High-velocity Gas Research Articles

Extreme Variation in Star Formation Efficiency across a Compact, Starburst Disk Galaxy

Abstract We report on the internal distribution of star formation efficiency in IRAS 08339+6517 (hereafter IRAS08), using ∼200 pc resolution CO(2 − 1) observations from NOEMA. The molecular gas depletion time changes by 2 orders-of-magnitude from disk-like values in the outer parts to less than 108 yr inside the half-light radius. This translates to a star formation efficiency per freefall time that also changes by 2 orders-of-magnitude, reaching 50%–100%, different than local spiral galaxies and the typical assumption of constant, low star formation efficiencies. Our target is a compact, massive disk galaxy that has a star formation rate 10× above the z = 0 main sequence; Toomre Q ≈ 0.5−0.7 and high gas velocity dispersion (σ mol ≈ 25 km s−1). We find that IRAS08 is similar to other rotating, starburst galaxies from the literature in the resolved Σ SFR ∝ Σ mol N relation. By combining resolved literature studies we find that the distance from the main sequence is a strong indicator of the Kennicutt-Schmidt power-law slope, with slopes of N ≈ 1.6 for starbursts from 100 to 104 M ⊙ pc−2. Our target is consistent with a scenario in which violent disk instabilities drive rapid inflows of gas. It has low values of Toomre-Q, and also at all radii, the inflow timescale of the gas is less than the depletion time, which is consistent with the flat metallicity gradients in IRAS08. We consider these results in light of popular star formation theories; in general observations of IRAS08 find the most tension with theories in which star formation efficiency is a constant. Our results argue for the need of high-spatial-resolution CO observations for a larger number of similar targets.

M 1–92 Revisited: New Findings and Open Questions: New NOEMA Observations of Minkowski’s Footprint

PN M 1–92, also known as Minkowski’s Footprint, is a textbook example of a massive pre-planetary nebula. It presents all the characteristics of this type of source: non-spherical symmetry (bipolar cylindrical symmetry in this case), high-velocity gas emission, large amounts of linear momentum and kinetic energy (momentum excess), and a self-similar growing structure. We have revisited this object by performing new NOEMA observations (with half arc-second resolution) of a wealth of molecules, including the rare isotopologues of CO, as well as other less abundant species. These maps provide new insights into the origin of this source. Our findings include the discovery of molecular species in the ionised regions of the nebula, confirming its shocked origin; the structure of the massive equatorial component, including the presence of active wind collisions; and the strong evidence that the AGB evolution of the source was terminated prematurely, probably due to the huge mass loss event that resulted in the formation/acceleration of the present nebula.

Reinforcement of the Ceramic Matrix of CaO-ZrO2-MgO with Al2O3 Coarse Particles

A thermal protection system is subject to high forces, in particular compression, bending and wear, to aggressive environments of high temperatures, high velocity gases and particle shock. Typically, ceramic materials appear as a first barrier or outer shield over a metallic substrate responsible for the structure. When it comes to a coating due to the small thickness, the particles of the raw material are sub-micron scale, but when a shield with a few centimeters is built its structural and economic viability requires the use of wider particle size distributions. In this work, a ceramic fine-grained matrix of CaO-ZrO2-MgO was reinforced with commercial coarse Al2O3 particles. The results show that for larger size distributions, CZM-4A, replacing 63% of fine-grained matrix by coarse Al2O3 particles, the dimensional stability is obtained (ΔL = 5%) and the good mechanical properties such as flexural strength of 154 MPa, elastic modulus of 286 GPa, and hardness of 8.5 GPa, which allows to propose this ceramic composite for a structural application.

Numerical simulation and an innovative design of the inlet gas distributor in an industrial adsorption tower

Gas distributor plays an important role in operation performance of gas-solid and gas-liquid reactions and separation processes. In this work, computational fluid dynamics method was used to simulate the gas distribution of the inlet gas distributor in an industrial pressure swing adsorption tower. The employed model has been validated with available empirical formula. The simulation results show that the industrial perforated plate gas distributor brings a strong flow along the elliptical head wall and large vortexes. It shows bad gas distribution performance. Therefore, a conical shell gas distributor is proposed. Its structural parameters, such as cone angle and hole distribution are optimized. The optimal cone angle is 166°. Furthermore, an imperforated area with a diameter of 290 mm is necessary to decrease the gas velocity at the center area. The optimal distributor can effectively weaken the large vortexes above the distributor and the high gas velocity at axial center. Compared with the industrial distributor, the inhomogeneity index M of the gas distribution is decreased from 5.61 to 2.48, and the pressure drop △P of the distributor is decreased from 59.3 Pa to 46.0 Pa. In addition, the designed distributor is also suitable for towers with larger diameters.

Achieving Adequate Circulation in Chemical Looping Combustion─Design Proposal for a 200 MWth Chemical Looping Combustion Circulating Fluidized Bed Boiler

Chemical looping combustion (CLC) has unique potential for avoiding the large costs and energy penalties of existing CO2 capture technologies. Oxygen is transferred to the fuel using an oxygen carrier, thus avoiding contact between air and fuel. Consequently, the combustion products, CO2 and H2O, come in a separate stream, and more or less pure CO2 is obtained after condensation of H2O. CLC is normally conceived as a dual fluidized bed process, with high gas velocities in an air reactor driving the circulation, similar to circulating fluidized beds (CFBs), except that the material is led to a fuel reactor before being returned to the air reactor. Crucial for the process is the properties of the oxygen carrier and that circulation is sufficient to transfer needed oxygen and heat to the fuel reactor. Comprehensive literature shows successful use of many oxygen carriers in sustained pilot operation. In contrast, the need for reaching adequate circulation in an industrial-scale system has been given little consideration. Normally, a system similar to CFB boilers is assumed to give sufficient circulation. However, literature data indicate that circulation in CFB boilers is 5–50% of what is needed. Measures to provide sufficient circulation may cause difficulties, such as erosion or bed material loss in the cyclone. Here, a circulation system based on collection of the downflow of particles along the walls is proposed, and a design of a 200 MWth combined CLC–CFB boiler based on this principle is presented. Further, operational strategies and the need for flexibility are discussed. The design is focused on making an industrial-scale demonstration boiler, which can be used in CLC operation with different oxygen carriers and different fuels and that can explore different operational strategies to find optimal conditions. It is recommended that the upscaling of the technology aims directly at the industrial scale.

The SEDIGISM survey: A search for molecular outflows

Context. The formation processes of massive stars are still unclear, but a picture is emerging involving accretion disks and molecular outflows in what appears to be a scaled-up version of low-mass star formation. A census of outflow activity toward high-mass star-forming clumps in various evolutionary stages has the potential to shed light on high-mass star formation. Aims. We conducted an outflow survey toward ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) clumps using SEDIGISM (structure, Excitation, and Dynamics of the Inner Galactic InterStellar Medium) data and aimed to obtain a large sample of clumps exhibiting outflow activity in different evolutionary stages. Methods. We identify the high-velocity wings of the 13CO lines, which indicate outflow activity, toward ATLASGAL clumps by (1) extracting the simultaneously observed 13CO (2–1) and C18O (2–1) spectra from SEDIGISM, and (2) subtracting Gaussian fits to the scaled C18O (core emission) from the 13CO line after considering opacity broadening. Results. We detected high-velocity gas toward 1192 clumps out of a total sample of 2052, corresponding to an overall detection rate of 58%. Outflow activity has been detected in the earliest (apparently) quiescent clumps (i.e., 70 μm weak) to the most evolved H II region stages (i.e., 8 μm bright with tracers of massive star formation). The detection rate increases as a function of evolution (quiescent = 51%, protostellar = 47%, YSO = 57%, UC H II regions = 76%). Conclusions. Our sample is the largest outflow sample identified so far. The high detection rate from this large sample is consistent with the results of similar studies reported in the literature and supports the scenario that outflows are a ubiquitous feature of high-mass star formation. The lower detection rate in early evolutionary stages may be due to the fact that outflows in the early stages are weak and difficult to detect. We obtain a statistically significant sample of outflow clumps for every evolutionary stage, especially for outflow clumps in the earliest stage (i.e., 70 μm dark). The detections of outflows in the 70 μm dark clumps suggest that the absence of 70 μm emission is not a robust indicator of starless and/or pre-stellar cores.

Development, Application and Effect Evaluation of the Remote-controlled Automated Needle Valve Intermittent Production System in the L Well Block in China

In order to solve the problem of liquid loading, some water-produced gas wells use intermittent production mode to produce: shut in gas wells to restore energy during the closing phase, and open up to carry the liquid to surface by the high velocity gas during well opening phase, which is cost effective. However, some wells need frequent opening and closing or adjusting gas flow, manual opening and closing is easily influenced by external interference factors (road conditions, weather, public relation issue, etc.), and cannot guarantee production time for intermittent producing well. In order to realize the remote-control and automation for these wells, the remote-control automated needle valve intermittent production system was developed and successfully applied to the L well block. The gas rate, production time and economy before and after the smart needle valve installed was compared to do the performance assessment. The results show that: (1) the stability of the remote-control automated needle valve intermittent production system is good, and it can meet the requirments of the remote automated opening and closing of gas wells. (2) After the installation of the remote-controlled automated needle valve system, 71% of the gas wells have a stable gas increase, 100% of the gas wells have a higher well opening time, and the liquid unloading in the gas wells has been significantly improved. The average gas production increased from 1.75×10⁴ m³/d to 1.87×10⁴ m³/d, which was 6.86% higher than that before installation. The well opening time of 7 wells increased by 5.16% on average. (3) Compared with manual operation, the comprehensive economic performance of the remote-controlled automated needle valve opening system is more excellent. The remote-controlled automated needle valve opening system can remotely intelligently control the intermittent production of gas wells, which has significant economic benefits and high application value and worth further spreading.

Multipath Flow Metering of High-Velocity Gas Using Ultrasonic Phased-Arrays

In this work we combine a multipath ultrasonic gas flow meter (UFM) with an ultrasonic air-coupled phased-array. This allows complementing the advantages of a multipath UFM, i.e. higher accuracy and more robustness to irregular flow, with the extended velocity measuring range due to sound drift compensation via a phased-array. We created a 3D-printed flow meter consisting of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8\,\,\lambda /2$ </tex-math></inline-formula> phased-array for transmission and 14 individual receivers for seven upstream and seven downstream sound paths. Measurements were conducted in a test rig with a maximum gas flow rates of 8.3 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> (107 ms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ). A differential pressure nozzle was used as reference sensor. Three configurations were compared: Parallel sound paths with a single transmitter; parallel sound paths with the phased-array as transmitter; and fan-shaped sound paths with the phased-array as transmitter. The signal-to-noise ratio (SNR) and deviation of measured flow were used as comparison criteria. In addition, we measured the optimum steering angles of the phased-array required to compensate the sound drift effect. Using the phased-array with the sound drift effect compensation enabled and disabled, the SNR increases by 10.6 dB and 4.95 dB, respectively, compared to the single transmitter setup at 83 m s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . Furthermore, the phased-array with compensation active, extends the velocity measuring range by 29%, from 83 ms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> to 107 m s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , while maintaining a similar standard deviation of the flow measured. Besides demonstrating that a phased-array in a gas flow meter significantly extends the measurement range, our setup qualifies as versatile research platform for designing future high-velocity gas flow meters.

Smart detection of fractures in formation image logs for enhanced CO2 storage

Carbon capture and storage (CCS) has attracted strong interest from industry and the scientific community alike due to the ability of storing CO2 in subsurface reservoirs. Deep saline aquifers may be well suited for the safe and long-term storage given their geological structure. The long term underground storage in saline aquifers depends on variety of interrelated trapping mechanisms in addition to the caprock sealing efficiency. Fractures are commonplace in many geological settings and represent a crucial role for hydrocarbon migrations and entrapment. Fracture impact fluid flow in variety of forms, particularly due to the complexity and varying natures of the fractures, which channel the injected CO2 throughout the reservoir formation. This is especially important for tight gas reservoirs and low permeable cap rock structures whose permeability is primarily characterized by the fault and fractures. This outlines the importance of determining accurately fracture penetration in wellbores for CO2 injection. We present a new deep learning framework for the detection of fractures in formation image logs for enhancing CO2 storage. Fractures may represent high velocity gas flow channels which may make CO2 storage a challenge. The novel deep learning framework incorporates both acoustic and electrical formation image logs for the detection of fractures in wellbores for CO2 storage enhancement and injection optimization. The framework was evaluated on the Pohokura-1 well for the detection of fractures, with the framework exhibiting strong classification accuracy. The framework could accurately classify the fractures based on acoustic and electrical image logs in 98.1% for the training and 85.6% for the testing dataset. Furthermore, estimates of the fracture size are strong, indicating the ability of the framework to accurately quantify fracture sizes in order to optimize CO2 injection and storage.

Integrated wellbore-reservoir simulations to design sand retention tests for flowback scenarios in SAGD injection wells

In the past, sand retention testing (SRT) research for steam-assisted gravity drainage (SAGD) injector was a parametric study, or general solution, rather than a case-specific solution for a particular problem in terms of testing parameters. Testing parameters were assigned based on hypothetical assumptions due to a lack of necessary field data to perform such a study. Field data are often confidential and nearly impossible to obtain for a hazardous scenario like a thermal injector flowback. The literature is rich with multiple proposed slotted liner (SL) design criteria for SAGD production wells. The SRT designed for SAGD producer takes into consideration some measurable factors to specify suitable aperture size. In contrast, SRT for the SAGD injector seems to rely on industry experience or rules of thumb. A systematic methodology, consisting of three steps, was developed for SL design using the SRT setup for SAGD injector wells. The first step involves estimating the laboratory testing variables or operational parameters based on case-specific data and reservoir simulations to assess the consequences of steam flowback. A 2D Computer Modelling Group (CMG) thermal simulator was coupled with gas flow correlation and used to predict the outcomes of SAGD injector flowback. The second step involves developing a new SRT setup dedicated to SAGD injector flowback laboratory testing. Intensive testing was performed to troubleshoot the problems associated with a high-velocity gas flow. The third and final step involves conducting six tests to verify the developed setup's performance. The consideration of thermodynamic equilibrium improved testing by avoiding inconsistent assumptions used in the previous studies. Neither low steam quality (SQ) nor high SQ flowback scenarios used in the past are found to fully represent SAGD injector flowback. SAGD injector depth and other operational parameters are linked to flowback differential pressure. In other words, one set of testing parameters cannot be representative for all SAGD injector, which makes developing design criteria a challenge. The preliminary results of SRT for SAGD injector indicate the possibility of using small aperture size slots of 0.010 inch that do not cause significant permeability reduction at laboratory scale, unlike the case for SAGD producer SRT. This may justify why the industry tends to prefer small aperture size slotted liner for SAGD injector completion. Eventually, this research should be considered as a first step only in SRT for SAGD injector flowback, and necessary methodology enhancements and facility upgrades should be investigated in future work.

Investigation of mass transfer characteristics under turbulent condition in adsorption separation process for CO2 capture

Turbulence caused by high superficial gas velocity has significant impact on the CO2 capture process by adsorption. However, the poor consideration of turbulent diffusion in existing methods limits the further analysis of mass and heat transfer in CO2 adsorber. In this study, a novel computational fluid dynamics (CFD) model was introduced for CO2 capture with fixed bed, which is based on the methodology of computational mass transfer (CMT)[1]. Compared with traditional CFD models, it rigorously considers turbulent diffusion and can more accurately predict the mass and heat transfer behavior of CO2 capture processes at high gas superficial velocity while reducing computer resources. Through the comparison of simulation with breakthrough experiment, the feasibility of proposed approach was verified. In addition, the simulated results indicated that the turbulent mass diffusion causes a more uniform distribution of CO2 in the radial direction of adsorption bed. As Reynolds number decreases, turbulent mass diffusivity gradually weakens, and it could be neglected when the Reynolds number is below 10. Besides, adsorbent size and adsorber size was found to have significant influences on turbulent mass diffusion. They affect turbulent diffusion by changing the condition of fluid flow, then having influences on the mass transfer characteristics in CO2 capture process. Our results can provide a valuable guide for the structural design and optimization of industrial CO2 adsorber.

Dry Reforming of Methane over Ni/MgO@Al Catalysts with Unique Features of Sandwich Structure

AbstractDry reforming of methane (DRM) reaction can eliminate CH4 and CO2, the two main greenhouse gases. However, the industrialization of Ni‐based catalysts has been restricted by the problems of sintering and carbon deposition in common use. In this work, a series of sandwich structure catalyst Ni/MgO@Alx with traditional Ni/MgO and core‐shell Ni@Al2O3 were characterized and analyzed. Extensive catalyst characterization using N2 adsoptron‐desorption isotherms, X‐ray diffraction (XRD), transmission electron microscope (TEM), temperature‐programmed reduction/ desorption (TPR/D), Raman and thermogravimetric analysis (TGA) indicates that the sandwich structure catalyst has high activity, and the suitable shell thickness directly determines the mass transfer and surface acidity and basicity of the catalyst. However, in the process of reaction, the carbon tube grows on the top of the active component, resulting in its stability is not as good as Ni@Al2O3. Under the conditions of high gas velocity of 18000 mL gcat−1 h−1 with a reaction gas ratio of CO2 : CH4=1 : 1, after 30 hours of reaction with Ni/MgO@Al0.6 catalyst at 750 °C, the conversion of CH4 and CO2 remained at 79 % and 83 %, respectively.

A novel horizontal gas–liquid pipe separator for wet gas based on the phase-isolation

This paper proposes a novel horizontal gas–liquid pipe separator with a compact structure based on the phase-isolation. In the separator, the gas–liquid two-phase flow is firstly isolated as a swirling annular flow by a swirler, where gas core and liquid film spiral and flow forward in parallel. Based on the flow characteristics of the swirling liquid film, a downward tangential liquid extraction channel is designed, which is tangent to the swirl trajectory of the liquid film. Then the swirling liquid film can be directly separated by falling into the downward tangential channel under the combined action of its kinetic energy and gravity. On the basis of this structure, the inner thread on the wall, different lengths of liquid extraction channel and tangential gas return channel are designed individually to study their effect on the separation efficiency. Experiments were carried out to investigate the separation performance of the separator. The results show that when the superficial velocity of gas reaches 20 m/s, the separation efficiency can be higher than 94% with the superficial velocity of liquid in a large range of 0.02–0.264 m/s. The design of inner thread is beneficial for separation when the liquid film has a certain thickness. The length of liquid extraction channel has an opposite influence on separation efficiency at low gas velocity and high gas velocity. The gas return flow channel deteriorates the separation performance for the reason that the returning gas will carry a large number of liquid droplets into the main pipe.

Interaction between high-velocity gas and liquid in gas atomization revealed by a new coupled simulation model

Due to the high efficiency and low cost, gas atomization (GA) has been widely applied to produce metal powders. In this paper, the GA process is first modeled by combining the volume of fluid (VOF) model with dynamic adaptive mesh and the discrete phase model (DPM) to simulate the formation of the powders and the evolution of the defects. Simulation results show that the Kelvin-Helmholtz instability in the primary atomization and the membranous droplet breakup and closure in secondary atomization can form the hollow powder. While the presence of the satellite powder is caused by the collisions between the large and small droplets with different velocities. Moreover, the irregular powder is produced when the drag force is not enough to separate the droplets but deforms them. The estimated morphology and size distribution of the particles have a good agreement with the experimental ones. Finally, the possible measures to reduce the defects of the powders have been put forward based on the revealed mechanism of defect evolution. This work provides a deep simulation insight into the GA process, towards producing high-quality metal powders for additive manufacturing on a large scale.

Top of line corrosion in gas-condensate pipelines

Low alloyed carbon steel is the only viable material of construction for long pipelines transporting unprocessed gas-condensate. The water that condenses is highly corrosive because it contains dissolved acid gases, i.e., CO2, H2S and organic acids like acetic and formic acid. The high velocity gas also contains droplets of water and condensate, and these will deposit if they hit the steel surface. Monoethylene glycol (MEG) injected to prevent ice and hydrates must be considered when predicting the composition and corrosivity of the aqueous phases in the pipeline. The liquids gathering at the bottom of the pipe have a higher heat capacity than the gas, and the temperature at the top of the pipe will be slightly lower than at the bottom. As the produced fluids cool during the transport from the hot wells to the process plant, water will condense on the cold pipe surface and more at the top than at the bottom. The literature on Top-of-line corrosion (ToLC) has grown steadily since the first reported case in 1960. There are also several prediction models for ToLC. This review is an overview of the main factors that cause ToLC and how these are modelled. Mass transfer from the aqueous phase at the bottom to the top contribute to the condensation. Despite the low MEG to water ratio in the gas due to the difference in vapour pressure, the fraction of MEG in the condensing water may be considerable. The concentration of MEG in the aqueous phase at the top depends on the mass transfer from bottom. The same is the case for organic acids. Liquid droplets entrained in the gas may deposit top of line and contribute to the chemistry of the aqueous phase. Models for ToLC must thus not only predict the composition of the condensing phases but also the mass transfer to be able to estimate the corrosion rate.

Comprehensive Optimization of the Dispersion of Mixing Particles in an Inert-Particle Spouted-Bed Reactor (IPSBR) System

Effective gas dispersion and liquid mixing are significant parameters in the design of an inert-particle spouted-bed reactor (IPSBR) system. Solid particles can be used to ensure good mixing and an efficient rate of mass and heat transfer between the gas and liquid. In this study, computational fluid dynamics (CFD) coupled with the discrete phase model (DPM) were developed to investigate the effect of the feed gas velocity (0.5–1.5 m/s), orifice diameter (0.001–0.005 m), gas head (0.15–0.35 m), particle diameter (0.009–0.0225 m), and mixing-particle-to-reactor-volume fraction (2.0–10.0 vol.%) on the solid mass concentration, average solid velocity, and average solid volume fraction in the upper, middle, and conical regions of the reactor. Statistical analysis was performed using a second-order response surface methodology (RSM) with central composite design (CCD) to obtain the optimal operating conditions. Selected parameters were optimized to maximize the responses in the middle and upper regions, and minimize them in the conical region. Such conditions produced a high interfacial area and fewer dead zones owing to good particle dispersion. The optimal process variables were feed gas velocity of 1.5 m/s, orifice diameter of 0.001 m, gas head of 0.2025 m, a particle diameter of 0.01 m, and a particle load of 0.02 kg. The minimum average air velocity and maximum air volume fraction were observed under the same operating conditions. This confirmed the novelty of the reactor, which could work at a high feed gas velocity while maintaining a high residence time and gas volume fraction.

Modeling transient flow behavior with the high velocity non-Darcy effect in composite naturally fractured-homogeneous gas reservoirs

A gas reservoir with composite properties contains two distinct regions, where one develops natural fractures and the other does not. To investigate the pressure transient behavior of the non-Darcy flow in composite naturally fractured-homogeneous gas reservoirs, a radial bi-zonal composite non-Darcy flow model was developed based on Izbash's equation. The inner region was considered as a dual-porosity medium to simulate the non-Darcy flow, whereas the outer region was considered as a homogeneous medium to simulate the Darcy flow. This model was solved using the Laplace transform, linearization and Stehfest numerical inversion. Then, the standard bi-logarithmic characteristic curves of the non-Darcy flow model were plotted. The flow stages were recognized and the influence of vital characteristic parameters on the transient behavior was analyzed and discussed in detail, such as the empirical constant, radius of the non-Darcy region, storage ratio, crossflow coefficient, etc. It is found that the values of the empirical constant n have a significant influence on the pressure transient behavior of the non-Darcy region. Moreover, three reduced models of the model proposed in this study were analyzed and discussed. Finally, it was found from the field application that this model had an excellent agreement between the measured and simulated pressure responses. The research results can be a helpful guide for researchers in the related fields when studying the transient behavior of high-velocity non-Darcy gas flow in composite naturally fractured-homogeneous gas reservoirs.

Experiment and numerical simulation investigation on wire-plate electrostatic precipitator with expanded-shrunk spoilers

In this paper, three types of wire-plate electrostatic precipitators with expanded-shrunk spoilers (ESP-ESSs) were proposed. The influences of different geometric characteristics and arrangements of the expanded-shrunk spoilers (ESSs) on the electric field intensity, airflow field, particle trajectory, and collection efficiency were investigated by experiment and numerical simulation. The ESP-ESSs was compared with ESP with parallel plates (ESP-PP). The numerical results were relatively in agreement with the experimental data. The maximum error was 6.5%. The results showed that with the increase of the ESS height, the electric field intensity increased. The ESSs could generate low-velocity vortices contributing to extend the retention time of particles, which was conducive to particle collection. In general, the collection efficiency of the ESP-ESS was superior to the ESP-PP, but there was no advantage for fine particles at high inlet gas velocity and low applied voltage.

Quantitative comparison of measurement quality of cross-correlation based particle velocity instruments in different gas fluidization regimes

Particle velocity measurement based on cross-correlation algorithm is used widely in various multiphase flow systems. In this study, an optical fiber probe, i.e. Labasys® 100 from MSE Meili was used to systematically compare the qualities of its measured particle velocities in a pair of hydrodynamically distinct regimes, i.e. a fast fluidized bed (FFB) and a bubbling fluidized bed (BFB). Compared to FFBs, the measured particle velocities in BFBs show lower data repeatability, higher percentage of invalid data and higher sensitivity to the selection of the threshold value of maximum cross-correlation coefficient, which corresponds to much lower measurement qualities in this regime. Comparatively, higher measurement qualities were observed in the FFB based on the same evaluating methods. The highest measurement qualities appear in the core region of the riser and under high superficial gas velocities. A matchup relationship between the measurement quality and the shape of the probability density function (PDF) curves of maximum cross-correlation coefficient is found. Narrower PDF curves correspond to higher measurement quality and vice versa.

Fast Pyrolysis of Hydrolysis Lignin in Fluidized Bed Reactors

Fast pyrolysis of hydrolysis lignin was studied in fluidized bed units. Hydrolysis lignin, a bioproduct from the lignocellulosic ethanol production process (St1 Cellunolix), was processed in bench scale bubbling fluidized bed (BFB) and pilot scale circulating fluidized bed (CFB) units. Utilization of steam and ethanol as hydrogen sources was tested in a BFB unit. Major technical challenges identified were related to slow reaction rates of lignin degradation and the rapid secondary reactions in the vapor phase resulting in deposit formation and pressure buildup in product gas lines. The carbohydrate content of hydrolysis lignin had a clear correlation to its processability. More challenges with clogging and bed agglomeration were observed with lignin feedstock having lower carbohydrate content. The challenges with the bed agglomeration in the BFB unit were overcome by adding a rapidly rotating mixer in the reactor to break the agglomerates. With the CFB unit, bed agglomeration was not a problem, due to high gas velocities and forces applied to sand and lignin particles. In the BFB unit, the screw feeder was cooled and no significant melting problems were observed. In the CFB unit, melting problems were avoided by feeding the raw material in the cold section of reactor. However, severe increases in the pressure buildup and deposit formation rates were observed in both units. Steam and ethanol was tested, separately, in the BFB unit, to provide excess hydrogen in the system. Based on the product analyses both added hydrogen into the system, but hydrogen ended up mostly in the gas phase. To enhance the hydrogen transfer to the organic liquid, a catalyst active in hydrogen transfer is probably needed.