Natural Gas Pipeline Network System Research Articles

Allocation of transportation capacity for complex natural gas pipeline network under fair opening

China has formed a national natural gas pipeline network, and reasonable and accurate pipeline capacity allocation scheme has important significance for improving the utilization rate of pipeline network, improving the income of pipeline network operators and ensuring the gas consumption of downstream users, which poses greater challenges to the formulation of pipeline capacity allocation rules and mechanisms. This paper takes the natural gas pipeline network system as the research object, and studies the rules and mechanisms of pipeline capacity allocation. A capacity allocation model of natural gas pipeline network is proposed with the net present value of pipeline network operator's income as the goal, considering the gas consumption characteristics of downstream users, the dynamic change of gas source node capacity, pipeline hydraulic characteristics, pipeline flow direction, compressor and other constraints. Based on the simulation of the actual pipeline network by the proposed model, seven allocation rules and one mechanism are proposed. Specifically, the user priority of non-interruptible type, the pipeline path adjustable type and the gas source node adjustable type is higher than the corresponding comparison type. In the pipeline capacity allocation mechanism, the amount compensation mechanism for pipeline capacity transactions is as follows: When the pipeline capacity transaction occurs between users, the transaction information is submitted to the pipeline network operator. The pipeline network operator proposes the corresponding amount compensation according to the transaction information, and the transaction parties negotiate the proportion of the amount compensation and submit it to the pipeline network operator. In addition, it is recommended that pipeline network operators vigorously develop LNG receiving stations and downstream interruptible and compressible users in the future.

New method for the transient simulation of natural gas pipeline networks based on the fracture-dimension-reduction algorithm

The transient simulation technology of natural gas pipeline networks plays an increasingly prominent role in the scheduling management of natural gas pipeline network system. The increasingly large and complex natural gas pipeline network requires more strictly on the calculation efficiency of transient simulation. To this end, this paper proposes a new method for the transient simulation of natural gas pipeline networks based on fracture-dimension-reduction algorithm. Firstly, a pipeline network model is abstracted into a station model, inter-station pipeline network model and connection node model. Secondly, the pressure at the connection node connecting the station and the inter-station pipeline network is used as the basic variable to solve the general solution of the flow rate at the connection node, reconstruct the simulation model of the inter-station pipeline network, and reduce the equation set dimension of the inter-station pipeline network model. Thirdly, the transient simulation model of the natural gas pipeline network system is constructed based on the reconstructed simulation model of the inter-station pipeline network. Finally, the calculation accuracy and efficiency of the proposed algorithm are compared and analyzed for the two working conditions of slow change of compressor speed and rapid shutdown of the compressor. And the following research results are obtained. First, the fracture-dimension-reduction algorithm has a high calculation accuracy, and the relative error of compressor outlet pressure and user pressure is less than 0.1%. Second, the calculation efficiency of the new fracture-dimension-reduction algorithm is high, and compared with the nonlinear equations solving method, the speed-up ratios under the two conditions are high up to 17.3 and 12.2 respectively. Third, the speed-up ratio of the fracture-dimension-reduction algorithm is linearly related to the equation set dimension of the transient simulation model of the pipeline network system. The larger the equation set dimension, the higher the speed-up ratio, which means the more complex the pipeline network model, the more remarkable the calculation speed-up effect. In conclusion, this new method improves the calculation speed while keeping the calculation accuracy, which is of great theoretical value and reference significance for improving the calculation efficiency of the transient simulation of complex natural gas pipeline network systems.

Supply reliability analysis of natural gas pipeline network based on demand-side economic loss risk

• An evaluation method for the economic loss risk on the demand side of a natural gas pipeline network system in a certain period is proposed. • User priorities are considered when there is a shortage of gas in the pipeline network. • The economic consequences on the demand side are quantified in terms of the alternative energy costs. • The effect of supply sequence of users on gas supply reliability is described. Most studies on the natural gas supply reliability evaluation have reflected on whether the volume of gas supply to users is sufficient. However, different types of users suffer from the same natural gas shortage, the consequences of loss are different. The abundance of the supplied gas volumes does not reflect the actual losses incurred by users. Moreover, when a gas shortage occurs, the supply flow of different types of users is redistributed according to the supply order. Therefore, this study proposes an evaluation method for the gas supply reliability based on demand-side economic risk. The user's supply sequence is integrated into the cost matrix to optimize the distribution of the user's demand flow under gas shortage. A calculation model of the economic loss cost is established using alternative energy sources. Finally, a reliability index is established based on economic risk to evaluate the degree of supply security. The results showed that the reliability based on the economic risk assessment was slightly higher than that based on the gas quantity assessment. The reliabilities were 99.988% and 99.991%, respectively. The economic risk is reduced and the reliability is improved for the important users after considering the influence of the demand-side supply order.

Supply resilience assessment of natural gas pipeline network systems

Resilience is one of the important components of system safety evaluation and optimization, the research of which for natural gas pipeline network system (NGPNS) is still in initial stage, especially for the resilience indexes and process description. To evaluate the resilience of NGPNS more synthetically and practically, considering different types of disturbances, an integrated framework is proposed for evaluating the supply resilience of NGPNS, involving the topology and operating conditions. The characteristics of both deterministic and probabilistic disturbances are analyzed. The innovations and corresponding methodology are that global resilience, temporal resilience and threshold resilience are proposed as the resilience evaluation indicators; the maximum flow method and shortest path method are integrated with operation and structural parameters to calculate the amounts and routes of gas supply, before and after disturbance; based on complex networks theory and graph theory, the traditional view point is changed from whole system to the affected area. The results can contribute to the guidance of NGPNS topological designing and the building of prewarning scheme, including spare gas sources and gas routes optimization, and the strategy of pipeline maintenance, also can help the rapid analysis of disturbance consequences and the enhancement of evaluating accuracy in NGPS resilience.

Prediction of fluctuation loads based on GARCH family-CatBoost-CNNLSTM

An accurate prediction on natural gas load is always a guarantee of a safe and reliable operation of the natural gas pipeline network system, however, natural gas daily load variations are instability and fluctuation. Therefore, accurate prediction fluctuation loads can be challenging. Concerning that many influencing factors of natural gas daily load are non-linear and time-varying, a combined prediction model combining GARCH family models, CatBoost algorithm, CNN and LSTM is proposed in this paper. The model combines two important techniques. The first technique is to visualize the fluctuation of the daily load of natural gas through the classical GARCH family model. and characterize the fluctuation through parameters. The second one is a new gradient boosting algorithm that can take into account factors such as the parameters of the GARCH family of models and the meteorological environment, and screen for suitable and important prediction features. It also combines CNN with LSTM to predict natural gas daily load with large fluctuations and calculates 95% confidence intervals. The experimental results show that the natural gas load prediction based on GARCH family-CatBoost-CNNLSTM is reduced by an average of 26.555%, 30.892%, and 26.283% in the three relative evaluation indicators of RMSE, MAE and MAPE, and an average increase of 0.914% in R2 compared with other single or combined control models such as LSTM, CNN and MLP. The model effectively combines the advantages of econometric methods, machine learning algorithms, deep learning algorithms and other techniques, as a result, it can be better applied to the prediction of fluctuation loads.

Multi-period optimal infrastructure planning of natural gas pipeline network system integrating flowrate allocation

The purpose of flow allocation is to give full play to the transmission capacity of the pipeline network system and complete the transportation task with less operation cost. When the flow allocation cannot balance the changes of upstream gas source and downstream demand, the pipeline network system needs to be planned and constructed. Therefore, this paper aims to propose an optimization method allowing the simultaneous optimization of infrastructure planning and the flowrate allocation in each decide cycle by explicit consideration of the corresponding operational constraints. The constraints include the limit of gas supply and user demand, the transmission capacity of pipeline network, the balance of node flowrate, and the capacity of gas storage. The injection, storage and production capacity of gas storage is considered. A case study including multi scene settings shows the feasibility of the proposed method. The results show that compared with the annual scale, the half-year scale can better consider the peak regulation effect of gas storage, and the utilization rate of gas storage is improved by 12.88%. Multiple options that allow for both expansion and new pipelines are more economical than a single option. Specifically, the total cost under multi-option planning is 8.24% lower than only expansion is allowed, and 8.32% lower than only new construction is allowed. In addition, the sensitivity analysis is carried out to study the impact of the unit pipeline transmission cost, unit construction cost and lead time of pipeline on the pipeline construction scheme. The improvement of gas storage utilization rate, gas storage operation and pipeline network transmission capacity verify that the proposed planning model has the ability to improve the system operation efficiency and reduce the total cost.

Security region of natural gas pipeline network system: Concept, method and application

This paper proposes the security region of natural gas pipeline network system (NGS-SR), which provides a new perspective to analyze the security of the system. Firstly, the definition of NGS-SR is proposed, that is, the closed set of all secure operating points in the state space. NGS-SR is then modeled considering variety of operation constraints, such as the hydraulic balance constraint, the node gas pressure constraint, etc. Secondly, an observation-based method is proposed to solve the security boundary of NGS-SR. Thirdly, the approaches of security assessment and preventive control based on NGS-SR are illustrated. Finally, the NGS-SR of two typical systems are observed, analyzed and compared with the existing methods of security analysis. The results show the validity and precision of the proposed model and method, as well as the advantages of NGS-SR: 1) NGS-SR can describe the secure operating range of the system in a geometric and visualized way; 2) NGS-SR is beneficial to realize online security analysis, the analysis speed is increased up to 1944 times in the cases; 3) NGS-SR can provide the security margin information for system operation.

Reliability assessment of integrated energy system considering the uncertainty of natural gas pipeline network system

Natural gas, as a clean fossil energy, has been widely used in power generation system by converting chemical energy into electrical energy through gas turbines. However, the natural gas pipeline network system (NGPNS) is comprised of many equipments, and the failure of any equipment will probably cause the outage of gas turbines. Therefore, this study proposes an analytical method which can incorporate the uncertainty of NGPNS into the reliability assessment of integrated energy system. Firstly, on the basis of an analytical technique, NGPNS's operating states and the corresponding state probabilities are simulated. Secondly, a state transferring and equivalence technique is proposed for transferring the unreliability of NGPNS to the involved outage of gas turbines. Thirdly, an equivalent reliability model of gas turbine is established for taking into account the uncertainty of NGPNS. Finally, the NGPNS is connected to the Roy Billinton Test System through the coupling of gas turbines between electrical and gas networks. The results of case studies verify the correctness and effectiveness of the proposed algorithm.

Economic Imperative of Flow Optimization in Natural Gas Pipeline Network System

Economic evaluation of gas pipelines assets and facilities are three-fold in nature. Design, construction and operation costs are the three aspects of the economic evaluation implications. Installation cost of a gas pipeline network system is pressure and flow throughput dependent. The work considers single phase flow of gas in gas pipeline network system. The economic assessment of capital cost savings accruable operating gas pipeline at optimal level of performance considers five operating gas pipelines network system in Nigerian terrain. The case study Natural gas pipelines are ElfTotal Nig. Ltd, Shell Petroleum Development Company (SPDC), Agip Nig. Ltd, Nigeria Gas Company (NGC)-Eastern Division and Nigeria Gas Company NGC)-Western Division. The economic viability or feasibility of a facility is dependent on the cost of development, operation and service life. The consideration also applies to the capital cost savings that could accrue if gas pipeline is designed and operated at their optimal capacities condition. The economic evaluation results for optimized pipelines operated on Panhandle-A and Modified Panhandle-B were remarkable. Potential capital cost savings for Elf Total optimized Panhandle-A and optimized Modified Panhandle-B was within a margin of 3% to 31%. That of Shell Petroleum Development Company (SPGC) was within 5% to 40%. Agip Nig. Ltd was to the tune of 3% TO 44%. Nigeria Gas Company (NGC) Eastern Division potential savings in installation cost is within 5% to 36%. Nigeria Gas Company (NGC) Western Division potential savings in investment cost is in the range of 5% to 56%.

Flow Optimization Sensitivity in Natural Gas Pipeline Network System

Three control variables of interest namely upstream pressure, downstream pressure and gas specific gravity were considered to determine the sensitivities of the optimal flow capacity to changes in the aforementioned control variables. The sensitivity scheme covered five case study Pipelines namely: Elf Total Nig. Ltd, Shell Petroleum Development Company (SPDC), Agip Nig. Ltd and Nigeria Gas Company (NGC) Eastern Division. The Panhandle A and Modified Panhandle B models equations were both applied to each of the pipelines in the sensitivity evaluation scheme. The sensitivities were calculated with respect to small changes in upstream pressure P 1 , downstream pressure P 2 and the gas specific gravity G, within the limit of ± 20 %. It was seen that changes in optimal flow capacities were insignificant and therefore insensitive to changes in flow variables in the range upto ± 20 %. This gives credence, authenticates and establish the stability of the results of optimization of flow capacities carried out in the researcher’s previous works. The Panhandle-A flow model yielded lower values of changes in optimal flow capacities upto the limit of 1.0 %. In comparison, the Panhandle-B flow model gave sensitivities upto a maximum of 9.0 %, for all the Pipelines covered in the study and the flow control variables. In more explicit manner, the response of optimal flows capacities to changes in control variables for the transformed Panhandle-A and Modified Panhandle-B models for ElfTotal Nig. Ltd with respect to upstream pressure, downstream and gas specific gravity are respectively 0.4 %, 0.9 % and 0.16 % (Tables 1 a to 1b). Applying the same concept to Shell petroleum Development Company (SPDC), the response are respectively 3.2 %, 1.7 % and 0.16 % (Tables 2a to 2b). In the same vein, with respect to Agip Nig. Ltd, the respective data are 7.11 %, 0.03 % and 3.7 % (Tables 3a to 3b) and for the Nigeria Gas Company (NGC) Eastern Division the respective data are 7.11 %, 0.03 % and 3.7 % (Tables 4a and 4b). The graphical illustrations are in accordance with Figures (Fig.1a & b to 4a & b). The operating threshold based on off design analysis (Tables 6 to 10) confirmed that the line flow throughput could be varied within 1 m 3 /s to 6.5 m 3 /s. The nominal line diameter could be fixed within 30” and 65”. These condition are possible within the limit of pressure variation in the range of 30 bar to 170 bar at stream temperature of 40 0 C.

Analogical Approach for Optimizing Natural Gas Transmission Pipeline Network System

The increase in demand for natural gas in different sectors attracted different scholars in optimizing the operation and configurations of natural gas pipeline network (NGPN) systems. Even though there have been reports regarding the attempts of solutions for optimizing NGPN problems, the issues of NGPN regarding energy minimizations are not fully address yet. This paper proposed robust solution for NGPN system energy consumption minimization at compressor stations based on analogical approach. The analogies between NGPN system and inventory model were observed and applied in the analysis of steady state NGPN system. The proposed technique is based on the inventory model to find optimal operations for natural gas pipeline network system. The method for the determination of the optimal pressures was efficient and handled the non-linearity that occurs on both objective and the constraint equations. Results on a gunbarrel NGPN showed the proposed method assisted in determining the discharge and suction pressures to minimized energy consumption at compressor stations.

A Mixed-Integer Optimization Model for Compressor Selection in Natural Gas Pipeline Network System Operations

This paper presents a Mixed-Integer Linear Programming (MILP) model to optimize the compressor selection operations in natural gas pipeline network system. The objectives of natural gas pipeline network system operations are to minimize the operation costs and provide sufficient gas to the local customers. A pipeline network system is the most cost effective way for moving fluid products over long distances. In this case, it is used for transmitting natural gas from a producer to customers. To ensure demand for natural gas can be met, a dispatcher turns on or off compressor(s) in order to increase or decrease the amount of natural gas in the pipeline system. Compressor selection is one of the most critical operations in the natural gas pipeline network system because the costs associated with turning on or off the compressor make up a large percentage of the total operating costs. In order to minimize the operating costs of the pipeline system, the three most crucial factors that affect the costs are integrated into the MILP model. The three factors include the capacities of compressors, the energy used to turn on the compressors, and the energy used to turn them off. The MILP model provides the decision support in determining the optimal solutions for controlling the compressors. It was developed and verified using the operation data supplied by a gas pipeline company in Saskatchewan, Canada.

Computer-Aided Simulation Model for Natural Gas Pipeline Network System Operations

This paper presents the development of a computer-aided simulation model for natural gas pipeline network system operations. The simulation model is a useful tool for simulating and analyzing the behavior of natural gas pipeline systems under different operating conditions. Historical data and knowledge of natural gas pipeline system operations are crucial information used in formulating the simulation model. This model incorporates the natural gas properties, energy balance, and mass balance that lay the foundation of knowledge for natural gas pipeline network systems. The user can employ the simulation model to create a natural gas pipeline network system, selecting the components of natural gas, pipe diameters, and compressor capacities for different seasons. Because the natural gas consumption rate continuously varies with time, the dynamic simulation model was built to display state variables of the natural gas pipeline system and to provide guidance to the users on how to operate the system properly...