Experimental Study On Heavy Oil Oxy-fuel Combustion Characteristics

As a technique of the CO2 capture, oxy-fuel combustion has received attentions from scholars since it was put forward. It has a high efficiency of CO2 capture and a relatively good technical advantage of energy saving and emission reduction. The heavy oil oxy-fuel combustion technology can be applied to the oil field steam injection boiler, which can be used to realize the resource utilization of heavy oil and CO2, and also reduce the emission of pollutants by burning heavy oil. At present, there are few studies about the heavy oil oxy-fuel combustion technology, the research of flame characteristics, temperature characteristics and pollutants emission characteristics and the selection of optimum combustion condition are of great significance.The biggest difference between oxy-fuel combustion and air condition is the change of combustion atmosphere and oxygen concentration, the excess air coefficient will be renamed the excess oxygen coefficient in this paper, the increase of oxygen concentration will cause reduction in gas flow. If the gas flow is too low, the jet velocity is insufficient, the stability of combustion flame is poor, it may cause backfire. Increase the gas flow will also increase the excess oxygen coefficient, which means higher oxygen cost. Through the observation of flame and flue gas, select the minimum excess oxygen coefficient of each condition, and then calculate the flue gas volume, the concentration of each composition of flue gas and the average heat capacity of flue gas. The selection result shows that with the increasing of oxygen concentration the minimum excess oxygen coefficient is increased, but the gas flow is reduced. The calculation results show that under 27%～35% oxygen concentration, dry flue gas CO2 concentration can be reached more than 90%. The increase of excess oxygen coefficient leads to more oxygen content remaining in flue gas, the average heat capacity of oxy-fuel combustion flue gas is larger than air combustion, and will increase with the rise of temperature.Experimental study is taken on flame characteristics, temperature characteristics and pollutant emission characteristics under the minimum excess oxygen coefficient. The flame shape and temperature field distribution is most similar to air combustion when the oxygen concentration is at the range of 27%-29%, as the oxygen concentration increased, the flame color is turned from orange to yellow with the flame shortened and thickened, also the flame temperature level increased and high temperature region is closer to the burner. Due to the differences in physical properties of nitrogen and oxygen, the flame propagation speed is slower than air conditon. The overall temperature level of oxy-fuel combustion is lower than that of O2/N2 atmosphere under the same oxygen concentration.For pollutant emission, under the atmosphere of high CO2 concentration, CO as the intermediate product of the combustion process has longer residence time in furnace, the generation of NO in the core reaction zone is inhibited, with the increase of oxygen concentration, combustion rate and the highest concentration value of NO are increased, but the residence time of CO is decreased. The reduction of flue gas volume makes the overall concentration levels of NO rise, but no obvious change in the emission volume under different conditions.Compare with the diesel experiment, they show a roughly same temperature distribution, the combustion speed of diesel is faster than heavy oil, and the flame temperature level is higher than heavy oil, also the temperature change of core reaction region is more intense. In heavy oil experiments NO emission is more than air condition, and in diesel experiment NO emission is about half of the air condition, two experiments get the opposite results, it is considered that fuel may be one of the important factors that influences the formation of NO.The oxygen concentration range suitable for the oil field steam injection boiler is about 27%～31%,The economic performance of technology is limited by crude oil prices, it need careful consideration under the low oil price and the rising domestic production cost.