Numerical Modeling Of Key Equipment For Coal Gasification In Supercritical Water

With the aggregation of the global energy crisis, the direct use of primary energy,including oil and coal resources causes the enviroment degradation increasingseriously. Therefore, it is urgent to use highly efficient process to transform the coalresources into clean energy. In recent years, the technique of coal gasification insupercritical water (SCW) has drawn much attention as an effective method to convertcoal into clean fuel gas, such as CH4, H2. SCW coal gasification process would beinvolved in multiphase flow, heat transfer and reaction. The particle deposition andtube wear problems would be an inevitable problem. In order to alleviate thoseproblems, CFD simulations have been adopted to study the key equipment depositioncondition and the heat transfer process in reactor as well as the phase transfer processin heat exchanger.Firstly, a solid-phase and supercritical water two-phase three-dimensionaltransient CFD model, adopting IAPWS properties database for the physical propertiesof supercritical water has been established. The reliability of the established modelwas confirmed by pressure drop results under different temperature and mass ratio ofwater to coal. The results showed that the pressure increases with increasingtemperature and wall roughness. Corrosion was more serious on the outside andbottom of bending pipe. The study also researched the coal particle sedimentcondition in vertically placed elbow segment. The results showed that conveying typeof different size particle was varying. The particle deposition condition insupercritical water heat exchanger tube box was also explored using the samesimulating method. The results showed that vertical inlet type was better than theother type and proper height of the tube box could reduce the deposition mass.Then, this research established a CFD model of supercritical water coalgasification to simulate the high temperature region heated by ethanol combustion.The combustion model of ethanol in supercritical water was successfully establishedwhich provide the temperature distribution for various inlet mass flow of ethanol. Theoptimum feed amount of ethanol was proposed to ensure high temperature ignition,while providing the assurance of heat from the reactor to achieve heat balance.Finally, a three-dimensional model of a shell and tube heat exchanger including tube side and shell side was established. The temperature field and distribution ofpressure and heat transfer coefficient was also studied. The inner tube supercriticalwater phase change position was given. The results showed that the pressure on theshell side and heat transfer coefficient would increase when increasing the shell sidemassflow.The impact of varying shell side inlet mass flow to the pressure drop wasalso analyzed. The plate spacing had little effect on heat transfer enhancement. Theeffects of radiation for heat transfer was non-ignorable.