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.     

食用氯化钾生产工艺节能改造

在蒸发结晶法生产食用氯化钾工艺中,存在高能耗、高碳排放的问题。每生产1 t食用氯化钾需消耗2 t蒸汽,而80%的蒸汽消耗产生在氯化钾的结晶过程中。为了解决这个问题,利用DTB结晶器和MVR蒸汽压缩技术对结晶工艺进行了改造。结果表明：改造后工艺与原工艺相比,结晶工段蒸汽实现零消耗,总的蒸汽消耗降至0.4 t,蒸汽消耗减少80%,每1 t产品成本节约了 280元,以年产1万t食用氯化钾计,生产系统可节约成本 280万元;同时,二氧化碳的排放量也比过去减少80%以上,实现了节能减排的目的。     

含氯废弃物燃烧过程中HCl排放特性

引　言生活垃圾中含有的有机氯主要以PVC塑料的形式存在 ,我国塑料制品中PVC占 30 %以上 ;无机氯通常以NaCl的形式存在于厨余中 ,单独焚烧厨余物 (主要含无机氯化物 )会导致大部分氯化物转化为HCl[1] .郭小汾等[2 ] 研究了PVC的燃烧特性和HCl的析出机理 ,认为PVC的燃烧过程分为     

Modelling wood combustion under fixed bed conditions

A computer model describing the conversion of wood under packed-bed conditions is presented. The packed bed is considered to be an arrangement of a finite number of particles, typically sized between 5 and 25 mm, with a void space left between them. Each particle is undergoing a thermal conversion process, which is described by a one-dimensional and transient model.Within the single-particle model, heating, drying, pyrolysis, gasification and combustion are considered, whereby each particle exchanges energy due to conduction and radiation with its neighbours. Because of the one-dimensional discretization of the particles, heat transfer and mass transfer is taken into account explicitly. Therefore, no macrokinetic data are needed within the model. For ease of implementation and access, kinetic data and property data are stored in a database. The global conversion of the packed bed is represented by the contributions of single particles, where each particle is coupled to the surrounding gas phase by heat and mass transfer. For gas phase flow through the porous bed, the conservation equations for mass, momentum and energy are solved on a Cartesian mesh by a Finite Volume method.Experiments have been performed to validate the single particle model for the conversion of beech wood during pyrolysis and char combustion. Agreement between experimental and predictions obtained by the model is very satisfactory. However, for wet wood, changes in structure seem to enhance the heat transfer to the solid which is not yet covered in the model.     

Effect of Turbulence of the Freeboard on Fluidized-Bed Biomass Combustion

Fluidized-bed combustion is a very popular technology used to convert solid biomass into thermal energy, which has many advantages over other conversion technologies. However, these advantages strongly depend on the freeboard combustion. This study focuses on the effect of turbulence of the freeboard via developing a comprehensive mathematical model including four-way coupling, biomass thermal decomposition, and turbulent combustion by means of an Eulerian-Lagrangian framework. The validated model predicts with significant accuracy for all gas species when turbulence modeling is improved. The optimum amount of the secondary air ratio and the optimum excess air ratio were determined, which give a higher freeboard temperature while maintaining minimum emission.     

川东达州地区地下卤水75 ℃等温蒸发析盐规律研究

四川东部达州地区地下卤水资源丰富,卤水储量约为8.23×10⁸ m³,富含钠、钾、锂、硼、铷、溴等元素。实验研究了该卤水在75 ℃等温蒸发过程中溶液pH变化规律、各种元素在溶液和固相中的富集规律,并通过X射线衍射（XRD）检测析出矿物的种类,确定了矿物的析出顺序。实验研究结果表明：溶液pH随着蒸失率的增加而降低;氯化钠在整个蒸发过程中大量析出,氯化钾在蒸失率达到77.3%时开始大量析出,蒸发接近末尾时钙、硼都有部分析出;蒸发过程中矿物的析出顺序为氯化钠→氯化钠+氯化钾→氯化钠+氯化钾+硼酸,蒸发过程中的析盐规律与K⁺,Na⁺,Mg²⁺//Cl^--H₂O（75 ℃）四元相图吻合。根据蒸发实验数据初步设计出卤水资源利用工艺路线。该研究结果为川东地下卤水的开发和综合利用提供了可靠的基础数据。     

硫酸镁型光卤石转化钾盐镁矾的过程机制与动态规律

硫酸镁的存在影响光卤石矿加工的钾盐收率和产品质量。通过对一里坪盐湖硫酸镁型光卤石进行等温不完全分解实验,研究了钾盐分解转化机制和动态特征,并建立了钾盐转化过程的动态模型。结果表明：（1）硫酸镁型光卤石在加水过程迅速分解,而经过3~4 h诱导期,氯化钾与硫酸镁会逐渐转化为钾盐镁矾,经过50 h系统达到平衡,总钾量的近55%转化为钾盐镁矾,约20%溶于分解液,仅25%以固相氯化钾存在;（2）转化过程中,如有硫酸镁水合物存在,会出现“固、液相点不动的介稳态”假象,而实际上是氯化钾和硫酸镁水合物转化为钾盐镁矾的动态过程,当固相硫酸镁水合物缺失,液相点会向氯化钠、氯化钾、钾盐镁矾、光卤石的四盐共饱点移动;（3）钾盐镁矾生成的动力学方程的反应推动力（离子活度积与共饱点活度积之差）级数为1.5,产物存量的影响指数为2/3,反应速率常数为3.907×10^-4 mol^1/3·min^-1,动力学方程与全组分物料方程构成了动态模型,可量化表达转化过程中任意时刻固液混合体系的状态。这一研究结果对改善盐湖钾资源利用过程具有重要指导意义。     

硫酸镁型光卤石转化钾盐镁矾的过程机制与动态规律

硫酸镁的存在影响光卤石矿加工的钾盐收率和产品质量。通过对一里坪盐湖硫酸镁型光卤石进行等温不完全分解实验,研究了钾盐分解转化机制和动态特征,并建立了钾盐转化过程的动态模型。结果表明：(1)硫酸镁型光卤石在加水过程迅速分解,而经过3～4 h诱导期,氯化钾与硫酸镁会逐渐转化为钾盐镁矾,经过50 h系统达到平衡,总钾量的近55%转化为钾盐镁矾,约20%溶于分解液,仅25%以固相氯化钾存在;(2)转化过程中,如有硫酸镁水合物存在,会出现“固、液相点不动的介稳态”假象,而实际上是氯化钾和硫酸镁水合物转化为钾盐镁矾的动态过程,当固相硫酸镁水合物缺失,液相点会向氯化钠、氯化钾、钾盐镁矾、光卤石的四盐共饱点移动;(3)钾盐镁矾生成的动力学方程的反应推动力(离子活度积与共饱点活度积之差)级数为1.5,产物存量的影响指数为2/3,反应速率常数为3.907×10^-4mol^1/3·min^-1,动力学方程与全组分物料方程构成了动态模型,可量化表达转化过程中任意时刻固液混合体系的状态。这一研究结果对改善盐湖钾资源利用过程具有重要指导意义。     

丙烯腈装置尾气催化燃烧本征动力学

消除内外扩散影响后, 在微型固定床积分反应器中开展了国产HPA型负载贵金属催化剂上一氧化碳、丙烯和丙烷单组分及其三组分混合物催化燃烧的实验研究。采用程序升温脱附（TPD）手段考察了反应物在催化剂上的吸附脱附情况, 据此推测可能的反应机理, 建立了单组分催化燃烧的Eley-Rideal速率模型。运用最小二乘估计和单纯形优化搜索方法对模型参数进行了估值, 反应物转化率的模型计算值与实验值吻合良好。同时, 将所得单组分动力学模型叠加用于预测多组分催化燃烧时, 转化率的计算值与多组分实验结果相容。     

节能技术在硝酸钾生产中应用

在硝酸钾生产中采用节能技术主要有:蒸汽直接加热溶解氯化钾、空气冷却结晶、蒸发后溶解硝酸铵、二效蒸发、干燥机空气加热器串联进蒸汽等,这些节能技术应用后能显著降低硝酸钾能耗与生产成本,可使吨硝酸钾降低2622kg蒸汽消耗。     

三效错流降膜真空蒸发低浓度氯化铵废水工艺

离子交换法生产碳酸钾流程中排出的废液严重污染环境。分析了含氯化铵工业废水蒸发回收过程中的技术难点，确定了回收的工艺流程，采用三效错流降膜真空蒸发工艺，有效地解决了能耗过高、设备腐蚀严重、氯化铵升华等技术难题。该工艺具有流程简单、设备和运行费用低的特点，经实际应用，取得了很好的经济效益和社会效益。     

烘焙生物质燃烧过程中钾的赋存形态及析出迁移特性

选取稻秆和棉秆为原料,在烘焙预处理后,通过固定床燃烧实验结合HSC Chemistry热力学平衡计算,获得了烘焙生物质燃烧过程中碱金属K的析出和迁移规律。结果表明：烘焙过程中存在着少量水溶性K的释放及其向醋酸铵溶态K的转化,而其转化和释放能力与Cl/K呈正相关。烘焙生物质的成灰率随着燃烧温度的升高而下降,而K的释放率随温度的变化则相反,其主要释放形式为K的氯化物和KOH;此外,600℃时,水溶性K和醋酸铵溶态K主要转化为char-K,700~900℃时其主要转化为K的硅酸盐,随着温度的上升,其转化量不断增加。相比于原生生物质,烘焙生物质有更高的成灰率;此外,烘焙促进了生物质燃烧过程中醋酸铵溶态K向酸溶态或残渣态K转化,同时抑制了水溶性K的释放,这些使得烘焙生物质燃烧过程中K的释放率更低,而烘焙对生物质燃烧过程中K释放的抑制与烘焙过程中Cl的释放率呈正相关。     

Formation and reduction of nitric oxide in fixed-bed combustion of straw

Mechanisms of nitric oxide (NO) formation and reduction in fixed-bed combustion of straw have been modeled mathematically and verified experimentally. The model for the straw combustion and nitrogen chemistry consists of sub-models for evaporation, pyrolysis, tar and char combustion, nitrogen conversion, and energy and mass conservation. Twenty chemical reactions are included, of which 12 belong to the fuel nitrogen reaction network. Volatile nitrogen is assumed to be NO, NH₃, HCN and HNCO, and char nitrogen is converted to NO during char oxidation. The model predictions are in qualitative agreement with the measurements during the ignition phase, i.e. when the combustion front passes through the un-burnt fuel. The yield of NO can be reduced considerably by using a low primary air flow due to the longer gas residence in the fixed-bed, while the NO exhaust concentration is insensitive to the bed temperature. The NO exhaust concentration initially reaches a maximum and then decreases towards a stable value after the straw bed is ignited. Variations of NO, NH₃, HCN, and HNCO concentrations in the ignition flame front indicate that a large quantity of NO can be reduced in the thin flame front zone. The developed model is further validated by separate experiments in which NO or NH₃ was added at the middle through tubes or at the bottom of the bed with the primary air flow. Both the simulations and measurements showed that the variation of the NO exhaust concentration is small as compared with the injected NO or NH₃ concentration. According to the simulations and experiments, it is proposed that flue gas recirculation may be a very effective method of reducing NO emissions from flue gas in the fixed-bed combustion of straw. Calculations indicated that about 20% of the flue gas may be recirculated without significantly affecting the combustion behavior.     

In-field direct combustion fuel property changes of switchgrass harvested from summer to fall

Switchgrass, a perennial warm-season grass and potential energy crop, is usually harvested during the time between full maturity in the fall to the following spring. During this wide harvest window, the changes in fuel properties that could occur are important for making appropriate decisions with respect to the optimum harvest time for maximum fuel quality. A field plot study was carried out to investigate the quantitative fuel properties (proximate, ultimate and mineral analyses) of switchgrass over a harvest period from crop maturity in July through November. Harvest moisture decreased from July to November and moisture was uniformly distributed in the switchgrass plant at all times in the harvest period. There were significant differences in ash, volatiles, fixed carbon and nitrogen among months of harvest. Nitrogen, ash and fixed carbon contents decreased while oxygen and volatiles increased through the harvest period. Also, there were significant differences in oxides of silicon, calcium, potassium, phosphorus and sulfur among harvest times. The concentration of oxides of potassium and sulfur decreased at the end of the harvesting period. Fouling and slagging indices decreased as harvest was delayed but remained low throughout harvest. However, the decreases are small and might not dramatically impact fouling and slagging. Overall, the results appear to favor a later harvest for switchgrass used for direct combustion. This study will benefit feedstock producers as well as biomass feedstock facility operators by providing a better understanding of how the properties of switchgrass vary over a typical harvest period and their potential effect on boiler equipment.     

CH4掺混H2的燃烧数值模拟及掺混比合理性分析

本工作针对天然气掺氢燃烧技术在燃气锅炉的最佳掺混比开展数值模拟研究,以小火焰燃烧器为研究对象,计算了在空气氛围、恒定过氧系数、不同甲烷掺混氢气比条件下,掺氢比对燃料燃烧温度、燃烧速率、主要污染物排放浓度的影响.其中燃烧机理采用GRI-MECH 3.0简化机理,该反应包含24个基元反应,涉及17种组分.计算结果表明,随掺...     

煤化工高盐废水复分解法制备硫酸钾实验研究

煤化工厂生产甲醇和轻烃过程会产生大量废液,将废液经过反渗透和纳滤膜浓缩以及减量处理可以得到高盐废水。以高盐废水为原料,将其浓缩至对硫酸钠饱和,然后采用两步转化法（复分解法）制备硫酸钾：第一步,向浓缩废水中加入氯化钾制备钾芒硝,产生的母液蒸发一部分水分得到氯化钠,向蒸发后的母液中加入硫酸钠得到浓缩母液,回收利用母液;第二步,以钾芒硝为原料加入氯化钾制备硫酸钾。考察了高盐废水浓缩倍率、氯化钾加入量、蒸发水量对钾芒硝纯度及产率的影响;考察了加水量、氯化钾加入量对硫酸钾纯度及产率的影响。得出以高盐废水为原料制备硫酸钾的适宜条件：制备钾芒硝过程,高盐废水浓缩倍率为4.35,以500 g浓缩废水为基准,氯化钾加入量为84.25 g,蒸发水量为100 g;制备硫酸钾过程,以100 g氯化钾为基准,钾芒硝用量为153.08 g,加水量为322.06 g。在此条件下得到的硫酸钾中水溶性氧化钾的质量分数为52.96%、氯离子质量分数为1.09%,符合GB/T20406—2017《农业用硫酸钾》优等品的要求。制备钾芒硝过程,母液循环利用3次,总有机碳（TOC）对钾芒硝的纯度影响不大,对白度有影响;钾芒硝与氯化钾制备硫酸钾产生的母液K,经过投加硫酸钠制备钾芒硝得到母液K″,母液K″与浓缩废水制备钾芒硝产生的母液F组成基本一致,验证了循环工艺路线的可行性。     

热重-红外联用分析制革污泥的燃烧特性

利用TG-FTIR对制革污泥的燃烧特性和燃烧过程气体释放情况进行了研究。研究发现,制革污泥挥发分和灰分含量较高,固定碳含量低、热值低。不同升温速率下,制革污泥的燃烧在800℃时已经比较充分,随着升温速率的增加,制革污泥碳燃烧的失重速率和峰值温度有所增加。运用Ozawa法进行活化能计算表明,制革污泥燃烧所需活化能随着反应程度的深入而增加。制革污泥的挥发分燃烧阶段符合三维扩散的Z-L-T方程反应模型,固定碳燃烧阶段符合自催化反应的P-T方程反应模型,且制革污泥在不同升温速率下燃烧动力学参数存在动力学补偿效应。TG-FTIR分析表明,不同升温速率对气体析出基本特征没有影响,在低温阶段,制革污泥的燃烧产物中有少量的有机酸组分析出。     

Study of the Radiation Emitted During the Combustion of Pyrotechnic Charges. Part II: Characterization by Fast Visualization and Spectroscopic Measurements

Ignition and combustion of pyrotechnical mixtures in a closed volume are studied with an inflammatory device. In a previous study, both, measurements and numerical simulations showed, that the burning phenomena are very fast, with a typical duration of about 200 μs. Temperature measurements by a two‐color pyrometer made it possible to evaluate the temperature as a function of time. The temperature seems to reach a constant level during the first 50 μs of combustion. Then the radiance continues to increase, obtaining a decrease of the temperature which reaches approximately 3000 K. These temperature measurements indicate that the radiative medium (the flame) is a gaseous phase with a high density of particles. In order to check this assumption, spectroscopic measurements have been made and are presented in this study. The results are commented by visualization of fast camera recordings confirming that the combustion phenomena can be separated into two stages: before 50 μs and after 50 μs. The first part of the process corresponds to the optical emission of a very hot gas which can be a potassium plasma, assumption justified by the presence of an intense emission line of neutral potassium identified at 770 nm. In this first stage, a few particles contribute to the optical emission. The second stage of the process reveals a typical grey body spectrum, being a medium charged with particles. The experimental spectrum reveals gradually the absorption lines at the wavelengths of the atomic lines observed in the first stage. The assumption of a cold gas surrounding a hotter reacting area seems to be confirmed for the second part of the combustion.     

Nitric oxide conversion in hydrocarbon-fuel flames in two-step combustion

On the basis of the kinetic model of nitrogen oxide conversion in hydrocarbon-fuel combustion, the stages of NO conversion are calculated and the degree of conversion in multistage combustion is determined. The calculation results are compared with industrial test data. The limiting degree of conversion in industrial-furnace conditions is estimated.Alma-Ata. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 4, pp. 16–20, July–August, 1993.     

Kinetic model of the medium for formation of combustible nitrogen oxides in a coal-dust flare

A kinetic model of the medium (least complicated kinetic mechanism) is constructed for the formation of combustible nitrogen oxides in coal-dust flares. The model includes both the yield kinetics of volatiles from the coal with formation of a fuel gas mixture and the chemical reaction kinetics in the gaseous phase, which describe the conversion of nitrogen-containing components into NO during the combustion of the volatiles. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 2, pp. 23–29, Mach–April 1999.