Adaptive Internal Model Control of a High‐Purity Heat‐Integrated Air Separation Column

An internal model control scheme based on a second‐order internal model (SI‐IMC) is proposed for the heat‐integrated air separation column (HIASC). An adaptive internal model control (ASI‐IMC) scheme is further presented to make the model more accurate. The IMC scheme based on the first‐order model (F‐IMC) and the multi‐loop PID (M‐PID) scheme are also explored as the comparison basis of ASI‐IMC and SI‐IMC schemes. Comparative researches among these four control schemes are carried out in detail. The results indicate that ASI‐IMC presents the best performances among the four control schemes in both servo control and regulatory control, which proves the improvement of ASI‐IMC over the SI‐IMC and the superiority of ASI‐IMC for the high‐purity HIASC.     

Dynamic modeling and collocation‐based model reduction of cryogenic air separation units

High purity distillation columns and multi‐stream heat exchangers (MSHXs) are critical units in cryogenic air separation plants. This article focuses on modeling approaches for the primary section of a super‐staged argon plant. A full‐order stage‐wise model for distillation columns in air separation units (ASUs) that considers key process phenomena is presented, followed by a reduced‐order model using a collocation approach. The extent of model reduction that can be achieved without losing significant prediction accuracy is demonstrated. A novel moving boundary model is proposed to handle MSHXs with phase change. Simulation results demonstrate the capability of the proposed model for tracking the phase change occurrence along the length of the heat exchanger. Dynamic simulation studies of the integrated plant show that the thermal integration between the feed and product streams captured in the primary heat exchanger is critical to accurately capture the behavior of ASUs. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1602–1615, 2016     

Sidestream Analysis and Optimization of Full Tower Internal Thermally Coupled Air Separation Columns

An appropriate sidestream is the key to improve the yields and purities of products in the cryogenic air separation process. The sidestream of a full tower internal thermally coupled air separation column is characterized. Sensitivity analysis indicates that heat duty distribution, purities, and yields of the products are strongly influenced by the withdrawn position and the flow rate of the sidestream. Optimization models are proposed by adopting the minimum flow rate of the low‐purity liquid nitrogen product and with maximum flow rates of the oxygen product or nitrogen product as optimization target. The optimization research allows selecting the optimum operating conditions with different production requirements.     

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.     

Reducing total annualized cost and CO2 emissions in batch distillation: Dynamics and control

In this contribution, the direct vapor recompression approach is introduced in a batch distillation operated at an unsteady state condition. This vapor recompressed batch distillation (VRBD) accompanies an isentropic compressor that runs at a fixed as well as variable speed. Aiming to ensure the optimal use of internal heat source, an open‐loop control policy is proposed for the VRBD that adjusts either the overhead vapor splitting or the external heat supply to the reboiler. Again, the variable speed VRBD additionally involves the manipulation of compression ratio. Developing two alternative configurations of VRBD column, the best heat integrated scheme is attempted to identify in the aspects of energy efficiency and total annualized cost for further advancement. A closed‐loop control algorithm for the best performing variable speed VRBD aiming to meet the end objective of relatively high‐purity product discharged at a constant composition is developed. The separation of a reactive system is considered to illustrate these results and demonstrate the effectiveness of the novel VRBD scheme. Performing simulation tests, it is investigated that the closed‐loop control operation substantially improves not only the distillate purity but also the total amount of product. Achieving significant improvement in thermodynamic efficiency and cost by the controlled heat integrated scheme over its conventional counterpart, finally the attractiveness of the VRBD column by investigating its potential to reduce the greenhouse gas (i.e., CO₂) emissions is shown. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2821–2832, 2013     

Production of argon free oxygen by adsorptive air separation on Ag‐ETS‐10

The purification of different components of air, such as oxygen, nitrogen, and argon, is an important industrial process. Pressure swing adsorption (PSA) is surpassing the traditional cryogenic distillation for many air separation applications, because of its lower energy consumption. Unfortunately, the oxygen product purity in an industrial PSA process is typically limited to 95% due to the presence of argon which always shows the same adsorption equilibrium properties as oxygen on most molecular sieves. Recent work investigating the adsorption of nitrogen, oxygen and argon on the surface of silver‐exchanged Engelhard Titanosilicate‐10 (ETS‐10), indicates that this molecular sieve is promising as an adsorbent capable of producing high‐purity oxygen. High‐purity oxygen (99.7+%) was generated using a bed of Ag‐ETS‐10 granules to separate air (78% N₂, 21% O₂, 1% Ar) at 25°C and 100 kPa, with an O₂ recovery rate greater than 30%. © 2012 American Institute of Chemical Engineers AIChE J, 59: 982–987, 2013     

Pilot‐scale studies of process intensification by cyclic distillation

Process intensification in distillation systems receives much attention with the aim of increasing both energy and separation efficiency. Several technologies have been investigated and developed, as for example: dividing‐wall column, HiGee distillation, or internal heat‐integrated distillation. Cyclic distillation is a different method based on separate phase movement—achievable with specific internals and a periodic operation mode—that leads to key advantages: increased column throughput, reduced energy requirements, and better separation performance. This article is the first to report the performance of a pilot‐scale distillation column for ethanol‐water separation, operated in a cyclic mode. A comparative study is made between a pilot‐scale cyclic distillation column and an existing industrial beer column used to concentrate ethanol. Using specially designed trays that truly allow separate phase movement, the practical operation confirmed that 2.6 times fewer trays and energy savings of about 30% are possible as compared with classic distillation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2581–2591, 2015     

Theoritical analysis and simulation of five‐zone simulating moving bed for ternary mixture separation

In the present work a mathematical model has been presented to study the behaviour of five‐zone simulating moving bed (SMB) system for the separation of a ternary mixture of certain amino acids. These are methionine, phenylalanine and tryptophan, possessing linear isotherms values. Safety margin method has been used to design the SMB system while triangle theory became the basis to calculate the operating conditions at fixed feed flow rate. It was found that for same safety factor (β) value in each zone, increase in β value causes the purity values of all product streams to increase up to a definite value. Further increase in β value shows the effect of decrease in separation efficiency, because of dominance of axial dispersion and mass transfer resistances. The effect of zone safety factor (zone flow rate β_II, β_III and β_IV) values on the separation performance of five‐zone SMB have also been investigated which remained an important issue in SMB current research. Increase in β_II value results in rising tryptophan purity, phenylalanine purity improves due to increase in β_III value and increase in β_IV value becomes the basis for enhancing methionine purity. In column profile study, the solute concentration profile diminishes due to increase in particular separation zone safety factor value. This happened due to low column switching time with high desorbent flow rate to the system. The developed mode was run in Aspen Chromatography vis 12.1. (2004) simulator for simulation studies.     

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     

Development of an efficient electroflocculation technology integrated with dispersed‐air flotation for harvesting microalgae

BACKGROUND: Various methods, including centrifugation, filtration, electroflocculation, flocculation and flotation, have been developed for harvesting microalgae. However, some economic or technical problems still remain with current methods for algal recovery, such as high capital, energy and running costs, flocculant toxicity or low separation efficiency. Therefore, there is great interest in developing new efficient approaches for harvesting microalgae. RESULT: An efficient electroflocculation method integrated with dispersed‐air flotation has been developed for harvesting Botryococcus braunii. The recovery efficiency of B. braunii reached 93.6% after 30 min using an electroflocculation process. Microalgae recovery was improved significantly when the electroflocculation process was integrated with dispersed‐air flotation; the recovery efficiency of B. braunii reached 98.9% after 14 min. CONCLUSION: The present work demonstrated that electroflocculation integrated with dispersed‐air flotation is a promising method suitable for microalgae harvesting. The strategic air supply obviously shortened the algal recovery time in the process of electroflocculation due to facilitating algal aggregation and flotation to the solution surface. Copyright © 2010 Society of Chemical Industry     

Hydrogen Production by Sorption‐Enhanced Steam Glycerol Reforming: Sorption Kinetics and Reactor Simulation

Sorption‐enhanced glycerol reforming, an integrated process involving glycerol catalytic steam reforming and in situ CO₂ removal, offers a promising alternative for single‐stage hydrogen production with high purity, reducing the abundant glycerol by‐product streams. This work investigates this process in a fixed‐bed reactor, via a two‐scale, nonisothermal, unsteady‐state model, highlighting the effect of key operating parameters on the process performance. CO₂ adsorption kinetics was investigated experimentally and described by a mathematical reaction‐rate model. The integrated process presents an opportunity to improve the economics of green hydrogen production via an enhanced thermal efficiency process, the exothermic CO₂ adsorption providing the heat to endothermic steam glycerol reforming, while reducing the capital cost by removing the processing steps required for subsequently CO₂ separation. The operational time of producing high‐purity hydrogen can be enhanced by increasing the adsorbent/catalyst volume ratio, by adding steam to the reaction system and by increasing the inlet reactor temperature. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2105–2118, 2013     

Performance and Energy Consumption of Membrane‐Distillation Hybrid Systems for Olefin‐Paraffin Separation

Light olefin and paraffin are commonly separated by energy‐intensive cryogenic distillation. Membrane/distillation hybrid systems constitute an economical alternative separation process. Different configurations of this hybrid system are studied for olefin‐paraffin separation with emphasis on C₃ separation. An approach based on the McCabe‐Thiele method is applied to analyze different process configurations. A facilitated transport membrane is considered as membrane type. Both new column design and augmentation of an existing distillation column by a membrane module are considered. Numerical examples are considered for the separation of propane from propylene through different hybridization shapes with facilitated transport membranes. The energy requirement can be halved using hybrid systems.     

Simultaneous Drying and Cleaning of Guava Seeds in a Spout‐Fluid Bed with Draft Tube

A half sectional spout‐fluid bed column with draft tube was used for the cleaning and drying of guava seeds in one single operation. The process took place on a batch basis with a constant spouting velocity of 1.5 U_ms and an additional annular air flow rate equivalent to 0.5 and 0.7 U_mf. A regression model based on the spouting air temperature T_s, the annular inlet air temperature T_a and the additional annular air flow rate xU_mf was obtained to calculate the drying time. An additional cleaning step was necessary to increase the separation efficiency of the dried pulp from about 70% obtained during the drying process to 84%.     

Separation of methanol‐tetrahydrofuran mixtures by heteroazeotropic distillation and pervaporation

The experimental investigation of the separation of tetrahydrofuran‐methanol by heteroazeotropic‐batch‐distillation and methanol‐hexane by pervaporation is presented. In particular for this last task, four different specialty commercial membranes were tested (varying feed concentration and temperature). The “pore filling” PolyAn membranes show methanol permeance values higher than 5100 GPU (Typ M2^®); separation factor of 19; and a selectivity of about 119 (Typ M1^®). From the results, a coupling phenomenon was observed. An assessment of the temperature effect in the pervaporation process corroborates the hypothesis of the presence of a coupling phenomenon. Finally, a discussion is made on two industrial scale units for the separation of the same mixture: a system of a distillation column integrated with a decanter and stand‐alone pervaporation unit. The energetic comparison shows that when using pervaporation a large reduction of the energetic consumption compared to a conventional distillation system (up to 29%) can be obtained. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2584–2595, 2014     

Modeling and analysis of conventional and heat‐integrated distillation columns

A generic model that can cover diabatic and adiabatic distillation column configurations is presented, with the aim of providing a consistent basis for comparison of alternative distillation column technologies. Both a static and a dynamic formulation of the model, together with a model catalogue consisting of the conventional, the heat‐integrated and the mechanical vapor recompression distillation columns are presented. The solution procedure of the model is outlined and illustrated in three case studies. One case study being a benchmark study demonstrating the size of the model and the static properties of two different heat‐integrated distillation column (HIDiC) schemes and the mechanical vapor recompression column. The second case study exemplifies the difference between a HIDiC and a conventional distillation column in the composition profiles within a multicomponent separation, whereas the last case study demonstrates the difference in available dynamic models for the HIDiC and the proposed model. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4251–4263, 2015     

A Novel Sol–Gel Method for Large‐Scale Production of Nanopowders: Preparation of Li1.5Al0.5Ti1.5(PO4)3 as an Example

Sol–gel synthesis is an extensively used method for the preparation of nanopowders. However, complicated or expensive precursors, and the necessity of using organic solvent and/or heat assistance limit the method to laboratory‐scaled level. An aqueous‐based sol–gel method with spontaneous sol and gel formation is developed in this study. It can be applied on a large scale to synthesize compounds with Ti⁴⁺ and PO₄^3? as major components with low cost. Al‐substituted LiTi₂(PO₄)₃ (LATP) has been widely investigated as a promising candidate for solid electrolyte in Li‐ion or Li‐air batteries. Major challenges such as unsatisfactory phase purity, low sintering activity, and high production costs are faced during the fabrication of LATP. In this study, as a sample application, Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP05) is conveniently prepared on a large scale by the novel sol–gel method with high phase purity, active densification behavior and high conductivity.     

Anatomy of a rapid pressure swing adsorption process performance

A detailed numerical study of the individual and cumulative effects of various mass, heat, and momentum transfer resistances, which are generally present inside a practical adiabatic adsorber, on the overall separation performance of a rapid pressure swing adsorption (RPSA) process is performed for production of nearly pure helium gas from an equimolar binary (N₂ +He) gas mixture using 5 A zeolite. Column bed size factor (BSF) and helium recovery (R) from the feed gas are used to characterize the separation performances. All practical impediments like column pressure drop, finite gas‐solid mass and heat transfer resistances, mass and heat axial dispersions in the gas phase, and heats of ad(de)sorption causing nonisothermal operation have detrimental impacts on the overall process performance, which are significantly accentuated when the total cycle time of a RPSA process is small and the product gas helium purity is high. These impediments also prohibit indefinite lowering of BSF (desired performance) by decreasing process cycle time alone. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2008–2015, 2015     

Effects of Oxygen Supply Modes on the Production of Human Growth Hormone in Different Scale Bioreactors

Recombinant Escherichia coli has been studied as a main host for recombinant protein productions, but it is still difficult to cultivate E. coli in a large industrial‐scale process due to the oxygen supply limitation. In this study, E. coli BL(21) harboring a new constructed plasmid (pEHUb‐hGH) was used for producing recombinant human growth hormone (r‐hGH) in 5‐L and 30‐L scale fermentors by supplying air and high purity oxygen, respectively, where the high purity oxygen was produced from a vacuum pressure swing adsorption (PSA). The impact of oxygen supply modes, i.e., air and high purity oxygen, on cell growth and r‐hGH production was investigated in different scale fermentors. In the case of high purity oxygen supply, the final cell density and r‐hGH concentrations were 63.0 and 4.8 g/L in the 5‐L fermentor, 51.6 and 4.0 g/L in the 30‐L fermentor, respectively. In addition, the productivity of r‐hGH was doubled in the 5‐L fermentor, and increased 4‐fold in the 30‐L fermentor, compared to the results obtained in the case of the air supply. The supply of high purity oxygen eliminated the oxygen limitation and acetate formation effectively, and apparently, did not affect the degradation of r‐hGH. This shows that the recombinant E. coli cultivation with high purity oxygen produced from PSA may provide an effective method for large‐scale industrial production of recombinant proteins.     

Generalized generic model control of high‐purity internal thermally coupled distillation column based on nonlinear wave theory

A new model‐based control strategy for the internal thermally coupled distillation column (ITCDIC) is presented. Based on the nonlinear wave theory that describes the nonlinear dynamics in the separation processes, a simplified nonlinear wave model is established that concerns both the wave propagation and the profile shape. An advanced controller (WGGMC) is formulated by combining the nonlinear wave model with a generalized generic model control (GGMC). Compared with a conventional generic model controller based on a data‐driven model (TGMC), and another wave‐model based generic model controller (WGMC) developed in our previous work, WGGMC exhibits the best performances in both servo control and regulatory control. Furthermore, WGGMC can handle a very‐high‐purity system of ITCDIC with top product composition of 0.99999, while the other two controllers fail to work. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4133–4141, 2013     

High‐rate hydrogen separation using an MIEC oxygen permeable membrane reactor

In this study, we propose using mixed ionic‐electronic conducting (MIEC) oxygen permeable membrane to separate hydrogen via the water splitting reaction. To do that, steam was fed to one side of the membrane (side I) and a low‐purity hydrogen was fed to the other side (side II). Oxygen from water splitting on side I permeates through the membrane driven by an oxygen chemical potential gradient across the membrane to react with the low‐purity hydrogen on side II. After condensation and drying, high‐purity hydrogen is acquired from side I. Thus, the hydrogen separation process is realized based on the fact that the low‐purity hydrogen is consumed and high‐purity hydrogen is acquired. We achieved a high hydrogen separation rate (13.5 mL cm^?2 min^?1) at 950°C in a reactor equipped with a 0.5‐mm‐thick Ba_0.98Ce_0.05Fe_0.95O_3‐δ membrane. This research proofed that it is feasible to upgrade hydrogen purity using an MIEC oxygen permeable membrane. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1278–1286, 2017