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。     

催化裂化装置防结焦技术研究

结焦是影响催化裂化装置长周期运行的重要原因之一。本文从催化裂化工艺和实际生产出发,根据沉降器的结焦部位、焦块的形态和构成归纳出导致沉降器结焦的三大成因——湿催化剂粘附结焦、重组分油冷凝结焦和缩合反应结焦。文章认为湿催化剂粘附是提升管、旋分器料腿和沉降器内结焦的主要原因;重组分冷凝是旋分器升气管外壁、沉降器内和转油线结焦的主要原因。本文还论述了包括原料性质、原料汽化率、油气停留时间、粗旋与顶旋的连接方式和设备等五大影响沉降器结焦的主要因素,并总结提出避免或减缓沉降器结焦的措施。     

乙烯裂解的结焦及抑制

分析了乙烯裂解中的结焦现象,讨论了影响结焦的主要因素,并综述了抑制结焦的方法。     

催化裂化装置防结焦技术研究

从催化裂化工艺和实际生产出发,根据沉降器的结焦部位、焦块的形态和构成归纳出导致沉降器结焦的三大成因-湿催化剂粘附结焦、重组分油冷凝结焦和缩合反应结焦。原料油在催化剂上不能完全汽化形成湿催化剂,油浆中重组分在沉降器内以汽液两相形式存在,缩合反应生成液相的重组分,这些为结焦提供了物质基础。分析认为湿催化剂粘附结焦是提升管、旋分器料腿和沉降器内结焦的主要原因;重组分冷凝是旋分器升气管外壁、沉降器内和转油线结焦的主要原因。论述了包括原料性质、原料汽化率、油气停留时间、粗旋与顶旋的连接方式和设备的影响等五大影响沉降器结焦的主要因素,并总结提出避免或减缓沉降器结焦的措施。     

催化裂化装置防止结焦措施

本文介绍了呼和浩特石化公司催化裂化装置的防止结焦的措施，分析了结焦的主要部位和结焦原因，提出了减轻结焦的措施。     

CFB锅炉结焦分析与预防

分析了循环流化床锅炉结焦的影响因素，认为主要是床料对结焦的影响、燃料特性对结焦的影响、密相区的燃烧份额对结焦的影响，从而提出结焦事故预防措施，保证了循环流化床锅炉的正常稳定运行。     

合成氨多级压缩级间换热器结焦机理分析

合成氨生产中多级压缩级间换热器的结焦是一个普遍存在且急需解决的共性问题。以贵州开磷集团公司合成氨作为研究对象,对结焦现象和结焦机理进行了分析研究。通过对级间换热器中的焦垢及退役结焦换热管进行了XRD、SEM、IR以及金相学表征分析,发现原料气杂质硫化氢是影响结焦的主要因素,结焦机理主要以金属催化结焦和硫化氢腐蚀生焦占主导地位,同时还伴有腐蚀和渗碳现象。     

S Zorb装置反应进料换热器E101快速结焦情况分析

某石化S Zorb装置反应进料换热器E101开工三天内快速结焦,装置被迫隔离换热器进行检修,通过分析结焦过程,对垢样化验分析,说明此次结焦与行业普遍结焦情况不同,认为催化汽油性质极差是导致此次快速结焦的主要原因,并提出相应预防措施。     

溶剂油系统结焦问题的研究

针对溶剂油系统结焦问题开展了室内试验研究,研究表明氧气是造成结焦问题的主要原因,并探讨了解决结焦问题的对策.     

溶剂油系统结焦问题的研究

针对溶剂油系统结焦问题开展了室内试验研究，研究表明氧气是造成结焦问题的主要原因，并探讨了解决结焦问题的对策。     

Modelling coke formation in an industrial ethane-cracking furnace for ethylene production

The development of a model for predicting coke formation in an industrial ethylene cracking furnace is described. Expressions for predicting the rates of catalytic and pyrolytic coke formation are developed and a differential equation is derived to predict changes in coke thickness with time and position. An expression is developed to account for a decline in the rate of catalytic coke formation with increasing thickness of the coke layer. The proposed coke model equations are used to extend a previously developed ethane pyrolysis furnace model that ignored coke. Three model parameters related to coke formation are estimated using industrial data to obtain reliable model predictions. Two of these parameters are coefficients that appear in the catalytic and pyrolytic coke formation rate expressions. The third is a characteristic-length parameter used to reduce the rate of catalytic coke formation as the coke layer grows. The resulting dynamic model matches the industrial data well and can be used to simulate furnace operation and predict coke thickness profiles over a variety of the operating conditions, thereby helping process engineers who plan the decoking process.     

石油加工过程中焦炭形成的原因、类型及影响因素

回顾了多种烃类分子裂解生焦的机理,指出多环芳烃是石油加工过程中焦炭形成的反应中间体。从分子化学反应水平上综述了3种生焦机理:多相催化结焦、多相非催化结焦、均相非催化结焦,研究表明:较高温度下烷烃催化裂解过程中,焦炭的组成与裂解反应深度有关,但不受烷烃分子结构的影响;热裂解过程中,异构烷烃的生焦速率大于正构烷烃,烯烃、芳烃具有较大的生焦趋势,且芳烃裂化的生焦量与物质的碱性对数线性相关。依据显微结构的不同,焦炭可以分为3类:点状焦炭、镶嵌状焦炭和纤维状焦炭,相关研究表明:焦的结构特性与中间相形态有关,可塑性好的碳质中间相易聚合、溶并形成各向异性的纤维状焦炭。工艺过程中,原料的性质、催化剂及添加剂种类、工艺操作条件等因素都会影响焦炭的生成。     

催化裂化结焦反应的研究进展

综述了近年来催化裂化结焦反应的研究进展情况,重点介绍了结焦反应的影响因素、焦炭对催化反应的影响、结焦机理以及焦炭的表征4个方面。研究认为,原料的性质、反应温度、催化剂的类型等因素均会对焦炭的生成产生影响。焦炭可以导致催化剂的失活,而位于孔道内部的焦炭对反应物或产物的扩散不利,进而影响产物的分布。研究表明,各种烃类组分形成焦炭的过程都必须经历芳香烃这一步。对于结焦催化剂可以采取多种表征手段,其中利用XPS以及GC-MS对焦炭进行表征的报道日益增多。尽管国内外对于催化裂化结焦反应的研究开展较早,然而探究焦炭的具体成分仍存在不小的困难,通过先进的表征手段鉴定焦炭中高缩合度芳烃组分以及如何减小催化裂化催化剂的结焦量将成为未来的研究方向。     

In situ Monitoring of Coke Deposits during Coking and Regeneration of Solid Catalysts by Electrical Impedance‐based Sensors

The activity of solid catalysts is often substantially reduced by the formation of coke. The in situ monitoring of the coke load of catalyst particles could therefore be a controlling instrument of high value. Such sensors could be useful to measure the axial coke profile in a fixed bed reactor, both during coke formation and regeneration by coke burn‐off. As a contribution to the development of such sensors, single particles of an alumina oxide catalyst were used as a model system. The particles were electrically contacted and characterized by electrical impedance spectroscopy. The coke formation/burn‐off and the impedance were simultaneously measured in a magnetic suspension balance. A clear relationship between the coke loading and the respective electrical impedance signal could be observed, both during coke formation and during the regeneration by coke burn‐off. Kinetic studies were conducted to verify the influence of mass transfer limitations on the impedance signal.     

Coke Formation on Pt?CSn/Al2O3 Catalyst in Propane Dehydrogenation: Coke Characterization and Kinetic Study

The influences of gas compositions on the rates of coke formation over a Pt?CSn/Al₂O₃ catalyst are studied. The coke formed on the catalyst is characterized by thermal gravimetric analysis, IR spectroscopy, Raman spectroscopy and elemental analysis. Two kinds of coke are identified from the TPO profiles and assigned to the coke on the metal and the coke on the support, respectively. The coke formed on the metal is softer (containing more hydrogen) than that formed on the support. The rate of coke formation on the metal is weakly dependent on the propylene and hydrogen pressures but increasing with the propane pressure, while the rate of coke formation on the support is increasing with the propane and propylene pressures and decreasing with the hydrogen pressure. Based on the kinetic analysis, a mechanism for the coke formation on the Pt?CSn/Al₂O₃ catalyst is proposed, and the dimerization of adsorbed C₃H₆ is identified to be the kinetic relevant step for coke formation on the metal.     

Coke formation during cracking of hydrocarbons. I. The effect of pre-sulphiding on coke formation on a nickel-chromium-iron alloy under steam cracking conditions

Studies have been carried out on the effect of pre-sulphiding a nickel-chromium-iron alloy on coke formation under steam cracking conditions. Pre-sulphiding has no great effect on the gaseous product spectrum as long as some sulphur is present, but the coking rate is dependent on the amount of sulphur pre-deposited. Small amounts of sulphur reduce the coke formation, but the coking rate increases with increasing amounts of pre-deposited sulphur. As the sulphur content increases still further, coke formation passes through a maximum. A tentative explanation of these observations is advanced in terms of the effect of metal sulphides on the established mechanism of coke formation. Initial sulphiding is suggested to increase grain boundary penetration by coke and to result in the accumulation of iron sulphide on the surface. Eventually this may act to seal off grain boundaries, thereby inhibiting further coke formation.     

Residua coke formation predictability maps

The dispersed particle solution model of petroleum residua structure was used to develop predictors for pyrolytic coke formation. Coking Indexes were developed in prior years that measure how near a pyrolysis system is to coke formation during the coke formation induction period. These have been demonstrated to be universally applicable for residua regardless of the source of the material. Coking onset is coincidental with the destruction of the ordered structure and the formation of a multi-phase system. The amount of coke initially formed appears to be a function of the free solvent volume of the original residua. In the current work, three-dimensional coke make predictability maps were developed at 400, 450 and 500 °C for four residua with nominal H/C atomic ratios of 1.4. The maps relate residence time and free solvent volume to the amount of coke formed at a particular pyrolysis temperature. Coke formation reactions can be modeled with zero-order kinetics which occur in two stages. The first stage produces 22.5-27.0 wt% coke with activation energies ranging from 22,000 to 38,000 cal/mol. The second stage continues the reaction to completion, producing 58.1-63.6 wt% coke with activation energies ranging from 54,000 to 83,000 cal/mol. The activation energies correlate with the original residua free solvent volumes. The results provide a new tool for ranking residua, gauging proximity to coke formation, and predicting initial coke make tendencies.     

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.     

Inductive effect of basic nitrogen compounds on coke formation during the catalytic cracking process

This paper proposes a mechanism for the inductive effect of quinoline on coke formation during the catalytic cracking of o-xylene. Quinoline preferentially adsorbs on the acidic sites to induce coke formation and promote the conversion of o-xylene via electrophilic substitutions and hydrogen transfer reactions. The presence of naphthyl-quinolines and benzyl-quinolines in soluble coke identified by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and the characterization of two types of nitrogen species in coke by XPS both confirm that the mechanism is reasonable. Basic nitrogen compounds poison the acidic sites of catalysts and induce the coke formation from aromatics.