MATHEMATICAL MODEL FOR REDUCTION OF COKE FORMATION DURING HYDROCARBON PYROLYSIS USING ADDITIVES

A mathematical model has been developed to simulate reduction of coke formation by additives during hydrocarbon pyrolysis. In this model it is assumed that the formation of coke is mainly due to surface catalytic reactions. The adsorption of additive agents on the reactor surface, therefore, effectively reduces the formation of coke. Using this model, it is found that the higher the additive concentration the faster the formation of the protective layer, and hence the rate of coke formation approaches its steady state value more quickly. The developed model is simple and the predicted results are reasonable.     

二氯乙烷裂解管式反应器二维模拟

建立了二氯乙烷在管式反应器中进行气相热裂解的二维模型 ,模型考虑了二氯乙烷热解生成氯乙烯的主反应和生成焦前体的副反应以及气体密度变化对裂解反应的影响 .模拟计算表明 ,二氯乙烷和氯乙烯的浓度沿径向分布平坦 ;但是管内近壁面处由于存在边界层 ,始终存在着明显的径向温差 ;近管壁处始终是裂解的高速率区 ,副反应也主要发生在管壁区 .表明确定最优的炉管管径时必须考虑提高裂解速率与降低结焦速率之间的平衡 .在距进口量纲 1管程 0 .3左右的管壁处裂解速率达到最高 ;副反应速率的最大点位于出口管壁处 .与工业数据比较后发现 ,炉管出口的转化率、选择性、出口压力和温度等数据与模型预测值一致 ,表明模型具有较高的可信度     

应用经遗传算法优化的BP神经网络预测催化裂化装置焦炭产率

焦炭是催化裂化装置的主要副产物,准确预测催化裂化焦炭产率对提高装置的操作平稳度和经济效益具有重要意义。人工神经网络(ANN)具有强大的自学习和自适应能力,在非线性预测方面具有明显的优势。本研究将遗传算法(GA)与BP神经网络相结合,基于某炼厂催化裂化装置的生产数据,分别从原料、催化剂和操作条件3个方面选取28个关键影响参数建立了催化裂化焦炭产率预测模型,分别将BP神经网络和经遗传算法优化的BP神经网络(GA-BP)的预测结果与工业数据进行对比。结果表明,经遗传算法优化的预测模型无论在预测结果的准确性还是稳定性方面效果更好。最后,本研究还通过考察原料残炭、反应温度等单一关键参数对焦炭产率的影响,进一步证明了经遗传算法优化的BP神经网络预测模型的准确性。     

Coke deposition and run length in industrial naphtha thermal cracking furnaces via a quasi-steady state coupled CFD model

Mathematical modelling of the thickness of the coke layer growing over months in millisecond cracking reactors is a dilemma in computational fluid dynamics (CFD) simulation. To address the time scale issue, a quasi-steady state (QSS) approach was employed through a comprehensive coupled reactor/firebox CFD model in the current study. The model was applied to predict the time-dependent behaviour of coke deposition and to determine the appropriate operating conditions for maximum olefin yields over an industrial furnace run length. A novel algorithm was designed to overcome the complexity of QSS simulation of the CFD model, which is a combination of reactive turbulence flow, combustion, and radiation models. The furnace parameters were studied as a function of two variables: the dilution steam-to-feed ratio and the liberated heat by the burners. The results indicated that the run length can be extended by up to 20% while retaining the main product yields. This study offers practical suggestions to maximize the run length in the operation.     

Outlet Temperature Correlation and Prediction of Transfer Line Exchanger in an Industrial Steam Ethylene Cracking Process

Predicting the best shutdown time of a steam ethylene cracking furnace in industrial practice remains a challenge due to the complex coking process. As well known, the shutdown time of a furnace is mainly determined by coking condition of the transfer line exchangers （TLE） when naphtha or other heavy hydrocarbon feedstocks are cracked. In practice, it is difficult to measure the coke thickness in TLE through experimental method in the complex industrial situation. However, the outlet temperature of TLE （TLEOT） can indirectly characterize the coking situation in TLE since the coke accumulation in TLE has great influence on TLEOT. Thus, the TLEOT could be a critical factor in deciding when to shut down the furnace to decoke. To predict the TLEOT, a paramewic model was proposed in this work, based on theoretical analysis, mathematic reduction, and parameters estimation. The feasibility of the proposed model was further checked through industrial data and good agreements between model prediction and industrial data with maximum deviation 2% were observed.     

Systematics and modelling representations of LPG thermal cracking for olefin production

Pyrolysis of hydrocarbons is an important commercial process for the production of ethylene, propylene and 1,3 butadiene. These low molecular weight olefins are among the most important base chemicals for the petrochemical industries for polymer production. A simulation program of the reaction kinetics and coke formation inside the coils of a thermal cracking unit can provide information on the effects of operating conditions on the product distribution. The aim of this study was to develop a mechanistic reaction model for the pyrolysis of LPG that can be used to predict the yields of the major products from a given LPG sample with commercial indices. A complete reaction network, using a rigorous kinetic model, for the decomposition of the LPG feed has been developed, which is used for the simulation of industrial LPG crackers. This model has been adapted using industrial data for the pyrolysis yields of LPG. The present paper attends on the asymptotic coking mechanism and describes the development of a kinetic coking model in the pyrolysis of LPG. Detailed and accurate information about the product distribution, growth of coke layer, the evolution of the tube skin temperatures can be obtained from this simulation. Simulations of this kind can be used to optimize the furnace operation. They can be used as a guide for the adaptation of the operating variables aiming at prolonging the run length of the furnace. The reactor model, as well as kinetic scheme, is tested in an industrial cracking furnace.     

烃类裂解结焦机理的研究

烃类高温裂解生产乙烯过程中 ,炉管管壁结焦不仅导致传热系数下降 ,压力降增大 ,管子腐蚀 ,还会堵塞炉管 ,影响裂解炉正常运转 ,因此研究结焦机理 ,从而更有效地抑制结焦一直受到人们的重视。结焦过程涉及到不同形式的焦油和炭的复杂过程 ,虽报道的文章很多 ,但确切机理尚不清楚。目前综合国内外的有关文献报道 ,对烃类热裂解过程中的结焦机理进行了详细综述 ,着重阐述了以金属碳化物为中间产物的金属催化反应 ,即金属催化结焦 ;非催化结焦 ;自由基结焦三种结焦机理。同时叙述了用此三种结焦机理如何解释实验室和工业装置的结焦状况。为进一步探索结焦机理开发新的结焦抑制技术奠定了一定的基础。     

Investigation of the effect of presulphidation on coke deposition on 25Cr-35Ni alloy during ethane steam cracking

The process of hydrocarbons cracking is carried out in the presence of heat-resistant alloys Fe-Ni-Cr, which HP40 alloy (25Cr-35Ni) has the most applications among olefin plants. Since these alloys naturally tend to form coke, the industry has always tried to reduce the coke formation by reducing the catalytic properties of the coils. In this research, the effect of dimethyl disulphide (DMDS) concentration (200–900 ppm) on the HP40 alloy of industrial coils at the presulphidation stage is evaluated. In the presulphidation stage, the alloy surface is in contact with sulphur in the absence of hydrocarbons, and this affects the amount of coke formation in the cracking process. Also, the surface composition and morphology of coke are identified using EDX and SEM analysis. These results showed that at the 500 ppm concentration of DMDS, coke deposition is minimized. Additionally, our findings indicated that coke morphology has not changed under different presulphidation conditions, and coke is still a filament type, but the size of the filaments has changed. Moreover, the study of HP40 composition in both preoxidized and presulphide stages shows that presulphidation reduces the amount of Fe and Ni in the coke layer significantly.     

Carbonization of pitch

An overview is presented of the many factors which influence the process of carbonization of pitch and hence the properties of pitch cokes. The controlling factors include type of starting material, the industrial process of carbonization, the role of quinoline-insoluble material and carbonization conditions. Several coke parameters are studied and related to the carbonization process by multiple regression analysis. Kinetic data are presented together with a schematic model of coke formation.     

煤系针状焦生产用延迟焦化加热炉清焦技术的研究

针对延迟焦化生产中延迟焦化加热炉炉管结焦的现象,研究了现有清焦工艺,提出对于煤系针状焦延迟焦化加热炉采用传统的蒸汽-空气清焦工艺技术是可行的,并给出了具体实施方案与操作要点。     

乙烯裂解炉结焦抑制技术研究

介绍了乙烯裂解炉的结焦机理、影响结焦的主要因素和抑制炉管结焦的主要技术。     

光纤内窥图像法测量MTO催化剂表观形貌及其积炭量的实验研究

催化反应过程中的多尺度现象一直是近年来颗粒学领域研究的热点，其中颗粒形貌、积炭都是影响催化剂流态及活性的关键参数。为了从颗粒尺度深入探究积炭对催化剂颗粒表观形貌的影响，选取了DMTO工艺中第二代分子筛SAPO-34催化剂，在实验室微型固定流化床反应器中制备了停留时间分别为0、30、60、90、120 min等多种催化剂样品。使用课题组研制的光纤内窥显微成像平台，拍摄了催化剂样品的微尺度图像，并以此构建了基于深度学习的样本形貌图像库，实现批量统计催化剂颗粒表观特性（包括粒径、球形度、椭圆比、色度等参数及其分布）的功能。测量结果表明：积炭会明显改变催化剂的粒径及其分布，但是对催化剂的球形度或椭圆比等参数的影响较小。通过比较这些催化剂样本图像的色度信息与其对应的热重法测得的积炭量数据，建立了催化剂色度信息与其积炭量之间的定量关系，并预测了两种来自某企业DMTO生产装置反应器内催化剂的平均积炭量。实验数据表明：图像色度法与热重法测量结果的相对误差小于10%，具有较好的一致性。这将有助于发展基于图像色度法测量催化剂积炭量的工业仪表，为工业过程从颗粒尺度认识反应器内催化剂的状态提供便携的观测手段，进而指导操作人员对DMTO工艺进行优化调控。     

乙烯裂解炉结焦抑制技术研究

介绍了乙烯裂解炉的结焦机理、影响结焦的主要因素和抑制炉管结焦的主要技术。     

生物油非催化热转化过程中受热结焦特性研究进展

生物油在受热条件下极易结焦,结焦是影响生物油规模化利用的重要因素之一,因此深入理解生物油受热结焦特性是实现生物油高效热转化利用的基础。本文从生物油热解过程的关键反应参数（温度、升温速率、气氛、压力、灰分）、生物油化学成分、生物油有机组分间交互作用、自由基反应特性等方面综述了生物油受热结焦特性相关研究进展,总结了反应参数对生物油热解结焦反应网络的影响,梳理了生物油各特征组分单独热解结焦及特征组分间交互作用对结焦特性的影响机制,并基于生物油结焦机理和焦炭的物化特性,总结了通过定向调控生物油结焦反应过程,将焦炭作为燃料和炭材料的潜在利用途径。最后,指出了明晰生物油受热结焦机理还需从生物油组分间交互作用机制和自由基反应机理的角度进一步探究。本文为实现生物油高效热转化利用提供了理论参考和借鉴。     

RC031连续重整催化剂的工业试生产

在不降低RC031（生产型号）催化剂比表面积的情况下,可实现降低高铂型连续重整催化剂积炭速率和提高芳烃收率。催化剂的工业试生产结果表明,在反应条件相同情况下,与原有高铂型连续重整催化剂相比,具有选择性高、积炭速率低、水热稳定性好、持氯性能强和再生性能优良等特点。连续重整装置在不增加再生能力的前提下,可以在更高苛刻度或更高处理量下操作,最大限度地增加装置的经济效益。     

单孔炭化室底砖更换的工艺过程

焦炉是由各种耐火砖砌筑而成结构复杂的工业窑炉。焦炉在生产过程中由于很多原因,会使焦炉耐火砖出现剥蚀或损坏,为了保证焦炉的连续生产,炉体的各项维修一般都在热态修补下进行。文章简要介绍了单孔炭化室底砖整体更换的工艺过程,供同行参考。     

应用煤岩理论预测焦炭强度

以 4 0kg焦炉试验为基础 ,用数理统计法优选出镜质体最大反射率平均值及胶质层最大厚度 ,建立了预测生产焦炉焦炭强度的数学模型。     

钢铁工业技术进步及焦炭生产能力布局变化对焦炭市场的影响

分析了炼铁、炼钢工艺技术进步,以及焦炭生产能力布局变化对焦炭市场的影响。指出在近期内高炉炼铁仍是主要炼铁工艺,焦炭有稳定的市场需求。目前焦炭市场供大于求的局面通过国家产业政策的调控和优胜劣汰的市场竞争,可望在短期内达到供求关系的基本平衡。     

电炉制磷对焦炭质量要求

介绍了焦炭理化特性，分析了焦炭各组分对电炉法生产黄磷的影响，部结了黄磷生产经验，指出了炉料中焦炭粒度大小变化对电炉制磷生产的影响十分敏感。提出了加强科学管理，严把焦炭质量关，逐步完善焦炭加工工艺和设备，建议推广使用料斗式电子称配料计量设备，使炉料称量准确和混合均匀，使电炉生产正常。     

焦炭质量预测方法的应用

以太原煤炭气化(集团)有限责任公司的工业焦炉数据为基础,建立了该公司的焦炭质量预测模型。利用单种煤和配合煤的各种性质指标预测焦炭质量,并指导配煤,以获得稳定的焦炭质量。