Alternative Gas Research Articles

Introduction to Domestic and International Sulfur Hexafluoride (SF6) Greenhouse Gas Emission Reduction Technologies for Power Grid Enterprises

Since its introduction in 1930, sulfur hexafluoride (SF6) has rapidly become the primary insulation material for high-voltage electrical equipment such as transmission lines, switches, transformers, circuit breakers, and reactors, owing to its exceptional electrical properties. However, the flip side of its excellent performance is its extremely high global warming potential (GWP), which is over 23,000 times that of carbon dioxide (CO2). Managing SF6 has thus become a key aspect of emission reduction efforts. The primary strategies for reducing SF6 emissions include minimizing gas leakage during the production, operation, and maintenance of electrical equipment, as well as purifying and recycling emitted SF6 gas. Various purification and monitoring methods have been developed for routine operations and have already been implemented by power grid companies globally. In addition to ongoing daily monitoring, research is also underway concerning the transformation, degradation, and substitution of SF6 gases. Degradation and transformation methods primarily focus on high-temperature degradation, photocatalysis, and arc degradation. In the context of substitution, the idea is to use conventional gases or various organic compounds to form SF6 mixtures or alternative gases, with the aim of reducing effect of leakage while maintaining performance. Finally, recommendations are made for power grid enterprises to reduce SF6 emissions, emphasizing the importance of source control and the exploration of alternatives. Effective equipment management to prevent gas leakage, comprehensive monitoring and assessment, as well as the proper handling of unusable SF6 devices, are also crucial steps in emission reduction efforts.

In-situ growth of zeolite-A in the fiber surface for methane adsorption

Methane as an anthropogenic gas has an effect on the atmosphere and can be used as an alternative natural gas using adsorbent material. This research aims to determine the impact of activation conditions on the surface of fibers for zeolite-A crystal growth utilized for CH4 adsorption. Glass fiber and pineapple fiber have been treated with an alkali used in this research. The concentration of NaOH and fiber immersion time determine the activation conditions. The activation process altered the crystallinity of the surface-deposited zeolite-A. Characterization by XRD and SEM revealed that zeolite-A covered the surface of those fibers when the NaOH concentration was 4M and the immersion time was 24 h. Thermal analysis revealed that the composite of zeolite-A/fibers undergoes two weight loss processes prior to achieving stability. The methane adsorption gravimetric measurements for zeolite-A supported glass fiber (glass wool) and pineapple fiber with high crystallinities are 4.644% wt and 3.461% wt, respectively.

Improving Simultaneous Water Alternative Associate Gas Tests in the Presence of Newly Synthesized γ-Al2O3/ZnO/Urea Nano-Composites: An Experimental Core Flooding Tests.

Nano-composites positively impact subsurface porous media's properties during enhanced oil recovery. In this paper, γ-Al2O3/ZnO/urea nano-composites were selected to improve simultaneous water alternative associate gas (SWAG) tests based on better results in comparison to pure γ-Al2O3 in the static phase. According to the interfacial tension (lowest), contact angle (lowest), zeta potential (highest absolute value), and viscosity (lowest) tests in the presence of nano-composites, 80 ppm was chosen as the optimum concentration (OP) to perform SWAG experiments. The interfacial tension (mN m-1) and contact angle (°) values of nano-fluids at concentrations of 20, 40, 60, 80, 100, and 120 ppm were higher than that of alumina and were (27.50, 130.12), (24.38, 80.32), (21.63, 70.98), (15.63, 40.69), (10.75, 8.50), and (6.80, 46.01) mN m-1, respectively. It was evident that considering effective, efficient parameters before performing the main SWAG test was important, and due to using OP, the recovery factor increased from 55.9 to 83.1% at a constant SWAG ratio (1:1) and temperature (40 °C). Furthermore, higher instant oil and lower produced water were seen as OP during the nano-composite-assisted SWAG test at 80 ppm.

A Minireview of the Influence of CO2 Injection on the Pore Structure of Reservoir Rocks: Advances and Outlook

The recoverable hydrocarbon reserves of conventional oil and gas resources are very limited in China. As important alternative resources, unconventional oil and gas have become a research hotspot. Though tight reservoirs have great potential to alleviate the increasing demand, issues during the development process, such as the rapid pressure depletion, fast decline in production, low productivity, and difficulties in water injection, are usually encountered due to poor physical properties like small pore throats and strong heterogeneity of the pore structure. The CO2 flooding technique could effectively replace crude oil from micro-nanopores, which is considered as a promising way to enhance the development performance of tight oil. However, precipitation and dissolution phenomena usually occur along with the CO2 injection process into reservoirs, affecting the pore structure evolution and oil displacement efficiency. In addition, artificial and natural fractures will even make this process more complicated. This paper presents the commonly used experimental approaches for CO2 injection into tight reservoirs and summarizes the main methods for investigating the influence of CO2 injection on the pore structure of reservoir rocks. Based on this, we highlighted that more attention should be paid to the influence of fractures and their dynamic changes on the evolution of pore structure during CO2 injection and the study of the solid–liquid interactions. To establish a method that could quantitatively evaluate the full-scale evolution of pore throats after CO2 injection is necessary. Meanwhile, the interaction strength of precipitation and dissolution and their effects on pore structure also remain open. Finally, a rigorous framework that could reveal the evolution mechanism and characterize the multiscale pore structure involving multiple influencing factors is urgently warranted.

An Experimental Study of Short-Circuit Current Making Operation of Air Medium-Voltage Load Break Switches

Replacing SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> , the most potent greenhouse gas, with an alternative gas is a challenge faced by medium-voltage load break switches (MV-LBS). Air is a possible alternative, but there are some challenges regarding low dielectric strength leading to high arcing time and dissipated energy. Therefore, understanding the switching processes for both interruption and making operations in air MV-LBS is crucial to designing efficient compact switchgear. This work focuses on making operations in air MV-LBS. A synthetic test circuit and a model switch are designed based on the standards to simulate making operations under fault conditions similar to a real test. The test condition is set to achieve high pre-strike arcing time and energy. The results show that the most destructive impact of the making short-circuit current occurs in the first half-cycle of the load current when the pre-strike arc is formed. For an average short-circuit current with a peak of 22 kA and a breakdown voltage of 20 kV, the switch failed to re-open due to the arcing contacts welding after four successive making operations without main contacts and seven successive operations with main contacts. It has been shown that the total arcing contact mass loss occurs mainly during the pre-arcing time.Increasing the closing speed could be a possible solution to minimize the impact of arcing.

Long-Term Partial Discharge Behavior of Protrusion Defect in HVDC GIS

This article investigates the partial discharge (PD) behavior of protrusion defects in real-size high-voltage direct current gas insulated switchgear (HVDC GIS) for SF6 and SF6 alternative gases including fluoronitrile–CO2 mixture (10%) and fluoroketone–dry air mixture (6.6%). The evolution of PD apparent charge and PD repetition rate for all investigated gases is presented and discussed. The measurement results indicate that PD behavior changes as a function of time. The PD apparent charge increases and the PD repetition rate decreases with the increase of voltage application time. This evolution can be related to the change in protrusion tip radius due to electrochemical etching: radius of the protrusion’s tip being enlarged. In addition, the pulse sequence analysis (PSA) plots of the PDs caused by this defect are presented. It is observed that the PSA plots change over time. Therefore, for the development of a robust PD monitoring and defect-recognition tool, as well as for the assessment of risks in the operation of HVDC GIS, it is crucial to take these changes into account.

Reduction of recombination effects in large plane parallel beam monitors for FLASH radiotherapy with scanned ion beams

Purpose:Radiotherapy escalating dose rates above 50Gys−1, might offer a great potential in treating tumours while further sparing healthy tissue. However, these ultra-high intensities of FLASH-RT lead to new challenges with regard to dosimetry and beam monitoring. FLASH experiments at HIT (Heidelberg Ion Beam Therapy Center) and at GSI (GSI Helmholtz Centre for Heavy Ion Research) have shown a significant loss of signal in the beam monitoring system due to recombination effects. To enable accurate beam monitoring, this work investigates the recombination loss of different fill gases in the plane parallel ionisation chambers (ICs). Methods:Therefore, saturation curves at high intensities were measured for the currently used fill gases Ar/CO2 (80/20) and pure He and also for He/CO2 mixtures as alternative fill gases. Furthermore, breakdown voltages and ion mobilities were measured in ICs filled with He/CO2 mixtures. A numerical model for volume recombination in plane parallel ionisation chambers was developed and implemented in Python. This includes a novel simulation method of the space charge effect from the charge carriers in the detector volume and predicts a significant effect on the electric field for high intensity beams. Results:Even at high intensities the He/CO2 mixtures allow operation of the ICs at an electric field strength of 2 kVcm−1 or more which reduces recombination to negligible levels at intensities larger than 3 × 101012C-ions per second. Our measurements show that added fractions of CO2 to He decrease the ion mobility in the fill gas but significantly increase the breakdown voltage in the ICs compared to pure He.

USE OF BIOGAS AS A RAW MATERIAL AND ENGINE FUEL IN ENERGY AND TRANSPORT

In the article, based on existing global trends, legislative incentives for climate-friendly development of economic sectors, the place of biogas as a raw material and engine fuel in the decarbonization of energy and transport in Ukraine is substantiated. To reduce greenhouse gas emissions, most countries are making the transition from fossil fuels to renewable energy sources. In EU countries, renewable energy with a Green Deal label was equated with energy obtained from the combustion of natural gas. In Ukraine, biomethane is legislated as an alternative gas fuel similar to natural gas. The raw material for biomethane is biogas. In Ukraine, biomethane is not produced on an industrial scale due to the lack of special purification and enrichment technologies at biogas stations. In Ukraine, it is necessary to start producing biomethane on an industrial scale and use the natural gas infrastructure for transporting biomethane. An existing quantity and quality of treatment technologies of biogas plants allow the use of biogas as an independent fuel in cogeneration plants in the immediate vicinity of biogas plants. Calculation of the heat balance of the drive gas engine (8-cylinder, 100 mm cylinder diameter, 88 mm stroke) showed that in addition to generating 30 kW of electrical energy, it is possible to obtain additionally up to 162 MJ of thermal energy without taking heat from the lubrication system. When generating only electrical energy, the efficiency installation in nominal mode is about 30%, and with cogeneration – it increases to 75%. The next step is – the use of biogas as an additive to natural gas in reciprocating internal combustion engines on cars, buses and special agricultural machinery at the local or regional level. The results of research on the 8Ch10/8.8 gas combustion engine ensured the transition from quantitative to qualitative regulation of the fuel mixture of natural gas with biogas additives. An interdependent regulation algorithm has been developed for mixed fuel. With an increase in load, the share of biogas decreases, the mixture is enriched with natural gas. At a load of 75% or more, the enrichment of the fuel mixture occurs more intensively.

The Comprehensive Overview of Large-Volume Surfactant Slugs Injection for Enhancing Oil Recovery: Status and the Outlook

Despite the development of alternative energy sources, oil and gas still remain the predominant energy sources in most countries in the world. Due to gradual hydrocarbon reserve depletion and the existing downward trend in the production level, there is a need to search for methods and technical approaches to level off the falling rates. Chemically enhanced oil recovery methods (EOR) by surfactant solution injections are one of the possible approaches for addressing this issue in already developed fields. Most often, surfactants are injected together with polymers or alkalis. These technologies are called surfactant–polymer (SP) and alkali–surfactant–polymer (ASP) flooding. Basically, SP and ASP have been distributed in China and Canada. In this article, in addition to these countries, we paid attention to the results of pilot and full-scale tests of SP and ASP in Russia, Hungary, and Oman. This study was a comprehensive overview of laboratory and field tests of surfactant solutions used for oil displacement in SP and ASP technologies. The first part of the article discussed the physical fundamentals of the interaction of oil with surfactants. The second part presented the main chemical reagents used to increase oil recovery. In the third part, we described the main facilities used for the preparation and injection of surfactants. Further, the results of field tests of SP and ASP in the abovementioned countries were considered. In the discussion part, based on the considered results, the main issues and uncertainties were identified, based on which some recommendations were proposed for improving the process of preparation and injection of surfactants to increase oil recovery. In particular, we identified an area of additional laboratory and scientifically practical research. The outcomes of this work will provide a clearer picture of SP and ASP, as well as information about their limitations, current challenges, and potential paths forward for the development of these technologies from an economic and technological point of view.

Potential Solutions for the Short to Medium-Term Natural Gas Shortage Issues of Europe: What Can Qatar Do?

European countries are required to look for alternative gas suppliers to deliver energy security for Europe. Qatar has been proposed to be an alternative gas supplier; however, there are problems that limit Qatar from exporting more gas to Europe, namely: the limited LNG quantities available for export, the long-term fixed contracting strategy, and the lack of room to receive additional gas in European LNG terminals. As these problems are critical and limit Qatar from exporting more gas to Europe, this research aims to propose potential solutions to overcome them. The results show that to solve the issue of the limited LNG quantities available for export, Qatar can produce electricity from renewable sources and export the gas consumed for power production, and can produce renewable natural gas (RNG) from green hydrogen and captured carbon dioxide. Two BCM of natural gas can be exported if 15% of the electricity required is produced from renewables in Qatar. In addition, 0.45 BCM of RNG can be exported if Qatar uses its natural resources to produce 5000 MW of renewable power. Redirecting contracts coming to an end and increasing dependence on spot markets can resolve the issue of a long-term fixed contracting strategy. Finally, using floating import terminals may alleviate the problem of European LNG terminals running out of room to receive more gas.

Voltage–Current Characteristic of Free Burning Arcs in SF₆ Alternative Gas Mixtures

Voltage–current characteristics of free burning arcs in SF6 and air have been known for decades. As the demand for an SF6-free solution is increasing, there is an accompanying need to determine arc parameters in the alternative gases. An unblown arc experiment has been established to determine the voltage–current characteristics of SF6 alternative gases, which have not yet been thoroughly studied. In this experiment, free burning arc measurements were performed in a number of gases under consideration of SF6 alternatives, including CO2 and mixtures of CO2/O2 with and without C4F7N or C5F10O additives at the concentrations of up to 10 %. Measurements were also performed in air and SF6 for comparison. Arc voltage was measured in each gas at pressures ranging from 1- to 5-bar absolute, and electrode separations ranging from 20 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$95 \mathrm {~mm}$ </tex-math></inline-formula> . Voltage–current characteristic measurements for air and SF6 show good agreement with previously published results. A linear relationship of the arc voltage to the arc length is shown as well as the fourth root dependence of the arc voltage on the gas pressure. It was shown that neither the O2 nor the fluorinated additives to CO2 have any significant influence on the voltage–current characteristic. The minimum arc voltage in all measured gases was slightly higher than in SF6, but the arc in SF6 was the least stable and had the highest elongations resulting in high-voltage peaks. The arc voltage in air had a similar minimum value to the CO2-based gases, but the arc was much more stable, resulting in lower effective voltage, especially at low currents.

Technoeconomic and Environmental Assessment of Alternative Biorefineries for Bioenergy and Polyphenolic Production from Pomace Biomass

Pomace is generated during fruit processing and is regarded as a highly polluting waste stream due to its high moisture content, biological instability, and acidic properties. To facilitate pomace management, this study has applied the biorefinery concept to develop systems that facilitate value extraction. To this regard, alternative scenarios for the production of polyphenolic compounds and bioenergy from apple pomace were investigated using ASPEN Plus for process modeling, simulation, and analysis. Systems facilitating the production of polyphenols via the use of the green solvents (i.e. subcritical water in scenario (a) and ethanol in scenario (b)), while also co-producing bioenergy, were compared to a system that produced only bioenergy (i.e. scenario (c)). Comparisons of profitabilities and environmental performances were achieved via considerations of the net present values (NPVs) and potential environmental impacts (PEIs) of all scenarios. The study was able to show that scenario (a) constituted the only economically viable strategy, with a NPV of US$ 19.86 million, while scenarios (b) and (c) were determined to have NPVs of US$ − 88.12 million and US$ − 4.05 million respectively. Scenario (b) was also determined to have the poorest environmental performance with a PEI of 148 kPEI/h. Notably, although scenario (c) (PEI of 0.21 kPEI/h) was determined to present a better environmental performance than scenario (a) (PEI of 47 kPEI/h), its economic infeasibility indicated that it will be impractical to consider it as a viable pomace valorization strategy in a scaled-up system. This study therefore proposed that scenario (a) may constitute a preferred pomace valorization strategy provided technological innovations, i.e., use of alternative energy sources and gas filters, are explored to reduce the major existing challenge of enhanced global warming potential due to greenhouse gas emissions. This study therefore provides information regarding the sustainability implication of executing different biorefinery scenarios for pomace management in the fruit processing industry.

Analysis of Energy Distribution and Lubrication Characteristics in an Internal Combustion Engine Fueled with Percentages of Alternative Gas

In the current investigation, the influence of hydrogen gas on the energy and exergetic distribution and the properties of the lubricating oil in gasoline engines were studied. For the development of the investigation, four loads (25%, 50%, 75%, and 100%) and three percentages of hydrogen gas injection (5%, 10%, and 15%) were defined. The mixture of gasoline and hydrogen gas leads to an improvement in the combustion process of the engine. It was found that the injection of 15% hydrogen in the gasoline engine causes an increase of 5.09% and 5.70% in energy and exergetic efficiency. Additionally, a reduction in brake specific fuel consumption was demonstrated by 0.43%, 0.86%, and 1.58% with mixtures G(100%) + H2(5%), G(100%) +H2(10%), and G(100%) + H2(15%) compared to pure gasoline. The mixture of gasoline and hydrogen gas allows to the improvement of the combustion characteristics of the engine. However, hydrogen injection produces negative effects on the lubricating oil system, such as the increased presence of wear metal debris and decreased lubricant viscosity. The foregoing implies a shortening in the useful life of the lubricating oil and an increased risk of wear on engine parts.

Surface discharge pattern of C4F7N/CO2 mixture under negative impulse voltages

Due to the excellent properties, C4F7N/CO2 mixture is the most concerned eco-friendly SF6 alternative gas. For a better understanding of the surface discharge characteristics, the surface discharge pattern of C4F7N/CO2 mixture under negative impulse voltages is investigated in this work. The morphology of the surface discharge is obtained by an optical method and a dust figure method. The structure of the surface discharge is established, which from the outside to the inside consists of electron cloud, streamer, streamer stem, and leader. The propagation pattern of the surface discharge in C4F7N/CO2 mixture under negative impulse follows the stepwise expansion pattern. The structure of the surface discharge in C4F7N/CO2 mixtures with different ratios and SF6 has no obvious difference, and the propagation pattern is also the same. The results of this work can help to better understand the surface discharge phenomenon and the insulation characteristics of C4F7N/CO2 mixture.

Research on the adsorption of environmentally friendly insulating gas C4F7N decomposed components on the surface of γ‐Al2O3

AbstractC4F7N is considered to be the most potential alternative gas for SF6. However, harmful decomposition by‐products generated by the discharge or overheating faults will pose threat to safe operation and service life of gas insulated equipment (GIE). Herein, we investigated the adsorption performance of γ‐Al2O3 on C4F7N and its decomposition products to evaluate the possibility of using it as by‐products adsorbent or exhaust treatment material. It is found that γ‐Al2O3 demonstrates superior adsorption capacity for CF4, C2F6, C3F8, C3F6, C2F4, and keeps stable after the interaction. The first‐principles calculation infers that γ‐Al2O3 has stronger interaction with C4F7N, C3F6 and C3F8 than that of C2F4, C2F6 and CF4. There exists obvious charge transfer between C4F7N and γ‐Al2O3, which belongs to chemisorption. The interaction between F 2p orbital and C=C π orbital determines the gas‐solid adsorption performance. The desorption properties were also explored and the recovery time was in order of CF4 &lt; C2F6 &lt; C2F4&lt; C3F8 &lt; C4F7N &lt; C3F6. Overall, the γ‐Al2O3 is inappropriate to be used as the adsorbent for decomposition by‐products of C4F7N gas mixture‐based GIE, while it can be used as exhaust treatment material for C4F7N wasted gas.

Decarbonisation options of existing thermal power plant burning natural gas

Nowadays power industry faces deepest crises ever with unprecedented prices shocks and climate challenges at the same time. From one hand we realise the need of energy transformation of power industry towards more sustainable future with climate neutral technologies. From the other hand it become obvious that this change could not happen immediately, and transition period is needed with some fossil fuel technology still playing an important role as a back-up for renewable energy sources. The biggest question what the best and cost-efficient way is to decarbonise existing thermal power generation. We try to address it on the example of existing combined cycle gas turbine (CCGT) power plant fuelled by natural gas. Clearly the following possible options were identified: 1) replacement of natural gas with alternative gases, such as green hydrogen, bio or synthetic methane, 2) carbon capture and underground storage (CCS) in geological formations, 3) carbon capture, liquefaction and export, 4) carbon capture and utilization (CCU) or 5) replacement of power generation technology. In this publication we try to compare these different options, despite they are not clearly comparable. For the analysis we take natural gas fired CCGT plant Riga TPP-2 in Latvia with installed capacity of 881 MW (in condensing mode).Option 1. In order to completely (100 % in energy values) replace natural gas by green hydrogen, we need electroliers with capacity of at least 2600 MW. Very roughly this is an investment of at least 2,6 billion EUR for hydrogen production, storage and supply. Additionally, we shall take into account necessary modernisation of CCGT plant to be capable for 100 % hydrogen firing as well as necessity to construct additional wind or solar capacity. Conversion efficiency from power to gas is approximately 60 %, while from gas to power – around 55-57 %. Overall conversion efficiency is 33-35 %. The main advantages of this option are a) possibility for wide use of renewable energy sources (wind and solar) in hydrogen production, b) avoidance of carbon dioxide emissions during the electricity production, c) possibility to supply a surplus of hydrogen to transport sector and industry, d) avoidance of all problems associated with CCS option, including the ban for geological storage of CO2. The main disadvantages of this option: a) very high costs of hydrogen production, b) very low conversion efficiency, c) necessity to convert CCGT plant for hydrogen combustion and to install considerable wind and solar capacity.

Underground hydrogen storage in a naturally fractured gas reservoir: The role of fracture

As hydrogen provides a high heating value with the least environmental impact, it can be considered as an energy carrier pioneer in following the global zero-carbon policies. Then, since storing hydrogen in large quantities can also be a valuable technique for alleviating energy shortages due to energy consumption fluctuations, underground hydrogen storage (UHS) is being explored further in today's world. To the best of our knowledge, the role of fracture on underground hydrogen storage performance has not comprehensively been evaluated. For the first time, in this study, the effects of fracture on hydrogen storage and production were investigated in a naturally fractured gas reservoir in the Middle East using a numerical simulation. Then, to determine whether the fracture was able to accelerate hydrogen production, UHS was evaluated under various conditions, including the fracture system, condensate presence, Initial hydrogen injection stage, cushion gas type, hydrogen storage commence time and different injection/production cycle duration. The results of this study proves that although a huge amount of hydrogen is invaded into the matrix during hydrogen injection, the fracture accelerates hydrogen production, resulting in higher hydrogen recovery and purity, which indicates fractures are suitable media for hydrogen storage. However, it should be noted that the purity of hydrogen produced from naturally fractured reservoirs (NFR) decreases more rapidly than a conventional one during a single cycle due to the higher mixing of gases in the fracture. In the case of the initial stage of hydrogen injection, fractures are not found to be attractive as storage media. Therefore, it is necessary to analyze the fracture effects as a storage media under various situations and stages. In addition, alternative gas injection revealed that nitrogen injection into cushion gas resulted in the highest hydrogen production in the entire porous media, whereas methane injection led to the highest hydrogen recovery in the fracture media. Also, the rapid injection/production cycle duration improved hydrogen recovery, indicating that the required time for high hydrogen invasion into the matrix is not provided during hydrogen injection.

Swarm Parameters and Critical Breakdown Fields in CO₂ Subjected to Time-Invariant Uniform × Fields

This article presents swarm data in CO2 under crossed uniform time-invariant fields. CO2 is used as an alternative gas in switching applications, and however, its dielectric properties in crossed fields are limited in the literature. The dielectric response under crossed fields is investigated together with excitation rates and ionization and attachment frequencies. Critical breakdown fields evaluated indicate that it is possible to increase the dielectric strength of CO2 with the application of crossed magnetic field in the parameter range of the present investigation. Furthermore, the electron energy distribution functions in crossed fields are analyzed, and employing the evaluated electron mean energies and magnetic deflection angles, the validity of the equivalent reduced electric field concept is investigated.

The role of natural gas in facilitating the transition to renewable electricity generation in South Africa

As is being done in most of the world, South Africa has commenced the transition from a fossil fuel-based electricity generation system to one based on renewable sources to meet greenhouse gas emission reduction goals. This paper explores the role of natural gas in South Africa to support the transition to a renewable energy-driven power grid. Specifically, the paper quantifies the firm and dispatchable power requirement to accommodate variability in solar and wind generation sources based on real-time series data from current renewable energy power plants for the country, and demonstrates that natural gas could be one of the elements to meet the medium-term need for this dispatchable power requirement, based on current regional gas resources. A range of alternative natural gas sources are considered in this analysis, covering existing gas resources from Mozambique, deep-water offshore potential from the southern Cape, shale gas from the Karoo basin, as well as liquefied natural gas imports. In addition, the alternatives to natural gas to supply the required dispatchable energy are considered. The analysis shows that the major challenge is to have sufficient gas storage available to be able to provide gas at the very high instantaneous rates required, but where the gas is only used for short periods of time and at low annual rates.

A Multiphysics Co-Simulation Framework of a Gas Engine and Three-Way Catalyst toward a Complete Vehicle Design Model

In view of the increasingly stringent emission regulations, the automotive sector needs considerable support from the development of robust and reliable engine and aftertreatment models. Accurate reproduction of engine-out and tailpipe pollutants plays a crucial role in complying with these legislations. Given the difficulty in characterizing some critical phenomena, frequently caused by strong dynamics and related to experimental uncertainties, communication between several calibrated and reliable models is mandatory. This is certainly valid for powertrains that will be powered with alternative gas fuels such as natural gas, bio-methane and hydrogen in the future. This paper describes a methodology to co-simulate a 1D CNG HD 6-cyl engine model and a 1D quasi-steady Three-Way Catalyst model in a global framework for high-fidelity virtual prototyping of the vehicle system. Through the implementation of a dedicated control logic in MATLAB/Simulink, the modeling architecture allows for the reproduction of the engine performance parameters together with the evaluation of the TWC pollutants’ conversion efficiency. An extensive database of experimental tests was used to assess the model response. The latter was validated in multiple steady-state operating conditions of the engine workplan. Using a semi-predictive combustion model, the validation was carried out over a wide range of different air-to-fuel ratios and during fast rich/lean transitions to evaluate the formation and conversion phenomena of the main chemical species, both engine-out and tailpipe. Subsequently, the complete model was validated in dynamic conditions throughout a WHTC, accurately reproducing the cut-off phases and their sudden accelerations. The numerical–experimental agreement on pollutant reproduction is generally good and globally below 3%. Larger deviations occur in extremely rich conditions and in CH4 emission evaluation due to the lack of information related to the combustion process and chemical mechanisms involving the Pd surface.