuel-N to NO conversion.     

石灰石和白云石高温循环脱除CO2过程分析

在N2气氛和高浓度CO2气氛两种典型锻烧气氛下,对石灰石和白云石在循环煅烧/碳酸化捕集CO2过程中的主要系统参数包括长周期循环碳酸化转化率、平均碳酸化转化率、CO2捕集效率和煅烧炉能量需求进行了实验研究和计算分析.结果表明,吸收剂补充流率和吸收剂循环流率对平均碳酸化转化率、CO2捕集效率和煅烧炉所需能量具有直接影响.在...     

Measurement of residence time distribution in a rotary calciner

Rotary calcination is widely used in catalyst manufacturing and many other industrial processes. In this article, the influence of operational variables and material properties on the mean residence time (MRT), hold up, and axial dispersion was investigated in a pilot plant rotary calciner. Residence time distributions (RTD) of spherical, cylindrical, and quadrilobe catalyst particles were measured and contrasted. The Saeman's model was successfully applied to predict the experimental bed depth and the MRT as particles flowed through the calciner. It was observed that increasing the feed rate did not significantly affect the MRT. Results for the different particles indicated that cylinders and quadrulobes exhibited less axial dispersion than spheres due to the decreased flowability. A reliable method was developed to provide a reasonable RTD prediction in rotary calcination systems. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4068–4076, 2013     

聚磷酸钙镁的制备研究

针对湿法磷酸渣和磷尾矿难以利用的问题,提出了一种焙烧湿法磷酸渣和磷尾矿的混合物制备聚磷酸钙镁肥的策略。基于磷尾矿分解率得出磷尾矿与磷酸渣的适宜质量比为0.30,在此条件下磷尾矿的分解率为80.18%。煅烧工艺结果表明,升高温度和延长时间都能促使聚磷酸盐链的增长。在焙烧时间为1 h条件下焙烧温度从105 ℃逐渐升高到460 ℃,聚磷酸钙镁中磷的平均聚合度从1.00逐渐增加至3.23。其中,焙烧温度为340 ℃时,聚磷酸钙镁中磷的聚合率超过85%,但是聚合度还在增加。尽管肥料的水溶性随着聚磷酸盐链的增长而逐渐降低,但是当焙烧温度≤340 ℃时有效磷含量依然大于90%（质量分数）。在340 ℃焙烧1.0~2.0 h后发现,当焙烧时间为1.0 h时,聚磷酸钙镁中磷的聚合率和平均聚合度分别达到87.4%和2.80。通过工艺条件优化,可在聚合度分布水平上实现聚磷酸盐的可控制备,这也开辟了一种构建缓释肥的新方向。在340 ℃聚合1.0 h优选出聚合度为1~10分布的聚磷酸钙镁,表现为多孔的非晶态结构,其中有效磷、钙、镁养分含量超过85%（质量分数）,可作为一种新型的多元缓释肥。     

LiFePO_4材料的溶胶凝胶法合成及其粒度研究

采用溶胶凝胶法合成了橄榄石型LiFePO4材料。运用XRD、SEM和激光粒度分布仪等手段对材料进行表征。研究了反应体系pH值、煅烧温度、煅烧升温速率和柠檬酸用量等工艺参数对LiFePO4粒径和粒度分布、物相组成和结构等物性的影响。得到的适宜工艺条件为：反应体系pH值为3.57,煅烧温度800℃,煅烧升温速率7℃/min,柠檬酸用量3.5∶1.0。同时分析了各因素对LiFePO4材料粒度分布的影响机制,重点讨论了反应过程机理和煅烧过程机理。     

Numerical modelling of flow and transport processes in a calciner for cement production

Controlling the calcination process in industrial cement kilns is of particular importance because it affects fuel consumption, pollutant emission and the final cement quality. Therefore, understanding the mechanisms of flow and transport phenomena in the calciner is important for efficient cement production. The main physico-chemical processes taking place in the calciner are coal combustion and the strongly endothermic calcination reaction of the raw materials. In this paper a numerical model and a parametric study are presented of the flow and transport processes taking place in an industrial calciner. The numerical model is based on the solution of the Navier-Stokes equations for the gas flow, and on Lagrangean dynamics for the discrete particles. All necessary mathematical models were developed and incorporated into a computational fluid dynamics model with the influence of turbulence simulated by a two-equation (k-ε) model. Distributions of fluid velocities, temperatures and concentrations of the reactants and products as well as the trajectories of particles and their interaction with the gas phase are calculated. The results of the present parametric study allow estimations to be made and conclusions to be drawn that help in the optimization of a given calciner.     

Thermal Decomposition of Potassium Titanium Hexacyanoferrate（Ⅱ） Loaded with Cesium in a Fixed Bed Calciner

The thermal decomposition of potassium titanium hexacyanoferrate（ Ⅱ ） （KTiFC） loaded with cesium （referred to as Used Exchanger,or UE） was-studied at different flow rate of air in a fixed bed calciner. The calcina t ign processconsisted of four stages：ambient temperature- 180℃ （stageⅠ ）, 180-250℃（stage Ⅱ）, 250-400℃ （stage Ⅲ）, and constant 400℃ （stage Ⅳ）.The most intense reaction occurred in stage .Ⅱ. The rate of thermal decomposition was controlled, depending on the O2 flux, by O2 or CN concentration in ditterent stages. Results from differential thermal analysis （DTA） showed that the calcination reaction of the anhydrous UE was exothermic, with an approximate heat output of 4.6kJ·g^-1, which was so large to cause the possible agglomeration of calcined residues. The agglomeration could be avoided by enhancing heat transfer and controlling the O2 flux. It was found that there was no cyanides in the calcined residues and no CN-bearing gases such as HCN and （CN）2 in the off-gas. It seemed that the catalytic oxidation furnace behind the fixed bed calciner could be cancelled.     

Modeling of in-line low-NOx calciners—a parametric study

Simulations with a heterogeneous model of an in-line low-NO_x calciner, based on non-isothermal diffusion-reaction models for char combustion and limestone calcination combined with a kinetic model for NO formation and reduction, are reported. The analysis shows that the most important hydrodynamic parameter is the mixing rate of preheated combustion air into the sub-stoichiometric suspension leaving the reducing zone and the most important combustion parameter is the char reactivity. Also, the calcination rate modifies very much the temperature in the calciner, char and limestone conversion and NO emission. Carbon monoxide is a key component for the reduction of NO and reliable data for the kinetics of NO reduction by CO over CaO are very important for the prediction of the NO emission. The internal surface area of char and limestone particles influences the combustion and calcination rates and thereby the char and limestone conversion and the NO emission.     

Removal of Phosphate from Aqueous Solution with Modified Bentonite

Bentonite combined with sawdust and other metallic compounds was used to remove phosphate from aqueous solutions in this study. The adsorption characteristics of phosphate on the modified bentonite were investigated, including the effects of temperature, adsorbent dosage, initial concentration of phosphate and pH on removal of phosphate by conducting a series of batch adsorption experiments. The results showed that 98% removal rate of phosphate was obtained since sawdust and bentonite used in this investigation were abundantly and locally available. It is concluded that modified bentonite is a relatively efficient, low cost and easily available adsorbent for the removal of phosphate from aqueous solutions.     

磷酸铵镁沉淀与沸石吸附组合工艺处理海水中的氨氮

大量陆源营养物质的输入是导致我国近岸海域富营养化问题的主要原因, 传统生化法对海水中氮磷处理能力有限, 天然沸石凭借较强的选择性离子交换性能已成为一种较为经济和高效的水处理材料。本研究通过穿透实验考察了天然沸石对海水中氨氮的动态吸附性能, 采用磷酸铵镁(MAP)沉淀和沸石吸附组合工艺对海水中氨氮进行处理。实验结果表明, 天然沸石吸附氨氮达平衡时间随过滤速度的增大而减小, 随滤层高度的增加而增大, Logistic模型能较好反映天然沸石对海水中氨氮的动态吸附过程。MAP沉淀法与沸石吸附法联用可以将海水中氨氮含量降低至较低水平, 适宜的滤柱过滤条件为:滤速20L/h, 滤层高度100cm。通过焙烧或NaCl浸洗处理能够恢复天然沸石对海水中氨氮的吸附能力, 300℃焙烧2h和1.5mol/L NaCl溶液浸洗24h条件下的再生率分别为99.38%和122.22%。     

对罐式煅烧炉几个问题的讨论及设计改进

能否取消炭素罐式煅烧炉蓄热室,关键在于当空气预热程度降低时挥发分燃烧能否达到煅烧所需的温度(质的要求);能否取消外加燃料系统,真正作到无燃料煅烧,关键在于挥发分燃烧提供的热量能否满足煅烧需要的热量(量的要求)。从理论计算和实际经验两个方面对罐式煅烧炉的几个问题进行具体的分析和探讨,并从炉子设计的角度提出了改进措施。     

高温煅烧脱除磷酸铁中硫的研究

磷酸铁是合成磷酸铁锂电池正极材料的主要原料,目前多采用硫酸亚铁和磷酸盐共沉淀方法制备。硫酸体系内共沉淀获得的磷酸铁中硫杂质含量较高,目前采用水洗方式脱除,吨磷酸铁洗水用量需60~100吨,硫酸盐废水处理成本高。为从源头削减磷酸铁脱硫过程产生的大量废水,根据硫酸盐高温分解的性质,提出磷酸铁高温煅烧脱硫新方法,开展了热力学可行性计算与高温煅烧脱硫动力学研究。结果表明,磷酸铁中硫元素主要以硫酸根形式存在,高温煅烧可有效促进含硫杂质分解,温度越高,脱硫效果越好。高温煅烧脱硫过程反应动力学级数为2,活化能为88.075 kJ/mol,属于化学反应控制。在温度1173 K、煅烧时间10 min的条件下,磷酸铁中硫杂质含量可降至0.01wt%以下。     

分解炉内煤矸石悬浮煅烧的数值模拟

煤矸石制备水泥辅助胶凝材料的应用研究对水泥行业的节能减排与大宗固废的高值利用均具有重要意义。本文以河北某地不同矿区的6种煤矸石为原料，采用XRD，热重等方法分析判断其化学成分和矿物组成，通过静态煅烧实验研究了其煅烧活化条件，并通过胶砂实验测定其胶凝活性。结果表明，煅烧温度和时间会影响产品的胶凝活性，煤矸石经过适当的热处理后，可用作辅助胶凝材料替代部分水泥熟料，在实现煤矸石资源化利用的同时，也为水泥工业碳减排提供了新路径。但煤矸石成分复杂，活化煅烧需要注意煅烧制度。采用CPFD（Computational Particle Fluid Dynamics）数值模拟方法模拟了分解炉内煤矸石传热、传质及化学反应，分析了不同工况下分解炉内气固两相流场。结果表明：入炉空气的温度较低时无法点燃煤矸石中的可燃组分，通过高温烟气点火和分级司料可有效解决这一问题。     

回转煅烧炉窑制取轻质氧化镁的技术经济评价

根据装置的实际运行状况，从技术经济角度具体分析了以煤为燃料的新型连续回转煅烧炉窑与土法间歇式固定炉窑的差别，认为新法在诸多方面都优于旧法，从而为碳酸镁的煅烧制取轻质氧化镁提供了一条先进有效的途径。     

Characteristics and applications of flash metakaolins

This paper presents physical, chemical and mechanical characteristics of metakaolins obtained from an industrial flash calciner, in order to compare their properties with standard industrial metakaolin produced in a rotary kiln calciner. Three kaolins, with three levels of purity, were calcined by these two different methods to give six different metakaolins for the study. The results showed that the method of calcination did not affect the chemical composition of the metakaolins formed but did influence their physical properties and performance as a supplementary cementitious material when blended with Portland cement, and in geopolymer synthesis. Flash metakaolins have a lower water demand than rotary metakaolins, which can be explained by the morphological properties of the flash metakaolin, induced by the calcination process. Traditional rotary-calcined metakaolins tend to be angular layered particles, whereas flash metakaolins contain spherical particles. Mechanical test results showed that the two methods of calcination can lead to metakaolins with equivalent performance in the synthesis of construction materials.     

Removal of phosphates from aqueous solutions by using bauxite. I: Effect of pH on the adsorption of various phosphates

In this study, the effect of pH on adsorption of various forms of phosphate onto bauxite was investigated. For this purpose, the adsorption and desorption of inorganic (ortho and condensed) and organic phosphate species were studied. It was observed that the adsorption tendency of the various phosphate forms was different and depended on pH. Maximum adsorption efficiencies for all phosphate forms were achieved in slightly acidic conditions (pH 3.2–5.5). The results of adsorption and desorption studies showed that the adsorption of phosphates onto bauxite is based on a ligand exchange mechanism. The adsorption mechanism of inorganic condensed phosphates and organic phosphates is thought to be more complex than that of orthophosphate. It can be stated that the adsorption of organic phosphates is dependent on the functionality, number, and variety of organic groups. The results of experiments carried out with mixed phosphate solutions showed that the adsorption yields of various phosphate forms are dependent on the composition of the solution. The relative adsorptivity of various phosphates was found to be in the general order of hexametaphosphate > pyrophosphate > orthophosphate > tripolyphosphate > adenosine triphosphate > glycerophosphate > glucose‐1‐phosphate. © 2001 Society of Chemical Industry     

磷矿研磨细度与酸解转化率的关系

磷矿粉研磨细度与磷矿酸解转化率关系的研究结果表明,磷矿粉细度是影响过磷酸钙生产中磷矿酸解反应速率和分解率的敏感因素.只有将磷矿粉的细度过100目的比例控制在95%以上,并且使其中通过200目的达50%以上,才能使磷矿酸解转化率达到95%以上.     

无水磷酸氢钙的制备研究

研究以二水磷酸氢钙为原料,采用煅烧法生产无水磷酸氢钙。通过生成的水蒸汽压,煅烧时间为3h,煅烧温度140℃,产品质量可达孟山都公司食品用无水磷酸氢钙标准。