Experimental Study on the Co-Combustion Characteristics of Brown Gas (HHO) and Bituminous Coal/Anthracite with Different Injection Modes in a One-Dimensional Furnace

As the energy structure evolves, low-load operation of coal-fired boilers is becoming common, posing challenges to combustion stability. This study explored the co-combustion of brown gas (HHO) with bituminous coal and anthracite in a one-dimensional furnace. Results indicate that introducing HHO significantly elevated combustion temperatures, with maximum increases of 158 °C and 207 °C, respectively. In the premixed mode, the flame front shifted upstream, indicating advanced ignition timing. Moreover, HHO co-combustion notably enhanced the combustion stability of anthracite, as reflected in stabilized furnace temperatures. With increasing HHO flow rate, CO concentrations from both bituminous coal and anthracite were reduced by over 80%. The combustion efficiency of bituminous coal reached 98%, while the combustion efficiency of anthracite increased by 19% (premixed) and 13% (staged), confirming the premixed mode’s superiority in promoting complete combustion. HHO co-combustion increased SO2 emissions but had a complex effect on NOX emissions due to the competition between NOX reduction caused by HHO and NOX formation caused by the increased combustion temperature. HHO co-combustion changed the melting point of fly ash, increased the content of Al2O3, and reduced the content of Na2O, K2O, and MgO, influencing the slagging behavior of the boiler and the subsequent management of fly ash.