Experimental investigation of the thermal behavior for oxy-fired and air-fired high temperature furnaces for the vitreous ceramic industry

•Specific Energy Consumption of 3.9 MJ/kg for oxy-combustion, twice lower than the air-fired process.•Higher emission of tons of CO2 per ton of product for the air-fired furnace.•Higher concentration of NO ppm per ton of product for the oxy-fuel furnace.•Load, flue gas and walls absorb most of the energy in the oxy-combustion, respectively.•Flue gas, load and walls absorb most of the energy for air-fired conditions, respectively.•Presence of air infiltration in the operation of oxy-fired furnace. Oxy-fired and air-fired furnaces are commonly employed in the ceramic and glass industry due to the high temperature and intensive energy required for the melting of glassy material. In this work an experimental analysis of a 0.96 MW oxy-fired furnace is presented and compared to the experimental analysis of two others: a 1.3 MW air-fired furnace and a 1.0 MW oxy-fired furnace. All three furnaces are used in the ceramic industry with operational temperature between 1200 and 1500 °C, processing a similar product and with equivalent dimensions. Experimental results for the presented oxy-fired furnace indicate an elevated mass flow infiltration of ambient air due to negative manometric pressure inside the combustion chamber. The release of CO2 by the load was detected and quantified. Comparison between the three furnaces show that the oxy-fired furnaces have higher efficiency with an energy input per kilogram of product of approximately one half of the one encountered for the air-fired furnace. Emission of CO2 and NO were measured and results indicate higher emission of tons of CO2 per ton of product for the air-fired furnace, while higher concentration of NO ppm per kg/h of product for the oxy-fuel furnace. Dissimilar behavior was found in the energy distribution among furnaces. For the air-fired furnace most of the energy is lost through the flue gas while for the oxy-fired furnaces most of the energy leaves the furnace with the load, indicating more available energy for the load processing. The results are interesting for understanding the behavior of industrial furnaces with different oxidizers and can be used for operational cost estimation and design of new equipment.