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.     

“CHCT”催化剂在水泥煅烧中的催化作用探讨

“CHCT”催化剂在水泥熟料煅烧过程中通过对煤炭的催化燃烧进而促进固相反应、液相反应、熟料急冷 ,使用该催化剂可降低水泥生产成本、增加企业经济效益     

Burnability of cement raw materials at rapid calcination conditions

Cement raw materials (clay, limestone and pyrite cinders) were mixed, pressed into pellets, burnt at high temperatures, cooled and the resulting clinkers analysed for free CaO content. The effect of the following parameters and their interactions on the free CaO was studied: top temperature of burning (in three levels: 1300, 1350, 1400°C), soaking time at top temperature (in three levels: 5, 30 and in some cases 60 min), method of heating (in two levels: rapid and normal), method of cooling (in two levels, rapid and slow), lime saturation factor of the mix, LSF (in three levels, 0.95, 0.85, 0.76). Experiments were planned to enable a statistical evaluation (calculation of error variance at various levels of significance). Rapid calcination improves the burnability of cement raw materials, as contrasted to normal calcination. This indicates that rapid calcination enables the use of lower calcination temperatures. A long soaking at top temperature is unnecessary in case of rapid calcination. The free CaO content of the clinker is affected primarily by the LSF of the mix and the top temperature of firing; all other parameters are less effective.     

水泥熟料岩相分析在水泥生产中的作用

预分解窑与湿法窑的工艺差异,其熟料的微观结构能够明显反映;熟料的晶体结构取决于工艺过程,并能判断操作水平的高低;从分解炉结渣的微观结构可以准确地找出原燃材料存在的问题。也就是说,水泥生产过程中的不良环节均能从熟料岩相结构中反映出来。     

水泥窑低氮煅烧自适应控制系统的设计与研发

水泥回转窑系统是连续进出料的高温热工设备,它的热工参数离散,是一个多变量、非线性、强干扰、大滞后的复杂系统。使用传统的机理建模和常规的控制方法,烧成系统污染物排放勉强能够达到环保国标要求,但要进一步降低氮氧化物排放极其困难。利用Elman神经网络进行建模,通过分析及预处理变量数据,优化多维模糊规则表,控制低氮燃烧器,基于理论分析及系统设计,形成一套水泥炉窑低氮煅烧自适应控制系统。试验结果表明,系统对多变量的预测误差低于6%,且实现连续稳定运行近100天。     

C_4烷烃混合热裂解反应机理的数值模拟

通过对蒸汽热裂解反应机理实验研究困难的分析,提出了将Materials studio模拟和Aspen Plus模拟计算相结合的烃类热裂解自由基反应机理的理论研究方法。并用该理论方法对正丁烷和异丁烷及其混合物的相互作用机理进行了研究。结果表明:正丁烷热裂解主要是1-C4H9·中β-C—C键发生的断裂生成乙烯,由2-C4H9·断β-C—C键生成丙烯;异丁烷热裂解主要是i-C4H9·中β-C—C键的断裂生成丙烯。采用与文献[1]同样的原料数据进行模拟,并与该文献中混合C4烷烃热裂解的实验数据进行了对比,说明该理论方法计算得到的结果与实验结果吻合较好。     

Thermodynamic modelling of the hydration of Portland cement

A thermodynamic model is developed and applied to calculate the composition of the pore solution and the hydrate assemblage during the hydration of an OPC. The calculated hydration rates of the individual clinker phases are used as time dependent input. The modelled data compare well with the measured composition of pore solutions gained from OPC as well as with TGA and semi-quantitative XRD data. The thermodynamic calculations indicate that in the presence of small amounts of calcite typically included in OPC cements, C-S-H, portlandite, ettringite and calcium monocarbonates are the main hydration products. The thermodynamic model presented in this paper helps to understand the interactions between the different components and the environment and to predict the influence of changes in cement composition on the hydrate assemblage.     

AOS生产反应机理描述及相关工艺计算

简述了α-烯基磺酸盐(AOS)的特性,通过对AOS磺化反应机理的分析,就反应过程物料组成及相关控制指标进行了理论计算,提供了一系列理论数据,阐述了AOS生产工艺控制关键点。     

Numerical modelling for rotational moulding with non-isothermal heating

Abstract

In the rotational moulding process, the internal air temperature has been widely recognised as a tool to predict an optimum cycle time. This paper presents a new numerical approach to predict the internal air temperature in a two-dimensional (2-D) static model without requiring the consideration of the tumbling motion of polymer powder. The initial non-isothermal heating of the static model is actually formed by two changeable plastic beds (stagnant and mixing beds), which represent the actual stagnant and mixing pools inside a rotating mould respectively. In the numerical approach, the lumped-parameter system and coincident node technique are proposed to incorporate with the Galerkin Finite Element Method in order to account for the complex thermal interaction of the internal air. It helps to overcome the difficulty of multidimensional static models in predicting an accurate internal air temperature during the heating stage of rotationally powdery plastic. Importantly, the predicted temperature profiles of the internal air, oven times for different part thicknesses and process conditions accord with the available experimental results.     

浅谈核电站工程用水泥的生产

介绍了根据核电站建设用水泥的品质要求,通过制订合理的配料方案,选择适合的原、燃料,以及加强对生产过程的控制,终于生产出合格的核电站建设用水泥。     

Continuum lumping modelling for step growth polymerisation mechanism

Polymerisation occurs by chain addition or step-growth mechanisms. The yield and the concentration distribution of monomers, dimers, trimers and higher order polymers can depend on the molecular weight or some other variable which can be unequivocally linked to any given compound. Continuum lumping is a methodology widely used to describe the kinetic and thermodynamic behaviour of complex reactive mixtures of diverse components all undergoing similar types of reactions (e.g., cracking, pyrolysis, oligomerisation). The methodology is particularly convenient when the number of species involved is very large and the species can be characterised by properties which are measured in a continuous fashion, as for instance in a chromatogram. By applying the lumping methodology, a large reactive system can be reduced to a simpler and more tractable one. A model, based on the continuum lumping approach, is proposed to predict the molecular weight distribution of polymers during polymerisation. The main aim of this work is to assess the suitability of the application of the continuum lumping approach to polymerisation. The results obtained from a continuous model are assessed, at this stage, only qualitatively; nevertheless, by analysing the weight distribution and the average of such distribution, conclusions can be reached to assess the predictive capability of the lumping methodology. The model is tested for two selected case studies and the product distribution is obtained at various times.     

脱硫石膏代替天然石膏在水泥生产中的应用

<正>天然石膏是目前水泥行业使用最广泛的缓凝剂原材料,但由于天然石膏为不可再生资源,随着我国水泥工业的不断发展、水泥产量的不断增加,优质的天然石膏资源日益匮乏,价格也是逐年升高。我公司也同样遇到了天然石膏的资源问题以及价格成本     

磷渣用于水泥熟料生产的试验

磷渣是电热法生产黄磷时排出的一种具有潜在活性的低熔点工业废渣。在水泥熟料烧成过程中掺入磷渣能降低熟料烧成热耗、改善熟料矿物组成、提高熟料性能,但在实际使用过程中,会引起结皮加速、烧成工况波动等问题。在生产试验过程中,磷渣掺入量由1%~3%逐渐增加,通过生料配料调整、烧成系统精细控制,最终达到改善生料易烧性、降低熟料热耗、提高熟料质量的目标。     

An integrated knowledge-based approach for modelling biochemical reaction networks

This paper presents a new methodology for constructing cellular network topologies by searching for new binding species and new reactions catalysed by the enzymes present. Our technique is knowledge-based and integrates several steps. Starting from a pre-determined list of enzymes in the system it (i) generates lists of binding species, (ii) constructs a reaction network using these species and (iii) finds pathways through this network, which link different substrates (raw materials) with target metabolites (pathway products). Graph-theory-based analysis of the two-dimensional structures of known binding species is used to compute pharmacophores, the structures and functional groups binding at the corresponding enzymes’ sites. New binding species are obtained by searching in appropriate databases for existing compounds, which contain these pharmacophores. Reactions are constructed by generating all possible combinations of the binding species identified and by testing the feasibility (i.e. the ability to conserve atomic/molecular mass) of each constructed reaction. Generated reactions are required to be linearly independent in order to minimise the complexity of subsequent steps. Finally, pathways through the reaction network are computed to assess important reactions and metabolites for a given process. Our integrated procedure has been applied to two illustrative systems, the glycolysis and the citric acid cycle in Homo sapiens and Saccharomyces cerevisiae, respectively. New binding species and reactions were found for the enzymes involved. It was observed that some enzymes are very specific and only catalyse a small number of very similar reactions. Pathways were also constructed and analysed to demonstrate the relative importance of the metabolites involved.     

The effect of calcination on reactive milling of anthracite as potential precursor for graphite production

The effect of a pretreatment using reactive ball milling and calcination on the graphitizability of an anthracite coal is explored. A thermal anneal of Buck Mountain anthracite at 1400 °C in argon increased the L_c crystallite dimension (from 12 to 20 Å) and led to an increase in the oxidation temperature of the product. Ball milling of the coal reduced particle size with a nominal effect on carbon order and the degree of graphitization after the 1400 °C thermal anneal (L_c from 18 to 29 Å). Ball milling in cyclohexene led to a substantial increase in the graphitizability at 1400 °C (L_c from 12 to 50 Å). The enhanced reactivity was due to both carbon structure and introduced metal. The products of the mechano-chemical pretreatment and thermal anneal consisted of nanographene ribbons and multi-walled nanopolyhedral particles. It oxidized at moderate temperatures and had a high (74.3%) degree of graphitization based on X-ray diffraction analysis; the derived material has potential as filler for production of graphite.     

白水泥生产之浅见

白水泥是一种主要用于建筑装饰的特种水泥,白水泥的矿物组成及生产工艺与普通硅酸盐水泥相似,但是对原料要求十分严格,其生料易烧性差,熟料煅烧温度高。详细介绍了白水泥生产用原燃材料的选择范围和质量要求;采用与普通水泥生产的对比方法,全面分析了白水泥的生产工艺过程及其特点;重点介绍了白水泥白度的影响因素及其提高白度的工艺控制措施。最后,还介绍了白水泥生产的技术进步。     

丙烯生成苯和甲苯反应机理的数值模拟

结合Material Studio软件和Aspen Plus软件计算结果,通过自由基与不饱和烃的加成反应生成大自由基,大自由基再经过环化、脱氢生成五元环,再经由生成苯或甲苯的路径生成相应产物。其中生成苯的路径为环戊二烯基和CH_3·加成、链传递、脱氢、成桥环、桥键断裂,最终脱氢生成苯;生成甲苯的路径为乙炔和环戊二烯基加成、分子内加成、分子内氢转移、桥键断裂,最终链终止反应生成甲苯。将得到的模拟数据分布与文献中的数据进行对比可知,两者吻合良好。     

脱硫石膏在水泥生产中的应用实践

研究了脱硫石膏和天然石膏对水泥性能影响的差异,探讨了脱硫石膏完全代替天然石膏生产水泥的途径,并在实际生产中成功应用脱硫石膏作水泥缓凝剂生产出符合国标要求的水泥。