Insoo Ye

Modeling and analysis of a syngas cooler with concentric evaporator channels in a coal gasification process

Coal gasification offers a flexible and efficient conversion of the solid fuel into CO- and H2-rich synthetic gas (syngas) for production of various chemicals and energy products. Since the hot syngas leaving a gasifier contains various impurities such as acidic gases and particulates, it needs to be cooled down for cleaning prior to conversion into the final product. A dedicated heat exchanger called a syngas cooler (SGC) is used to lower the gas temperature while recovering the thermal energy. This study investigated the heat transfer characteristics in a commercial-scale SGC consisting of a series of concentric helical coil channels. First, the detailed flow and heat transfer pattern in the unique heat exchanger were analyzed using computational fluid dynamics (CFD) for various operating loads and fouling conditions. The predicted heat transfer rate was used to derive correlations for Nusselt number for the channel sections of the SGC. Second, a one-dimensional model of the equipment was proposed for fast-response process simulations. In terms of heat transfer rate and gas temperature, the process model showed a reasonable accuracy compared to the CFD results for the tested cases.

NUMERICAL INVESTIGATION OF THE SPREADING AND HEAT TRANSFER CHARACTERISTICS OF EX-VESSEL CORE MELT

The flow and heat transfer characteristics of the ex-vessel core melt (corium) were investigated using a commercial CFD code along with the experimental data on the spreading of corium available in the literature (VULCANO VE-U7 test). In the numerical simulation of the unsteady two-phase flow, the volume-of-fluid model was applied for the spreading and interfacial surface formation of corium with the surrounding air. The effects of the key parameters were evaluated for the corium spreading, including the radiation, decay heat, temperature-dependent viscosity and initial temperature of corium. The results showed a reasonable trend of corium progression influenced by the changes in the radiation, decay heat, temperature-dependent viscosity and initial temperature of corium. The modeling of the viscosity appropriate for corium and the radiative heat transfer was critical, since the front progression and temperature profiles were strongly dependent on the models. Further development is required for the code to consider the formation of crust on the surfaces of corium and the interaction with the substrate.

Effect of slag viscosity model on transient simulations of wall slag flow in an entrained coal gasifier

The viscosity-temperature relation of slag determines its behavior inside an entrained flow coal gasifier. However, existing prediction models give results with large variations among them. We investigated the influence of different viscosity models in the prediction of the steady and transient behaviors of slag flow on the wall of a gasifier undergoing gas temperature changes. Five viscosity models adopted showed differences in the temperature (T250) at 25 Pa∙s as large as 97 K for the selected slag composition, which was used as the interface temperature between the solid and liquid slag. When the predicted viscosity and corresponding T250 increased, the solid slag became thicker and the dynamic response of the slag became slower. In contrast, the differences in the liquid slag thickness were small. The influence of T250 predicted was dominant, compared to that of different viscosity curves of the liquid slag.

Effect of Operating Pressure on the Heat Transfer and Particle Flow Characteristics in the Syngas Quench System of an IGCC Process

In a coal gasifier for IGCC, hot syngas leaving the gasifier at about 1550oC is rapidly quenched by cold syngas recycled from the gas cleaning process. This study investigated the flow and heat transfer characteristics in the gas quench system of a commercial IGCC process plant under different operating pressures. As the operating pressure increased from 30 bar to 50 bar, the reduced gas velocity shortened the hot syngas core. The hot fly slag particles were retained within the core more effectively, and the heat transfer became more intensive around the hot gas core under higher pressures. Despite the high particle concentrations, the wall erosion by particle impaction was estimated not significant. However, large particles became more stagnant in the transfer duct due to the reduced gas velocity and drag force under higher pressures.

Numerical Simulation on the Spreading and Heat Transfer of Ex-Vessel Core Melt in a Channel

In the unlikely of nuclear reactor meltdown, the leaked core melt or corium must be contained in a device called core-catcher so that the corium can be cooled and stabilized. The ex-vessel behavior of corium involves complex physical and chemical mechanisms of flow propagation, heat transfer, and reactions with sacrificial substrates. In this study, the detailed characteristics of corium flow and heat transfer were investigated by using a commercial CFD code for VULCANO VE-U7 test reported in the literature. The volume-of-fluid (VOF) model was used to predict the interfacial surface formation of corium and the surrounding air, and the discrete ordinate model was adopted to calculate radiation between corium and the surroundings. It was found that cooling via radiation through the top surface of corium had a dominant effect on the temperature and viscosity profiles at the front of the corium flow.