Study On The Disciminant Index Of Coking Characteristic For Coal Combustion In Stoker-fired Boiler

In China,the industrial stoker-fired boiler is the second most commonly used equipment for coal combustion while the first is the power plant boiler.With the implementation of central heating in major cities,the safe and efficient operation of the stoker-fired boiler has received more and more attention.In the operation of the stoker-fired boiler,the coking problem has been prominent all the time.And the different types of coal show different degrees of coking in the combustion process.At present,the main basis for the coking judgment of coal combustion in the stoker boiler is the char residue characteristic method(CRC).However,because the CRC is not fully combined with the coal quality data and the measurement condition is single,the accuracy of the judgment results remain to be discussed.Therefore,in this paper,based on the data of coal quality characteristics,the results of different experimental conditions including ambient temperature,ambient atmosphere and the residence time,and the synthetic weight mark method,a new discriminant index of coking characteristic for coal combustion in stoker-fired boiler is proposed.In this paper,five coal samples were selected as experimental materials which contained Fuyuan coal,Muleng coal,MianDuhe coal,Sanxinyuan coal and Baorixile coal.The characteristics of coal quality were analyzed by means of proximate analysis,ultimate analysis and maceral analysis.And the coking characteristics of five coal samples were studied by experiments under different conditions were conducted,which included different temperatures(700?,900?,1000?,1200?,1300?),different atmosphere(oxidation and reduction)and different residence time(7min,14 min,21min).and the coking characteristic was analyzed by using the methods of Scanning electron microscopy(SEM),X-ray diffraction(XRD)and X-ray fluorescence(XRF).Moreover,the fusion characteristic of five coal ashes and its effect on coking were analyzed,by the way,the accuracy of some discriminant index of coking were compared.From the analysis of coal quality and experimental results,it is found that in the range of bituminous coal and lignite,with the increase of C/H and FC/V,the CRC value of coal increases,which means the coking characteristics was enhanced.However,the correlation is not linear,there is an extreme value,Indicating that when the degree of coal metamorphosis is much high,such as anthracite,the coking characteristics will be very weak.Based on the maceral analysis,it can be inferred that the vitrinite is the key component of coal for coking.All of the large content,high average reflectance value and high reflectivity distribution interval can represent strong coking characteristic.In the analysis of ash fusion characteristics,it was found that there was a large deviation between the coking prediction results obtained by the ratio of acid to alkali,silicon,silica-alumina,iron-calcium ratio and composite index.Among them,the prediction results of acid-base ratio and silicon ratio are in agreement with the fusion temperature measured by the triangular pyramid method.Moreover,it is concluded that the ambient temperature has an obvious effect on the coking characteristics,which because the high temperature can strengthen the graphitization,make the agglomeration is more dense,and lead to larger amount of amorphous phase eutectic produced.The influence of ambient atmosphere on coking characteristics is mainly reflected in the change of mineral composition in the char,while the residence time has little effect on coking characteristics.Moreover,based on all the test and experimental results,firstly,this paper used the synthetic weight mark method to analyze the influence weight of C/H,FC/V,vitrinite content,vitrinite average reflectance,ash deformation temperature,acid ratio and silica ratio to the coking characteristics.Then the comprehensive index of coal quality was proposed,the empirical equation and the boundaries of discrimination were obtained.Finally,based on the comprehensive index of coal quality and the influence of the external environment on the coking characteristics,the discriminant index of coal coking characteristics of the stoker-fired boiler is further proposed.