Mixing unit burns natural gas with particularly low emissions

A gas-air mixing unit - manufactured in an additive process - promises a reduction of the nitrogen oxide value by a factor of ten below the maximum permitted limit value. And all this without any further catalytic reductions in the combustion process. This is how the component works.

The physical basis of combustion is that the cleaner the combustion of two gases is, the fewer foreign residues there are. This is exactly where Kueppers Solutions, in cooperation with RWTH Aachen University, comes in. The company from Gelsenkirchen is developing a gas-air mixer which ensures that almost no NOx residues occur compared to normal burners. Through a special feed of the gases to be burned, a clean air flow is created. This burns at maximum efficiency on the one hand and ensures uniform heating in the furnace on the other.

The component primarily mixes the fuel gas and oxygen in a star pattern, which then distributes the gases evenly over the largest possible space. A further, angled metal disc additionally swirls the mixture in order to achieve an optimum level of efficiency.

Furthermore, the system uses combustion air, which can be preheated in advance with the exhaust gas by means of a heat exchanger. This increases the overall efficiency; however, more nitrogen oxides will be emitted.

The component, which was manufactured using the laser sintering process, was researched between 2017 and 2019. A first prototype consisted of hundreds of individual nozzles that were to distribute the gases evenly. The performance of the gas mixer was already good. It was the complexity of the component in particular that led to the development of new iterations.

At the end of 2018, the final design was produced, again using a 3D printer. The combustion power that can be achieved with this component is up to 150 kilowatts. The design has been changed from individual nozzles to a multitude of channels, reducing the overall surface area as well as the component, making printing faster and easier.

Due to its small size, the mixing unit can be produced in most selective industrial laser printers. Important factors here are manufacturing accuracy and material strength of the metal powder used.

Kueppers has been building reference plants since the beginning of 2019. With Gelsenwasser and Stadtwerke Bochum, Kueppers has acquired two major partners in the Ruhr area who want to use the technology themselves and sell it in the future. The demand is there - and not only in the industrial sector. Large-scale bakeries, natural gas heating systems and combined heat and power plants are just a few examples where a similar mixing unit could provide advantages.

Due to the standardisation of gas burners in industrial plants, it is also possible to retrofit the technology easily. However, even without constant dimensions, it would be possible to develop a gas mixer equipped for special requirements with just a few iterations. Modernisation is not only worthwhile from the point of view of environmental performance, but also from the point of view of production quality and efficiency. After all, a catalytic converter is no longer absolutely necessary for further exhaust gas purification.

Kueppers Solutions' mixing unit won the award "Top Innovator 2019" in June, presented by science journalist Ranga Yogeshwar. The low-emission combustion convinced the jury, so that Kueppers is now one of the 100 most innovative companies in Germany.

Kueppers Solutions offers the RooN-SI as a mixing unit in a completely finished burner, which has all the positive features of the 3D-printed mixer: Low nitrogen oxide values, compatibility with existing burner systems, flexible use at various temperatures and the possibility of working with combustion air preheated up to 600 degrees.