Lateral Gas Research Articles

Lateral gas transport in soil adjacent to an old landfill: factors governing emissions and methane oxidation.

Field investigations of lateral gas transport and subsequent emissions in soil adjacent to an old landfill in Denmark have been conducted during a one-year period. A significant seasonal variation in the emissions with high carbon dioxide and low methane fluxes in the summer (May to October) was observed. This was attributed to methane oxidation. Diumal measurements during a drop in barometric pressure showed that the fluxes of landfill gas changed dramatically within a very short time. The concentrations and the soil moisture content in the upper part of the soil profile had significant influence on the fluxes, as did the distance from the landfill border, temperature, barometric pressure and the pressure gradient. Statistical analyses proved that soil moisture described the largest part of the variation. No methane at all emitted during the summer. Calculations and isotope analyses showed that very high fractions of the laterally migrating methane were oxidised.

Lateral gas transport in soil adjacent to an old landfill: factors governing gas migration.

Field experiments investigating lateral gas transport in soil adjacent to an old landfill in Denmark during a one-year period were conducted. A significant seasonal variation, with low concentrations of methane and high concentrations of carbon dioxide in the summer, caused by methane oxidation was observed. There was a good correlation between pressure above the barometric pressure and the methane concentration in the soil, indicating that advective flow was the controlling process. This was confirmed by calculations. Diurnal measurement during a drop in barometric pressure showed that lateral migration of landfill gas was a very dynamic system and the concentrations of LFG at a specific place and depth changed dramatically within a very short time. The experiments showed that change in barometric pressure was an important factor affecting gas migration at the Skellingsted landfill in Denmark.

Lateral gas transport in soil adjacent to an old landfill: factors governing emissions and methane oxidation.

Field investigations of lateral gas transport and subsequent emissions in soil adjacent to an old landfill in Denmark were conducted during a 1-year period. A significant seasonal variation in the emissions with high carbon dioxide and low methane fluxes in the summer (May to October) was observed. This was attributed to methane oxidation. Diurnal measurements during a drop in barometric pressure showed that the fluxes of landfill gas changed dramatically within a very short time. The concentrations and the soil moisture content in the upper part of the soil profile had significant influence on the fluxes, as did the distance from the landfill border, temperature, barometric pressure and the pressure gradient. Statistical analyses proved that soil moisture described the largest part of the variation. No methane is emitted during the summer. Calculations and isotope analyses showed that very high fractions of the laterally migrating methane were oxidised.

Modeling Lateral Gas Transport in Soil Adjacent to Old Landfill

Lateral migration of landfill gases in soils surrounding old (closed) municipal landfills can lead to explosion hazards and damage to vegetation. Landfill gas production and migration is controlled by microbial activity and soil physical properties such as gas (air) permeability, gas diffusivity, and atmospheric pressure variations. Gas diffusivity and air permeability were measured on undisturbed samples collected at an agricultural field adjacent to an old Danish municipal landfill. Empirical expressions for predicting gas diffusivity and air permeability from soil-water content were fitted to the data. An empirical expression for calculating methane oxidation rate as a function of soil temperature was developed using site-specific measurements of methane oxidation rate. The transport and degradation parameter expressions were incorporated into a numerical model for simulating landfill gas transport, using soil-water content, temperature, and soil organic matter content as measured input parameters (fun...

A pilot plant study and 2-D dispersion-reactor model for a high-density riser reactor

The radial concentration profiles of reactant concentrations in a pilot plant high-density riser propylene ammoxidation reactor were sampled and analyzed and the extreme maldistribution of the profiles were found. A two-dimensional dispersion-reactor model was proposed to simulate the selective oxidization that taken place in the riser, which considered the influences of axial and lateral gas mixing, the non-uniformity of radial solids concentration and gas-velocity profiles on the reactor. The model can successfully predict the axial and radial profiles of concentrations sampled in the pilot plant. Simulation results indicate that the non-uniformity in radial catalyst concentration and gas-velocity distribution as well as insufficient lateral gas mixing result in a significant loss of selectivity and yield of acrylonitrile. The scale-up effect and the interdependence of the reaction rate, the non-uniformity of catalyst concentration and the requirement of gas mixing are discussed in details.

Numerical simulation of the gas–solid flow in a bed with lateral gas blasting

This paper presents a numerical study of the gas–solid flow in a bed by a Combined Continuum and Discrete Model (CCDM). Numerical experiments are carried out to simulate the motion of 10,000 spherical particles of 4 mm diameter caused by lateral gas blasting into a bed with its thickness equal to the diameter of particles. It is shown that, depending on the gas velocity, the bed can transform from a fixed bed to a fluidised bed or vice versa. Two zones can be identified in such a bed: a stagnant zone in which particles remain in their initial positions, and a mobile zone in which particles can move in various flow patterns. If the gas velocity is in a certain range, the mobile zone is confined in front of the gas inlet, forming the so-called raceway in which particles can circulate. If the gas velocity is higher than a critical value, fluidisation results, with the mobile zone growing by the combined effect of bubble penetration and shearing between moving and static particles until a stable state where the boundary separating the mobile and stagnant zones is unchanged. The dependence of raceway and fluidisation phenomena on gas velocity has been examined in terms of the size and shape of the mobile zone, gas-solid flow patterns and forces acting on individual particles. It is found that large interparticle forces occur along the boundary between the mobile and stagnant zones, whereas large fluid drag forces occur at the roof of a raceway or bubble. The predictions of transition between the static and dynamic states, and the complicated hysteretic behaviour in terms of either bed pressure drop or raceway size are in good agreement with the experimental observations.

Respiratory system of arachnids I: morphology of the respiratory system of Salticus scenicus and Euophrys lanigera (Arachnida, Araneae, Salticidae)

The book-lungs and the tracheal systems of two species of jumping spider, Salticus scenicus and Euophrys lanigera, were investigated using gross anatomical, light and electron microscopic methods. Both species possess well-developed book-lungs of similar size and tracheal systems with a basically similar branching pattern. The tracheal spiracle opens into a single atrium, where it gives rise to four thick ‘tube tracheae’, from which small secondary tube tracheae originate in groups. The secondary tracheae (diameter 1–5 μm) run parallel, without further branching, into the prosoma. In the opisthosoma, they lie ventrolaterally, where they contact muscles and internal organs. In the prosoma, the secondary tracheae may penetrate the gut epithelium and central nervous tissue. The structure of the tracheal walls is very similar to that of insects, consisting of a striated inner cuticular layer with taenidial structures and a surrounding outer hypodermal layer. The wall thickness appears similar in all secondary tracheae, indicating that lateral gas diffusion may be possible through the walls of all small tube tracheae.

Self-Organized Quasiparticles: Breathing Filaments in a Gas Discharge System

A quasi-two-dimensional, lateral ac-powered gas discharge system is investigated experimentally from the point of view of pattern formation. In a certain parameter range, well localized self-organized quasiparticles in the shape of current density filaments are observed. By varying the supply voltage, such objects can be destabilized and stationary filaments with a circular symmetry undergo a transition towards breathing filaments of dumbbell shape.

Observation of Q-spoiling effects on the resonance modes from a noncircularly deformed liquid jet

Spectral changes in fluorescence and lasing spectra were observed from a noncircularly deformed ink-doped ethanol jet, which was induced by a lateral gas flow. The distortion parameter was determined from the analysis of diffraction patterns to be as much as ~10%. Q -spoiling effects were clearly observed in the appearance of high- Q (~10(7)) modes in fluorescence and their disappearance in lasing. From the behavior of resonance modes, we concluded that the effective Q does not decrease so rapidly as predicted by the relation obtained from the ray-optics model. We also found that the signals leak out, with a wide angular spreading, mainly from near the boundary of the major axis, even for a large distortion parameter.

OIL AND GAS POTENTIAL OF THE PRERIF FORELAND BASIN, ONSHORE NORTHERN MOROCCO

The PreRif Basin in northern onshore Morocco may contain major oil and gas reserves. This foreland basin is located between the Tertiary‐Recent Rif Orogen to the north and the stable Moroccan Meseta to the south; for the purposes of this paper, it includes the Rharb Basin, an area of strong Neogene subsidence which extends offshore to the west.Prospective sandstone and carbonate reservoirs are present at a number of stratigraphic levels, ranging in age from Triassic and Jurassic to Miocene and Pliocene. Lower and Middle Jurassic shales and carbonates constitute potential source beds for “thermal” oil and gas; biogenic gas is generated within Miocene/Pliocene shales. Potential source beds are expected to have reached thermal maturity in the deepest portions of the present basinal area since the Late Miocene. Seals are provided by intraformational shales, transgressive shales of Tertiary age, Triassic evaporites, and by a thick, complex glidemass (or “olistostrome”) of late Miocene (Tortonian) age. Multiple traps can be expected; they will include anticlines, fault closures, salt‐tectonic features, and structural‐stratigraphic traps.Gravity‐defined low areas in the northern portion of the basin are probably the main generative depocentres. Lateral oil and gas migration has occurred on a regional scale since the Late Miocene, and has continued to the present day.A Jurassic Petroleum System includes the surface oil seeps and shut‐in oilfields of the Sidi Cacem area along the basin's southern flank. A Miocene Petroleum System supplies gas production in the Rharb Basin.The prospective area covers some 15,000 sq. km. Available reconnaissance data include published gravity, magnetic, seismic, and surface‐geological surveys. Modern airborne surveys of prospective areas should be followed by detailed exploration, including 3‐D seismic surveys.New recoverable field reserves may lie in the range of 50 to 150 million barrels oil‐equivalent per discovery; several new discoveries can be expected, leading to new total reserves possibly totalling 0.5 billion barrels oil‐equivalent.

Mixing of a lateral gas stream in a two‐dimensional riser of a circulating fluidized bed

AbstractA cold model of a circulating fluidized bed having a two‐dimensional riser, with a 12 × 120 mm section and a 6.4 m height, was equipped with a device to inject a lateral gas stream along the riser. The apparatus was operated under conditions ranging from those characteristic of combustors to those of gas‐conversion processes. Flow structures in the interaction region between the rising gas—solids suspension and the lateral gas stream were studied by means of a motion analysis system. Three main configurations were identified. The ratio between the momentum of the lateral gas stream and that of the rising suspension was found to be the parameter able to discriminate among the three configurations. A satisfactory agreement was found with mixing data obtained using a cylindrical riser.

Retroperitoneal laparoscopic nephrectomy: animal and human anatomic studies.

Retroperitoneal laparoscopic nephrectomy with CO2 insufflation was performed in 11 goats. The hemodynamic and blood gas repercussions of retroperitoneal laparoscopy were compared during the first 30 minutes with those induced by intraperitoneal laparoscopy. With the animal placed in the left lateral supine position, the hemodynamic and blood gas changes were similar with the two techniques and had a similar time course. The technical feasibility of retroperitoneal laparoscopy in animals was confirmed in the fresh human cadaver. The technical feasibility of retroperitoneal laparoscopy and the absence of any particular hemodynamic and blood gas repercussions encourage us to develop this approach for clinical upper urinary tract surgery.

Experimental and theoretical analysis of shadow-masked growth using organometallic vapor-phase epitaxy: The reason for the absence of facetting

Shadow-masked growth using organometallic vapor-phase epitaxy allows the creation of nonplanar regions having smoothly varying profiles devoid of macroscopic facets. The shape of these profiles is independent of gas flow direction and stripe orientation, suggesting that they are determined by lateral gas phase gradients. It is proposed that the absence of facets is due to the unique growth regime underneath the shadow mask, where organic radicals combine with group-III surface species, temporarily returning them to the vapor phase. This process has been simulated using a two-dimensional finite-element analysis that accurately describes the experimental behavior. Furthermore, this hypothesis predicts other experimentally observed phenomena.

A novel circulating cross-flow moving bed reactor system for gas—solids contacting

A novel circulating cross-flow moving bed reactor system for gas—solids contacting is presented. The system comprises a bunker, an inclined reactor, a stripper, a regenerator, a second stripper, a vertical transport system, and a gas—solids separator. It is an option for highly selective regenerative solid catalytic processes with a short gas residence time (up to seconds) and a moderate catalyst residence time (up to minutes). A laboratory-scale test rig of the circulating cross-flow moving bed reactor system is described along with an experimental study to verify its practical feasibility. The set-up operates under ambient conditions and 1.6 mm porous spherical alumina particles have been used. The feasibility of obtaining a stable continuous solids flow in the circulating system was shown. Further research focused on the reactor which has been constructed from four geometric equal compartments. The minimum superficial gas velocity below which the solids do not flow has been determined, as well as the maximum superficial gas velocity in the reactor above which fluidisation and the formation of gas bubbles occurs. Radioactive gas and solids tracer experiments have been performed to study the gas and solids flow patterns in the reactor. The lateral gas flow to neighbouring compartments in the reactor has been quantified. The solids move in plug flow unless gas bubble formation occurs.

Continuous monitoring of distal gas emanations at Vulcano, southern Italy

The increasing activity of Vulcano Island (Italy) since 1985 led to the initiation of continuous geochemical monitoring of the lateral soil gas emissions. On the basis both of their relative geochemical characteristics and of local considerations, three gaseous components were selected for monitoring, namely CO2, He and 222Rn. Monitoring has been performed by means of specific analysers. Gases extracted from a water well located at the foot of the active cone were selected for monitoring, on the basis of their geochemical and isotopic characters that indicate their genetic link with central high temperature fumarolic gases emitted at the crater. Very strong variations of gas composition can be observed within one day (from 1 to about 94% for CO2). Some variations display a daily character and can be correlated with that of atmospheric pressure. The three monitored gases are highly correlated, suggesting very high kinetics of gas transfer in the system. Because of these considerable variations of chemical composition, bulk concentrations obviously are not suitable for monitoring at Vulcano. However, the evolution with time of ratios such as 222Rn/CO2 and He/CO2 (the latter being corrected for atmospheric contamination) supplies numerical parameters that the expected to characterize the intensity of the degassing process. A new input of magmatic gases, that would lead to an increase in the 222Rn/CO2 and He/CO2 ratios, should therefore be detected by such a monitoring station.

MOCVD growth of AlGaAs/GaAs structures on nonplanar {111} substrates: Evidence for lateral gas phase diffusion

We investigate the MOCVD growth characteristics of AlGaAs on nonplanar {111}A and {111}B substrates. Growth over features etched into the {111} substrates is found to be highly anisotropic and asymmetric. The ratio of growth rates on adjacent facets is strongly dependent on the depth of the etched feature during growth, and is strikingly different between AlGaAs and GaAs layers. These observations suggest a large difference in the surface chemistry of Al and Ga species under these growth conditions and indicate that the column III element determines the relative growth rates of different facets during nonplanar growth. The results also provide strong evidence that lateral gas phase diffusion of reactants can be perhaps more significant than surface migration as a mechanism determining the incorporation sites of column III elements. Growth characteristics on nonplanar {111} substrates are markedly different than those observed for nonplanar growth on {100} substrates, creating a new set of design tools for the single step growth of guided wave devices such as lasers, modulators and waveguides.

Origin and migration of hydrocarbon gases and carbon dioxide, Békés Basin, southeastern Hungary

The Békés Basin is a sub-basin within the Pannonian Basin, containing about 7000 m of post-Cretaceous sedimentary rocks. Natural gases are produced from reservoirs (Precambrian to Tertiary in age) located on structural highs around the margins of the basin. Gas composition and stable carbon isotopic data indicate that most of the flammable gases were derived from humic kerogen contained in source rocks located in the deep basin. The depth of gas generation and vertical migration distances were estimated using quantitative source rock maturity-carbon isotope relationships for methane compared to known Neogene source rock maturity-depth relationships in the basin. These calculations indicate that as much as 3500 m of vertical migration has occured in some cases. Isotopically heavy (> − 7 >0) CO2 is the predominant species present in some shallow reservoirs located on basin-margin structural highs and has probably been derived via long-distance vertical and lateral migration from thermal decompositon of carbonate minerals in Mesozoic and older rocks in the deepest parts of the basin. A few shallow reservoirs (< 2000m) contain isotopically light (−50 to −60%0) methane with only minor amounts of C2+ homologs (< 3% v/v). This methane is probably mostly microbial in origin. Above-normal pressures, occuring at depths greater than 1800 m, are believed to be the principal driving force for lateral and vertical gas migration. These pressures are caused in part by active hydrocarbon generation, undercompaction, and thermal decomposition of carbonates.

Stability of Emission-Line Clouds in Seyfert Galaxies

Otherwise acceptable kinematic and dynamic models for emission line regions may be ruled out if the line-emitting clouds are unstable. We discuss the stability of radially-moving clouds to lateral gas flows. Such flows result from internal overpressures arising from the absorption of continuum radiation.

Gas Migration from Low-Level Radioactive Waste Repositories in Hard Rocks

A mathematical model is used to describe the migration of gas from radioactive waste repositories. Calculations are presented for rock properties characteristic of the Forsmark area. In Sweden, the repository of medium- and low-level radioactive waste is in fractured hard rock formations at a depth of --50 m below sea level. Chemical reactions in the stored waste produce hydrogen, which displaces the water from the fractures and migrates toward the surface, where it is finally released into the atmosphere. The lateral gas movement is considered negligible, and computations are performed under the assumption of vertical flow. Rock permeability was determined by flow tests in vertical boreholes. Calculations were performed for two cases: a constant gas flow rate corresponding to a gas production of 33000 kg/yr and a constant pressure corresponding to a gas cushion of 0.5m.

GEOLOGICAL AND RESERVOIR ENGINEERING CONSIDERATIONS FOR THE NORTH RANKIN GAS RECYCLING PROJECT

The North Rankin Field, situated in the Dampier Sub-basin offshore north-western Australia, is being developed as part of the North West Shelf Development Project. Substantial excess production capacity from the field exists until liquified natural gas exports to Japan plateau in late 1993. A recycling project was proposed to utilise this spare capacity. Gas produced in excess of current sales volumes is stripped of its condensate, and the lean gas is reinjected into the reservoir thereby increasing condensate production and the total recovery.The North Rankin A Gas Recycling Project was commissioned in June 1987 and its performance to date has been better than original expectations. The average recycling rate during the first few months of operation was approximately 13 x 106sm3/d (450 MMscfd) with associated condensate production of 1600 m3/d (10,000 STB/d). Studies suggest that the total recycled volume for the project, up until late 1993, may be in the order of 19 x 109sm3 (0.7 Tcf) with additional condensate recovery of approximately 2 million cubic metres (13 MMSTB).The design and implementation of subsurface aspects of the recycling project required close co-operation between the geological and reservoir engineering disciplines. Detailed studies were undertaken to determine reservoir extent and communication within the field in order to identify likely paths for lateral and vertical gas movement. Estimates of swept reservoir volumes were used to determine injected lean gas distributions. These gas distributions, in conjunction with operational aspects, formed the basis for the production and injection policy developed to maximise sweep efficiency and optimise condensate recovery from the recycling project.Multiple zone through tubing perforation was needed in most injection wells. The initial perforation was performed with an optimal underbalance pressure. Subsequent perforation was neutrally balanced. The degree of underbalance while perforating has a significant effect on perforation efficiency and simple models were used to predict this.Accurate estimates of well injectivity must be made to ensure that the perforation design allows well target rates to be met. Numerical reservoir and wellbore models were constructed to evaluate well injection potentials and gas distributions.To verify the design procedures and well performance, well testing and production logging was carried out before and after the start up of gas recycling. Production logging surveys in the injection wells and measuring condensate gas ratios in the producers are essential in monitoring the performance of gas recycling.