Formation And Emission Characteristics Of Volatile Organic Compounds During Coal Combustion

Volatile organic compounds（VOCs）are one of the most important atmospheric pollutants.They have poor chemical stability and are easily converted into secondary pollutants such as PM_2.5 and ozone in the atmospheric environment,which can cause haze,photochemical pollution and other atmospheric pollution issue.Coal combustion is an important man-made emission source of VOCs,and the temperature,oxygen concentration,residence time and other factors at the initial stage of pulverized coal combustion will have an important impact on the generation of VOCs.However,due to the limitations of equipment and the difficulty of sampling VOCs,the existing research seldom conducts direct sampling and measurement of VOCs in the early stage of coal combustion and explores the generation mechanism.In this paper,a flat-flame burner reaction platform is built independently,and the VOCs generation characteristics of typical lignite Pingdingshan low-sulfur coal at the initial stage of combustion are explored,and the VOCs emission characteristics of actual coal-fired power plants are obtained.First,based on the flat flame burner reaction platform,the research on the generation characteristics of VOCs in the initial stage of coal combustion was carried out.The qualitative and quantitative analysis of VOCs was carried out using adsorption tube sampling and offline measurement methods,and the influence of combustion temperature on the generation of VOCs was explored.The results show that the organic products of Pingdingshan low-sulfur coal at the initial stage of combustion mainly include aliphatic hydrocarbons（decane,1-undecene,etc.）,monocyclic aromatic hydrocarbons（toluene,1,3-dimethylbenzene,ethylbenzene,etc.）.Cyclic aromatic hydrocarbons（naphthalene,2-methylnaphthalene,1,6-dimethylnaphthalene）and nitrogen/oxygen organics（nonanal,benzonitrile）.The increase in combustion temperature will aggravate the decomposition of active functional groups in unstable compounds such as olefins and oxygen/nitrogen compounds,promote the transfer of compounds to small molecule compounds,and ultimately lead to the reduction of VOCs content and species.Secondly,in order to further explore the effects of the complex furnace environment and various conventional pollutant control equipment on the generation and emission characteristics of VOCs in actual coal-fired power plants,a coal-fired power plant in Wuhan was used to sample VOCs in order to obtain its generation and emission characteristics.The results showed that the aromatic hydrocarbon content was the highest among the 4 measuring points,accounting for more than 30%,Followed by halogenated hydrocarbons,which occupied more than 25%of the concentrations.The total concentration of VOCs is slightly different.The total concentration of VOCs collected at the furnace outlet is 21969.37μg/m³,and the total concentration of VOCs collected at the chimney inlet is 13252.0μg/m³,the total concentration is reduced by 39.68%.Existing conventional pollution control equipment has different effects on VOCs.After passing through the SCR denitration system,the total concentration of VOCs in the flue gas decreases by 41.60%;after passing through the bag dust removal system,the total concentration increases by 27.04%;thanks to the WFGD desulfurization system,the total concentration dropped by 18.69%.It shows that the existing pollution control system has a certain synergistic effect on the removal of VOCs,but the total export concentration is still high,and further targeted treatment is needed.