From Natural Gas to H₂: Hydrogen Combined Heat and Power Plants (CHP) and Their Valves

What is a CHP? The Principle of Cogeneration 

A combined heat and power plant (CHP) is a compact system for the simultaneous generation of electricity and heat. It operates on the principle of cogeneration: Unlike conventional power plants, which often release the heat generated during electricity production unused into the environment, a CHP deliberately utilizes this thermal energy – for heating systems or industrial processes.

The heart of a CHP is typically a combustion engine that drives a generator to produce electricity. The resulting engine waste heat is transferred to the heating network via a heat exchanger. This dual use enables CHPs to achieve overall efficiency ratings of up to 90 percent, while conventional power plants only reach 30-60%. CHPs are often installed close to consumers, with their size varying according to purpose. There are small systems for single-family homes, medium-sized systems for commercial operations and public facilities, as well as large systems for industrial processes. 

Conventional CHPs run on various fuels. Natural gas is most commonly used due to its high availability and relatively clean combustion. Additionally, liquid petroleum gas (especially in areas without natural gas connections), biogas, heating oil, and in special engines, vegetable oil or rapeseed oil are also used. More recently, hydrogen has been gaining importance.

Hydrogen CHP: Advantages of an Alternative Fuel 

Hydrogen-powered CHPs combine the advantages of decentralized cogeneration technology with the possibility of potentially CO₂-neutral energy supply. Unlike conventional CHPs, they use either pure hydrogen or hydrogen-natural gas mixtures. The electrical efficiency of modern systems is up to 45 percent, while the overall efficiency can rise to over 90 percent through heat utilization.

A pioneering achievement in practical application was accomplished by CHP manufacturer 2G Energy in 2019 with the Haßfurt Municipal Utilities: The company from Westphalia expanded an existing power-to-gas plant with a hydrogen CHP for reconverting regeneratively produced hydrogen into electricity.

The integrated hydrogen storage enables continuous operation of the plant for about 12 hours. Additionally, the CHP has a second gas connection to switch to natural gas operation if necessary. A plus point is therefore the flexibility of the overall system: If hydrogen is available, the CHP works with it – and if it runs out, it uses natural gas. The project was scientifically supervised by the Institute for Energy Technology at the East Bavarian Technical University of Amberg-Weiden to gain practical insights into hydrogen operation. For 2G, this was already their second hydrogen CHP: In 2012, the manufacturer had already installed a system at BER Airport in Berlin – one of the first ever. 

Since 2020, Tyrolean manufacturer INNIO Jenbacher has also been offering its gas engines for CHPs with a "Ready for H2" option, which allows a 25% hydrogen blend and later conversion from natural gas to 100% hydrogen. In a high-profile test run, a converted Jenbacher CHP was already operated with up to 100% hydrogen for several weeks.

A demonstrative project went into operation in October 2024 in Gampern, Upper Austria: Gas storage operator RAG Austria AG is using a 1 MW hydrogen CHP from INNIO Jenbacher there. What makes this special: At the site, hydrogen is produced in summer using solar power and stored in an underground porous rock reservoir. During the heating period, it is extracted and converted into electricity and heat in the CHP. The underground porous reservoir should be able to hold surplus solar electricity with a volume of up to 4.2 GWh in hydrogen form. This corresponds to the production of about 1,000 residential-scale PV systems over the course of a summer. 

Challenges for Valve Technology 

The physical properties of hydrogen place high demands on the components installed in the CHP. The first and most important is tightness: With a molecular diameter of only 0.24 nm, hydrogen is extremely diffusible and can penetrate even the smallest gaps. Standards from the natural gas sector cannot simply be adopted: Valves and control fittings for hydrogen CHPs must comply with much stricter leakage rates. This in turn has direct implications for the sealing materials and concepts used.

Another critical issue is material selection. Many materials used in conventional valves are unsuitable for hydrogen applications as they tend to suffer from hydrogen embrittlement. This phenomenon, in which hydrogen atoms penetrate the metal lattice and alter the mechanical properties, can lead to sudden material failure. Austenitic stainless steels with increased nickel content are therefore preferably used for hydrogen valves. Alternatively, special coatings or completely different material concepts such as ceramic-metal composites are being developed and used.

For this reason, corrosion-resistant pipes and fittings are essential in the fuel system. Highly precise pressure control valves are also needed for the safe control of hydrogen pressure, while only special delivery pumps and filters ensure a stable fuel supply. 

Safety is the Top Priority 

In addition, hydrogen CHPs require a sophisticated system of safety valves – particularly due to the wide ignition limits of hydrogen (4 to 76 volume percent in air) and the very low ignition energy required to ignite the gas. Quick-closing valves that interrupt the hydrogen supply within fractions of a second during malfunctions, pressure relief valves to protect against inadmissible pressure increases, and backflow preventers that prevent flame flashback into the supply line are therefore required.

In engine and fuel preparation, heat-resistant cylinder head valves are designed to prevent unwanted ignitions. The injection system requires precise injection nozzles for controlled combustion. Particularly critical are fuel supply lines and mixture preparation: Here, the valves must not only be absolutely tight but also have precise control characteristics that ensure an optimal air-hydrogen mixture. It is important that the control valves deliver consistent performance under highly fluctuating operating conditions.

Retrofitting or New Procurement? 

When converting existing CHP plants to hydrogen, operators often face the question: Retrofitting or complete replacement of valves? The answer depends significantly on the planned hydrogen content. Generally, with a hydrogen content of up to 30 percent, retrofitting existing natural gas valves is usually possible. If the content is between 30 and 75 percent, more comprehensive adaptations are often required, while with a hydrogen content above 75 percent, new procurement of valves is usually recommended.

Decisive for these thresholds are the requirements from mechanical explosion protection due to the change in gas group. According to studies by the Federal Institute for Materials Research and Testing (BAM), the maximum experimental safe gap behaves almost linearly to the ratio of natural gas to hydrogen: At about 30 percent hydrogen blending, the explosion subgroup changes from IIA to IIB, and at around 75 percent, from IIB to IIC.

This change affects the requirements for valves. With a higher hydrogen concentration, there is a greater risk that, for example, at spindle seals, too much heat is generated during frequent and rapid operation, which could cause ignition of the flammable medium. To prevent this, among other things, the gap dimensions must be reduced to prevent flame propagation.

Outlook: Standardization as the Key to Success 

The future of hydrogen CHPs will depend significantly on the performance and reliability of the valves used, because ultimately, every hydrogen project stands or falls with the quality of its components. However, better standardization is necessary for the further development of the market. Various standardization committees are currently working on specific standards for hydrogen valves. The "Hydrogen Technologies Standardization Roadmap" initiated by the Federal Ministry of Economics explicitly addresses the CHP sector.

In this context, the Valve World Expo is becoming an important industry meeting point to promote exchange between manufacturers, users, and standardization experts. With numerous technical presentations, product presentations, and a wide selection of hydrogen valves, the trade fair in December 2026 will provide an overview of the current state of the art.

For more information on Valve World Expo 2025, visit www.valveworldexpo.com