Investigation on boiler efficiency and pollutant emissions of water/heavy oil emulsions using edge-tone resonant homogenizer

Water/heavy oil emulsion prepared by an edge-tone resonant homogenizer without a surfactant is investigated. The three aims of this study are: (1) the spectrum analysis of pressure vibration inside the resonant chamber of the homogenizer, (2) the production of droplets with the desired mean size and a suitable distribution, and (3) the determination of the boiler efficiency using a thermal input–output method. The homogenizer is designed to generate resonant vibrations through the interaction between the jet exit and a knife-like blade under the conditions of high temperature and pressure. The desired mean droplet size (on the order of micrometers) and the proper size distribution for the water/heavy oil emulsion are achieved using the homogenizer. It is found that the amplitude of pressure fluctuation is at its maximum at the first-stage resonant frequency. The boiler efficiency calculated using the thermal input–output method shows that the water/heavy oil emulsion has the potential to reduce energy consumption by 15% compared to that obtained with pure heavy oil. The NOx emissions in the boiler furnace increase with increasing amount of excess air. Additionally, lower CO emissions are found for the boiler firing water/heavy oil emulsions because of the occurrence of micro-explosion, also known as secondary atomization.