Study On Gasification Of Coal Char With Steam And CO₂

Coal gasification plays an important role in coal utilization with the development ofIGCC and chemical processes. Understanding of char gasification kinetics and charstructure is essential for the design and modeling of a coal gasifier. Although manyresearchers have constructed CO₂gasification model and H₂O gasification modelseparately, in coal gasifier, CO₂gasification and H₂O gasification occur at the same time.Hence，it is important to determine the gasification kinetic of co-existing of H₂O and CO₂and apply to more realistic gasification systems.Chars were made with different pyrolysis conditions from two different rank of rawcoals, and specific surface area and pore diameter distribution of coal chars were tested.Themorphology of the chars was observed by ESEM, and carbon crystal structure of chars wastested by XRD. The gasification kinetics of CO₂gasification and H₂O gasification and theirmixtures gasification were tested. The experimental results can be concluded as following:（1）The results from XRD show that char structure as reflected by crystallite sizebecomes more ordered with decreasing heating rate. The porosity of Datong chars becomeslager with increasing heating rate, and Dayan chars become to fragments at rapid pyrolysis.The pyrolysis rate obviously affected the char gasification rate, and the chars becomes moreactive with increasing heating rate.（2）Gasification rate of char with H₂O is much higher than the rate with CO₂.Thedifference between the rate of Char-H₂O and Char-CO₂of the same char is: DT slowchar>DT fast char>DY slow char>DY fast char.（3）The reactivity of chars with CO₂from high to low are: DY fast char> DY slowchar> DT fast char, and the reactivity of chars with H₂O and H₂O&CO₂from high to loware: DY fast char> DT fast char> DY slow char.（4） Homogeneous reaction model were used to deal with experimental data. For Dayancoals, the higher the activity the larger the pre-exponential, kinetic compensation effectwere observed between them. （5）Gasification reaction of Char-CO₂and char-H₂O competes for the common activesites of char partially, and the rank of the competition is: DT slow char>DT fast char>DYslow char>DY fast char.