The gas chain: influence of its specificities on the liberalisation process. NBB Working Papers. No. 122, 16 November 2007

Like other network industries, the European gas supply industry has been liberalised, along the lines of what has been done in the United Kingdom and the United States, by opening up to competition the upstream and downstream segments of essential transmission infrastructure. The aim of this first working paper is to draw attention to some of the stakes in the liberalisation of the gas market whose functioning cannot disregard the network infrastructure required to bring this fuel to the consumer, a feature it shares with the electricity market. However, gas also has the specific feature of being a primary energy source that must be transported from its point of extraction. Consequently, opening the upstream supply segment of the market to competition is not so obvious in the European context, because, contrary to the examples of the North American and British gas markets, these supply channels are largely in the hands of external suppliers and thus fall outside the scope of EU legislation on the liberalisation and organisation of the internal market in gas. Competition on the downstream gas supply segment must also adapt to the constraints imposed by access to the grid infrastructure, which, in the case of gas in Europe, goes hand in hand with the constraint of dependence on external suppliers. Hence the opening to competition of upstream and downstream markets is not "synchronous", a discrepancy which can weaken the impact of liberalisation. Moreover, the separation of activities necessary for ensuring free competition in some segments of the market is coupled with major changes in the way the gas chain operates, with the appearance of new markets, new price mechanisms and new intermediaries. Starting out from a situation where gas supply was in the hands of vertically-integrated operators, the new regulatory framework that has been set up must, on the one hand, ensure that competitive forces can be given free rein, and, on the other hand, that free and fair competition helps the gas chain to operate coherently, at lower cost and in the interests of consumers, for whom the stakes are high as natural gas is an important input for many industrial manufacturing processes, even a "commodity" almost of basic necessity

Automation and Control Architecture for Hybrid Pipeline Robots

The aim of this research project, towards the automation of the Hybrid Pipeline Robot (HPR), is the development of a control architecture and strategy, based on reconfiguration of the control strategy for speed-controlled pipeline operations and self-recovering action, while performing energy and time management. The HPR is a turbine powered pipeline device where the flow energy is converted to mechanical energy for traction of the crawler vehicle. Thus, the device is flow dependent, compromising the autonomy, and the range of tasks it can perform. The control strategy proposes pipeline operations supervised by a speed control, while optimizing the energy, solved as a multi-objective optimization problem. The states of robot cruising and self recovering, are controlled by solving a neuro-dynamic programming algorithm for energy and time optimization, The robust operation of the robot includes a self-recovering state either after completion of the mission, or as a result of failures leading to the loss of the robot inside the pipeline, and to guaranteeing the HPR autonomy and operations even under adverse pipeline conditions Two of the proposed models, system identification and tracking system, based on Artificial Neural Networks, have been simulated with trial data. Despite the satisfactory results, it is necessary to measure a full set of robot’s parameters for simulating the complete control strategy. To solve the problem, an instrumentation system, consisting on a set of probes and a signal conditioning board, was designed and developed, customized for the HPR’s mechanical and environmental constraints. As a result, the contribution of this research project to the Hybrid Pipeline Robot is to add the capabilities of energy management, for improving the vehicle autonomy, increasing the distances the device can travel inside the pipelines; the speed control for broadening the range of operations; and the self-recovery capability for improving the reliability of the device in pipeline operations, lowering the risk of potential loss of the robot inside the pipeline, causing the degradation of pipeline performance. All that means the pipeline robot can target new market sectors that before were prohibitive

Bond graph modeling of centrifugal compression systems

A novel approach to model unsteady fluid dynamics in a compressor network by using a bond graph is presented. The model is intended in particular for compressor control system development. First, we develop a bond graph model of a single compression system. Bond graph modeling offers a different perspective to previous work by modeling the compression system based on energy flow instead of fluid dynamics. Analyzing the bond graph model explains the energy flow during compressor surge. Two principal solutions for compressor surge problem are identified: upstream energy injection and downstream energy dissipation. Both principal solutions are verified in bond graph modelings of single compression system equipped with a surge avoidance system (SAS) and single compression system equipped with an active control system. Moreover, the bond graph model of single compressor equipped with SAS is able to show the effect of recycling flow to the compressor upstream states which improves the current available model. The bond graph model of a single compression system is then used as the base model and combined to build compressor network models. Two compressor networks are modeled: serial compressors and parallel compressors. Simulation results show the surge conditions in both compressor networks.© SAGE. This is the authors’ accepted and refereed manuscript to the article

Real-time receding horizon optimisation of gas pipeline networks

Real-time optimisation of gas pipelines in transient conditions is considered to be a challenging problem. Many pipeline systems are, however, only mildly non-linear. It is shown, that even the shutdown event of a compressor station can be described using a linear model. A dynamic, receding horizon optimisation problem is defined, where the free response prediction of the pipeline is obtained from a pipeline simulator and the optimal values of the decision variables are obtained solving a Quadratic Programming (QP) problem set up by using linear models, linearised constraints and quadratic approximations of the cost function, which is the energy consumption of the compressor stations (CSs). The problem is extended with discrete decision variables, the shutdown/start-up commands of CSs. A Mixed Logical Dynamical (MLD) system is defined, but the resulting Mixed Integer QP problem is shown to be very high-dimensional. Instead, a series of QP problems, each containing linear constraints modelling the shut down state of CSs, results in an optimisation problem with considerably smaller dimension. The receding horizon optimisation is tested in a simulation environment and comparison with data from the Finnish natural gas pipeline shows that 5 to 8 % savings in compressor energy consumption can be achieved using optimisation. A new idea, maximisation of energy consumption, is used to calculate maximal energy savings potential of the pipeline. A new result is that step response models used in conjunction with MLD systems do not produce the same model change behaviour than state space models.reviewe

Liquid Transport Pipeline Monitoring Architecture Based on State Estimators for Leak Detection and Location

This research presents the implementation of optimization algorithms to build auxiliary signals that can be injected as inputs into a pipeline in order to estimate —by using state observers—physical parameters such as the friction or the velocity of sound in the fluid. For the state estimator design, the parameters to be estimated are incorporated into the state vector of a Liénard-type model of a pipeline such that the observer is constructed from the augmented model. A prescribed observability degree of the augmented model is guaranteed by optimization algorithms by building an optimal input for the identification. The minimization of the input energy is used to define the optimality of the input, whereas the observability Gramian is used to verify the observability. Besides optimization algorithms, a novel method, based on a Liénard-type model, to diagnose single and sequential leaks in pipelines is proposed. In this case, the Liénard-type model that describes the fluid behavior in a pipeline is given only in terms of the flow rate. This method was conceived to be applied in pipelines solely instrumented with flowmeters or in conjunction with pressure sensors that are temporarily out of service. The design approach starts with the discretization of the Liénard-type model spatial domain into a prescribed number of sections. Such discretization is performed to obtain a lumped model capable of providing a solution (an internal flow rate) for every section. From this lumped model, a set of algebraic equations (known as residuals) are deduced as the difference between the internal discrete flows and the nominal flow (the mean of the flow rate calculated prior to the leak). The residual closest to zero will indicate the section where a leak is occurring. The main contribution of our method is that it only requires flow measurements at the pipeline ends, which leads to cost reductions. Some simulation-based tes

Model Order Reduction for Gas and Energy Networks

To counter the volatile nature of renewable energy sources, gas networks take a vital role. But, to ensure fulfillment of contracts under these circumstances, a vast number of possible scenarios, incorporating uncertain supply and demand, has to be simulated ahead of time. This many-query gas network simulation task can be accelerated by model reduction, yet, large-scale, nonlinear, parametric, hyperbolic partial differential(-algebraic) equation systems, modeling natural gas transport, are a challenging application for model order reduction algorithms. For this industrial application, we bring together the scientific computing topics of: mathematical modeling of gas transport networks, numerical simulation of hyperbolic partial differential equation, and parametric model reduction for nonlinear systems. This research resulted in the "morgen" (Model Order Reduction for Gas and Energy Networks) software platform, which enables modular testing of various combinations of models, solvers, and model reduction methods. In this work we present the theoretical background on systemic modeling and structured, data-driven, system-theoretic model reduction for gas networks, as well as the implementation of "morgen" and associated numerical experiments testing model reduction adapted to gas network models

The gas chain : influence of its specificities on the liberalisation process

Like other network industries, the European gas supply industry has been liberalised, along the lines of what has been done in the United Kingdom and the United States, by opening up to competition the upstream and downstream segments of essential transmission infrastructure. The aim of this first working paper is to draw attention to some of the stakes in the liberalisation of the gas market whose functioning cannot disregard the network infrastructure required to bring this fuel to the consumer, a feature it shares with the electricity market. However, gas also has the specific feature of being a primary energy source that must be transported from its point of extraction. Consequently, opening the upstream supply segment of the market to competition is not so obvious in the European context, because, contrary to the examples of the North American and British gas markets, these supply channels are largely in the hands of external suppliers and thus fall outside the scope of EU legislation on the liberalisation and organisation of the internal market in gas. Competition on the downstream gas supply segment must also adapt to the constraints imposed by access to the grid infrastructure, which, in the case of gas in Europe, goes hand in hand with the constraint of dependence on external suppliers. Hence the opening to competition of upstream and downstream markets is not "synchronous", a discrepancy which can weaken the impact of liberalisation. Moreover, the separation of activities necessary for ensuring free competition in some segments of the market is coupled with major changes in the way the gas chain operates, with the appearance of new markets, new price mechanisms and new intermediaries. Starting out from a situation where gas supply was in the hands of vertically-integrated operators, the new regulatory framework that has been set up must, on the one hand, ensure that competitive forces can be given free rein, and, on the other hand, that free and fair competition helps the gas chain to operate coherently, at lower cost and in the interests of consumers, for whom the stakes are high as natural gas is an important input for many industrial manufacturing processes, even a "commodity" almost of basic necessity.network industries, gas industry, gas utility, liberalisation, regulation, deregulation, market structure, European gas supply, oligopoly, OPEG