一种天然气液化和CO2捕集相结合的余热回收发电系统

针对余热回收和能源利用的问题,以液化天然气(LNG)作为冷源,稠油开采废气作为热源,提出了一种结合天然气液化和废气发电与CO₂捕集的余热回收利用系统。分析了关键热力学参数对系统热力学性能的影响。结果表明：对于有机朗肯循环和制冷循环,增加透平膨胀机的进口温度,降低其出口压力以及减少制冷循环压缩机进出口的压缩比,可获得最大净输出功为454.9 kW,余热回收效率为34.2%。对于天然气液化系统,采用C++进行非线性约束优化计算,以氮膨胀制冷循环压缩机总功耗为目标函数进行优化,得到压缩机最优总功耗为101.54 kW。降低天然气压缩机(K110)进口温度,氮气膨胀机(T3)出口压力以及氮气质量流量,可获得最大LNG调峰量为378.8 kg/h,反之,CO₂捕集量可提高28.6%。     

Equation‐oriented simulation and optimization of process flowsheets incorporating detailed spiral‐wound multistream heat exchanger models

Multiple chemical processes rely on multistream heat exchangers (MHEXs) for heat integration, particularly at cryogenic temperatures. Owing to their geometric complexity, the detailed design of MHEXs is typically iterative: the exchanger geometric parameters are selected to match process specifications resulting from a flowsheet optimization step; then, the flowsheet is reoptimized with the predictions of the MHEX model, and these steps are repeated until a convergence criterion is met. This paper presents a novel framework that allows—for the first time, to our knowledge—for the simultaneous optimization of the process flowsheet and the detailed MHEX design. Focusing on spiral‐wound MHEXs, we develop an equation‐oriented exchanger model using industry‐accepted heat transfer and pressure drop correlations for single‐phase and multiphase streams. We embed this model in our previously developed pseudo‐transient equation‐oriented process simulation and optimization framework. We demonstrate our approach on an industrial case study, the PRICO^® natural gas liquefaction process. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3778–3789, 2017     

高压管输天然气利用压力能液化技术

通过火用分析得出,高压管网输送的天然气在调压过程中释放巨大的压力能,在调压站利用膨胀机回收天然气的压力能,用于天然气液化,以增加管网运行的经济性。并介绍了国内外几种天然气液化流程,阐述和分析了其液化方法和特点。     

焦炉多余热回收系统的分析及优化

为了研究焦炉多余热回收系统中能量的利用情况，依据分析理论，通过对某焦化厂实际案例的计算，对现有的余热回收方案进行分析，指出3个子系统运行过程中的能量回收的薄弱环节。结果表明：干熄焦、荒煤气、烟气余热回收系统的效率分别为55.16%、17.18%、51.75%，干熄焦系统的损主要为换热过程中产生的不可逆换热损失，荒煤气系统的损主要为出口损以及不可逆换热损失，烟道系统的损主要为烟气出口损。在此基础上依据各等级能量匹配利用的原则对原方案进行优化，并使用分析理论对其计算并分析。结果表明：优化过后的余热回收系统的总效率为58.72%，相比优化之前提高了11.07%，系统总不可逆换热损降低了155.49MJ/t干煤。     

初始压力对冰冻石英砂中CO2水合物生成特性的影响

利用冰冻石英砂模拟冻土水合物的赋存条件，研究了压力对二氧化碳水合物生成特性的影响，在300 mL高压水合物反应釜中于271 K下进行了多组CO2液化压力以上及以下的霰状冰粉包裹的石英砂中水合物生成实验。结果表明，充入的CO2未液化时，初始压力越大，水合反应速率越快，压力越早达稳定状态；充入压力达液化压力后，注入的CO2越多，水合反应速率越快。压力作为水合反应的驱动力，压力越高水合物生成越多，冰的最终转化率越高。采用CO2置换冻土区中甲烷水合物时，控制压力低于液化压力或注入过量的CO2，置换效果更好。     

Kinetic separation of carbon dioxide from hydrocarbons using carbon molecular sieve

Experimental results are reported on a pressure swing adsorption (PSA) process using carbon molecular sieve (CMS) for the separation of a gas mixture containing carbon dioxide, hydrocarbons (methane, ethane, propane, etc.) and nitrogen. This PSA process has direct applications in carbon dioxide removal or purification from landfill gas, natural gas processing plants and tertiary oil recovery effluent streams. The CMS-based PSA process separates the carbon dioxide in a single stage by using the differences in component diffusivities. This approach, therefore, provides a significant advantage compared to conventional equilibrium adsorption processes which require one separation stage for removing components such as ethane and propane that are more strongly adsorbed than carbon dioxide and another separation stage for removing components such as methane and nitrogen that are less strongly adsorbed than carbon dioxide. The CMS-based PSA process operates between a feed pressure of 20 to 40 bars and a regeneration pressure of 1.5 bars at ambient temperature and produces a 98+% carbon dioxide product. The PSA process can be integrated with a liquid carbon dioxide plant to produce food grade product.     

Gas Mixture Fractionation to Produce Two High Purity Products by Pressure Swing Adsorption

Abstract

Pressure swing adsorption processes have been traditionally used to produce one high purity gas stream from a gas mixture. One of the most common uses of this technology is in the production of ultrahigh purity hydrogen from various gas streams such as steam methane reformer (SMR) off-gas. However, many of these gas streams contain a second gas in sufficiently high concentrations, e.g., carbon dioxide in SMR off-gas, that the recovery of this secondary gas stream along with the primary product is extremely desirable. A new pressure swing adsorption (PSA) process, GEMINI-8, has been developed at Air Products and Chemicals, Inc., to achieve this goal. Process cycle steps for the GEMINI-8 PSA process are illustrated by SMR off-gas fractionation for the production of hydrogen and carbon dioxide. Capital and power savings of this process as well as other advantages compared with the previous technology are discussed.     

Multistream heat exchangers: Equation‐oriented modeling and flowsheet optimization

Multistream heat exchangers (MHEXs), typically of the plate‐fin or spiral‐wound type, are a key enabler of heat integration in cryogenic processes. Equation‐oriented modeling of MHEXs for flowsheet optimization purposes is challenging, especially when streams undergo phase transformations. Boolean variables are typically used to capture the effect of phase changes, adding considerable difficulty to solving the flowsheet optimization problem. A novel optimization‐oriented MHEX modeling approach that uses a pseudo‐transient approach to rapidly compute stream temperatures without requiring Boolean variables is presented. The model also computes an approximate required heat exchange area to determine the optimal tradeoff between operating and capital expenses. Subsequently, this model is seamlessly integrated in a previously‐introduced pseudo‐transient process modeling and flowsheet optimization framework. Our developments are illustrated with two optimal design case studies, an MHEX representative of air separation operation and a natural gas liquefaction process. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1856–1866, 2015     

Design process of LNG heavy hydrocarbons fractionation: Low LNG temperature recovery

The liquefied natural gas (LNG) includes light hydrocarbons heavier than methane, such as ethane, propane and butane, which not only may increase the calorific values of the natural gas beyond specification limits, but also may have greater market values. During the gasification of the LNG, the energy invested in it during liquefaction process may be recovered and re-used. This paper relates to two regasification processes for separating natural gas liquids from liquefied natural gas using the low LNG temperature to produce natural gas meeting pipeline or other commercial specifications. From the two processes studied, the fractionated methane-rich stream is pressurized to pipeline pressure by pumps instead of compressors and the liquefied ethane, propane and butane are obtained directly at atmospheric pressure. Among the processes studied, the low pressure process sounds economically attractive with a saving in TAC of 4.6% over the high pressure process; however the high pressure process is more preferable for the cases where the space is limited.     

A superstructure‐based model for multistream heat exchanger design within flow sheet optimization

Multistream heat exchangers (MHEXs) are often used in energy‐intensive cryogenic processes. Modeling them within a process optimization formulation has been a challenge due to the needs to accommodate phase changes and ensure temperature approach. In this work, we present a nonlinear model for MHEXs based on a novel single‐stage superstructure of two‐stream exchangers. Our formulation guarantees a minimum temperature approach for all heat exchanges, estimates heat exchange areas for individual stream matches, requires no prior knowledge of phase changes, uses no Boolean variables, and enables seamless optimization of a process with multiple MHEXs. Furthermore, it facilitates dedicated constant‐phase intervals that allow accurate estimation of heat‐transfer parameters for various stream matches. We optimize two natural gas liquefaction processes involving MHEXs, and report better solutions than the existing literature. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3764–3777, 2017     

集成NGL回收的新型天然气液化系统AP-XTM的概念设计与模拟分析

为提高液化天然气能量集成与设备共用水平,提出了一种基于大型AP-X^TM液化流程，综合气体过冷技术（GSP）的集成NGL（天然气凝液）回收工艺的天然气液化系统的概念设计。基于化工流程模拟软件Aspen HYSYS进行模拟和分析，将集成工艺多流股换热器性能、全流程的单位功耗和乙烷回收率作为衡量系统性能的三项指标。模拟和分析的结果表明，集成NGL回收的AP-X^TM液化工艺单位功耗降低至0.45 kW·h·(kg LNG)^-1，较单产系统能耗降低了6%，同时乙烷回收率达到93%，实现了NGL的高效分离。通过热力学分析、?分析和经济性分析得出本设计流程具有较高的性能和经济价值，可为天然气液化工艺的集成设计和技术改造提供指导借鉴。     

Exergoeconomic (Thermoeconomic) Analysis and Performance Assessment of a Gas Engine–Driven Heat Pump Drying System Based on Experimental Data

Exergoeconomic analysis has been used as a powerful tool to study and optimize various types of energy-related systems. In this study, we use the specific exergy cost (SPECO) method to calculate exergy-related parameters and display cost flows for all streams and components in a gas engine–driven heat pump drying system based on the experimental data. We analyze and evaluate the performance of the drying system components and the drying process for three different medicinal and aromatic plants from an exergoeconomic point of view. We also investigate the effect of varying dead (reference) state temperatures on exergoeconomic performance parameters for the drying system components and drying process. Although the condenser and drying chamber of the gas engine–driven heat pump dryer were significantly affected by the ambient temperature, the gas engine was slightly influenced by the ambient temperature. At low ambient temperatures, the exergy rates increased and the most effective performance obtained from this dryer was at 0°C. The performance of the drying process also increased at low ambient temperatures. This study demonstrated that exergoeconomic analysis can provide more information than exergy analysis, and the results obtained from the exergoeconomic analysis provided cost-based information, suggesting potential locations for drying system improvement.     

Globally optimal design of Minimal WHEN systems using enumeration

The process synthesis problem referred to as work and heat exchange networks (WHENs) asks to determine the optimal heat exchanger network intertwined with compressors, expanders, and valves, all integrated into one single network, such that streams with certain initial temperature and pressure attain their temperature and pressure targets at minimum cost. This article presents a procedure that obtains the globally optimal solution of Minimal WHEN systems using an enumeration scheme, using only a few subproblems, each one solved using mathematical programming to global optimality. Minimal structures feature one compression/decompression task and one heat exchange task per stream. In addition, we depart from the ideal gas assumption and use a cubic equation of state for stream properties. Finally, the approach allows for the use of turboexpanders. Four examples are presented to show the effectiveness and accuracy of the proposed method.     

新型双压Linde-Hampson氢液化工艺设计与分析

为降低氢液化厂的生产能耗与投资成本,加快我国氢能商业化、民用化的发展,本文提出了一种采用液化天然气（LNG）预冷的新型双压Linde-Hampson（L-H）氢液化工艺系统。系统的设计液氢产量为5t/d,采用膨胀降温与换热冷却相结合的方法实现了对氢气的深冷。借助Aspen HYSYS软件对工艺流程展开了详细的模拟计算与分析,结果表明,该氢液化系统的比能耗为9.802,?效率为41.4%,系统的总?损失为1373.3kW,其中换热设备的?损失占主要部分;在对系统中关键参数进行的灵敏度分析中发现,氢气预压缩压力在2~4MPa范围内变化对液化系统的比能耗和氢气液化率影响较大,而LNG的加压压力对系统性能影响较小。新型氢液化工艺系统设备简单,投资成本较低,具备良好的液化性能,在未来中小型氢液化厂的建设中优势明显。     

高含氮天然气液化工艺的探讨

在不同气源中,含氮量较高的天然气热值低、集输过程中能耗大,为脱除天然气中过高含量的氮气,设计了深冷脱氮的天然气液化工艺。利用过程系统软件HYSYS模拟了深冷脱氮及液化天然气的过程,并分析了原料天然气特性、制冷剂特性及精馏塔操作条件对液化单元能耗的影响,对工艺条件进行了优化。结果表明,在制冷剂循环压力和温度为0.4MPaG和35℃,原料天然气压力和温度分别为2.6MPaG和20℃,精馏塔压力为0.6MPaG,氮气所占比例为0.5时,该液化单元的功耗最小,为0.527kW/Nm3,该工艺模拟和优化为高含氮气源进行液化利用提供了重要的参考。     

Simultaneous synthesis of heat exchanger networks with pressure recovery: Optimal integration between heat and work

The optimal integration between heat and work may significantly reduce the energy demand and consequently the process cost. This article introduces a new mathematical model for the simultaneous synthesis of heat exchanger networks (HENs), in which the pressure levels of the process streams can be adjusted to enhance the heat integration. A superstructure is proposed for the HEN design with pressure recovery, developed via generalized disjunctive programming, and mixed‐integer nonlinear programming formulation. The process conditions (stream temperature and pressure) must be optimized. Furthermore, the approach allows for coupling of the turbines and compressors and selection of the turbines and valves to minimize the total annualized cost, which consists of the operational and capital expenses. The model is tested for its applicability in three case studies, including a cryogenic application. The results indicate that the energy integration reduces the quantity of utilities required, thus decreasing the overall cost. © 2013 American Institute of Chemical Engineers AIChE J, 60: 893–908, 2014     

Framework for work‐heat exchange network synthesis (WHENS)

Work and heat are the two predominant forms of energy in the process industry. Considerable savings can be achieved by synergizing the work and heat requirements of process streams. A generalized framework for integrating heat and work simultaneously is proposed based on a mixed‐integer nonlinear programing model for work‐heat exchange network synthesis. Starting with a set of streams with known flows, temperatures, and pressures, a network of single‐shaft‐turbine‐compressors with motors/generators, valves, heat exchangers, and utility heaters/coolers is synthesized for minimized total annualized cost. In contrast to existing works, (1) streams are not preclassified as hot/cold or high/low pressure, (2) pressure changes are allowed for streams with no net pressure change, (3) liquid‐vapor phase changes are allowed, and (4) phase‐based property correlations are used. Successful application of our approach to C3 splitting yields a nonintuitive configuration. Another application of an offshore natural gas liquefaction process is also studied. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2472–2485, 2018     

基于余热利用的活化MDEA法脱除CO2的天然气液化系统

沼气以及CO₂驱采油的伴生气中都含有大量的CO₂。为降低高含CO₂天然气液化的能耗,提出了活化甲基二乙醇胺（MDEA）法脱除CO₂的天然气液化系统,将液化厂中驱动压缩机的燃气轮机烟气余热用于吸收剂的再生过程,实现能耗的降低。采用HYSYS软件对系统进行了模拟研究并对脱碳过程的关键参数进行了分析。结果表明,CO₂含量不超过10%时,脱碳再生的热耗可全部由烟气余热提供,CO₂含量为30%时,烟气余热可提供接近50%的再生热耗;CO₂含量为1%～30%时,系统的比功耗为0.577～0.611 kW·h/kg。     

热管式蒸汽发生器的火用分析

以热力学第一、第二定律为基础的热平衡分析法和火用平衡分析法相结合，对热管式蒸汽发生器进行了火用分析，给出了热管式蒸发器中各部分的火用损失情况，指出其合理的布置方式     

FLNG绕管式换热器晃动实验分析

浮式液化天然气生产储卸装置（FLNG,又称LNG-FPSO）是一种用于海上天然气田开发的浮式生产装置。由于FLNG装置海上作业的特殊环境,FLNG液化工艺不仅要实现最基本的天然气液化功能,还需考虑海上恶劣的环境条件对FLNG液化工艺的影响。海洋中海浪的波动对液化系统中的关键设备--换热器影响较大。为了研究绕管式换热器在海上晃荡条件下的性能,通过建立双混合制冷剂液化工艺小试实验装置,进行绕管式换热器实验装置的晃动实验。结果表明实验装置晃动时,节流阀节流前压力降低,节流后压力升高,节流阀的节流效果变差,绕管式换热器换热效果变差。换热器的换热效果受到晃动的方向和FLNG中设备安装方向的耦合影响,倾斜工况下换热器换热效果受影响最大,受横摇影响较纵摇影响大。