Dynamic Modeling of Detachment, Transport, and Flow of Slag in an Entrained-Flow Gasifier

Accelerating Fossil Energy Technology Development Through Integrated Computation and Experimentation
AIChE Annual Meeting
October 31, 2012 - 5:15pm-5:35pm
Dynamic Modeling of Detachment, Transport, and Flow of Slag in an Entrained-Flow Gasifier

 

Pratik Pednekar, PhD Student, West Virginia University

Department of Chem. Eng., West Virginia University, Morgantown WV  26506

ppedneke@mix.wvu.edu

 

Debangsu Bhattacharyya, Assoc. Professor, West Virginia University

Department of Chem. Eng., West Virginia University, Morgantown WV  26506

Debangsu.Bhattacharyya@mail.wvu.edu

Tel: 3042939335, Fax: 3042934139

 

Richard Turton, Professor, West Virginia University

Department of Chemical Engineering, WVU, Morgantown, WV 26506

Richard.Turton@mail.wvu.edu

Tel: 3042939364, Fax 3042934139

 

Raghunathan Rengaswamy, Professor, Texas Tech University

Department of Chemical Engineering, Texas Tech University, Lubbock, TX 26507

Raghu.Rengasamy@ttu.edu

Tel: 8067421765, Fax 3042850903

Abstract

The harsh environment inside slagging gasifiers causes degradation of the refractory lining. Replacement of the refractory lining is carried out every 1-2 years and is very expensive and leads to significant down-time, which lowers the overall availability of hot-wall slagging gasifiers. Due to the harsh operating condition inside a slagging gasifier, direct, in-situ measurements of either the transport variables or refractory degradation are not possible with current state-of-the-art technology. Therefore, a dynamic model describing the detachment, transport, and flow of slag has been developed for better understanding of the effects of various operating conditions and physicochemical properties on the degradation of the refractory. This can eventually lead to the development of better monitoring and prevention techniques.

Several models exist in the open literature for calculating the thickness of the slag layer flowing along the gasifier wall. However, there is a dearth of models that consider detachment of slag droplets from the char particles and the subsequent transport of the slag particles to the wall. In this work, a detachment model is developed by considering the dominating forces acting on the slag droplets attached to the unconverted char. In addition, a model of the turbulent deposition of the slag to the gasifier wall is developed. Furthermore, a model of the molten slag that flows along the refractory lining has been developed by considering mass, momentum, and energy balance equations. Due to the temperature gradient along the molten slag layer, a solid slag layer exists below the molten slag layer. A model of the solid slag layer is also developed using energy balance equations.  

The slag sub-model is integrated with a 1D steady-state model of a single-stage, downward-firing, oxygen-blown, slurry-fed, entrained-flow gasifier developed previously at WVU in the Aspen Custom Modeler® (ACM) environment. The gasifier model includes mass, momentum and energy balance equations for solid and gas phases. The model also includes a number of heterogeneous and homogeneous chemical reactions along with devolatilization and evaporation of the slurry feed.  It was assumed that the size of the char particles did not change as the ash remains attached to the unconverted char. Therefore, a shrinking core model was appropriate. However, in the current model, droplets of molten slag are considered to detach from the unconverted char when their diameters exceeds a critical value. Therefore, the shrinking core assumption is replaced with a shrinking particle description that is more appropriate for the current model. A discussion of the effect of various operating parameters on the formation and deposition of the slag will be given in this presentation.

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