High-pressure Gas Release Research Articles

Consequence analysis of vapour cloud explosion from the release of high-pressure hydrogen storage

Gaseous hydrogen is commonly stored under high pressures due to its low volumetric storage density. The safety concerns about its release and potential accidents, such as vapour cloud explosions, were of the highest importance in industries. This research work established a methodology for consequence analysis of compressed hydrogen releases, considering various stages of event escalation, including high-pressure gas release, gas jet dispersion, and overpressure evaluations. Specifically, compressed hydrogen release was defined as an under-expanded flow, characterised by a transition from sonic to supersonic velocities. The notional nozzle theory was employed to tackle the flow regime transition and provide revised nozzle size and gas velocity as inputs to the CFD model for gas jet dispersion. The model was validated against experimental results, exhibiting a good agreement with a deviation of less than 20%. The flammable gas mass in the cloud was determined using the dispersion model and then used for overpressure predictions. This approach proved to be more realistic than relying solely on the total hydrogen release amount. In a case study, release parameters such as release direction, wind speed and release hole size were investigated. It was observed that a downward release resulted in less gas dissipation, leading to larger overpressures compared to other release directions. Wind speed had a relatively lower impact compared to other parameters. The release hole size had the most significant influence on explosion overpressure, with the case of a larger release size (e.g., 50.8 mm) exhibiting a few hundred times higher of hazardous area compared to a small hole size (e.g., 3 mm).

Simulation of localized electron density enhancement caused by high-pressure H2O gas release in ionosphere

Based on the continuity and momentum equations, a self-consistent simulation model is developed for describing the localized electron density enhancement caused by high-pressure H2O gas release in the ionosphere. The chemical reaction and momentum exchange process between the neutral gas and ionospheric plasma species are considered in the theoretical simulation model. The finite element method is used to solve the simulation model for H2O gas release, and the expansion and ionospheric disturbance process at the early stage of high-pressure gas release are studied. It is shown that the space expansion of the released gas is mainly dominated by the pressure difference between the H2O gas and the ionospheric plasma at the early stage of release. Then the diffusion process becomes the dominant process of the space transport of H2O molecules. An electron depletion region forms near the center of the release region due to the chemical reaction and collision process with H2O molecules. Meanwhile, an electron density enhancement region forms on both sides along the magnetic field direction due to the electron snowplow effect. With the increase in the released mass of H2O gas, the intensity and duration of the electron density enhancement increase gradually. With the release position rising, it is found that the intensity of the electron density enhancement has a peak near 380 km and the duration increases slightly with the increasing release height.

High-pressure gas release from subsea pipelines: Multiphase modelling and CFD simulation for consequences analysis in risk assessment

The aim of this work is to assess the time evolution of natural gas release from high-pressure subsea pipelines (117 and 137 barg) to both assess the consequences of it on the sea surface and delimit the hazard areas for offshore structures, vessels, ships and workers. Such a hazard analysis is applied for the first time to risk assessment by a quantitative determination of the area of the different hazard zones on the sea surface as a function of the following parameters: i) water depth of release, ii) release flow rate, iii) sea current and iv) wind velocity. In this way, safety maps are developed from the obtained results based on different scenarios of accidental events. In detail, when a fire scenario is developed, the hazard area is delimited by the inflammable limits of natural gas in air. To perform this investigation, multiphase computational fluid dynamic simulations involving three phases – i.e., released gas, seawater and air – are carried out using the open-source software OpenFOAM®. The methodology introduced in this work goes beyond the current state-of-the-art simulations, as it takes into account the mutual interactions among all the three phases present in the system, for which there is no analytical model able to describe the behaviour of the three phases with a certain degree of precision. In particular, a multiphase hybrid model pairing Euler-Euler and VOF methods is implemented. As main results, the shape of the release gas subsea cone and superficial plume are precisely evaluated as a function of the above-mentioned operating conditions, determining the evolution of the gas dispersion also in the seawater, which is crucial in the description of accidental scenarios resulting from the consequences analysis. In particular, it is found that, at a water depth of release of 55 m, the cone diameter at the sea level is larger than that at 15 m due to dispersion of gas in the sea. On the other side, wind velocity does not affect significantly the cone diameter.

Failure Mechanism of Gas-Bearing Coal during Outburst and a New Method for Outburst Prediction.

Coal and gas outbursts are among the most serious disasters affecting the safety of coal mines. Gas is an important factor in these types of disasters. To analyze the characteristics of the damage caused by gas to the coal body during the sudden release of the gas process, a self-developed high-pressure gas release cause coal particle ejection experiment device was used to conduct gas release experiments under different conditions. The results show that at the moment of gas release, coal particles and gas are ejected at high speed, crushing coal particles into smaller particles. With the increase in gas pressure and gas adsorption performance, the crushing effect will increase. Also, the coal ejection strength (CES) will increase nonlinearly. By analyzing the mass ratio of ejected coal particles, based on the theory of crushing work and energy, we developed a new coal particle fragmentation index, which can be fitted linearly to CES. The index is based on the f value, which makes up for the limitations of the forecasting method, and can be used more flexibly to predict the coal sample crushing situation. Moreover, the fitting parameter values can more accurately describe the coal particle crushing grade.

Pore structure changes induced by hydrate dissociation: An example of the unconsolidated clayey-silty hydrate bearing sediment reservoir in the South China Sea

The natural gas hydrates (NGHs) in the South China Sea are found in unconsolidated clayey-silty sediments, featured by very weak mechanical strength and low permeability. During gas extraction from such unstable, low permeability reservoirs, hydrate dissociation can result in distinct changes in pore properties and flow capability. Thus, it is extremely important to investigate the pore characteristics and gas flow mechanisms in such reservoirs. In this study, five sediment samples including two from the hydrate bearing layer (HBL) and three from the underlying layer (ULL), were taken from an exploration well in the Shenhu area, South China Sea. The pore morphology, pore specific surface area (SSA), total pore volume, porosity, and pore size distribution of these samples have been analyzed to compare the reservoir physical properties of the HBL (after the hydrate has dissociated and disappeared) with the ULL. Results from scanning electron microscopy reveal that the HBL samples without the hydrate present feature larger grain sizes, larger pore apertures and better connectivity than ULL samples. Results of NMR analysis and low temperature N2/CO2-adsorption show that both HBL and ULL samples have high total porosities (42.4%–48.8%) and high SSA (21.17–30.09 m2/g), while the results from centrifugal experiments demonstrate that the producible porosity (defined as the pore volume available for hydrocarbon emplacement) of the HBL samples is about twice (26.6%–30.3%) that of the ULL samples (15.5%–19.6%). The pores in the two sample types are dominated by intra-particle pores of 80 nm, and inter-particle and inter-aggregate pores of 0.2–3 μm. The above differences between HBL and ULL can be used to analyze the pore structure changes occurring as a result of the dissociation of NGHs in the HBL. We assume that on the one hand, formation of NGHs reduces pore pressure, thus resulting in higher effective stress, then compacts the pore space and reduces the total porosity. On the other hand, the release of high-pressure gas during hydrate dissociation could increase the pore aperture and improve pore connectivity, and thus increase the producible porosity of the HBL reservoir. It is also assumed that the flow capacity in the methane production zone in the HBL can be improved by the NGHs dissociation, suggesting that not only the hydrate saturation but also the pore structure changes should be considered when estimating the permeability during the gas production process.

Scaling procedure for designing accidental gas release experiment

PurposeThe purpose of this paper is to present a procedure to design an experimental setup meant to validate an innovative approach for simulating, via computational fluid dynamics, a high-pressure gas release from a rupture (e.g. on an offshore oil and gas platform). The design is based on a series of scaling exercises, some of which are anything but trivial.Design/methodology/approachThe experimental setup is composed of a wind tunnel, the instrumented scaled (1:10) mock-up of an offshore platform and a gas release system. A correct scaling approach is necessary to define the reference speed in the wind tunnel and the conditions of the gas release to maintain similarity with respect to the real-size phenomena. The scaling of the wind velocity and the scaling of the gas release were inspired by the approach proposed by Hall et al. (1997): a dimensionless group was chosen to link release parameters, wind velocity and geometric scaling factor.FindingsThe theoretical scaling approaches for each different part of the setup were applied to the design of the experiment and some criticalities were identified, such as the existence of a set of case studies with some release parameters laying outside the applicability range of the developed scaling methodology, which will be further discussed.Originality/valueThe resulting procedure is one of a kind because it involves a multi-scaling approach because of the different aspects of the design. Literature supports for the different scaling theories but, to the best of the authors’ knowledge, fails to provide an integrated approach that considers the combined effects of scaling.

Complex thermal analysis and runaway reaction of 2,2′-azobis (isobutyronitrile) using DSC, STA, VSP2, and GC/MS

A severe manufacturing accident involving 2,2′-azobis (isobutyronitrile) (AIBN) occurred in China on April 14, 2011, which created high-pressure gas release killing nine people and severely damaging equipment and buildings. Eliminating chemical catastrophes in the petrochemical industry is a global concern. A new approach, which combines non-isothermal kinetic modeling, runaway reaction, and product analysis, was employed to determine decomposition mechanisms of AIBN by separately using differential scanning calorimetry, simultaneous thermogravimetric analyzer, vent sizing package 2, and gas chromatography/mass spectrometer. The results indicated that azo compound AIBN exhibits higher level of thermal decomposition with a maximum temperature of 294 °C and maximum pressure of 367 psig in comparison to the other azos. Moreover, various critical thermokinetic parameters, such as time to maximum rate, exothermic onset temperature, adiabatic temperature rise, and pressure gradients were obtained. A combination of thermal hazards and reaction pathways was subsequently employed to investigate the thermokinetics and mechanisms of AIBN decomposition.

Consequences of a 12-mm diameter high pressure gas release on a buried pipeline. Experimental setup and results

When considering the transportation of gas through high pressure pipeline and associated permitting, the 12-mm diameter breach is one of those commonly considered as accidental scenarios and the associated consequences must to be calculated for determining the required safety measures. Up to now this “12-mm” scenario was modeled at the convenience of each risk analyst with no certitude on the real behaviour of the gas in the soil for these types of releases.To obtain concrete information on the “12-mm” scenario considered as the sizing event for safety distances associated to a little breach due to corrosion for instance, AIR LIQUIDE, ENGIE, NATIONAL GRID, PETROBRAS and TIGF decided to launch in 2013 a JIP (Joint Industrial Program) named “CRATER”. The aim of this project was to improve knowledge on the consequences of leakages occurring on buried high pressure pipes, and to determine what were their behaviour and their impact on the soil – i.e. crater formation, or not, according to release parameters – in order to use the appropriate methodology for risk and consequences assessment. Thus by changing several parameters – like nature of gas, initial gas pressure, type of soil … – the threshold between crater formation and gas dispersion in the soil following such leakages was investigated (specifically for methane and hydrogen, flammable and light gases). INERIS was chosen as subcontractor to perform nearly-full scale tests on its experimental site in order to collect reference data, understand phenomena and correctly assess the gas behaviour for accurate risk evaluation.

New sedimentary structures in seismites from SW Tanzania: Evaluating gas- vs. water-escape mechanisms of soft-sediment deformation

Seismite horizons are abundant in Cretaceous sandstones of the Rukwa Rift Basin, southwestern Tanzania. Diverse morphologies of soft-sediment deformation are preserved, including two new, unusual sedimentary structures, herein referred to as 1) balloon-shaped inflation structures and 2) surface fractures with linked sandstone splays. This original description of new sedimentary structures contributes to the growing catalogue of seismically induced deformation features. Their unusual morphologies bring to the forefront an important, though seldom touched upon, question of how to differentiate between gas- and water-escape in soft-sediment deformation features. The recognition of the spectrum of soft-sediment deformation structures contained in strata and their deformational mechanisms is important because it permits the differentiation between triggering mechanisms, particularly seismic activity, and can constrain such events spatially and temporally. We interpret the surface fractures and linked sandstone splays to reflect a high gas effusion rate, formed by the release of high-pressure gas followed by a limited expulsion of water. The balloon-shaped inflation structures reflect lower gas effusion rates due to expulsion of lower pressure gas that did not breach the Cretaceous surface seal. When these gas pulses did breach the paleosurface, they formed gas-discharge pits. These seismogenic structures are consistent with deposition of Cretaceous strata in the Rukwa Rift during periods of active carbonatite volcanism, seismicity, and possibly hot spring activity. This documentation serves as an important data point for the re-examination of the classification scheme of soft-sediment deformation structures as primarily water-escape structures to accommodate for the genesis of some secondary sedimentary features by gas-escape.

Experimental investigation on shock waves generated by pressurized gas release through a tube

An experimental investigation on the flow structures and the strength of shock waves generated by high-pressure gas release through a tube into air was conducted. The results demonstrated that a leading shock wave was generated in front of the compressed gas jet and the shock wave speed increased firstly, then decreased and finally kept constant with an increase of the propagation distance in the tube. The experimentally measured Mach numbers of shock waves were close to those calculated from the theory of ideal shock tube flow. After spouting out of the tube, the normal shock quickly developed into a hemispherical shape. The Mach disk was observed in the under-expanded jet. For high-pressure combustible gas release, the concept of theoretical critical pressure of ignition was introduced and several theoretical critical pressures of common gaseous fuels were obtained.

Assessment of Noise Pollution in the Ashuganj Fertilizer Industrial Area, Ashuganj

Noise pollution in industries is now a serious environmental concern in Bangladesh. In this study sound levels are observed inside the Ashuganj Fertilizer Company Ltd (AFCL) Ashuganj. Continuous running of high speed turbo machinery, vibration of pipelines and structures, transmission of high pressure gas, sudden release of high pressure gas generate noise hazard inside the factory during the time of production. The sound level data was collected at seventeen different locations in the ammonia production plant, ten different locations in the urea production plant and ten different locations in the residential area of AFCL. In the ammonia plant, significantly high level of sound was observed (>90dB) from the process gas cooler, let-down station, boiler-feed water pump, synthesis-gas compressor, process air compressor, alternator and ammonia compressor areas. In the Urea plant, Prill tower (top), Prill tower (absorber vent) are the most noise vulnerable areas with sound level >90 dB. Residential area found less affected by noise pollution (43-53 dB) but in some areas like playground, main gate of the residential area sound level sometimes cross the standard sound level of residential area (50 dB). In the ammonia and urea plant, the sound levels are much higher than the standard sound level (75 dB) for the industrial area, which is considered a hazard of noise may induce hearing loss, annoyance and other adverse effects on the health of the workers of AFCL. Therefore, some remedial measures should be taken to reduce the sound level inside the factory. Key words: Noise pollution; Ashuganj Fertilizer Company Ltd (AFCL); Ammonia production plant; Urea production plant; Sound level; Health hazard. DOI: http://dx.doi.org/10.3329/bjsir.v46i2.8184 Bangladesh J. Sci. Ind. Res. 46(2), 183-190, 2011