The volatiles released by the volcanic structures of the world contribute to natural environmental pollution both during the passive and active degassing stages. The Island of Vulcano is ...characterized by solfataric degassing mainly localized in the summit part (Fossa crater) and in the peripheral part in the Levante Bay. The normal solfataric degassing (high-temperature fumarolic area of the summit and boiling fluids emitted in the Levante Bay area), established after the last explosive eruption of 1888–90, is periodically interrupted by geochemical crises characterized by anomalous degassing that are attributable to increased volcanic inputs, which determine a sharp increase in the degassing rate. In this work, we have used the data acquired from the INGV (Istituto Nazionale di Geofisica e Vulcanologia) geochemical monitoring networks to identify, evaluate, and monitor the geochemical variations of the extensive parameters, such as the SOsub.2 flux from the volcanic plume (solfataric cloud) and the COsub.2 flux from the soil in the summit area outside the fumaroles areas. The increase in the flux of volatiles started in June–July 2021 and reached its maximum in November of the same year. In particular, the mean monthly flux of SOsub.2 plume of 22 tons daysup.−1 (t dsup.−1) and of COsub.2 from the soil of 1570 grams per square meter per day (g msup.2 dsup.−1) increased during this event up to 89 t dsup.−1 and 11,596 g msup.2 dsup.−1, respectively, in November 2021. The average annual baseline value of SOsub.2 output was estimated at 7700 t dsup.−1 during normal solfataric activity. Instead, this outgassing increased to 18,000 and 24,000 t dsup.−1 in 2021 and 2022, respectively, indicating that the system is still in an anomalous phase of outgassing and shows no signs of returning to the pre-crisis baseline values. In fact, in the first quarter of 2023, the SOsub.2 output shows average values comparable to those emitted in 2022. Finally, the dispersion maps of SOsub.2 on the island of Vulcano have been produced and have indicated that the areas close to the fumarolic source are characterized by concentrations of SOsub.2 in the atmosphere higher than those permitted by European legislation (40 μg msup.−3 for 24 h of exposition) on human health.
Extraction of natural gas from shale rock in the United States (US) is one of the landmark events in the 21st century. The combination of horizontal drilling and hydraulic fracturing can extract huge ...quantities of natural gas from impermeable shale formations, which were previously thought to be either impossible or uneconomic to produce. This review offers a comprehensive insight into US shale gas opportunities, appraising the evolution, evidence and the challenges of shale gas production in the US. The history of US shale gas in this article is divided into three periods and based on the change of oil price (i.e., the period before the 1970s oil crisis, the period from 1970s to 2000, and the period since 2000), the US has moved from being one of the world's biggest importers of gas to being self-sufficient in less than a decade, with the shale gas production increasing 12-fold (from 2000 to 2010). The US domestic natural gas price hit a 10-year low in 2012. The US domestic natural gas price in the first half of 2012 was about $2 per million British Thermal Unit (BTU), compared with Brent crude, the world benchmark price for oil, now about $ 80–100/barrel, or $14–17 per million BTU. Partly due to an increase in gas-fired power generation in response to low gas prices, US carbon emissions from fossil-fuel combustion fell by 430millionton CO2 – more than any other country – between 2006 and 2011. Shale gas also stimulated economic growth, creating 600,000 new jobs in the US by 2010. However, the US shale gas revolution would be curbed, if the environmental risks posed by hydraulic fracturing are not managed effectively. The hydraulic fracturing is water intensive, and can cause pollution in the marine environment, with implications for long-term environmental sustainability in several ways. Also, large amounts of methane, a powerful greenhouse gas, can be emitted during the shale gas exploration and production. Hydraulic fracturing also may induce earthquakes. These environmental risks need to be managed by good practices which is not being applied by all the producers in all the locations. Enforcing stronger regulations are necessary to minimize risk to the environment and on human health. Robust regulatory oversight can however increase the cost of extraction, but stringent regulations can foster an historic opportunity to provide cheaper and cleaner gas to meet the consumer demand, as well as to usher in the future growth of the industry.
In comparison to legacy engine technology, natural gas vehicles have become cleaner and more efficient. Improved fueling infrastructure has supported the growth of natural gas vehicles in the ...heavy-duty sector. The heavy-duty transportation industry greatly favors the use of diesel engine technology compared to alternative fuel strategies. Local regulations and economic incentives, however, have helped to spur adoption of natural gas vehicles in certain heavy-duty vocations. Studies have shown lower distance-specific oxides of nitrogen (NOx) emissions from the stoichiometric three-way catalyst (TWC) equipped natural gas engines compared to diesel engines equipped with diesel particulate filters (DPF) and selective catalytic reduction (SCR). This review details the progress in natural gas engine technology, presents changes to emissions rate due to technology advancements, and compares natural gas engine emissions to those of modern diesel engines.
•Natural gas engines are favorable to achieve regional air quality standards, especially NOx.•Important to control fugitive methane emissions to realize low GHG emissions.•Effect of natural gas engine aging on the regulated emissions rate is seldom reported.
With the continuous growth of the global natural gas trade, the accurate prediction of natural gas prices has become one of the most critical issues in the planning and operation of public utilities. ...In order to further improve the prediction accuracy of natural gas prices, we have developed a novel hybrid method based on the CEEMDAN-SE (complete ensemble empirical mode decomposition with an adaptive noise-sample entropy) and the PSO-ALS-GRU (gated recurrent unit network optimized by the particle swarm optimization algorithm with an adaptive learning strategy (PSO-ALS)) for predicting the natural gas prices. The proposed approach can address the limitations of the traditional forecasting approaches and perform accurate predictions. First, the original natural gas price series is decomposed into a series of sub-sequences with obvious differences in a complex degree by using the CEEMDAN-SE. Then, the forecasting model PSO-ALS-GRU is developed, and each sub-sequence is individually predicted. Finally, the prediction results of each sub-sequence are superimposed and reconstructed in order to form the overall forecast result. This hybrid model combines the methodology of complex systems with deep-learning techniques, making it more appropriate for analyzing relationships such as long-term dependences and solving complex nonlinear problems. By finding the key hyperparameters in the GRU network using the PSO-ALS, the data feature of natural gas prices matches the network topology structure, and the prediction accuracy of the model is improved. For illustration and verification purposes, the simulation is performed by using real data. The results show that the novel hybrid model can accurately predict the weekly prices of natural gas. In a comparison of prediction errors with other individual models, the proposed model demonstrates the highest prediction ability among all of the investigated models.
•A novel hybrid method based on CEEMDAN-SE and PSO-ALS optimized GRU network is proposed.•The PSO-ALS is used to find hyperparameters of GRU network model.•The model actively learns data dependencies and can better reflect complex changes of prices.•The proposed hybrid network model has better performance than other prediction models.
Recent advances in satellite observations of methane provide increased opportunities for inverse modeling. However, challenges exist in the satellite observation optimization and retrievals for high ...latitudes. In this study, we examine possibilities and challenges in the use of the total column averaged dry-air mole fractions of methane (XCHsub.4) data over land from the TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel 5 Precursor satellite in the estimation of CHsub.4 fluxes using the CarbonTracker Europe-CHsub.4 (CTE-CHsub.4) atmospheric inverse model. We carry out simulations assimilating two retrieval products: Netherlands Institute for Space Research's (SRON) operational and University of Bremen's Weighting Function Modified Differential Optical Absorption Spectroscopy (WFM-DOAS). For comparison, we also carry out a simulation assimilating the ground-based surface data. Our results show smaller regional emissions in the TROPOMI inversions compared to the prior and surface inversion, although they are roughly within the range of the previous studies. The wetland emissions in summer and anthropogenic emissions in spring are lesser. The inversion results based on the two satellite datasets show many similarities in terms of spatial distribution and time series but also clear differences, especially in Canada, where CHsub.4 emission maximum is later, when the SRON's operational data are assimilated. The TROPOMI inversions show higher CHsub.4 emissions from oil and gas production and coal mining from Russia and Kazakhstan. The location of hotspots in the TROPOMI inversions did not change compared to the prior, but all inversions indicated spatially more homogeneous high wetland emissions in northern Fennoscandia. In addition, we find that the regional monthly wetland emissions in the TROPOMI inversions do not correlate with the anthropogenic emissions as strongly as those in the surface inversion. The uncertainty estimates in the TROPOMI inversions are more homogeneous in space, and the regional uncertainties are comparable to the surface inversion. This indicates the potential of the TROPOMI data to better separately estimate wetland and anthropogenic emissions, as well as constrain spatial distributions. This study emphasizes the importance of quantifying and taking into account the model and retrieval uncertainties in regional levels in order to improve and derive more robust emission estimates.
Pressurized liquefied natural gas (PLNG) is a new natural gas liquefaction solution proposed in recent years for reducing the construction and operating costs of floating liquefied natural gas ...(FLNG). For natural gas, the liquefaction temperature is strongly influenced by the pressure; when the pressure increases, the liquefaction temperature of natural gas increases accordingly. The increase in the liquefaction temperature of natural gas leads to a higher solubility of impurities such as carbon dioxide, which means that the pretreatment standards for liquefied natural gas can be reduced. Therefore, the use of PLNG technology can simplify pretreatment plants and significantly reduce construction and operating costs. In order to better apply PLNG technology to FLNG, it is necessary to understand the solubility of carbon dioxide in pressurized LNG and the phase change during liquefaction. To achieve this, experimental setups are needed to simulate the temperature and pressure environment of the LNG to obtain the relevant data and observe the relevant phenomena. After a literature research and analysis of the advantages and disadvantages of previous experimental setups, several improvements are proposed in this paper, and based on this, a visualization device is designed for studying the liquid-solid-phase equilibrium experiment of COsub.2 in PLNG. The device has a pressure resistance of 20 MPa, a minimum operating temperature of 77 K, and a variable volume function. It is also equipped with a sapphire window to be able to observe the inside of the device. In order to verify the superiority of the device, experiments were conducted using the device to verify the pressure resistance, variable volume, and visualization functions of the device. The experimental results show that the experimental device designed in this paper does have a certain superiority.
Display omitted
•We investigated the costs and GHG emissions of three blue hydrogen production technologies.•Blue hydrogen cost ranges from $1.69-$2.55 per kg H2 depending on the production ...technology.•Autothermal reforming (ATR) with carbon capture and storage (CCS) and natural gas decomposition with CCS produce H2 has the lowest and highest cost, respectively.•Blue hydrogen from ATR process has the lowest GHG emissions, 3.91 kgCO2eq/kg H2.•The economics of a steam reforming plant depends on the CO2 capture rate.
Interest in blue hydrogen production technologies is growing. Some researchers have evaluated the environmental and/or economic feasibility of producing blue hydrogen, but a holistic assessment is still needed. Many aspects of hydrogen production have not been investigated. There is very limited information in the literature on the impact of plant size on production and the extent of carbon capture on the cost and life cycle greenhouse gas (GHG) emissions of blue hydrogen production through various production pathways. Detailed uncertainty and sensitivity analyses have not been included in most of the earlier studies. This study conducts a holistic comparative cost and life cycle GHG emissions’ footprint assessment of three natural gas-based blue hydrogen production technologies – steam methane reforming (SMR), autothermal reforming (ATR), and natural gas decomposition (NGD) to address these research gaps. A hydrogen production plant capacity of 607 tonnes per day was considered. For SMR, based on the percentage of carbon capture and capture points, we considered two scenarios, SMR-52% (indicates 52% carbon capture) and SMR-85% (indicates 85% carbon capture). A scale factor was developed for each technology to understand the hydrogen production cost with a change in production plant size. Hydrogen cost is 1.22, 1.23, 2.12, 1.69, 2.36, 1.66, and 2.55 $/kg H2 for SMR, ATR, NGD, SMR-52%, SMR-85%, ATR with carbon capture and sequestration (ATR-CCS), and NGD with carbon capture and sequestration (NGD-CCS), respectively. The results indicate that when uncertainty is considered, SMR-52% and ATR are economically preferable to NGD and SMR-85%. SMR-52% could outperform ATR-CCS when the natural gas price decreases and the rate of return increases. SMR-85% is the least attractive pathway; however, it could outperform NGD economically when CO2 transportation cost and natural gas price decrease. Hydrogen storage cost significantly impacts the hydrogen production cost. SMR-52%, SMR-85%, ATR-CCS, and NGD-CCS have scale factors of 0.67, 0.68, 0.54, and 0.65, respectively. The hydrogen cost variation with capacity shows that operating SMR-52% and ATR-CCS above hydrogen capacity of 200 tonnes/day is economically attractive. Blue hydrogen from autothermal reforming has the lowest life cycle GHG emissions of 3.91 kgCO2eq/kg H2, followed by blue hydrogen from NGD (4.54 kgCO2eq/kg H2), SMR-85% (6.66 kgCO2eq/kg H2), and SMR-52% (8.20 kgCO2eq/kg H2). The findings of this study are useful for decision-making at various levels.
The injection of carbon dioxide (COsub.2) into gas reservoirs has become an important way to enhance gas recovery and reduce COsub.2 emissions. Large discrepancies are observed when predicting ...natural gas compressibility factors with high COsub.2 content by several well-known empirical correlations. An explicit correlation is proposed to improve the prediction accuracy in the estimation of compressibility factors on condensate gases with variable COsub.2 contents. The analysis of the results is carried out on the basis of 202 experimental data from 9 various mixtures of natural gases. The results show that relative deviations of compressibility factors predicted by conventional empirical correlations increase with the increase in COsub.2 mole fraction with an average error of 8%. The average error of the new method is less than 4%. The effect of compressibility factors on the estimations of dynamic reserves is studied and the compressibility factor causes a 3% reduction in dynamic reserves estimation. The proposed correlation has fewer uncertainties and more accurate results than other correlations that involve the iterative process in calculating compressibility factors of natural gases with variable COsub.2 contents.
The uncertainty of market demand and dynamic behaviour of the pipeline system are usually ignored in previous gas supply reliability assessments. With the intent of overcoming these deficiencies, a ...novel methodology to assess the gas supply reliability of natural gas transmission pipeline systems is proposed in this paper. Considering both gas supply capacity and market demand uncertainties, calculations of these two items are integrated into a single Monte Carlo simulation. On each Monte Carlo trial, the hydraulic analysis of unsteady flow is combined with the state transition process simulation to calculate the gas supply capacity. In terms of market demand, the load duration curve technology is employed to predict the amount of demand. Then, the indicator proposed to quantify gas supply reliability is calculated on each trial. Finally, the average gas supply reliability is obtained based on N Monte Carlo trials. Applications of this methodology are demonstrated through a real transmission pipeline system. Thereafter, the method is compared with previous approaches and differences are discussed. Furthermore, the impacts of supply capacity and market demand uncertainties on the gas supply reliability are investigated and suggestions to improve the gas supply reliability are proposed.
•A methodology to assess gas supply reliability of pipeline systems is proposed.•Demand uncertainty and system's dynamic behaviour are considered.•A real pipeline system is adopted to demonstrate the feasibility of methodology.•The impacts of supply capacity and market demand uncertainties are investigated.
•Relevant studies of gas production from natural gas hydrate are reviewed.•The limitations, challenges and some questions of NGH are discussed.•NGH exploitation are mainly carried out from numerical ...simulation, experiments and field tests.•Characteristics of the flow, heat and mass transfer are still not comprehensively recognized.•Environmental impacts and economics are still unclear and await further research.
Natural gas hydrates (NGHs), which extensively exist in sea-floor and permafrost regions, are considered as an alternative energy in the future for the fossil fuels approaching depletion with the gradually increasing energy consumption. Because of the particularity of NGH stabilizing only in the conditions of the high pressure and the low temperature, the exploitation of NGH is distinguished from those of petroleum and natural gas. Researchers over the world are devoting themselves to developing the technologies of NGH exploitation. However, till now, few NGH exploitation technology is identified and employed to exploit commercially NGH. Although there do be two cases of short-term NGH exploitation in Mackenzie Delta (CAN), Alaska North Slope (USA) and Nankai Trough (JAP) in the past 10years. It is mainly because some characteristics of the flow (gas, water, gas-hydrate slurry, quicksand, etc.), the issues of heat and mass transfer, the risk assessment and the economic evaluation are still not comprehensively recognized. Presently, the researches of NGH exploitation are mainly carried out from three aspects, numerical simulation and analysis, experimental simulation and field trial exploitation for the different technologies. In this paper, we comprehensively review the relevant studies of NGHs and propose our comments. We not only represent the achievements for the NGH exploitation researches, but also discuss the limitations and challenges, raise some questions and put forward some suggestions from our points of view.
PDF
