Argon Column Research Articles

Detailed Design and Economic Evaluation of a Cryogenic Air Separation Unit with Recent Literature Solutions

Cryogenic air separation is a well-established technology. However, due to its associated energy intensity and hazardousness, new studies are always emerging on this topic. Nevertheless, economic feasibility studies of cryogenic separation plants are still scarce. Studies of this type are essential because installing an air separation unit can also be considered at the design stage of other common industrial projects, such as oxidation/combustion processes and ammonia production. This study aims to elucidate the technical and economic aspects of a real-size air separation unit and analyze the feasibility of incorporating some alternatives recently proposed in the literature, such as multistage compression with and without an organic Rankine cycle for energy saving, integrated argon column, energy recovery systems in turbines, and a PSA unit for CO2 removal, and in the implementation of a new plant. For this, we performed a rigorous simulation and a robust economic evaluation. Thus, it was possible to identify the main bottlenecks of the process, which may become the subject for future work. As a result, the relevance of the compression (34–36%) and refrigeration (54–55%) stages in the capital cost and the importance of conscious electricity (29–32% of the production costs) and maintenance spending for the process’ economic viability were shown. Flowsheets and economic analysis are presented in detail so that they could be used as a base case for future developments in this field.

Comparisons of thermodynamic and economic performances of cryogenic air separation plants designed for external and internal compression of oxygen

Cryogenic air separation plants producing pressurized gaseous oxygen (PGOX) near 40 bara at purities 99.8% and 95% and gaseous nitrogen at 5 bara above 99.99% purity are analyzed. Oxygen is compressed either by external compression process (EC) or by internal compression (IC). IC is gasification of pumped liquid oxygen in the main heat exchanger (MHX). IC plants require appropriate combinations of pressure and flow of air and size of the MHX to vaporize PGOX with reasonable specific power consumption (SPC). Based on exergy and economic analyses of the ASU after simulating the plant in Aspen HYSYS®™8.6, the values of parameters which give high exergy efficiency with low capital and operating expenditures are determined. SPC of IC is 7–8% higher than that of EC. Addition of crude argon column improves the purity of oxygen from 96.3% to 99.8%. Recovery of oxygen improves by 5% with 3–4% reduction of SPC for both types of plants. Capital requirement for both EC and IC plants is about 50% higher with argon separation than without it. HP air between 33% and 31% of total air flow at 70 bara and 80 bara respectively is the most preferred range of operation of IC plants for 95% purity of oxygen. The corresponding flow of HP air is 5% lower for 99.8% purity of oxygen.

Membrane-assisted Cryogenic Distillation for Energy-efficient Argon Production from Air

High-purity argon is produced from air by cryogenic distillation; the process is energy intensive because of the similar volatilities of oxygen and argon. This work investigates the potential to reduce the energy consumption of argon production by using membrane-assisted distillation in the crude argon column of an air separation unit (ASU). Membrane-assisted distillation flowsheets are developed and simulated in Aspen Plus®. A customised model for the membrane separation is implemented in Aspen Plus as a user-defined unit. The built-in optimisation tool in Aspen Plus is used to optimise process operating conditions and the location of the membrane unit along the distillation column with the objective of minimising the overall power demand of the process. The performance of ambient polymeric membrane separations and low-temperature carbon molecular sieve membranes separations is evaluated.Detailed simulation and optimisation results show that membrane-assisted distillation offers considerable power savings when the membrane is placed in parallel to the distillation column. For both types of membrane material, the reduction in specific power demand (i.e. per unit of argon produced) is greatest when the membrane is placed close to the feed stage of the distillation column. A reduction in specific power demand of 12 %, relative to conventional distillation, is found for commercially available polymeric membranes. The decrease in specific power demand would be even greater (up to 32 %), if carbon molecular sieve membranes operating at low temperatures could be used.

Reduced electric field in the positive column of the glow discharge in argon

In this paper we report the measurements we performed of the reduced electric field strength E/p in the positive column in the range of the gas pressure and tube radius product of 0.01 < pR < 30 Torr·cm. We got good agreements with numerical models and experimental data of other authors. We also present two analytical models for the reduced electric field E/p. The first model deals with the ambipolar mode of the positive column of the dc discharge in noble gases. We consider the case of low discharge current values when one observes a balance between the rate of charged particle production due to direct ionization of gas molecules through electron impact and their escape to the discharge tube walls. Simple expressions for the reduced electric field E/p in the positive column in argon are obtained. The second model consists in considering the production and loss of charged particles and metastable atoms and obtaining a simple equation for the reduced electric field E/p depending on the discharge current density, gas pressure and tube radius. These models furnish a good description of experimental data in the whole range of pR values studied.

ПУСКОВОЙ РЕЖИМ ВОЗДУХОРАЗДЕЛИТЕЛЬНЫХ УСТАНОВОК С УЗЛОМ ПОЛУЧЕНИЯ АРГОНА

The starting conditions of the technical argon column included in the air separation plant (ASP) is described. The results of calculation of argon rectification over a wide range of parameters are presented. The conditions of argon accumulation in the liquid inside the technical argon column have been analyzed. Starting period duration — gaseous argon fraction argon content relationship for standard parameters of argon rectification units is shown, the comparison with actual data of operational ASPs is made. Recommended is the range of gaseous fraction composition for the technical argon column starting period, wherein the technical oxygen of the designed purity can be produced.

Gas-discharge acoustically induced laser

The generation of superluminescent flashes from a positive argon column induced by an acoustic wave upon a stepwise transition of the high-pressure gas discharge from the noncontracted state to the contracted state is considered. The conditions for the acoustically induced population inversion in the plasma column are described. The creation of a gas-discharge acoustically induced laser is proposed.

Heat and mass transfer model approach to optimum design of cryogenic air separation plant by packed columns with structured packing

Abstract A process simulator for design of a cryogenic air separation plant by packed columns with structured packing was developed by use of our heat and mass transfer model. The heat and mass transfer rates were estimated by correlations which were proposed in our previous work (J. Chem. Eng. Japan 33 (2000) 245). Comparison of the predicted separation performance of a pilot-scale cryogenic air separation plant by the developed simulator with the observed data was made. Predicted concentration profiles in the low pressure column and the ones in the argon column showed good agreement with observed data. The effects of the side-cut location to the argon column, the liquid-feed location to the low pressure column, and the vapor–liquid ratio in the feeds to the low pressure column for a commercial-scale cryogenic air separation plant, which consisted of a high pressure column with 50 sieve trays, a 3.2-m diameter low pressure packed column with structured packing, and a 2.5-m diameter argon column with structured packing, on purity of the product nitrogen, oxygen and crude argon were also discussed.

Heat and Mass Transfer Model Approach to Prediction of Separation Performance of Cryogenic Air Separation Plant by Packed Columns with Structured Packing.

A process simulator for prediction of separation performance of a cryogenic air separation plant by packed columns with structured packing is developed by use of our heat and mass transfer model. The basic equations for the simulation are mass transfer correlations which were proposed in our previous work (Egoshi et al., 2000). Comparison of observed data from a pilot-scale cryogenic air separation plant, which consisted of a 710 mm-diameter high pressure sieve plate column for feed to low pressure column, a 500 mm-diameter low pressure packed column with structured packing for production of pure grade nitrogen and oxygen, and a 380 mm-diameter argon column with structured packing for production of crude argon is made. Predicted concentration profiles in the low pressure column and the ones in the argon column show good agreement with observed data. The effect of liquid feed location, side-cut location, vapor-liquid ratio of the feeds to the low pressure column on purity of the product nitrogen, oxygen and crude argon are also discussed.

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

Abstract 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.

Dynamics of an argon gas-embedded Z-pinch micro-channel as a function of the initial preionization

We have studied experimentally the relation between the preionization of a plasma micro-channel in Argon at atmospheric pressure and the dynamics of the discharge initiated by preionization. Preionization is obtained in two different ways: (a) injecting the soft X rays produced by a 3 J, 3 ns YAG laser focused on a copper target through a pinhole (b) direct focusing of a 4ω laser (0·26 μm) along the Argon column. Both experiments and simple numerical models are presented in this paper.

Anoxic contractile failure in rat heart myocytes is caused by failure of intracellular calcium release due to alteration of the action potential.

Anoxia of the heart causes failure of contraction before any irreversible injury occurs; the mechanism by which anoxia blocks cardiac excitation-contraction coupling is unknown. Studies in whole muscle are confounded by heterogeneity; however, achieving the low oxygen tensions required to study anoxia in a single myocyte during electrophysiological recording has been a barrier in experimental design. Guided by calculations of oxygen transport, we developed a system to insulate myocytes in an open dish from oxygen by a laminar counterflowing argon column, permitting free access to the cell by microelectrodes while maintaining a PO2 less than 0.02 torr (1 torr = 133 Pa). In the absence of glucose, the amplitude of stimulated contraction of anoxic ventricular myocytes fell to zero over 2 min after a lag period attributable to the consumption of endogenous glycogen. The cytosolic calcium concentration transient, measured by indo-1 fluorescence, fell to zero simultaneously with contraction. After the twitch had failed, microinjection of caffeine around the cell still caused a large calcium release and contraction, indicating that sarcoplasmic reticular calcium stores were not depleted. Twitch failure was accompanied by shortening and then failure of the action potential; under voltage clamp, large outward currents, reversing at the resting potential, developed during contractile failure. After failure of action potential-mediated contraction, voltage-clamp depolarization, with a large command voltage to compensate for the series-resistance error due to outward currents, restored normal twitch contraction. We conclude that anoxic contractile failure in the rat myocyte is due to alteration of the action potential and the distal pathways of excitation-contraction coupling remain essentially intact.

Modelling of the low-pressure argon positive column

The properties and operating characteristics of the positive column of a low-pressure positive column in argon have been investigated experimentally and theoretically. In the experiments the pressure was varied from 5×10−2 to 1 Torr, the discharge current from 0.2–20 mA, and the discharge tube was 2.6 cm inside diameter. Measurements of the axial electric field, electron density and population in 3P2 metastable states are reported for various discharge conditions. A test is made of the usefulness of a two-moment theory which is applicable in the intermediate pressure range of this work, i.e., in the transition from inertia-limited to mobility-limited flow of ions to the wall, for the prediction of the operating characteristics. For this purpose, the electron excitation and ionization rates, and transport parameters were calculated from the homogeneous Boltzmann equation. The predicted similarity laws for the positive column are in reasonable agreement with the measurements only in the lower pressure region, i.e., for a pressure-radius product less than about 0.1 Torr cm. The discrepancy between theory and experiment at the higher pressure is, presumably, the result of our failure to correct the calculated ionization rate and effective electron loss rate for the effects caused by ionization from metastables and by space-charge fields.

空気分離装置アルゴン塔の特性解析

空気分離装置アルゴン塔の特性解析

Design calculations for the argon column of an air-fractionating unit

Design calculations for the argon column of an air-fractionating unit

Ultrashort electromagnetic waves from arc discharges at the plasma frequency and its second harmonic

The radiation detected at four discrete frequency bands from the positive column in argon at low pressure is compatible with that from a source comprising two modes of plasma waves—oscillations of a plasma plate and cylinder.

The pressure gradient in positive columns

In a positive column in argon in a tube with radius much greater than the molecular free path, the pressure at the anode is greater than that at the cathode. The resulting axial gas and peripheral counterstreaming velocities, for which direct measurements are not available, have been calculated. The former varies in a typical case as (E/p)0.53. The velocities are smaller than those of ion drift and moving striations.

A simple and continuous level indicator for liquefied gases

Cryogenic air separation plants producing pressurized gaseous oxygen (PGOX) near 40 bara at purities 99.8% and 95% and gaseous nitrogen at 5 bara above 99.99% purity are analyzed. Oxygen is compressed either by external compression process (EC) or by internal compression (IC). IC is gasification of pumped liquid oxygen in the main heat exchanger (MHX). IC plants require appropriate combinations of pressure and flow of air and size of the MHX to vaporize PGOX with reasonable specific power consumption (SPC). Based on exergy and economic analyses of the ASU after simulating the plant in Aspen HYSYS®™8.6, the values of parameters which give high exergy efficiency with low capital and operating expenditures are determined. SPC of IC is 7–8% higher than that of EC. Addition of crude argon column improves the purity of oxygen from 96.3% to 99.8%. Recovery of oxygen improves by 5% with 3–4% reduction of SPC for both types of plants. Capital requirement for both EC and IC plants is about 50% higher with argon separation than without it. HP air between 33% and 31% of total air flow at 70 bara and 80 bara respectively is the most preferred range of operation of IC plants for 95% purity of oxygen. The corresponding flow of HP air is 5% lower for 99.8% purity of oxygen.

Striations in High Frequency Discharges

IN the course of an investigation on the starting and maintenance potentials of the luminous column in argon, produced by applying a high frequency potential of wave-length from 10 to 300 metres to external sleeve electrodes, we found that steady striations were frequently developed. Using the method described by Townsend and Donaldson (Phil. Mag., January 1928), an attempt was made to measure the potential fall over single striations to see whether any definite value could be assigned to it.