Investigation On The Coal Char Reactivity Based On The Molecular Simulation Technology

The carbon solution loss reaction in the blast furnace is a physical and chemical process containing gas mass-transfer and heterogeneous gas solid reaction which is important for coking process. In order to understand the mechanism of the carbon solution loss reaction, the kinetics experiments of the reaction were carried out on the premise that the influence of internal and external diffusion was eliminated. On the basis of that, one coal molecular model, one char molecular model and some other coal char molecular models containing different minerals(Na2CO3, Ca Cl2, Fe Cl3 and H3BO3) were built by Materials Studio(MS) 7.0 referred to many reported coal char models. Furthermore, Molecular Mechanics(MM) and Molecular Dynamics(MD) optimization simulation of those models were calculated by MS 7.0. The adsorption capability and diffusion coefficients of CO2 in different coal char models were also calculated. Simultaneously, the coke model structure was built to study its reaction process under catalytic effect of different minerals with CO2 by ADF(Amsterdam Density Function) based on Reax FF(Reactive Force Field). The results show:(1) On the premise of the elimination of the influence of internal and external diffusion, the kinetics of carbon solution loss reaction was investigated under catalytic effect of different minerals(Na2CO3, Ca Cl2, Fe Cl3 and H3BO3) in CO2, at 1223 K, 1248 K, 1273 K and 1298 K. Research shows that the reaction kinetics parameters, like the pre-exponential factor and activation energies were calculated by homogeneous model and shrinking core model and the results are 1.5303 s-1 and 101.3905 k J·mol-1, 0.5675 s-1 and 92.7428 k J·mol-1. The reaction activation energies of the samples adsorbed Na2CO3, Ca Cl2 and Fe Cl3 decreased compared with the original sample results while the reaction activation energies of the samples adsorbed H3BO3 increased compared with the original ones.(2) The construction of coal char molecular models and MM, MD optimization simulation of their structures were carried out by MS 7.0. And related energy parameters were calculated. The results show that the non bond energy of van der Waals force and Coulomb energy and the bond energy of torsion energy play a stabilizing role during the construction of coal molecule structure model, and only van der Waals force and torsion energy play a stabilizing role during the construction of char molecular structure model.(3) The diffusion coefficients of CO2 in different models at different temperatureswere calculated by MS 7.0. The diffusion coefficients of CO2 in char model are much higher than in coal model. The addition of Na2CO3, Ca Cl2 and Fe Cl3 enhanced the degree of CO2 diffusion in the model, while addition of H3BO3 hindered the diffusion of CO2. The diffusion activation energies of CO2 in coal and char model were 32.31 k J·mol-1and 146.26 k J·mol-1, respectively. And the addition of H3BO3 increased the diffusion activation energies.(4) Coke model structure of carbon solution loss reaction was built and proposed by ADF based on Reax FF. The catalytic effects of Na, Fe and B on the carbon solution loss reaction were analyzed as follows: Na with the positive charge will produce attractive force to the aromatic molecules with negative charge, which make van der Waals force between the aromatic molecules weakened and cause them unable to arrange orientation smoothly. Therefore, the reactivity of coke increased. The presence of Fe promotes the formation of semi quinoid oxygen complexes, which prompts the reaction through the decomposition, and accelerated the rate of solution loss reaction. Moreover, the carbon solution loss reaction occurs easily in the defect surface, which makes the B-O-B key has a tendency to gather here, thus blocking the solution loss reaction active sites, then hindered the solution loss reaction.