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Fuel flexibility analysis of conventional and low-NOx gas water heater burners on renewable fuel introduction

Creative Commons 'BY-SA' version 4.0 license

Residential water heating is the single most significant end-use for natural gas in California-- more than half of the net energy consumption for a typical Californian household goes into fulfilling hot water demands. Aided by cost-effective natural gas available in the state, about 90% of water heaters are natural gas-fueled storage tank systems, with 40-50-gallon capacity. In order to decarbonize residential spaces, a strong focus on water heating is essential.

This research focuses on the impact of renewable fuel (biogas and renewable hydrogen) injection into pipelines for gas-fired storage water heaters. Two representative models of storage water heaters were chosen for experiments. First, a conventional storage unit; meeting 40 ng/J NOx emission requirement, second, a low-NOx storage water heater meeting 10 ng/J NOx emission requirement. This research answers how much CO2/H2 content in natural gas can be tolerated without loss of critical performance parameters with reliable operation.

Characteristics like ignition delay, flashback, blow-off, ignition, flame structure, and emissions (NO2, N2O, NO, CO, CO2, UHC, and NH3) at different concentrations of CO2/H2 mixed with natural gas is investigated. The study found less than 10% H2 tolerance for both the water heaters, less than 15% CO2 tolerance for low-NOx water heater and no CO2 tolerance for the conventional storage model. NOx/NO emission reduction is achieved for both the water heaters with increased CO2/H2 and a simultaneous CO/UHC increase is observed. Further, both the water heater emission and stability performance were simulated using a chemical reactor network (CRN).

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