Experimental Study On Oil Oxy-fuel Combustion Characteristics

Oxy-fuel combustion technology can improve combustion efficiency of boilers and achieve simultaneous control of different pollutants. The flue gas with high CO2concentration can be used for enhanced oil recovery (EOR) which is an economic method for CO2capture and storage. At present, most of the researches about oxy-combustion focus on coal and biomass while little on oil. So, it shows significance to carry out oil oxy-fuel combustion experiment to investigate the flame characteristics, combustion characteristics and kinetic parameters. In our study, two sets of combustion system were established to investigate oxy-fuel combustion characteristics from different aspects.Experiments were carried out on thermogravimetric system to investigate the influences of heating rate, oxygen concentration and inert components on oxy-fuel combustion characteristics and kinetic parameters. Four stages of mass loss during combustion can be observed due to different classes of hydrocarbons. Low molecular mass hydrocarbons release in the first stage; medium molecular mass hydrocarbons are oxidized at low temperature in the second stage; heavy compounds are oxidized rapidly in the third and fourth stages. With the increase of heating rate, the mass loss peaks reduce and heat flux increases in oxidation-combustion stage. At low-temperature zone, oxygen concentration shows little influence on combustion characteristics, while the combustion process is shortened and peaks of DTG and DSC increase with the increase of oxygen concentration at high-temperature zone. Kinetic analysis indicates that activation energy at rapid oxidation stage is higher than that at slow oxidation stage, but it decreases with the increase of oxygen concentration. The results obtained at single heating rate are similar to that got at different heating rates at high-temperature zone, but different at low-temperature zone.Different kinds of fuel oil share some similar combustion principles and models. So we choose the widely used diesel oil to carry out oxy-fuel thermodynamic test in80kW combustion system. Because of its low load, the system is suitable for small-scale test. In this dissertation, the differences under O2/CO2and O2/N2atmospheres are analyzed. Moreover, the influence of oxygen concentration and inert components on flame propagation, temperature field and pollutants emission are investigated. At lower oxygen concentration, the oxy-fuel combustion is not stable. With the increase of oxygen concentration, the flame stability and brightness increase as temperature gradient increasing. Compared with the combustion under O2/N2atmosphere, oxy-fuel combustion shows lower temperature and flame propagation velocity at the same oxygen concentration. Besides, the change of flame shapes is not obvious with the change of oxygen concentration under O2/CO2atmosphere. For pollutants emission, CO and SO2concentration stay at lower levels while NO concentration is much higher under O2/N2atmosphere than that under O2/CO2atmosphere. When the oxygen concentration is at the range31%-33%, oil oxy-fuel combustion could achieve similar flame temperature as air-fuel combustion. However, the required oxygen concentration is relatively lower than that for coal oxy-fuel combustion.