Natural Gas Distribution Systems Research Articles

Development of Company-Specific Emission Factors with Confidence Intervals for Natural Gas Customer Meters in Southern California.

Methane is both a significant and short-lived greenhouse gas compared to CO2, and reducing methane emissions from natural gas distribution systems may offer cost-effective reduction opportunities. We report substantial new direct leak rate measurements from customer meter set assemblies (MSAs) in Southern California. In a novel way, emission factors are defined in terms of aboveground Hazardous and Nonhazardous leak categories, which take direct advantage of readily available industry leak data. We also studied leaks that were not detected as part of normal leak survey procedures. As a result, this yields company-specific emission factors that can be used to track progress in reducing methane emissions. This approach also has the advantage of explicitly accounting for the skewed or fat-tail distribution of leak rates by treating high flow rate MSA leaks separately from low flow rate MSA leaks. The Southern California Gas (SoCalGas) methane emission factors, based on 485 leak rate measurements by direct enclosure, were 4.55 (95% confidence interval: 2.32 to 7.14) kg/day for Hazardous leaks, 0.149 (0.119 to 0.183) kg/day for Nonhazardous leaks, and 0.0039 (0.0003 to 0.0198) kg/day for Non-Detected leaks. The percentage of surveyed meters with nondetected leaks was 29.1% (24.3 to 34.6%). Based on a robust Monte Carlo analysis, total leak emissions from MSAs for the SoCalGas system were reduced by 35% based on data from 2015 to 2022. These reductions were attributed to surveying a larger number of MSAs and accelerated leak repair rates. In traditional population-based emission inventories, an individual emission factor for a given asset category is multiplied by the total population of MSAs within the category. This approach simply cannot capture the reduction in leak numbers and methane emissions resulting from leak mitigation and prevention programs.

Iterative convex relaxation of unbalanced power distribution system integrated multi-energy systems

This study describes a multi-period, multi-energy operation of a three-phase unbalanced Electric Distribution System (EDS) that coordinates with a District Heating System (DHS) and a Natural Gas (NG) distribution system. The electrical subsystem problem is formulated as a bi-level programming problem, with levels 1 and 2 solving the subsystem’s linearized and relaxed nonlinear versions, respectively. Second-Order Cone Programming (SOCP) and polyhedral relaxations are availed to circumvent the non-convexities involved in the subsystems. The SOCP relaxation for an unbalanced power distribution network is inexact; also, the subsystems applying polyhedral relaxation may not generate a meaningful solution as the relaxations are not tight. Therefore, a solution recovery algorithm is developed for each subsystem to recover a feasible solution from their relaxed counterparts. The successive bound tightening algorithm employing a solution recovery procedure is proposed for each subsystem, improving solution quality and strengthening the relaxations with the desired computational efficiency. The proposed solution strategy to optimize the Multi-Energy System (MES) operation cost is verified on the three-phase IEEE-13 and IEEE-123 bus systems, each coordinating with a 30-node DHS and a 6-bus NG network. The results analyses demonstrate that the proposed solution strategy efficiently achieves an optimal solution, reducing maximum relaxation error below 0.1% for each subsystem. The proposed strategy delivered a 14.58% reduction in real power losses and a 12.73% decrease in phase voltage unbalance rate for the EDS in MES. Furthermore, a 1.96% decrease in operational cost demonstrates the techno-economic benefits of the proposed strategy.

A Multi-Agent Distributed Operation Solution to Electricity and Natural Gas Distribution Systems for Enhancing Resilience

A Multi-Agent Distributed Operation Solution to Electricity and Natural Gas Distribution Systems for Enhancing Resilience

Ground-Based Mobile Measurements to Track Urban Methane Emissions from Natural Gas in 12 Cities across Eight Countries.

To mitigate methane emission from urban natural gas distribution systems, it is crucial to understand local leak rates and occurrence rates. To explore urban methane emissions in cities outside the U.S., where significant emissions were found previously, mobile measurements were performed in 12 cities across eight countries. The surveyed cities range from medium size, like Groningen, NL, to large size, like Toronto, CA, and London, UK. Furthermore, this survey spanned across European regions from Barcelona, ES, to Bucharest, RO. The joint analysis of all data allows us to focus on general emission behavior for cities with different infrastructure and environmental conditions. We find that all cities have a spectrum of small, medium, and large methane sources in their domain. The emission rates found follow a heavy-tailed distribution, and the top 10% of emitters account for 60-80% of total emissions, which implies that strategic repair planning could help reduce emissions quickly. Furthermore, we compare our findings with inventory estimates for urban natural gas-related methane emissions from this sector in Europe. While cities with larger reported emissions were found to generally also have larger observed emissions, we find clear discrepancies between observation-based and inventory-based emission estimates for our 12 cities.

Electricity generation potential from natural gas pressure reduction turbines in Brazil

This paper addresses the urgent need to meet increasing energy demand while avoiding greenhouse gas emissions by improving energy efficiency. One significant challenge is the energy losses that occur during gas pressure reduction at city gates in natural gas distribution systems. To tackle this issue, this study proposes installing pressure reduction turbines (PRTs) parallel to existing reduction valves, which can generate electricity and enhance system efficiency. This research mainly focuses on Brazil’s natural gas supply, where the potential for installing PRTs is evaluated. The methodology analyzes the country’s distribution network and estimates the electricity generation capacity achievable from PRTs. The results indicate a potential power generation of 66 MW, capable of avoiding the emission of 235,800 tons of CO2 annually and generating 333 GWh/year of electricity, all at a LCOE of $27/MW. These contribute to the environment using the energy efficiency achieved through the installation of PRTs, consequently, Brazil can help to a cleaner and more sustainable energy future.

Gas Leakage Identification and Prevention by Pressure Profiling for Sustainable Supply of Natural Gas

In the strive for an environmentally conscious energy sector, a sustainable supply of natural gas necessitates comprehensive strategies that prioritise the prevention of gas leakages, ensuring minimal ecological harm while harnessing the benefits of this valuable resource. Though all sectors are putting their efforts into coping with the problems associated with the energy crisis, one of the many ways is to reduce distribution losses, particularly in the gas sector. The loss impacts include methane escaping to the environment to affect ozone, direct financial loss, non-availability of gas to the domestic, commercial, and industrial sectors, public safety hazards and indirect environmental impacts. There is a dire need to improve the natural gas distribution system, which has its own insight problems to be addressed. This work aims to investigate leakages in domestic, commercial and industrial gas distribution lines with different times, volumes and pressures using a pressure profiling technique. As a result of this investigation, around 293 million cubic feet (MMCF) of natural gas is saved, which is enough volume to feed approximately 16,000 domestic consumers for 365 days. The same energy content is equivalent to 21 million pounds of coal, which emits 64 million pounds of carbon dioxide, whereas natural gas would have 50% less CO2 emissions, and that is apart from the tangible pollution and waste associated with the use of coal.

Evaluation of Hydrogen Blend Stability in Low-Pressure Gas Distribution

Natural gas distribution companies are developing ambitious plans to decarbonize the services that they provide in an affordable manner and are accelerating plans for the strategic integration of renewable natural gas and the blending of green hydrogen produced by electrolysis, powered with renewable electricity being developed from large new commitments by states such as New York and Massachusetts. The demonstration and deployment of hydrogen blending have been proposed broadly at 20% of hydrogen by volume. The safe distribution of hydrogen blends in existing networks requires hydrogen blends to exhibit similar behavior as current supplies, which are also mixtures of several hydrocarbons and inert gases. There has been limited research on the properties of blended hydrogen in low-pressure natural gas distribution systems. Current natural gas mixtures are known to be sufficiently stable in terms of a lack of chemical reaction between constituents and to remain homogeneous through compression and distribution. Homogeneous mixtures are required, both to ensure safe operation of customer-owned equipment and for safety operations, such as leak detection. To evaluate the stability of mixtures of hydrogen and natural gas, National Grid experimentally tested a simulated distribution natural gas pipeline with blends containing hydrogen at up to 50% by volume. The pipeline was outfitted with ports to extract samples from the top and bottom of the pipe at intervals of 20 feet. Samples were analyzed for composition, and the effectiveness of odorant was also evaluated. The new results conclusively demonstrate that hydrogen gas mixtures do not significantly separate or react under typical distribution pipeline conditions and gas velocity profiles. In addition, the odorant retained its integrity in the blended gas during the experiments and demonstrated that it remains an effective method of leak detection.

Integrated planning of natural gas and electricity distribution systems for enhancing resilience

Integrated power and gas systems (IPGSs) have developed a critical infrastructure in multi-energy systems. The bi-directional energy conversion between the two systems may cause disturbances in one system spread to the other one by coupling components. Especially under extreme events, this coupling relationship can cause the system to collapse. Therefore, it is urgent to enhance the resilience of IPGS at the planning stage. Based on this requirement, the integrated planning model of IPGS considering cascading effects for enhancing resilience is proposed in this paper. Firstly, the two-phase framework contains phases of “demand reachability evaluation” and “integrated planning” is proposed. Furthermore, capacity accessibility considering load level is defined to evaluate the reachability of the power system and the natural gas system (NGS) under extreme events. In this period, the Monte Carlo simulation (MCS) technique is used to represent the random failure of components. Based on this, an integrated planning model considering cascading effects is developed to optimize the location and capacity of coupling elements for enhancing IPGS resilience. Numerical results on the IPGS test system demonstrate the effectiveness of the proposed methods.

Gas Losses in the Distribution Networks: An Interdisciplinary Analysis

This work focuses on a very important and current problem in the gas field: gas losses in natural gas distribution networks and their impact on the environment, as well as on the company operating the network. The paper starts with a bibliographic study and aims to identify the sources leading to losses, estimate loss volumes, reduce these losses by replacing high-risk pipeline sections, as well as trace the economic, environmental, and social impact. The calculation methodologies used in various countries in estimating these consumptions are very diverse. Romania uses a very dense methodology that can prompt very broad variations in the values obtained for technological consumption calculations using Order 18/2014, due to the multitude of parameters that must be estimated. To reduce some of the uncertainties in estimating these parameters, a study was proposed and carried out on the ill-fittings in the natural gas distribution systems. The article presents the experimental stand, the analysis of the experimental data, the methodology for calculating gas losses in the natural gas distribution system through leaking equipment, as well as the results obtained and the conclusions. Moreover, an application was made for a dynamic area check of the gas balance. Based on the correlations between the annual values in M&R stations, AMR, the volume for small consumers, technological consumption, linepack, and the equipment and materials used in the network, useful data were obtained in the diagnosis of problem areas. The end of the paper shows an economic calculation regarding the replacement of problematic pipeline sections in natural gas distribution networks. The difference between the volume of investments and the income from loss reduction is very large, but the aspect of protecting the environment and eliminating technological risks intervenes, thus increasing social security and health.

Hierarchical Microenergy Hub Sizing and Placement in Integrated Electricity and Natural Gas Distribution Systems

The integration of different energy carriers is a key factor to improve the energy network performance. A micro-energy hub (μEH) concept has recently been proposed in the integrated electricity and natural gas distribution systems (IENGDSs), for generating, converting, storing, and managing different types of energy at the customer level. To improve the performance of μEH, this paper proposes a hierarchical optimization-based model to optimize the sizes of μEH components and locations of μEHs in the IENGDS. The operation and structural sizing constraints of the μEHs are first determined. Then the optimal electricity network buses and natural gas nodes for installing μEHs are determined, considering the operational constraints of IENGDS. The objective in both steps is to minimize operation and investment costs. Moreover, the impacts of seasonal climate changes on energy demands and prices are considered during the planning horizon. Furthermore, the uncertainties in demands and renewable energy generation are quantified with a two-stage stochastic programming framework. The effectiveness of the proposed method is evaluated on an IENGDS that consists of an IEEE 33-bus distribution system and a Belgian 20-node natural gas system. Numerical simulations demonstrate that the optimal hierarchical planning model can improve total line losses and reduce the total purchased electricity from the upstream network and total imported natural gas from gas wells. The simulation results show that if the hierarchical optimization process is not performed in determining optimal placement of μEHs, then IENGDS may operate with electricity network congestion or natural gas pressure violations during the planning horizon.

Data-driven modelling for gas consumption prediction at City Gate Stations

City Gate Stations (CGS) are critical elements of Natural Gas (NG) distribution systems, as they connect national high-pressure transmission networks with local low-pressure networks. One of their main tasks is to pre-heat the gas to avoid dangerous sub-cooling due to the Joule-Thompson effect after the pressure reduction stage. For this process, significant amounts of thermal energy are required, usually obtained by burning part of the gas flow rate. This work aims to develop a data-driven model that will serve as a tool to predict and monitor the thermal consumption of the CGS. The plant chosen as a case study for this activity is in a region of central Italy. A Multiple Linear Regression (MLR) model is developed and trained, and its predictive performance is evaluated. The model results achieved an accuracy of over 95% for the coefficient of determination. The method makes it possible to create a baseline consumption model and evaluate the performance of the CGS over time using the CUSUM technique to find variations between actual and modelled gas consumption, being an essential tool for monitoring the effectiveness of the NG preheating system.

Low-Cost Representative Sampling for a Natural Gas Distribution System in Transition.

Natural gas distribution systems within municipalities supply a substantial fraction of energy consumed in the United States. As decarbonization of the natural gas system necessitates new modes of operation outside original design purposes, for example, increased hydrogen or biogas blending, it becomes increasingly important to understand in advance how existing infrastructure will respond to these changes. Such an analysis will require detailed information about the existing asset base, such as local soil composition, plastic type, and other characteristics that are not systematically tracked at present or have substantial missing data. Opportunistic sampling, for example, collecting measurements at assets that are already undergoing maintenance, has the potential to substantially reduce the cost of gathering such data but only if the results are representative of the full asset base. To assess prospects for such an approach, we employ a dataset including the entire service line and leak database from a large natural gas distribution utility (∼66,700 km of service pipelines and over 530,000 leaks over decades of observations). This dataset shows that service lines affected by excavation damage produce an approximately random sample of plastic and steel service lines, with similar distributions of component age, operating pressure, and pipeline diameter, as well as a relatively uniform spatial distribution. This means that opportunistic measurements at these locations will produce a first-order estimate of the relative prevalence of key characteristics across the utility's full asset base of service lines. We employ this approach to estimate the plastic type, which is unknown for roughly 80% of plastic service lines in the database. We also find that while 32% of leaks across all components occur in threaded steel junctions, excavation damage accounts for 75% of hazardous grade 1 leaks in plastic service lines and corrosion accounts for 47% in steel service lines. Insights from this sampling approach can thus help natural gas utilities collect the data they need to ensure a safe and reliable transition to a lower-emission system.

Differentiating and Mitigating Methane Emissions from Fugitive Leaks from Natural Gas Distribution, Historic Landfills, and Manholes in Montréal, Canada.

Rapidly reducing urban methane (CH4) emissions is a critical component of strategies aimed at limiting climate change. Individual source measurements provide the details necessary to develop actionable mitigation strategies and are highly complementary to mobile surveys and other top-down methods. Here, we perform 615 individual source measurements in Montréal, Canada, to quantify CH4 emissions from historic landfills, manholes, and fugitive emissions from natural gas (NG) distribution systems. We find that in 2020, historic landfills produced 901 (452 to 1541, 95% c.i.) tons of CH4, manholes emitted 786 (32 to 2602, 95% c.i.) tons of CH4, and NG distribution systems emitted 451 (176-843, 95% c.i.) tons of CH4, placing them all within the top four CH4 sources in Montréal. Methane emissions from both historic landfills and manholes are not accounted for in any greenhouse gas inventory. We find that geochemistry alone cannot positively identify source subcategories (e.g., type of manhole or NG infrastructure) in almost all cases, although C2/C1 ratios can distinguish NG distribution sources from biogenic sources (historic landfills and manholes). Using our individual source measurement data, we show that historic landfills have the greatest potential for CH4 reductions but the highest mitigation costs, unless we target the highest emitting landfills. In contrast, CH4 emissions from manholes can be reduced at low costs, but reduction methods are commercially unavailable. For NG distribution, methods such as increasing repair rates for high-emitting industrial meters can greatly reduce mitigation costs and emissions. Overall, our results highlight the role of individual source measurements in developing actionable CH4 mitigation strategies to meet municipal, regional, and national climate action plans.

Collaborative Resilience to Extreme Weather in Decentralized Co-operation of Electricity and Natural Gas Distribution Systems

• A model to enhance the resilience of the integrated electrical distribution and gas networks. • A min-max robust optimization model considering worst-case scenarios. N-k and wind power generation • A multi-stage and multi-zone model to capture the spatial-temporal dynamic of extreme hurricane. • A hybrid column-and-constraints optimization solution. The flexibility of the power-to-gas (P2G) technologies and natural gas units (NGUs) can enhance the resilience of the electric distribution system (EDS) considering the high penetration of renewable energy resources (RERs). The decentralized collaborative operation (co-operation) of electric distribution systems and natural gas systems (EDSs&NGSs) considering information privacy preserving can enhance the resilience during an extreme hurricane. To address this issue, this paper proposes a three-level hierarchal solution to decompose the centralized co-operation of the EDS&NGS framework in which an independent decision-making strategy and information privacy preserving for both network operators are simultaneously addressed. Furthermore, in this paper, a min–max robust resilience-constrained co-optimization model is presented to enhance the resilience of the integrated EDS&NGS against worst-case N − k contingencies and wind power generation uncertainty under extreme hurricane events. To attain the spatial dynamics of extreme hurricanes, a the multi-zone and multi-time extreme hurricanes model is considered. Then, a column-and-constraints generation (C&CG) algorithm is used to solve the proposed robust resilience-constrained co-optimization model. To verify the effectiveness of the model, we conducted experiments on a modified IEEE-33-bus-10-node/123-bus-20-node EDS&NGS. The numerical results show that the proposed robust resilience-constrained co-operation of EDS&NGS problem is an effective model for enhancing EDS resilience.

Coordinated Planning of Electric Power and Natural Gas Distribution Systems With Refueling Stations for Alternative Fuel Vehicles in Transportation System

The alternative fuel vehicles (AFVs) which include electric vehicles (EVs) and natural gas vehicles (GVs) have gained much attention in recent years for delivering a clean and low-carbon urban mobility. The AFV development is promoting the coordination among electric power, natural gas, and transportation (ENT) networks. This paper proposes a coordinated planning method for investment on and operation of emerging urban energy infrastructures. The sites and sizes of refueling stations are optimized along with the expansion strategies for electric power distribution network (PDN) and natural gas distribution network (GDN). First, AFV refueling demands are analyzed according to the refueling station constraints and options, and transportation network (TN) constraints. Second, the coordinated planning model for PDN and GDN is formulated along with respective operation constraints in PDN, GDN, and TN. An efficient MILP solution method is developed for the proposed optimization problem. Finally, several case studies verify the effectiveness of the proposed model and its solution method. Compared with existing solutions, the proposed panning method offers a more accurate AFV refueling demand model with various refueling options. It is demonstrated that the coordinated planning can reduce investment and operation costs of urban energy infrastructures by exploring the pertinent interactions among constrained PDN, GDN, and TN.

Hydrogen–Natural Gas Blending in Distribution Systems—An Energy, Economic, and Environmental Assessment

Taking into account the international policies in the field of environmental protection in the world in general, and in the European Union in particular, the reduction of greenhouse gas (GHG) emissions, and primarily of carbon dioxide, has become one of the most important objectives. This can be obtained through various renewable energy sources and non-polluting technologies, such as the mixing of hydrogen and natural gas. Combining hydrogen with natural gas is an emerging trend in the energy industry and represents one of the most important changes in the efforts to achieve extensive decarbonisation. The importance of this article consists of carrying out a techno-economic study based on the simulation of annual consumptions regarding the construction and use of production capacities for hydrogen to be used in mixtures with natural gas in various percentages in the distribution network of an important operator in Romania. In order to obtain relevant results, natural gas was treated as a mixture of real gases with a known composition as defined in the chromatographic bulletin. The survey presents a case study for the injection of 5%, 10%, and 20% hydrogen in the natural gas distribution system of Bucharest, the largest city in Romania. In addition to conducting this techno-economic study, the implications for final consumers of this technical solution in reducing greenhouse gas emissions—mainly those of carbon dioxide from combustion—are also presented.

Study on leakage and explosion consequence for hydrogen blended natural gas in urban distribution networks

It appears to be the most economical means of transporting large quantities of hydrogen over great distances by the existing natural gas pipeline network. However, the leakage and diffusion behavior of urban hydrogen blended natural gas and the evolution law of explosion characteristics are still unclear. In this work, a Computational Fluid Dynamics three-dimensional simulation model of semi-confined space in urban streets is developed to study the diffusion process and explosion characteristics of hydrogen-blended natural gas. The influence mechanism of hydrogen blending ratio and ambient wind speed on the consequences of explosion accident is analyzed. And the dangerous area with different environmental wind effects is determined through comparative analysis based on the most dangerous scenarios. Results indicate that the traffic flow changes the diffusion path of the jet, the flammable gas cloud forms a complex profile in many obstacles, high congestion level lead to more serious explosion accidents. Wind effect keeps the flammable gas cloud near the vehicle flow, the narrow gaps between the vehicles aggravate the expansion of the flammable gas cloud. When the wind direction is consistent with the leakage direction, hydrogen blended natural gas is gathered in the recirculation zone due to the vortex effect, which results in more serious accident consequences. With the increase in hydrogen blending ratio, the higher content of H and OH in the gas mixture significantly increases the premixed burning rate, the maximum overpressure rises rapidly when the hydrogen blend level increases beyond 40%. The results can provide a basis for construction safety design, risk assessment of leakage and explosion hazards, and emergency response in hydrogen blended natural gas distribution systems.

REORGANIZATION OF THE NATURAL GAS DISTRIBUTION COMPLEX OF JSC “MOLDOVAGAZ”

For the reorganization of the gas distribution companies affiliated to JSC “Moldovagaz”, a bibliographic study of the experience of foreign countries in this field was carried out, analyzing the production, financial and economic conditions of the activity of the mentioned companies. In order to improve the organizational structure of the 12 existing natural gas distribution companies, the analysis of technical and economic indicators and their evaluation were performed as well as the development of three management models of the natural gas distribution system. The comparative analysis of the functions and responsibilities of the management of natural gas distribution companies as well as the organizational structural options was performed, thе tаrgеt struсturе оf thе singlе gаs distributiоn соmраny wаs аnаlyzеd. Thе аdvаntаgеs аnd disаdvаntаgеs оf еасh rеоrgаnizаtiоn mоdеl wеrе аnаlyzеd sо thаt in thе еnd it wаs determined and rесоmmеndеd thе орtimаl model.

Environmental Injustices of Leaks from Urban Natural Gas Distribution Systems: Patterns among and within 13 U.S. Metro Areas.

Natural gas leaks in local distribution systems can develop as underground pipeline infrastructure degrades over time. These leaks lead to safety, economic, and climate change burdens on society. We develop an environmental justice analysis of natural gas leaks discovered using advanced leak detection in 13 U.S. metropolitan areas. We use Bayesian spatial regression models to study the relationship between the density of leak indications and sociodemographic indicators in census tracts. Across all metro areas combined, we found that leak densities increase with increasing percent people of color and with decreasing median household income. These patterns of infrastructure injustice also existed within most metro areas, even after accounting for housing age and the spatial structure of the data. Considering the injustices described here, we identify actions available to utilities, regulators, and advocacy groups that can be taken to improve the equity of local natural gas distribution systems.

On the effectiveness of the use of polyethylene pipes with coextrusion layers in natural gas distribution systems

The article analyzes the efficiency factors of the use of polyethylene pipes with coextrusion layers of PE100-RC on the outer and / or inner surface of the pipe in the natural gas distribution systems. It is noted that efficiency factors are manifested at the construction stage and allow reducing capital investments in the construction of gas distribution networks. The proposals for amendments to the current regulatory documentation specifying the requirements to the design, technical characteristics, application, design and installation of polyethylene pipes in gas distribution networks are formulated, the features of the application of PE100-RC polyethylene pipes are presented. An assessment of the economic efficiency of the use of polyethylene pipes with PE100-RC co-extruded layers on the outer and/or inner surface of the pipe in gas distribution networks was carried out.