Influence of Blending Hydrogen and Biogas Into Natural Gas on the Combustion Performance of a Tankless Water Heater

Abstract

Utilizing renewable gases including biogas and renewable hydrogen instead of natural gas helps reduce greenhouse gases from fossil fuel combustion. Due to the fuel property variation, it is not practical to replace pipeline natural gas with these renewable fuels while still keeping the combustion devices at its designed operating condition. Therefore, this study mixes renewable hydrogen and simulated biogas into pipeline natural gas and investigates the combustion performance of a commercial tankless water heater. Up to around 10 vol% carbon dioxide and 20 vol% hydrogen are mixed into natural gas, then the mixtures are supplied to the water heater. Appliance performance such as operability, emissions (CO, UHC, NO, NO2, N2O, NH3) and efficiency are examined. The feasibility of injecting renewable gases into the existing natural gas infrastructure is evaluated from the perspective of the representative tankless water heater performance. The results show a positive sign for mixing hydrogen into pipeline natural gas, due to the small variation of the water heater emissions and an increase of the efficiency.