Sustainably heating up the industry

Porous radiation burners provide heat for industrial applications for drying and heating. In conventional operation with natural gas, a gas-air mixture is ignited and burned in the burner chamber. Combustion takes place almost flamelessly within a porous ceramic plate. As a result, this molded body heats up, begins to glow and radiates heat at a high intensity. The temperature of the burner is controlled by the ratio of air and natural gas. Several individual burners are usually connected in a row to form a burner field, creating a large glowing surface of up to 100 burners. Managing Director Heiko Schneider gives an insight into the GoGaS customer base: "Due to their very high radiation output of up to 1,000 kw/m², such burners are mainly used in drying and heating systems, for example in the paper industry for drying coated papers, in the paint and textile industry, in glass forming or in the steel industry for metal coating."

Alternative technologies, such as infrared burners as surface burners, are physically limited to around 1,000 degrees Celsius. For processes that require much more heat, porous radiation burners with up to 1,400 degrees Celsius are indispensable. The joint development project WAPS has succeeded in producing a new type of hydrogen porous radiation burner. For the first time, the burner can be operated flexibly with hydrogen and natural gas (dual fuel), enabling carbon-free operation within high-temperature technologies. Schneider emphasizes: "With the porous burners, we achieve much more intensive irradiation and thus enable shorter dwell times and faster processes for industry. The icing on the cake is now the hydrogen operation."

From the goal to the solution

Projektleiter Weis vom KIT erklärt: „In der technischen Entwicklung ging es darum, den Zulauf des Brenners auf ein anderes Medium umzustellen. Die Schwierigkeit dabei war, beim Funktionsprinzip des Porenbrenners den unterschiedlichen verbrennungstechnischen und physikalischen Eigenschaften von Erdgas und Wasserstoff gerecht zu werden. Wenn ich Wasserstoff anstatt Erdgas benutze, hat das natürlich unmittelbar Einfluss auf weitere Komponenten.“ Zusätzlich zur bestehenden Erdgaszufuhr im Zentrum des Brenners wurde eine separate Zufuhr für reinen Wasserstoff integriert. „Anders als Erdgas und Luft, die sich in einer Art Vormischzone verbinden und gemischt in die Verbrennungszone gelangen, wird Wasserstoff erst nahe der Verbrennungszone mit der Luft diffundiert. Die Herausforderung lag dabei in der gleichmäßigen Verteilung von Wasserstoff und der Mischung mit der Luft in diesem lokal begrenzten Bereich“, so Weis weiter. Die Forschenden vom EBI fanden die Lösung in einer mehrschichtigen Misch- und Verteileinheit aus einem metallischen Werkstoff, die zwischen Vormischzone und Keramik platziert ist.

„Beim neuen Brenner ist die oberste, poröse Keramikschicht nahezu identisch zu konventionellen Produkten. Den Unterschied macht unser darunterliegender Multi-Layer als Hauptverteiler. Er besteht zum einen aus mehreren verbundenen Feinverteilerplatten mit sehr kleinen, gefrästen Kanälen senkrecht zur Hauptströmungsrichtung für das Wasserstoffgas. Zum anderen ist er mit einer Lochplatte mit Bohrungen für die Luftzufuhr aus der vorgelagerten Vormischzone versehen. Indem wir erst kurz vor der porösen Keramik den Wasserstoff dazugeben, vermeiden wir potenzielle Flammenrückschläge“, führt der Verbrennungstechniker Weis aus. Die vielen feinen Kanäle der Metallschichten dienen einerseits dazu, den sauberen Brennstoff flächendeckend zu verteilen, andererseits auch zur thermischen Entkopplung. Über die Strömung wird gleichzeitig aktiv das Gehäuse gekühlt, sodass die Wärmeenergie zielgerichtet abstrahlt.

Upgrade for high-temperature technologies

Schneider is pleased to report: "The good thing about this is that the natural gas-air path can be followed in the old way in fossil fuel mode. The natural gas-air mixture flows through the larger holes in the perforated plate as usual. This means that the porous burner can continue to be operated with natural gas without any problems." Weis adds: "Despite the new technology, we are sticking to the dimensions of existing products. The new porous radiant burners are therefore recommended both for new installations and for retrofitting relatively old systems." Schneider from GoGaS, the Dortmund-based specialist for heating technology, sees a further advantage: "Compared to a natural gas burner, the hydrogen burner has more than twice the heat transfer coefficient. This means that the heating process only takes half as long."

Preparations for the future of hydrogen

The great interest in hydrogen technologies that Schneider encounters in his company is still disproportionate to the availability of hydrogen: "When asked whether we offer hydrogen solutions, I often respond with the counter-question of whether the gas is always available. And no customer can say yes to that at the moment. Until a hydrogen network can be expanded and operated in a stable manner, I believe it is absolutely essential to offer a porous radiator that can do both. We listen to our customers and try to offer the best possible solutions. In KIT, we have found a committed partner who specializes in developing solutions." The experts from EBI made a significant contribution to the implementation and technical development. "Although the framework conditions for completely carbon-free operation are generally not yet in place, it is the right step to become less dependent on available fuels. With the help of dual-fuel technology, different fuels can be used flexibly. This means that as soon as hydrogen is available, I can switch the heater from natural gas to hydrogen and become CO2-neutral in no time at all," emphasizes Weis.

Hydrogen burners on the road to success

However, the cooperation project not only focused on the functionality of the burner, but also on production technology and cost-effectiveness. Over the course of the project, a wide variety of techniques were experimented with, such as diffusion bonding and selective laser melting (SLM), also known as 3D metal printing. Weis looks back: "We manufactured the new hydrogen pore burner using different techniques and investigated how well it works. For example, we looked at heat radiation, flame propagation and material stability. The best results were achieved with the multi-layer variant, for which we then further optimized the production technology." From the outset, the prerequisite and objective was that the new product could ultimately be finished using GoGaS production systems. The medium-sized company makes it clear: " With the developed dual-fuel pore burner, we offer a solution for drying systems to replace climate-damaging natural gas. We have a lot of customers who are still using conventional porous burners at the moment. Our aim is to get the pricing right so that customers from industry and research can buy the new technology for a relatively low additional price in order to gradually replace conventional natural gas pore heaters. A good investment in the future of hydrogen!"