Argon production from air distillation: Use of a heat pump in a ternary distillation with a side rectifier

A ternary feed mixture ABC can be separated into individual components through the use of a main distillation column with a thermally linked side rectifier. To enhance such a separation, a heat pump can be implemented to transfer heat from the condenser at the top of the side rectifier to the reboiler at the bottom of the main column. In this paper, one such heat pump is described and applied to an air distillation system separating the ternary mixture containing nitrogen, oxygen and argon. The separation is performed by a conventional double column with a crude argon side column. When this system is operated at an elevated pressure to obtain higher product pressures, the separation of oxygen and argon becomes very difficult and leads to reduced argon recovery. The proposed heat pump enhances the separation by providing a supplementary crude argon condensing duty through the vaporization of a liquid oxygen stream from the bottom of the low pressure (LP) column. This scheme improves the liquid/vapour ratio (L/V) in the bottom section of the LP column and, more importantly, increases the vapour feed to the crude argon column. This increased feed rate leads to a substantial increase in argon recovery for the elevated pressure air distillation process.     

NMP萃取精馏分离醋酸和水的过程模拟

利用化工模拟软件Aspen Plus采用萃取精馏法,以N-甲基吡咯烷酮(NMP)为萃取剂,对生产中醋酸和水分离进行了模拟计算,并与普通精馏法进行比较。结果表明,NMP是一种良好的萃取剂,能够很好的实现醋酸和水的分离;与普通精馏法相比,同样分离指标下萃取精馏法的能耗降低了69.8%,每吨醋酸蒸汽消耗量由10.5 t降低至3.2 t,表明萃取精馏分离醋酸和水,节能显著,优于普通精馏,为醋酸和水分离的优化操作和设计提供依据。     

Preparation of high purity methylal by extractive distillation using N,N-dimethylformamide (DMF) as solvent

通过溶剂选择原理粗选出萃取精馏制备甲缩醛产品的溶剂,既而通过Chemcad软件模拟和汽液平衡实验确定合适的溶剂及溶剂比。结果表明,N,N-二甲基甲酰胺（DMF）能够消除甲缩醛-甲醇共沸物系的共沸点;采用UNIQUAC模型对常压下甲缩醛-甲醇物系和加入溶剂N,N-二甲基甲酰胺的汽液平衡进行模拟,模拟结果和实验数据吻合较好。用间歇萃取精馏实验对甲缩醛粗品进行了分离,在实验条件下,可以从塔顶得到质量浓度为99.9%的高纯度甲缩醛产品。     

Separation process of butanol-butyl acetate-methyl isobutyl ketone system by the analysis to residual curve and the double effect pressure-swing distillation

The separation of ternary mixture of butanol,butyl acetate,and methyl isobutyl ketone (MIBK) was initially analyzed by the residual curve.In this process,MIBK was chosen as the azeotropic agent during the first step of separation.The optimum mass ratio of extra MIBK was 1.6 in the modified feed stream according to the residual curve.Thus on this condition the top product was butanol-MIBK azeotrope while the bottom product was butyl acetate in the preliminary separation of the mixture.Then the butanol and MIBK azeotrope was separated by the double effect pressureswing distillation with the low pressure column performing at 30 kPa and the atmosphetic pressure column at 101 kPa.The optimal operating conditions were then obtained by using Aspen Plus to simulate and optimize the process.The results showed that the mass purities of butanol,butyl acetate,and MIBK were all more than 99％ and reached the design requirements.Additionally,compared with the traditional distillation with outside heating,the double effect pressure swing distillation saved the reboiler duty by 48.6％ and the condenser duty by 44.6％.     

全回流-全馏出与变塔压联合的间歇精馏过程

A novel operation of batch distillation-combination of varying colum pressure and total reflux-total efflux is studied experimentally. In the operation, the product is accumulated at the top of the column under total reflux and then drained off completely, and the column pressure is varying in the whole process. This process has been industrialized successfully with large profits. The conventional mode of batch distillation is improved by this method effectively: the separation eficiency and the yield of product are increased greatly, the operation time is shortened and the production cost is cut down. Moreover, the amount of condensation water is decreased and the over-high reboiler temperature is lowered.     

Moderate-pressure cryogenic air separation process

A new cryogenic air separation process has been developed which complements the traditional double column low pressure air separation cycle^1,2. The process, designated the M-Plant cycle (for moderate pressure), focuses upon high fractional recovery of argon and production of moderate pressure gaseous nitrogen. The M-Plant cycle distillation system inverts product pressures and provides crude argon and high purity nitrogen at about 200 kPa pressure with high purity oxygen slightly above atmospheric pressure. The traditional T-Plant cycle uses a standard low pressure double column distillation system which furnishes the oxygen at about 140 kPa pressure and crude argon and high purity nitrogen at slightly above atmospheric pressure. Since nitrogen and argon comprise the larger part (79%) of the processed air, the M-Plant cycle conserves product pressure energy and results in a physically smaller upper column and nitrogen piping which reduces capital cost. Customers requiring large amounts of gaseous nitrogen at about 200 kPa pressure and above can realize as much as 10% energy savings and up to 5% greater argon recovery over the traditional T-Plant.     

DCS控制系统在粗苯蒸馏工艺中的应用

针对传统粗苯蒸馏工艺人工调节频繁,调节不及时、不准确,产品质量不稳定,劳动负荷大等问题,通过引入DCS控制系统,建立计算机自动调节模型,调整函数的微分和积分变量实现脱苯塔塔顶回流量、进再生塔的蒸汽量和管式加热炉富油出口温度的自动控制,从而实现粗苯生产工艺的稳定、高产、优质和低耗。     

Using hot-vapor bypass for pressure control in distillation columns

Distillation column control is widely explored in literature due to its complexity and importance in chemical and petrochemical industries.In this process,pressure represents one of the most important variables to be controlled.However,there are few studies about how pressure affects the dynamic behavior of distillation columns and most research on distillation column control involve direct manipulation of cooling fluid through the condenser.Nevertheless,such an approach demands constant changes in cooling fluid flowrates that are commonly by the order of tons per hour,which can be difficult to work or even unfeasible in a real plant.Furthermore,this strategy is usually avoided,as it can cause fouling and corrosion acceleration.The hot-vapor bypass strategy fits well as a solution for these issues,eliminating the need to dynamically manipulate cooling fluid flowrates in the condensation unit.This work presents the modeling and simulation of a conventional distillation column for the separation of water and ethanol,in which a comparative study between a conventional pressure control and a control using hot-vapor bypass was performed.The main results were obtained through dynamic simulations which considered various disturbances in the feed stream,and demonstrated superior performance by the hot-vapor bypass system over the usual scheme proposed in literature,while evaluating the Integral Absolute Error (IAE) norm as the control performance index.     

DMC-甲醇-水三元混合物的萃取精馏分离工艺

运用Aspen Plus软件回归文献数据校正了碳酸二甲酯（DMC）-水（H₂O）混合物的UNIQUAC热力学模型参数,并以该模型为基础分析了水作为萃取剂萃取精馏分离DMC-甲醇（CH₃OH）-水三元混合物的分离原理,结合混合组分的三角相图和物料组成设计了反向萃取精馏工艺,发现选用水为萃取剂可以利用DMC-水的部分互溶特性,通过三塔精馏即可分离DMC-甲醇-水三元混合物,沸点较高的DMC和少量水由塔顶馏出,而沸点较低的甲醇和大部分水由塔底采出,避免了DMC-甲醇二元共沸物的形成。同时,在相同分离要求下设计了变压精馏工艺,通过对两个精馏工艺参数模拟优化,发现萃取精馏工艺的总冷凝负荷和总加热负荷分别为888.7kW和898.2kW,其总能耗较变压精馏工艺节约了47.2%,萃取精馏工艺的年总费用（TAC）比变压精馏工艺下降了48.8%。     

焦炉气制甲醇联产甲烷工艺模拟

介绍了焦炉气制甲醇联产甲烷工艺,并利用Aspen Plus对该联产工艺进行了模拟。模拟结果显示,在给定焦炉气进料条件下,联产工艺可实现日产摩尔分数93.01%的甲烷6.31×105m3,年产摩尔分数99.43%的甲醇2.04×105t。分析了补碳量、新鲜合成气温度、压力及第二级精馏塔塔板数对甲醇产品的影响。结果表明,当补碳量约为625.00 kmol/h、新鲜合成气温度约为240℃、反应压力为6 000.00 kPa、第二级精馏塔理论塔板数为25块左右时,甲醇产品中甲醇摩尔分数达到最大值,为99.75%。     

甲基氯硅烷精馏流程的模拟与优化

采用Aspen plus软件对工业七塔精馏过程进行全流程建模与模拟,优化工艺参数,研究了新的精馏节能工艺。对一甲塔等7个精馏塔采用双因素水平的灵敏度分析,考察了塔釜采出率、回流比、进料位置和塔顶压力对产品浓度和热负荷的影响,确定一甲塔最优的工艺参数：塔釜摩尔采出率为0.92,摩尔回流比为130,塔顶压力为0.18 MPa,总理论板数为400,在210块理论板位置进料。在此基础上,针对高能耗的脱高塔/脱低塔,模拟研究了双效精馏新工艺,新工艺可节省39.70%的年总成本;针对一甲塔模拟研究了热泵精馏新工艺,新工艺可降低41.42%的年总成本。     

Optimal design of mixed acid esterification and isopropanol dehydration systems via incorporation of dividing-wall columns

This study explores the design of a reactive distillation system and that of a heterogeneous azeotropic system by incorporating dividing-wall column (DWC). The first system involves the esterification of mixed acid (acetic acid and propionic acid) with methanol. Simulation studies are carried out for conventional reactive distillation sequence as well as for reactive dividing-wall distillation system. Both systems are optimized by an iterative optimization procedure. Optimal design results show that the reactive dividing-wall system saves steam consumption by 45.2% and reduces total annual costs (TAC) by 34.5%. The second case investigated is a heterogeneous azeotropic distillation system involving dehydration of crude isopropyl alcohol with cyclohexane as entrainer. Two optimal separation systems are generated, including one with a single-dividing wall column and one with a double-dividing wall column. In comparison with an energy-efficient azeotropic distillation sequence containing two stripping columns by Chang et al. (2012) [1], simulation results show that the former two systems can cut steam usage further by 6.0%. The two systems save about 5.4–6.1% in terms of TAC. DWCs prove to be superior to the convention distillation systems with respect to both cost and energy efficiency.     

A REACTIVE DISTILLATION PROCESS FOR AN AZEOTROPIC REACTION SYSTEM: TRANSESTERIFICATION OF ETHYLENE CARBONATE WITH METHANOL

A reactive distillation process is proposed for manufacturing dimethyl carbonate (DMC) through the transesterification reaction of ethylene carbonate (EC) with methanol. Modeling and simulation of the reactive distillation column have been carried out to study the effects of operating conditions, such as the reflux ratio, the number of theoretical plates, the feed ratio, the top effluent, the liquid holdup, and the feed location, on EC conversion and product composition at the top of the reactive distillation column. The calculated results show that a complete EC conversion can be achieved. The model reliability is analyzed under different Murphree tray efficiencies, showing no considerable difference between the equilibrium and nonequilibrium models for this system. And the calculated results are verified by experimental data and commercial operation of a dimethyl carbonate plant of 10,000 tons per year.     

A REACTIVE DISTILLATION PROCESS FOR AN AZEOTROPIC REACTION SYSTEM: TRANSESTERIFICATION OF ETHYLENE CARBONATE WITH METHANOL

A reactive distillation process is proposed for manufacturing dimethyl carbonate (DMC) through the transesterification reaction of ethylene carbonate (EC) with methanol. Modeling and simulation of the reactive distillation column have been carried out to study the effects of operating conditions, such as the reflux ratio, the number of theoretical plates, the feed ratio, the top effluent, the liquid holdup, and the feed location, on EC conversion and product composition at the top of the reactive distillation column. The calculated results show that a complete EC conversion can be achieved. The model reliability is analyzed under different Murphree tray efficiencies, showing no considerable difference between the equilibrium and nonequilibrium models for this system. And the calculated results are verified by experimental data and commercial operation of a dimethyl carbonate plant of 10,000 tons per year.     

常压塔回流取热流程的讨论

根据一套500万t/a常减压蒸馏装置的数据,采用ASPEN PLUS软件对目前常减压蒸馏装置设计中采用的3种常压塔回流取热流程进行了模拟计算,并从产品分离精度、对换热网络终温的影响等方面进行了对比.对比结果认为流程1和流程3产品的分离精度比较好,流程2的换热网络终温较高、但产品的分离精度和常压塔的操作弹性较差.     

新型复合塔板在甲醇回收中的应用

介绍了由新型复合塔板组成的精馏塔 ,采用直接蒸汽加热用于甲醇和水的分离 ,具有回收率高和操作费用低的优点。精馏塔及工艺改进后 ,塔顶产品甲醇含量在 98.5 %以上 ,塔釜废水中甲醇残留≤ 0 .3% ,甲醇回收率 99%以上 ,甲醇每小时回收量比改造前增加约 1 80kg,取得了明显的经济效益和环保效益。     

己烷油和异己烷油精馏分离系统的设计

采用6号溶剂油为原料,进行了分离过程的工艺模拟计算。根据工艺计算结果,进行了精馏塔的水力学核算,设计出同时生产异己烷油与己烷油的精馏装置,并确保精馏塔的分离效果达到了厂方的要求。该设计采用了高效规整填料与新型塔内件,使整塔压降控制在合理范围之内,并且保证了液体分布的均匀程度。实践证明,该设计不但保证了产品质量,同时也满足了对产品收率的要求。     

Purification of specific structured lipids by distillation: Effects on acyl migration

The cause and effects of acyl migration during the purification of specific structured lipids by distillation were studied in a conventional batch deodorizer with stripping steam. The mixture of specific structured lipids produced by lipase-catalyzed acidolysis between rapeseed oil and capric acid contained a large amount of free fatty acids and a small amount of partial acylglycerols besides triacylglycerols. Therefore, the effect of steam, free fatty acids, diacylglycerols, and monoacyl-glycerols on acyl migration was studied in a palm oil midfraction model. The results showed that all these factors influenced the rate of acyl migration, and their combinations made the effect more severe. However, diacylglycerols were found to be the main reason for acyl migration. In the distillation of the specific structured lipid product mixture, distillation temperature and time were the main factors to determine the degree of acyl migration and the extent of separation of free fatty acids. The results indicate that more efficient separation technology should be used to improve the quality of the purified structured lipids. In order to reduce the distillation temperature, vacuum should be made as low as possible with more effective pumps. To reduce the distillation time, thin-film principle in a packed column should be used, or other more efficient distillation techniques such as molecular distillation or short-path distillation should be exploited.     

草酸二乙酯加氢制乙二醇产品精馏试验研究

通过减压间歇精馏对草酸二乙酯加氢制乙二醇产品进行精制.试验表明该方法切实可行,获得了纯度≥99.8％的乙二醇产品;同时探讨了塔顶压强、回流比变化对产品纯度的影响,获得了试验条件下的最佳操作条件,为工业化提纯草酸二乙酯加氢制乙二醇产品提供了有益信息.     

聚酯工艺塔节能降耗技术探讨

概述了在聚酯工艺塔装置中增加板式换热器,利用塔顶蒸汽制取热水,再将热水进行综合利用。系统运行后,热水型制冷机每月可节约用电121.88万度;浆料配制过程每天可节约1.64×107k J能耗;长丝空调每天可节能7.4 t标煤的发热量。