Study On The Mixture Pyrolysis Combustion And Heavy Metal Migration Of Coal And Biomass

Biomass is a renewable and large amount of energy with the characteristics of low carbon and clean;Low-quality coal is the coal with high ash content,low volatile content and low calorific value.Some poor quality coal is produced when coal is mined.With the acceleration of industrialization in China,the utilization of biomass and coal is concerned by people from all walks of life.The mixed pyrolysis and combustion of biomass and coal has practical application value.In this paper,corn stalks from Hetao Plain,a grain producing area in Inner Mongolia,and raw coal from Xilinhot Coalfield in Inner Mongolia were selected as raw materials.The main research contents are as follows:First thermogravimetric experiments were carried out on coal and biomass and their mixtures under nitrogen atmosphere to study their pyrolysis characteristics,Kinetic characteristics and synergistic effects.It was found that at the same heating rate,with the increase of corn stalk content,the volatiles were more,the comprehensive pyrolysis index was larger,the pyrolysis performance was better,and the activation energy decreased gradually.In the range of 200℃ to 550℃,the difference of conversion rate increases first and then decreases.When the mixture ratio of coal and corn straw is 8:2,the volatiles from coal samples can be precipitated in advance most obviously.At the same mixing ratio,the weight loss rate of volatilization analysis in pyrolysis stage is the largest and its ratio of total weight loss is the highest.When the heating rate is 15 K/min,the weight loss ratio of volatilization analysis is the largest.Second thermogravimetric experiments were carried out on coal,biomass and their mixtures under air atmosphere to study their combustion characteristics,Kinetic characteristics and synergistic effects.It was found that the weightlessness changes of coal and corn stalk were different when they were burned alone.At the same heating rate,with the increase of the content of corn straw,the overall combustion performance of the samples after mixed firing improved,but the activation energy in the high temperature section decreased,and the catalytic effect increased first and then decreased.When the mixture ratio of coal and corn straw was 8:2,the catalytic effect reached the maximum.At the same mixing ratio,the ignition temperature,flammability index and comprehensive combustion characteristic index all increased with the increase of heating rate,and the heat release showed a trend of first increasing and then decreasing,and the heat release reached the maximum when the heating rate was 15 K/min.Finally inductively Coupled Plasma Mass Spectrometer(ICP-MS)was used to determine the content of heavy metals in ash samples after combustion.The results show that the Hg element exists in the gas phase at 900℃.With the increase of corn straw content,the ash formation rate decreased gradually,the release rate of As and Cd increased,the release rate of Zn decreased,and the release rate of volatile heavy metals(Co,Ni,Cu,Mn)decreased.Different residence times have different effects on different heavy metal elements,especially on semi-volatile heavy metal elements,especially Pb elements,but less on difficult volatile metal elements.