Experimental Study on Hydrogen‐Blended Combustion of In‐Service Gas‐Fired Heating and Hot Water Boilers

Against the backdrop of the “carbon peaking and carbon neutrality” goals, hydrogen‐blended natural gas (HBNG) has emerged as a pivotal pathway for the low‐carbon transition of the gas industry. However, the combustion characteristics of HBNG in in‐service gas‐fired heating and hot‐water boilers remain underexplored, particularly regarding systematic experimental data on combustion stability, pollutant emissions, and thermal performance under high hydrogen blending ratios. To investigate the combustion characteristics of gas‐fired heating and hot‐water boilers using HBNG, the paper established an experimental system; typical in‐service conventional atmospheric gas‐fired boilers, as well as fully premixed condensing gas‐fired boilers, were selected as test samples; pure methane (0% H 2 + 100% CH 4 ) and blends of 20% H 2 + 80% CH 4 , 40% H 2 + 60% CH 4 , 60% H 2 + 40% CH 4 were used as test gas. Experiments were conducted on heat input, thermal efficiency, exhaust gas temperature, combustion products (O 2 , CO 2 , CO, NO x ), combustion flame, ignition flame, ignition, and operational noise. The results indicate that the thermal performance under hydrogen blending can still meet the requirements stipulated in the corresponding national standard GB 25034. However, several issues were identified: as the hydrogen blending ratio increased, noticeable flame light‐back was observed in the atmospheric boilers; the length of the combustion flame gradually shortened, with a maximum reduction of nearly 70%. One boiler experienced momentary deflagration when the gas source was 60% hydrogen, and abnormal noise was observed during the operation of some prototypes. It was confirmed that the use of hydrogen‐blended gas in in‐service heating boilers alters the original combustion process. This study reveals the influence of hydrogen blending ratios on the combustion and heat transfer of in‐service gas‐fired boilers, providing a reference for proposing optimization methods for the combustion and heat transfer of in‐service boilers using hydrogen‐blended gas.