| In this thesis, a laboratory-scale direct coal liquefaction (DCL) reactor (0.101 m ID and 4.04 m height) of an engineer company was studied experimentally and numerically. A coal model experimental apparatus was constructed, and the gas-liquid/gas-liquid-solid fluid dynamics in the reactor was tested. Hot model simulations were performed by using CFD software, and the gas-slurry flow and the chemical reactions under the conditions of high temperature and elevated pressure were both investigated. A comprehensive mathematic model was developed to successfully predict the multiphase flow and chemical reactions in the DCL reactor. The subjects and the major conclusions were summarized as follows:(1) Hydrodynamic parameters in the newly built Plexiglas experimental setups were measured, including bubble dynamics, overall gas-holdup and liquid velocity. Air and tap water or paraffin were used as the gas and liquid phase, respectively, and glass beads as the solid phase. At a superficial gas velocity lower than 2cm/s, spherical and elliptical bubbles were observed with uniform size distribution, and the gas-liquid or gas-liquid-solid flow were predicted to be a homogeneous bubbly flow. Furthermore, it was verified that the mean gas holdup was determined mainly by the superficial gas velocities, namely, a low gas velocity produced a low gas holdup, whereas other parameters such as the superficial liquid velocity and the height/diameter aspect ratio (H/D) made insignificant effects on the overall gas holdup. Of particular note, the overall gas holdups decreased with the increases in the solid concentrations of the gas-liquid-solid system, mainly due to the decreases of the small bubbles’volume fraction. In addition, it was noted that the radial distributions of liquid velocities were largely affected by the superficial gas velocity, and by the superficial liquid velocity, H/D and the height of testing point in a less extent. Based on the study, it was predicted that the DCL reactor operating at a superficial gas velocity of 0.4cm/s, was in a homogeneous bubble flow regime characterized by a uniform dispersion of small bubbles, a low overall gas holdup and a plain radial distribution of liquid velocity.(2) With the assumption of a gas-slurry Euler-Euler two-fluid model, a 3-dimensional time-dependent simulation was conducted by using Fluent 14.0 for the gas-liquid-solid flow in the lab-scale DCL reactor at high temperature and pressure. The following results were obtained:the overall gas holdup in the reactor was relatively low at a level of about 0.0165, and an obvious liquid back-flow was observed near the reactor wall and a vortex flow near the inlet of the reactor, which could made a positive contribution to the mixing of reactants. The averaged residence time of slurry in the reactor was about 70 minutes, which was in the reasonable range of the reaction time required for a complete coal conversion.(3) Based on the experimental results of lignite liquefaction by Liu Ming, a new kinetic model was constructed and a set of kinetic parameters were obtained by using the Matlab toolbox of the least-square parameter regression method. Via programming a user defined function (UDF), the reaction model was coupled with fluid dynamics solver of the ANSYS Fluent 14.0 software, and a simulation of coal liquafaction at T=430 ℃, P=10 MPa was performed. The computational results indicate that the coal conversion at the outlet is about 90.83%, and the predicted yields of oil and gas (OG) are 64.67%, which are in good agreements with the experimental results of the lab-scale reactor operated under the same conditions. |
PDF Full Text Request