乙烯装置冷箱及脱甲烷系统模拟

以化工流程模拟软件ASPEN PLUS为应用平台,建立能良好描述裂解气在冷箱中预冷和脱甲烷塔中分离的工艺模型。应用该模型对扬子乙烯装置老区冷箱和脱甲烷塔系统进行了流程模拟、参数灵敏度分析和过程优化;研究了裂解气负荷、裂解气组成等几个因素,对冷箱与脱甲烷塔系统的影响以及相应操作参数的优化调整;找到了现有冷箱与脱甲烷系统的用能瓶颈;解决了工艺操作参数的优化问题;实现了装置高负荷情况下的经济运行。     

新节能脱甲烷系统

在某30万t乙烯装置低压脱甲烷系统的基础上,应用流程模拟技术开发出一套新的节能的脱甲烷系统。新系统在流程中引入膨胀机,有效避免了气体节流的能量损失;调整、优化了原有的工艺参数,减少了直接节流到塔压的裂解气量;对系统换热网络重新进行了匹配,更加合理利用了各股物料的冷量,使脱甲烷塔回流比、甲烷压缩机负荷以及乙烯冷剂消耗均有所降低。模拟结果表明,新系统总计节能达到1377 kW。     

脱甲烷塔塔顶冷凝器运行问题分析及对策

介绍了四川石化乙烯装置脱甲烷塔的基本流程及塔顶冷凝器运行存在的问题,分析了脱甲烷塔塔顶冷凝器冷剂侧液位不能建立的原因,并在保证装置不停车的前提下对现有流程进行整改和优化。利用乙烯制冷压缩机三段吸入罐的设备预留口对脱甲烷塔塔顶冷凝器冷剂入口管道优化改造,解决了脱甲烷塔塔顶冷凝器冷剂供给不足、脱甲烷塔顶温高及塔顶甲烷气中乙烯损失大等问题。以最低的改造成本获得最大的经济效益,在节能降耗的同时也为装置的稳定操作和高负荷生产创造了条件,保障了装置裂解原料轻质化条件下的高负荷工况下的稳定运行。     

顺序流程乙烯装置冷区扩能改造方案探讨

乙烯装置分离冷区工艺流程复杂,技术难度高,是全装置工艺设计的关键。以某200 kt/a乙烯挖潜改造、1100 kt/a乙烯装置改造和1190 kt/a乙烯装置改造为例,着重论述了顺序分离流程冷区改造的工艺技术特点,对深冷及脱甲烷系统、制冷系统和碳二分离系统的工艺改造方案进行了说明,分析了各装置在具体改造方案上的工艺技术特点,最后总结出顺序流程深冷系统、制冷系统以及乙烯全装置扩能改造的最佳方案和改造原则。     

乙烯装置急冷系统的流程模拟与热量回收优化分析

利用PROII化工流程模拟软件,对乙烯装置急冷系统进行了流程模拟,将模拟结果与实际数据进行对比。在对模拟数据进行提取后,找到影响急冷油热量回收关键操作参数。分析得出裂解气进塔温度、粗汽油回流量、裂解柴油采出量等操作参数与急冷油热量回收值的关系曲线,结合装置的实际生产提出了优化急冷油热量回收的操作条件,为乙烯装置急冷系统的优化生产和操作提供了理论依据和数据支持。     

乙烯深冷分离中变温冷却过程制冷系统的设计与优化

根据乙烯装置中的用冷需求,将乙烯装置的深冷分离过程分为变温冷却过程和定温冷凝过程,变温冷却过程指的是裂解气的预冷过程,定温冷凝过程指的是乙烯装置中各塔塔顶冷凝器中的换热;分析了乙烯-丙烯复叠制冷系统的换热集成曲线,可知在裂解气的预冷阶段,冷热物流换热温差大。提出一种组合制冷系统,它集成了纯工质复叠制冷和混合冷剂制冷,其中的多元混合冷剂制冷系统为乙烯深冷分离的变温换热过程提供冷量。并用Aspen Plus软件对混合冷剂系统进行建模,使用遗传算法优化,优化结果表明在替代原制冷系统6895.5 kW冷量负荷的情况下,功耗降低521.6 kW,节能14.7%。     

丙烯制冷系统模拟优化

丙烯制冷压缩机是乙烯装置的核心设备。兰州石化分公司460 kt/a乙烯装置的丙烯制冷系统为各用户提供-42℃、-15℃和7℃3个温位等级冷剂。目前该系统的7℃丙烯冷剂还存在富裕情况,还有较大的节能空间。利用Aspen plus建立7℃丙烯冷剂系统的模型,通过模拟对比该系统初步设计和现阶段的运行工况,为丙烯冷剂系统的优化提供依据。     

高低压脱甲烷流程方案的比较

通过对乙烯装置高低压脱甲烷塔流程方案，设备投资，冷剂和三机功率消耗等不同方面的优化及比较，为今后大型乙烯装置深冷分离系统的设计提供理论基础。     

大庆裂解老区乙烯分离工艺优化探讨

脱甲烷系统是乙烯裂解装置能量消耗的大户。通过分析大庆乙烯装置裂解老区分离流程,在不改变老区分离进料量的前提下,对前冷、脱甲烷塔及脱乙烷塔部分进行工艺优化,将前冷的前两股进料直接进入脱乙烷塔处理,降低脱甲烷塔和脱乙烷塔负荷;重新启用膨胀机、压缩机,并将再生气、燃料气二者合做驱动力,循环利用冷量,进而达到节能降耗的目的。     

混合冷剂组成对天然气轻烃回收乙烷工艺流程的影响

天然气中所含有丰富的C_2+组分,回收后可以得到乙烷、液化石油气和稳定轻烃等产品。其中,乙烷是优质的乙烯原料,乙烯产量是衡量一个国家石油化工水平的重要标志,其众多下游产品应用广泛。其中,混合制冷工艺是目前油田伴生气回收乙烷工艺流程中比较高效的工艺之一。利用Aspen HYSYS软件搭建模拟流程。混合冷剂的组成对整个工艺的压缩机功耗、混合冷剂流量等工艺参数影响较大。例如,变化混合冷剂的组成可以影响冷箱的冷热换热曲线,同时也影响着冷箱的夹点温差,而这些参数直接决定着冷箱的工作性能。因此,对冷剂的组成进行研究,合理的优化混合冷剂的配比,是混合冷剂制冷工艺至关重要的一个方面。     

Product Loss Minimization of an Integrated Cryogenic Separation System

The integrated cold box and demethanizer system as one of the most critical production sections in an ethylene plant couples multistage refrigeration and cryogenic separation to extract hydrogen and methane from the cracked gas feed. Ethylene and the heavier components are liquefied for recovery in the downstream process. During separation, ethylene contained in the methane and hydrogen streams is accounted as the product loss which in reality is significant. To reduce the ethylene loss with energy consumption consideration, a systematic methodology has been developed to optimize the process operation of the integrated cold box and demethanizer system. It covers rigorous simulation model development and validation, sensitivity analysis, operational optimization, and result analysis. The optimization results demonstrate the significant economic benefits of the proposed methodology.     

乙烯装置中气相冷剂过热度的设定及其影响评述

介绍了乙烯装置上传统的丙烯、乙烯和甲烷单组分制冷以及近年出现的混合制冷中,返回压缩的气相冷剂过热度设定情况。评述了它们跟所使用换热设备的型号、出口温度的控制方式与中间冷却器的设置等实施要素的相互制约关系;并就过热度对段间吸入罐的引入、淬冷线和排液系统的优化设计方面的影响进行了分析。     

Cascade refrigeration system synthesis based on exergy analysis

Refrigeration systems are very important to chemical/petrochemical process industries because their performances are closely related to product quality, energy usage efficiency, and plant profitability. Hitherto, the optimal synthesis of a cascade refrigeration system with multiple refrigerants and multiple temperature levels presents considerable challenges and systematic studies combined with thermodynamic insights and mathematical-programming approaches in this area are still lacking. In this paper, a general methodology for the optimal synthesis of such cascade refrigeration system to maximize the energy efficiency has been developed. The exergy-temperature chart combined with the exergy analysis is presented to comprehensively analyze the thermodynamic nature of a refrigeration system, which provides a solid foundation for the conceptual design/retrofit of the complex refrigeration system. An exergy-embedded MINLP model has also been developed for the optimal synthesis of a general cascade refrigeration system. The efficacy of the developed methodology is demonstrated through a case study on the retrofit of a cascade refrigeration system for an ethylene plant.     

乙烯分离与复叠制冷系统用能的综合优化

乙烯装置的分离过程要在低温下进行,由乙烯制冷系统提供所需冷量。乙烯制冷系统为封闭式循环,独立于分离单元之外。将乙烯分离单元与制冷系统同时优化,能有效提高装置用能效率。复叠式制冷级数是当前乙烯工业中使用最为广泛的制冷技术。本文针对乙烯分离过程和配套的复叠制冷系统,采用Aspen Hysys进行模拟并进行(火用)分析,发现系统主要的(火用)损失发生在换热与压缩两部分,其占总(火用)损失的83%,为节能的重点。进而通过夹点技术对冷剂配置进行分析,发现-56℃以上各温位的冷量配置不合理,远超过理论最小值,-56℃以下各温位的冷量基本达到理论最小值。提出了采用多股流换热器的换热网络理论设计方法,并对冷剂进行重新配置,该理论方案可以降低丙烯制冷压缩机约30%的功耗,并节约部分乙烯制冷压缩机功耗,显著降低了乙烯深冷分离能耗。     

Optimal synthesis of compression refrigeration system using a novel MINLP approach

The optimal design of a compression refrigeration system (CRS) with multiple temperature levels is very important to chemical process industries and also represents considerable challenges in process systems engineering. In this paper, a general methodology for the optimal synthesis of the CRS, which simultaneously integrates CRS and Heat Exchanger Networks (HEN) to minimize the total compressor shaft work consumption based on an MINLP model, has been proposed. The major contribution of this method is in addressing the optimal design of refrigeration cycle with variable refrigeration temperature levels. The method can be used to make major decisions in the CRS design, such as the number of levels, temperature levels, and heat transfer duties. The performance of the developed methodology has been illustrated with a case study of an ethylene CRS in an industrial ethylene plant, and the optimal solution has been examined by rigorous simulations in Aspen Plus to verify its feasibility and consistency.     

Synthesis of refrigeration system based on generalized disjunctive programming model

Refrigeration system holds an important role in process industries. The optimal synthesis cannot only reduce the energy consumption, but also save the production costs. In this study, a general methodology is developed for the optimal design of refrigeration cycle and heat exchanger network (HEN) simultaneously. Taking the heat integration between the external heat sources/sinks and the refrigeration cycle into consideration, a superstructure with sub-coolers is developed. Through defining logical variables that indicate the relative temperature positions of refrigerant streams after sub-coolers, the synthesis is formulated as a Generalized Disjunctive Programming (GDP) problem based on LP transshipment model, with the target of minimizing the total compressor shaft work in the refrigeration system. The GDP model is then reformulated as a Mixed Integer Nonlinear Programming (MINLP) problem with the aid of binary variables and Big-M Constraint Method. The efficacy of the process synthesis model is demonstrated by a case study of ethylene refrigeration system. The result shows that the optimization can significantly reduce the exergy loss as well as the total compression shaft work.     

低温蒸馏塔与冷冻系统的热泵流程集成

本文复合夹点分析方法和　分析原理,建立了低温蒸馏塔与冷冻系统热泵流程集成的优化方法。其中首次构造了低温过程系统热泵流程集成的　总组合曲线,用以目标化低温蒸馏塔与冷冻系统的热泵流程集成;并提出低温过程系统热泵流程集成的　效能系数,预测冷冻系统通过热泵流程集成所得到的轴功节省目标。所提出的方法已成功地应用于乙烯精馏塔与冷冻系统联合解瓶颈工程实例,经济效益显著。     

三元制冷系统分析

乙烯装置产品分离过程需要在低温下进行,为此需配置压缩制冷系统为深冷分离提供冷量。三元压缩制冷由于能提供温位连续的制冷曲线,与工艺物流降温曲线更好地匹配,相比传统的复叠制冷具有热力学效率高、制冷能耗低的特点。为了分析三元压缩制冷的节能潜力,本文对某乙烯装置的三元制冷系统进行了(火用)分析。从(火用)总复合曲线(EGCC)图的分析可以得出该系统三元冷剂配置是比较合理的,(火用)损失较小。将该制冷系统划分为换热器、压缩机、节流阀、闪蒸罐等子系统,并分别计算了各子系统的(火用)损失。三元制冷系统的(火用)损失总计为24238.1kW,90%(火用)损失集中在换热器和压缩机两个子系统。然后将(火用)损失分为可避免的和不可避免的(火用)损失两类,其中不可避免的(火用)损失为13539.9kW,可避免的(火用)损失为10698.2kW,最后指出节能重点应该放在降低可避免的(火用)损失。