Research On Combustion-Supporting Characteristic Of Oxygen In Process Of Boiler Starting-up And Combustion-Stabilizing

China is lack of fuel oil resource and have to import the large amount of oil every year. However, power plant boiler consumes vast fuel oil in the process of cold starting-up and combustion-stabilizing. Therefore, the study on new oil saving technology is great practical significance.Aiming at the above-mentioned problems, a new method of substituting oil with oxygen is proposed, which introduce oxygen into the combustion process of pulverized coal stream, the method take full advantage of combustion-supporting performance of oxygen to improve the ignition characteristics of pulverized coal stream, realizing the purpose of reducing the oil consumption in power plant boiler.The main research contents and conclusions of this dissertation are as follows:1. Oxygen-enriched combustion theory of the pulverized coal stream in specific oxygen atmosphere is studied. And this part included four aspects:(1)The influence of oxygen concentration on combustion mode of the pulverized coal is analyzed with the help of mathematical model. The research results shows that the increase of oxygen concentration will change combustion mode of the pulverized coal from homogeneous phase ignition to heterogeneous phase ignition. (2)The formula of the heating time of pulverized coal stream is derived, the calculation results show that the heating time of pulverized coal is reduced by 80% when the fuel flame temperature rises from 1000℃ to 2000℃,which prove that increasing the flame temperature with the help of oxygen is an effective method to reduce the the heating time of pulverized coal stream. (3)The relationship among the reaction rate constant k of pulverized coal combustion, reaction temperature and oxygen concentration is analyzed, the research results shows that the combustion reaction rate constant k increases 11.56 times when the flame temperature rises from 1000℃ to 2000℃, which prove that increasing the flame temperature with the help of oxygen is an effective method to accelerate the combustion speed of pulverized coal. (4)The influence of oxygen concentration on the ignition heat of the pulverized coal stream is analyzed, which indicates that the ignition heat of the pulverized coal stream in pure oxygen condition is half of that in air condition.2. The method of high-temperature oxygen ignition is proposed. In a special designed high-temperature oxygen generator, a tiny amount of oil is ignited to heat oxygen up to high-temperature state as high as 1480 ℃, then the high-temperature oxygen is injected into pulverized coal burner to ignite the inferior pulverized coal steam. This dissertation adopted the research methods of thermal state ignition experiments and simulation to verify the feasibility and effectiveness of the described technology. In the experiments part, the features of high-temperature oxygen generator is tested firstly, then Jinzhong lean coal and Yangquan Anthracite from Shanxi Province is chosen as experimental coal to conduct pulverized coal ignition experiments under various working conditions. It is proved that high-temperature oxygen is able to ignite inferior pulverized coal, and furthermore, the optimal heat source parameter of the method is provided. In the simulation part, high-temperature generator is simulated to obtain the distribution characteristics of several major parameters, such as velocity, temperature, oxygen concentration, etc. After that, Yangquan anthracite is selected as research object to be simulated under the same conditions, which theoretically proved that the method is feasible and effective to ignite the pulverized coal.3. The application of high temperature oxygen ignition technology in W-flame boiler is studied with the method of simulation. The combustion characteristic of cyclone burner is simulated, summarizing the performance feature of the burner. The research results shows that the high-temperature oxygen is capable to ignite the pulverized anthracite stream in W-shape flame boiler. Thus the technology is a new and effective ignition method of oil-saving for W-flame boiler.4. The superhigh-temperature flame ignition method is put forward. The feature of this method is to support diesel oil combustion with a part of oxygen, which produce a pure white flame with the temperature of 1895℃, and the rest oxygen is injected to the pulverized coal stream to creat the oxygen-enriched atmosphere. The performance feature of the super-high temperature flame generator is tested by hot-state experiment, revealing the inner relations among flame temperature, oil flow rate, oxygen flow rate. The practical application of the method is introduced through an example of swirl-opposed boiler firing inferior-coal (300MW unit) and the optimal pulverized coal concentration rage and coal-oxygen flow rate are concluded. The performance of the method are tested in process of boiler start-up, the low carbon content in the fly ash and the reasonable curves of boiler starting-up validate that the method is appropriate for the boiler firing inferior coal.5. A stabling combustion method that replace fuel oil with oxygen is presented. Pure oxygen will be sent to the dense pulverized coal stream in burner, forming a partial oxygen enrichment atmosphere in which the ignition characteristics of pulverized coal stream is improve. Research method of numerical simulation is adopted. It is studied that the mixture distribution character of the pure oxygen and pulverized coal stream in burner, which research result reveals inner relationship of the oxygen-injecting position and oxygen-enriched concentration, oxygen-enriched range. The combustion-stabilized effects of oxygen under different working conditions are analyzed. Through the data analysis for the distribution characteristics of temperature field and CO2 concentration field, the ignition distance of pulverized coal stream are compared under different condition through the variation of the oxygen flow and oxygen-injected position, and then the required minimum oxygen flow to stabiliz combustion and the optimal oxygen-injected position in the simulated conditions are summarized. The simulated results proves that stabilizing combustion with oxygen instead of oil is feasible in condition of the oxygen flow rate is 600Nm3/h.