PSI Blog

Into the Future With Hydrogen: Using a New Gas in Old Networks

11 Jun 2020 - Energy, Sustainability

Source: iStock (edited by PSI)
Source: iStock (edited by PSI)

CO2 reduction targets and rising energy prices are necessitating the development of new approaches to how gas networks and pipelines will be used in the future. One such approach is making use of existing infrastructures to transport hydrogen. As a secondary and virtually emission-free source of energy, hydrogen has long been regarded as crucial for the creation of a sustainable energy supply. At PSI, we are supporting network operators by providing the software they need to convert gas network pipelines into hydrogen pipelines.

There are many different ways of producing and storing hydrogen and safely transporting it over long distances. There are now millions of kilometers of pipeline and gas network infrastructure around the world, which play a vital role in our energy supply and will continue to be indispensable in the future.

Hydrogen can be stored for long periods of time with very little loss of energy. For example, electricity generated by wind turbines in  the fall in the north of Germany can be stored using hydrogen and then used by consumers in the south of the country several months later. Network capacity is currently limited which restricts the expansion of renewable energies — but hydrogen could potentially solve this problem in the future.

Safely Turning Gas Network Pipelines into Hydrogen Pipelines

The efficient use of hydrogen has been a key focus at PSI for many years and is part of the company's wider goal of establishing a sustainable energy supply for the future. As early as 1997, our leak detection software  helped the successful operation of the Buna (Schkopau) hydrogen transport pipeline to Böhlen.. In addition to the technical requirements for connecting hydrogen pipelines, different regulatory frameworks had to be taken into account and implemented in the corresponding software.

Since our very first pipeline project, we have been working closely with the relevant experts and monitoring authorities. We use our decades of expert knowledge to guide our customers through the entire process; from obtaining the required operating license to maintaining operations for the long term. The same applies for all other pipelines that are used to safely and reliably transport a wide variety of liquids and gases to their destinations.

Our software helps operators of gas networks and pipelines to integrate hydrogen and other gases, such as bio methane, into the existing infrastructure and track them.

Every Gas Is Different: What Should Be Taken Into Account When Converting the Existing Infrastructure?

When converting gas network pipelines into hydrogen pipelines, it is important to remember that hydrogen and natural gas have very different physical properties. Hydrogen behaves like an ideal gas and has a considerably lower density and significantly lower combustion energy than natural gas. This means that network operators need to transport a considerably larger quantity of hydrogen in order to supply the same amount of energy.

The higher the hydrogen content, the more the gas in the network behaves like an ideal gas. Our software is able to accurately model this behavior.

The diagram below shows the control factor curve when hydrogen is fed into a typical gas.

Simulation Software Enables Precise Calculation of the CO2 Footprint

Every time hydrogen is fed into the gas network, the CO2 content can be accurately tracked during the transportation and calculated for the past, present and immediate future at all offtake points. This is also true for energy networks that utilize the principles of integrated energy, where electricity is used to produce green gas that is then fed into the gas networks. This makes it possible to measure and predict the CO2 footprint of each gas delivery.

Our online simulation software enables the gas composition to be precisely calculated at the relevant intakepoints as well as all other points along the gas network including all offtake points. Furthermore, predictive simulation can be used for extrapolation.

Hydrogen distribution in a network. The different colors represent different hydrogen levels, graded in 10 percent intervals: blue represents a low level and red a high level. Source: PSI
Hydrogen distribution in a network. The different colors represent different hydrogen levels, graded in 10 percent intervals: blue represents a low level and red a high level. Source: PSI

Accurate Characteristic Diagrams are Essential

Characteristic diagrams provide a graphical representation of multiple characteristics of machines that are influenced by variable parameters in a single diagram. These realistic characteristic diagrams are of great importance in determining the optimal mode of operation. Characteristic diagrams display the operating point and operating point history in relation to various different parameters, such as pressure ratio, speed and efficiency.

We have improved the accuracy of the characteristic diagrams in our PSIganopt software and also developed a method for correcting the increasing inaccuracy of the characteristic diagram caused by plant aging. Although the cost of taking accurate compressor readings and approaching operating points throughout the permissible characteristic diagram range is quite high, this cost is worthwhile when compared to the increasing cost of energy and CO2 emissions.

Compressor characteristic diagram with speed curves (black), efficiency curves (green), maximum output power (red), operating point curve (purple) and current operating point (brown dot). This demonstrates the limits of the compressor's working range within which the operating point can fluctuate. Source: PSI
Compressor characteristic diagram with speed curves (black), efficiency curves (green), maximum output power (red), operating point curve (purple) and current operating point (brown dot). This demonstrates the limits of the compressor's working range within which the operating point can fluctuate. Source: PSI

The principles for improving the accuracy of the characteristic diagram are currently being researched intensively as part of the MathEnergy (german only) research project. PSI is part of a consortium of universities and industrial partners jointly researching key mathematical techniques for power supply networks. The objective is to provide faster and more accurate results for simulation as well as to optimize multimodal power supply networks.

Energy Optimization for Compressors

Compressors are by far the largest energy consumers in gas transportation. Energy efficiency can be significantly improved if the correct operating point for each compressor is known at all times and used for operational and setpoint optimization. The provision of this data is just one of the advantages of our software.

Our new characteristic diagram provides users with higher accuracy in budget calculations for compressor use. Thus they are able to determine optimal modes of operation and ideal setpoints for compressors and controllers in steady-state operation.

What is a Compressor?

A compressor is a device used to compress gases. Gases steadily lose pressure while they are being transported from the source to the consumer. Compressor stations help to maintain the required gas pressure by taking the intake volume and compressing it to a smaller volume using the operating pressure. Compressing the gas reduces its volume and thus allows more energy to be transported through the pipelines.

The compressors in use today are designed to transport natural gas. However these compressors, also known as gas turbine engine compressors, are not capable of compressing hydrogen with a similarly high pressure ratio. This means that compressor characteristic diagrams that were originally designed for natural gas need to be adapted to simulate the transportation of hydrogen.

Although there is a way to do this, the laws of similitude are stretched to their limits when converting characteristic diagrams for natural gas into characteristic diagrams for hydrogen. Hydrogen's velocity of sound, for example, is about three times as high as that of natural gas and the standard density is almost ten times lower. This adjustment is sufficient for initial analyses, but when working with high hydrogen levels, the characteristics should instead be measured.

Software Supports the Efficient Transportation of Hydrogen

Since very few companies have experience  transporting hydrogen in large transport networks, determining optimal modes of operation represents a significant planning challenge. This requires help from software-based simulation and optimization tools. Optimizing compressor modes of operation and compressor setpoints allow feasible transport requirements to be determined and evaluated (e.g. using different optimization targets such as increasing energy efficiency, reducing CO2 levels and reducing the number of compressors).

PSI is supporting the HYPOS initiative (german only) by aiming to make hydrogen pipelines cost-effective and suitable for industrial use.

HYPOS Initiative

HYPOS stands for Hydrogen Power Storage & Solutions East Germany and is one of the ten innovation projects of the "Twenty20 — Partnership for Innovation" initiative led by the Federal Ministry of Education and Research. The aim of the project is the manufacture, storage, distribution and widespread use of green hydrogen in the chemical, refining, mobility and energy supply industries.

The importance of hydrogen in securing the energy supply of the future will only increase in the coming years. The operators of pipelines and gas networks are preparing for this reality. For example, research is being conducted into how different hydrogen intakes, e.g. in different quantities, times or locations, affect the gas network.

PSI recognized this development in the industry very early on and adapted our software accordingly. Our software has been successfully used to monitor leaks in  hydrogen transport pipelines for over 20 years. The significance of hydrogen as a source of energy will continue to increase over the coming years thanks in part to the hydrogen strategy of the German Federal Ministry of Education and Research.

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Walter Verhoeven

Manager Gas Simulation and Pipelines PSI Gas & Oil
Telefon +49 201 7476-180