# GasLib—A Library of Gas Network Instances

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## Abstract

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`GasLib`is to provide a set of publicly available gas network instances that can be used by researchers in the field of gas transport. The advantages are that researchers save time by using these instances and that different models and algorithms can be compared on the same specified test sets. The library instances are encoded in an XML (extensible markup language) format. In this paper, we explain this format and present the instances that are available in the library.

**Data Set:**http://gaslib.zib.de

**Data Set License:**CC BY 3.0

## 1. Summary

`GasLib`, we provide a set of network instances that can be used to test and compare such models and the algorithms for solving them.

`GasLib`networks and to the chapter [4] in the book [1] for a physical and technical description of the network elements as well as for several mathematical models.

`GasLib`aims to fix these problems by providing publicly available small- to large-scale academic and real-world networks. It currently contains stationary instances only. The contained real-world data originates from the completed industrial research project ForNe, the project “Investigation of the technical capacities of gas networks” (2009–2012) that was funded by the German Federal Ministry of Economic Affairs and Energy, and from the collaborative research center TRR 154 “Mathematical Modelling, Simulation and Optimization using the Example of Gas Networks”, which is funded by the German Research Foundation. Because some of the original data from our former industry partner Open Grid Europe GmbH (http://www.open-grid-europe.com) and from the Greek network operator DESFA is confidential, the corresponding

`GasLib`instances are distorted versions of the original transport networks. See Section 2.1 for a more detailed description of the instances. The complete library is freely available at http://gaslib.zib.de.

`GasLib`is useful for different target groups: First, researchers that develop new mathematical models and simulation or optimization algorithms can use

`GasLib`to test and evaluate these algorithms on network instances of different sizes. Second, developers of optimization and simulation solvers can use

`GasLib`to improve the performance and robustness of their solvers using the example of challenging models from a real-world problem.

`GasLib`are composed of different data that can be used to set up simulation or optimization models for stationary gas transport problems. First, every instance includes a structural and technical description of the network and all contained network elements. Second, several sets of nominations are provided. More detailed information on the provided data and the data format is given in Section 2.2.

`GasLib`additionally provides

`GAMS`[6] models of specific mixed-integer nonlinear models based on the corresponding network instances. This collection of models can be used to test and improve solvers for mixed-integer nonlinear optimization (MINLP). The corresponding models are feasibility problems, that is, no objective function is given, as described in [1], and the modeling decisions are the same as for the MINLP model described in [7]. For instance, the MINLP instances arising from the

`GasLib-582`network have roughly 2200 variables (of which roughly 250 are binary) and 3700 constraints (of which roughly 900 are nonlinear). Numerical results on an earlier version of these models can be found in [2].

`GasLib`instances. We give the corresponding references in Section 2.1, where we present the instances in detail.

## 2. Data Description

`GasLib`and explain the different data formats.

#### 2.1. Overview of the Instances

`GasLib`currently contains seven instances: four handmade networks with 11, 24, 40, and 135 nodes intended for testing purposes, one medium-scale real-world network with 134 nodes, and two large real-world networks with 582 and 4197 nodes, respectively. In the following, we describe all the networks in detail. We note that the number of nodes is always part of the name of the network.

#### 2.1.1. `GasLib-11`

#### 2.1.2. `GasLib-24`

`GasLib-24`is also provided for testing purposes. It is an extended variant of the network used in [8]; see the description in the cited paper for more details. Its small size again allows for fast computations as well as for testing and comparing different models of network elements. The network consists of 3 entries, 5 exits, 19 pipes, 3 compressor stations, and 1 control valve, short pipe, and resistor each; see Figure 2. The single nomination requires routing 544.32 $\mathrm{N}{\mathrm{m}}^{3}/\mathrm{h}$ units of flow from the entries to the exits. This network has already been used in the papers [9,10].

#### 2.1.3. `GasLib-40`

#### 2.1.4. `GasLib-134`

`GasLib-134`is a close approximation of the real-world tree-like gas transport network of Greece and consists of a main pipeline connecting the Greek–Bulgarian border with southern Greece and additional 16 branches, comprising an overall length of 1412 km. The network consists of 3 entries, 45 exits, 86 inner nodes, 86 pipes, 45 short pipes, 1 turbo compressor machine, and 1 control valve with preset pressure; see Figure 4. Because of the confidential nature of the compressor’s technical data, it has been replaced by a random example that roughly approximates its main characteristics, namely, a maximum mechanical power of 7500 kW and an adiabatic efficiency of 0.84. The associated 1234 daily nominations have been taken from the transmission system operator’s website [16] and processed so that they only represent balanced samples between the entries and the exits. Moreover, all nomination data have been converted from heat power to volumetric units by utilizing a conversion with a single calorific value, thus neglecting the gas mixing within the network. This instance has been used in the papers [17,18,19].

#### 2.1.5. `GasLib-135`

`GasLib-135`is also provided for testing purposes. It allows the testing of models on a larger network. The network consists of 6 entries, 99 exits, 30 inner nodes, 141 pipes, and 29 compressor stations. It roughly represents a part of the German high-calorific gas transport network; see Figure 5. We note that this network also contains cycles, which is not the case for the almost equally sized

`GasLib-134`network. This aspect typically makes the network harder to solve than

`GasLib-134`. Again, a single nomination is provided, in which the same amount of gas (40 $\mathrm{N}{\mathrm{m}}^{3}/\mathrm{h}$) is discharged at every exit. The entries equally provide the gas; that is, the inflow at every entry is 660 $\mathrm{N}{\mathrm{m}}^{3}/\mathrm{h}$. Numerical results for these instances can be found in [11,12,13,14].

#### 2.1.6. `GasLib-582`

`GasLib-582`is based on a real-world gas transport network, which covers approximately one-fourth of the area of Germany. Because the original network data from Open Grid Europe GmbH are confidential, we have carefully distorted these such that no direct conclusion regarding the true operational capability of the network can be drawn, while still maintaining a realistic behavior. In particular, the feasibility of the edited instances is comparable to that of the original instances.

`GasLib-582`contains 31 entries, 129 exits, and 422 inner nodes, which are connected by 278 pipes, 5 compressor stations, 23 control valves, 8 resistors, and 269 short pipes; see Figure 6. We note that this network again contains cycles. The compressor stations contain 8 turbo compressors and 1 piston compressor in total.

#### 2.1.7. `GasLib-4197`

`GasLib-4197`is based on a real-world gas transport network spanning one-third of Germany. Because the original network data from Open Grid Europe GmbH again are confidential, we have carefully distorted these as described for the

`GasLib-582`network.

`GasLib-582`; see [20] for a detailed description of the sampling process.

#### 2.2. Description of the Data Files

`GasLib`are XML files. XML is a language for describing data in a hierarchical format; see [27]. A multitude of software to read and write XML files on different platforms is available, rendering XML useful for collecting and publishing data that should be easy to read, to parse, and to write.

`GasLib`network is described using different files. First, the network topology itself is specified in a

`net`file. The contained compressor machines are described in a

`cs`file, and the interplay of different controllable elements of the network is given in a

`cdf`file. Finally, a nomination is specified by a separate

`scn`file. Thus, the full set for specifying a single stationary demand scenario (nomination) for a gas transport network requires four files. However, the

`cdf`file is optional and does not need to be given. We note further that there may be arbitrarily many

`scn`files but only one

`cs`and one

`cdf`file for a given network description (

`net`) file.

`GasLib`provides the usage of many different units for the same physical or technical quantity. Examples are given in Table 1, and a full list can be found in the documentation on the

`GasLib`website or in the XSD files.

#### 2.2.1. The `net` File

`net`file together with the technical parameters of the network elements.

`source`), exit nodes (

`sink`), and junctions (

`innode`). Common to all types of nodes are bounds for the pressure, but

`source`and

`sink`nodes have additional bounds on the supplied and discharged amount of flow at the node. Positive flow at a

`source`node refers to the injection of gas, while positive flow at a

`sink`stands for the discharge of gas. The

`source`nodes have additional parameters, describing the composition of the supplied gas. For example, for source nodes, we have to state the values of, for example, the calorific value or the pseudocritical temperature; see Figure 8. The flow bounds at the nodes in the

`net`file are usually very wide. Fixed values for the nominated flows at nodes are given in the

`scn`file that complements the

`net`file; see Section 2.2.4.

`height`value of the nodes is needed to compute the slope of pipes, which typically has an impact on the pressure losses in the network. See Figure 8 for examples of the three node types.

`net`file: pipes (

`pipe`), short pipes (

`shortPipe`), resistors (

`resistor`), valves (

`valve`), control valve stations (

`controlValve`), and compressor stations (

`compressorStation`). All arcs have bounds restricting the flow through the arc (

`flowMin`and

`flowMax`) and specify their incident nodes as well as their orientation in the network. In addition, every arc type has its specific set of parameters.

`length`,

`diameter`, and

`roughness`; see Figure 9. These are used to compute the friction factor in the pressure loss equation. The

`pressureMax`element specifies the maximum pressure that the material of the pipe can withstand. It is typically used to also bound the pressure on the incident nodes. The

`heatTransferCoefficient`element specifies the heat transfer coefficient of the material of the pipe’s wall, and, finally, the

`speedLimit`element specifies the maximum velocity of the gas in the pipe. The latter parameter is optional. A typical value is 50 $\mathrm{m}\text{}{\mathrm{s}}^{-1}$.

`shortPipe`has no further attributes; see Figure 10 for an example.

`GasLib`instances. One results in a constant pressure loss (in the direction of the flow), which is specified by the element

`pressureLoss`. The other type induces a pressure loss that continuously depends on the flow rate through the resistor as specified by the tags

`dragFactor`and

`diameter`. An example for both types of resistors is given in Figure 11.

`valve`can be open or closed. In the open state, the pressures at the end nodes attain the same value, while in the closed state, the flow rate is zero. They only have one specific parameter

`pressureDifferentialMax`that restricts the difference of pressures between the

`from`and

`to`node when the valve is closed; see Figure 12 for an example.

`controlValve`elements, as shown in Figure 13. These elements can be set to three states: active, bypass mode, and closed. In the active state, gas pressure can be reduced (in the direction of the orientation of the arc), and the parameters

`pressureDifferentialMin`and

`pressureDifferentialMax`define the range of possible pressure reductions. The bypass and closed states are equivalent to the corresponding states of valves. This means that a control valve in bypass mode may have nonzero flow and does not influence the pressures, whereas a closed control valve blocks the gas flow. The attribute

`internalBypassRequired`specifies whether the bypass state needs to be modeled (if

`1`) or whether a bypass valve is already given in the network topology. The

`controlValve`elements have resistors at their inlet and outlet, which are described with the same data as stand-alone resistors. The resistors only have to be considered if the

`controlValve`is active. Otherwise, they do not have any impact on the gas flow. Finally, the attribute

`gasPreheaterExisting`specifies if a gas preheater is present at the control valve station.

`fuelGasVertex`specifies the node from which the fuel gas is taken, and the attribute

`gasCoolerExisting`specifies whether a gas cooler is installed at the station or not. We note that the description of the

`compressorStation`in the

`net`file is not complete. The hosted machines are the most complicated elements of the considered networks, which is the reason why they are described in a separate

`cs`file; see Section 2.2.2.

#### 2.2.2. The `cs` File

`net`file is given in a

`cs`file. These files describe all compressor machines and their drives. In addition, a list of configurations is given that defines the set of possible interconnections of the machines in the station.

`cs`files, both a parameterization of the fitted functions as well as the measurements are given.

`GasLib`distinguishes two types of compressor machines: turbo and piston compressors. Turbo compressors are described by characteristic diagrams in the $(Q,{H}_{\mathrm{ad}},n,{\eta}_{\mathrm{ad}})$-space, where Q is the volumetric flow rate through the compressor, ${H}_{\mathrm{ad}}$ is the adiabatic change in specific enthalpy, n is the speed of the machine, and ${\eta}_{\mathrm{ad}}$ denotes the adiabatic efficiency of the compression process. The meaning of this quadruple can be summarized as follows: the turbo compressor is able to compress a volumetric flow rate Q with an adiabatic change in specific enthalpy ${H}_{\mathrm{ad}}$ using a compressor speed of n and yielding an efficiency of ${\eta}_{\mathrm{ad}}$; see Figure 15.

`characteristicDiagramMeasurements`element of the turbo compressor; see Figure 16. The biquadratic fits are given in the

`cs`file by the coefficients

`n_isoline_coeff_1`,…,

`n_isoline_coeff_9`for the biquadratic isolines of the speed of the machine (solid lines in Figure 15), and the coefficients

`eta_ad_isoline_coeff_1`,…,

`eta_ad_isoline_coeff_9`for the biquadratic isolines of adiabatic efficiency (dashed lines in Figure 15). The upper and lower bounds of the characteristic diagram are given by the isolines of speed together with the minimum speed

`speedMin`as well as the maximum speed

`speedMax`, respectively. The left and right border, that is, the surgeline and the chokeline of the machine, are given separately as quadratic functions (of the volumetric flow rate Q) with coefficients

`surgeline_coeff_1`,…,

`surgeline_coeff_3`and

`chokeline_coeff_1`,…,

`chokeline_coeff_3`, respectively. The chokeline efficiency is given explicitly in the element

`efficiencyOfChokeline`, whereas the surgeline is specified by its measurements contained in the element

`surgelineMeasurements`. These measurements are given by triples of

`speed`,

`adiabaticHead`, and

`volumetricFlowrate`. All other measurements of the characteristic diagram are given in the element

`characteristicDiagramMeasurements`, which lists sets of such triples for every measured

`adiabaticEfficiency`.

`operatingVolume`), which fits into their compression cylinder, and by the minimal speed (

`speedMin`) and maximal speed (

`speedMax`) they can be operated in. Additionally, the maximal torque (

`maximalTorque`) of the piston compressor’s crankshaft, the maximal compression ratio (

`maximalCompressionRatio`), and the adiabatic efficiency (

`adiabaticEfficiency`) of the compression process are specified. The volumetric flow rate through the piston compressor depends on the rotational speed of the crankshaft. Operating the piston compressor at its minimal speed therefore gives a lower bound on the volumetric flow rate. However, for some piston compressors, decreasing the volumetric flow by technical means to a level that is lower than the aforementioned bound is required. If this is the case, the reducing factor is given by the element

`additionalReductionVolFlow`.

`energy_rate_fun_coeff_1`,…,

`energy_rate_fun_coeff_3`and the maximum power function. This depends on the specific drive type if the latter is modeled by a quadratic function of the compressor’s speed (with coefficients

`power_fun_coeff_1`,…,

`power_fun_coeff_3`) or by a biquadratic function of the compressor’s speed and the ambient temperature at the station (with coefficients

`power_fun_coeff_1`,…,

`power_fun_coeff_9`). For exemplary XML specifications, see Figure 18. For further details on modeling drives, we refer the reader to [4,21,29].

`cs`file contains a list of configurations for every compressor station; see Figure 19. A configuration is a serial arrangement of parallel combinations of compressor machines, and the element

`configurations`lists all possible configurations for the corresponding station.

#### 2.2.3. The `cdf` File

`cdf`file optionally complements the

`net`file by describing additional restrictions for the switching of certain sets of controllable elements (

`valve`,

`controlValve`, and

`compressorStation`).

`cdf`file. We call the grouped sets of controllable elements “subnetworks”, and the restrictions of their interplay are called “combined decisions”. A subnetwork is modeled as a

`decisionGroup`in the data format, and the corresponding set of possible switching decisions for the elements of the subnetwork are modeled as a list of the element

`decision`; see Figure 20 for examples. One

`decision`must be chosen, with implications for the arcs in the

`decisionGroup`: For a

`value`of

`0`, the corresponding network element is closed. For a

`value`of

`1`, it is open and maybe active or in bypass mode. Optionally, for each arc, a

`flowDirection`(

`0`or

`1`for backward or forward flow) and a

`mode`(

`active`or

`bypass`) may be given. If a

`decisionGroup`contains only a single

`decision`, this effectively fixes the switching decisions for the affected arcs. This is used, for example, in the

`GasLib-4197`instance to fix certain

`valve`elements that are not remote-controlled.

#### 2.2.4. The `scn` File

`scn`file specifies a demand and supply scenario for a network. Thus, a gas transport instance is only given completely by the combination of a network (with a

`net`, a

`cs`, and an optional

`cdf`file) together with an

`scn`file.

`GasLib`contains a single scenario file for the four small- to medium-scale networks

`GasLib-11`,

`GasLib-24`,

`GasLib-40`, and

`GasLib-135`and many different

`scn`files for the real-world networks

`GasLib-134`,

`GasLib-582`, and

`GasLib-4197`.

`net`and

`scn`files of

`GasLib`are expressed in normal volumetric flow, as this is the standard unit in gas transport.

`source`nodes equals the sum of the discharged flows at the

`sink`nodes. The

`flow`values in all

`scn`files of

`GasLib`are fixed to values that satisfy this balance constraint. Thus, all provided

`scn`files define nominations, as described in the introduction.

`node`in the

`scn`file, a

`type`is specified:

`entry`or

`exit`. Typically, nodes that are a

`source`(

`sink`) in the

`net`file should be an

`entry`(

`exit`) in the

`scn`file. Otherwise, the sign of the corresponding flow value has to be changed.

`pressure`bounds may be specified for the nodes. These bounds should be intersected with the bounds from the

`net`file, that is, the tightest bound holds. Typically, lower pressure bounds are given for exits, and upper pressure bounds are given for entries. Optionally,

`contractPressure`bounds may be specified for further restricting the allowed pressure values.

`scn`file.

## 3. Outlook

`GasLib`are to add more and even larger instances. Moreover, we also plan to provide transient data in the near future. In any case,

`GasLib`will only be successful if it is used. Moreover, we are always grateful for constructive remarks and, of course, for providing new data.

## Acknowledgments

## Author Contributions

`GasLib`. All authors jointly wrote the paper.

## Conflicts of Interest

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Physical/Technical Quantity | Units |
---|---|

Gas flow | ${\mathrm{m}}^{3}\xb7{\mathrm{s}}^{-1}$, ${\mathrm{m}}^{3}\xb7{\mathrm{h}}^{-1}$, 1000 ${\mathrm{m}}^{3}\xb7{\mathrm{h}}^{-1}$, … |

Gas temperature | ${}^{\xb0}$C, $\mathrm{K}$, … |

Length | $\mathrm{mm}$, $\mathrm{cm}$, $\mathrm{m}$, $\mathrm{km}$, … |

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## Share and Cite

**MDPI and ACS Style**

Schmidt, M.; Aßmann, D.; Burlacu, R.; Humpola, J.; Joormann, I.; Kanelakis, N.; Koch, T.; Oucherif, D.; Pfetsch, M.E.; Schewe, L.; Schwarz, R.; Sirvent, M. GasLib—A Library of Gas Network Instances. *Data* **2017**, *2*, 40.
https://doi.org/10.3390/data2040040

**AMA Style**

Schmidt M, Aßmann D, Burlacu R, Humpola J, Joormann I, Kanelakis N, Koch T, Oucherif D, Pfetsch ME, Schewe L, Schwarz R, Sirvent M. GasLib—A Library of Gas Network Instances. *Data*. 2017; 2(4):40.
https://doi.org/10.3390/data2040040

**Chicago/Turabian Style**

Schmidt, Martin, Denis Aßmann, Robert Burlacu, Jesco Humpola, Imke Joormann, Nikolaos Kanelakis, Thorsten Koch, Djamal Oucherif, Marc E. Pfetsch, Lars Schewe, Robert Schwarz, and Mathias Sirvent. 2017. "GasLib—A Library of Gas Network Instances" *Data* 2, no. 4: 40.
https://doi.org/10.3390/data2040040