Study of high-temperature oxygen combustion (HiTOx) and its heating performance using a laboratory-scale test furnace

•The process is designated as high-temperature oxygen combustion (HiTOx).•HiTOx uses a preheated mixture of O2 and recirculated burned gas.•It provides better heating performance than high-temperature air combustion.•Its high heat flux is attributed to strong gas-phase radiation of H2O and CO2.•Objects with complex external shapes can be heated efficiently and uniformly in HiTOx. High-temperature air combustion technology (HiCOT), which uses air preheated by heat recirculation, has had a great impact on reduction of CO2 and NOx emissions from combustion furnaces. In this study, a lab-scale test furnace was developed to examine the novel combustion method termed as high-temperature oxygen combustion, HiTOx. HiTOx uses combustion with a preheated mixture of oxygen and burned gas. Testing was conducted with liquefied petroleum gas. HiTOx has the following three characteristics because nitrogen is excluded from the working gas: (1) in principle, no thermal NOx is generated; (2) combustion gas is almost entirely water vapor and carbon dioxide, providing better heating performance because of its strong gas-phase radiation; and (3) the method has good compatibility with carbon dioxide capture, utilization and storage (CCUS) technologies because carbon dioxide can be separated easily from the combustion gas of HiTOx furnace by condensation of water vapor. Heating performance tests in a lab-scale test furnace were conducted using stainless steel rectangular rods as heating objects. Gas temperature, object temperature, and heat fluxes on the objects were measured. Compared to HiCOT, HiTOx enables stable operation with a lower flow rate of flue gas, better gas temperature uniformity in the furnace, faster heating, and higher heat flux. The heat flux of HiTOx was slightly higher than that of HiCOT (7%) when the furnace temperature was low (973 K) and the temperature difference between the gas and object was large (280 K). On the other hand, the heat flux of HiTOx was much higher than that of HiCOT (22%) when the furnace temperature was high (1323 K) and the temperature difference was small (60 K). Radiative heat transfer at high temperature was greater in HiTOx than in HiCOT at small temperature difference between the gas and object. A furnace body can be greatly downsized by the good radiation performance of combustion gas in HiTOx, resulting in a remarkable improvement in energy-saving performance.