Characteristics of syngas reburning in a natural gas firing furnace - Effects of combustible gas species in the syngas

Co-firing of synthesis gas (syngas) produced from biomass/waste gasification is a promising option for increasing renewable energy production from existing boilers burning fossil fuels. This study presents an experimental approach to utilizing syngas as reburn fuel for NOx emissions reduction. In a 65 kWth furnace firing natural gas, the reburning characteristics for simulated syngas representing main syngas components, such as CH4, CO and H2, were evaluated for co-firing ratios up to 20%. The heating value and gas residence time of the syngas were maintained in the reburn zone by adjusting the N2 concentration. Detailed distribution of temperature, O2 and NOx concentrations within the furnace were measured for the test conditions. The lower stoichiometric ratios of the primary combustion zone by reburning were favorable in reducing NOx formation from the main fuel. Among the syngas components, CH4 was most efficient, exhibiting an immediate decrease in NOx concentration after injection through the formation of HCN. CO and H2 also contributed to the reduction of NOx emissions by suppressing further formation of NOx in the reburn zone. The NOx removal efficiency was diminished by an increase in NOx concentrations in the burnout zone.