Numerical Simulation Of New Multi-burner Entrained Flow Coal Gasifier

Coal gasification is a major approach to utilize coal cleanly with high efficiency. Entrained flow coal gasification technology has been the first choice of coal gasification due to its high carbon conversions and flexible coal applicability. Zhejiang University and Shanghai United Chem Tech Investment & Development Co., Ltd. jointly developed a new multi-burner entrained flow coal gasifier to solve the blockup trouble of slag hole and the problem of low thermal efficiency which easily arised in current entrained flow coal gasifier, and it’s essential to research the characteristic of fluid flow of this new gasifier even though there wasn’t any operation experience of this new gasifier. This paper established a three-dimensional mathematical model of this new gasifier, In this model, Euler-Lagrange model and non-premixed combustion model were performed to analyses the regularity of flow field properties in cold and hot condition, and assisting the optimization and operation of this new coal gasifier.In the numerical simulation research of this new gasifier at cold conditon, Euler-Lagrange model was adapted to simulate the gas-solid flow field properties. Species transport model and realizable k-s model were performed to model the turbulent flow of continuous phase, discrete phase model and stochastic trajectory model were utilized to describle the motion of coal powder. The simulation results showed that, the multi-burner coal gasifier had more homogeneous flow field distribution and longer particle residence time than the single burner gasifier. Taking account of the influence of particle residence time, forty percent of feed stock supplied by the main burner will bring the best flow field characteristics than others percentage; The outlet gas velocity increased with the enlargement of feed stock velocity of main burner, while the feed stock velocity of auxiliary burner didn’t effect the flow field largely; With the increase of auxiliary burner inclination, both of the particle residence time and turbulent kinetic energy increased consequently, while the gasifier outlet gas velocity decreased. When the auxiliary burner inclination change to 30°, the flow field distribution will get its optimal condition at the range of 15-30°.In the thermogravimetric analyzer experiment, two different controversial assumptions, common or separate active sites assumptions, existed in the Langmuir-Hinshelwood (L-H) kinetic model when coal char gasified by the mixture of H2O and CO2. Two potential factors, specific surface area and ash content, were proposed to elucidate the reason for this controversial issue. Experiments were conducted at atmospheric condition and a temperature of 1223K, using a modified thermogravimetric analyzer (TGA) system at various reactant partial pressures. The experimental results showed that both specific surface area and ash content will affect the mechanisms of coal char gasification. The experimental data of coal char with large specific surface area fit the calculation of separate active sites assumption, while the experimental data of coal char with small specific surface area fit the calculation of another assumption very well. The experimental data of demineralized char didn’t fit the calculation which based on both of these two active sites assumptions.In the numerical simulation research of this new gasifier at hot conditon, non-premixed combustion model was performed to simulate the gasification process in this gasifer. The two competing rates model was adapted to model the emission of volatile component, while the kinetics/diffusion-limited model were utilized to describle the heterogeneous reaction of coal powder. The probability density function (PDF) of β-function was used to model the turbulence-chemistry interaction. The simulation results showed that, the new gasifier had more homogeneous flow field distribution and more available components than single burner gasifier. With the increase of feed stock percentage in main burner, the available components in syngas first increased and then decreased, and got its highest level at fifty percent; The available components gradually increased with the enlargement of feed stock velocity of main burner; With the increased of feed stock velocity of auxiliary burner, the the available components in syngas first increased and then decreased; In different conditions, the wider the auxiliary burner inclination was, the lower available components and temperature the syngas were,20° of the auxiliary burner inclination was the most suitable angle of this new gasifier.