Low Gas Loading Research Articles

A Comparative CFD Study on Gas-Liquid Dispersion in A Stirred Tank with Low and High Gas Loadings

Abstract The computational fluid dynamics (CFD) combined with a population balance model (PBM) was applied to simulate gas-liquid dispersion in a stirred tank with low and high gas loadings. The model predictions were validated by using the data in the literature. The simulation results show that the flow patterns and gas dispersion characteristics are very different in the stirred tank for low and high gas loadings. A typical two-loop flow pattern forms as that in single-phase stirred tank for low gas loadings, while a triple-loop flow pattern, with two recirculation loops above and one below the impeller is found in the tank for high gas loadings. Shaft power input of impeller agitation plays a major role for gas dispersion with low gas loadings. For high gas loadings, the potential energy due to gas sparging has significant effect on gas dispersion and can not be neglected. Compared to low gas loading, high gas loading causes average gas holdup increased in the stirred tank, while relative local gas holdup in the lower circulation-loop region and near-wall region reduced. The ability of impeller agitation for gas dispersion reduces with high gas loadings, and mean bubble size becomes larger and the volume-averaged bubble size distribution is wider.

Modeling the solubility of CO2 in aqueous methyl diethanolamine solutions with an electrolyte model based on COSMO-RS

A new COSMO-RS based electrolyte model (COSMO-RS-ES) was applied to the prediction of the solubility of CO2 in aqueous MDEA solutions. For this purpose, the model was combined with the Soave-Redlich-Kwong equation of state to describe the gas phase non-ideality. First, it was shown that the model can successfully describe the phase equilibria in the CO2 + water, as well as in alkanolamine + water systems. Using a region specific interaction parameter for the amine, the accuracy of the model for the prediction of the phase equilibrium in alkanolamine + water systems was further improved. Additionally, a detailed investigation of different amine + water systems based on the calculation of the partial molar enthalpies and entropies provided valuable insights on the properties of the systems. The description of the ternary CO2 + MDEA + H2O system was successful after a readjustment of selected interaction energy equations of the model using few parameters. The model was then applied to the prediction of the species distribution as well as the prediction of the partial pressure of CO2 at low gas loading.

Discontinuous atmospheric pressure interface for mass spectrometry using a solenoid pulse valve.

For the development of on-site mass spectrometry for security and safety, point-of-care analysis, etc., the gas volume introduced into the vacuum should be reduced to a minimum. To cope with this demand, a discontinuous atmospheric pressure interface using a solenoid pulse valve was developed. The sample gas was introduced discontinuously into the ionization cell with a volume of 0.17cm(3) . The sampled gas in the cell was ionized by an alternating current (ac) corona discharge. The generated ions were sampled through a 0.25mm i.d. and 12mm long nickel capillary into the vacuum of a time-of-flight mass spectrometer. A gas flow rate of ~25mL/min was achieved with the 1Hz pulse valve operation and 20ms valve opening time. Sub-ng limits of detection for less volatile compounds such as explosives and drugs were obtained. Due to its compact size and low gas load to the vacuum, this new interface may be useful for applications in miniaturized mass spectrometry. Copyright © 2016 John Wiley & Sons, Ltd.

Some notes on process intensification of amine based gas sweetening process for better temperature distribution in contactor to reduce the amount of amine as a result of corrosion and foaming

The conventional processes of acid gas removal from natural gas have the disadvantages of low acid gas loading capacity, high equipment corrosion rate and energy demand. To address these issues and to better control of corrosion and temperature in the contactor, the temperature based techniques such as supersonic gas separation, mixed amines and multi-lean amine streams processes are simulated and proposed using computational fluid dynamics and process simulator software, respectively. The results of multi-lean amine streams approach confirmed a lower corrosion and temperature along the contactor and proposed a promising process.

Solubility and thermodynamic modeling of hydrogen sulfide in aqueous (diisopropanolamine + 2-amino-2-methyl-1-propanol + piperazine) solution at high pressure

Natural gas as a clean source of energy contains several contaminates such as CO2 and H2S that is treated through a natural gas purification unit in gas industry. Moreover, for design and construction of gas contactor equipment, it is necessary to obtain experimental values of solubility for H2S and CO2 in aqueous amine/alkanolamines. In this work, the solubility of H2S in the blended aqueous diisopropanolamine (DIPA), 2-amino-2-methyl-1-propanol (AMP) and piperazine (Pz) are measured using a static high pressure apparatus through volumetric method. The values are measured at fixed 45 mass per cent of total amine so that the solubility of H2S in the present system is investigated under isothermal conditions at T=(313.15, 328.15 and 343.15)K and in the pressure range of (0.1 to 2.1)MPa. The experimental results are presented as the partial pressure of H2S against acid gas loading (moles H2S per total moles of amine). Also for modeling the solubility of H2S in the blended amine/alkanolamines, the Electrolyte-NRTL activity coefficient function is applied to the correlation and prediction of the partial pressure of H2S versus the acid gas loading. Considering the present results at the given conditions, it is observed that in the low gas loading region, the effect of enhancing Pz on the solubility of H2S is very low, but at high gas loading the absorption of H2S is intensified by enhancing mass fraction of Pz in alkanolamine.

A novel intensified reactive absorption of ethanol gas sweetening plant

The conventional acid gas removal processes from natural gas have the disadvantages of low acid gas loading capacity, high equipment corrosion rate and energy demand. In order to address these issues, the novel process based on the non-aqueous system of ethanol is simulated and proposed for first time. Simulation results showed that significant energy saving, low corrosivity and high acid gas removal are expected for the new process.

Solubility of Carbon Dioxide in Activated Potash Solutions in the Low and High Gas Loading Regions

In the Hot Potassium Carbonate Process, carbon dioxide (CO2) is removed from gaseous streams by chemical absorption in an aqueous solution of potassium carbonate (K2CO3). It is common to activate the solvent by adding borates and vanadates as promoters. In the present investigation, we investigate the influence of borates and vanadates on the equilibrium solubility of CO2 in aqueous solutions of K2CO3. The solubility of CO2 in four activated aqueous solutions of K2CO3 was determined experimentally at two temperatures that are typical for CO2 absorption (343 K) and solvent regeneration (383 K) in the Hot Potassium Carbonate Process. The mass fraction of K2CO3 in the solvent was 0.26 g/g, and the mass fractions of boron (vanadium) was varied between 0.006 g/g and 0.013 g/g (0.01 g/g and 0.02 g/g). Two experimental setups were used: A headspace gas chromatography technique was applied to determine the solubility of CO2 at partial pressures of CO2 between 1 kPa and 140 kPa, and the synthetic gas solubility te...

Solubility of Carbon Dioxide in Aqueous Solutions of Monoethanolamine in the Low and High Gas Loading Regions

Reliable data for the solubility of carbon dioxide in aqueous solutions of monoethanolamine are required for the design and evaluation of postcombustion carbon capture processes. As published experimental data for the solubility of carbon dioxide in aqueous solutions of monoethanolamine show considerable scatter, the solubility of carbon dioxide in aqueous solutions containing (15 and 30) mass percent of monoethanolamine; that is, (2.9 and 7.0) mol·(kg H2O)−1 respectively, was measured at molar ratios of carbon dioxide to monoethanolamine in the liquid solution from 0.1 to 1.3 at (313, 353 and 393) K. An apparatus based on headspace gas chromatography (on the synthetic gas solubility method) was used for the experiments at low (high) gas loadings, that is, at partial pressures of carbon dioxide from (1 to 80) kPa (from (0.4 to 8.6) MPa). The new experimental results are compared to literature data and used to parametrize a physicochemical thermodynamic model based on the extended Pitzer equation for the G...

Experimental Study on Internal Flow Field of Wet Desulphurization Tower

In order to study the flue gas velocity distribution and pressure drop characteristics inside wet desulfurization Tower, experimental study has been carried out. Flow model is built with geometric scale of 1 / 12 , flue gas velocity ratio of 1 / 1 and different gas entrance angle as 12°and 7°. Experiment result shows that Spray liquid droplets made gas more evenly; The evenness of gas velocity distribution is very poor with very low gas load (<35%);The pressure drop in tower increases with increase of sprayer and increases with increase of gas load; The evenness of gas velocity distribution becomes poor and the pressure drop increases when gas inlet angle changes from 12°to 7°.

High pressure solubility of carbon dioxide (CO 2) in aqueous piperazine solutions

The absorption of carbon dioxide in aqueous solutions of piperazine (PZ) in a high pressure Jerguson cell was studied at high gas loadings (1.06–2.77) mo l C O 2 /mol PZ. Because of its cyclic and diamine characteristics, the reactivity and solubility of piperazine are higher than in other secondary amines. The solubility of CO 2 in aqueous solutions of piperazine was measured at (313 and 343) K for (0.3 and 1.2) M piperazine up to a pressure of 7400 kPa. The Electrolyte-NRTL model was used to correlate the solubility of CO 2 in aqueous solutions of piperazine. Eight adjustable ionic pair interaction parameters were estimated allowing for the correlation of the available experimental solubility data with an average deviation of 1–2% in CO 2 partial pressure. The model was tested by predicting published experimental literature data for both low and high gas loadings.

A short pulse (7 μs FWHM) and high repetition rate (dc-5kHz) cantilever piezovalve for pulsed atomic and molecular beams

In this paper we report on the design and operation of a novel piezovalve for the production of short pulsed atomic or molecular beams. The high speed valve operates on the principle of a cantilever piezo. The only moving part, besides the cantilever piezo itself, is a very small O-ring that forms the vacuum seal. The valve can operate continuous (dc) and in pulsed mode with the same drive electronics. Pulsed operation has been tested at repetition frequencies up to 5 kHz. The static deflection of the cantilever, as mounted in the valve body, was measured as a function of driving field strength with a confocal microscope. The deflection and high speed dynamical response of the cantilever can be easily changed and optimized for a particular nozzle diameter or repetition rate by a simple adjustment of the free cantilever length. Pulsed molecular beams with a full width at half maximum pulse width as low as 7 micros have been measured at a position 10 cm downstream of the nozzle exit. This represents a gas pulse with a length of only 10 mm making it well matched to for instance experiments using laser beams. Such a short pulse with 6 bar backing pressure behind a 150 microm nozzle releases about 10(16) particles/pulse and the beam brightness was estimated to be 4x10(22) particles/(s str). The short pulses of the cantilever piezovalve result in a much reduced gas load in the vacuum system. We demonstrate operation of the pulsed valve with skimmer in a single vacuum chamber pumped by a 520 l/s turbomolecular pump maintaining a pressure of 5x10(-6) Torr, which is an excellent vacuum to have the strong and cold skimmed molecular beam interact with laser beams only 10 cm downstream of the nozzle to do velocity map slice imaging with a microchannel-plate imaging detector in a single chamber. The piezovalve produces cold and narrow (Delta v/v=2%-3%) velocity distributions of molecules seeded in helium or neon at modest backing pressures of only 6 bar. The low gas load of the cantilever valve makes it possible to design very compact single chamber molecular beam machines with high quality cold and intense supersonic beams. The high speed cantilever piezovalve may find broad applicability in experiments where short and strong gas pulses are needed with only modest pumping, the effective use of (expensive) samples, or the production of cold atomic and molecular beams.

Solubility of Hydrogen Sulfide in Aqueous Solutions of Piperazine in the Low Gas-Loading Region

The solubility of hydrogen sulfide in 2 m (about 0.146 mass fraction) aqueous solutions of 1,4-diazacyclohexane (piperazine, PIPH2) was measured at low gas loadings (at stochiometric molar ratios of hydrogen sulfide to PIPH2 between about 0.14 and 1.04) and low partial pressures of hydrogen sulfide (from about (1.3 to 98.7) kPa) at (313.5 and 392.2) K by headspace gas chromatography. The new experimental results are a supplement to previously published data in the high gas-loading region. The new experimental data are compared to prediction results from a thermodynamic model that was based only on gas solubility data in the high gas-loading area. That thermodynamic model for describing the vapor−liquid equilibrium uses Pitzer’s molality-based equation for the excess Gibbs energy of the aqueous solution. The average relative deviation between the new experimental results and the predictions for the partial pressure of hydrogen sulfide amounts to 10 %.

Solubility of Carbon Dioxide in Aqueous Solutions of N-Methyldiethanolamine and Piperazine in the Low Gas Loading Region

A synthetic technique was used to measure the solubility of carbon dioxide in three aqueous solutions of 2,2′-methyliminodiethanol (N-methyldiethanolamine, MDEA) and piperazine (PZ) at around (313, 333, 353, and 393) K and pressures between about (0.2 and 10) MPa. The molalities of (MDEA + PZ) in the aqueous solutions were (2.2 + 1.97), (4.22 + 2.01), and (7.83 + 2.07), respectively. The loading of the amines by carbon dioxide (i.e., the molar ratio of (MDEA + PZ) and CO2 varied between 0.2 and 2.0 The new experimental results are to supplement previously published experimental data of our research group for a single solution of both amines {molalities of (MDEA + PZ) in the aqueous solutions: (2.0 + 2.0)}. The new experimental results are compared to predictions from a model that combines previously published models for (CO2 + MDEA + H2O) and (CO2 + PZ + H2O).

PRODUCTION OF HYDROGEN, NITROGEN AND ARGON PELLETS WITH THE MOSCOW-JÜLICH PELLET TARGET

Targets of frozen droplets ("pellets") from various liquefiable gases like H 2, D 2, N 2, Ne , Ar , Kr and Xe are very promising for high luminosity experiments with a 4π detector geometry at storage-rings. High effective target densities (> 1015 atoms / cm 2), a small target size (⊘ ≈ 20–30 μ m ), a low gas load and a narrow pellet beam are the main advantages of such targets. Pioneering work on pellet targets has been made at Uppsala, Sweden.1 A next generation target has been built at the IKP of FZJ in collaboration with two institutes (ITEP and MPEI) from Moscow, Russia. It is a prototype for the future pellet target at the PANDA experiment at FAIR/HESR (supported by INTAS 06-1000012-8787, 2007/08) and makes use of a new cooling and liquefaction method, based on cryogenic liquids instead of cooling machines.2 The main advantages of this method are the vibration-free cooling and the possibility for cryogenic jet production from various gases in a wide range of temperatures. Different regimes of pellet production from H 2, N 2 and Ar have been observed and their parameters have been measured.3 For the first time, mono-disperse and satellite-free droplet production was achieved for cryogenic liquids from H 2, N 2 and Ar .

Supercritical carbon dioxide fractionation of Lavandin essential oil: Experiments and modeling

The two main components of Lavandin essential oil are linalool and linalyl acetate. These components have different applications in the food and fragrance industry, and also for producing natural herbicides and insecticides in the case of linalool. Thus there is a commercial interest in the separation of the essential oil into linalool- and linalyl acetate-rich fractions. This work presents a study of this fractionation using supercritical CO 2 in a continuous operating high-pressure counter-current packed column. The influence of process parameters like flowrate, pressure and temperature has been determined. The separation is limited by the low gas load achieved, and it has been observed that in order to increase the load, high temperatures and CO 2/oil phase ratios were necessary with operating pressures close to the mixture critical point. Additionally, a detailed mathematical model of the fractionation column has been developed and validated with the pilot plant results. This model has been used to study the operation with conditions that exceed the capabilities of the pilot plant such as a higher CO 2/oil phase ratio or a longer fractionation column, and to propose the optimum conditions for this fractionation.

Solubility of Carbon Dioxide in Aqueous Solutions of N-Methyldiethanolamine in the Low Gas Loading Region

A headspace gas chromatography technique was applied to determine the solubility of carbon dioxide in aqueous solutions of 2,2‘-methyliminodiethanol (N-methyldiethanolamine, MDEA) at low gas loadings (at stoichiometric molar ratios of carbon dioxide to MDEA between about 0.003 and 0.8). A temperature range T ≈ 313−393 K was covered. The stoichiometric molality of MDEA in water amounted to about 2, 4, and 8 mol/(kg of water) (mass fraction of MDEA ≈ 0.192, 0.323, and 0.488). The partial pressure of carbon dioxide was between about 0.1 and 70 kPa. A thermodynamic model for describing the vapor−liquid equilibrium (which applies Pitzer's molality-scale-based equation for describing the Gibbs excess energy of the aqueous phase) is revised and extended using the new data.

Solubility of Carbon Dioxide in Aqueous Solutions of Piperazine in the Low Gas Loading Region

The solubility of carbon dioxide in aqueous solutions of piperazine was determined at low gas loadings (stoichiometric molar ratios of carbon dioxide to piperazine between about 0.05 and 0.95) and temperatures between (313 and 393) K by means of headspace gas chromatography. The stoichiometric molality of piperazine amounted to about (1 and 2) mol·(kg of water)-1 {mass fraction of piperazine ≈ (8 and 15) %} at T ≈ 313 K and to about (2 and 4) mol·(kg of water)-1 {mass fraction of piperazine ≈ (15 and 26) % } at T ≈ (353 and 393) K. The partial pressure of carbon dioxide was between about (0.1 and 95) kPa. A thermodynamic model for describing the vapor−liquid equilibrium (which applies Pitzer's molality scale based equation for describing the Gibbs excess energy of the aqueous phase) is revised and extended using the new data.

Advanced performance of small diaphragm vacuum pumps through the use of mechatronics

Oil-free diaphragm vacuum pumps have proven to be the best way in vacuum generation for the chemical laboratory and they also find increasing use as backing pumps for modern wide-range turbo molecular pumps. The majority of vacuum pumps in practical use pump only a rather small percentage of their lifetime at full gas load. A pump backing a turbo molecular pump does not have to pump a significant gas load when the high-vacuum pump is running at ultimate vacuum pressure. Also, for a vacuum distillation the vacuum pump has to operate at full speed only at the beginning to lower the pressure inside the system to a vacuum level where evaporation starts. In a rather leak-tight system the distillation process continues by evaporating from the hot liquid and condensing at the cold condenser without the need of a mechanical vacuum pump. Rotational speed controlled diaphragm pumps are now available through progress in mechatronics and offer high pumping speed capability for fast pump-down cycles and precise pressure control for distillations. At low gas load the rotational speed can be reduced, improving maintenance intervals, power consumption, noise, vibration and – surprisingly – also ultimate pressure. The different behaviour in pumping speed and ultimate pressure of rotational speed controlled diaphragm pumps in comparison to constant-speed pumps is related to the mechanical properties of the valves and gas dynamics .

GENAP—the code for a pressure distribution calculation

The program for calculating the pressure distribution in long vacuum chambers, evacuated by several pumping units, was written for the general case of random location of different pumps, connected by the cylindrical pipes of varying cross-sections. The fast but simplified version compiled as GENAP4 was applied to compute the pressure distribution in the axial injection lines of heavy-ion cyclotrons. It is based on calculating the partial distribution corresponding to one pump, provided the rest of the pumps are off. The total pressure distribution is then obtained by inverse summation of the partial distributions. The results are in good agreement with measured values for the case of low gas load. For higher gas loads several correcting routines were incorporated into the program version GENAP7. This code was used to calculate the pressure distributions over a linear accelerator, where very good agreement with the measured values has been observed.

A Thermodynamic Model of Methyldiethanolamine−CO2−H2S−Water

The electrolyte−nonrandom two-liquid model has been used to represent the thermodynamic behavior of the system: methyldiethanolamine−CO2−H2S−water. The Data Regression System (DRS) of Aspen Plus was used to regress parameters of the model to experimental data. pH and conductivity data were utilized to supplement vapor−liquid equilibria (VLE) data and improve confidence in model predictions at low acid gas loadings. Predictions for the mixed acid gas systems can be accurately made from the single acid gas parameter sets without the need to regress additional parameters. VLE data were fit well and the calculated heat of absorption matches calorimetric data.