Study On Pyrolysis And NO Precipitation Characteristics Of Large Coal Particles In Low Oxygen Atmosphere

China’s current energy situation determines that coal will still be the mainstay of the country’s energy consumption in the future,and the development of clean and efficient use of coal is still the focus of the current stage.The current status of energy consumption in China has led to a certain proportion of the use of large-particle coal in the process of coal utilization.Decoupling combustion technology is a clean coal technology with high efficiency and low pollution emission,which has certain guiding significance for the utilization of large particle coal.In this paper,a series of studies on large particle coal are carried out to provide theoretical guidance for efficient and clean utilization of large particle coal.The pyrolysis and volatilization characteristics of bituminous coal were studied.The pyrolysis process of pulverized coal can be divided into three stages.The temperature range of the mass release of volatiles is consistent with that of the active pyrolysis stage according to the thermogravimetric curve.When oxygen concentration is lower than 6%,increasing oxygen can promote CH4 precipitation,while increasing oxygen can promote CO release.The study on the pyrolysis process of large particle coal shows that the increase of reaction temperature and oxygen concentration can promote the generation of pyrolytic gas,and reduce the yield of carbon black and tar at the same time.When the oxygen concentration exceeds 10%,the yield of coke decreases obviously,and when the temperature exceeds 700℃,the influence of temperature on the pyrolysis products increases.The addition of CO2 at low temperature and oxygen concentration can inhibit the precipitation of gas products and promote the production of carbon black and tar.At higher temperatures and oxygen concentrations,the effect is completely opposite.There is a coupling critical value between reaction temperature and oxygen concentration,where CH4 is more sensitive to oxygen.The addition of CO2 can not change the law of gas precipitation with temperature and oxygen concentration,but can affect the total amount of gas precipitation.The distributed activation energy model can well predict the volatiles precipitation during large particle pyrolysis.Then,the pyrolyzed coal char was analyzed.The increase of reaction temperature and oxygen concentration in the pyrolysis process could reduce the volatile content of pyrolyzed coal char gradually and the H/C decreased.When the oxygen concentration is 10%,the gas at 700℃ mainly comes from endophenols,lactones,C-O stretching vibration in anhydride,O-H bending vibration and C-H cleavage of fat.When the pyrolysis reaction temperature is 700℃,the pyrolyzed coal char is easy to ignite.The higher the oxygen concentration in the pyrolysis atmosphere,the less conducive to ignition.Finally,the migration of nitrogen elements in large coal during pyrolysis was studied.Lower concentration of oxygen can promote the precipitation of NH3 and HCN.At lower reaction temperatures,the reduction effect of NO is not obvious,and the release of NO is mainly affected by the formation rate of NO.When the reaction temperature exceeds 800℃,the reduction effect of coke and volatiles on NO increases,and the release of NO is affected.With the increase of particle size,the amount of NO released during coal pyrolysis decreases obviously.During the pyrolysis process,each nitrogen-containing functional group will not only crack and release nitrogen-containing products,but also transform into each other.Homogeneous and heterogeneous reduction processes of NO during low oxygen pyrolysis of large coal particles are one of the main factors affecting NO precipitation.