Effects of Design/Operating Parameters and Physical Properties on Slag Thickness and Heat Transfer during Coal Gasification

Abstract

Abstract:The behaviors of the slag layers formed by the deposition of molten ash onto the wall are important for the operation of entrained coal gasifiers. In this study, the effects of design/operation parameters and slag properties on the slag behaviors were assessed in a commercial coal gasifier using numerical modeling. The parameters influenced the slag behaviors through mechanisms interrelated to the heat transfer, temperature, velocity, and viscosity of the slag layers. The velocity profile of the liquid slag was less sensitive to the variations in the parameters. Therefore, the change in the liquid slag thickness was typically smaller than that of the solid slag. The gas temperature was the most influential factor, because of its dominant effect on the radiative heat transfer to the slag layer. The solid slag thickness exponentially increased with higher gas temperatures. The influence of the ash deposition rate was diminished by the high-velocity region developed near the liquid slag surface. The slag viscosity significantly influenced the solid slag thickness through the corresponding changes in the critical temperature and the temperature gradient (heat flux). For the bottom cone of the gasifier, steeper angles were favorable in reducing the thickness of the slag layers.

Simulation of Deposition and Flow Characteristics of Slag in Entrained Flow Gasifiers

“…The context of assumption 2 was to ignore the slag flow at temperatures below T cv . Assumption 2 was adopted and confirmed by Ye et al , Brid et al studied particle movement on a vertical wall surface and found that the liquid film flow behaved as a laminar flow without radial pulsation when the Reynolds number was less than 4–25. Because the Reynolds number is typically less than 0.02–0.03 when the viscosity and surface tension of the slag flow were relatively large, the slag flow was laminar.…”

Rare earth elements enrichment of fixed-bed coal ash from a pilot plant gasification by physical methods

“…However, by developing a new generation of the gasification process, the waste char is relatively rare (Pomykała and Mazurkiewicz, 2015). Ye, Oh and Ryu (2015) reported that coal gasification process often obtained a granular charcoal, as a result of the improper reaction of fixed residual carbon. Gasification reaction of carbon element in the fixed carbon with a gas reactant such as CO 2 , H 2 O or H 2 is relatively more difficult than the reaction between the carbon element in the volatile matter (Hosseini, 2015).…”