Many manufacturers are working on converting their condensing units to clean energy supply with as few technical changes as possible. Hydrogen is the chemical element with the lowest density, which is why components in condensing boilers have to be adapted. The combustion behavior requires special attention. As the flame speed is eight times higher than with methane, the ignition times in the combustion controller have to be checked and adjusted if necessary. Hydrogen has a lower heating value than methane but its Wobbe index, important for the interchangeability of fuel gas, is almost as high. For an optimal mixture in the venturi, the gas/air ratio controls have to be designed correctly. As a result, the interaction between the gas blowers, venturi and gas valve is of great importance.
NRV 118 ready for H2
The established NRV 118 composite system from ebm-papst is already designed for use with a hydrogen content of up to 10% without any changes. Thanks to a few changes, the composite system is even suitable for use with 100% hydrogen. This has now been proven in several investigations and initial field tests. The leak tightness of the gas valve and blower has been increased and the materials used checked for their suitability. Thanks to a special pre-mixing device, the NRV 118 hydrogen is ideally suited for hydrogen use. The "premix" gas blower compensates for the disadvantage of the lower Wobbe index and calorific value of hydrogen, while at the same time increasing burner pressure loss due to the gas/air mixture upstream of the fan. Complex control cables, as for operation in excess pressure, are not required. Furthermore, higher modulations can be run because the gas valve can be optimally controlled by negative pressure.
It will be some time before the clean fuel can be used extensively for heating, but if developments continue in science, politics and industry, this could become reality in the not-too-distant future.