Techno-economic analysis of potential natural gas liquid (NGL) recovery processes under variations of feed compositions

This paper presents the different process schemes used for known NGL recovery methods with respect to their economic performance. The original turbo-expander (ISS) was considered as base case plant. The GSP, CRR and RSV process schemes focus on improvement at the top of the demethanizer column. The IPSI-1 and IPSI-2 schemes focus on the bottom of the demethanizer column. All the process schemes were initially built using Aspen HYSYS with a common set of operating criteria. Numerous simulation runs were made by taking various typical feed compositions classified as lean and rich. The economic assessment for each process scheme was later made by considering the capital cost, operating cost and profitability analysis. Results showed that the IPSI-1 process scheme gives the best economic performance with lowest TAC and payback time compared to the other process schemes. On the other hand, the RSV process gives higher TAC and payback time compared to others.     

天然气轻烃回收装置工艺优化

本文以某套轻烃浅冷回收装置为研究对象,运用HYSIM烃类工艺模拟软件,对其进行了工艺参数的优化。同时,还考察了原料气的轻重程度不同对最优工艺参数的影响。结果表明:重原料组成时,装置的操作压力可适当降低;轻原料组成时,适当提高装置的操作压力可使轻烃的收率达到最大,实现以最小的能耗获得最大的C 组分收率这一优化目标。     

Recovery enhancement of liquid hydrocarbons in dew point control unit of natural gas processing plant

ABSTRACT

The low temperature absorption method is currently used in a gas-processing unit to control the natural gas dew point. The major problem of this unit is the simultaneous absorption of high amount of methane within heavier hydrocarbons, which leads to low purity of ethane and propane streams. Considering the operational conditions, the mentioned method used in second and third phases, will control the dew point at ?23° c at the best condition. This temperature is not proper for dew point and shows very high amount of hydrocarbons in product gas. In this study, a new process has been introduced in order to drop the gas liquid dew point (natural gas liquid) to ?85° c by self-refrigeration technology. Due to the advanced nature of absorption process, the problem of methane existence in the product of gas liquids is noticeably overcome. In this process, natural gas enters the turbo expander after passing through a refrigeration cycle at ?37° c and it is then expanded in an isotropic process to 2896 kPa pressure. Expander outlet with reflux and condensate produced from a cold separator are fed to an absorption tower with a reboiler and the separation will occur. The advantage of this method is controlling the concentration of methane in the product streams. Simulation results show that the process can daily produce 22,280 barrels of gas liquids with a concentration of 0.5 mole% of methane. In addition, the recovery efficiencies of propane and butane in the newly proposed method are 97.3% and 99.99%, respectively, which show a remarkable advantage over the current trend.     

一种新的利用LNG冷能的回收油田伴生气凝液的工艺

A novel process to recovery natural gas liquids from oil field associated gas with liquefied natural gas (LNG)cryogenic energy utilization is proposed.Compared to the current electric refrigeration process,the proposed process uses the cryogenic energy of LNG and saves 62.6%of electricity.The proposed process recovers ethane, liquid petroleum gas(propane and butane)and heavier hydrocarbons,with total recovery rate of natural gas liquids up to 96.8%.In this paper,exergy analysis and the energy utilization diagram method(EUD)are used to assess the new process and identify the key operation units with large exergy loss.The results show that exergy efficiency of the new process is 44.3%.Compared to the electric refrigeration process,exergy efficiency of the new process is improved by 16%.The proposed process has been applied and implemented in a conceptual design scheme of the cryogenic energy utilization for a 300 million tons/yr LNG receiving terminal in a northern Chinese harbor.     

天然气深冷分离装置的(火用)分析及用能改进建议

将天然气深冷分离装置划分为6个子系统,采用“三箱”分析方法,建立了NGL装置的火用分析模型,并给出了具体分析过程和评价指标。利用实测数据,对某一实际运行的NGL装置进行了分析计算,根据测算结果提出了改进建议。实际应用表明,对NGL装置进行火用分析,能更全面地反映装置的用能情况。     

An Optimization of Capital and Operating Alternatives in a NGL Recovery Unit

A natural gas liquids (NGL) recovery unit currently in operation has been simulated and compared with a real unit. Optimized operating conditions have been determined, in which the objective function is based on cost analysis. Following this, different turboexpansion processes have been analyzed and the best flow sheet selected, based on capital analysis and operating limitations. Parameter optimization of the entire modified plant has been performed using an advanced genetic algorithm program, to determine optimal operating conditions. The best revamping alternative is a turboexpander‐exchanger process, in which case the profit is increased by 28 %.     

天然气脱水系统现状分析及优化

针对陕北某天然气净化厂脱水系统中原料气水含量偏高、产品气无法满足国标要求这一生产难题,本文利用ChemCAD对该脱水系统进行了全流程模拟,研究分析得到最佳的优化操作参数为：TEG循环量为6.16 m3/h,原料气进气温度为33 ℃。通过FRI、HTRI和Pipe Flow Expert等专业软件对系统改造后的关键设备及管线进行优化,核算结果表明,脱水塔的各个流体力学参数均可满足生产需要;套管换热器换热能力不足,通过对比分析可知选用高效板式换热器替代在役套管换热器是一种较为经济、合理的优化方案;通过提高原料气预冷器换热管束的表面翅化率可以有效改善它的换热效果,使其达到系统指定的换热要求。研究结果可为该脱水系统的升级改造提供可靠的理论依据,对同类型装置亦具有一定的借鉴作用。     

A power plant for integrated waste energy recovery from liquid air energy storage and liquefied natural gas

Liquefied natural gas(LNG)is regarded as one of the cleanest fossil fuel and has experienced significant developments in recent years.The liquefaction process of natural gas is energy-intensive,while the regasification of LNG gives out a huge amount of waste energy since plenty of high grade cold energy(-160℃)from LNG is released to sea water directly in most cases,and also sometimes LNG is burned for regasification.On the other hand,liquid air energy storage(LAES)is an emerging energy storage tech-nology for applications such as peak load shifting of power grids,which generates 30％-40％of compres-sion heat(～200℃).Such heat could lead to energy waste if not recovered and used.The recovery of the compression heat is technically feasible but requires additional capital investment,which may not always be economically attractive.Therefore,we propose a power plant for recovering the waste cryo-genic energy from LNG regasification and compression heat from the LAES.The challenge for such a power plant is the wide working temperature range between the low-temperature exergy source(-160℃)and heat source(～200℃).Nitrogen and argon are proposed as the working fluids to address the challenge.Thermodynamic analyses are carried out and the results show that the power plant could achieve a thermal efficiency of 27％and 19％and an exergy efficiency of 40％and 28％for nitrogen and argon,respectively.Here,with the nitrogen as working fluid undergoes a complete Brayton Cycle,while the argon based power plant goes through a combined Brayton and Rankine Cycle.Besides,the economic analysis shows that the payback period of this proposed system is only 2.2 years,utilizing the excess heat from a 5 MW/40MWh LAES system.The findings suggest that the waste energy based power plant could be co-located with the LNG terminal and LAES plant,providing additional power output and reducing energy waste.     

常规及创新高压凝液回收流程对比

塔里木盆地地区的英买、迪那等大型高压凝析气田目前仅对原料天然气进行了烃水露点控制,重烃回收率低,经济效益没有实现最大化,对此类气田进行凝液回收可显著提升气田的经济效益。现今适用于高压天然气凝液回收的流程主要为HPA（high pressure absorber）流程,本文在HPA流程基础上提出两种改进流程,即改进Ⅰ型流程和改进Ⅱ型流程。并通过SQP（sequential quadratic programming）算法以单位能耗最低为目标函数对3种流程进行操作参数优化, 并通过能耗分析表明：3种流程具有不同原料气贫富和压力适应范围,在贫气条件下,原料气压力在7000~8000kPa范围内,改进Ⅰ型比HPA流程更节能,而当原料气压力高于7500kPa时,改进Ⅱ型流程能耗开始低于前两者,且随原料气压力增加,节能效果更加明显。而对于富气,改进Ⅱ型流程能耗最高,改进Ⅰ型与HPA流程区别不明显。     

硫磺回收装置过程气加热方式比较

介绍了国内硫磺回收工艺特点及过程气加热方式。分析比较高温热掺合法、在线加热炉加热法、蒸汽加热法、气-气换热法和电加热法等过程气加热方式的优缺点,并探讨了高温掺合阀的安装位置及选材、Claus尾气加热方式选择等。建议设计人员根据各企业热源的可靠性、装置规模、装置操作弹性、酸性气组成、装置平面布局及投资情况等综合考虑,选择最佳的过程气加热方式。     

天然气脱硫装置的系统模拟与优化

针对陕北某天然气净化厂脱硫装置CO2体积分数偏高﹑生产设备和输送管线故障频繁这一问题,文中利用ChemCAD 6.0.1对脱硫系统进行了全流程模拟优化,并通过FRI-Tray Rating 1.0.7,HTRI Xchanger Suit 4.00等专业软件对关键设备进行了校核。结果表明:适当提高MDEA循环量可使产品气达到国标相关要求;此外,MDEA吸收塔的各项流体力学指标均满足新工艺条件的要求;MDEA贫富液换热器的换热能力不足,可在原有换热器基础上串联一台同型号换热器来满足换热负荷;提高酸气空冷器的表面翅化率可使其满足换热要求;将原有MDEA循环泵更换为大功率机泵以保证MDEA循环量达到系统指定要求。     

多晶硅生产氯化氢回收工艺的模拟与优化

建立了多晶硅生产氯化氢回收工艺过程的热力学模型,考察了吸收塔进气的氯化氢摩尔分数、吸收塔的液气比、解吸塔回流比等因素对吸收尾气中氯化氢摩尔分数、回收氯化氢中氯化氢摩尔分数的影响,并考察了闪蒸脱氢的最优条件。最终得出CVD尾气的最优吸收液气比和解吸回流比分别为1.4和0.3;STC氢化尾气的最优吸收液气比和解吸回流比分别为2.0和0.3;闪蒸的最优条件是0.2 MPa、-40℃。     

Control structure synthesis for operational optimization of mixed refrigerant processes for liquefied natural gas plant

The best control structures for the energy optimizing control of propane precooled mixed refrigerant (C₃MR) processes were examined. A first principles‐based rigorous dynamic model was developed to analyze the steady‐state and dynamic behaviors of the C₃MR process. The steady‐state optimality of the C₃MR process was then examined in a whole operation space for exploring the feasibility of the energy optimizing control for possible control structures. As a result, the temperature difference (TD) between the warm‐end inlet and outlet MR streams was exploited as a promising controlled variable to automatically keep the liquefaction process close to its optimum. The closed‐loop responses were finally evaluated for every possible control structure candidate. Based on the steady‐state optimality and the dynamic performance evaluation, several control structures with a TD loop were proposed to be most favorable for the energy optimizing control of the C₃MR process. The proposed optimality approach can be applied to any natural gas liquefaction process for determining a proper controlled variable for optimizing operation. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2428–2441, 2014     

Natural gas conversion to liquid fuels in a zone reactor

A process for conversion of natural gas to liquid fuels is described. The process can be conducted in a “zone reactor” in which oxygen or air is first contacted with solid metal bromide, producing bromine and metal oxide. The bromine passes into a second zone, in which it reacts with natural gas, producing alkyl bromides and hydrogen bromide. The products of the second zone pass into a third zone, in which they react with metal oxide, producing metal bromide and liquid product. At the end of the cycle the oxygen feed and product streams are switched and the flow reversed. The advantages of the process including safety and capital cost reduction are presented and results discussed.     

天然气轻烃回收工艺设计及操作参数的优化

以廉价天然气中的乙烷和丙烷为原料的乙烯成本仅是石脑油等重质原料成本的30%,高压管输天然气进入城市门站分输需调压,调压过程中有大量压力能可利用。本文以某段高压管输天然气为原料,提出了处理量60×10⁴m³/h的轻烃分离回收工艺流程,综合考虑轻烃回收率、系统功耗、CO₂冻堵、冷箱传热温差等因素,优化操作参数,完成了系统能量的高效集成,实现了轻烃分离工艺的节能降耗。该方案C₂回收率达90%以上,可为乙烯装置提供优质的乙烷等轻烃原料50.75万吨/年,有利于解决乙烯工业发展的原料瓶颈,提高天然气、乙烯工业的整体经济效益。     

Simulation and energy consumption analysis of a propane plus recovery plant from natural gas

This paper deals with the investigation of a cryogenic plant for the recovery of propane plus compounds from natural gas. The commercially available software ASPEN Plus® has been used to simulate the process, and to investigate the effect of the main operating variables on the efficiency of propane plus recovery and on the energy required by the various pieces of equipment of the plant. With respect to the base case considered, the optimized plant allows to reduce the heat required up to 25%; besides, the refrigeration required can be reduced up to 60%, without significantly affecting the propane plus recovery.     

A novel conceptual design by integrating NGL recovery and LNG regasification processes for maximum energy savings

Natural gas liquids (NGL) recovery from shale gas needs large amounts of cold energy for cooling, while liquefied natural gas (LNG) regasification requires tremendous hot energy for heating. Thus, recycling the cold energy from LNG regasification process at a receiving terminal to assist the NGL recovery process has great economic benefits on both energy saving and high‐value product recovery. A novel conceptual design by integrating NGL recovery from shale gas and LNG regasification at receiving terminals has been developed. It first generates a process superstructure. Then, a simulation‐assisted mixed‐integer linear programming (MILP) model is developed and solved for the optimal process synthesis. Next, heat exchange network (HEN) design and analysis are performed to accomplish the maximum energy‐saving target. Finally, rigorous plant‐wide simulations are conducted to validate the feasibility and capability of the entire conceptual design coupling of separation and heat integration. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4673–4685, 2013     

Solute recovery from ionic liquids: A conceptual design study for recovery of styrene monomer from [4-mebupy][BF4]

Extractive distillation using ionic liquids (ILs) is a promising technology to separate the close-boiling mixture ethylbenzene/styrene. A proper solvent regeneration is crucial to obtain a technical and economic feasible process. In this work, several regeneration technologies were studied to recover styrene from the IL [4-mebupy][BF₄] using Aspen Plus. Stripping with a hot gas (N₂ or ethylbenzene), supercritical CO₂ extraction, distillation by adding a co-solvent, and evaporation were investigated. It was found that the IL that was fed as solvent to the extractive distillation column should have a purity of at least 99.6 wt% to maintain the purities of the top and bottom products from the extractive distillation column. This purity could not be obtained with an evaporator using mild conditions (T = 130 °C, T_condenser ≥ 20 °C). From the process models and the economic evaluation for a typical production capacity of 500,000 mta, the conclusion can be drawn that evaporation using very low pressures (P < 10 mbar) and stripping with ethylbenzene are the most promising technologies to recover styrene monomer from the IL [4-mebupy][BF₄].     

Techno-economical and environmental optimization of natural gas network operation

In the present study, a multi-objective approach is proposed to find optimum operating condition of natural gas network. For this purpose, a thermodynamic modeling of natural gas through the main elements of the network i.e. pipelines and compressor stations (CSs) is performed. This study aims to find optimum values of three conflicting objective functions namely maximum gas delivery flow and line pack, and minimum operating cost (sum of fuel consumption and carbon dioxide emission costs), simultaneously. Here, fast and elitist non-dominated sorting genetic-algorithm (NSGA-II) is applied by considering fourteen decision variables: number of running turbo-compressors (TCs) and rotational speed of them in compressor stations as well as gas flow rate and pressure at injection points. The results of multi-objective optimization are obtained as a set of multiple optimum solutions, called ‘the Pareto optimal solutions’. Furthermore, a set of typical constraints, governing the pipeline operation, is subjected to obtain more practical solutions. To control the constraints satisfaction and to find better solutions in optimization process, the penalty functions are defined and applied. Sensitivity analysis of change in the objective functions, when the optimum decision variables vary, is also conducted and the degree of each parameter on conflicting objective functions is investigated.     

萃取蒸馏脱除油品中硫的过程模拟与优化

汽车尾气严重污染环境,为了生产满足环保法规的硫含量低于10μg/g的汽油,提出了在传统的萃取蒸馏中以有机溶剂+离子液体（IL）为复合萃取剂的脱硫法。以与真实催化裂化（FCC）汽油组成及物性相近的模型油为模拟汽油,利用COSMO-RS模型计算了30种常见IL对环己烷-噻吩的选择性和溶解能力,筛选出用于萃取蒸馏脱硫添加剂的最佳离子液体为[EMIM][BF₄]。通过Aspen Plus软件以N-甲酰吗啉（NFM）+[EMIM][BF₄]为复合萃取剂进行了汽油脱硫的工艺流程模拟与优化。优化结果为萃取剂由NFM（质量分数98%）和[EMIM][BF₄]（质量分数2%）构成,萃取蒸馏塔质量回流比R=0.4,剂油质量比S/F=1,采出率为70%。模拟结果表明：萃取蒸馏可高效地脱除苯并噻吩、硫醚及噻吩类硫化物,上述硫化物总量可从1581μg/g降低至5.37μg/g,脱硫率达98.1%,质量收率为70%,体积收率为75%。此外,通过对比计算值与文献中实验值,验证了COSMO-RS预测IL热力学性质、UNIFAC预测有机硫化物-烃类汽液相平衡的准确性和模拟工艺流程的可靠性。