Natural Vents Research Articles

Associated natural gas flare in the integrated market of the southern cone

Reducing greenhouse gas is a major challenge. The oil and gas industry must contribute to this goal, primarily by controlling natural gas flaring and venting, which is a multibillion revenue loss. More than 4000 billion cubic feet of gas is flared every year in the world, leading to almost 400 million tonnes of greenhouse gases. In Latin America, 7.4% of the total gas produced in the region is flared or vented. This article evaluates the status of the flaring and venting of gas in Latin America, focusing on the southern cone countries (Argentina, Bolivia, Brazil and Chile). It also develops a long-term perspective analysis for the region, using an integrated optimization model. Findings indicate that, when transport infrastructure is limited or there is no domestic demand to absorb the associated gas, flaring becomes the least-cost solution in the optimization model. This can be critical in the next decade, due to the excess gas supply or the lack of gas demand to absorb it. Particularly, the natural gas demand associated with the electricity generation in Brazil is reduced by the hydroelectric expansion and a sluggish economy. Therefore, policies must promote options to monetize the stranded gas.

Wind action on natural smoke exhaust in atria

Performance of natural vents installed at height would be affected under strong wind. Smoke might even be pulled downward or inward by wind action if the building is located near to a tall building or on the hillside. The importance of studying aerodynamics around a building located adjacent to a vertical wall while designing static smoke exhaust system will be illustrated in this paper. Air flow pattern around the buildings depends on many factors including wind speed, fire size, height of the vertical wall and distance away from the building, theoretical study is difficult. Numerical simulations with Computational Fluid Dynamics is appropriate to design smoke exhaust system design under these conditions. Key equations of calculating the smoke exhaust rates and the required vent area will be reviewed. Modified equations on smoke exhaust rates with wind effects discussed earlier will be applied.

Noise-silencing technology for upright venting pipe jet noise

When a natural gas transmission and distribution station performs a planned or emergency venting operation, the jet noise produced by the natural gas venting pipe can have an intensity as high as 110 dB, thereby severely affecting the production and living environment. Jet noise produced by venting pipes is a type of aerodynamic noise. This study investigates the mechanism that produces the jet noise and the radiative characteristics of jet noise using a computational fluid dynamics method that combines large eddy simulation with the Ffowcs Williams–Hawkings acoustic analogy theory. The analysis results show that the sound pressure level of jet noise is relatively high, with a maximum level of 115 dB in the low-frequency range (0–1000 Hz), and the sound pressure level is approximately the average level in the frequency range of 1000–4000 Hz. In addition, the maximum and average sound pressure levels of the noise at the same monitoring point both slightly decrease, and the frequency of the occurrence of a maximum sound pressure level decreases as the Mach number at the outlet of the venting pipe increases. An increase in the flow rate can result in a shift from low-frequency to high-frequency noise. Subsequently, this study includes a design of an expansion-chamber muffler that reduces the jet noise produced by venting pipes and an analysis of its effectiveness in reducing noise. The results show that the expansion-chamber muffler designed in this study can effectively reduce jet noise by 10–40 dB and, thus, achieve effective noise prevention and control.

Natural Ventilation of Smoke Subject to Wind Pressure Within Fire Safety Engineering Approach

This paper presents an analytical model able to explore the design method of natural smoke evacuation through an exhaust vent subject to wind pressure. The proposed model can be used to determine the flow rate of smoke and the optimal section of the exhaust vent according to the geometric parameters of the room, the heat release rate and the pressure exerted by the wind forces at the exhaust vent. The numerical resolutions of the mathematical equations of the model were performed using the dichotomy method. The proposed analytical approach is built progressively by, (i) the examination of interaction forces between buoyancy forces and wind pressure forces, (ii) a numerical validation of the analytical model using the numerical simulation software Fire Dynamics Simulator, and (iii) proposal of a method of approximation of the optimal section of the exhaust vent for a maximum smoke evacuation rate. The results show very satisfactory and provide adequate prediction of the optimal size of the exhaust vent between the theoretical approximation and various configurations of numerical simulation. The feasibility and effectiveness of the proposed approach lead to an accurate and reliable analytical model able to analyze the influence of the size of natural smoke evacuation vents subjected to the pressure of wind forces.

Ciliates as bioindicators of CO2 in soil

The effect of controlled sub-surface CO2 emissions on edaphic ciliate communities was examined in experimental mesocosms and then compared with the effect of natural CO2 emissions from natural vents on edaphic ciliate communities to analyse the potential of ciliates as bioindicators of soil CO2 increments. The relative abundance of each taxonomic family formed the basis for developing the metrics of the ciliate assemblages in order to obtain a quantitative soil quality bioassessment, the edaphic ciliate bioindex. Twenty-four mesocosms filled with soil and equipped with controlled CO2 injection were built for the experiment. To evaluate the potential of soil ciliates as bioindicators, the same CO2 fluxes were analyzed in both study conditions, from 0 to more than 150mlCO2d−1. Several diversity indices and other group ratios and percentages of community structure were calculated.Biodiversity of ciliates (Equitability, Margalef and Shannon indices) decreased with the increase in CO2 fluxes, and Colpodid/Polyhymenophorean ratio increased. This indicated adverse conditions for the ciliates in the soil. There was a positive significant relationship between the observed CO2 values measured in the test set and the values expected according to their inhabiting ciliate community. The weighted averaging of taxonomic group indicator method supported the experimental results attesting to the potential of edaphic ciliates as bioindicators of CO2 flux increments. The ecological profiles estimated within the training test, based on the taxonomic level of family, were reliable and provided a basis for the use of ciliates to monitor soil CO2 flux increments in a wide range of ecological conditions.

Experimental and numerical study of interactions between sprinklers and natural smoke vents

AbstractReal scale experimentations have been conducted in order to investigate interactions that may occur in a compartment where sprinklers and Smoke and Heat Exhaust Vent Systems coexist. Fuel oil spray was used as fire source with steady heat release rate of 400 and 800 kW. Both sprinkler system and natural Smoke and Heat Exhaust Vent Systems were designed according to the French standards. Effect of vent on sprinkler activation time was studied. An analysis of the temperature field inside the compartment was conducted while vent was opened prior or after sprinkler activation. Simulations of the experiments were also carried out with Fire Dynamics Simulator v.6 for validation purpose and also to provide supplementary data regarding soot flow rate and energy extracted at the vent.

Multi-criteria numerical analysis of factors influencing the efficiency of natural smoke venting of atria

Smoke management in the atrium with natural smoke venting is influenced by many parameters. The analysis presented considered the impact of atrium height, atrium shape and layout of air inlets, wind direction, wind speed and location of the fire outbreak. Experimental research is here very awkward due to the costs, thus the numerical analysis is a convenient way to examine such a large parameters domain. So wide range of research was feasible thanks to the use of Taguchi method of experiment design. The flow volume through the exhaust vents and the soot mass fraction at the ground floor were chosen as criteria to evaluate the efficiency of the smoke removal system As a result, the relative importance of examined parameters were obtained, and above all the interactions between parameters were revealed. This allows to formulate some hints for designers to make the smoke removal systems robust on the wind influence and other unpredictable factors.

Dimensionless analytical solutions for steady-state fire smoke spread through high-rise shaft

Analytical solutions in terms of dimensionless numbers for the smoke spread through high-rise shafts during fires are essential to provide a fundamental understanding of smoke transport physics, which is a complex coupled heat and mass transfer problem. Existing solutions are often dimensional based on simplification of the problem such as assuming adiabatic conditions. In order to obtain the dimensionless analytical solutions, energy balance equation, mechanical energy equation and mass balance equation were established for smoke spread in high-rise buildings under both mechanical and natural venting conditions. Experiments were designed and conducted on two scaled shafts with different sizes and materials, and the measured results were compared to the dimensionless analytical solutions. It was found that the dimensionless analytical solutions could predict temperature profiles, mass flow rate and neutral plane level accurately. The effect of the adiabatic assumption on the accuracy was also discussed. For example, due to the adiabatic assumption, the error of the calculated mass flow rate required during mechanical venting to maintain a high-rise shaft smoke free was found to increase with a dimensionless number, ω, defined by the geometrical and thermal properties of the shaft.

The stable microbiome of inter and sub-tidal anemone species under increasing pCO2.

Increasing levels of pCO2 within the oceans will select for resistant organisms such as anemones, which may thrive under ocean acidification conditions. However, increasing pCO2 may alter the bacterial community of marine organisms, significantly affecting the health status of the host. A pH gradient associated with a natural volcanic vent system within Levante Bay, Vulcano Island, Italy, was used to test the effects of ocean acidification on the bacterial community of two anemone species in situ, Anemonia viridis and Actinia equina using 16 S rDNA pyrosequencing. Results showed the bacterial community of the two anemone species differed significantly from each other primarily because of differences in the Gammaproteobacteria and Epsilonproteobacteria abundances. The bacterial communities did not differ within species among sites with decreasing pH except for A. viridis at the vent site (pH = 6.05). In addition to low pH, the vent site contains trace metals and sulfide that may have influenced the bacteria community of A. viridis. The stability of the bacterial community from pH 8.1 to pH 7.4, coupled with previous experiments showing the lack of, or beneficial changes within anemones living under low pH conditions indicates that A. viridis and A. equina will be winners under future ocean acidification scenarios.

One-dimensional analysis for optimizing smoke venting in tunnels by combining roof vents and longitudinal ventilation

A hybrid mode that combines both longitudinal ventilation and natural roof venting is proposed for thermal and smoke control in tunnel fires. This hybrid strategy creates safe environments at the upstream side of the fire and shortens the smoke spreading distance at the downstream side, if the longitudinal ventilation and roof smoke venting are well cooperated. It is advantageous to the urban traffic tunnels that are adjacent to other underground facilities. The pressure rise of the longitudinal ventilation system and the geometrical parameters of the roof vents are the two key factors affecting the effectiveness of the proposed hybrid mode. The heat and smoke convection patterns under this hybrid mode are investigated with both a one-dimensional hydraulic analysis method and numerical simulations. The simulation results demonstrate that the smoke can be exhausted by the roof vents downstream of the fire, and thus, the gas temperatures downstream of the vents can be significantly decreased. The maximum deviation between the theoretical smoke exhaust rate and simulation result is approximately 17%, indicating the analytical model and numerical simulation results are in good agreement. The one-dimensional analysis method and the equations associated with it can be directly used to optimize the design parameters.

Numerical studies on the wind effects on natural smoke venting of atria

ABSTRACTSmoke management in the atrium with natural smoke venting is influenced by many parameters. These include the geometry of a building, external temperature and wind. The article presents the analyses of the impact of two wind speeds: 2.5 m/s and 7.5 m/s on conditions in the atrium. Volume flow rate of air inflowing to the atrium and the velocity of supply air in make-up air inlets were considered. The wind inflow from each direction was examined for two wind speed. This enabled the analyses of operation of particular make-up air inlets in variable external wind conditions. The possible impact of other buildings has been omitted. Moreover, the operation of exhaust openings was analysed. The subsequent step was examination of conditions in the atrium. The influence of wind, its speed and direction on soot mass fraction and its distribution in relation to the height of the atrium were considered. In addition, for some cases, visibility has been shown. It was proved that make-up air inlets located near the corner on the side wall parallel to the wind direction do not work properly, usually air flows through these openings to the outside. This allows to formulate guidelines for designers on the best locations of the inlet vents in buildings.

Microbial communities in a range of carbon dioxide fluxes from a natural volcanic vent in Campo de Calatrava, Spain

A natural carbon dioxide (CO2) vent sited in Ciudad Real (Spain) was studied to understand how CO2 emissions affect microbial communities along a CO2 gradient. We used different molecular methods (quantitative PCR, DGGE and Biolog EcoPlates™) to assess changes in abundance, diversity and functionality of the main groups of soil microbiota (bacteria, archaea and fungi). A general decrease for all studied variables (gene copies and band richness of bacteria, archaea and fungi, and Biolog activities) was observed from control (7–19gm−2d−1) to high CO2 fluxes (260–1600gm−2d−1). On the contrary, at extreme fluxes (more than 10kgm−2d−1) the microbial community increased their abundance and activity, though remained less diverse. PCA from carbon use substrate pattern and DGGE dendograms clearly differentiated low fluxes from high and extreme. This paper proves that high CO2 fluxes (between 260 and 1600gm−2d−1) cause losses in both structural and functional community diversity, and a decrease in metabolic activities.

Soil communities are affected by CO2 belowground emissions at a natural vent in Spain

Natural CO2 vents have received growing interest in the last years due to their relation to CO2 capture and storage (CCS) risk assessment studies. Despite the increasing body of knowledge, mostly focused on microbial communities, scarce information is available on how geological CO2 affects mesofauna and microfauna, and their interactions. We studied microorganisms, microfauna i.e. protists and nematodes, and mesofauna communities, i.e. collembola and mites and their relationships in a natural CO2 vent at La Sima (Spain). Four CO2 flux intensities from Control (7–19 g m−2 d−1) to low (40–55 g m−2 d−1) and high fluxes (260–1600 g m−2 d−1), including extreme emissions (more than 104 g m−2 d−1) were studied. We found that increasing CO2 emissions from Control to high fluxes strongly affected biota abundances and richness, cascading from microorganisms to mesofauna, and resulting in reduced and less diverse populations in each of the groups levels assayed. Nevertheless, at extreme fluxes edaphic biota biomass recovered in most of the communities, suggesting that the extreme CO2 conditions are associated with high abundances of well adapted communities, although with very low diversity. Increases in abundance of bacteria, fungi and amoebae, but not ciliates, were related to increases in mesofauna richness and nematode and mesofauna abundances. Our results help to indicate the CO2 threshold from which accidental losses from CCS operations can be detected in the long-term.

The evacuation safety analysis of fire scenarios in the entire acoustic barriers of elevated Mass Rapid Transit System

The entire acoustic barrier is similar to a tunnel for the elevated Mass Rapid Transit (MRT) System. Current smoke ventilation designs for the elevated MRT system have no precedent standards to follow, and therefore are all designed based on experience. For the entire acoustic barrier design in the MRT system in Taiwan, this research used FDS to simulate fires under the compartments with different heat release rates and varying number of compartments in varying lengths of entire acoustic barriers. The effects of the smoke layers produced by the fires on the evacuation of the personnel were observed. This research used a 1000m entire acoustic barrier without smoke vent for discussion, and it was discovered that evacuation proved to be ineffective when the heat release rates were 10, 20, 30 and 40MW. However, under circumstances where openings of different sizes were used at the top of the barriers, or changes were made to the heat release rates, or alterations were made to the number of passengers and compartments, a formula was developed in which all passengers could be evacuated under these varying circumstances; and this formula can be used as reference during the designing of natural ventilation vents in acoustic barriers for elevated MRT systems.

Techno-economic evaluation of an integrated hydrogen and power co-generation system with CO2 capture

An integrated hydrogen and power co-generation system with CO2 capture has been proposed and evaluated techno-economically. The proposed system is an alternative low cost clean power generation while supplying hydrogen for process plants. The baseline configuration has been designed based on the literature. Different cases are simulated in Aspen Plus and are evaluated economically. Thermodynamic models have been validated against the results of previous publications. The co-generation system with different product shares of hydrogen and power has been compared with CO2 captured and CO2-vented hydrogen plants by means of defined techno-economic-environmental indicators. Sensitivity analysis has been carried out for input parameters of natural gas and electricity prices. The simulation results demonstrate that in CO2 capture studied cases, system total efficiency is slightly greater (1–1.5%) in co-generation cases than in hydrogen only production case with electricity importing from natural gas combined cycle and CO2 venting. Economic evaluation results indicate that although hydrogen cost increases with power co-generation (5–8%), the CO2 avoidance cost is significantly lower than in power plants alone (73–83% lower).

Response of key stress-related genes of the seagrass <i>Posidonia oceanica</i> in the vicinity of submarine volcanic vents

Abstract. Submarine volcanic vents are being used as natural laboratories to assess the effects of increased ocean acidity and carbon dioxide (CO2) concentration on marine organisms and communities. However, in the vicinity of volcanic vents other factors in addition to CO2, which is the main gaseous component of the emissions, may directly or indirectly confound the biota responses to high CO2. Here we used for the first time the expression of antioxidant and stress-related genes of the seagrass Posidonia oceanica to assess the stress levels of the species. Our hypothesis is that unknown factors are causing metabolic stress that may confound the putative effects attributed to CO2 enrichment only. We analyzed the expression of 35 antioxidant and stress-related genes of P. oceanica in the vicinity of submerged volcanic vents located in the islands of Ischia and Panarea, Italy, and compared them with those from control sites away from the influence of vents. Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) was used to characterize gene expression patterns. Fifty-one percent of genes analyzed showed significant expression changes. Metal detoxification genes were mostly down-regulated in relation to controls at both Ischia and Panarea, indicating that P. oceanica does not increase the synthesis of heavy metal detoxification proteins in response to the environmental conditions present at the two vents. The up-regulation of genes involved in the free radical detoxification response (e.g., CAPX, SODCP and GR) indicates that, in contrast with Ischia, P. oceanica at the Panarea site faces stressors that result in the production of reactive oxygen species, triggering antioxidant responses. In addition, heat shock proteins were also activated at Panarea and not at Ischia. These proteins are activated to adjust stress-accumulated misfolded proteins and prevent their aggregation as a response to some stressors, not necessarily high temperature. This is the first study analyzing the expression of target genes in marine plants living near natural CO2 vents. Our results call for contention to the general claim of seagrasses as "winners" in a high-CO2 world, based on observations near volcanic vents. Careful consideration of factors that are at play in natural vents sites other than CO2 and acidification is required. This study also constitutes a first step for using stress-related genes as indicators of environmental pressures in a changing ocean.

Feasibility of Using More Geothermal Energy to Generate Electricity

Human population is ever-increasing and, thus, demand for energy is escalating. Consequently, seeking clean methods of producing electricity is a most crucial endeavor at this time. The shrinking reserves of oil have added urgency to the matter as well. One other recognized source of renewable energy besides wind, water, and solar (WWS) is geothermal energy, which has been proven to be useful in baseload power generation, a significant advantage over WWS. As compared to fossil fuels, geothermal energy is not subjected to the supply and cost fluctuations of which fuel is at risk. To date, there have been a number of innovative procedures explored to use geothermal energy to produce electricity. A relatively innovative yet not uncommon method has been to use hot solid rocks to heat water and pump the superheated water to use in power plants. These rocks are generally underground and at higher temperatures due to their proximity to volcanoes or natural geothermal vents. The water goes deeper down into the earth's crust to become superheated by the rocks, and then is pumped out to power turbines, and subsequently returned into the ground to repeat the process. In Krafla, Iceland, during their Icelandic Deep Drilling Project (IDDP) in 2009, a borehole was accidentally dug into the magma at 2100 m. The temperature of this magma was about 900–1000 °C. A steel casing with perforations on the flat side was cemented into the well bottom. This design was to slow the heat flow, and superheated steam was made for the following two years till July 2012. The steam reached temperatures of 450 °C and was at high pressures. Krafla was the world's first magma-enhanced geothermal system (EGS) to generate electricity. This paper will explore the feasibility of using geothermal power plant methods as a sustainable source of clean energy. Geothermal energy has tremendous potential if the right methods can be found to tap that potential, as well as if the cost may be brought down by innovation and demand. In addition, an innovative method, which already exists in some form, is proposed in the current review to harness more geothermal energy for use.

Bubble Transport Mechanism: Indications for a gas bubble-mediated inoculation of benthic methanotrophs into the water column

The importance of methanotrophic microorganisms in the sediment and water column for balancing marine methane budgets is well accepted. However, whether methanotrophic populations are distinct for benthic and pelagic environments or are the result of exchange processes between the two remains an area of active research. We conducted a field pilot study at the Rostocker Seep site (Coal Oil Point seep field, offshore California, USA) to test the hypothesis that bubble-mediated transport of methane-oxidizing microorganisms from the sediment into the water column is quantifiable. Measurements included dissolved methane concentration showed a strong influence of methane seepage on the water-column methane distribution with strongly elevated sea surface concentrations with respect to atmospheric equilibrium (saturation ratio ~17,000%).Using Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD FISH) analysis, aerobic methane oxidizing bacteria (MOB) were detected in the sediment and the water column, whereas anaerobic methanotrophs (ANME-2) were detected exclusively in the sediment. Critical data for testing the hypothesis were collected using a novel bubble catcher that trapped naturally emanating seep gas bubbles and any attached particles approximately 15cm above the seafloor. Bubble catcher experiments were carried out directly above a natural bubble seep vent and at a nearby reference site, for which an “engineered” nitrogen bubble vent without sediment contact was created. Our experiments indicate the existence of a “Bubble Transport Mechanism”, which transports MOB from the sediment into the water column. In contrast, ANME-2 were not detected in the bubble catcher. The Bubble Transport Mechanism could have important implications for the connectivity between benthic and pelagic methanotrophic communities at methane seep sites.

Spatio-temporal variability of polychaete colonization at volcanic CO2 vents indicates high tolerance to ocean acidification

Ocean acidification is predicted to have negative effects on marine biota, resulting in the loss of biodiversity and changes in marine ecosystem structure and function. However, some species and life stages may be capable of thriving in low pH conditions, either due to their natural ability to tolerate stressful low pH–high pCO2 conditions and/or alteration of species interactions caused by changes in pH profiles, or due to evolutionary trade-offs. A better understanding of which species may be capable of tolerating ocean acidification can guide future research into the mechanisms for physiological and ecological resilience to future carbon dioxide (CO2) conditions. We investigated the colonization of selected polychaete species along a pH gradient originating from shallow, coastal volcanic CO2 vents (Ischia, Italy). Colonization was quantified by exposing artificial invertebrate collectors attached to the substratum for 30 days during different periods of the year (late spring, fall and late winter). Three species, Amphiglena mediterranea, Platynereis dumerilii and Syllis prolifera, were present and abundant along the gradient throughout the year. All three species were significantly more abundant in the most acidified areas, confirming their high tolerance and capacity to cope with very low pH. Abundances of all three species were compared to data previously collected via collectors suspended in the water column. More individuals were found in the collectors attached to the substratum, suggesting that abundances may have previously been underestimated. This is likely due to the close proximity of these collectors with the natural rocky substratum. All three species exhibited similar temporal variability, consistent with their life cycle and reproductive biology. Our results demonstrate high tolerance of the species for low and variable pH and corroborate their use as robust models to explore the capacity to cope with low pH–high pCO2 conditions, both in the natural vent systems and in the laboratory.

Performance of smoke elimination and confinement with modified hybrid ventilation for subway station

Smoke is the element of a fire that causes the greatest loss of life. The importance of eliminating smoke is underscored in the fire safety engineering of underground subway stations. In this study, an experiment and a numerical simulation were performed to determine the efficacy of different ventilation modes. The experiment was conducted on a 1:50 scale model of a subway station and a complementary Fire Dynamics Simulator (FDS) simulation was performed on a full scale station. The influences of natural ventilation, mechanical ventilation and hybrid ventilation were examined.The results indicated that natural ventilation was good for smoke elimination when the fire source was under the dome, and the gas temperature measured in the middle of the basement 1 decreased significantly as the size of the vent increased. Smoke was exhausted from the basement 1 and fresh air supplied into the basements 2 and 3, which had the best efficacy when managing the smoke diffusion. No matter that the fire source was under the dome or out of the atrium, the carbon monoxide (CO) concentration was the smallest when the modified hybrid ventilation system was in operation. At the same time, changes in the natural ventilation vent had an influence on smoke elimination and the efficacy of smoke elimination became better with the increasing of the dimension of the vent when the fire location was under the dome.