Pyrolysis And Combustion Characteristics And Their Kinetic Analysis Of Coal Slime And Sewage Sludge

Sewage sludge(SS)and coal slime(CS)are solid combustible wastes with high water content.After drying,they can be used by thermochemical conversion processes such as pyrolysis and combustion to recover heat energy or produce high value-added products.In this paper,two kinds of SS and one kind of CS were selected to investigate their pyrolysis and combustion performance by thermal gravimetric analyzer,and the kinetic characteristics of typical processes were analyzed.Gauss function was used to analyze the pyrolysis process of dried SS and CS.The results showed that the pyrolysis process of dried SS and CS included the following stages:(1)Below 300℃ the release of bound water and decomposition of carboxylic acid groups were the main processes.(2)In the temperature range of 400～500℃,the cleavage of aliphatic carbon covalent bond is the main one.(3)In the temperature range of 500～600℃,the aromatic carbon covalent bond is broken.(4)Above 600℃,including aromatic ring polycondensation and release of H2.The results show that the pyrolysis weight loss of the CS samples mainly comes from the covalent bond breaking of aliphatic carbon and aromatic carbon,both of which account for more than 20%of the total weight loss;The weight loss of SS mainly comes from the decomposition of carboxylic acid,in which sample 1 accounts for more than 20%of the total weight loss and sample 2 accounts for more than 50%.Furthermore,the kinetic analysis of pyrolysis weight loss curve shows that the desorption process of surface water is below 110℃,and the most probable mechanism function is the random nucleation and subsequent growth model.The most probable mechanism function of the subsequent pyrolysis process can be written as 2(1-α)3/2,which belongs to the chemical reaction of order 3/2.The co-pyrolysis results of the blended SS and CS show that the weight loss increases before 700℃,but decreases after 700℃,and there is no obvious change overall;The co-combustion results show that the influence mainly occurs after 600℃.The results of non-isothermal combustion show that the weight gain of coal slime is about 260℃ and reaches the peak at about 350℃.The total weight gain is less than 1.2%.With the increase of heating rate,the lag effect of the thermal gravimetric curve of CS is more obvious than that of SS.The particle size and temperature have certain influences on the isothermal combustion process of CS.When the particle size of the selected sample does not exceed 100～200μm,the particle size has no effect on the mass of residual solid after combustion,on the contrary,the mass of residual solid increases with the increase of particle size.The mass spectrum analysis results of the isothermal combustion process of CS at 850℃,900℃ and 950℃ show that the CO2 released at 950℃ is more than that at other temperatures,and the production of NO2 and SO2 also increases.The most probable mechanism function of isothermal combustion process of CS can be written as 6(1-a)2/3[1-(1-a)1/3]1/2 which belongs to three-dimensional diffusion model.The effects of 850℃,900℃ and 950℃ on the isothermal burnout time of CS were compared,it was found that the burnout time decreases by 0.5～2 min with the increase of temperature only for CS of 53～100 μm and 100～200 μm;for other partical sizes,the change in burnout time was not obvious.