乙烯裂解炉耦合模拟中湍流模型的影响分析

配备底部烧嘴和侧壁烧嘴的乙烯裂解炉应用越来越广泛，不同燃烧模式影响着炉膛内湍流流动状态，考虑到裂解炉中湍流流动与燃气喷料、燃烧和传热有较强的非线性耦合作用，为此探究不同湍流模型在裂解炉/反应器耦合模拟中的影响对于裂解炉的精确设计和优化至关重要。针对不同湍流模型对某十万吨工业乙烯裂解炉进行了耦合模拟，利用CFD数值模拟对采用标准k-ε模型、RNG k-ε和Realizable k-ε模型所建立的湍流流动模型进行评估。将三种湍流模型的模拟结果与工业数据进行比较，重点分析了裂解炉内的速度、温度、湍流能力等参数的分布情况，表明Realizable k-ε模型在火焰稳定性、反应效率等方面优于其他两种模型，且基于Realizable k-ε湍流方程的反应管模型在热通量、炉管外壁温度分布计算结果更接近实际工况。     

Coupled simulation of combustion with heat transfer and cracking reaction in SL-Ⅱ industrial ethylene pyrolyzer

采用计算流体力学(CFD)方法对SL-Ⅱ型工业乙烯裂解炉辐射段炉膛内的燃烧传热及管内石脑油裂解反应过程进行耦合模拟,建模及耦合求解在CFX中完成。计算时采用标准k-ε双方程湍流模型、旋涡耗散/有限化学速率(EDM/FRC)燃烧模型和离散传播(DT)辐射模型,其中介质辐射特性采用多灰气加权模型;石脑油裂解反应采用Kumar分子反应模型,流体流动方程组由全隐式的耦合算法求解。模拟结果与工业数据吻合良好,验证了模型的可靠性。结果表明,管内裂解产物丙烯和丁烯收率先增后减,甲烷和乙烯收率一直增大;出口管外壁温度沿管长分布因侧壁烧嘴的加入而更加均匀;炉膛中部的回流区使该区温度更加均匀;裂解炉结构的非对称性引起烟气流速分布不对称,进而导致后墙上侧壁烧嘴的供热效率相对前墙侧较低,本文模拟结果为裂解炉进一步设计与改造提供理论指导。     

乙烯裂解炉耦合模拟中湍流模型的影响分析

配备底部烧嘴和侧壁烧嘴的乙烯裂解炉应用越来越广泛,不同燃烧模式影响着炉膛内湍流流动状态,考虑到裂解炉中湍流流动与燃气喷料、燃烧和传热有较强的非线性耦合作用,为此探究不同湍流模型在裂解炉/反应器耦合模拟中的影响对于裂解炉的精确设计和优化至关重要。针对不同湍流模型对某十万吨工业乙烯裂解炉进行了耦合模拟,利用CFD数值模拟对采用标准k-ε模型、RNG k-ε和Realizable k-ε模型所建立的湍流流动模型进行评估。将三种湍流模型的模拟结果与工业数据进行比较,重点分析了裂解炉内的速度、温度、湍流能力等参数的分布情况,表明Realizable k-ε模型在火焰稳定性、反应效率等方面优于其他两种模型,且基于Realizable k-ε湍流方程的反应管模型在热通量、炉管外壁温度分布计算结果更接近实际工况。     

SL-Ⅱ型工业乙烯裂解炉内燃烧传热与裂解反应的耦合模拟

采用计算流体力学(CFD)方法对SL-Ⅱ型工业乙烯裂解炉辐射段炉膛内的燃烧传热及管内石脑油裂解反应过程进行耦合模拟,建模及耦合求解在CFX中完成.计算时采用标准k-ε双方程湍流模型、旋涡耗散/有限化学速率(EDM/FRC)燃烧模型和离散传播(DT)辐射模型,其中介质辐射特性采用多灰气加权模型;石脑油裂解反应采用Kuma...     

天津乙烯6台裂解炉全部投用空气预热器

裂解炉空气预热器项目是中石化集团公司2006年重点推广的节能降耗项目，其思路是利用乙烯装置中的余热来加热裂解炉的燃烧空气，以达到节省裂解炉燃料气，降低装置能耗的目的。在乙烯装置的能耗中，燃料气占80％左右，因此降低燃料消耗是降低装置能耗的重要手段。为此，天津乙烯装置在6台裂解炉上投用了空气预热器。     

乙烯在线

天津乙烯6台裂解炉全部投用空气预热器裂解炉空气预热器项目是中石化集团公司2006年重点推广的节能降耗项目,其思路是利用乙烯装置中的余热来加热裂解炉的燃烧空气,以达到节省裂解炉燃料气,降低装置能耗的目的。在乙烯装置的     

大型乙烯裂解炉用低NOx燃烧器的结构优选

随着大能力大型化裂解炉的不断发展,国内首台单炉膛20万吨/年产能乙烯裂解炉对燃烧器提出了更高的设计要求,在稳定燃烧的同时还要满足特定的工艺要求和严苛的环保要求。采用CFD技术和热态试验方法优选新型乙烯裂解炉用低NO_x燃烧器,通过数值分析方法研究不同底部与侧壁供热比(底侧比)下裂解炉内的燃烧状态(火焰形状、火焰长度、炉内温度分布及NO_x排放量等),结果表明：在底侧比为70:30时燃烧状态最优,炉膛内温度分布均匀且满足工艺要求和环保要求。在热态试验炉上对最终设计工况(底侧比72:28)进行热态试验,结果显示:炉内燃烧状态良好,温度分布均匀且满足热通量曲线,NO_x排放量也较低。     

低NOx燃烧器在扬子石化10万吨乙烯裂解炉上的应用

为满足环保要求,扬子石化烯烃厂10万吨裂解炉低氮改造选用低NO_x燃烧器并对其炉膛燃烧情况进行了CFD模拟。将该燃烧器应用于扬子10万吨乙烯裂解炉后,实际操作和运行情况表明,完全满足裂解炉的工艺和环保要求。     

空气预热器在乙烯裂解炉上的应用

为减少乙烯装置燃料气消耗,采用急冷水的热量对裂解炉空气进行预热,并对国内某乙烯装置裂解炉进行了改造,在裂解炉底部空气入口安装空气预热器。通过对比空气预热器投用前后的相关数据得出,该装置燃料气单耗降低了3 kg/t,每年产生的经济效益500万元。     

乙烯装置裂解炉的烧焦过程模拟

裂解炉炉管内壁的烧焦过程是个炉管温度、压力、浓度和焦炭厚度随时间,沿空间变化的动态过程。基于蒸汽-空气法烧焦机理分析,假定沿炉管烧焦反应动力学参数和反应热不变,建立了蒸汽-空气烧焦过程机理模型。针对中石化镇海炼化分公司乙烯装置裂解炉BA104的实际烧焦参数结合有限元求解进行了流程模拟。流程模拟结果与实际过程的对比证实了所建立的工业裂解炉蒸汽-空气烧焦过程模型的可行性和有效性,为实现烧焦过程的闭环优化控制奠定了基础。     

Analysis of low NO emission in high temperature air combustion for pulverized coal

High temperature air combustion experiments for pulverized coal in a large-scale furnace have been done before and shown that the NO emission in the high temperature air combustion is significantly lower than that in the normal temperature air combustion. This paper numerically studies the NO evolution in the large-scale experiments with a simplified chemical reaction model. Through an analysis of numerical results a low NO emission mechanism in the high temperature air combustion has been presented. If the HCN concentration is high, the NO generation is fast. But, the high HCN and NO concentrations together will make NO destruction fast. It is found that, by properly arranging flow patterns, the high HCN and NO concentrations can be obtained in the vicinity of primary air nozzle. Thus, the generation and destruction of NO can reach an equilibrium point so that the net NO emission rate is low.     

含氨燃料预混火焰的层流火焰速度及NO排放特性

将甲烷或氢气与氨气共燃可以克服NH₃火焰的点火能量高、燃烧速度慢的缺点。为了解NH₃作为燃料的燃烧特性,对含NH₃燃料进行一维层流预混火焰数值模拟,研究其层流火焰速度及NO排放特性。采用文献中5个简化反应机理进行数值计算,发现Okafor机理模拟NH₃/CH₄/air火焰精度更高;Xiao机理模拟NH₃/H₂/air、NH₃/air精度适中,计算时间较短。此外,开展了当量比、燃料混合物组分比例、压力等参数对含NH₃燃料燃烧时烟气中NO浓度影响的研究。研究发现：含NH₃燃料燃烧时NO主要通过OH、H、O自由基和O₂分子的消耗而生成,主要通过与NH_i（i=0, 1, 2）自由基反应消耗;含NH₃燃料在富燃状态下燃烧可有效减少NO排放,但富燃燃烧效率低,可采用富燃-贫燃分级燃烧技术来提高燃烧效率,同时保持NO的低排放;掺有较多NH₃的含NH₃燃料在中高压下燃烧时可有效减少NO排放。     

Numerical simulation on flow, combustion and heat transfer of ethylene cracking furnaces

With the study object of an 100kt/a SL-II ethylene cracking furnace, this paper used Computational Fluid Dynamics (CFD) method to carry out coupled simulation studies on the flow, combustion, radiative heat transfer and thermal cracking reaction processes in the cracking furnace. The standard k–ε two-equation model was applied to turbulence simulation. The finite-rate/eddy-dissipation model was used for modeling of non-premixed combustion of the bottom burners and premixed combustion of the sidewall burners. The Discrete Ordinates (DO) model was applied to the simulation of radiative heat transfer of furnace. The simulation results show the detailed information about velocity, temperature and concentration fields in the furnace and heat flux distribution on the reactor tubes skin. This work will provide a theoretical basis for the optimization of the geometrical structure and operational parameters of the cracking furnace.     

Mathematical modelling of NO emissions from high-temperature air combustion with nitrous oxide mechanism

A study of the mathematical modelling of NO formation and emissions in a gas-fired regenerative furnace with high-preheated air was performed. The model of NO formation via N₂O-intermediate mechanism was proposed because of the lower flame temperature in this case. The reaction rates of this new model were calculated basing on the eddy-dissipation-concept. This model accompanied with thermal-NO, prompt-NO and NO reburning models were used to predict NO emissions and formations. The sensitivity of the furnace temperature and the oxygen availability on NO generation rate has been investigated. The predicted results were compared with experimental values.The results show that NO emission formed by N₂O-intermediate mechanism is of outstanding importance during the high-temperature air combustion (HiTAC) condition. Furthermore, it shows that NO models with N₂O-route model can give more reasonable profile of NO formation. Additionally, increasing excess air ratio leads to increasing of NO emission in the regenerative furnace.     

Computational study of the combustion process and NO formation in a small-scale wood pellet furnace

This paper presents a computational study of the combustion process of wood pellets in a small-scale grate fired furnace. The objectives were to obtain detailed information on the combustion characteristics and NO formation in the furnace, and to examine the effect of secondary air on the combustion process. The simulation results were compared with experimental data in terms of flame temperature and distributions of species concentrations, including CO and NO. It was shown that the combustion process is strongly controlled by the inflow turbulence from the secondary and tertiary air jets. The combustion process is not sensitive to the bed combustion process in the present test case. The high speed air flow from the secondary and tertiary air inlets ‘destroys’ the history of the effluent volatile gases from the fuel bed. Different paths for the NO emission were investigated, including the thermal NO, the fuel-NO and NO from the N₂O intermediate mechanisms. The fuel-NO path is responsible for the rapid NO increase and the high NO peak near the fuel bed. Fuel-NO is rather low far downstream owing to the rather low nitrogen content in the fuel (less than 0.1% on mass basis), and the de-NO_x reactions with NH₃. NO is likely formed from the N₂O intermediate mechanism far downstream.     

Characteristics of sodium compounds on NO reduction at high temperature in NOx control technologies

Characteristics of sodium compounds additives on NO reduction at high temperature were investigated in a tube stove and a drop tube furnace. Sodium carbonate, sodium hydroxide and sodium acetate were chosen as Na additives to research the effect on NO reduction. It was found that sodium compounds could reduce NO emission and promoted NO reduction efficiency during pulverized coal combustion, coal reburning and urea-SNCR process. Adding sodium carbonate into crude coal gained 3.2%–34.8% of NO reduction efficiency on different combustion conditions during the coal combustion process. NO reduction efficiency was affected by sodium content and coal rank. Na additive performed NO reduction effect in whole Shenhua coal combustion process and in char rear combustion of Gelingping coal. Adding sodium hydroxide into the reburning coal increased NO reduction efficiency of the reburning technology. NO reduction efficiency was increased to 82.7% from 50.0% when the weight ratio sodium to the reburning coal was 3% and the ratio of the supplied air to the theoretical air of reburning fuel was 0.6. Sodium carbonate, sodium hydroxide and sodium acetate performed the promotion of NO reduction efficiency in urea-SNCR. Sodium acetate promoted NO reduction efficiency best while sodium hydroxide promoted worst at 800 °C. Sodium additives as SNCR promoter performed much better at lower temperature than at higher temperature, and they promoted NO reduction weakly in urea-SNCR when the temperature was greater than 900 °C.     

影响裂解炉热效率的原因分析及处理方法

从设备、分析仪表以及裂解炉生产运行等方面,分析了影响乙烯装置裂解炉热效率的原因,并提出了解决处理方法,从而提高了裂解炉热效率,降低了装置能耗。     

基于交叉迭代BLSTM网络的乙烯裂解炉建模

数据驱动的乙烯裂解炉模型通常忽视了裂解炉结构和反应机理，存在预测误差偏大的缺点，为此提出基于知识和数据融合驱动的乙烯裂解炉乙烯收率等关键参数的双向长短时间记忆网络(BLSTM)预测模型。为了解决BLSTM建模缺少可用数据的问题，提出了一种采用交叉迭代的BLSTM(CIBLSTM)模型。所提CIBLSTM模型采用了正反向交叉迭代方法，逐步逼近所缺数据的真实值，进而建立乙烯裂解炉的预测模型。为了验证所提CIBLSTM模型的有效性，选取9种工业实际原料与分析数据进行仿真测试，仿真结果验证了所提的CIBLSTM模型的有效性与实用性，所提方法也可应用于其他复杂化工过程建模。     

提高裂解炉热效率的有效途径

从完善设备结构、提高管束清洁度、减少辐射段热量损失、改善燃烧环境以及生产调优等五方面论述了提高裂解炉热效率的有效途径。旨在为同行改善裂解炉效能,节能降耗提供借鉴。