Gas Throughput Research Articles

Using wavelet analysis to characterize the transition from bubbling to turbulent fluidization

Turbulent fluidized bed (TFB) regime has demonstrated many advantages such as a combination of enhanced gas-solids contact and increased gas throughput, making it an optimal reactor in many industrial chemical and metallurgical processes. While the transition from bubbling to turbulent bed has been extensively investigated, some details still remain unclear such as the local transition velocity and the corresponding flow characteristics during the transition process. In this work, experiments were conducted in a conventional fluidized column with 0.267 m in diameter and 2.46 m in height and solids holdup was measured using an optical fiber probe in a superficial velocity range of 0.1–1.0 m/s. A discrete wavelet analysis method was proposed to extract quantitative information of bubbles/voids including the count and the lasting time. The local transition details and the onset velocity to the TFB regime in the fluidized bed were more clearly identified based on the extracted bubble/void information.

Experimental Investigation of Stability and Structure of Vertical LPG Inverse Diffusion Flames Issuing from an Elliptic Burner

The present paper experimentally examines the influence of the progressive variations of the central air jet velocity in a concentric circular-elliptical inverse diffusion flame (IDF) on the visual and thermal structure and stability of the developed flames. All experiments are conducted at a fixed fuel flow rate (liquefied petroleum gas) throughput that emerges from the annular elliptic passage having an aspect ratio of 2:1. The visual images are aided via a digital camera and shadowgraphs, while the thermal structure (axial and radial temperature profiles) is acquired using a bare fine wire (125 μm) thermocouple; rendering radiation loss insignificant. The visual images and shadowgraphs clearly indicate the existence of four regimes: (i) an annular partially premixed region at the burner rim, (ii) an inner central premixed blue flame, (iii) an outer luminous yellowish post combustion zone and (iv) the flame tip buoyant zone. The progressive increases of the central average air velocity (𝑉𝑎 = 7.4 m/s up to 31.3 m/s) result in shortening the visible flame length and narrowing the flame width. These are coupled with changing the flame appearance from a yellowish diffusion flame with a sooty core regime to an intense central premixed flame surrounded by a soot ring to blue flames exhibiting intense central radiation regime associated with soot oxidation. At extremely high air velocity > 21 m/s, locals flame extinction and re-ignition occurs at the boundaries of the ellipse minor axis and further increase of 𝑉𝑎 causes complete extinction of the main flame. These findings are very much supported by the mean gas temperature measurements that indicate steep temperature rise associated with the formation of a central premixed combustion within the flame core which is followed by the diffusion mode of combustion. A plateau of the axial temperature profiles is observed in the transition zone between the two regions whereby the rise in temperature due to soot oxidation is balanced by the radiation loss.

The CO2/CH4 Separation Potential of ZIF-8/Polysulfone Mixed Matrix Membranes at Elevated Particle Loading for Biogas Upgradation Process

Biogas is a renewable energy that has been explored widely in Indonesia to substitute non-renewable energy. However, the presence of certain gas, such as carbon dioxide (CO2), can decrease the calorific value and generate greenhouse gas. Hence, the separation of CO2 from methane (CH4) occurs as a crucial step to improve the utilization of biogas. The separation of CH4/CO2 can be conducted using a polymeric membrane that needs no chemical, hence considered as an environmentally friendly technique. However, the utilization of polymeric membrane in gas separation processes is hampered by the trade-off between gas throughput and selectivity. To solve this problem, the incorporation of inorganic particles, such as Zeolitic Imidazolate Framework-8 (ZIF-8) particles, into the polymer matrix to improve the gas separation performance of the membrane has been conducted recently. In this research, ZIF-8 has been incorporated into Polysulfone matrix to form ZIF-8/Polysulfone-based membrane by simple blending and phase inversion techniques in flat sheet configuration. The pure gas permeation tests showed an increase in gas permeability (26 Barrer compared to 17 Barrer) after the inclusion of ZIF-8 particles with a slight decrease in CO2/CH4selectivity for particle loading more than 15wt. %. Therefore, the membrane with 15wt. % of particles showed the best performance in terms of gas selectivity. This result was due to the aggregation of ZIF-8 particles at particle loading higher than 15wt. %. Chemical analysis indicated an interaction between filler and polymer, and there were increases in the degree of crystallinity after the incorporation of ZIF-8.

Shock-free ion transmission in a skimmer-based MEMS mass spectrometer vacuum interface

Shock-free ion transmission from atmospheric pressure to a microelectromechanical system (MEMS)-based mass spectrometer has been achieved using micro-engineered nickel skimmers. The signal level has increased 70-fold compared with a previous configuration in which the skimmer did not sample the supersonic flow. The skimmers are formed by electroplating internal surfaces of anisotropically etched, pyramidal holes in (100) silicon. Etching from the reverse of the wafer exposes free-standing, open-ended skimmers supported by remaining silicon. High-resolution schlieren imaging has been used to visualise gas flow within the interface. Signal enhancement and increased gas throughput are observed when the skimmer attaches to the supersonic gas expansion via oblique shocks. The silicon back wall interacts with the flow field, causing the free jet Mach disc to evolve into a bowl-shaped surface shock whose position asymptotically approaches a stand-off separation as the interface pressure decreases. Ideally, the skimmer entrance should be located approximately midway between the inlet and the back wall. This development should allow a sensitivity increase in MEMS mass spectrometers using pumps of moderate capacity.

Investigation of spatiotemporal output beam profile instabilities from differentially pumped capillaries.

Differentially pumped capillaries, i.e., capillaries operated in a pressure gradient environment, are widely used for nonlinear pulse compression. In this work, we show that strong pressure gradients and high gas throughputs can cause spatiotemporal instabilities of the output beam profile. The instabilities occur with a sudden onset as the flow evolves from laminar to turbulent. Based on the experimental and numerical results, we derive guidelines to predict the onset of those instabilities and discuss possible applications in the context of nonlinear flow dynamics.

Update of Techno-Economic Benchmarks for Fossil Fuel Power Plants with CO2 Capture

Carbon capture and storage (CCS) has long been recognized as a key component of an effective mitigation strategy to decarbonize the power and industrial sectors. For many reasons, however, the commercial deployment of CCS technologies has been slow and must accelerate to contribute effectively to mitigating climate change. This paper presents the outcome of a study that Amec Foster Wheeler Italiana, a Wood Company, performed on behalf of IEAGHG, aimed at updating the technical and economical assessment of coal and natural gas fired power plants with and without CO2 capture, considering the benefits of recent technology improvements. The work has focused on ultra-supercritical pulverized coal (USC PC) boiler and natural gas combined cycle (NGCC) power plants, with and without CO2 capture. Post combustion capture based on solvent scrubbing only has been considered; this is currently the commercially leading option for capture on both pulverized coal and natural gas-fired power plants. Two different capture unit designs are studied: a 90% CO2 recovery scenario, and a high capture rate scenario (around 99%). Starting from the benchmark NGCC cases described above, the work has also addressed: • The impacts of Flue Gas Recirculation (FGR) on power plant performances and economics. The recirculation of part of the flue gas back to the GT compressor has the beneficial effects of enriching the exhaust gas in CO2 and significantly reducing the gas throughput of the absorption section in the CO2 capture unit, but also shows some drawbacks, such as the cost of the recirculation system and a slight efficiency drop. • Improvements to the operational flexibility of both natural gas and coal fired power plants with carbon capture from a simplified techno-economic optimization standpoint, updating the main outcomes of the work presented in “Operating flexibility of power plants with CCS” (2011, Foster Wheeler) with state-of-the-art technologies. The trade-off between flexibility and efficiency is also analyzed for the coal cases, including a literature review of the possible impacts on operating flexibility of adopting Advanced-Ultra Super Critical (A-USC) technologies (700°C). • Consideration of mid-term future advancements on power generation technologies for the NGCC plant, including the use of novel improved materials in the hot gas path of the for the gas turbine and integration with Molten Carbon Fuel Cells (MCFCs), in which hydrogen is provided via natural gas steam reforming (using MCFC waste heat). The MCFC, besides contributing to power generation, allows separation of CO2 from the NGCC flue gas and its release into a syngas stream that needs a relatively simple purification method to remove the CO2 (like cryogenic technology) and can then be re-covered as auxiliary fuel to the power island.

Comparison of Two-Phase Porosity Models for High Capacity Random Packing

High capacity random packing is used in absorption applications where a large throughput of gas is required while simultaneously maintaining as low a pressure loss as possible. Utilising computational fluid dynamics to capture the internal flow patterns and transients when designing packed bed towers can be advantageous in respect to expected performance and cost optimisation. However, capturing the direct interaction between gas, liquid and packing is not computationally feasible and therefore the packed bed is modelled as a porous media. In this work four different porosity model are calibrated with idealised equations to data for the high capacity packing IMTP or I-Ring. The different models are evaluated based on their ability to predict pressure loss and liquid holdup in the packed bed. An Eulerian two-phase model with a porous zone representing the packed bed is setup in a cylindrical tower. The CFD results are compared to the predictions of the best performing porosity model. It was found that the best performing model had an absolute mean error of 6.7% when calibrated with the idealised equations. This error increased to 10.5% when the porosity model was implemented into the CFD model.

Study on Mass Transfer Characteristics of Hydrate-based Gas Absorber

Hydrated-based gas separation is a method capable of selectively separating and recovering greenhouse gases. Although a conventional hydrate-based gas separation apparatus is a batch or a semi-batch system, continuous operation is preferable to increase the throughput of gas without changing the apparatus volume. Recently, we proposed a flow type apparatus to allow continuous operation of hydrate formation (absorption) and subsequent decomposition (desorption). The aim of this study is to investigate the mass transfer characteristics of the continuous apparatus using the HFC134a-N2 mixed gas system. The volumetric mass transfer coefficient was calculated especially during a steady state of gas absorption. Besides, we compared mass transfer performance between the hydrate-based gas absorber and a conventional bubble column. Sodium dodecyl sulfate was used as a hydrate dispersant. In the flow type apparatus, the gas-liquid contact was good and the hydrate slurry state was observed during hydrate formation. In the surfactant solution, the volumetric mass transfer coefficient increased in comparison with that in water. The volumetric mass transfer coefficient with hydrate was higher than that of the bubble column. These results suggest that hydrate formation improves gas absorption performance.

Assessment of ITER divertor performance during early operation phases

During the ITER design phase, the focus of ITER boundary plasma modeling activities has been on divertor performance under baseline H-mode, fusion power operation (FPO) conditions. However, early ITER operation will be primarily with hydrogen fuel in L-mode, in the pre-fusion power operation 1 (PFPO-1) phase. Here, the SOLPS-ITER code is used to evaluate divertor performance during this non-active phase. To verify the assumptions used in the existing high power simulation database, gas throughput scans were performed for two types of divertor surface material (beryllium and tungsten) and two gas puff locations (divertor and main chamber). The adoption of beryllium target surfaces simulates the effect of main chamber material erosion and migration and, along with main chamber gas injection, is the current default for the high power database. Depending on the divertor surface material, the atom to molecule ratio of the recycled neutral particles varies. This modifies the momentum and power loss mechanisms arising from plasma–neutral interactions. However, since the effect of atomic and molecular reactions are compensatory, the ‘total’ power and momentum losses are relatively insensitive to the target surface material. Similarly, the impact of gas puff location on divertor plasma parameters is not significant, though main chamber injection provides an additional ionization source in the upstream scrape-off layer (SOL) and leads to moderate changes in the upstream density and far SOL parameters. However, these effects can be neglected within the available range of the gas puff and pump rates in ITER. Since beryllium and tungsten are materials at both extremes in terms of surface reflection properties, the conclusions may be applicable to other divertor surface materials. An important additional finding of the study is that the insensitivity of upstream density to divertor neutral pressure found in the FPO database is also recovered in these PFPO-1 simulations.

Development of Electrochemically-Driven CO2 Separator for Hydroxide Exchange Membrane Fuel Cells in Transportation Applications

Hydrogen fuel cell vehicles are a promising, emerging alternative to the internal combustion engine but the commercialized proton exchange membrane fuel cells (PEMFCs) are comparatively expensive. Hydroxide exchange membrane fuel cells (HEMFCs) are a potentially lower cost hydrogen fuel cell technology under development; unfortunately, ambient levels of CO2 in air reduce HEMFC performance and impede HEMFCs from becoming competitive with the incumbent fuel cell technology.1 Current levels of atmospheric CO2 have been shown to decrease fuel cell performance up to 200 mV.2 The hydroxide produced during the electrochemical reaction in a HEMFC reacts readily with CO2 in air at the cathode due to its acid-base reaction and transports CO2 across the hydroxide exchange membrane. At the anode, the bicarbonates build up lowering the local pH until CO2 evolution is favorable, concurrently the pH gradient saps cell voltage. However, this transport results in the effective separation of CO2 from air. By optimizing a HEMFC for CO2 capture, rather than power production, an electrochemically-driven CO2 separator (EDCS) was developed using a poly(aryl piperidinium) membrane.3 The continuous and compact EDCS has the potential to enable HEMFCs to operate efficiently with ambient air in automotive applications.This work will demonstrate the ability of the EDCS to effectively and continuously remove CO2 from air at ambient levels using minimal hydrogen flow to power the separation. This work will explore the effect of operating conditions such as flow rates, current density, and relative humidity on CO2 separation performance with the innovative EDCS. A carbon-ionomer interlayer between the catalyst layer and membrane was added to improve CO2 capture by creating an accessible volume for hydroxide and CO2 gas to react. Additionally, various design features of the cell were investigated to improve the mass transport such as flow fields and gas diffusion layers. The CO2 removal performance of a single-cell 25 cm2 EDCS is shown in Figure 1. Currently, the optimal design configuration of the EDCS has achieved 98% CO2 removal for 100 hours (Figure 2) with the potential to improve CO2 removal as well as processed gas throughput by further development of the module’s design.

Effect of Soot-Inhibitor Additives on the Thermal Structure and Soot Volume Fraction Inside Laminar Diffusion Natural Gas Flames

Abstract Soot study is a fundamental issue for the combustion process of hydrocarbon fuels. Losses in combustion efficiency, health risks, environmental loosestrife, and damage in furnaces may appear as a result of soot existence. This present paper aims at providing an experimental mapping of the changes in the soot volume fraction and axial flame mean temperature associated with the addition of different percentages of soot inhibitor additives (namely, Argon, Nitrogen, and Helium) in a vertical laminar diffusion natural gas flame issuing from a honeycomb circular burner. The soot volume fraction is acquired by the laser extinction technique, while the axial variations of the mean flame temperature are accomplished by a bare 51 µm (Pt-30%Rh versus Pt-6%Rh) thermocouple to render radiation loss insignificant. The concentration of the individual additives is varied from 5% to 25% (step 5%) and the experiments are conducted at a fixed natural gas throughput (350 mL/min) to ensure unvaried thermal input. Measurement traverses along and across (at fixed radial locations) are conducted. The fuel flowrate is measured by a precision digital gas flowmeter (type: Varian intelligent), while the flow of the individual additive is admitted via solenoid valves (handled with labview program) and is injected through mixing pipes located at burner entry. The different regimes of the soot inception (molecular; zone 1), soot growth zone (zone 2), and soot oxidation (zone 3) are accurately defined and assessed in relation to the temperature results for the different cases under investigation.

Structural Design for ITER Gas Injection System Gas Fueling Gas Valve Box

The ITER gas injection system delivers gases from the tritium plant to the vacuum vessel, fueling pellet injection system, and neutral beam for plasma operation and fusion power shutdown. In this system, the gas fueling (GF) gas valve box (GVB) is an indispensable part that mainly provides functions of gas throughput control and measurement of gas pressure, flow rate, and temperature. The preliminary structure design is largely driven by the requirements of magnetic field compatibility and limited integration space. A strong magnetic field of over 0.2 T exists around the GVB locations, so a magnetic shielding design is required to ensure the normal function of susceptible components. Instead of the previous overall shielding, a local magnetic shielding has been developed by a validated analysis method. As a result, the total weight of the shield has been reduced from over 7000 kg to about 200 kg. Furthermore, considering the limited space reservation, a highly compact flat layout for the GF GVB has been developed to ensure enough maintenance space in front of it. In addition, other requirements such as structure integrity under various load combinations, leak detectability, in situ maintainability, etc., have all been taken into account.

Analysis of an electrochemical compressor stack

Electrochemical compression (ECC) of gases offers advantages over conventional mechanical compression such as higher efficiency and noiseless operation. However, ECC performance can be affected by back-diffusion of the gas across the membrane which is exacerbated at high pressures. Practical systems employ multiple cells in a stack configuration to achieve higher flowrates and gas pressures. Here, we analyze two different stack configurations in order to understand their influence on gas throughput and exit pressure in the presence of back-diffusion. Both the stack configurations examined here are connected electrically in series such that the external voltage applied to the stack terminals is divided equally across each individual cell. On the other hand, the flow of gas within the stack can occur either in parallel or in series. Accordingly, we name these stack configurations Electrically in Series/Flow in Parallel (ESFP), and Electrically in Series/Flow in Series (ESFS). The ESFP configuration can deliver higher gas throughput but at limited pressures, whereas the ESFS configuration can deliver higher pressures but at lower flowrates. A theoretical performance analysis has been conducted for both configurations to gain insights into the compressed gas flux, pressure rise, back diffusion, and efficiency. Furthermore, it is also possible to design a hybrid configuration that combines both parallel and series flow aspects to deliver flow and pressure that is optimized for a given application.

A New Analytical Model for Predicting Natural Gas Transportation Compressor Power

The compressor power requirement for gas pipelines is critical to the efficient delivery of natural gas over long distances. Existing models for predicting compressor power using pipeline length and gas throughput as input parameters are limited. This study focused on developing a new analytical model using the general energy equation to capture better interrelationships between compressor power and other parameters affecting compressor power requirements of horizontal natural gas pipelines. The developed model was validated using Bryan Research and Engineering (BRE) ProMax 2.0 process simulation software. The results indicated that the developed model was reliably consistent and accurate when compared with ProMax results. In other to improve the efficiency of the developed model, correction factors for both pipe length and gas throughput were developed. The percentage average absolute deviation (% AAD) was 4.37 for the fixed pipe length with variable throughput and 0.68 for the fixed throughput with variable length, scenarios.

Simulation of a reactor for thermal processing of coal-water fuel to produce syngas of specified composition

The main physical and chemical regularities for development of a flow gasifier for thermal processing of coal-water fuel (CWF) on condition of the set structure received syngas are presented in this article. Based on the calculations made on the residence time of a CWF drop in the reactor and the time of gasification reactions the gasifier was designed with vertical heating surfaces. Calculation of the main sizes of a gas generator for gas productivity on synthesis gas 500, 1000 and 1500 m3/h is carried out. The results of a constructive calculation show that in order to ensure the required residence time of a CWF particle in the volume of the gasifier it is necessary to ensure a certain length of the reactor, regardless of the gas throughput.

Organically modified activated bentonites for the reversible capture of CO2

Abstract Effective adsorbents for the reversible capture of CO2 at ambient temperature were prepared by acid activation of bentonite (AAB) and chemical grafting of 3-amino-propyltriethoxysilane (γ-APTES) or 3-diethanolamino-propyltriethoxysilane (3-diEtOH-APTES). Full characterization of the resulting organo-AAB materials through X-ray diffraction, nitrogen adsorption-desorption isotherms, thermogravimetric analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry and 29Si solid-state nuclear magnetic resonance (NMR) revealed thermally stable porous structures with higher affinity towards CO2. Thermal programmed desorption analyses (TPD) gave appreciable CO2 retention capacity (CRC) with easy release of ca. 90% of the absorbed CO2 at temperature not exceeding 80 °C. Total regeneration of adsorbents was achieved at less than 160 °C, without affecting the stability of the grafted groups. Acid activation produced an increase of the number of silanol groups and of the silylation capacity, but unavoidably a marked CRC decay. Further grafting of amino and diethanol-amino groups was found to revive the affinity towards CO2. The CRC increase with increasing amount of impregnating CO2 and decreasing carrier gas throughput allows predicting even much higher CO2 uptakes than those obtained in the present work through predominant non-stoichiometric physical condensation around the amino groups. Such low-cost hybrid materials appear as promising alternative to others prepared by physical incorporation of amine, and the results obtained herein allow envisaging effective reversible capture of CO2 without amine loss upon thermal stresses.

Reaction kinetics and temperature effects in syngas photo-initiated chemical vapor deposition on single-walled carbon nanotubes

Photo-initiated chemical vapor deposition (PICVD) is a solvent-free process that can be used to produce thin films on a variety of substrates, with applications in fields ranging from biomedicine to optics and microelectronics. This study presents a kinetic analysis for this process using syngas (CO + H2) as a precursor for the surface treatment of single-walled carbon nanotubes (SWCNT) with average dimensions of 1.5 × 100 nm (diameter × length), and addresses the role of iron pentacarbonyl (Fe(CO)5), a photo-active contaminant found in CO. This work builds upon previously developed reaction schemes for PICVD, based mainly on surface characterizations, by coupling these analyses with gas-phase monitoring. This allows us to propose two separate reaction schemes for the gas and surface phase reactions and consider temperature effects. Online FTIR, offline GC-MS, and online GC characterized the gas phase, while for surface characterizations, XPS and TGA were used. Characterizations showed that a coating with a general formula of CnO3nFen was deposited, corresponding to 0.29 ± 0.04 mg carbon and 0.49 ± 0.03 mg iron on the SWCNT substrate over the course of treatment. The Fe(CO)5 was identified as the key reactant in syngas/PICVD reactions and was nearly completely consumed (94%). Mass balances derived from the gas phase characterization showed that Fe(CO)5 inputted to the plug flow reactor could potentially contribute all the amount of 0.49 ± 0.03 mg of Fe and 0.29 ± 0.04 mg of C to the coating on the SWCNT, indicating that syngas/PICVD can be optimized in the future to decrease gas throughput. Temperature did not show a significant effect in the case of PICVD. However, in the absence of ultraviolet light, its role becomes determinant, with rising temperatures causing more Fe deposition.

Characterization of ZAO® sintered getter material for use in fusion applications

The use of non-evaporable getter (NEG) pumps is common in many UHV applications, and the properties of the new sintered getters based on the ZAO®alloy make them appealing for applications dealing with large fluxes of hydrogen and its isotopes, as typically occurs in fusion research. In particular, the use of NEG pumps is interesting for the vacuum system of negative ion-based neutral beam injectors, which require huge deuterium gas throughputs for long durations. The key advantages of a NEG pumping solution are the high specific pumping speed and capacity, the ability to withstand a large number of absorption/desorption cycles, the ease of integration. In addition, NEG do not release hydrogen unless power is supplied to heat them, addressing an important safety issue related to uncontrolled release in case of power outage or subsystem failures.This paper reports the experimental characterization of ZAO®sintered getters, in pressure regimes and sorption amounts relevant for the use in the next generation NBI. Single discs and complete pumps were characterized in different conditions of H2/D2 pressure between 10−4 and 10-1Pa and operating temperatures up to 150°C. In particular, the feasibility of getter regeneration within time windows compatible with current NBI operation scenarios was demonstrated.

Investigating Effects of the Ball Size on the Gas Throughput Using Partially Curved and Wholly Curved Seats

Investigating Effects of the Ball Size on the Gas Throughput Using Partially Curved and Wholly Curved Seats

Environmental Protection Improvement of Fabric-Filter Cleaning of Process and Ventilation Gases at the Kazzinc LLC Ust-Kamenogorsk Metallurgical Complex

The Ust-Kamenogorsk Metallurgical Complex (UKMC) is an independent division of Kazzinc LLC with a closed-loop manufacturing process. The company is primarily engaged in production of rare nonferrous metals and alloys. RFG and URFM bag filter models are the most commonly used at UKMC. Bag regeneration is by blowback and shaking; the filters have been in operation for over 50 years, and the residual dust content is 10–15 mg/m3 of gas. The company is actively working to upgrade these filters through introduction of a pulsed bag regeneration system to increase gas throughput by 50% and reduce the residual dust content to a maximum of 1 mg/m3 of gas. The authors’ proposed upgrade of the URFM-1 filter to FRKI-3800 filters will reduce fugitive intake of ambient air by 15% and lower atmospheric emissions of lead-containing dust by 4 metric tons/yr. The annual cost savings from the upgrade will exceed 40 million tenge (approximately 116,000 U.S. dollars), in the form of reduced emission fees and lower electric power consumption for handling process gases.