CCS and Power Systems
Advanced Energy Systems - Gasification Systems
Performer: National Energy Technology Laboratory
Project No: FWP-2012.03.03
Accurate physical models to predict the rates of slag buildup in a gasifier or ash deposition in a syngas convective cooler are currently not available. Demonstration plants are currently experiencing problems such as lower carbon conversion and plugging of syngas coolers with fly ash, which reduce the thermal efficiency of a gasifier, place additional strain on solids handling and greywater circuits, and reduce the overall reliability of the gasifier. Molten ash chemistry and viscosity are crucial aspects of carbon feedstock ash impacting slag properties in a gasifier and refractory corrosion. The roles of iron sulfide (FeS) and oxides of trace elements on plastic viscosity are well understood. Studies on fouling caused by ash deposition are plentiful in the combustion community, but there are far fewer such studies under gasification. The published literature suggests that iron sulfides (FeS, FeS2) play a primary role in ash deposition and agglomeration because they may become &"sticky” at convective syngas cooler (CSC) temperatures. More recent reports suggest that other compounds may behave in a similar fashion, although there are no studies that quantify how ash deposition occurs as a function of carbon feedstock.
Researchers will develop reduced order models (ROMs) with higher fidelity computational fluid dynamics models coupled to the ROMs to enable more accurate prediction of gasifier performance. The proposed devolatization and char kinetics subtasks will attempt to identify the factors responsible for the formation of fly ash particles by using the traditional mineral processing approach of particle partitioning, and by superimposing kinetics of char and mineral transformations. In the slag viscosity and unburnt carbon effort, slag viscosity will be investigated using a high-temperature rotating-bob viscometer and a temperature gradient furnace in which slag infiltration in a controlled atmosphere can be studied. Particle deposition testing will initially be conducted at temperatures relevant to the convective syngas coolers in order to generate ash particle chemistry; ash adhesion probabilities as a function of particle size, temperature, and velocity; surface temperature; and contact angle. Ash particles from the High Pressure Entrained Flow Reactor (HPEFR) at Pennsylvania State University (Penn State) will be generated from coal and petcoke feedstocks that are separated into multiple size and density fractions, each containing various amounts of mineral matter, which will be used to determine the characteristics of the fly ash particles. The effect of FeS and other coatings on particle deposition will also be investigated in the latter stages of the project, and a comprehensive model for ash deposition at CSC conditions will be generated.