Combustion of low-calorific waste liquids in high temperature air

Waste liquids with low-calorific values are not easy to burn. In this experiment, a furnace with a pair of burners for high-cycled alternate firing was utilized to burn the low-calorific value liquids. In a 1383 K furnace, 1173 K preheated air was achieved via these burners equipped with regenerators. It was observed that the alternate firing with highly preheated air was an effective way to ignite and burn the low-calorific value liquids. The preheated air temperature was higher than the auto-ignition temperature of the flammable mixture of the waste liquids. The combustion gas temperature in the furnace was quite uniform via the high-cycled alternate firing, resulting in a longer residence time of combustion in the furnace as compared to the conventional incinerator. The convective heat transfer in this furnace was higher than that of the conventional incinerator, and more useful energy was extracted from the waste liquids for end users. For the waste liquids with lower heating values of 15.0 MJ/kg (19 wt.% water) and 10.4 MJ/kg (42 wt.% water), it was found that 49% and 10% of the heating values of the waste liquids, respectively, could be used for utility energy. Furthermore, the waste liquid with a lower heating value of 7.1 MJ/kg (45 wt.% water) could burn itself in this furnace without the need of co-firing of any auxiliary fuels. NO_x and CO emissions were lower than 60 ppmv (6% O₂) and 50 ppmv (6% O₂), respectively, for all tests.