Investigation On The Enthalpy And Kinetics Parameter Of Pulverized Coal/Char Combustion

Calorific value of coals and chars are particularly important in spontaneouscombustion, ignition of the coal, temperature distribution of the furnace and adjustment ofheat load as it has a significant effect on the construction of the energy balance. Averageheat released from the whole combustion process often measured by Oxygen Bombcalorimeter is adopted. It is obviously not accurate and appropriate. The components andcalorific values of combustible mass released from the fuels at different stage ofcombustion process vary greatly. Better insights into the transient enthalpy can improve theperformance and economics of the pulverized coal power plant.Characteristics of three different coals (including JWY anthracite, ZCY bituminous,and SLH lignite) and char corresponded combustion in an air atmosphere were studied andcompared by using thermo-gravimetric-differential scanning calorimeter (TG-DSC)simultaneous thermal analyzer. The chars were prepared by horizontal tube furnace andTGA, respectively. It was found that active specific surface area and kinetics parameterscalculated using SCT model were in change at any time of the coal/char combustion. Withthe burning of coal/char, apparent activation energy of reaction gradually decreased to aminimum value, and then increased. At the major combustion zone, activation energychanged in the value of50-200kJ/mol.The transient enthalpy h of coal/char combustion which represents the calorificvalue (CV) of combustible matter released at different time was determined as a function ofburn-out degree. It was found that in the initial stage, hof JWY and ZCY coals weregreater than that of the char pyrolysized from parent coal, mainly because volatiles ofJWY/ZCY contained more a great deal of heat per unit mass oxidized at low temperature; in the middle stage, all the hof coals were lower than that of the char pyrolysized, so thepyrolysized char oxidation can supply more thermo-energy per unit mass. hwas almosta constant when the burn-off degree was equal to between0.3/0.15and0.92/0.85forJWY/char, between0.36/0.18and0.95/0.88for JWY/char, between0.45and0.95for SLHchar; For SLH, there are more oxygen content and lower (C/H)dafof volatiles which resultsthat hwas reduced sharply to a minimum at the burnout rate of0.27, Then coke wascombusted, h increased. In the later stage, the h of the coal/char decreased with theburn-off degree, which implies that the activity of the coal/char decreases.The rates of heat release during combustion of coal at different heating rates werepredicted by both transient enthalpy and constant calorific value. The results showed thatthe rate of heat release can be well predicted using transient enthalpy, while the predictedresult using constant calorific was smaller than the experimental measurement result at theearly stage, bigger at the mid-stage, which made the forecast of ignition of pulverized coaland furnace temperature not accurate.