Implications of Increased Renewable Natural Gas on Appliance Emissions and Stability

This project examines how adding renewable biogas or renewable hydrogen to fossil-derived natural gas affects the performance of commercial and residential appliances. Displacing fossil natural gas with renewable gas decreases the net carbon emissions of these devices. Adding renewable biogas or hydrogen to the existing natural gas infrastructure can also help with near-term, low-cost carbon emissions reduction. The project included studies for nine typical combustion-based appliances with an unknown fuel mix: cooktop burner, oven burner, gas fireplace, low-oxides-of-nitrogen storage water heater, tankless water heater, space heater, pool heater, outdoor grill, and laundry dryer. The results showed that all devices can accept some level of biogas or hydrogen. Generally, adding renewable fuels tends to reduce emissions of oxides of nitrogen, carbon dioxide, and unburned hydrocarbons. Overall, the project results indicated that 5 percent to 10 percent (by volume) of hydrogen could be added without affecting general operation of these devices. The limiting behavior is flashback upon ignition or relight. Up to 10 percent biogas can be added but degraded cooking efficiency and flame stability so adding hydrogen is preferable from an operational and performance viewpoint. Adding 10 percent hydrogen to the existing natural gas infrastructure would remove 1.28 million tons of carbon dioxide emissions, equivalent to removing 278,000 gasoline vehicles from the road.